Abstract A072: Ghrelin deletion reduces mammary tumor growth and enhances response to immunotherapy
Authors: II William H Walker , Elliott Brittany D , Kisamore Claire O , Nelson Randy J , DeVries A. Courtney 
Published: December 2023

Abstract
Ghrelin is a peptide hormone, primarily produced in the stomach, best known for its role as a regulator of nutrient sensing, appetite, and meal initiation. However, increasing evidence supports a more complex and nuanced role for ghrelin in a diverse array of biological processes, including cancer. Ghrelin’s effects on breast cancer development and progression are not clear, as the literature detailing its effects is conflicting. Several studies in breast cancer survivors have concluded that higher expression of ghrelin is correlated with better recurrence-free and breast cancer-specific survival. However, additional clinical and foundational science studies have suggested greater complexity for ghrelin’s role in breast cancer development as a splice variant of ghrelin, namely In1-ghrelin, is associated with increased tumor proliferation and reduced disease-free survival of breast cancer patients. Thus, the current study sought to determine the effects of ghrelin deletion within mammary tumor cells (67NR) on subsequent tumor growth. Specifically, we hypothesized that ghrelin deletion would significantly alter tumor growth. Adult female mice received bilateral orthotopic injections of the nonmetastatic murine breast carcinoma cell line 67NR or one of two CRISPR generated ghrelin deleted cell lines 1G9 or 2G2 (derived from the 67NR cell line). Ghrelin deletion significantly reduced tumor volume and tumor mass by ~60% and ~55%, respectively. Additionally, ghrelin deletion significantly increased median survival duration by ~30%. When examining changes within the tumor microenvironment we observed a significant increase in macrophage colonization in ghrelin knockouts relative to the parental 67NR tumors. Notably, the percent F4/80 staining within the tumor positively correlated with length of survival. To determine the role of these F4/80 cells on tumor progression, we ablated these macrophages by feeding chow containing the colony stimulating factor receptor 1 inhibitor, PLX5622, for the entirety of the study. Ablating macrophages significantly increased tumor volume and tumor mass and rendered the previous beneficial effects of ghrelin deletion null, suggesting that the positive effects of ghrelin deletion may be due to actions on macrophages. Lastly, because of the increased macrophage infiltration within ghrelin knockout tumors, we sought to determine their repose to an immunotherapy targeting macrophages, namely anti-CD47. Notably, ghrelin deleted tumors displayed a positive response to the immunotherapy and further reduction in tumor growth (~80% reduction in tumor volume compared to 67NR tumors). Whereas, 67NR tumors were unresponsive to the immunotherapy. These data add to the literature detailing the complex effects of ghrelin on tumor growth and suggest that ghrelin may be a druggable target to slow tumor development.
Citation Format: William H Walker II, Brittany D Elliott, Claire O Kisamore, Randy J Nelson, A. Courtney DeVries. Ghrelin deletion reduces mammary tumor growth and enhances response to immunotherapy [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr A072.