Peptide-based therapeutics hold great promise in precision medicine, yet their clinical translation remains restricted by poor conformational stability, rapid enzymatic degradation, and low membrane permeability. Microneedle (MN) technology provides a minimally invasive, patient-friendly delivery platform that is particularly suitable for peptides, as it offers an attractive alternative to frequent injections while enabling efficient transdermal absorption. However, MNs alone cannot fully address peptide limitations: peptides remain vulnerable to proteolytic enzymes present in the skin, exhibit short systemic half-lives after absorption, and often lack the conformational stability needed to maintain bioactivity. 

Previously, we introduced the i,i+4 amine-containing hydrocarbon (ACH) stapling system, which improved aqueous compatibility and proteolytic resistance compared to conventional all-hydrocarbon staples. Yet, the i,i+4 constraint stabilizes only a single helical turn, limiting long-range conformational control. To overcome these limitations, we have now developed an i,i+7 ACH stapling strategy, which spans two full helical turns and provides broader structural reinforcement. The optimized i,i+7 ACH stapled peptides exhibited exceptional helicity (>90%) and up to a 17-fold increase in proteolytic stability relative to unstapled controls.

We suggest that the combination of i,i+7 ACH stapling and MN technology could provide a synergistic platform: MNs enable efficient, non-invasive delivery, while i,i+7 staples confer molecular stability and biochemical durability. Compared with i,i+4 variants, i,i+7 ACH stapling may be particularly advantageous for MN delivery, offering stronger protease resistance, extended helical coverage, and greater formulation compatibility. Together, this approach may expand the potential of stapled peptides as next-generation therapeutics for patient-friendly transdermal administration.

This research was supported by a grant (RS-2024-00332929) from Ministry of Food and Drug Safety in 2025.