Tumor-associated macrophages (TAMs) are pivotal for tumor development and progression. Reprogramming the M2-like pro-tumoral behavior of TAMs towards the M1-like anti-tumor phenotype to unleash their potential against tumors has become one of the most promising anti-tumor immunotherapy strategies. In this work, the natural product pseudolaric acid B (PAB, 1) was found to markedly decrease ARG1 mRNA expression and significantly increase NOS2 expression in the IL-4/IL-13-pre-stimulated RAW 264.7 cells through cellular phenotype screening of a series of pseudolaric acid-related natural products, suggesting its potential to reprogram the pro-tumoral TAMs towards the M1-like phenotype against tumors. Further chemical modification of the carboxylic acid moiety of 1 led to a series of amide or pyranoside derivatives with ARG1- and NOS2-modulating activity. Among them, hydrazineyl amide 12 stands out as the most potent, without significant diminution in cell viability. It inhibited the M2-like polarized tumor-promoting phenotype of macrophages, as evidenced by a decrease in CD206 expression and an increase in CD86 expression in flow cytometry, as well as a decrease in ARG1 protein level in Western blot assays. In addition, 12 could reverse the suppression of Ki67+, IFN γ+, and granzyme B+ CD8+ T cell proliferation and activation induced by pro-tumoral macrophages. More importantly, it could reshape the tumor immune microenvironment and inhibit tumor growth in immunocompetent murine tumor models. Hsp90 was predicted to be a potential target of 12 by a target fishing software, which was further demonstrated by molecular docking. Collectively, the amide derivative 12 of PAB demonstrated promising anti-tumor TAM-reprogramming activity, which is worthy of further investigation.
