Surfactant Protein A–Polylysine Conjugates for Delivery of DNA to Airway Cells in Culture

Abstract

Surfactant protein A (SP-A) was modified by covalent linkage with polylysine of average M_r 21 kD ([Lys]_21kd-SP-A) and utilized to transfect human airway epithelial cells (H441) in vitro. Transfection of H441 cells was more efficient with [Lys]_21kd-SP-A than with polylysine–DNA or unmodified SP-A–DNA complexes. Transfection with [Lys]_21kd-SP-A was effective at a protein-to-DNA molar ratio of 400:1 and in the presence of an exogenous surfactant preparation, Survanta. Transfection with [Lys]_21kd-SP-A was reduced in the presence of unmodified SP-A consistent with the concept of a receptor mediated uptake of protein–DNA complexes. Increased transfection efficiency correlated with decreasing diameter of the [Lys]_21kd-SP-A–DNA complexes, and these complexes bound to the cell surface and pseudopodia of H441 cells. Transfection was enhanced by co-incubation with replication-deficient adenovirus. Cotransfection by [Lys]_21kd-SP-A–DNA and [Lys]_10kd-SP-B resulted in an additive level of reporter gene (CAT) expression. [Lys]_21kd-SP-A–DNA is likely to be useful as a component of a surfactant-based DNA delivery system for transfection of airway cells. Pulmonary surfactant is a complex mixture of phospholipids and proteins lining the airway epithelium. Surfactant proteins are synthesized, secreted, and recycled by the pulmonary epithelium. Synthetic surfactant preparations are used safely in repetitive treatment of infants with neonatal respiratory distress syndrome. Surfactant protein A (SP-A) is an abundant surfactant associated protein, normally recycled in the airway. SP-A covalently complexed with polylysine is active in transfection of plasmid DNA to human respiratory cells in vitro. The modified SP-A–DNA complex is likely internalized through receptor- and nonreceptor-mediated processes and transported through endosomal routing. SP-A transfects efficiently in the presence of surfactant lipids and transfects additively with surfactant protein B covalently linked to polylysine. SP-A complexed with polylysine may be useful alone or in combination with other modified surfactant proteins in plasmid DNA delivery to airway cells to treat human genetic diseases of the lung.