IMPACT OF INTRATUMORAL MICROBIOTA IN SOFT TISSUE SARCOMA TREATMENT EFFICACY

Tumor resident microbiota is an emerging component of the tumor microenvironment with undefined biological function. Among all microorganisms harbored within tumor tissue, bacteria are currently the most studied interaction with the host. To date, the tumor microbiome is reported as composed of tumor type-specific bacteria, commonly found within host cells, which can affect tumor biology as well as play a role in cancer formation, progression, and response to therapy. So far, the contribution of intratumoral microbiota in the context of soft tissue sarcoma (STS) has been underestimated; therefore, this project aims to characterize the STS microbiota and understand if it can impair the sensitivity to chemotherapeutic regimens. STS are heterogeneous cancers with more than 70 histological subtypes, different in molecular alterations, which make its personalized therapy very complex. Thus, doxorubicin, characterized by an agnostic mechanism of action, is the gold standard of chemotherapy for advanced STS but it is effective for less than 50% of patients. Doxorubicin is a natural anthracycline produced by different strains of Streptomycetaceae which exploit the toxic properties of this molecule for inter-specific competition. Hence, the hypothesis that certain bacteria developed drug-inactivating mechanisms seems evolutionarily plausible. Targeting the bacterial 16S rRNA gene through a Fluorescence in situ hybridization, we were able to detect bacteria within different histotypes of sarcoma. In addition, we analyzed the microbiome composition performing the bacterial 16S rRNA gene sequencing on sarcoma tissues and adjacent healthy tissues. This analysis showed that sarcomas harbor a distinct microbiome composition if compared to adjacent healthy tissues and seems to be shaped according to histological features. Moreover, we were able to isolate live bacteria harbored within sarcoma tissues. To date, isolated bacteria were mainly strictly or facultative anaerobes; thus, well adapted to live in the hypoxic environment of tumors. These bacteria gave us the opportunity to investigate their ability to interfere with chemotherapy. We exposed several sarcoma-isolated bacteria strains to doxorubicin, and we found that certain bacteria strains were responsible for drug degradation. This result was confirmed through mass spectrometry and with functional experiments evaluating drug toxicity after bacterial exposure. In addition, we showed in vivo that the intratumoral presence of doxorubicin-degrading bacteria is sufficient to promote the occurrence of chemoresistance in a doxorubicin-sensitive mouse model of fibrosarcoma. This study offers new insights about the relationship between the intratumoral microbiota and the occurrence of chemoresistance in cancer therapies, suggesting that microbial communities hosted within the tumor should be deeply investigated, and then manipulated, to improve the outcome of therapies.