Metal-based anti-diabetic drugs: advances and challenges

Synthesis, characterization, and enzyme inhibition evaluation of sitagliptin derivatives and their metal complexes

AIMS

This study focuses on the synthesis and characterization of novel sitagliptin derivatives, aiming to develop potent, orally active anti-diabetic agents with minimal side effects for the management of type 2 diabetes mellitus. Copper (II) (SCu1-SCu9) and zinc (II) (SZn1-SZn9) metal complexes of sitagliptin-based derivatives were synthesized via a template reaction.

MATERIAL & METHOD

The synthesized complexes were comprehensively characterized using elemental analysis, FTIR, UV-Vis, 1 h NMR, and 13C NMR spectroscopy. The biological efficacy of these compounds was assessed through α-amylase and α-glucosidase enzyme inhibition assays, with molecular simulation studies providing additional confirmation of their inhibitory activity.

RESULTS

Among the tested derivatives, SD7, SD4, SD3, SD5, and SD9 demonstrated enzyme inhibition profiles comparable to the standard inhibitors. However, the metal complexes exhibited absorption challenges, which may influence their bioavailability.

CONCLUSION

These findings highlight the significant anti-diabetic potential of the synthesized compounds against targeted enzymes, establishing a foundation for their development as lead molecules in future therapeutic research.

Exploring the Biological Effects of Anti-Diabetic Vanadium Compounds in the Liver, Heart and Brain

The prevalence of diabetes mellitus and diabetes-related complications is rapidly increasing worldwide, placing a substantial financial burden on healthcare systems. Approximately 537 million adults are currently diagnosed with type 1 or type 2 diabetes globally. However, interestingly, the increasing morbidity rate is primarily influenced by the effects of long-term hyperglycemia on vital organs such as the brain, the liver and the heart rather than the ability of the body to use glucose effectively. This can be attributed to the summation of the detrimental effects of excessive glucose on major vascular systems and the harmful side effects attributed to the current treatment associated with managing the disease. These drugs have been implicated in the onset and progression of cardiovascular disease, hepatocyte injury and cognitive dysfunction, thereby warranting extensive research into alternative treatment strategies. Literature has shown significant progress in utilizing metal-based compounds, specifically those containing transition metals such as zinc, magnesium and vanadium, in managing hyperglycaemia. Amongst these metals, research carried out on vanadium reflected the most promising anti-diabetic efficacy in cell culture and animal studies. This was attributed to the ability to improve glucose management in the bloodstream by enhancing its uptake and metabolism in the kidney, brain, skeletal muscle, heart and liver. Despite this, organic vanadium was considered toxic due to its accumulative characteristics. To alleviate vanadium's toxic nature while subsequently manipulating its therapeutic properties, vanadium complexes were synthesized using either vanadate or vanadyl as a base compound. This review attempts to evaluate organic vanadium salts' therapeutic and toxic effects, highlight vanadium complexes' research and provide insight into the novel dioxidovanadium complex synthesized in our laboratory to alleviate hyperglycaemia-associated macrovascular complications in the brain, heart and liver.

Vanadium(V) Pyridine-Containing Schiff Base Catecholate Complexes are Lipophilic, Redox-Active and Selectively Cytotoxic in Glioblastoma (T98G) Cells

Two new series of complexes with pyridine-containing Schiff bases, [VV O(SALIEP)L] and [VV O(Cl-SALIEP)L] (SALIEP=N-(salicylideneaminato)-2-(2-aminoethylpyridine; Cl-SALIEP=N-(5-chlorosalicylideneaminato)-2-(2-aminoethyl)pyridine, L=catecholato(2-) ligand) have been synthesized. Characterization by 1 H and 51 V NMR and UV-Vis spectroscopies confirmed that: 1) most complexes form two major geometric isomers in solution, and [VV O(SALIEP)(DTB)] (DTB=3,5-di-tert-butylcatecholato(2-)) forms two isomers that equilibrate in solution; and 2) tert-butyl substituents were necessary to stabilize the reduced VIV species (EPR spectroscopy and cyclic voltammetry). The pyridine moiety within the Schiff base ligands significantly changed their chemical properties with unsubstituted catecholate ligands compared with the parent HSHED (N-(salicylideneaminato)-N'-(2-hydroxyethyl)-1,2-ethanediamine) Schiff base complexes. Immediate reduction to VIV occurred for the unsubstituted-catecholato VV complexes on dissolution in DMSO. By contrast, the pyridine moiety within the Schiff base significantly improved the hydrolytic stability of [VV O(SALIEP)(DTB)] compared with [VV O(HSHED)(DTB)]. [VV O(SALIEP)(DTB)] had moderate stability in cell culture media. There was significant cellular uptake of the intact complex by T98G (human glioblastoma) cells and very good anti-proliferative activity (IC50 6.7±0.9 μM, 72 h), which was approximately five times higher than for the non-cancerous human cell line, HFF-1 (IC50 34±10 μM). This made [VV O(SALIEP)(DTB)] a potential drug candidate for the treatment of advanced gliomas by intracranial injection.

Substitution Kinetics, Albumin and Transferrin Affinities, and Hypoxia All Affect the Biological Activities of Anticancer Vanadium(V) Complexes

Limited stability of most transition-metal complexes in biological media has hampered their medicinal applications but also created a potential for novel cancer treatments, such as intratumoral injections of cytotoxic but short-lived anticancer drugs. Two related V(V) complexes, [VO(Hshed)(dtb)] (1) and [VO(Hshed)(cat)] (2), where H2shed = N-(salicylideneaminato)-N'-(2-hydroxyethyl)-1,2-ethanediamine, H2dtb = 3,5-di-tert-butylcatechol, and H2cat = 1,2-catechol, decomposed within minutes in cell culture medium at 310 K (t1/2 = 43 and 9 s for 1 and 2, respectively). Despite this, both complexes showed high antiproliferative activities in triple-negative human breast cancer (MDA-MB-231) cells, but the mechanisms of their activities were radically different. Complex 1 formed noncovalent adducts with human serum albumin, rapidly entered cells via passive diffusion, and was nearly as active in a short-term treatment (IC50 = 1.9 ± 0.2 μM at 30 min) compared with a long-term treatment (IC50 = 1.3 ± 0.2 μM at 72 h). The activity of 1 decreased about 20-fold after its decomposition in cell culture medium for 30 min at 310 K. Complex 2 showed similar activities (IC50 ≈ 12 μM at 72 h) in both fresh and decomposed solutions and was inactive in a short-term treatment. The activity of 2 was mainly due to the reactions among V(V) decomposition products, free catechol, and O2 in cell culture medium. As a result, the activity of 1 was less sensitive than that of 2 to the effects of hypoxic conditions that are characteristic of solid tumors and to the presence of apo-transferrin that acts as a scavenger of V(V/IV) decomposition products in blood serum. In summary, complex 1, but not 2, is a suitable candidate for further development as an anticancer drug delivered via intratumoral injections. These results demonstrate the importance of fine-tuning the ligand properties for the optimization of biological activities of metal complexes.

Medicinal applications of vanadium complexes with Schiff bases

Many transition metal complexes have been explored for their therapeutic properties after the discovery of cisplatin. Schiff bases have an efficient complexation tendency with the transition metals and several medicinal properties have been reported. However, fewer studies have reported the medicinal utility of vanadium and its Schiff base complexes. This paper provides a comprehensive overview of vanadium complexes with Schiff bases along with their mechanistic insight. Vanadium complexes in + 4 and + 5 oxidation states have exhibited well-defined geometry and found to be thermodynamically stable. The studies have reported the G0/G1 phase cell cycle arrest and decreased delta psi m, inducing mitochondrial membrane depolarization in cancer cell lines along with the alterations in the metabolism of the cancer cells upon dosing with the vanadium complexes. Cancer cell invasion and growth are also found to be markedly reduced by peroxo complexes of vanadium. The studies included in the review paper have been taken from leading indexing databases and focus was laid on recent reports in literature. The biological potential of vanadium complexes of Schiff bases opens new horizons for future interdisciplinary studies and investigation focussed on understanding the biochemistry of these complexes, along with designing new complexes which have better bioavailability, solubility and low or non-toxicity.

Vanadium Chloro-Substituted Schiff Base Catecholate Complexes are Reducible, Lipophilic, Water Stable, and Have Anticancer Activities

A hydrophobic Schiff base catecholate vanadium complex was recently discovered to have anticancer properties superior to cisplatin and suited for intratumoral administration. This [VO(HSHED)(DTB)] complex, where HSHED is N-(salicylideneaminato)-N'-(2-hydroxyethyl)-1,2-ethanediamine and the non-innocent catecholato ligand is di-t-butylcatecholato (DTB), has higher stability compared to simpler catecholato complexes. Three new chloro-substituted Schiff base complexes of vanadium(V) with substituted catecholates as co-ligands were synthesized for comparison with their non-chlorinated Schiff base vanadium complexes, and their properties were characterized. Up to four geometric isomers for each complex were identified in organic solvents using ⁵¹V and ¹H NMR spectroscopies. Spectroscopy was used to characterize the structure of the major isomer in solution and to demonstrate that the observed isomers are exchanged in solution. All three chloro-substituted Schiff base vanadium(V) complexes with substituted catecholates were also characterized by UV-vis spectroscopy, mass spectrometry, and electrochemistry. Upon testing in human glioblastoma multiforme (T98g) cells as an in vitro model of brain gliomas, the most sterically hindered, hydrophobic, and stable compound [t_1/2 (298 K) = 15 min in cell medium] was better than the two other complexes (IC₅₀ = 4.1 ± 0.5 μM DTB, 34 ± 7 μM 3-MeCat, and 19 ± 2 μM Cat). Furthermore, upon aging, the complexes formed less toxic decomposition products (IC₅₀ = 9 ± 1 μM DTB, 18 ± 3 μM 3-MeCat, and 8.1 ± 0.6 μM Cat). The vanadium complexes with the chloro-substituted Schiff base were more hydrophobic, more hydrolytically stable, more easily reduced compared to their corresponding parent counterparts, and the most sterically hindered complex of this series is only the second non-innocent vanadium Schiff base complex with a potent in vitro anticancer activity that is an order of magnitude more potent than cisplatin under the same conditions.

Therapeutic Potential of miRNAs for Type 2 Diabetes Mellitus: An Overview

MicroRNA(miRNA)s have been identified as an emerging class for therapeutic interventions mainly due to their extracellularly stable presence in humans and animals and their potential for horizontal transmission and action. However, treating Type 2 diabetes mellitus using this technology has yet been in a nascent state. MiRNAs play a significant role in the pathogenesis of Type 2 diabetes mellitus establishing the potential for utilizing miRNA-based therapeutic interventions to treat the disease. Recently, the administration of miRNA mimics or antimiRs in-vivo has resulted in positive modulation of glucose and lipid metabolism. Further, several cell culture-based interventions have suggested beta cell regeneration potential in miRNAs. Nevertheless, few such miRNA-based therapeutic approaches have reached the clinical phase. Therefore, future research contributions would identify the possibility of miRNA therapeutics for tackling T2DM. This article briefly reported recent developments on miRNA-based therapeutics for treating Type 2 Diabetes mellitus, associated implications, gaps, and recommendations for future studies.

An Overview of Herbal-Based Antidiabetic Drug Delivery Systems: Focus on Lipid- and Inorganic-Based Nanoformulations

Diabetes is a metabolic pathology with chronic high blood glucose levels that occurs when the pancreas does not produce enough insulin or the body does not properly use the insulin it produces. Diabetes management is a puzzle and focuses on a healthy lifestyle, physical exercise, and medication. Thus far, the condition remains incurable; management just helps to control it. Its medical treatment is expensive and is to be followed for the long term, which is why people, especially from low-income countries, resort to herbal medicines. However, many active compounds isolated from plants (phytocompounds) are poorly bioavailable due to their low solubility, low permeability, or rapid elimination. To overcome these impediments and to alleviate the cost burden on disadvantaged populations, plant nanomedicines are being studied. Nanoparticulate formulations containing antidiabetic plant extracts or phytocompounds have shown promising results. We herein aimed to provide an overview of the use of lipid- and inorganic-based nanoparticulate delivery systems with plant extracts or phytocompounds for the treatment of diabetes while highlighting their advantages and limitations for clinical application. The findings from the reviewed works showed that these nanoparticulate formulations resulted in high antidiabetic activity at low doses compared to the corresponding plant extracts or phytocompounds alone. Moreover, it was shown that nanoparticulate systems address the poor bioavailability of herbal medicines, but the lack of enough preclinical and clinical pharmacokinetic and/or pharmacodynamic trials still delays their use in diabetic patients.

Advantageous Reactivity of Unstable Metal Complexes: Potential Applications of Metal-Based Anticancer Drugs for Intratumoral Injections

Injections of highly cytotoxic or immunomodulating drugs directly into the inoperable tumor is a procedure that is increasingly applied in the clinic and uses established Pt-based drugs. It is advantageous for less stable anticancer metal complexes that fail administration by the standard intravenous route. Such hydrophobic metal-containing complexes are rapidly taken up into cancer cells and cause cell death, while the release of their relatively non-toxic decomposition products into the blood has low systemic toxicity and, in some cases, may even be beneficial. This concept was recently proposed for V(V) complexes with hydrophobic organic ligands, but it can potentially be applied to other metal complexes, such as Ti(IV), Ga(III) and Ru(III) complexes, some of which were previously unsuccessful in human clinical trials when administered via intravenous injections. The potential beneficial effects include antidiabetic, neuroprotective and tissue-regenerating activities for V(V/IV); antimicrobial activities for Ga(III); and antimetastatic and potentially immunogenic activities for Ru(III). Utilizing organic ligands with limited stability under biological conditions, such as Schiff bases, further enhances the tuning of the reactivities of the metal complexes under the conditions of intratumoral injections. However, nanocarrier formulations are likely to be required for the delivery of unstable metal complexes into the tumor.

Living with the enemy: from protein-misfolding pathologies we know, to those we want to know

Conformational diseases are caused by the aggregation of misfolded proteins. The risk for such pathologies develops years before clinical symptoms appear, and is higher in people with alpha-1 antitrypsin (AAT) polymorphisms. Thousands of people with alpha-1 antitrypsin deficiency (AATD) are underdiagnosed. Enemy-aggregating proteins may reside in these underdiagnosed AATD patients for many years before a pathology for AATD fully develops. In this perspective review, we hypothesize that the AAT protein could exert a new and previously unconsidered biological effect as an endogenous metal ion chelator that plays a significant role in essential metal ion homeostasis. In this respect, AAT polymorphism may cause an imbalance of metal ions, which could be correlated with the aggregation of amylin, tau, amyloid beta, and alpha synuclein proteins in type 2 diabetes mellitus (T2DM), Alzheimer's and Parkinson's diseases, respectively.

Evaluation of Insulin-Like Activity of Novel Zinc Metal-Organics toward Adipogenesis Signaling

Diabetes mellitus is a debilitating disease, plaguing a significant number of people around the globe. Attempts to develop new drugs on well-defined atoxic metalloforms, which are capable of influencing fundamental cellular processes overcoming insulin resistance, has triggered an upsurge in molecular research linked to zinc metallodrugs. To that end, meticulous efforts were launched toward the design and synthesis of materials with insulin mimetic potential. Henceforth, trigonelline and N-(2-hydroxyethyl)-iminodiacetic acid (HeidaH₂) were selected as organic substrates seeking binding to zinc (Zn(II)), with new crystalline compounds characterized by elemental analysis, FT-IR, X-rays, thermogravimetry (TGA), luminescence, NMR, and ESI-MS spectrometry. Physicochemical characterization was followed by in vitro biochemical experiments, in which three out of the five zinc compounds emerged as atoxic, exhibiting bio-activity profiles reflecting enhanced adipogenic potential. Concurrently, well-defined qualitative–quantitative experiments provided links to genetic loci responsible for the observed effects, thereby unraveling their key involvement in signaling pathways in adipocyte tissue and insulin mimetic behavior. The collective results (a) signify the quintessential role of molecular studies in unearthing unknown facets of pathophysiological events in diabetes mellitus II, (b) reflect the close associations of properly configured molecular zincoforms to well-defined biological profiles, and (c) set the stage for further physicochemical-based development of efficient zinc antidiabetic metallodrugs.

Ruthenium compounds as potential therapeutic agents for type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) is a chronic metabolic disorder which is globally responsible for millions of fatalities per year. Management of T2DM typically involves orally administered anti-hyperglycaemic drugs in conjunction with dietary interventions. However, the current conventional therapy seems to be largely ineffective as patients continue to develop complications such as cardiovascular diseases, blindness and kidney failure. Existing alternative treatment entails the administration of organic therapeutic pharmaceuticals, but these drugs have various side effects such as nausea, headaches, weight gain, respiratory and liver damage. Transition metal complexes have shown promise as anti-diabetic agents owing to their diverse mechanisms of activity. In particular, selected ruthenium compounds have exhibited intriguing biological behaviours as Protein Tyrosine Phosphatase (PTP) 1B and Glycogen Synthase Kinase 3 (GSK-3) inhibitors, as well as aggregation suppressants for the human islet amyloid polypeptide (hIAPP). This focussed review serves as a survey on studies pertaining to ruthenium compounds as metallo-drugs for T2DM. Herein, we also provide perspectives on directions to fully elucidate in vivo functions of this class of potential metallopharmaceuticals. More specifically, there is still a need to investigate the pharmacokinetics of ruthenium drugs in order to establish their biodistribution patterns which will affirm whether these metal complexes are substitutionally inert or serve as pro-drugs. In addition, embedding oral-administered ruthenium complexes into bio-compatible polymers can be a prospective means of enhancing stability during drug delivery.

Vanadium-protein complex inhibits human adipocyte differentiation through the activation of β-catenin and LKB1/AMPK signaling pathway

Obesity is a common disease over the world and is tightly associated with diabetes mellitus, cardiovascular and cancer disease. Although our previous study showed that the synthetic vanadium-protein (V-P) complex had a better effect on antioxidant and antidiabetic, the relative molecular mechanisms are still entirely unknown. Hence, we investigated the effect of the synthetic V-P complex on adipocyte differentiation (adipogenesis) using human preadipocytes to clarify its molecular mechanisms of action. The primary human preadipocytes were cultured with and without V-P complex during adipocyte differentiation. The cell proliferation, lipid accumulation, and the protein expression of transcription factors and related enzymes were determined for the differentiated human preadipocytes. In this study, the 20 μg/mL of V-P complex reduced the lipid and triglyceride (TG) content by 74.47 and 57.39% (p < 0.05), respectively, and down-regulated the protein expressions of peroxisome proliferator-activated receptor-γ (PPARγ), CCAAT/enhancer-binding protein alpha (C/EBPα), sterol regulatory element-binding protein 1 (SREBP-1) and fatty acid synthase (FAS). Additionally, the V-P complex significantly up-regulated the protein levels of total β-catenin (t-β-catenin), nuclear β-catenin (n-β-catenin), phosphorylated adenosine monophosphate-activated protein kinase alpha (p-AMPKα) and liver kinase B1 (p-LKB1). These showed that the inhibitory effect of V-P complex on human adipogenesis was mediated by activating Wnt/β-catenin and LKB1/AMPK-dependent signaling pathway. Therefore, the synthetic V-P complex could be considered as a candidate for prevention and treatment of obesity.

A Short-Lived but Highly Cytotoxic Vanadium(V) Complex as a Potential Drug Lead for Brain Cancer Treatment by Intratumoral Injections

The chemistry and short lifetimes of metal-based anti-cancer drugs can be turned into an advantage for direct injections into tumors, which then allow the use of highly cytotoxic drugs. The release of their less toxic decomposition products into the blood will lead to decreased toxicity and can even have beneficial effects. We present a ternary V^V complex, 1 ([VOL¹ L² ], where L¹ is N-(salicylideneaminato)-N'-(2-hydroxyethyl)ethane-1,2-diamine and L² is 3,5-di-tert-butylcatechol), which enters cells intact to induce high cytotoxicity in a range of human cancer cells, including T98g (glioma multiforme), while its decomposition products in cell culture medium were ≈8-fold less toxic. 1 was 12-fold more toxic than cisplatin in T98g cells and 6-fold more toxic in T98g cells than in a non-cancer human cell line, HFF-1. Its high toxicity in T98g cells was retained in the presence of physiological concentrations of the two main metal-binding serum proteins, albumin and transferrin. These properties favor further development of 1 for brain cancer treatment by intratumoral injections.

Biguanide-transition metals complexes as potential drug for hyperglycemia treatment

Coordination compounds of Cu(ii), Ni(ii), Co(ii), and Zn(ii) with a type of biguanide (known commercially as metformin) have been synthesized and characterized using spectroscopic techniques (FT-IR, UV/VIS), X-ray diffraction techniques and thermal analysis. For all compounds, single crystals were obtained for single-crystal X-ray diffraction. For the first time, an octahedral cobalt compound with the formula [Co(C₄H₁₁N₅)₃]Cl₂·2H₂O that crystallizes in the monoclinic space group C2/c with one molecule in the asymmetric unit has been obtained. Also, a novel nickel compound with the formula [Ni(C₄H₁₁N₅) (C₄H₁₀N₅)]Cl·H₂O that crystallizes in the monoclinic space group P2₁/c with two molecules in the asymmetric unit was obtained. Finally, we obtained copper and zinc compounds that crystallize in the monoclinic space groups P2₁/n and P2₁/c with the general formula [Cu(C₄H₁₁N₅)₂]Cl₂·H₂O and [Zn(C₄H₁₂N₅)Cl₃], respectively. A structural and supramolecular analysis was developed for all compounds using Hirshfeld surface analysis and electrostatic potential maps. The cell viability of the obtained compounds was evaluated in C2C12 (ATCCCRL-1772™) mouse muscle cells and HepG2 (ATCC HB-8065™) human liver carcinoma cells by the MTT assay to determine the potential of the compounds as new safe drugs. The results demonstrate that the compounds exhibit low cytotoxicity at doses less than 250 μg mL⁻¹ with a cell viability greater than 80%.

Coordination compounds of Cu(ii), Ni(ii), Co(ii), and Zn(ii) with a type of biguanide were obtained and structurally characterized. The new metal-drugs present biological applications as potential drugs for diabetes and metabolic syndrome.

Insulin‐Sensitizing Activity of Sub‐Nanoscaled Polyalkoxyvanadate Clusters

Sub‐nanoscaled polyalkoxyvanadates (PAOVs) functionalized with various aliphatic acids are evaluated for their insulin‐sensitizing activity in lowering the blood glucose levels of diabetic mice in typical glucose tolerance tests. All the PAOVs can restore the blood glucose to normal levels after a single oral administration of PAOVs. Among them, the myristic acid‐modified PAOVs enable the response of insulin to the repeated glucose challenges, lasting for up to 13 h. The combined administration of PAOVs exerts better glucose control over insulin alone, while the capric acid‐ and myristic acid‐modified ones can enhance the responsiveness of insulin to glucose challenge and is comparable to a clinical‐used derivative of insulin. Interestingly, continuous glucose monitoring shows that myristic acid‐modified PAOV derivatives sensitize the responsiveness of insulin, almost matching with that of a healthy pancreas. These discoveries open up new opportunities for the application of PAOVs to promote glucose‐responsive and long‐lasting activity of insulin, which are expected to aid the accurate blood glucose control in insulin therapy while reducing the number of insulin administrations.

Bis(ethylmaltolato)oxidovanadium (IV) mitigates neuronal apoptosis resulted from amyloid-beta induced endoplasmic reticulum stress through activating peroxisome proliferator-activated receptor γ

Neuronal apoptosis caused by amyloid-beta (Aβ) overproduction is one of the most important pathological features in Alzheimer's disease (AD). Endoplasmic reticulum (ER) stress induced by Aβ overload plays a critical role in this process. Bis(ethylmaltolato)oxidovanadium (IV) (BEOV), a vanadium compound which had been regarded as peroxisome proliferator-activated receptor γ (PPARγ) agonist, was reported to exert an antagonistic effect on ER stress. In this study, we tested whether BEOV could ameliorate the Aβ-induced neuronal apoptosis by inhibiting ER stress. It was observed that BEOV treatment ameliorated both tunicamycin-induced and/or Aβ-induced ER stress and neurotoxicity in a dose-dependent manner through downgrading ER stress-associated and apoptosis-associated proteins in primary hippocampal neurons. Consistent with in vitro results, BEOV also reduced ER stress and inhibited neuronal apoptosis in hippocampi and cortexes of transgenic AD model mice. Moreover, by adopting GW9662 and salubrinal, the inhibitor of PPARγ and hyperphosphorylated eukaryotic translation initiation factor 2α, respectively, we further confirmed that BEOV alleviated Aβ-induced ER stress and neuronal apoptosis in primary hippocampal neurons by activating PPARγ. Taken together, these results provided scientific evidences to support the concept that BEOV ameliorates Aβ-induced ER stress and neuronal apoptosis through activating PPARγ.

DNA binding, cytotoxic effects and probable targets of an oxindolimine–vanadyl complex as an antitumor agent

The vanadyl–oxindolimine complex as an antitumor agent.

Hydrophobicity may enhance membrane affinity and anti-cancer effects of Schiff base vanadium(v) catecholate complexes

Anti-cancer activities of vanadium compounds have generated recent interest because of a combination of desirable properties for chemotherapy, i.e., strong cytotoxicities, anti-metastatic activities and relatively low systemic toxicities. Certain hydrophobic vanadium(v) Schiff base/catecholate compounds, which as shown herein, have increased stability in aqueous media and affinity for membrane interfaces. Depending on their hydrophobicity, they may be able to enter cells intact. In this manuscript, two hydrophobic V(v) catecholate substituted analogues, [VO(Hshed)(cat)] and [VO(Hshed)(dtb)], (Hshed = N-(salicylideneaminato)-N'-(2-hydroxyethyl)-1,2-ethanediamine, cat = pyrocatechol, and dtb = 3,5-di(tert-butyl)catechol and the vanadium(v) precursor [V(O)2(Hshed)]) were synthesized for their ability to interact with membranes and their anti-cancer effects. Using 51V and 1H NMR spectroscopy, the presence and location of the free ligand, H2shed, and the three V(v) complexes were examined in a model membrane microemulsion system. The stability of the three complexes was measured in aqueous solution, cell media and an inhomogeneous microemulsion system. Our results demonstrated that free ligand H2shed and the intact V(v) complexes associated with the interface but that the V-complexes hydrolyzed to some extent because oxovanadates were observed by 51V NMR spectroscopy and decreasing complex by absorption spectroscopy in cell media. When determining the effects of V(v) catecholate complexes on bone cancer cells, the strongest effects were observed with the more stable hydrophobic complex [VO(Hshed)(dtb)] that was able to best associate and penetrate the model membrane system intact. These studies are consistent with the membrane permeability studies being a good predictor for in vitro cytotoxicity assays because [VO(Hshed)(dtb)] can pass through the cellular membrane intact, which may enhance its anti-cancer activities.

EPR and 51V NMR studies of prospective anti-diabetic bis(3-hydroxy-4-pyridinonato)oxidovanadium(iv) complexes in aqueous solution and liposome suspensions

EPR/⁵¹V-NMR parallel studies of [VO(3,4-HPO)₂] complexes in MOPS buffer and POPC liposome suspensions provide information regarding solvents for oral administration.

Bis(picolinato) complexes of vanadium and zinc as potential antidiabetic agents: synthesis, structural elucidation and in vitro insulin-mimetic activity study

The studied vanadium(iv), vanadium(v) and zinc(ii) complexes show inhibition of the free fatty acid release from rat adipocytes.

A potent, selective, and orally bioavailable inhibitor of the protein-tyrosine phosphatase PTP1B improves insulin and leptin signaling in animal models

The protein-tyrosine phosphatase PTP1B is a negative regulator of insulin and leptin signaling and a highly validated therapeutic target for diabetes and obesity. Conventional approaches to drug development have produced potent and specific PTP1B inhibitors, but these inhibitors lack oral bioavailability, which limits their potential for drug development. Here, we report that DPM-1001, an analog of the specific PTP1B inhibitor trodusquemine (MSI-1436), is a potent, specific, and orally bioavailable inhibitor of PTP1B. DPM-1001 also chelates copper, which enhanced its potency as a PTP1B inhibitor. DPM-1001 displayed anti-diabetic properties that were associated with enhanced signaling through insulin and leptin receptors in animal models of diet-induced obesity. Therefore, DPM-1001 represents a proof of concept for a new approach to therapeutic intervention in diabetes and obesity. Although the PTPs have been considered undruggable, the findings of this study suggest that allosteric PTP inhibitors may help reinvigorate drug development efforts that focus on this important family of signal-transducing enzymes.

Stabilities and Biological Activities of Vanadium Drugs: What is the Nature of the Active Species?

Diverse biological activities of vanadium(V) drugs mainly arise from their abilities to inhibit phosphatase enzymes and to alter cell signaling. Initial interest focused on anti-diabetic activities but has shifted to anti-cancer and anti-parasitic drugs. V-based anti-diabetics are pro-drugs that release active components (e.g., H₂ VO₄^- ) in biological media. By contrast, V anti-cancer drugs are generally assumed to enter cells intact; however, speciation studies indicate that nearly all drugs are likely to react in cell culture media during in vitro assays and the same would apply in vivo. The biological activities are due to V^V and/or V^IV reaction products with cell culture media, or the release of ligands (e.g., aromatic diimines, 8-hydroxyquinolines or thiosemicarbazones) that bind to essential metal ions in the media. Careful consideration of the stability and speciation of V complexes in cell culture media and in biological fluids is essential to design targeted V-based anti-cancer therapies.

Investigation of Biodistribution and Speciation Changes of Orally Administered Dual Radiolabeled Complex, Bis(5-chloro-7-[131I]iodo-8-quinolinolato)[65Zn]zinc

Many zinc (Zn) complexes have been developed as promising oral antidiabetic agents. In vitro assays using adipocytes have demonstrated that the coordination structures of Zn complexes affect the uptake of Zn into cells and have insulinomimetic activities, for which moderate stability of Zn complexes is vital. The complexation of Zn plays a major role improving its bioavailability. However, investigation of the speciation changes of Zn complexes after oral administration is lacking. A dual radiolabeling approach was applied in order to investigate the speciation of bis(5-chloro-7-iodo-8-quinolinolato)zinc complex [Zn(Cq)₂], which exhibits the antidiabetic activity in diabetic mice. In the present study, ⁶⁵Zn- and ¹³¹I-labeled [Zn(Cq)₂] were synthesized, and their biodistribution were analyzed after an oral administration using both invasive conventional assays and noninvasive gamma-ray emission imaging (GREI), a novel nuclear medicine imaging modality that enables analysis of multiple radionuclides simultaneously. The GREI experiments visualized the behavior of ⁶⁵Zn and [¹³¹I]Cq from the stomach to large intestine and through the small intestine; most of the administered Zn was transported together with clioquinol (5-chloro-7-iodo-8-quinolinol) (Cq). Higher accumulation of ⁶⁵Zn for [Zn(Cq)₂] than ZnCl₂ suggests that the Zn associated with Cq was highly absorbed by the intestinal tract. In particular, the molar ratio of administered iodine to Zn decreased during the distribution processes, indicating the dissociation of most [Zn(Cq)₂] complexes. In conclusion, the present study successfully evaluated the speciation changes of orally administered [Zn(Cq)₂] using the dual radiolabeling method.

Characterization and cytotoxic effect of aqua-(2,2',2''-nitrilotriacetato)-oxo-vanadium salts on human osteosarcoma cells

The use of protonated N-heterocyclic compound, i.e. 2,2'-bipyridinium cation, [bpyH+], enabled to obtain the new nitrilotriacetate oxidovanadium(IV) salt of the stoichiometry [bpyH][VO(nta)(H2O)]H2O. The X-ray measurements have revealed that the compound comprises the discrete mononuclear [VO(nta)(H2O)]- coordination ion that can be rarely found among other known compounds containing nitrilotriacetate oxidovanadium(IV) moieties. The antitumor activity of [bpyH][VO(nta)(H2O)]H2O and its phenanthroline analogue, [phenH][VO(nta)(H2O)](H2O)0.5, towards human osteosarcoma cell lines (MG-63 and HOS) has been assessed (the LDH and BrdU tests) and referred to cis-Pt(NH3)2Cl2 (used as a positive control). The compounds exert a stronger cytotoxic effect on MG-63 and HOS cells than in untransformed human osteoblast cell line. Thus, the [VO(nta)(H2O)]- containing coordination compounds can be considered as possible antitumor agents in the osteosarcoma model of bone-related cells in culture.

A Small Insulinomimetic Molecule Also Improves Insulin Sensitivity in Diabetic Mice

Dramatic increase of diabetes over the globe is in tandem with the increase in insulin requirement. This is because destruction and dysfunction of pancreatic β-cells are of common occurrence in both Type1 diabetes and Type2 diabetes, and insulin injection becomes a compulsion. Because of several problems associated with insulin injection, orally active insulin mimetic compounds would be ideal substitute. Here we report a small molecule, a peroxyvanadate compound i.e. DmpzH[VO(O2)2(dmpz)], henceforth referred as dmp, which specifically binds to insulin receptor with considerable affinity (KD-1.17μM) thus activating insulin receptor tyrosine kinase and its downstream signaling molecules resulting increased uptake of [14C] 2 Deoxy-glucose. Oral administration of dmp to streptozotocin treated BALB/c mice lowers blood glucose level and markedly stimulates glucose and fatty acid uptake by skeletal muscle and adipose tissue respectively. In db/db mice, it greatly improves insulin sensitivity through excess expression of PPARγ and its target genes i.e. adiponectin, CD36 and aP2. Study on the underlying mechanism demonstrated that excess expression of Wnt3a decreased PPARγ whereas dmp suppression of Wnt3a gene increased PPARγ expression which subsequently augmented adiponectin. Increased production of adiponectin in db/db mice due to dmp effected lowering of circulatory TG and FFA levels, activates AMPK in skeletal muscle and this stimulates mitochondrial biogenesis and bioenergetics. Decrease of lipid load along with increased mitochondrial activity greatly improves energy homeostasis which has been found to be correlated with the increased insulin sensitivity. The results obtained with dmp, therefore, strongly indicate that dmp could be a potential candidate for insulin replacement therapy.

Influence of Primary Ligands (ODA, TDA) on Physicochemical and Biological Properties of Oxidovanadium (IV) Complexes with Bipy and Phen as Auxiliary Ligands

The influence of the oxydiacetate (ODA) and thiodiacetate (TDA) ligands on the physicochemical and biological properties of the oxidovanadium(IV) ternary complexes of the VO(L)(B) type, where L denotes ODA or TDA and B denotes 2,2'-bipyridine (bipy) or 1,10-phenanthroline (phen), has been investigated. The stability of the complexes in aqueous solutions, assessed based on the potentiometric titration method, increases in the following direction: VO(TDA)(bipy) < VO(ODA)(bipy) < VO(TDA)(phen) < VO(ODA)(phen). Furthermore, the influence of the TDA and ODA ligands on the antioxidant activity of the oxidovanadium(IV) complexes toward superoxide free radical (O₂^•-), 2,2'-azinobis(3-ethylbenzothiazoline-6 sulfonic acid) cation radical (ABTS^+•) and 2,2-diphenyl-1-picrylhydrazyl radical (DPPH^•) has been examined and discussed. The reactivity of the complexes toward O₂^•- increases in the following direction: VO(TDA)(phen) < VO(TDA)(bipy) ≈ VO(ODA)(bipy) < VO(ODA)(phen). The antioxidant activity against ABTS^+• and DPPH^• free radicals is higher for phen complexes, whereas the thiodiacetate complexes are more reactive than are the corresponding oxydiacetate ones. Finally, herein, the cytoprotective activity of the complexes against the oxidative damage generated exogenously by hydrogen peroxide in the hippocampal neuronal HT22 cell line (the MTT and LDH tests) is reported. In a low concentration (1 μM), the cytoprotective action of thiodiacetate complexes is much higher than that of the corresponding oxydiacetate complexes. However, in the higher concentration range (10 and 100 μM), the antioxidant activity of the complexes is overcompensated by their cytotoxic effect.

Selective speciation improves efficacy and lowers toxicity of platinum anticancer and vanadium antidiabetic drugs

Improving efficacy and lowering resistance to metal-based drugs can be addressed by consideration of the coordination complex speciation and key reactions important to vanadium antidiabetic drugs or platinum anticancer drugs under biological conditions. The methods of analyses vary depending on the specific metal ion chemistry. The vanadium compounds interconvert readily, whereas the reactions of the platinum compounds are much slower and thus much easier to study. However, the vanadium species are readily differentiated due to vanadium complexes differing in color. For both vanadium and platinum systems, understanding the processes as the compounds, Lipoplatin and Satraplatin, enter cells is needed to better combat the disease; there are many cellular metabolites, which may affect processing and thus the efficacy of the drugs. Examples of two formulations of platinum compounds illustrate how changing the chemistry of the platinum will result in less toxic and better tolerated drugs. The consequence of the much lower toxicity of the drug, can be readily realized because cisplatin administration requires hospital stay whereas Lipoplatin can be done in an outpatient manner. Similarly, the properties of Satraplatin allow for development of an oral drug. These forms of platinum demonstrate that the direct consequence of more selective speciation is lower side effects and cheaper administration of the anticancer agent. Therefore we urge that as the community goes forward in development of new drugs, control of speciation chemistry will be considered as one of the key strategies in the future development of anticancer drugs.

EPR and DFT analysis of biologically relevant chromium(V) complexes with d-glucitol and d-glucose

1,2-diolato ligands, such as carbohydrates and glycoproteins, tend to stabilize chromium(V), thus forming important intermediates that have been implicated in the genotoxicity of Cr(VI). Since many years, room-temperature continuous-wave electron paramagnetic resonance (EPR) at X-band microwave frequencies has been used as a standard characterization tool to study chromium(V) intermediates formed during the reduction of Cr(VI) in the presence of biomolecules. In this work, the added value is tested of using a combination of pulsed and high-field EPR techniques with density functional theory computations to unravel the nature of Cr(V) complexes with biologically relevant chelators, such as carbohydrates. The study focuses on the oxidochromium(V) complexes formed during reduction of potassium dichromate with glutathione in the presence of the monosaccharide d-glucose or the polyalcohol d-glucitol. It is shown that although the presence of a multitude of Cr(V) intermediates may hamper a complete structural determination, the combined EPR and DFT approach reveals unambiguously the effect of freezing on the location of the counterions, the gradual replacement of water ligands by the diols, and the preference of Cr(V) to bind certain conformers.

Cooperative adsorption of critical metal ions using archaeal poly-γ-glutamate

Antimony, beryllium, chromium, cobalt (Co), gallium (Ga), germanium, indium (In), lithium, niobium, tantalum, the platinoids, the rare-earth elements (including dysprosium, Dy), and tungsten are generally regarded to be critical (rare) metals, and the ions of some of these metals are stabilized in acidic solutions. We examined the adsorption capacities of three water-soluble functional polymers, namely archaeal poly-γ-glutamate (L-PGA), polyacrylate (PAC), and polyvinyl alcohol (PVA), for six valuable metal ions (Co(2+), Ni(2+), Mn(2+), Ga(3+), In(3+), and Dy(3+)). All three polymers showed apparently little or no capacity for divalent cations, whereas L-PGA and PAC showed the potential to adsorb trivalent cations, implying the beneficial valence-dependent selectivity of anionic polyelectrolytes with multiple carboxylates for metal ions. PVA did not adsorb metal ions, indicating that the crucial role played by carboxyl groups in the adsorption of crucial metal ions cannot be replaced by hydroxyl groups under the conditions. In addition, equilibrium studies using the non-ideal competitive adsorption model indicated that the potential for L-PGA to be used for the removal (or collection) of water-soluble critical metal ions (e.g., Ga(3+), In(3+), and Dy(3+)) was far superior to that of any other industrially-versatile PAC materials.

Carcinogenic Chromium(VI) Compounds Formed by Intracellular Oxidation of Chromium(III) Dietary Supplements by Adipocytes

Chromium(III) nutritional supplements are widely consumed for their purported antidiabetic activities. X-ray fluorescence microscopy (XFM) and X-ray absorption near-edge structure (XANES) studies have now shown that non-toxic doses of [Cr3 O(OCOEt)6 (OH2 )3 ](+) (A), a prospective antidiabetic drug that undergoes similar H2 O2 induced oxidation reactions in the blood as other Cr supplements, was also oxidized to carcinogenic Cr(VI) and Cr(V) in living cells. Single adipocytes treated with A had approximately 1 μm large Cr hotspots containing Cr(III) , Cr(V) , and Cr(VI) (primarily Cr(VI) thiolates) species. These results strongly support the hypothesis that the antidiabetic activity of Cr(III) and the carcinogenicity of Cr(VI) compounds arise from similar mechanisms involving highly reactive Cr(VI) and Cr(V) intermediates, and highlight concerns over the safety of Cr(III) nutritional supplements.