Structural development of p-carborane-based potent non-secosteroidal vitamin D analogs

Non-secosteroidal vitamin D receptor (VDR) ligands are promising candidates for many clinical applications. We recently developed novel non-secosteroidal VDR agonists based on p-carborane (an icosahedral carbon-containing boron cluster) as a hydrophobic core structure. Here, we report the design, synthesis and biological evaluation of carborane-based vitamin D analogs bearing various substituents at the diol moiety. Among the synthesized compounds, methylene derivative 31 exhibited the most potent vitamin D activity, which was comparable to that of the natural hormone, 1α,25(OH)₂D₃. This compound is one of the most potent non-secosteroidal VDR agonists reported to date, and is a promising lead for development of novel drug candidates.     

Novel nucleotide phosphonate analogues with potent antitumor activity

We have identified several nucleotide phosphonates demonstrating in vitro antiproliferative activity in several human cancer cell lines with IC(50) values in the microM range. The synthesis as well as structure-activity relationship are described.     

Enhancement by other compounds of the anti-cancer activity of vitamin D(3) and its analogs

Differentiation therapy holds promise as an alternative to cytotoxic drug therapy of cancer. Among compounds under scrutiny for this purpose is the physiologically active form of vitamin D(3), 1,25-dihydroxyvitamin D(3), and its chemically modified derivatives. However, the propensity of vitamin D(3) and its analogs to increase the levels of serum calcium has so far precluded their use in cancer patients except for limited clinical trials. This article summarizes the range of compounds that have been shown to increase the differentiation-inducing and antiproliferative activities of vitamin D(3) and its analogs, and discusses the possible mechanistic basis for this synergy in several selected combinations. The agents discussed include those that have differentiation-inducing activity of their own that is increased by combination with vitamin D(3) or analogs, such as retinoids or transforming growth factor-beta and plant-derived compounds and antioxidants, such as curcumin and carnosic acid. Among other compounds discussed here are dexamethasone, nonsteroidal anti-inflammatory drugs, and inhibitors of cytochrome P450 enzymes, for example, ketoconazole. Thus, recent data illustrate that there are extensive, but largely unexplored, opportunities to develop combinatorial, differentiation-based approaches to chemoprevention and chemotherapy of human cancer.     

Novel, potent THC/anandamide (hybrid) analogs

The structure–activity relationship (SAR) of the end pentyl chain in anandamide (AEA) has been established to be very similar to that of Δ⁹-tetrahydrocannabinol (Δ⁹-THC). In order to broaden our understanding of the structural similarities between AEA and THC, hybrid structures 1–3 were designed. In these hybrids the aromatic ring of THC–DMH was linked to the AEA moiety through an ether linkage with the oxygen of the phenol of THC. Hybrid 1 (O-2220) was found to have very high binding affinity to CB1 receptors (K_i = 8.5 nM), and it is interesting to note that the orientation of the side chain with respect to the oxygen in the phenol is the same as in THCs. To further explore the SAR in this series the terminal carbon of the side chain was modified by adding different substituents. Several such analogs were synthesized and tested for their CB1 and CB2 binding affinities and in vivo activity (tetrad tests). The details of the synthesis and the biological activity of these compounds are described.     

Novel vitamin D3 antipsoriatic antedrugs: 16-En-22-oxa-1alpha,25-(OH)2D3 analogs

A series of 16-en-22-oxa-derivatives of vitamin D3 based on the structure of maxacalcitol (2) were prepared. Maxacalcitol is currently used topically for the treatment of psoriasis and is recognized as the most successful antedrug of natural vitamin D(3) because it retains the original antiproliferative activity of calcitriol without increased calcemic activity. We introduced 16-olefinic functionality to accelerate the oxidative metabolism of the drug in liver, presumed to be essential for the reduction of calcemic activity, and modified the side-chain moiety by placing the 22-oxygen on the more labile allylic carbon center. Novel 22-oxa analogs (7a-i), carrying either the 24-alkynyl bond or 24-hydroxy functionality in addition to the 16-double bond were synthesized and their pharmacokinetics were evaluated.     

The synthesis and biological activity of 25-hydroxy-26,27-dimethylvitamin D3 and 1,25-dihydroxy-26,27-dimethylvitamin D3: highly potent novel analogs of vitamin D3

We synthesized 25-hydroxy-26,27-dimethylvitamin D3, 9, and 1,25-dihydroxy-26,27-dimethylvitamin D3, 14, from chol-5-enic acid-3 beta-ol and tested their biological activity in vivo and in vitro. 9 was found to be highly potent vitamin D analog with bioactivity similar to that of 25-hydroxyvitamin D3. 9 bound to rat plasma vitamin D binding protein with approximately one-third the affinity of 25-hydroxyvitamin D3. In a duodenal organ culture system and in a competitive binding assay with chick intestinal 1,25-dihydroxyvitamin D receptor, 9 was significantly more potent than 25-hydroxyvitamin D3. 1,25-Dihydroxy-26,27-dimethylvitamin D3, 14 was also highly active in vivo. At doses of 1000-5000 pmol/rat, its action was more sustained than that of 1,25-dihydroxyvitamin D3. 14 bound to vitamin D binding protein about 18 times less effectively than 1,25-dihydroxyvitamin D3. 14 bound to the chick intestinal cytosol receptor with an affinity one-half that of 1,25-dihydroxyvitamin D3. In a duodenal organ culture system, 14 was about half as active as 1,25-dihydroxyvitamin D3. Extension of the sterol side chain, at C-26 and C-27, by methylene groups, prolongs the bioactivity of a vitamin D sterol hydroxylated at C-1 and C-25; the corresponding sterol, hydroxylated only at C-25, does not show any alteration of its bioactivity in vivo. These newly synthesized analogs may potentially be of therapeutic use in various mineral disorders.     

Novel nonsecosteroidal vitamin D3 carboxylic acid analogs for osteoporosis, and SAR analysis

Novel vitamin D(3) analogs with carboxylic acid were explored, focusing on a nonsecosteroidal analog, LG190178, with a bisphenyl skeleton. From X-ray analysis of these analogs with vitamin D receptor (VDR), the carboxyl groups had very unique hydrogen bonding interactions in VDR and mimicked 1α-hydroxy group and/or 3β-hydroxy group of 1α,25-dihydroxyvitamin D(3). A highly potent analog, 6a, with good in vitro activity and pharmacokinetic profiles was identified from an SAR study. Compound 6a showed significant prevention of bone loss in a rat osteoporosis model by oral administration.     

Novel morpholine ketone analogs as potent histamine H3 receptor inverse agonists with wake activity

Structure-activity relationship on a novel ketone class of H(3)R antagonists/inverse agonists is disclosed. Compound 4 showed excellent target potency, selectivity and brain penetration. Evaluation of antagonist 4 in the rat EEG/EMG model demonstrated robust wake activity thereby establishing preclinical proof of concept.     

Novel stable PACAP analogs with potent activity towards the PAC1 receptor

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a 38- or 27-amino acid neuropeptide with promising therapeutic applications for the treatment of several pathophysiological states related to neurodegenerative diseases. However, its use for therapeutic applications is actually limited by its restricted bioavailability and rapid degradation. Therefore, metabolically stable PACAP analogs represent promising tools to further investigate the physiological roles of PACAP and ascertain its usefulness in some clinical conditions. In this study, derivatives of PACAP27 and PACAP38 have been rationally designed to develop PAC1 receptor agonists resistant to peptidase action. Results showed that N-terminal modifications confer resistance to dipeptidyl peptidase IV, a major proteolytic process involved in PACAP degradation. Moreover, in vitro incubation of both PACAP isoforms in human plasma revealed that PACAP38 is rapidly metabolized, with a half-life of less than 5 min, while PACAP27 was stable in these experimental conditions. Hence, following the elucidation of its plasmatic metabolites, PACAP38 was modified at its putative endopeptidase and carboxypeptidase sites of cleavage. All peptide analogs were tested for their ability to bind the PAC1 receptor, as well as for their potency to induce calcium mobilization and inhibit PC12 cell proliferation through the PAC1 receptor. This approach revealed two leading compounds, i.e. acetyl-[Ala¹⁵, Ala²⁰]PACAP38-propylamide and acetyl-PACAP27-propylamide, which exhibited improved metabolic stability and potent biological activity. This study describes innovative data related to PACAP metabolism in human plasma and depicts the development of a metabolically stable PACAP38 analog, acetyl-[Ala¹⁵, Ala²⁰]PACAP38-propylamide, which behaves as a super-agonist towards the PAC1 receptor.     

Use of vitamin D(4) analogs to investigate differences in hepatic and target cell metabolism of vitamins D(2) and D(3)

In this study, we used molecules with either of the structural differences in the side chains of vitamin D(2) and vitamin D(3) to investigate which feature is responsible for the significant differences in their respective metabolism, pharmacokinetics and toxicity. We used two cell model systems-HepG2 and HPK1A-ras-to study hepatic and target cell metabolism, respectively. Studies with HepG2 revealed that the pattern of 24- and 26-hydroxylation of the side chain reported for 1alpha-hydroxyvitamin D(2) (1alpha-OH-D(2)) but not for 1alpha-OH-D(3) is also observed in both 1alpha-OH-D(4) and Delta(22)-1alpha-OH-D(3) metabolism. This suggests that the structural feature responsible for targeting the enzyme to the C24 or C26 site could be either the C24 methyl group or the 22-23 double bond. In HPK1A-ras cells, the pattern of metabolism observed for the 24-methylated derivative, 1alpha,25-(OH)(2)D(4), was the same pattern of multiple hydroxylations at C24, C26 and C28 seen for vitamin D(2) compounds without evidence of side chain cleavage observed for vitamin D(3) derivatives, suggesting that the C24 methyl group plays a major role in this difference in target cell metabolism of D(2) and D(3) compounds. Novel vitamin D(4) compounds were tested and found to be active in a variety of in vitro biological assays. We conclude that vitamin D(4) analogs and their metabolites offer valuable insights into vitamin D analog design, metabolic enzymes and maybe useful clinically.     

A-ring analogs of 1,25-dihydroxyvitamin D(3)

The growing interest in1α,25(OH)(2)D(3), the hormonally active form of vitamin D(3), has prompted numerous efforts to synthesize vitamin D analogs as potential therapeutic agents, and some of these are already on the market and in clinical development. Although most vitamin D preparations developed thus far have focused on side-chain modifications, providing many useful analogues with high potency and selectivity, in recent years, modifications of the A-ring has attracted much attention because it can afford useful analogues exhibiting unique activity profiles as well. In this review we will focus on the current understanding of the relationship between selected modifications in the A-ring of the 1α,25(OH)(2)D(3) molecule, such as epimerization and/or substitution at C-1 and C-3, substitution at C-2, and removal of the 10,19-exocyclic methylene group, and their effect on biological potency and selectivity. Finally, suggestions for the structure-based design of therapeutically valuable A-ring vitamin D analogs will conclude the review.     

Molecular structure and antitumor activity of platinum(II) complexes containing purine analogs

Platinum(II) compounds containing purine analogs as ligands have gained increasing attention in pharmaceutical applications as, for example, antitumor drugs. This article reviews the molecular and antitumor properties of this class of compounds. The large amount of available spectroscopic and crystollographic data allows possible elucidation of geometrical parameters, such as bond lengths and angles, which may have an impact on the behavior of platinum(II) complexes against tumor cells.     

Synthesis and antitumor activity of simplified ecteinascidin-saframycin analogs

Two series of simplified analogs of the ecteinascidin-saframycin type alkaloids were prepared from l-DOPA. Their in vitro antitumor activity was tested against three human cancer cell lines (HCT-8 colon carcinoma, Bel-7402 liver carcinoma, and BGC-823 gastric carcinoma). Among these compounds, the ester analogs have stronger activities than those of amide analogs in general. Among them, 1-naphthalene carboxylate ester analog 31 has the strongest activity against BGC-823 cells.     

Novel benzodifuran analogs as potent 5-HT2A receptor agonists with ocular hypotensive activity

A series of 8-substituted benzodifuran analogs was prepared and evaluated for 5-HT(2A) receptor binding and activation. Several compounds containing ether and ester functionality were found to be potent agonists. Topical ocular administration of 5, 18, and 25 effectively reduced intra-ocular pressure in the hypertensive cynomolgus monkey eye in the range of 25-37%.     

Synthesis and antitumor activity of 2'-bromo- and 2'-chloro-3'-acetoxy-3'-deaminodaunorubicin analogs

Bromination of 3,4-di-O-acetyl-L-rhamnal (7) and subsequent glycosidic coupling under Koenigs-Knorr conditions with daunomycinone gave a mixture of three compounds having the beta-L-gluco (10), alpha-L-gluco (11), and alpha-L-manno (12) configurations. Analogous bromination of 3,4-di-O-acetyl-L-fucal (13) followed by coupling with daunomycinone gave a mixture of three glycosides having the beta-L-galacto (16), alpha-L-galacto (17), and alpha-L-talo (18) configurations. Chlorination of 7 and coupling with daunomycinone in the presence of silver triflate gave products having the alpha-L-gluco (21) and alpha-L-manno (22) configurations, whereas 13, under similar conditions, gave only one stereoisomeric product, that having the alpha-L-galacto (24) configuration. Compounds 12 and 22 showed high in vivo activity in the P-388 lymphocytic leukemia assay.     

1Alpha,25-dihydroxyvitamin D3 receptor: competitive binding of vitamin D analogs

The intestinal nuclear receptor for lα,25-dihydroxyvitamin D₃ has been utilized to determine the ability of vitamin D-active sterols to compete with this hormone at the molecular level. 25-Hydroxyvitamin D₃ and lα-hydroxyvitamin D₃ must be present in 150 and 450 times the concentration respectively of lα,25-dihydroxyvitamin D₃, $\text{in}$$\text{vitro}$, to displace the physiologic hormone. These data indicate that: i) superphysiologic levels of 25-hydroxyvitamin D₃ may simulate lα,25-dihydroxyvitamin D₃ and act directly on isolated target organs and ii) the biologic potency observed for low doses of lα-hydroxyvitamin D₃, $\text{in}$$\text{vivo}$, is probably the result of 25-hidroxylation of the lα-derivative to form lα,25-dihydroxyvitamin D₃.     

Autoradiographic studies with 3H 1,25 (OH)2 vitamin D3 and 3H 25 (OH) vitamin D3 in rat parathyroid glands

Summary After injection of radiolabeled 1,25 (OH)₂ vitamin D₃, nuclear concentration of radioactivity is observed in parenchymal cells of the parathyroid gland in pregnant, adult male, and 10-day male neonatal rats. In competition studies with unlabeled 1,25 (OH)₂ vitamin D₃, but not with 25 (OH) vitamin D₃, nuclear uptake is prevented. Experiments with ³H 25 (OH) vitamin D₃, in contrast to ³H 1,25 (OH)₂ vitamin D₃, do not show nuclear concentration in cells of the parathyroid. The results of the autoradiographic studies suggest the presence of receptors for a direct effect of 1,25 (OH)₂ vitamin D₃ on the parathyroid gland for modulation of parathyroid hormone secretion.