Medivation's mystery cancer drug gets out from an FDA hold

Medivation ($MDVN) alarmed regulators earlier this year with the revelation that its mid-stage cancer drug, purported to block the protein PD-1, didn't do that at all, leading the FDA to put the program on hold. Now the company says it has satisfied the agency's curiosity, clearing the way for clinical trials, but the biotech's still not disclosing how its drug works.

The treatment, pidilizumab, was on the verge of a Phase II trial in patients with diffuse large B-cell lymphoma when the FDA placed a partial clinical hold on development last month. Medivation said it has since revised all study protocols to note that pidilizumab is not a PD-1 blocker, updating consent documents to ensure patients know what they're getting.

But just what pidilizumab does do remains unclear. Medivation hasn't disclosed the drug's actual mechanism of action, and the company didn't return phone messages Tuesday. In a statement, CEO David Hung said Medivation is "working to determine the compound's exact binding mechanism." He's also spinning pidilizumab's mystery science as a positive, adding that Medivation believes the undisclosed mechanism "modulates the body's innate immune response and differentiates (pidilizumab) from the heavily crowded immuno-oncology space that targets the adaptive side of immunity."

In the meantime, the San Francisco biotech is moving forward with its Phase II trial, planning to enroll about 180 patients whose lymphoma has withstood chemotherapy or stem cell transplants. The open-label study will measure pidilizumab's effect on overall survival across both patient groups, and Medivation has said the trial could support an FDA filing if results are positive.

Medivation picked up pidilizumab in a $335 million deal with CureTech in 2014, paying just $5 million up front for full rights to the antibody. Teva ($TEVA) bankrolled much of pidilizumab's early development under a partnership with CureTech but cut its ties to the treatment in 2013 when then-CEO Jeremy Levin decided his company was too far behind the likes of Merck ($MRK) and Bristol-Myers Squibb ($BMY) to compete in immuno-oncology.

- read the statement