(P 297) UNVEILING THE IMPACT OF INTRATUMORAL MICROBIOTA IN THE TREATMENT EFFICACY OF SOFT TISSUE SARCOMA

Objective: Tumor resident microbiota is an emerging component of the tumor microenvironment with poorly defined biological function. Among all microorganism harbored within tumor tissue, bacteria are currently arising as unexpected factors able to play a role in cancer formation, progression, and response to therapy. This project is aimed to characterize soft tissue sarcoma microbiota and understand if it can impair patients’ sensitivity to chemotherapeutic regimens.

Methods: To characterize microbiome composition of soft tissue sarcomas we applied, as an explorative approach, a Fluorescent In-Situ Hybridization targeting the bacterial 16S rRNA and an innovative 16S rRNA gene sequencing method on DNA extracted from sarcoma tissues and adjacent healthy tissues.

To investigate bacterial capability to interfere with anticancer treatments, and particularly with doxorubicin administration, we adopted culturomic approaches to isolate bacteria from fresh sarcoma tissues. We found some bacteria able to metabolize doxorubicin and we confirm their capability to interfere with doxorubicin efficacy in vitro using human and murine sarcoma cell lines, and in vivo with a doxorubicin sensitive murine model of fibrosarcoma (MCA205 injected subcutaneously in C57Bl/6 mice). In addition, products of bacterial biotrasformation of doxorubicin were assessed through mass spectrometry approaches.

Results: We were able to detect bacteria within different histotypes of sarcoma targeting the bacterial 16S rRNA. (Fig.1A) In addition, the 16S rRNA gene sequencing showed that sarcomas arbor a distinct microbiome composition if compared to adjacent healthy tissues. (Fig.1B) Furthermore, comparison of different sarcoma histotypes revealed that microbiome composition seems to be shaped according to histological features. (Fig.1D) We successfully isolated different strains of bacteria from fresh sarcoma tissues, these bacteria were exposed to doxorubicin, and we found that some bacteria have the capacity to completely degrade the drug. (Fig.2A) Functional in vitro experiments confirmed that bacterial exposure can cause, not only the degradation, but also the complete abrogation of drug toxicity. (Fig.2B) In addition, we showed in a doxorubicin sensitive murine model of fibrosarcoma that the presence of doxorubicin-degraders bacteria within the tumor microenvironment promoted the occurrence of chemoresistance.

Conclusion: We revealed that several sarcoma histotypes are colonized by bacteria which constitute the soft tissue sarcoma microbiota. Moreover, we found a direct proof that tumor resident bacteria can degrade doxorubicin impairing the efficacy of chemotherapy. 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.