Inhibitory Effects of Metabolites of Nobiletin and 5‐hydroxy Nobiletin on Human Lung Cancer Cells

Nobiletin (NBT) and 5‐hydroxy nobiletin (5HN) are unique polymethoxyflavones found in citrus fruits. We investigated the effects of NBT, 5HN, and their major metabolites, namely 4′‐hydroxy nobiletin (M1), 3′,4′‐dihydroxy nobiletin (M2), 3′,5‐dihydroxy nobiletin (M3), 4′,5‐dihydroxy nobiletin (M4), and 3′,4′,5‐trihydroxy nobiletin (M5) on human lung cancer cells. All metabolites showed much stronger inhibitory effects on lung cancer cells than NBT and 5HN. M3 produced the strongest inhibition among all metabolites. Cell cycle analyses revealed that M1 and M4 induced G 0 /G 1 cell cycle arrest, while M3 and M5 caused G 2 /M cell cycle arrest after 24h treatments. Moreover, annexin V‐FITC/PI co‐staining assay showed that M2, M3 and M5 induced extensive apoptosis after 48h treatments. Consistent with these results, immunoblotting showed that M3 and M5 decreased expression levels of cyclinB1 and cdc‐2 (cdk‐1), while increased expression levels of p21 (Cip1/Waf1) . M1 and M4 decreased expression levels of cdk‐4. Furthermore, M2, M3, and M5 caused significant Increases in the expression levels of Bax, cleaved PARP, and cleaved caspase‐3. In contrast, NBT and 5HN did not cause any changes in these proteins at the same concentrations as the metabolites. In conclusion, our results demonstrated strong inhibitory effects of metabolites of NBT and 5HN on human lung cancer cells. Grant Funding Source : NIH: CA139174 , AICR: 10A044