TZ9 is a novel inhibitor of Rad6 ubiquitin conjugating enzyme(E2 enzyme); inhibits MDA-MB-231 cell proliferation with IC50 of ~6 uM. IC50 value: 6 uM  Target: Rad6 inhibitor The bulk of MDA-MB-231 cells treated with 10 μmol/L or more SMI #9 displayed a round morphology compared with controls and less than 5 μmol/L doses of SMI #9. Simultaneous comparison of SMIs #8 and 9 confirmed SMI #9 inhibits Matrigel-induced migration of MDA-MB-231 cells in a dose-dependent manner compared with SMI #8. 5 μmol/L SMI #9 treatment triggered morphologic changes consistent with apoptosis in a time-dependent manner. 5 μmol/L SMI #9 treatment of MDA-MB-231 cells for 24 hours increased the proportion of G2–M-arrested cells by 2-fold and was accompanied by a proportional decrease in S-phase cells. SMIs #8 or 9 treatments dramatically reduced β-catenin staining as visualized by reduced merged Rad6/β-catenin yellow fluorescence.