Introduction: BAY 869766 (RDEA119) is an orally available, allosteric MEK1/2 inhibitor, targeting the central switch in the MAP kinase pathway. BAY 869766 demonstrates potent in vitro and in vivo activity in different human cancer cell lines and preclinical models. BAY 869766 is currently in clinical phase I/II studies in the indications HCC (hepatocellular carcinoma) and pancreatic cancer (PaCa). In the described preclinical studies BAY 869766 was studied in two orthotopic, syngeneic HCC and PaCa models and five subcutaneous PaCa xenografts as a single agent and combination therapy. In contrast to subcutaneous xenografts, orthotopic syngeneic models provide additional important information about microenvironment-dependent tumor growth, metastatic spread, immune response and survival.

Results: To establish a syngeneic, orthotopic HCC model, the rat HCC cell line MH3924a was first evaluated in vitro. BAY 869766 induced antiproliferative effects in MH3924a HCC cells in monotherapy and showed synergistic effects in combination with sorafenib. In the corresponding rat allograft model efficacy of BAY 869766 in mono- and combination therapy with sorafenib was confirmed. Primary tumor growth and metastatic spread were strongly reduced. These effects were accompanied by a reduction of pERK levels, proliferation index and microvessel density. Finally, the median overall survival in combination treatment was increased by 100% in comparison with vehicle treatment. To characterize BAY 869766 in an orthotopic syngenic PaCa model, the Panc02 mouse allograft model was established. BAY 869766 was tested in mono- and combination therapy with Gemcitabine. Especially, combination treatment led to significant lower tumor weight, reduction of metastatic spread and increase of median survival by 135%. To test BAY 869766 in further clinical relevant pancreatic cancer models, five patient-derived pancreatic cancer tumor samples were subcutaneously implanted in mice and subsequently treated with BAY 869766. Significant tumor growth inhibition in these patient-derived pancreatic cancer xenograft models was observed (Treatment/Control ratios from 23,5% − 44%).

Conclusion: These preclinical results support the clinical development of the MEK inhibitor BAY 869766 in HCC and pancreatic cancer. Inhibition of Ras-Raf-MEK-Erk-signaling, direct antiproliferative effects on tumor cells, reduction of metastatic spread and anti-angiogenic properties were demonstrated in these studies. In combination with the respective SoC drugs a significant benefit in survival could be achieved in the orthotopic models.

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 B247.