Abstract 6186: Patient-derived tumor organoids with p53 mutations, and not wild-type p53, demonstrate synergistic sensitivity to treatment with temozolomide in combination with talazoparib PARP inhibitor
Authors: Rowdo Florencia P. Madorsky , Xiao Gu , Davis Melissa B. , Martin Laura , Elemento Olivier , Bargonetti Jill 
Published: April 2023

Abstract
Mutations in the TP53 gene can be found in more than 50% of tumors. We recently showed in 2D breast cancer cell lines that mutant p53 (mtp53) proteins tightly associate with replicating DNA, chromatin and Poly (ADP-ribose) polymerase (PARP) protein. In addition, missense mtp53 R273H causes an increase in the chromatin association of replication proteins including PARP, and mini-chromosome maintenance complex 2-7 (MCM2-7). The expression of mtp53 R273H enhances overall MCM2 levels, promotes cell proliferation, and improves the synergistic cytotoxicity of treatment with the alkylating agent temozolomide in combination with the PARP inhibitor (PARPi) talazoparib. Currently, PARPis are indicated for patients that present BRCA1/2 mutations, but there might be patients with other alterations associated with DNA damage repair that could benefit from PARPi treatment; this includes expression of mtp53. Patient-derived Tumor Organoids (PDTO) are 3D culture models that retain cell-cell and cell-matrix interactions and are shown to reproduce drug responses observed in patients. Here, we evaluated the sensitivity of wild-type BRCA1/2 breast and lung PDTO with either mtp53 or wild-type p53 (wtp53) to the combination of DNA damaging agent temozolomide plus the PARPi talazoparib. First, we tested the sensitivity of the organoids to talazoparib and temozolomide individually. To determine if there was synergy between the two treatments, the organoids were treated with an inhibitor matrix to evaluate multiple combinatorial concentrations. Three breast cancer and two lung cancer PDTO with mtp53 presented synergistic cytotoxicity of the combination treatment. Two breast organoid lines with wtp53 showed no synergistic interaction between the two drugs, and the same was observed in a wtp53 lung organoid line. We analyzed wtp53 and mtp53 PDTO cell extracts by western blot to assess the activation of downstream p53 effectors and DNA damage markers after treatment with temozolomide and/or talazoparib. Combination of talazoparib and temozolomide induced higher DNA double-strand breaks in mtp53 organoids as shown by increased gamma-H2AX expression. The results obtained demonstrated that in mtp53 PDTO synergism is achieved with combined talazoparib-temozolomide treatment supporting the idea that tumors expressing mtp53 may be potential candidates for this combination PARPi treatment.
Citation Format: Florencia P. Madorsky Rowdo, Gu Xiao, Melissa B. Davis, Laura Martin, Olivier Elemento, Jill Bargonetti. Patient-derived tumor organoids with p53 mutations, and not wild-type p53, demonstrate synergistic sensitivity to treatment with temozolomide in combination with talazoparib PARP inhibitor. [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 6186.