Combination of lipopolysaccharide and polygalacturonic acid exerts antitumor activity and augments anti-PD-L1 immunotherapy.

Polygalacturonic acid (PGA) restored the alpha-diversity of gut microbiota and promoted T cells infiltration in tumors. Here, we investigated whether oral administration of PGA could improve the anti-cancer effect of lipopolysaccharide-encapsulated PLGA-PEG-PLGA (LPS/PPP) in mice bearing CT26 tumors. Hydrogels with rapid thermogelling properties can achieve localized and controlled release of LPS, thus retaining the anti-cancer effect of LPS and avoiding a robust inflammatory storm. LPS/PPP promoted M1 macrophage polarization, TLR4 expression, and phagocytosis in tumors. The combination of PGA and LPS/PPP (PGA&#95;LPS) notably repressed CT26 tumor growth and the inhibition rate reached 67.6 %. PGA&#95;LPS triggered the recruitment of helper and cytotoxic T cells, IFN-γ level, decreased the proportion of immunosuppressive regulatory T cells. PGA&#95;LPS also restored the beta-diversity of gut microbiota and increased short chain fatty acids abundance (butyric acid, 608.93 % vs. model group, P < 0.01). PGA&#95;LPS followed by αPD-L1 resulted in obvious inhibition of both CT26 and 4T1 tumor growth, promoted cleaved-caspase 3 and Bax expression, T cell responses and the rescue of T cells exhaustion. These results confirmed that PGA&#95;LPS reinforced the anticancer effect of αPD-L1, probably by reshaping the tumor microenvironment and intestinal flora, which sheds light on the combination approach to intensify the effect of immune checkpoint inhibitors.
Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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