Merck-Gilead Drug Duel Is Heating Up

A couple of experimental drugs designed to fight HIV in new ways will highlight an important and closely watched medical meeting next week.

Drugmakers Merck(MRK Quote) and Gilead Sciences(GILD Quote) are expected to present new clinical data at the annual Conference on Retroviruses and Opportunistic Infections, Feb. 25-28 in Los Angeles.

The CROI meeting brings together scientists and researchers from around the world and is generally viewed as one of the most important forums for the presentation of new HIV drug research. CROI is also a bit unique in that it bars entry to anyone connected to Wall Street, including sell-side analysts and fund managers. Even the financial press -- myself included -- isn't allowed to attend.

I may need to watch from the outside, but I'll still be covering the data duel between Merck and Gilead, both of which are developing similar HIV drugs known as integrase inhibitors. Merck is in the lead with about a 12-month time advantage over Gilead. But in HIV treatment, speed and being first to market don't guarantee victory.

The Hows of HIV

To understand why, start with a short lesson in the science behind HIV: In order for HIV (human immunodeficiency virus) to successfully replicate itself, the virus must first infect a host cell and integrate itself into the cell's genome. Three enzymes in the body help the virus accomplish this task: reverse transcriptase, protease and integrase. Once HIV gets cozy inside a host cell, it turns that cell into an HIV factory, capable of churning out new copies of the virus to seek out and infect new cells.

There are currently three major classes of antiretroviral drugs used to treat HIV. Two of these classes work by inhibiting the action of the reverse transcriptase enzyme; the third class inhibits the protease enzyme. Modern HIV therapy, which involves patients taking a cocktail of these drugs, does a remarkable job of tamping down the virus to undetectable levels. HIV and AIDS (acquired immune deficiency syndrome) used to kill patients quickly but now have been somewhat defanged, and HIV infection is treated more like a chronic disease. (There is still no "cure" for HIV because under current therapies, the virus is never 100% eliminated from the body.)

The problem, however, is that HIV is a smart virus and over time can mutate into forms that are resistant to existing drugs. That's why the development of new classes of HIV drugs that fight the virus in novel ways is important.