TMG-123, a novel glucokinase activator, exerts durable effects on hyperglycemia without increasing triglyceride in diabetic animal models

Abstract

Glucokinase (GK) plays a critical role for maintaining glucose homeostasis with regulating glucose uptake in liver and insulin secretion in pancreas. GK activators have been reported to decrease blood glucose levels in patients with type 2 diabetes mellitus. However, clinical development of GK activators has failed due to the loss of glucose-lowering effects and increased plasma triglyceride levels after chronic treatment. Here, we generated a novel GK activator, TMG-123, examined its in vitro and in vivo pharmacological characteristics, and evaluated its risks of aforementioned clinical issues. TMG-123 selectively activated GK enzyme activity without increasing Vmax. TMG-123 improved glucose tolerance without increasing plasma insulin levels in both insulin-deficient (Goto-Kakizaki rats) and insulin-resistant (db/db mice) models. The beneficial effect on glucose tolerance was greater than results observed with clinically available antidiabetic drugs such as metformin and glibenclamide in Zucker Diabetic Fatty rats. TMG-123 also improved glucose tolerance in combination with metformin. After 4 weeks of administration, TMG-123 reduced the Hemoglobin A1c levels without affecting liver and plasma triglyceride levels in Goto-Kakizaki rats and Diet-Induced Obesity mice. Moreover, TMG-123 sustained its effect on Hemoglobin A1c levels even after 24 weeks of administration without affecting triglycerides. Taken together, these data indicate that TMG-123 exerts glucose-lowering effects in both insulin-deficient and -resistant diabetes, and sustains reduced Hemoglobin A1c levels without affecting hepatic and plasma triglycerides even after chronic treatment. Therefore, TMG-123 is expected to be an antidiabetic drug that overcomes the concerns previously reported with other GK activators.

Fig 1. TMG-123 decreases S_0.5 value of GK without increasing Vmax.

Glucose concentration-versus-human liver GK activity relationships in the presence of 30 μM TMG-123 or vehicle alone (5% DMSO).

Fig 2. TMG-123 increases glucose uptake in rat primary hepatocytes and insulin secretion in MIN6 cells.

(a) Glucose uptake in rat primary hepatocytes in the presence of 4 mM glucose is calculated by determining uptake of 2-[1,2-³H(N)]deoxyglucose after 8 hours of treatment with several concentrations of TMG-123. (b) Insulin secretion from MIN6 cells in the presence of 4 mM glucose after 1 hour of treatment with several concentrations of TMG-123.

Fig 3. Administration of TMG-123 improves glucose tolerance without stimulating insulin secretion in animal models of insulin-deficient and -resistant diabetes.

(a-d) OGTTs with Goto-Kakizaki rats and Wistar rats. TMG-123 (1–10 mg/kg) or vehicle (Gelucire/PEG400 = 3/2) were orally administered at -0.5 hr, and 2 g/kg of glucose was orally gavaged at 0 hr (n = 8, each). (a) Plasma glucose curves and (b) Glucose AUC_0-4hr following OGTTs in Goto-Kakizaki and Wistar rats. (c) Plasma insulin curves and (d) plasma insulin levels at 0.25 hr following OGTTs in Goto-Kakizaki and Wistar rats. (e-h) OGTTs in db/db mice. TMG-123 (3–30 mg/kg) or vehicle were orally administered at -1 hr and 5 g/kg glucose was orally gavaged at 0 hr (n = 8, each). (e) Plasma glucose curves and (f) Glucose AUC_0-4hr following OGTTs in db/db mice. (g) Plasma insulin curves and (h) plasma insulin levels at 0.25 hr following OGTTs in db/db mice. **p < 0.025, ***p < 0.001, NS = not significant.

Fig 4. Administration of TMG-123 improves glucose tolerance more than metformin and glibenclamide, and exerts additional efficacy in combination with metformin.

(a-e) OGTTs in ZDF rats. TMG-123 (3–30 mg/kg), metformin (30–300 mg/kg), glibenclamide (1–10 mg/kg), TMG-123 plus metformin or vehicle (Gelucire/PEG400 = 3/2) were orally administered at -0.5 hr and 2 g/kg of glucose was orally gavaged at 0 hr (n = 9–10). (a, c, d, e) Glucose AUC_0-4hr and (b) plasma insulin levels at 0.25 hr following OGTTs in ZDF rats. **p < 0.025, ***p < 0.001, NS = not significant.

Fig 5. TMG-123 produces a sustained reduction in HbA1c levels in animal models of insulin-deficient and -resistant diabetes.

(a) HbA1c levels in Goto-Kakizaki rats after once daily administration of TMG-123 per oral for 4 weeks (n = 9–10). (b) HbA1c levels in DIO mice after administration of TMG-123 as a diet admixture for 4 weeks (n = 10). (c-f) 24 weeks study in DIO mice (n = 8). (c) Time courses of HbA1c levels during a 24-week administration period of TMG-123. HbA1c levels at 4 (d) and 24 (e) weeks after initiating treatment. (f) Time courses of plasma insulin levels. **p < 0.025, ***p < 0.001.

Fig 6. Sub-chronic and chronic administration of TMG-123 does not induced hypertriglyceridemia and liver TG accumulation in animal models of insulin-deficient and -resistant diabetes.

(a, b) Plasma TG levels and liver TG contents after a 4-week administration in Goto-Kakizaki rats (n = 9–10). (c, d) Plasma and liver TG after a 4-week administration (n = 10) and (e, f) those after a 24-week administration (n = 8) in DIO mice. *p < 0.05, ***p < 0.001, NS = not significant.