(282e) Expression-Targeted Gene Therapy for the Treatment of Transitional Cell Carcinoma

Gene therapy holds great promise for providing a clinical treatment for many cancers. Although clinical trials have used mainly viral transduction for gene delivery, non-viral methods have drawn more and more attention primarily due to issues regarding immunogenicity. A challenge common to both delivery methods is the attainment of gene expression in only the cells of interest. The attachment of ligands or antibodies to gene delivery complexes has been utilized toward this end, but this type of construct modification alters size and charge distributions in addition to marking the complexes with molecules that may be recognized by the liver or immune system. The complexes may face premature clearance from the body due to issues involving microvascularity, inflammation, immunogenicity, or simple attachment to serum albumin in vivo. In an alternative targeting approach, cell- or behavior-specific DNA control elements are included as part of the delivered gene to elicit transcription by only the cells of interest, regardless of whether additional cell types received the gene via delivery. This technique, known as expression-targeting, is at the core of this investigation.

Cyclooxygenase-2 (Cox-2) is overexpressed in most carcinomas but is weak to undetectable in normal, unstressed tissues. Normal cells induced to express Cox-2 do so at levels below those observed in certain tumor cell lines. Experiments in our laboratory utilized the murine cox2 promoter successfully to target the expression of delivered pro-apoptotic genes to transitional cell carcinoma MB49 tumors in vivo in immunocompetent C57Bl6 mice. The pro-apoptotic genes, delivered via the branched polycation poly(ethylenimine), coded for inducible forms of caspases 3 and 9, which remained inactive until the administration of a chemical inducer of dimerization on subsequent days. Statistical analysis of treatment data revealed no significant difference between normal bladder weights and the bladders of mice belonging to groups that received optimized transfections with subsequent dimerization. Negative controls showed no statistical difference between groups that received sham treatments or gene delivery treatments without the dimerization. There was, however, a significant difference between the mice that received the full treatment regimen and mice receiving the treatment without subsequent product activation (p=0.04). The investigations show that the cox2 promoter is and effective means for achieving expression-targeted gene delivery to transitional cell carcinoma cells in vivo, and that expression-targeted delivery of apoptotic genes is an effective means to bring about apoptosis even in apoptosis-resistant cell lines. The delivery of genes that code for inducible forms of caspases 3 and 9, with subsequent product activation, can be used to significantly inhibit the progression of transitional cell carcinoma in mice. Because of the levels of Cox-2 expression seen in other carcinomas (including colon and prostate cancers), this treatment regimen could have wide applicability in the future.