Bystander effects of nucleoside analogs phosphorylated in the cytosol or mitochondria

The efficiency of nucleoside kinase suicide gene therapy for cancer is high ly dependent on "bystander" cell killing, i.e., the transfer of cytotoxic p hosphorylated nucleoside analogs to cells adjacent to those expressing the suicide enzyme. We have recently studied the possible use of mitochondrial. nucleoside kinases as suicide genes. In the present study, we investigated if nucleoside analogs phosphorylated in the mitochondrial matrix cause bys tander killing. We used deoxycytidine kinase-deficient Chinese hamster ovar y cells reconstituted with deoxycytidine kinase targeted to either the cyto sol or mitochondria matrix and determined the bystander cell killing when t hese cells were incubated with the nucleoside analogs 1-beta -D-arabinofura nosylcytosine and 2,2'-difluorodeoxycytidine. A bystander effect occurred w hen nucleoside analogs were phosphorylated in the cytosol, but not when the se compounds were phosphorylated in the mitochondria. These findings sugges t that nucleoside kinases targeted to the mitochondrial matrix have limited use in suicide gene therapy when efficient bystander cell killing is requi red. (C) 2001 Academic Press.