Bristol-Myers Squibb's aspirations to build a lucrative franchise in hepatitis C virus (HCV) treatment suffered a setback after the company was forced to suspend dosing in a mid-stage trial of a combination therapy.
The phase II study was testing BMS' NS5a inhibitor daclatasvir with nucleotide polymerase (NS5b) inhibitor BMS-986094 (formerly INX-189), which was one of the key assets behind the company's $2.5bn acquisition of Inhibitex earlier this year.
The decision to halt the trial was taken "to protect patient safety based on the emergence of a serious safety issue", said BMS, which added that it is now reviewing data on all the patients in the study to try to determine whether the side effect is linked to the drug or some other factor.
The company is remaining tight-lipped about the nature of the safety issue, but it has been reported that at least one patient in the study developed congestive heart failure.
The announcement - so early after the Inhibitex acquisition closed - is a major blow to BMS as the firm races with a number of other pharma companies to develop an all-oral treatment regimen that could replace current HCV therapies based on injectable interferon alpha.
The company is exploring other drugs in combination with daclatasvir in HCV, including Tibotec's NS3 protease inhibitor TMC435, but the regimen with BMS-986094 was considered a cornerstone of its HCV treatment strategy, according to analysts.
HCV treatment has been transformed in recent years with the introduction of new orally-active agents, namely the protease inhibitor class represented by Johnson & Johnson/Vertex/Mitsubishi Tanabe's Incivek/Incivo (telaprevir) and Merck & Co's Victrelis (boceprevir).
Nucleotide polymerase inhibitors or 'nukes' such as BMS-986094 have been tipped as the next big class in HCV, and if BMS is forced to halt development of its compound it will benefit Gilead Sciences, whose own nuke candidate GS-7977 is a little further ahead in development.
BMS had a partnership in place with GS-7977 when it was owned by Pharmasset - a company acquired by Gilead last year for $11bn - but the latter company is now developing the drug in tandem with its own NS5a inhibitor GS-5885.