Gemcitabine intercellular diffusion mediated by gap junctions: new implications for cancer therapy

We first showed with a dye transfer assay that the glioblastoma and the osteosarcoma cells used in this study have functional gap junctions. These cells were genetically engineered to express the herpes simplex virus thymidine kinase (TK), and induced a "bystander effect" as demonstrated by the killing of TK-negative cells in presence of the nucleoside analogue ganciclovir (GCV). The ability of gemcitabine to induce a similar bystander effect was then tested by mixing cells treated with 3 μM gemcitabine for 24 hours with untreated cells at different ratios. In all cell lines tested, bystander cells were killed with ratios containing as low as 5% treated cells, and this toxic effect was reduced in presence of α-glycyrrhetinic acid (AGA), a specific gap junction inhibitor. We also showed that a 2- or a 24-hour gemcitabine treatment was more efficient to inhibit the growth of spheroids with functional gap junctions as compared to the same treatment made in presence of AGA. Finally, after a 24-hour gemcitabine treatment, the cell viability in spheroids was reduced by 92% as opposed to 51% in presence of AGA.These results indicate that gemcitabine-mediated toxicity can diffuse through gap junctions, and they suggest that gemcitabine treatment could be more efficient for treating solid tumors that display gap junctions. The presence of these cellular channels could be used to predict the responsiveness to this nucleoside analogue therapy.Nucleoside analogues are drugs commonly used in the clinic as antiviral and anticancer agents. Gemcitabine (2', 2'-difluorodeoxycytidine, dFdC; Gemzar？) is a pyrimidine analogue that has a well established place in the treatment of several types of solid tumors; it is indicated as a single agent for the treatment of metastatic pancreatic cancer and, in combination regimens, for the treatment of non-small cell lung carcinoma, ovarian and breast cancer [1]. The use of gemcitabine is currently being tested in bladder cancer, mesothelioma and