In vitro selection and analysis of SARS-CoV-2 nirmatrelvir resistance mutations contributing to clinical virus resistance surveillance.

To facilitate the detection and management of potential clinical antiviral resistance, in vitro selection of drug-resistant severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) against the virus Mpro inhibitor nirmatrelvir (Paxlovid active component) was conducted. Six Mpro mutation patterns containing T304I alone or in combination with T21I, L50F, T135I, S144A, or A173V emerged, with A173V+T304I and T21I+S144A+T304I mutations showing >20-fold resistance each. Biochemical analyses indicated inhibition constant shifts aligned to antiviral results, with S144A and A173V each markedly reducing nirmatrelvir inhibition and Mpro activity. SARS-CoV-2 surveillance revealed that in vitro resistance-associated mutations from our studies and those reported in the literature were rarely detected in the Global Initiative on Sharing All Influenza Data database. In the Paxlovid Evaluation of Protease Inhibition for COVID-19 in High-Risk Patients trial, E166V was the only emergent resistance mutation, observed in three Paxlovid-treated patients, none of whom experienced COVID-19-related hospitalization or death.

A Second-Generation Oral SARS-CoV-2 Main Protease Inhibitor Clinical Candidate for the Treatment of COVID-19.

Despite the record-breaking discovery, development and approval of vaccines and antiviral therapeutics such as Paxlovid, coronavirus disease 2019 (COVID-19) remained the fourth leading cause of death in the world and third highest in the United States in 2022. Here, we report the discovery and characterization of PF-07817883, a second-generation, orally bioavailable, SARS-CoV-2 main protease inhibitor with improved metabolic stability versus nirmatrelvir, the antiviral component of the ritonavir-boosted therapy Paxlovid. We demonstrate the in vitro pan-human coronavirus antiviral activity and off-target selectivity profile of PF-07817883. PF-07817883 also demonstrated oral efficacy in a mouse-adapted SARS-CoV-2 model at plasma concentrations equivalent to nirmatrelvir. The preclinical in vivo pharmacokinetics and metabolism studies in human matrices are suggestive of improved oral pharmacokinetics for PF-07817883 in humans, relative to nirmatrelvir. In vitro inhibition/induction studies against major human drug metabolizing enzymes/transporters suggest a low potential for perpetrator drug-drug interactions upon single-agent use of PF-07817883.

Designing small molecules for therapeutic success: A contemporary perspective.

Successful small-molecule drug design requires a molecular target with inherent therapeutic potential and a molecule with the right properties to unlock its potential. Present-day drug design strategies have evolved to leave little room for improvement in drug-like properties. As a result, inadequate safety or efficacy associated with molecular targets now constitutes the primary cause of attrition in preclinical development through Phase II. This finding has led to a deeper focus on target selection. In this current reality, design tactics that enable rapid identification of risk-balanced clinical candidates, translation of clinical experience into meaningful differentiation strategies, and expansion of the druggable proteome represent significant levers by which drug designers can accelerate the discovery of the next generation of medicines.

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.

Design and synthesis of pyridazinone-based 5-HT(2C) agonists.

The SAR of a series of pyridazinone derived 5-HT(2C) agonists has been explored and resulted in identification of a compound with excellent levels of 5-HT(2C) functional agonism and selectivity over 5-HT(2A) and 5-HT(2B). This compound displayed good in vivo efficacy in pre-clinical models of stress urinary incontinence, despite having physiochemical properties commensurate with impaired CNS penetration.

Design and synthesis of piperazinylpyrimidinones as novel selective 5-HT(2C) agonists.

This Letter reports the design and synthesis of several novel series of piperazinyl pyrimidinones as 5-HT(2C) agonists. Several of the compounds presented exhibit good in vitro potency and selectivity over the closely related 5-HT(2A) and 5-HT(2B) receptors. Compound 11 was active in in vivo models of stress urinary incontinence.

Design and synthesis of a functionally selective D3 agonist and its in vivo delivery via the intranasal route.

This paper reports the synthesis and biological activity of a novel series of aryl-morpholine dopamine receptor agonists. Several compounds show high levels of functional selectivity for the D3 over the D2 dopamine receptor. Compound 26 has >1000-fold functional selectivity and has been successfully progressed in vivo using an intranasal delivery route.

A novel series of potent and selective PDE5 inhibitors with potential for high and dose-independent oral bioavailability.

Sildenafil (5-[2-ethoxy-5-(4-methyl-1-piperazinylsulfonyl)phenyl]-1-methyl-3-n-propyl-1,6-dihydro-7H-pyrazolo[4,3-d]pyrimidin-7-one), a potent and selective phosphodiesterase type 5 (PDE5) inhibitor, provided the first oral treatment for male erectile dysfunction. The objective of the work reported in this paper was to combine high levels of PDE5 potency and selectivity with high and dose-independent oral bioavailability, to minimize the impact on the C(max) of any interactions with coadministered drugs in the clinic. This goal was achieved through identification of a lower clearance series with a high absorption profile, by replacing the 5'-piperazine sulfonamide in the sildenafil template with a 5'-methyl ketone. This novel series provided compounds with low metabolism in human hepatocytes, excellent caco-2 flux, and the potential for good aqueous solubility. The in vivo oral and iv pharmacokinetic profiles of example compounds confirmed the high oral bioavailability predicted from these in vitro screens. 5-(5-Acetyl-2-butoxy-3-pyridinyl)-3-ethyl-2-(1-ethyl-3-azetidinyl)-2,6-dihydro-7H-pyrazolo[4,3-d]pyrimidin-7-one (2) was selected for progression into the clinic.

Design, synthesis and biological activity of beta-carboline-based type-5 phosphodiesterase inhibitors.

The SAR of a series of beta-carboline derived type 5 phosphodiesterase inhibitors has been explored and we have discovered compounds with excellent levels of PDE5 potency and selectivity over PDE6. However, the series exhibits low levels of selectivity over PDE11, a phosphodiesterase with unknown function.