Microbial-derived immunostimulatory small molecule augments anti-PD-1 therapy in lung cancer

We previously showed that enrichment of the Bacteroides genus is associated with improved anti-PD-1-mediated tumor therapy. Here, we isolate 183 Bacteroides isolates from the feces of humanized anti-PD-1 responder mice. Supernatants from 6 of 183 isolates stimulate IFNγ production from primary CD8⁺ T cells. These six isolates (6-consort) enhance anti-PD-1-induced anti-tumor efficacy in syngeneic and orthotopic lung cancer models compared to non-responder feces-colonized mice, an effect dependent on the production of IFNγ. Bioassay-guided fractionation and comparative metabolomics lead to the discovery of an active N-acyl amide (cis-Bac429) produced by Bacteroides. cis-Bac429 stimulates IFNγ production by CD8⁺ T cells but not synthetic saturated Bac429 (sat-Bac429), indicating structural specificity. Intratumorally administered cis-Bac429, but not sat-Bac429, significantly decreases subcutaneous lung and colon tumor growth in combination with anti-PD-1 therapy and drives IFNγ+ CD8⁺ T cell tumor infiltration. These findings pave the way for development of Bacteroides-type N-acyl-amides as adjuvant treatments for anti-PD-1-refractory NSCLC.