Discovery of orally active SARS-CoV-2 papain-like protease (PLpro) inhibitors (preprint)

Vaccines and first-generation antiviral therapeutics have provided important protection against coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). However, there remains a need for additional therapeutic options that provide enhanced efficacy and protection against potential viral resistance. The SARS-CoV-2 papain-like protease (PLpro) is one of two essential cysteine proteases involved in viral replication. While inhibitors of the SARS-CoV-2 main protease (Mpro) have demonstrated clinical efficacy, known PLpro inhibitors have to date lacked the inhibitory potency and requisite pharmacokinetics to demonstrate that targeting PLpro translates to in vivo efficacy in a preclinical setting. Herein, we report the machine learning-driven discovery of potent, selective, and orally available SARS-CoV-2 PLpro inhibitors, with lead compound PF-07957472 (4) providing robust efficacy in a mouse-adapted model of COVID-19 infection.

CORNEAL GRAFT REJECTIONS DUE TO COVID 19 INFECTION OR VACCINATIONS : A CASE SERIES

Purpose : To report 4 cases of corneal graft rejections which occurred due to COVID19 infection or vaccination. Methods : Case 1 A 24-year old woman presented with corneal scar in her right eye (due to a resolved microbial keratitis) for which she underwent optical penetrating keratoplasty (PK). The patient presented with hyperacute endothelial rejection 5 weeks later. She had epithelial and endothelial corneal graft rejection (Figure 1) for which she was treated with intravenous methylprednisolone, along with topical steroids prescribed hourly and systemic steroids. 3 days later, she was diagnosed with COVID 19 infection. In spite of adequate treatment, her corneal graft could not be salvaged. Case 2 A 31-year old male who had history of chemical injury in the right eye in 2017, underwent second PK in 2020, and had graft rejection 4 weeks after 1st dose of COVID vaccine (COVISHIELD). He was successfully treated with hourly topical steroids along with systemic steroids and the corneal graft cleared up. Case 3 Another 29-year old male diagnosed with Macular corneal dystrophy underwent corneal transplantation in 2016 had graft rejection following 1st dose of COVID vaccine (COVISHIELD) 3 weeks later. The patient was treated with topical and systemic steroids. Though most part of the graft cleared up but inferior graft edema was found to persist (Figure 2). Case 4 A 17-year old girl, underwent PK for Congenital Hereditary Endothelial Dystrophy and had corneal graft rejection 1 month after the 2nd dose of COVID vaccine (COVISHIELD). With adequate treatment of topical and systemic steroids, the patient's corneal graft improved and cleared up, and the patient reports an improvement in visual acuity as well. Results :-Conclusions : COVID 19 infection and vaccination can induce graft rejection. Hyperacute endothelial rejection is possible with COVID 19 infection. COVID vaccine related corneal graft rejections may be less severe and may be reversed with adequate treatment.

Disposition of Nirmatrelvir, an Orally Bioavailable Inhibitor of SARS-CoV-2 3C-Like Protease, across Animals and Humans.

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) 3C-like protease inhibitor PF-07321332 (nirmatrelvir), in combination with ritonavir (Paxlovid), was recently granted emergency use authorization by multiple regulatory agencies for the treatment of coronavirus disease 2019 (COVID-19) in adults and pediatric patients. Disposition studies on nirmatrelvir in animals and in human reagents, which were used to support clinical studies, are described herein. Plasma clearance was moderate in rats (27.2 ml/min per kg) and monkeys (17.1 ml/min per kg), resulting in half-lives of 5.1 and 0.8 hours, respectively. The corresponding oral bioavailability was moderate in rats (34%-50%) and low in monkeys (8.5%), primarily due to oxidative metabolism along the gastrointestinal tract in this species. Nirmatrelvir demonstrated moderate plasma protein binding in rats, monkeys, and humans with mean unbound fractions ranging from 0.310 to 0.478. The metabolism of nirmatrelvir was qualitatively similar in liver microsomes and hepatocytes from rats, monkeys, and humans; prominent metabolites arose via cytochrome P450 (CYP450)-mediated oxidations on the P1 pyrrolidinone ring, P2 6,6-dimethyl-3-azabicyclo[3.1.0]hexane, and the tertiary-butyl group at the P3 position. Reaction phenotyping studies in human liver microsomes revealed that CYP3A4 was primarily responsible (fraction metabolized = 0.99) for the oxidative metabolism of nirmatrelvir. Minor clearance mechanisms involving renal and biliary excretion of unchanged nirmatrelvir were also noted in animals and in sandwich-cultured human hepatocytes. Nirmatrelvir was a reversible and time-dependent inhibitor as well as inducer of CYP3A activity in vitro. First-in-human pharmacokinetic studies have demonstrated a considerable boost in the oral systemic exposure of nirmatrelvir upon coadministration with the CYP3A4 inhibitor ritonavir, consistent with the predominant role of CYP3A4 in nirmatrelvir metabolism. SIGNIFICANCE STATEMENT: The manuscript describes the preclinical disposition, metabolism, and drug-drug interaction potential of PF-07321332 (nirmatrelvir), an orally active peptidomimetic-based inhibitor of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) 3CL protease, which has been granted emergency use authorization by multiple regulatory agencies around the globe for the treatment of coronavirus disease 2019 (COVID-19) in COVID-19-positive adults and pediatric patients who are at high risk for progression to severe COVID-19, including hospitalization or death.

An oral SARS-CoV-2 Mpro inhibitor clinical candidate for the treatment of COVID-19.

The worldwide outbreak of COVID-19 caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has become a global pandemic. Alongside vaccines, antiviral therapeutics are an important part of the healthcare response to countering the ongoing threat presented by COVID-19. Here, we report the discovery and characterization of PF-07321332, an orally bioavailable SARS-CoV-2 main protease inhibitor with in vitro pan-human coronavirus antiviral activity and excellent off-target selectivity and in vivo safety profiles. PF-07321332 has demonstrated oral activity in a mouse-adapted SARS-CoV-2 model and has achieved oral plasma concentrations exceeding the in vitro antiviral cell potency in a phase 1 clinical trial in healthy human participants.