title: Lysosomal sequestration of sunitinib: a novel mechanism of drug resistance.
abstract: OBJECTIVE
  Resistance to antiangiogenic tyrosine kinase inhibitors such as sunitinib is an important clinical problem, but its underlying mechanisms are largely unknown. We analyzed tumor sunitinib levels in mice and patients and studied sensitivity and resistance mechanisms to sunitinib.
  
  
  METHODS
  Intratumoral and plasma sunitinib concentrations in mice and patients were determined. Sunitinib exposure on tumor cell proliferation was examined. Resistant tumor cells were derived by continuous exposure and studied for alterations in intracellular sunitinib accumulation and activity.
  
  
  RESULTS
  Intratumoral concentrations of sunitinib in mice and patients were 10.9 ± 0.5 and 9.5 ± 2.4 μmol/L, respectively, whereas plasma concentrations were 10-fold lower, 1.0 ± 0.1 and 0.3 ± 0.1 μmol/L, respectively. Sunitinib inhibited tumor cell growth at clinically relevant concentrations in vitro, with IC(50) values of 1.4 to 2.3 μmol/L. Continuous exposure to sunitinib resulted in resistance of 786-O renal and HT-29 colon cancer cells. Fluorescent microscopy revealed intracellular sunitinib distribution to acidic lysosomes, which were significantly higher expressed in resistant cells. A 1.7- to 2.5-fold higher sunitinib concentration in resistant cells was measured because of increased lysosomal sequestration. Despite the higher intracellular sunitinib accumulation, levels of the key signaling p-Akt and p-ERK 1/2 were unaffected and comparable with untreated parental cells, indicating reduced effectiveness of sunitinib.
  
  
  CONCLUSIONS
  We report that sunitinib inhibits tumor cell proliferation at clinically relevant concentrations and found lysosomal sequestration to be a novel mechanism of sunitinib resistance. This finding warrants clinical evaluation whether targeting lysosomal function will overcome sunitinib resistance.
authors: Department of Medical Oncology, VU University Medical Center, Amsterdam, the Netherlands.
authors: Kristy J
authors: KJ
authors: Gotink
authors: Henk J
authors: HJ
authors: Broxterman
authors: Mariette
authors: M
authors: Labots
authors: Richard R
authors: RR
authors: de Haas
authors: Henk
authors: H
authors: Dekker
authors: Richard J
authors: RJ
authors: Honeywell
authors: Michelle A
authors: MA
authors: Rudek
authors: Laurens V
authors: LV
authors: Beerepoot
authors: René J
authors: RJ
authors: Musters
authors: Gerrit
authors: G
authors: Jansen
authors: Arjan W
authors: AW
authors: Griffioen
authors: Yehuda G
authors: YG
authors: Assaraf
authors: Roberto
authors: R
authors: Pili
authors: Godefridus J
authors: GJ
authors: Peters
authors: Henk M W
authors: HM
authors: Verheul
mesh_terms: D020533:Angiogenesis Inhibitors / Q000097:blood / Q000378:metabolism* / Q000494:pharmacology; D000818:Animals; D002292:Carcinoma, Renal Cell / Q000188:drug therapy / Q000378:metabolism; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D019008:Drug Resistance, Neoplasm; D005260:Female; D045325:HCT116 Cells; D019073:HT29 Cells; D006801:Humans; D007211:Indoles / Q000097:blood / Q000378:metabolism* / Q000494:pharmacology; D007680:Kidney Neoplasms / Q000188:drug therapy / Q000378:metabolism / Q000473:pathology; D008247:Lysosomes / Q000378:metabolism*; D051379:Mice; D009369:Neoplasms / Q000188:drug therapy / Q000378:metabolism / Q000473:pathology; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors; D011758:Pyrroles / Q000097:blood / Q000378:metabolism* / Q000494:pharmacology; D000077210:Sunitinib
chemical_list: D020533:Angiogenesis Inhibitors; D007211:Indoles; D011758:Pyrroles; D011505:Protein-Tyrosine Kinases; D000077210:Sunitinib