Calithera Biosciences Inc., of South San Francisco, said it inked two clinical trial collaborations involving its glutaminase inhibitor CB-839 with New York-based Pfizer Inc. to test CB-839 plus Ibrance (palbociclib) and CB-839 plus PARP inhibitor talazoparib. As part of the collaboration, Pfizer will provide palbociclib and talazoparib, as well as financial support.