Abstract 2317: SGI-110 alters ovarian cancer stem cells to prevent recurrent and chemoresistant ovarian cancer

Abstract

Abstract Ovarian cancer stem cells (OCSCs) are associated with drug resistance and tumor relapse. Epigenetic aberrations, especially DNA methylation, result in silencing of tumor suppressor and differentiation-associated genes and regulate OCSCs' survival. To test the hypothesis that DNA hypomethylating agents can “reset” OCSCs towards differentiation, we investigated the effect of the DNA methytransferase inhibitor SGI-110 on OCSCs, defined by aldehyde dehydrogenase 1 (ALDH)(+) cells. We treated ALDH(+) cells from platinum-sensitive A2780 and platinum-resistant A2780-cp OC cells with SGI-110 (100nM, 72 hr) or with cisplatin (CDDP; 1.67M, 24hr). After a 4 day recovery period, %ALDH+ was analyzed using FACS, cell viability was determined, and ALDH(+) cells were grown as spheroids in culture or as xenografts in mice. The overall %ALDH+ cells was higher (P<0.05) at baseline in the SKOV3 (0.65%) and A2780-cp (1.07%) cells vs. A2780 (0.3%). SGI-110 inhibited (P<0.001) the growth and %ALDH+ of A2780, A2780-cp cells. SGI-110-CDDP inhibited cell growth vs. CDDP alone (p<0.001) and decreased (P<0.05) ALDH(+) cells in A2780 and A2780-cp. MTT assay showed A2780-cp-ALDH(+) cells were 3-fold more resistant than ALDH(-) cells to CDDP. SGI-110 decreased by 2 and 6-fold respectively the CDDP IC50 in A2780 and A2780-cp (P<0.05). SGI-110 induced both transient and prolonged inhibitory (P<0.05) effects on ALDH(+) cell migration and sphere and colony formation. DNA methylation and gene expression changes in the ALDH(+) spheres were assessed by pyrosequencing and qRT-PCR. HOXA10 and HOXA11 (differentiation-associated genes) were upregulated and the stemness markers ALDH1A1, Bmi1, Nanog, Notch3 and Oct4 were down regulated by SGI-110. ALDH+ cells treated with SGI-110 (100nM) showed prolonged tumor formation latency and reduced tumor growth in mice compared to ALDH+ cells alone, whereas ALDH- cells were non-tumorigenic. In an ip xenograft model derived from A2780 cells, CDDP decreased (P<0.001) tumor growth. The %ALDH(+) cells and spheroid numbers were increased (p<0.001) in the cell population dissociated from residual OC xenografts after CDDP treatment (3 weeks) compared to control (44% vs. 2.3%). Maintenance therapy with SGI-110 after maximal response induced by CDDP decreased recurrent tumor growth and metastases (P=0.05). DNA methylome assessed with Infinium 450K methylation arrays showed global demethylation of xenografts by SGI-110 vs. control (6% decrease in average β-value, p=0.05 and over 60,000 hypomethylated sites). In summary, our in vitro and in vivo data demonstrate that low dose SGI-110 or with CDDP, reduced the stemness capability of OCSCs and SGI-110 alone increased CDDP sensitivity and induced reexpression of differentiation-associated genes in ALDH+ cells. Therefore, SGI-110 in combination with cisplatin has the potential to alter OCSC in patients to prevent recurrent and chemoresistant OC. Citation Format: Yinu Wang, Horacio Cardenas, Fang Fang, Salvatore Condello, Pietro Taverna, Gavin Choy, Mohammad Azab, Kenneth Nephew, Daniela Matei. SGI-110 alters ovarian cancer stem cells to prevent recurrent and chemoresistant ovarian cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2317. doi:10.1158/1538-7445.AM2014-2317