Synthetic vitamins and natural plant pigments could help prevent major cancers, recent studies suggests. Scientists gathered at the 92nd Annual Meeting of the American Association for Cancer Research (AACR) this week to present and examine a range of cancer preventive research. In an initial study of heavy smokers, researchers at the University of Texas M. D. Anderson Cancer Center in Houston, Texas, recently found that a synthetic vitamin A compound significantly reduced the activity of telomerase, an enzyme important in carcinogenesis. Telomerase activity is evident in up to 90 per cent of human lung cancers but is rare in normal cells. Other studies have shown that telomerase activity is important in the early stages of cancer development and that vitamin A compounds known as retinoids can prevent cancer in animals and humans. The Houston scientists pursued both those findings in research with 57 heavy smokers who had no evidence of cancer. In the double-blinded study, 27 subjects were randomly assigned to receive N-(4-hydroxyphenyl) retinamide (4-HPR), a synthetic retinoid. The other 30 subjects received a placebo. Lung biopsies were taken from the same sites in both groups before and after the six-month treatment period. In prevention studies, a particular challenge is finding meaningful ways to measure the impact of the intervention without waiting decades to see if high-risk subjects remain free of disease. The M. D. Anderson investigators used hTERT, the catalytic subunit of telomerase, as a biomarker to measure the effectiveness of 4-HPR. At baseline, expression of hTERT was similar in both groups (4-HPR group, 62.4%; placebo group, 65.3%). Treatment with 4-HPR, however, significantly reduced expression of hTERT (45.6%, compared with 68.1% of the placebo group), indicating reduced telomerase activity and reduced risk of lung cancer. In another study investigators reported that quercetin, a natural substance found in common fruits and vegetables, significantly reduced the expression of androgen receptor (AR) in a prostate cancer cell line, investigators reported here. AR is an important hormone mediator in the development and progression of prostate cancer, which will strike 198,100 men and will cause 31,500 deaths in the United States during 2001, estimates the American Cancer Society. In another presentation at the AACR meeting, researchers reported that a synthetic version of vitamin D - called Ro 26-9114 - demonstrated significant antitumor activity in mice with colon cancer, without the serious toxic effects that limit use of the natural vitamin as a cancer prevention agent. "The activated form of vitamin D has anticancer effects against many common cancers, but it produces abnormally high levels of calcium in the blood, which can lead to toxic effects such as fatigue, headache, nausea, vomiting, and loss of appetite," explained Sergio Huerta, M.D., a postdoctoral fellow at UCLA's Center for Human Nutrition in Los Angeles. "Our study found that Ro 26-9114 displayed the beneficial antitumor properties of vitamin D but with only modest loss of appetite and weight."