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Abstract 368A: Functional assessment of DNA damage repair defects and the anti-tumor immune response in high grade serous ovarian cancers using patient-derived organoids

Patients with high grade serous ovarian cancer (HGSC) have limited additional therapeutic options beyond traditional carboplatin and paclitaxel. Immuno-oncologic (IO) agents have had limited effect, and despite the fact that 50% of HGSCs have genomic alterations in DNA damage repair genes, we still have no means of predicting which of these tumors actually harbor repair defects and will respond to these agents. Using patient-derived organoids which contain patient immune cells, we have developed functional assays to test the DNA damage repair capacity, anti-tumor immune response, and therapeutic vulnerability of HGSCs. These assays include testing for defects in the two key DNA damage repair pathways, homologous recombination (HR) and stalled replication fork protection, testing for activity and specificity of the immune cells in the cultures against the tumor cells when exacerbated by specific therapeutic combinations, and testing for therapeutic sensitivity to targeted and traditional chemotherapy agents and IO agents either alone or in rational combinations. In parallel, many of the tumors and organoids have undergone genomic and RNA sequencing, searching for relevant alterations to explain detected defects. Flow cytometry analysis of the parent tumors and short term (7-10 day) organoids reveal that organoids contain an immune milieu with IO receptor expression levels similar to the parent tumors. Upon treatment with IO agents alone or in combination with chemotherapeutic agents, we have found that specific IO receptor expression is altered, certain combinations lead to induction of cytokine expression that may repress an anti-tumor response, and that some combinations do not induce the expected cytotoxicity. The DNA damage repair functional assays have revealed that in HGSC, stalled fork protection defects are more common than HR defects, regardless of the repair gene mutational status of the tumors. Importantly, there is a wider array of therapies available to target these defects. For instance, organoids with unstable replication forks are more sensitive to ATR and CHK1 inhibitors. Organoids with stable forks are more sensitive to combinations of drugs which confer replication stress, such as the combination of a CHK1 inhibitor plus gemcitabine. Overall, the repair assays will allow for a better understanding of the types and mechanisms of repair defects present in tumors and a more accurate prediction of sensitivity to targeted agents. The immune functional assays will allow for a better mechanistic understanding of what response specific agents actually induce in immune and tumor cells and allow for better rational therapeutic pairings. Through assessment of a larger number of patients, we hope to demonstrate that these functional assays can have a clinical impact in rapidly predicting patient response. Citation Format: Sarah J. Hill, Patrick Lizotte, Neil S. Horowitz, Michael G. Muto, Michael J. Worley, Colleen M. Feltmate, Bose Kochupurakkal, Khanh T. Do, Panagiotis Konstantinopoulos, Marisa R. Nucci, Joyce F. Liu, Ursula A. Matulonis, Geoffrey I. Shapiro, Ross S. Berkowitz, Christopher P. Crum, Alan D. D9Andrea. Functional assessment of DNA damage repair defects and the anti-tumor immune response in high grade serous ovarian cancers using patient-derived organoids [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 368A.