Recent development of gold(I) and gold(III) complexes as therapeutic agents for cancer diseases

Metal complexes have demonstrated significant antitumor activities and platinum complexes are well established in the clinical application of cancer chemotherapy. However, the platinum-based treatment of different types of cancers is massively hampered by severe side effects and resistance development. Consequently, the development of novel metal-based drugs with different mechanism of action and pharmaceutical profile attracts modern medicinal chemists to design and synthesize novel metal-based agents. Among non-platinum anticancer drugs, gold complexes have gained considerable attention due to their significant antiproliferative potency and efficacy. In most situations, the gold complexes exhibit anticancer activities by targeting thioredoxin reductase (TrxR) or other thiol-rich proteins and enzymes and trigger cell death via reactive oxygen species (ROS). Interestingly, gold complexes were recently reported to elicit biochemical hallmarks of immunogenic cell death (ICD) as an ICD inducer. In this review, the recent progress of gold(I) and gold(III) complexes is comprehensively summarized, and their activities and mechanism of action are documented.

Gold (III) Derivatives in Colon Cancer Treatment

Cancer is one of the leading causes of morbidity and mortality worldwide. Colorectal cancer (CRC) is the third most frequently diagnosed cancer in men and the second in women. Standard patterns of antitumor therapy, including cisplatin, are ineffective due to their lack of specificity for tumor cells, development of drug resistance, and severe side effects. For this reason, new methods and strategies for CRC treatment are urgently needed. Current research includes novel platinum (Pt)- and other metal-based drugs such as gold (Au), silver (Ag), iridium (Ir), or ruthenium (Ru). Au(III) compounds are promising drug candidates for CRC treatment due to their structural similarity to Pt(II). Their advantage is their relatively good solubility in water, but their disadvantage is an unsatisfactory stability under physiological conditions. Due to these limitations, work is still underway to improve the formula of Au(III) complexes by combining with various types of ligands capable of stabilizing the Au(III) cation and preventing its reduction under physiological conditions. This review summarizes the achievements in the field of stable Au(III) complexes with potential cytotoxic activity restricted to cancer cells. Moreover, it has been shown that not nucleic acids but various protein structures such as thioredoxin reductase (TrxR) mediate the antitumor effects of Au derivatives. The state of the art of the in vivo studies so far conducted is also described.

Anticancer Activity and Apoptosis Induction of Gold(III) Complexes Containing 2,2'-Bipyridine-3,3'-dicarboxylic Acid and Dithiocarbamates

Three novel gold(III) complexes (1–3) of general composition [Au(Bipydc)(S₂CNR₂)]Cl₂ (Bipydc = 2,2′-bipyridine-3,3′-dicarboxylic acid and R = methyl for dimethyldithiocarbamate (DMDTC), ethyl for diethyldithiocarbamate (DEDTC), and benzyl for dibenzyldithiocarbamate (DBDTC)) have been synthesized and characterized by elemental analysis, FTIR and NMR spectroscopic techniques. The spectral results confirmed the presence of both the Bipydc and dithiocarbamate ligands in the complexes. The in vitro cytotoxic studies demonstrated that compounds 1–3 were highly cytotoxic to A549, HeLa, MDA-231, and MCF-7 cancer cells with activities much higher (about 25-fold) than cisplatin. In order to know the possible mode of cell death complex 2, [Au(Bipydc)(DEDTC)]Cl₂ was further tested for induction of apoptosis towards the MCF-7 cells. The results indicated that complex 2 induces cell death through apoptosis.

Au(III) and Pt(II) Complexes of a Novel and Versatile 1,4-Disubstituted 1,2,3-Triazole-Based Ligand Possessing Diverse Secondary and Tertiary Coordinating Groups

A novel 1,4-disubstituted 1,2,3-triazole-based ligand, 2-(4-(pyridin-2-yl)-1 H-1,2,3-triazol-1-yl)propane-1,3-diamine (ptpd), which possesses pyridyl and diamino secondary and tertiary coordinating groups was synthesized in excellent yield. The reactivity of 2-(1-phenyl-1 H-1,2,3-triazol-4-yl)pyridine (ptp), di- tert-butyl (2-azidopropane-1,3-diyl)dicarbamate (Boc₂-ptpd), and ptpd·3HCl was investigated with Au(III) and Pt(II) precursors. Analysis including X-ray crystal structures of [Au(III)Cl₃(ptp)] (1), [Au(III)Cl₂(ptpd)][Au(I)Cl₂][OH]{[NaAuCl₄·2H₂O]} n (3), and [Pt(II)Cl₂(ptpdH₂)][PtCl₄] (4) revealed that ptpd (i) serves as a monodentate ligand for Au(III) coordinating to the metal center via the pyridine nitrogen only, (ii) preferentially coordinates Au(III) via the bidentate diamino group over the monodentate pyridine group, (iii) can coordinate Pt(II) in a bidentate fashion via the pyridyl nitrogen and the triazole N-3, and (iv) can bridge two Pt(II) centers through bidentate chelation at the diamino group and bidentate chelation via the pyridyl nitrogen and the triazole N-3. ptpd represents a versatile ligand template for the development of mixed metal complexes.