title: The tyrosine kinase inhibitor imatinib mesylate enhances the efficacy of photodynamic therapy by inhibiting ABCG2.
abstract: OBJECTIVE
  The ATP-binding cassette protein ABCG2 (breast cancer resistance protein) effluxes some of the photosensitizers used in photodynamic therapy (PDT) and, thus, may confer resistance to this treatment modality. Tyrosine kinase inhibitors (TKI) can block the function of ABCG2. Therefore, we tested the effects of the TKI imatinib mesylate (Gleevec) on photosensitizer accumulation and in vitro and in vivo PDT efficacy.
  
  
  METHODS
  Energy-dependent photosensitizer efflux and imatinib mesylate's effects on intracellular accumulation of clinically used second- and first-generation photosensitizers were studied by flow cytometry in murine and human cells with and without ABCG2 expression. Effects of ABCG2 inhibition on PDT were examined in vitro using cell viability assays and in vivo measuring photosensitizer accumulation and time to regrowth in a RIF-1 tumor model.
  
  
  RESULTS
  Energy-dependent efflux of 2-(1-hexyloxethyl)-2-devinyl pyropheophorbide-a (HPPH, Photochlor), endogenous protoporphyrin IX (PpIX) synthesized from 5-aminolevulenic acid, and the benzoporphyrin derivative monoacid ring A (BPD-MA, Verteporfin) was shown in ABCG2+ cell lines, but the first-generation multimeric photosensitizer porfimer sodium (Photofrin) and a novel derivative of HPPH conjugated to galactose were minimally transported. Imatinib mesylate increased accumulation of HPPH, PpIX, and BPD-MA from 1.3- to 6-fold in ABCG2+ cells, but not in ABCG2- cells, and enhanced PDT efficacy both in vitro and in vivo.
  
  
  CONCLUSIONS
  Second-generation clinical photosensitizers are transported out of cells by ABCG2, and this effect can be abrogated by coadministration of imatinib mesylate. By increasing intracellular photosensitizer levels in ABCG2+ tumors, imatinib mesylate or other ABCG2 transport inhibitors may enhance efficacy and selectivity of clinical PDT.
authors: Department of Dermatology, Medicine, Roswell Park Cancer Institute, Buffalo, New York 14263, USA.
authors: Weiguo
authors: W
authors: Liu
authors: Maria R
authors: MR
authors: Baer
authors: Mary Jo
authors: MJ
authors: Bowman
authors: Paula
authors: P
authors: Pera
authors: Xiang
authors: X
authors: Zheng
authors: Janet
authors: J
authors: Morgan
authors: Ravindra A
authors: RA
authors: Pandey
authors: Allan R
authors: AR
authors: Oseroff
mesh_terms: D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters / Q000502:physiology*; D000970:Antineoplastic Agents / Q000627:therapeutic use; D001549:Benzamides; D002294:Carcinoma, Squamous Cell; D045744:Cell Line, Tumor; D003131:Combined Modality Therapy; D006801:Humans; D007012:Hypopharyngeal Neoplasms; D000068877:Imatinib Mesylate; D009363:Neoplasm Proteins / Q000502:physiology*; D010778:Photochemotherapy; D017319:Photosensitizing Agents / Q000037:antagonists & inhibitors / Q000627:therapeutic use*; D010879:Piperazines / Q000627:therapeutic use*; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors; D011743:Pyrimidines / Q000627:therapeutic use*
chemical_list: C116614:ABCG2 protein, human; D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters; D000970:Antineoplastic Agents; D001549:Benzamides; D009363:Neoplasm Proteins; D017319:Photosensitizing Agents; D010879:Piperazines; D011743:Pyrimidines; D000068877:Imatinib Mesylate; D011505:Protein-Tyrosine Kinases