Expression of p16(INK4A) induces dominant suppression of glioblastoma growth in situ through necrosis and cell cycle arrest

Tumor suppressor genes may represent an important new therapeutic modality in the treatment of human glioblastoma (GBM). p16(INK4A) is a tumor suppres sor gene with mutation and/or deletion found in many human tumors, includin g glioblastomas, melanoma, and leukemias. RT-2 rat GEM cell line was used t o investigate if the p16 gene induces dominant suppression of glioblastoma growth. Close to 100% of tumor cells were infected by high titer pCL retrov irus encoding the full-length human p16 cDNA at 5 m.o.i. Infected cells sho wed a 98% reduction in colony forming assay and a 60% reduction in growth c urves in oih compared to vector control. Exogenous overexpression of p16 in duced hypophosphorylation of Rb protein by Western blot analysis. Intracran ial injection of p16-infected tumor cells into syngeneic rats resulted in a 95% reduction in tumor volume compared to the controls. Intratumoral injec tion of p16 retrovirus resulted in tumor necrosis and prominent human p16 t ransgene expressions. Proliferation marker PCNA was not detected in these h uman pie-expressed RT-2 tumor cells, suggesting the cells were unable to en ter into S phase after p16 expression In addition, direct repeat intracrani al injections of pie retrovirus prolonged animal survival 3.2-fold compared to the controls (48.4 +/- 13.4 vs 15.0 +/- 2.1 days, p < 0.001). Two out o f ten rats were found with dormant tumors at day 60 after p16 retrovirus in jection, These results showed that p16 is effective in inhibiting GEM growt h in situ. The mechanisms of tumor growth reduction and necrosis in vivo mi ght be due to G1 arrest triggered by pie expression, (C) 2000 Academic Pres s.