Berberine enhances gemcitabine­induced cytotoxicity in bladder cancer by downregulating Rad51 expression through inactivating the PI3K/Akt pathway.

Although gemcitabine (GEM) has been used to treat bladder cancer (BC) for a number of years, severe adverse events or drug resistance frequently develops. A series of drugs have been proved to sensitize patients to GEM and reduce the side effects. The aim of the present study was to evaluate the potential effects of berberine (BER) on GEM­induced cytotoxicity in BC and to explore the possible underlying mechanisms. T24 and 5637 human BC cell lines were treated with GEM and/or BER before cell proliferation, apoptosis and migration were studied. Oncomine databases and Gene Expression Profiling Interactive Analysis (GEPIA) were used to retrieve RAD51 recombinase (Rad51) mRNA expression. Overexpression plasmid or specific Rad51 small interfering RNA were used to examine the role of Rad51 in drug­treated BC cells. BC model mice were administered with GEM and/or BER before changes in tumor volume, size and Ki67 expression were assessed. BER enhanced GEM­induced cytotoxicity, apoptosis and inhibition of migration, whilst attenuating the GEM­induced upregulation of phosphorylated Akt and Rad51 expression. According to Oncomine and GEPIA analyses, Rad51 was found to be significantly upregulated in BC tissues compared with that in normal tissues, where there was a weak positive correlation between Rad51 and Akt1 expression. Knockdown of Rad51 enhanced GEM­induced cytotoxicity, whilst overexpression of Rad51 reversed the suppressed cell viability induced by BER and GEM. Inactivation of the PI3K/Akt pathway by LY294002 or BER enhanced GEM­induced cytotoxicity and downregulated Rad51 expression, whilst overexpression of constitutively active Akt restored Rad51 expression and cell viability that was previously decreased by BER and GEM. BER additively inhibited tumor growth and Ki67 expression when combined with GEM in vivo. These results suggest that BER can enhance GEM­induced cytotoxicity in BC by downregulating Rad51 expression through inactivating the PI3K/Akt pathway, which may represent a novel therapeutic target for BC treatment.