title: Effect of DOTA position on melanoma targeting and pharmacokinetic properties of 111In-labeled lactam bridge-cyclized alpha-melanocyte stimulating hormone peptide.
abstract: The purpose of this study was to examine the effect of DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) position on melanoma targeting and pharmacokinetics of radiolabeled lactam bridge-cyclized alpha-melanocyte stimulating hormone (alpha-MSH) peptide.
  
  
  METHODS
  A novel lactam bridge-cyclized alpha-MSH peptide, Ac-GluGlu-CycMSH[DOTA] {Ac-Glu-Glu-c[Lys-Nle-Glu-His-DPhe-Arg-Trp-Gly-Arg-Pro-Val-Lys(DOTA)]}, was synthesized using standard 9-fluorenylmethyloxycarbonyl (Fmoc) chemistry. DOTA was directly attached to the alpha-amino group of Lys in the cyclic ring, while the N-terminus of the peptide was acetylated to generate Ac-GluGlu-CycMSH[DOTA]. The MC1 receptor binding affinity of Ac-GluGlu-CycMSH[DOTA] was determined in B16/F1 melanoma cells. Melanoma targeting and pharmacokinetic properties of Ac-GluGlu-CycMSH[DOTA]-111In were determined in B16/F1 melanoma-bearing C57 mice and compared to that of 111In-DOTA-Gly-Glu-c[Lys-Nle-Glu-His-DPhe-Arg-Trp-Gly-Arg-Pro-Val-Asp] (111In-DOTA-GlyGlu-CycMSH; DOTA was coupled to the N-terminus of the peptide).
  
  
  RESULTS
  Ac-GluGlu-CycMSH[DOTA] displayed 0.6 nM MC1 receptor binding affinity in B16/F1 cells. Ac-GluGlu-CycMSH[DOTA]-111In was readily prepared with greater than 95% radiolabeling yield. Ac-GluGlu-CycMSH[DOTA]-111In exhibited high tumor uptake (11.42 +/- 2.20% ID/g 2 h postinjection) and prolonged tumor retention (9.42 +/- 2.41% ID/g 4 h postinjection) in B16/F1 melanoma-bearing C57 mice. The uptake values for nontarget organs were generally low (<1.3% ID/g) except for the kidneys 2, 4, and 24 h postinjection.
  
  
  CONCLUSIONS
  DOTA position exhibited profound effect on melanoma targeting and pharmacokinetic properties of Ac-GluGlu-CycMSH[DOTA]-111In, providing a new insight into the design of lactam bridge-cyclized peptide for melanoma imaging and therapy.
authors.affiliation: College of Pharmacy, Cancer Research Treatment Center, Department of Cell Biology and Physiology, Department of Pathology, Department of Dermatology, University of New Mexico, Albuquerque, New Mexico 87131, USA.
authors.forename: Haixun
authors.initials: H
authors.lastname: Guo
authors.forename: Jianquan
authors.initials: J
authors.lastname: Yang
authors.forename: Fabio
authors.initials: F
authors.lastname: Gallazzi
authors.forename: Eric R
authors.initials: ER
authors.lastname: Prossnitz
authors.forename: Larry A
authors.initials: LA
authors.lastname: Sklar
authors.forename: Yubin
authors.initials: Y
authors.lastname: Miao
mesh_terms: D000818:Animals; D002614:Chelating Agents / Q000737:chemistry; D016503:Drug Delivery Systems / Q000379:methods*; D015195:Drug Design; D006573:Heterocyclic Compounds, 1-Ring / Q000737:chemistry*; D007205:Indium Radioisotopes / Q000737:chemistry* / Q000493:pharmacokinetics; D007668:Kidney / Q000378:metabolism; D007769:Lactams; D008546:Melanoma, Experimental / Q000188:drug therapy*; D051379:Mice; D008810:Mice, Inbred C57BL; D010599:Pharmacokinetics; D019275:Radiopharmaceuticals / Q000008:administration & dosage / Q000138:chemical synthesis* / Q000493:pharmacokinetics; D013329:Structure-Activity Relationship; D000521:alpha-MSH / Q000737:chemistry / Q000493:pharmacokinetics*
chemical_list: D002614:Chelating Agents; D006573:Heterocyclic Compounds, 1-Ring; D007205:Indium Radioisotopes; D007769:Lactams; D019275:Radiopharmaceuticals; C071349:1,4,7,10-tetraazacyclododecane- 1,4,7,10-tetraacetic acid; D000521:alpha-MSH