In situ gel formulations for delivery: Release and myotoxicity studies

The in vitro release of plasmid DNA and salmon sperm DNA from in situ gel formulations was investigated. Two in situ gel systems were studied: (a) an interpolymeric complex (IPC) of water-soluble polymers polymethacrylic acid (PMA) and polyethylene glycol (PEG) and (b) a hydroxypropylmethylcellulose-carbopol system (H:C). Two-way analysis of variance with replication demonstrated that both gel composition and medium pH influenced significantly the release of plasmid DNA from in situ gel formulations. When the release of both types of DNA was compared, higher release was observed for plasmid DNA compared to genomic salmon sperm DNA. Conformational analysis of the released plasmid DNA showed that DNA was released without degradation, but with remarkable conversion from supercoiled (SC) to open circular (OC). In addition, the tested in situ gel systems demonstrated protection from DNAse I degradation. The myotoxicity of the injectable gelling solutions was assessed by the cumulative release of creatine kinase (CK) over 120 min from the isolated rodent extensor digitorum longus (EDL) muscle. A higher level of cumulative CK was observed for IPC when compared to H:C (2:1). These results demonstrate that the in situ gelling systems can be considered as a valuable injectable controlled- delivery system for pDNA in their role to provide protection from DNAse degradation.