Combined epigenetic and metabolic inhibition blocks platinum-induced ovarian cancer stem cell enrichment

Abstract

High grade serous ovarian cancer (HGSOC) is the most common and aggressive type of ovarian cancer. Platinum resistance is a common occurrence in HGSOC and a main cause of tumor relapse resulting in high patient mortality rates. Recurrent ovarian cancer is enriched in aldehyde dehydrogenase (ALDH)+ ovarian cancer stem cells (OCSCs), which are resistant to platinum agents. We demonstrated that acute platinum treatment induced a DNA damage-dependent decrease in BRCA1 levels through BRCA1 promoter DNA hypermethylation. In a parallel pathway associated with G2/M arrest, platinum treatment also induced an increase in expression of NAMPT, the rate limiting regulator of NAD+ production from the salvage pathway, and NAD+ levels, the cofactor required for ALDH activity. Both decreased BRCA1 and increased NAD+ levels were required for the platinum-induced enrichment of OCSCs, and inhibition of both DNA methyltransferases (DNMT) and NAMPT synergistically abrogated the platinum-induced increase in OCSCs. We conclude that these two separate pathways lead to platinum-induced OCSC enrichment, providing preclinical evidence that in the neoadjuvant setting, combining DNMT and NAMPT inhibitors with platinum has the potential to reduce OC reoccurrence.

Platinum-Induced Mitochondrial OXPHOS Contributes to Cancer Stem Cell Enrichment in Ovarian Cancer

“…Furthermore, high expression and activity of the ALDH1A isoform strongly correlates with platinum resistant OC cells (8–10) and negatively correlates with survival of OC patients (11, 12). Our group as well as others have demonstrated that acute treatment of OC cells with platinum-based agents results in enrichment of ALDH+ OCSCs (7, 13, 14). Collectively, the evidence suggests that platinum-induced enrichment of ALDH+ OCSCs contributes to OC recurrence and relapse.…”

“…Approximately 24 hours after plating, cells were treated with cisplatin alone or in combination with DMSO or appropriate inhibitors and incubated at 37°C, 5% CO 2 for 16 hours. After the incubation time ALDEFLUOR assay (Stem Cell Technologies, #01700) was performed as described previously (14).…”

“…All the animal studies were performed in accordance with the Association for Assessment and Accreditation of Laboratory Animal Care International and approved by Indiana University Bloomington Institutional Animal Care and Use Committee as described previously (14). 2 × 10 6 OVCAR3 cells were injected subcutaneously in the flanks of NSG mice (IUSCCC In Vivo Therapeutics Core).…”

“…IACS-010759 was administered orally at 7.5 mg/kg five days a week for 3 weeks. At the end of the treatment schedule, mice were sacrificed and tumors were collected, disassociated and used for ALDEFLUOR assay as we have done previously (7, 14). Tumor dissociation kit and gentle MACS dissociator (Miltenyi Biotech) was used to dissociate the tumors into single cells as per manufacturer’s protocol.…”

“…We and others have demonstrated that acute platinum treatment results in an increase in expression of nictotinamide phosphoribosyltransferase (NAMPT) – a rate limiting enzyme in NAD+ biosynthesis salvage pathway. The subsequent increase in cellular NAD+ levels promotes ALDH+ OCSC enrichment and contributes to platinum resistance (13, 14). However, it is well-established that platinum resistance is a multifactorial phenomenon (22) and it likely that additional metabolic pathways contribute to the enrichment of ALDH+ OCSCs and chemoresistance.…”