title: HDAC-inhibition counteracts everolimus resistance in renal cell carcinoma in vitro by diminishing cdk2 and cyclin A.
abstract: BACKGROUND
  Targeted therapies have improved therapeutic options of treating renal cell carcinoma (RCC). However, drug response is temporary due to resistance development.
  
  
  METHODS
  Functional and molecular changes in RCC Caki-1 cells, after acquired resistance to the mammalian target of rapamycin (mTOR)-inhibitor everolimus (Cakires), were investigated with and without additional application of the histone deacetylase (HDAC)-inhibitor valproic acid (VPA). Cell growth was evaluated by MTT assay, cell cycle progression and apoptosis by flow cytometry. Target molecules of everolimus and VPA, apoptotic and cell cycle regulating proteins were investigated by western blotting. siRNA blockade was performed to evaluate the functional relevance of the proteins.
  
  
  RESULTS
  Everolimus resistance was accompanied by significant increases in the percentage of G2/M-phase cells and in the IC50. Akt and p70S6K, targets of everolimus, were activated in Cakires compared to drug sensitive cells. The most prominent change in Cakires cells was an increase in the cell cycle activating proteins cdk2 and cyclin A. Knock-down of cdk2 and cyclin A caused significant growth inhibition in the Cakires cells. The HDAC-inhibitor, VPA, counteracted everolimus resistance in Cakires, evidenced by a significant decrease in tumor growth and cdk2/cyclin A.
  
  
  CONCLUSIONS
  It is concluded that non-response to everolimus is characterized by increased cdk2/cyclin A, driving RCC cells into the G2/M-phase. VPA hinders everolimus non-response by diminishing cdk2/cyclin A. Therefore, treatment with HDAC-inhibitors might be an option for patients with advanced renal cell carcinoma and acquired everolimus resistance.
authors.forename: Eva
authors.initials: E
authors.lastname: Juengel
authors.forename: Snigdha
authors.initials: S
authors.lastname: Nowaz
authors.forename: Jasmina
authors.initials: J
authors.lastname: Makarevi
authors.forename: Iyad
authors.initials: I
authors.lastname: Natsheh
authors.forename: Isabella
authors.initials: I
authors.lastname: Werner
authors.forename: Karen
authors.initials: K
authors.lastname: Nelson
authors.forename: Michael
authors.initials: M
authors.lastname: Reiter
authors.forename: Igor
authors.initials: I
authors.lastname: Tsaur
authors.forename: Jens
authors.initials: J
authors.lastname: Mani
authors.forename: Sebastian
authors.initials: S
authors.lastname: Harder
authors.forename: Georg
authors.initials: G
authors.lastname: Bartsch
authors.forename: Axel
authors.initials: A
authors.lastname: Haferkamp
authors.affiliation: Department of Urology, Goethe-University, Interdisciplinary Science Building, Building 25A, Room 404, Theodor-Stern-Kai 7, Frankfurt / Main D-60590, Germany. blaheta@em.uni-frankfurt.de.
authors.forename: Roman A
authors.initials: RA
authors.lastname: Blaheta
mesh_terms: D002292:Carcinoma, Renal Cell / Q000188:drug therapy* / Q000235:genetics* / Q000473:pathology; D045744:Cell Line, Tumor; D019925:Cyclin A / Q000378:metabolism*; D051357:Cyclin-Dependent Kinase 2 / Q000378:metabolism*; D019008:Drug Resistance, Neoplasm / Q000187:drug effects; D000068338:Everolimus; D059565:G2 Phase Cell Cycle Checkpoints / Q000187:drug effects; D055785:Gene Knockdown Techniques; D056572:Histone Deacetylase Inhibitors / Q000008:administration & dosage; D006655:Histone Deacetylases / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D020123:Sirolimus / Q000031:analogs & derivatives / Q000627:therapeutic use; D014635:Valproic Acid / Q000008:administration & dosage
chemical_list: D019925:Cyclin A; D056572:Histone Deacetylase Inhibitors; D014635:Valproic Acid; D000068338:Everolimus; C495894:CDK2 protein, human; D051357:Cyclin-Dependent Kinase 2; D006655:Histone Deacetylases; D020123:Sirolimus