title: Acquired resistance to sunitinib in human renal cell carcinoma cells is mediated by constitutive activation of signal transduction pathways associated with tumour cell proliferation.
abstract: WHAT'S KNOWN ON THE SUBJECT? AND WHAT DOES THE STUDY ADD?: Although there have been a few studies investigating the molecular mechanism mediating the acquisition of resistance to molecular-targeted agents, including sunitinib, by renal cell carcinoma (RCC) cells, this mechanism remains largely unclear. The maintenance of protein kinase activation during sunitinib treatment may be involved in the acquisition of a phenotype resistant to sunitinib in RCC, and additional treatment with agents targeting activated protein kinases could be a promising approach for overcoming resistance to sunitinib in RCC.
  
  
  OBJECTIVE
  To characterise the mechanism involved in the acquired resistance to sunitinib, a potential inhibitor of multiple receptor tyrosine kinases (RTKs), in renal cell carcinoma (RCC).
  
  
  METHODS
  A parental human RCC cell line, ACHN (ACHN/P), was continuously exposed to increasing doses of sunitinib, and a cell line resistant to sunitinib (ACHN/R), showing an ≈5-fold higher IC50 (concentration that reduces the effect by 50%) than that of ACHN/P, was developed.
  
  
  RESULTS
  ACHN/R appeared to acquire significant cross resistance to sorafenib; however, there were no significant differences in sensitivities to the Mammalian target of rapamycin inhibitors, temsirolimus and everolimus, between ACHN/P and ACHN/R. After sunitinib treatment, the expression levels of phosphorylated Akt and p44/42 mitogen-activated protein kinase in ACHN/P, but not those in ACHN/R, were significantly inhibited. RTK assay showed that treatment of ACHN/P with sunitinib resulted in the marked downregulation of several phosphorylated RTKs compared with that of ACHN/R. Additional treatment with a specific inhibitor of Akt significantly increased the sensitivity of ACHN/R to sunitinib, but not that of ACHN/P. There were no significant differences between in vivo growth patterns of ACHN/P and ACHN/R in mice before and after the administration of sunitinib; however, the proportion of cells positive for TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling) staining in ACHN/P tumour was significantly greater than that in ACHN/R tumour in mice treated with sunitinib.
  
  
  CONCLUSIONS
  The maintenance of protein kinase activation during sunitinib treatment may be involved in the acquisition of resistant phenotype to sunitinib in RCC cells.
authors.affiliation: Division of Urology, Kobe University Graduate School of Medicine, Kobe, Japan.
authors.forename: Iori
authors.initials: I
authors.lastname: Sakai
authors.forename: Hideaki
authors.initials: H
authors.lastname: Miyake
authors.forename: Masato
authors.initials: M
authors.lastname: Fujisawa
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000627:therapeutic use*; D002292:Carcinoma, Renal Cell / Q000188:drug therapy* / Q000473:pathology*; D049109:Cell Proliferation / Q000187:drug effects*; D019008:Drug Resistance, Neoplasm; D006801:Humans; D007211:Indoles / Q000627:therapeutic use*; D007680:Kidney Neoplasms / Q000188:drug therapy* / Q000473:pathology*; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D011758:Pyrroles / Q000627:therapeutic use*; D015398:Signal Transduction / Q000187:drug effects*; D000077210:Sunitinib; D014407:Tumor Cells, Cultured
chemical_list: D000970:Antineoplastic Agents; D007211:Indoles; D011758:Pyrroles; D000077210:Sunitinib