Hybridon Drops GEM 91 Antisense For AIDS

Hybridon has decided to halt clinical development of itsfirst-generation antisense drug, GEM 91, based on a preliminary review of new data from an open-label Phase II study in patients with advanced HIV infection. The company will now focus its resources on four of its second-generation drugs, spearheaded by GEM 132, in Phase II trials for systemic cytomegalovirus infection and retinitis.

Hybridon's share price fell 32% from $4.63 on the day of the announcement (July 25) to $3.13, and remained in the low $3s range through the end of the Marketletter's reporting period. The company has pulled back from a primary offering which it had registered with the Securities and Exchange Commission.

GEM 91 is a phosphorothioate antisense oligonucleotide which targets the gag site in the HIV genome. Hybridon had been encouraged by earlier data from trials in which the drug was administered as a monotherapy at doses up to 4.4mg/kg/day for eight days, which uncovered promising decreases in cellular viremia at some doses. A dose of 3.2mg/kg/day was selected for further assessment in the 14-day, open-label study.