Creative synthesis of novel vitamin D analogs for health and disease

Secondary Prevention of Diabetes Type 1 with Oral Calcitriol and Analogs, the PRECAL Study

Screening for Type 1 Diabetes (T1D, incidence 1:300) with T1D autoantibodies (T1Ab) at ages 2 and 6, while sensitive, lacks a preventive strategy. Cholecalciferol 2000 IU daily since birth reduced T1D by 80% at 1 year. T1D-associated T1Ab negativized within 0.6 years with oral calcitriol in 12 children. To further investigate secondary prevention of T1D with calcitriol and its less calcemic analog, paricalcitol, we initiated a prospective interventional non-randomized clinical trial, the PRECAL study (ISRCTN17354692). In total, 50 high-risk children were included: 44 were positive for T1Ab, and 6 had predisposing for T1D HLA genotypes. Nine T1Ab+ patients had variable impaired glucose tolerance (IGT), four had pre-T1D (3 T1Ab+, 1 HLA+), nine had T1Ab+ new-onset T1D not requiring insulin at diagnosis. T1Ab, thyroid/anti-transglutaminase Abs, glucose/calcium metabolism were determined prior and q3-6 months on calcitriol, 0.05 mcg/Kg/day, or paricalcitol 1-4 mcg × 1-3 times/day p.o. while on cholecalciferol repletion. Available data on 42 (7 dropouts, 1 follow-up < 3 months) patients included: all 26 without pre-T1D/T1D followed for 3.06 (0.5-10) years negativized T1Ab (15 +IAA, 3 IA2, 4 ICA, 2 +GAD, 1 +IAA/+GAD, 1 +ICA/+GAD) within 0.57 (0.32-1.3) years or did not develop to T1D (5 +HLA, follow-up 3 (1-4) years). From four pre-T1D cases, one negativized T1Ab (follow-up 1 year), one +HLA did not progress to T1D (follow-up 3.3 years) and two +T1Ab patients developed T1D in 6 months/3 years. Three out of nine T1D cases progressed immediately to overt disease, six underwent complete remission for 1 year (1 month-2 years). Five +T1Ab patients relapsed and negativized again after resuming therapy. Four (aged <3 years) negativized anti-TPO/TG, and two anti-transglutaminase-IgA. Eight presented mild hypercalciuria/hypercalcemia, resolving with dose titration/discontinuation. Secondary prevention of T1D with calcitriol and paricalcitol seems possible and reasonably safe, if started soon enough after seroconversion.

The Vitamin D Analog, MART-10, Attenuates Triple Negative Breast Cancer Cells Metastatic Potential

Regarding breast cancer treatment, triple negative breast cancer (TNBC) is a difficult issue. Most TNBC patients die of cancer metastasis. Thus, to develop a new regimen to attenuate TNBC metastatic potential is urgently needed. MART-10 (19-nor-2α-(3-hydroxypropyl)-1α,25(OH)₂D₃), the newly-synthesized 1α,25(OH)₂D₃ analog, has been shown to be much more potent in cancer growth inhibition than 1α,25(OH)₂D₃ and be active in vivo without inducing obvious side effect. In this study, we demonstrated that both 1α,25(OH)₂D₃ and MART-10 could effectively repress TNBC cells migration and invasion with MART-10 more effective. MART-10 and 1α,25(OH)₂D₃ induced cadherin switching (upregulation of E-cadherin and downregulation of N-cadherin) and downregulated P-cadherin expression in MDA-MB-231 cells. The EMT(epithelial mesenchymal transition) process in MDA-MB-231 cells was repressed by MART-10 through inhibiting Zeb1, Zeb2, Slug, and Twist expression. LCN2, one kind of breast cancer metastasis stimulator, was also found for the first time to be repressed by 1α,25(OH)₂D₃ and MART-10 in breast cancer cells. Matrix metalloproteinase-9 (MMP-9) activity was also downregulated by MART-10. Furthermore, F-actin synthesis in MDA-MB-231 cells was attenuated as exposure to 1α,25(OH)₂D₃ and MART-10. Based on our result, we conclude that MART-10 could effectively inhibit TNBC cells metastatic potential and deserves further investigation as a new regimen to treat TNBC.

MART-10, the new brand of 1α,25(OH)2D3 analog, is a potent anti-angiogenic agent in vivo and in vitro

BACKGROUND

Angiogenesis is the hall marker for cancer growth and metastasis. Thus, anti-angiogenesis emerges as a new way to treat cancer. 1α,25(OH)2D3 is recently getting popular due to the non-mineral functions, which have been applied fore cancer treatment. The newly-synthesized 1α,25(OH)2D3 analog, MART-10, has been proved to be much more potent than 1α,25(OH)2D3 regarding inhibiting cancer cells growth and metastasis without inducing hypercalcemia in vivo. In this study, we aimed to investigate the effect of MART-10 and 1α,25(OH)2D3 on angiogenesis in vitro and in vivo.

METHODS AND RESULTS

MART-10 and 1α,25(OH)2D3 were able to repress VEGFA-induced human umbilical vein endothelial cells (HUVECs) migration, invasion and tube formation, but not proliferation, with MART-10 much more potent than 1α,25(OH)2D3. The Chick Chorioallantoic Membrane (CAM) assay and matrigeal angiogenesis assay further confirmed the in vivo more potent anti-angiogenesis effect of MART-10. MART-10 inhibited the VEGFA-induced HUVECs angiogenesis process through downregulation of Akt and Erk 1/2 phosphorylation. The VEGFA-VEGFR2 (VEGF receptor 2) axis is the main signal transducing pathway to stimulate angiogenesis. A positive autocrine manner was found for the first time in HUVECs as treated by VEGFA, which induced VEGFA expression and secretion, and VEGFR2 expression. MART-10 and 1α,25(OH)2D3 were demonstrated to be able to repress this positive autocrine manner, thus inhibiting angiogenesis.

CONCLUSIONS

MART-10 and 1α,25(OH)2D3 both are effective anti-angiogenesis agents. Given MART-10 is much more potent than 1α,25(OH)2D3 and active in vivo without obvious side effect, MART-10 should be deemed as a promising anti-cancer agent.

The vitamin D analog, MART-10, represses metastasis potential via downregulation of epithelial-mesenchymal transition in pancreatic cancer cells

Pancreatic cancer (PDA) is a devastating disease and there is no effective treatment available at present. To develop new regiments against PDA is urgently needed. Previously we have shown that vitamin D analog, MART-10 (19-nor-2α-(3-hydroxypropyl)-1α,25(OH)2D3), exerted potent antiproliferative effect on PDA in vitro and in vivo without causing hypercalcemia. Since metastasis is the major cause of PDA-related death, we therefore investigate the anti-metastasis effect of MART-10 on PDA. Our results showed that both 1α,25(OH)2D3 and MART-10 repressed migration and invasion of BxPC-3 and PANC cells with MART-10 much more potent than 1α,25(OH)2D3. 1α,25(OH)2D3 and MART-10 inhibited epithelial-mesenchymal transition (EMT) in pancreatic cancer cells through downregulation of Snail, Slug, and Vimentin expression in BxPC-3 and PANC cells. MART-10 further blocked cadherin switch (from E-cadherin to N-cadherin) in BxPC-3 cells. The F-actin synthesis in the cytoplasm of BxPC-3 cells was also repressed by 1α,25(OH)2D3 and MART-10 as determined by immunofluorescence stain. Both 1α,25(OH)2D3 and MART-10 decreased MMP-2 and -9 secretion in BxPC-3 cells as determined by western blot and zymography. Collectively, MART-10 should be deemed as a promising regimen against PDA.

MART-10, a less calcemic vitamin D analog, is more potent than 1α,25-dihydroxyvitamin D3 in inhibiting the metastatic potential of MCF-7 breast cancer cells in vitro

With the recent advance in breast cancer therapy, the survival rate of breast cancer patients has improved greatly. In spite of the progress, 25-50% of breast cancer patients eventually will develop metastasis. Due to limited early detection methods, metastasis is usually diagnosed at the late stages beyond recovery likely due to resistance to currently available breast cancer therapies. Thus, a new strategy to prevent cancer cell growth and repress tumor metastasis is desirable. The active form of vitamin D3, 1α,25-dihydroxyvitamin D3 [1α,25(OH)2D3], has anti-invasion and anti-migration properties in pre-clinical studies, yet its clinical application has been hampered by its hypercalcemic side effect. Previously, we have demonstrated that a new class of less-calcemic vitamin D analog, 19-nor-2α-(3-hydroxypropyl)-1α,25-dihydroxyvitamin D3 (MART-10), is 1000-fold more active than 1α,25(OH)2D3 in suppressing MCF-7 cells growth through cell cycle arrest and apoptosis induction. In the current study, we show for the first time that MART-10 is more active than 1α,25(OH)2D3 in preventing MCF-7 cell invasion and migration likely mediated through the upregulation of E-cadherin, and the downregulation of Snail, Slug, and Twist, the transcription factors implicated in epithelial-mesenchymal transition (EMT), as well as MMP-13. Based on the current in vitro and the highly anti-tumor characteristics of MART-10 in a pancreatic xenograft model, MART-10 is deemed as a promising candidate for breast cancer treatment. Further in vivo animal study comparing MART-10 with 1α,25(OH)2D3 and other potent and less calcemic analogs of vitamin D is warranted.

Recent developments of 19-nor-1,25-dihydroxyvitamin D3 analogues

The vitamin D hormone, 1α,25-dihydroxyvitamin D3 [1,25-(OH)2 D3 ], exerts its hormonal effects predominantly on intestine, bone, and kidney, where it plays a crucial role in calcium and phosphorus homeostasis and bone mineralization. In addition to its classical actions, 1,25(OH)2 D3 exerts pleiotropic effects in a wide variety of target tissues and cell types, often in an autocrine/paracrine fashion. These biological activities of 1,25(OH)2 D3 have suggested a multitude of potential therapeutic applications for the vitamin D hormone in the treatment of hyperproliferative disorders (e.g. cancer and psoriasis), immune dysfunction (autoimmune diseases), and endocrine disorders (e.g. hyperparathyroidism). However, the calcemic effects induced by 1,25(OH)2 D3--hypercalcemia, increased bone resorption, and soft tissue calcification--limit the use of the natural ligand in these clinical applications. Therefore, numerous 1,25(OH)2 D3 analogues have been synthesized with the intent of producing therapeutic agents devoid of hypercalcemic and hyperphosphatemic side effects. To this aim, much attention has been focused on the development of 19-nor-vitamin D3 derivatives that lack the ring-A exocyclic methylene group (C19). In this review, the 19-nor-1,25(OH)2 D3 analogues are classified according to modifications made at the A-ring, the side chain, or both the A-ring and side chain, as well as other positions. The biological activities of these 19-nor-1,25(OH)2 D3 analogues are summarized and their structure-activity relationships and binding features with the vitamin D receptor (VDR) are discussed.

Potent 19-norvitamin D analogs for prostate and liver cancer therapy

The active form of vitamin D(3), 1α,25(OH)(2)D(3) or calcitriol, is known to inhibit the proliferation and invasiveness of many types of cancer cells, including prostate and liver cancer cells. These findings support the use of 1α,25(OH)(2)D(3) for prostate and liver cancer therapy. However, 1α,25(OH)(2)D(3) can cause hypercalcemia, thus, analogs of 1α,25(OH)(2)D(3) that are less calcemic but exhibit potent antiproliferative activity would be attractive as therapeutic agents. We have developed 2α-functional group substituted 19-norvitamin D(3) analogs with and without 14-epimerization. Among them, 2α- and 2β-(3-hydroxypropyl)-1α,25-dihydroxy-19-norvitamin D(3) (MART-10 and -11, respectively) and 14-epi-2α- and 14-epi-2β-(3-hydroxypropyl)-1α,25-dihydroxy-19-norvitamin D(3) (14-epi-MART-10 and 14-epi-MART-11, respectively) were found to be the most promising. In this review, we discuss the synthesis of this unique class of vitamin D analogs, the molecular mechanism of anticancer actions of vitamin D, and the biological evaluation of these analogs for potential application to the prevention and treatment of prostate and liver cancer.

Vitamin D receptor ligands: the impact of crystal structures

INTRODUCTION

In the past years, the biologically active form of vitamin D(3), 1α,25-dihydroxyvitamin D(3) (1α,25(OH)(2)D(3)), has received large appreciation due to the broad physiological impact of the hormone and its nuclear receptor, the transcription factor vitamin D receptor (VDR). Recently, the understanding of VDR actions has progressed greatly, due to VDR crystal structures with various ligands.

AREAS COVERED

This review will present and discuss new synthetic agonistic and antagonistic 1α,25(OH)(2)D(3) analogs in the context of the recent insights provided by VDR crystal structures.

EXPERT OPINION

During the last 5 years, a large number of new 1α,25(OH)(2)D(3) analogs, many of which have an interesting functional profile, have been patented. Moreover, for a surprisingly high number of 1α,25(OH)(2)D(3) analogs, the crystal structure data of their complex with the VDR is available. This structural information provides important insight into the functional potential of the VDR ligands and explains their agonistic and antagonistic action. However, so far, only for a few VDR ligands, a rational design, based on crystal structure information, has been applied. The design of future analogs may also take the specificity of co-factor interaction into account, in order to create selective VDR modulators.

Novel vitamin d analogs for prostate cancer therapy

Prostate cells contain specific receptors for 1α,25-dihydroxyvitamin D [1α,25(OH)₂D] or calcitriol, the active form of vitamin D. 1α,25(OH)₂D is known to inhibit the proliferation and invasiveness of prostate cancer cells. These findings support the use of 1α,25(OH)₂D for prostate cancer therapy. However, 1α,25(OH)₂D can cause hypercalcemia, analogs of 1α,25(OH)₂D that are less calcemic but exhibit potent antiproliferative activity would be attractive as therapeutic agents. To accomplish these goals, different strategies, based on metabolism, molecular mechanism of actions, and structural modeling, have been taken to modify the structure of vitamin D molecule with the aims to improve the efficacy and decrease the toxicity of vitamin D to treat different diseases. During the past four decades, over 3,000 analogs have been synthesized. In this paper, we discuss the development and the biological analysis of a unique class of vitamin D analogs with a substitution at the carbon 2 of 19-nor-1α,25(OH)₂D₃ molecule for potential application to the prevention and treatment of prostate cancer as well as other cancers.

22S-butyl-1alpha,24R-dihydroxyvitamin D3: recovery of vitamin D receptor agonistic activity

We recently reported that 22S-butyl-1alpha,24R-dihydroxyvitamin D(3)3 recovers the agonistic activity for vitamin D receptor (VDR), although its 25,26,27-trinor analog 2 is a potent VDR antagonist. To investigate the structural features involved in the recovery of agonism, we crystallized the ternary complex of VDR-ligand-binding domain, ligand 3 and coactivator peptide, and conducted X-ray crystallographic analysis of the complex. Compared with the complex with 2, the complex with 3 recovered the following structural features: a pincer-type hydrogen bond between the 24-hydroxyl group and VDR, the conformation of Leu305, the positioning of His301 and His393, the stability of the complex, and intimate hydrophobic interactions between the ligand and helix 12. In addition, we evaluated the potency of both compounds for recruiting RXR and coactivator. The results indicate that the complex with 3 generates a suitable surface for coactivator recruitment. These studies suggest that the action of 2 as an antagonist is caused by the generation of a surface not suitable for coactivator recruitment due to the lack of hydrophobic interactions with helix 12 as well as insufficient hydrogen bond formation between the 24-hydroxyl group and VDR. We concluded that the action of 3 as an agonist is based on the elimination of these structural defects in the complex with 2.

Structural refinement of seco-steroidal skeleton and the biological activity through nuclear receptors

1alpha,25-Dihydroxyvitamin D(3) (1) regulates a variety of biological actions through vitamin D receptor (VDR), including calcium and phosphorus homeostasis, bone remodeling, cellular proliferation and differentiation and many other functions. To enhance its potency and to study the structure/function relationship, we synthesized a series of analogs of 1 with a modification at the C-2alpha position. Introducing 2alpha-methyl, 2alpha-(3-hydroxypropyl), or 2alpha-(3-hydroxypropoxy) group increased its binding affinity for the VDR 2- to 4-fold compared to 1. The crystal structures of the VDR bound to these analogs provide a molecular explanation for the interaction between the 2alpha-substituents and water molecules exist in the VDR-ligand binding domain. Based on the accumulated knowledge in VDR agonists, we synthesized 2-substituted analogs of 'double side chain' (gemini), 19-norvitamin D(3) (MART-10), TEI-9647 (VDR antagonist), 1-alkylated vitamin D(3), 14-epi-previtamin D(3) etc. Gemini analogs showed potent HL-60 cell differentiation activity (13-38 times compared to 1), and MART-10 exhibited remarkable antiproliferative activity on PZ-HPV-7 cells even at 10(-10) M. (24S)-2alpha-(3-Hydroxypropoxy)-24-propyl-TEI-9647 showed potent VDR antagonism, and its IC(50) value was 7.4 pM against 10 nM of 1. 1alpha-Methyl-2alpha-(3-hydroxypropyl)-25-hydroxyvitamin D(3) improved the binding affinity for the mutant VDR(Arg274Leu), which causes hereditary vitamin D resistant rickets. 1alpha,25-Dihydroxy-2alpha-methyl-14-epi-previtamin D(3) showed moderate osteocalcin transcriptional activity on HOS cells. We theorize that modification at A-ring alone and in combination with functionalization of the other parts of the vitamin D molecule would provide important new information on the mechanism of vitamin D actions that could lead to the development of new therapeutic regimes for the treatment of various diseases.

Inherited disorders of calcium homeostasis

In mammals a complicated homeostatic mechanism has evolved to maintain near consistency of extracellular calcium ion levels. The homeostatic mechanism involves several hormones, which comprise among others, parathyroid hormone and vitamin D. The recent resurge in vitamin D deficiency, as a global health issue, has increased interest in the hormone. In addition to vitamin D deficiency, other causes of rickets are calcium deficiency and inherited disorders of vitamin D and phosphorus metabolism. Vitamin D-resistant syndromes are caused by hereditary defects in metabolic activation of the hormone or by mutations in the vitamin D receptor, which binds the hormone with high affinity and regulates the expression of genes through zinc finger mediated DNA binding and protein-protein interaction. Current interest is to correlate the type/position of mutations that result in disorders of vitamin D metabolism or in vitamin D receptor function with the variable phenotypic features and clinical presentation. The calcium sensing receptor plays a key role in calcium homeostasis. Loss of function mutations in the calcium sensing receptor can cause familial benign hypocalciuric hypercalcemia in heterozygotes and neonatal severe hyperparathyroidism when homozygous mutations occur in the calcium sensing receptor. Gain of function mutation can cause the opposite effect causing autosomal dominant hypocalcemia. Mouse models using targeted gene disruption strategies have been valuable tools to study the effect of mutations on the calcium sensing receptor or in the vitamin D activation pathway. Dysfunctional calcium sensing receptors with function altering mutations may be responsive to treatment with allosteric modulators of the calcium sensing receptor. Vitamin D analogs which induce unusual structural conformations on the vitamin D receptor may have a variety of therapeutic indications. This review summarises recent advances in knowledge of the molecular pathology of inherited disorders of calcium homeostasis.