Gemini Vitamin D Analogues Inhibit Estrogen Receptor–Positive and Estrogen Receptor–Negative Mammary Tumorigenesis without Hypercalcemic Toxicity

Abstract

Numerous preclinical, epidemiologic, and clinical studies have suggested the benefits of vitamin D and its analogues for the prevention and treatment of cancer. However, the hypercalcemic effects have limited the use of 1α,25(OH) 2 D 3 , the hormonally active form of vitamin D. To identify vitamin D analogues with better efficacy and low toxicity, we have tested >60 novel Gemini vitamin D analogues with a unique structure of two side chains for growth inhibition of breast cancer cells. Our initial studies found that some Gemini analogues are 5-15 times more active than 1α,25(OH) 2 D 3 in growth inhibition assay. In vivo experiments were designed to study the inhibitory effect of selected Gemini vitamin D analogues against mammary carcinogenesis by using -hexafluoro-19-nor-cholecalciferol] administration inhibited by 60% the NMUinduced mammary tumor burden compared with the NMU-treated control group, but these compounds were devoid of hypercalcemia toxicity. In an ER-negative xenograft model, Gemini 0097 significantly suppressed tumor growth without hypercalcemia toxicity. We found that the inhibitory effect of Gemini 0097 was associated with an increased level of cyclin-dependent kinase inhibitor p21 and the insulin-like growth factor binding protein 3 in both ER-positive and ER-negative mammary tumors. Our results suggest that Gemini vitamin D analogues may be potent agents for the prevention and treatment of both ER-positive and ER-negative breast cancer without hypercalcemia toxicity.In the United States, breast cancer remains the most frequently diagnosed cancer and the second leading cause of cancer death in women according to Cancer Statistics from the American Cancer Society. Because of the complexity and heterogeneity of mammary carcinogenesis (1), many pharmacologic agents have been studied for their effects on the prevention of breast cancer. For example, selective estrogen receptor (ER) modulators such as tamoxifen and raloxifene have achieved significant reduction of breast cancer incidence in women at high risk (2, 3). However, selective ER modulators are not effective in preventing ER-negative breast cancer, which corresponds to at least one third of the breast cancer cases (4). The vitamin D receptor (VDR), a member of the nuclear receptor superfamily, has been suggested as a target for both ER-positive and ER-negative breast cancer prevention (5, 6) because it is present in most breast tumors (4), and VDR ablation in mice was reported to enhance carcinogeninduced formation of mammary tumors (7). These results suggest a role of vitamin D signaling in the regulation of mammary tumorigenesis.The ligand for VDR, 1α,25-dihydroxyvitamin D 3 (1α,25(OH) 2 D 3 ; the key hormone in calcium/phosphate homeostasis) is a hormonally active metabolite synthesized from vitamin D 3 predominantly through hydroxylation by a 25-hydroxylase in the

A Novel Gemini Vitamin D Analog Represses the Expression of a Stem Cell Marker CD44 in Breast Cancer

“…Therefore, numerous synthetic vitamin D 3 analogs have been developed for better anticancer efficacy with lower toxicity (Hines et al, 2010). Our studies demonstrated that Gemini vitamin D analogs inhibited the formation and growth of estrogen receptor-positive mammary tumors in vivo without hypercalcemic toxicity (Lee et al, 2008) and suppressed mammary tumor growth in the ErbB2-overexpressing transgenic mice . In the present study, because of the importance of CD44 as a cancer stem cell marker and its suggested functional roles in breast cancer, we examined the effects of Gemini BXL0124 on regulation of CD44 in cultured MCF10DCIS.com cells in vitro and in MCF10DCIS.com xenograft tumors in vivo.…”

“…Our recent report of in vivo and in vitro inhibitory activities of novel Gemini vitamin D analogs on MCF10DCIS.com cells (Lee et al, 2008) led us to study whether 1␣,25(OH) 2 D 3 or Gemini vitamin D analogs regulate cancer stem cell markers such as CD44, which eventually results in inhibition of breast tumorigenesis. 1␣,25(OH) 2 D 3 is the key hormone in calcium/phosphate homeostasis and bone mineralization, and an epidemiological study indicates an association between low serum vitamin D levels and increased risk for breast cancer (Deeb et al, 2007).…”

Hydroxylation of CYP11A1-Derived Products of Vitamin D3 Metabolism by Human and Mouse CYP27B1

“…This has led to the search for new vitamin D analogs that retain the antiproliferative and prodifferentiative properties of 1,25(OH) 2 D3 but are not calcemic (Masuda and Jones, 2006;Takahashi and Morikawa, 2006;Lee et al, 2008;Slominski et al, 2010). Vitamin D analogs that have such properties are produced by the action of cytochrome P450scc (CYP11A1) on vitamin D Wang et al, 2012), and several of them show antimelanoma activity in cell culture models Slominski et al, 2012aSlominski et al, , 2013b.…”

Purified Mouse CYP27B1 Can Hydroxylate 20,23-Dihydroxyvitamin D3, Producing 1α,20,23-Trihydroxyvitamin D3, Which Has Altered Biological Activity

“…However, the supraphysiological doses required for the anticancer effects result in toxic hypercalcemia, which limits the use of 1,25(OH) 2 D 3 for therapeutic purposes. As a result, other vitamin D analogs are being tested that retain the antiproliferative and prodifferentiative properties of 1,25(OH) 2 D 3 but are not calcemic (Masuda and Jones, 2006;Takahashi and Morikawa, 2006;Lee et al, 2008;Slominski et al, 2010). A new source of vitamin D analogs with such properties arises from the action of cytochrome P450scc on vitamin D 3 (Slominski et al, 2006;Zbytek et al, 2008;Janjetovic et al, 2009;Slominski et al, 2010).…”