Valproic acid inhibits adhesion of vincristine- and cisplatin-resistant neuroblastoma tumour cells to endothelium

Drug resistance to chemotherapy is often associated with increased malignancy in neuroblastoma (NB). In pursuit of alternative treatments for chemoresistant tumour cells, we tested the response of multidrug-resistant SKNSH and of vincristine (VCR)-, doxorubicin (DOX)-, or cisplatin (CDDP)-resistant UKF-NB-2, UKF-NB-3 or UKF-NB-6 NB tumour cell lines to valproic acid (VPA), a differentiation inducer currently in clinical trials. Drug resistance caused elevated NB adhesion (UKF-NB-2(VCR), UKF-NB-2(DOX), UKF-NB-2(CDDP), UKF-NB-3(VCR), UKF-NB-3(CDDP), UKF-NB-6(VCR), UKF-NB-6(CDDP)) to an endothelial cell monolayer, accompanied by downregulation of the adhesion receptor neural cell adhesion molecule (NCAM). Based on the UKF-NB-3 model, N-myc proteins were enhanced in UKF-NB-3(VCR) and UKF-NB-3(CDDP), compared to the drug naïve controls. p73 was diminished, whereas the p73 isoform deltaNp73 was upregulated in UKF-NB-3(VCR) and UKF-NB-3(CDDP). Valproic acid blocked adhesion of UKF-NB-3(VCR) and UKF-NB-3(CDDP), but not of UKF-NB-3(DOX), and induced the upregulation of NCAM surface expression, NCAM protein content and NCAM coding mRNA. Valproic acid diminished N-myc and enhanced p73 protein level, coupled with downregulation of deltaNp73 in UKF-NB-3(VCR) and UKF-NB-3(CDDP). Valproic acid also reverted enhanced adhesion properties of drug-resistant UKF-NB-2, UKF-NB-6 and SKNSH cells, and therefore may provide an alternative approach to the treatment of drug-resistant NB by blocking invasive processes.

Valproic acid induces expression of neutrophil chemoattractants of the CXC chemokine family in endothelial cells

The branched-chain fatty acid valproate (valproic acid; VPA) displays antitumoral properties by blocking tumor growth, progression and invasion. Recent data have shown that VPA reduces the angiogenic activity of endothelial cells. The object of this study was to investigate whether endothelial modulation might also influence the level of chemotactic mediators. Endothelial cells were isolated from human umbilical cord veins (HUVEC) and treated with VPA-concentrations ranging from 0.125 mM to 1 mM. The mRNA level of CXC-chemokines was investigated by reverse transcriptase-polymerase chain reaction. The proliferative activity of HUVEC was measured as well. VPA evoked a striking increase in the neutrophil chemoattractants CXCL1, CXCL3, CXCL4, CXCL5 and a moderate increase in CXCL6 with maximal effects after a 3-day incubation period. Other CXC-chemokines and CXC-receptors remained unaffected. HUVEC growth was diminished time- and dose-dependently by VPA. We conclude that VPA treatment leads to alterations in the chemokine expression profile of endothelial cells. This might allow more neutrophils to reach the tumor area and trigger cytolysis.