Pfizer says maraviroc suppresses AIDS virus

Pfizer Inc. said on Tuesday pivotal-stage trials found that adding its experimental HIV drug maraviroc to a regimen of the best-available drugs resulted in twice as many patients achieving suppression of the virus.

If approved by regulators, maraviroc would be the first in a new class of oral HIV drugs, said Dr. Howard Mayer, a Pfizer executive in charge of the drug's development.

Maraviroc is designed to block the human immunodeficiency virus from taking up residence in T cells, a type of white blood cell vital to the immune system, by jamming receptors - or docking stations - that dot the surface of T cells and act as doorways in. If HIV cannot enter, it cannot replicate.

As the receptors are made of a protein called CCR5, maraviroc and others in this new crop of drugs are called CCR5 inhibitors.

About 80 percent of recently infected HIV patients and 50 percent of treatment-experienced patients have so-called CCR5-tropic virus, said Chris Petropoulos, chief scientific officer at Monogram Biosciences, which makes a CCR5 test.

Over time, the virus in most patients develops the ability to use an alternate pathway known as CXCR4, he explained.

Pfizer, the world's top drugmaker, unveiled 24-week results of two Phase III trials involving patients with CCR5-tropic HIV who had stopped responding to other treatments at the 14th Conference on Retroviruses and Opportunistic Infections.

The first trial of 601 patients showed 60.4 percent of those who took maraviroc twice a day along with a background regimen of current HIV drugs achieved a level of less than 400 HIV copies per milliliter of blood, compared to 54.7 percent on a once-daily dose and 31.4 percent on just background therapy.

The second trial, involving 475 patients, found that 61.3 percent of twice-daily maraviroc patients achieved target HIV levels, compared with 55.5 percent on once-daily therapy and 23.1 percent treated only with other drugs.

Mayer said even though maraviroc patients were on therapy for longer - because most did not become resistant - side effect profiles were similar between both arms of the trials.

"We are not seeing any evidence of hepatotoxicity ... there has been no evidence of increased risk of lymphoma or other malignancies," he said, referring to side effects such as liver damage seen with other CCR5 inhibitors under development.

The Pfizer executive said the company has not observed any increased infection risk in patients treated with maraviroc.

Because CCR5 inhibitors do not attack the virus itself, as with existing HIV treatment classes, Mayer said HIV might be less likely to develop ways of resisting their effects.

The virus that causes AIDS infects more than 1 million people in the United States and nearly 40 million worldwide.