Target Identification in Anti-Tuberculosis Drug Discovery.

Mycobacterium tuberculosis (Mtb) is the etiological agent of tuberculosis (TB), a disease that, although preventable and curable, remains a global epidemic due to the emergence of resistance and a latent form responsible for a long period of treatment. Drug discovery in TB is a challenging task due to the heterogeneity of the disease, the emergence of resistance, and uncomplete knowledge of the pathophysiology of the disease. The limited permeability of the cell wall and the presence of multiple efflux pumps remain a major barrier to achieve effective intracellular drug accumulation. While the complete genome sequence of Mtb has been determined and several potential protein targets have been validated, the lack of adequate models for in vitro and in vivo studies is a limiting factor in TB drug discovery programs. In current therapeutic regimens, less than 0.5% of bacterial proteins are targeted during the biosynthesis of the cell wall and the energetic metabolism of two of the most important processes exploited for TB chemotherapeutics. This review provides an overview on the current challenges in TB drug discovery and emerging Mtb druggable proteins, and explains how chemical probes for protein profiling enabled the identification of new targets and biomarkers, paving the way to disruptive therapeutic regimens and diagnostic tools.

An Overview of Drug Resistance in Protozoal Diseases.

Protozoan diseases continue to be a worldwide social and economic health problem. Increased drug resistance, emerging cross resistance, and lack of new drugs with novel mechanisms of action significantly reduce the effectiveness of current antiprotozoal therapies. While drug resistance associated to anti-infective agents is a reality, society seems to remain unaware of its proportions and consequences. Parasites usually develops ingenious and innovative mechanisms to achieve drug resistance, which requires more research and investment to fight it. In this review, drug resistance developed by protozoan parasites Plasmodium, Leishmania, and Trypanosoma will be discussed.

From hybrid compounds to targeted drug delivery in antimalarial therapy.

The discovery of new drugs to treat malaria is a continuous effort for medicinal chemists due to the emergence and spread of resistant strains of Plasmodium falciparum to nearly all used antimalarials. The rapid adaptation of the malaria parasite remains a major limitation to disease control. Development of hybrid antimalarial agents has been actively pursued as a promising strategy to overcome the emergence of resistant parasite strains. This review presents the journey that started with simple combinations of two active moieties into one chemical entity and progressed into a delivery/targeted system based on major antimalarial classes of drugs. The rationale for providing different mechanisms of action against a single or additional targets involved in the multiple stages of the parasite's life-cycle is highlighted. Finally, a perspective for this polypharmacologic approach is presented.

Necroptosis induced by ruthenium (II) complexes as mitochondrial disruptors.

Inducing necroptosis in cancer cells has emerged as an effective strategy to overcome drug resistance. However, while organic small molecules have been extensively studied for this purpose, metal-based compounds have received relatively little attention as triggers of necroptosis. The development of ruthenium (II) hybrid compounds, particularly those containing triazene (Ru-TRZ), highlights a novel avenue for modulating necroptotic cell death. Here we show that incorporating a methyltriazene moiety, a known alkylating warhead, confers superior mitochondrial-targeting properties and enhances cell death compared to amide-containing counterparts. Ru-hybrid TRZ2 exhibits also antitumor efficacy against in vivo drug-resistant cancer cells. Mechanistically, we demonstrate that Ru-TRZ hybrids induce apoptosis. In addition, by activating downstream RIPK3-driven cell death, TRZ2 proficiently restrains normal mitochondrial function and activity, leading to cancer cell necroptosis. Finally, TRZ2 synergizes anti-proliferative activity and cell death effects induced by conventional drugs. In conclusion, Ru-TRZ2 stands as a promising ruthenium-based chemotherapeutic agent inducing necroptosis in drug resistant cancer cells.

Structural Optimization of Antimycobacterial Azaaurones Towards Improved Solubility and Metabolic Stability.

While N-acetyl azaaurones have already been disclosed for their potential against tuberculosis (TB), their low metabolic stability remains an unaddressed liability. We now report a study designed to improve the metabolic stability and solubility of the azaaurone scaffold and to identify the structural requirements for antimycobacterial activity. Replacing the N-acetyl moiety for a N-carbamoyl group led to analogues with sub- and nanomolar potencies against M. tuberculosis H37Rv, as well as equipotent against drug-susceptible and drug-resistant M. tuberculosis isolates. The new N-carbamoyl azaaurones exhibited improved microsomal stability, compared to their N-acetylated counterparts, with several compounds displaying moderate to high kinetic solubility. The frequency of spontaneous resistance to azaaurones was observed to be in the range of 10-8 , a value that is comparable to current TB drugs in the market. Overall, these results reveal that azaaurones are amenable to structural modifications to improve metabolic and solubility liabilities, and highlight their potential as antimycobacterial agents.

Design and evaluation of primaquine-artemisinin hybrids as a multistage antimalarial strategy.

It is widely accepted that the struggle against malaria depends on the development of new strategies to fight infection. The "magic bullet" thought to be necessary to reach eradication should not only provide treatment for all Plasmodium spp. that infect human red blood cells but should also eliminate the replicative and dormant liver forms of the parasite. Moreover, these goals should ideally be achieved by using different mechanisms of action so as to avoid the development of resistance. To that end, two hybrid molecules with covalently linked primaquine and artemisinin moieties were synthesized, and their effectiveness against the liver and blood stages of infection was compared in vitro and in vivo with those of the parent compounds. Both hybrids displayed enhanced in vitro activities, relative to those of the parent compounds, against Plasmodium berghei liver stages. Both compounds were about as potent as artemisinin against cultured Plasmodium falciparum (50% inhibitory concentration [IC(50)], ∼10 nM). When used to treat a murine P. berghei infection, one of the molecules displayed better efficacy than an equimolar mixture of the parent pharmacophores, leading to improved cure and survival rates. These results reveal a novel approach to the design and evaluation of antimalarials based on the covalent combination of molecules acting on different stages of the parasite life cycle.

Artemisinin-dipeptidyl vinyl sulfone hybrid molecules: design, synthesis and preliminary SAR for antiplasmodial activity and falcipain-2 inhibition.

A series of artemisinin-vinyl sulfone hybrid molecules with the potential to act in the parasite food vacuole via endoperoxide activation and falcipain inhibition was synthesized and screened for antiplasmodial activity and falcipain-2 inhibition. All conjugates were active against the Plasmodium falciparum W2 strain in the low nanomolar range and those containing the Leu-hPhe core inhibited falcipain-2 in low micromolar range.

Endoperoxide-8-aminoquinoline hybrids as dual-stage antimalarial agents with enhanced metabolic stability.

Hybrid compounds may play a critical role in the context of the malaria eradication agenda, which will benefit from therapeutic tools active against the symptomatic erythrocytic stage of Plasmodium infection, and also capable of eliminating liver stage parasites. To address the need for efficient multistage antiplasmodial compounds, a small library of 1,2,4,5-tetraoxane-8- aminoquinoline hybrids, with the metabolically labile C-5 position of the 8-aminoquinoline moiety blocked with aryl groups, was synthesized and screened for antiplasmodial activity and metabolic stability. The hybrid compounds inhibited development of intra-erythrocytic forms of the multidrug-resistant Plasmodium falciparum W2 strain, with EC50 values in the nM range, and with low cytotoxicity against mammalian cells. The compounds also inhibited the development of P. berghei liver stage parasites, with the most potent compounds displaying EC50 values in the low µM range. SAR analysis revealed that unbranched linkers between the endoperoxide and 8-aminoquinoline pharmacophores are most beneficial for dual antiplasmodial activity. Importantly, hybrids were significantly more potent than a 1:1 mixture of 8-aminoquinoline-tetraoxane, highlighting the superiority of the hybrid approach over the combination therapy. Furthermore, aryl substituents at C-5 of the 8-aminoquinoline moiety improve the compounds' metabolic stability when compared with their primaquine (i.e. C-5 unsubstituted) counterparts. Overall, this study reveals that blocking the quinoline C-5 position does not result in loss of dual-stage antimalarial activity, and that tetraoxane-8- aminoquinoline hybrids are an attractive approach to achieve elimination of exo- and intraerythrocytic parasites, thus with the potential to be used in malaria eradication campaigns.

Imidazolidin-4-one derivatives of primaquine as novel transmission-blocking antimalarials.

Imidazolidin-4-one derivatives of primaquine were synthesized as potential double prodrugs of the parent drug. The title compounds inhibit the development of the sporogonic cycle of Plasmodium berghei, affecting the appearance of oocysts in the midguts of the mosquitoes. The imidazolidin-4-ones are very stable, both in human plasma and in pH 7.4 buffer, indicating that they are active per se. Thus, imidazolidin-4-ones derived from 8-aminoquinolines represent a new entry in antimalarial structure-activity relationships.

Bundle Approach to Reduce Bloodstream Infections in Neutropenic Hematologic Patients with a Long-Term Central Venous Catheter.

INTRODUCTION: The objective of the study was to reduce, by a bundle of interventions, the global bloodstream infections and catheter-related bloodstream infections rates in neutropenic hematology patients with a long-term central venous catheter. MATERIAL AND METHODS: This was a non-randomized prospective study. It was conducted in a 20-bed hematology oncology unit (Portuguese Institute of Oncology, Porto, Portugal) between 1st of August 2010 and 31st of January 2012. In this period we introduced a bundle of interventions (study group) and compared the results with the six months prior to implementation (control group). The interventions consisted in the use of a neutral pressure mechanical valve connector instead of a positive pressure mechanical valve connector, a more frequent change of this connector and a more efficient clean solution. One hundred and sixteen hematology patients with a long-term central venous catheter at time superior of 72 h, with 8 867 central venous catheter days [6 756 central venous catheter days in the study group and 2 111 central venous catheter days in the control group] were included in the study. RESULTS: A significant reduction in bloodstream infections rates and catheter-related bloodstream infections rates was achieved. Bloodstream infections rates: [32.69 (control group) vs. 9.43 (study group)], incidence reduction 71% [relative risk 0.2886, CI 95% (0.1793 - 0.4647), p < 0.001] and catheter-related bloodstream infections rates: [17.53 (control group) vs. 4.73 (study group)], incidence reduction 71% [relative risk 0.2936, CI 95% (0.1793 - 0.5615), p < 0.014]. No significant difference (p > 0.05) was found in the neutrophil count at the time of blood culture samples between groups: 69% (< 500 neutrophils/mm3) [71% (study group) vs. 68% (control group)]. CONCLUSIONS: The introduction of this bundle of interventions based on the variables of patient, product and practice, supported by the Healthcare and Technology Synergy framework, quickly resulted in a significant reduction of bloodstream infections and catheter-related bloodstream infections rates.

Introdução: O objetivo deste estudo foi reduzir através de um pacote de medidas as infeções sistémicas e as taxas de infeções com origem no cateter venoso central nos doentes hematológicos em neutropenia com cateter venoso central de longa duração. Material e Métodos: Estudo prospetivo não randomizado realizado na unidade onco-hematológica do Instituto Português de Oncologia do Porto no período compreendido entre 1 de agosto de 2010 até 31 de janeiro de 2012. Durante este período foi introduzido um pacote de medidas (grupo estudo) e comparados os resultados nos 6 meses anteriores à sua implementação (grupo de controlo). As medidas consistiram na utilização de conectores de pressão neutra em detrimento dos conectores de pressão positiva, na sua troca mais frequente e numa solução anti-séptica mais eficaz. Foram incluídos neste estudo 116 doentes hematológicos com cateter venoso central de longa duração inserido por um período superior a 72 h. Foram contabilizados 8 867 dias de cateter (6 756 dias de cateter venoso central no grupo estudo e 2 111 dias de cateter venoso central no grupo de controlo). Resultados: Obteve-se uma redução significativa nas taxas de infeções sistémicas e infeções com origem no cateter venoso central. As taxas de infeções sistémicas: [32,69 (grupo de controlo) vs. 9,43 (grupo estudo)], com uma redução de incidência de 71% [risco relativo 0,2886, CI 95% (0,1793 - 0,4647), p < 0,001] e taxas de infeções com origem no cateter venoso central: [17,53 (grupo de controlo) vs. 4,73 (grupo estudo)], com redução de incidência de 71% [risco relativo 0,2936, CI 95% (0,1793 - 0,5615), p < 0,014]. Não foi encontrada diferença significativa (p > 0,05) na contagem de neutrófilos à data da colheita das amostras de hemoculturas entre ambos os grupos: 69% (< 500 neutrófilos/mm3) [71% (grupo estudo) vs. 68% (grupo de controlo)]. Conclusões: A introdução deste pacote de medidas baseado nas variáveis do paciente, produto e prática, suportado pela estrutura Healthcare and Technology Synergy, resultou numa redução significativa das taxas de infeções sistémicas e infeções com origem no cateter venoso central.

Novel endoperoxide-based transmission-blocking antimalarials with liver- and blood-schizontocidal activities.

In a search for effective compounds against both the blood- and liver-stages of infection by malaria parasites with the ability to block the transmission of the disease to mosquito vectors, a series of hybrid compounds combining either a 1,2,4-trioxane or 1,2,4,5-tetraoxane and 8-aminoquinoline moieties were synthesized and screened for their antimalarial activity. These hybrid compounds showed high potency against both exoerythrocytic and erythrocytic forms of malaria parasites, comparable to representative trioxane-based counterparts. Furthermore, they efficiently blocked the development of the sporogonic cycle in the mosquito vector. The tetraoxane-based hybrid 5, containing an amide linker between the two moieties, effectively cleared a patent blood-stage P. berghei infection in mice after i.p. administration. Overall, these results indicate that peroxide-8-aminoquinoline hybrids are excellent starting points to develop an agent that conveys all the desired antimalarial multistage activities in a single chemical entity and, as such, with the potential to be used in malaria elimination campaigns.

Structure-activity relationships for dipeptide prodrugs of acyclovir: implications for prodrug design.

A series of water-soluble dipeptide ester prodrugs of the antiviral acyclovir (ACV) were evaluated for their chemical stability, cytotoxicity, and antiviral activity against several strains of Herpes Simplex-1 and -2, vaccinia, vesicular stomatitis, cytomegalovirus and varicella zoster viruses. ACV dipeptide esters were very active against herpetic viruses, independently of the rate at which they liberate the parent drug. Their minimum cytotoxic concentrations were above 100 microM and the resulting MCC/EC(50) values were lower than those of ACV. When comparing the reactivity of Phe-Gly esters and amides (ACV, zidovudine, paracetamol, captopril and primaquine) in pH 7.4 buffer it was found that the rate of drug release increases with drug's leaving group ability. Release of the parent drug from Phe-Gly in human plasma is markedly faster than in pH 7.4 buffer, thus suggesting that the dipeptide-based prodrug approach can be successfully applied to bioactive agents containing thiol, phenol and amine functional groups.