Wednesday, February 20, 2013
A natural, nontoxic product called genistein-combined polysaccharide, or GCP, which is commercially available in health stores, could help lengthen the life expectancy of certain prostate cancer patients, UC Davis researchers have found.
Men with prostate cancer that has spread to other parts of the body, known as metastatic cancer, and who have had their testosterone lowered with drug therapy are most likely to benefit. The study, recently published in Endocrine-Related Cancer, was conducted in prostate cancer cells and in mice.
Lowering of testosterone, also known as androgen-deprivation therapy, has long been the standard of care for patients with metastatic prostate cancer, but life expectancies vary widely for those who undergo this treatment. Testosterone is an androgen, the generic term for any compound that stimulates or controls development and maintenance of male characteristics by binding to androgen receptors.
The current findings hold promise for GCP therapy as a way to extend life expectancy of patients with low response to androgen-deprivation therapy.
Paramita Ghosh, an associate professor in the UC Davis School of Medicine, led the pre-clinical study with a team that included UC Davis Comprehensive Cancer Center Director Ralph de Vere White, a UC Davis distinguished professor of urology. Ruth Vinall in the UC Davis Department of Urology and Clifford Tepper in the UC Davis Department of Biochemistry and Molecular Medicine directed the studies in mice; Ghosh’s laboratory conducted the cell studies.
The research focused on GCP, a proprietary extract cultured from soybeans and shiitake mushrooms and marketed by Amino-Up of Sapporo, Japan. Researchers found that the combination of the compounds genistein and daidzein, both present in GCP, helps block a key mechanism used by prostate cancer cells to survive in the face of testosterone deprivation.
The research team had earlier shown that when a patient’s androgen level goes down, cancerous prostate cells kick out a protein known as filamin A, which is otherwise attached to the androgen receptor in the cell’s nucleus. The androgen receptor regulates growth of prostate cancer cells. Once filamin A leaves the cancerous cell’s nucleus, that cell no longer requires androgens to survive. Thus, loss of filamin A allows these cells to survive androgen deprivation, at and the cancer essentially becomes incurable.
The paper, titled “Enhancing the effectiveness of androgen deprivation in prostate cancer by inducing Filamin A nuclear localization,” shows for the first time that GCP keeps filamin A in the nucleus. As long as this protein remains attached to the androgen receptor, the cancerous cells need androgens to survive and grow. They die off when starved of androgens, thus prolonging the effects of androgen deprivation, which ultimately prolongs the patient’s life.
The team’s hypothesis is that metastatic prostate cancer patients with the weakest response to androgen-deprivation therapy could be given GCP concurrently with androgen deprivation therapy to retain Filamin A in the nucleus, thereby allowing cancer cells to die off.
De Vere White is now pursuing funding to begin GCP human clinical trials. Because GCP is a natural product rather than a drug, and requires fewer government approvals, it’s expected that these trials will proceed rapidly once funded.
“We should know within the first eight months or so of human clinical trials if GCP works to reduce PSA levels,” says de Vere White, referring to prostate-specific antigen levels, a tumor marker to detect cancer. “We want to see up to 75 percent of metastatic prostate cancer patients lower their PSA levels, and GCP holds promise of accomplishing this goal. If that happens, it would probably be a greater therapy than any drug today.”
Chemists at the University of California, Riverside have developed a compound that holds much promise in the laboratory in fighting renal (kidney) cancer.
Named TIR-199, the compound targets the "proteasome," a cellular complex in kidney cancer cells, similar to the way the drug bortezomib, approved by the Food and Drug Administration, targets and inhibits the proteasome in multiple myeloma cells, a cancer coming from bone marrow.
Michael Pirrung, a distinguished professor of chemistry at UC Riverside, announced the development of TIR-199 in a lecture he gave on Feb. 19 at the 5th International Conference on Drug Discovery and Therapy, held in Dubai, UAE.
Operating like the garbage dump of a cell, the proteasome breaks down proteins. Drugs that block the action of proteasomes are called proteasome inhibitors, and have been shown to have activity against a variety of cancer cell lines, albeit with mixed results. For example, bortezomib, though effective against multiple myeloma, has many side effects because cells other than bone marrow cells are affected.
"The novel feature of our new proteasome inhibitor, TIR-199, is that it is nearly as potent as bortezomib, but is selective in inhibiting the growth of only renal cancer cell lines," Pirrung said. "It's what makes TIR-199 attractive."
The TIR-199 research project at UC Riverside began about four years ago after a multidisciplinary, international team reported on a class of compounds that act on the proteasome. These compounds are the "syringolin" natural products -- such as a compound produced naturally by the wheat-infecting bacterium Pseudomonas syringae. TIR-199 is a synthetic relative of syringolin.
"At UCR we began to work on, and completed the synthesis of, two compounds from this class of compounds," Pirrung said. "Of the two, TIR-199 showed most promise."
Pirrung's lab first shipped TIR-199 samples to the University of Hawaii, Hilo, where André Bachmann, an associate professor of pharmaceutical sciences and Pirrung's collaborator, studied TIR-199 in test-tube assays for how it worked against the proteasome. Bachmann then tested the compound against a limited number of cancer cell lines that showed that TIR-199 was effective against the cancer cells. What remained unclear, however, was if TIR-199 was toxic to normal cells.
Encouraged by these results, Pirrung submitted TIR-199 samples to the National Cancer Institute at the National Institutes of Health, where the compound was subjected to a rigorous 60-cell screening used routinely to test compounds for their effectiveness in battling 60 kinds of cancer, including leukemia, lung, colon, brain, breast, ovarian prostate and renal cancers.
"We were very excited when the NCI informed us that TIR-199 has excellent potential to be moved to drug development because of its selective activity against renal cancer," Pirrung said. "This is good news also because the NCI scientists told us there really are no good drugs out there to fight renal cancer."
Next, the NCI will test TIR-199 on cells grown in a hollow fiber that partially mimics the body by offering a three-dimensional environment. If the test results are positive, TIR-199 will be tested on mice.
The UCR Office of Technology Commercialization has filed a patent application on TIR-199 and is currently seeking partners in industry interested in developing the compound commercially. Several biotechnology companies have already shown interest.
"We still have to fine-tune TIR-199 in the lab because some aspects -- certain structural elements within it -- make it easily metabolized," Pirrung said. "But now that we have a good handle on how structural changes in the compound affect anticancer activity and how the parent drug binds to the proteasome, we are pretty confident of making a better version -- the second generation -- of TIR-199."
The project was funded by a grant from the University of California Institute for Mexico and the United States (UC MEXUS), to Tannya Ibarra-Rivera, a former postdoctoral researcher in Pirrung's lab who helped discover TIR-199 and after whose initials the compound is named; and to Pirrung from the UC Cancer Research Coordinating Committee.