Abstract B085: Carcinoma-associated mesenchymal stem cells promote high-grade serous ovarian cancer metastasis and drive tumor heterogeneity at the metastatic site through direct mitochondrial transfer

Abstract High-grade serous ovarian cancer (HGSC) is the most common and lethal form of ovarian cancer, accounting for over 70% of ovarian cancer cases. HGSC mortality is largely driven by early and diffuse transcoelomic spread from the primary site throughout the peritoneal cavity, resulting in roughly three-quarters of cases presenting with advanced stage disease at time of diagnosis. Following detachment from the primary tumor, disseminated ovarian cancer cells are spread by the peritoneal fluid and ascites where they must adapt to their new microenvironment to survive and successfully form metastases. Crucial to this spread is the formation of multicellular aggregates containing both cancer and non-malignant stromal cells, which enhance cancer cell survival and are associated with poor clinical outcome. While most studies on HGSC multicellular aggregates have focused on ovarian cancer cells alone, the interactions between ovarian cancer cells and other non-malignant cells have yet to be fully elucidated. Prior work by our group have shown that stromal-progenitor cells, termed carcinoma-associated mesenchymal stem/stromal cells (CA-MSCs), enhance HGSC metastasis through direct cellular interaction and formation of heterocellular CA-MSC: cancer cell complexes. Here we demonstrate CA-MSCs enhance metastasis by preferentially donating their mitochondria to cancer cells with the least amount of endogenous mitochondria content (‘mito poor’ cancer cells), increasing their ability to survive and driving tumor heterogeneity at the metastatic site in vivo. Mito poor cancer cells were shown to have decreased proliferative capacity, increased sensitivity to platinum-based chemotherapy and display decreased oxidative phosphorylation (OXPHOS) compared to ‘mito rich’ cancer cells. Primary patient-derived CA-MSCs rescue this vulnerable phenotype by increasing proliferation, chemoresistance and OXPHOS in mito poor cancer cells. These findings were validated in a fully autologous system using CA-MSCs and cancer cells derived from the same patient to prevent confounding effects of cellular response to foreign organelle/DNA. Through lentiviral knockdown of the mitochondrial motor protein MIRO1 we further demonstrate mitochondrial transfer is necessary for CA-MSC-mediated rescue of mito poor cancer cells. Further, we developed a haplotype-specific quantification of mitochondrial DNA to differentiate CA-MSC from endogenous cancer cell mitochondria which was used to quantify the amount of CA-MSC mitochondrial donation and demonstrate donated mitochondria persist in cancer cells up to 14 days. Importantly, CA-MSC mitochondrial donation occurred in vivo and was associated with decreased survival in an orthotopic ovarian cancer murine model. Genomic barcoding was used to quantify tumor cell clonal heterogeneity; using this system we demonstrate CA-MSC mitochondrial donation significantly enhance tumor cell heterogeneity at the metastatic site in vivo. Collectively, we report CA-MSC mitochondrial transfer as a driver of HGSC progression, heterogeneity and metastasis. Citation Format: Leonard G. Frisbie, Catherine A. Pressimone, Roja Baruwal, Geyon L. Garcia, Zanib Javed, Claudette St. Croix, Simon Watkins, Michael Calderone, Huda I. Atiya, Nadine Hempel, Alexander Pearson, Lan G. Coffman. Carcinoma-associated mesenchymal stem cells promote high-grade serous ovarian cancer metastasis and drive tumor heterogeneity at the metastatic site through direct mitochondrial transfer abstract. In: Proceedings of the AACR Special Conference on Ovarian Cancer; 2023 Oct 5-7; Boston, Massachusetts. Philadelphia (PA): AACR; Cancer Res 2024;84 (5 Suppl₂): Abstract nr B085.