New AIDS drugs aim to combat resistant HIV strains

By Deena Beasley and Ransdell Pierson

LOS ANGELES/NEW YORK (Reuters) - More than 25 years into the AIDS epidemic, many drugs are used to treat HIV, but an alarming number of patients have become resistant to therapy, driving research into new ways to combat the virus.

Data from clinical trials of several promising new products will be unveiled at a conference of leading HIV researchers in Los Angeles next week.

"There is a confluence of new drugs in the pipeline that people are pretty excited about," said Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases.

These include next-generation versions of long-standing HIV drugs as well as new agents that combat the virus through innovative mechanisms.

More than 1 million people in the United States and nearly 40 million worldwide are infected with HIV, the virus that causes AIDS. An estimated 40,000 Americans become infected each year.

About half of U.S. patients treated for HIV infection have stopped responding to at least one drug, said Dr. John Mellors, chief of infectious diseases at the University of Pittsburgh.

Resistance is becoming a problem because the virus can mutate, particularly if patients fail to rigorously follow complicated drug regimens.

On Tuesday, Merck & Co. will release results of a trial of MK-0518, which is likely to be the first in a new class of drugs, known as integrase inhibitors. Merck plans to seek U.S. approval for the drug in the second quarter.

"It looks like a very exciting result," said Mellors. He said clinicians are starting to see response rates in heavily treated patients that are similar to those of patients being treated for the first time.

On Wednesday, Gilead Sciences Inc., maker of Truvada, a combination of emtricitabine and tenofovir disoproxil fumarate, will present data from a mid-stage trial of its experimental integrase inhibitor GS-9137.

Norbert Bischofberger, head of research for Gilead, said comparisons with Merck's data would be problematic because patients in the Gilead study were not allowed to use other therapies until the company obtained information on potential drug interactions.

About 6 months into the 6-month Gilead study, patients were allowed to use protease inhibitors, a commonly used family of HIV drugs, he said.

Another promising new class of medicines works by blocking HIV from entering and taking up residence in the T cells, a type of white blood cell vital to the immune system.

The drugs work by blocking the receptors -- or "docking stations" - on the surface of the T cell and allow entry into the cells. If HIV is barred entry, the virus cannot infect or replicate.

Another type of drug candidate is called a CCR5 inhibitor, which prevents chemokine co-receptor 5 from entering T cells.

On Tuesday, Pfizer Inc. will present data from a late-stage trial of its CCR5 inhibitor maraviroc now awaiting U.S. and European approval. Patients in the trial had fared poorly on previous HIV treatments.

"If maraviroc is approved, it would change the landscape of treatment and be the first new oral class of HIV treatments in a decade, since the approval of protease inhibitors," said Howard Mayer, a Pfizer executive in charge of maraviroc's development.

Because CCR5 inhibitors do not attack the virus itself, as other classes of HIV treatments do, Mayer said HIV might be less able to develop resistance.

On Wednesday, Johnson & Johnson, which last year launched its first AIDS drug Prezista, a protease inhibitor called darunavir, will announce results from a mid-stage trial of its next-generation non-nucleoside reverse transcriptase inhibitor, known as TMC278, which works by blocking an enzyme the HIV virus needs to replicate.

The 14th Conference on Retroviruses and Opportunistic Infections will be held at the Los Angeles Convention Center.