Valproic acid blocks adhesion of renal cell carcinoma cells to endothelium and extracellular matrix

Treatment strategies for metastatic renal cell carcinoma (RCC) have been limited due to chemotherapy and radiotherapy resistance. The development of targeted drugs has now opened novel therapeutic options. In the present study, anti-tumoral properties of the histone deacetylase inhibitor valproic acid (VPA) were tested in vitro and in vivo on pre-clinical RCC models. RCC cell lines Caki-1, KTC-26 or A498 were treated with various concentrations of VPA to evaluate tumour cell adhesion to vascular endothelial cells or to immobilized extracellular matrix proteins. In vivo tumour growth was conducted in subcutaneous xenograft mouse models. VPA was also combined with low dosed interferon-alpha (IFN-alpha) and the efficacy of the combination therapy, as opposed to VPA monotherapy, was compared. VPA significantly and dose-dependently prevented tumour cell attachment to endothelium or matrix proteins, accompanied by elevated histones H3 and H4 acetylation. VPA altered integrin-alpha and -beta subtype expression, in particular alpha(3), alpha(5) and beta(3), and blocked integrin-dependent signalling. In vivo, VPA significantly inhibited the growth of Caki-1 in subcutaneous xenografts with the 200 mg/kg being superior to the 400 mg/kg dosing schedule. VPA-IFN-alpha combination markedly enhanced the effects of VPA on RCC adhesion, and in vivo tumour growth was further reduced by the 400 mg/kg but not by the 200 mg/kg VPA dosing schedule. VPA profoundly blocked the interaction of RCC cells with endothelium and extracellular matrix and reduced tumour growth in vivo. Therefore, VPA should be considered an attractive candidate for clinical trials.