Merck Will Not Request Approval of CCR5 Antagonist Vicriviroc for Treatment-experienced HIV Patients

		SUMMARY: Merck informed investors on January 20, 2010 that it does not plan to seek approval from the U.S. Food and Drug Administration (FDA) of vicriviroc for treatment-experienced people with HIV, due to disappointing clinical trial results. The company said it would, however, continue to evaluate vicriviroc as first-line therapy for treatment-naive patients.

By Liz Highleyman

Vicriviroc is a CCR5 antagonist -- like the recently approved maraviroc (Selzentry) -- intended for use by people with exclusively CCR5-tropic virus, meaning it makes use of only one of the 2 cell surface receptors (CCR5 and CXCR4) that HIV can use to infect cells.

HIV-1 interacts with a cell-surface receptor, primarily CD4, and through conformational changes becomes more closely associated with the cell through interactions with other cell-surface molecules, such as the chemokine receptors CXCR4 and CCR5.

In a Merck Investor Relations FAQ, the company stated: "In two Phase III studies in this patient population, vicriviroc did not meet the primary efficacy endpoint. These studies enrolled a high percentage of patients who had three or more active drugs in their optimized background therapy regimen."

Researchers reported as recently as last September that vicriviroc produced "sustained antiviral effect, including full virologic suppression and durable CD4+ cell count increases," at 96 weeks in an extension of the Phase 2b VICTOR-E1 study. The drug was also reported to be well tolerated.

Furthermore, investigators reported in the December 1, 2009 Journal of Infectious Diseases that vicriviroc appeared more effective than previously demonstrated when eligible patients were selected using a newer, more sensitive Trofile CCR5 tropism test.

Merck said that the study data that led to the company's decision have been shared with the FDA and would be presented at the upcoming Conference on Retroviruses and Opportunistic Infections (CROI) in February.

Merck acquired vicriviroc as part of its recent merger with Schering-Plough. Maraviroc, the only approved drug in the same class, has not sold as well as manufacturers hoped, in part due to the fact that prospective users require an expensive CCR5 tropism test to ensure they have susceptible virus. Maraviroc may gain additional market share, however, with its new approval for treatment-naive patients.

1/22/10

Sources
Merck Investor Relations. Vicriviroc FAQ. January 20, 2010.

P Loftus. Merck Won't Seek FDA Approval For HIV Drug. Dow Jones Newswires. January 20, 2010.