Abstract 2317: SGI-110 alters ovarian cancer stem cells to prevent recurrent and chemoresistant ovarian cancer
Authors: Wang Yinu , Cardenas Horacio , Fang Fang , Condello Salvatore , Taverna Pietro , Choy Gavin , Azab Mohammad , Nephew Kenneth , Matei Daniela 
Published: May 2015

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&lt;0.05) at baseline in the SKOV3 (0.65%) and A2780-cp (1.07%) cells vs. A2780 (0.3%). SGI-110 inhibited (P&lt;0.001) the growth and %ALDH+ of A2780, A2780-cp cells. SGI-110-CDDP inhibited cell growth vs. CDDP alone (p&lt;0.001) and decreased (P&lt;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&lt;0.05). SGI-110 induced both transient and prolonged inhibitory (P&lt;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&lt;0.001) tumor growth. The %ALDH(+) cells and spheroid numbers were increased (p&lt;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