ABSTRACT
Colorectal cancer (CRC) is a global health problem being the fourth most common cause of death due to cancer worldwide. Oxaliplatin plays a key role in current CRC treatment but shows serious drawbacks, such as a high systemic toxicity and the frequent insurgence of Pt resistance. In search of novel and more efficacious Pt-based drugs for CRC treatment, we synthesized and characterised PtI2(DACH), an oxaliplatin analogue. PtI2(DACH) was obtained through the replacement of bidentate oxalate with two iodides. PtI2(DACH) turned out to be more lipophilic than oxaliplatin, a fact that led to an enhancement of its cellular uptake. In contrast to oxaliplatin, PtI2(DACH) showed a scarce reactivity towards model proteins, while maintaining affinity for a standard DNA oligo. Notably, PtI2(DACH) induced cytotoxicities roughly comparable to those of oxaliplatin in three representative CRC cell lines. Moreover, it was able to trigger cell apoptosis, to an extent even better than cisplatin and oxaliplatin. Overall, a rather promising picture emerges for this novel Pt drug that merits, in our opinion, a deeper and more extensive preclinical evaluation.
ABSTRACT
Gold metallodrugs form a class of promising antiproliferative agents showing a high propensity to react with proteins. We exploit here X-ray absorption spectroscopy (XAS) methods [both X-ray absorption near-edge spectroscopy (XANES) and extended X-ray absorption fine structure (EXAFS)] to gain insight into the nature of the adducts formed between three representative gold(I, III) metallodrugs (i.e., auranofin, [Au(2,2'-bipyridine)(OH)(2)](PF(6)), Aubipy, and dinuclear [Au(2)(6,6'-dimethyl-2,2'-bipyridine)(2)(µ-O)(2)](PF(6))(2), Auoxo6) and two major plasma proteins, namely, bovine serum albumin (BSA) and human serum apotransferrin (apoTf). The following metallodrug-protein systems were investigated in depth: auranofin/apoTf, Aubipy/BSA, and Auoxo6/apoTf. XANES spectra revealed that auranofin, upon protein binding, conserves its gold(I) oxidation state. Protein binding most probably takes place through release of the thiosugar ligand and its subsequent replacement by a thiol (or a thioether) from the protein. This hypothesis is independently supported by EXAFS results. In contrast, the reactions of Aubipy with serum albumin and of Auoxo6 with serum apoTf invariantly result in gold(III) to gold(I) reduction. Gold(III) reduction, clearly documented by XANES, is accompanied, in both cases, by release of the bipyridyl ligands; for Auoxo6 cleavage of the gold-gold dioxo bridge is also observed. Gold(III) reduction leads to formation of protein-bound gold(I) species, with deeply modified metal coordination environments, as evidenced by EXAFS. In these adducts, the gold(I) centers are probably anchored to the protein through nitrogen donors. In general, these two XAS methods, i.e., XANES and EXAFS, used here jointly, allowed us to gain independent structural information on metallodrug/protein systems; detailed insight into the gold oxidation state and the local environment of protein-bound metal atoms was achieved in the various cases.