Introduction:Melanoma is considered the deadliest form of skin cancer.
While monoclonal-antibodies and molecular targets marked milestones in melanoma therapy,
more research is needed to overcome the advanced stages of this disease.Objective:To explore the possible use of the yeast cytosine deaminase::uracil phosphoribosyltransferase
fusion enzyme/5-fluorocytosine (CD::UPRT/5FC) suicide gene (SG) system for human
melanoma.Methods:In eight metastatic human melanoma cell lines, we determined: cytotoxicity, lipofection
efficiencies, colony forming capacity and bystander effects due to soluble and/or particulate
factors secreted to the conditioned media after treatments.Results:CD::UPRT induced cell death in a prodrug (5FC) concentration-dependent manner and
was able to eliminate the sub-population of surviving cells with clonogenic capacity. Compared
with human interferon-β gene transfer or the herpes simplex virus thymidine kinase/ganciclovir
system, at 100 μM 5FC, CD::UPRT was more efficient in inducing cell death. The strong cytotoxic
response contrasted with the low lipofection efficiencies (<5%), indicating a potent bystander
effect. We analyzed the contribution of soluble and particulate factors released by SG
lipofected cells to the conditioned media (CM) finding that they were able to deliver CD::UPRT
genetic information and/or recombinant enzyme to recipient cells. When exposed to 5FC, the
cells that received either supernatant or 12000×g pellet fractions of CM, efficiently activated the
prodrug because of the acquired CD::UPRT activity and caused cell death.Conclusion:This suicide gene therapy approach, amplified by the release of free 5-fluorouracil
and soluble and particulate factors containing CD::UPRT genetic information and/or enzyme,
could have a great clinical potential for malignant melanoma.