Gene therapy of rat medullary thyroid cancer by naked nitric oxide synthase II DNA injection

Background Nitric oxide (NO), produced by NO synthase II (NOS II), is the m ain mediator of the tumoricidal action of activated macrophages. In the pre sent study we examined the potential of the NOS n gene as a suicide gene fo r medullary thyroid cancer (MTC) therapy. Methods We orthotopically transplanted rMTC 6-23 cells into the inbred stra in of Wag/Rij rats and constructed a plasmid carrying the NOS II gene under the control of the cytomegalovirus (CMV) promoter. Results Successive injections of tumor cells (Day 0) and naked DNA (Day 2) caused strong inhibition of tumor growth (50%, p < 0.05). Plasmid injection into established tumors (14-day tumors) resulted in the development of lar ge cavities due to tumor cell. destruction, with a significant reduction in tumor tissue Volume (35%, p < 0.05). Adjacent quiescent tissues were unaff ected. Cell death occurred by apoptosis as demonstrated by specific labelin g. Macrophages and CD4(+) lymphocytes were recruited in the treated tumors. However, tumor-specific T lymphocytes were undetectable in the spleen of t reated rats. In control experiments using Lac Z as a reporter gene, express ion of beta-galactosidase was detected in only 1% of the tumor cells. Conclusions Despite a low gene transfer efficiency, NOS II plasmid produced a strong anti-tumor action resulting from its marked 'bystander' effect ma inly due to NO production and diffusion. Therefore the NOS IT gene appears to be a promising suicide gene therapy of human canter. Copyright (C) 2000 John Wiley & Sons, Ltd.