Abstract 1547: Acquisition of resistance to the β1 integrin antagonist HYD1 correlates with decreased α4, α6, αV and β1 integrin expression and decreased adhesion to fibronectin, VCAM-1 and vitronectin

Proceedings: AACR 101st Annual Meeting 2010‐‐ Apr 17‐21, 2010; Washington, DC Our laboratory recently reported that the D amino acid-containing β1 integrin inhibitory peptide HYD1 causes caspase independent cell death in multiple myeloma (MM) cell lines as a single agent in vitro and in vivo (Nair et al Molecular Cancer Therapeutics, 2009). Exposure of MM cells to HYD1 induces autophagy, but autophagy was shown to contribute to survival following HYD1 treatment. HYD1 treatment induces cell death in MM cell lines indicative of necrosis. These characteristics included: (a) an increase in the levels of reactive oxygen species (ROS), (b) ATP depletion and (c) loss of mitochondrial membrane potential. To further characterize the mechanism of HYD1 induced cell death an isogenic drug resistant variant was developed. This variant, referred to as H929-60, was developed by chronically exposing parental H929 cells to increasing doses of HYD1. Acquired resistance correlated with decreased HYD1 induced TO-PRO-3 positivity, decreased levels of ROS, reduced ATP depletion and reduced mmp loss compared to the H929 cell line. Additionally, the drug resistant variant H929-60 cells displayed decreased cell surface binding of FAM-HYD1 compared to H929 cells. These data indicate that decreased expression of the binding target(s) of HYD1 may contribute to drug resistance. Gene expression profiling (GEP) was used as an unbiased approach to identify changes in gene expression that may contribute to HYD1 resistance. Differentially expressed genes were mined in silico using the pathway analysis programs Ingenuity and GeneGo. The integrin signaling hub showed substantial changes in gene expression in the drug resistant variant compared to the parental cell line. Specifically, α4, α6, αV and β1 integrins were all down regulated along with the integrin associated protein CD47 in the HYD1 resistant cell line. These changes were consistent with decreased protein expression of integrins on the cell membrane and decreased functional adhesion to fibronectin, vitronectin and VCAM-1. Reducing the expression of α4 integrin using shRNA in the parental H929 cell line conferred partial resistance to HYD1 induced cell death. Together our data show that the acquisition of resistance to HYD1 correlated with decreased integrin expression and functional binding to extracellular matrixes. Future studies aim to determine whether a decrease in α6, αV and β1 integrins on the cell surface contributes to HYD1 resistance. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1547.