Abstract 1638: Validation of a novel pan-Ras inhibitor, ADT-007, against lethal variants of prostate cancer

Abstract Metastatic prostate cancer is the second leading cause of cancer deaths in US men. Most early-stage PCa are dependent on overexpression of the androgen receptor (AR) and are therefore sensitive to androgen deprivation therapies. However, eventual resistance to standard medical castration and secondary chemotherapies including next-generation AR-targeting agents like abiraterone or enzalutamide and taxanes (Docetaxel or cabazitaxel) is nearly universal. Further, neuroendocrine PCa or NEPC, a poorly differentiated aggressive variant of PCa that lacks AR expression, and the presence of cancer stem-like cells with self-renewal and differentiation (epithelial to mesenchymal trans-differentiation or EMT) capacities significantly contribute to the development of clinically most aggressive and lethal variants of PCa. Endogenous Ras/ERK/MAPK signaling is known to drive prostate tumor formation, cancer progression, cell migration, and the acquisition of mesenchymal phenotype (EMT) in metastatic prostate cancers. Ras family members are responsible for modulating the function of most of the receptors upregulated in advanced PCa, including AR, so that AR can be functional even in the absence of physiologic levels of androgen. Previous studies have reported that the NSAID, sulindac, inhibits Ras-induced transformation and directly binds Ras. In this study, we show that a non-COX inhibitory sulindac derivative, ADT-007, is a potent drug candidate against lethal PCa. First, we performed single-cell RNA sequencing as a biomarker-based drug screen and showed that chemo-resistant, drug-tolerant, stem-cell-like PCa cell clusters had high expression of Ras genes, indicating that the Ras inhibitor, ADT-007, may be effective in targeting these aggressive subclones. Next, using several cell-based assays on a large panel of lethal PCa cell lines representing metastatic castration-resistant PCa (mCRPC), NEPC as well as African American ancestry, we showed that ADT-007 is highly effective as a single-agent and in combination with taxanes. Combination index values were <0.7, and BLISS scores were >10, indicating very high synergy. Finally, using pre-vs-post-treatment bulk RNAseq, we demonstrated that ADT-007 is indeed effective in downregulating KRas and NRas in a dose-dependent manner. In addition, ingenuity pathway analysis (IPA) predicted significant downregulation of cell cycle, DNA replication, CCND1, AR, and the lncRNA ELDR, and upregulation of autophagy and interferon pathway genes, and the microRNA miR-96. Finally, using PCa patient datasets, we showed that ADT-007 is potentially capable of reversing the expression of several genes associated with biochemical recurrence. Thus, our results show that ADT-007 is a novel drug candidate that circumvents subclonal aggressiveness, drug resistance, and stemness in lethal PCa through simultaneous inhibition of multiple oncogenic factors/pathways. Citation Format: Taraswi Mitra Ghosh, Adam B. Keeton, Xi Chen, Salsabil Ahmed, Razan S. Waliagha, Gary A. Piazza, Amit K. Mitra. Validation of a novel pan-Ras inhibitor, ADT-007, against lethal variants of prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1638.