Effects of a glycogen synthase kinase-3 inhibitor, lithium, in adenomatous polyposis coli mutant mice.

Glycogen synthase kinase-3 (GSK-3) is an intermediary enzyme in various cellular pathways, and has been implicated in the pathophysiology and treatment of numerous diseases, including Alzheimer's disease, diabetes, and bipolar disorder. There is therefore in developing potent, selective GSK-3 inhibitors for the treatment of these devastating illnesses. A concern, however, is that the Wnt-signaling pathway-of which GSK-3 is an important intermediary molecule-has been implicated in many human cancers. It is thus of considerable importance to determine if GSK-3 inhibitors have tumorigenic potential in systems predisposed to developing tumors by virtue of mutations of the Wnt-signaling pathway. We therefore investigated the effects of a GSK-3 inhibitor, lithium, in a murine model predisposed to the formation of tumors due to activation of the Wnt pathway-the adenomatous polyposis coli (APC) multiple intestinal neoplasia (min) mouse. We found that 60 days of lithium treatment did not produce a significant increase in the number of tumors in these genetically predisposed mice. Lithium treatment resulted in a modest overall increase in the tumor size. The APC (min) mouse has previously been shown to be a robust indicator of tumorigenesis, with large increases in tumor number observed in response to a variety of agents; thus, our results suggest that lithium-and perhaps other inhibitors of GSK-3-pose a low risk for the development of cancers of the Wnt pathway. These results are consistent with the available epidemiological evidence that long-term lithium therapy does not increase cancer morbidity or mortality, but rather is associated with reduced overall mortality in bipolar disorder.