Marcelo Santos Castilho

Discovery of new inhibitors of Schistosoma mansoni PNP by pharmacophore-based virtual screening.

Schistosomiasis is considered the second most important tropical parasitic disease, with severe socioeconomic consequences for millions of people worldwide. Schistosoma mansoni , one of the causative agents of human schistosomiasis, is unable to synthesize purine nucleotides de novo, which makes the enzymes of the purine salvage pathway important targets for antischistosomal drug development. In the present work, we describe the development of a pharmacophore model for ligands of S. mansoni purine nucleoside phosphorylase (SmPNP) as well as a pharmacophore-based virtual screening approach, which resulted in the identification of three thioxothiazolidinones (1-3) with substantial in vitro inhibitory activity against SmPNP. Synthesis, biochemical evaluation, and structure-activity relationship investigations led to the successful development of a small set of thioxothiazolidinone derivatives harboring a novel chemical scaffold as new competitive inhibitors of SmPNP at the low-micromolar range. Seven compounds were identified with IC(50) values below 100 μM. The most potent inhibitors 7, 10, and 17 with IC(50) of 2, 18, and 38 μM, respectively, could represent new potential lead compounds for further development of the therapy of schistosomiasis.

Structural basis for selective inhibition of purine nucleoside phosphorylase from Schistosoma mansoni: Kinetic and structural studies

Selectivity plays a crucial role in the design of enzyme inhibitors as novel antiparasitic agents, particularly in cases where the target enzyme is also present in the human host. Purine nucleoside phosphorylase from Schistosoma mansoni (SmPNP) is an attractive target for the discovery of potential antischistosomal agents. In the present work, kinetic studies were carried out in order to determine the inhibitory potency, mode of action and enzyme selectivity of a series of inhibitors of SmPNP. In addition, crystallographic studies provided important structural insights for rational inhibitor design, revealing consistent structural differences in the binding mode of the inhibitors in the active sites of the SmPNP and human PNP (HsPNP) structures. The molecular information gathered in this work should be useful for future medicinal chemistry efforts in the design of new inhibitors of SmPNP having increased affinity and selectivity.

2D QSAR studies on series of human beta-secretase (BACE-1) inhibitors.

β-secretase (BACE-1) plays a pivotal role in the β-Amyloid plaques formation, which is responsible for progressive cognitive and memory loss commonly found in Alzheimer disease patients. As a consequence, it has been considered as a good target for drug development efforts. Early work focused on the synthesis of peptidomimetics, but poor pharmacokinetics profile prevented advancing lead compounds to clinical trials. As an alternative, aminoimidazoles, aminohydantoins and aminopyridines derivatives that inhibit BACE-1 were designed. Herein we report statistically sound descriptor- based (r(2) = 0.87, q(2) = 0.85, 6 PCs) and fragment-based (r(2) = 0.91, q(2) = 0.84, 6 PCs) QSAR models, that show high predictive ability (r(2)pred = 0.84, averaged r(2)m=0.78) and underscore polar interactions that are important for BACE-1 inhibition.

Enzyme kinetics, structural analysis and molecular modeling studies on a series of Schistosoma mansoni PNP inhibitors

The enzyme purine nucleoside phosphorylase from Schistosoma mansoni (SmPNP) is an attractive molecular target for the development of novel drugs against schistosomiasis, a neglected tropical disease that affects about 200 million people worldwide. In the present work, enzyme kinetic studies were carried out in order to determine the potency and mechanism of inhibition of a series of SmPNP inhibitors. In addition to the biochemical investigations, crystallographic and molecular modeling studies revealed important molecular features for binding affinity towards the target enzyme, leading to the development of structure-activity relationships (SAR).

2D QSAR studies on a series of bifonazole derivatives with antifungal activity

Candida albicans (CA) has been identified as the major opportunistic pathogen in immunosuppressed patients. Most of currently available drugs are either highly toxic or becoming ineffective against resistant strains. An approach to overcome this burden relies on azole derivatives with increased potency and selectivity. Aiming at shedding some light on structural and chemical features that are important for the antifungal activity of azole derivatives, classical 2D QSAR and hologram QSAR (HQSAR) studies were performed for a diverse set of 52 bifonazole derivatives with antifungal activity. Topological descriptors, employed in Classical QSAR studies, resulted in models with low correlation (r2 = 0.38, q2 = 0.27) and lack of predictive power (r2pred = -0.6). On the other hand molecular holograms afforded HQSAR models with good correlation coefficients (r2 = 0.92, q2 = 0.65) and good predictive ability (r2pred = 0.79).

Estudos de QSAR 3D para um conjunto de inibidores de butirilcolinesterase humana

Alzheimers disease (AD) is considered the main cause of cognitive decline in adults. The available therapies for AD treatment seek to maintain the activity of cholinergic system through the inhibition of the enzyme acetylcholinesterase. However, butyrylcholinesterase (BuChE) can be considered an alternative target for AD treatment. Aiming at developing new BuChE inhibitors, robust QSAR 3D models with high predictive power were developed. The best model presents a good fit (r2=0.82, q2=0.76, with two PCs) and high predictive power (r2predict=0.88). Analysis of regression vector shows that steric properties have considerable importance to the inhibition of the BuChE.

In vitro screening and chemometrics analysis on a series of azole derivatives with fungicide activity against moniliophthora perniciosa

Moniliophthora perniciosa, o agente causal da vassoura-de-bruxa do cacaueiro, diminuiu significativamente a producao de cacau, especialmente no estado da Bahia, a maior regiao produtora de cacau do continente americano. As formas de controle desenvolvidas ate o momento tem baixa eficiencia. Derivados de azol sao ativos tanto in vitro quanto in loco contra M. perniciosa, porem nao ha um estudo sistematico sobre a atividade dos azois contra este fitopatogeno. Dados biologicos, obtidos em um ensaio padronizado, foram utilizados para criacao de modelos quimiometricos, que destacam caracteristicas fisico e estruturais importantes para a atividade fungicida de derivados de azol frente a M. perniciosa. De acordo com os modelos de PCA e SIMCA, caracteristicas eletronicas, representadas pelos descritores BEHe3 e JGI4, paralelamente a possibilidadde de realizar ligacoes de H e ausencia de atomos de cloro, distantes de 6-8 ligacoes dos nitrogenios do anel azolico, parecem contribuir para atividade fungicida dos compostos estudados Moniliophthora perniciosa, the causal agent of witches’ broom disease in Theobroma cacao, significantly decreased cacao production, especially in Bahia State, the largest cocoa producing of the American continent. Control programs developed so far have low efficiency. Azole derivatives are active both in vitro and in loco against M. perniciosa, however there is no comprehensive study on the activity of azoles against this phytopatogen. Standardized in vitro biological data were employed to develop supervised and unsupervised chemometric models that highlight physicochemical and structural features that are crucial for azole’s fungicidal activity against M. perniciosa. Thus, PCA and SIMCA models suggest that electronegativity (BEHe3) and dipolar moment (JGI4), as well as H-bonding to M. pernciosa’s lanosterol 14α-desmethylase active site and lack of Cl atoms 6 to 8 bonds from the azole’s nitrogen atoms play a major role to azoles’ fungicide activity.

Analysis of the ergosterol biosynthesis pathway cloning, molecular characterization and phylogeny of lanosterol 14α-demethylase (ERG11) gene of Moniliophthora perniciosa

The phytopathogenic fungus Moniliophthora perniciosa (Stahel) Aime & Philips-Mora, causal agent of witches’ broom disease of cocoa, causes countless damage to cocoa production in Brazil. Molecular studies have attempted to identify genes that play important roles in fungal survival and virulence. In this study, sequences deposited in the M. perniciosa Genome Sequencing Project database were analyzed to identify potential biological targets. For the first time, the ergosterol biosynthetic pathway in M. perniciosa was studied and the lanosterol 14α-demethylase gene (ERG11) that encodes the main enzyme of this pathway and is a target for fungicides was cloned, characterized molecularly and its phylogeny analyzed. ERG11 genomic DNA and cDNA were characterized and sequence analysis of the ERG11 protein identified highly conserved domains typical of this enzyme, such as SRS1, SRS4, EXXR and the heme-binding region (HBR). Comparison of the protein sequences and phylogenetic analysis revealed that the M. perniciosa enzyme was most closely related to that of Coprinopsis cinerea.

2D Chemometrics Analyses of Tetrahydroquinoline and Ethylenediamine Derivatives with Antimalarial Activity

Malaria, one of the most widespread and deadly infectious diseases continues to kill over 1 million people every year. This scenario is getting even worse as P. falciparum develops resistance to existing drugs. Thus, there is an imperative need for novel and more effective antimalarials. Farnesyltransferase (PFT) appears to be a promising therapeutic target to development of antimalarial drugs and many analogs of PFT inhibitors have proved active against P. falciparum. In order to shed some light on the structure-activity relationships of 192 tetrahydroquinoline and ethylenediamine derivatives that are active against P.falciparum, exploratory analysis as well as classical and hologram QSAR strategies were employed. No global QSAR could be developed for the whole dataset, instead local QSAR models were developed for 118 compounds (classical QSAR r2=0.78, q2=0.75, r2 pred= 0.77 with 2 PCs; HQSAR r2=0.82, q2=0.72, r2 pred= 0.79 with 3 PCs) and 74 compounds (r2=0.79, q2=0.74, r2 pred= 0.57 with 2PCs; r2=0.86, q2=0.77, r2 pred= 0.75 with 4 PCs) using partial least square (PLS) regression. Furthermore, the careful and integrated analysis of contribution maps and regression vector suggest that these inhibitors might have dissimilar requirements to their biological activity.

Descriptor-and fragment-based QSAR models for a series of Schistosoma mansoni purine nucleoside inhibitors

The enzyme purine nucleoside phosphorylase from Schistosoma mansoni (SmPNP) is an attractive molecular target for the treatment of major parasitic infectious diseases, with special emphasis on its role in the discovery of new drugs against schistosomiasis, a tropical disease that affects millions of people worldwide. In the present work, we have determined the inhibitory potency and developed descriptor- and fragment-based quantitative structure-activity relationships (QSAR) for a series of 9-deazaguanine analogs as inhibitors of SmPNP. Significant statistical parameters (descriptor-based model: r2 = 0.79, q2 = 0.62, r2pred = 0.52; and fragment-based model: r2 = 0.95, q2 = 0.81, r2pred = 0.80) were obtained, indicating the potential of the models for untested compounds. The fragment-based model was then used to predict the inhibitory potency of a test set of compounds, and the predicted values are in good agreement with the experimental results