Abstract B35: Validation of a multiplex method for detection of several oncosignaling proteins with potential utility for assessment of pharmacodynamic activity of hsp90 inhibitors

Biomarkers are increasingly being used in early phase clinical trials not only to determine pharmacodynamic activity but also as surrogate end points of clinical efficacy. BIIB021 is a synthetic small molecule that inhibits the activity of Hsp90, a molecular chaperone involved in the folding of multiple oncogenic signaling proteins. Treatment of tumor models and cancer patients with BIIB021 resulted in proteosomal degradation of key cancer survival proteins e.g., AKT, RAF, IGF‐1R, ER and HER‐2. BIIB021 is currently undergoing Phase I/II testing in GIST, Breast Cancer and Solid tumors. We are exploring robust methods for assessing multiple signaling markers with an objective of using them to confirm inhibition of Hsp90 activity and support dose/schedule finding studies. To that end, we have evaluated the utility of a sensitive multiplex assay on the Meso Scale Discovery (MSD) platform. This platform measures the levels of total and phosphorylated proteins of the MAPK and AKT signaling pathways. Peripheral blood mononuclear cells from healthy, breast and prostate cancer patients were treated ex vivo with BIIB021 and the levels of multiple signaling proteins were determined in the MSD assay. A significant decrease in the AKT family of signaling proteins was observed in all of the donors tested, while up to 75% of the subjects showed a marked reduction in the MAPK family of proteins over a period of 24hrs. The depletion of the similar oncosignaling proteins by BIIB021 was also confirmed in mouse models of human breast cancer and in vitro studies using the MSD platform 1 . Furthermore, to support the future development of BIIB021 in oncology, the multiplex assay will be validated for various clinical parameters (i.e., Quantitation range, reproducibility, accuracy, precision, linearity, longitudinal variability, and stability). We anticipate a rationally developed and rigorously validated multiplex assay measuring key signaling proteins involved in the survival of tumor cells would fully support the clinical development of BIIB021 and a wide range of anti‐cancer agents affecting the AKT/MAPK pathways. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):B35.