Third Place-Resident Research Competition, AAO-2000 - Antisense cyclin D1 inhibits growth of head and neck cancer xenografts in nude mice

PROBLEM: Cyclin DI is a regulatory factor essential in the progression of t he cell cycle from G1 through S phase. Amplification and overexpression of cyclin DI have been observed in many human cancers including head and neck squamous cell carcinoma (HNSCC). We have previously transfected a HNSCC con trol cell line (CCL23) with an antisense cyclin DI plasmid and demonstrated inhibition of cell proliferation in vitro. In this study, we examine wheth er antisense cyclin DT could inhibit tumor growth in vivo. METHODS/MEASURES: The CCL23 and its antisense cyclin D1 transfected clone ( CCL23 AS) were injected into the flanks of nude mice. Tumor growth was moni tored weekly, After 5 weeks, tumors were removed and studied for tumor size , cyclin D1 expression, cyclin D1-dependent kinase activity, and retinoblas toma (Rb) phosphorylation. RESULTS: Compared with the control tumors, 11 of 19 antisense tumors were s maller, 7 tumors were of equal size, and I tumor was larger. Immunohistoche mical analysis with an anti-cyclin D1 antibody demonstrated decreased cycli n D1 expression in CCL23 AS and the smaller antisense tumors. Cyclin D1-dep endent kinase activity was reduced in CCL23 AS and the smaller anti-sense t umors, and this was accompanied by a relative decrease in phosphorylated Rb in these samples. CONCLUSION: Antisense cyclin D1 inhibits growth of HNSCC tumors. Cyclin D1 expression, cyclin D1-dependent kinase activity, and Rb phosphorylation: ar e decreased in these tumors. CLINICAL SIGNIFICANCE: These findings lend support for the potential use of antisense cyclin D1 as gene therapy for HNSCC.