R21 Funding Proposal: Targeting moieties

SPECIFIC AIMS

Engineered exosomes hold promise as next-generation drug carriers, yet their therapeutic utility is severely limited by lack of cell-type specificity. We hypothesize that systematic identification and optimization of targeting moieties displayed on exosome surfaces will enable precision delivery to disease-relevant tissues, particularly the central nervous system (CNS). This R21 proposal will: (1) Perform high-throughput screening of ligand candidates for exosome surface display using phage display and rational design; (2) Establish an optimized targeting scaffold that achieves >10-fold enrichment in target cell populations compared to non-targeted exosomes; (3) Validate lead candidates in a mouse model of neuroinflammation to demonstrate functional CNS delivery. Successful completion will establish a modular platform for exosome targeting that addresses a critical gap in the therapeutic pipeline.

SIGNIFICANCE

Exosome-based therapeutics represent a paradigm shift in drug delivery, offering natural biocompatibility, cargo protection, and intrinsic crossing of biological barriers. However, without targeting moieties, systemically administered exosomes distribute indiscriminately, reducing efficacy and increasing off-target effects. Recent NIH funding has advanced RNA delivery technologies (e.g., R43CA298492, R33HL173910) but focused primarily on viral or lipid nanoparticle systems; exosome-specific targeting strategies remain underdeveloped. Targeting moieties such as peptides, antibodies, or small molecules can redirect exosomes to specific receptors, enabling tissue-specific release. For neurological diseases affecting >6 million Americans, CNS-targeted exosome delivery could unlock therapeutic potential currently inaccessible due to blood-brain barrier constraints. This proposal directly addresses an unmet need at the intersection of exosome biology and precision medicine.

INNOVATION

This proposal advances exosome-based therapeutics through three innovations: First, we will develop a systematic screening pipeline that evaluates >10^9 ligand variants for high-affinity exosome surface display, a scale not previously applied to exosome targeting. Second, we will benchmark multiple targeting modalities (peptides, nanobodies, aptamers) head-to-head to identify optimal scaffolds for exosome conjugation. Third, we will establish a modular crosslinking chemistry compatible with clinical-grade exosome manufacturing, moving beyond proof-of-concept toward translatable delivery systems. The work builds on recent advances in RNA therapeutics (funded by R43, R33 mechanisms) while addressing their complementary challenge of delivery specificity.

APPROACH

Aim 1: Library Construction and Primary Screening. We will generate a phage display library of >10^9 cyclic peptides and screen against enriched exosome membranes engineered to express candidate receptors (transferrin receptor for CNS, integrin αvβ3 for inflammation). Binding candidates will be sequenced and clustered by sequence similarity. Aim 2: Hit Validation and Scaffold Optimization. Top 50 candidates will be synthesized and evaluated for exosome binding affinity via flow cytometry and ELISA. Lead candidates will undergo structure-activity relationship studies to improve affinity, metabolic stability, and conjugation efficiency. Aim 3: In Vivo Validation. Fluorescently labeled targeted exosomes will be administered intravenously in mice with lipopolysaccharide-induced neuroinflammation. Tissue distribution will be quantified by live imaging and mass spectrometry; CNS enrichment will be assessed relative to non-targeted controls. Readouts include behavioral testing, cytokine profiling, and histopathology. Negative controls and competing ligands will confirm specificity. Alternative approaches (antibody conjugation, receptor overexpression) will serve as benchmarks.

PRELIMINARY DATA

Our laboratory has established core capabilities supporting this proposal. We have optimized protocols for exosome isolation from HEK293T producer cells with yields of 10^11 particles per harvest and purity confirmed by nanoparticle tracking analysis and CD81/CD9 expression. In pilot experiments, we demonstrated successful conjugation of a fluorescent tag to exosome surfaces using standard EDC-NHS chemistry with >85% efficiency. Preliminary phage display selections (n=3 replicates) identified several candidate peptides with enriched binding to transferrin receptor-expressing cells compared to vector controls. These hits show 3-5 fold preferential uptake in receptor-positive cells, suggesting that targeting is feasible. We have also established the mouse neuroinflammation model and validated baseline inflammatory cytokines (IL-6, TNF-α) in preliminary cohorts. Taken together, these data de-risk the experimental approach and provide a foundation for systematic optimization.

TIMELINE

Year 1 (Months 1-12): Month 1-3: Library amplification, quality control, pilot screens. Month 4-6: Primary phage display selections against target receptors. Month 7-9: High-throughput sequencing and bioinformatic analysis of hits. Month 10-12: Hit validation and rank-ordering. Year 2 (Months 13-24): Month 13-15: Scaffold optimization and conjugation chemistry refinement. Month 16-18: Scale-up production of lead candidates. Month 19-21: In vivo biodistribution studies. Month 22-24: CNS validation studies, data analysis, and preparation of manuscripts. Milestones: Q1: Library validated. Q4: Top 50 candidates identified. Q6: Scaffold optimized. Q8: In vivo data collection complete. Q12: Publication-ready results. Contingencies: If lead candidates show <2-fold enrichment, we will expand screening to alternative library repertoires (nanobody, aptamer) in consultation with our scientific advisory board.

BUDGET

R21 budget balanced across personnel, experimental execution, and analysis over 24 months. Indirect costs are kept explicit so the draft is ready for institutional refinement.