Abstract B11: Collective extrusion initiates dissemination in organotypic model of high-grade serous carcinoma

Abstract

Abstract Development of serous tubal intraepithelial carcinoma (STIC) from transformed fallopian tube secretory epithelial cells (FTSEC) is considered to be an initiating event for a significant proportion of high-grade serous carcinomas (HGSCs). Some regions of STIC lesions can form multicellular loosely cohesive outgrowths that apically extend out of the tubal epithelium. These outgrowths can detach and disseminate within the peritoneal cavity, causing organ obstruction. Immunohistochemical analysis of STICs suggests the possibility that molecular pathways associated with proliferation, DNA repair, cytoskeletal dynamics, and extracellular matrix adhesion contribute to outgrowth formation. Due to limited availability of transformed FTSEC in vitro culture models that faithfully capture outgrowth dynamics, the role of these pathways in STIC/HGSC outgrowth formation remains unknown. Here we present the development of an organotypic model of outgrowth formation. Long-term live-cell imaging of transformed human, and mouse FTSEC and STIC-like multicellular organotypic assemblies, have shown that outgrowths are initiated by collective apical extrusion of less-cohesive, loosely attached cell populations that can proliferate outside of the organotypic assembly. mRNA and immunofluorescence analysis of loosely attached cell populations revealed: (i) activation of Rho pathway, (ii) increased expression of several alpha integrin subunits that form heterodimers with beta 1 integrin, and (iii) nonpolarized apical and junctional localization of activated integrin beta 1. Pharmacologic or genetic inhibition of Rho-associated kinase (ROCK) blocked outgrowth formation without affecting cell proliferation. Conversely, activation of Rho significantly accelerated outgrowths, indicating that Rho-ROCK is a critical regulator of early steps of HGSC dissemination. Quantitative image-based evaluation of ROCK target phosphorylated myosin light chain expression in patient-derived xenograft cells revealed the presence of cell populations with high ROCK activation. Blocking integrin beta 1 activity resulted in the disintegration of already formed outgrowths. Our data indicate that cell populations with high Rho/ROCK activity remodel integrin beta 1-dependent adhesion to initiate apical extrusion and peritoneal dissemination. Citation Format: Sarah Alshehri, Sadaf Farsinejad, Douglas Kung, Estefan Santi, Yali Zhai, Thomas Cattabiani, Hongjun Wang, Kathleen Cho, Marcin Iwanicki. Collective extrusion initiates dissemination in organotypic model of high-grade serous carcinoma [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research; 2019 Sep 13-16, 2019; Atlanta, GA. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(13_Suppl):Abstract nr B11.