(UPDATED: See below.)For at least a decade, biotech futurists have been predicting that the genomics revolution will lead to medical treatments tailored to the genetic quirks of individuals. And for at least as long, we’ve all been waiting for evidence that this “personalized medicine” revolution is coming to pass.
On Monday, the field took a baby step forward when the FDA approved Selzentry, a new AIDS drug from Pfizer. Selzentry is unique in a number of ways — for instance, it’s the first drug that tries to “lock down” T-cells to prevent HIV (that’s the culprit, above and to the left) from entering and infecting them. Fuzeon, a less-than-successful drug from Roche and Trimeris, does something similar, although it works to gum up HIV’s “landing gear,” not the T-cell’s docking port.
But the particularly interesting thing about Selzentry is that it only works against a particular sub-strain of HIV — those that dock to a T-cell surface protein called CCR5 in order to invade. (Most HIV strains use another protein called CXCR4 or a combination of the two.) That means would-be Selzentry users first have to be tested to ensure that their HIV strain will respond to the drug. And that, in turn, makes Selzentry one of the first drugs to be paired with a diagnostic test that limits the number of people who can try it, but which also greatly enhances the odds that it will work in those who do.
That test, offered by Monogram Biosciences, requires “amplifying” the HIV genome in the lab, producing scads of genetically identical viruses that are used to infect cultures of T-cells that lack either CCR5 or CXCR4. When infection occurs, a transplanted gene in the cell cultures begins to produce fluorescent proteins, making it easy to tell whether the viral strain is CCR5-specific. (There’s more info in this Monogram press release.)
Of course, Selzentry — generically known as maraviroc — most likely wouldn’t appear to work at all if tested in a general population, which helps explain why Pfizer was willing to pair it with a diagnostic. Genentech’s breast-cancer drug Herceptin — long the sole poster-child for the nascent field of personalized medicine — likely would have gone the same way had researchers not realized that it appeared to work particularly well in an identifiable subset of tumors.
So far, however, there aren’t too many other similar personalized treatments out there, or even in development. One exception is the beta blocker bucindolol being developed by Arca Discovery, which aims to test the drug in patients who have specific genetic variants; I wrote about them here.
Why aren’t there more? The simplest explanation is that most drug developers, whether pharma companies or biotechs, don’t want to risk circumscribing their patient population unless they have to, since doing so by definition limits the potential sales of a new drug. Up to now, drug makers haven’t really faced much economic pressure to embrace personalized medicine, or “pharmacogenomics,” as it’s technically known. With pipelines drying up and the patent environment getting a lot harsher for the me-too drugs drug giants have long relied on, however, they may soon have little choice.
(Brief aside: Pharmacogenomics, of course, is also the answer to the oft-touted assertion that me-too drugs — meaning a variety of drugs that all target the same biological mechanism, such as the half-dozen statins approved to lower cholesterol — aren’t the waste that drug-industry critics often assert. This argument holds that patients who, for instance, don’t respond to one statin might actually benefit from a different one. The short and simple response is, Where’s the proof? If the makers of statins, or of the depressants known as SSRIs, really want to know which patients their drugs work best in, it’s certainly within their ability to find out. The fact that no one is conducting such tests tells you quite a bit of what you need to know about decision-making in the drug industry.)
UPDATE: Apropos of nothing, I just stumbled across this Reuters story describing a Royal Society report on personalized medicine. The bottom line:
“Personalized medicines show promise but they have undoubtedly been over-hyped,” said David Weatherall, who chairs the working group that produced the report.
UPDATE REDUX: For more on the FDA’s big push behind personalized medicine, see this more recent post.