Part I: Research Update
Note: This CME/CE activity expired on Oct. 14, 2009. For a list of currently available activities, click here.
This is Dr. David Hardy, director of the Division of Infectious Diseases at Cedars-Sinai Medical Center and associate professor of medicine at the David Geffen School of Medicine, both in Los Angeles, Calif. I'm going to be discussing a new class of medications called CCR5 antagonists, or coreceptor antagonists.
Targets for Treatment of HIV Infection
Before I go into the details of the CCR5-related clinical trials, I want to provide some background about how chemokine coreceptors are involved in HIV entry, how they evolve over the course of HIV infection and how they are a new target for the treatment of HIV infection.
As you all know, the treatment of HIV infection has relied primarily upon viral targets, such as the enzymes that are useful in reproducing the virus once it has entered into a CD4+ T cell.1 Currently, in the United States, we have only one licensed HIV medication that's considered to be an entry inhibitor.2 Called enfuvirtide [T-20, Fuzeon], it blocks viral fusion after the virus has sufficiently attached to the outside of a CD4+ T cell, and is pushing its way inside that cell.
As you can see from the slide above, the retroviral life cycle has provided us with a multitude of targets.1 We have exploited several of these targets through the use of reverse transcriptase inhibitors, protease inhibitors, fusion inhibitors and now with a new class of medications called coreceptor inhibitors.
Another new class of medications, recently brought to market in the United States and in many countries around the world, is the integrase inhibitors, which block viral integration into the host cell genome.3
Finally, there are medications that are currently in phase 2/phase 3 studies called maturation inhibitors.4
Today I will focus on the coreceptor biology of HIV, and how this target can be therapeutically useful to us, in terms of blocking the earliest steps of viral entry outside a human T cell.
As we understand it today, HIV entry is composed of at least three steps.1 These steps are sequential, but they may overlap and have different sorts of activity over time.
As we can see in the above slide, the first step in HIV entry is the CD4+ cell binding, in which the CD4+ cell protein on the outside of a T cell binds to a specific part of the gp120 viral protein, a glycoprotein on the outside of HIV. This initial CD4+ cell binding causes a conformational change that exposes a part of the gp120 molecule, know as the V3 loop, that was previously unexposed.
In the second step, which is known as coreceptor binding, the V3 loop of the gp120 molecule binds to another particle, called the chemokine receptor, on the outside of the human T cell. I'll talk more about chemokine receptors in a few minutes.
The third step is virus-cell fusion: Once the virus is firmly attached to the cell via CD4+ and chemokine receptor binding, it basically harpoons the cell with its gp41 protein, shown in red in the slide above.
After this, gp41 folds over on itself, allowing for close contact between the viral envelope and the plasma cell membrane. These two membranes then fuse and allow for the genetic material and enzymes of HIV to be pushed inside the human cell, and thus, HIV infection has occurred.
There are many molecules that have been developed to block CD4+ cell binding, coreceptor binding and fusion. Enfuvirtide is licensed in the United States as a medication for blocking the fusion step.2 We also now have maraviroc [MVC, Selzentry, Celsentri] approved as a CCR5 antagonist,5 and a second CCR5 antagonist in development called vicriviroc [SCH 417690, SCH-D],6 plus several agents, such as PRO 1407 and AMD11070,8 that are still in either preclinical or clinical testing.
Biology of the HIV and T Cell Interaction
Let's break this down a little bit more to get a better feeling for the biology of the interaction between a human T cell and HIV.
In the above slide, you can see the surface of a CD4+ T cell with its CD4+ molecules (shown here in pink) and chemokine receptors, either CCR5 (shown in orange) or CXCR4 (shown in green).
These molecules are all arranged in groupings of three, or triads, so that it takes a triple binding each time for this interaction between virus and human T cell to occur.
In the slide above you can view the structure of the HIV-1 envelope glycoprotein. You can see how the viral particle descends upon a human T cell.
Note that gp120, the outermost part of the virus, is getting closer and closer to the CD4+ molecule.
When these two molecules become very close, there is a specific binding between gp120 and the three CD4+ cell molecules.1 This creates a conformational change, which basically flips open the part of the gp120 molecule previously hiding the V3 loop.
The V3 loop is now exposed, and with that exposure comes a second binding of the gp120 molecule and the chemokine receptor, in this case a CCR5 molecule. This is actually done in triplicate so that the viral particle is firmly bound to the human T cell.
Once firmly bound, there's a quick and efficient harpooning of the human T cell by gp41. With that, there is the folding over of the gp41 molecule, which pulls the envelope of HIV close to the plasma membrane of the cell.
Fusion occurs between these two surfaces and with this act, a pore is created, allowing for the entrance of the HIV RNA and other associated enzymes into the human T cell -- and thus, HIV infection has occurred.
HIV Natural History and Tropism Expression
Let's move on to the natural history of tropism. Our understanding of tropism expression is fairly new. Tropism was first discovered about 10 to 12 years ago and has offered us a huge new understanding of how HIV interacts with our human T cells.9
CCR5 and CXCR4 are chemokine receptors. Chemokine receptors are expressed on the outside of immune cells and other antigen presenting cells. They allow these cells to interact with each other through chemo-attractive cytokines. Some of the molecules that are the natural ligands, or binders, of these chemokine receptors include cytokines such as MIP-1α, MIP-1β and RANTES.
HIV has been able to evolve to where it can also utilize these chemokine receptors, not as immune correspondents, but as a way to bind and get inside the cell, as we saw before.10
We know that the normal function of chemokine receptors is to allow for T-cell migration to different inflammatory areas, as well as allow for the T cell immune response to various antigens.
The above slide demonstrates how CCR5 and CXCR4 -- the two most commonly used chemokine receptors for HIV infection -- are actually very similar in terms of their seven transmembrane proteins, meaning that they traverse the human T cell plasma membrane seven times and have both intracellular and extracellular regions. Those extracellular regions are important, in terms of the specificity of the amino acids within them, which allow HIV to recognize and attach in a very specific way.
CCR5 viruses, known for short as R5 viruses, are what we used to call M-tropic (macrophage-tropic) or NSI (non-syncytium-inducing) viruses. These viruses make up for around 98% to 99% of all new HIV infections and are prevalent early in HIV infection and disease.11
CXCR4 viruses -- or, for short, X4 viruses -- are also known as T-tropic (T-cell tropic) or SI (syncytium-inducing) viruses. As we know from studies of the evolution of HIV infection, these viruses emerge late in HIV disease and have been associated with rapid CD4+ cell decline.12 We also know that there are mixed or dual-tropic viruses.10
The above slide shows how X4 viruses infect primarily T-cell lines by using the CXCR4 coreceptors on those cells, and also primarily lymphocytes, such as naive and memory CD4+ cells. R5 viruses infect primarily macrophages, monocytes and dendritic cells, which is why new infections are associated with this type of virus. Primary lymphocytes can express both CXCR4 and CCR5 over different stages of their lifetime. A dual-tropic virus then would be able to infect this kind of cell because it expresses both coreceptors.
Over time we've learned about some interesting genetics regarding the CCR5 gene. As you all know, we receive an allele for CCR5 from each parent. It's been determined that about 5% to 14% of Caucasians, primarily of Northern European descent, carry a specific deletion in the CCR5 gene, called Δ32, which makes half of that person's genes unable to express the CCR5 protein.13
In addition, we have also learned that 1% of persons have dual Δ32 deleted genes, which they got from both parents, and are considered to be CCR5 Δ32 homozygotes. What this means is that their T cells cannot express any CCR5 molecules, and therefore they are unable to be infected by CCR5-tropic virus. They can, however, become infected by an X4 virus.
Interestingly, the origin of this CCR5 Δ32 allele has been traced back to Europe.13,14 It is thought that it arose about 1,000 years ago, possibly as a positive selection against a pandemic pathogen, such as smallpox or the bubonic plague.15 Persons who did not have wild-type genes, but had Δ32 deleted genes, were the ones who survived the pandemic pathogen.
As you can see from the above map, the area of Europe where Δ32 prevalence is highest is in Northern Europe.14 It decreases going southward, through Central and Southern Europe. It seems also to be rather high in areas where migration occurred from Northern Europe, such as in the United States, Canada and Australia, and appears to be very rare in other parts of the world, such as Africa, Asia and South America.
People who are considered to be wild type, or normal, for the CCR5 gene have the wild-type allele from both parents. They also have a normal amount of CCR5 expression on their T cells, normal progression of HIV infection, if infected, and also normal immune function.
People who are heterozygous for this gene -- meaning they have one wild-type and one Δ32 allele -- also express CCR5, but to a lesser degree, probably half of that of normal people.10 This can be associated with HIV infection, but it is also associated with delays in HIV progression, CD4+ cell depletion, AIDS and death.16-19 These people also have normal immune function.
Individuals who are Δ32 homozygous (i.e., both alleles are Δ32 in origin), have no CCR5 expression on their T cells. Therefore they cannot be infected with an R5-tropic virus. As mentioned, they can be infected with X4-tropic virus, though it is rare, but interestingly, they too do have normal immune function.20
There's been some concern that individuals who are homozygotes for Δ32 may not have entirely normal immune function, since there have been reports in the United States of a handful of these individuals developing neurologic involvement with West Nile infection.21
As mentioned above, patients who have been followed over time and who are known to be heterozygous for the CCR5 Δ32 gene experience a slower time to HIV progression, to developing AIDS and to death -- statistically different from individuals who are wild type for this gene -- indicating that there's some protection that seems to occur with the decrease in the amount of available CCR5.16-19 Of course, this provides some insight into how this decrease in CCR5 expression can be used in a therapeutic nature.
In order for us to better understand how we can characterize viruses, a new assay, called a tropism assay, has been developed. This assay extends our ability to characterize individual patients' viruses in order to better understand how their particular HIV may progress and what kind of therapeutic agents -- in this case, CCR5 antagonists -- may or may not be effective in treating them.
A tropism assay is in fact required before prescribing a CCR5 antagonist.5 Individuals who have CCR5-tropic virus will be expected to respond well to an HIV regimen containing a CCR5 antagonist. Patients who have either dual/mixed or primarily X4-type virus would not be expected to respond well to a CCR5-containing regimen.
Let's look at the assay that's now available in the United States, and has been clinically validated, in terms of being used in pretty much all of the currently completed and ongoing treatment protocols with R5 and X4 antagonists.6-8,22,23
The tropism assay is a further use of the platform that was developed to assess the phenotypic expression of resistance to reverse transcriptase inhibitors and protease inhibitors, and which has been available for many years.24 The tropism assay works in this way: A viral vector is created using the patient's HIV envelope gene, and then is cloned along with another vector, called a luciferase expression vector, which allows for light to be emitted in an infected cell.
When these two vectors are transfected, or forced inside of a virus-producing cell, particles called pseudovirions are generated that will express the patient's actual HIV envelope glycoproteins and emit light that can be detected when they have infected a CD4+ cell. These pseudovirions are then put in contact with two different kinds of cells. Both types of cells express CD4+ molecules on their surface, but one type expresses only CCR5 coreceptors while the other expresses only CXCR4 coreceptors.
When these pseudovirions are put into contact with these cells, one possible outcome may be that the pseudovirions infect the CCR5 expressing cells, but not the CXCR4-positive cells. In this case the virus they were derived from would be characterized as CCR5 or R5 tropic. If the pseudovirions infect only the CXCR4-expressing cells, then we know that the virus is only X4 tropic, because it cannot, and does not, infect the CCR5-expressing cells.
If the pseudovirions can infect both the CCR5- and CXCR4-expressing cells, then the virus is either dual tropic or mixed.
Let's look at how this can actually occur, in terms of what the tropism test can tell us. As the above slide shows in graphic form, an R5 virus (shown in orange) will infect a CCR5 expressing cell. Light is generated when the viral particle infects a cell and a readout of light expression is shown to be positive. When this same virus then tries to infect an X4-expressing cell, it cannot attach to the cell and therefore no light is generated.
Let's look at a dual-tropic virus. This virus expresses both CCR5 and CXCR4 binding molecules on its surface, and therefore it can infect both an R5 virus and an X4 virus, with light expressed from both cell populations.
Finally, let's look at a viral population, as shown in the above slide, in which some of the viruses are R5, some are X4 and some are dual tropic. Such a viral population could infect CCR5-expressing cells and express light. This viral population could also infect X4-expressing cells and express light.
Just as a little quiz, what kind of population do we see here? We see primarily R5-tropic viruses and one X4-tropic virus. So this population can infect both R5-expressing cells and a smaller number of X4-expressing cells. This really points out how important it is to be able to detect not so much the R5 population, but primarily the X4 population. It is especially important when we're talking about whether we can use the currently licensed class of medications called R5 inhibitors, because what we really want to know is, how much X4 virus is actually in that population that may not be affected by the R5 antagonist.
The above slide shows how this tropism test has been improved upon since it was made available about a year ago. The standard tropism test is able to detect X4-tropic virus if at least 10% of the viral population is X4 tropic.24 This assay is not able to accurately identify levels of X4 virus lower than 10%.
The standard assay has been improved upon using some specific enhancements. The new enhanced assay can actually detect down to an X4-using viral population of around 0.3%, markedly increasing the sensitivity of this assay to be able to identify any X4 virus that may be in the viral population.25 With this enhanced assay, we are able to more accurately characterize a virus's tropism, and thereby identify what kind of medications would work well against the virus.26
We know that coreceptor tropism evolves over time. Let's look at some of the epidemiologic data that we have available to us to see how this happens. From several cohorts of patients who were naive to therapy, but about to start therapy, we know that the majority of the viruses contained in these persons is R5 tropic. Somewhere between 80% to almost 90% of treatment-naive HIV-infected patients will have R5-tropic virus.27-30 A smaller proportion, somewhere between 10% to as high as 20%, will have dual/mixed virus. A very small population, less than 1%, will have only X4-tropic virus.
Over time, what we notice is that coreceptor usage evolves. When we look at populations of patients from the TORO,31 MOTIVATE 1 and MOTIVATE 2 studies,32 as shown in the above slide, we see that in these highly treatment-experienced patients the percentage of R5 viruses decreases from between 80% and 90%, down to around 40% to 50%. The proportion of patients' viruses that use R5 and X4 increases to around 40% to 50%. The proportion of X4-only using viruses increases a bit to between 2% and 4%. This evolution of tropism usage occurs over the course of the patient's HIV treatment history, and whether it's caused by that is really not clearly understood.
What we do know about HIV tropism, from this study by Brumme et al, is that as the CD4+ cell count decreased, the percentage of patients with X4-using virus increased.27 The median CD4+ cell count in patients who have X4 virus was 110 cells/mm3 versus a median CD4+ cell count of 290 cells/mm3 in those who had R5-using virus. The viral load was 175,000 copies/mL versus 120,000 copies/mL, in X4 versus R5 viruses, respectively.
Whether the use of X4 is caused by the drop in CD4+ cell count is still not clearly understood. All we know for sure right now is that these two things are, in fact, associated.
What happens to patients who are determined to be R5 or X4 over time? What happens when they get treated, in terms of their response to HAART [highly active antiretroviral therapy] regimens? A cohort of patients in London, in which individuals were naive to therapy and followed over time for the progression of HIV infection, had their viruses tested for tropism.30 Of the 402 treatment-naive patients, 326 were found to have R5 virus, 73 were found to have dual/mixed virus and three patients were found to have X4 virus. By August 2006, 340 of these 402 patients had started on HAART: 229 of the R5 virus patients, 60 of the dual/mixed patients and 51 had been excluded from analysis for various reasons.
Let's look at the two-year follow-through of these patients who were determined to have R5 or X4 virus. Looking at their CD4+ cell count progression over time, a statistically greater fall in CD4+ cell count occurred in those patients who were found to have some X4 virus in their viral population over two years of no treatment follow-up.
However, when treatment was in fact initiated in these patients, the proportion of patients achieving a viral load of less than 50 copies/mL, or becoming undetectable, was in fact no different in these patients whether they had a R5 or a dual/mixed viral population, showing that there does seem to be some natural history difference between these two viral populations, but no real difference in terms of treatment.
A similar sort of study, known as the TORO study, was done in those patients who had R5-only or X4-containing viral populations.33 As the above slide shows, in terms of response rates to HAART between those patients who were R5 tropic and those who had some X4-tropic virus, the CD4+ cell count rise at 12 and 24 months is really no different.30 In terms of the proportion of patients who had undetectable virus at 12 or 24 months, there's really no difference, as well. So, both by immunologic and virologic criteria, there was really no difference between patients with R5 virus and patients with X4 virus.
Let's move on to some of the clinical trials with CCR5 antagonists. There is one agent, called maraviroc, that has been approved by the FDA [U.S. Food and Drug Administration], specifically for patients who are highly treatment experienced.5 The MOTIVATE 1 and 2 studies are responsible for licensure of this medication in the United States and in several countries throughout the world.22
MOTIVATE 1 and 2 are international ongoing trials that enrolled a little over 1,000 patients worldwide. These patients had to have triple-class experience or proven triple-class resistance to nucleosides, non-nucleosides and protease inhibitors.
All these patients were, at screening, determined to have R5-tropic virus, which was necessary in order to participate in these trials. All patients were given an optimized background therapeutic regimen based upon a baseline genotype/phenotype NT20 sensitivity assay. Added to that optimized background regimen was a placebo, maraviroc given once a day or maraviroc given twice a day.
The above slide shows some of the baseline characteristics of the patients enrolled in the study. These individuals were in their mid- to late-40s; around 10% to 12% were female; the majority, around 80% to 85%, were Caucasian; CD4+ cell counts in the three arms of the studies were all less than 200 cells/mm3; the viral loads were somewhere around 70,000 copies/mL to 80,000 copies/mL; and the majority of patients -- two thirds of the patients -- had less than two active drugs in their background optimized regimen. Around 40% to 45% of the patients received enfuvirtide as part of their regimen, and a very small number of patients, around 12% to 15%, received tipranavir [TPV, Aptivus]. Of note: Darunavir [TMC114, Prezista], our newest protease inhibitor, was not allowed to be used in the study because of a lack of knowledge of the drug-to-drug interaction between maraviroc and darunavir.
The bottom line is that the difference in the primary endpoint of suppression of viral load from baseline to week 48 showed a statistically and clinically significant greater viral load suppression with both maraviroc once a day and maraviroc twice a day, compared to placebo. The difference was almost one log between placebo and both maraviroc treatment arms.
The studies' secondary endpoints were the proportion of patients who had viral loads of less than 400 copies/mL or less than 50 copies/mL at week 48. The proportion of patients who achieved the study endpoint of less than 50 copies/mL of virus was around 43% to 45% in the maraviroc arms, compared to just under 17% in the placebo arm. There was almost a tripling in terms of better viral suppression with the maraviroc-containing regimens.
The CD4+ cell count increase in these patients was also of note at 48 weeks. The maraviroc arms both had an increase of well over 100 new CD4+ cells compared to baseline: 124 cells/mm3 for the maraviroc twice-a-day arm and 116 cells/mm3 for the once-a-day maraviroc arm, compared to 61 cells/mm3 for the placebo arm.
As you can see from the above slide, there was a difference in terms of what the patient's baseline viral load was when they started. However, there were significant increases, in terms of better viral load suppression, with maraviroc compared to placebo, whether the patient's viral load was greater than or less than 100,000 copies/mL. Similar results were seen based upon baseline CD4+ cell count.
There was better suppression of HIV based upon the number of CD4+ cells at baseline with both maraviroc arms compared to placebo. However, this did vary as the CD4+ cell count increased. A patient's ability to suppress the virus was increasingly better the greater their CD4+ cell count, as one might expect. This trend is something that has been seen in pretty much all of our treatment-experienced protocols.
One of the most interesting things, I think, about this medication is that its adverse event profile seems to be very good, although the total exposure time to maraviroc versus placebo was in fact different -- almost three times longer in the maraviroc-treated patients. The proportion of patients having any kind of treatment emergent adverse events leading to discontinuation of therapy, serious adverse events, category C new AIDS events or malignancies, was really no different between the maraviroc-treated patients and those receiving placebo.
One concern, of course, about this class of agents has been what effect it may have on the liver. As one can see from the above slide, the proportion of patients in the maraviroc arms compared to the placebo arm was really no different for both grade 3 and grade 4 increases in AST [aspartate aminotransferase], ALT [alanine aminotransferase] or total bilirubin, indicating really no significant signal of any kind of hepatic toxicity with this agent.
In terms of patient-reported adverse events such as diarrhea, nausea, fatigue and headache, the most common events that usually occur in clinical trials with antiretroviral agents, there were really no differences between those patients receiving maraviroc and receiving placebo. The things that did stand out that were more commonly associated with maraviroc treatment were, in fact, upper respiratory tract infection, cough and nasal pharyngitis.
One of the hypotheses of why this occurred this way was simply that maraviroc patients were on treatment longer, so the opportunity for them to develop a seasonal URI [upper respiratory infection] was greater than for those patients who were in the placebo arm who stopped medication more quickly.
In summary, the MOTIVATE 1 and 2 studies showed us that maraviroc was an effective agent when added to an optimized background regimen compared to placebo -- it suppressed viral load by almost an additional log, almost doubled CD4+ cell count increases and was associated with few, if any, significant adverse events, either patient reported or laboratory events. It has a very good tolerance and toxicity profile.
A second CCR5 antagonist is also in clinical development. A medication called vicriviroc, being developed in treatment-experienced patients, has been shown in a phase 2b clinical trial to have significant antiviral activity.6 Patients who were triple-class experienced with nucleosides, non-nucleosides and protease inhibitors, and were also determined to be CCR5 tropic, in terms of viral tropism, were randomized to an optimized background regimen along with vicriviroc dosed at 20 mg once a day, vicriviroc dosed at 30 mg once a day or a placebo.
Of note: All patients' optimized background regimen had to contain a ritonavir [RTV, Norvir]-boosted PI [protease inhibitor] because of the boosting effect that ritonavir has on vicriviroc that allows for a lower dosage to be used on a once-a-day basis.
At 48 weeks of follow-up we see a significant decrease in viral load in the two vicriviroc arms of approximately 1.75/1.77 logs compared to baseline, which is almost an additional one-log increase over those patients who were receiving placebo.
The proportion of patients who had viral loads of less than 50 copies/mL at 48 weeks was 56% in the 30-mg vicriviroc arm and 53% in the 20-mg vicriviroc arm, compared to only 14% in those patients that received placebo -- showing a more than tripling effect in terms of the addition of vicriviroc to an optimized background medication.
There are really no significant clinical differences in adverse events seen between vicriviroc and placebo, and really no difference in terms of laboratory abnormalities, as well.
This was a small study, containing about 60 patients per arm, and therefore the phase 3 trial of this medication is to be done, and will be done in comparison to maraviroc, the only agent in this class that has been approved, as we saw before.
As one might expect, perhaps one of the best places in which to use CCR5 antagonists is where that type of virus, an R5-tropic virus, is most common -- and that is in patients who are naive to therapy.23 The MERIT study is a trial that is still ongoing, but actually compared maraviroc plus zidovudine [AZT, Retrovir] plus lamivudine [3TC, Epivir] to efavirenz [EFV, Sustiva, Stocrin] plus zidovudine/lamivudine [AZT/3TC, Combivir] in treatment-naive patients. All these patients were determined to have R5-tropic virus at screening into the trial, and were followed in this very stringent, non-inferiority-based study, to see whether the maraviroc arm was in fact not inferior to the efavirenz-containing arm.
This study was stratified not only by whether the baseline HIV RNA was above or below 100,000 copies/mL, but also by where the patient was treated -- in the Northern or Southern Hemisphere. We'll talk about that in just a minute.
In terms of the primary endpoint in the study, looking at the proportion of patients that had viral loads of less than 400 copies/mL at 48 weeks, there was really no significant difference. In fact, the two drugs were considered to be non-inferior, with 73% of patients in the efavirenz arm versus 71% in the maraviroc arm having well-suppressed virus at 48 weeks.
However, when one looked at the proportion of patients who had less than 50 copies/mL of virus at 48 weeks, this turned out to be 69% with efavirenz and 65% with maraviroc. This comparison did not reach non-inferiority and, in fact, it missed it by an approximately 0.9 percentage points difference. Therefore, this trial did not prove that maraviroc was non-inferior to efavirenz using a primary endpoint of less than 50 copies/mL at one-year follow-up.
In this study, it was more likely that patients in the efavirenz arm were discontinuing therapy due to an adverse event (13%) versus a lack of efficacy (only 4.2%). However, the opposite was seen with maraviroc. The patients in the maraviroc arm were more likely to discontinue therapy because of lack of efficacy (about 12%) versus discontinuation due to an adverse event (about 4%).
What we see here is that there's a difference in efficacy, as well as a difference in terms of adverse events. An interesting thing in the study was that when one looked at the proportion of patients who had viral loads of less than 50 copies/mL at 48 weeks, if a patient's baseline viral load was less than 100,000 copies/mL, there was really no difference between the efavirenz arm and the maraviroc arm. However, there was evidence of a drop-off in response rate with maraviroc at 48 weeks if a patient's viral load was greater than 100,000 copies/mL at baseline: 67% in the efavirenz arm versus 60% in the maraviroc arm.
Some of this may be due to the type of virus a patient had. In addition to the viral load stratification of above and below 100,000 copies/mL, these patients were also stratified by whether they lived in the Northern or Southern Hemisphere. This was done primarily because almost all of the patients enrolled in the study in areas such as North America, Western Europe, Australia and Argentina have clade B virus. However, in South Africa, one of the largest enrolling centers in the Southern Hemisphere, patients primarily have type C, or clade C, virus.
The reason the stratification occurred, therefore, was because it was not known whether the difference in clade would be responsible for differences in response rate. Whether this did have an effect on this trial has yet to be clearly understood.
When looking at the adverse event analysis, in terms of the MERIT study, there was a slightly increased amount of grade 3 and grade 4 adverse events associated with efavirenz, as well as more significant serious adverse events, increased category C events and more malignancies.
One important analysis that was done later in this study of the MERIT population looked at baseline tropism. While all patients coming into the study had to have R5-tropic virus at screening, approximately 3.5% of these patients did in fact not have R5-tropic virus at baseline -- meaning that there was a shift in viral tropism between the screening sample and the baseline sample.34 When one looks at patients who had R5-tropic virus, both at screening and at baseline, the difference in terms of response rate was actually really no different between the efavirenz and maraviroc arms at 48 weeks. However, if one looks at those patients who switched, that 3.5% of patients who had R5-tropic virus at screening but had switched to X4-containing virus at baseline, then the response rate for both arms was, in fact, very different: Only 55% of patients responded in the efavirenz arm, but an even smaller number, only 7% of patients, responded with a viral load of less than 50 copies/mL in the maraviroc arm, indicating that this change in tropism had a much greater deleterious effect in the maraviroc arm versus the efavirenz arm -- again, as one might expect.
It has been hypothesized that, if the new enhanced sensitivity assay had been used in this study, those patients would have been screened out and the results may have been very different in terms of non-inferiority.
One thing we also learned from the MERIT study was to get a really good look at the kind of effect maraviroc may have on lipid levels. As one can see in the above slide, increases in total cholesterol and LDL [low-density lipoprotein] cholesterol -- as demonstrated before in other trials with efavirenz -- were higher with efavirenz compared to with maraviroc.35 In fact, between baseline and week 48, there was really no significant difference in total cholesterol, HDL [high-density lipoprotein] cholesterol, LDL cholesterol or triglycerides across the board with maraviroc, indicating that this drug seems to have very little, if any, effect on lipid levels whatsoever.
Chemokine coreceptors do in fact play an important role in the early steps of HIV infection.1 This makes for a very useful target in the area of HIV therapeutics, in terms of interfering with the ability of HIV to initially infect a cell.
Viral coreceptor tropism evolves over the course of HIV infection and is associated with -- though it may or may not be caused by -- a decrease in CD4+ cell count and treatment experience.16
A tropism assay, which has now been clinically validated, is available. It can detect with great sensitivity a patient's viral tropism,25 which is important to know when choosing whether we want to use a CCR5 antagonist.
Maraviroc is the first CCR5 antagonist approved in the United States. It has demonstrated therapeutic activity, and also increases the CD4+ cell count, in treatment-experienced patients.22 Whether it can be used in treatment-naive patients still remains a question to be answered once we have more data over time.
Vicriviroc is a CCR5 antagonist currently in development, which is being studied primarily in patients who are treatment experienced. We await the results of a phase 3 trial comparing it to our first licensed agent from this class, maraviroc.36
This is where I'll end. I hope you were able to learn something new from this presentation, and will be able to use this information to treat your patients better.
I'll now answer some questions that have been collected by TheBodyPRO.com involving viral tropism and the use of CCR5 antagonists.
Question: Has anyone who was treated with a CCR5 antagonist -- either maraviroc or, through a clinical trial, vicriviroc -- developed West Nile virus infection or the severe complications associated with it?
In other words: Does the use of CCR5 antagonists prevent the immune system from mounting an effective defense against West Nile virus infection and its complications?
First, let me just expand a little bit on my comments about the association between patients who are known to be CCR5 homozygotes for the deleted gene -- meaning, they have no CCR5 molecules on the surface of their T cells or other immune cells, such as macrophages -- and West Nile virus. I have looked at the literature and I found less than five case reports of patients who are homozygous genetically for Δ32, who have West Nile and who have developed a more significant neurologic disease associated with it -- which is considered to be a more serious problem when coupled with West Nile virus infection.21
To my knowledge, no patient in a clinical trial of either maraviroc or vicriviroc, or anyone taking maraviroc in clinical practice, has developed West Nile or any serious complications from it.
This is probably because, while a patient on maraviroc is somewhat similar to a patient who is a CCR5 Δ32 homozygote, they are not exactly alike. It's likely that patients on maraviroc still have some expression of CCR5 on some of their immune cells. As good as maraviroc or vicriviroc could ever be, they cannot, in fact, completely block all CCR5 molecules on the surface of all CD4+ cells, so there is still the ability for these immune cells to use that coreceptor in a way that immune defenses could be continued. That's my hypothesis about it, anyway. Clinically, I do not know of any increase in West Nile virus infection with these two agents.
Question: Is the new enhanced tropism test sensitive enough to more accurately identify patients who may have some X4-tropic virus?
The ability of the assay to detect very low levels of X4-tropic virus has been significantly improved upon -- it can now detect X4-using virus down to 0.3% of the entire viral population.25
Looking at some of the trials in which the older assay was used, we see that it failed to identify some of the patients who had X4-tropic virus. The new enhanced assay has been about 70% effective in identifying X4 virus in those patients.26 This assay, I think, is going to do a much better job at finding the X4 virus, and letting the treating physician know about it.
My concern about it is that it may actually go the other way -- the new assay may be too sensitive. The situation may be similar to what we've seen with minority variant populations of HIV in which the presence of very low levels of NNRTI [non-nucleoside reverse transcriptase inhibitor] resistance mutations does not always predict whether a patient will fail on an NNRTI-based regimen.
Now, we don't know with 100% certainty that this is occurring yet, as this assay has only been available for three months in the United States -- it came out in June of 2008.37
What we do know is that it is doing a very good job of finding very, very low levels of X4, and with that we're going to be able to use agents such as maraviroc and vicriviroc much, much more effectively.
Question: Is there going to be a second clinical trial of maraviroc in treatment-naive patients that uses the more sensitive assay?
One would think, based upon the post-hoc analysis from the MERIT study, in which it was determined that patients switched from R5 at screening to X4 at baseline,34 that a second study would be more effectively done if the new assay where used to exclude patients who have low level X4 virus that wouldn't have been detected in the first trial.
However, I doubt that the companies that are making these agents will want to repeat a study as large as the MERIT trial. The expenditures to do that trial, especially on an international basis, were I'm sure tremendous.
Probably what's going to happen is that maraviroc will continue to be studied in treatment-naive patients, but in a different way from that used in the MERIT study. It will probably be coupled with a more up-to-date or novel regimen -- perhaps with an unboosted protease inhibitor, perhaps boosted with one nucleoside analog or perhaps compared with one of our new second-generation NNRTIs, such as etravirine [TMC125, Intelence].
Of course the enhanced tropism assay will be used. It will, I think, identify a more well-defined population of patients in which to study this kind of agent. So look for that in the future.
Question: Who is the best patient to use a CCR5 antagonist?
The ideal patient would have been infected with HIV recently, since those are the patients with the highest likelihood of having R5-tropic virus, against which this medication works best.
However, the drug has been used most commonly in highly treatment-experienced patients; in fact, it is currently only approved for use in the United States in treatment-experienced patients because they are the ones who actually need brand new agents.
But I have not found its use to be the most beneficial in salvage patients (i.e., those who have very little, if any, kind of medication regimens available to them), as were studied in the MOTIVATE trials.22 This is because, oftentimes, the chances that a salvage patient has an R5-tropic virus are pretty low; it sometimes is less than 30% to 40%.
It would probably be better if this agent were used after the failure of a second regimen; the probability of a patient's virus being R5 tropic is much higher at that point then after the failure of a fifth, sixth or seventh regimen. Also, at that point, a patient usually has already gone through two nucleoside backbones, an NNRTI and a boosted PI. This may be the perfect situation in which to use maraviroc because of the chances of having the right kind of virus present.
I should also mention that the toxicity profile of the drug seems to be very good. Plus, it can be coupled with many other agents, because the drug-drug interactions have been clearly worked out.
In practice, as soon as I do the tropism assay and find out that the patient has R5-tropic virus, that's when I use the medication. Waiting to use the medication and hoping that the assay is going to continue to show the same result could be a big problem.
- Moore JP, Doms RW. The entry of entry inhibitors: a fusion of science and medicine. Proc Natl Acad Sci U S A. September 16, 2003;100(19):10598-10602.
- Food and Drug Administration. Fuzeon (T-20) approved in the U.S. Rockville, Md: Food and Drug Administration; March 13, 2003.
- Jegede O, Babu J, Di Santo R, McColl DJ, Weber J, Quiñones-Mateu ME. HIV type 1 integrase inhibitors: from basic research to clinical implications. AIDS Rev. July-September 2008;10(3):172-189.
- Stoddart CA, Joshi P, Sloan B, et al. Potent activity of the HIV-1 maturation inhibitor bevirimat in SCID-hu Thy/Liv mice. PLoS ONE. November 28, 2007;2(11):e1251.
- Food and Drug Administration. Approval of maraviroc. Rockville, Md: Food and Drug Administration; August 6, 2007.
- Zingman B, Suleiman J, DeJesus E, et al. Vicriviroc, a next generation CCR5 antagonist, exhibits potent, sustained suppression of viral replication in treatment-experienced adults: VICTOR-E1 48-week results. In: Program and abstracts of the 15th Conference on Retroviruses and Opportunistic Infections; February 3-6, 2008; Boston, Mass. Abstract 39LB.
- Jacobson JM, Saag MS, Thompson MA, et al. Antiviral activity of single-dose PRO 140, a CCR5 monoclonal antibody, in HIV-infected adults. J Infect Dis. November 1, 2008;198(9):1345-1352.
- Moyle G, DeJesus E, Boffito M, et al. CXCR4 Antagonism: proof of activity with AMD11070. In: Program and abstracts of the 14th Conference on Retroviruses and Opportunistic Infections; February 25-28, 2007; Los Angeles, Calif. Abstract 511.
View poster: Download PDF
- Zhang L, He T, Huang Y, et al. Chemokine coreceptor usage by diverse primary isolates of human immunodeficiency virus type 1. J Virol. November 1998;72(11):9307-9312.
- McNicholl JM, Smith DK, Qari SH, Hodge T. Host genes and HIV: the role of the chemokine receptor gene CCR5 and its allele (Δ32 CCR5). Emerg Infect Dis. July-September 1997;3(3):261-271.
- Eshleman SH, Husnik M, Hudelson S, et al. Antiretroviral drug resistance, HIV-1 tropism, and HIV-1 subtype among men who have sex with men with recent HIV-1 infection. AIDS. May 31, 2007;21(9):1165-1174.
- Poveda E, Briz V, de Mendoza C, et al. Prevalence of X4 tropic HIV-1 variants in patients with differences in disease stage and exposure to antiretroviral therapy. J Med Virol. August 2007;79(8):1040-1046.
- Libert F, Cochaux P, Beckman G, et al. The [delta]CCR5 mutation conferring protection against HIV-1 in Caucasian populations has a single and recent origin in Northeastern Europe. Hum Mol Genet. March 1, 1998;7(3):399-406.
- Stephens JC, Reich DE, Goldstein DB, et al. Dating the origin of the CCR5-Delta32 AIDS-resistance allele by the coalescence of haplotypes. Am J Hum Genet. June 1998;62(6):1507-1515.
- Galvani AP, Slatkin M. Evaluating plague and smallpox as historical selective pressures for the CCR5-Δ32 HIV-resistance allele. Proc Natl Acad Sci U S A. December 9, 2003;100(25):15276-15279.
- Huang Y, Paxton WA, Wolinsky SM, et al. The role of a mutant CCR5 allele in HIV-1 transmission and disease progression. Nat Med. November 1996;2(11):1240-1243.
- Eugen-Olsen J, Iversen AKN, Garred P, et al. Heterozygosity for a deletion in the CKR-5 gene leads to prolonged AIDS-free survival and slower CD4 T-cell decline in a cohort of HIV-seropositive individuals. AIDS. March 11, 1997;11(3):305-310.
- Michael NL, Louie LG, Rohrbaugh AL, et al. The role of CCR5 and CCR2 polymorphisms in HIV-1 transmission and disease progression. Nat Med. October 1997;3(10):1160-1162.
- Dean M, Carrington M, Winkler C, et al. Genetic restriction of HIV-1 infection and progression to AIDS by a deletion allele of the CKR5 structural gene. Science. September 27, 1996;273(5283):1856-1862.
- Oh D-Y, Jessen H, Kücherer C, et al. CCR5Δ32 genotypes in a German HIV-1 seroconverter cohort and report of HIV-1 infection in a CCR5Δ32 homozygous individual. PLoS ONE. July 23, 2008;3(7):e2747.
- Glass WG, McDermott DH, Lim JK, et al. CCR5 deficiency increases risk of symptomatic West Nile virus infection. J Exp Med. January 23, 2006;203(1):35-40.
- Hardy D, Reynes J, Konourina I, et al. Efficacy and safety of maraviroc plus optimized background therapy in treatment-experienced patients infected with CCR5-tropic HIV-1: 48-week combined analysis of the MOTIVATE studies. In: Program and abstracts of the 15th Conference on Retroviruses and Opportunistic Infections; February 3-6, 2008; Boston, Mass. Abstract 792.
View poster: [Download PDF](https://img.thebody.com/confs/retro2008/slides/792 Hardy poster.pdf)
- Saag M, Ive P, Heera J, et al. A multicenter, randomized, double-blind, comparative trial of a novel CCR5 antagonist, maraviroc versus efavirenz, both in combination with Combivir (zidovudine [ZDV]/lamivudine [3TC]), for the treatment of antiretroviral naive patients infected with R5 HIV 1: week 48 results of the MERIT study. In: Program and abstracts of the 4th International AIDS Society Conference on HIV Pathogenesis, Treatment and Prevention; July 22-25, 2007; Sydney, Australia. Abstract WESS104.
View slides: Download PowerPoint
- Whitcomb JM, Huang W, Fransen S, et al. Development and characterization of a novel single-cycle recombinant-virus assay to determine human immunodeficiency virus type 1 coreceptor tropism. Antimicrob Agents Chemother. February 2007;51(2):566-575.
- Reeves JD, Han D, Liu Y, et al. Enhancements to the Trofile HIV coreceptor tropism assay enable reliable detection of CXCR4-using subpopulations at less than 1%. In: Program and abstracts of the 47th Interscience Conference on Antimicrobial Agents and Chemotherapy; September 17-20, 2007; Chicago, Ill. Abstract H-1026.
- Reeves J, Han D, Wilkin T, et al. An enhanced version of the Trofile HIV co-receptor tropism assay predicts emergence of CXCR4 use in ACTG5211 vicriviroc trial samples. In: Program and abstracts of the 15th Conference on Retroviruses and Opportunistic Infections; February 3-6, 2008; Boston, Mass. Abstract 869.
View poster: [Download PDF](https://img.thebody.com/confs/retro2008/slides/869 Reeves poster.pdf)
- Brumme ZL, Goodrich J, Mayer HB, et al. Molecular and clinical epidemiology of CXCR4-using HIV-1 in a large population of antiretroviral-naive individuals. J Infect Dis. August 1, 2005;192(3):466-474.
- Moyle GJ, Wildfire A, Mandalia S, et al. Epidemiology and predictive factors for chemokine receptor use in HIV-1 infection. J Infect Dis. March 15, 2005;191(6):866-872.
- Demarest J, Bonny T, Vavro C, et al. HIV-1 co-receptor tropism in treatment naive and experienced subjects. In: Program and abstracts of the 44th Interscience Conference on Antimicrobial Agents and Chemotherapy; October 30 - November 2, 2004; Washington, D.C. Abstract H-1136.
- Waters LJ, Mandalia S, Wildfire A, Gazzard B, Moyle G. HIV co-receptor tropism in treatment-naive patients: impact on CD4 decline and subsequent response to HAART. In: Program and abstracts of the 46th Interscience Conference on Antimicrobial Agents and Chemotherapy; September 27-30, 2006; San Francisco, Calif. Abstract H-1667.
View slides: Download PowerPoint
- Paxinos EE, Fransen S, Huang W, Wrin T, Whitcomb JM, Petropoulos CJ. Measuring HIV-1 co-receptor tropism using a recombinant virus assay. In: Program and abstracts of the 42nd Interscience Conference on Antimicrobial Agents and Chemotherapy; September 27-30, 2002; San Diego, Calif. Abstract H-2040.
- Coakley E, Benhamida J, Chappey C, et al. An evaluation of tropism profiles and other characteristics among 3988 individuals screened from A4001026, A4001027 (MOTIVATE 1) and A4001028 (MOTIVATE 2) studies for maraviroc. In: Program and abstracts of the 2nd International Workshop on Targeting HIV Entry; October 20-21, 2006; Boston, Mass. Abstract 8.
- Melby T, Sista P, DeMasi R, et al. Characterization of envelope glycoprotein gp41 genotype and phenotypic susceptibility to enfuvirtide at baseline and on treatment in the phase III clinical trials TORO-1 and TORO-2. AIDS Res Hum Retroviruses. May 2006;22(5):375-385.
- Heera J, Saag M, Ive P, et al. Virological correlates associated with treatment failure at week 48 in the phase 3 study of maraviroc in treatment-naive patients. In: Program and abstracts of the 15th Conference on Retroviruses and Opportunistic Infections; February 3-6, 2008; Boston, Mass. Abstract 40LB.
- DeJesus E, Walmsley S, Cohen C, et al. Fasted lipid changes after administration of maraviroc or efavirenz in combination with zidovudine and lamivudine for 48 weeks to treatment-naive HIV-infected patients. In: Program and abstracts of the 15th Conference on Retroviruses and Opportunistic Infections; February 3-6, 2008; Boston, Mass. Abstract 929.
View poster: Download PDF
- Schering-Plough initiates phase III studies with vicriviroc in treatment-experienced HIV patients. Kenilworth, NJ: Schering-Plough; September 17, 2008.
- Monogram biosciences announces immediate availability of enhanced sensitivity Trofile(TM) HIV tropism assay. South San Francisco, Calif: Monogram Biosciences; June 5, 2008.
Copyright © 2008 Body Health Resources Corporation. All rights reserved.
Part II: Case Studies
Note: This CME/CE activity expired on Oct. 14, 2009. For a list of currently available activities, click here.
How can HIV therapy that makes use of CCR5 antagonists and tropism testing be applied in everyday patient case management? Let's go through a couple of cases.
Our first patient is a 37-year-old male with an extensive history of antiretroviral therapy beginning in 1995.
His past antiretroviral agents included all the NRTIs [nucleoside reverse transcriptase inhibitors] except for zalcitabine [ddC, Hivid], all the NNRTIs [non-nucleoside reverse transcriptase inhibitors] except for delavirdine [DLV, Rescriptor] and all the PIs [protease inhibitors] except for fosamprenavir [FPV, Lexiva, Telzir] and full-dose ritonavir [RTV, Norvir].
He has a history of buffalo hump, which occurred while he was taking indinavir [IDV, Crixivan]. It was removed by liposuction.
In addition, he participated in the RESIST 1 trial between 2003 and 2005.1 At that time, he received an antiretroviral regimen consisting of ritonavir-boosted tipranavir [TPV, Aptivus], the fixed-dose combination of tenofovir/emtricitabine [TDF/FTC, Truvada], efavirenz [EFV, Sustiva, Stocrin], didanosine [ddI, Videx] and enfuvirtide [T-20, Fuzeon].
During the time that he was in the study, his HIV RNA decreased from 510,000 copies/mL to 5,200 copies/mL and his CD4+ cell count increased from 75 cells/mm3 to 120 cells/mm3. However, he never reached a viral load of less than 50 copies/mL.
He continued on this regimen for approximately 2.5 years, after which he discontinued the enfuvirtide, because of the difficulty he had in taking it due to the lack of any available injection sites.
The patient was also a participant in the MOTIVATE 1 trial, which evaluated maraviroc [MVC, Selzentry, Celsentri] versus placebo in treatment-experienced patients.2
In this study, he was -- as we later found out -- randomized to the placebo arm. The optimized background regimen that was selected for him contained ritonavir-boosted saquinavir [SQV, Invirase], combination tenofovir/emtricitabine, didanosine and efavirenz.
Although ritonavir-boosted indinavir was predicted to have full activity against his virus by baseline resistance testing, the patient initially refused to take this medication due to the lipodystrophy he experienced while on it in the past.
After eight weeks in the study, the patient's viral load had changed very little, going from 1,162,500 copies/mL to just 734,000 copies/mL. Because this was a less-than-half-log decrease, the patient's therapy was considered to be a virologic failure and he was allowed to switch over to open-label maraviroc at 150 mg twice a day. At this point, he also accepted ritonavir-boosted indinavir, which genotypically and phenotypically looked to have the best activity against his virus, and he continued on tenofovir/emtricitabine plus didanosine.
On this regimen, he achieved a viral load of less than 50 copies/mL by week 24. His CD4+ cell count increased to 155 cells/mm3, 22% of total lymphocytes, and he maintained this for the next six months.
However, he soon developed bilateral hip pain. An orthopedic exam found advanced aseptic necrosis of the right hip. He underwent right total hip replacement surgery for this problem.
At this time, do you think we should consider this new complication to be a good reason to change the patient's therapy?
- Not sure
Keep in mind that the patient is, in fact, undetectable on his current regimen of maraviroc, ritonavir-boosted indinavir, combination tenofovir/emtricitabine and didanosine. However, the aseptic necrosis of his right hip is a significant complication that may or may not be related to his indinavir therapy.3
Because the patient is not experiencing virologic failure, there are many ways in which the situation could be handled. In fact, in the more than 10 years that he has been taking antiretroviral medications, this is the first time that his HIV has been suppressed to less than 50 copies/mL. But, because he only reluctantly agreed to take indinavir (due to his concerns about developing lipodystrophy) and because the aseptic necrosis of his right hip may be related to the use of indinavir, we are concerned that the patient's adherence to his regimen may suffer. In fact, he's said that this may be a problem. So there are strong reasons for and against changing his regimen.
To answer my question: We do not change the patient's regimen, because our first priority is to maintain his undetectable viral load. We convince the patient to remain on his current regimen so that he will be able to maintain his HIV RNA of less than 50 copies/mL. However, over the next several weeks, the patient's HIV RNA increases -- initially to 580 copies/mL and then, on repeat testing, up to 1,280 copies/mL. We suspect that the patient's confidence in his antiretroviral therapy regimen is waning, due to his concern about hip surgery on his right hip, and the possibility of the same on his left hip.
We determine that a change in his regimen is in fact indicated. Because the patient's viral load is now detectable, we order a new genotype/phenotype, as well as a tropism test, so that we can access his viral characteristics.
The results of the tropism test indicate that the patient's virus, which initially had been R5 tropic before he enrolled in the MOTIVATE study in 2005, is still R5 tropic. This indicates that maraviroc would still be a useful agent against this patient's virus.
The patient's genotype/phenotype is shown above. As you can see, on this genotype/phenotype, there are few choices for therapy from the three classes of medications that were available at the time. We see that there are multiple mutations in the reverse transcriptase gene, affecting both nucleosides and non-nucleosides, and multiple mutations within the protease gene.
Only one medication, tenofovir, demonstrates any activity based upon phenotype. We are a bit concerned, however, in reading this test, because based upon his genotype the patient has mutations at positions 41, 210 and 215, which genotypically predict resistance to tenofovir.
The fact that he has an additional thymidine analog mutation, a TAM, at position 67, is also of concern. However, the phenotype is saying that there's not only susceptibility, but perhaps even hypersusceptibility, of this patient's virus to tenofovir. So this may be one medication that we could continue to use based upon what other drugs we use with it.
In addition, we see that according to this particular resistance test, because the patient has five NNRTI-associated mutations, all first-generation NNRTIs would no longer be effective against his virus. What effect a new medication like etravirine [TMC125, Intelence] will have against this virus is not shown on this particular genotype/phenotype, but we will pick it up in just a minute.
As we can see from the bottom of the genotype/phenotype readout, he has 13 protease inhibitor mutations, with many primary mutations, particularly at sites 33, 47, 54 and 90. This, of course, presents a rather concerning picture because every protease inhibitor mutation listed there has been shown to be associated with high-level resistance. Some of the genotypes are showing that there may be some susceptibility to boosted and unboosted fosamprenavir, but there is no other indication of susceptibility to this class whatsoever.
Based upon this particular phenotype/genotype and the fact that boosted PIs have been a cornerstone of many of our regimens for highly treatment-experienced people, should we include a boosted PI in this patient's regimen?
- Not sure
Even though there is high-level resistance here, using a medication in this class may have some partial benefit, particularly in coordination with other medications. We see that genotypically there is some activity with fosamprenavir, although phenotypically there is none, and even though our newest protease inhibitor, darunavir [TMC114, Prezista], is shown to have a fold change of over 100, greater than its upper cutoff. So it's unclear whether continuing a boosted PI would be of any help.
The other situation we're dealing with, of course, is the fact that this patient is currently still on ritonavir-boosted indinavir. As our genotype/phenotype shows, both genotypically and phenotypically, there is no susceptibility to this medication. In addition, the patient had a significant adverse event -- the right hip aseptic necrosis -- that might be due to this medication. I can see good reasons why continuing this class of medication probably is not going to be very effective and, in fact, may only be fraught with more toxicity for the patient. But let's still consider the next question.
If we were going to include a PI in the patient's regimen, what should it be?
- Ritonavir-boosted atazanavir [ATV, Reyataz]
- Ritonavir-boosted darunavir
- Lopinavir/ritonavir [LPV/r, Kaletra]
- Ritonavir-boosted saquinavir
- Ritonavir-boosted tipranavir
This is a really difficult question, because none of the PIs on this phenotype/genotype are shown to have significantly good activity.
The best way for us to approach this would be to include one that may be close, in terms of its upper cutoff. But we really don't see that there's great activity with any of the PIs. So it is tough to say which, if any, boosted PI may be helpful.
Should we switch the nucleoside component of this patient's regimen?
- Yes, I would drop didanosine.
- Yes, I would drop tenofovir/emtricitabine.
- Yes, I would not use NRTIs in his new regimen.
The patient is currently taking the fixed-dose combination of tenofovir plus emtricitabine. As you can see from the above resistance test, his virus is susceptible to tenofovir by phenotypic testing. Probably the best thing to do here -- because we have some glimmer of activity with tenofovir -- is to continue him on tenofovir/emtricitabine. The emtricitabine will be continued not so much because it's going to have any significant activity against his virus, but primarily because the mutation M184V conferred by emtricitabine could be helpful in maintaining susceptibility to the tenofovir. The M184 mutation that he has may be suppressing some of the action of the mutations on tenofovir -- which is why the genotype is showing resistance, while the phenotype, which can show the interactions between mutations, shows sensitivity.
In terms of continuing didanosine, this really looks pretty ineffective. This medication has no activity and continuing it may in fact be only fraught with more problems.
How about new drug classes? Would we want to include raltegravir [MK-0518, Isentress], the first FDA [U.S. Food and Drug Administration]-approved integrase inhibitor, in this patient's regimen?
- Not sure
The answer has to be an overwhelming yes because of the lack of good options from among the initial three classes that we used (i.e., nucleosides, non-nucleosides and protease inhibitors). Raltegravir can be assumed to be highly active against this patient's virus because he had never received an integrase inhibitor before. Therefore, I think including it would definitely be a good idea.
Should we include etravirine in this patient's regimen?
Although the patient's older genotype/phenotype did not include new drugs such as etravirine, it did indicate that this patient has at least three NNRTI mutations, which are now considered to be resistance-associated mutations for this drug.
Let's look at some new information that just came to light regarding resistance and etravirine. At the International HIV Drug Resistance Workshop, in the summer of 2008, the clinical cutoffs for the phenotypic susceptibility of etravirine were established.4 An additional four etravirine mutations were identified, increasing the number from 13 up to 17.5 The new mutations occurred at positions 101 (specifically the K101H mutation, which involved a new substitution at this position), 136, 170 and 230. Most importantly, a weighted scoring system was developed to help us understand that of the 17 mutations that affect etravirine not all are equal.4
We know, for example, that the mutations that occur at position 181 -- particularly Y181I and Y181V -- have more of an effect against etravirine than other mutations, such as G190A. Because Y181I and Y181V are considered to be significant mutations against etravirine, they carry a weight of 3, whereas G190A is given a weight of 1. So, this is an instance in which the weighted scoring system has come in handy.
When we add up all the mutations that occur in this patient's particular genotype -- including Y181C (given a weight of 2.5), K101H (given a weight of 1) and G190A (given a weight of 1) -- we get a score of 4.5.
Based upon the results from the DUET 1 and 2 studies,6,7 we see in the above slide that patients who have an etravirine genotypic weighted score of 4.5, have a reduced response rate of 38% or less to etravirine, indicating that etravirine is not going to be too promising in this patient.
Should we continue the maraviroc in this patient's new regimen?
The patient has been on maraviroc for approximately three years now. It continued to be effective until the patient, perhaps through his own lack of good adherence, had low-level viremia of around 1,500 copies/mL. However, testing with the new enhanced sensitivity test, which can detect the presence of X4 virus down to 0.3%, shows that the majority of the patient's virus remains R5 tropic.
With an assay that has 99.7% sensitivity, we can feel sure that this patient's virus is still susceptible to maraviroc, and therefore continuing it in his new regimen would be a good idea.
For his new regimen, we decide to give the patient maraviroc, darunavir and etravirine, based upon the good results that this combination demonstrated in the DUET 1 and DUET 2 studies,6,7 although we're aware that darunavir and etravirine will not have full activity given the patient's resistance profile. We are a bit concerned about not having some more potent agents, which is why we'll also be giving him raltegravir. We decide to also continue the patient on tenofovir/emtricitabine.
On this regimen, the patient's HIV RNA again falls below 50 copies/mL and his CD4+ cell count slowly rises to over 280 cells/mm3, 28% of total lymphocytes, over the next eight months.
His left hip pain stabilizes and an MRI shows no further progression. He continues to tolerate this antiretroviral regimen well. Our selection of two active drugs -- raltegravir based upon the assumption of susceptibility and maraviroc based upon demonstrated susceptibility -- plus tenofovir (to which the patient had full phenotypic susceptibility), darunavir and etravirine seems to have worked. Our ability to get the patient's viral load to less than 50 copies/mL and get him off of what we considered to be an offending protease inhibitor (i.e., indinavir) has been associated with improvement of not only his CD4+ cell count, but also his hip, which had caused him to show poor adherence to his regimen. We will continue to follow this patient over time and assess whether we need to maintain him on all these particular agents. If side effects occur in the future, there may be cause to simplify this patient's regimen, perhaps by discontinuing etravirine or darunavir.
In this second case, we have a 45-year-old man who was diagnosed with HIV in 1994, when he first presented to his doctor with cutaneous Kaposi's sarcoma.
At that time, his CD4+ cell count was 360 cells/mm3. Unfortunately, because HIV RNA testing was unavailable in 1994, we don't have an initial HIV RNA to work with.
His past medical history included mild hypertension, which was well controlled with diuretics. He had a family history of both diabetes and cardiovascular disease.
His antiretroviral history began in 1994 with zidovudine [AZT, Retrovir] monotherapy. He took this because the Kaposi's sarcoma diagnosis also gave him a diagnosis of AIDS and, for that reason, zidovudine was recommended. However, he had to stop the zidovudine after about six months due to progressive anemia, as well as nausea.
He then went on didanosine monotherapy -- didanosine was the second HIV agent licensed in the United States in the early '90s. He tolerated the didanosine monotherapy for nine months, but he then developed chronic pancreatitis, with elevated pancreatic enzymes and abdominal pain.
He discontinued the didanosine then because his Kaposi's sarcoma had been quiescent, there were no new lesions and his CD4+ cell count was stable at 360 cells/mm3. Again, viral load testing was not available at that time.
Starting in 1996, he began a series of various regimens. Of course, this was very typical of the early HAART [highly active antiretroviral therapy] era: When new medications became available, they were oftentimes added sequentially, and usually not in very good order, since we had no understanding at that time what medication sequencing would be most effective.
During this period of time, his first HAART regimen was a combination of stavudine [d4T, Zerit], lamivudine [3TC, Epivir] and saquinavir. That was followed by a single substitution of the saquinavir for nelfinavir [NFV, Viracept]. Next, the stavudine was switched to abacavir [ABC, Ziagen], lamivudine was maintained and he began taking efavirenz.
Finally, he was switched back to stavudine and lamivudine, with the first fixed-dose combination boosted-PI lopinavir/ritonavir. When tenofovir [TDF, Viread] became available, as well as fosamprenavir, he switched from stavudine to tenofovir, maintained the lamivudine, maintained the lopinavir/ritonavir and added fosamprenavir.
Let's review what kinds of intolerance this patient had to his antiretrovirals. As mentioned, he was intolerant to zidovudine due to anemia, intolerant to didanosine due to pancreatitis and while on stavudine he developed peripheral neuropathy. Nelfinavir caused significant diarrhea, as well as significant GI [gastrointestinal] symptoms, including bloating and abdominal cramps, with the dual-boosted PIs of his last regimen.
His HIV RNA had reached less than 400 copies/mL on a few occasions, but had never become less than 50 copies/mL. In terms of his resistance testing over this period of time, his first genotypic assay after failure of the stavudine, lamivudine and saquinavir regimen showed mutations in the reverse transcriptase gene at positions 41, 74, 184 and 215, as one might expect, as well as in the protease gene at positions 10, 63 and 90 -- again, as one might expect in response to the saquinavir.
His second genotypic test -- after failure of the abacavir, lamivudine and efavirenz -- showed a continued increase in the number of mutations in the RT [reverse transcriptase] gene, including at positions 41, 74, 101, K103N, Y181C, M184V, 215 and 219. He also developed more mutations in the PR [protease] gene, most likely related to his previous use of nelfinavir.
During this time, his CD4+ cell count rose and fell, and had reached a nadir of 240 cells/mm3 at one point.
So now it's 2008. The patient is currently taking a regimen of tenofovir, lamivudine and lopinavir/ritonavir. He has persistent low-level viremia, between 1,500 copies/mL and 2,500 copies/mL. His current CD4+ cell count is between 300 cells/mm3 and 350 cells/mm3.
His other medical problems have progressed, as well. His hypertension has now become poorly controlled with an ACE [angiotensin-converting enzyme] inhibitor, a diuretic combination and a beta blocker. A test of his fasting glucose finds it to be over 180 mg/dL, indicating pre-diabetic abnormalities.
His serum creatinine, which at baseline had been between 1.0 mg/dL and 1.4 mg/dL, is now 1.9 mg/dL and is starting to be of concern. The patient has read about new medications being available, particularly in new drug classes, and he wants to consider a new regimen, because he knows that persistent viremia, although of a low level, is not good for him.
We get a genotype/phenotype (shown below). It demonstrates some good news. Even though he has mutations in the reverse transcriptase gene at 41, 74, 184V, 215 and 219, there's still some activity with zidovudine, stavudine and tenofovir.
We know that his tolerance of stavudine and zidovudine has not been good in the past. Even though today's doses of zidovudine (300 mg twice a day) are not as high as those that have been used (up to 1,200 mg a day), which may have been part of the reason why he could not tolerate it previously, we're concerned about using either one of those medications. The only medication that may still be of use to him is the tenofovir.
With respect to the NNRTI class, he has the mutations K101P and K103S. The K103S mutation is an intermediate for the K103N mutation. All first-generation NNRTIs show high-level resistance. We'll have to see what we can count up, in terms of mutations for etravirine.
Finally, with respect to the protease inhibitors, he has 10 protease inhibitor mutations, with particularly major mutations at sites 33, 54, 84 and 90. While he has high-level resistance to many of the protease inhibitors, he has some intermediate susceptibility to darunavir, as indicated by a fold change on the phenotype of 17 -- falling above the lower cutoff but below the upper cutoff of 40.
Let's look at the patient's viral tropism. Although he is treatment experienced, his CD4+ cell count is over 300 cells/mm3, so the possibility that his virus will be R5 tropic is still pretty good. We get a tropism test and find that the majority of his virus is R5 tropic, predicting that maraviroc should be highly active against his virus.
Darunavir and tipranavir have historically had the best susceptibility in situations in which patients have had a lot of treatment experience with boosted PIs.1,8 Looking specifically at these two PIs, we see that the patient has overlapping mutations that confer resistance to both of these drugs, particularly the darunavir resistance mutations at positions 33 and 84 have activity against tipranavir. The mutation at 54V also has a resistance profile against tipranavir.
The patient has two darunavir mutations, three tipranavir mutations and his phenotype does in fact support some activity with darunavir. We find that the phenotypic fold change at 10 is above the upper cutoff at 8 for the drug, indicating that probably there is going to be very little good susceptibility to this agent. So darunavir boosted with ritonavir is probably the best medication we could use from that class here.
Should we use a nucleoside analog or two in this regimen?
The continuation of drugs from this class sometimes may or may not make sense because many highly treatment-experienced patients, such as this individual, have experienced not only resistance, but also side effects to NNRTIs and to many nucleosides. This is where, I think, we're starting to change that paradigm of always using a dual nucleoside backbone in patients who have high treatment experience.
Reviewing the phenotypic information, we see that the patient's virus has susceptibility to tenofovir, zidovudine and stavudine. However, we know that there have been significant side effects with zidovudine and stavudine in the past.
We're a little concerned about the change in his renal function, although we don't know exactly where that's coming from. So the answer to this question could go either way, depending upon how many other agents we have available to us from our current armamentarium.
This brings up a very important question.
How many additional active agents does this patient need in order to get his viral load to less than 50 copies/mL?
- Individualized for patient's viral resistance
Remember that this patient has never had a viral load of less than 50 copies/mL. Therefore, looking at what's available to us, we would predict that maraviroc would be a fully active agent, based upon the tropism test showing R5 virus. We would predict that raltegravir would be a fully active agent, based upon assumed susceptibility -- because he's never been on an integrase inhibitor before. But we don't know about etravirine because there's no clear phenotype with it and we have some concerns about ritonavir-boosted darunavir because of the intermediate resistance the patient has to darunavir.
Let's look at a little bit of data to help us decide whether we need one, two, three or more than three active agents to suppress HIV in a patient with this much treatment experience.
The BENCHMRK study evaluated the use of an optimized background regimen based upon resistance testing, and allowed the use of ritonavir-boosted darunavir or ritonavir-boosted tipranavir in the regimens, and then used placebo or raltegravir.9
Looking at the phenotypic data from this study, we see that as the number of active agents in the background regimen increased from 0 to 1 to 2, there was an increasingly good response in the proportion of patients who had viral loads of less than 50 copies/mL at 24 weeks of treatment, going from 61% to 79% to 87%.
However, the genotypic analysis shows a leveling off at 71% between one and two active agents, indicating that no particular improvement occurred with the addition of more active agents to the background regimen. So, again, a little bit of controversial data there.
Let's also look at the DUET 1 and DUET 2 studies.6,7 All participants had ritonavir-boosted darunavir as part of their optimized background therapy regimen and then added either a placebo or etravirine to that.
In terms of the phenotypic susceptibility score of the background agents, there's a pretty clear topping out between 2 and 3 -- no further improvement occurs in terms of response by adding more than two active agents to the background regimen.
Finally, let's look at the MOTIVATE 1 and MOTIVATE 2 studies, which evaluated the use of either once-a-day maraviroc or twice-a-day maraviroc, as shown on the slide below, compared to placebo in the context of an optimized background regimen.10,11 It should be noted that these regimens could not contain darunavir because of a lack of drug interaction data at the time.
Again, we see the same thing. Focusing on the twice-a-day maraviroc arm, the percentage of patients achieving a viral load of less than 50 copies/mL increased from 29% to 43% to 53% to only a small increase of 58% as the number of agents increased from 0 to 1 to 2 to 3 in the optimized background regimen.
All these clinical trials only allowed one investigational agent. If we were to add multiple agents from new classes together, we may be able to get past this apparent 60% to 70% response rate ceiling we get with these agents individually.
Which regimen should we choose for this patient?
- tenofovir/emtricitabine, darunavir + ritonavir, etravirine, maraviroc
- tenofovir/emtricitabine, darunavir + ritonavir, maraviroc, raltegravir
- tenofovir/emtricitabine, darunavir + ritonavir, etravirine, raltegravir
- tenofovir/emtricitabine, darunavir + ritonavir, etravirine, maraviroc, raltegravir
- Something else
We decided to keep the patient on tenofovir/emtricitabine because of the activity of the tenofovir. We also decided to include ritonavir-boosted darunavir based on the fact that it has some partial activity.
What are we going to add to that? We have what we consider to be full activity with tenofovir and partial activity with boosted darunavir. We could add etravirine plus maraviroc, maraviroc plus raltegravir, etravirine plus raltegravir or all three -- etravirine, maraviroc and raltegravir.
This is a situation in which, while we have the luxury of many new active medications for these highly experienced patients, there has not been a clear indication of how these agents may be used most effectively.
Many physicians are now left to their own devices in this way, because the clinical trial data have really been very few and far between, in terms of suggesting how many new agents we really need.
It was decided that the patient needed to use all the agents (answer D) -- tenofovir/emtricitabine, ritonavir-boosted darunavir, etravirine, maraviroc and raltegravir -- because of the concern that there may be some decreased response with etravirine.
We did, in fact, choose correctly, because the patient's viral load dropped to less than 50 copies/mL at six weeks. His CD4+ cell count, a few weeks later, increased to 420 cells/mm3. However, we encountered an adverse event of concern. The serum creatinine increased to 2.7 from 1.9, and a measured creatinine clearance of 24-hour urine collection showed creatinine clearance to be 48 mL/min.
What do we do next with the tenofovir/emtricitabine?
- Continue tenofovir/emtricitabine once a day
- Continue tenofovir/emtricitabine but decrease the dose to once every other day
- Change tenofovir/emtricitabine to abacavir/lamivudine [ABC/3TC, Epzicom, Kivexa]
- Discontinue tenofovir/emtricitabine
In this case, I think the fact that we were continuing it based upon weak phenotypic data, and because we have now encountered a significant side effect, stopping the medication would probably be best.
I think dropping the dose to every other day would not be a good option because this patient has other issues with his kidneys -- particularly, long-standing hypertension that now indicates diabetes, and that may indicate that he will not do well with another possible renal toxin added to it. Remember that abacavir did not show good activity against his virus on the last genotype/phenotype we had.
We decided to stop the tenofovir/emtricitabine altogether and keep him on ritonavir-boosted darunavir, etravirine, maraviroc and raltegravir. His viral load remains less than 50 copies/mL, his CD4+ cell count increased to 550 cells/mm3, thankfully, his creatinine dropped down to 1.8 and his 24-hour collection shows a creatinine clearance of 80 mL/min.
In this case we were able, through trial and error, to improve on this patient's therapy and suppress his viral load effectively using new agents, plus avert some toxicity associated with old agents and offer him something that could be very promising for the future.
Thanks very much for your attention.
This transcript has been lightly edited for clarity.
- Hicks CB, Cahn P, Cooper DA, et al, on behalf of the RESIST investigator group. Durable efficacy of tipranavir-ritonavir in combination with an optimised background regimen of antiretroviral drugs for treatment-experienced HIV-1-infected patients at 48 weeks in the Randomized Evaluation of Strategic Intervention in multi-drug reSistant patients with Tipranavir (RESIST) studies: an analysis of combined data from two randomised open-label trials. Lancet. August 5, 2006;368(9534):466-475.
- Hardy D, Reynes J, Konourina I, et al. Efficacy and safety of maraviroc plus optimized background therapy in treatment-experienced patients infected with CCR5-tropic HIV-1: 48-week combined analysis of the MOTIVATE studies. In: Program and abstracts of the 15th Conference on Retroviruses and Opportunistic Infections; February 3-6, 2008; Boston, Mass. Abstract 792.
View poster: [Download PDF](https://img.thebody.com/confs/retro2008/slides/792 Hardy poster.pdf)
- Begovac J, Bayer K, Krpan D, Kušec V. Osteosclerosis and periostal new bone formation during indinavir therapy. AIDS. March 29, 2002;16(5):803-804.
- Peeters M, Nijs S, Vingerhoets J, et al. Determination of phenotypic clinical cut-offs for etravirine (ETR): pooled week 24 results of the DUET-1 and DUET-2 trials. In: Program and abstracts of the XVII HIV Drug Resistance Workshop; June 10-14, 2008; Sitges, Spain. Abstract 121.
- Vingerhoets J, Peeters M, Azijn H, et al. An update of the list of NNRTI mutations associated with decreased virological response to etravirine (ETR): multivariate analyses on the pooled DUET-1 and DUET-2 clinical trial data. In: Program and abstracts of the XVII HIV Drug Resistance Workshop; June 10-14, 2008; Sitges, Spain. Abstract 24.
- Mills A, Cahn P, Grinsztejn B, et al, on behalf of the DUET-1 study group. DUET-1: 24 week results of a phase III randomised double-blind trial to evaluate the efficacy and safety of TMC125 versus placebo in 612 treatment-experienced HIV-1 infected patients. In: Program and abstracts of the 4th International AIDS Society Conference on HIV Pathogenesis, Treatment and Prevention; July 22-25, 2007; Sydney, Australia. Abstract WESS204-1.
View slides: Download PowerPoint
- Katlama C, Campbell T, Clotet B, et al, on behalf of the DUET-2 study group. DUET-2: 24 week results of a phase III randomised double-blind trial to evaluate the efficacy and safety of TMC125 versus placebo in 591 treatment-experienced HIV-1 infected patients. In: Program and abstracts of the 4th International AIDS Society Conference on HIV Pathogenesis, Treatment and Prevention; July 22-25, 2007; Sydney, Australia. Abstract WESS204-2.
- Clotet B, Bellos N, Molina J-M, et al, on behalf of the POWER 1 and 2 study groups. Efficacy and safety of darunavir-ritonavir at week 48 in treatment-experienced patients with HIV-1 infection in POWER 1 and 2: a pooled subgroup analysis of data from two randomised trials. Lancet. April 7, 2007;369(9568):1169-1178.
- Kumar PN, Cooper DA, Steigbigel RT, Zhao J, Teppler H, Nguyen B-Y, for the BENCHMRK-1 and BENCHMRK-2 Study Groups. Efficacy of raltegravir, an HIV integrase inhibitor, in combination with regimens containing efuvirtide, darunavir, or tipranavir in patients with triple-class resistant virus: combined results from BENCHMRK-1 and BENCHMRK-2. In: Program and abstracts of the 11th European AIDS Conference; October 24-27, 2007; Madrid, Spain. Abstract P7.2/06.
View poster: Download PDF
- Nelson M, Fätkenheuer G, Konourina I, et al. Efficacy and safety of maraviroc plus optimized background therapy in viremic, ART-experienced patients infected with CCR5-tropic HIV-1 in Europe, Australia, and North America: 24-week results. In: Program and abstracts of the 14th Conference on Retroviruses and Opportunistic Infections; February 25-28, 2007; Los Angeles, Calif. Abstract 104aLB.
- Lalezari J, Goodrich J, DeJesus E, et al. Efficacy and safety of maraviroc plus optimized background therapy in viremic ART-experienced patients infected with CCR5-tropic HIV-1: 24-week results of a phase 2b/3 study in the US and Canada. In: Program and abstracts of the 14th Conference on Retroviruses and Opportunistic Infections; February 25-28, 2007; Los Angeles, Calif. Abstract 104bLB.
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