Gemcitabine intercellular diffusion mediated by gap junctions: new implications for cancer therapy.
BACKGROUND
Solid tumors are often poorly vascularized, with cells that can be 100 microm away from blood vessels. These distant cells get less oxygen and nutrients and are exposed to lower doses of chemotherapeutic agents. As gap junctions allow the passage of small molecules between cells, we tested the possibility that the chemotherapeutic agent gemcitabine can diffuse through gap junctions in solid tumors.


RESULTS
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 microM 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 alpha-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.


CONCLUSIONS
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.
Centre de Recherche en Cancérologie de l'Université Laval, L'Hôtel-Dieu de Québec, Centre Hospitalier Universitaire de Québec, Qc G1R 2J6, Canada.
Sylvine
S
Cottin
Karim
K
Ghani
Pedro Otavio
PO
de Campos-Lima
Manuel
M
Caruso
D000964:Antimetabolites, Antineoplastic / Q000493:pharmacokinetics* / Q000627:therapeutic use; D000998:Antiviral Agents / Q000493:pharmacokinetics*; D024201:Bystander Effect; D045744:Cell Line, Tumor; D003841:Deoxycytidine / Q000031:analogs & derivatives* / Q000493:pharmacokinetics / Q000627:therapeutic use; D005455:Fluorescent Antibody Technique; D017629:Gap Junctions / Q000502:physiology*; D006801:Humans; D009369:Neoplasms / Q000188:drug therapy; D000093542:Gemcitabine
D000964:Antimetabolites, Antineoplastic; D000998:Antiviral Agents; D003841:Deoxycytidine; D000093542:Gemcitabine