Aerobic glycolysis is an important metabolic adaptation of cancer cells. There is growing evidence that oxidative phosphorylation is also an active metabolic pathway in many tumors, including in high grade serous ovarian cancer. Metastasized ovarian tumors use fatty acids for their energy needs. There is also evidence of ovarian cancer stem cells privileging oxidative phosphorylation (OXPHOS) for their metabolic needs. Metformin and thiazolidinediones such as rosiglitazone restrict tumor growth by inhibiting specific steps in the mitochondrial electron transport chain. These observations suggest that strategies to interfere with oxidative phosphorylation should be considered for the treatment of ovarian tumors. Here, we review the literature that supports this hypothesis and describe potential agents and critical control points in the oxidative phosphorylation pathway that can be targeted using small molecule agents. In this review, we also discuss potential barriers that can reduce the efficacy of the inhibitors of oxidative phosphorylation.

The Na + /K + -ATPase (NKA) complex is the master regulator of membrane potential and a target for anti-cancer therapies. Here, we investigate the effect of drug-induced oxidative stress on NKA activity. The natural product, plumbagin increases oxygen radicals through inhibition of oxidative phosphorylation. As a result, plumbagin treatment results in decreased production of ATP and a rapid increase in intracellular oxygen radicals. We show that plumbagin induces apoptosis in canine cancer cells via oxidative stress. We use this model to test the effect of oxidative stress on NKA activity. Using whole-cell patch-clamp electrophysiology we demonstrate that short-term exposure (4 min) to plumbagin results in 48% decrease in outward current at +50 mV. Even when exogenous ATP was supplied to the cells, plumbagin treatment resulted in 46% inhibition of outward current through NKA at +50 mV. In contrast, when the canine cancer cells were pre-treated with the oxygen radical scavenger, N-acetylcysteine, the NKA inhibitory activity of plumbagin was abrogated. These experiments demonstrate that the oxidative stress-causing agents such as plumbagin and its analogues, are a novel avenue to regulate NKA activity in tumors.

Background: MUC16 is a transmembrane protein that is overexpressed by ovarian cancer. The role of MUC16 in the pathogenesis of ovarian cancer is unknown; however, MUC16 may facilitate binding of ovarian tumor cells to mesothelial cells lining the peritoneal cavity. Traditional antibody drug conjugates, with conjugation through inter-chain disulfides, are heterogeneous mixtures of drug antibody ratios (DAR) ranging from 0-8, resulting in complex pharmacokinetics (PK) and potentially unfavorable safety and efficacy. In contrast, THIOMABTM drug conjugates (TDCs) use novel technology that achieves site-directed drug conjugation yielding a homogeneous DAR. DMUC4064A is a cysteine-engineered TDC comprising a humanized anti-MUC16 IgG1 and 2 potent anti-mitotic monomethyl auristatin E (MMAE) molecules. Methods: The dose-escalation component of the Phase I study evaluated safety, tolerability, PK, pharmacodynamics, and early activity of DMUC4064A given Q3W to patients with platinum-resistant ovarian cancer. A standard 3+3 design was used to determine the maximum-tolerated dose. Archival tumor tissue was used to assess expression of MUC16 and other markers. Clinical activity was evaluated per RECIST v4.0 criteria. Results: Forty-four female patients, median age 63 (35-84), ECOG PS 0-1, received a median of 4 doses (range 1-12) of DMUC4064A at 1.0-5.6 mg/kg. At 5.6 mg/kg, one patient experienced three adverse events (AE) each qualifying as a DLT (colitis, hyperglycemia, and hypokalemia; all Grade 3). At 5.2 mg/kg, another patient experienced a DLT of Grade 5 septic shock. Grade ≥ 3 AE occurring in ≥ 5% of patients included hyponatremia (1 each at 1.8, 3.2, and 5.2 mg/kg; 2 at 2.4 mg/kg; 11% total), ascites (2 at 2.4 mg/kg and 1 at 3.2 mg/kg; 7% total) and hyperglycemia (3 at 5.6 mg/kg; 7% total), all unrelated except hyperglycemia. The most common (≥20%) related AEs for all dose levels were fatigue (34%), nausea (32%), diarrhea (23%) and abdominal pain (21%). Ocular toxicities (related, Grade ≥ 2) included keratitis (Grade 3, n=2), blurred vision (Grade 3, n=1; Grade 2, n=3), and dry eye (Grade 2, n=1). Total antibody and conjugated MMAE showed dose-dependent PK; neither were impacted by circulating CA125. Total antibody, conjugated and free MMAE accumulation was minimal. At doses ≥2.4 mg/kg, DMUC4064A had decreased clearance and achieved higher exposures versus MUC16 MMAE ADC. Confirmed responses (1 CR and 6 PRs) occurred at ≥ 3.2 mg/kg (n=30). Tumor MUC16 IHC scores were 2+/3+ in responders for whom data were available (n=5). Conclusions: These data are the first reported for an MMAE-containing TDC in a clinical trial (clinicaltrials.gov NCT02146313). DMUC4064A has an acceptable safety profile with improved stability compared to MUC16 MMAE ADC and shows evidence of anti-tumor activity, warranting further evaluation in ovarian cancer. Citation Format: Joyce F. Liu, Kathleen N. Moore, Judy S. Wang, Manish Patel, Michael J. Birrer, Erika Hamilton, Lisa Barroilhet, William M. Flanagan, Yulei Wang, Amit Garg, Xuyang Lu, Anjali Vaze, Dilip Amin, Doug Leipold, S Renee Commerford, Eric W. Humke, Harold A. Burris. Targeting MUC16 with the THIOMABTM-drug conjugate DMUC4064A in patients with platinum-resistant ovarian cancer: a Phase I escalation study [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr CT009. doi:10.1158/1538-7445.AM2017-CT009

Current therapeutic strategies for endometriosis focus on symptom management and are not curative. Here, we provide evidence supporting inhibition of oxidative phosphorylation (OXPHOS) as a novel treatment strategy for endometriosis. Additionally, we report an organotypic organ-on-a chip luminal model for endometriosis. The OXPHOS inhibitors, curcumin, plumbagin and the FDA approved anti-malarial agent, atovaquone, were tested against the endometriosis cell line, 12Z, in conventional as well as the new organotypic model. The results suggest that all three compounds inhibit proliferation and cause cell death of the endometriotic cells by inhibiting OXPHOS and causing an increase in intracellular oxygen radicals. The oxidative stress mediated by curcumin, plumbagin and atovaquone cause DNA double strand breaks as indicated by elevation of phospho-γH2Ax. Mitochondrial energetics shows significant decrease in oxygen consumption in 12Z cells. These experiments also highlight differences in mechanism of action as curcumin and plumbagin inhibit Complex I whereas atovaquone blocks Complex I, II and III. Real time assessment of cells in the lumen model showed inhibition of migration in response to the test compounds. Additionally, using two-photon lifetime imaging, we demonstrate that the 12Z cells in the lumen show decreased redox ratio (NAD(P)H/FAD) and lower fluorescence lifetime of NAD(P)H in the treated cells confirming major metabolic changes in response to inhibition of mitochondrial electron transport. The robust chemotoxic responses observed with atovaquone suggest that this anti-malarial agent may be repurposed for effective treatment of endometriosis.