ABSTRACT
The bystander effect (BSE) is an interesting and important property of the herpes thymidine kinase/ganciclovir (hTK/GCV) system of gene therapy for cancer. With the BSE, not only are the hTK expressing cells killed upon ganciclovir (GCV) exposure but also neighboring wild-type tumor cells. On testing a large number of tumor cell lines in vitro, a wide range of sensitivity to bystander killing was found. Since transfer of toxic GCV metabolites from hTK-modified to wild-type tumor cells via gap junctions (GJ) seemed to be a likely mechanism of the BSE, we tested GJ function in these various tumors with a dye transfer technique and pharmacological agents known to affect GJ communication. We confirmed that mixtures of tumor cell resistant to the BSE did not show dye transfer from cell to cell while bystander-sensitive tumor cells did. Dieldrin, a drug known to decrease GJ communication, diminished dye transfer and also inhibited the BSE. Forskolin, an upregulator of cAMP did increase GJ, but directly inhibited hTK and therefore its effect on BSE could not be determined. We conclude that these observations further support port the concept that functional GJ play an important role in the BSE and further suggest that pharmacological manipulation of GJ may influence the outcome of cancer therapy with hTK/GCV.
Subject(s)
Antiviral Agents/therapeutic use , Ganciclovir/therapeutic use , Gap Junctions , Genetic Therapy/methods , Protein Kinases/genetics , Transfection/methods , Animals , Colforsin/pharmacology , Coloring Agents , Dieldrin/pharmacology , Fluoresceins , Gap Junctions/drug effects , Genetic Vectors , Histidine Kinase , Humans , Insecticides/pharmacology , Mice , Organophosphorus Compounds , Rats , Retroviridae , Tumor Cells, CulturedABSTRACT
'Bystander' killing of adjacent wild-type tumor cells was seen when tumors transduced with the herpes thymidine kinase gene were treated with the antiviral agent ganciclovir (GCV). Some tumors were 'bystander-sensitive' while others were 'bystander-resistant'. Mixtures of different 'sensitive' tumor lines showed cross-transfer of bystander killing, while in mixtures of 'resistant' with 'sensitive' tumors, the resistant phenotype was predominant. Using 3H-GCV with 'sensitive' mixtures, phosphorylated 3H-GCV was found in both herpes thymidine kinase transduced and unmodified cells, while 'resistant' cell combinations showed little or no transfer of phosphorylated GCV between cells. The capacity of intracellularly produced nucleotide toxin to spread from cell to cell within a tumor mass effectively amplifies the apparent efficiency of gene transfer in the tumor and makes feasible the use of this system for therapy of localized cancer.