Baseline phosphorylated ERK levels in renal cell carcinoma patients from a phase II study of BAY 43–9006.

3677 BAY 43–9006 is a novel signal transduction inhibitor that prevents tumor growth by combining two anti-cancer activities: inhibition of tumor cell proliferation and tumor angiogenesis. BAY 43–9006 inhibits tumor cell proliferation by targeting the Raf/MEK/ERK pathway at the level of Raf kinase. BAY 43–9006 also exerts an anti-angiogenic effect by blocking the receptor tyrosine kinases VEGFR-2 and PDGFR and their associated signaling cascades. The Raf/MEK/ERK signaling pathway is an important mediator of tumor cell proliferation and angiogenesis. Activated Raf kinase phosphorylates and activates MEK (mitogen-activated protein kinase kinase), which in turn phosphorylates and activates ERK (extracellular signal-regulated kinase), which translocates to the nucleus and modifies gene expression. This pathway is often aberrantly activated in tumor cells due to the presence of activated ras, mutant BRAF, or elevation of growth factor receptors. Therefore, inhibition of the Raf/MEK/ERK signaling pathway may be therapeutically relevant. We have developed a semi-quantitative immunohistochemical method to detect phosphorylated ERK (pERK) in human tumor biopsies as a potential patient selection biomarker for the clinical development of BAY 43–9006. The antibody used is a polyclonal antibody (rabbit) that detects the phosphorylation status of p44 and p42 (phospho-p44/42 MAPK (Thr202/Tyr204)) MAP kinases (ERK1 and ERK2). The procedure has been formatted for performance on the DAKO Autostainer Universal Staining System but can also be done manually. After staining, slides are subjected to semi-quantitative analysis that uses a four quartile system for scoring percent nuclei expressing pERK and a 1+ to 4+ system for scoring staining intensity. This assay has been utilized to analyze renal cell carcinoma (RCC), hepatocellular and melanoma primary tumor biopsies from patients in Phase II clinical trials of BAY 43–9006. We report here on the methodology for detection of pERK and on the baseline status of pERK in the Phase II RCC patients.