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

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.