Tripodal tris(hydroxypyridinone) ligands for immunoconjugate PET imaging with super(89)Zr super(4+): comparison with desferrioxamine-B

• Published in: Dalton transactions : an international journal of inorganic chemistry 2015-03, Vol.44 (11), p.4884-4900
• Main Authors: Ma, Michelle T, Meszaros, Levente K, Paterson, Brett M, Berry, David J, Cooper, Maggie S, Ma, Yongmin, Hider, Robert C, Blower, Philip J
• Format: Article
• Language: English
• Subjects: Bones; Carrier density; Chelating; Derivatives; Imaging; Serums; Stability
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/c4dt02978j

Due to its long half-life (78 h) and decay properties (77% electron capture, 23% beta super(+), E sub(max) = 897 keV, E sub(av) = 397 keV, E gamma = 909 keV, I gamma = 100%) super(89)Zr is an appealing radionuclide for immunoPET imaging with whole IgG antibodies. Derivatives of the siderophore desferrioxamine-B (H sub(3)DFO) are the most widely used bifunctional chelators for coordination of super(89)Zr super(4+) because the radiolabeling of the resulting immunoconjugates is rapid under mild conditions. super(89)Zr-DFO complexes are reportedly stable in vitro but there is evidence that super(89)Zr super(4+) is released in vivo, and subsequently taken up by the skeleton. We have evaluated a novel tripodal tris(hydroxypyridinone) chelator, H sub(3)CP256 and its bifunctional maleimide derivative, H sub(3)YM103, for coordination of Zr super(4+) and compared the NMR spectra, and the super(89)Zr super(4+) radiolabeling, antibody conjugation, serum stability and in vivo distribution of radiolabelled immunoconjugates with those of H sub(3)DFO and its analogues. H sub(3)CP256 coordinates super(89)Zr super(4+) at carrier-free concentrations forming [ super(89)Zr(CP256)] super(+). Both H sub(3)DFO and H sub(3)CP256 were efficiently radiolabelled using [ super(89)Zr(C sub(2)O sub(4)) sub(4)] super(4-) at ambient temperature in quantitative yield at pH 6-7 at millimolar concentrations of chelator. Competition experiments demonstrate that super(89)Zr super(4+) dissociates from [ super(89)Zr(DFO)] super(+) in the presence of one equivalent of H sub(3)CP256 (relative to H sub(3)DFO) at pH 6-7, resulting largely in [ super(89)Zr(CP256)] super(+). To assess the stability of H sub(3)DFO and H sub(3)YM103 immunoconjugates radiolabelled with super(89)Zr, maleimide derivatives of the chelators were conjugated to the monoclonal antibody trastuzumab via reduced cysteine side chains. Both immunoconjugates were labelled with super(89)Zr super(4+) in >98% yield at high specific activities and the labeled immunoconjugates were stable in serum with respect to dissociation of the radiometal. In vivo studies in mice indicate that super(89)Zr super(4+) dissociates from YM103-trastuzumab with significant amounts of activity becoming associated with bones and joints (25.88 plus or minus 0.58% ID g super(-1) 7 days post-injection). In contrast,