Chalk another “nuc” up to the FDA’s growing list of safety-related development interruptions. On Tuesday, BioCryst Pharmaceuticals (NASDAQ:BCRX) announced that it has withdrawn an Investigational New Drug application for BCX5191 after the FDA communicated unease over toxicity issues. The drug is a nucleoside NS5B inhibitor in preclinical development for the treatment of Hepatitis C (HCV). The FDA has repeatedly expressed concern over so-called “nucs” in the last few months, suspending Bristol-Myers Squibb’s (NYSE:BMY) BMS-986094 and placing a clinical hold on Idenix Pharmaceuticals’ (NASDAQ:IDIX) IDX-184, both nucleotide polymerase inhibitors. While BioCryst indicated that they will continue to test BCX5191 in animals and believe that the drug holds human potential, shares of BioCryst fell 30% Wednesday.
The FDA’s concerns create a new headwind in the face of this hepatitis program. BioCryst is in the process of acquiring Presidio Pharmaceuticals specifically to harness Presidio’s HCV compounds in combination with BCX5191. It’s not the possible loss of the asset alone that caused Wednesday’s decline, but what it means for the HCV regimen that the two companies hope to develop. PropThink covered the acquisition earlier this month and expressed concern about the possibility for a major setback when dealing with so many early-stage compounds; Presidio’s PPI-668, a NS5A inhibitor, and PPI-383, a Non-nucleoside NS5B inhibitor, are pre-Phase 2 and -Phase 1 respectively. And, BioCryst’s treatment for Hereditary Angioedema, BCX4161, hasn’t entered its first Phase 1 trial. Investors might look to BioCryst’s gout candidate, ulodesine, as a value-driver, but the company has yet to partner the drug, which management stresses is a priority.
Whether or not BioCryst can salvage BCX5191 and move it into clinical development may be determinant of long-term merit for this hepatitis franchise. Biotech investors will be well-aware of the crowding HCV segment, led by Gilead (NASDAQ:GILD) and its GS7977 compound. Even if BioCryst and Presidio can steer their hepatitis franchise back on track, they have a long way to go in becoming a genuine competitor in the segment. And without BCX5191, the Presidio merger looks much less applicable than it once did.