Induction of apoptosis and inhibition of prostate and breast cancer growth by BGP-15, a new calcipotriene-derived vitamin D3 analog.

The role of vitamin D3 in cancer prevention and its potential as an anticancer therapeutic agent have been researched and are well established. However, the clinical use of the natural vitamin D3 metabolite, 1alpha,25-dihydroxyvitamin D3 [1,25(OH)2D3 or calcitriol] is limited by a possible cause of hypercalcemia and hypercalciuria. A new 24-chloro calcipotriene-based vitamin D3 analog (BGP-15) was synthesized and examined for antiproliferative activity in the androgen-dependent cell lines of prostate cancer (LNCaP) and breast cancer (MCF-7). The new analog led to significant decrease in cell viability in cultured LNCaP and MCF-7 cell lines compared with calcipotriene and 1,25(OH)2D3. We observed elevated vitamin D receptor protein levels in both LNCaP and MCF-7 cells, which were treated with 5 micromol/l of 1,25(OH)2D3, calcipotriene or BGP-15 for 20 h, indicating vitamin D receptor-binding ability. Treatments of LNCaP and MCF-7 cells with 5 micromol/l BGP-15 and calcipotriene for 20 h generated procaspase-3 cleavage and therefore, apoptosis. Interestingly, BGP-15, and to a lesser extent calcipotriene, but not 1,25(OH)2D3, activated caspase-3 in MCF-7 cells, a cell line that normally lacks this specific caspase (and procaspase). It is presumed that management of MCF-7 with BGP-15 modulates procaspase-3 expression and cleavage, and a subsequent activation of caspase-3. Similar treatments of LNCaP cells induced procaspase-9 cleavage and therefore caspase-9 activation, whereas similar treatments of MCF-7 cells failed to induce caspase-9 activation. Cytochrome c release was, however, detected in both cell lines, LNCaP and MCF-7. In-vivo results suggested that BGP-15 (similar to its parent drug) did not cause calcium-related toxic side effects after chronic treatment.