Cryptotanshinone Inhibits Proliferation Yet Induces Apoptosis by Suppressing STAT3 Signals in Renal Cell Carcinoma

It has been established that signal transducer and activator of transcription 3 serves as an oncoprotein in various human cancers; targeting it is therefore a reasonable approach for emerging cancer therapies. Cryptotanshinone, a natural compound extracted from the root of Salvia miltiorrhiza Bunge, has been identified as a potential STAT3 inhibitor. However, its functional role in renal cell carcinomas remains largely unknown. Therefore, we investigated the mode of action for cryptotanshinone. We found that cryptotanshinone substantially suppressed cancer cell growth while it promoted cell apoptosis by inhibiting the phosphorylation of STAT3 at Tyr705 and its blocking nuclear translocation. Coordinately, P-AKT, CyclinD1, C-MYC, MEKK2, and HGF were down-regulated and cell cycle progression was arrested at the G0/G1 phase, thereby attenuating cell proliferation. Moreover, the level of Cleaved-Caspase-3 was elevated while Bcl-2 and Survivin were down-regulated, accounting for the increased apoptosis. Furthermore, in vivo results revealed that cryptotanshinone effectively inhibits tumorigenesis in an A498-xenografted mouse model. Taken together, our data gives a more comprehensive understanding of how cryptotanshinone functions in renal cell carcinomas and demonstrates its potential as a powerful therapeutic approach to treat renal cell carcinomas.