Abstract PR05: Development of new immune therapy combinations for ovarian cancer using genetically defined organoid platform
Authors: Zhang Shuang , Iyer Sonia , Ran Hao , wei Wei , Weinberg Robert A , Neel Benjamin G 
Published: March 2020

Abstract
High-grade serous ovarian cancer (HGSOC) is the most common and deadly subtype of ovarian epithelial cancer. HGSOC typically presents at an advanced stage, with widespread peritoneal metastasis. Although surgical debulking and platinum/taxane-based chemotherapy can result in complete responses, disease almost always recurs, eventually in drug-resistant forms. Although the recent addition of Avastin and PARP inhibitors benefits a subset of patients, survival has improved only marginally in the past 30 years. Responses to immune checkpoint inhibitors have also been disappointing. Genomic studies (e.g., by TCGA) have shown that HGSOC is a complex, diverse disease with widespread copy number abnormalities affecting multiple pathways. Nevertheless, most studies aimed at developing new therapies treat HGSOC as a single entity. The absence of genomically relevant, immune-competent HGSOC models poses a major barrier to developing new therapies. Capitalizing on a mouse fallopian tube organoid system that we developed, along with lentiviral gene transduction and/or CRISPR/Cas9 technology, we generated multiple new HGSOC models containing combinations of mutations seen in human HGSOC, including homologous recombination (HR)-proficient (Tp53-/-;Ccne1OE;Akt2OE and Tp53-/-;Ccne1OE;KrasOE) and -deficient (Tp53-/-;Brca1-/-;Pten-/-and Tp53-/-;Brca1-/-;MycOE), and poorly characterized (Tp53-/-;Pten-/-;Nf1-/-) models. These models differ in proliferation, differentiation, and polarity/organoid structure in vitro, as well as tumorigenic capacity and behavior upon orthotopic injection into syngeneic mice. Organoids bearing different mutational spectra show differential sensitivity to conventional HGSOC chemotherapies and PARP inhibitors, and evoke distinctly different immune microenvironment in vivo. The immune microenvironment induced by Brca1-/- and CcneOE tumors show significant T cell infiltration/Treg cells, the latter also has increased myeloid-derived suppressor cells (MDSCs), and Pten-/-lines show lower T cell infiltration but higher levels of MDSCs and macrophages. To test the utility of this platform for new therapeutic development, we focused on CcneOE tumors, because human CCNE-amplified HGSOC responds poorly to current therapy. CcneOE organoids were sensitive to gemcitabine (GEM), probably due to CCNE-evoked replication stress. GEM treatment reduced pro-MDSC cytokines in organoid conditioned media, and decreased tumor burden in mice. Consistent with the in vitro data, residual tumors had decreased MDSCs (CD11b+Ly6CloLy6Ghi), but persistent Treg (CD24+CD25+FoxP3+) and “exhausted” CD8 T cells (CD8+PD1+) in their microenvironment. Intriguingly, a combination regimen aimed at attacking tumor cells (gemcitabine) and the residual microenvironment (CTLA4 and PDL1 antibodies) produced complete responses in mice with widepresad metastatic disease, Our results argue that genotype-informed combination therapies will be necessary for better outcomes for this devastating disease.
Citation Format: Shuang Zhang, Sonia Iyer, Hao Ran, Wei wei, Robert A Weinberg, Benjamin G Neel. Development of new immune therapy combinations for ovarian cancer using genetically defined organoid platform [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr PR05. doi:10.1158/1535-7163.TARG-19-PR05