Synthesis and biological activities of vitamin D-like inhibitors of CYP24 hydroxylase

Abstract

Selective inhibitors of CYP24A1 represent an important synthetic target in a search for novel vitamin D compounds of therapeutic value. In the present work, we show the synthesis and biological properties of two novel side chain modified 2-methylene-19-nor-1,25(OH)2D3 analogs, the 22-imidazole-1-yl derivative 2 (VIMI) and the 25-N-cyclopropylamine compound 3 (CPA1), which were efficiently prepared in convergent syntheses utilizing the Lythgoe type Horner–Wittig olefination reaction. When tested in a cell-free assay, both compounds were found to be potent competitive inhibitors of CYP24A1, with the cyclopropylamine analog 3 exhibiting an 80–1 selective inhibition of CYP24A1 over CYP27B1. Addition of 3 to a mouse osteoblast culture sustained the level of 1,25(OH)2D3, further demonstrating its effectiveness in CYP24A1 inhibition. Importantly, the in vitro effects on human promyeloid leukemia (HL-60) cell differentiation by 3 were nearly identical to those of 1,25(OH)2D3 and in vivo the compound showed low calcemic activity. Finally, the results of preliminary theoretical studies provide useful insights to rationalize the ability of analog 3 to selectively inhibit the cytochrome P450 isoform CYP24A1.

24,25-Dihydroxyvitamin D3 cooperates with a stable, fluoromethylene LPA receptor agonist to secure human (MG63) osteoblast maturation

“…To ascertain whether 24,25D might be converted to 1,24,25D we took advantage of ketoconazole, an antifungal recognised as inhibiting the actions of CYP27B1, the hydroxylase required for 1,24,25D synthesis. Indeed the inhibitory constant of ketoconazole for CYP27B1 is rather low at 50nM [47]. However, when ketoconazole (5M) was applied to cells co-treated with FHBP and 24,25D, the attenuation of the differentiation response (i.e., enhanced total ALP expression) was essentially similar for cells exposed to the antifungal, 1,25D and FHBP (Fig 9).…”

Cytochromes P450 and Skin Cancer: Role of Local Endocrine Pathways

“…For instance, while 1,25(OH)2D3 was found to inhibit growth of several cancer cell lines including melanomas (for recent review see [207]), the beneficial effects could be attenuated by high levels of CYP24A1 [222]. Thus, application of selective CYP24A1 inhibitors [223, 224] may substantially increase and extend the effects of treatment with vitamin D or its analogs. Moreover, CYP3A4, well known as a detoxifying enzyme, possess 24/25-hydroxylase activity and may also inactive vitamin D analogs, especially when therapeutic concentration are used [225].…”

Impaired Vitamin D Metabolism in CKD

“…50 A CYP24A1 inhibitor has been developed, in part to mitigate the ability of cancer cells to escape the anti-proliferative effects of 1,25(OH) 2 D by inducing CYP24A1. 142,143 This inhibitor would theoretically raise tissue and circulating 25(OH)D and 1,25(OH) 2 D concentrations, which could be beneficial in CKD. However, use of such an inhibitor must be approached with caution because it may exacerbate a CKD-related impairment of vitamin D catabolism and impair the ability of target tissues to protect against 1,25(OH) 2 D intoxication.…”