Valproic Acid Represses Autophagy And Enhances The Anti-myeloma Activity Of DNA-damaging Drugs

Background Multiple myeloma(MM) is a malignant disease originated from the proliferation of clonal plasma cells in bone marrow and accompanied with the monoclonal immunoglobulin detected in the serum and urine. Although many new treatments emerged recently, it still remained an uncurable disease. The progression and relapse of MM is a common problem we faced when the clinic therapy undergoing, besides the reason probably related to the resistance to radiation and chemotherapy conferred by autophagy occured in tumor cells.Therefore it makes a huge difference to study the treatment about MM on autophagy.Valproic acid(VPA) belongs to one of the histone deacetylase inhibitor(HDACi), and the modification of histone is connected with autophagy. Thus, the research about the mechanism of VPA would help to the treatment of MM in clinic.ObjectiveThis study is aimed to explore the autophagy effect of VPA on human MM cell lines and the effects of VPA combined with Doxorubicin(DOX) or Melphalan(MEL) on anti-myeloma activity. To observe the relationship between VPA and autophagy in human MM cell lines and to see whether VPA can alleviate the side effects induced byDNA-damage drugs and improve the anti-myeloma activity at the same time.MethodsHuman MM cells were treated with VPA/DOX/MEL at different concentrations.The cell proliferation of each single group was detected by MTT assay. According to the inhibitory concentration(IC) detect the non-toxic dose of VPA in presence of DOX or MEL at different concentrations(ie.IC10, IC20, IC40) by MTT. The groups of Western blot were set as follows: VPA alone; DOX alone; MEL alone; VPA of non-toxic dose(IC5)in presence of DOX(IC10); VPA of non-toxic dose(IC5) in presence of MEL(IC10).Western blot was used to detect and compare the expression levels of autophagy-related proteins(LC3, ATG5, ATG7) and histone H4K16 acetylation in each single group and co-treatment group.ResultsThe results showed that as the treatment concentration going up, the cell proliferation inhibition ascending. Besides cell proliferation inhibition was markedly increased in VPA plus DOX or MEL compared with DOX or MEL alone(P<0.05). The level of LC3 in VPA alone group was decreased while the level of H4K16 ac was increased. The level of LC3 in DOX or MEL alone group was increased while the level of H4K16 ac was decreased. Both LC3 and H4K16 ac expression levels in co-treatment were between VPA and DOX or MEL co-treatment and alone.ConclusionImportantly, VPA of non-toxic dose not only augments the anti-myeloma activity of DOX or MEL, but also down-regulates the autophagy-related protein expression and increases H4K16 ac protein levels. Taking in consideration that H4K16 ac can inhibit the transcription of autophagy-related genes, the data presented here suggests that VPA enhance the anti-myeloma activity of DNA-damaging drugs via, at least in part,H4K16ac-mediated suppression of cytoprotective autophagy.