Development of Koronis Pharmaceuticals’ KP-1461, an experimental antiretroviral (ARV), has been suspended after an analysis of existing data failed to show anti-HIV activity, according to a report by Project Inform. These results came as a surprise to Koronis and stand in contrast to the drug’s earlier lab studies that showed promise.

Though KP-1461 is technically a nucleoside reverse transcriptase inhibitor (NRTI), its mechanism of action is quite different from other drugs in this class of ARVs. Whereas current NRTIs are incorporated into developing DNA to stop the chains of genetic material from becoming fully formed and infectious, the integration of KP-1461 into developing chains of viral DNA causes the virus to produce defective, harmless versions of itself.

The U.S. Food and Drug Administration (FDA) had asked Koronis to do some additional lab studies to determine if HIV becomes resistant to KP-1461. During these lab studies, Koronis found that the drug had no measurable effect on HIV, a stark contrast to earlier studies that supported the drug’s clinical development. With the new results in hand, Koronis then analyzed blood samples from people enrolled in its ongoing clinical trial and, to their surprise, again found no anti-HIV activity.

Stephen Becker, MD, the lead investigator for Koronis, told Project Inform that the company is, “committed to understanding these discordant results and will attempt to validate the original 2002 research,” on KP-1461. Becker estimated that it will take at least two months to fully investigate this setback, and determine what comes next.