Polyethylenimine (PEI)-Mediated DNA Delivery in Rat Tumor Xenografts

Polyethylenimine (PEI) is a widely used cationic polymer for nonviral gene delivery, known for its ability to compact plasmid DNA into nanoscale polyplexes that facilitate cellular uptake and endosomal escape via the “proton sponge” effect. In rat tumor xenograft models, PEI-mediated DNA delivery is employed to introduce therapeutic or reporter genes directly into tumor tissue, allowing assessment of gene function, tumor biology, and therapeutic efficacy. However, achieving efficient transfection within solid tumors requires careful optimization of PEI properties, dosing, and delivery methods to balance transfection efficiency with toxicity.

PEI’s molecular weight and branching pattern critically influence its transfection performance and cytotoxicity profile. Branched PEI with molecular weights of 25 kDa is commonly used due to its favorable balance of transfection efficiency and biocompatibility. The nitrogen to phosphate (N/P) ratio—reflecting the ratio of positively charged amines in PEI to negatively charged DNA phosphate groups—is a key parameter that affects particle size, charge, and stability. Ratios typically range from 5 to 15, with higher ratios increasing transfection but also cytotoxicity.

For intratumoral delivery, PEI-DNA complexes are injected directly into the xenograft using fine needles, often with multiple injection sites to enhance distribution. Systemic administration is less common due to rapid clearance and nonspecific accumulation in organs such as the liver and lungs. Formulation buffers containing glucose or saline maintain isotonicity and stabilize polyplexes, while PEGylation or surface modification with targeting ligands can improve tumor penetration and reduce nonspecific interactions.

Transfection efficiency is monitored by measuring reporter gene expression through bioluminescence imaging, quantitative PCR, or immunohistochemistry. Tumor growth kinetics, apoptosis markers, and angiogenesis assays provide functional readouts of therapeutic gene effects. Toxicity evaluation involves histological examination of tumor and adjacent tissues, as well as systemic monitoring of body weight and organ function markers.

Despite its advantages, PEI-mediated delivery can induce inflammatory responses, oxidative stress, and necrosis in tumor and surrounding tissues, necessitating careful dose escalation and monitoring. Advances in PEI modification, including biodegradable linkers and targeting moieties, are being developed to enhance specificity and reduce toxicity. In summary, PEI represents a versatile platform for DNA delivery in rat tumor xenografts, enabling in vivo evaluation of gene therapies and molecular mechanisms underlying cancer progression.