Generation of quinolone antimalarials targeting the Plasmodium falciparum mitochondrial respiratory chain for the treatment and prophylaxis of malaria.

There is an urgent need for new antimalarial drugs with novel mechanisms of action to deliver effective control and eradication programs. Parasite resistance to all existing antimalarial classes, including the artemisinins, has been reported during their clinical use. A failure to generate new antimalarials with novel mechanisms of action that circumvent the current resistance challenges will contribute to a resurgence in the disease which would represent a global health emergency. Here we present a unique generation of quinolone lead antimalarials with a dual mechanism of action against two respiratory enzymes, NADH:ubiquinone oxidoreductase (Plasmodium falciparum NDH2) and cytochrome bc(1). Inhibitor specificity for the two enzymes can be controlled subtly by manipulation of the privileged quinolone core at the 2 or 3 position. Inhibitors display potent (nanomolar) activity against both parasite enzymes and against multidrug-resistant P. falciparum parasites as evidenced by rapid and selective depolarization of the parasite mitochondrial membrane potential, leading to a disruption of pyrimidine metabolism and parasite death. Several analogs also display activity against liver-stage parasites (Plasmodium cynomolgi) as well as transmission-blocking properties. Lead optimized molecules also display potent oral antimalarial activity in the Plasmodium berghei mouse malaria model associated with favorable pharmacokinetic features that are aligned with a single-dose treatment. The ease and low cost of synthesis of these inhibitors fulfill the target product profile for the generation of a potent, safe, and inexpensive drug with the potential for eventual clinical deployment in the control and eradication of falciparum malaria.

Predicting the parasite killing effect of artemisinin combination therapy in a murine malaria model.

OBJECTIVES: To develop a mechanism-based model that describes the time course of the malaria parasite in infected mice receiving a combination therapy regimen of dihydroartemisinin and piperaquine. METHODS: Total parasite density-time data from Swiss mice inoculated with Plasmodium berghei were used for the development of population models in S-ADAPT. The mice were administered a single intraperitoneal dose of 30 mg/kg dihydroartemisinin, 10 mg/kg piperaquine phosphate or a combination of both antimalarials at 64 h post-inoculation. In a separate study, mice received multiple dihydroartemisinin doses (5 × 10 mg/kg or 30 mg/kg dihydroartemisinin followed by two 10 mg/kg doses). Parasite recrudescence after treatment was defined using a model that incorporated each erythrocytic stage of the P. berghei life cycle. RESULTS: The disposition of dihydroartemisinin and piperaquine was described by a one-compartment and two-compartment model, respectively. The estimated clearance was 1.95 L/h for dihydroartemisinin and 0.109 L/h for piperaquine. A turnover model described the parasite killing curve after single-agent dosing, with an estimated mean IC50 of 0.747 µg/L for dihydroartemisinin and 16.8 µg/L for piperaquine. In addition, the rate of parasite killing by dihydroartemisinin was almost 50-fold faster than for piperaquine. Parameters from the monotherapy models adequately described the parasite density-time curve following dihydroartemisinin/piperaquine combination therapy or multiple-dose regimens of dihydroartemisinin. CONCLUSIONS: This study has developed mechanistic models that describe the parasite-time curve after single, multiple or combination dosing of antimalarials to mice. These structural models have potential application for pre-clinical investigations to design and refine artemisinin-based combination therapy dosage regimens.

Mechanism-based model of parasite growth and dihydroartemisinin pharmacodynamics in murine malaria.

Murine models are used to study erythrocytic stages of malaria infection, because parasite morphology and development are comparable to those in human malaria infections. Mechanism-based pharmacokinetic-pharmacodynamic (PK-PD) models for antimalarials are scarce, despite their potential to optimize antimalarial combination therapy. The aim of this study was to develop a mechanism-based growth model (MBGM) for Plasmodium berghei and then characterize the parasiticidal effect of dihydroartemisinin (DHA) in murine malaria (MBGM-PK-PD). Stage-specific (ring, early trophozoite, late trophozoite, and schizont) parasite density data from Swiss mice inoculated with Plasmodium berghei were used for model development in S-ADAPT. A single dose of intraperitoneal DHA (10 to 100 mg/kg) or vehicle was administered 56 h postinoculation. The MBGM explicitly reflected all four erythrocytic stages of the 24-hour P. berghei life cycle. Merozoite invasion of erythrocytes was described by a first-order process that declined with increasing parasitemia. An efflux pathway with subsequent return was additionally required to describe the schizont data, thus representing parasite sequestration or trapping in the microvasculature, with a return to circulation. A 1-compartment model with zero-order absorption described the PK of DHA, with an estimated clearance and distribution volume of 1.95 liters h(-1) and 0.851 liter, respectively. Parasite killing was described by a turnover model, with DHA inhibiting the production of physiological intermediates (IC(50), 1.46 ng/ml). Overall, the MBGM-PK-PD described the rise in parasitemia, the nadir following DHA dosing, and subsequent parasite resurgence. This novel model is a promising tool for studying malaria infections, identifying the stage specificity of antimalarials, and providing insight into antimalarial treatment strategies.

Synthesis, in vitro and in vivo antimalarial assessment of sulfide, sulfone and vinyl amide-substituted 1,2,4-trioxanes prepared via thiol-olefin co-oxygenation (TOCO) of allylic alcohols.

Thiol-Olefin Co-Oxygenation (TOCO) methodology has been applied to the synthesis of a small library of weak base and polar 1,2,4-trioxanes. The 1,2,4-trioxane units synthesised exhibit remarkable stability as they survive base catalysed hydrolysis and mixed anhydride/amine coupling reactions. This unique stability feature has enabled a range of novel substitution patterns to be incorporated within the spiro 1,2,4-trioxane unit. Selected analogues express potent in vitro nM antimalarial activity, low cytotoxicity and oral activity in the Plasmodium berghei mouse model of malaria.

Two-step synthesis of achiral dispiro-1,2,4,5-tetraoxanes with outstanding antimalarial activity, low toxicity, and high-stability profiles.

A rapid, two-step synthesis of a range of dispiro-1,2,4,5-tetraoxanes with potent antimalarial activity both in vitro and in vivo has been achieved. These 1,2,4,5-tetraoxanes have been proven to be superior to 1,2,4-trioxolanes in terms of stability and to be superior to trioxane analogues in terms of both stability and activity. Selected analogues have in vitro nanomolar antimalarial activity and good oral activity and are nontoxic in screens for both cytotoxicity and genotoxicity. The synthesis of a fluorescent 7-nitrobenza-2-oxa-1,3-diazole (NBD) tagged tetraoxane probe and use of laser scanning confocal microscopy techniques have shown that tagged molecules accumulate selectively only in parasite infected erythrocytes and that intraparasitic formation of adducts could be inhibited by co-incubation with the iron chelator desferrioxamine (DFO).

Design and synthesis of novel 2-pyridone peptidomimetic falcipain 2/3 inhibitors.

The structure-based design, chemical synthesis and in vitro activity evaluation of various falcipain inhibitors derived from 2-pyridone are reported. These compounds contain a peptidomimetic binding determinant and a Michael acceptor terminal moiety capable of deactivating the cysteine protease active site.

Development of a pharmacodynamic model of murine malaria and antimalarial treatment with dihydroartemisinin.

Antimalarial treatment strategies based on in vitro studies are limited by the paucity of pharmacodynamic information for dosage regimen design. We postulated that a murine model could be used for pre-clinical stages of drug development, especially in dose-response studies and evaluation of combination therapies. Swiss mice infected with Plasmodium berghei parasites (2-5% starting parasitaemia) were given dihydroartemisinin (0-100 mg/kg single dose). Parasite density was regularly determined from thin blood films. A parasite population growth model comprising parasite multiplication, decline in erythrocyte count with increasing parasitaemia and parasite clearance after drug administration was developed. This model described the rise in parasitaemia following inoculation, the nadir following dihydroartemisinin administration, and the subsequent resurgence of parasitaemia (analogous to 'recrudescence'). At doses of 10, 30 and 100 mg/kg dihydroartemisinin, there was a graded response with 2.5+/-1, 5+/-1 and 12+/-4-fold decreases in parasitaemia, respectively. The nadir parasitaemia (at 21-27 h) was also dose-dependent. This study demonstrates that a murine malaria pharmacodynamic model is a valuable tool for understanding how single drugs and their dosing schedules alter the time course and level of infection.

Image-Guided Surgical Robotic System for Percutaneous Reduction of Joint Fractures.

Complex joint fractures often require an open surgical procedure, which is associated with extensive soft tissue damages and longer hospitalization and rehabilitation time. Percutaneous techniques can potentially mitigate these risks but their application to joint fractures is limited by the current sub-optimal 2D intra-operative imaging (fluoroscopy) and by the high forces involved in the fragment manipulation (due to the presence of soft tissue, e.g., muscles) which might result in fracture malreduction. Integration of robotic assistance and 3D image guidance can potentially overcome these issues. The authors propose an image-guided surgical robotic system for the percutaneous treatment of knee joint fractures, i.e., the robot-assisted fracture surgery (RAFS) system. It allows simultaneous manipulation of two bone fragments, safer robot-bone fixation system, and a traction performing robotic manipulator. This system has led to a novel clinical workflow and has been tested both in laboratory and in clinically relevant cadaveric trials. The RAFS system was tested on 9 cadaver specimens and was able to reduce 7 out of 9 distal femur fractures (T- and Y-shape 33-C1) with acceptable accuracy (≈1 mm, ≈5°), demonstrating its applicability to fix knee joint fractures. This study paved the way to develop novel technologies for percutaneous treatment of complex fractures including hip, ankle, and shoulder, thus representing a step toward minimally-invasive fracture surgeries.

Intra-operative fiducial-based CT/fluoroscope image registration framework for image-guided robot-assisted joint fracture surgery.

PURPOSE: Joint fractures must be accurately reduced minimising soft tissue damages to avoid negative surgical outcomes. To this regard, we have developed the RAFS surgical system, which allows the percutaneous reduction of intra-articular fractures and provides intra-operative real-time 3D image guidance to the surgeon. Earlier experiments showed the effectiveness of the RAFS system on phantoms, but also key issues which precluded its use in a clinical application. This work proposes a redesign of the RAFS's navigation system overcoming the earlier version's issues, aiming to move the RAFS system into a surgical environment. METHODS: The navigation system is improved through an image registration framework allowing the intra-operative registration between pre-operative CT images and intra-operative fluoroscopic images of a fractured bone using a custom-made fiducial marker. The objective of the registration is to estimate the relative pose between a bone fragment and an orthopaedic manipulation pin inserted into it intra-operatively. The actual pose of the bone fragment can be updated in real time using an optical tracker, enabling the image guidance. RESULTS: Experiments on phantom and cadavers demonstrated the accuracy and reliability of the registration framework, showing a reduction accuracy (sTRE) of about [Formula: see text] (phantom) and [Formula: see text] (cadavers). Four distal femur fractures were successfully reduced in cadaveric specimens using the improved navigation system and the RAFS system following the new clinical workflow (reduction error [Formula: see text], [Formula: see text]. CONCLUSION: Experiments showed the feasibility of the image registration framework. It was successfully integrated into the navigation system, allowing the use of the RAFS system in a realistic surgical application.

Rational Design, Synthesis, and Biological Evaluation of Heterocyclic Quinolones Targeting the Respiratory Chain of Mycobacterium tuberculosis.

A high-throughput screen (HTS) was undertaken against the respiratory chain dehydrogenase component, NADH:menaquinone oxidoreductase (Ndh) of Mycobacterium tuberculosis (Mtb). The 11000 compounds were selected for the HTS based on the known phenothiazine Ndh inhibitors, trifluoperazine and thioridazine. Combined HTS (11000 compounds) and in-house screening of a limited number of quinolones (50 compounds) identified ∼100 hits and four distinct chemotypes, the most promising of which contained the quinolone core. Subsequent Mtb screening of the complete in-house quinolone library (350 compounds) identified a further ∼90 hits across three quinolone subtemplates. Quinolones containing the amine-based side chain were selected as the pharmacophore for further modification, resulting in metabolically stable quinolones effective against multi drug resistant (MDR) Mtb. The lead compound, 42a (MTC420), displays acceptable antituberculosis activity (Mtb IC50 = 525 nM, Mtb Wayne IC50 = 76 nM, and MDR Mtb patient isolates IC50 = 140 nM) and favorable pharmacokinetic and toxicological profiles.

Alpha-lithio quinuclidine N-oxide (Li-QNO): a new base for synthetic chemistry.

A-Lithio quinuclidine N-oxide (Li-QNO) behaves as a strong non-nucleophilic base and an HMPA mimetic in a tandem process, in a range of synthetically useful reactions.

The electromyographic activity of thoracic paraspinal muscles identified as abnormal with palpation.

OBJECTIVE: The aim of this study was to compare the electromyographic (EMG) activity of deep muscles in the thoracic paravertebral gutter (PVG) detected as abnormal to palpation (AbPT) and reported as tender by the subject with muscles underlying nontender (NT), normal to palpation sites under various experimental conditions. METHODS: Twelve subjects (mean age, 25.42 years; range, 22-43 years) participated in this study. Fine-wire, bipolar intramuscular electrodes were inserted, under real-time ultrasonic guidance, into the deep paravertebral muscle mass underlying 1 AbPT and 2 NT sites (1 segment above and below the AbPT site) in the thoracic PVG regions. Electromyographic activity was recorded under the following conditions: resting prone, prone active trunk extension, application of pressure (300 kPa) to adjacent spinous processes, resting seated, passive and active seated trunk rotation, and supporting 2-kg weights in outstretched arms. RESULTS: Mean EMG activity was highest at the AbPT site, relative to NT sites, under all conditions, with a significant between-group effect of site (F2,31 = 4.13, P = .03) and large between-group effect size (eta2 = 0.21). There was also a trend for lower percentage change from baseline resting at the AbPT sites, relative to the NT sites, in response to the demand of other conditions. There were large variations in EMG activity within and between individuals, and large SDs accompanied the mean values of EMG activity in all cases. CONCLUSION: Increased motor activity may be a contributing factor to tissue changes in the PVG detected with palpation. However, caution must be used when interpreting these results because of the large variations, small sample size, and issues associated with EMG normalization.

Referencing and quotation accuracy in four manual therapy journals.

The aim of the study was to investigate the reference and quotation accuracy in four peer-reviewed manual therapy journals. A stratified random sample of original research (n=7) was collected from each of the journals spanning the years January 2000 to December 2001. A further random selection of 80 references from each journal paper sampled was then reviewed (Total N=320) for citation and quotation accuracy. Numbers of citations with errors were determined, then classified as either major or minor and categorized by bibliographic headings (author, title, journal, year, volume, page and irretrievable). Each quotation was individually assessed for accuracy and judged to be either correct or incorrect. A quotation was deemed correct if it accurately substantiated and reported the original authors assertions. One hundred and fifteen citations across all journals contained errors (35.9%). Some citations exhibited multiple major and minor errors. Bibliographically classified errors for all journals showed 61 author, 51 title, 6 journal, 4 year, 12 volume and 25 page errors. JMPT showed the lowest referencing error rate (20%) while JBWMT recorded the highest (58.8%). The total number of quotation errors across all journals was 69 (12.3%). JMPT showed the lowest quotation error rate of 6 (4.7%), MT had 12 errors (7.3%), JOM produced 21 errors (13.3%), while JBWMT recorded the highest error rate with 32 (27.6%). Poor citation and quotation is a reflection on the scholarly work of the authors and the journal. The trend for errors in quotation is more worrying than citation errors as it reflects poor diligence on the part of the investigators.

Paraspinal muscles and intervertebral dysfunction: part two.

BACKGROUND: One of the diagnostic characteristics of the manipulable spinal lesion--a musculoskeletal disturbance that is claimed to be detected with manual palpation and corrected with manipulation--is said to be altered segmental tissue texture. Little evidence for the nature of abnormal paraspinal tissue texture exists, but indirect evidence from experimental studies supports the plausibility of the concept of protective muscle spasm, although investigations of increased paraspinal electromyography (EMG) associated with low back pain suggests complex changes in motor control rather than simple protective reflexes. OBJECTIVES: To review the literature for evidence that may support or refute proposed explanations for clinically observed altered paraspinal tissue texture associated with the manipulable spinal lesion. This review aims to highlight areas that require further research and make recommendations for future studies. Data Source MEDLINE and CINAHL databases were searched using various combinations of the keywords paraspinal, muscle, palpation, EMG, spine, low back pain, pain, myofascial, hardness, manipulation, reliability, and somatic dysfunction, along with searching the bibliographies of selected articles and textbooks. Data Extraction All relevant data were used. RESULTS: Decreased paraspinal muscle activity and strength associated with low back pain is well established, and there is evidence of changes in muscle fiber composition and localized selective multifidus atrophy. Disturbances in microcirculation have been implicated in nonparaspinal muscle pain. The effect of spinal manipulation on paraspinal EMG activity is inconclusive but promising. CONCLUSION: Little direct evidence exists to support the existence or nature of paraspinal tissue texture change that is claimed to be detected with palpation. The proposal of segmental reflex paraspinal muscle contraction was not supported, at least in association with low back pain. There appears to be a complex relationship between deep paraspinal muscle inhibition during dynamic activity and nonvoluntary guarding behavior during static activity. The relationship between these findings and palpable tissue change is speculative, but increased activity, decreased activity, or both may be responsible for paraspinal tissues detected as abnormal with palpation. Recommendations are outlined for future research.

Identification, design and biological evaluation of bisaryl quinolones targeting Plasmodium falciparum type II NADH:quinone oxidoreductase (PfNDH2).

A program was undertaken to identify hit compounds against NADH:ubiquinone oxidoreductase (PfNDH2), a dehydrogenase of the mitochondrial electron transport chain of the malaria parasite Plasmodium falciparum. PfNDH2 has only one known inhibitor, hydroxy-2-dodecyl-4-(1H)-quinolone (HDQ), and this was used along with a range of chemoinformatics methods in the rational selection of 17 000 compounds for high-throughput screening. Twelve distinct chemotypes were identified and briefly examined leading to the selection of the quinolone core as the key target for structure-activity relationship (SAR) development. Extensive structural exploration led to the selection of 2-bisaryl 3-methyl quinolones as a series for further biological evaluation. The lead compound within this series 7-chloro-3-methyl-2-(4-(4-(trifluoromethoxy)benzyl)phenyl)quinolin-4(1H)-one (CK-2-68) has antimalarial activity against the 3D7 strain of P. falciparum of 36 nM, is selective for PfNDH2 over other respiratory enzymes (inhibitory IC(50) against PfNDH2 of 16 nM), and demonstrates low cytotoxicity and high metabolic stability in the presence of human liver microsomes. This lead compound and its phosphate pro-drug have potent in vivo antimalarial activity after oral administration, consistent with the target product profile of a drug for the treatment of uncomplicated malaria. Other quinolones presented (e.g., 6d, 6f, 14e) have the capacity to inhibit both PfNDH2 and P. falciparum cytochrome bc(1), and studies to determine the potential advantage of this dual-targeting effect are in progress.

Identification, design and biological evaluation of heterocyclic quinolones targeting Plasmodium falciparum type II NADH:quinone oxidoreductase (PfNDH2).

Following a program undertaken to identify hit compounds against NADH:ubiquinone oxidoreductase (PfNDH2), a novel enzyme target within the malaria parasite Plasmodium falciparum, hit to lead optimization led to identification of CK-2-68, a molecule suitable for further development. In order to reduce ClogP and improve solubility of CK-2-68 incorporation of a variety of heterocycles, within the side chain of the quinolone core, was carried out, and this approach led to a lead compound SL-2-25 (8b). 8b has IC(50)s in the nanomolar range versus both the enzyme and whole cell P. falciparum (IC(50) = 15 nM PfNDH2; IC(50) = 54 nM (3D7 strain of P. falciparum) with notable oral activity of ED(50)/ED(90) of 1.87/4.72 mg/kg versus Plasmodium berghei (NS Strain) in a murine model of malaria when formulated as a phosphate salt. Analogues in this series also demonstrate nanomolar activity against the bc(1) complex of P. falciparum providing the potential added benefit of a dual mechanism of action. The potent oral activity of 2-pyridyl quinolones underlines the potential of this template for further lead optimization studies.

Identification of novel antimalarial chemotypes via chemoinformatic compound selection methods for a high-throughput screening program against the novel malarial target, PfNDH2: increasing hit rate via virtual screening methods.

Malaria is responsible for approximately 1 million deaths annually; thus, continued efforts to discover new antimalarials are required. A HTS screen was established to identify novel inhibitors of the parasite's mitochondrial enzyme NADH:quinone oxidoreductase (PfNDH2). On the basis of only one known inhibitor of this enzyme, the challenge was to discover novel inhibitors of PfNDH2 with diverse chemical scaffolds. To this end, using a range of ligand-based chemoinformatics methods, ~17000 compounds were selected from a commercial library of ~750000 compounds. Forty-eight compounds were identified with PfNDH2 enzyme inhibition IC(50) values ranging from 100 nM to 40 µM and also displayed exciting whole cell antimalarial activity. These novel inhibitors were identified through sampling 16% of the available chemical space, while only screening 2% of the library. This study confirms the added value of using multiple ligand-based chemoinformatic approaches and has successfully identified novel distinct chemotypes primed for development as new agents against malaria.