S 50131 and S 51434, two novel small molecule glucokinase activators, lack chronic efficacy despite potent acute antihyperglycaemic activity in diabetic mice

Abstract

Background and purpose: Small molecule glucokinase activators (GKAs) have been associated with potent antidiabetic efficacy and hepatic steatosis in rodents. This study reports the discovery of S 50131 and S 51434, two novel GKAs with an original scaffold and an atypical pharmacological profile.

Experimental approach: Activity of the compounds was assessed in vitro by measuring activation of recombinant glucokinase, stimulation of glycogen synthesis in rat hepatocytes and increased insulin secretion from rat pancreatic islets of Langerhans. Efficacy and safety in vivo were evaluated after oral administration in db/db mice by measuring glycaemia, HbA1c and dyslipidaemia-associated events.

Key results: S 50131 and S 51434 activated GK and stimulated glycogen synthesis in hepatocytes and insulin secretion from pancreatic islets. Unexpectedly, while both compounds effectively lowered glycaemia after acute oral administration, they did not decrease HbA1c after a 4-week treatment in db/db mice. This lack of antidiabetic efficacy was associated with increased plasma free fatty acids (FFAs), contrasting with the effect of GKA50 and N00236460, two GKAs with sustained HbA1c lowering activity but neutral regarding plasma FFAs. S 50131, but not S 51434, also induced hepatic steatosis, as did GKA50 and N00236460. However, a shorter, 4-day treatment resulted in increased hepatic triglycerides without changing the plasma FFA levels, demonstrating dynamic alterations in the lipid profile over time.

Conclusions and implications: In addition to confirming the occurrence of dyslipidaemia with GKAs, these findings provide new insights into understanding how such compounds may sustain or lose efficacy over time.

Figure 1

Chemical structures of the novel glucokinase activators S 49164, S 50612 and their enantiomers.

Figure 2

Glucose-dependent and dose-dependent effect of S 49164 and its enantiomers (A), and S 50612 and its enantiomers (B) on human recombinant glucokinase. Data are means ± SEM of one representative experiment (out of two) performed in four replicates for each point.

Figure 3

In vitro pharmacological profiles of S 49164, S 50612 and their enantiomers (A,C). Glycogen synthesis in primary rat hepatocytes after 3 h of treatment with S 49164 and its enantiomers (A) or S 50612 and its enantiomers (C). Data are means ± SEM of four independent experiments performed in quadruplicate wells. (B, D). Insulin secretion from rat islets of Langherans cells after 90 min of treatment with S 49164 and its enantiomers (B) or S 50612 and its enantiomers (D). Data are means ± SEM of three independent experiments performed in eight replicate wells (containing four islets per well). *P < 0.05, **P < 0.01, ***P < 0.001, significantly different from controls; in A and C, anova and Dunnett's t-test; in B and D, Student's t-test.

Figure 4

Antihyperglycaemic action of tetrahydrocyclopropa[a]indene glucokinase activators after acute oral administration in db/db mice. Data are means ± SEM of 10 animals. *P < 0.05, **P < 0.01, ***P < 0.001 significantly different from vehicle; Dunnett's t-test. FFA, free fatty acid; TG, triglyceride.

Figure 5

Evaluation of the efficacy and safety of S 50131 and S 51434 compared to GKA50 and N00236460, after 4 weeks of daily oral administration in db/db mice. The doses expressed as mg·kg⁻¹ correspond to 120 μmol·kg⁻¹ for GKA50 and N00236460, to 60 and 180 μmol·kg⁻¹ for S 50131, and to 1.5-fold lower doses (40 and 120 μmol·kg⁻¹) for S 51434, considering its 1.5-fold greater acute hypoglycaemic potency after 4 h, as shown in Figure 4. (A–F) Efficacy and safety profile of S 50131; (G–L) Efficacy and safety profile of S 51434. (A,G) Differences in plasma HbA1c levels between day 1 and day 28; (B,H) Relative liver weights after 4 weeks; (C,I) Hepatic glycogen content after 4 weeks; (D, J) Plasma free fatty acid (FFA) levels after 4 weeks; (E,K) Plasma triglyceride (TG) levels after 4 weeks; (F,L) Hepatic TG content after 4 weeks. Data are means ± SEM of 12 animals per group. *P < 0.05, **P < 0.01, ***P < 0.001 significantly different from vehicle; anova and Dunnett's multiple comparison test for S 50131 and S 51434; Student's t-test for N00236460 or GKA50.

Figure 6

S 50131 and S 51434 increase the hepatic triglyceride (TG) content without any effect on plasma free fatty acids (FFAs) after 4 days of daily oral treatment in db/db mice. (A,C), Hepatic TG content. (B,D), Plasma FFA levels. S 50131 (A,B) and S 51434 (C,D) were evaluated in independent experiments with GKA50 being used as positive control. All compounds were administered once daily at 130 μmol·kg⁻¹, corresponding to 60.4 mg·kg⁻¹ for GKA 50, 40.0 mg·kg⁻¹ for S 50131 and 43.9 mg·kg⁻¹ for S 51434. Data are means ± SEM of 10 animals. **P < 0.01, ***P < 0.001, significantly different from vehicle; Student's t-test.