Targeting the cell cycle for cancer therapy in rhabdomyosarcoma.

Abstract

10535 Background: Rhabdomyosarcoma (RMS) is an aggressive malignancy of childhood with a poor prognosis in patients with metastatic or recurrent disease. Inhibitors of Wee1 kinase and heat shock protein 90 (HSP90) have in vitro activity in RMS and have emerged as potential novel treatment strategies. We performed a comprehensive preclinical phase III study to compare the Wee1 inhibitor AZD1775 and HSP90 inhibitor ganetespib (GANET) in combination with irinotecan (IRN) and vincristine (VCR). Methods: Orthotopic xenografts (O-PDXs) were created by injecting luciferase labeled RMS cells into the hind-leg muscle of CD-1 nude mice. Pharmacokinetic studies on RMS O-PDXs were performed to determine matched human AUC-guided dosing. A total of 540 O-PDXs derived from 4 high risk RMS patients, 2 alveolar and 2 embryonal, were randomly enrolled into 14 treatment groups. Six courses of blinded placebo-controlled therapy were given on a clinically relevant schedule. Mice were classified as having progressive disease if tumor approached 20% body weight at any time in the study. For mice completing all 6 courses, bioluminescence was used to determine complete response (CR), partial response (PR), stable disease (SD), and progressive disease (PD). Results: The addition of AZD1775 to IRN and VCR demonstrated the most significant response for all 4 O-PDX lines tested; 70% of mice achieved a CR or PR. GANET combined with IRN and VCR had a 54% response (CR + PR) which was not significantly better than IRN plus VCR for most O-PDXs tested. Overall response data for select treatment groups is shown in the table below. Conclusions: Comprehensive preclinical testing using multiple O-PDX models of RMS that represent the clinical spectrum of disease is feasible. Comparison of novel treatment regimens to standard of care at clinically relevant doses is warranted as justification for future clinical trials. Observation to assess durable response following completion of therapy is ongoing to determine if AZD1775 remains a promising treatment strategy. [Table: see text]