Apoptotic Regression of MCF-7 Xenografts in Nude Mice Treated with the Vitamin D3 Analog, EB1089

Abstract

1,25-Dihydroxyvitamin D3 [1,25-(OH)2D3] and its synthetic analog EB1089 induce characteristic morphological features of apoptosis in MCF-7 cells in vitro that coincide with up-regulation of clusterin and cathepsin B, proteins associated with apoptosis in the mammary gland, and with down-regulation of Bcl-2, an antiapoptotic protein. To determine whether vitamin D3 compounds could mediate apoptosis of breast tumors in vivo, we treated nude mice carrying established MCF-7 xenografts with the low calcemic vitamin D3 analog EB1089 via daily injection or sustained release pellets for up to 5 weeks. The volume of tumors from mice treated with 45 pmol/day EB1089 was 4-fold lower than that of tumors from vehicle-treated control mice after 5 weeks. The reduced growth of tumors from EB1089-treated mice was associated with characteristic apoptotic morphology and a marked reduction in the proportion of epithelial cells to stroma. After 5 weeks of treatment with EB1089, MCF-7 tumors exhibited a 6-fold increase in DNA fragmentation (as measured by in situ end labeling) relative to that in control tumors. The enhanced rate of apoptosis in tumors from EB1089-treated mice was coupled to a 2-fold reduction in proliferation (as measured by expression of proliferating cell nuclear antigen) compared with that in tumors from control mice. The antitumor effects of EB1089 were evident at doses that had minimal effects on serum calcium and body weight. EB1089 treatment did not alter the growth of xenografts derived from a vitamin D3-resistant variant of MCF-7 cells (MCF-7(D3Res) cells), which display resistance to EB1089 in vitro, indicating that resistance to EB1089 is maintained in vivo. Tumors derived from both MCF-7 and MCF-7(D3Res) cells underwent apoptotic regression upon estradiol withdrawal, indicating comparable estrogen dependence of tumors with differential sensitivity to vitamin D3 compounds. These are the first studies to demonstrate apoptotic morphology and regression of human breast tumors in response to treatment with a vitamin D3 analog in vivo and support the concept that vitamin D3 compounds can effectively target human breast cancer.

Plasma 25‐hydroxyvitamin D and premenopausal breast cancer risk in a German case‐control study

“…26 Effects of vitamin D and analogues have been reported in early initiation and promotion phases of cancer development 44,45 as well as in late phases when used as a chemotherapeutic agent. 46 To overcome these problems, repeated measurements at different time points before diagnosis would be most valuable.…”

Potentiation by vitamin D analogs of TNFα and ceramide-induced apoptosis in MCF-7 cells is associated with activation of cytosolic phospholipase A2

“…It is suggested that vitamin D analogs, through altered transcription of target genes, increase generation of ceramide and cPLA 2 activation such that apoptosis can be initiated in response to suboptimal concentrations of TNFa Vitamin D analogs, TNFa and apoptosis in breast cancer cells G Pirianov et al xenografts in nude mice. 31 The novel vitamin D analog CB1093 has been shown to display potent antitumor effects in vivo and in vitro and its effects on induction of apoptosis are evident at concentrations approximately tenfold lower than EB1089. 10 Furthermore, induction of apoptosis has been reported to be accompanied by decreased bcl-2 protein expression.…”

Antiproliferative effects of 1,25-dihydroxyvitamin D3 on breast cells: a mini review

“…in breast cancer cells (43 (38). Vitamin D-stimulated apoptotic regression in mice bearing MCF-7 xenografts was also described (49). The underlying mechanism of the antiproliferative effects of 1,25-(OH) 2 D 3 on HC11 cells has yet to be clarified.…”