Synthesis, characterization and biological evaluation of In(III) complexes anchored by DOTA-like chelators bearing a quinazoline moiety.

Following previous studies with a DOTA-like bifunctional chelator (H(3)L1) containing an ethylenic linker between the macrocycle backbone and a quinazoline pharmacophore, we synthesized and fully characterized a congener macrocyclic ligand (H(3)L2) having a longer, five-carbon spacer for the linkage of the quinazoline moiety. Both H(3)L1 and H(3)L2 were used to prepare indium(III) complexes aiming at their evaluation as radioactive probes for in vivo targeting of EGFR-TK. The protonation constants (log K(Hi)) of H(3)L2 were determined by potentiometry and UV-Vis spectrophotometry and the values found are 12.18, 9.74, 4.99, 3.91 and 2.53. The stability and protonation constants of InL (L = L1, L2) were also obtained from a combined potentiometry and UV-VIS spectrophotometry study. The reaction of InCl(3) with H(3)L1 and H(3)L2 led to the formation of the well-defined complexes InL1 and InL2, containing In(iii) ions coordinated by a seven (N(4),O(3)) donor atom set. These new complexes were fully characterized by spectroscopic methods (IR, NMR, ESI-MS), HPLC and by X-ray diffraction analysis in the case of InL1. The radioactive congener (111)InL2 was prepared from the reaction of (111)In-chloride with H(3)L2, in high yield and high radiochemical purity. (111)InL2 is a neutral complex that presents a hydrophilic character and exhibits a high in vitro and in vivo stability. H(3)L2 and InL2 do not inhibit the cell growth of A431 cervical carcinoma cells. In this EGFR-expressing cell line, (111)InL2 has shown very low cell internalization. These findings indicate that these DOTA-like chelators are not the best suited bifunctional ligands to obtain In(iii) complexes with adequate biological properties for targeting the EGFR-TK.

A quinazoline-derivative DOTA-type gallium(III) complex for targeting epidermal growth factor receptors: synthesis, characterisation and biological studies.

The novel DOTA-like chelator 1,4,7,10-tetraazacyclododecane-1-{4-[(3-chloro-4-fluorophenyl)amino]quinazoline-6-yl}propionamide-4,7,10-triacetic acid (H(3)L) was synthesised by alkylation of 1,4,7,10-tetraazacyclododecane-1,4,7-tris(t-butyl acetate) with N-{4-[(3-chloro-4-fluorophenyl)amino]quinazoline-6-yl}-3-bromopropionamide, followed by hydrolysis of the ester groups with trifluoracetic acid. H(3)L has been fully characterised by multinuclear NMR spectroscopy, mass spectrometry and high-performance liquid chromatography (HPLC). Five protonation constants, log K (Hi ), of H(3)L were determined by potentiometry and UV-vis spectrophotometry and the values found are 10.47, 9.18, 5.24, 4.00 and 2.23. These methods, complemented with variable-pH (71)Ga NMR studies, allowed us to ascertain the stability constant of the Ga(III) complex of L. GaL has a remarkably high thermodynamic stability constant (log K (ML) = 24.5). The radioactive complex (67)GaL was prepared in high yield and high radiochemical purity. Its HPLC chromatogram is identical to that obtained for the GaL complex prepared at the macroscopic level. At pH 7.4, (67)GaL has an overall neutral charge, is highly hydrophilic (log D = -1.02 +/- 0.03) and presents high in vitro stability in physiological media and in the presence of an excess of diethylenetriaminepentaethanoic acid . In vitro studies indicated that H(3)L and GaL do not inhibit the cell growth of epidermal growth factor receptor expressing cell lines, such as A431 cervical carcinoma cells, a result which agrees with the very low cell internalisation found for (67)GaL in the same cell line. Biodistribution studies in mice indicated high in vivo stability for (67)GaL, a high total excretion rate and a relatively slow blood clearance, in full accordance with its hydrophilic character and the relatively important protein binding.