retaspimycin hydrochloride + trastuzumab

A combination therapy consisting of retaspimycin hydrochloride (IPI-504), a potent heat shock protein 90 (Hsp90) inhibitor, and trastuzumab, a HER2-targeted monoclonal antibody. This combination was investigated for the treatment of HER2-positive metastatic breast cancer, particularly in patients who had progressed on prior trastuzumab-based therapies. The rationale behind this combination is that Hsp90 inhibition leads to degradation of client proteins including HER2, potentially enhancing the anti-tumor effects of trastuzumab. ## Mechanism of Action Retaspimycin hydrochloride works by binding to and inhibiting the cytosolic chaperone functions of Hsp90, which maintains the stability of key oncoproteins, including HER2[6]. As a hydroquinone hydrochloride salt derivative of 17-AAG, retaspimycin is converted in the systemic circulation to its free base form and subsequently oxidized to 17-AAG[5][9]. Trastuzumab specifically targets the HER2 receptor, which is overexpressed in approximately 20-25% of breast cancers. The combination therapy leverages the ability of retaspimycin to destabilize HER2 through Hsp90 inhibition while trastuzumab directly targets the receptor, potentially overcoming trastuzumab resistance mechanisms[3]. ## Clinical Development A phase 2 trial evaluated this combination in patients with previously treated, locally advanced or metastatic HER2-positive breast cancer. The study used a Simon two-stage design with the following parameters: - Dosing: 300 mg/m² retaspimycin HCl weekly with 6 mg/kg trastuzumab every 3 weeks - Patient population: Heavily pretreated patients (median of 6 prior regimens, range 2-20) - Median age: 52.5 years (range 33-72) - Median treatment duration: 3 cycles (range 1-12)[3][7] ## Efficacy Results The clinical activity observed was modest and did not meet the prespecified criteria for trial expansion: - No confirmed responses were observed in the once-weekly dosing cohort - Stable disease was achieved in 16 patients (62%), with a median duration of 2.4 months (range 1.1-8.2)[1][2] - One partial response was reported in some analyses based on central, independent radiology review[3][7] ## Safety Profile The combination was generally well tolerated: - No dose-limiting toxicities were reported - Most adverse events were grade 1 or 2 - Common treatment-related adverse events included fatigue (46%), nausea (31%), and diarrhea (23%) - Serious adverse events were rare, with one patient experiencing grade 1 diarrhea and grade 3 hypokalemia - Only one patient (4%) developed grade 3 transaminase elevation, who had metastatic liver disease[2][3][7] The safety profile raised the possibility that retaspimycin HCl may have been underdosed at 300 mg/m², potentially limiting efficacy[1][2].

Other names

Retaspimycin hydrochloride + trastuzumabRetaspimycin HCl + trastuzumab