Identification of Small Molecule Inhibitors of PPM1D Using a Novel Drug Discovery Platform.

Protein phosphatase, Mg2+/Mn2+ dependent 1D (PPM1D), is a serine/threonine phosphatase that is recurrently activated in cancer, regulates the DNA damage response (DDR), and suppresses the activation of p53. Consistent with its oncogenic properties, genetic loss or pharmacologic inhibition of PPM1D impairs tumor growth and sensitizes cancer cells to cytotoxic therapies in a wide range of preclinical models. Given the therapeutic potential of targeting PPM1D specifically and the DDR and p53 pathway more generally, we sought to deepen our biological understanding of PPM1D as a drug target and determine how PPM1D inhibition differs from other therapeutic approaches to activate the DDR. We performed a high throughput screen to identify new allosteric inhibitors of PPM1D, then generated and optimized a suite of enzymatic, cell-based, and in vivo pharmacokinetic and pharmacodynamic assays to drive medicinal chemistry efforts and to further interrogate the biology of PPM1D. Importantly, this drug discovery platform can be readily adapted to broadly study the DDR and p53. We identified compounds distinct from previously reported allosteric inhibitors and showed in vivo on-target activity. Our data suggest that the biological effects of inhibiting PPM1D are distinct from inhibitors of the MDM2-p53 interaction and standard cytotoxic chemotherapies. These differences also highlight the potential therapeutic contexts in which targeting PPM1D would be most valuable. Therefore, our studies have identified a series of new PPM1D inhibitors, generated a suite of in vitro and in vivo assays that can be broadly used to interrogate the DDR, and provided important new insights into PPM1D as a drug target.

Target-driven machine learning-enabled virtual screening (TAME-VS) platform for early-stage hit identification.

High-throughput screening (HTS) methods enable the empirical evaluation of a large scale of compounds and can be augmented by virtual screening (VS) techniques to save time and money by using potential active compounds for experimental testing. Structure-based and ligand-based virtual screening approaches have been extensively studied and applied in drug discovery practice with proven outcomes in advancing candidate molecules. However, the experimental data required for VS are expensive, and hit identification in an effective and efficient manner is particularly challenging during early-stage drug discovery for novel protein targets. Herein, we present our TArget-driven Machine learning-Enabled VS (TAME-VS) platform, which leverages existing chemical databases of bioactive molecules to modularly facilitate hit finding. Our methodology enables bespoke hit identification campaigns through a user-defined protein target. The input target ID is used to perform a homology-based target expansion, followed by compound retrieval from a large compilation of molecules with experimentally validated activity. Compounds are subsequently vectorized and adopted for machine learning (ML) model training. These machine learning models are deployed to perform model-based inferential virtual screening, and compounds are nominated based on predicted activity. Our platform was retrospectively validated across ten diverse protein targets and demonstrated clear predictive power. The implemented methodology provides a flexible and efficient approach that is accessible to a wide range of users. The TAME-VS platform is publicly available at https://github.com/bymgood/Target-driven-ML-enabled-VS to facilitate early-stage hit identification.

Mitigating the risk of antimalarial resistance via covalent dual-subunit inhibition of the Plasmodium proteasome.

The Plasmodium falciparum proteasome constitutes a promising antimalarial target, with multiple chemotypes potently and selectively inhibiting parasite proliferation and synergizing with the first-line artemisinin drugs, including against artemisinin-resistant parasites. We compared resistance profiles of vinyl sulfone, epoxyketone, macrocyclic peptide, and asparagine ethylenediamine inhibitors and report that the vinyl sulfones were potent even against mutant parasites resistant to other proteasome inhibitors and did not readily select for resistance, particularly WLL that displays covalent and irreversible binding to the catalytic ß2 and ß5 proteasome subunits. We also observed instances of collateral hypersensitivity, whereby resistance to one inhibitor could sensitize parasites to distinct chemotypes. Proteasome selectivity was confirmed using CRISPR/Cas9-edited mutant and conditional knockdown parasites. Molecular modeling of proteasome mutations suggested spatial contraction of the ß5 P1 binding pocket, compromising compound binding. Dual targeting of P. falciparum proteasome subunits using covalent inhibitors provides a potential strategy for restoring artemisinin activity and combating the spread of drug-resistant malaria.

Discovery of mobocertinib, a potent, oral inhibitor of EGFR exon 20 insertion mutations in non-small cell lung cancer.

In the treatment of non-small cell lung cancer (NSCLC), patients harboring exon 20 insertion mutations in the epidermal growth factor receptor (EGFR) gene (EGFR) have few effective therapies because this subset of mutants is generally resistant to most currently approved EGFR inhibitors. This report describes the structure-guided design of a novel series of potent, irreversible inhibitors of EGFR exon 20 insertion mutations, including the V769_D770insASV and D770_N771insSVD mutants. Extensive structure-activity relationship (SAR) studies led to the discovery of mobocertinib (compound 21c), which inhibited growth of Ba/F3 cells expressing the ASV insertion with a half-maximal inhibitory concentration of 11 nM and with selectivity over wild-type EGFR. Daily oral administration of mobocertinib induced tumor regression in a Ba/F3 ASV xenograft mouse model at well-tolerated doses. Mobocertinib was approved in September 2021 for the treatment of adult patients with advanced NSCLC with EGFR exon 20 insertion mutations with progression on or after platinum-based chemotherapy.

Susceptibilities of Ugandan Plasmodium falciparum Isolates to Proteasome Inhibitors.

The proteasome is a promising target for antimalarial chemotherapy. We assessed ex vivo susceptibilities of fresh Plasmodium falciparum isolates from eastern Uganda to seven proteasome inhibitors: two asparagine ethylenediamines, two macrocyclic peptides, and three peptide boronates; five had median IC50 values <100 nM. TDI8304, a macrocylic peptide lead compound with drug-like properties, had a median IC50 of 16 nM. Sequencing genes encoding the ß2 and ß5 catalytic proteasome subunits, the predicted targets of the inhibitors, and five additional proteasome subunits, identified two mutations in ß2 (I204T, S214F), three mutations in ß5 (V2I, A142S, D150E), and three mutations in other subunits. The ß2 S214F mutation was associated with decreased susceptibility to two peptide boronates, with IC50s of 181 nM and 2635 nM against mutant versus 62 nM and 477 nM against wild type parasites for MMV1579506 and MMV1794229, respectively, although significance could not be formally assessed due to the small number of mutant parasites with available data. The other ß2 and ß5 mutations and mutations in other subunits were not associated with susceptibility to tested compounds. Against culture-adapted Ugandan isolates, two asparagine ethylenediamines and the peptide proteasome inhibitors WLW-vinyl sulfone and WLL-vinyl sulfone (which were not studied ex vivo) demonstrated low nM activity, without decreased activity against ß2 S214F mutant parasites. Overall, proteasome inhibitors had potent activity against P. falciparum isolates circulating in Uganda, and genetic variation in proteasome targets was uncommon.

Reaction hijacking of tyrosine tRNA synthetase as a new whole-of-life-cycle antimalarial strategy.

Aminoacyl transfer RNA (tRNA) synthetases (aaRSs) are attractive drug targets, and we present class I and II aaRSs as previously unrecognized targets for adenosine 5'-monophosphate-mimicking nucleoside sulfamates. The target enzyme catalyzes the formation of an inhibitory amino acid-sulfamate conjugate through a reaction-hijacking mechanism. We identified adenosine 5'-sulfamate as a broad-specificity compound that hijacks a range of aaRSs and ML901 as a specific reagent a specific reagent that hijacks a single aaRS in the malaria parasite Plasmodium falciparum, namely tyrosine RS (PfYRS). ML901 exerts whole-life-cycle-killing activity with low nanomolar potency and single-dose efficacy in a mouse model of malaria. X-ray crystallographic studies of plasmodium and human YRSs reveal differential flexibility of a loop over the catalytic site that underpins differential susceptibility to reaction hijacking by ML901.

Design of proteasome inhibitors with oral efficacy in vivo against Plasmodium falciparum and selectivity over the human proteasome.

The Plasmodium falciparum proteasome is a potential antimalarial drug target. We have identified a series of amino-amide boronates that are potent and specific inhibitors of the P. falciparum 20S proteasome (Pf20S) ß5 active site and that exhibit fast-acting antimalarial activity. They selectively inhibit the growth of P. falciparum compared with a human cell line and exhibit high potency against field isolates of P. falciparum and Plasmodium vivax They have a low propensity for development of resistance and possess liver stage and transmission-blocking activity. Exemplar compounds, MPI-5 and MPI-13, show potent activity against P. falciparum infections in a SCID mouse model with an oral dosing regimen that is well tolerated. We show that MPI-5 binds more strongly to Pf20S than to human constitutive 20S (Hs20Sc). Comparison of the cryo-electron microscopy (EM) structures of Pf20S and Hs20Sc in complex with MPI-5 and Pf20S in complex with the clinically used anti-cancer agent, bortezomib, reveal differences in binding modes that help to explain the selectivity. Together, this work provides insights into the 20S proteasome in P. falciparum, underpinning the design of potent and selective antimalarial proteasome inhibitors.

Canine pedal papilloma identification and management: a retrospective series of 44 cases.

BACKGROUND: Papillomavirus infections in dogs have a variety of manifestations and involve multiple viral genera. Canine pedal papillomas have been infrequently studied and reported in the literature. OBJECTIVE: To report the signalment, history, treatment and outcome of biopsy-confirmed cases of canine pedal papillomatosis, collected from veterinarians across the United States and Canada ANIMALS: Medical records from 44 dogs were submitted by North American veterinarians. METHODS AND MATERIALS: Surveys were submitted through the Veterinary Information Network for biopsy-confirmed cases of canine pedal papillomatosis. Submissions included information on patient signalment, history, biopsy report, treatment and outcome. RESULTS: Forty-four cases were reviewed. The median age of presentation was four years old. Dogs most commonly presented with lameness and/or paw licking/chewing. Only one paw was affected in 35 cases, and front paws were more often affected than back paws. Twenty-eight dogs presented with one mass. Histopathological evaluation documented 33 cases of noninverted papillomas and 11 cases of inverted papillomas. Thirty-four papillomas resolved in total; 25 resolved within three weeks after biopsy collection. Twenty-one dogs received no additional treatment and 15 of those cases resolved. Azithromycin was the most commonly reported treatment initiated after biopsy was collected. CONCLUSIONS AND CLINICAL IMPORTANCE: The biological behaviour of canine pedal papillomas in this case series was similar to oral papillomas, and most lesions resolved with or without additional treatment. Further research is needed to better characterise the causative papillomavirus types and genera involved in the development of canine pedal papillomas.

Efficacy of ulipristal acetate in women with fibroid induced menorrhagia: A systematic review and meta-analysis.

AIM: To evaluate the efficacy of UPA in women with fibroid induced menorrhagia. METHODS: Embase, MEDLINE, CAB Abstracts, Cochrane Central Register of Controlled Trials, PsychInfo were searched up to 18th May 2020 and updated on 7th February 2021. Randomised controlled trials evaluating the efficacy of UPA in women with fibroid induced menorrhagia were included in the study. RESULTS: Two authors independently reviewed and extracted the study data. Statistical heterogeneity was quantified using I2 statistics. Publication bias and data asymmetry was assessed by funnel plots. A meta-analysis was conducted where appropriate. Six studies were eligible for inclusion. UPA (5 mg and 10 mg) achieved statistically significant amenorrhoeic outcome when compared to placebo (p<0.00001). Increased adverse events (AE) profile was observed in the higher UPA dose, however, did not reach statistical significance. CONCLUSIONS: This review demonstrates the efficacy of UPA in achieving amenorrhoea in women with fibroid induced menorrhagia. However, the favourable dose of UPA remains inconclusive when AE profile is taken into account. Evidence remains obscure regarding liver damage and further research is warranted to attain a conclusive outcome.

Identification of Novel Carbocyclic Pyrimidine Cyclic Dinucleotide STING Agonists for Antitumor Immunotherapy Using Systemic Intravenous Route.

Stimulator of Interferon Genes (STING) plays an important role in innate immunity by inducing type I interferon production upon infection with intracellular pathogens. STING activation can promote increased T-cell activation and inflammation in the tumor microenvironment, resulting in antitumor immunity. Natural and synthetic cyclic dinucleotides (CDNs) are known to activate STING, and several synthetic CDN molecules are being investigated in the clinic using an intratumoral administration route. Here, we describe the identification of STING agonist 15a, a cyclic dinucleotide structurally diversified from natural ligands with optimized properties for systemic intravenous (iv) administration. Our studies have shown that STING activation by 15a leads to an acute innate immune response as measured by cytokine secretion and adaptive immune response via activation of CD8+ cytotoxic T-cells, which ultimately provides robust antitumor efficacy.

Mobocertinib (TAK-788): A Targeted Inhibitor of EGFR Exon 20 Insertion Mutants in Non-Small Cell Lung Cancer.

Most EGFR exon 20 insertion (EGFRex20ins) driver mutations in non-small cell lung cancer (NSCLC) are insensitive to approved EGFR tyrosine kinase inhibitors (TKI). To address the limitations of existing therapies targeting EGFR-mutated NSCLC, mobocertinib (TAK-788), a novel irreversible EGFR TKI, was specifically designed to potently inhibit oncogenic variants containing activating EGFRex20ins mutations with selectivity over wild-type EGFR. The in vitro and in vivo activity of mobocertinib was evaluated in engineered and patient-derived models harboring diverse EGFRex20ins mutations. Mobocertinib inhibited viability of various EGFRex20ins-driven cell lines more potently than approved EGFR TKIs and demonstrated in vivo antitumor efficacy in patient-derived xenografts and murine orthotopic models. These findings support the ongoing clinical development of mobocertinib for the treatment of EGFRex20ins-mutated NSCLC. SIGNIFICANCE: No oral EGFR-targeted therapies are approved for EGFR exon 20 insertion (EGFRex20ins) mutation-driven NSCLC. Mobocertinib is a novel small-molecule EGFR inhibitor specifically designed to target EGFRex20ins mutants. Preclinical data reported here support the clinical development of mobocertinib in patients with NSCLC with EGFR exon 20 insertion mutations.See related commentary by Pacheco, p. 1617.This article is highlighted in the In This Issue feature, p. 1601.

Discovery and optimization of pyrazolopyrimidine sulfamates as ATG7 inhibitors.

Autophagy is postulated to be required by cancer cells to survive periods of metabolic and/or hypoxic stress. ATG7 is the E1 enzyme that is required for activation of Ubl conjugation pathways involved in autophagosome formation. This article describes the design and optimization of pyrazolopyrimidine sulfamate compounds as potent and selective inhibitors of ATG7. Cellular levels of the autophagy markers, LC3B and NBR1, are regulated following treatment with these compounds.

Recovery of meticillin-resistant Staphylococcus species from pet-grooming salons.

BACKGROUND: Meticillin-resistant (MR) staphylococcal species have been cultured from veterinary hospital environments and veterinary instruments. Pet-grooming salon environments and grooming tools may pose a risk for dissemination of MR staphylococcal bacteria into the pet population. OBJECTIVE: The objectives of this study were to investigate the frequency of MR staphylococcal colonization of pet-grooming salons and to collect information regarding cleaning procedures in grooming salons. METHODS AND MATERIALS: A nonrandomized, observational study was performed in 2018. Locations inside 19 grooming salons near Tacoma, WA, USA, were sampled and selectively cultured for MR, coagulase-positive staphylococci. Sampled sites included clipper blades and handles, leashes, rims of bathtub drains, insides of shampoo caps, and bathtub spray hoses or faucet handles. Grooming salons were asked to complete surveys regarding their cleaning practices. RESULTS: Meticillin-resistant coagulase-positive staphylococci were isolated from 12 of 19 grooming salons and 25 of 112 total samples. Meticillin-resistant S. pseudintermedius, S. aureus and S. schleiferi were isolated from multiple salons, most commonly from electric clipper blades, clipper handles and grooming leashes. No statistically significant correlations were identified between cleaning practices and the isolation of MR coagulase-positive staphylococci. CONCLUSIONS AND CLINICAL IMPORTANCE: Clipper blades, clipper handles and leashes are potential fomites for MR staphylococci in a grooming salon; increased disinfection practices for these items are indicated. A prospective, controlled, large-scale study is warranted to examine the effect of grooming salon hygiene practices on the isolation of MR staphylococci in salons.

The proteasome as a target for protozoan parasites.

Introduction: The proteasome is a multi-subunit enzyme complex responsible for the turnover of short-lived, abnormal or damaged proteins in eukaryotic cells. As organisms that undergo rapid growth and cell division, protozoan parasites exist on the knife-edge of proteotoxic catastrophe and thus rely heavily on their protein quality control machinery for survival. Because of this, the proteasome has recently emerged as a desirable drug target.Area covered: This review focuses on efforts to identify protozoan parasite-specific proteasome inhibitors using substrate profiling, library screening, and in vitro evolution of resistance approaches to inform medicinal chemistry. Targeting the parasite's 20S proteasome chymotrypsin-like (ß5) activity and selectively inhibiting protein turnover in parasites compared to human cells are critical properties of potent, selective inhibitors.Expert opinion: Proteasome inhibitors have the potential for rapid action against all stages, all species and all strains of plasmodium and kinetoplastid parasites. Given the high level of conservation of proteasome active sites in eukaryotes, an important challenge is achieving inhibitors that show sufficient selectivity while maintaining properties consistent with drug development.

Target Validation and Identification of Novel Boronate Inhibitors of the Plasmodium falciparum Proteasome.

The Plasmodium proteasome represents a potential antimalarial drug target for compounds with activity against multiple life cycle stages. We screened a library of human proteasome inhibitors (peptidyl boronic acids) and compared activities against purified P. falciparum and human 20S proteasomes. We chose four hits that potently inhibit parasite growth and show a range of selectivities for inhibition of the growth of P. falciparum compared with human cell lines. P. falciparum was selected for resistance in vitro to the clinically used proteasome inhibitor, bortezomib, and whole genome sequencing was applied to identify mutations in the proteasome ß5 subunit. Active site profiling revealed inhibitor features that enable retention of potent activity against the bortezomib-resistant line. Substrate profiling reveals P. falciparum 20S proteasome active site preferences that will inform attempts to design more selective inhibitors. This work provides a starting point for the identification of antimalarial drug leads that selectively target the P. falciparum proteasome.

Cardiac arrest in an American Cocker Spaniel during a deep ear flush procedure.

CASE DESCRIPTION A 14-year-old spayed female American Cocker Spaniel with bilateral otitis media and no evidence of cardiovascular instability was anesthetized to allow performance of a deep ear flush. CLINICAL FINDINGS Otoscopic examination of the left ear revealed evidence of chronic inflammation; the ear was flushed with sterile saline (0.9% NaCl) solution. Examination of the right ear revealed more severe chronic inflammation than in the left ear, including a ruptured tympanum (timing of rupture unknown). The right ear was flushed with sterile saline solution, and several drops of otic medication were instilled. During infusion of saline solution, the ECG revealed a rapid decrease in heart rate until no more electrical activity was noted. Pulse also ceased to be detectable via pulse oximetry and femoral artery palpation. TREATMENT AND OUTCOME Isoflurane was discontinued immediately after recognition of cardiac arrest. Shortly after, atropine (0.04 mg/kg [0.02 mg/lb]) and epinephrine (0.3 mg/kg [0.14 mg/lb]) were administered IV, chest compressions and ventilation were performed for 2 to 3 minutes, and 3 boluses (each 5 mL/kg) of lactated Ringer solution were administered IV. The dog was extubated 8 minutes after anesthesia was discontinued, and its recovery was monitored for the next 5 hours. No further incidents of cardiac arrest occurred after recovery from anesthesia. CLINICAL RELEVANCE This case represented a rarely documented potential complication associated with otic manipulation in a dog: cardiac arrest secondary to stimulation of the auricular branch of the vagus nerve. Veterinarians should be prepared for and warn clients of this possibility prior to otic flushing.

Optimization of tetrahydronaphthalene inhibitors of Raf with selectivity over hERG.

Investigations of a biaryl ether scaffold identified tetrahydronaphthalene Raf inhibitors with good in vivo activity; however these compounds had affinity toward the hERG potassium channel. Herein we describe our work to eliminate this hERG activity via alteration of the substituents on the benzoic amide functionality. The resulting compounds have improved selectivity against the hERG channel, good pharmacokinetic properties and potently inhibit the Raf pathway in vivo.

Histone deacetylase inhibitors derived from 1,2,3,4-tetrahydropyrrolo[1,2-a]pyrazine and related heterocycles selective for the HDAC6 isoform.

Acyl derivatives of 4-(aminomethyl)-N-hydroxybenzamide are potent sub-type selective HDAC6 inhibitors. Constrained heterocyclic analogs based on 1,2,3,4-tetrahydropyrrolo[1,2-a]pyrazine show further enhanced HDAC6 selectivity and inhibitory activity in cells. Homology models suggest that the heterocyclic spacer can more effectively access the wider catalytic channel of HDAC6 compared to other HDAC sub-types.

Mechanistic study of Uba5 enzyme and the Ufm1 conjugation pathway.

E1 enzymes activate ubiquitin or ubiquitin-like proteins (Ubl) via an adenylate intermediate and initiate the enzymatic cascade of Ubl conjugation to target proteins or lipids. Ubiquitin-fold modifier 1 (Ufm1) is activated by the E1 enzyme Uba5, and this pathway is proposed to play an important role in the endoplasmic reticulum (ER) stress response. However, the mechanisms of Ufm1 activation by Uba5 and subsequent transfer to the conjugating enzyme (E2), Ufc1, have not been studied in detail. In this work, we found that Uba5 activated Ufm1 via a two-step mechanism and formed a binary covalent complex of Uba5∼Ufm1 thioester. This feature contrasts with the three-step mechanism and ternary complex formation in ubiquitin-activating enzyme Uba1. Uba5 displayed random ordered binding with Ufm1 and ATP, and its ATP-pyrophosphate (PPi) exchange activity was inhibited by both AMP and PPi. Ufm1 activation and Uba5∼Ufm1 thioester formation were stimulated in the presence of Ufc1. Furthermore, binding of ATP to Uba5∼Ufm1 thioester was required for efficient transfer of Ufm1 from Uba5 to Ufc1 via transthiolation. Consistent with the two-step activation mechanism, the mechanism-based pan-E1 inhibitor, adenosine 5'-sulfamate (ADS), reacted with the Uba5∼Ufm1 thioester and formed a covalent, tight-binding Ufm1-ADS adduct in the active site of Uba5, which prevented further substrate binding or catalysis. ADS was also shown to inhibit the Uba5 conjugation pathway in the HCT116 cells through formation of the Ufm1-ADS adduct. This suggests that further development of more selective Uba5 inhibitors could be useful in interrogating the roles of the Uba5 pathway in cells.