title: Synthesis and preliminary evaluation of n.c.a. iodoquine: a novel radiotracer with high uptake in cells with high ALDH1 expression.
abstract: OBJECTIVE
  Chloroquine has demonstrated high affinity for aldehyde dehydrogenase 1A1 (ALDH1), an enzyme expressed in the highly tumorigenic CD133+ brain tumor initiating subpopulation. The purpose of this study is to report the novel synthesis of a chloroquine analogue, n.c.a. iodoquine, and the in vitro and in vivo uptake in cells with high ALDH1 content.
  
  
  METHODS
  Iodoquine was synthesized in novel no-carrier-added forms (n.c.a.) for both 125I and 123I. I25I IQ and 18F FDG cell uptake assays were performed in the L1210 and L1210cpa (cyclophosphamide resistant), A549, and MG456 glioblastoma cell lines. Uptake was expressed as a percent of the administered activity. 125I IQ biodistribution studies assessed organ uptake at 1, 4, and 24 hours after IV administration (n= 15 total; 5 mice/timepoint). Radiation dosimetry estimates were calculated using standard OLINDA/EXM software. In vivo imaging of 123I IQ uptake in MG456 glioblastoma mouse model (n=10) was performed with small animal high resolution micro-SPECT. Autoradiography and histology co-localized radiotracer and tumor biodistribution. Uptake in MG456 glioblastoma tumors was quantified with gamma counting.
  
  
  RESULTS
  L1210 cpa (high ALDH1) showed significantly higher 125I IQ uptake compared to the parental L1210 (low ALDH1) for all time points through 4 hours (20.7% ± 1.4% versus 11.0% ± 0.5%; 21.3% ± 0.9% versus 11.0% ± 0.4%; 20.6% ± 0.7% versus 9.4% ± 0.3%; and 15.7% ± 0.7% versus 7.5% + 0.4% at 30 minutes, and 1, 2 and 4 hours, respectively; p < 0.001 for all time points). In the CD133+ fraction of MG456 glioblastoma cell line, IQ uptake was significantly higher compared to FDG at all time points through 4 hours (81.5% ± 0.9% versus 1.3% ± 0.1%; 88.8% ± 0.4% versus 1.3% ± 0.1%; 87.8% ± 2.1% versus 1.7% ± 0.2%; and 87.0% ± 2.4% versus 1.8% ± 0.1 at 30 minutes, and 1, 2 and 4 hours, respectively; p > 0.001 for all time points). The A549 lung cancer cell line also showed high IQ uptake through 4 hours. IQ normal biodistribution studies showed rapid renal excretion and very low normal background brain activity after IV administration. In vivo micro-SPECT images showed mild uptake in larger MG456 glioblastomas (n=6) as verified with autoradiography and histology. Gamma well counter uptake in large tumors was 2.3% ± 0.48% ID/g (n=5).
  
  
  CONCLUSIONS
  Iodoquine localizes to cells with high ALDH1 content. Cell assays show high 125I IQ uptake in the MG456 cell line, and in vivo micro-SPECT imaging showed mild 123I IQ uptake in MG456 glioblastomas. Further studies are necessary to investigate 131I IQ as a potential therapeutic agent targeting the highly tumorigenic CD133+ brain tumor stem cell subpopulation.
authors.affiliation: Duke University Medical Center, DUMC, Durham, NC 27710, USA. chin0004@mc.duke.edu
authors.forename: Bennett B
authors.initials: BB
authors.lastname: Chin
authors.forename: Anita
authors.initials: A
authors.lastname: Hjelemand
authors.forename: Jeremy
authors.initials: J
authors.lastname: Rich
authors.forename: Haijing
authors.initials: H
authors.lastname: Song
authors.forename: Christopher
authors.initials: C
authors.lastname: Lascola
authors.forename: Robert
authors.initials: R
authors.lastname: Storms
authors.forename: Roger
authors.initials: R
authors.lastname: McLendon
authors.forename: Robert
authors.initials: R
authors.lastname: Reiman
authors.forename: Kim L
authors.initials: KL
authors.lastname: Greer
authors.forename: Scott D
authors.initials: SD
authors.lastname: Metzler
authors.forename: Darryl
authors.initials: D
authors.lastname: McDougald
authors.forename: Diana
authors.initials: D
authors.lastname: Dai
authors.forename: Ganesan
authors.initials: G
authors.lastname: Vaidyanathan
mesh_terms: D000080924:Aldehyde Dehydrogenase 1 Family; D000818:Animals; D015153:Blotting, Western; D001932:Brain Neoplasms / Q000000981:diagnostic imaging / Q000201:enzymology; D045744:Cell Line, Tumor; D002738:Chloroquine / Q000031:analogs & derivatives* / Q000493:pharmacokinetics; D019008:Drug Resistance, Neoplasm; D005260:Female; D005909:Glioblastoma / Q000000981:diagnostic imaging / Q000201:enzymology; D007457:Iodine Radioisotopes / Q000493:pharmacokinetics*; D007527:Isoenzymes / Q000378:metabolism*; D007939:Leukemia L1210 / Q000201:enzymology; D008297:Male; D051379:Mice; D008819:Mice, Nude; D009369:Neoplasms / Q000000981:diagnostic imaging* / Q000201:enzymology; D011829:Radiation Dosage; D019275:Radiopharmaceuticals / Q000138:chemical synthesis / Q000493:pharmacokinetics*; D050697:Retinal Dehydrogenase / Q000378:metabolism*; D015899:Tomography, Emission-Computed, Single-Photon / Q000379:methods
chemical_list: D007457:Iodine Radioisotopes; D007527:Isoenzymes; D019275:Radiopharmaceuticals; D002738:Chloroquine; D000080924:Aldehyde Dehydrogenase 1 Family; C515028:ALDH1A1 protein, mouse; D050697:Retinal Dehydrogenase; C572571:iodoquine