Abstract 4409: A quantitative MSD assay to measure c-IAP1 degradation in PBMC, cell lines and tumor cells as a pharmacodynamic biomarker following antagonism of IAP family members

Abstract

Abstract The Inhibitor of Apoptosis (IAP) protein family members are widely expressed in many cancers, providing a mechanism to protect these cancer cells from apoptosis. The IAP proteins block activation of the canonical and non-canonical NF-kB pathway, the subsequent expression of TNFα and its initiation of the extrinsic apoptosis pathway. IAP proteins also directly bind and inhibit caspases activated during the induction of apoptosis. Using MDA-MB-231 cells as a model system to assess the effect of candidate IAP antagonists on markers of extrinsic and intrinsic pathway inhibition, we observe that the antagonism of the major IAP family members results in apoptosis in vitro and inhibits their tumor growth in nude mice in vivo. These effects are coincident with changes in the cellular levels of IAP family members such as c-IAP1, detected by Western analysis. These data are consistent with previously described autoubiquitination and subsequent proteasomal degradation of c-IAP1 following IAP antagonism. We have developed a high-throughput, quantifiable and sensitive assay to measure c-IAP1 levels in multiple cell lines, xenografts and in PBMCs using the MesoScale Discovery (MSD) Platform. The c-IAP1 MSD assay has a lower limit of quantification of 1.6 ng/ml of cell lysate, has precision of <10% CV and is linear down to at least a 4-fold dilution of lysate. Quantifiable changes in cellular c-IAP1 protein may serve as an ideal proximal pharmacodynamic (PD) biomarker to measure IAP family inhibition and degradation in the cell, particularly in the evaluation of candidate inhibitors targeting the IAP pathway in the clinical setting. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4409. doi:10.1158/1538-7445.AM2011-4409