We have synthesized 3β,21-dihydroxypregna-5,7-dien-20-one (
21(OH) 7DHP) and used UVB radiation to induce its photoconversion to analogues of
vitamin D (pD),
lumisterol (pL) and tachysterol (pT). The number and character of the products and the dynamics of the process were dependent on the UVB dose. The main products: pD and pT compounds were characterized by UV absorption, MS and NMR spectroscopy after RP-HPLC chromatography. In addition, formation of multiple oxidized derivatives of the primary products was detected and one of these derivatives was characterized as oxidized 21-hydroxyisotachysterol compound (21(OH)oxy-piT). These newly synthesized compounds inhibited growth of human
melanoma cells in a dose dependent manner, with greater or equal potency to
calcitriol. 3β,21-Dihydroxy-9β,10α-pregna-5,7-dien-20-one (21(
OH)pL) and 21(OH)oxy-piT had higher potency against pigmented
melanoma cells, while the EC(50) for compounds
21(OH)7DHP and (5Z,7E)-3β,21-dihydroxy-9,10-secopregna-5,7,10(19)-trien-20-one (21(
OH)pD) were similar in both pigmented and non-pigmented cells. Moreover,
21(OH)7DHP and its derivatives inhibited proliferation of human epidermal HaCaT keratinocytes, albeit at a lower activity compared to
melanoma cells. Importantly,
21(OH)7DHP derivatives strongly inhibited the colony formation of human
melanoma cells with 21(
OH)pD being the most potent. The potential mechanism of action of newly synthesized compounds was similar to that mediated by
1,25(OH)(2)D(3) and involved
ligand-induced translocation of
vitamin D receptor into the nucleus. In summary, we have characterized for the first time products of UVB-induced conversion of
21(OH)7DHP and documented that these compounds have selective, inhibitory effects on
melanoma cells.