Novel Deuterated Gemini-Vitamin D₃ Analogs Have Potent Antitumor Activity.

The active form of vitamin D₃, 1,25(OH)₂D₃, is an important regulator of calcium and bone metabolism. Also, it inhibits proliferation and induces differentiation of a variety of malignant cells. Here, we synthesized a new class of vitamin D₃ analogs, which have a C-20 methyl group and a deuterium substituted basic side chain [Deuterated Gemini (DG)]. Six DG analogs were evaluated for their ability to inhibit growth of myeloid leukemia (HL-60), prostate (LNCaP and PC-3), lung (H520) and breast (MCF-7) cancer cell lines. All 6 DG analogs inhibited growth in a dose-dependent manner and had very similar potency. Most effective DG, BXL-01-0120, was over 70-fold more potent than 1,25(OH)₂D₃ in inhibiting 50% clonal growth (ED₅₀) of HL-60, LNCaP, PC-3, H520 and MCF-7 cells with ED₅₀s ranging from 10⁻¹¹ M to 10⁻¹³ M. Focusing on this analog for further analyses, pulse-exposure, wash and culture experiments showed that 48 hours exposure of HL-60 cells to BXL-01-0120 (10⁻⁹ M) had potent anti-proliferative activity (82% growth inhibition compared to diluent control cells). Cell cycle assays found that BXL-01-0120 (10⁻¹⁰ M, 4 days) increased the percent of cells in the G₀/G₁-phase (61%, diluent control 47%) associated with a decrease S-phase (18%, diluent control 42%). BXL-01-0120 (10⁻¹⁰ M, 4 days) caused apoptosis in approximately 15% of cells. 1,25(OH)₂D₃ at the same concentration and duration changed neither the cell cycle nor number of cells undergoing apoptosis compared to control HL-60 cells. BXL-01-0120 (10⁻¹⁰ M, 4 days) strongly induced expression of the CD11b and CD14 (monocyte / macrophage differentiation markers) on HL-60 cells (87%); in contrast, 1,25(OH)₂D₃(10⁻¹⁰ M) stimulated a mean 43% of the cells to express these cell surface proteins. In summary, DGs strongly inhibited clonal proliferation, induced differentiation and cell cycle arrest in several types of cancer cells, especially HL-60 cells, suggesting that further preclinical and clinical studies to explore their anticancer potential are warranted.