Abstract 5467: NTX301 targets platinum resistant ovarian cancer
Authors: Wang Yinu , Situ Xiaolei , Cardenas Horacio , Matei Daniela 
Published: June 2022

Abstract
Background: The majority of patients with ovarian cancer (OC) experience tumor relapse and develop chemoresistant tumors, which are fatal. Epigenetic alterations, especially DNA methylation, result in silencing of tumor suppressor and differentiation-associated genes, confer chemoresistance and are linked to stemness. Although our and others’ previous studies demonstrated that hypomethylating agents (HMA) could re-sensitize OC cells to chemotherapy, translation to the clinic has been slow due the poor stability and bioavailability of existing HMAs. Novel agents are critically needed.
Methods: NTX 301 is a novel, highly potent and orally bioavailable HMA, in early clinical development, provided by PinotBio. Here, we assessed its anti-tumor effects in OC models by using cell proliferation, stemness assays, and RNA sequencing and validation.
Results: OC cells (SKOV3, IC50=5.089nM; OVCAR4, IC50=29.68nM; and OVCAR5 IC50=3.664nM) were highly sensitive to NTX301 (p&lt;0.05) compared to immortalized fallopian tube epithelial cells (FT-190) (IC50=103.3nM). Treatment with NTX301 induced more significant downregulation of the DNA methyltransferases (DNMTs) 1-3 expression in SKOV3 and OVCAR5 cells compared with decitabine (p&lt;0.05). Treatment with low dose NTX301 (100nM) reset the transcriptome of OC cells, inducing about 15,000 differentially expressed genes (DEGs) compared to DMSO (P&lt;0.05). Gene Ontology Enrichment analysis classified upregulated DEGs enriched in biological processes related to cellular response to DNA damage stimulus, DNA repair, positive regulation of cell cycle process; down-regulated DEGs enriched in processes of regulation of alcohol, cholesterol, and fatty acid biosynthesis and regulation of cell migration. GO analysis indicated NTX301 down-regulated molecular functions related to aldehyde dehydrogenase (ALDH) and oxidoreductase activity, known features of cancer stem cells (CSCs). Indeed, treatment with low dose NTX301 (100nM, 4 days) reduced ALDH(+) cell population, inhibited their self-renewal ability, and repressed the stemness-related transcription factor, Sox2 (P&lt;0.05). We next tested the effects NTX301 in cisplatin (CDDP) resistant OC cells, developed by repeated treatments with CDDP. Priming with NTX301 reduced the IC50 (~two-fold) to CDDP in OVCAR5_CDDP (5.43μM vs. 9.79μM) and OVCAR4_CDDP (2.19μM vs. 9.29μM) resistant cells (p&lt;0.05). NTX301 with CDDP induced phospho-γH2AX and cleaved caspase 3. To discover the mechanisms by which NTX301 restored chemosensitivity, we measured its effects on Schlafen-11 (SLFN11), a DNA damage response regulator silenced through methylation. SLFN11 expression was repressed in CDDP resistant compared to parental cells (P&lt;0.05) and treatment with NTX301 induced its re-expression (P&lt;0.05).
Conclusions: Our data indicate that NTX301 is a potent HMA which targets ovarian CSCs and re-sensitizes OC cells to chemotherapy, supporting its further development in OC.
Citation Format: Yinu Wang, Xiaolei Situ, Horacio Cardenas, Daniela Matei. NTX301 targets platinum resistant ovarian cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5467.