ORF50-06 - Novel Penetration Enhancers Enable Non-Invasive Sublingual and Transdermal Delivery of GLP-1 Receptor Agonists: Preclinical Evidence from Stearic Acid-Conjugated Protamine and Protamine Dimer Systems

Background: Injectable GLP-1 receptor agonists have transformed diabetes and obesity management but face significant adherence challenges. Needle phobia affects 20-30% of patients, while injection-site reactions and administration burden contribute to discontinuation rates exceeding 40% within the first year. Non-invasive delivery routes face formidable physiological barriers: sublingual mucin layers and tight epithelial junctions restrict protein absorption, while the stratum corneum excludes hydrophilic macromolecules from transdermal penetration. Current penetration enhancers demonstrate poor efficacy-to-toxicity ratios, limiting clinical translation.

Objectives: To evaluate whether stearic acid-conjugated protamine (C18-P) and protamine dimer (P2) enable therapeutic glycemic control when delivering GLP-1 receptor agonists via sublingual and transdermal routes in diabetic mouse models, comparing efficacy to standard subcutaneous administration.

Methods: C18-P was synthesized via EDC/NHS coupling chemistry. P2 was generated through NHS-PEG-NHS crosslinking to create dimeric protamine with enhanced mucoadhesive properties and enzymatic resistance. Diabetic mice received: sublingual semaglutide with C18-P (1:5 w/w ratio) in tablet formulation, transdermal liraglutide with P2 (1:10 w/w ratio) in patch formulation, or subcutaneous GLP-1 agonist controls. Blood glucose was monitored continuously for two hours post-administration.

Results: Sublingual semaglutide formulated with C18-P achieved blood glucose reduction comparable to subcutaneous injection, demonstrating successful mucosal barrier penetration. The lipophilic stearic acid modification enhanced membrane interaction while maintaining the guanidinium-rich protamine core essential for cellular uptake. Transdermal liraglutide with P2 produced sustained glycemic control over the two-hour observation period compared to untreated diabetic controls. The dimeric P2 structure provided enhanced mucoadhesion and protected liraglutide from enzymatic degradation. Neither formulation showed visible signs of tissue irritation.

Conclusions: Rationally designed protamine derivatives enable therapeutic delivery of GLP-1 receptor agonists via non-invasive routes with glycemic efficacy comparable to injection. The distinct mechanisms-C18-P's enhanced lipophilicity for sublingual absorption and P2's dimeric structure for transdermal stability-suggest pathway-specific optimization strategies. These findings address critical clinical needs by potentially eliminating injection barriers while maintaining therapeutic benefit. Future work should assess pharmacokinetic profiles, dose-response relationships, and safety in larger animal models prior to clinical translation.