ONC201 induces the unfolded protein response (UPR) in high- and low-grade ovarian carcinoma cell lines and leads to cell death regardless of platinum sensitivity

Abstract

Objectives: Treatment of both platinum resistant high grade (HG) and low-grade (LG) ovarian cancer (OVCA) poses significant challenges as neither respond well to conventional chemotherapy leading to morbidity and mortality. Identification of novel agents that can overcome chemoresistance is therefore critical. Previously, we have demonstrated that OVCA has basal upregulated unfolded protein response (UPR) and that targeting cellular processes leading to further and persistent upregulation of UPR leads to cell death. ONC201 is an orally bioavailable Dopamine Receptor D2 inhibitor demonstrating anticancer activity and was found to induce UPR. Given its unique properties, we hypothesized that ONC201 would overcome platinum resistance in OVCA.

Methods: Cisplatin sensitive and resistant HG OVCA and two primary LG OVCA cell lines were studied. Cell viability was determined using MTT assay. Cell migration was studied using wound healing assay. Apoptosis and mitochondrial membrane potential were investigated using flow cytometry. Analysis of pathway inhibition was performed by Western Blot. mRNA expression of UPR related genes were measured by qPCR. In vivo studies were completed utilizing axillary xenograft models. Co-testing with conventional chemotherapy was performed to study synergy.

Results: ONC201 significantly inhibited cell viability and migration in a dose dependent manner with IC50's from 1-20 µM for both cisplatin sensitive and resistant HG and LG-OVCA cell lines. ONC201 lead to upregulation of the pro-apoptotic arm of the UPR, specifically ATF-4/CHOP/ATF3 and increased the intrinsic apoptosispathway. The compensatory, pro-survival PI3K/AKT/mTOR pathway was downregulated. In vivo, weekly dosing of single agent ONC201 decreased xenograft tumor size by ~50% compared to vehicle. ONC201 also demonstrated significant synergy with paclitaxel in a highly platinum resistant OVCA cell-line (OV433).

Conclusions: Our findings demonstrate that ONC201 can effectively overcome chemoresistance in OVCA cells by blocking pro-survival pathways and inducing the apoptotic arm of the UPR. This is a promising, orallybioavailable therapeutic agent to consider in clinical trials for patients with both HG and LG OVCA.

Keywords: ONC201; apoptosis; high-grade ovarian cancer; low-grade ovarian cancer; unfolded protein response.