Abstract LB215: Polymerase θ (POLθ) inhibitors (novobiocin, ART-558, RP6685) were tested with 22 approved and investigational agents in multi-cell type spheroids of genetically selected patient-derived human tumor cell lines

Abstract The potential of novobiocin to augment cancer chemotherapy was explored in the late 1980s and early 1990s in tumor cells and tumor-bearing mice and in Phase 1 clinical trials with cyclophosphamide or cisplatin. The molecular target of novobiocin was identified to be DNA POLθ which has a role in repair of DNA double strand breaks (DSB) during mitosis. Genetic alterations which may increase or decrease POLθ inhibitor effects have been elucidated. Thirty patient-derived tumor cell lines with known BRCA, ATM, ATR, POLQ, XRCC1, PALB2, PARP1, and LIG3 alterations were screened in a complex spheroid assay (tumor cells, endothelial cells, mesenchymal stem cells) with a POLθ inhibitor (novobiocin, ART-558, or RP6685), alone or in simultaneous combination with a FDA approved or investigational anticancer small molecule, using a 7-day exposure and a CellTiter-Glo 3D luminescence endpoint. As single agents, the POLθ inhibitors had little or no cytotoxicity. Potentiation of the topoisomerase II inhibitors doxorubicin (DOX) and etoposide by the POLθ inhibitors ART-558 or RP6685 was observed in spheroids grown from the serous endometrial adenocarcinoma 922993-354-T-J3, which has ATM and BRCA2 variants. The 379773-124-R-J2 endometrioid endometrial adenocarcinoma which harbors mutant POLθ demonstrated antagonism with ART-558 in combination with PARP inhibitors and less than additive to additive cytotoxicity in combination with DOX. Activity of the Chk1/2 inhibitor prexasertib was potentiated by either ART-558 or RP6685 in the 922993-354-T-J3 complex spheroids. The combination of POLθ inhibitor ART-558 and the Chk1/2 inhibitor prexasertib produced up to 1 log increase in cytotoxicity in the 922993-354-T-J3 complex spheroids. KRAS G12D inhibitor MRTX-133 cytotoxicity against 186277-243-T-J2 colon adenocarcinoma with the KRAS G12D variant was potentiated by either ART-558 or RP6685. Potential combinations to advance into in vivo studies will be presented. This project was funded in part with federal funds from the NCI, NIH, under contract no. HHSN261201500003I. Citation Format: Beverly A. Teicher, Thomas S. Dexheimer, Thomas Silvers, Nathan P. Coussens, J Paul Eder, James H. Doroshow. Polymerase θ (POLθ) inhibitors (novobiocin, ART-558, RP6685) were tested with 22 approved and investigational agents in multi-cell type spheroids of genetically selected patient-derived human tumor cell lines abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (7Suppl): Abstract nr LB215.