Schering-Plough Corporation has reported that results from a phase II clinical trial showed vicriviroc, its investigational CCR5 antagonist, demonstrated potent and sustained viral suppression through 48 weeks of therapy in treatment-experienced HIV patients, when administered in once-daily doses in combination with an optimized ritonavir-boosted protease inhibitor (PI)- containing antiretroviral regimen.

Vicriviroc is an extracellular inhibitor of HIV infection designed to block entry of infectious virions into uninfected CD4 cells via antagonism of the CCR5 co-receptor. These results represent the longest follow-up data reported to date for any CCR5 antagonist.

Researchers from the NIH-sponsored AIDS Clinical Trial Group (ACTG), which conducted the study, reported the data here today in an oral presentation at the International AIDS Society 4th IAS Conference on HIV Pathogenesis, Treatment and Prevention.

At 48 weeks, patients in the 10 mg and 15 mg vicriviroc treatment groups achieved a median decrease in viral load of 1.92 and 1.44 (log10 copies/mL) and a median increase in CD4 cell count of 130 and 96 (cell/uL) from baseline, respectively. More patients in the vicriviroc groups had undetectable virus at 48 weeks compared to those in the placebo group and fewer patients in the vicriviroc groups experienced virological failure compared to those in the placebo group.

In the study, there was no significant difference in grade three or four adverse events across the vicriviroc and placebo groups. Eight patients randomised to vicriviroc and two patients randomised to placebo developed malignancies. No cases of seizure were reported.

"These 48-week data establish the durability of viral suppression with a vicriviroc-containing regimen in treatment-experienced patients with advanced HIV disease, and are the first to demonstrate the sustained effects of a CCR5- based regimen through 48 weeks," said Roy Gulick, MD, principal investigator and professor, Weill Medical College of Cornell University, New York, who presented the data. "New antiviral agents with novel mechanisms of action and unique resistance profiles are urgently needed for this challenging patient population, and we look forward to the further clinical evaluation of vicriviroc in combination with antiretroviral regimens."