Project Summary
Bladder cancer represents a major public health burden. The cost per bladder cancer patient from diagnosis to
death is the highest among all cancers ($96,000 to $187, 000 per patient in the US). Our long-term goal is to
develop new chemopreventive agents to reduce the burden of bladder cancer. Because exposure to
carcinogens is the major risk factor for bladder cancer and many potentially protective compounds contained in
plant-derived food are concentrated in the urine, it is plausible that bioactive agents in plants may play a role in
bladder cancer chemoprevention. Flavokawain A is the predominant chalcone identified from kava root extract.
The promise of flavokawain A is based on the following data : 1) an epidemiological study reported that high
kava consumption correlated with lower incidences of cancers despite the presence of many smokers in the
populations of the South Pacific Islands; 2) In vitro cell culture studies showed that flavokawains but not
kavalactones in kava extracts exhibited strong antiproliferative and apoptotic effects on human bladder cancer
cells characterized as low- and high- grades; 3) Flavokawain A inhibited tumor growth in xenograft models of
superficial and invasive bladder cancer without any noticeable side effects; and 4) The chemical structure of
flavokawain A, similar to some other chalcones, leads us to predict that it would cause no direct damage to
DNA, bind to beta-tubulin, and induce phase II enzymes to protect against carcinogenesis. We hypothesize
flavokawain A has chemopreventive effects on bladder epithelium via enhancing cell cycle regulation
and increasing the sensitivity of apoptotic mechanisms. Three mouse models will be used to test this
hypothesis: a carcinogen [4-hydroxybutyl (butyl) nitrosamine (OH-BBN)]-induced carcinogenesis model in mice
bladders, and two spontaneous mouse bladder transgenic carcinogenesis models, each of which will address
distinct issues. The OH-BBN model in mice will be used to examine flavokawain A's utility in primary
prevention; for preventing the first occurrence of bladder cancer in those with risk factors such as cigarette
smoking and industrial exposures. The transgenic models each induce a separate precursor state to advanced
bladder cancer: either papillary tumors or carcinoma in situ, as seen in early stages of clinical bladder cancer.
Examining flavokawain A in these transgenic models will provide information about its usefulness in secondary
prevention, which clinically will address preventing bladder cancer recurrence and progression. Our microarray
analysis has identified a few potential transcriptional targets (i.e. BIM, BID, survivin, Plk1, 14-3-3gamma, and
SKP-2) for flavokawain A when inducing apoptosis and cell cycle arrests. We will validate these targets by
examining their expression in vivo in these tested animal models and by using RNA interference and
overexpression vectors to determine their contributions to flavokawain A's action in vitro, as well as by studying
the down-stream events of these targets. Together, these studies will provide a firm answer to the promise of
flavokawin A as a chemoprventative and/or chemotherapeutic agent. |