Abstract 612: Microbial determinants of immune checkpoint inhibition response in a murine model of obesity and metastatic basal-like breast cancer
Authors: McFarlane Tori L. , Carson Meredith S. , Glenny Elaine M. , Kiesel Violet A. , Taylor Ashlee , Roth Daniel , Albright Jody , VerHague Melissa , French John E. , Coleman Michael F. , Hursting Stephen D. 
Published: June 2022

Abstract
Introduction: Breast cancer (BC) is the second leading cause of cancer-related mortality among American women and is exacerbated by obesity. The basal-like (BL) subtype accounts for 10-15% of all BCs and is a particularly aggressive disease due to its extreme intrinsic diversity compared with other subtypes. Paradoxically, obesity promotes immune checkpoint inhibition (ICI) response in some cancers. Further, obesity promotes altered intestinal microbial composition, and recent clinical studies of fecal microbiota transplants suggest causal links between the microbiome and immunotherapy responses. Hence, we evaluated the correlation of tumoral and cecal microbiota with anti-Programmed Cell Death Protein 1 (PD1) immunotherapy response in a murine model of BLBC and obesity.
Methods: In an initial study, normoweight female C57BL/6J mice (n=8/group) received orthotopic injection of one of two novel C3TAg BLBC cell lines (1.02 and 2.51) syngeneic to C57BL/6J derived from a spontaneous tumor excised from B6-C3TAg transgenic mice. Gene expression profiling (Affymetrix arrays) with Gene Set Enrichment Analysis (GSEA) was performed on the resulting transplanted tumors. In a second study, female C57BL/6J mice were divided into a diet-induced obesity (DIO) group (n=30), promoted by high-fat diet feeding, and a lean control group (n=30). After 24 weeks, 2.51 cells were orthotopically injected into the fourth mammary fat pad of all mice, followed by treatment with anti-PD1 or IgG control antibodies (n=15/diet group). Tumor and cecal DNA was extracted and subjected to 16S rRNA amplicon sequencing.
Results: GSEA from the initial study revealed that orthotopically transplanted line 2.51 tumors, relative to line 1.02 tumors, had lower levels of stromal remodeling as indicated by significant enrichment of gene sets related to extracellular matrix proteoglycans, collagen chain trimerization, and collagen biosynthesis and modification. Gene sets related to insulin and IGF-1 signaling were also lower in line 2.51 tumors than line 1.02 tumors. The in-life portion of the second study revealed a heterogeneous response to ICI therapies among lean and obese mice. To understand this diversity of response, 16S rRNA sequencing analysis of tumoral and cecal microbiota in response to DIO and ICI therapy is underway.
Discussion: These data reveal striking differences in tumor microenvironment and nutrient sensing as being potentially important determinants of differential tumor growth in BLBC. Ultimately, this research may contribute to the development of precision nutrition approaches using pro-/pre-biotics to promote microbial communities, targeting the tumor microenvironment, which may improve immunotherapy response and disrupt the obesity-associated exacerbation of breast cancer.
Financial Support: This work was supported by R35CA197627 to SDH.
Citation Format: Tori L. McFarlane, Meredith S. Carson, Elaine M. Glenny, Violet A. Kiesel, Ashlee Taylor, Daniel Roth, Jody Albright, Melissa VerHague, John E. French, Michael F. Coleman, Stephen D. Hursting. Microbial determinants of immune checkpoint inhibition response in a murine model of obesity and metastatic basal-like breast cancer [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 612.