In vivo gene therapy for colon cancer using adenovirus-mediated, transfer of the fusion gene cytosine deaminase and uracil phosphoribosyltransferase

Virus-directed enzyme prodrug therapy (VDEPT) utilising cytosine deaminase (CD) converts 5-fluorocytosine (5-FC) into the chemotherapy agent, 5-fluoro uracil (5-FU), and has entered into a clinical trial for metastatic colon c ancer. To improve this system, a replication-deficient adenovirus, containi ng a bifunctional fusion gene, CD:uracil phosphoribosyltransferase (UPRT), was constructed (AdCDUPRT). UPRT enhances the conversion of 5-FU into its a ctive metabolites, which inhibit DNA and RNA synthesis. In vitro, AdCDUPRT infection of colon cancer cells resulted in a marked increase in sensitisat ion to 5-FU, compared with AdCD-infected or uninfected cells. The corollary is a similar to 100-fold and similar to 10 000-fold increase in sensitisat ion to 5-FC in AdCDUPRT-infected cells, compared to AdCD-infected and uninf ected cells, respectively. There was a strong bystander effect in vitro, 70 % of tumour cells were killed by 5-FC when only 10% of cells expressed CDUP RT. In vivo, athymic mice with colon cancer xenografts treated with intratu moral AdCDUPRT and intraperitoneal 5-FC, significantly reduced tumour growt h rates compared with untreated controls (P = 0.02), whereas AdCD/5-FC trea ted mice did not. At higher AdCDUPRT virus doses, 5-FC and 5-FU were equall y effective at delaying tumour growth compared with controls. In summary, V DEPT for colon cancer utilising AdCDUPRT is more effective than AdCD and th e bifunctional CDUPRT gene enables the use of either 5-FC or 5-FU as prodru gs.