Evaluation of the multi-kinase inhibitor regorafenib in the Pediatric Preclinical Testing Consortium osteosarcoma, rhabdomyosarcoma, and Ewing sarcoma in vivo models.
10038 Background: Regorafenib is a multi-kinase inhibitor, developed by adding a fluorine atom to the phenyl ring of sorafenib. Regorafenib inhibits multiple kinases including BRAF, FGFR1, KIT, PDGFRB, RAF, RET, and VEGFR1-3, many at a higher potency than sorafenib. Prior studies within the Pediatric Preclinical Testing Consortium (PPTC) demonstrated sorafenib exhibited intermediate activity for tumor growth inhibition in more than 50% of the sarcoma models tested at a dose of 60mg/kg by oral gavage daily (5 days/wk for 6 consecutive weeks). The in vivo effects of regorafenib were studied in the PPTC osteosarcoma (OS), rhabdomyosarcoma (Rh) and Ewing (EW) sarcoma xenograft models. Methods: The in vivo anticancer effects of regorafenib were assessed in a panel of 6 osteosarcoma models (OS2, OS9, OS31, OS33, OS36, OS60), two rhabdomyosarcoma models (Rh30, Rh41), and one Ewing sarcoma model (EW5). Regorafenib was administered by oral gavage at a dose of 30 mg/kg/day given daily for 21 consecutive days. Time to event and tumor volume responses were defined and analyzed utilizing standard PPTC statistical methods. Results: Regorafenib induced significant improvements in event-free survival (EFS) compared to control in 100% (9/9) of sarcoma models tested. Most models showed pronounced slowing of tumor growth compared to control during the 21 days of regorafenib treatment, with tumor growth generally approximating control rates soon after completion of regorafenib treatment. Three out of 8 sarcoma models demonstrated EFS T/C values > 2 (1/6 OS, 2/2 Rh, 0/1 EW). Minimum relative tumor volumes ranged from 0.74 to 1.60, with no models meeting criteria for objective response. Conclusions: Regorafenib induced modest inhibition of tumor growth in the PPTC sarcoma models evaluated. The overall pattern of response to the multi-kinase inhibitor regorafenib against the PPTC sarcoma models appears similar to that of the kinase inhibitor sorafenib, with pronounced slowing of tumor growth in some models that is limited to the period of agent administration being the primary treatment effect.