A continued saga of Boc5, the first non-peptidic glucagon-like peptide-1 receptor agonist with in vivo activities

Abstract

Glucagon-like peptide-1 (GLP-1)-based therapy presents a promising option for treating type 2 diabetes. However, there are several limitations relative to the peptidic GLP-1 mimetics currently on the market or under development. This concern has led to a continued interest in the search for non-peptidic agonists for GLP-1 receptor (GLP-1R). Here, we briefly review the discovery, characterization and current status of a novel class of cyclobutane-derivative-based non-peptidic agonists for GLP-1R, including Boc5 and its newly discovered analogue WB4-24. Although the oral bioavailability of such compounds still poses great challenges, the progress made so far encourages us to identify a truly 'druggable' small molecule agonist for GLP-1R.

Figure 1

The structures of Boc5 and WB4-24.

Figure 2

Effects of WB4-24 treatment on body weight and food intake in diet-induced obese (DIO) mice. Animals were maintained on high fat diet (HFD) for 12 weeks and then randomly assigned into 4 treatment groups with matched body weight. They were injected (ip), 3 times a week (Monday, Wednesday and Friday), with 0 (obese control), 0.3, 1, or 3 mg of WB4-24 (1% DMSO, 20% PEG400 in saline, pH 7.4, 0.5 mL) for 12 weeks. To compare the in vivo effects of WB4-24 and Boc5, a positive control group treated with 3 mg of Boc5, previously proven to be effective in combating obesity, was presented. A further comparator group of mice consuming standard chow diet (lean control) was used to index responses to normal values. Except for animals in 3 mg WB4-24, obese and lean control groups, all mice were sacrificed at the end of therapy. The remaining mice were kept under observation without therapeutic intervention. An 8-week new treatment regimen (3 mg WB4-24) was introduced two months after the cessation of the initial therapy. Time course of body weight changes (A) and daily food intake (C) over the 28-week investigational period were monitored. The changes of body weight (Δ-body weight, B) and daily food intake (Δ-daily food intake, D) over the first 12-week period were analyzed. Statistical analysis was performed using GraphPad Prism software (GraphPad, San Diego, CA, USA) by one-way analysis of variance (ANOVA), followed by Bonferroni post hoc analysis. Values are presented as mean±SEM. n=6–9 per group. ^bP<0.05, ^cP<0.01 compared with lean controls. ^eP<0.05, ^fP<0.01 compared with obese controls. ^hP<0.05, ⁱP<0.01 compared with 3 mg Boc5-treated mice. ^lP<0.01 compared with 0.3 mg WB4-24-treated mice. ^oP<0.05 compared with 1 mg WB4-24-treated mice.

Figure 3

Effects of WB4-24 on glucose homeostasis in DIO mice. The experiments were conducted as described in Figure 1 legend and intraperitoneal glucose tolerance tests (IPGTTs) were carried out at week 0 (A), 4 (B), 12 (C), 20 (D), and 28 (E) after initial treatment with WB4–24. The glucose area-under-curve integrated from 0–120 min (AUC₁₂₀) was calculated for each mouse (F). Statistical analysis was performed using GraphPad Prism software by one-way analysis of ANOVA, followed by Bonferroni post hoc analysis. Values are presented as mean±SEM. n=6–9 per group. ^bP<0.05, ^cP<0.01 compared with lean controls. ^eP<0.05, ^fP<0.01 compared with obese controls.

Figure 4

Effects of WB4-24 on serum satiety hormone concentrations in DIO mice. The experiments were conducted as described in Figure 1 legend . At the end of 12-week treatment, blood samples were collected from WB4-24-treated (3 mg), Boc5-treated (3 mg), lean and obese control groups. Fasting satiety hormones including insulin, leptin, active GLP-1 and glucagon levels were analyzed using Luminex 200 system (Luminex, Austin, USA) with the mouse endocrine MILLIPLEX MAP kit supplied by Millipore (Billerica, MA, USA). Statistical analysis was performed using GraphPad Prism software by one-way analysis of ANOVA, followed by Bonferroni post hoc analysis. Values are presented as mean±SEM. n=6–9 per group. ^cP<0.01 compared with lean controls; ^eP<0.05, ^fP<0.01 compared with obese controls.

Figure 5

Correlation between plasma antibody titers and therapeutic efficacy in DIO mice treated with WB4–24. WB4-24 antibody titers had no statistically significant correlation with body weight (r=0.7758, P=0.698, n=6; A) or AUC₁₂₀ of IPGTT (r=0.5627, P=0.245, n=6; C). The line in column B represents the positive correlation between WB4-24 antibody titers and daily food intake (r=0.8227, P=0.0444, n=6). Statistical analysis was performed using GraphPad Prism software by Pearson's correlation analysis.