Organometallic Gold(III) Complex [Au(Hdamp)(L14)]+ (L1 = SNS-Donating Thiosemicarbazone) as a Candidate to New Formulations against Chagas Disease

Review on the Applications of Selected Metal-Based Complexes on Infectious Diseases

Fatalities caused by infectious diseases (i.e., diseases caused by parasite, bacteria, and viruses) have become reinstated as a major public health threat globally. Factors such as antimicrobial resistance and viral complications are the key contributors to the death numbers. As a result, new compounds with structural diversity classes are critical for controlling the virulence of pathogens that are multi-drug resistant. Derivatization of bio-active organic molecules with organometallic synthons is a promising strategy for modifying the inherent and enhanced properties of biomolecules. Due to their redox chemistry, bioactivity, and structural diversity, organometallic moieties make excellent candidates for lead structures in drug development. Furthermore, organometallic compounds open an array of potential in therapy that existing organic molecules lack, i.e., their ability to fulfill drug availability and resolve the frequent succumbing of organic molecules to drug resistance. Additionally, metal complexes have the potential towards metal-specific modes of action, preventing bacteria from developing resistance mechanisms. This review's main contribution is to provide a thorough account of the biological efficacy (in vitro and in vitro) of metal-based complexes against infectious diseases. This resource can also be utilized in conjunction with corresponding journals on metal-based complexes investigated against infectious diseases.

Potential of sulfur-selenium isosteric replacement as a strategy for the development of new anti-chagasic drugs

Current treatment for Chagas disease is based on only two drugs: benznidazole and nifurtimox. Compounds containing sulfur (S) in their structure have shown promising results in vitro and in vivo against Trypanosoma cruzi, the parasite causing Chagas disease. Notably, some reports show that the isosteric replacement of S by selenium (Se) could be an interesting strategy for the development of new compounds for the treatment of Chagas disease. To date, the activity against T. cruzi of three Se- containing groups has been compared with their S counterparts: selenosemicarbazones, selenoquinones, and selenocyanates. More studies are needed to confirm the positive results of Se compounds. Therefore, we have investigated S compounds described in the literature tested against T. cruzi. We focused on those tested in vivo that allowed isosteric replacement to propose their Se counterparts as promising compounds for the future development of new drugs against Chagas disease.

Insight into Recent Drug Discoveries against Trypanosomatids and Plasmodium spp Parasites: New Metal-based Compounds

Scaffolds of metal-based compounds can act as pharmacophore groups in several ligands to treat various diseases, including tropical infectious diseases (TID). In this review article, we investigate the contribution of these moieties to medicinal inorganic chemistry in the last seven years against TID, including American trypanosomiasis (Chagas disease), human African trypanosomiasis (HAT, sleeping sickness), leishmania, and malaria. The most potent metal-based complexes are displayed and highlighted in figures, tables and graphics; according to their pharmacological activities (IC50 > 10µM) against Trypanosomatids and Plasmodium spp parasites. We highlight the current progresses and viewpoints of these metal-based complexes, with a specific focus on drug discovery.

Development of new dinuclear Fe(III) coordination compounds with in vitro nanomolar antitrypanosomal activity

Chagas disease is a neglected tropical disease caused by the protozoan pathogen Trypanosoma cruzi. The disease is a major public health problem affecting about 6 to 7 million people worldwide, mostly in Latin America. The available therapy for this disease is based on two drugs, nifurtimox and benznidazole, which exhibit severe side effects, including resistance, severe cytotoxicity, variable efficacy and inefficiency in the chronic phase. Therefore, new drugs are urgently needed. Coordination compounds may be an interesting alternative for antiparasite therapy against Leishmania spp., Toxoplasma gondii and T. cruzi. Herein, we tested the in vitro effect on T. cruzi epimastigotes (Y strain) of two new μ-oxo Fe(III) dinuclear complexes: [(HL1)(Cl)Fe(μ-O)Fe(Cl)(HL2)](Cl)₂·(CH₃CH₂OH)₂·H₂O (1) and [(HL2)(Cl)Fe(μ-O)Fe(Cl)(HL2)](Cl)₂·H₂O (2) where HL1 and HL2 are ligands which contain two pyridines, amine and alcohol moieties with a naphthyl pendant unit yielding a N₃O coordination environment. Complexes (1) and (2), which are isomers, were completely characterized, including X-ray diffraction studies for complex (1). Parasites were treated with the complexes and the outcome was analyzed. Complex (1) exhibited the lowest IC₅₀ values, which were 99 ± 3, 97 ± 2 and 110 ± 39 nM, after 48, 72 and 120 h of treatment, respectively. Complex (2) showed IC₅₀ values of 118 ± 5, 122 ± 6 and 104 ± 29 nM for the same treatment times. Low cytotoxicity to the host cell LLC-MK2 was found for both complexes, resulting in impressive selectivity indexes of 106 for complex (1) and 178 for (2), after 120 h of treatment. Treatment with both complexes reduced the mitochondrial membrane potential of the parasite. Ultrastructural analysis of the parasite after treatment with complexes showed that the mitochondria outer membrane presented swelling and abnormal disposition around the kinetoplast; in addition, reservosomes presented anomalous spicules and rupture. The complexes showed low nanomolar IC₅₀ values affecting mitochondria and reservosomes, essential organelles for the survival of the parasite. The low IC₅₀ and the high selectivity index show that both complexes act as a new prototype of drugs against T. cruzi and may be used for further development in drug discovery to treat Chagas disease.

Metallodrugs for the Treatment of Trypanosomatid Diseases: Recent Advances and New Insights

Trypanosomatid parasites are responsible for many Neglected Tropical Diseases (NTDs). NTDs are a group of illnesses that prevail in low-income populations, such as in tropical and subtropical areas of Africa, Asia, and the Americas. The three major human diseases caused by trypanosomatids are African trypanosomiasis, Chagas disease and leishmaniasis. There are known drugs for the treatment of these diseases that are used extensively and are affordable; however, the use of these medicines is limited by several drawbacks such as the development of chemo-resistance, side effects such as cardiotoxicity, low selectivity, and others. Therefore, there is a need to develop new chemotherapeutic against these tropical parasitic diseases. Metal-based drugs against NTDs have been discussed over the years as alternative ways to overcome the difficulties presented by approved antiparasitic agents. The study of late transition metal-based drugs as chemotherapeutics is an exciting research field in chemistry, biology, and medicine due to the ability to develop multitarget antiparasitic agents. The evaluation of the late transition metal complexes for the treatment of trypanosomatid diseases is provided here, as well as some insights about their mechanism of action.

Gold(III) complexes with thiosemicarbazonate ligands as potential anticancer agents: Cytotoxicity and interactions with biomolecular targets

Gold(III) complexes have been studied for the past years due to their anticancer properties and great affinity to biotargets, such as enzymes and proteins, which support their pharmacological applications. Within this scope, in this work the antiproliferative activities of two Au(III)-thiosemicarbazonate complexes, [AuClL₁] (1, L₁: (E,Z)-N-ethyl-N'-(3-nitroso-kN)butan-2-ylidene)carbamohydrazonothioato-k²N²,S) and [Au(Hdamp)L₂]Cl (2, L₂: N-(N'',N''-diethylaminothiocarbonyl)-N'(N''', N'''-dimethylcarbothioamide)benzamidineto-kN,k²S and Hdamp: 2-(N,N-dimethylaminomethyl)-phenyl-C¹), and their affinities to possible biological targets were investigated. Three different tumor cell lines were used to perform the cytotoxicity assays, including one cisplatin-resistant model, and the results showed lower EC₅₀ for 1 over 2 in every case: B16F10 (4.1 μM and 15.6 μM), A431 (4.0 μM and >50 μM) and OVCAR3 (4.2 μM and 24.5 μM). However, a lower toxicity to fibroblast 3T3 cell line was observed for 2 (30.58 μM) when compared to 1 (7.17 μM), resulting in comparable therapeutic indexes. Both complexes presented strong affinity to HSA: they distorted the secondary structure of the protein, as verified by circular dichroism, but 1 additionally presented the apparent fluorescence quenching constant (K_app) ten times greater than 2, which was probably due to the fact of 1 being able to denature HSA. The ethidium bromide displacement assay showed that neither 1 nor 2 are strong DNA intercalators, which is in agreement with what was observed through the UV-vis titration. In both cases, the 260 nm band presented hyperchromism, which can indicate ionic interactions or DNA damage. In fact, 1 was able to damage the pGEM plasmid, similarly to cisplatin, as verified by agarose gel electrophoresis and Atomic Force Microscopy. Biophysical studies in cancer cells model membranes were also performed in order to investigate the interaction of the gold complexes to lipid bilayers and revealed that the compounds interact with the membranes by exhibiting partition coefficients of 10³ order of magnitude. Overall, both complexes were found to be promising candidates for the development of a future anticancer drug against low sensitive or cisplatin resistant tumors.

Challenges in Chagas Disease Drug Development

The protozoan parasite Trypanosoma cruzi causes Chagas disease, an important public health problem throughout Latin America. Current therapeutic options are characterised by limited efficacy, long treatment regimens and frequent toxic side-effects. Advances in this area have been compromised by gaps in our knowledge of disease pathogenesis, parasite biology and drug activity. Nevertheless, several factors have come together to create a more optimistic scenario. Drug-based research has become more systematic, with increased collaborations between the academic and commercial sectors, often within the framework of not-for-profit consortia. High-throughput screening of compound libraries is being widely applied, and new technical advances are helping to streamline the drug development pipeline. In addition, drug repurposing and optimisation of current treatment regimens, informed by laboratory research, are providing a basis for new clinical trials. Here, we will provide an overview of the current status of Chagas disease drug development, highlight those areas where progress can be expected, and describe how fundamental research is helping to underpin the process.