Abstract 2536: Investigating the mechanisms of HER2+ breast cancer cell redirection
Authors: Campbell Caroline J. , Booth Brian W. 
Published: June 2022

Abstract
Introduction: Breast cancer research has advanced understanding of breast cancer development and progression greatly over the past few decades. Despite progress in research, breast cancer is the second leading cause of cancer death in North America and is the most frequent type of cancer for women. Better treatments and diagnostic tools have increased breast cancer survival rates, but there is still a fundamental lack of understanding in tumor progression. Previous studies show the normal mammary microenvironment can influence non-mammary cells and tumor-derived cancer cells to participate in normal mammary gland development. The tumorigenic cells lose their tumor-forming capabilities and are “redirected” into phenotypically normal, non-tumorigenic cells. The purpose of this study is to obtain knowledge of the mechanisms that play a role in cancer cell redirection and therefore be able manipulate those mechanisms for therapeutic treatment in a clinical setting. Our hypothesis is that microenvironmental elements control whether a tumorigenic cell will enter a redirected state. We have developed and validated an in vitro model to mimic the mammary microenvironment to study cancer cell redirection. We found that when cancer cells that overexpress HER2+ are redirected in our cancer redirection model, phospho-HER2+ is silenced. We use HER2+ phosphorylation as a marker for cancer cell redirection though not a mechanism for cancer cell redirection.
Materials and Methods: HER2+ breast cancer cells and normal breast epithelial cells (BECs) were co-cultured in ratios of 1:1 or 1:50. Monocultures of breast cancer cells and BECs were used as controls. Western analysis and immunostaining was used to assess attenuation of HER2+ and phospho-HER2+ receptors and RNAseq was used for pathway analyses. Images were taken using a Leica confocal microscope. For comparison of 2 or more groups, a one-way analysis of variance was performed. A p-value of less than 0.05 was considered significant.
Results and Discussion: We found that the redirected cells underwent a phenotype shift in which the redirected cells adopted a normal mammary epithelial phenotype based on gene expression profiles. Furthermore, when HER2+ breast cancer cells were redirected in vitro they lost their tumor-forming potential in vivo. Signal pathway analyses revealed that redirected cancer cells are adopting a normal phenotype compared to breast cancer cells.
Conclusions: These results indicate that epithelial cells provide signals that influence HER2+ breast cancer cells to undergo a shift in phenotype. The phenotypic shift in cancer cell redirection includes multiple intracellular signaling pathways that may be the key towards effective cancer treatment.
Acknowledgements: This research was supported by South Carolina Idea Networks of Biomedical Research Excellence (SC INBRE).
Citation Format: Caroline J. Campbell, Brian W. Booth. Investigating the mechanisms of HER2+ breast cancer cell redirection [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2536.