Restoration of virulence in the attenuated Candid#1 vaccine virus requires reversion at both positions 168 and 427 in the envelope glycoprotein GPC.

Live-attenuated virus vaccines provide long-lived protection against viral disease but carry inherent risks of residual pathogenicity and genetic reversion. The live-attenuated Candid#1 vaccine was developed to protect Argentines against lethal infection by the Argentine hemorrhagic fever arenavirus, Junín virus. Despite its safety and efficacy in Phase III clinical study, the vaccine is not licensed in the US, in part due to concerns regarding the genetic stability of attenuation. Previous studies had identified a single F427I mutation in the transmembrane domain of the Candid#1 envelope glycoprotein GPC as the key determinant of attenuation, as well as the propensity of this mutation to revert upon passage in cell culture and neonatal mice. To ascertain the consequences of this reversion event, we introduced the I427F mutation into recombinant Candid#1 (I427F rCan) and investigated the effects in two validated small-animal models: in mice expressing the essential virus receptor (human transferrin receptor 1; huTfR1) and in the conventional guinea pig model. We report that I427F rCan displays only modest virulence in huTfR1 mice and appears attenuated in guinea pigs. Reversion at another attenuating locus in Candid#1 GPC (T168A) was also examined, and a similar pattern was observed. By contrast, virus bearing both revertant mutations (A168T+I427F rCan) approached the lethal virulence of the pathogenic Romero strain in huTfR1 mice. Virulence was less extreme in guinea pigs. Our findings suggest that genetic stabilization at both positions is required to minimize the likelihood of reversion to virulence in a second-generation Candid#1 vaccine.IMPORTANCELive-attenuated virus vaccines, such as measles/mumps/rubella and oral poliovirus, provide robust protection against disease but carry with them the risk of genetic reversion to the virulent form. Here, we analyze the genetics of reversion in the live-attenuated Candid#1 vaccine that is used to protect against Argentine hemorrhagic fever, an often-lethal disease caused by the Junín arenavirus. In two validated small-animal models, we find that restoration of virulence in recombinant Candid#1 viruses requires back-mutation at two positions specific to the Candid#1 envelope glycoprotein GPC, at positions 168 and 427. Viruses bearing only a single change showed only modest virulence. We discuss strategies to genetically harden Candid#1 GPC against these two reversion events in order to develop a safer second-generation Candid#1 vaccine virus.

Use of Cryopreserved Hepatocytes as Part of an Integrated Strategy to Characterize In Vivo Clearance for Peptide-Antibody Conjugate Inhibitors of Nav1.7 in Preclinical Species.

The identification of nonopioid alternatives to treat chronic pain has received a great deal of interest in recent years. Recently, the engineering of a series of Nav1.7 inhibitory peptide-antibody conjugates has been reported, and herein, the preclinical efforts to identify novel approaches to characterize the pharmacokinetic properties of the peptide conjugates are described. A cryopreserved plated mouse hepatocyte assay was designed to measure the depletion of the peptide-antibody conjugates from the media, with a correlation being observed between percentage remaining in the media and in vivo clearance (Pearson r = -0.5525). Physicochemical (charge and hydrophobicity), receptor-binding [neonatal Fc receptor (FcRn)], and in vivo pharmacokinetic data were generated and compared with the results from our in vitro hepatocyte assay, which was hypothesized to encompass all of the aforementioned properties. Correlations were observed among hydrophobicity; FcRn binding; depletion rates from the hepatocyte assay; and ultimately, in vivo clearance. Subsequent studies identified potential roles for the low-density lipoprotein and mannose/galactose receptors in the association of the Nav1.7 peptide conjugates with mouse hepatocytes, although in vivo studies suggested that FcRn was still the primary receptor involved in determining the pharmacokinetics of the peptide conjugates. Ultimately, the use of the cryopreserved hepatocyte assay along with FcRn binding and hydrophobic interaction chromatography provided an efficient and integrated approach to rapidly triage molecules for advancement while reducing the number of in vivo pharmacokinetic studies. SIGNIFICANCE STATEMENT: Although multiple in vitro and in silico tools are available in small-molecule drug discovery, pharmacokinetic characterization of protein therapeutics is still highly dependent upon the use of in vivo studies in preclinical species. The current work demonstrates the combined use of cryopreserved hepatocytes, hydrophobic interaction chromatography, and neonatal Fc receptor binding to characterize a series of Nav1.7 peptide-antibody conjugates prior to conducting in vivo studies, thus providing a means to rapidly evaluate novel protein therapeutic platforms while concomitantly reducing the number of in vivo studies conducted in preclinical species.

Sustained inhibition of the NaV1.7 sodium channel by engineered dimers of the domain II binding peptide GpTx-1.

Many efforts are underway to develop selective inhibitors of the voltage-gated sodium channel NaV1.7 as new analgesics. Thus far, however, in vitro selectivity has proved difficult for small molecules, and peptides generally lack appropriate pharmacokinetic properties. We previously identified the NaV1.7 inhibitory peptide GpTx-1 from tarantula venom and optimized its potency and selectivity via structure-guided analoging. To further understand GpTx-1 binding to NaV1.7, we have mapped the binding site to transmembrane segments 1-4 of the second pseudosubunit internal repeat (commonly referred to as Site 4) using NaV1.5/NaV1.7 chimeric protein constructs. We also report that select GpTx-1 amino acid residues apparently not contacting NaV1.7 can be derivatized with a hydrophilic polymer without adversely affecting peptide potency. Homodimerization of GpTx-1 with a bifunctional polyethylene glycol (PEG) linker resulted in a compound with increased potency and a significantly reduced off-rate, demonstrating the ability to modulate the function and properties of GpTx-1 by linking to additional molecules.

A replicating RNA vaccine confers protection in a rhesus macaque model of Crimean-Congo hemorrhagic fever.

Crimean-Congo hemorrhagic fever (CCHF) is a tick-borne febrile illness with a wide geographic distribution. In recent years the geographic range of Crimean-Congo hemorrhagic fever virus (CCHFV) and its tick vector have increased, placing an increasing number of people at risk of CCHFV infection. Currently, there are no widely available vaccines, and although the World Health Organization recommends ribavirin for treatment, its efficacy is unclear. Here we evaluate a promising replicating RNA vaccine in a rhesus macaque (Macaca mulatta) model of CCHF. This model provides an alternative to the established cynomolgus macaque model and recapitulates mild-to-moderate human disease. Rhesus macaques infected with CCHFV consistently exhibit viremia, detectable viral RNA in a multitude of tissues, and moderate pathology in the liver and spleen. We used this model to evaluate the immunogenicity and protective efficacy of a replicating RNA vaccine. Rhesus macaques vaccinated with RNAs expressing the CCHFV nucleoprotein and glycoprotein precursor developed robust non-neutralizing humoral immunity against the CCHFV nucleoprotein and had significant protection against the CCHFV challenge. Together, our data report a model of CCHF using rhesus macaques and demonstrate that our replicating RNA vaccine is immunogenic and protective in non-human primates after a prime-boost immunization.

Liver-specific mitochondrial amidoxime-reducing component 1 (Mtarc1) knockdown protects the liver from diet-induced MASH in multiple mouse models.

BACKGROUND: Human genetic studies have identified several mitochondrial amidoxime-reducing component 1 (MTARC1) variants as protective against metabolic dysfunction-associated steatotic liver disease. The MTARC1 variants are associated with decreased plasma lipids and liver enzymes and reduced liver-related mortality. However, the role of mARC1 in fatty liver disease is still unclear. METHODS: Given that mARC1 is mainly expressed in hepatocytes, we developed an N-acetylgalactosamine-conjugated mouse Mtarc1 siRNA, applying it in multiple in vivo models to investigate the role of mARC1 using multiomic techniques. RESULTS: In ob/ob mice, knockdown of Mtarc1 in mouse hepatocytes resulted in decreased serum liver enzymes, LDL-cholesterol, and liver triglycerides. Reduction of mARC1 also reduced liver weight, improved lipid profiles, and attenuated liver pathological changes in 2 diet-induced metabolic dysfunction-associated steatohepatitis mouse models. A comprehensive analysis of mARC1-deficient liver from a metabolic dysfunction-associated steatohepatitis mouse model by metabolomics, proteomics, and lipidomics showed that Mtarc1 knockdown partially restored metabolites and lipids altered by diet. CONCLUSIONS: Taken together, reducing mARC1 expression in hepatocytes protects against metabolic dysfunction-associated steatohepatitis in multiple murine models, suggesting a potential therapeutic approach for this chronic liver disease.

PADLOC: a powerful tool to assign disulfide bond connectivities in peptides and proteins by NMR spectroscopy.

The determination of the disulfide bond connectivity in a peptide or protein represents a significant challenge. It is notoriously difficult to use NMR spectroscopy to assign disulfide connectivities because NMR spectra lack direct evidence for disulfide bonds. These bonds are typically inferred from three-dimensional structure calculations, which can result in ambiguous disulfide assignment. Here, we present a new NMR based methodology, in which the disulfide connectivity is obtained by applying Bayesian rules of inference to the local topology of cysteine residues. We illustrate how this approach successfully predicts the disulfide connectivity in proteins for which crystal structures are available in the protein data bank (PDB). We also demonstrate how this methodology is used with experimental NMR data for peptides with complex disulfide topologies, including hepcidin, Kalata-B1, and µ-Conotoxin KIIIA. In the case of µ-Conotoxin KIIIA, the PADLOC connectivity (1-15,2-9,4-16) differs from previously published results; additional evidence is presented demonstrating unequivocally that this newly proposed connectivity is correct.

Purification of N-acetylgalactosamine-modified-oligonucleotides using orthogonal anion-exchange and mixed-mode chromatography approaches.

N-acetylgalactosamine (GalNAc)-modified small interfering ribonucleic acids (siRNA) have shown promising outcomes for targeted siRNA delivery resulting in gene silencing in vivo; however, their structural complexity requires development of new purification methods to address high purity and recovery requirements. The current study evaluates complementary purification approaches using a mixed-mode Scherzo SS-C18 and anion-exchange (AEX) TSK-gel SuperQ-5PW for a range of single-stranded triantennary GalNAc-oligonucleotides. Initially, the semi-preparative mixed-mode support (10 × 250 mm, 3 µm) was compared against the preparative AEX analogue (21.5 × 300 mm, 13 µm), with the former affording double the recovery and higher purity of 95% over its AEX counterpart displaying 91% for a selected siRNA conjugate. An assortment of GalNAc-modified oligonucleotides was later purified using the mixed-mode resin revealing good recoveries (∼30-60%) and high purities of 90-94% ranging from straightforward to more challenging purifications. High sample loading in the 20 mg range was achieved, which was comparable with the larger preparative TSKgel SuperQ-5PW support. The Scherzo-SS-C18 resin also afforded some degree of resolution between diastereomers containing phosphorothioate functionalities. The TSKgel SuperQ-5PW support was later investigated to provide orthogonal separation selectivity to the Scherzo-SS-C18 column enabling purification of a selected, GalNAc-siRNA conjugate. The developed pH (8.5-11) and salt (0.3-0.7 M) gradients method provided enhanced separation selectivity between the free and conjugated siRNA, while minimizing formation of secondary structures and highlighting a complementary approach to deal with challenging purifications of oligonucleotide-GalNAc conjugates. Together, the use of AEX and mixed-mode columns provide much needed orthogonality to deal with complex GalNAc-modified oligonucleotides and potentially other upcoming modalities.

An antiangiogenic neurokinin-B/thromboxane A2 regulatory axis.

Establishment of angiogenic circuits that orchestrate blood vessel development and remodeling requires an exquisite balance between the activities of pro- and antiangiogenic factors. However, the logic that permits complex signal integration by vascular endothelium is poorly understood. We demonstrate that a "neuropeptide," neurokinin-B (NK-B), reversibly inhibits endothelial cell vascular network assembly and opposes angiogenesis in the chicken chorioallantoic membrane. Disruption of endogenous NK-B signaling promoted angiogenesis. Mechanistic analyses defined a multicomponent pathway in which NK-B signaling converges upon cellular processes essential for angiogenesis. NK-B-mediated ablation of Ca2+ oscillations and elevation of 3'-5' [corrected] cyclic adenosine monophosphate (cAMP) reduced cellular proliferation, migration, and vascular endothelial growth factor receptor expression and induced the antiangiogenic protein calreticulin. Whereas NK-B initiated certain responses, other activities required additional stimuli that increase cAMP. Although NK-B is a neurotransmitter/ neuromodulator and NK-B overexpression characterizes the pregnancy-associated disorder preeclampsia, NK-B had not been linked to vascular remodeling. These results establish a conserved mechanism in which NK-B instigates multiple activities that collectively oppose vascular remodeling.

Identification and Optimization of a Minor Allele-Specific siRNA to Prevent PNPLA3 I148M-Driven Nonalcoholic Fatty Liver Disease.

Human genome wide association studies confirm the association of the rs738409 single nucleotide polymorphism (SNP) in the gene encoding protein patatin like phospholipase domain containing 3 (PNPLA3) with nonalcoholic fatty liver disease (NAFLD); the presence of the resulting mutant PNPLA3 I148M protein is a driver of nonalcoholic steatohepatitis (NASH). While Pnpla3-deficient mice do not display an adverse phenotype, the safety of knocking down endogenous wild type PNPLA3 in humans remains unknown. To expand the scope of a potential targeted NAFLD therapeutic to both homozygous and heterozygous PNPLA3 rs738409 populations, we sought to identify a minor allele-specific small interfering RNA (siRNA). Limiting our search to SNP-spanning triggers, a series of chemically modified siRNA were tested in vitro for activity and selectivity toward PNPLA3 rs738409 mRNA. Conjugation of the siRNA to a triantennary N-acetylgalactosamine (GalNAc) ligand enabled in vivo screening using adeno-associated virus to overexpress human PNPLA3I148M versus human PNPLA3I148I in mouse livers. Structure-activity relationship optimization yielded potent and minor allele-specific compounds that achieved high levels of mRNA and protein knockdown of human PNPLA3I148M but not PNPLA3I148I. Testing of the minor allele-specific siRNA in PNPLA3I148M-expressing mice fed a NASH-inducing diet prevented PNPLA3I148M-driven disease phenotypes, thus demonstrating the potential of a precision medicine approach to treating NAFLD.

PRX-08066, a novel 5-hydroxytryptamine receptor 2B antagonist, reduces monocrotaline-induced pulmonary arterial hypertension and right ventricular hypertrophy in rats.

Pulmonary arterial hypertension (PAH) is a life-threatening disease that results in right ventricular failure. 5-((4-(6-Chlorothieno[2,3-d]pyrimidin-4-ylamino)piperidin-1-yl)methyl)-2-fluorobenzonitrile monofumarate (PRX-08066) is a selective 5-hydroxytryptamine receptor 2B (5-HT2BR) antagonist that causes selective vasodilation of pulmonary arteries. In the current study, the effects of PRX-08066 were assessed by using the monocrotaline (MCT)-induced PAH rat model. Male rats received 40 mg/kg MCT or phosphate-buffered saline and were treated orally twice a day with vehicle or 50 or 100 mg/kg PRX-08066 for 5 weeks. Pulmonary and cardiac functions were evaluated by hemodynamics, heart weight, magnetic resonance imaging (MRI), pulmonary artery (PA) morphology, and histology. Cardiac MRI demonstrated that PRX-08066 (100 mg/kg) significantly (P < 0.05) improved right ventricular ejection fraction. PRX-08066 significantly reduced peak PA pressure at 50 and 100 mg/kg (P < 0.05 and < 0.01, respectively) compared with MCT control animals. PRX-08066 therapy also significantly reduced right ventricle (RV)/body weight and RV/left ventricle + septum (P < 0.01 and < 0.001, respectively) compared with MCT-treated animals. Morphometric assessment of pulmonary arterioles revealed a significant reduction in medial wall thickening and lumen occlusion associated with both doses of PRX-08066 (P < 0.01). The 5-HT2BR antagonist PRX-08066 significantly attenuated the elevation in PA pressure and RV hypertrophy and maintained cardiac function. Pulmonary vascular remodeling was also diminished compared with MCT control rats. PRX-08066 prevents the severity of PAH in the MCT rat model.

Dipeptidyl-quinolone derivatives inhibit hypoxia inducible factor-1α prolyl hydroxylases-1, -2, and -3 with altered selectivity.

Intracellular levels of the hypoxia-inducible transcription factor (HIF) are regulated under normoxic conditions by prolyl hydroxylases (PHD1, 2, and 3). Treatment of cells with PHD inhibitors stabilizes HIF-1α, eliciting an artificial hypoxic response that includes the transcription of genes involved in erythropoiesis, angiogenesis, and glycolysis. The different in vivo roles of the three PHD isoforms are not yet known, making a PHD-selective inhibitor useful as a biological tool. Although several chemical series of PHD inhibitors have been described, significant isoform selectivity has not been reported. Here we report the synthesis and activity of dipeptidyl analogues derived from a potent but non-selective quinolone scaffold. The compounds were prepared by Pd-catalyzed reductive carbonylation of the 6-iodoquinolone derivative to form the aldehyde directly, which was then attached to a solid support via reductive amination. Amino acids were coupled, and the resulting dipeptidyl-quinolone derivatives were screened, revealing retention of PHD inhibitory activity but an altered PHD1, 2, and 3 selectivity profile. The compounds were found to be ∼10-fold more potent against PHD1 and PHD3 than against PHD2, whereas the specific parent compound had shown no appreciable selectivity among the different PHD isoforms.

Purification of guanine-quadruplex using monolithic stationary phase under ion-exchange conditions.

The current study investigates a method for purification of the G-quadruplex secondary structure, naturally formed by a guanine-rich 21-mer oligonucleotide strand using a monolithic convective interaction media-quaternary amine (CIM-QA) column under ion-exchange conditions. The monolithic support was initially evaluated on a preparative scale against a highly efficient TSKgel SuperQ-5PW ion-exchange support designed for oligonucleotide purification. The CIM analogue demonstrated clear advantages over the particle-based support on the basis of rapid separation times, while also affording high purity of the G-quadruplex. Various parameters were investigated including the type of mobile phase anion, cation, pH and injection load to induce and control quadruplex formation, as well as enhance chromatographic separation and final purity. Potassium afforded the most prominent quadruplex formation, yet sodium allowed for the highest resolution and purity to be achieved with a 30 mg injection on an 8 ml CIM-QA monolithic column. This method was applied to purify in excess of 300 mg of the quadruplex, with excellent retention time precision of under 1% RSD. Native mass spectrometry was utilized to confirm the identity of the intact G-quadruplex under non-denaturing conditions, while ion-pairing reversed-phase methods confirmed the presence of the single-stranded oligonucleotide in high purity (92%) under denaturing conditions. The key advantage of the purification method enables isolation of the G-quadruplex in its native state on a milli-gram scale, allowing structural characterization to further our knowledge of its role and function. The G-quadruplex can also be subsequently denaturated at elevated temperature causing single strand formation if additional reactions are to be pursued, such as annealing to form a duplex, and evaluation in in vitro or in vivo studies.

A combination of ultrahigh throughput PathHunter and cytokine secretion assays to identify glucocorticoid receptor agonists.

The use of ultrahigh throughput screens (uHTS) is a well-accepted mechanism to identify agonists and antagonists of target receptors. We used the Path Hunter [Path Hunter technology is a registered trademark of DiscoveRx Corporation.] technology from DiscoveRx to screen the entire Merck compound library for glucocorticoid receptor (GR) agonists in a 2.2-microl total reaction volume assayed in a 3456-well plate format. This single addition, homogenous assay which utilizes the principle of enzyme fragment complementation (EFC) to detect nuclear translocation of GR, an initial step of receptor activation, was used to successfully screen a large library of small molecules as indicated by an average signal to background ratio of approximately 4-fold and an average Z-factor value of 0.45. Hits from the HTS campaign were studied in a cytokine secretion assay in primary human monocytes to gain functional information regarding these compounds in a phenotypic and physiologically relevant setting. Our data indicate that using the PathHunter assay, we successfully identified compounds that showed agonism for the GR receptor in primary human monocytes and due to their performance in a physiologically relevant model they likely will have a better chance to evoke clinical efficacy.

Engineering NaV1.7 Inhibitory JzTx-V Peptides with a Potency and Basicity Profile Suitable for Antibody Conjugation To Enhance Pharmacokinetics.

Drug discovery research on new pain targets with human genetic validation, including the voltage-gated sodium channel NaV1.7, is being pursued to address the unmet medical need with respect to chronic pain and the rising opioid epidemic. As part of early research efforts on this front, we have previously developed NaV1.7 inhibitory peptide-antibody conjugates with tarantula venom-derived GpTx-1 toxin peptides with an extended half-life (80 h) in rodents but only moderate in vitro activity (hNaV1.7 IC50 = 250 nM) and without in vivo activity. We identified the more potent peptide JzTx-V from our natural peptide collection and improved its selectivity against other sodium channel isoforms through positional analogueing. Here we report utilization of the JzTx-V scaffold in a peptide-antibody conjugate and architectural variations in the linker, peptide loading, and antibody attachment site. We found conjugates with 100-fold improved in vitro potency relative to those of complementary GpTx-1 analogues, but pharmacokinetic and bioimaging analyses of these JzTx-V conjugates revealed a shorter than expected plasma half-life in vivo with accumulation in the liver. In an attempt to increase circulatory serum levels, we sought the reduction of the net +6 charge of the JzTx-V scaffold while retaining a desirable NaV in vitro activity profile. The conjugate of a JzTx-V peptide analogue with a +2 formal charge maintained NaV1.7 potency with 18-fold improved plasma exposure in rodents. Balancing the loss of peptide and conjugate potency associated with the reduction of net charge necessary for improved target exposure resulted in a compound with moderate activity in a NaV1.7-dependent pharmacodynamic model but requires further optimization to identify a conjugate that can fully engage NaV1.7 in vivo.

Exploration of structure--activity relationships among foldamer ligands for a specific protein binding site via parallel and split-and-mix library synthesis.

We describe the use of parallel and split-and-mix library synthesis strategies for exploration of structure-activity relationships among peptidic foldamer ligands for the BH3-recognition cleft of the anti-apoptotic protein Bcl-xL. This effort began with a chimeric (alpha/beta+alpha)-peptide oligomer (composed of an alpha/beta-peptide segment and an alpha-peptide segment) that we previously identified to bind tightly to the target cleft on Bcl-xL. The side chains that interact with Bcl-xL were varied in a 1000-member one-bead-one-compound library. Fluorescence polarization (FP) screening identified four new analogues with binding affinities similar to that of the lead compound but no analogues with enhanced affinity. These results suggested that significant improvements in affinity were unlikely in this series. We then used library synthesis to examine backbone variations in the C-terminal alpha-peptide segment of the lead compound. These studies provided an opportunity for direct comparison of parallel and split-and-mix synthesis formats for foldamer libraries with respect to synthetic variability and assay sensitivity. We found that compounds from both the parallel and one-bead-one-compound libraries could be reliably screened in a competition FP assay without purification of library members. Our findings should facilitate the use of combinatorial library synthesis for exploration of foldamers as inhibitors of protein-protein interactions.

Discovery of Tarantula Venom-Derived NaV1.7-Inhibitory JzTx-V Peptide 5-Br-Trp24 Analogue AM-6120 with Systemic Block of Histamine-Induced Pruritis.

Inhibitors of the voltage-gated sodium channel NaV1.7 are being investigated as pain therapeutics due to compelling human genetics. We previously identified NaV1.7-inhibitory peptides GpTx-1 and JzTx-V from tarantula venom screens. Potency and selectivity were modulated through attribute-based positional scans of native residues via chemical synthesis. Herein, we report JzTx-V lead optimization to identify a pharmacodynamically active peptide variant. Molecular docking of peptide ensembles from NMR into a homology model-derived NaV1.7 structure supported prioritization of key residues clustered on a hydrophobic face of the disulfide-rich folded peptide for derivatization. Replacing Trp24 with 5-Br-Trp24 identified lead peptides with activity in electrophysiology assays in engineered and neuronal cells. 5-Br-Trp24 containing peptide AM-6120 was characterized in X-ray crystallography and pharmacokinetic studies and blocked histamine-induced pruritis in mice after subcutaneous administration, demonstrating systemic NaV1.7-dependent pharmacodynamics. Our data suggests a need for high target coverage based on plasma exposure for impacting in vivo end points with selectivity-optimized peptidic NaV1.7 inhibitors.

Pharmacological characterization of potent and selective NaV1.7 inhibitors engineered from Chilobrachys jingzhao tarantula venom peptide JzTx-V.

Identification of voltage-gated sodium channel NaV1.7 inhibitors for chronic pain therapeutic development is an area of vigorous pursuit. In an effort to identify more potent leads compared to our previously reported GpTx-1 peptide series, electrophysiology screening of fractionated tarantula venom discovered the NaV1.7 inhibitory peptide JzTx-V from the Chinese earth tiger tarantula Chilobrachys jingzhao. The parent peptide displayed nominal selectivity over the skeletal muscle NaV1.4 channel. Attribute-based positional scan analoging identified a key Ile28Glu mutation that improved NaV1.4 selectivity over 100-fold, and further optimization yielded the potent and selective peptide leads AM-8145 and AM-0422. NMR analyses revealed that the Ile28Glu substitution changed peptide conformation, pointing to a structural rationale for the selectivity gains. AM-8145 and AM-0422 as well as GpTx-1 and HwTx-IV competed for ProTx-II binding in HEK293 cells expressing human NaV1.7, suggesting that these NaV1.7 inhibitory peptides interact with a similar binding site. AM-8145 potently blocked native tetrodotoxin-sensitive (TTX-S) channels in mouse dorsal root ganglia (DRG) neurons, exhibited 30- to 120-fold selectivity over other human TTX-S channels and exhibited over 1,000-fold selectivity over other human tetrodotoxin-resistant (TTX-R) channels. Leveraging NaV1.7-NaV1.5 chimeras containing various voltage-sensor and pore regions, AM-8145 mapped to the second voltage-sensor domain of NaV1.7. AM-0422, but not the inactive peptide analog AM-8374, dose-dependently blocked capsaicin-induced DRG neuron action potential firing using a multi-electrode array readout and mechanically-induced C-fiber spiking in a saphenous skin-nerve preparation. Collectively, AM-8145 and AM-0422 represent potent, new engineered NaV1.7 inhibitory peptides derived from the JzTx-V scaffold with improved NaV selectivity and biological activity in blocking action potential firing in both DRG neurons and C-fibers.

Ultra-high-throughput screening for antagonists of a Gi-coupled receptor in a 2.2-microl 3,456-well plate format cyclicAMP assay.

3',5'-Cyclic adenosine monophosphate (cAMP) is a common intracellular second messenger that enables cells to respond to external stimuli. Measurement of intracellular cAMP concentrations is thus widely used for studying guanosine triphosphate binding protein-coupled receptors (GPCRs), which make up a large class of pharmaceutical drug targets. Although several assay technologies exist to measure cAMP, most are not suitable for ultra-high-throughput screening (uHTS), as is often required for screening large (greater than 1 million) chemical libraries for the identification of suitable leads for drug development. Here we report that the enzyme fragment complementation assay, a homogeneous gain of signal assay based on complementation of two fragments of a beta-galactosidase enzyme, is compatible with uHTS requirements of a 2.2-microl total assay volume in 3,456-well plate format. We describe the miniaturization of this assay into 3,456-well plate format exhibiting comparable sensitivity and plate statistics to those of a 384-well assay and the application of this assay in uHTS for the identification of antagonists of a Gi-coupled receptor.

Miniaturization and automation of an ubiquitin ligase cascade enzyme-linked immunosorbent assay in 1,536-well format.

Enzyme-linked immunosorbent assays (ELISAs) are a long established and widely used assay format for drug discovery and diagnostics. They offer many advantages over homogeneous assay formats, including high sensitivity and separation (wash) steps that remove detection-interfering compounds. Many high-throughput screening assays are now performed in miniaturized formats (1,536- and 3,456-well plates) for higher throughput and lower reagent consumption. With miniaturization, separation steps in assays such as ELISA can become difficult to implement. Here we report on the implementation of the Kalypsys, Inc. (San Diego, CA) 1,536-well plate washer to enable the successful miniaturization and full automation of an ELISA that monitors ubiquitin ligase activity. The 1,536-well plate ELISA was robust and used for the high-throughput screening of a large screening collection (>1 million compounds).

Engineering Antibody Reactivity for Efficient Derivatization to Generate NaV1.7 Inhibitory GpTx-1 Peptide-Antibody Conjugates.

The voltage-gated sodium channel NaV1.7 is a genetically validated pain target under investigation for the development of analgesics. A therapeutic with a less frequent dosing regimen would be of value for treating chronic pain; however functional NaV1.7 targeting antibodies are not known. In this report, we describe NaV1.7 inhibitory peptide-antibody conjugates as an alternate construct for potential prolonged channel blockade through chemical derivatization of engineered antibodies. We previously identified NaV1.7 inhibitory peptide GpTx-1 from tarantula venom and optimized its potency and selectivity. Tethering GpTx-1 peptides to antibodies bifunctionally couples FcRn-based antibody recycling attributes to the NaV1.7 targeting function of the peptide warhead. Herein, we conjugated a GpTx-1 peptide to specific engineered cysteines in a carrier anti-2,4-dinitrophenol monoclonal antibody using polyethylene glycol linkers. The reactivity of 13 potential cysteine conjugation sites in the antibody scaffold was tuned using a model alkylating agent. Subsequent reactions with the peptide identified cysteine locations with the highest conversion to desired conjugates, which blocked NaV1.7 currents in whole cell electrophysiology. Variations in attachment site, linker, and peptide loading established design parameters for potency optimization. Antibody conjugation led to in vivo half-life extension by 130-fold relative to a nonconjugated GpTx-1 peptide and differential biodistribution to nerve fibers in wild-type but not NaV1.7 knockout mice. This study describes the optimization and application of antibody derivatization technology to functionally inhibit NaV1.7 in engineered and neuronal cells.