Abstract 796: Novel mechanisms of drug resistance in leukemia cells associated with changes in HoxA9 and microRNA expression

Abstract

Abstract The acquisition of resistance to anticancer drugs is a key obstacle to successful cancer therapy. An increasing number of studies have investigated the roles of microRNAs in drug resistance. We previously reported that the upregulation of miR-135b and miR-196b correlated positively with acquired drug resistance in the human T-cell leukemia cell line, CCRF-CEM (CEM), and that the elevation of expression of these two microRNAs in response to the DNA damaging agent etoposide appears to be histiotype-specific (T-T Ho et al, Proceedings of the 102nd Annual Meeting of the AACR 2011). To develop a mechanistic understanding of why these microRNAs are differentially expressed, we have studied miR-196b, which maps between the HoxA9 and HoxA10 genes on chromosome 7p15.2, suggesting that miR-196b and HoxA genes might be co-activated. Indeed, we found upregulation of HoxA9 mRNA after short-term (48 h) exposure of CEM cells to the topoisomerase II inhibitors etoposide and doxorubicin. Of note, we also found that HoxA9 is constitutively overexpressed in multidrug-resistant CEM/VM-1-5 cells. Of interest, we found that HoxA9 is clearly associated with drug resistance, as knockdown of HoxA9 using esiRNA (a heterogeneous mixture of siRNAs that all target the same mRNA) partially sensitized multidrug-resistant CEM/VM-1-5 cells to etoposide. This indicates that the expression of miR-196b is linked to HoxA gene transcription and to drug responsiveness. We subsequently confirmed that the expression of HoxA9 mRNA follows the same pattern in other leukemia cells. For example, both miR-196b and HoxA9 are upregulated in response to short-term etoposide exposure in HL-60 (acute promyelocytic leukemia), but not in solid tumor-derived MCF7 (breast cancer cell line) and its etoposide-resistant subline MCF7/VP, or Rh30 (rhabdomyosarcoma cell line) and its etoposide-resistant subline, Rh30/V1. We are presently assessing the role of HoxA9 in drug resistance in other leukemia cell lines and investigating the mechanistic basis for this effect. In summary, we report here a novel mechanism of anticancer drug resistance in leukemia cells that is associated with HoxA9 and specific changes in microRNA expression. This is the first report that HoxA9 may impact on anticancer drug resistance. (Supported in part by R01 CA40570 from NCI to WTB, and in part by UIC.) Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 796. doi:1538-7445.AM2012-796