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Inhibition of DHODH induces differentiation in AML
regulated by isobavachalcone in a time-dependent manner (Figure 4E). MYC has been reported to be an unstable pro- tein that is degraded rapidly via the proteasome pathway.30 As shown in Figure 4F, isobavachalcone induced significant degradation of MYC, and treatment with MG132 (a pro-
teasome inhibitor) blocked MYC deregulation. Moreover, extended isobavachalcone treatment (24 h) reduced MYC gene transcription in a MYC reporter assay (Figure 4G). Figure 4H further confirms down-regulation of MYC and p21 gene expression following isobavachalcone treatment.
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Figure 5. Isobavachalcone suppresses tumor growth in a subcutaneous HL60 xenograft mouse model. (A) Measurements of tumor volume in an HL60 xenograft mouse model treated with vehicle or the indicated dosages of compounds for 18 days. Changes in mean tumor sizes compared with the control group. Bars repre- sent mean ± SD for eight animals in each group. (B) Effect of isobavachalcone on tumor weights. (C) The body weight of mice was measured every 3 days. (D) Histological morphology of tumor tissue, stained with hematoxylin and eosin, from the different groups. (E) Images of the major organ tissues, stained with hema- toxylin and eosin, from the different groups of animals. (F) DHODH protein expression in tumors was examined at the time the animals were sacrificed. (G) The enzyme activity of DHODH in xenograft tumor tissues treated with vehicle, isobavachalcone or leflunomide was measured by fluorescence assay. (H) Western blot analysis of the changes of apoptosis-associated proteins at day 18 of HL60 xenograft tumors treated with vehicle, isobavachalcone or leflunomide. (I) Expression levels of MYC and p21 in tumors treated with vehicle, isobavachalcone, or leflunomide were estimated by western blot. Data represent means ± SD. A one-way ANOVA test was performed, **P<0.01 and ***P<0.001. IBC: isobavachalocone; LEF: leflunomide.
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