title: Comparative study on DOTA-derivatized bombesin analog labeled with 90Y and 177Lu: in vitro and in vivo evaluation.
abstract: BACKGROUND
  The aim of the study was to compare in vitro and in vivo a novel DOTA-chelated bombesin (BN) analog of the amino acid sequence, QRLGNQWAVGHLM-CONH(2) (BN[2-14]NH(2)), labeled with (90)Y and (177)Lu, for its potential use in targeted radiotherapy of tumors expressing gastrin releasing peptide (GRP) receptors. The same amino acid sequence, but with different chelator, referred as BN1.1 (Gly-Gly-Cys-Aca-QRLGNQWAVGHLM-CONH(2)), has already been studied and reported; however, the DOTA-chelated one, suitable for labeling with M(+3) type radiometals, was not yet described.
  
  
  METHODS
  The conditions for labeling of DOTA-BN[2-14]NH(2) with noncarrier added (90)Y and with (177)Lu [specific activity (SA), 15 Ci/mg Lu] were investigated and optimized to provide (90)Y-DOTA-BN[2-14]NH(2) and (177)Lu-DOTA-BN[2-14]NH(2) of high SA. The stability of the radiolabeled compounds in human serum was evaluated over a period of 24 h. The human prostate cancer cell line PC-3, known to express GRP receptors, was used for in vitro evaluation of radiolabeled peptide affinity to GRP receptors and for assessment of cytotoxicity of both nonlabeled and radiolabeled peptide. Biodistribution accompanied by receptor blocking was studied in normal Swiss mice.
  
  
  RESULTS
  (90)Y-DOTA-BN[2-14]NH(2) and (177)Lu-DOTA-BN[2-14]NH(2) were obtained with radiochemical yield >98% and high SA (67.3 GBq (90)Y/mumol and 33.6 GBq (177)Lu/mumol, respectively). They were stable when incubated in human serum for up to 24 h. The binding affinities of DOTA-BN[2-14]NH(2) and both (nat)Y- and (nat)Lu-labeled analogs to GRP receptors were high (IC(50)=1.78, 1.99, and 1.34 nM, respectively), especially for the (nat)Lu-DOTA-BN[2-14]NH(2) complex. The cytotoxicity study of DOTA-BN[2-14]NH(2) to PC-3 cells revealed an IC(50)=6300 nM after 72 h of exposition, while the labeled derivatives showed no significant cytotoxic effect. The internalization rate to PC-3 cells was more rapid for (177)Lu-labeled peptide (84.87%) than for the (90)Y-labeled one (80.79%), while the efflux rate was slower for (177)Lu-DOTA-BN[2-14]NH(2) (46.8% vs. 61.74%). The biodistribution study of both derivatives in normal mice revealed a specific binding to GRP receptor-positive tissues, which could be blocked by coinjection of cold peptide. The effect of receptor blockage in vivo was also more pronounced for the (177)Lu-labeled peptide than that for the (90)Y-labeled (81% vs. 42%, respectively).
  
  
  CONCLUSIONS
  Our studies demonstrated that DOTA-BN[2-14]NH(2) can be labeled with (90)Y (NCA) and (177)Lu (CA) with high radiochemical yields. The in vitro and in vivo comparison between (90)Y-DOTA-BN[2-14]NH(2) and (177)Lu-DOTA-BN[2-14]NH(2) indicated that the change of radiometal in the complex from Y to Lu influence the binding affinity to the GRP receptors with preference to the (177)Lu-labeled derivative.
authors: Institute R-RP, NCSR "Demokritos", Athens, Hellas; IAE, Radioisotope Centre POLATOM, 05-400 Swierk-Otwock, Poland. eytyxiak@yahoo.com
authors: Eftychia
authors: E
authors: Koumarianou
authors: Renata
authors: R
authors: Mikołajczak
authors: Dariusz
authors: D
authors: Pawlak
authors: Xhristos
authors: X
authors: Zikos
authors: Pinelopi
authors: P
authors: Bouziotis
authors: Piotr
authors: P
authors: Garnuszek
authors: Urszula
authors: U
authors: Karczmarczyk
authors: Michał
authors: M
authors: Maurin
authors: Spyridon C
authors: SC
authors: Archimandritis
mesh_terms: D000818:Animals; D001692:Biological Transport; D001839:Bombesin / Q000097:blood / Q000737:chemistry* / Q000378:metabolism* / Q000633:toxicity; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D006573:Heterocyclic Compounds, 1-Ring / Q000737:chemistry*; D006801:Humans; D007553:Isotope Labeling; D008187:Lutetium / Q000737:chemistry*; D008297:Male; D051379:Mice; D019275:Radiopharmaceuticals / Q000097:blood / Q000737:chemistry / Q000378:metabolism / Q000633:toxicity; D018004:Receptors, Bombesin / Q000378:metabolism; D014018:Tissue Distribution; D015021:Yttrium Radioisotopes / Q000737:chemistry
chemical_list: D006573:Heterocyclic Compounds, 1-Ring; D019275:Radiopharmaceuticals; D018004:Receptors, Bombesin; D015021:Yttrium Radioisotopes; C071349:1,4,7,10-tetraazacyclododecane- 1,4,7,10-tetraacetic acid; D008187:Lutetium; D001839:Bombesin