pubs.acs.org/jmc Published on Web 06/02/2010 r 2010 American Chemical Society J. Med. Chem. 2010, 53, 4633–4641 4633 DOI: 10.1021/jm1001293 Evaluation of Re and 99m Tc Complexes of 2-(4 0 -Aminophenyl)benzothiazole as Potential Breast Cancer Radiopharmaceuticals Stamatia Tzanopoulou, † Marina Sagnou, † Maria Paravatou-Petsotas, ‡ Eleni Gourni, ‡ George Loudos, § Stavros Xanthopoulos, ‡ Daniel Lafkas, ) Hippokratis Kiaris, ) Alexandra Varvarigou, ‡ Ioannis C. Pirmettis, ‡ Minas Papadopoulos, ‡ and Maria Pelecanou* ,† † Institute of Biology, and ‡ Institute of Radioisotopes-Radiodiagnostic Products, National Centre for Scientific Research “Demokritos”, 15310 Athens, Greece, § Department of Medical Instruments Technology, Technological Educational Institute of Athens, 12210 Athens, Greece, and ) Department of Biological Chemistry, University of Athens Medical School, 75 M. Asias Street, 11527 Athens, Greece Received January 31, 2010 The synthesis of M(I)(CO) 3 (NNO) (M = Re, 99m Tc) complexes conjugated to the antitumor agent 2-(4 0 - aminophenyl)benzothiazole and to its 6-methyl derivative, as well as their in vitro and in vivo biological evaluation as breast cancer radiopharmaceuticals, is reported. The Re complexes displayed under the fluorescence microscope clear uptake by the sensitive to the 2-(4 0 -aminophenyl)benzothiazole pharmaco- phore breast cancer cell lines MCF-7 and T47D, while uptake by less sensitive lines and by normal fibroblasts was much weaker. In accordance, uptake of the corresponding radioactive 99m Tc complexes was clearly higher in the breast cancer cell lines MCF-7 and MDA-231 compared to normal fibroblasts. Biodistribution of the 99m Tc complexes in SCID mice bearing MCF-7 xenografts showed appreciable tumor uptake. A tumor/muscle ratio of 2.2 was measured for the complex conjugated to 2-(4 0 -aminophenyl)benzothiazole that led to successful tumor imaging. The results render the 2-(4 0 -aminophenyl)benzothiazole complexes potential candidates for imaging ( 99m Tc) and targeted radiotherapy ( 188 Re) of breast cancer. Introduction Members of the 2-(4 0 -aminophenyl)benzothiazole class (Figure 1A) possess highly selective, potent antitumor proper- ties in vitro and in vivo. 1,2 The original lead compound in this series, 2-(4 0 -aminophenyl)benzothiazole (1), exhibits nanomo- lar in vitro activity against certain human breast cancer cell lines with a characteristic biphasic dose-response relationship. 3 Its discovery in 1996 was followed by the synthesis and evaluation of a series of substituted analogues with more potent and diverse activity and the identification of the 2-(4 0 -amino-3 0 - methylphenyl)benzothiazole (DF 203) 1,4 as the lead compound in this series on the basis of superior in vivo performance. 5-7 The result of this chemistry-driven approach to drug disco- very encompassing synthesis, in vitro and in vivo biological evaluation, and mechanistic studies culminated in the develop- ment of the novel clinical candidate 2-(4 0 -amino-3 0 -methyl- phenyl)-5-fluorobenzothiazole lysylamide prodrug (Phortress, Figure 1B), 2 which is in phase I clinical trial in the U.K. 2,8 The specificity of the action of the 2-(4 0 -aminophenyl)- benzothiazoles that are taken up and metabolized only by sensitive cancer cell lines with negligible uptake by unresponsive cell lines 1-8 makes this class of compounds ideal pharmaco- phores for the development of tumor-specific radiopharma- ceuticals, serving as vehicles that carry the radionuclide of choice to the diseased tissue for diagnostic or therapeutic applications. 9 In a previous communication 10 we have re- ported the synthesis and initial biological evaluation of rhe- nium ( 185/187 Re) and technetium-99m ( 99m Tc) complexes of 2-(4 0 -aminophenyl)benzothiazole of the general formula M(I)- (CO) 3 (NNO) (M = Re, 99m Tc) (2a and 2b, respectively, Figure 2) for breast cancer imaging and targeted radiotherapy. 99m Tc (monoenergetic γ photons of 140 keV, t 1/2 of 6 h, lack of particulate emission) is widely used in clinical diagnostic imaging, while Re, the group VIIB congener of Tc, has two β-emitting isotopes suitable for therapeutic applications, 186 Re (t 1/2 = 3.8 d, E max = 1.07 MeV) and 188 Re (t 1/2 = 0.7 d, E max = 2.12 MeV). 11 Tc and Re form analogous complexes with very similar physical and chemical properties that are expected to have the same pharmacokinetic behavior and are therefore considered a “matched pair” for diagnosis and therapy. 12 Figure 1. Chemical structures of (A) the antitumor 2-(4 0 -amino- phenyl)benzothiazoles (1 being the original lead compound in the series) and (B) the clinical candidate phortress. *To whom correspondence should be addressed. Phone: þ 30 210 6503555. Fax: þ 30 210 6511767. E-mail: pelmar@bio.demokritos.gr.