Pharmacodynamic monitoring of BAY 43‐9006 (Sorafenib) in phase I clinical trials involving solid tumor and AML/MDS patients, using flow cytometry to monitor activation of the ERK pathway in peripheral blood cells

Background We previously reported a flow cytometry technique to monitor pharmacodynamic effects of the raf kinase inhibitor BAY 43‐9006 based on the ability of phorbol ester (PMA) to phosphorylate extracellular‐regulated kinase (ERK) in peripheral blood (Chow et al., Cytometry 2001;46:72–78). In this article, we describe its application to phase I trials of BAY 43‐9006 in solid tumor and AML/MDS patients. Methods The previously described whole blood lysis method was used to monitor BAY 43‐9006 effects on peripheral T‐cells of solid tumor patients. A modified whole blood fixation protocol was developed for the AML/MDS trial, using the c‐kit ligand stem cell factor (SCF) to activate ERK as an alternative to PMA, and incorporating immunophenotypic markers to identify leukemic blasts. Results At all dose levels of BAY 43‐9006 used to treat solid tumor patients, ERK could be activated by PMA in peripheral T‐cells and we were not able to show inhibition of raf kinase. A similar effect was seen in the lymphocytes of AML/MDS patients during treatment with BAY 43‐9006. However, we found strong inhibition when ERK was activated via c‐kit using SCF. Furthermore, normal donor CD34+ve stem cells were much more sensitive to BAY 43‐9006 when ERK was activated by SCF, compared to PMA. Conclusions These findings support the further development of flow cytometry applications to monitor signal transduction inhibitors during early phase clinical trials. © 2006 International Society for Analytical Cytology