Synthesis and in vitro examination of [ 124 I]-, [ 125 I]- and [ 131 I]-2-(4-iodophenylamino) pyrido[2,3-d]pyrimidin-7-one radiolabeled Abl kinase inhibitors Darren R. Veach a,1 , Mohammad Namavari a,1 , Tatiana Beresten a , Julius Balatoni b,c,2 , Maria Minchenko a , Hakim Djaballah a , Ronald D. Finn a,b , Bayard Clarkson a , Juri G. Gelovani b,c,2 , William G. Bornmann a,2 , Steven M. Larson a,b, T a Department of Molecular Pharmacology and Chemistry, Memorial Sloan-Kettering Cancer Center, New York, NY 10021, USA b Department of Radiology, Memorial Sloan-Kettering Cancer Center, New York, NY 10021, USA c Department of Neurology, Memorial Sloan-Kettering Cancer Center, New York, NY 10021, USA Received 29 October 2004; received in revised form 20 January 2005; accepted 28 January 2005 Abstract The pyridopyrimidinones are a potent class of inhibitors of c-Abl kinase and Bcr–Abl kinase, the causative fusion protein in chronic myelogenous leukemia and Src family kinases. A novel method for routine, high-yield no-carrier-added synthesis of [ 124 I]-, [ 125 I]- and [ 131 I]-6- (2,6-dichlorophenyl)-2-(4-iodophenylamino)-8-methyl-8H-pyrido[2,3-d ]pyrimidin-7-one has been developed. The 4V -trimethylstannyl- or 4V - tri-n -butylstannyl-pyridopyrimidinone precursors were prepared from the aryl bromide via a palladium-mediated coupling with hexaalkylditin (dioxane/microwave irradiation/10 min at 1608C). The radioiodination of 4V -stannylpyridopyrimidinones was found to optimally occur via an iododestannylation with Na 124 I, Na 125 I or Na 131 I in the presence of an oxidant [30% H 2 O 2 /HOAc (1:3)/10 min] in 79 – 87% radiochemical yield with N 99% radiochemical purity. The total radiosynthesis time was 30 min. The 4-iodophenylpyridopyrimidinone 2 inhibited recombinant Abl kinase activity with an IC 50 of 2.0 nM. Cell proliferation of K562 and A431 cells was inhibited with an IC 50 of 2.0 and 20 nM, respectively. Rapid cellular uptake and equilibrium were observed within 10–15 min using [ 131 I]-4-iodophenylpyridopyrimidinone 6c in K562 and A431 cells and demonstrated a 2.8-fold uptake selectivity for the Bcr–Abl-expressing K562 cells at 60 min. These results suggest that pyridopyrimidinone radiotracers may be useful in imaging Abl-, Bcr–Abl- or Src-expressing malignancies. D 2005 Elsevier Inc. All rights reserved. Keywords: Pyridopyrimidinone; Tyrosine kinase inhibitor; Iododestannylation; Iodine-124; Iodine-125; Iodine-131 1. Introduction Kinase inhibitors represent the latest generation of small- molecule drug therapies applicable to cancer and other illnesses. Complementary kinase-targeted radiolabeled probes are evolving rapidly alongside therapeutics. Primar- ily, this is fueled by the increasing demand for advanced in vivo characterization of drugs and drug candidates as early as possible during development. The pyrido[2,3-d ]pyrimi- din-7-ones are a class of potent tyrosine kinase inhibitors that are known to strongly inhibit Abl, Bcr–Abl and Src kinases among others [1–3]. These key cellular signaling proteins are implicated in a variety of cancers, Bcr–Abl most notably in chronic myelogenous leukemia (CML) [4]. CML arises from a reciprocal translocation mutation between chromosomes 9 and 22, forming the Philadelphia chromosome, the hallmark karyotypic marker. At the site of the crossover, a chimeric fusion oncogene, BCR–ABL, is formed from the Ableson tyrosine kinase (ABL) and break- point cluster region (BCR) genes. The gene product, Bcr–Abl, has an intact Abl kinase domain that is constitu- tively activated and dysregulated. The progression of CML 0969-8051/$ – see front matter D 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.nucmedbio.2005.01.008 T Corresponding author. Memorial Sloan-Kettering Cancer Center, Box 77, New York, NY 10021, USA. E-mail address: larsons@mskcc.org (S.M. Larson). 1 Darren R. Veach and Mohammad Namavari contributed equally to this paper. 2 Current address: Department of Experimental Diagnostic Imaging, The University of Texas M.D. Anderson Cancer Center, Houston, TX 77030, USA. Nuclear Medicine and Biology 32 (2005) 313 – 321 www.elsevier.com/locate/nucmedbio