Abstract A041: Treating liver metastases by reversing cell competition between metastatic cancer cells and hepatocytes
Authors: Lake Katherine E , Mohta Sakshi , Smith Clayton A , Repaka Venkata , Xu Lily , Saunders Kaitlyn , Pandit Vrushali , Goff Emily , Pena Jacob , Chinea Luise , Froessl Luisa , Reddy Sangeetha M , McArthur Heather L , Hodges Christine , Maues Julia , Chen Elizabeth , Chan Isaac S 
Published: February 2024

Abstract
Background Although breast cancer liver metastases (BCLM) are common events, with 40-50% of patients with metastatic breast cancer developing liver metastases, their development indicates particularly poor prognosis. Targeted treatments for liver metastases are virtually non-existent, partly because the key events of early liver metastasis formation remain unknown. The liver is a dense organ, and metastatic breast cancer cells (MCC) must first clear space among hepatocytes, the primary cell population in the liver, to form. Cell competition is a process that explains how organs or primary tumors form from two populations of competing cells with varied fitness levels. The expansion of one population of cells creates space through the induction of apoptosis in the other. Objectives In this study, we tested the hypothesis that MCC use cell competition with hepatocytes to create space and expand within the liver, resulting in hepatocyte apoptosis. Methods We develop new in-vitro and mouse lineage-traced models to assay cell competition between MCC and hepatocytes. These models directly capture MCC and hepatocyte interactions and we can assess modes of cell competition, including apoptosis, through immunostaining. Because prior literature suggests that the developing mammary gland informs both cell competition and metastasis, we performed a bioinformatics screen to identify potential signals that contribute to cell competition between MCC and hepatocytes. We generate a new single-cell RNA-seq dataset that incorporates information from the developing mammary gland and breast cancer cells and identify genes enriched in both. Next, we validated genes by testing for their high expression in MCC when compared to hepatocytes. Then, we determined the impact of target genes on cell competition in our models. Results/Discussion Our models demonstrate that MCC use cell competition to create space in the liver by inducing apoptosis in neighboring hepatocytes. MCC induce apoptosis in neighboring hepatocytes through cell competition in in-vitro co-cultures by 11.7-fold compared to MCC apoptosis. Hydrodynamic tail-vein engraftment in NOD-scid-gamma mice with MCC also resulted in increased neighboring hepatocyte apoptosis. Using our bioinformatics screen, we identified SerpinE2, a protease inhibitor, as a target that could drive breast cancer metastasis and cell competition. Knock-out of SerpinE2 in MCC did not affect their viability or growth but resulted in MCC apoptosis adjacent to hepatocyte neighbors by 16.9-fold when compared to wild-type (WT) conditions. Further, co-culture of MCC that lacked SerpinE2 with hepatocytes resulted in decreased hepatocyte apoptosis by 2.3-fold compared to hepatocytes co-cultured with WT MCC. These findings suggest that perturbation of SerpinE2 successfully modulates competition between MCC and hepatocytes: Hepatocytes can selectively outcompete and kill MCC that lack SerpinE2. Future work focused on the perturbation of SerpinE2 may lead to novel therapies for patients at risk for or with BCLM.
Citation Format: Katherine E Lake, Sakshi Mohta, Clayton A Smith, Venkata Repaka, Lily Xu, Kaitlyn Saunders, Vrushali Pandit, Emily Goff, Jacob Pena, Luise Chinea, Luisa Froessl, Sangeetha M Reddy, Heather L McArthur, Christine Hodges, Julia Maues, Elizabeth Chen, Isaac S Chan. Treating liver metastases by reversing cell competition between metastatic cancer cells and hepatocytes [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Breast Cancer Research; 2023 Oct 19-22; San Diego, California. Philadelphia (PA): AACR; Cancer Res 2024;84(3 Suppl_1):Abstract nr A041.