A Modified Cell-Penetrating Peptide Boosts Insulin Transport Across Nasal Cells Nearly 8-Fold | Research

The takeaway

The cell-penetrating peptide PLR (P21-LK15-8R) enhanced insulin transcytosis across human nasal epithelial cells by 7.8-fold at a 2:1 molar ratio, demonstrating potential for needle-free nose-to-brain and systemic peptide drug delivery.

7.8× insulin transport enhancement
PLR boosted insulin crossing of human nasal epithelial cells by nearly 8-fold without damaging the cells, demonstrating potential for needle-free delivery

What the researchers found

PLR enhanced insulin transcytosis across RPMI 2650 human nasal epithelial cells by 7.8-fold at 2:1 insulin/PLR molar ratio (p<0.05), with each PLR domain (membrane docking, uptake, endosomal escape) contributing to the enhancement.

Why it matters

Needle-free delivery of peptide drugs would be transformative — especially for insulin, which currently requires injection for systemic delivery. Nasal delivery also offers a direct route to the brain, which could benefit oxytocin-based therapies for neuropsychiatric conditions. PLR's ability to enhance transport without cellular damage makes it a practical delivery platform.

The numbers in context

GET system enhanced transport of both insulin and oxytocin across nasal epithelial barriers compared to unassisted controls.

How the study worked

RPMI 2650 human nasal epithelial cells cultured at air-liquid interface served as a nasal barrier model. PLR (P21-LK15-8R, 44 residues) was tested with insulin (51 residues, negative charge) and oxytocin (9 residues, positive charge) at various molar ratios. Transcytosis was measured over 6 hours. Individual PLR domains were tested to establish structure-function relationships.

Who was studied

RPMI 2650 nasal epithelial cell barrier model

What this study cannot tell us

In vitro only — the RPMI 2650 cell model doesn't fully replicate the human nasal environment (mucus, mucociliary clearance, enzymes). The 7.8-fold enhancement is relative to baseline, and absolute transport percentages aren't provided. No in vivo nasal delivery data. Ciliotoxicity and long-term safety not assessed. Oxytocin enhancement was less impressive, suggesting the approach is cargo-dependent.

How to read the evidence

Preliminary evidence from an in vitro cell model study. The enhancement is impressive but translation to in vivo nasal delivery with therapeutically relevant drug levels remains to be demonstrated.

When this study was published

Published in 2024, part of ongoing efforts to develop non-invasive delivery platforms for peptide therapeutics.

The bigger picture

The quest for needle-free insulin delivery has been one of pharmaceutical science's holy grails. Nasal delivery is particularly attractive because the nasal mucosa is thin, highly vascularized, and bypasses first-pass liver metabolism. Adding a direct nose-to-brain pathway makes it doubly valuable for peptide drugs targeting neurological conditions. PLR represents a sophisticated approach — a single peptide that solves three separate delivery challenges (membrane binding, cellular uptake, and endosomal escape).

Questions still open

Does PLR-enhanced insulin nasal delivery achieve therapeutically relevant blood insulin levels in animal models?
Can PLR be optimized for positively charged peptides like oxytocin, or is it best suited for negatively charged cargo?
What is the long-term safety profile of repeated PLR application to nasal epithelium?

Common questions

Could this lead to insulin nasal spray instead of injections?

That's the goal, though significant hurdles remain. This study shows that PLR can dramatically boost insulin transport across nasal cells in the lab, but translating this to a real nasal spray requires overcoming additional challenges: nasal mucus, enzymatic degradation, mucociliary clearance (the nose's self-cleaning mechanism), and achieving consistent, therapeutically effective drug levels. Previous attempts at nasal insulin have struggled with these issues, but PLR's multi-functional design addresses several of them.

What is a cell-penetrating peptide and how does PLR work?

Cell-penetrating peptides (CPPs) are short amino acid sequences that can cross cell membranes — essentially molecular skeleton keys. PLR is a sophisticated version with three built-in functions: P21 helps it dock onto cell membranes, 8R (eight arginines) promotes uptake into cells, and LK15 helps the cargo escape from endosomes (cellular recycling compartments that would otherwise trap and destroy the drug). This three-part design addresses the major barriers to getting peptide drugs across epithelial tissues.

Read the original research

A Modified Cell-Penetrating Peptide Enhances Insulin and Oxytocin Delivery across an RPMI 2650 Nasal Epithelial Cell Barrier In Vitro.

Pharmaceutics, 16(10)

View on PubMed ↗Publisher’s paper ↗

Citation

Wong, Sara; Brown, Alexander D; Abrahams, Abigail B; Nurzak, An Nisaa; Eltaher, Hoda M; Sykes, David A; Veprintsev, Dmitry B; Fone, Kevin C F; Dixon, James E; King, Madeleine V. (2024). A Modified Cell-Penetrating Peptide Enhances Insulin and Oxytocin Delivery across an RPMI 2650 Nasal Epithelial Cell Barrier In Vitro.. Pharmaceutics, 16(10). https://doi.org/10.3390/pharmaceutics16101267