Abstract 4650: RalBP1, a novel approach for ovarian cancer therapy

Abstract Ovarian cancer (OC) is the most devastating gynecologic cancer. The ever-climbing incidence rate of OC makes it the most lethal female reproductive disorder. Triggering apoptosis is one of the potential strategies to overcome chemoresistance. Recent evidence suggests that the failure of drug-induced apoptosis may be an underlying cause of drug-resistance. Molecular mechanisms of failed apoptosis in chemoresistant OC cells include p53 mutations, abnormal expression of the Bcl2 family proteins, and upregulation of other inhibitors of apoptosis that block caspases and stabilize the mitochondrial permeability pore. RalBP1 (Ral-binding protein) is a required stress-defense protein for OC, and its specific depletion or inhibition will cause apoptosis in cancer cells expressing RalBP1. RalBP1 is a multifunctional 76 kDa protein encoded as a splice variant in the human RALBP1 gene (18p11. 22). RalBP1 is an ATP dependent efflux transporter for glutathione (GSH) conjugates (GS-E) of products of oxidative stress, like 4HNE and GSH-conjugates of chemotherapy drugs. Our recent studies indicate that upon depletion/inhibition of RalBP1, malignant cells are significantly more sensitive to apoptosis than non-malignant cells, suggesting that the stress-protective, anti-apoptotic activity of RalBP1 is necessary for malignant cells. This differential sensitivity to RalBP1 translates into tumor regression, a lack of toxicity, and the prolonged survival of mice bearing subcutaneous OC cells in which RalBP1 is inhibited by anti-RalBP1 IgG or depleted using RalBP1 antisense oligonucleotides. These studies demonstrate that inhibition or depletion of RalBP1 exerts anti-neoplastic effects in OC and indicate that this GS-E and xenobiotic transporter occupies an important position in the hierarchy of stress defense mechanisms necessary for cancer cell survival. Overall, the present research focuses on hypothesis-driven studies to define novel relationships between RalBP1 and signaling pathways, and to determine the suitability of RalBP1 as an anticancer target for OC. Citation Format: Sharad S. Singhal, Sravani Ramisetty, Atish Mohanty, Prakash Kulkarni, David Horne, Sanjay Awasthi, Ravi Salgia. RalBP1, a novel approach for ovarian cancer therapy abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 4650.