c-Met is a receptor tyrosine kinase whose activation by hepatocyte growth factor (HGF) can lead to transformation and tumorigenicity in a variety of tumors. We investigated the effects of suppressing c-Met protein expression in human non-small cell lung tumors. Expression plasmids containing either sense or antisense sequences of the human c-met gene were constructed under control of the U6 snRNA promoter. A U6 control plasmid was also constructed that did not contain any c-met sequence. These constructs have been examined both in vitro and in an in vivo tumor xenograft model. The c-Met protein was downregulated by 50-60% in two lung cancer cell lines that were transiently transfected with the c-Met antisense versus U6 control. Tumor cells treated with the c-Met antisense construct also show decreased phosphorylation of c-Met and MAP kinase when exposed to exogenous HGF. Lung cancer cells were grown as xenografts in mice and treated by intratumoral liposome-mediated transfer of the c-Met sense, antisense or U6 control plasmids. The treatment of lung tumors with c-Met antisense versus U6 control plasmid resulted in the downregulation of the c-Met protein expression, a 50% decrease in tumor growth over a 5-week treatment period and an increased rate of apoptosis. These results suggest that targeting the HGF/c-Met pathway may be an effective novel strategy to treat lung cancer patients.