Current Medicinal Chemistry - Volume 26, Issue 4, 2019

Biospeciation of essential and toxic metal ions, metal complexes with biological or medicinal activity are discussed in the paper in order to emphasize the importance of the distribution of metal ions in biological milieu. The exact knowledge of the chemical species present in the different organs/compartments/fluids/cells may provide essential information about the pharmacokinetic properties and the biological effect of the metal ion or the drug candidate metal complex. The transport of essential and toxic metal ions in the blood serum is discussed first, which is followed by the description of biodistribution of several important metal complexes with medicinal interest such as (i) anticancer, (ii) insulin-enhancing and (iii) MRI contrast agents in biological fluids.

Tumor cell chemoresistance is a major challenge in cancer therapeutics. Major select metal-based drugs are potent anticancer mediators yet they exhibit adverse sideeffects and are efficient against limited types of malignancies. A need, therefore, arises for novel metallodrugs with improved efficacy and decreased toxicity. Enhancement of antitumor drugs based on anticancer metals is currently a very active research field, with considerable efforts having been made toward elucidating the mechanisms of immune action of complex metalloforms and optimizing their immunoregulatory bioactivity through appropriate synthetic structural modification(s) and encapsulation in suitable nanocarriers, thereby enhancing their selectivity, specificity, stability, and bioactivity. In that respect, comprehending the molecular factors involved in drug resistance and immune response may help us develop new approaches toward more promising chemotherapies, reducing the rate of relapse and overcoming chemoresistance. In this review, a) molecular immunerelated mechanisms in the tumor microenvironment, responsible for lower drug sensitivity and tumor relapse, along with b) strategies for reversing drug resistance and targeting immunosuppressive tumor networks, while concurrently optimizing the design of complex metalloforms bearing anti-tumor activity, are discussed in an effort to identify and overcome chemoresistance mechanisms for effective tumor immunotherapeutic approaches.

Silver is a non-essential element with promising antimicrobial and anticancer properties. This work is a detailed summary of the newest findings on the bioinorganic chemistry of silver, with a special focus on the applications of Ag+ complexes and nanoparticles. The coordination chemistry of silver is given a reasonable amount of attention, summarizing the most common silver binding sites and giving examples of such binding motifs in biologically important proteins. Possible applications of this metal and its complexes in medicine, particularly as antibacterial and antifungal agents and in cancer therapy, are discussed in detail. The most recent data on silver nanoparticles are also summarized.

Heterocyclic compounds containing nitrogen ions, like pyrazoles, aziridines, diaziridines and their metal ion complexes with Cu(II), Zn(II) and Ru(III) and others exhibit a wide range of biological activity, including mainly anti-inflammatory, antioxidant, anticancer, and antimicrobial properties. Biological significance of these molecules and thus their potential use in medicine has driven growing interest into their coordination chemistry. A knowledge of the relationship between the structure of chemical compounds and their activity is needed for the synthesis of the preparations possessing the most beneficial features. The choice of interposed substituents may improve biocidal and antitumor action, reduce the toxicity of the initial substance, or even completely eliminate its adverse effects for healthy tissues. The main aim of this review paper is to present the current state of knowledge concerning the synthesis and biological activity of complexes with small heterocyclic ligands containing transition metal ions.

Antibiotic resistance acquired by various bacterial fungal and viral pathogens poses therapeutic problems of increasing severity. Among the infections that are very difficult to treat, biofilm-associated cases are one of the most hazardous. Complex structure of a biofilm and unique physiology of the biofilm cells contribute to their extremely high resistance to environmental conditions, antimicrobial agents and the mechanisms of host immune response. Therefore, the biofilm formation, especially by multidrugresistant pathogens, is a serious medical problem, playing a pivotal role in the development of chronic and recurrent infections. These factors create a limitation for using traditional chemiotherapeutics and contribute to a request for development of new approaches for treatment of infectious diseases. Therefore, early reports on antimicrobial activity of several complexes of metal ions, bearing thiosemicarbazide or thiosemicarbazones as the ligands, gave a boost to worldwide search for new, more efficient compounds of this class, to be used as alternatives to commonly known drugs. In general, depending on the presence of other heteroatoms, these ligands may function in a di-, tri- or tetradentate forms (e.g., of N,S,-, N,N,S-, N,N,N,S-, N,N,S,S-, or N,S,O-type), which impose different coordination geometries to the resultant complexes. In the first part of this review, we describe the ways of synthesis and the structures of the ligands based on the thiosemicarbazone motif, while the second part deals with the antimicrobial activity of their complexes with selected metal ions.

Background: Since the serendipitous discovery of the antitumor activity of cisplatin there has been a continuous surge in studies aimed at the development of new cytotoxic metal complexes. While the majority of these complexes have been designed to interact with nuclear DNA, other targets for anticancer metallodrugs attract increasing interest. In cancer cells the mitochondrial metabolism is deregulated. Impaired apoptosis, insensitivity to antigrowth signals and unlimited proliferation have been linked to mitochondrial dysfunction. It is therefore not surprising that mitochondria have emerged as a major target for cancer therapy. Mitochondria-targeting agents are able to bypass resistance mechanisms and to (re-) activate cell-death programs. Methods: Web-based literature searching tools such as SciFinder were used to search for reports on cytotoxic metal complexes that are taken up by the mitochondria and interact with mitochondrial DNA or mitochondrial proteins, disrupt the mitochondrial membrane potential, facilitate mitochondrial membrane permeabilization or activate mitochondria-dependent celldeath signaling by unbalancing the cellular redox state. Included in the search were publications investigating strategies to selectively accumulate metallodrugs in the mitochondria. Results: This review includes 241 references on antimitochondrial metal complexes, the use of mitochondria-targeting carrier ligands and the formation of lipophilic cationic complexes. Conclusion: Recent developments in the design, cytotoxic potency, and mechanistic understanding of antimitochondrial metal complexes, in particular of cyclometalated Au, Ru, Ir and Pt complexes, Ru polypyridine complexes and Au-N-heterocyclic carbene and phosphine complexes are summarized and discussed.

Background: Application of coordination chemistry in nanotechnology is a rapidly developing research field in medicine. Bismuth complexes have been widely used in biomedicine with satisfactory therapeutic effects, mostly in Helicobacter pylori eradication, but also as potential antimicrobial and anti-leishmanial agents. Additionally, in recent years, application of bismuth-based compounds as potent anticancer drugs has been studied extensively. Methods: Search for data connected with recent trends on bismuth compounds in cancer chemo- and radiotherapy was carried out using web-based literature searching tools such as ScienceDirect, Springer, Royal Society of Chemistry, American Chemical Society and Wiley. Pertinent literature is covered up to 2016. Results: In this review, based on 213 papers, we highlighted a number of current problems connected with: (i) characterization of bismuth complexes with selected thiosemicarbazone, hydrazone, and dithiocarbamate classes of ligands as potential chemotherapeutics. Literature results derived from 50 papers show that almost all bismuth compounds inhibit growth and proliferation of breast, colon, ovarian, lung, and other tumours; (ii) pioneering research on application of bismuth-based nanoparticles and nanodots for radiosensitization. Results show great promise for improvement in therapeutic efficacy of ionizing radiation in advanced radiotherapy (described in 36 papers); and (iii) research challenges in using bismuth radionuclides in targeted radioimmunotherapy, connected with choice of adequate radionuclide, targeting vector, proper bifunctional ligand and problems with 213Bi recoil daughters toxicity (derived from 92 papers). Conclusion: This review presents recent research trends on bismuth compounds in cancer chemo- and radiotherapy, suggesting directions for future research.