Efficient and versatile synthesis of novel 2alpha-substituted 1alpha,25-dihydroxyvitamin D(3) analogues and their docking to vitamin D receptors

Simmons-Smith Cyclopropanation: A Multifaceted Synthetic Protocol toward the Synthesis of Natural Products and Drugs: A Review

Simmons-Smith cyclopropanation is a widely used reaction in organic synthesis for stereospecific conversion of alkenes into cyclopropane. The utility of this reaction can be realized by the fact that the cyclopropane motif is a privileged synthetic intermediate and a core structural unit of many biologically active natural compounds such as terpenoids, alkaloids, nucleosides, amino acids, fatty acids, polyketides and drugs. The modified form of Simmons-Smith cyclopropanation involves the employment of Et2Zn and CH2I2 (Furukawa reagent) toward the total synthesis of a variety of structurally complex natural products that possess broad range of biological activities including anticancer, antimicrobial and antiviral activities. This review aims to provide an intriguing glimpse of the Furukawa-modified Simmons-Smith cyclopropanation, within the year range of 2005 to 2022.

Development of In Vitro and In Vivo Evaluation Systems for Vitamin D Derivatives and Their Application to Drug Discovery

We have developed an in vitro system to easily examine the affinity for vitamin D receptor (VDR) and CYP24A1-mediated metabolism as two methods of assessing vitamin D derivatives. Vitamin D derivatives with high VDR affinity and resistance to CYP24A1-mediated metabolism could be good therapeutic agents. This system can effectively select vitamin D derivatives with these useful properties. We have also developed an in vivo system including a Cyp27b1-gene-deficient rat (a type I rickets model), a Vdr-gene-deficient rat (a type II rickets model), and a rat with a mutant Vdr (R270L) (another type II rickets model) using a genome editing method. For Cyp27b1-gene-deficient and Vdr mutant (R270L) rats, amelioration of rickets symptoms can be used as an index of the efficacy of vitamin D derivatives. Vdr-gene-deficient rats can be used to assess the activities of vitamin D derivatives specialized for actions not mediated by VDR. One of our original vitamin D derivatives, which displays high affinity VDR binding and resistance to CYP24A1-dependent metabolism, has shown good therapeutic effects in Vdr (R270L) rats, although further analysis is needed.

Design, synthesis and biological evaluation of novel 2-alkylidene 19-norcalcitriol analogs

Continuing our studies aimed at A-ring modified vitamin D compounds, we designed novel 19-norcalcitriol derivatives bearing at C-2 pegylated chains of different lengths. The terminal fragments of these substituents contain hydroxyls or moieties possessing nitrogen and/or sulfur atoms capable of transition metal ions complexation. Also, two conjugate-type platinum(II) complexes of 19-norcalcitriol were obtained in which l-methionine served as chelating moiety. The convergent synthesis of the target 19-norcalcitriol analogs involved several steps with the crucial one being condensation of A-ring phosphine oxide and the known Grundmann ketone by Wittig-Horner reaction. Further elaboration of the 2-alkylidene substituent provided all final compounds which were then tested to determine their affinity for the vitamin D receptor and cytotoxic activity.

Synthetic Chemical Probes That Dissect Vitamin D Activities

Vitamin D₃ metabolites are capable of controlling gene expression in mammalian cells through two independent pathways: vitamin D receptor (VDR) and sterol regulatory element-binding protein (SREBP) pathways. In the present study, we dissect the complex biological activity of vitamin D by designing synthetic vitamin D₃ analogs specific for VDR or SREBP pathway, i.e., a VDR activator that lacks SREBP inhibitory activity, or an SREBP inhibitor devoid of VDR activity. These synthetic vitamin D probes permitted identification of one of the vitamin D-responsive genes, Soat1, as an SREBP-suppressed gene. The chemical probes developed in the present study may prove useful in dissecting the intricate interplay of vitamin D actions, thereby providing insights into how vitamin D target genes are regulated.

Effects of 2-substitution on 14-epi-19-nortachysterol-mediated biological events: based on synthesis and X-ray co-crystallographic analysis with the human vitamin D receptor

Both 2α- and 2β-hydroxypropyl substituted 14-epi-1α,25-dihydroxy-19-nortachysterols were synthesized to study the human vitamin D receptor (hVDR) binding affinity, binding configurations, and interactions with amino acid residues in the ligand binding domain of hVDR by X-ray co-crystallographic analysis. In conjunction with our previous results on 14-epi-19-nortachysterol, 2-methylidene-, 2α-methyl-, 2β-methyl, and 2α-hydroxypropoxy-14-epi-19-nortachysterol, we propose a variety of effects of substitution at the C2 position in the 14-epi-19-nortachysterol skeleton on biological activities.

Mutation goals in the vitamin D receptor predicted by computational methods

The mechanism through which nuclear receptors respond differentially to structurally distinct agonists is a poorly understood process. We present a computational method that identifies nuclear receptor amino acids that are likely involved in biological responses triggered by ligand binding. The method involves tracing how structural changes spread from the ligand binding pocket to the sites on the receptor surface, which makes it a good tool for studying allosteric effects. We employ the method to the vitamin D receptor and verify that the identified amino acids are biologically relevant using a broad range of experimental data and a genome browser. We infer that surface vitamin D receptor residues K141, R252, I260, T280, T287 and L417 are likely involved in cell differentiation and antiproliferation, whereas P122, D149, K321, E353 and Q385 are linked to carcinogenesis.

Nature-Inspired Bioorthogonal Reaction: Development of β-Caryophyllene as a Chemical Reporter in Tetrazine Ligation

A nature-inspired bioorthogonal reaction has been developed, hinging on an inverse-electron-demand Diels-Alder reaction of tetrazine with β-caryophyllene. Readily accessible from the cheap starting material through a scalable synthesis, the newly developed β-caryophyllene chemical reporter displays appealing reaction kinetics and excellent biocompatibility, which renders it applicable to both in vitro protein labeling and live cell imaging. Moreover, it can be used orthogonally to the strain-promoted alkyne-azide cycloaddition for dual protein labeling. This work not only provides an alternative to the existing bioorthogonal reaction toolbox, but also opens a new avenue to utilize naturally occurring scaffolds as bioorthogonal chemical reporters.

Synthesis of 19-norcalcitriol analogs with alkylidene moieties at C-2 based on succinic acid and l-methionine

On the basis of the literature data, our previous research work and docking experiments, we designed novel 19-norvitamin D compounds having elongated 2-alkylidene substituents. These 19-norcalcitriol derivatives have attached 2-(3'-aminopropylidene) substituent in which the nitrogen atom bears acyl residue derived from succinic acid and l-methionine. Both compounds were obtained by the same synthetic strategy involving Julia coupling of the A-ring ketone with the known C/D-ring sulfone. In the obtained 1α,25-dihydroxy-19-norvitamin D₃ derivative, the alkylidene substituent at C-2 was further elaborated to the desired structures.

Novel screening system for high-affinity ligand of heredity vitamin D-resistant rickets-associated vitamin D receptor mutant R274L using bioluminescent sensor

Hereditary vitamin D-resistant rickets (HVDRR) is caused by mutations in the vitamin D receptor (VDR) gene. Arg274 located in the ligand binding domain (LBD) of VDR is responsible for anchoring 1α,25-dihydroxyvitamin D3 (1α,25(OH)₂D₃) by forming a hydrogen bond with the 1α-hydroxyl group of 1α,25(OH)₂D_3. The Arg274Leu (R274L) mutation identified in patients with HVDRR causes a 1000-fold decrease in the affinity for 1α,25(OH)₂D₃, and dramatically reduces vitamin D- related gene expression. Recently, we successfully constructed fusion proteins consisting of split-luciferase and LBD of the VDR. The chimeric protein LucC-LBD-LucN, which displays the C-terminal domain of luciferase (LucC) at its N-terminus, can detect and discriminate between VDR agonists and antagonists. The LucC-LBD (R274L)-LucN was constructed to screen high-affinity ligands for the mutant VDR (R274L). Of the 33 vitamin D analogs, 5 showed much higher affinities for the mutant VDR (R274L) than 1α,25(OH)₂D₃, and 2α-[2-(tetrazol-2-yl)ethyl]-1α,25-(OH)₂D₃ showed the highest affinity. These compounds might be potential therapeutics for HVDRR caused by the mutant VDR (R274L).

MART-10, a newly synthesized vitamin D analog, represses metastatic potential of head and neck squamous carcinoma cells

Even with multidisciplinary treatment, the prognosis and quality of life of patients diagnosed with head and neck squamous cell carcinoma (HNSCC) are still not satisfactory. Previously, 19-Nor-2α-(3-hydroxypropyl)-1α,25(OH)₂D₃ (MART-10), the new brand 1α,25(OH)₂D₃ analog, has been demonstrated to be an effective drug to inhibit HNSCC growth in vitro. Since most cancer patients die of metastasis, in this study, the antimetastatic effect of MART-10 on HNSCC was investigated. Our results reveal that both 1α,25(OH)₂D₃ and MART-10 effectively repressed the migration and invasion of HNSCC cells, with MART-10 being much more potent than 1α,25(OH)₂D₃. The antimetastatic effect of 1α,25(OH)₂D₃ and MART-10 was mediated by attenuation of epithelial–mesenchymal transition (EMT), which was supported by the finding that the expression of EMT-inducing transcriptional factors, Sail and Twist, was inhibited by 1α,25(OH)₂D₃ and MART-10. The upregulation of E-cadherin and downregulation of N-cadherin in FaDu cells induced by both drugs further confirmed the repression of EMT. In addition, 1α,25(OH)₂D₃ and MART-10 treatment inhibited intracellular MMP-9 expression and extracellular MMP activity in FaDu cells. Collectively, our results suggest that the less-calcemia 1α,25(OH)₂D₃ analog, MART-10, is a promising drug for HNSCC treatment. Further clinical studies are warranted.

Vitamin D Analogs with Nitrogen Atom at C2 Substitution and Effect on Bone Formation

The Arg274 residue of the ligand binding domain of human vitamin D receptor (hVDR) is important for 1α,25-dihydroxyvitamin D3 (1α,25(OH)2D3) binding as a specific ligand through forming a hydrogen bond with the 1α-OH group of the active vitamin D3, 1α,25(OH)2D3. An additional pincer-type hydrogen bond formation with Arg274 from a 2α-substituent of a synthetic 1α,25(OH)2D3 analog would enhance the binding affinity and biological activity. A series of 2α-[2-(heteroaryl)ethyl]-, 2α-(4-cyanobutyl)-, 2α-(ω-cyanoalkoxy)-, and 2β-(3-cyanopropoxy)-1α,25(OH)2D3 were designed and synthesized based on our original hVDR super agonists of 2α-(3-hydroxypropyl)- and 2α-(3-hydroxypropoxy)-1α,25(OH)2D3. Their potential biological activities, i.e., hVDR binding affinity, transactivation activity in HOS cells, and therapeutic effect on enhancing the bone mineral density of OVX rats, were studied.

19-Norvitamin D analogs for breast cancer therapy

The active form of vitamin D3, 1α,25-dihydroxyvitamin D3 (1α,25(OH)2D3 or calcitriol), is known to inhibit the proliferation and invasiveness of many types of cancer cells, including breast, colon, pancreatic, prostate, and liver cancer cells. These findings support the use of 1α,25(OH)2D3 for the treatment of these types of cancer. However, 1α,25(OH)2D3 can cause hypercalcemia, so analogs of 1α,25(OH)2D3 that are less calcemic but exhibit more potent anti-tumor activity would be good candidates as therapeutic agents. Therefore, a series of 19-norvitamin D analogs, in which the methylidene group on C19 is replaced with 2 hydrogen atoms, have been synthesized by several laboratories. In our laboratory, we have designed and synthesized a series of 2α-functional group substituted 19-norvitamin D3 analogs and examined their anti-proliferative activity. Among them, 2α- and 2β-(3-hydroxypropyl)-1α,25-dihydroxy-19-norvitamin D3 (MART-10 and MART-11) were found to be the most promising. Here, we review the rationale and approaches for the synthesis of different 19-norvitamin D analogs, and the pre-clinical studies using these analogs in breast cancer cells, in particular, we chose MART-10 for its potential application to the prevention and treatment of breast cancer.

Design and synthesis of 2α-(tetrazolylethyl)-1α,25-dihydroxyvitamin D3 as a high affinity ligand for vitamin D receptor

X-ray cocrystallographic studies of the human vitamin D receptor (hVDR)-[2α-(3-hydroxypropyl)-1α,25-dihydroxyvitamin D3 (O1C3)] complex showed that the terminal hydroxy group of the 2α-functional group of O1C3 formed a hydrogen bond with Arg274 in the ligand binding domain (LBD) of hVDR to stabilize the complex; therefore, O1C3 showed 3-times greater binding affinity for VDR than the natural hormone. Here, the effects of a heteroaromatic ring on binding to hVDR instead of the terminal OH group of O1C3 and also on preliminary biological activities were studied. We synthesized 2α-[2-(tetrazol-2-yl)ethyl]-1α,25(OH)2D3 (1a) and its regioisomer 2α-[2-(tetrazol-1-yl)ethyl]-1α,25(OH)2D3 (1b), in which 1a showed much higher hVDR binding affinity and greater osteocalcin promoter transactivation activity in human osteosarcoma (HOS) cells than those of 1b. X-ray cocrystallographic analysis of the hVDR-1a complex showed new hydrogen bond formation between one of the nitrogen atoms of the tetrazole ring and Arg274. This article is part of a Special Issue entitled '16th Vitamin D Workshop'.

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 novel vitamin D analog, inhibits head and neck squamous carcinoma cells growth through cell cycle arrest at G0/G1 with upregulation of p21 and p27 and downregulation of telomerase

For the head and neck squamous cell carcinoma (HNSCC), surgery in combination with radiation therapy is the current standard treatment. However, the complex anatomy and important functions over the head and neck region often make HNSCC patients with severe comorbidities. Even after aggressive treatment, the 5year survival for HNSCC patients is only around 61%. Thus, new therapeutic regimens against HNSCC are urgently needed. 1α,25-Dihydroxyvitamin D3 [1α,25(OH)2D3] is a potent anti-tumor agent in a variety of pre-clinical studies, but its clinical application is impeded by hypercalcemic side effect. A new class of less-calcemic 1α,25(OH)2D3 analog, MART-10 (19-nor-2α-(3-hydroxypropyl)- 1α,25-Dihydroxyvitamin D3), has been shown to be much more potent than 1α,25(OH)2D3 in inhibiting cancer cell growth in vitro and in vivo without inducing hypercalcemia. In this study, we compared the antiproliferative activity of MART-10 with 1α,25(OH)2D3 and the mechanism responsible for the inhibition in FaDu and SCC-25 squamous carcinoma cells. Our results demonstrate that MART-10 is more potent than 1α,25(OH)2D3 in suppressing FaDu and SCC-25 cell growth through greater cell cycle arrest at G0/G1, accompanied by a greater downregulation of ki-67 expression and upregulation of p21 and p27. We also showed that telomerase expression in SCC-25 was suppressed to a greater extent by MART-10 than by 1α,25(OH)2D3. Thus, given the previously-proven in vivo antitumor effect and safety of MART-10 and bleak background of HNSCC, based on our current result, we concluded that MART-10 has a potential as a chemo-preventive and - therapeutic agent to treat HNSCC.

Synthesis of 2α-heteroarylalkyl active vitamin d3 with therapeutic effect on enhancing bone mineral density in vivo

2α-Heteroarylethyl-1α,25-dihydroxyvitamin D3 analogues, which were designed to form a hydrogen bond between Arg274 of human vitamin D receptor (hVDR) and a nitrogen atom of the heteroaromatic ring at the 2α-position, were synthesized. Among them, 2α-[2-(tetrazol-2-yl)ethyl]-1α,25-dihydroxyvitamin D3 showed higher osteocalcin promoter transactivation activity in human osteosarcoma (HOS) cells and a greater therapeutic effect in ovariectomized (OVX) rats, osteoporosis model animals, on enhancing bone mineral density than those of active vitamin D3. X-ray cocrystallographic analysis of the hVDR-ligand complex confirms that the new hydrogen bond formation stabilized the complex.

Synthesis of novel C-2 substituted vitamin D derivatives having ringed side chains and their biological evaluation on bone

Up to the present, numerous vitamin D derivatives have been synthesized, but most of them have straight side chains, and there are few publications described about in vitro and in vivo evaluations on bone by vitamin D derivatives. In our previous paper, we reported the synthesis of various C-2 substituted vitamin D derivatives (2b-2i) with a 2,2-dimethylcyclopentanone unit in the CD-ring side chains, and that the derivatives have strong activity for enhancing bone growth. On the basis of results, this time, we report the synthesis of 2α-substituted vitamin D3 derivatives with chiral cyclopentanone (3-6 and 12-16). These derivatives were obtained by Pd-coupling reaction with A-ring precursor and CD-rings precursor. We evaluated novel derivatives in vitro assays, for affinities for VDR and transactivation assays by human osteosarcoma (HOS) cells. In this research, we demonstrated that some novel vitamin D derivatives (12-MP, 13-MP, 15-MP and 16-LP) have strong transactivation activities in spite of lower affinity for VDR than 1. In addition, we also demonstrated that these derivatives have strong activities for enhancing bone growth using OVX therapeutic rats. This article is part of a Special Issue entitled 'Vitamin D Workshop'.

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.

Evaluation of the potential therapeutic role of a new generation of vitamin D analog, MART-10, in human pancreatic cancer cells in vitro and in vivo

Pancreatic cancer is a lethal disease with no known effective chemotherapy and radiotherapy, and most patients are diagnosed in the late stage, making them unsuitable for surgery. Therefore, new therapeutic strategies are urgently needed. 1α,25-dihydroxyvitamin D3 [1α,25(OH)2D3] is known to possess antitumor actions in many cancer cells in vitro and in vivo models. However, its clinical use is hampered by hypercalcemia. In this study, we investigated the effectiveness and safety of a new generation, less calcemic analog of 1α,25(OH)2D3, 19-nor-2α-(3-hydroxypropyl)-1α,25-dihydroxyvitamin D3 (MART-10), in BxPC-3 human pancreatic carcinoma cells in vitro and in vivo. We demonstrate that MART-10 is at least 100-fold more potent than 1α,25(OH)2D3 in inhibiting BxPC-3 cell proliferation in a time- and dose-dependent manner, accompanied by a greater upregulation of cyclin-dependent kinase inhibitors p21 and p27 and a greater downregulation of cyclin D3 and cyclin-dependent kinases 4 and 5, leading to a greater increase in the fraction of cells in G0/G1 phase. No induction of apoptosis and no effect on Cdc25 phosphatases A and C were observed in the presence of either MART-10 or 1α,25(OH)2D3. In a xenograft mouse model, treatment with 0.3 µg/kg body weight of MART-10 twice/week for 3 weeks caused a greater suppression of BxPC-3 tumor growth than the same dose of 1α,25(OH)2D3 without inducing hypercalcemia and weight loss. In conclusion, MART-10 is a promising agent against pancreatic cancer growth. Further clinical trial is warranted.

Human cytochrome P450-dependent differential metabolism among three 2α-substituted-1α,25-dihydroxyvitamin D(3) analogs

Our previous studies revealed that C2α-substituted-1α,25(OH)(2)D(3) analogs had unique biological activities. For example, 19-nor-2α-(3-hydroxypropyl)-1α,25(OH)(2)D(3) (MART-10), which has a high affinity for vitamin D receptor (VDR), is more bioavailable and more potent than 1α,25(OH)(2)D(3) in inhibiting cancer cell growth and invasion because of its weaker binding to vitamin D binding protein (DBP), and more resistance to CYP24A1-dependent metabolism. In this study, we examined the metabolism of MART-10 and two other 2α-substituted analogs, 2α-(3-hydroxypropoxy)-1α,25(OH)(2)D(3) (O2C3) and 2α-(3-hydroxypropyl)-1α,25(OH)(2)D(3) (O1C3) by using human liver microsomes and human P450s. We demonstrated that O2C3 was converted to 1α,2α,25(OH)(3)D(3) in human liver microsomes, whereas both O1C3 and MART-10 were hardly metabolized. The metabolism of O2C3 was significantly inhibited by ketoconazole, and the recombinant human CYP3A4 converted O2C3 to 1α,2α,25(OH)(3)D(3), which suggests that CYP3A4 is responsible for the metabolism of O2C3 in human liver. The k(cat)/K(m) values of CYP3A4 for O1C3 and MART-10 are much smaller than that for O2C3. The k(cat)/K(m) values of human CYP24A1 for the three analogs are 1% (MART-10), 3% (O2C3), and 4% (O1C3) of that for 1α,25(OH)(2)D(3), indicating that MART-10 is the most resistant to CYP24A1 hydroxylation. On the other hand, 1α,2α,25(OH)(3)D(3), the metabolite of O2C3 by CYP3A4, was metabolized by CYP24A1 via multiple pathways similar to 1α,25(OH)(2)D(3), which suggests that O2C3 can be metabolized by two sequential hydroxylations, first by CYP3A4 and then by CYP24A1 in human body. These results suggest that modification at C-2α position and C-19 demethylenation markedly change metabolic profiles and biological activities of vitamin D analogs.

MART-10, a New Generation of Vitamin D Analog, Is More Potent than 1α,25-Dihydroxyvitamin D(3) in Inhibiting Cell Proliferation and Inducing Apoptosis in ER+ MCF-7 Breast Cancer Cells

Hormone antagonist therapy for estrogen receptor positive (ER+) breast cancer patients post radical surgery and radiation therapy has a poor prognosis and also causes bone loss. 1α,25-dihydroxyvitamin D₃ [1α,25(OH)₂D₃] is a potent antitumor agent in pre-clinical studies, but caused hypercalcemia when its effective antitumor doses were used. Therefore, we investigated the effects of a less-calcemic 1α,25(OH)₂D₃ analog, 19-nor-2α-(3-hydroxypropyl)-1α,25-dihydroxyvitamin D₃ (MART-10), on ER+MCF-7 cells. We demonstrate that MART-10 is 500- to 1000-fold more potent than 1α,25(OH)₂D₃ in inhibiting cell growth in a dose- and time-dependent manner. MART-10 is also much more potent in arresting MCF-7cell cycle progression at G₀/G₁ phase as compared to 1α,25(OH)₂D₃, possibly mediated by a greater induction of p21 and p27 expression. Moreover, MART-10 is more active than 1α,25(OH)₂D₃ in causing cell apoptosis, likely through a higher BAX/Bcl expression ratio and the subsequent cytochrome C release from mitochondria to cytosol. Based on our in vitro findings, MART-10 could be a promising vitamin D analog for the potential treatment of breast cancer, for example, ER+ patients, to decrease the tumor relapse rate and the side effect on bone caused by antihormone regimens. Thus, further in vivo animal study is warranted.

Mechanism of the anti-proliferative action of 25-hydroxy-19-nor-vitamin D(3) in human prostate cells

According to the prevailing paradigm, 1α-hydroxylation of 25-hydroxyvitamin D(3) (25(OH)D(3)) and its analogs is a pre-requisite step for their biological effects. We previously reported that 25-hydroxy-19-nor-vitamin D(3) (25(OH)-19-nor-D(3)) had anti-proliferative activity in a cell line, PZ-HPV-7, which was derived from human non-cancerous prostate tissue, and suggested that 25(OH)-19-nor-D(3) acted after 1α-hydroxylation by vitamin D 1α-hydroxylase (CYP27B1). However, metabolic studies of 25(OH)-19-nor-D(3) using recombinant CYP27B1 revealed that 25(OH)-19-nor-D(3) was rarely subjected to 1α-hydroxylation. Therefore, in this report, we attempted to clarify the mechanism of 25(OH)-19-nor-D(3) action in intact cells using PZ-HPV-7 prostate cells. After incubating the cells with 25(OH)-19-nor-D(3), eight metabolites of 24-hydroxylase (CYP24A1) were detected, whereas no products of CYP27B1 including 1α,25-dihydroxy-19-nor-vitamin D(3) (1α,25(OH)(2)-19-nor-D(3)) were found. Furthermore, the time-dependent nuclear translocation of vitamin D receptor (VDR) and the subsequent transactivation of cyp24A1 gene in the presence of 25(OH)-19-nor-D(3) were almost identical as those induced by 1α,25(OH)(2)-19-nor-D(3). These results strongly suggest that 25(OH)-19-nor-D(3) directly binds to VDR as a ligand and transports VDR into the nucleus to induce transcription of cyp24A1 gene. In addition, knock down of cyp27B1 gene did not affect the anti-proliferative activity of 25(OH)-19-nor-D(3), whereas knock down of VDR attenuated the inhibitory effect. Thus, our results clearly demonstrate that the anti-proliferative activity of 25(OH)-19-nor-D(3) is VDR dependent but 1α-hydroxylation independent, suggesting that 25(OH)D(3) analogs such as 25(OH)-19-nor-D(3) could be attractive candidates for anticancer therapy.

Vitamin D analogs

Vitamin D has gone through a renaissance with the association of vitamin D deficiency with a wide array of common diseases including breast, colorectal and prostate cancers, cardio-vascular disease, autoimmune conditions and infections. Vitamin D analogs constitute a valuable group of compounds which can be used to regulate gene expression in functions as varied as calcium and phosphate homeostasis, as well as cell growth regulation and cell differentiation of a wide spectrum of cell types. This review will discuss the full range of vitamin D compounds currently available, some of their possible uses, and potential mechanisms of action.

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.

[Creation of highly potent vitamin D receptor antagonists]

Vitamin D receptor antagonist has attracted significant level of interests because of its potential utility in the treatment of Paget's disease, which is known as the most flagrant example of disordered bone remodeling and the second most common bone disease after osteoporosis in Anglo-Saxons. Recent studies on Paget's disease suggested a specific increase in osteoclasts sensitivity to the differentiation activity of active vitamin D(3) as the principal mechanism for abnormal bone formation. We set out to conduct a structure-activity relationship study on the first VDR antagonists of TEI-9647 and TEI-9648 (25-dehydro-1alpha-hydroxyvitamin D(3)-26,23-lactone) toward improved VDR antagonistic activity. Given that both potent agonists and antagonists must have high affinity for the VDR, we hoped that our accumulated knowledge in VDR agonists would help us identify potent antagonists. First, 2alpha-modified TEI-9647 analogs were synthesized, and then, 24-substitution was next investigated to stabilize its lactone structure under the physiological conditions. Finally, 2alpha-modified 24-methyl-, 24,24-dimethyl-25-dehydro-1alpha-hydroxyvitamin D(3)-26,23-lactone analogs were synthesized. It was found that 2alpha,24,24-trimethyl-TEI-9647 was found to possess approximately 90-fold improved antagonistic activity (IC(50) 0.093 nM) over the original TEI-9647 (IC(50) 8.3 nM).

Easy and Stereoselective Approach to α,β-Unsaturated γ-Lactones Fused to Pyranoses from Furanose Scaffolds

The first facile and efficient route to pyranose-fused butenolides from furanose scaffolds, convenient for scaling up production, is described. Wittig olefination of 1,2-O-isopropylidene pentofuranos- or hexofuranos-3-uloses with a resonance-stabilized ylide led to the stereoselective formation of the (Z)-alpha,beta-unsaturated ester. In the presence of acid labile 5-O- or 5,6-di-O-protecting groups, acid hydrolysis of the Wittig product resulted in isomerization to the pyranose form and spontaneous lactonization to give the target molecules in good overall yield.

Kinetic Studies of 25-Hydroxy-19-nor-vitamin D3 and 1α,25-Dihydroxy-19-nor-vitamin D3 Hydroxylation by CYP27B1 and CYP24A1

Our previous study demonstrated that 25-hydroxy-19-nor-vitamin D(3) [25(OH)-19-nor-D(3)] inhibited the proliferation of immortalized noncancerous PZ-HPV-7 prostate cells similar to 1 alpha,25-dihydroxyvitamin D(3) [1 alpha,25(OH)(2)D(3)], suggesting that 25(OH)-19-nor-D(3) might be converted to 1 alpha,25-dihydroxy-19-nor-vitamin D(3) [1 alpha,25(OH)(2)-19-nor-D(3)] by CYP27B1 before exerting its antiproliferative activity. Using an in vitro cell-free model to study the kinetics of CYP27B1-dependent 1 alpha-hydroxylation of 25(OH)-19-nor-D(3) and 25-hydroxyvitamin D(3) [25(OH)D(3)] and CYP24A1-dependent hydroxylation of 1 alpha,25(OH)-19-nor-D(3) and 1 alpha,25(OH)(2)D(3), we found that k(cat)/K(m) for 1 alpha-hydroxylation of 25(OH)-19-nor-D(3) was less than 0.1% of that for 25(OH)D(3), and the k(cat)/K(m) value for 24-hydroxylation was not significantly different between 1 alpha,25(OH)(2)-19-nor-D(3) and 1 alpha,25(OH)(2)D(3). The data suggest a much slower formation and a similar rate of degradation of 1 alpha,25(OH)(2)-19-nor-D(3) compared with 1 alpha,25(OH)(2)D(3). We then analyzed the metabolites of 25(OH)D(3) and 25(OH)-19-nor-D(3) in PZ-HPV-7 cells by high-performance liquid chromatography. We found that a peak that comigrated with 1 alpha,25(OH)(2)D(3) was detected in cells incubated with 25(OH)D(3), whereas no 1 alpha,25(OH)(2)-19-nor-D(3) was detected in cells incubated with 25(OH)-19-nor-D(3). Thus, the present results do not support our previous hypothesis that 25(OH)-19-nor-D(3) is converted to 1 alpha,25(OH)(2)-19-nor-D(3) by CYP27B1 in prostate cells to inhibit cell proliferation. We hypothesize that 25(OH)-19-nor-D(3) by itself may have a novel mechanism to activate vitamin D receptor or it is metabolized in prostate cells to an unknown metabolite with antiproliferative activity without 1 alpha-hydroxylation. Thus, the results suggest that 25(OH)-19-nor-D(3) has potential as an attractive agent for prostate cancer therapy.

Creative synthesis of novel vitamin D analogs for health and disease

We report new analogs of 1alpha,25-dihydroxyvitamin D(3) (1) in three categories. First, design and synthesis of ligands for a mutant vitamin D receptor (VDR)(Arg274Leu), which possess proper functional groups at both C1alpha and C2alpha positions of 1 to study the biological activity of the mutant VDR. Among our synthetic analogs, 1alpha-methyl-2alpha-(3-hydroxypropyl)-25-hydroxyvitamin D(3) (8) showed 7.3-fold greater transcriptional activity for the VDR(Arg274Leu) than that of 1. Next, we examined the antiproliferative activity of 2-substituted 19-norvitamin D(3) analogs on an immortalized normal prostate cell line, PZ-HPV-7, and we found MART 10 (14) showed the activity even at very low concentration of 10(-10) to 10(-11)M. We also synthesized 25-hydroxy-19-norvitamin D(3) (13) using Julia-type olefination to connect between the C5 and C6 positions, effectively, to test it as a prohormone type agent for antiprostate diseases. Synthesized compound 13 showed potent antiproliferative activity in PZ-HPV-7, which has high 1alpha-hydroxylase activity. Finally, we describe design and synthesis of a new TEI-9647 analog, 2alpha-(3-hydroxypropoxy)-24-propyl-25-dehydro-1alpha-hydroxyvitamin D(3)-26,23-lactone (17), which showed the strongest VDR antagonism. Its IC(50) value is 7.4pM to inhibit differentiation of HL-60 cells induced by 10nM of 1.

Efficient synthesis and biological evaluation of ω-oxygenated analogues of vitamin K2: Study of modification and structure–activity relationship of vitamin K2 metabolites

Novel omega-oxygenated vitamin K2 analogues, which are candidates for metabolites of vitamin K2 homologues, were efficiently synthesized and their apoptosis-inducing activity was evaluated. We revealed that some of those analogues were biologically active and the side-chain part played an important role in apoptosis-inducing activity. Our results can provide useful information to develop the structure-activity relationship of vitamin K2 analogues for new drugs based on vitamin K.