Agaritine purified from Agaricus blazei Murrill exerts anti-tumor activity against leukemic cells

Background: Mushrooms of the genus Agaricus are a common folk remedy against carcinoma. The active ingredients, polysaccharides and protein-polysaccharide complexes containing β-glucan, have been isolated and shown to have indirect tumor-suppressing activity via an immunological activation. Methods: The diffusible fraction of a hot-water extract of Agaricus blazei Murrill (ABM) powder was fractionated by HPLC based on the anti-tumor activity against leukemic cells in vitro. The structure of the anti-tumor substance was determined by NMR and MS analyses. Results: We purified a tumorcidal substance from the diffusible fraction of ABM and identified it as agaritine, β-N-(γ-l(+)-glutamyl)-4-(hydroxymethyl) phenylhydrazine, having a molecular mass of 267Da. This compound inhibited the proliferation of leukemic cell lines such as U937, MOLT4, HL60 and K562 with IC₅₀ values of 2.7, 9.4, 13.0, and 16.0μg/mL, respectively, but showed no significant effect on normal lymphatic cells at concentrations up to 40μg/mL. Although agaritine has been suspected of having genotoxic or carcinogenic properties, agaritine did not activate the umu gene of Salmonella, which reacts to carcinogens. General significance: The results indicate that agaritine from ABM has direct anti-tumor activity against leukemic tumor cells in vitro. This is in contrast to the carcinogenic activity previously ascribed to this compound. Our results also show that this activity is distinct from that of β-glucan, which indirectly suppresses proliferation of tumor cells.