Phase I Study of BIIB028, a Selective Heat Shock Protein 90 Inhibitor, in Patients with Refractory Metastatic or Locally Advanced Solid Tumors

Purpose: Heat shot protein 90 (Hsp90) is a ubiquitous molecular chaperone involved in protein folding, activation, and assembly, including key mediators of signal transduction, cell-cycle control, and transcriptional regulation. We conducted a phase I dose-finding and pharmacokinetic/pharmacodynamic study of BIIB028, a prodrug designed to inhibit Hsp90 activity. Experimental Design: Patients with advanced solid tumors were enrolled and received escalating doses of BIIB028 intravenously twice a week in 21-day cycles (3 + 3 design). Response was evaluated after two cycles. Results: Forty-one patients received doses of 6 to 192 mg/m(2). The maximum tolerated dose was 144 mg/m(2). Dose-limiting toxicities were syncope (n = 1) and fatigue (n = 1). Common toxicities at least possibly related to drug were grades 1 to 2, including fatigue (46%), diarrhea (44%), nausea (44%), vomiting (29%), hot flushes (29%), and abnormal dreams (17%). The concentration-time curves for day 1 and day 18 for both prodrug and active metabolite (CF2772) showed a negligible difference. There was a dose-dependent increase in plasma exposure for BIIB028 (CF3647) and CF2772 with plasma half-life of 0.5 and 2.1 hours, respectively. Pharmacodynamic analyses showed significant increases in Hsp70 in peripheral blood mononuclear cells and significantly decreased circulating human EGF receptor-2 extracellular domain in all patients who received BIIB028 at dose levels of 48 mg/m(2) or more. Stable disease for at least eight cycles (24 weeks) was achieved in 5 (12%) patients (for durations of 6, 6, 8, 12.5, and 19 months). Conclusion: BIIB028 is a well-tolerated molecule that showed target impact and was associated with prolonged stable disease in two patients. (C) 2013 AACR.