title: Cross-resistance to clinically used tyrosine kinase inhibitors sunitinib, sorafenib and pazopanib.
abstract: OBJECTIVE
  When during cancer treatment resistance to a tyrosine kinase inhibitor (TKI) occurs, switching to another TKI is often considered as a reasonable option. Previously, we reported that resistance to sunitinib may be caused by increased lysosomal sequestration, leading to increased intracellular lysosomal storage and, thereby, inactivity. Here, we studied the effect of several other TKIs on the development of (cross-) resistance.
  
  
  METHODS
  TKI resistance was induced by continuous exposure of cancer cell lines to increasing TKI concentrations for 3-4 months. (Cross-) resistance was evaluated using MTT cell proliferation assays. Intracellular TKI concentrations were measured using LC-MS/MS. Western blotting was used to detect lysosome-associated membrane protein-1 and -2 (LAMP1/2) expression.
  
  
  RESULTS
  The previously generated sunitinib-resistant (SUN) renal cancer cells (786-O) and colorectal cancer cells (HT-29) were found to be cross-resistant to pazopanib, erlotinib and lapatinib, but not sorafenib. Exposure of 786-O and HT-29 cells to sorafenib, pazopanib or erlotinib for 3-4 months induced drug resistance to pazopanib and erlotinib, but not sorafenib. Intracellular drug accumulation was found to be increased in pazopanib- and erlotinib-, but not in sorafenib-exposed cells. Lysosomal capacity, reflected by LAMP1/2 expression, was found to be increased in resistant cells and, in addition, to be transient. No cross-resistance to the mTOR inhibitor everolimus was detected.
  
  
  CONCLUSIONS
  Our data indicate that tumor cells can develop (cross-) resistance to TKIs, and that such resistance includes increased intracellular drug accumulation accompanied by increased lysosomal storage. Transient (cross-) resistance was found to occur for several of the TKIs tested, but not for everolimus, indicating that switching from a TKI to a mTOR inhibitor may be an attractive therapeutic option.
authors: Department of Medical Oncology, VU University Medical Center, Rm 3A46, De Boelelaan 1117, 1081 HV, Amsterdam, The Netherlands.
authors: Kristy J
authors: KJ
authors: Gotink
authors: Maria
authors: M
authors: Rovithi
authors: Richard R
authors: RR
authors: de Haas
authors: Richard J
authors: RJ
authors: Honeywell
authors: Henk
authors: H
authors: Dekker
authors: Dennis
authors: D
authors: Poel
authors: Kaamar
authors: K
authors: Azijli
authors: Godefridus J
authors: GJ
authors: Peters
authors: Henk J
authors: HJ
authors: Broxterman
authors: Henk M W
authors: HM
authors: Verheul
mesh_terms: D015153:Blotting, Western; D045744:Cell Line, Tumor; D019008:Drug Resistance, Neoplasm / Q000187:drug effects*; D006801:Humans; D007191:Indazoles; D007211:Indoles / Q000494:pharmacology; D009536:Niacinamide / Q000031:analogs & derivatives / Q000494:pharmacology; D010671:Phenylurea Compounds / Q000494:pharmacology; D047428:Protein Kinase Inhibitors / Q000494:pharmacology*; D011743:Pyrimidines / Q000494:pharmacology; D011758:Pyrroles / Q000494:pharmacology; D000077157:Sorafenib; D013449:Sulfonamides / Q000494:pharmacology; D000077210:Sunitinib; D053719:Tandem Mass Spectrometry
chemical_list: D007191:Indazoles; D007211:Indoles; D010671:Phenylurea Compounds; D047428:Protein Kinase Inhibitors; D011743:Pyrimidines; D011758:Pyrroles; D013449:Sulfonamides; D009536:Niacinamide; C516667:pazopanib; D000077157:Sorafenib; D000077210:Sunitinib