Abstract 1194: MEK inhibition in combination with PI3K/AKT/MTOR is a promising therapeutic in basal bladder cancer

Abstract

Abstract There are diverse resources available for data relevant to the drug screening of bladder cancer cell lines in 2D culture, such as the Cancer Cell Line Encyclopedia (CCLE) and Genomics of Drug Sensitivity in Cancer (GDSC) databases; however, 3D culture is more representative of in vivo response in patients. Moreover, drug screens in 3D reveal differential drug response and expression of genes and proteins that indicate the potential of more effective selection of drugs for specific patients: the basic tenet of personalized oncology. Therefore, we screened bladder cancer cell lines in 3D culture using a library of curated small-molecule inhibitors to identify compounds and classes of compounds with efficacy in bladder cancer. Genomic and transcriptomic data for these bladder cancer cell lines were used to correlate genomic molecular parameters with drug response with the aim of discerning biomarkers of response or to suggest plausible drug combinations. This allowed us to identify groups of tumors that are vulnerable to specific drugs or classes of drugs. We found that MEK inhibitors were a promising target among basal bladder cancers, an RNA-based molecular subtype of bladder cancer, especially aggressive and exhibiting poor prognosis. Furthermore, trametinib was found to be a “very active” MEK inhibitor in basal cancers, classified using drug sensitivity 3 (DSS3) scoring. PI3K/AKT/MTOR inhibitors target a parallel signaling pathway to MEK inhibition; therefore, we tested PI3K/AKT/MTOR combinations with trametinib in basal bladder cancer to query for synergistic properties. Additionally, we tested PI3K/AKT/MTOR combinations with trametinib using ex vivo organoids of bladder cancer patient samples collected directly at operation. Taken together, MEK inhibition is a promising therapeutic strategy in the basal subtype of bladder cancer, particularly in combination with parallel pathway inhibition. Moving forward, we plan to test PI3K/AKT/MTOR combinations with trametinib in trametinib-resistant basal bladder cancer cell lines to investigate how this affects signaling and re-sensitization to trametinib. Citation Format: Athena M. Apfel, Nathan M. Merrill, Nathalie M. Vandecan, Liwei Bao, Xu Cheng, Lluis A. Lopez-Barcons, Kathleen C. Day, Phillip L. Palmbos, Mark L. Day, Aaron M. Udager, Matthew B. Soellner, Sofia D. Merajver. MEK inhibition in combination with PI3K/AKT/MTOR is a promising therapeutic in basal bladder cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1194.