Apoptotic and antiproliferative effects of components of kava extracts on bladder cancer cells.

2220

Kava (the piper methysticum Forst.f. plant) is a sterile plant limited to growth in the South Pacific Tropics. Time required for its growth before root harvest is approximately four to five years. The root extract of kava has been part of the Pacific Islanders’ culture for thousands of years, serving as a beverage, medicine and in socio-religious functions similar to wine in Western cultures. Consumption of traditional aqueous kava preparation has not been documented with any major side effects for centuries, and has correlated with low and uncustomary sex ratios (more cancer in women than men) of cancer incidences in three kava-drinking countries such as Fiji, Vatu and Western Samoa. Kavalactones and chalcones are two major classes of chemicals isolated from kava extracts. The major kavalactones in kava extracts are kawain, mehtysticin, desmethoxyyangonin, Yangonin, dihydrokawain and dihydromethysticin, whereas chalcones include flavokawain A, B and C. We found that the kava extract standardized with 70% kavalactones inhibits proliferation of bladder cancer cell lines RT24, T24 and EJ in a dose-dependent manner. The IC_50s of a kava extract for RT24, T24 and EJ cells were estimated to be about 20.1, 6.2 and 5.1 μg/ml at 48 hours, respectively. Invasive bladder cancer cell lines T24 and EJ cells with mutant p53 are more sensitive to the treatment of kava extract than superficial bladder cancer RT24 cells with wild-type p53. The anti-proliferative effect of the kava extract was involved in typical apoptotic morphologies including cell shrinkage and rounding up, cell membrane blebbing as well as nuclear fragmentation and condensation. Further study showed the differential abilities of kawain, a major kavalactone in kava extract, and flavokawain A, B and C on proliferation of bladder cancer cells. At doses up to 25 μg/ml, no inhibitory effect on proliferation of RT 24 and EJ cells, and less than 27 % inhibition of T24 cell proliferation were observed with kawain treatment. On the contrary, compared to 0.1% DMSO treated controls, flavokwain A, B and C at a dose of 25 μg/ml caused almost complete inhibition of RT24, T24 and EJ cell proliferation. Western blot analysis showed that 12.5 μg/ml flavokawain A induced a significant cleavage of PARP and caspase 3, two hallmarks of apoptosis, but that kawain, methysticin and yangonin at doses of 40 and 80 μg/ml did not. Microarray analysis for comparing gene expression profiles of the kava extract and its components on treated bladder cancer cells are in progress to determine the active principles of kava extracts in induction of apoptosis in bladder cancer cells.