# Rewriting Tumor Entry Rules: Microfluidic Polyplexes and Tumor-Penetrating Strategies—A Literature Review

## TL;DR

This review explores how polyplexes can be engineered to improve the delivery of nucleic acid-based cancer vaccines, focusing on design principles and strategies to overcome tumor barriers.

## Contribution

The paper provides a comprehensive review of polyplex design and tumor-penetrating strategies, emphasizing microfluidic fabrication and stepwise delivery mechanisms.

## Key findings

- Polyplexes offer advantages over lipid nanoparticles and viral vectors in terms of tunability and reduced immunogenicity.
- Engineering strategies like size-switching systems and charge-reversal polymers enhance intratumoral distribution.
- Preclinical and early clinical data show on-target effects of polyplex-based therapies in multiple tumor types.

## Abstract

Cancer immunotherapy increasingly relies on nucleic acid-based vaccines, yet achieving efficient and safe delivery remains a critical limitation. Polyplexes—electrostatic complexes of cationic polymers and nucleic acids—have emerged as versatile carriers offering greater chemical tunability and multivalent targeting capacity compared to lipid nanoparticles, with lower immunogenicity than viral vectors. This review summarizes key design principles governing polyplex performance, including polymer chemistry, architecture, and assembly route—emphasizing microfluidic fabrication for improved size control and reproducibility. Mechanistically, effective systems support stepwise delivery: tumor targeting, cellular uptake, endosomal escape (via proton-sponge, membrane fusion, or photochemical disruption), and compartment-specific cargo release. We discuss therapeutic applications spanning plasmid DNA, siRNA, miRNA, mRNA, and CRISPR-based editing, highlighting preclinical data across multiple tumor types and early clinical evidence of on-target knockdown in human cancers. Particular attention is given to physiological barriers and engineering strategies—including size-switching systems, charge-reversal polymers, and tumor-penetrating peptides—that improve intratumoral distribution. However, significant challenges persist, including cationic toxicity, protein corona formation, manufacturing variability, and limited clinical responses to date. Current evidence supports polyplexes as a modular platform complementary to lipid nanoparticles in selected oncology indications, though realizing this potential requires continued optimization alongside rigorous translational development.