Rhizopus nigricans polysaccharide activated macrophages and suppressed tumor growth in CT26 tumor-bearing mice

•A homogeneous polysaccharide (RPS-1) was extracted from Rhizopus nigricans.•RPS-1 was non-starch α-1,6 branched α-1,4-glucan and its Mw was 1.617 × 107 g/mol.•MAPKs and NF-κB pathways were involved in macrophages activation induced by RPS-1.•Intragastric administration of RPS-1 inhibited tumor growth of CT26 tumor-bearing mice.