A high-molecular-weight polysaccharide from Polygonatum sibiricum inhibits distant tumor growth associated with gut microbiota remodeling and Enhances with αPD-1 therapy.

BACKGROUND: Defined polysaccharide fractions can reshape the gut microbiome and influence systemic antitumor immunity. We investigated whether an operationally defined high-molecular-weight Polygonatum sibiricum polysaccharide fraction (PSP-H) enriched by 100 kDa ultrafiltration suppresses growth of subcutaneous MC38 tumors via microbiota-associated mechanisms and potentiates anti-PD-1 therapy.

MATERIALS AND METHODS: PSP-H was isolated by cascade ultrafiltration and compared with a total polysaccharide extract (PSP-T) and lower-MW fractions. We profiled fecal metagenomes, serum metabolites, tumor molecular readouts (immunoblotting; HDAC activity), and immunity. Fecal microbiota transplantation (FMT) tested the microbiota dependence and sufficiency of PSP-H-remodeled communities to transfer the immunometabolic phenotype. Combination with anti-PD-1 (RMP1-14) was evaluated.

RESULTS: PSP-H showed minimal direct cytotoxicity while suppressing tumor growth, selectively enriching butyrate-producing taxa (e.g., Lachnospiraceae) and elevating serum butyrate and inosine, with TNF-α reduced. In vitro, butyrate enhanced T-cell production of IFN-γ, IL-2 and granzyme-B and counteracted IFN-γ-induced PD-L1 expression. In vivo, PSP-H reduced tumor HDAC activity and increased histone acetylation while inducing adaptive STAT1/PD-L1 upregulation. FMT recapitulated the key metabolite/cytokine signature. PSP-H + anti-PD-1 synergistically increased intratumoral CD8+ T cells and yielded superior tumor control versus monotherapy.

CONCLUSION: PSP-H is a defined microbiota-modulating adjuvant that engages a microbiome-butyrate-immune axis to restrain subcutaneous tumors and sensitizes them to PD-1 blockade by reprogramming systemic immunity while inducing targetable adaptive resistance.