Intercellular delivery of thymidine kinase prodrug activating enzyme by the herpes simplex virus protein, VP22

We demonstrate that fusion proteins consisting of the herpes simplex virus (HSV) transport protein VP22 linked in frame to HSV thymidine kinase (tk) r etain the ability to be transported between cells. In vivo radiolabelling e xperiments and in vitro assays show that the fusion proteins also retain tk activity. When transfected COS cells. acting as a source of the VP22-tk ch imera, were co-plated on to gap junction-negative neuroblastoma cells, ganc iclovir treatment induced efficient cell death in the recipient neuroblasto ma cell monolayer. No such effect was observed with COS cells transfected w ith tk alone. Tumours established in mice with neuroblastoma cell lines exp ressing VP22-tk regressed upon administration of ganciclovir. Furthermore t umours established from 50:50 mixtures of VP22-tk transduced and nontransdu ced cells also regressed while no significant effect was observed in simila r experiments with cells transduced with tk alone. VP22 mediated transport may thus have application in a clinical setting to amplify delivery of the target protein in enzyme-prodrug protocols.