Antileukemic effect of a synthetic vitamin D-3 analog, HY-11, with low potential to cause hypercalcemia

Abstract

1 alpha,25-dihydroxyvitaminD(3) [1,25(OH)(2)D-3] is capable of inhibiting the proliferation of acute myelogenous leukemia (AML). However, toxicity of hypercalcemia has limited the use of 1,25(OH)(2)D-3 in clinical trials. We have evaluated 11 synthesized vitamin D-3 analogs for their ability to inhibit clonal growth of HL-60 mycloid leukemic cells. Among the 11 vitamin D-3 analogs, HY-11 (code name) showed the most potent antileukemic activity with 2.5x10(-6) M of IC50, however, it did not affect the cellular growth of normal peripheral blood mononuclear cells until 10(-6) M. Flow cytometric analysis indicated that HY-11 induced the G1 arrest in a dose-dependent manner, which was mediated via inactivation of CDK4 and CDK6 in association with upregulation of CDKI (cyclin-dependent kinase inhibitor), p27 and Rb protein. Induction of apoptosis was mediated via caspase-3 pathway in HY-11-treated HL-60. In addition, HY-11 enhanced the expression of TGF-beta 1, TGF-beta receptor type I and II and vitamin D3 receptor (VDR). VDR expression was increased by TGF-beta 1, suggesting that TGF-beta 1 might be involved in the antiproliferative effect of HY-11 on HL-60 cells by autocrine and paracrine regulation. Serum calcium levels were within normal limit when HY-11 was given intraperitoneally (i.p.) every other day for 5 weeks to BALB/c mice at the doses of 10(-7), 10(-6) and 10(-5) M. HY-11 inhibited the growth of WEHI-3BD(+) mouse leukemic cells in vitro, and syngeneic BALB/c mice that received WEHI-3BD(+) mouse leukemic cells and HY-11 had a significantly longer survival without producing hypercalcemia compared to control group. In summary, HY-11 is a vitamin D-3 analog that inhibited the proliferation of human AML cell line, HL-60, through induction of cell cycle arrest, triggering apoptosis as well as modulation of TGF-beta 1 and its receptors. In particular, HY-11 significantly increased the survival of mice that had myeloid leukemia without producing hypercalcemia.