Linear gold(I) complex with tris-(2-carboxyethyl)phosphine (TCEP): Selective antitumor activity and inertness toward sulfur proteins.

The search for modulating ligand substitution reaction in gold complexes is essential to find new active metallo compounds for medical applications. In this work, a new linear and hydrosoluble goldI complex with tris-(2-carboxyethylphosphine) (AuTCEP). The two phosphines coordinate linearly to the metal as solved by single crystal X-ray diffraction. Complete spectroscopic characterization is also reported. In vitro growth inhibition (GI50) in a panel of nine tumorigenic and one non-tumorigenic cell lines demonstrated the complex is highly selective to ovarium adenocarcinoma (OVCAR-03) with GI50 of 3.04 nmol mL-1. Moreover, non-differential uptake of AuTCEP was observed between OVCAR-03 (tumor) and HaCaT (non-tumor) two cell lines. Biophysical evaluation with the sulfur-rich biomolecules showed the compound does not interact with two types of zinc fingers, bovine serum albumin, N-acetyl-l-cysteine and also l-histidine, revealing to be inert to ligand substitution reactions with these molecules. However, AuTCEP demonstrated to cleave plasmidial DNA, suggesting DNA as a possible target. No antibacterial activity was observed in the strains evaluated. Besides, it inhibits 15% of the activity of a mixture of serine-β-lactamase and metallo-β-lactamase from Bacillus cereus in the enzymatic activity assay, similarly to EDTA. These results suggest AuTCEP is selective to metallo-β-lactamase but the cell uptake is hindered, and the compound does not reach the periplasmic space of Gram-positive bacteria. The unique inert behavior of AuTCEP is interesting and represent the modulation of the reactivity through coordination chemistry to decrease the toxicity associated with AuI complexes and its lack of specificity, generating very selective compounds with unexpected targets.