Bystander effect from cytosine deaminase and uracil phosphoribosyl transferase genes in vitro: A partial contribution of gap junctions

Among gene therapy strategies elaborated to kill cancer cells, one uses the CodA gene, coding for cytosine deaminase (CD) that converts 5-fluorocytosine (5-FC) into toxic 5-fluorouracil (5-FU). To enhance 5-FC metabolic activation, we prepared a vector carrying CodA and upp (uracil phosphoribosyl transferase) genes which rendered HeLa cells sensitive to 5-FC and enhanced a bystander effect not mediated by gap junctions. However, 1% CD+–UPP+ cells were able to kill 40% of the cell population if the cells were communicating. This suggests that, at very low percentages of CD+–UPP+ cells, CodA and upp induce a bystander effect through gap junction-dependent mechanisms.