Role of bacterial-derived small molecules in immunotherapy

There is an urgent unmet need in the clinic to improve response rates to immune checkpoint inhibition (ICI) treatment and extend overall survival in these treatment-refractory non-small cell lung cancer (NSCLC) patients, which is an estimated 68% of all lung cancer patients. We recently showed that microbiota transplantation feces from ICI responder (R) patients into gnotobiotic lung cancer allograft mice decreased tumor growth compared to non-responders (NR) colonized mice following anti-PD-1 therapy, a phenomenon associated with enrichment of the Bacteroides genus. Our preliminary work identified 183 culturable Bacteroides isolates from feces of R mice, with 6 out of these strains able to stimulate IFNγ production from primary CD8+ T cells. A consortium composed of these six stimulatory isolates (6-Consort) decreased tumor growth compared to NR feces-colonized mice following treatment with ICI and increased intratumoral and systemic IFNγ production. A combination of bioassay-guided fractionation with metabolomics performed on the supernatant of these bacteria identified novel small molecule Bac429, which was synthesized and found to induce IFNγ production from primary CD8+ T cells. Moreover, intra-tumor Bac429 injection in xenograft mice augmented anti-PD-1 mediated anti-tumor effect. These exciting findings suggest that some bacteria from ICI-responsive patients produce small molecules that augment immunotherapy responsiveness. Our central hypothesis is that specific bacteria produce small molecules that determine ICI efficacy and toxicity by engaging host immune responses. The rationale for the proposed research is that once we understand the interplay between bacteria and cancer therapy, it would be possible to design selective bacteria-derived drugs to augment responsiveness to immunotherapy. We plan to test our central hypothesis and fulfill the overall objective of this application with the following specific aims. Aim 1: Define the functional impact of Bac429 on experimental NSCLC. Our hypothesis is that Bac429 is a microbially-regulated small molecule with immunostimulatory effect impacting response to anti-PD-1 treatment in lung cancer. Aim 2: Establish the relationship between diet and Bac429 production in 6-consort mediated anti-PD-1 synergistic effect. Our hypothesis is that selective dietary glycan modulation will affect bacterial metabolism and Bac429 production and that this gene-diet interaction can be harnessed to modulate anti-tumor immunity. Aim 3: Design of cis-Bac429 to improve anti-tumor immunity properties. Our hypothesis is that key structural modifications of Bac429 will improve solubility, bioavailability and anti-tumor immune effect. At completion, this project will characterize bacterial-derived metabolite Bac429 and its mechanism of action implicated in the anti-tumor efficacy of anti-PD-1 treatment. This knowledge will serve as a springboard for future studies expanding to other forms of solid tumors.