Systemic therapeutic gene delivery for cancer: crafting Paris' arrow

Tremendous strides have been made in proteogenomics and RNA interference technologies. Hence "personalized" cancer gene therapy has become a foreseeable rather than a predictable reality. Currently, the lack of an optimized, systemic gene delivery vehicle remains a key limiting factor for developing effective treatment applications. Since their introduction by Felgner in 1987, cationic lipids have been an attractive consideration for gene delivery, in view of their biocompatibility, biodegradability, low toxicity, and low immunogenicity. Successful in vivo transgene expression by cationic lipid- or cationic polymer-based delivery depends critically on a long circulating half life (>48 h), a definable systemic biodistribution with target-specific cancer localization, and efficient cell entry and internalization. Ideally, the agent should have a hydrophobic, stabilized core that ensures integrity of the therapeutic entity in vivo, a biocompatible, neutrally charged shell (zeta potential of approximately +/-10 mv) for enhanced, "stealth" circulation, and a suitable size (approximately 50-200 nm in diameter) for access into the tumor neovasculature and reduced reticuloendothelial system (RES) uptake. "Smart" receptor-targeting moieties can redirect intracellular trafficking. Additional engineered features have also been incorporated to minimize lysosomal degradation (membrane fusogenic lipids or proton sponge), promote endosomal escape into cytoplasm (cell penetrating peptides, triblock copolymer construction), and enhance nuclear entry and activate the endogenous transcriptional machinery (inclusion of a nuclear localization signal). Improvements in each of these respective areas of study have converged to yield promising in vivo results.