Effects of the Kava Chalcone Flavokawain A Differ in Bladder Cancer Cells with Wild-type versus Mutant p53

Abstract

Flavokawain A is the predominant chalcone from kava extract. We have assessed the mechanisms of flavokawain A's action on cell cycle regulation. In a p53 wild-type, low-grade, and papillary bladder cancer cell line (RT4), flavokawain A increased p21/WAF1 and p27/ KIP1, which resulted in a decrease in cyclin-dependent kinase-2 (CDK2) kinase activity and subsequent G 1 arrest. The increase of p21/WAF1 protein corresponded to an increased mRNA level, whereas p27/KIP1 accumulation was associated with the down-regulation of SKP2, which then increased the stability of the p27/KIP1 protein. The accumulation of p21/ WAF1 and p27/KIP1 was independent of cell cycle position and thus not a result of the cell cycle arrest. In contrast, flavokawain A induced a G 2 -M arrest in six p53 mutant-type, highgrade bladder cancer cell lines (T24, UMUC3, TCCSUP, 5637, HT1376, and HT1197). Flavokawain A significantly reduced the expression of CDK1-inhibitory kinases, Myt1 and Wee1, and caused cyclin B1 protein accumulation leading to CDK1 activation in T24 cells. Suppression of p53 expression by small interfering RNA in RT4 cells restored Cdc25C expression and down-regulated p21/WAF1 expression, which allowed Cdc25C and CDK1 activation, which then led to a G 2 -M arrest and an enhanced growth-inhibitory effect by flavokawain A. Consistently, flavokawain A also caused a pronounced CDK1 activation and G 2 -M arrest in p53 knockout but not in p53 wild-type HCT116 cells. This selectivity of flavokawain A for inducing a G 2 -M arrest in p53-defective cells deserves further investigation as a new mechanism for the prevention and treatment of bladder cancer.

Flavokawain B induces apoptosis of human oral adenoid cystic cancer ACC-2 cells via up-regulation of Bim and down-regulation of Bcl-2 expression

“…Cells were stained using 50 µg/mL propidium iodide for 30 min. Approximately 10 000 cells per sample were analyzed by FACScan flow cytometer (BD Biosciences) and the percentage of cells in the G1, S, and G2-M phases of the cell cycle was determined using Mod-FIT software as described previously (Tang et al 2008). …”

“…Flavokawain A, B, and C, constitute approximately 0.46%, 0.015%, and 0.012% of kava extracts, respectively (Dharmaratne et al 2002). Previous studies have shown that the chalcone flavokawain A (FKA), the predominant chalcone in kava extracts, induces apoptosis of bladder cancer cells via Bax-and mitochondriadependent apoptosis and cell-cycle arrest, and the anti-tumor action of the chalcone flavokawain B (FKB) isolated from kava extracts is even stronger than that of FKA (Zi and Simoneau 2005;Tang et al 2008Tang et al , 2010.…”

Diterpenoids from the root bark of Jatropha curcas and their cytotoxic activities

“…The cytotoxic activities of compounds 1-12 were evaluated against HEPG2 (liver) and LOVO (colon) tumor cell lines using the MTT assay (Tang et al, 2008). Compounds 8, 9 and 10 showed In conclusion, we have isolated three new diterpenoids whose chemical structures were determined based on extensive spectroscopic studies and chemical methods.…”

Dietary chalcones with chemopreventive and chemotherapeutic potential

“…In p53 mutated cell lines, however, flavokavain A (23) prevented the G2/M transition via persistent activation of Cdk1 kinase activity and increased levels of cyclin B1, which counteracted the decreased level of Cdc25C. The Cdk1-inhibitory kinases Myt1 and Wee1 were suppressed, allowing Cdk1 to remain dephosphorylated [167].…”