Background: Gastric cancer (GC) is a prevalent and deadly disease. Because the Ras/Raf/MEK/ERK signaling cascade plays a critical role in signal transduction pathways that regulate growth factor response, angiogenesis, tumor cell proliferation, and apoptosis, blocking this signaling pathway could thus have therapeutic efficacy. This study aims to target this pathway in preclinical models of GC with refametinib (BAY 86-9766, RDEA119), an orally available, allosteric inhibitor of MEK1/2.

Methods: Eight patient-derived GC xenograft models with different histotypes were treated orally with refametinib or vehicle and tumor growth was monitored using caliper measurements. Tissue sections of vehicle- or refametinib-treated xenografts were analyzed by immunohistochemistry for cell proliferation, apoptosis and microvessel area, using antibodies against p-Histone H3Ser10, cleaved PARP and CD31, respectively. Tumor lysates were analyzed by Western Blotting with antibodies for effects on marker proteins for proliferation, apoptosis and angiogenesis.Results: Refametinib demonstrated significant tumor growth inhibition ranging from 66-87% in eight GC models at a dose of 15 mg/kg/d. Refametinib inhibited cell proliferation by 2-4 fold as observed by reduced staining for p-Histone H3Ser10. Increased staining for caspase-cleaved p85 PARP by 1.5 to 9 fold was detected, indicating that refametinib induced apoptosis. Furthermore the compound significantly inhibited angiogenesis in 2 of 8 models by 3-fold compared to the vehicle-treated group as indicated by reduced CD31 staining. Reduced cell proliferation and induction of apoptosis were associated with decreased levels of p-ERK1/2, p-cdk2Thr14/Tyr15, p-p90RSKSer359/363, p-p70S6KThr421/Ser424, p-4EBP1Thr70, p-S6RSer235/236 and p-eIF4ESer209 and elevation of p-AktSer473, Bim and cleaved PARP. Conclusion: We show that single-agent refametinib has significant anti-tumor activity in patient-derived gastric cancer preclinical models. Our findings support further investigation of refametinib either in monotherapy or in combination with inhibitors of the PI3K-AKT-mTOR pathway in the treatment of GC.

Citation Format: Huynh T. Hung, Richard Ong, Khee Chee Soo, Florian Puehler, Arne Scholz, Dominik Mumberg, Dieter Zopf, Karl Ziegelbauer. Refametinib (BAY 86-9766): An allosteric inhibitor of MEK1/2, potently inhibits tumor growth in patient-derived xenograft models of gastric cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1052. doi:10.1158/1538-7445.AM2013-1052