|in the pipeline...
Jun 13, 2002
Dr. Cohen, What do you make of the 24 week results of the Phase 3 trial of T-20. Do you think this drug will be be used in standard practice as part of combination therapy in the near future? What information is available (or will soon be) regarding antivirals that can be taken safely/effectively with this new drug. And finally what do you think will be the next available drug that is effective against resistant virus / what should we be looking for. Thanks for your help with a look into the future.
| Response from Dr. Cohen
The 24 week results of now TWO phase 3 trials of T20 confirmed the same outcome - when T20 was added to a combo of up to 5 other antivirals, there was a clear benefit of better viral control.
These studies were done in people who have very difficult to control HIV - due to lots of drug resistance. Over the years this group are those who have been on all three classes of antivirals - nucleosides, nonnukes, and the protease inhibitors. And this group has historically had very low rates of suppression on most new combinations tested - in part due to all the resistance and cross resistance there is with the current antivirals. So - what to do?
Well, T-20 will be the first of a fourth class of antivirals. These are called entry inhibitors - more precisely, T-20 (brand name yet to be announced...) is the first fusion inhibitor to get this far. It blocks the ability to HIV to actually fuse with our own cells after attachment occurs. By blocking this step, HIV cannot enter, and this blocks the damage done when the genetic material of HIV enters our cells. And fortunately, HIV lives less than one day outside of our cells - so these virus's die off. Now - this is NOT a cure - HIV, shortly after initial infection, enters cells and becomes integrated into our own DNA - and so even if new HIV cannot gain entry - our cells can still produce more HIV. That is where the other antivirals come into play.
But blocking entry has a key advantage - as it is a completely new class - most everyone should be able to respond to this drug since there is little resistance to it so far. And we've known now for years that T20, even as a single drug - works. The studies have shown it is about as potent as most of our more potent drugs. But, as with many drugs, HIV can develop resistance to this one as well - unless we establish full suppression with T20 and a combo of other active agents.
And that is what the phase 3 trials did show - that a combo based on T20 can work far better than a combo without T20 in those with lotsa resistance to the standard meds. There was about a 0.9 log difference at week 24 in the T20 arm vs the control. (There were actually two trials done - they showed about the same difference, although the one in the Americas did slightly better than the one in Europe, not that it was a competition...) More details about these results are expected to be presented in Barcelona at the upcoming AIDS meetings.
Now, the big issue with T20 is that it is not a pill - it is, like insulin, a drug that, at least for now, has to be taken via an injection that is taken just under the skin (subcutaneous) twice a day. Which has some plusses and minuses. For some, the idea of an injection is just too much to deal with, while for others who have been on these studies, the injection issue has not been a big deal overall. There can be some nuisance issues to this part of it - but in a survey done of those who were in the studies, it had minimal overall impact on daily life. There can be some nodules at the site of injection, but in most, these fade away in a day or so. And, since it is not a pill, there have not been problems with nausea, diarrhea and those other GI upset type side effects... which is the plus.
But, no single drug is enough. And yes, HIV can develop resistance to this one as well. And so it must be taken with other active meds to work. And for those with significant resistance to the current meds - this can sometimes be a challenge. There are some new meds coming and some general concepts that seem to help. For example, a resistance test can help identify which agents retain activity despite the current resistance. And "boosting" the blood levels of protease inhibitors with low dose norvir has been very helpful in reestablishing control with these meds. And the newest antiviral viread might be a part of the nucleosides selected - or others can be, depending on how much resistance there is, and what type of mutations there are on that side of the equation.
And other new meds are slowly arriving as well. On the PI side - the next to arrive through expanded access (preapproval) protocols is atazanavir. This drug may have some benefits in controlling HIV even after there is resistance to other PIs - although this role is still under active investigation and not as fully defined so far. Also coming along is tipranavir - another PI - where the data are good about its ability to control HIV even after resistance to other PIs. Those two are the furthest along - and behind them are others in each of the now four classes of antivirals.
We've learned over the years that one component of reestablishing control over HIV is to have a class of antivirals that is completely new as the "backbone" of the new combo. T20 can be that new backbone for many. No guarantee that any combo containing T20 will work of course - like all meds, it needs the help of other meds to be durable after the first few weeks. But for many this drug has been pivotal to reestablishing control.
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