Abstract 5905: Enterotoxigenic Bacteroides fragilis, a colon microbe, dysregulates polyamine catabolism to promote breast cancer progression
Authors: Nandi Deeptashree , Parida Sheetal , Thatikonda Sowjanya , Foley Jackson , Stewart Tracy , Sears Cynthia L. , Casero Robert A. , Sharma Dipali 
Published: June 2023

Background: With more than 2.3 million cases worldwide, breast cancer persists as a major health burden and warrants a greater understanding of the molecular triggers underlying this disease. Focusing on microbial dysbiosis, our lab discovered the pivotal role of the enterotoxigenic Bacteroides fragilis (ETBF) in promoting breast tumorigenesis through activation of key oncogenic pathways. A gap in knowledge exists regarding how microbes/microbial toxins modulate the oncogenic pathways in cancer cells. Polyamines are imperative for various physiological processes, including cell growth, survival, differentiation and apoptosis and are strongly associated with breast cancer. We questioned the involvement of polyamine pathway in mediating the oncogenic effects of microbial dysbiosis on breast cancer.

Methods: Human Her2 expressing spontaneous breast cancer model, MMTV.f.HuHer2 mice, were infected with ETBF and tumor incidence and progression were monitored for 18 months. We used qRT-PCR, western blotting, immunocytochemistry and immunohistochemistry to examine expression of key nodes of polyamine pathway. Various growth, migration and invasion assays were performed to assess carcinogenic properties in breast cancer cells. We employed a colorimetric-based assay to analyze enzymatic activities of key polyamine metabolic members. ROS generation was examined via DCFA staining.

Results: Our in vivo data showed that ETBF colonization in mice led to a considerable increase in the level of spermine oxidase (SMOX) in breast tumors, hinting at a correlation between ETBF and polyamine metabolism. Moreover, a marked rise in expression of γH2AX foci was observed in these tumors and in breast cancer cells, suggesting a critical role of ETBF in SMOX-related DNA damage. In agreement, we found SMOX upregulation in breast cancer cells. Our findings displayed a substantial increase in SMOX enzymatic activity in the presence of ETBF toxin, BFT, in breast tumor cells. BFT caused a marked rise in ROS generation of breast tumor cells, suggesting a plausible association of ETBF in SMOX-mediated oxidative stress. Interestingly, we noted a significant induction of ornithine decarboxylase (ODC) expression and activity in response to ETBF or BFT in breast cancer cells. Treatment of BFT-exposed breast cancer cells with SMOX inhibitors led to a sharp inhibition of neoplastic transformations, like cellular migration and γH2AX induction.

Conclusion: Our collated evidences suggest the existence of an important cross-talk between key polyamine metabolic enzymes and ETBF that aids in exacerbating breast tumorigenesis. Of importance, therapeutic inhibition of SMOX dramatically impeded BFT-related breast tumorigenesis. Collectively, our results demonstrated the attractive potential of intervening the polyamine catabolic pathway for the management of breast cancer.

Citation Format: Deeptashree Nandi, Sheetal Parida, Sowjanya Thatikonda, Jackson Foley, Tracy Stewart, Cynthia L. Sears, Robert A. Casero, Dipali Sharma. Enterotoxigenic Bacteroides fragilis, a colon microbe, dysregulates polyamine catabolism to promote breast cancer progression. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5905.