The Coming Crisis in HIV Drug Development
June 16, 2008
The last few years have seen tremendous progress in treating people with advanced and drug-resistant HIV. Four powerful drugs became available that either overcame drug resistance (Prezista [darunavir, TMC-114], Intelence [etravirine, TMC-125]) or were from entirely new classes [Selzentry (maraviroc), Isentress (raltegravir)].
This marked an important and unique moment in HIV drug development. Never before have so many new and effective drugs come out so close together. People with extensive experience taking HIV drugs have been able to put together powerful regimens with two or more fully active agents -- often for the first time.
Project Inform took pains to highlight both the tremendous promise of these new drugs as well as the importance of using them correctly -- emphasizing that this moment, or anything resembling it, is unlikely to recur. Our message was clear: 'Seize this opportunity, use the new drugs carefully, and don't waste this once-in-a-lifetime chance'.
As good as some of these newer drugs have looked in studies, there are emerging signs of trouble in the real world. Dr. Steven Deeks, a prominent HIV physician and researcher says, "Although the current generation of drugs are generally doing great, many patients are not responding in a durable manner. We are now following about 25 individuals who have failed all six drug classes. The key now is to design regimens to maintain immunologic and clinical stability while we wait for more drugs. I am concerned, however, as it will likely be a few years before we have another shot at getting the virus under control. We desperately need a second generation integrase inhibitor that works against viruses resistant to raltegravir."
Dr. Deeks' experience is far from typical. He follows many of the most treatment experienced people in the San Francisco Bay Area, many of whom have been on therapy since 1987. Although not typical, his experiences have been reported elsewhere, if in smaller numbers.
This suggests a burgeoning problem of people beginning to run out of treatment options, as has happened a couple of times during the epidemic. Project Inform is concerned that the most vulnerable people living with HIV will be left with few or no viable treatment options, possibly for many years.
One of the unintended effects of the recent successes in drug development is that fewer people are available for studies of experimental drugs aimed at treatment experienced folks. We saw this coming and have been counseling drug companies and the Food and Drug Administration (FDA) that the era of 'TORO-like' studies was coming to a close. These studies give volunteers optimized background therapy (the best combination of HIV drugs chosen with resistance test results) with either the experimental drug or a placebo. The design allows regulators, scientists and activists to clearly see the benefit of the new drug. (Some call these studies 'TORO-like' after those that led to the approval of Fuzeon [enfuvirtide, T20]).
This contrasts with how studies of first line treatment are done. When studying HIV drugs as first line, the basic model is head-to-head non-inferiority studies, which are designed to tease out the relative contribution of the entire regimens rather than the individual drugs. (Non-inferiority means that one drug or regimen is equivalent or 'close enough' to another.)
The FDA has allowed non-inferiority studies for drugs being studied as first line, but has insisted on placebo controlled superiority studies for treatment experienced studies. This made a good deal of sense when there were many people signing up for these studies. The situation is now quite different.
While there aren't enough people signing up for these kinds of studies, there's still a sizeable need for studying new HIV drugs. This, combined with the thin drug pipeline and the current difficulty recruiting for studies, may add up to real trouble down the line.
In meetings with many drug companies Project Inform has warned of this impending problem and recommended that they adopt new ways of studying their drugs. The reaction has been mixed. While some companies have been quite open to new ideas, it's fair to say that most would prefer to stick with models that have proven successful.
We have struggled to argue -- to the companies and the FDA -- that ways of studying and developing drugs are both necessary and possible. Gilead Sciences is one of the first to grapple with this. When it came time to do large, pivotal studies of their experimental integrase inhibitor, elvitegravir, there simply were not enough people in the US to enroll a typical study for treatment experienced people. Project Inform had warned Gilead, and others, of this eventuality and argued for studies that would more closely resemble the head-to-head, non-inferiority studies used for studying first-line drugs.
Over time Gilead came to agree that this was the way forward and submitted such a plan to the FDA. The FDA eventually allowed Gilead to move forward with this study design for elvitegravir. This is a great victory for people living with HIV. There is a great need for new treatments to be developed and for the FDA and companies to think and act creatively to ensure this happens.
An Overview of the Current State of HIV Drug Development
As a whole, pharma has done a tremendous job developing HIV drugs. However, many visible signs are showing their fading commitment to HIV. Fewer new companies are getting into HIV, and some well established ones are either cutting back or eliminating their drug development plans. The marketplace for HIV drugs is both crowded and competitive. The scientific hurdles for developing new HIV drugs have also grown more difficult, making it a less attractive market for companies.
The FDA is responsible for ensuring that drugs are safe and effective before they become available outside clinical studies. Recent media stories that focused on drug safety, particularly on Vioxx and Heparin, have created a somewhat fearful climate inside the FDA where new ideas are met skeptically. Their recent decision to green light elvitegravir's development shows that at least its antiviral division is open to creative drug development plans.
The Current Pipeline
All in all, the pipeline is both thin and unimpressive. There are a few 'me too' drugs (slight changes in existing drugs) which are helpful but not game changing. A few novel compounds may prove promising down the line, but they're struggling right now, due to either study results or in one case the company being bought by a company that doesn't want to work in HIV.
As for those drugs in human studies, the closest to approval is rilpivarine (TMC-278), an NNRTI for first line treatment being studied against Sustiva. Vicriviroc, Schering's CCR5 drug, continues to flounder but is still viable. Bevirimat, a maturation inhibitor from Panacos, has been hamstrung by formulation problems. Other drugs we are following are Pharmasset's racivir, and Avexa's apricitabine.
The Bottom Line
The past two years have been a boon to people with extensive treatment experience. Four successful new drugs, including two new classes, have meant most people can put together powerful, effective and tolerable regimens, even if they've never been able to get to undectable before. However, this period is now over, and we're experiencing a major downturn in the number of promising drugs in the pipeline.
This reinforces the importance of using the current crop of new drugs correctly. Your best chance at getting to and staying undetectable is to start a regimen with at least two and hopefully three fully active drugs. If you're able to do this and get your HIV level to undetectable, good adherence is the best way of keeping it there.
This also points to the need for treatment activists, like Project Inform, to continue to work with the companies, scientists and regulators to ensure that new drugs are developed.
The only real solution is a cure. While some may discount its possibility, we do not. Many promising approaches are under study, as well as a resurgence in community activism aimed at cure research. A conscientious program mounted by academia, industry, government and community is necessary to reach this goal.
This article was provided by Project Inform. Visit Project Inform's website to find out more about their activities, publications and services.
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