title: Differential sensitivity in cell lines to photodynamic therapy in combination with ABCG2 inhibition.
abstract: BACKGROUND
  ABCG2 is an ATP-binding cassette transporter protein which has a role in the regulation of endogenous protoporphyrin IX (PpIX) levels.
  
  
  OBJECTIVE
  To understand the influence of ABCG2 on porphyrin-based photodynamic therapy (PDT) and fluorescence diagnosis (FD), we examined the role of endogenous ABCG2 in four human cell lines from the epidermis (HaCaT keratinocytes), oesophagus (OE19 adenocarcinoma), brain (SH-SY5Y neuroblastoma) and bladder (HT1197 carcinoma).
  
  
  METHODS
  Cells were incubated with ALA or MAL in the presence or absence of the ABCG2 activity inhibitor Ko-143. Porphyrin accumulation was detected by spectrofluorimetric analysis and high performance liquid chromatography (HPLC) with porphyrin localisation observed by confocal laser scanning microscopy. PDT efficacy was assessed 24h post irradiation (1.5J/cm(2) red light) by the neutral red (NR) assay.
  
  
  RESULTS
  We show cell-specific differences when Ko-143 was co-incubated with ALA or, in particular with, MAL. Enhanced PDT-induced cell kill was shown in HaCaT, OE19 and HT1197 cells, but not SH-SY5Y cells and could be explained by porphyrin accumulation and expression of ABCG2. We have also found that despite high levels of intracellular PpIX, the OE19 cells were protected from phototoxic cell death by PpIX compartmentalisation. This could be reversed by Ko-143.
  
  
  CONCLUSIONS
  The results from this study show a possible cause of reduced sensitivity to ALA/MAL-PDT, with a potential solution to overcome this effect in certain tissue types. The potential to improve PDT with Ko-143 remains promising.
authors.affiliation: Photobiology Unit, University of Dundee, Ninewells Hospital and Medical School, Dundee, Scotland DD1 9SY, United Kingdom. g.a.barron@dundee.ac.uk
authors.forename: Gemma A
authors.initials: GA
authors.lastname: Barron
authors.forename: Harry
authors.initials: H
authors.lastname: Moseley
authors.forename: Julie A
authors.initials: JA
authors.lastname: Woods
mesh_terms: D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters / Q000037:antagonists & inhibitors* / Q000378:metabolism; D000241:Adenosine / Q000031:analogs & derivatives* / Q000494:pharmacology; D000622:Aminolevulinic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology* / Q000627:therapeutic use; D045744:Cell Line, Tumor; D054659:Diketopiperazines; D004952:Esters; D005110:Extracellular Space / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects / Q000528:radiation effects; D006576:Heterocyclic Compounds, 4 or More Rings; D006801:Humans; D042541:Intracellular Space / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects; D007536:Isomerism; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D010778:Photochemotherapy; D011524:Protoporphyrins / Q000378:metabolism
chemical_list: C541506:3-(6-isobutyl-9-methoxy-1,4-dioxo-1,2,3,4,6,7,12,12a-octahydropyrazino(1',2'-1,6)pyrido(3,4-b)indol-3-yl)propionic acid tert-butyl ester; C116614:ABCG2 protein, human; D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters; D054659:Diketopiperazines; D004952:Esters; D006576:Heterocyclic Compounds, 4 or More Rings; D009363:Neoplasm Proteins; D011524:Protoporphyrins; D000622:Aminolevulinic Acid; C028025:protoporphyrin IX; D000241:Adenosine
keywords: ABCG2; Aminolaevulinic acid; Chemo sensitivity; Ko-143; Photodynamic therapy; Protoporphyrin IX