Methyl Scanning and Revised Binding Mode of 2-Pralidoxime, an Antidote for Nerve Agent Poisoning

Organophosphorus nerve agents (OPNAs) inhibit acetylcholinesterase (AChE) and, despite the Chemical Weapons Convention arms control treaty, continue to represent a threat to both military personnel and civilians. 2-Pralidoxime (2-PAM) is currently the only therapeutic countermeasure approved by the United States Food and Drug Administration for treating OPNA poisoning. However, 2-PAM is not centrally active due to its hydrophilicity and resulting poor blood-brain barrier permeability; hence, these deficiencies warrant the development of more hydrophobic analogs. Specifically, gaps exist in previously published structure activity relationship (SAR) studies for 2-PAM, thereby making it difficult to rationally design novel analogs that are concomitantly more permeable and more efficacious. In this study, we methodically performed a methyl scan on the core pyridinium of 2-PAM to identify ring positions that could tolerate both additional steric bulk and hydrophobicity. Subsequently, SAR-guided molecular docking was used to rationalize hydropathically feasible binding modes for 2-PAM and the reported derivatives. Overall, the data presented herein provide new insights that may facilitate the rational design of more efficacious 2-PAM analogs.

S-(4-Methoxyphenyl)-4-methoxybenzenesulfonothioate as a Promising Lead Compound for the Development of a Renal Carcinoma Agent

Organosulfur compounds show cytotoxic potential towards many tumor cell lines. Disulfides and thiosulfonates act through apoptotic processes, inducing proteins associated with apoptosis, endoplasmic reticulum stress, and the unfolded protein response. Three p-substituted symmetric diaryl disulfides and three diaryl thiosulfonates were synthesized and analyzed for inhibition of tubulin polymerization and for human cancer cell cytotoxic activity against seven tumor cell lines and a non-tumor cell line. S-(4-methoxyphenyl)-4-methoxybenzenesulfonothioate (6) exhibited inhibition of tubulin polymerization and showed the best antiproliferative potential, especially against the 786-0 cell line, being six times more selective as compared with the non-tumor cell line. In addition, compound 6 was able to activate caspase-3 after 24 and 48 h treatments of the 786-0 cell line and induced cell-cycle arrest in the G2/M stage at the highest concentration evaluated at 24 and 48 h. Compound 6 was able to cause complete inhibition of proliferation, inducing the death of 786-0 cells, by increasing the number of cells at G2/M and greater activation of caspase-3.

Next-Generation Cell-Active Inhibitors of the Undrugged Oncogenic PTP4A3 Phosphatase

Oncogenic protein tyrosine phosphatases (PTPs) are overexpressed in numerous human cancers but they have been challenging pharmacological targets. The emblematic oncogenic PTP4A tyrosine phosphatase family regulates many fundamental malignant processes. 7-Imino-2-phenylthieno[3,2-c]pyridine-4,6(5H,7H)-dione (JMS-053) is a novel, potent, and selective PTP4A inhibitor but its mechanism of action has not been fully elucidated, nor has the chemotype been fully investigated. Because tyrosine phosphatases are notoriously susceptible to oxidation, we interrogated JMS-053 and three newly synthesized analogs with specific attention on the role of oxidation. JMS-053 and its three analogs were potent in vitro PTP4A3 inhibitors, but 7-imino-5-methyl-2-phenylthieno[3,2-c]pyridine-4,6(5H,7H)-dione (NRT-870-59) appeared unique among the thienopyridinediones with respect to its inhibitory specificity for PTP4A3 versus both a PTP4A3 A111S mutant and an oncogenic dual specificity tyrosine phosphatase, CDC25B. Like JMS-053, NRT-870-59 was a reversible PTP4A3 inhibitor. All of the thienopyridinediones retained cytotoxicity against human ovarian and breast cancer cells grown as pathologically relevant three-dimensional spheroids. Inhibition of cancer cell colony formation by NRT-870-59, like JMS-053, required PTP4A3 expression. JMS-053 failed to generate significant detectable reactive oxygen species in vitro or in cancer cells. Mass spectrometry results indicated no disulfide bond formation or oxidation of the catalytic Cys104 after in vitro incubation of PTP4A3 with JMS-053 or NRT-870-59. Gene expression profiling of cancer cells exposed to JMS-053 phenocopied many of the changes seen with the loss of PTP4A3 and did not indicate oxidative stress. These data demonstrate that PTP4A phosphatases can be selectively targeted with small molecules that lack prominent reactive oxygen species generation and encourage further studies of this chemotype. SIGNIFICANCE STATEMENT: Protein tyrosine phosphatases are emerging as important contributors to human cancers. We report on a new class of reversible protein phosphatase small molecule inhibitors that are cytotoxic to human ovarian and breast cancer cells, do not generate significant reactive oxygen species in vitro and in cells, and could be valuable lead molecules for future studies of PTP4A phosphatases.

P6342Subcutaneous delivery of NPA7, first-in-class novel bispecific designer peptide: enhances cardiorenal function and suppresses renin and aldosterone in vivo and in vitro

Introduction

The rapid increase of patients of heart failure (HF) is a major health burden worldwide. Most importantly is the need to develop innovative new drugs for treatment of HF, such as sacubitril/valsartan which in part functions by enhancing the natriuretic peptides (NPs). We engineered NPA7 as a novel 30 amino acid bispecific designer peptide which activates the particulate guanylyl cyclase A receptor (pGC-A)/cGMP and for which the NPs both ANP and BNP are ligands and the Mas-receptor (MasR)/cAMP pathways for Angiotensin 1–7 (Ang1–7) is the endogenous ligand. We previously reported that acute intravenous (IV) administration of NPA7 shows cardiorenal protective and renin-aldosterone suppressing actions that go beyond the native peptides, BNP or Ang 1–7, which may have therapeutic potential for HF.

Purpose

To support the clinical development of NPA7 as a potential therapy in HF which promotes NP and MasR pathways, we investigated the actions and stability of subcutaneous (SQ) administration of NPA7 in normal canines. We also defined NPA7's peptide stability and metabolites in canine plasma.

Methods

Plasma and urinary cGMP, cardiorenal and renin-aldosterone responses to SQ injection (10μg/kg) were determined over 4 hours in normal canines (n=5) in vivo. Ex vivo, we established stability of NPA7 and key metabolites in canine serum using liquid chromatography-mass spectrometry (LC-MS). Data are expressed as mean ± SEM. * P<0.05 vs. BL.

Results

In vivo, SQ NPA7 resulted in a sustained increase at 2 hours in plasma (BL: 10±3; 120 min: 30±6* pmol/ml) and urinary (BL: 1033±198; 120 min: 5792±857* pmol/min) cGMP, GFR (BL: 29±6; 120 min: 70±12* ml/min) and sodium excretion (BL: 18±10; 120 min: 144±33* ueq/min). We observed a gradual reduction in BP at 60 min (BL: 109±4; 60 min: 99±7* mmHg) with a sustained decrease in PCWP at 4 hours (BL: 5±0.9; 240 min: 3.1±0.6* mmHg). SQ NPA7 also suppressed plasma renin and aldosterone up to 3 hours after SQ injection. LC-MS revealed that NPA7 was highly stable with both the pGC-A and MasR activating moieties intact ex vivo in canine serum with a disappearance time of 2 hours. We also identified 2 major NPA7 metabolites NPA71–27 and NPA71–28.

Conclusions

SQ NPA7 possesses cGMP activating, cardiac unloading, diuretic, natriuretic, and renin-aldosterone suppressing actions in normal canines. NPA7 is also highly stable in serum. These studies support SQ administration as an effective delivery strategy for NPA7, a first-in-class innovative bispecific dual pGC-A/MasR activator now in preclinical development for HF.

Specific RITA Modification Produces Hyperselective Cytotoxicity While Maintaining In Vivo Antitumor Efficacy

The preclinical antitumor agent RITA (2,5-bis[5-hydroxymethyl-2-thienyl] furan, NSC 652287), an analog of the natural product α-terthiophene, failed during the development phase due to acute pulmonary toxicity in animal models. A series of synthetic modifications to RITA's heterocyclic scaffold resulted in activity ranging from broadly cytotoxic to highly selective. In the NCI 60-cell line screen, these "hyperselective" agents (e.g., imatinib) are rare. A selectivity index (SI) was developed to quantify this desirable feature, which is 20 for imatinib, whereas RITA's SI is only 0.10. One of the described hyperselective RITA analogs (SI = 7.9) completely lost activity in the presence of a known SULT1A1 inhibitor. These results, coupled with previous evidence that RITA is a SULT1A1 substrate, suggest that carbinol modification by a sulfate leaving group and subsequent formation of a reactive carbocation may explain RITA's broad cytotoxicity. Although SULT1A1 expression is required for susceptibility, hyperselective analogs exhibited reduced association of activity with SULT1A1 mRNA expression compared with RITA, apparently requiring some additional target(s). In support of this hypothesis, there is a strong correlation (P < 0.01, r = 0.95) between quantum mechanically calculated energy barriers for carbocation formation from sulfonated analogs and SI, indicating that hyperselective RITA analogs generate reactive carbocations less readily after sulfate activation. Importantly, narrowing the cytotoxicity profile of RITA did not eliminate its analogs' in vivo antitumor activity, as several new hyperselective agents, NSC 773097 (1), 773392 (2), and 782846 (6), displayed impressive activity against A498 xenografts in mice.

Tapping the therapeutic potential of protein tyrosine phosphatase 4A with small molecule inhibitors

Protein tyrosine phosphatases (PTPs) are emerging new targets for drug discovery. PTPs and protein tyrosine kinases (PTKs) maintain cellular homeostasis through opposing roles: tyrosine O-dephosphorylation and -phosphorylation, respectively. An imbalance in the phosphorylation equilibrium results in aberrant protein signaling and pathophysiological conditions. PTPs have historically been considered 'undruggable', in part due to a lack of evidence defining their relationship to disease causality and a focus on purely competitive inhibitors. However, a better understanding of protein-protein interfaces and shallow active sites has recently renewed interest in the pursuit of allosteric and orthosteric modulators of targets outside the major druggable protein families. While their biological mechanism of action still remains to be clarified, PTP4A1-3 (also referred to as PRL1-3) are validated oncology targets and play an important role in cell proliferation, metastasis, and tumor angiogenesis. In this Digest, recent syntheses and structure-activity relationships (SAR) of small molecule inhibitors (SMIs) of PTP4A1-3 are summarized, and enzyme docking studies of the most potent chemotype are highlighted. In particular, the thienopyridone scaffold has emerged as a potent lead structure to interrogate the function and druggability of this dual-specificity PTP.

Do Zebrafish Obey Lipinski Rules?

The use of zebrafish in whole organism phenotypic assays has become a valuable strategy throughout the drug discovery process. Zebrafish assays can be used not only to screen libraries of compounds at the earliest stages but also to evaluate advanced leads for their effects on specific biological pathways or for toxicity. However, when confronted with inactivity of a compound in a zebrafish assay, there are little data that can be used to judge if the compound is truly biologically inert or inactive due to a lack of permeability into the model organism. While medicinal chemistry principles suggest parameters that are predictive of human oral bioavailability, cellular permeability, and even bacterial permeability, there have been no such parameters developed for zebrafish absorption. To address this question, we compiled a set of 700 compounds reported in the literature to be active in zebrafish assays, evaluated their properties, and compared them to properties derived from a set of historical drugs and a set of recently approved oral drugs. While some properties overlap, the averages and 10th and 90th percentiles of molecular weight, octanol-water partition coefficient (logP), H-bond counts, and polar surface area for zebrafish-active compounds are statistically different from those of known drugs. This analysis should be useful to scientists interpreting structure-activity relationships based on data from zebrafish assays and help to inform the translation from fish to mammals.

In-flow photooxygenation of aminothienopyridinones generates iminopyridinedione PTP4A3 phosphatase inhibitors

A continuous flow photooxygenation of 7-aminothieno[3,2-c]pyridin-4(5H)-ones to produce 7-iminothieno[3,2-c]pyridine-4,6(5H,7H)-diones has been developed, utilizing ambient air as the sole reactant. N-H Imines are formed as the major products, and excellent functional group tolerance and conversion on gram-scale without the need for chromatographic purification allow for facile late-stage diversification of the aminothienopyridinone scaffold. Several analogs exhibit potent in vitro inhibition of the cancer-associated protein tyrosine phosphatase PTP4A3, and the SAR supports an exploratory docking model.

Optimization of Phenyl Indole Inhibitors of the AAA+ ATPase p97

Optimization of the side-chain of a phenyl indole scaffold identified from a high-throughput screening campaign for inhibitors of the AAA+ ATPase p97 is reported. The addition of an N-alkyl piperazine led to high potency of this series in a biochemical assay, activity in cell-based assays, and excellent pharmaceutical properties. Molecular modeling based on a subsequently obtained cryo-EM structure of p97 in complex with a phenyl indole was used to rationalize the potency of these allosteric inhibitors.

A threonine turnstile defines a dynamic amphiphilic binding motif in the AAA ATPase p97 allosteric binding site

The turnstile motion of two neighboring threonines sets up a dynamic side chain interplay that can accommodate both polar and apolar ligands in a small molecule allosteric protein binding site. A computational model based on SAR data and both X-ray and cryo-EM structures of the AAA ATPase p97 was used to analyze the effects of paired threonines at the inhibitor site. Specifically, the Thr side chain hydroxyl groups form a hydrogen bonding network that readily accommodates small, highly polar ligand substituents. Conversely, diametric rotation of the χ₁ torsion by 150-180° orients the side chain β-methyl groups into the binding cleft, creating a hydrophobic pocket that can accommodate small, apolar substituents. This motif was found to be critical for rationalizing the affinities of a structurally focused set of inhibitors of p97 covering a > 2000-fold variation in potencies, with a preference for either small-highly polar or small-apolar groups. The threonine turnstile motif was further validated by a PDB search that identified analogous binding modes in ligand interactions in PKB, as well as by an analysis of NMR structures demonstrating additional gear-like interactions between adjacent Thr pairs. Combined, these data suggest that the threonine turnstile motif may be a general feature of interest in protein binding pockets.

Targeting ovarian cancer and endothelium with an allosteric PTP4A3 phosphatase inhibitor

Overexpression of protein tyrosine phosphatase PTP4A oncoproteins is common in many human cancers and is associated with poor patient prognosis and survival. We observed elevated levels of PTP4A3 phosphatase in 79% of human ovarian tumor samples, with significant overexpression in tumor endothelium and pericytes. Furthermore, PTP4A phosphatases appear to regulate several key malignant processes, such as invasion, migration, and angiogenesis, suggesting a pivotal regulatory role in cancer and endothelial signaling pathways. While phosphatases are attractive therapeutic targets, they have been poorly investigated because of a lack of potent and selective chemical probes. In this study, we disclose that a potent, selective, reversible, and noncompetitive PTP4A inhibitor, JMS-053, markedly enhanced microvascular barrier function after exposure of endothelial cells to vascular endothelial growth factor or lipopolysaccharide. JMS-053 also blocked the concomitant increase in RhoA activation and loss of Rac1. In human ovarian cancer cells, JMS-053 impeded migration, disrupted spheroid growth, and decreased RhoA activity. Importantly, JMS-053 displayed anticancer activity in a murine xenograft model of drug resistant human ovarian cancer. These data demonstrate that PTP4A phosphatases can be targeted in both endothelial and ovarian cancer cells, and confirm that RhoA signaling cascades are regulated by the PTP4A family.

Insulin/glucose induces natriuretic peptide clearance receptor in human adipocytes: a metabolic link with the cardiac natriuretic pathway

Cardiac natriuretic peptides (NP) are involved in cardiorenal regulation and in lipolysis. The NP activity is largely dependent on the ratio between the signaling receptor NPRA and the clearance receptor NPRC. Lipolysis increases when NPRC is reduced by starving or very-low-calorie diet. On the contrary, insulin is an antilipolytic hormone that increases sodium retention, suggesting a possible functional link with NP. We examined the insulin-mediated regulation of NP receptors in differentiated human adipocytes and tested the association of NP receptor expression in visceral adipose tissue (VAT) with metabolic profiles of patients undergoing renal surgery. Differentiated human adipocytes from VAT and Simpson-Golabi-Behmel Syndrome (SGBS) adipocyte cell line were treated with insulin in the presence of high-glucose or low-glucose media to study NP receptors and insulin/glucose-regulated pathways. Fasting blood samples and VAT samples were taken from patients on the day of renal surgery. We observed a potent insulin-mediated and glucose-dependent upregulation of NPRC, through the phosphatidylinositol 3-kinase pathway, associated with lower lipolysis in differentiated adipocytes. No effect was observed on NPRA. Low-glucose medium, used to simulate in vivo starving conditions, hampered the insulin effect on NPRC through modulation of insulin/glucose-regulated pathways, allowing atrial natriuretic peptide to induce lipolysis and thermogenic genes. An expression ratio in favor of NPRC in adipose tissue was associated with higher fasting insulinemia, HOMA-IR, and atherogenic lipid levels. Insulin/glucose-dependent NPRC induction in adipocytes might be a key factor linking hyperinsulinemia, metabolic syndrome, and higher blood pressure by reducing NP effects on adipocytes.

Recent advances in botulinum neurotoxin inhibitor development

Botulinum neurotoxins (BoNTs) are endopeptidases that target motor neurons and block acetylcholine neurotransmitter release. This action results in the muscle paralysis that defines the disease botulism. To date, there are no FDA-approved therapeutics to treat BoNT-mediated paralysis after intoxication of the motor neuron. Importantly, the rationale for pursuing treatments to counter these toxins is driven by their potential misuse. Current drug discovery efforts have mainly focused on small molecules, peptides, and peptidomimetics that can directly and competitively inhibit BoNT light chain proteolytic activity. Although this is a rational approach, direct inhibition of the Zn(2+) metalloprotease activity has been elusive as demonstrated by the dearth of candidates undergoing clinical evaluation. Therefore, broadening the scope of viable targets beyond that of active site protease inhibitors represents an additional strategy that could move the field closer to the clinic. Here we review the rationale, and discuss the outcomes of earlier approaches and highlight potential new targets for BoNT inhibition. These include BoNT uptake and processing inhibitors, enzymatic inhibitors, and modulators of neuronal processes associated with toxin clearance, neurotransmitter potentiation, and other pathways geared towards neuronal recovery and repair.

Phosphatase Inhibitors Function as Novel, Broad Spectrum Botulinum Neurotoxin Antagonists in Mouse and Human Embryonic Stem Cell-Derived Motor Neuron-Based Assays

There is an urgent need to develop novel treatments to counter Botulinum neurotoxin (BoNT) poisoning. Currently, the majority of BoNT drug development efforts focus on directly inhibiting the proteolytic components of BoNT, i.e. light chains (LC). Although this is a rational approach, previous research has shown that LCs are extremely difficult drug targets and that inhibiting multi-serotype BoNTs with a single LC inhibitor may not be feasible. An alternative approach would target neuronal pathways involved in intoxication/recovery, rather than the LC itself. Phosphorylation-related mechanisms have been implicated in the intoxication pathway(s) of BoNTs. However, the effects of phosphatase inhibitors upon BoNT activity in the physiological target of BoNTs, i.e. motor neurons, have not been investigated. In this study, a small library of phosphatase inhibitors was screened for BoNT antagonism in the context of mouse embryonic stem cell-derived motor neurons (ES-MNs). Four inhibitors were found to function as BoNT/A antagonists. Subsequently, we confirmed that these inhibitors protect against BoNT/A in a dose-dependent manner in human ES-MNs. Additionally, these compounds provide protection when administered in post-intoxication scenario. Importantly, the inhibitors were also effective against BoNT serotypes B and E. To the best of our knowledge, this is the first study showing phosphatase inhibitors as broad-spectrum BoNT antagonists.

SRC family kinase inhibitors antagonize the toxicity of multiple serotypes of botulinum neurotoxin in human embryonic stem cell-derived motor neurons

Botulinum neurotoxins (BoNTs), the causative agents of botulism, are potent inhibitors of neurotransmitter release from motor neurons. There are currently no drugs to treat BoNT intoxication after the onset of the disease symptoms. In this study, we explored how modulation of key host pathways affects the process of BoNT intoxication in human motor neurons, focusing on Src family kinase (SFK) signaling. Motor neurons derived from human embryonic stem (hES) cells were treated with a panel of SFK inhibitors and intoxicated with BoNT serotypes A, B, or E (which are responsible for >95 % of human botulism cases). Subsequently, it was found that bosutinib, dasatinib, KX2-391, PP1, PP2, Src inhibitor-1, and SU6656 significantly antagonized all three of the serotypes. Furthermore, the data indicated that the treatment of hES-derived motor neurons with multiple SFK inhibitors increased the antagonistic effect synergistically. Mechanistically, the small molecules appear to inhibit BoNTs by targeting host pathways necessary for intoxication and not by directly inhibiting the toxins' proteolytic activity. Importantly, the identified inhibitors are all well-studied with some in clinical trials while others are FDA-approved drugs. Overall, this study emphasizes the importance of targeting host neuronal pathways, rather than the toxin's enzymatic components, to antagonize multiple BoNT serotypes in motor neurons.

Second generation steroidal 4-aminoquinolines are potent, dual-target inhibitors of the botulinum neurotoxin serotype A metalloprotease and P. falciparum malaria

Significantly more potent second generation 4-amino-7-chloroquinoline (4,7-ACQ) based inhibitors of the botulinum neurotoxin serotype A (BoNT/A) light chain were synthesized. Introducing an amino group at the C(3) position of the cholate component markedly increased potency (IC50 values for such derivatives ranged from 0.81 to 2.27 μM). Two additional subclasses were prepared: bis(steroidal)-4,7-ACQ derivatives and bis(4,7-ACQ)cholate derivatives; both classes provided inhibitors with nanomolar-range potencies (e.g., the Ki of compound 67 is 0.10 μM). During BoNT/A challenge using primary neurons, select derivatives protected SNAP-25 by up to 89%. Docking simulations were performed to rationalize the compounds' in vitro potencies. In addition to specific residue contacts, coordination of the enzyme's catalytic zinc and expulsion of the enzyme's catalytic water were a consistent theme. With respect to antimalarial activity, the compounds provided better IC90 activities against chloroquine resistant (CQR) malaria than CQ, and seven compounds were more active than mefloquine against CQR strain W2.

PTH: Potential role in management of heart failure

Biomarkers play an important role for the diagnosis and prognosis of heart failure (HF), a disease with high morbidity and mortality as well as a huge impact on healthcare budgets. Parathyroid hormone (PTH) is a major systemic calcium-regulating hormone and an important regulator of bone and mineral homeostasis. PTH testing is important for differential diagnosis of calcemia related disorders and for the management of patients with chronic kidney disease. As secondary hyperparathyroidism has been evidenced in HF patients, PTH testing might be relevant in HF patients for risk stratification and more personalized selection of treatment.

Recent developments in cell-based assays and stem cell technologies for botulinum neurotoxin research and drug discovery

Botulinum neurotoxins (BoNTs) are exceptionally potent inhibitors of neurotransmission, causing muscle paralysis and respiratory failure associated with the disease botulism. Currently, no drugs are available to counter intracellular BoNT poisoning. To develop effective medical treatments, cell-based assays provide a valuable system to identify novel inhibitors in a time- and cost-efficient manner. Consequently, cell-based systems including immortalized cells, primary neurons and stem cell-derived neurons have been established. Stem cell-derived neurons are highly sensitive to BoNT intoxication and represent an ideal model to study the biological effects of BoNTs. Robust immunoassays are used to quantify BoNT activity and play a central role during inhibitor screening. In this review, we examine recent progress in physiologically relevant cell-based assays and high-throughput screening approaches for the identification of both direct and indirect BoNT inhibitors.

4-Amino-7-chloroquinolines: probing ligand efficiency provides botulinum neurotoxin serotype A light chain inhibitors with significant antiprotozoal activity

Structurally simplified analogues of dual antimalarial and botulinum neurotoxin serotype A light chain (BoNT/A LC) inhibitor bis-aminoquinoline (1) were prepared. New compounds were designed to improve ligand efficiency while maintaining or exceeding the inhibitory potency of 1. Three of the new compounds are more active than 1 against both indications. Metabolically, the new inhibitors are relatively stable and nontoxic. 12, 14, and 15 are more potent BoNT/A LC inhibitors than 1. Additionally, 15 has excellent in vitro antimalarial efficacy, with IC90 values ranging from 4.45 to 12.11 nM against five Plasmodium falciparum (P.f.) strains: W2, D6, C235, C2A, and C2B. The results indicate that the same level of inhibitory efficacy provided by 1 can be retained/exceeded with less structural complexity. 12, 14, and 15 provide new platforms for the development of more potent dual BoNT/A LC and P.f. inhibitors adhering to generally accepted chemical properties associated with the druggability of synthetic molecules.

Synthesis and evaluation of diaryl sulfides and diaryl selenide compounds for antitubulin and cytotoxic activity

We have devised a procedure for the synthesis of analogs of combretastatin A-4 (CA-4) containing sulfur and selenium atoms as spacer groups between the aromatic rings. CA-4 is well known for its potent activity as an inhibitor of tubulin polymerization, and its prodrugs combretastatin A-4 phosphate (CA-4P) and combretastatin A-1 phosphate (CA-1P) are being investigated as antitumor agents that cause tumor vascular collapse in addition to their activity as cytotoxic compounds. Here we report the preparation of two sulfur analogs and one selenium analog of CA-4. All synthesized compounds, as well as several synthetic intermediates, were evaluated for inhibition of tubulin polymerization and for cytotoxic activity in human cancer cells. Compounds 3 and 4 were active at nM concentration against MCF-7 breast cancer cells. As inhibitors of tubulin polymerization, both 3 and 4 were more active than CA-4 itself. In addition, 4 was the most active of these agents against 786, HT-29 and PC-3 cancer cells. Molecular modeling binding studies are also reported for compounds 1, 3, 4 and CA-4 to tubulin within the colchicine site.

A limited structural modification results in a significantly more efficacious diazachrysene-based filovirus inhibitor

Ebola (EBOV) and Marburg (MARV) filoviruses are highly infectious pathogens causing deadly hemorrhagic fever in humans and non-human primates. Promising vaccine candidates providing immunity against filoviruses have been reported. However, the sporadic nature and swift progression of filovirus disease underlines the need for the development of small molecule therapeutics providing immediate antiviral effects. Herein we describe a brief structural exploration of two previously reported diazachrysene (DAAC)-based EBOV inhibitors. Specifically, three analogs were prepared to examine how slight substituent modifications would affect inhibitory efficacy and inhibitor-mediated toxicity during not only EBOV, but also MARV cellular infection. Of the three analogs, one was highly efficacious, providing IC(50) values of 0.696 µM ± 0.13 µM and 2.76 µM ± 0.21 µM against EBOV and MARV infection, respectively, with little or no associated cellular toxicity. Overall, the structure-activity and structure-toxicity results from this study provide a framework for the future development of DAAC-based filovirus inhibitors that will be both active and non-toxic in vivo.

The synthesis of 2,5-bis(4-amidinophenyl)thiophene derivatives providing submicromolar-range inhibition of the botulinum neurotoxin serotype A metalloprotease

Botulinum neurotoxins (BoNTs), composed of a family of seven serotypes (categorized A-G), are the deadliest of known biological toxins. The activity of the metalloprotease, light chain (LC) component of the toxins is responsible for causing the life-threatening paralysis associated with the disease botulism. Herein we report significantly more potent analogs of novel, lead BoNT serotype A LC inhibitor 2,5-bis(4-amidinophenyl)thiophene (K(i) = 10.88 μM ± 0.90 μM). Specifically, synthetic modifications involved simultaneously replacing the lead inhibitor's terminal bis-amidines with secondary amines and the systematic tethering of 4-amino-7-chloroquinoline substituents to provide derivatives with K(i) values ranging from 0.302 μM (± 0.03 μM) to 0.889μM (± 0.11 μM).

Interactions of halichondrin B and eribulin with tubulin

Compounds that modulate microtubule dynamics include highly effective anticancer drugs, leading to continuing efforts to identify new agents and improve the activity of established ones. Here, we demonstrate that [(3)H]-labeled halichondrin B (HB), a complex, sponge-derived natural product, is bound to and dissociated from tubulin rapidly at one binding site per αβ-heterodimer, with an apparent K(d) of 0.31 μM. We found no HB-induced aggregation of tubulin by high-performance liquid chromatography, even following column equilibration with HB. Binding of [(3)H]HB was competitively inhibited by a newly approved clinical agent, the truncated HB analogue eribulin (apparent K(i), 0.80 μM) and noncompetitively by dolastatin 10 and vincristine (apparent K(i)'s, 0.35 and 5.4 μM, respectively). Our earlier studies demonstrated that HB inhibits nucleotide exchange on β-tubulin, and this, together with the results presented here, indicated the HB site is located on β-tubulin. Using molecular dynamics simulations, we determined complementary conformations of HB and β-tubulin that delineated in atomic detail binding interactions of HB with only β-tubulin, with no involvement of the α-subunit in the binding interaction. Moreover, the HB model served as a template for an eribulin binding model that furthered our understanding of the properties of eribulin as a drug. Overall, these results established a mechanistic basis for the antimitotic activity of the halichondrin class of compounds.

Embryonic stem cell-derived motoneurons provide a highly sensitive cell culture model for botulinum neurotoxin studies, with implications for high-throughput drug discovery

Botulinum neurotoxins (BoNTs) inhibit cholinergic synaptic transmission by specifically cleaving proteins that are crucial for neurotransmitter exocytosis. Due to the lethality of these toxins, there are elevated concerns regarding their possible use as bioterrorism agents. Moreover, their widespread use for cosmetic purposes, and as medical treatments, has increased the potential risk of accidental overdosing and environmental exposure. Hence, there is an urgent need to develop novel modalities to counter BoNT intoxication. Mammalian motoneurons are the main target of BoNTs; however, due to the difficulty and poor efficiency of the procedures required to isolate the cells, they are not suitable for high-throughput drug screening assays. Here, we explored the suitability of embryonic stem (ES) cell-derived motoneurons as a renewable, reproducible, and physiologically relevant system for BoNT studies. We found that the sensitivity of ES-derived motoneurons to BoNT/A intoxication is comparable to that of primary mouse spinal motoneurons. Additionally, we demonstrated that several BoNT/A inhibitors protected SNAP-25, the BoNT/A substrate, in the ES-derived motoneuron system. Furthermore, this system is compatible with immunofluorescence-based high-throughput studies. These data suggest that ES-derived motoneurons provide a highly sensitive system that is amenable to large-scale screenings to rapidly identify and evaluate the biological efficacies of novel therapeutics.

Post-intoxication inhibition of botulinum neurotoxin serotype A within neurons by small-molecule, non-peptidic inhibitors

Botulinum neurotoxins (BoNTs) comprise seven distinct serotypes that inhibit the release of neurotransmitter across neuromuscular junctions, resulting in potentially fatal flaccid paralysis. BoNT serotype A (BoNT/A), which targets synaptosomal-associated protein of 25kDa (SNAP-25), is particularly long-lived within neurons and requires a longer time for recovery of neuromuscular function. There are currently no treatments available to counteract BoNT/A after it has entered the neuronal cytosol. In this study, we examined the ability of small molecule non-peptidic inhibitors (SMNPIs) to prevent SNAP-25 cleavage post-intoxication of neurons. The progressive cleavage of SNAP-25 observed over 5 h following 1 h BoNT/A intoxication was prevented by addition of SMNPIs. In contrast, anti-BoNT/A neutralizing antibodies that strongly inhibited SNAP-25 cleavage when added during intoxication were completely ineffective when added post-intoxication. Although Bafilomycin A1, which blocks entry of BoNT/A into the cytosol by preventing endosomal acidification, inhibited SNAP-25 cleavage post-intoxication, the degree of inhibition was significantly reduced versus addition both during and after intoxication. Post-intoxication application of SMNPIs, on the other hand, was nearly as effective as application both during and after intoxication. Taken together, the results indicate that competitive SMNPIs of BoNT/A light chain can be effective within neurons post-intoxication.

A chemotype that inhibits three unrelated pathogenic targets: the botulinum neurotoxin serotype A light chain, P. falciparum malaria, and the Ebola filovirus

A 1,7-bis(alkylamino)diazachrysene-based small molecule was previously identified as an inhibitor of the botulinum neurotoxin serotype A light chain metalloprotease. Subsequently, a variety of derivatives of this chemotype were synthesized to develop structure-activity relationships, and all are inhibitors of the BoNT/A LC. Three-dimensional analyses indicated that half of the originally discovered 1,7-DAAC structure superimposed well with 4-amino-7-chloroquinoline-based antimalarial agents. This observation led to the discovery that several of the 1,7-DAAC derivatives are potent in vitro inhibitors of Plasmodium falciparum and, in general, are more efficacious against CQ-resistant strains than against CQ-susceptible strains. In addition, by inhibiting β-hematin formation, the most efficacious 1,7-DAAC-based antimalarials employ a mechanism of action analogous to that of 4,7-ACQ-based antimalarials and are well tolerated by normal cells. One candidate was also effective when administered orally in a rodent-based malaria model. Finally, the 1,7-DAAC-based derivatives were examined for Ebola filovirus inhibition in an assay employing Vero76 cells, and three provided promising antiviral activities and acceptably low toxicities.

Small molecule inhibitors as countermeasures for botulinum neurotoxin intoxication

Botulinum neurotoxins (BoNTs) are the most potent of known toxins and are listed as category A biothreat agents by the U.S. CDC. The BoNT-mediated proteolysis of SNARE proteins inhibits the exocytosis of acetylcholine into neuromuscular junctions, leading to life-threatening flaccid paralysis. Currently, the only therapy for BoNT intoxication (which results in the disease state botulism) includes experimental preventative antibodies and long-term supportive care. Therefore, there is an urgent need to identify and develop inhibitors that will serve as both prophylactic agents and post-exposure ‘rescue’ therapeutics. This review focuses on recent progress to discover and develop small molecule inhibitors as therapeutic countermeasures for BoNT intoxication.

Pharmacophore Refinement Guides the Rational Design of Nanomolar-Range Inhibitors of the Botulinum Neurotoxin Serotype A Metalloprotease

Botulinum neurotoxins (BoNTs) are the deadliest of microbial toxins. The enzymes' Zinc(II) metalloprotease, referred to as the light chain (LC) component, inhibits acetylcholine release into neuromuscular junctions, resulting in the disease botulism. Currently, no therapies counter BoNT poisoning post-neuronal intoxication; however, it is hypothesized that small molecules may be used to inhibit BoNT LC activity in the neuronal cytosol. Herein, we describe the pharmacophore-based design and chemical synthesis of potent (non-Zinc(II) chelating) small molecule (non-peptidic) inhibitors (SMNPIs) of the BoNT serotype A LC (the most toxic of the BoNT serotype LCs). Specifically, the three-dimensional superimpositions of 2-[4-(4-amidinephenoxy)-phenyl]-indole-6-amidine-based SMNPI regioisomers (K(i) = 0.600 μM (± 0.100 μM)), with a novel lead bis-[3-amide-5-(imidazolino)-phenyl]-terephthalamide (BAIPT)-based SMNPI (K(i) = 8.52 μM (± 0.53 μM)), resulted in a refined 4-zone pharmacophore. The refined model guided the design of BAIPT-based SMNPIs possessing K(i) values = 0.572 μM (± 0.041 μM) and 0.900 μM (± 0.078 μM).

Iterative structure-based peptide-like inhibitor design against the botulinum neurotoxin serotype A

The botulinum neurotoxin serotype A light chain (BoNT/A LC) protease is the catalytic component responsible for the neuroparalysis that is characteristic of the disease state botulism. Three related peptide-like molecules (PLMs) were designed using previous information from co-crystal structures, synthesized, and assayed for in vitro inhibition against BoNT/A LC. Our results indicate these PLMS are competitive inhibitors of the BoNT/A LC protease and their K_i values are in the nM-range. A co-crystal structure for one of these inhibitors was determined and reveals that the PLM, in accord with the goals of our design strategy, simultaneously involves both ionic interactions via its P1 residue and hydrophobic contacts by means of an aromatic group in the P2′ position. The PLM adopts a helical conformation similar to previously determined co-crystal structures of PLMs, although there are also major differences to these other structures such as contacts with specific BoNT/A LC residues. Our structure further demonstrates the remarkable plasticity of the substrate binding cleft of the BoNT/A LC protease and provides a paradigm for iterative structure-based design and development of BoNT/A LC inhibitors.

Analysis of Botulinum Neurotoxin Serotype A Metalloprotease Inhibitors: Analogs of a Chemotype for Therapeutic Development in the Context of a Three-Zone Pharmacophore

Botulinum neurotoxins (BoNTs), and in particular serotype A, are the most poisonous of known biological substances, and are responsible for the flaccid paralysis of the disease state botulism. Because of the extreme toxicity of these enzymes, BoNTs are considered highest priority biothreat agents. To counter BoNT serotype A (BoNT/A) poisoning, the discovery and development of small molecule, drug-like inhibitors as post-intoxication therapeutic agents has been/is being pursued. Specifically, we are focusing on inhibitors of the BoNT/A light chain (LC) (ie, a metalloprotease) subunit, since such compounds can enter neurons and provide post-intoxication protection of the enzyme target substrate. To aid/facilitate this drug development effort, a pharmacophore for inhibition of the BoNT/A LC subunit was previously developed, and is continually being refined via the incorporation of novel and diverse inhibitor chemotypes. Here, we describe several analogs of a promising therapeutic chemotype in the context of the pharmacophore for BoNT/A LC inhibition. Specifically, we describe: 1) the pharmacophoric 'fits' of the analogs and how these 'fits' rationalize the in vitro inhibitory potencies of the analogs and 2) pharmacophore refinement via the inclusion of new components from the most potent of the presented analogs.

Low-dose nesiritide in human anterior myocardial infarction suppresses aldosterone and preserves ventricular function and structure: a proof of concept study

BACKGROUND

B-type natriuretic peptide (BNP, nesiritide) has anti-fibrotic, anti-hypertrophic, anti-inflammatory, vasodilating, lusitropic and aldosterone-inhibiting properties but conventional doses of BNP cause hypotension, limiting its use in heart failure.

OBJECTIVE

To determine whether infusion of low-dose BNP within 24 h of successful reperfusion for anterior acute myocardial infarction (AMI) would prevent adverse left ventricular (LV) remodelling and suppress aldosterone.

METHODS

A translational proof-of-concept study was carried out to determine tolerability and biological activity of intravenous BNP at 0.003 and 0.006 microg/kg/min, without bolus started within 24 h of successful reperfusion for anterior AMI. 24 patients with first anterior wall ST elevation AMI and successful revascularisation were randomly assigned to receive 0.003 (n = 12) or 0.006 (n = 12) microg/kg/min of IV BNP for 72 h in addition to standard care during hospitalisation for anterior AMI.

RESULTS

Baseline characteristics, drugs and peak cardiac biomarkers for myocardial damage were similar between both groups. Infusion of BNP at 0.006 microg/kg/min resulted in greater biological activity than infusion at 0.003 microg/kg/min as measured by higher mean (SEM) plasma cGMP levels (8.6 (1) vs 5.5 (1) pmol/ml, p<0.05) and suppression of plasma aldosterone (8.0 (2) to 4.6 (1) ng/dl, p<0.05), which was not seen in the 0.003 microg/kg/min group. LV ejection fraction (LVEF) improved significantly from baseline to 1 month (40 (4)% to 54 (5)%, p<0.05) in the 0.006 group but not in the 0.003 group. Infusion of BNP at 0.006 microg/kg/min was associated with a decrease of LV end-systolic volume index (61 (9) to 43 (8) ml/m(2), p<0.05) at 1 month, which was not seen in the 0.003 group. No drug-related serious adverse events occurred in either group.

CONCLUSIONS

72 h infusion of low BNP at the time of anterior AMI is well tolerated and biologically active. Patients treated with low-dose BNP had improved LVEF and smaller LV end-systolic volume at 1 month.

Three-dimensional database mining identifies a unique chemotype that unites structurally diverse botulinum neurotoxin serotype A inhibitors in a three-zone pharmacophore

A search query consisting of two aromatic centers and two cationic centers was defined based on previously identified small molecule inhibitors of the botulinum neurotoxin serotype A light chain (BoNT/A LC) and used to mine the National Cancer Institute Open Repository. Ten small molecule hits were identified, and upon testing, three demonstrated inhibitory activity. Of these, one was structurally unique, possessing a rigid diazachrysene scaffold. The steric limitations of the diazachrysene imposed a separation between the overlaps of previously identified inhibitors, revealing an extended binding mode. As a result, the pharmacophore for BoNT/A LC inhibition has been modified to encompass three zones. To demonstrate the utility of this model, a novel three-zone inhibitor was mined and its activity was confirmed.

A potent peptidomimetic inhibitor of botulinum neurotoxin serotype A has a very different conformation than SNAP-25 substrate

Botulinum neurotoxin serotype A is the most lethal of all known toxins. Here, we report the crystal structure, along with SAR data, of the zinc metalloprotease domain of BoNT/A bound to a potent peptidomimetic inhibitor (K(i)=41 nM) that resembles the local sequence of the SNAP-25 substrate. Surprisingly, the inhibitor adopts a helical conformation around the cleavage site, in contrast to the extended conformation of the native substrate. The backbone of the inhibitor's P1 residue displaces the putative catalytic water molecule and concomitantly interacts with the "proton shuttle" E224. This mechanism of inhibition is aided by residue contacts in the conserved S1' pocket of the substrate binding cleft and by the induction of new hydrophobic pockets, which are not present in the apo form, especially for the P2' residue of the inhibitor. Our inhibitor is specific for BoNT/A as it does not inhibit other BoNT serotypes or thermolysin.

Novel 4-aminoquinolines active against chloroquine-resistant and sensitive P. falciparum strains that also inhibit botulinum serotype A

We report on the initial result of the coupling of 4-amino-7-chloroquinoline with steroidal and adamantane constituents to provide small molecules with excellent in vitro antimalarial activities (IC90 (W2) down to 6.74 nM). The same entities also inhibit the botulinum neurotoxin serotype A light chain metalloprotease at low micromolar levels (7-31 microM). Interestingly, structural features imparting increased antimalarial activity also provide increased metalloprotease inhibition, thus allowing for simultaneous compound optimizations against distinct targets.

A Refined Pharmacophore Identifies Potent 4-Amino-7-chloroquinoline-Based Inhibitors of the Botulinum Neurotoxin Serotype A Metalloprotease

We previously identified structurally diverse small molecule (non-peptidic) inhibitors (SMNPIs) of the botulinum neurotoxin serotype A (BoNT/A) light chain (LC). Of these, several (including antimalarial drugs) contained a 4-amino-7-chloroquinoline (ACQ) substructure and a separate positive ionizable amine component. The same antimalarials have also been found to interfere with BoNT/A translocation into neurons, via pH elevation of the toxin-mediated endosome. Thus, this structural class of small molecules may serve as dual-function BoNT/A inhibitors. In this study, we used a refined pharmacophore for BoNT/A LC inhibition to identify four new, potent inhibitors of this structural class (IC50's ranged from 3.2 to 17 muM). Molecular docking indicated that the binding modes for the new SMNPIs are consistent with those of other inhibitors that we have identified, further supporting our structure-based pharmacophore. Finally, structural motifs of the new SMNPIs, as well as two structure-based derivatives, were examined for activity, providing valuable information about pharmacophore component contributions to inhibition.

Inhibition of metalloprotease botulinum serotype A from a pseudo-peptide binding mode to a small molecule that is active in primary neurons

An efficient research strategy integrating empirically guided, structure-based modeling and chemoinformatics was used to discover potent small molecule inhibitors of the botulinum neurotoxin serotype A light chain. First, a modeled binding mode for inhibitor 2-mercapto-3-phenylpropionyl-RATKML (K(i) = 330 nM) was generated, and required the use of a molecular dynamic conformer of the enzyme displaying the reorientation of surface loops bordering the substrate binding cleft. These flexible loops are conformationally variable in x-ray crystal structures, and the model predicted that they were pivotal for providing complementary binding surfaces and solvent shielding for the pseudo-peptide. The docked conformation of 2-mercapto-3-phenylpropionyl-RATKML was then used to refine our pharmacophore for botulinum serotype A light chain inhibition. Data base search queries derived from the pharmacophore were employed to mine small molecule (non-peptidic) inhibitors from the National Cancer Institute's Open Repository. Four of the inhibitors possess K(i) values ranging from 3.0 to 10.0 microM. Of these, NSC 240898 is a promising lead for therapeutic development, as it readily enters neurons, exhibits no neuronal toxicity, and elicits dose-dependent protection of synaptosomal-associated protein (of 25 kDa) in a primary culture of embryonic chicken neurons. Isothermal titration calorimetry showed that the interaction between NSC 240898 and the botulinum A light chain is largely entropy-driven, and occurs with a 1:1 stoichiometry and a dissociation constant of 4.6 microM.

Comparison of the activities of the truncated halichondrin B analog NSC 707389 (E7389) with those of the parent compound and a proposed binding site on tubulin

The complex marine natural product halichondrin B was compared with NSC 707389 (E7389), a structurally simplified, synthetic macrocyclic ketone analog, which has been selected for clinical trials in human patients. NSC 707389 was invariably more potent than halichondrin B in its interactions with tubulin. Both compounds inhibited tubulin assembly, inhibited nucleotide exchange on beta-tubulin, and were noncompetitive inhibitors of the binding of radiolabeled vinblastine and dolastatin 10 to tubulin. Neither compound seemed to induce an aberrant tubulin assembly reaction, as occurs with vinblastine (tight spirals) or dolastatin 10 (aggregated rings and spirals). We modeled the two compounds into a shared binding site on tubulin consistent with their biochemical properties. Of the two tubulin structures available, we selected for modeling the complex of a stathmin fragment with two tubulin heterodimers with two bound colchicinoid molecules and a single bound vinblastine between the two heterodimers (Nature (Lond) 435:519-522, 2005). Halichondrin B and NSC 707389 fit snugly between the two heterodimers adjacent to the exchangeable site nucleotide. Fitting the compounds into this site, which was also close to the vinblastine site, resulted in enough movement of amino acid residues at the vinblastine site to cause the latter compound to bind less well to tubulin. The model suggests that halichondrin B and NSC 707389 most likely form highly unstable, small aberrant tubulin polymers rather than the massive stable structures observed with vinca alkaloids and antimitotic peptides.

A common pharmacophore for a diverse set of colchicine site inhibitors using a structure-based approach

Modulating the structure and function of tubulin and microtubules is an important route to anticancer therapeutics, and therefore, small molecules that bind to tubulin and cause mitotic arrest are of immense interest. A large number of synthetic and natural compounds with diverse structures have been shown to bind at the colchicine site, one of the major binding sites on tubulin, and inhibit tubulin assembly. Using the recently determined X-ray structure of the tubulin:colchicinoid complex as the template, we employed docking studies to determine the binding modes of a set of structurally diverse colchicine site inhibitors. These binding models were subsequently used to construct a comprehensive, structure-based pharmacophore that in combination with molecular dynamics simulations confirms and extends our understanding of binding interactions at the colchicine site.

The rapidly advancing field of biodefense benefits many other, critical public health concerns

Extract: In 2001, the public was introduced to one of the deadliest of biowarfare agents -- Bacillus anthracis -- the bacterium that causes anthrax. At the time, it was unimaginable that one might come into contact with such a deadly pathogen by simply opening the mail. Today anthrax is a nearly ubiquitous household word. This single act of bioterrorism had a profound effect in that it clearly demonstrated that even a small-scale attack could incur huge repercussions: the loss of life, the need for thousands to be treated with prophylaxis, public panic, and a large economic toll. Following this realization, a major government effort to find new and more effective ways to detect, diagnose, and therapeutically counter biothreat agents was initiated. So, how has this initiative fared?

ANSWER

in a very short period of time the scientific community has responded with a massive and productive effort. Driving the research advances described in this review: 1) a vastly improved understanding of the biological mechanisms and machinery used by biothreat agents; 2) state-of-the-art high-throughput screening technologies; and 3) more efficient, standardized methods and improved protocols for detecting, identifying, and diagnosing biowarfare agents. Furthermore, as with all good science, many recent biodefense research discoveries/advances have also directly facilitated our understanding and ability to treat other diseases, including antibiotic resistant bacteria and viruses (such as HIV and SARS).

An all-atom model of the pore-like structure of hexameric VP40 from Ebola: Structural insights into the monomer–hexamer transition

The matrix protein VP40 is an indispensable component of viral assembly and budding by the Ebola virus. VP40 is a monomer in solution, but can fold into hexameric and octameric states, two oligomeric conformations that play central roles in the Ebola viral life cycle. While the X-ray structures of monomeric and octameric VP40 have been determined, the structure of hexameric VP40 has only been solved by three-dimensional electron microscopy (EM) to a resolution of approximately 30 A. In this paper, we present the refinement of the EM reconstruction of truncated hexameric VP40 to approximately 20 A and the construction of an all-atom model (residues 44-212) using the EM model at approximately 20 A and the X-ray structure of monomeric VP40 as templates. The hexamer model suggests that the monomer-hexamer transition involves a conformational change in the N-terminal domain that is not evident during octamerization and therefore, may provide the basis for elucidating the biological function of VP40.

The evolving field of biodefence: therapeutic developments and diagnostics

Bioweapons are a clear threat to both military and civilian populations. Here, the latest advances in the pursuit of inhibitors against biothreat threat toxins, current therapeutic strategies for treating biodefence related pathogens, and strategies for improving detection and exposure survivability are covered.

There are numerous lead therapeutics that have emerged from drug discovery efforts. However, many of these are toxic and/or fail to possess conventional drug-like properties. One clear advantage of small (non-peptidic) molecules is that they possess scaffolds that are inherently more likely to evolve into real therapeutics.

One of the major obstacles impeding the translation of these lead therapeutics into viable drugs is the lack of involvement of the pharmaceutical industry, which has been discovering leads and translating them into drugs for decades. The expertise of the pharmaceutical industry therefore needs to be more effectively engaged in developing drugs against biothreat agents.

New methods for rapidly detecting and diagnosing biothreat agents are also in development. The detection and diagnosis of biothreats is inherently linked with treatment. The means for detecting the release of bioweapons are being deployed, and new technologies are shortening the timeframe between initial sample collection and conclusive agent determination. However, the organization of this process is imperfect.

At present, a unifying entity that orchestrates the biodefence response is clearly needed to reduce the time-to-drug process and redundancies in drug development efforts. Such a central entity could formulate and implement plans to coordinate all participants, including academic institutions, government agencies and the private sector. This could accelerate the development of countermeasures against high probability biothreat agents.

The threat of bioterrorism and the potential use of biological weapons against both military and civilian populations has become a major concern for governments around the world. For example, in 2001 anthrax-tainted letters resulted in several deaths, caused widespread public panic and exerted a heavy economic toll. If such a small-scale act of bioterrorism could have such a huge impact, then the effects of a large-scale attack would be catastrophic. This review covers recent progress in developing therapeutic countermeasures against, and diagnostics for, such agents.

Conformational sampling of the botulinum neurotoxin serotype a light chain: implications for inhibitor binding

Botulinum neurotoxins (BoNTs) are the most potent of the known biological toxins, and consequently are listed as category A biowarfare agents. Currently, the only treatments against BoNTs include preventative antitoxins and long-term supportive care. Consequently, there is an urgent need for therapeutics to counter these enzymes--post exposure. In a previous study, we identified a number of small, nonpeptidic lead inhibitors of BoNT serotype A light chain (BoNT/A LC) metalloprotease activity, and we identified a common pharmacophore for these molecules. In this study, we have focused on how the dynamic movement of amino acid residues in and surrounding the substrate binding cleft of the BoNT/A LC might affect inhibitor binding modes. The X-ray crystal structures of two BoNT/A LCs (PDB refcodes=3BTA and 1E1H) were examined. Results from these analyses indicate that the core structural features of the examined BoNT/A LCs, including alpha-helices and beta-sheets, remained relatively unchanged during 1 ns dynamics trajectories. However, conformational flexibility was observed in surface loops bordering the substrate binding clefts in both examined structures. Our analyses indicate that these loops may possess the ability to decrease the solvent accessibility of the substrate binding cleft, while at the same time creating new residue contacts for the inhibitors. Loop movements and conformational/positional analyses of residues within the substrate binding cleft are discussed with respect to BoNT/A LC inhibitor binding and our common pharmacophore for inhibition. The results from these studies may aid in the future identification/development of more potent small molecule inhibitors that take advantage of new binding contacts in the BoNT/A LC.

Structural basis for the potent antisickling effect of a novel class of five-membered heterocyclic aldehydic compounds

Naturally occurring five-membered heterocyclic aldehydes, including 5-hydroxymethyl-2-furfural, increase the oxygen affinity of hemoglobin (Hb) and strongly inhibit the sickling of homozygous sickle red blood (SS) cells. X-ray studies of Hb complexed with these compounds indicate that they form Schiff base adducts in a symmetrical fashion with the N-terminal alphaVal1 nitrogens of Hb. Interestingly, two cocrystal types were isolated during crystallization experiments with deoxygenated Hb (deoxyHb): one crystal type was composed of the low-affinity or tense (T) state Hb quaternary structure; the other crystal type was composed of high-affinity or relaxed state Hb (with a R2 quaternary structure). The R2 crystal appears to be formed as a result of the aldehydes binding to fully or partially ligated Hb in the deoxyHb solution. Repeated attempts to crystallize the compounds with liganded Hb failed, except on rare occasions when very few R state crystals were obtained. Oxygen equilibrium, high performance liquid chromatography (HPLC), antisickling, and X-ray studies suggest that the examined heterocyclic aldehydes may be acting to prevent polymerization of sickle hemoglobin (HbS) by binding to and stabilizing liganded Hb in the form of R2 and/or various relaxed state Hbs, as well as binding to and destabilizing unliganded T state Hb. The proposed mechanism may provide a general model for the antisickling effects of aldehyde containing small molecules that bind to N-terminal alphaVal1 nitrogens of Hb. The examined compounds also represent a new class of potentially therapeutic agents for treating sickle cell disease (SCD).

Novel small molecule inhibitors of botulinum neurotoxin A metalloprotease activity

Botulinum neurotoxins (BoNTs) are among the most lethal biological substances to have been weaponized and are listed as biodefense category A agents. Currently, no small molecule (non-peptidic) therapeutics exist to counter this threat; hence, identifying and developing compounds that inhibit BoNTs is a high priority. In the present study, a high-throughput assay was used to identify small molecules that inhibit the metalloprotease activity of BoNT serotype A light chain (BoNT/A LC). All inhibitors were further verified using a HPLC-based assay. Conformational analyses of these compounds, in conjunction with molecular docking studies, were used to predict structural features that contribute to inhibitor binding and potency. Based on these results, a common pharmacophore for BoNT/A LC inhibitors is proposed. This is the first study to report small molecules (non-peptidics) that inhibit BoNT/A LC metalloprotease activity in the low microM range.

Molecular mechanisms of filovirus cellular trafficking

The filoviruses, Ebola and Marburg, are two of the most pathogenic viruses, causing lethal hemorrhagic fever in humans. Recent discoveries suggest that filoviruses, along with other phylogenetically or functionally related viruses, utilize a complex mechanism of replication exploiting multiple cellular components including lipid rafts, endocytic compartments, and vacuolar protein sorting machinery. In this review, we summarize these recent findings and discuss the implications for vaccine and therapeutics development.