Biological Evaluation of Double Point Modified Analogues of 1,25-Dihydroxyvitamin D2 as Potential Anti-Leukemic Agents

Abstract

Structurally similar double-point modified analogues of 1,25-dihydroxyvitamin D2 (1,25D2) were screened in vitro for their pro-differentiating activity against the promyeloid cell line HL60. Their affinities towards human full length vitamin D receptor (VDR) and metabolic stability against human vitamin D 24-hydroxylase (CYP24A1) were also tested. The analogues (PRI-1730, PRI-1731, PRI-1732, PRI-1733 and PRI-1734) contained 5,6-trans modification of the A-ring and of the triene system, additional hydroxyl or unsaturation at C-22 in the side chain and reversed absolute configuration (24-epi) at C-24 of 1,25D2. As presented in this paper, introduction of selected structural modifications simultaneously in two distinct parts of the vitamin D molecule resulted in a divergent group of analogues. Analogues showed lower VDR affinity in comparison to that of the parent hormones, 1,25D2 and 1,25D3, and they caused effective HL60 cell differentiation only at high concentrations of 100 nM and above. Unexpectedly, introducing of a 5,6-trans modification combined with C-22 hydroxyl and 24-epi configuration switched off entirely the cell differentiation activity of the analogue (PRI-1734). However, this analogue remained a moderate substrate for CYP24A1, as it was metabolized at 22%, compared to 35% for 1,25D2. Other analogues from this series were either less (12% for PRI-1731 and PRI-1733) or more (52% for PRI-1732) resistant to the enzymatic deactivation. Although the inactive analogue PRI-1734 failed to show VDR antagonism, when tested in HL60 cells, its structure might be a good starting point for our design of a vitamin D antagonist.

Antiproliferative Activity of Non-Calcemic Vitamin D Analogs on Human Melanoma Lines in Relation to VDR and PDIA3 Receptors

“…Recently, we described vitamin D 3 -resistant clone of SK-MEL1-88 (SK-MEL-188b) [ 55 ]. Contrary to parental SK-MEL-188, this clone was insensitive to the treatment with 1,25(OH) 2 D 3 , or with several analogs of vitamin D 2 , except of PRI-1731 with the inverse orientation of A ring in comparison to parental 1,25(OH) 2 D 3 by the introduction of ( 5Z , 7Z ) modification [ 55 , 78 , 79 ]. This clone does not express the coding region of VDR and of CYP27B1 .…”

The Biological Activities of Vitamin D and Its Receptor in Relation to Calcium and Bone Homeostasis, Cancer, Immune and Cardiovascular Systems, Skin Biology, and Oral Health

“…The major function of 1,25(OH) 2 D is to regulate calcium homeostasis [ 4 , 9 , 10 ]; other biological activities include regulation of proliferation and differentiation of several cell lines including keratinocytes, endothelial cells, osteoblasts, and lymphocytes. Most of these biological functions are mediated via the vitamin D nuclear receptor (VDR) which acts as a transcription factor regulating transcription of target genes [ 1 , 4 , 10 , 11 ].…”

“…The physiological levels of vitamin D may vary: supplementation may be required by the debilitated, the elderly, and those with insufficient exposure to sunlight [ 5 , 6 , 13 ]. The serum level of biologically active 1,25(OH) 2 D depends on multiple factors including the efficacy of synthesis of vitamin D precursor in the skin, on its absorption from dietary sources, on the conversion of 25(OH)D to 1,25(OH) 2 D, and on its transport and its degradation [ 5 , 11 ]. Common causes of vitamin D deficiency and functional impairment are listed in Table 1 .…”

Vitamins D: Relationship between Structure and Biological Activity

“…For reference, we used a new compound (not shown) with all the functional groups (C-25 carboxy and 1- and 3-hydroxyl) protected and, therefore, deprived of electrostatic interactions [ 20 ]. The correlation of the structures of the new analogues with their biological activities [ 21 , 22 ] allowed us to solve a long-lasting enigma [ 23 , 24 ] surrounding the 1α-hydroxylated analogues of vitD. We have proposed a new general rule (see below), confirmed by theoretical calculations, which applies to all of our crystallographic data and which has been obtained for 1α -hydroxylated analogues of vitD over the last 25 years.…”

“…As expected, 5,6- trans modification of the A-ring was advantageous to enhancing the anti-proliferative activity of the analogues but not as a single point modification. Very unexpectedly, the additional 22-hydroxyl in the side-chain, conceived to enhance VDR binding, reduced significantly the anti-proliferative activity of both the natural and 5,6- trans series of analogues [ 21 ].…”