Radioiodination of new EGFR inhibitors as potential SPECT agents for molecular imaging in cancer

1. Radioiodination of new EGFR inhibitors as potential SPECT agents for molecular imaging in cancer Maria Cristina Oliveira, Célia Fernandes, Isabel Santos Departamento de Química, ITN, Estrada Nacional 10, 2686-953, Sacavém Codex, Portugal email: cmelo@itn.mces.pt Introduction The epidermal growth factor receptor (EGFR) belongs to the ErbB family of receptor tyrosine kinases (TK) involved in the proliferation of normal and malignant cells. EGFR is often over expressed in cancer cells, namely in 45% of breast tumours.1 A suitable radioligand that selectively binds EGFR will allow the mapping of this receptor kinase by nuclear medicine techniques. Recently, there has been a growing interest in the use of EGFR-TK inhibitors, such as quinazoline derivatives, as radiotracers for molecular imaging.2 In our search for the development of novel SPECT radioligands for EGFR positive tumours, new irreversible TK inhibitors are being explored. Herein, we describe the synthesis and the iodination (127I/125I) of N-4-[(3-chloro-4-fluorphenyl) amino] quinazoline-6-yl-3-bromopropionamide (2), a novel EGFR-TK inhibitor synthesized in our laboratory.3 Synthesis of EGFR inhibitors + NEt3 Acetone, rt 1 2 NaI/Na125I acetone, reflux 1H NMR (CD3OD)  (ppm) 3.07 (t, 2H,-CH2-CH2-Br) 3.78 (t, 2H, -CH2-CH2-Br) 7.27 (t, 1H, arom) 7.80-7.68 (m, 3H, arom) 8.06 (dd, 1H, arom) 8.53 (s, 1H, arom) 8.78 (s, 1H, arom) 1H NMR (CD3OD)  (ppm) 3.14 (t, 2H,-CH2-CH2-I) 3.24 (t, 2H, -CH2-CH2-I) 7.36 (t, 1H, arom) 7.69 (m, 1H, arom) 7.97-7.85 (m, 3H, arom) 8.72 (s, 1H, arom) 8.97 (d, 1H, arom) 3,127I; 3a, 125I Results and Discussion The radiolabelling of 2 was accomplished via halogen exchange. Purification by RP-HPLC yielded N-4-[(3-chloro-4-fluorphenyl) amino] quinazoline-6-yl-3-125Iiodopropionamide (3a) with a radiochemical purity higher than 98%. The radioiodinated quinazoline (3a) was well separated from its bromo precursor (2) leading to high specific activity, a very important issue in molecular imaging. Quinazoline 3a was characterized by HPLC co-elution with cold standard 3, characterized by conventional analytical methods. 3 3a CH3CN/TFA 0.1% (35:65) 1 mL/min RP C18 Nucleosil Optimization of eluting conditions for the separation of iodinated from bromo precursor 2 chloropropionamide Bromopropionamide (2) Iodopropionamide (3) CH3CN/TFA 0.1% (35:65) 1 mL/min RP C18 Nucleosil Concluding Remarks The radiolabelled compound was obtained with  high radiochemical purity (> 98%)  high specific activity high in vitro stability in the eluting solvent (> 95% after 2 weeks) The in vitro and in vivo properties and the potential of this novel compound as a SPECT biomarker for molecular imaging of EGFR positive tumours is currently under investigation. References: 1 - C. Arteaga, Seminars in Oncology, (2003) Vol 30, nº 3, Suppl 7, 3-14 2 - N. Vasdev et al, J Label Compd Radiopharm (2005) Vol 48, 109-115 3 - I. Santos, Synthesis and Characterization of Quinazoline Derivatives, 2st RCM on Development of 99mTc-Based Small Biomolecules Using Novel 99mTc Cores/ IAEA, Viena, Austria, November 2004, oral