Convenient microwave-assisted synthesis of lipophilic sulfenamide prodrugs of metformin

Metformin derivatives - Researchers' friends or foes?

Metformin has been used for ages to treat diabetes mellitus due to its safety profile and low cost. However, metformin has variable pharmacokinetics in patients, and due to its poor oral absorption, the therapeutic doses are relatively high, causing unpleasant gastrointestinal adverse effects. Therefore, novel derivatives of metformin have been synthesized during the past decades. Particularly, after the mid-2000 s, when organic cation transporters were identified as the main metformin carriers, metformin derivatives have been under intensive investigation. Nevertheless, due to the biguanide structure, derivatives of metformin have been challenging to synthesize. Moreover, the mechanisms of metformin's action are not fully understood to date, and since it has multifunctional properties, the interests have switched to re-purposing for other diseases. Indeed, metformin derivatives have been demonstrated in many cases to be more effective than metformin itself and have the potential to be used in different diseases, including several types of cancers and neurodegenerative diseases. On the other hand, the pleiotropic nature of metformin and its derivatives can also create challenges. Not all properties are fit for all diseases. In this review, the history of the development of metformin-like compounds is summarized, and insights into their potential for future drug discovery are discussed.

Design, synthesis and chemical stability of indolizine derivatives for antidiabetic activity

Prodrugs of metformin were synthesized with the goal of enhancing biological activity of metformin. They were synthesized by combining metformin with 2-substituted indolizine (C7-C12). The synthesized prodrugs were characterized by IR, ¹H NMR, ¹³C NMR, and mass spectroscopy. The chemical hydrolysis of C7-C12 was carried out at pH 1.2, 6.8, and 7.4. All compounds showed encouraging chemical stability at pH 1.2 and 6.8, whereas mild hydrolysis was shown at pH 7.4. Further prodrugs were screened for antidiabetic activity using a streptozotocin-induced model in rat. These derivatives showed substantial results. Among them C8 showed significant activity in the reduction of streptozotocin-induced blood glucose in rats when compared to that of metformin, indicating the effectiveness of prodrug.

Design, synthesis and chemical stability of indolizine derivatives for antidiabetic activity

Prodrugs of metformin were synthesized with the goal of enhancing biological activity of metformin. They were synthesized by combining metformin with 2-substituted indolizine (C7-C12). The synthesized prodrugs were characterized by IR, ¹H NMR, ¹³C NMR, and mass spectroscopy. The chemical hydrolysis of C7-C12 was carried out at pH 1.2, 6.8, and 7.4. All compounds showed encouraging chemical stability at pH 1.2 and 6.8, whereas mild hydrolysis was shown at pH 7.4. Further prodrugs were screened for antidiabetic activity using a streptozotocin-induced model in rat. These derivatives showed notable results. Among them C8 showed significant activity in the reduction of STZ-induced blood glucose in rats when compared to that of metformin, indicating the effectiveness of prodrug.

Type 2 Diabetes Complicated With Heart Failure: Research on Therapeutic Mechanism and Potential Drug Development Based on Insulin Signaling Pathway

Type 2 diabetes mellitus (T2DM) and heart failure (HF) are diseases characterized by high morbidity and mortality. They often occur simultaneously and increase the risk of each other. T2DM complicated with HF, as one of the most dangerous disease combinations in modern medicine, is more common in middle-aged and elderly people, making the treatment more difficult. At present, the combination of blood glucose control and anti-heart failure is a common therapy for patients with T2DM complicated with HF, but their effect is not ideal, and many hypoglycemic drugs have the risk of heart failure. Abnormal insulin signaling pathway, as a common pathogenic mechanism in T2DM and HF, could lead to pathological features such as insulin resistance (IR), myocardial energy metabolism disorders, and vascular endothelial disorders. The therapy based on the insulin signaling pathway may become a specific therapeutic target for T2DM patients with HF. Here, we reviewed the mechanisms and potential drugs of insulin signaling pathway in the treatment of T2DM complicated with HF, with a view to opening up a new perspective for the treatment of T2DM patients with HF and the research and development of new drugs.

Deciphering the Roles of Metformin in Alzheimer's Disease: A Snapshot

Alzheimer’s disease (AD) is a prevalent neurodegenerative disease predominantly affecting millions of elderly people. To date, no effective therapy has been identified to reverse the progression of AD. Metformin, as a first-line medication for Type 2 Diabetes Mellitus (T2DM), exerts multiple beneficial effects on various neurodegenerative disorders, including AD. Evidence from clinical studies has demonstrated that metformin use contributes to a lower risk of developing AD and better cognitive performance, which might be modified by interactors such as diabetic status and APOE-ε4 status. Previous mechanistic studies have gradually unveiled the effects of metformin on AD pathology and pathophysiology, including neuronal loss, neural dysfunction, amyloid-β (Aβ) depositions, tau phosphorylation, chronic neuroinflammation, insulin resistance, impaired glucose metabolism and mitochondrial dysfunction. Current evidence remains ambiguous and even conflicting. Herein, we review the current state of knowledge concerning the mechanisms of metformin in AD pathology while summarizing current evidence from clinical studies.

An investigation into the pleiotropic activity of metformin. A glimpse of haemostasis

The most characteristic features of type 2 diabetes mellitus (T2DM) are hyperglycaemia and insulin resistance, however, patients with T2DM are at higher risk of cardiovascular disease (CVD) and atherosclerosis. Diabetes, frequently related to metabolic and vascular impairments, is also associated with thrombosis, increased blood coagulation and an imbalance between coagulation and fibrinolysis. Metformin is the most often used oral glucose-lowering agent; its beneficial properties include lowering insulin resistance, weight reduction and cardioprotection. Available data suggest that the advantageous properties of metformin stem from its favourable effects on endothelium, and anti-oxidative and anti-inflammatory properties. This paper reviews the favourable impact of metformin on endothelial function, with particular emphasis on the release of endogenous molecules modulating the state of the vascular endothelium and coagulation. It also summarizes the present knowledge on the influence of metformin on platelet activity and plasma haemostasis, including clot formation, stabilization and fibrinolysis. Its findings confirm that metformin should constitute first line therapy of T2DM subjects; however, more comprehensive methodical studies are required to discover the full potential of this drug.

Pleiotropic Activity of Metformin and Its Sulfonamide Derivatives on Vascular and Platelet Haemostasis

As type 2 diabetes mellitus (T2DM) predisposes patients to endothelial cell injury and dysfunction, improvement of vascular function should be an important target for therapy. The aim of this study was to evaluate the effects of metformin, its sulfenamide and sulfonamide derivatives on selected parameters of endothelial and smooth muscle cell function, and platelet activity. Metformin was not found to significantly affect the viability of human umbilical vein endothelial cells (HUVECs) or aortal smooth muscle cells (AoSMC); however, it decreased cell migration by approximately 21.8% in wound healing assays after 24 h stimulation (wound closure 32.5 µm versus 41.5 µm for control). Metformin reduced platelet aggregation manifested by 19.0% decrease in maximum of aggregation (Amax), and 20% reduction in initial platelet aggregation velocity (v0). Furthermore, metformin decreased spontaneous platelet adhesion by 27.7% and ADP-induced adhesion to fibrinogen by 29.6% in comparison to control. Metformin sulfenamide with an n-butyl alkyl chain (compound 1) appeared to exert the most unfavourable effects on AoSMC cell viability (IC50 = 0.902 ± 0.015 μmol/mL), while 4-nitrobenzenesulfonamide (compound 3) and 2-nitrobenzenesulfonamide (compound 4) derivatives of metformin did not affect AoSMC and HUVEC viability at concentrations up to 2.0 μmol/mL. These compounds were also found to significantly reduce migration of smooth muscle cells by approximately 81.0%. Furthermore, sulfonamides 3 and 4 decreased the initial velocity of platelet aggregation by 11.8% and 20.6%, respectively, and ADP-induced platelet adhesion to fibrinogen by 76.3% and 65.6%. Metformin and its p- and o-nitro-benzenesulfonamide derivatives 3, 4 appear to exert beneficial effects on some parameters of vascular and platelet haemostasis.

Novel halogenated sulfonamide biguanides with anti-coagulation properties

Apart from its hypoglycaemic properties, metformin also offers beneficial effects for the cardiovascular system resulting in significant reduction of diabetes-related death, and all-cause mortality. The aim of this study was to synthesize nine new benzenesulfonamide derivatives of metformin with a halogen substituent, and estimate their influence on selected parameters of plasma and vascular hemostasis. The study describes the synthesis of nine benzenesulfonamide biguanides with o-, m-, and p- chloro-, bromo-, and fluoro substituents. All orto- derivatives (chloro- (1), bromo- (4), and fluoro- (7)) significantly prolong prothrombin time (PT) and partially activated thromboplastin time (APTT). In addition compounds 4 and 7 slow the process of fibrin polymerization, and contribute to increased TT. Multiparametric CL-test revealed that compounds 1, 4, 7 and p-fluorobenzenesulfonamide (9) significantly prolong the onset of clot formation, decrease initial clot formation velocity, and maximum clotting. Analysis of human endothelial cell (HUVECs) and human aortal smooth muscle cell (AoSMCs) viability over the entire tested concentration range (0.001-3.0 μmol/mL) indicated that the examined compounds can undergo further tests up to 1.5 µmol/mL concentration without decreasing cellular viability. Furthermore, none of the synthesized compounds exert an unfavourable effect on erythrocyte integrity, and thus do not interact strongly with the lipid-protein bilayer. In summary, chemical modification of the metformin backbone into benzenesulfonamides containing halogen substituents at the o- position leads to the formation of potential agents with stronger anti-coagulant properties than the parent drug, metformin. Therefore, o-halogenated benzenesulfonamides can be regarded as an initial promising step in the development of novel biguanide-based compounds with anti-coagulant properties.

Sulfenamide and Sulfonamide Derivatives of Metformin - A New Option to Improve Endothelial Function and Plasma Haemostasis

Type 2 diabetes mellitus (T2DM) is a multi-factorial disease which can cause multiple organ dysfunction, including that of the vascular endothelium. The aim of the present study was to evaluate the effects of metformin, and its sulfenamide and sulfonamide derivatives (compounds 1–8) on the selected markers of endothelial function and blood coagulation. The integrity of endothelial cells(ECs) was examined using the real-time cell electric impedance system. Tissue Factor(TF) production, the release of von Willebrand Factor (vWF) and tissue plasminogen activator(t-PA) from ECs were determined using immunoenzymatic assays, while the process of platelet thrombus formation using the Total Thrombus-Formation Analysis System. Sulfenamide with n-butyl alkyl chain(3) does not interfere with ECs integrity, and viability (nCI_(24h) = 1.03 ± 0.03 vs. 1.06 ± 0.11 for control), but possesses anticoagulation properties manifested by prolonged platelet-dependent thrombus formation (Occlusion Time 370.3 ± 77.0 s vs. 286.7 ± 65.5 s for control) in semi-physiological conditions. Both p- and o-nitro-benzenesulfonamides (compounds7,8) exhibit anti-coagulant properties demonstrated by decreased vWF release and prolonged parameters of platelet thrombus formation and total blood thrombogenicity. In conclusion, chemical modification of metformin scaffold into sulfenamides or sulfonamides might be regarded as a good starting point for the design and synthesis of novel biguanide-based compounds with anticoagulant properties and valuable features regarding endothelial function.

Sulfenamide derivatives can improve transporter-mediated cellular uptake of metformin and induce cytotoxicity in human breast adenocarcinoma cell lines

Metformin, the most frequently administered oral anti-diabetic drug, is a substrate for organic cation transporters (OCTs). This determines not only its pharmacokinetic properties but also its biochemical effects in humans, including its recently-discovered antiproliferative properties. The aim of the study was to verify the hypothesis whether chemical modification of its biguanide backbone may increase the cellular uptake and antiproliferative efficacy of metformin. The study examines five sulfenamide derivatives of metformin with differing lengths of alkyl chains. It determines their cellular uptake and the role of OCTs in their transport in human breast adenocarcinoma cells (epithelial-like MCF-7, and MDA-MB-231). It also evaluates whether increased cellular uptake of metformin derivatives is associated with their cytotoxic properties. Sulfenamide derivatives were characterized by a greater ability to bind to OCTs than metformin. Compound 2 with n-octyl alkyl chain was found to possess the greatest affinity towards OCTs, as measured by determination of [¹⁴C]choline uptake inhibition (IC₅₀ = 236.1 ± 1.28 μmol/L, and 217.4 ± 1.33 μmol/L, for MCF-7 and MDA-MB-231 respectively). Sulfenamides were also found to exhibit better cellular uptake in comparison with the parent drug, metformin. For instance, the uptake of cyclohexyl derivative 1 was 1.28 ± 0.19 nmol/min/mg of proteins and thus was 12-fold higher than the metformin in MCF-7 cells. Furthermore, higher uptake was associated with the greatest antiproliferative properties expressed as the lowest IC₅₀ value i.e. inhibiting the growth of 50% of the cells (IC₅₀ = 0.72 ± 1.31 μmol/L). Collectively, chemical modification of metformin into sulfenamides with different alkyl substituents obtains better substrates for OCTs, and subsequently higher cellular uptake in MCF-7 and MDA-MB-231 cells. Additionally, the length of alkyl chain introduced to the sulfenamides was found to influence selectivity and transport efficiency via OCT1 compared to other possible transporters, as well as potential intracellular activity and cytotoxicity.

Metformin and its sulphonamide derivative simultaneously potentiateanti-cholinesterase activity of donepezil and inhibit beta-amyloid aggregation

The aim of this study was to assess in vitro the effects of sulphenamide and sulphonamide derivatives of metformin on the activity of human acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE), establish the type of inhibition, and assess the potential synergism between biguanides and donepezil towards both cholinesterases (ChEs) and the effects on the β-amyloid aggregation. Sulphonamide 5 with para-trifluoromethyl- and ortho-nitro substituents in aromatic ring inhibited AChE in a mixed-type manner at micromolar concentrations (IC50 = 212.5 ± 48.3 µmol/L). The binary mixtures of donepezil and biguanides produce an anti-AChE effect, which was greater than either compound had alone. A combination of donepezil and sulphonamide 5 improved the IC50 value by 170 times. Compound 5 at 200 µmol/L inhibited Aβ aggregation by ∼20%. In conclusion, para-trifluoromethyl-ortho-nitro-benzenesulphonamide presents highly beneficial anti-AChE and anti-Aβ aggregation properties which could serve as a promising starting point for the design and development of novel biguanide-based candidates for AD treatment.

A preclinical overview of metformin for the treatment of type 2 diabetes

Type 2 diabetes (T2D) is the most common type of diabetes mellitus and is mainly characterized by insulin resistance, β-cell dysfunction, and elevated hepatic glucose output. Metformin is a first-line antihyperglycemic agent that works mainly by regulating hepatic glucose production and peripheral insulin sensitivity. Metformin has been clinically applied for more than half a century, although the underlying pharmacological mechanisms remain elusive. This current review mainly focused on the development history of metformin and related preclinical studies on structural modification, pharmacological mechanisms for treatment of T2D, toxicology, pharmacokinetics, and pharmaceutics. The pharmacological function of metformin in lowering hyperglycemia suggests that multi-targeting could be an effective strategy for the discovery of new anti-diabetic drugs. A number of discoveries have revealed the pharmacologic mechanisms of metformin; however, precise mechanisms remain unclear. Deeper investigations on the biological features of metformin are expected to provide more rational applications and indications of this evergreen anti-T2D agent, which will in turn help to better understand the complicated pathogenesis of T2D.

Biocompatible sulfenamide and sulfonamide derivatives of metformin can exert beneficial effects on plasma haemostasis

As the pharmacokinetic properties of metformin are unfavourable, several analogues and prodrugs have been synthesised to improve its bioavailability. The aim of this study was to assess the plasma stability of sulfenamide and sulfonamide derivatives of metformin and establish their effects on plasma haemostasis and integrity of red blood cells (RBCs). The overall haemostasis potential was evaluated spectrophotometrically by clot formation and lysis test (CL-test). PT (Prothrombin Time) and APTT (Activated Partial Tromboplastin Time) were used to evaluate the effects if the compounds on the extrinsic and intrinsic coagulation pathway. Haemolysis assay, microscopy and flow cytometry studies were conducted to determine the effect of the compounds on RBCs. Two sulfonamide and one sulfenamide derivatives of metformin were associated with a statistically significant decrease in the overall potential of clot formation and fibrinolysis (↓ CL_AUC), suggesting that these compounds may exert beneficial effects regarding plasma haemostasis, which is frequently impaired in diabetic patients. p- and o-Nitrobenzene sulfonamides contributed to the beneficial change in kinetic parameters of clot formation and fibrinolysis. o-Nitrobenzene sulfonamide significantly increased thrombin generation time (↑ TGt) and was also found to prolong both APTT and PT. All compounds did not exert any effects on the integrity of RBCs over the concentration range 0.006-0.6 μmol/mL which constitutes the expected therapeutic concentration. In conclusion, sulfonamide derivatives of metformin present potentially beneficial properties in terms of plasma haemostasis which is frequently impaired in T2DM patients. Therefore, metformin sulfonamides may become a prototype for further design and synthesis of novel metformin analogues and prodrugs with improved pharmacokinetic properties.

Metformin - a Future Therapy for Neurodegenerative Diseases : Theme: Drug Discovery, Development and Delivery in Alzheimer's Disease Guest Editor: Davide Brambilla

Type 2 diabetes mellitus (T2DM) is a complex, chronic and progressive metabolic disease, which is characterized by relative insulin deficiency, insulin resistance, and high glucose levels in blood. Esteemed published articles and epidemiological data exhibit an increased risk of developing Alzheimer's disease (AD) in diabetic pateints. Metformin is the most frequently used oral anti-diabetic drug, which apart from hypoglycaemic activity, improves serum lipid profiles, positively influences the process of haemostasis, and possesses anti-inflammatory properties. Recently, scientists have put their efforts in establishing metformin's role in the treatment of neurodegenerative diseases, such as AD, amnestic mild cognitive impairment and Parkinson's disease. Results of several clinical studies confirm that long term use of metformin in diabetic patients contributes to better cognitive function, compared to participants using other anti-diabetic drugs. The exact mechanism of metformin's advantageous activity in AD is not fully understood, but scientists claim that activation of AMPK-dependent pathways in human neural stem cells might be responsible for the neuroprotective activity of metformin. Metformin was also found to markedly decease Beta-secretase 1 (BACE1) protein expression and activity in cell culture models and in vivo, thereby reducing BACE1 cleavage products and the production of Aβ (β-amyloid). Furthermore, there is also some evidence that metformin decreases the activity of acetylcholinesterase (AChE), which is responsible for the degradation of acetylcholine (Ach), a neurotransmitter involved in the process of learning and memory. In regard to the beneficial effects of metformin, its anti-inflammatory and anti-oxidative properties cannot be omitted. Numerous in vitro and in vivo studies have confirmed that metformin ameliorates oxidative damage.

Metformin and Its Sulfenamide Prodrugs Inhibit Human Cholinesterase Activity

The results of epidemiological and pathophysiological studies suggest that type 2 diabetes mellitus (T2DM) may predispose to Alzheimer's disease (AD). The two conditions present similar glucose levels, insulin resistance, and biochemical etiologies such as inflammation and oxidative stress. The diabetic state also contributes to increased acetylcholinesterase (AChE) activity, which is one of the factors leading to neurodegeneration in AD. The aim of this study was to assess in vitro the effects of metformin, phenformin, and metformin sulfenamide prodrugs on the activity of human AChE and butyrylcholinesterase (BuChE) and establish the type of inhibition. Metformin inhibited 50% of the AChE activity at micromolar concentrations (2.35 μmol/mL, mixed type of inhibition) and seemed to be selective towards AChE since it presented low anti-BuChE activity. The tested metformin prodrugs inhibited cholinesterases (ChE) at nanomolar range and thus were more active than metformin or phenformin. The cyclohexyl sulfenamide prodrug demonstrated the highest activity towards both AChE (IC₅₀ = 890 nmol/mL, noncompetitive inhibition) and BuChE (IC₅₀ = 28 nmol/mL, mixed type inhibition), while the octyl sulfenamide prodrug did not present anti-AChE activity, but exhibited mixed inhibition towards BuChE (IC₅₀ = 184 nmol/mL). Therefore, these two bulkier prodrugs were concluded to be the most selective compounds for BuChE over AChE. In conclusion, it was demonstrated that biguanides present a novel class of inhibitors for AChE and BuChE and encourages further studies of these compounds for developing both selective and nonselective inhibitors of ChEs in the future.

New prodrugs of metformin do not influence the overall haemostasis potential and integrity of the erythrocyte membrane

Although metformin, an oral anti-diabetic drug, has been found to have multidirectional effects over the past decade, it is characterised by unfavourable pharmacokinetic properties. This study discusses the effects of metformin, phenformin and three prodrugs of metformin on the haemostasis and integrity of Red Blood Cells (RBCs). The influence of examined biguanide derivatives on haemostasis was evaluated spectrophotometrically by clot formation and lysis test (CL-test) at 405nm. The extrinsic and intrinsic coagulation pathway were examined by measuring the PT (Prothrombin Time) and aPTT (Activated Partial Tromboplastin Time). Haemolysis assay, microscopy and flow cytometry studies were used to assess the effect of the tested compounds on RBCs. Although none of the tested biguanide derivatives significantly influenced the overall potential of clot formation and fibrinolysis (CL_AUC constants), statistically significant changes were seen in the values of the kinetic parameters of fibrinolysis. Furthermore, only prodrug 2, with an 8-carbon alkyl chain, unfavourably affected RBCs by interaction with the erythrocyte membrane leading to significant haemolysis. Our results provide a further insight into the effects of metformin and its prodrugs on haemostasis and RBCs and underscore the necessity for further research.