Targeting strategies in cancer gene therapy.

Targeting to the tumor tissues can improve the therapeutic effect of gene transfer by preventing damage of healthy tissues and decreasing the risk of germ line transduction. Although targeting seems not important for intratumoral gene delivery, it becomes crucial when systemic gene transfer is performed. Targeted gene therapy of malignancies can be achieved through targeted gene delivery or targeted gene transcription. Recent advances in targeted delivery include the successful use of bifunctional crosslinkers to target adenoviral and retroviral vectors, inserting short targeting peptides and larger polypeptide-binding domains into the coat proteins of a number of different viral vectors, and replication-competent vectors which have been shown to be promise as anti-cancer agents. Some other non-viral therapeutic agents, including receptor-mediated DNA or liposome-DNA complex, and bacteria vehicles have also been developed. Some of these delivery systems are currently in clinical trials. For targeted and regulable gene transcription, tissue or tumor specific promoters and some manual regulatory systems are used to regulate therapeutic gene expression. Antisense oligonucleotides, some ribozyme and DNAzyme molecules are developed to inactivate genes that are essential to the development of many tumors.