Abstract 6842: The effect of intra-tumoral Candida albicans on host gene expression
Authors: Loncar Alexander , Grencewicz Dennis , Hoyd Rebecca , Pallerla Aaditya , Williams Nyelia , Benej Martin , Mehra Yogita , Jahanbakhshi Shiva , Anderson Matthew , Denko Nicholas , Spakowicz Daniel 
Published: March 2024

Abstract
The gut and tumor microbiome have been shown to affect tumorigenesis, tumor immune infiltration, and response to traditional cancer therapeutics such as radiation therapy. Further, specific microbe-cancer relationships have been established. One such microbe is Candida albicans, which has been identified within several gastrointestinal cancers and is associated with an increased risk of metastases and decreased overall survival. By completing RNA-sequencing on murine rectal tumors colonized with C. albicans, we can better understand whether intratumoral changes in gene expression exist based on colonization of specific microbes. This study utilizes gut-to-tumor translocation and whole transcriptome analysis for a discovery-based approach to identify the effects of C. albicans on the host tumor.
We established a rectal tumor model with C57BL/6 mice using MC38 rectal cancer cells subcutaneously injected on the right flank, local radiation to the tumor (standard-of-care for rectal cancer), and gavage with either C. albicans (Ca) or PBS. Fungal presence within tumors was validated by staining with calcofluor white and subsequently, tumors were sent for bulk RNA-sequencing to determine differences in gene expression using DeSeq2 and a gene set enrichment analysis (GSEA).
In unsupervised analysis of gene expression differences between PBS-gavaged and Ca-gavaged with bulk RNA sequencing, tumors gavaged with C. albicans possessed unique gene expression and pathway analysis when compared to PBS-gavaged mice. Global differential gene expression showed 1,947 genes upregulated in Ca gavage and 593 genes upregulated in the PBS gavage (p &lt; 0.05). C. albicans colonized tumors showed decreased expression in gene pathways relating to immune activation (interferon alpha response, IL-6 and STAT3 signaling), p53 expression, DNA repair, oxidative phosphorylation, NOTCH signaling, and apoptosis. We subsequently used a network-based approach to identify the most important genes driving the differences in the tumors, calculating the degree, closeness, and betweenness centralities.
Several microbes have been regarded as potential contributors to decreased treatment response and survival in rectal cancer. In the case of tumors colonized with C. albicans, bulk RNA-sequencing indicates down regulation of gene pathways related to cell proliferation, immune activation, and DNA maintenance. Down regulation of gene pathways related to cell cycle control and arrest suggests that intratumoral colonization of C. albicans may causally affect tumorigenesis. Decreases in immune signaling in tumors suggest a potentially causal role of C. albicans immune suppression. These results highlight initial steps to understand how intratumoral C. albicans may be affecting rectal cancer progression and treatment response and serve as a technique to allow better insight to individual microbial impact on tumors.
Citation Format: Alexander Loncar, Dennis Grencewicz, Rebecca Hoyd, Aaditya Pallerla, Nyelia Williams, Martin Benej, Yogita Mehra, Shiva Jahanbakhshi, Matthew Anderson, Nicholas Denko, Daniel Spakowicz. The effect of intra-tumoral Candida albicans on host gene expression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6842.