Early GLP-1 Receptor Agonists: From Physiology to Pharmacotherapy

Incretin Historical Guideline Series | Milestone 13

Executive summary

Identifying GLP-1 as a functional incretin was not enough to turn it into a drug. Rapid degradation of native peptide and its short half-life required design solutions: resistant molecules, structural modifications, albumin binding or extended-release systems [4,7,8].

This milestone documents the first stage of GLP-1 pharmacotherapy: exendin-4/exenatide as the first clinical agonist, liraglutide as a once-daily long-acting human analogue, and early weekly formulations as the transition toward the modern GLP-1 receptor agonist era [1-7].

1. Historical context

The previous milestone established the pharmacological problem of native GLP-1: the signal was potent, but sustained systemic exposure was limited by enzymatic degradation. Therefore, the next stage was not only to demonstrate receptor-ligand activity, but to construct agonists capable of sustaining that signal in clinical conditions [6-8].

Exendin-4, isolated from Heloderma suspectum venom, showed functional homology with GLP-1 and the ability to activate the GLP-1 receptor. Its synthetic version, exenatide, was later introduced as the first GLP-1 receptor agonist approved for type 2 diabetes in the United States [1-3].

2. Scientific development of the milestone

Exenatide represented a first pharmacological solution: it was not a copy of human GLP-1, but a functional receptor agonist with relative resistance to DPP-4 degradation and clinical utility as an incretin mimetic [2,3].

Liraglutide represented a second solution: a human GLP-1 analogue modified to prolong exposure through acylation and albumin binding, enabling once-daily administration and opening the route toward rationally designed analogues [4,5].

Extended-release formulations and weekly agonists then expanded the field. GLP-1 pharmacotherapy moved from proof-of-possibility into a therapeutic platform with differences in duration, potency, tolerability and adherence [6,7].

3. HMD figure: from physiological hormone to pharmacotherapy

Figure 1. HMD representation of the conceptual jump: turning a brief physiological hormone into a pharmacological platform required solving stability, duration and exposure.

4. Documentary sequence

5. HMD chronological table

6. Independent HMD analysis

From the HMD perspective, early GLP-1 receptor agonists did not only inaugurate a pharmacological class; they inaugurated a method of metabolic translation. The question was no longer whether GLP-1 had activity, but how to design molecules capable of preserving that activity long enough to modify clinical parameters.

The exenatide-liraglutide-weekly formulation sequence shows three solution routes: using a resistant functional agonist, modifying a human analogue to prolong half-life, or altering formulation to extend exposure. These routes directly prepared the expansion toward semaglutide, obesity and later coagonism [4,7,8].

7. Early routes of GLP-1 agonism

Figure 2. HMD synthesis of the early pharmacological routes that solved native GLP-1 fragility through molecular origin, structural modification or formulation.

8. Relationship with later milestones

This milestone prepares the transition toward GLP-1 and obesity. Once the pharmacological exposure problem was addressed, the GLP-1 class could move from glycemic control toward body-weight control, satiety, cardiometabolic risk reduction and next-generation molecular systems [5,7,8].

References

1. Eng J, Kleinman WA, Singh L, Singh G, Raufman JP. Isolation and characterization of exendin-4, an exendin-3 analogue, from Heloderma suspectum venom. J Biol Chem. 1992;267(11):7402-7405.

2. Bond A. Exenatide (Byetta) as a novel treatment option for type 2 diabetes mellitus. Proc (Bayl Univ Med Cent). 2006;19(3):281-284. doi:10.1080/08998280.2006.11928187.

3. Briones M, Bajaj M. Exenatide: a GLP-1 receptor agonist as novel therapy for Type 2 diabetes mellitus. Expert Opin Pharmacother. 2006;7(8):1055-1064. doi:10.1517/14656566.7.8.1055.

4. Knudsen LB, Lau J. The discovery and development of liraglutide and semaglutide. Front Endocrinol (Lausanne). 2019;10:155. doi:10.3389/fendo.2019.00155.

5. Crane J, McGowan B. The GLP-1 agonist, liraglutide, as a pharmacotherapy for obesity. Ther Adv Chronic Dis. 2016;7(2):92-107. doi:10.1177/2040622315620180.

6. Prasad-Reddy L, Isaacs D. A clinical review of GLP-1 receptor agonists: efficacy and safety in diabetes and beyond. Drugs Context. 2015;4:212283. doi:10.7573/dic.212283.

7. Nauck MA, Quast DR, Wefers J, Meier JJ. GLP-1 receptor agonists in the treatment of type 2 diabetes - state-of-the-art. Mol Metab. 2021;46:101102. doi:10.1016/j.molmet.2020.101102.

8. Müller TD, Finan B, Bloom SR, D'Alessio D, Drucker DJ, Flatt PR, et al. Glucagon-like peptide 1 (GLP-1). Mol Metab. 2019;30:72-130. doi:10.1016/j.molmet.2019.09.010.