Targeting MEIS2 in platinum resistant ovarian cancer

Background: Recurrent ovarian cancer (OC) develops chemoresistance, which is fatal. Cancer stem cells (CSCs) have been hypothesized to be responsible for driving chemoresistance and tumor relapse. Myeloid Ecotropic Insertion Site 2 (MEIS) is a homeobox transcription factor (TF) that is deregulated in various cancers, playing critical roles in regulating stem cell identity and cell fate decisions. Here, I examined the role of MEIS2 in regulating stemness features that promote chemoresistance of OC, and the impact of a MEIS2 blockade on OC initiation and progression. ​ Methods: Paired isogenic OC cell lines (platinum sensitive (Pt-S) and resistant (Pt-R)) were used. MEIS2 expression level in these cells was assessed by q-RT-PCR and Western Blotting. The effects of MEIS2 inhibition (by using a pharmacological inhibitor MEISi and biological knockdown (KD)) and overexpression (OE) on OC cell survival and chemosensitivity were assessed using colony formation and cell viability assay, and on stemness features by flow cytometry for analysis of ALDH+ CSC population and measurement of stemness-related gene expression. ​MEIS2 direct binding targets in OC cells were examined using ChIP-seq and validated using q-PCR. The anti-tumor effects of MEIS2 inhibition on Pt-R OC cells and tumor initiation were tested in vivo. Results: MEIS2 expression levels were increased in Pt-R vs. Pt-S OC cells at mRNA and protein levels. Treatment with MEIS2i (500nM-1µM) reduced the number of colonies in OC cells by at least 2-fold and resensitized Pt-R OC cells to cisplatin (p<0.05). Treatment with MEIS2i (250nM-1uM, 48 hours) decreased ALDH+ CSCs population by at least ~2-fold (p<0.05) and inhibited the expression of stemness-associated genes ALDH1 isoforms and Sox2 (p<0.05), compared to vehicle control. MEIS2 KD decreased the CSC population by two-fold (p<0.05) and inhibited stemness gene expression (p<0.05). By integrating ChIP-seq and RNA-seq, we identified that stemness-associated gene ALDH1A2 is a direct binding target of MEIS2 in OC cells, contributing to the maintenance of stemness and chemoresistant features. We further validated the MEIS2 binding region on the enhancer region of the ALDH1A2 genes using ChIP-qPCR, which is highly conserved across multiple species. In vivo, OC xenografts derived from MEIS2 KD OVCAR5 cells were more responsive to carboplatin (p<0.05) compared with control xenografts, and MEIS2 KD inhibited tumor-initiating capacity. Importantly, MEISi treatment alone (25μM/100μL, 5 days, 2 weeks) or in combination with carboplatin (25mg/kg, once/week, 2 weeks) suppressed OVCAR5 Pt-R xenograft tumor growth and inhibited ALDH+ CSC population in the tumor residuals. Conclusions: Altogether, blocking MEIS2 in OC cells inhibits stemness traits that contribute to chemoresistance and tumor relapse, suggesting that MEIS2 is a potential new treatment target in OC therapy.