Antidiabetic treatments aiming to reduce body weight are currently gaining increased interest. Exendin-4, a glucagon-like peptide-1 (GLP-1) receptor agonist administered twice daily via s.c. injection, improves glycemic control, often with associated weight reduction. To further improve the therapeutic efficacy of exendin-4, we have developed a novel peptide engineering strategy that incorporates a serum protein binding motif onto a covalent side-chain staple and applied to the peptide to enhance its helicity and, as a consequence, its potency and serum half-life. We demonstrated that one of the resulting peptides, E6, has significantly improved half-life and glucose tolerance in an oral glucose tolerance test in rodents. Chronic treatment of E6 significantly decreased body weight and fasting blood glucose, improved lipid metabolism, and also reduced hepatic steatosis in diet-induced obese mice. Moreover, the high potency of E6 allowed us to administer this peptide using a dissolvable microstructure-based transdermal delivery system. Pharmacokinetic and pharmacodynamic studies in guinea pigs showed that a single 5-min application of a microstructure system containing E6 significantly improved glucose tolerance for 96 h. This delivery strategy may offer an effective and patient-friendly alternative to currently marketed GLP-1 injectables and can likely be extended to other peptide hormones.GLP-1 receptor agonist | helix stabilization | half-life extension | microstructure array | lipidated cross-linker B -family G protein-coupled receptors (GPCRs) include receptors for peptide hormones such as glucagon, glucagonlike peptides 1 and 2 (GLP-1 and -2), parathyroid hormone (PTH), and corticotropin-releasing factor. Attempts to generate smallmolecule modulators of these receptors have had limited success, whereas peptide ligands have been proven as effective therapeutic agents, as exemplified by exenatide (aka exendin-4 or Ex-4), a GLP-1 receptor agonist for diabetes, and teriparatide, a PTH1 receptor agonist for osteoporosis (1). However, peptide-based drugs generally suffer from short half-lives due to proteolytic degradation and fast renal clearance, rendering higher doses and frequent injections necessary, which negatively affects patient compliance (2). To improve their pharmacological properties, peptides have been chemically modified by conformational restriction (3-13) to increase potency and reduce proteolysis, and also by lipidation (14-16), polymer conjugation (17-23), and protein fusion (24-26) to decrease renal clearance. Although these latter conjugates can have enhanced circulatory half-lives, they often suffer from reduced potency and, as a result, require injection of relatively large quantities of the modified peptides.GLP-1 receptor agonists (GLP-1RAs) represent a unique approach to the treatment of diabetes, with benefits beyond glucose control, including favorable effects on body weight, blood pressure, cholesterol levels, and beta-cell function (27). Two short-acting (exenatide and liraglutide; on...