Abstract 3059: Microbiota mediated CHI3L1 expression as a novel candidate biomarker for breast cancer progression
Authors: Mozzarelli Alessandro Mauro , Carloni Sara , Ferrrari Valentina , Giugliano Silvia , Tiraboschi Luca , Cascio Antonino Lo , Fornasa Giulia , Braga Daniele , Golzato Davide , Segata Nicola , Penna Giuseppe , Rescigno Maria 
Published: June 2022

Abstract
Over the past decade, infectious agents, including bacteria, have come under scrutiny for contributing to almost 16% of all tumors. Indeed, emerging data report a microbial presence in many cancer types, with breast cancer accumulating the most diverse bacterial population. Pathogen defense mechanisms, such as CHI3L1, contribute to bacterial elimination; however, CHI3L1 is overexpressed in several cancer types and correlates with poor prognosis and shorter survival. However, the connection between intra-tumoral bacteria and CHI3L1 and how they contribute to cancer growth has not been fully characterized.To investigate if microbiota and CHI3L1 are connected, female BALB/c mice harboring 4T1-Luc cells were exposed to a broad-spectrum antibiotic mix to deplete the microbiota and to evaluate tumor growth and circulating CHI3L1 levels. 9 and 14 days after tumor inoculation, feces were collected and bacterial DNA isolated for 16S rRNA sequencing, and tumors were plated to identify intratumoral bacteria. To assess whether a specific bacterial strain could modulate CHI3L1 expression, we incubated 4T1 cells with supernatants from isolated bacteria, which contain metabolites and extracellular factors. Isolated bacteria that could upregulate CHI3L1 expression were then used to infect 4T1 cells prior to subcutaneous injection in the mammary fat pad of BALB/c mice to evaluate if bacterial infection changes tumor growth rate.In the 4T1 mouse breast cancer model, a broad-spectrum antibiotic treatment was able to: deplete host microbiota, abrogate tumor growth, and reduce CHI3L1 levels in the sera and in CD45+ immune infiltrating cells in tumor and colon. When 4T1 cells were exposed to bacterial supernatants in vitro, we observed that CHI3L1 was upregulated by a specific strain of E. coli. To simulate the effect of intra-tumoral microbiota, we infected 4T1 cells with either the isolated E. coli or S. aureus (which did not induce any CHI3L1 modulation in vitro) prior to subcutaneous injection. Strikingly, E. coli infection increased tumor progression with respect to the control S. aureus infection (p&lt;0.01).Moreover, we observed an increase in CHI3L1 produced by tumor immune infiltrates in E. coli-infected 4T1, highlighting a key role for microbiota and CHI3L1 in tumor progression. Overall, our findings shed light on the important link between tumor associated bacteria and CHI3L1 in cancer progression. Identifying the mechanism of action through which microbiota and CHI3L1 influence cancer growth will open new possibilities for improved screening, prognosis, and survival for patients with breast cancer.
Citation Format: Alessandro Mauro Mozzarelli, Sara Carloni, Valentina Ferrrari, Silvia Giugliano, Luca Tiraboschi, Antonino Lo Cascio, Giulia Fornasa, Daniele Braga, Davide Golzato, Nicola Segata, Giuseppe Penna, Maria Rescigno. Microbiota mediated CHI3L1 expression as a novel candidate biomarker for breast cancer progression [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 3059.