DNA complex‐releasing system by injectable self‐setting apatite cement

Abstract

The therapeutic effect of plasmid DNA complexes is not satisfactory because of the short duration of their gene expression. However, an efficient DNA slow-release system has not been established owing to the low dispersion stability of the DNA/polycation (or cationic lipid) complexes. We have found that hyaluronan (HA) could deposit onto the DNA/polycation complexes, stabilize their dispersion and prepare very small particles. We have also reported that the injectable self-setting apatite cement has high biocompatibility and biodegradability. Thus, durable gene expression systems using injectable apatite cement, including DNA/polycation/HA complexes, were expected. Small DNA/polyethyleneimine (PEI)/HA complex particles were prepared by a lyophilizing and rehydration process, and the in vitro release ratio of DNA complex from the apatite cements by MLC-6 cells was examined. Apatite cement slurry with collagen including plasmid DNA (pDNA) complex [encoding granulocyte macrophage-colony stimulating factor (GM-CSF)] was injected close to the tumor subcutaneously inoculated into mice. The therapeutic effect and degradation ratio of the apatite cement were evaluated. Very fine DNA/PEI/HA complex particles kept being dispersed in the apatite cement. The DNA complexes were continuously released from the apatite cement by MLC-6 cells. Single injection of the apatite cement-including pDNA-GM-CSF complex induced complete disappearance of tumor in 60% of mice. Smooth degradation of the apatite cement was observed in the mice in which a high therapeutic effect was seen. Single injection of the apatite cement-including pDNA-GM-CSF complex showed a high therapeutic effect on solid tumor, and thus appears to be promising as a sustained gene expression device.