Abstract 4105: Dissecting the mechanisms of hepatocyte replacement in breast cancer liver metastases
Authors: Nathan Mark R. , Kostaras Lefteris , Bridgeman Victoria , Foo Shane , Vermeulen Peter , Reynolds Andrew 
Published: July 2016

The liver is a common site of metastasis in metastatic breast cancer and is associated with significant mortality. Histopathological examination of human breast cancer liver metastases (BCLMs) reveals that the majority of these tumours present with a ‘replacement growth pattern.’ In this growth pattern, the breast cancer cells freely invade the liver parenchyma and replace the resident hepatocytes. In advanced BCLMs, breast cancer cells can eventually replace a significant volume of the liver parenchyma which, ultimately, leads to organ failure and death. However, the mechanism through which breast cancer cells replace the resident hepatocytes is unknown.

Here we set out to establish how this replacement of hepatocytes by breast cancer cells occurs in BCLMs. To do so, we established two in vivo models of advanced BCLM: (a) an ER+PR+HER2- model using the MCF7 cell line, and (b) a triple negative patient-derived xenograft model using breast cancer cells isolated from a pleural effusion. We have also established an in vitro co-culture system, where MCF7 cells are co-cultured with HepG2 cells, which is designed to mimic the breast cancer cell-hepatocyte interaction observed in vivo.

Both in vivo models exhibit a histology that closely mimics the replacement growth pattern of human BCLMs, where breast cancer cells replace hepatocytes at the tumour-liver interface. To address whether hepatocytes are killed by adjacent breast cancer cells in vivo, we evaluated hepatocyte death by apoptosis using appropriate markers (cleaved-PARP and cleaved-caspase-3). Surprisingly, although extensive apoptotic death of breast cancer cells in the tumour mass could be observed, no evidence for apoptotic death of hepatocytes could be found. However, we observed extensive cell-in-cell invasion at the tumour-liver interface, where live breast cancer cells enter the cytoplasm of adjacent hepatocytes. We also observe a similar process of cell-in-cell invasion within in vitro cultures of MCF-7 cells with HepG2 cells.

Although cell-in-cell invasion has been described as a mechanism of non-apoptotic cell death in breast cancer cells, the role of cell-in-cell invasion between breast cancer cells and hepatocytes in BCLMs has not been investigated. Our current studies are focused in two areas: (a) we are using intra-vital microscopy and time-lapse microscopy to investigate whether cell-in-cell invasion between breast cancer cells and hepatocytes mediates non-apoptotic death of hepatocytes both in vivo and in vitro, and (b) we are investigating the molecular mechanisms that mediate cell-in-cell invasion between breast cancer cells and hepatocytes.

In conclusion, we present preliminary evidence for a novel mechanism via which breast cancer cells could replace hepatocytes in BCLMs. Further studies aimed at elucidating the molecular basis of this mechanism may reveal novel targets for preventing the replacement of the liver parenchyma by metastatic breast cancer cells.

Citation Format: Mark R. Nathan, Lefteris Kostaras, Victoria Bridgeman, Shane Foo, Peter Vermeulen, Andrew Reynolds. Dissecting the mechanisms of hepatocyte replacement in breast cancer liver metastases. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4105.