Abstract B2: Regorafenib, an oral multi-kinase inhibitor of angiogenic, stromal and oncogenic receptor tyrosine kinases, potently inhibits tumor growth and angiogenesis in patient-derived xenograft models of gastric cancer.

Abstract

Abstract Background: Gastric cancer (GC) is a prevalent and deadly disease. Because the VEGFR and PDGFR signaling cascade plays a critical role in the development and progression of gastric cancer and VEGF expression is correlated with angiogenesis, tumor progression and poor prognosis in patients with GC, blocking these signaling pathways could thus have therapeutic efficacy. This study aims to investigate the potential of a combined therapeutic approach to target these pathways in preclinical models of GC with regorafenib an oral multi-kinase inhibitor targeting VEGFR1–3, PDGFR, FGFR, TIE-2, RET and KIT. Methods: Eight patient-derived GC xenograft models with different histotypes were treated orally with regorafenib or vehicle and tumor growth was monitored using caliper measurements. Tissue sections of vehicle- or regorafenib-treated xenografts were analyzed by immunohistochemistry for apoptosis, microvessel area, and cell proliferation using antibodies against cleaved PARP, CD31 and phospho-Histone3Ser10, respectively. Tumor lysates were analyzed by Western Blotting with respective antibodies for effects on marker proteins for proliferation, apoptosis and angiogenesis. Results: Regorafenib demonstrated significant tumor growth inhibition of 81%, 85% and 88% in the GC09-0109 model after oral administration of 5, 10 and 15 mg/kg/d, respectively. In addition potent tumor growth inhibition ranging from 72–96% was observed in seven other GC models at a dose of 10 mg/kg/d. Regorafenib significantly inhibited angiogenesis in all models by 4–12 fold compared to the vehicle-treated group, independent of their degree of vascularization, as indicated by reduced CD31 staining. Furthermore inhibition of cell proliferation by 2–4 fold was observed by reduced staining for p-histone 3Ser10. Increased staining for caspase-cleaved p85 PARP by 2 to 20 fold was detected, indicating that regorafenib induced apoptosis. Finally, regorafenib also induced tumor necrosis as detected by histological staining. Inhibition of angiogenesis, reduced cell proliferation and induction of apoptosis and necrosis was associated with decreased levels of p-ERK1/2, p-cdk2Thr14/Tyr15, p-VEGFR2Tyr951, p-p70S6KThr421/Ser424, p-S6RSer235/236 and p-eIF4ESer209 and elevation of cleaved caspase-3 and cleaved PARP. Conclusion: We show that regorafenib is an efficacious anti-tumor targeted agent in patient-derived gastric cancer preclinical models. Our findings support further investigation of regorafenib in the treatment of GC. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr B2.