Cytotoxic Constituents of Propolis from Myanmar and Their Structure–Activity Relationship

Abstract

Thirteen cycloartane-type tritepenes (1—13) and four prenylated flavanones (14—17) isolated from propolis collected in Myanmar, were evaluated for their cytotoxic activity against a panel of six different cancer cell lines; three murine cancer cell lines (colon 26-L5 carcinoma, B16-BL6 melanoma, and Lewis lung carcinoma) and three human cancer cell lines (lung A549 adenocarcinoma, cervix HeLa adenocarcinoma and HT-1080 fibrosarcoma). Among them, a cycloartane-type triterpene, 3α,27-dihydroxycycloart-24E-en-26-oic acid (3), showed the most potent cytotoxicity against B16-BL6 cells with an IC₅₀ value of 5.91 μM, comparable to those of positive controls, doxorubicin (IC₅₀, 5.66 μM) and 5-fluorouracil (IC₅₀, 4.88 μM). In addition, (2S)-5,7-dihydroxy-4′-methoxy-8,3′-diprenylflavanone (14) exhibited strong cytotoxicity against all the tested cancer cell lines with the IC₅₀ values ranging from 14.0 to 26.4 μM. Based on the observed results, the structure–activity relationships are discussed.