Atorvastatin reversed MYC-induced tumorigenesis in vitro and in vivo. (A) The influence of statins on cell proliferation was analyzed in murine lymphoma cell lines derived from a conditional transgenic model of MYC-induced lymphomagenesis using the Tet-system. Tumor-derived cell lines were treated with 10 μM atorvastatin (AT), 10 μM simvastatin (SM), 10 μM lovastatin (LOV), and 10 μM pravastatin (PRA) and analyzed after 24 and 48 hours for survival. Representative data are shown for 1 of the 6 tumor-derived cell lines from our conditional MYC transgenic model. Growth was measured by [³H]thymidine incorporation. Results are presented as stimulation index (SI), measured as the incorporation of [³H]thymidine in the presence versus the absence of treatment. Results are shown as mean of 2 separate experiments performed in triplicate (± SEM). SEMs were within 10% of the means. (B) Atorvastatin induced a dose-dependent inhibition of proliferation in MYC-induced tumors. Conditional transgenic lymphoma cell lines were generated using the Tet-system by overexpressing MYC. Tumor cells were treated with different doses of atorvastatin as indicated, and growth was measured by [³H]thymidine incorporation. Results are presented as SI, measured as the incorporation of [³H]thymidine in the presence versus the absence of treatment with statins. Experiments were performed in triplicate. Cells were treated with different doses of atorvastatin and analyzed after 24 and 48 hours of treatment. Results are presented as the mean of 3 different experiments performed in triplicate. (C) Atorvastatin inhibited proliferation and induced apoptosis in MYC-expressing tumor cells. MYC lymphoma cells where MYC was expressed (MYC ON) or MYC was inactivated (MYC OFF) after doxycycline treatment (20 ng/mL) or in the presence of 10 μM atorvastatin (AT), 100 μM mevalonate (Mev), or 10 μM atorvastatin plus 100 μM mevalonate (AT + Mev) were pulsed with BRDU after 36 hours. Live cells were stained with PI and analyzed by FACS. Results are presented as the mean of 2 different experiments. See also Figures S2,S3. (D) Survival of mice transplanted with a MYC-induced lymphoma cell line. Mice were injected with tumor cells of 1 of the MYC-induced tumor derived cell lines and when they were moribund with tumor, were either not treated (MYC ON; squares) or treated with doxycycline in their drinking water (100 μg/mL) to inactivate MYC (MYC OFF; circles) or treated with atorvastatin after 5 weeks of tumor growth, at doses of 1 mg/kg (triangles) or 10 mg/kg (stars). Each cohort consisted of 5 mice. Significant difference in survival was determined by Chi square test (AT, 1 mg/kg P < .002; AT, 10 mg/kg P < .02). (E) Representative picture of mouse prior to treatment and (F) after treatment with atorvastatin (1 mg/kg) (magnification 20× insert 40×) for 8 days. (G) Histology of a tumor sections stained with hematoxylin and eosin prior to treatment, consisting of tumor cells with high nuclear to cytoplasmic ratio, and (magnification 20× insert 40×) (H) after treatment with atorvastatin (magnification 20× insert 40×), where (magnification 20×) tumor cells appear to be apoptotic. Images were acquired as in “Viral infections.” (I) TUNEL assay was performed to determine the presence of apoptotic cells prior to treatment (magnification 20×) and (J) after treatment with atorvastatin (magnification 20×). Representative data are shown. Similar results were observed for 3 different tumor-derived lymphoma cell lines. Images were acquired as in “TUNEL assay.”