Phase Ib study of heat shock protein 90 inhibitor, onalespib in combination with paclitaxel in patients with advanced, triple-negative breast cancer (NCT02474173).

TPS1127Background: Heat shock protein 90 (HSP90) is a molecular chaperone which is necessary for proper folding and stabilization of proteins. Client proteins of HSP90 include many oncogenic proteins known to be over-activated in triple negative breast cancer such as AKT, EGFR, members of RAS/MAPK signaling pathway and androgen receptor. High expression of HSP90 in breast cancer has been associated with poor outcome. In addition, over-expression of HSP90 client proteins such as AKT and c-RAF has been implicated in paclitaxel resistance. Onalespib (AT13387) is a synthetic non-ansamycin small molecule that acts as an inhibitor of HSP90 by binding to the amino terminal of the protein and has dissociation constant (Kd) of 0.71 nM. Methods: Patients with inoperable or metastatic, triple negative or < 10% hormone receptor positive breast cancer are treated with onalespib and paclitaxel on days 1, 8, 15 every 28 days. Paclitaxel is given at a standard dose of 80 mg/m2 while the dose of onalespib is gradually inc...