Alpha 4 Integrin Expression Is A Determinant For Activity Of The Integrin Antagonist Hyd1 In Multiple Myeloma Cell Lines And Patient Specimens

Proceedings: AACR 102nd Annual Meeting 2011‐‐ Apr 2‐6, 2011; Orlando, FL Our laboratory previously showed that the β1 integrin inhibitory peptide HYD1 causes caspase independent cell death in myeloma cell lines. To further characterize the mechanism of HYD1 induced cell death an isogenic drug resistant variant was developed. This variant, called H929-60, was developed by chronically exposing parental H929 cells to increasing doses of HYD1 over time until a drug resistant phenotype was observed. The resistant cell lines demonstrated reduced binding of FAM-conjugated HYD1 to the cell surface compared to the parental cell line. We previously reported that HYD1 blocks α4β1 mediated adhesion to fibronectin and thus we asked whether resistance towards HYD1 induced cell death correlated with reduced α4β1 integrin expression. The resistant variant showed deceased levels of α4 integrin protein expression despite no change in RNA levels, indicating a post-transcriptional regulation of α4 expression. These changes were consistent with decreased binding to fibronectin, VCAM-1 and HS-5 stromal cells. Moreover, we demonstrated that biotin conjugated HYD1 is able to pulldown a α4 containing complex and the amount of α4 bound to biotin-HYD1 was reduced in the drug resistant variant. Reducing the expression of α4 and β1 integrins on the cell surface in H929 cells was sufficient to confer partial resistance to HYD1 induced cell death. Because the H929 resistant variant showed reduced adhesion to stroma cells, we asked whether acquisition of resistance towards HYD1 resulted in reduced levels of drug resistance in the HS-5 co-culture model of drug resistance. Using the HS-5 co-culture model, we show that the drug resistant variant H929-60 cells treated with either melphalan or velcade were drug sensitive in the HS-5 stromal co-culture model of drug resistance. Thus the drug resistant variant failed to demonstrate a cell adhesion mediate drug resistance (CAM-DR), indicating that as cells acquire resistance to HYD1 they lose resistance initiated by the tumor microenvironment. Finally, we show that HYD1 was significantly more potent in relapsed/refractory patient specimens compared to newly diagnosed patient specimens. Additionally, we show that α4 integrin expression positively correlates with HYD1 sensitivity. Together our data indicate that HYD1 is an attractive novel agent for the treatment of relapsed/refractory multiple myeloma with high levels of α4 integrin expression. 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 1523. doi:10.1158/1538-7445.AM2011-1523