REG is a small-molecule multikinase inhibitor involved in normal cellular functions and pathologic processes such as oncogenesis, angiogenesis, and tumor immunity. REG is approved for the treatment of advanced colorectal cancer, gastrointestinal stromal tumors, and hepatocellular carcinoma. REG alone is currently being evaluated for its tolerability and safety in pediatric cancers in a clinical phase 1 study. Preclinically, we investigated a series of drugs, which are established or emerging for the treatment of pediatric patients with RMS, for their combination potential with REG to support its clinical development in pediatric indications.
Proliferation assays were performed in vitro. In vivo, subcutaneous xenografts derived from pediatric alveolar (RH30) and embryonal (RD) RMS tumor cell lines were treated with REG alone and in combination with 13 different compounds including a combination with irinotecan (IRI) and vincristine (VINC). A study design with one mouse per group and a stepwise dose escalation was applied. The body weight of the mice was closely monitored for tolerability and the tumor growth was determined by caliper measurements. Treatment was for four weeks and the time to tumor regression was followed thereafter.
The pattern of response was heterogeneous, ranging from complete regression (CR) to insensitivity. REG alone at an oral dose of 10mg/kg/d delayed the growth of both RMS xenografts. CRs were observed for IRI (both models), paclitaxel (RH30 model), and VINC (RD model) alone near their maximum tolerated doses in mice. The strong monotherapy effects of IRI and VINC preclude a clear demonstration of a combination benefit with REG in this study. Beneficial combination effects were observed for some other drugs. IRI appeared as the most favorable combination partner of REG of the tested drugs. Surprisingly, the RH30 model was insensitive to VINC in this study. Treatment interruptions were required in some cases of treatment intolerability, but no drug-related deaths were observed.
These results warrant further exploration of a combination of REG with IRI and VINC in pediatric RMS.
Clinical trial identification
Legal entity responsible for the study
D. Zopf, Y. Tsvetkova: Full-time employment: Bayer AG. J. Hoffmann: CEO and shareholder: EPO GmbH.