Abstract 1446: Mitochondrial transfer in the ovarian tumor microenvironment contributes to tumor stem cell phenotypes
Authors: Pressimone Catherine , Atiya Huda Issa , Frisbie Leonard , Coffman Lan 
Published: September 2020

Abstract
Introduction: Ovarian cancer is the deadliest gynecologic malignancy in the USA, and many patients incur diffuse metastases before diagnosis. In order to improve prognoses and reveal novel therapeutics, we must understand the mechanisms of ovarian tumor metastasis. Previous studies demonstrate that interactions between ovarian tumor cells (TCs) and Carcinoma-Associated Mesenchymal Stem Cells (CA-MSCs) are important drivers of metastasis. In addition, preliminary data exposes mitochondrial transfer between CA-MSCs and ovarian TCs as a potential contributor to cancer stem cell (CSC) development. Since CSCs contribute to cancer persistence, these new findings motivate current research exploring whether mitochondrial gain enhances TC metastatic fitness and CSC formation.
Methods: CA-MSC mitochondria were transiently stained with MitoTracker Green, and GFP+ CA-MSCs were co-cultured with RFP+ TCs for various durations. Immunofluorescence visualized mitochondrial transfer following co-culture. Mitochondrial transfer from CA-MSCs to TCs was quantified with flow cytometry, separating GFP+ TCs from GFP-TCs. To examine whether mitochondrial transfer requires direct cell-cell contact, CA-MSC were separated from TCs with 0.4um Transwell membranes during co-culture. To elucidate functional phenotypic differences associated with mitochondrial gain, TCs and GFP+ CA-MSCs were directly co-cultured and TCs that acquired GFP+ mitochondria were sorted out via FACS. The TC populations that did or did not gain mitochondria were compared for cell proliferation rates, chemotherapy resistance, and stem-like phenotypes via cell viability and sphere formation assays.
Results: We obtained fluorescent images illustrating that CA-MSC mitochondria transferred to adjacent TCs within 4 hours of direct co-culture. When CA-MSCs and TCs were indirectly co-cultured using Transwell membranes, mitochondria were not transferred as robustly as they were via direct co-culture. Interestingly, TCs that gained mitochondria appeared to grow more slowly and were less resistant to cisplatin treatment when compared to TCs that did not gain mitochondria. However, the TCs that gained mitochondria appeared to form more spheres and thus demonstrate a more CSC-like phenotype than TCs that did not gain mitochondria.
Conclusions: These data suggest that ovarian TCs receive mitochondria from adjacent CA-MSCs via direct interaction. The TCs that obtain mitochondria may functionally diverge from TCs that don't gain mitochondria, exhibiting phenotypes consistent with CSCs. Future experiments will further delineate the functional difference and translational significance attributable to TC mitochondrial gain, potentially demonstrating that mitochondrial transfer in ovarian tumors can be therapeutically exploited to reduce metastases.
Citation Format: Catherine Pressimone, Huda Issa Atiya, Leonard Frisbie, Lan Coffman. Mitochondrial transfer in the ovarian tumor microenvironment contributes to tumor stem cell phenotypes [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1446.