The Capacity of High-Grade Serous Ovarian Cancer Cells to Form Multicellular Structures Spontaneously along Disease Progression Correlates with Their Orthotopic Tumorigenicity in Immunosuppressed Mice

Many studies have examined the biology, genetics, and chemotherapeutic response of ovarian cancer's solid component; its liquid facet, however, remains critically underinvestigated. Floating within peritoneal effusions known as ascites, ovarian cancer cells form multicellular structures, creating a cancer niche in suspension. This study explores the pathobiology of spontaneously formed, multicellular, ovarian cancer structures derived from serous ovarian cancer cells isolated along disease evolution. It also tests their capacity to cause peritoneal disease in immunosuppressed mice. Results stem from an analysis of cell lines representing the most frequently diagnosed ovarian cancer histotype (high-grade serous ovarian cancer), derived from ascites of the same patient at distinct stages of disease progression. When cultured under adherent conditions, in addition to forming cellular monolayers, the cultures developed areas in which the cells grew upwards, forming densely packed multilayers that ultimately detached from the bottom of the plates and lived as free-floating, multicellular structures. The capacity to form foci and to develop multicellular structures was proportional to disease progression at the time of ascites extraction. Self-assembled in culture, these structures varied in size, were either compact or hollow, irregular, or spheroidal, and exhibited replicative capacity and an epithelial nature. Furthermore, they fully recreated ovarian cancer disease in immunosuppressed mice: accumulation of malignant ascites and pleural effusions; formation of discrete, solid, macroscopic, peritoneal tumors; and microscopic growths in abdominal organs. They also reproduced the histopathological features characteristic of high-grade serous ovarian cancer when diagnosed in patients. The following results encourage the development of therapeutic interventions to interrupt the formation and/or survival of multicellular structures that constitute a floating niche in the peritoneal fluid, which in turn halts disease progression and prevents recurrence.