Patient-derived tumor organoids with p53 mutations, and not wild-type p53, are sensitive to synergistic combination PARP inhibitor treatment

Poly (ADP-ribose) polymerase inhibitors (PARPi) are used for patients with BRCA1/2 mutations, but patients with other mutations may benefit from PARPi treatment. Another mutation that is present in more cancers than BRCA1/2 is mutation to the TP53 gene. In 2D breast cancer cell lines, mutant p53 (mtp53) proteins tightly associate with replicating DNA and Poly (ADP-ribose) polymerase (PARP) protein. Combination drug treatment with the alkylating agent temozolomide and the PARPi talazoparib kills mtp53 expressing 2D grown breast cancer cell lines. We evaluated the sensitivity to the combination of temozolomide plus PARPi talazoparib treatment to breast and lung cancer patient-derived tumor organoids (PDTOs). The combination of the two drugs was synergistic for a cytotoxic response in PDTOs with mtp53 but not for PDTOs with wtp53. The combination of talazoparib and temozolomide induced more DNA double-strand breaks in mtp53 expressing organoids than in wild-type p53 expressing organoids as shown by increased γ-H2AX protein expression. Moreover, breast cancer tissue microarrays (TMAs) showed a positive correlation between stable p53 and high PARP1 expression in sub-groups of breast cancers, which may indicate sub-classes of breast cancers sensitive to PARPi therapy. These results suggest that mtp53 could be a biomarker to predict response to the combination of PARPi talazoparib-temozolomide treatment.

Patient-derived tumor organoids with p53 mutations, and not wild-type p53, are sensitive to synergistic combination PARP inhibitor treatment

Poly (ADP-ribose) polymerase inhibitors (PARPi) are used for patients with BRCA1/2 mutations, but patients with other mutations may benefit from PARPi treatment. Another mutation that is present in more cancers than BRCA1/2 is mutation to the TP53 gene. In 2D breast cancer cell lines, mutant p53 (mtp53) proteins tightly associate with replicating DNA and Poly (ADP-ribose) polymerase (PARP) protein. Combination drug treatment with the alkylating agent temozolomide and the PARPi talazoparib kills mtp53 expressing 2D grown breast cancer cell lines. We evaluated the sensitivity to the combination of temozolomide plus PARPi talazoparib treatment to breast and lung cancer patient-derived tumor organoids (PDTOs). The combination of the two drugs was synergistic for a cytotoxic response in PDTOs with mtp53 but not for PDTOs with wtp53. The combination of talazoparib and temozolomide induced more DNA double-strand breaks in mtp53 expressing organoids than in wild-type p53 expressing organoids as shown by increased γ-H2AX protein expression. Moreover, breast cancer tissue microarrays (TMAs) showed a positive correlation between stable p53 and high PARP1 expression in sub-groups of breast cancers, which may indicate sub-classes of breast cancers sensitive to PARPi therapy. These results suggest that mtp53 could be a biomarker to predict response to the combination of PARPi talazoparib-temozolomide treatment.

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

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.

Abstract 6037: Kinome crispr cas9 screening in breast cancer organoids derived from Ghanaian patients

Breast cancer is a polygenic genetic disease caused by multifaceted factors which are often unique for each individual patient. In our prior studies we have demonstrated that west African ancestry is associated with more aggressive breast tumor phenotypes. Precision medicine approaches to cancer treatment exploit genetic differences to tailor therapy options that are specific to individual patients/groups. We hypothesize that shared genetic susceptibilities to cancer, which are harbored within populations of common ancestry, may translate to options for targeted therapies. Specifically, we will investigate whether genetic manipulation of kinases in Patient-Derived Tumor Organoids (PDTO) from West African breast cancer patients uncover novel drug targets in a genetic background that has not been investigated in this context to date. PDTO are three-dimensional cellular models grown in culture ex vivo from the tumor tissues obtained from patients retaining cell-cell and cell-matrix interactions. We established and characterized PDTO from Ghanaian patients and optimized the experimental conditions to perform a lentiviral-based CRISPR-Cas9 loss-of-function mutation screen targeting kinases in breast cancer organoids. We analyzed which kinases are essential for tumor viability or directly impact the response to current therapy/drugs. Tumor specimens were collected in Ghana from breast cancer patients and PDTO were stablished in Weill Cornell Medicine (USA). These PDTO were characterized by IHC, targeted panel sequencing and RNA-seq and biobanked. We established stable Cas9-expressing PDTO and we confirmed Cas9 expression by Western Blot and its activity by reporter-based assays, confirming that at least 80% of the cells present Cas9 activity. We performed a Kinome CRISPR Cas9 screen with 2 PDTO. The screening was performed in the presence of DMSO (vehicle to identify essential genes), a MEK inhibitor or an EGFR inhibitor. Preliminary analysis of the screening revealed efficient depletion of the positive controls as well as of previously proposed pan-cancer essential kinases, including CHEK1, ATR and AURKA. Additional analysis and validation of potential novel targets is currently ongoing. Conclusions: We successfully established the conditions to identify potential new therapeutic targets in PDTO derived from Ghanaian patients. Our Kinome Crispr Screen identified known as well as previously unknown essential kinases for breast cancer.

Citation Format: Florencia P. Madorsky Rowdo, Sarah Ackermann, Joseph K. Oppong, Ishmael Kyei, Colin Tang, Lisa Newman, Olivier Elemento, Lukas E. Dow, M. Laura Martin, Melissa B. Davis. Kinome crispr cas9 screening in breast cancer organoids derived from Ghanaian patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 6037.

High lipid content of irradiated human melanoma cells does not affect cytokine-matured dendritic cell function

Gamma irradiation is one of the methods used to sterilize melanoma cells prior to coculturing them with monocyte-derived immature dendritic cells in order to develop antitumor vaccines. However, the changes taking place in tumor cells after irradiation and their interaction with dendritic cells have been scarcely analyzed. We demonstrate here for the first time that after irradiation a fraction of tumor cells present large lipid bodies, which mainly contain triglycerides that are several-fold increased as compared to viable cells as determined by staining with Oil Red O and BODIPY 493/503 and by biochemical analysis. Phosphatidyl-choline, phosphatidyl-ethanolamine and sphingomyelin are also increased in the lipid bodies of irradiated cells. Lipid bodies do not contain the melanoma-associated antigen MART-1. After coculturing immature dendritic cells with irradiated melanoma cells, tumor cells tend to form clumps to which dendritic cells adhere. Under such conditions, dendritic cells are unable to act as stimulating cells in a mixed leukocyte reaction. However, when a maturation cocktail composed of TNF-alpha, IL-6, IL-1beta and prostaglandin E2 is added to the coculture, the tumor cells clumps disaggregate, dendritic cells remain free in suspension and their ability to efficiently stimulate allogeneic lymphocytes is restored. These results help to understand the events following melanoma cell irradiation, shed light about interactions between irradiated cells and dendritic cells, and may help to develop optimized dendritic cell vaccines for cancer therapy.