Data showing progress on the development of two new classes of HIV drugs were
presented at the 14th Conference on Retroviruses and Opportunistic Infections (CROI) on
February 25-28, 2007 in Los Angeles. These experimental drugs are primarily for HIV
patients who have been unresponsive to existing therapies—patients termed "multi-drug
Pfizer Inc., a global pharmaceutical company headquartered in New York, reported
significant advances in the development of maraviroc, part of a new class of drugs known
as CCR5 inhibitors. The inhibitors bind to receptors on the surface of cells, stopping the
HIV virus from latching on and inserting itself into other uninfected cells, preventing it
from replicating. Pfizer researchers reported that during a 24-week study, approximately
double the number of patients receiving maraviroc in combination with an optimized
treatment regimen showed undetectable levels of HIV in the blood when compared to a
control group that was given the optimized treatment regimen alone.
"Data from the two identical studies are remarkably consistent and demonstrate
significant decreases in viral load and increases in CD4 cells when maraviroc is added to
the standard optimized treatment regimen," said Howard Mayer, MD, Pfizer’s global
clinical lead for the maraviroc development program.
The other representative of a new class of HIV drugs is raltegravir (ISENTRESS™), a
type of oral integrase inhibitor being developed by Merck & Co., Inc. By blocking an
HIV enzyme called integrase, the drug prevents the virus from replicating in human
immune cells. Early results from two ongoing studies involving 699 patients were
reported at CROI. The HIV levels in approximately 62% of patients receiving raltegravir
with standard therapy dropped to undetectable levels after 16 weeks. The results
compared favorably to the lowered HIV levels in only 36% of patients receiving standard
The integrase studies will continue for 156 weeks. According to Merck, the brand name
ISENTRESS™, previously known as MK-0518, is currently under review by the FDA.
"The efficacy results and tolerability profile that have been seen thus far with
ISENTRESS™ in combination with optimized background therapy in this patient
population with multi-drug resistant virus are exciting," said David Cooper, MD, D.Sc.,
professor of medicine and director, National Centre in HIV Epidemiology and Clinical
Research, University of New Wales, Sydney, Australia. "HIV integrase inhibitors may be
a new promising class of antiretroviral agents."
Maraviroc may be the first of the new drugs to become available to HIV patients in the
U.S. If so, it represents the first new oral class of HIV drugs available in the U.S. since
the mid-1990s. Regulators in Canada, Europe and the U.S. have permitted accelerated
review of maraviroc. This fast-track approach to potential approval is typically given for
novel drugs that could be an effective therapy for hard-to-treat patients. Pfizer is currently
submitting marketing applications internationally for maraviroc. The U.S. Food and Drug
Administration’s Antiviral Drugs Advisory Committee will discuss the drug in April
2007. Approval is anticipated this year.
Source: The Los Angeles Times, February 28, 2007, Pfizer news release and Merck news
release both dated March 1, 2007