Intravenous delivery of GS-441524 is efficacious in the African green monkey model of SARS-CoV-2 infection.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of the COVID-19 pandemic, has infected over 260 million people over the past 2 years. Remdesivir (RDV, VEKLURY®) is currently the only antiviral therapy fully approved by the FDA for the treatment of COVID-19. The parent nucleoside of RDV, GS-441524, exhibits antiviral activity against numerous respiratory viruses including SARS-CoV-2, although at reduced in vitro potency compared to RDV in most assays. Here we find in both human alveolar and bronchial primary cells, GS-441524 is metabolized to the pharmacologically active GS-441524 triphosphate (TP) less efficiently than RDV, which correlates with a lower in vitro SARS-CoV-2 antiviral activity. In vivo, African green monkeys (AGM) orally dosed with GS-441524 yielded low plasma levels due to limited oral bioavailability of <10%. When GS-441524 was delivered via intravenous (IV) administration, although plasma concentrations of GS-441524 were significantly higher, lung TP levels were lower than observed from IV RDV. To determine the required systemic exposure of GS-441524 associated with in vivo antiviral efficacy, SARS-CoV-2 infected AGMs were treated with a once-daily IV dose of either 7.5 or 20 mg/kg GS-441524 or IV RDV for 5 days and compared to vehicle control. Despite the reduced lung TP formation compared to IV dosing of RDV, daily treatment with IV GS-441524 resulted in dose-dependent efficacy, with the 20 mg/kg GS-441524 treatment resulting in significant reductions of SARS-CoV-2 replication in the lower respiratory tract of infected animals. These findings demonstrate the in vivo SARS-CoV-2 antiviral efficacy of GS-441524 and support evaluation of its orally bioavailable prodrugs as potential therapies for COVID-19.

Prodrugs of a 1'-CN-4-Aza-7,9-dideazaadenosine C-Nucleoside Leading to the Discovery of Remdesivir (GS-5734) as a Potent Inhibitor of Respiratory Syncytial Virus with Efficacy in the African Green Monkey Model of RSV.

A discovery program targeting respiratory syncytial virus (RSV) identified C-nucleoside 4 (RSV A2 EC50 = 530 nM) as a phenotypic screening lead targeting the RSV RNA-dependent RNA polymerase (RdRp). Prodrug exploration resulted in the discovery of remdesivir (1, GS-5734) that is >30-fold more potent than 4 against RSV in HEp-2 and NHBE cells. Metabolism studies in vitro confirmed the rapid formation of the active triphosphate metabolite, 1-NTP, and in vivo studies in cynomolgus and African Green monkeys demonstrated a >10-fold higher lung tissue concentration of 1-NTP following molar normalized IV dosing of 1 compared to that of 4. A once daily 10 mg/kg IV administration of 1 in an African Green monkey RSV model demonstrated a >2-log10 reduction in the peak lung viral load. These early data following the discovery of 1 supported its potential as a novel treatment for RSV prior to its development for Ebola and approval for COVID-19 treatment.

Discovery of AMG 232, a potent, selective, and orally bioavailable MDM2-p53 inhibitor in clinical development.

We recently reported the discovery of AM-8553 (1), a potent and selective piperidinone inhibitor of the MDM2-p53 interaction. Continued research investigation of the N-alkyl substituent of this series, focused in particular on a previously underutilized interaction in a shallow cleft on the MDM2 surface, led to the discovery of a one-carbon tethered sulfone which gave rise to substantial improvements in biochemical and cellular potency. Further investigation produced AMG 232 (2), which is currently being evaluated in human clinical trials for the treatment of cancer. Compound 2 is an extremely potent MDM2 inhibitor (SPR KD = 0.045 nM, SJSA-1 EdU IC50 = 9.1 nM), with remarkable pharmacokinetic properties and in vivo antitumor activity in the SJSA-1 osteosarcoma xenograft model (ED50 = 9.1 mg/kg).

Structure-based design of novel inhibitors of the MDM2-p53 interaction.

Structure-based rational design led to the discovery of novel inhibitors of the MDM2-p53 protein-protein interaction. The affinity of these compounds for MDM2 was improved through conformational control of both the piperidinone ring and the appended N-alkyl substituent. Optimization afforded 29 (AM-8553), a potent and selective MDM2 inhibitor with excellent pharmacokinetic properties and in vivo efficacy.

Design of 1-piperazinyl-4-arylphthalazines as potent Smoothened antagonists.

The Hedgehog (Hh) signaling pathway regulates cell proliferation and differentiation in developing tissues, and abnormal activation of the Hh pathway has been linked to several tumor subsets. As a transducer of Hh signaling, the GPCR-like protein Smoothened (Smo) is a promising target for disruption of unregulated Hh signaling. A series of 1-amino-4-arylphthalazines was developed as potent and orally bioavailable inhibitors of Smo. A representative compound from this class demonstrated significant tumor volume reduction in a mouse medulloblastoma model.