Abstract 4205: Development of peritoneal carcinomatosis by multicellular structures of high-grade serous ovarian cancer

Poor prognosis in more than 70% of ovarian cancer (OC) patients is tightly associated with: (i) advanced presentation at initial diagnosis with nests of solid tumors widely distributed on the surface of the serous membrane lining peritoneal organs and cavities; and (ii) accumulation of peritoneal malignant effusions (ascites), which carry cells gathered as multicellular structures (MCS). The biology of the solid growths adhered to the peritoneal wall and abdominal organs has been intensively investigated. In contrast, the role of the MCS living in suspension in the peritoneal fluid is less known. Herein, utilizing series of high-grade serous OC (HGSOC) cell lines developed from ascites of the same patients during different stages of disease progression, we provide evidence of an active role of the MCS in the pathobiology of OC. When cultured under adherent conditions, these HGSOC cells, in addition to forming cellular monolayers, develop areas in which the cells grow upwards forming densely-packed multilayers that ultimately detach from the bottom of the plate and live as free-floating MCS. The capacity to form foci and develop MCS increased along the progression of the disease as represented in the PEO1/PEO4/PEO6 series derived from a patient diagnosed with a poorly-differentiated disease, as well as in the PEO14/PEO23 pair, derived from a patient with highly-differentiated OC. When we compared cultures of PEO6 cells vs. PEO23 cells, we observed that both cellular entities gave rise to MCS with two morphological arrangements, one coral-like or irregular, and another more organized and spheroidal. To study whether these MCS are sufficient to generate peritoneal carcinomatosis we injected, into the peritoneal cavity of immunosuppressed female mice, a mixture of MCS obtained from a culture of PEO6 cells. Six-to-seven months after injection, the PEO6-derived MCS were sufficient to recreate discrete solid nodules in the omentum, liver, and lower pelvic cavity, with associated accumulation of abundant bloody peritoneal fluid. The ascites had also a high content of MCS resembling the phenotype of those originally injected. Using inverted confocal microscope we were able to determine that several, yet not all, floating MCS were hollow and contained a well-differentiated lumen. In addition, fluorescence microscopy demonstrated that the cells forming the MCS had replicative capacity and displayed cell-cell interactions mediated by the E-cadherin/beta-catenin complex. Collectively, we provide evidence that HGSOC cell lines: (i) develop MCS in suspension resembling those found in patient9s ascites; and (ii) the MCS formed in culture retain the capacity to develop peritoneal carcinomatosis with both adherent (‘solid’) and non-adherent (‘floating’) components of the disease. Citation Format: Alicia A. Goyeneche, Rekha Srinivasan, Juan M. Valdez, Carlos M. Telleria. Development of peritoneal carcinomatosis by multicellular structures of high-grade serous ovarian cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4205. doi:10.1158/1538-7445.AM2015-4205