According to researchers, a new vitamin D derivative, still in the early stages of testing, may hold out hope in the fight against breast cancer. In mice injected with human breast cancer cells, the new compound blocked cancer growth almost as effectively as the widely-used breast cancer drug tamoxifen, says Julia Barsony of the National Institute of Diabetes and Digestive and Kidney Diseases in the US. Vitamin D is crucial for the development of strong, healthy bones, but its role in cancer is mixed. Calcitriol, the hormonal form of vitamin D, stimulates cancer growth at normal body concentrations, while blocking cancer growth at very high concentrations. Many researchers have tried using high concentrations of calcitriol to fight cancer, but this approach has been dogged by side effects. The problem is that high levels of calcitriol cause calcium levels to rise and thereby increase the risk that a person's heart will stop suddenly or that blood vessels will clog, says Barsony. Researchers took a new approach, attempting to develop compounds that blocked calcitriol's growth-promoting effects in breast tissue but mimicked its effects in protecting bone. In cancer cells grown in culture, Barsony showed that her new compound, BCA11, bound to the vitamin D receptor and inhibited the effects of low doses of calcitriol on cell growth. In mice with advanced human breast cancer tumours, five weekly injections of BCA11 reduced the size of the tumours by 25 per cent, while tamoxifen decreased tumour volume by about 50 per cent. The levels of calcium and phosphorus in the BCA11-treated mice remained within normal ranges, indicating that the compound was unlikely to induce bone weakness, she said. "This suggests that, just as for estrogens, there is the possibility of developing analogues that selectively target certain tissues, in this case affecting cancer cell growth but not disrupting the beneficial effects of vitamin D on bone," said Donald B. DeFranco, a pharmacologist at the University of Pittsburgh. Source: United Press International
