Synthesis, reactivity, and biological activity of gold(i) complexes modified with thiourea-functionalized tyrosine kinase inhibitors

Thiourea-modified 3-chloro-4-fluoroanilino-quinazoline derivatives have been studied as potential receptor-targeted carrier ligands in linear gold(I) complexes. The molecules mimic the epidermal growth factor receptor (EGFR) tyrosine kinase-targeted inhibitor gefitinib. Thiourea groups were either directly attached to quinazoline-C6 (compounds 4, 5, and 7) or linked to this position via a flexible ethylamino chain (compound 9). Compound 7 acts as a thiourea-S/quinazoline-N1 mixed-donor ligand, giving the unexpected dinuclear complex [{Au(μ-7-S,N)}₂]X₂ (X = Cl^-, SCN^-) (12a,b) (X-ray crystallography, electrospray mass spectrometry). Derivative 9 forms a stable linear complex, [Au(PEt₃)(9-S)](NO₃) (13). The biological activity of the carrier ligands and corresponding gold(I) complexes was studied in NCI-H460 and NCI-H1975 lung cancer cells. Compound 9 partially overcomes resistance to gefitinib in NCI-H1975, a lung cancer cell line characterized by a L858R/T790M mutation in EGFR (IC₅₀ values of 1.7 and 30 μM, respectively). The corresponding gold complex (13) maintains activity in the low-micromolar concentration range similar to the metal-free carrier. Compound 9 and the corresponding [Au(PEt₃)] complex, 13, inhibit EGFR kinase-mediated phosphorylation with sub-micromolar IC₅₀ values similar to those observed for gefitinib under the same assay conditions. Potential mechanisms of action and reactions in biological media of this new type of hybrid agent, as well as shortcomings of the current design are discussed.