Insights to the emerging potential of glucokinase activators as antidiabetic agent

ABSTRACT

The glucokinase enzyme (belongs to the hexokinase family) is present in liver cells and β-cells of the pancreas. Glucokinase acts as a catalyst in the conversion of glucose-6-phosphate from glucose which is rate-limiting step in glucose metabolism. Glucokinase becomes malfunctional or remains inactivated in diabetes. Glucokinase activators are compounds that bind at the allosteric site of the glucokinase enzyme and activate it. This article highlights the patent and recent research papers history with possible SAR from year 2014–2023. The data comprises the discussion of novel chemotypes (GKAs) that are being targeted for drug development and entered into clinical trials. GK activators have attracted massive interest since successful results have been reported from clinical trials data.

Plain language summary

Article highlights.

Background

• Glucokinase enzyme becomes malfunctional or remains inactivated in diabetes.

• Glucokinase activators act as novel target in the management of diabetes Type II by restoration of normal blood glucose without causing hypoglycemia (common side effect of currently available diabetes medicines).

Potential new treatments

• The data comprises the discussion of novel chemotypes (GKAs) that are being targeted for drug development and entered into clinical trials.

Discussion

• It is analyzed that the core nucleus was designed on the basis of crucial H-bond interaction with Arg 63 residue to act as glucokinase activator. So, all the potent compounds possess either N heterocyclic moieties or amide linkage to bind with Arg 63.

Conclusion

• There is an imperative need to focus on glucokinase activators for designing of new drugs that are potent, exhibit better efficacy and safety profile. These compounds (GKAs) can be used as an alternative for the treatment of Type II diabetes.

1. Introduction

One of the persistent diseases globally is diabetes which occurs either due to dysfunction of pancreatic β-cell which leads to the reduction in the production of insulin or body cells not being able to use the insulin produced efficiently [1–3]. The blood sugar level is maintained by insulin which helps in the uptake of glucose by body cells to generate ATP (Adenosine triphosphate) [4,5]. Diabetes is characterized by hyperglycemia, leads to severe damage to the body's system such as blood vessels and nerves [6–8]. Diabetes can be classified into different types.

1.1. Prediabetes

It is a persistent metabolic state which is diagnosed by a raise in the upper threshold than normal but below the threshold for considering under diabetes [9,10]. The prediabetes condition is manifested by the rise in blood sugar level as compared with the normal blood sugar level (70 mg/dL-100 mg/dL) but not in the range of rising such that can be considered under the class of diabetes [11,12]. Prior to diabetes mellitus, prediabetes is the predecessor. Most of the people are not aware of prediabetes as there are no signs and symptoms [13,14]. As per American Diabetes Association, prediabetes is manifested by elevated plasma glucose level (100 mg/dL-125 mg/dL) during the fasting state, a rise in plasma glucose level after an oral glucose tolerance test (140–199 mg/dL) [15,16]. Prediabetes is a reversible condition that can be modified back to normal by changing the lifestyle such as loss of weight, increase in physical activity and dietary changes [17–19]. The blood glucose level in different conditions as discussed below.

1.1.1. Gestational diabetes

In the pregnant women manifested with the increased blood sugar level which comes into existence due to some reasons such as insulin resistance, autoimmune disorders [20–22]. Obesity can be the major cause of the development of gestational diabetes mellitus. It leads to a rise in a foetus and maternal complications [23–25]. It is observed in 5% of the gestation cases but this number is continuously increasing due to unhealthy lifestyles such as obesity, lack of physical exercise, junk foods and increased sweet foods intake [26–28].

1.1.2. Diabetes type 1

It is a chronic metabolic state which is characterized by the destruction of the β-cell of the pancreas that leads to either litter or no insulin production [29,30]. It is determined by the rise in glucose level of blood (hyperglycemia) due to lack of insulin. The type 1 diabetes also referred to as insulin-dependent diabetes or juvenile diabetes affects 5–10 percent of diabetics [31,32]. It is most usual age to be diagnosed with type 1 Diabetes frequent in children, adolescents, or young adults. Here, the immune system and specifically T-cells are aware that insulin producing beta cells in the pancreas are foreign and proceed to destroy them [33–35]. Because insulin is so important in decreasing the amount of glucose in the blood through its transport into the cells, a lack of insulin results in increased blood sugar levels. People with type 1 diabetes stave their lives to insulin injections and their most basic need for regulating blood sugar. This disease requires a constant medical management as far as health is concerned in order to avoid adverse impacts [36,37].

1.1.3. Diabetes Type II

It is a disease that is characterized by a rise in blood glucose level than normal level. It is the most common class of diabetes. During this state, there is a reduced or no response to insulin which is known as insulin resistance [38–40]. It is also called non-insulin-dependent diabetes mellitus. The most affected people due to diabetes Type II belong to middle-aged or older people [41,42]. Various factors such as overweight, genetic, β-cell broken, or inability of cells to communicate and pass a signal that all contribute to insulin resistance [43,44]. There are a lot of risk factors that are responsible for inducing Type II diabetes (T2DM) like high blood pressure, prediabetes, gestational diabetes, depression and polycystic ovary syndrome [45,46].

1.2. Prevalence of diabetes Type II

Both developing and developed countries are being affected by this disease as it spreads across the globe with time [47,48]. Diabetes affects 537 million adults between 20 to 79 years old, according to the IDF (International diabetes federation) Diabetes Atlas 2021, the tenth edition [49,50]. As a consequence, diabetes is estimated to cause 6.7 million deaths in 2021. Diabetes patients are expected to increase from 643 million in 2030 to 783 million in 2045 as per estimates [51,52]. Diabetes affects more than four in five adults (81%) living in middle and low-income countries [53,54]. There have been at least USD 966 billion in health expenditures associated with diabetes in the past 15 years (an increase of 316%). Diabetes remains largely undiagnosed in about 46.5% of adults [55–57].

The cytoplasmic enzyme glucokinase is responsible for phosphorylating glucose into glucose-6-phosphate in the body. GK (glucokinase) expression is predominantly found in pancreatic β-cells and liver hepatocytes [58]. GSIR (glucose-stimulated insulin release) is elicited by GK in pancreatic β-cells. The rate of glucose phosphorylation in β-pancreatic cells is directly proportional to the level of glucose in the tissues. A glucose phosphorylation rate constrains insulin secretion. In order to maintain a balanced ATP/ADP (Adenosine diphosphate) ratio, glucokinase regulates oxidative ATP production and glycolysis. A rise in membrane potential stimulates the opening of the L-type calcium channel-mediated by GK. It has been observed that Ca²⁺ facilitates the release of insulin in this process [59]. Pancreatic islets can recover their calcium response to glucose and insulin secretion by activating GK (Figure 1). Glucose metabolism in hepatocytes is dependent on GK. Glucokinase regulatory protein (GKRP) acts as an endogenous inhibitor that modulates hepatic glucokinase activity, which provokes insulin release [60].

Figure 1.

Insulin secretion is aided by the activation of the glucokinase enzyme to control blood glucose levels in the body.

At low glucose concentrations, glucokinase is located in the nucleus as an inactive complex with GKRP. GKAs bind to the allosteric site of the glucokinase enzyme. GKAs could activate glucokinase both directly and by destabilizing the glucokinase/GKRP (Glucokinase regulatory protein) complex [61]. Glucokinase is dissociated from the glucokinase/GKRP complex when the blood glucose level increases and is translocated to the cytoplasm. Thus, increased GK activity in the high glucose state results from the fact that GK dissociates with its GKRP is true. Nevertheless, the employ of glucokinase activator molecules in diabetes treatment is useful not only for one but several reasons [62]. Firstly, GKAs increase the enzyme's affinity for glucose and stimulate additional accelerated catalytic activity that cannot be achieved solely on the presence of high glucose concentrations to ensure optimal glucose utilization. Secondly, in diabetes the regulatory steps through glucokinase and its transporter protein may not function as required because of the insulin resistance or β-cell dysfunction and GKAs prevent the complications by maintaining the uninterrupted activation of glucokinase [63]. Furthermore, GKAs keep the glucokinase activity within a certain baseline level, or turn it on and off as needed, so that the patient may avoid damaging spikes and dips in their blood sugar levels [64]. They also augment the deficiency of glucokinase quantities in some types of diabetics by increasing the effectiveness of the existing enzyme. Last but not least; GKAs can be combined with other diabetic therapies to manage glycemic levels effectively in patients who gets worst with conventional anti-diabetic medication singly [65]. Hence, although basal and hepatic glucokinase functions naturally increase with high glucose levels, glucokinase activators (GKAs) hold a significant function in glucose management in diabetic patients. GKAs improved glucose tolerance not only by stimulating insulin secretion, but also by promoting glycolysis and glycogen synthesis (Figure 1). GK in glucose metabolism differs in function in pancreatic β-cells and hepatocytes, where its prominence is essential. In the pancreatic β-cells precisely, GK grips the utility of a glucose receptor. GK controls glucose metabolism by phosphorylating glucose at numerous tissues therefore endorsing glycolysis and boosted ATP formation when blood glucose is high [66]. This outcome in the shutting of ATP sensitive K⁺ channels which in turn unlocks the Na⁺ channels and crafts membrane depolarization. This leads to an escalation in the inaugural of explicit voltage-gated Ca⁺² ion channels and permitting the invasion of Ca⁺² ions hence liberating insulin to diminish high levels of blood glucose. Lactate dehydrogenase is associated to glucose metabolism in firm specializations of hepatocytes, in which GK is also located [67,68]. Here, GK is repressed by GKRP exclusively at low glucose concentration meaning it is reserved within the nucleus and has no catalytic activity. Amplified glucose levels lead to glucose and fructose-1-phosphate instigating the proclamation of GK from its inhibitory protein, GKRP, thus stimulating GK. GK is then elicited and produce glucose-6-phosphate by phosphorylating glucose, this ensues to the glycogenesis or glycolysis alleyways [69]. This mechanism aids hepatocytes in facilitating control the glucose in the blood stream by storing an additional glucose as glycogen for imminent use so as to preserve a balance of glucose levels in the blood. Hoffmann-La Roche AG first reported the small molecule RO-281675 (Figure 7) as a GKA in 2003 [70,71]. At a concentration of 3 μM, RO-281675 induced a 1.5-fold increase in the maximum metabolic rate (V_max) of GK. In addition, the substrate concentration [S_0.5] glucose at half of the V_max was decreased from 86 mM to 20 mmol/L. This demonstrates that GK could be a potential target for diabetes management [72]. Unfortunately, this compound did not undergo clinical trials due to its cardiovascular risk. Despite not reaching clinical trials, this compound paved the way for pharmaceutical companies to develop efficient and safe GKAs [73,74]. A wide variety of molecules including benzamides [75–78], acrylamides [79], propenamide [80], carboxamides [81], acetamides [82,83], benzimidazoles [84], quinazolines [85], urea [86,87], pyrimidone [88] and pyridines [89] derivatives have been reported in the last few years to act as potential GK activators. These heterocycles molecules contain nitrogen, sulfur, oxygen and amide linkages that are vital for binding to the allosteric site of GK and activating its functions [90]. Taking into consideration these ligand-GK interaction data, the researchers explored the different core nucleus for developing a novel GKA with better potency, efficacy, improved physicochemical properties and reduced toxicity [91].

Figure 7.

5-alkyl-2-urea-substituted pyridine derivatives 16a-b and quinazolin-4-one derivatives 17a-b.

Patent review of GKAs is structured in sections, based on the parent nucleus of the patented ligands.

2. Patent review

2.1. Advinus Therapeutics Limited. US9340506B2

In 2016, Advinus Therapeutics Limited, claimed acetamide derivatives as potent glucokinase activators. Most of the synthesized compounds were found to be potent with EC₅₀ value of <0.5 μM against the GK enzyme. Compounds 1a-j (Figure 2) were claimed to show best activity by raising 90% (E_max) GK activity. The glycogen synthesis data demonstrated that compounds 1a-e has shown >2.5-fold activity at 10 μM. All the compounds were found to be potent glucokinase activator with significant increase in the glycogen synthesis as compared with control DMSO (Dimethyl sulfoxide). Further SAR (Structure activity relationship) data revealed that incorporation of c-propyl ring and 2-substituted phenyl-methanol 1a shown the best activity with EC₅₀ values of 0.064 μM having 93% E_max. Compound 1b with 2-methylbenzoic acid was the second-best compound with EC₅₀ value of 0.087 μM and 71% E_max. Further, it was found that compound 1c with 2-(cyclopentylsulfonyl)pyridine ring has shown moderate GK agonism with EC₅₀ value 0.13 μM and E_max 95% while compound 1d has shown less activity. Thus, it was established that heterocyclic ring substitution were having possess greater GK agonism as compared with aromatic ring. 3-substituted benzoic acid derivative 1e has shown EC₅₀ values of 0.19 μM with 91% E_max. Moreover, replacement of tetrahydro-2H-pyran of compound 1b with 2,4-difluorophenyl 1f results in reduced potency with an EC₅₀ value of 0.093 μM having E_max as 89%. It was also found that compound 1g-j has shown good to moderate activity with EC₅₀ value of 0.093–0.17 μM and E_max of 90–95% [92].

Figure 2.

Acetamide derivatives 1a-j and indole derivatives 2a-j.

2.2. Takeda Pharmaceutical Company Limited. US8957070B2

Takeda pharmaceutical company limited has continued to be active in the field of GKA research, advancing with their work on GKAs further submitted a patent application in 2015. A series of substituted indole derivatives 2a-j (Figure 2) were discovered and evaluation was done using GK enzyme-based assay. In vitro results, it was found that substitution with methyl and thiazol-5-yl methanol led to compound of series compound 2a with EC₅₀ value is 0.019 μM. The replacement with the trifluoromethoxy group led to compound to 2b (EC₅₀ = 0.022 μM) which has slightly decreased activity as compared with 2a. Furthermore, Compound 2c with 4,5-dihydrothiazole and 2d with 4,5-dihydrothiazole with a fluoro at 5th position of indole ring has shown equipotent activity with EC₅₀ value of 0.027 & 0.028 μM, respectively. Apart from that, it was also found that compound 2e with thiazole ring on indole has same activity as compared with compound 2d (EC₅₀ = 0.028 μM). The replacement with ethyl resulted in compound 2f which has weak activity with EC₅₀ value of 0.034 μM. Compound 2g holds ethyl and 4-(thiazol-5-ylmethoxy)benzoic acid along with substitution at 4th position of indole ring with chloro exhibits weak activity with an EC₅₀ value of 0.035 μM. Compound 2h, 2i & 2j were found to be weak compounds of the series with EC₅₀ value of 0.048, 0.077 & 0.08 μM, respectively [93].

2.3. F. Hoffmann-La Roche Ag. AU2009237792B2

F. Hoffmann-La Roche Ag filed a patent of pyridazinone derivatives as GK activators for the treatment of Type II diabetes (T2D). In vivo glucokinase activity of the synthesized derivatives was done, compound 3a-c (Figure 3) exhibits higher % glucose-lowering activity at 4 hours post 50 mg/kg dose in lean C57BL/6J mice along with good potency. Compound 3a appended with methyl and 2-methyl-1-(1H-pyrazol-1-yl)propan-2-ol exhibited an EC₅₀ value of 0.174 μM (62.7% glucose-lowering). In compound 3b substitution with c-pentyl and nicotinic acid results in elevated potency as EC₅₀ value is 0.063 μM (60.9% glucose-lowering). The substitution with fluoro and 2-methyl-1-(1H-pyrazol-1-yl)propan-2-ol resulted in compound 3c that illustrates lower potency with 0.312 μM (EC₅₀ value) and raised % glucose-lowering as 61.7%. In vitro GK enzyme assay revealed that the compounds 3d-g (Figure 3) exhibit potent antidiabetic activity by increasing the flux of glucose metabolism which results in increased insulin secretion. SC_1.5 value was calculated for compounds with the aid of in vitro GK enzyme assay and it is defined as the concentration of activator at which there was a 50% increase in the activity of GK. Compound 3d comprehends di-fluoro groups and methyl nicotinate substitution showed the most potent activity with EC₅₀ value 0.008 μM. While S isomer of compound 3d exhibit less potency (EC₅₀ = 0.013 μM) as compared with compound 3d. The substitution with fluoro and nicotinic acid escalate compound 3e with EC₅₀ value 0.026 μM. In compound 3f removal of fluoro group at R₂ results in decreased potency as EC₅₀ value 0.033 μM. The removal of other fluoro resulted in compound 3h that exhibits reduced potency with EC₅₀ value 0.034 μM. The replacement with methyl group gives rise to compound 3g showing equipotent activity as compared with 3h with EC₅₀ value 0.033 μM [94].

Figure 3.

Pyridazinone derivatives 3a-h and substituted pyridine-2-carboxamide derivatives 4a-h.

2.4. Merck Sharp & Dohme Corp. WO2014099578A1

Merck Sharp & Dohme Corp. has filed a patent application on glucokinase activators useful for the treatment of T2D, obesity and metabolic syndrome. A series of substituted pyridine based compounds were synthesized 4a-h (Figure 3) and evaluated them by the enzyme-based assay. From the results, it was revealed that compound 4a with sulfonyl-methane and methyl propionate exhibit an EC₅₀ value of 3.8 nM. In compound 4b increase in potency (EC₅₀ = 1.9 nM) was observed when replaced with sulfonyl-ethane. The replacement of pyridyl moiety of compound 4h with pyrazine escalates compound 4c which has enhanced potency with EC₅₀ value of 2.1 nM [95]. Compound 4d with methyl pentanoate (longer alkyl chain ester), escalates has moderate activity with EC₅₀ value of 4.3 nM. In contrast, substitution with acetic acid generated compound 4g with reduced potency as EC₅₀ value of 23.8 nM while substitution with propionic acid, illustrated compound 4e with enhanced potency as EC₅₀ value of 15.1 nM. Compound 4h with methyl propionate as substituent exhibit weaker activity with EC₅₀ values of 39.1 nM while compound 4f with a lower homologue as methyl acetate increased potency (EC₅₀ = 21 nM).

2.5. Pfizer Inc. CA2754681C

In 2014, Pfizer Inc, claimed benzofuranyl derivatives as a potent glucokinase activator. Seven compounds (5a-g) (Figure 4) has shown potent EC₅₀ value and were claimed to possess above 50% raise in the glucokinase enzyme activity (% E_max). The substitution with 5-methylpyrazine and methyl gives rise to compound 5b demonstrated an effective EC₅₀ value of 0.555 μM and E_max 54.7%. Currently, compound 5b (PB-201) is in the Phase 3 of clinical trials [96]. The alteration of an oxy-pyrimidine moiety of compound 5b with oxy-pyrazine escalates compound 5a has possessed EC₅₀ value 0.412 μM and E_max 60.8%. Compound 5c with 5-methoxypyrazine resulted in raised potency with glucokinase activity as EC₅₀ value 0.462 μM and E_max 69.5%. The substitution of 5-methylpyrazine and ethyl resulted in compound 5e which possessed almost equipotent activity as that of compound 5b with EC₅₀ value 0.546 μM and E_max 57.6%. The alteration of an oxy-pyrimidine moiety of compound 5c with oxy-pyrazine furnished compound 5g which exhibited elevated potency with EC₅₀ value 0.474 μM and E_max 63.4%. Compound 5d with 1-methyl-1H-pyrazole and N,N-dimethyl substitution exhibited moderate activity with EC₅₀ value of 0.629 μM and E_max 63.9%. Moreover, compound 5f with N-ethyl-N-methylamine has shown the enhanced activity with EC₅₀ value of 0.382 μM and E_max of 54.1% as compared with 5d [97].

Figure 4.

Benzofuranyl derivatives 5a-g and phosphonate derivatives 6a-j.

2.6. Bristol-Myers Squibb. EP2059522B1

Bristol-Myers Squibb filed a patent application for the preparation of phosphonate and phosphinate compounds as GK activators for the treatment of T2D. All the synthesized compounds 6a-j were biologically evaluated for the glucokinase activity and in vivo evaluation indicated that compound 6a-f (Figure 4) exhibits a higher % reduction in glucose at 30 mg/kg dose in male DIO (diet-induced obese) C57BL/6J mice along with good potency. Compound 6a which was substituted with diethyl(thiazol-4-ylmethyl)phosphonate exhibited EC₅₀ value of 34 nM (88% glucose-lowering) and replacement with ethyl methyl(thiazol-4-ylmethyl)phosphinate yielded compound 6b with moderate activity (EC₅₀ = 49 nM & 62–82% glucose-lowering). Compound 6d with diethyl(pyrazin-2-yl methyl)phosphonate has shown EC₅₀ value of 564 nM (62–80% glucose-lowering). Further, the replacement with diethyl(pyridin-3-ylmethyl)phosphonate was done which yielded compound 6c which was found to be moderate to weak activity with EC₅₀ value of 98 nM (66–78% glucose-lowering). In compound 6e, diethyl((1H-pyrazol-1-yl)methyl) phosphonate substitution has shown moderate activity with EC₅₀ value of 65 nM with a significant 79% glucose-lowering effect. Moreover, (thiazol-4-yl)methyl)methylphosphonate was incorporated to yield compound 6f with better activity with EC₅₀ value of 18 nM but lower % for glucose-lowering was weaker (44%). In vitro GK enzyme assay concluded that the compounds 6g-j exhibit potent antidiabetic activity. The compound 6g comprehend 2-(thiazol-4-ylmethyl)-1,4,2-dioxaphosphinane-2-oxide substitution results in an potent compound with an EC₅₀ value of 9 nM while compound 6h with diethyl((5-bromothiazol-4-yl)methyl)phosphonate has shown weaker activity (EC₅₀ = 15 nM) compared with 6g. Compound 6i with diethyl((5-chlorothiazol-4-yl)methyl)phosphonate and compound 6j with azetidin-1-yl(pyrazin-2-yl) has shown weaker activity with EC₅₀ value of 22 & 38 nM, respectively [98].

2.7. Foshan Saiweisi Pharmaceutical Technology Co. Ltd.

2.7.1. CN104892505A

Halogenated quinoline derivatives as GK activators for the treatment of T2D were patented by Foshan Saiweisi Pharmaceutical Technology Co. Ltd. In vitro GK enzyme assay revealed that compounds 7a-e (Figure 5) have shown strong antidiabetic action. Substitution with Iodo led compound 7e with an effective EC₅₀ value of 10.3 nM and S_0.5 (substrate concentration at which the rate of reaction is half of the limiting rate) value of 3.5 mM. Bromo appended compound 7d yielded in a better compound in terms of activity (EC₅₀ = 8.8 nM & S_0.5 = 3.0 mM). Compound 7b with chloro was the most potent compound (EC₅₀ = 4.5 nM & S_0.5 = 1.6 mM) when compared with rest of the compounds. Compound 7c with fluoro was the second-best compound of the series with EC₅₀ value of 6.7 nM & S_0.5 value of 2.1 mM. Moreover, unsubstituted compound 7a has shown the reduced activity with EC₅₀ value of 24.1 nM and S_0.5 (5.4 mM) [99].

Figure 5.

Quinoline derivatives 7a-e, adamantane amide derivatives 8a-e, glucosamide derivatives 9a-h, quinolyl derivatives 10a-f and N-substituted-3,5-disubstituted benzamide derivatives 11a-g.

2.7.2. CN104628617A

Foshan Saiweisi Pharmaceutical Technology Co. Ltd. patented N-adamantanyl acetamide based compounds (8a-e) as GK activators for the treatment of T2D. In vitro GK assay revealed that compounds (Figure 5) exhibited good antidiabetic effect. Results of in vitro assay stated that compound 8a with phenyl ring has shown weak activity with EC₅₀ of 21.6 nM and S_0.5 of 3.7 mM, while compound 8b with 4-methylphenyl was the best compound with EC₅₀ value of 5.9 nM & S_0.5 value of 2.6 mM. Compound 8c has shown moderate activity (EC₅₀ = 10.4 nM & S_0.5 = 3.2 mM) which was substituted with 4-ethylphenyl. Compounds 8d comprehends 3-methylphenyl exhibited EC₅₀ value of 8.2 nM, S_0.5 as 2.6 mM. The replacement with 2-methylphenyl escalates compound 8e resulted moderate activity with EC₅₀ value of 9.3 nM, S_0.5 value 3.7 mM. Thus, SAR data revealed that compounds 8b-e linked with phenylmethyl or phenylethyl (alkyl spacer) has better activity as compared with compound 8a which was directly linked to phenyl [100].

2.7.3. CN104672218A

Glucosamide derivatives as GK activators for the treatment of T2D were patented by Foshan Saiweisi Pharmaceutical Technology Co. Ltd. In vitro glucokinase activity of the synthesized derivatives 9a-g was done (Figure 5) and it was revealed that all the compounds exhibited promising antidiabetic activity. All these compounds had substitutions on the pyridine and pyrazine moieties of the common structure. Results of in vitro assay revealed that unsubstituted compound 9c was the weakest compound of the series with EC₅₀ value of 16.2 nM and S_0.5 value of 5.8 mM. Compound 9a with methyl has shown better efficacy (EC₅₀ = 11 nM & S_0.5 = 3.4 mM) as compared with compound 9c. Compound 9b with dimethyl was the most potent compound of the series with good GK activity (EC₅₀ = 4.9 nM & S_0.5 = 2.1 mM). Compound 9g has shown moderate activity with EC₅₀ value of 9.3 nM and S_0.5 value of 3.1 mM. Moreover, diethyl substituted compound 9f illustrated good to moderate activity with EC₅₀ value of 8.9 nM and S_0.5 value of 3 mM while compound 9d with mono ethyl substitution has shown reduced potency with EC₅₀ value of 11.4 nM and S_0.5 as 3.8 mM. Ethyl & methyl substituted compound 9e possessed effective EC₅₀ value of 7.1 nM and a S_0.5 of 2.7 mM as compared with all other compounds except 9b [101].

2.7.4. CN104557698A

In the realm of GKA research, Foshan Saiweisi Pharmaceutical Technology Co. Ltd. filed a patent application in 2015. A series of quinolyl and alkoxylphenyl derivatives was synthesized 10a-f (Figure 5) and biologically evaluated by GK enzyme-based assay. Compound 10a with methoxy and acetamide exhibited most potent activity with an EC₅₀ value of 9.4 nM, S_0.5 of 2.1 mM as compared with other derivatives of the same series. The substitution with hydroxy yielded compound 10b that displayed weaker activity with EC₅₀ value of 15.3 nM & S_0.5 of 3.6 mM. Ethoxy and acetamide appended compound 10c offered moderate activity with EC₅₀ value of 10.2 nM & S_0.5 of 2.7 mM. Furthermore, it was revealed that propionamide based compound 10f has also shown moderate and equipotent activity with EC₅₀ values of 11.7 nM & S_0.5 of 2.9 mM as compared with compound 10c. Compound 10e with methoxy and propionamide has shown moderate activity (EC₅₀ = 11 nM & S_0.5 = 3.9 mM) while conversion of methoxy to hydroxy yielded compound 10d with weaker activity (EC₅₀ = 16.6 nM & S_0.5 = 3.2 mM) [102].

2.8. Shanghai Inst. Materia Medica. WO2016112863A1

Shanghai Inst Materia Medica had filed a patent including the development of N-substituted-3,5-disubstituted benzamide derivatives 11a-g (Figure 5) as GK activators for the treatment of T2D. Result of biological evaluation revealed that compound 11c with N,N-dimethylformamide and tert-butyl formate has exhibited effective EC₅₀ value of 0.09 μmol/L. Moreover, it was also noticed that replacement of N,N-dimethylformamide with azetidine-1-carbonyl (11d) helped in retaining the activity (EC₅₀ = 0.1 μmol/L). Furthermore, it was also established that replacement of N,N-dimethylformamide with methylsulfonyl and tert-butyl formate with pyridyl (11d) did not cause any loss or gain in activity (EC₅₀ = 0.1 μmol/L). Compound 11a comprehends methylsulfonyl along with acetamide illustrated as the best compound with EC₅₀ of 0.04 μmol/L while replacement of 1-methoxy-propanoxy of 11a with i-propoxy (11b) has shown equipotent activity as EC₅₀ value of 0.05 μmol/L. Compound 11f with ethylsulfonyl and tert-butyl formate has shown reduction in activity with EC₅₀ value of 0.14 μmol/L while Compound 11g with methylsulfonyl and tert-butyl formate has shown weaker activity (EC₅₀ = 0.2 μmol/L) [103].

2.9. 3,5-disubstituted benzamide derivatives

Based on pharmacophoric requirements for ligand binding to the GK protein (with Arg63 residue by H-bond interaction, is vital for GK activity) various substitutions were employed on the benzamide nucleus in the search of a potent antidiabetic agent. Results revealed that compounds 12a-f were designed and docking studies of these compounds indicated that these exhibit significant binding interactions with the allosteric site of GK protein with Arg63. In vitro GK assay revealed that compounds 12a-f (Figure 6) showed promising GK activity with EC₅₀ value of ranging from 1.68–2.11 μM. Glucose lowering effect of these derivatives were assessed using OGTT (Oral glucose tolerance test) assays and AUC (Area under curve) & blood glucose levels were measured at different time intervals such as 0, 30, 60, 90 and 120 min following oral glucose administration. OGTT assay revealed that compound 12a-c hadn't shown any significance reduction in the blood glucose level and AUC while compounds 12d-f had shown significant reduction in blood glucose level i.e., 250, 240, 260 mg/dL at 120 min, respectively as compared with marketed drug metformin (230 mg/dL). From the results, it was identified that compound containing benzene sulphonamide substituted with N-(pyrimidin-2-yl)formamide were less potent as compared with compound containing benzene sulphonamide substituted with N-(thiophen-2-yl)formamide [104].

Figure 6.

Substituted benzamide derivatives 12a-f, 13a-e, 14a-d and 15a-g.

2.10. Sulfonamido-benzamide hybrids

The carboxyl (C=O) group and amino (-NH) group of benzamide are responsible for binding to the allosteric site of the GK enzyme while interacting with the key residue like Arg63 but poor oral bioavailability was one of the major concerns for these kinds of derivatives. In order to improve oral bioavailability, researchers modified the amino group of the benzamide by adding heterocyclic rings and synthesized compounds 13a-e (Figure 6) which revealed good GK activation upon biological evaluation. Compound 13a with methyl and 5-chloro-thiazole substitution was the most potent compound of the series with EC₅₀ value of 495 nM, while replacement with 4-methylphenyl (compound 13d) has lowered the GK activation (EC₅₀ as 657 nM). 6-methylbenzothiazole and methyl derivative 13b was shown to have better activity (EC₅₀ = 522 nM) as compared with 13d. Compound 13e with 6-methylbenzothiazole and 4-methylphenyl has shown weaker activity with EC₅₀ of 836 nM as compared with 13b. 5-methyl-1,3,4-thiadiazole replacement yielded compound 13c which was the weaker compound of the series (EC₅₀ = 958 nM). In-vivo OGTT assay revealed that compound 13a has shown maximum reduction in blood glucose level (135 mg/dL at 120 min) followed by compound 13b (142 mg/dL at 120 min) as compared with control. The compounds 13d and 13e showed a moderate reduction in blood glucose levels 168 mg/dL and 162mg/dL, respectively. Compound 13c showed a similar pattern of blood glucose reduction as that of control i.e. 172 mg/dL [105].

2.11. Thiazol-2-yl benzamide derivatives

The benzamide nucleus substituted with thiazol-2yl at amido nitrogen was known to enhance GK activation. So, further compounds 14a-d (Figure 6) were synthesized and biological evaluation was done. In vitro enzymatic assay revealed that all the synthesized compounds had a good profile of GK activation. Moreover, biological evaluation revealed that compounds 14a-d was found to have good GK activation by 1.65, 1.74, 1.48 and 1.82-fold respectively as compare to control. Results of OGTT assay revealed that compound 14d reduced blood glucose equipotent to that of the standard drug metformin (125 mg/dL at 120 min time interval). From the SAR data, it was assessed that EWGs like chloro was beneficial for anti-diabetic activity as compare to EDGs [106].

2.12. N-benzothiazol-2-yl benzamide derivatives

The N-benzothiazol-2-yl was attached to the benzamide nucleus to form novel GKA derivatives. Compound 15a-g (Figure 6) exhibited hydrogen bond interaction with Arg63 residue (essential for GK activity) and has dock scores in range of -9.9 to -8.4 kcal/mol. Compound 15a-d with N-(2-methylphenyl), N-4-bromophenyl, N-phenyl, N-2-chloro-4-nitrophenyl exhibited GK activation by 1.97, 1.84, 1.66, 1.69 folds, respectively as compared with control. Compounds 15a-d exhibited improved GK activity when phenyl moieties were substituted while compounds with aliphatic chain (15e) has reduced potential with 1.34-fold GK activation. In contrast substitution with a higher alkyl homologue such as N-propyl in compound 15f and N-butyl in compound 15g, both remain ineffective in the GK assay. The docking results were also in compliance with the in vitro GK assay [107].

2.13. 5-Alkyl-2-urea-substituted pyridines

Dransfield et al., designed, synthesized and evaluated 5-alkyl-2-urea-substituted pyridines derivatives 16a-b (Figure 7) for the GK activity. From the results, it was estimated that c-butanol appended compound 16a with higher S_0.5 with EC₅₀ value of 110 nM, S_0.5 of 0.66 and V_max of 0.97 as compared with AM-2394 (EC₅₀ = 65 nM, S_0.5 = 0.64 and V_max = 1) [108]. Further, OGTT assay was conducted at the doses of 3, 10, 30 and 100 mg/kg and it was assessed that compound 16a reduces blood glucose levels in a dose-dependent manner (32% OGTT-AUC reduction at 30 mg/kg). Moreover, compound 16b comprehends tetrahydro-2H-pyran exhibited EC₅₀ value of 160 nM, S_0.5 value of 0.65 and V_max value of 1.1. OGTT assay revealed a dose-proportional decrease in blood glucose levels with 16b at doses of 3, 10, 30 and 100 mg/kg. Compound 16b also displayed a 40% reduction in AUC at 100 mg/kg. Compounds 16a and 16b demonstrated acceptable clearance, better oral bioavailability and successfully reduced plasma glucose levels in rodents [109].

2.14. Quinazolin-4-one derivatives

Design, synthesis and evaluation of clubbed thiazole acetates and acetamide derivatives of quinazolin-4-one as GKA was studied by Khadse et al. Initially, a docking study was done to evaluate the binding mode and interactions of these derivatives for best-fit conformations in the allosteric site of the human glucokinase enzyme (PDB ID: 1V4S). The docking result concluded that compounds 17a and 17b (Figure 7) have the good & comparable docking scores as -6.44 & -6.24 kcal/mol, respectively as compared with standard RO-28-1675 (-6.39) and piragliatin (-7.89). Compound 17a shows two hydrogen bond interactions, first with carbonyl oxygen (C=O) of acetate group with Arg63 & second with N¹ of quinazolinone ring and Thr65. Compound 17b exhibited three hydrogen bond interactions; one with NH of the amide group and Tyr61, second with N of thiazole ring and Arg63 and third with N¹ of quinazolinone ring and Tyr214 (Figure 7). In vitro assay revealed that compound 17a (EC₅₀ = 632 nM) and compound 17b (EC₅₀ = 516 nM) demonstrated moderate GK activation as compared with RO-281675 (EC₅₀ = 382 nM) & Piragliatin (EC₅₀ = 393 nM). Moreover, OGTT assay revealed that compounds 17a and 17b exhibited significantly reduced blood glucose levels to almost normal at 133 mg/dL and 135 mg/dL, respectively [110].

3. Clinical trial status

Through the joint action of the pancreas and liver, GKA is a novel class of drugs for the treatment of diabetes, which provides the body with a greater sensitivity to glucose. Some small-molecule-reported GKAs have entered the clinical stage of research at present. Novel GKAs such as PB-201, Dorzagliatin (Phase 3), AZD-1656, TTP-399 (Phase 2) and Globalagliatin, MK-0941, ARRY-403 (Phase 1) (Table 1) are still attracting a lot of attention in the pharmaceutical business [96,111–116].

Table 1.

Glucokinase activator under clinical trials.

Sr. No.	Name/Code	Structure	Status	Ref.
1.	PB-201		Phase 3	[96]
2.	Dorzagliatin		Phase 3	[111]
3.	AZD-1656		Phase 2	[112]
4.	TTP399	ND	Phase 2	[113]
5.	Globalagliatin		Phase 1	[114]
6.	MK-0941		Phase 1	[115]
7.	ARRY-403		Phase 1	[116]

4. Discussion

There are numerous pathophysiological verdicts related to diabetes, mostly with T2D where the GK has been initiate to be depressed synchronized in hepatocytes and pancreatic β-cells impeding precise glucose regulation. When the mouse is in a normal state, GK is usually articulated together in α-TC1 and β-TC6 cells which demeanor glucose sensing, insulin exudation and glycogen production. Nevertheless, researchers have conveyed that abridged expression and movement of the enzyme known as GK predominant in diabetes. Consequently, a diminution in GK in pancreatic β-cells consequences in poor insulin secretion in response to glucose, which augments hyperglycemia. In the same esteem, hepatocytes involved declined levels of GK which principals to moderated glucose phosphorylation and thus glycogen formation, storage and enhanced blood glucose levels. On the other hand, the comparative decrease in the expression and activity of GK in diabetes invades the kinetic equilibrium that sustains glucose homeostasis. It is thus momentous in the diabetic state because GKAs endorse instigation of glucokinase regardless of its notch of downregulation. High levels of GKAs enrich the feasting of glucose in the liver and rouse the release of insulin in the β-cells, which directly counteracts the effects of low GK expression. Returning the glucose metabolism and control back to normal, this tactic authorizes the efficiency of GKAs in treating diabetes. The specific involvement of hepatic GK in glucose metabolism has been well documented in both the physiological and pathological condition. Lack of GK is identified in the pancreatic β-cells and hepatocytes and is noted for its great physiological importance. In the pancreatic β-cells located in the liver, there is a very important enzyme called glucokinase, also called hexokinase IV, which plays an essential role in recognizing glucose and the suppressing of insulin. However, when the glucose levels are high, the enzyme GK phosphorylates glucose resulting in the formation glucose-6-phosphate. The type of reaction is phosphate transfer. This in turn generates ATP and insulin secretion is required to balance blood sugar levels. In the liver cells glucokinase is involved in the conversion of glucose to glucose-6-phosphate, which either takes glucose to other metabolic pathways or stores it in glycogen form in the liver cell for later energy requirements. Surprisingly, it has been observed that in certain diseases such as T2D, GK has had symptoms of pathological changes in gene expression and protein synthesis. Reduced activity of GK in pancreatic β-cells reduces the secretion of insulin and when GK action in hepatocytes is suppressed, it reduces glycogen synthesis further contributing toward continuously elevated blood glucose levels. These are largely the dishevelled elements that are accountable for the interruption of metabolic control of the disorder characteristic of diabetes. Understanding these functions helps explain the potential therapeutic roles of GK activators (GKAs) in that they raise the activity of GK and thus help to return the glucose-sensing and -metabolizing capabilities of pancreatic beta-cells to normal levels to be of great use in enhancing glycemic control in individuals with diabetes.

5. Conclusion

Diabetes is a lifelong chronic metabolic disease that affects people all over the world. With the passage of time, the number of persons affected by this condition continues to rise. Small molecule glucokinase activators (GKAs) emerge as a promising treatment option for T2D. In pancreatic β-cells and hepatocytes, glucokinase exerts its influence primarily through modulatory activities. It affects two essential components of glucose homeostasis by coupling insulin secretion in the pancreas with plasma glucose levels and improving glucose utilization in the liver. The substantial glucose-lowering activity shown by GKAs in preclinical T2D animal models and early reports of benefit in T2D humans is the main drivers of this interest. The aim of this review is to put emphasis on the filed patent during the period of 2014–2022. Only compounds that were disclosed in various patent applications and in researches were discussed. Some of the novel GKAs currently under clinical trials have also been encompassed. Several companies that have made significant investments in diabetes research continue to file new patent applications. Marketed antidiabetic agents exhibit various drawbacks, including weight gain, hypoglycemia, gastrointestinal side effects and cardiovascular risks. Additionally, many of these drugs do not specifically address the primary liver dysfunction in T2D, which is increased hepatic glucose output. In contrast, novel GKAs can offer several advantages. GKAs directly enhance glucokinase activity, improving glucose metabolism in both the liver and pancreas. This targeted mechanism helps reduce hepatic glucose production and promotes insulin secretion more effectively. By addressing the core dysregulation in T2D, GKAs can potentially provide better glycemic control with fewer side effects, offering a more efficient and safer therapeutic option compared with conventional antidiabetic drugs. A solution for this unmet need may be found in glucokinase (GK), the enzyme member of the hexokinase family that is activated upon stimulation. Hepatocyte GK serves as a “glucose sensor” or “glucose receptor” that stimulates insulin secretion in response to glucose, as well as a glucose “gatekeeper” that stimulates glycogen synthesis and storage in the liver. In normal cell metabolism, the glucose sensor hepatocyte GK normalizes the signals that outcomes in insulin secretion and endorses glycogen synthesis and storage in liver cells. In the circumstance of T2D, this regulation is not continually attainable. Usually, high glucose levels prompt enzymatic activity of GK, though, in diabetes, it is mired by insulin deficiency and dysfunction of islet β-cells. Due to this, GK is “emphaetielly” complicated in glucose sensing and glycogen amalgamation and its competence to maintain glucose homeostasis and diminution of hyperglyaemia. GKAs act in this method to return this function in injury because they recover the GK's ability to bind glucose and its influence in catalytic processes. In this manner, GKAS upsurge glucose uptake and utilization processes in the liver, rise glycogen synthesis and ultimately bring more stability in the blood glucose level. This restoration of GK activity enables the patient to afford the normal physiological function of glucokinase in glucose sensing and metabolic control, making a complete amelioration of the diabetic patient's glycemic status in T2D. A novel method of restoring or improving glycaemic control in people with diabetes is based on the activation of GK by small molecules. Thus, scientific world can adopt this target as a part of research and develop molecules based on discussed scaffolds to treat and cure the diabetes mellitus.

6. Future perspective

Mono-target therapy can fail to control blood glucose levels in people with T2D mellitus due to its complex pathogenesis. Diabetes is usually managed with medication use over a long period of time, creating a considerable burden on the patient and society. Among antidiabetic drugs, metformin is associated with drug resistance when used in long-term use. Furthermore, traditional oral hypoglycemic drugs (e.g. sulfonylureas, pyrazolidines and acarbose) may cause severe side effects and have many disadvantages (e.g. poor efficacy). Thus, it is imperative to develop new anti-diabetic drugs. This review has discussed patent based on glucose kinase activator which can be used as a probe to treat the diabetes mellitus. While writing this many things had been noticed which can be implement to investigate the new molecules. Study of patent has suggested that benzamide or derivatives based on amides like sulphonamide, acetamide, etc. has more potential to treat the diabetes mellitus as GKA. Apart from that it was also noticed that compounds which contain amide along with heterocyclic ring has more potential as glucokinase activator. So, researchers can investigate or put focus on developing molecule with amide and heterocyclic moiety.

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