Investigating the Potential for NHE1 Inhibitors to Function as Adjuvant Therapies in the Treatment of Ovarian Cancer

Abstract

Each year in the United States over 22,000 women are diagnosed with ovarian cancer leading to more than 14,000 deaths. Differential expression and activity of the Na+-H+ Exchanger Isoform 1 (NHE1) has been demonstrated to regulate cell proliferation in ovarian cancer cells from patients. NHE1 is an 815 amino acid transmembrane transport protein that regulates intracellular pH. NHE1 is hyperactivated in various types of cancer cells leading to a pH inversion that supports both cell proliferation and invasion. A significant issue in ovarian cancer therapy is the development of drug resistance and disease recurrence. In an effort to combat these outcomes, it is hypothesized that combining common ovarian cancer therapeutic agents along with compounds that directly inhibit NHE1 activation will enhance the ability of the therapeutic agents to slow ovarian cancer progression. Two ovarian adenocarcinoma cell lines; CAOV-3 and SKOV-3 are used in this research. Utilizing a proliferation assay, the impact of the ovarian cancer therapeutics, Rucaparib, Olaparib, Carboplatin and Cisplatin, were assessed in the presence and absence of the NHE1 inhibitors Cariporide and Ethylisopropyl Amiloride (EIPA). Dose response curves have been generated for each therapeutic (mean ± SE n=36) to evaluate the impact of combination therapies and supplement IC50 and percent reduction values for each pair. One example includes a 46% reduction in IC50 value for carboplatin alone (47.09 mM) as compared to carboplatin plus Cariporide (25.28 mM) in CAOV-3 cells. Reductions in IC50 values for each of the therapeutics in combination with NHE1 inhibitors ranging from 24% to 92% were seen in both cell lines. This work has been expanded to a three-dimensional environment, investigating the impact of combination therapies in a spheroid assay. To begin to identify a mechanism for NHE1 involvement in ovarian cancer progression and treatment, a steady-state intracellular pH was performed. It has been shown that when chemotherapeutics are paired with NHE1 inhibitors, a synergistic effect is exhibited in which the combination is more proficient at reducing cancer growth than either compound can alone. To confirm this relationship, NHE1 knockout cell lines are being created via CRISPR-Cas9 gene editing. If this relationship is validated, it could allow a reduction in the required drug dosage while maintaining efficacy and hopefully reducing harmful side effects in patients. Our research indicates that the inhibition of NHE1 in combination with standard chemotherapeutics may serve as a potential therapeutic target in ovarian cancer treatment.