COVID-19 caused by the SARS-CoV-2 virus has become a global pandemic. 3CL protease is a virally encoded protein that is essential across a broad spectrum of coronaviruses with no close human analogs. ...PF-00835231, a 3CL protease inhibitor, has exhibited potent in vitro antiviral activity against SARS-CoV-2 as a single agent. Here we report, the design and characterization of a phosphate prodrug PF-07304814 to enable the delivery and projected sustained systemic exposure in human of PF-00835231 to inhibit coronavirus family 3CL protease activity with selectivity over human host protease targets. Furthermore, we show that PF-00835231 has additive/synergistic activity in combination with remdesivir. We present the ADME, safety, in vitro, and in vivo antiviral activity data that supports the clinical evaluation of PF-07304814 as a potential COVID-19 treatment.
SARS-CoV-2 has currently precipitated the COVID-19 global health crisis. We developed a medium-throughput drug-screening system and identified a small-molecule library of 34 of 430 protein kinase ...inhibitors that were capable of inhibiting the SARS-CoV-2 cytopathic effect in human epithelial cells. These drug inhibitors are in various stages of clinical trials. We detected key proteins involved in cellular signaling pathways mTOR-PI3K-AKT, ABL-BCR/MAPK, and DNA-damage response that are critical for SARS-CoV-2 infection. A drug-protein interaction-based secondary screen confirmed compounds, such as the ATR kinase inhibitor berzosertib and torin2 with anti-SARS-CoV-2 activity. Berzosertib exhibited potent antiviral activity against SARS-CoV-2 in multiple cell types and blocked replication at the post-entry step. Berzosertib inhibited replication of SARS-CoV-1 and the Middle East respiratory syndrome coronavirus (MERS-CoV) as well. Our study highlights key promising kinase inhibitors to constrain coronavirus replication as a host-directed therapy in the treatment of COVID-19 and beyond as well as provides an important mechanism of host-pathogen interactions.
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•Kinase inhibitor screen identified 34 compounds with anti-SARS-CoV-2 activity•Inhibitors targeted mTOR-PI3K-AKT and DNA-damage response (DDR) signaling pathways•ATR kinase inhibitor berzosertib blocked SARS-CoV-1, SARS-CoV-2, and MERS-CoV infection•Treatment with berzosertib blocks SARS-CoV-2 at post-entry level in epithelial cells
Garcia et al. screen a library of drug compounds and identify SARS-CoV-2-specific antiviral agents. These drugs have been shown to modulate cellular signaling cascades, including mTOR-PI3K-AKT and DNA-damage response (DDR) pathways. A highly effective drug candidate, berzosertib, blocked multiple coronaviruses, such as SARS-CoV-1, SARS-CoV-2, and MERS-CoV, thus providing a potential therapeutic against COVID-19.
HIV is a major driver of tuberculosis (TB) reactivation. Depletion of CD4+ T cells is assumed to be the basis behind TB reactivation in individuals with latent tuberculosis infection (LTBI) ...coinfected with HIV. Nonhuman primates (NHPs) coinfected with a mutant simian immunodeficiency virus (SIVΔGY) that does not cause depletion of tissue CD4+ T cells during infection failed to reactivate TB. To investigate the contribution of CD4+ T cell depletion relative to other mechanisms of SIV-induced reactivation of LTBI, we used CD4R1 antibody to deplete CD4+ T cells in animals with LTBI without lentiviral infection. The mere depletion of CD4+ T cells during LTBI was insufficient in generating reactivation of LTBI. Instead, direct cytopathic effects of SIV resulting in chronic immune activation, along with the altered effector T cell phenotypes and dysregulated T cell homeostasis, were likely mediators of reactivation of LTBI. These results revealed important implications for TB control in HIV-coinfected individuals.
Drug resistant Plasmodium falciparum parasites represent a major obstacle in our efforts to control malaria, a deadly vector borne infectious disease. This situation creates an urgent need to find ...and validate new drug targets to contain the spread of the disease. Several genes associated with the unfolded protein response (UPR) including Glucose-regulated Protein 78 kDa (GRP78, also known as BiP) have been deemed potential drug targets. We explored the drug target potential of GRP78, a molecular chaperone that is a regulator of the UPR, for the treatment of P. falciparum parasite infection. By screening repurposed chaperone inhibitors that are anticancer agents, we showed that GRP78 inhibition is lethal to drug-sensitive and -resistant P. falciparum parasite strains in vitro. We correlated the antiplasmodial activity of the inhibitors with their ability to bind the malaria chaperone, by characterizing their binding to recombinant parasite GRP78. Furthermore, we determined the crystal structure of the ATP binding domain of P. falciparum GRP78 with ADP and identified structural features unique to the parasite. These data suggest that P. falciparum GRP78 can be a valid drug target and that its structural differences to human GRP78 emphasize potential to generate parasite specific compounds.
There remains a need to develop novel SARS-CoV-2 therapeutic options that improve upon existing therapies by an increased robustness of response, fewer safety liabilities, and global-ready ...accessibility. Functionally critical viral main protease (Mpro, 3CLpro) of SARS-CoV-2 is an attractive target due to its homology within the coronaviral family, and lack thereof toward human proteases. In this disclosure, we outline the advent of a novel SARS-CoV-2 3CLpro inhibitor, CMX990, bearing an unprecedented trifluoromethoxymethyl ketone warhead. Compared with the marketed drug nirmatrelvir (combination with ritonavir = Paxlovid), CMX990 has distinctly differentiated potency (∼5× more potent in primary cells) and human in vitro clearance (>4× better microsomal clearance and >10× better hepatocyte clearance), with good in vitro-to-in vivo correlation. Based on its compelling preclinical profile and projected once or twice a day dosing supporting unboosted oral therapy in humans, CMX990 advanced to a Phase 1 clinical trial as an oral drug candidate for SARS-CoV-2.
The ongoing pandemic caused by the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), necessitates strategies to identify prophylactic and therapeutic drug candidates for rapid ...clinical deployment. Here, we describe a screening pipeline for the discovery of efficacious SARS-CoV-2 inhibitors. We screen a best-in-class drug repurposing library, ReFRAME, against two high-throughput, high-content imaging infection assays: one using HeLa cells expressing SARS-CoV-2 receptor ACE2 and the other using lung epithelial Calu-3 cells. From nearly 12,000 compounds, we identify 49 (in HeLa-ACE2) and 41 (in Calu-3) compounds capable of selectively inhibiting SARS-CoV-2 replication. Notably, most screen hits are cell-line specific, likely due to different virus entry mechanisms or host cell-specific sensitivities to modulators. Among these promising hits, the antivirals nelfinavir and the parent of prodrug MK-4482 possess desirable in vitro activity, pharmacokinetic and human safety profiles, and both reduce SARS-CoV-2 replication in an orthogonal human differentiated primary cell model. Furthermore, MK-4482 effectively blocks SARS-CoV-2 infection in a hamster model. Overall, we identify direct-acting antivirals as the most promising compounds for drug repurposing, additional compounds that may have value in combination therapies, and tool compounds for identification of viral host cell targets.
The atypical butyrylcholinesterase (aBuChE) from Oryzias latipes shares approximately 65% sequence similarity to both acetylcholinesterase and butyrylcholinesterase and was studied for its capacity ...to spontaneously reactivate following inhibition by organophosphorus nerve agents. Like other cholinesterases, aBuChE was inhibited by all G- and V-type nerve agents. Interestingly, aBuChE was able to undergo spontaneous reactivation after inhibition with VR (t1/2 = 5.5 ± 0.2 h). Mass spectrometry of aBuChE after VR inhibition confirmed the presence of a covalently bound adduct of the size expected for non-aged VR on the peptide containing the active site serine. To understand the effect of substrate volume on rates of reactivation, the capacity of aBuChE to bind and spontaneously reactivate after inhibition with five V-agent analogues was examined. No appreciable reactivation was detected for enzyme inhibited by V2 (VX with O-isopropyl on retained group), V4 (VX with N-diethyl leaving group termination), or V5 (VX with N-dimethyl leaving group termination). Minimal reactivation was detected with V1 (VX with O-propyl on retained group). Conversely, spontaneous reactivation was observed when aBuChE was inhibited by V3 (VX with O-isobutyl on retained group; t1/2 = 6.3 ± 0.4 h). The data suggest that the ability of aBuChE to spontaneously reactivate after inhibition by V-agent analogues is related to the structure of the retained group. These results provide structural information that may shed light on the design of improved small molecule reactivators of nerve agent-inhibited acetylcholinesterase or butyrylcholinesterase, and further suggest that re-engineering the active site of a cholinesterase could result in enzymes with clinically relevant rates of nerve agent hydrolysis.
•Atypical butyrylcholinesterase from Oryzias latipes is inhibited by nerve agents.•Spontaneous reactivation occurs after inhibition with VR and other V-analogues.•Reactivation half-time is related to functional group adducted on enzyme.
Poisoning via organophosphorus (OP) nerve agents occurs when the OP binds and inhibits the enzyme acetylcholinesterase (AChE). This enzyme is responsible for the metabolism of the neurotransmitter ...acetylcholine (ACh) which transmits signals between nerves and several key somatic regions. When AChE is inhibited, the signal initiated by ACh is not properly terminated. Excessive levels of ACh result in a cholinergic crisis, and in severe cases can lead to death. Current treatments for OP poisoning involve the administration of atropine, which blocks ACh receptors, and oximes, which reactivate AChE after inhibition. Efforts to improve the safety, efficacy, and broad spectrum utility of these treatments are ongoing and usually require the use of appropriate animal model systems. For OP poisoning, the guinea pig (
Cavia porcellus) is a commonly used animal model because guinea pigs more closely mirror primate susceptibility to OP poisoning than do other animals such as rats and mice. This is most likely because among rodents and other small mammals, guinea pigs have a very low relative concentration of serum carboxylesterase, an enzyme known to bind OPs
in vitro and to act as an endogenous bioscavenger
in vivo. Although guinea pigs historically have been used to test OP poisoning therapies, it has been found recently that guinea pig AChE is substantially more resistant to oxime-mediated reactivation than human AChE. To examine the molecular basis for this difference, we reverse transcribed mRNA encoding guinea pig AChE, amplified the resulting cDNA, and sequenced this product. The nucleotide and deduced amino acid sequences of guinea pig AChE were then compared to the human version. Several amino acid differences were noted, and the predicted locations of these differences were mapped onto a structural model of human AChE. To examine directly how these differences affect oxime-mediated reactivation of AChE after inhibition by OPs, human and guinea pig red blood cell ghosts were prepared and used as sources of AChE, and the relative capacity of several different oximes to reactivate each OP-inhibited AChE were determined. The differences we report between human and guinea pig AChE raise additional concerns about the suitability of the guinea pig as an appropriate small animal model to approximate human responses to OP poisoning and therapies.
The use of whole insect larvae as a source of recombinant proteins offers a more cost‐effective method of producing large quantities of human proteins than conventional cell‐culture approaches. Human ...carboxylesterase 1 has been produced in and isolated from whole Trichoplusia ni larvae. The recombinant protein was crystallized and its structure was solved to 2.2 Å resolution. The results indicate that the larvae‐produced enzyme is essentially identical to that isolated from cultured Sf21 cells, supporting the use of this expression system to produce recombinant enzymes for crystallization studies.
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