Kenny K. H. Ang

In Vivo Antimalarial Activity of the Beta-Carboline Alkaloid Manzamine A

ABSTRACT Manzamine A, a β-carboline alkaloid present in several marine sponge species, inhibits the growth of the rodent malaria parasitePlasmodium berghei in vivo. More than 90% of the asexual erythrocytic stages of P. berghei were inhibited after a single intraperitoneal injection of manzamine A into infected mice. A remarkable aspect of manzamine A treatment is its ability to prolong the survival of highly parasitemic mice, with 40% recovery 60 days after a single injection. Oral administration of an oil suspension of manzamine A also produced significant reductions in parasitemia. The plasma manzamine A concentration peaked 4 h after injection and remained high even at 48 h. Morphological changes of P. berghei were observed 1 h after treatment of infected mice. (−)-8-Hydroxymanzamine A also displayed antimalarial activity, whereas manzamine F, a ketone analog of manzamine A, did not. Our results suggest that manzamine A and (−)-8-hydroxymanzamine A are promising new antimalarial agents.

A screen against Leishmania intracellular amastigotes: comparison to a promastigote screen and identification of a host cell-specific hit.

The ability to screen compounds in a high-throughput manner is essential in the process of small molecule drug discovery. Critical to the success of screening strategies is the proper design of the assay, often implying a compromise between ease/speed and a biologically relevant setting. Leishmaniasis is a major neglected disease with limited therapeutic options. In order to streamline efforts for the design of productive drug screens against Leishmania, we compared the efficiency of two screening methods, one targeting the free living and easily cultured promastigote (insect–infective) stage, the other targeting the clinically relevant but more difficult to culture intra-macrophage amastigote (mammal-infective) stage. Screening of a 909-member library of bioactive compounds against Leishmania donovani revealed 59 hits in the promastigote primary screen and 27 in the intracellular amastigote screen, with 26 hits shared by both screens. This suggested that screening against the promastigote stage, although more suitable for automation, fails to identify all active compounds and leads to numerous false positive hits. Of particular interest was the identification of one compound specific to the infective amastigote stage of the parasite. This compound affects intracellular but not axenic parasites, suggesting a host cell-dependent mechanism of action, opening new avenues for anti-leishmanial chemotherapy.

Nonpeptidic Tetrafluorophenoxymethyl Ketone Cruzain Inhibitors As Promising New Leads for Chagas Disease Chemotherapy

A century after discovering that the Trypanosoma cruzi parasite is the etiological agent of Chagas disease, treatment is still plagued by limited efficacy, toxicity, and the emergence of drug resistance. The development of inhibitors of the major T. cruzi cysteine protease, cruzain, has been demonstrated to be a promising drug discovery avenue for this neglected disease. Here we establish that a nonpeptidic tetrafluorophenoxymethyl ketone cruzain inhibitor substantially ameliorates symptoms of acute Chagas disease in a mouse model with no apparent toxicity. A high-resolution crystal structure confirmed the mode of inhibition and revealed key binding interactions of this novel inhibitor class. Subsequent structure-guided optimization then resulted in inhibitor analogues with improvements in potency despite minimal or no additions in molecular weight. Evaluation of the analogues in cell culture showed enhanced activity. These results suggest that nonpeptidic tetrafluorophenoxymethyl ketone cruzain inhibitors have the potential to fulfill the urgent need for improved Chagas disease chemotherapy.

Vibration control of smart piezoelectric composite plates

This study on the vibration control of smart piezoelectric composite plates investigates the effect of the stretching-bending coupling of the piezoelectric sensor/actuator pairs on the system stability of smart composite plates. Based on first-order shear theory and consistent methodology, a smart isoparametric finite element is formulated and the classical negative velocity feedback control method is adopted for the active vibration control analysis of smart composite plates with bonded or embedded distributed piezoelectric sensors and actuators. It is shown mathematically and demonstrated numerically that generally the coupling effect tends to result in system instability unless the sensor/actuator pairs are collocated or the plate simply supported. The result of this study can be used to aid the placement of piezoelectric sensor/actuator pairs of smart composite plates as well as for robust controller design.

Divergent modes of enzyme inhibition in a homologous structure-activity series.

A docking screen identified reversible, noncovalent inhibitors (e.g., 1) of the parasite cysteine protease cruzain. Chemical optimization of 1 led to a series of oxadiazoles possessing interpretable SAR and potencies as much as 500-fold greater than 1. Detailed investigation of the SAR series subsequently revealed that many members of the oxadiazole class (and surprisingly also 1) act via divergent modes of inhibition (competitive or via colloidal aggregation) depending on the assay conditions employed.

Vibration Control of Composite Plates via Optimal Placement of Piezoelectric Patches

A simple optimal placement strategy of piezoelectric sensor/actuator (S/A) pairs for vibration control of laminated composite plate is presented, where the active damping effect under a classical control framework is maximized using the finite element approach. The classical direct pattern search method is employed to obtain the local optimum, where two optimization performance indices based on modal and system controllability are studied. The start point for the pattern search is selected based on the maxima of integrated normal strains consistent with the size of the collocated piezoelectric patches used. This would maximize the virtual work done by the equivalent actuation forces along the strain field of an initial state. Numerical simulation using a cantilevered and a clamped composite square plate illustrate the effectiveness of the proposed strategy, where the results coincide with the global optimal layout from exhaustive search for both modal and system controllability indices. The number of trials to reach the optimal position is few compared to an initial blind discrete pattern search approach. The reduced control effectiveness of both plates under constrained input voltages is illustrated.

Natural Product Libraries to Accelerate the High Throughput Discovery of Therapeutic Leads

A high-throughput (HT) paradigm generating LC-MS-UV-ELSD-based natural product libraries to discover compounds with new bioactivities and or molecular structures is presented. To validate this methodology, an extract of the Indo-Pacific marine sponge Cacospongia mycofijiensis was evaluated using assays involving cytoskeletal profiling, tumor cell lines, and parasites. Twelve known compounds were identified including latrunculins (1-4, 10), fijianolides (5, 8, 9), mycothiazole (11), aignopsanes (6, 7), and sacrotride A (13). Compounds 1-5 and 8-11 exhibited bioactivity not previously reported against the parasite T. brucei, while 11 showed selectivity for lymphoma (U937) tumor cell lines. Four new compounds were also discovered including aignopsanoic acid B (13), apo-latrunculin T (14), 20-methoxy-fijianolide A (15), and aignopsane ketal (16). Compounds 13 and 16 represent important derivatives of the aignopsane class, 14 exhibited inhibition of T. brucei without disrupting microfilament assembly, and 15 demonstrated modest microtubule-stabilizing effects. The use of removable well plate libraries to avoid false positives from extracts enriched with only one or two major metabolites is also discussed. Overall, these results highlight the advantages of applying modern methods in natural products-based research to accelerate the HT discovery of therapeutic leads and/or new molecular structures using LC-MS-UV-ELSD-based libraries.

Diverse inhibitor chemotypes targeting Trypanosoma cruzi CYP51

Background Chagas Disease, a WHO- and NIH-designated neglected tropical disease, is endemic in Latin America and an emerging infection in North America and Europe as a result of population moves. Although a major cause of morbidity and mortality due to heart failure, as well as inflicting a heavy economic burden in affected regions, Chagas Disease elicits scant notice from the pharmaceutical industry because of adverse economic incentives. The discovery and development of new routes to chemotherapy for Chagas Disease is a clear priority. Methodology/Principal Findings The similarity between the membrane sterol requirements of pathogenic fungi and those of the parasitic protozoon Trypanosoma cruzi, the causative agent of Chagas human cardiopathy, has led to repurposing anti-fungal azole inhibitors of sterol 14α-demethylase (CYP51) for the treatment of Chagas Disease. To diversify the therapeutic pipeline of anti-Chagasic drug candidates we exploited an approach that included directly probing the T. cruzi CYP51 active site with a library of synthetic small molecules. Target-based high-throughput screening reduced the library of ∼104,000 small molecules to 185 hits with estimated nanomolar KD values, while cross-validation against T. cruzi-infected skeletal myoblast cells yielded 57 active hits with EC50 <10 µM. Two pools of hits partially overlapped. The top hit inhibited T. cruzi with EC50 of 17 nM and was trypanocidal at 40 nM. Conclusions/Significance The hits are structurally diverse, demonstrating that CYP51 is a rather permissive enzyme target for small molecules. Cheminformatic analysis of the hits suggests that CYP51 pharmacology is similar to that of other cytochromes P450 therapeutic targets, including thromboxane synthase (CYP5), fatty acid ω-hydroxylases (CYP4), 17α-hydroxylase/17,20-lyase (CYP17) and aromatase (CYP19). Surprisingly, strong similarity is suggested to glutaminyl-peptide cyclotransferase, which is unrelated to CYP51 by sequence or structure. Lead compounds developed by pharmaceutical companies against these targets could also be explored for efficacy against T. cruzi.

Novel non-peptidic vinylsulfones targeting the S2 and S3 subsites of parasite cysteine proteases.

We describe here the identification of non-peptidic vinylsulfones that inhibit parasite cysteine proteases in vitro and inhibit the growth of Trypanosoma brucei brucei parasites in culture. A high resolution (1.75 A) co-crystal structure of 8a bound to cruzain reveals how the non-peptidic P2/P3 moiety in such analogs bind the S2 and S3 subsites of the protease, effectively recapitulating important binding interactions present in more traditional peptide-based protease inhibitors and natural substrates.

Weighted energy linear quadratic regulator vibration control of piezoelectric composite plates

In this paper on finite element linear quadratic regulator (LQR) vibration control of smart piezoelectric composite plates, we propose the use of the total weighted energy method to select the weighting matrices. By constructing the optimal performance function as a relative measure of the total kinetic energy, strain energy and input energy of the system, only three design variables need to be considered to achieve a balance between the desired higher damping effect and lower input cost. Modal control analysis is used to interpret the effects of three energy weight factors on the damping ratios and modal voltages and it is shown that the modal damping effect will increase with the kinetic energy weight factor, approaching √2/2 as the strain energy weight factor increases and decrease with the input energy weight factor. Numerical results agree well with those from the modal control analysis. Since the control problem is simplified to three design variables only, the computational cost will be greatly reduced and a more accurate structural control analysis becomes more attractive for large systems.