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simnotrelvir (SSD 8432 / Cenoxin / SIM0417)

✓ Approved

Simcere Pharmaceutical Group · · Small Molecule

What is simnotrelvir?

simnotrelvir is a small molecule developed by Simcere Pharmaceutical Group. It is approved for therapeutic indications via oral (po).

Drug Profile

Brand NamesSSD 8432, Cenoxin, SIM0417
CompanySimcere Pharmaceutical Group
Drug ClassSmall Molecule
RouteOral (PO)
StatusApproved
Sources: ClinicalTrials.gov, Simcere Pharmaceutical Group

Mechanism of Action

Molecular Targets

simnotrelvir acts on 1 molecular target:

(ORF1ab)
Want deeper analysis?Noah AI can explain complex mechanisms and compare to similar drugs.

Therapeutic Indications

simnotrelvir is developed for 1 unique indication across 1 therapeutic area.

Therapeutic AreaConditionPhase
Infections and infestationsCOVID-19✓ Approved

Related Research Articles

PubMedNature communications2026-05-20

Cross-resistance patterns in SARS-CoV-2 against 3CL protease inhibitors.

Chithelen Janice J, Lovett David H DH, Wang Kevin K, Torres Yanagisawa Akari E AE et al.

SARS-CoV-2 is now endemic, with infections commonplace. While much of the population now has immunity, some subsets remain at risk. For such individuals, small-molecule antivirals are the frontline treatment. However, studies have identified resistance-conferring mutations to these compounds, and there are now cases of resistant viruses emerging during treatment. These occurrences make clear the need to understand the resistance mechanisms for SARS-CoV-2 antivirals. Here, we report the pathways to resistance for atilotrelvir and simnotrelvir, two 3CL protease inhibitors used for COVID-19 treatment, and ibuzatrelvir, a compound in late-stage clinical development. Through high-throughput passaging, we reveal that resistance can readily arise, and that there is a large degree of overlap in the mutations which emerge. Moreover, viral inhibition assays demonstrate that there is not only strong cross-resistance between the emerged viruses against these three molecules, but also against two additional widely used antivirals, nirmatrelvir and ensitrelvir, as well. Cellular assays highlight S144A, E166A, and E166V as mediating broad resistance, with E166V having the strongest effects. These results have important clinical implications, including the need to carefully consider cross-resistance properties in salvage therapy and combination treatment, as well as emphasizing the need for the further development of SARS-CoV-2 antivirals with differing modalities.

PMID 42156379
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PubMedJournal of virology2026-04-27

SARS-CoV-2 3CLpro mutations T21I and E166A confer differential resistance to simnotrelvir, bofutrelvir, and ensitrelvir.

Chen Lu L, Su Haixia H, Shang Weijuan W, Nie Tianqing T et al.

Inhibiting the catalytic activity of 3CLpro is a mainstream strategy to block coronavirus replication. However, the appearance of SARS-CoV-2 3CLpro resistance to protease inhibitors raises concerns for effective therapies. In this work, we first investigated the resistance profile of simnotrelvir, an approved anti-SARS-CoV-2 drug that targets 3CLpro. We found that the T21I/E166A mutations in 3CLpro equally emerged when SARS-CoV-2 was passaged in the HEK293T-hACE2 cells with increasing concentrations of simnotrelvir. The SARS-CoV-2 isolate carrying 3CLproT21I/E166A (SARS2-T21I/E166A) showed cross-resistance to simnotrelvir, nirmatrelvir, and ensitrelvir, but not significant resistance to bofutrelvir. Biochemical and cellular assays confirmed that 3CLproT21I/E166A was associated with the differential resistance to these protease inhibitors. Crystallographic structural analysis indicated that the alanine substitution disrupted hydrogen bonding interactions surrounding the γ-lactam rings (P1) of the inhibitors, which is similar to the model rebuilding observed with the previously reported E166V mutation. However, in contrast to the valine substitution, the alanine substitution resulted in a more spacious S2 subsite, thereby causing stronger interaction between the P1 and residues F140 and Ser1 of protomer B. Further computational simulations demonstrated that the covalent binding of bofutrelvir preserves strong binding affinity despite modifications in the S2 subsite caused by the E166A mutation, suggesting that inhibitors containing an aldehyde warhead may partially overcome resistance. Notably, both simnotrelvir and bofutrelvir exhibited therapeutic efficacy against the SARS2-T21I/E166A variant in K18-hACE2 mice. These findings advance our understanding of the resistance profiles and mechanistic underpinnings of SARS-CoV-2 3CLpro and underscore the necessity for diversified antiviral therapeutic strategies. Considering that the nirmatrelvir-resistant SARS-CoV-2 has emerged in immunocompromised patients who received long-term Paxlovid therapy, it is essential to investigate the response of resistance 3CLpro mutants to various protease inhibitors. Simnotrelvir, a novel inhibitor targeting SARS-CoV-2 3CLpro, has been authorized for the treatment of mild-to-moderate COVID-19 in China and has treated over 1 million patients. However, the resistance profile of simnotrelvir to SARS-CoV-2 remains unknown. Here, we identified that 3CLpro with T21I/E166A mutations confers resistance to simnotrelvir and showed cross-resistance to nirmatrelvir and ensitrelvir, but not bofutrelvir. More importantly, we further revealed that E166A showed a novel resistance mechanism to both the covalent inhibitors consisting of a γ-lactam ring and non-covalent inhibitors like ensitrelvir, which is different from that of E166V previously reported. In contrast, bofutrelvir maintains high affinity to T21I/E166A, suggesting that inhibitors with aldehyde warhead can partly neutralize the resistance.

PMID 42037412
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PubMedBMC infectious diseases2026-04-02

Rapid pulmonary calcification within 10 days in a COVID-19 patient: a case report.

Li Jie J, Liu Peng P, Wei Tong T, Zhang Yanan Y et al.

BACKGROUND: Pulmonary calcification typically occurs months to years after chronic infections or metabolic disorders. In contrast, it is exceedingly rare in acute viral pneumonias. We report the first case of rapid intrapulmonary calcification within 10 days of SARS-CoV-2 infection. CASE PRESENTATION: An 82-year-old male was admitted with fever and cough. Chest CT revealed scattered calcified foci with a density of 250 HU. Following antiviral therapy (simnotrelvir/ritonavir) and corticosteroids, the calcified lesions exhibited dynamic changes correlating with the inflammatory status. Specifically, partial resolution in early stages, followed by an increase during clinical deterioration, and persistence at discharge. Laboratory tests excluded metabolic causes of calcification (serum calcium, alkaline phosphatase, and parathyroid hormone were within normal limits). CONCLUSION: COVID-19 may be associated with rapid pulmonary calcification, with serial CT imaging providing a means to track dynamic lesion changes. The underlying mechanisms and long-term clinical significance remain uncertain and warrant further investigation.

PMID 41922988
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PubMedMicrobial biotechnology2026-03-31

Antivirals Targeting Coronavirus RNA-Dependent RNA Polymerase and Main Protease: From Mechanisms of Action to Outcomes in COVID-19 Clinical Trials.

Brüssow Harald H

The rapid global spread of SARS-CoV-2 triggered an unprecedented effort to develop effective antivirals. Among the first approved agents was remdesivir, an injectable nucleoside analogue developed by Gilead Sciences, that led to chain termination of viral RNA synthesis and showed broad antiviral activity against RNA viruses. Early clinical results were mixed: The US ACTT-1 trial reported an accelerated recovery and reduced mortality in treated patients, while the WHO Solidarity and a European trial revealed no impact of remdesivir on mortality. In contrast, a US trial in outpatients demonstrated a clear clinical benefit when treatment was administered early. Molnupiravir, an orally applicable nucleoside analogue developed by Merck, induces lethal mutations in the viral genome rather than chain termination. Molnupiravir showed in vivo antiviral activity against coronaviruses in different animals. In MOVe-OUT trials, molnupiravir reduced the rate of hospitalisation in treated outpatients. In the PANORAMIC trial, molnupiravir reduced the time to recovery in outpatients but not their rate of hospitalisation. No drug effect of molnupiravir was seen in the RECOVERY trial with hospitalised COVID-19 patients. Using structural biology and medicinal chemistry approaches, Pfizer developed nirmatrelvir, an oral inhibitor of the major coronavirus protease. In high-risk but not in standard-risk COVID-19 patients, the combination nirmatrelvir/ritonavir reduced the rate of hospitalisation (EPIC HR and SR trials). Retrospective cohort studies showed treatment effects in defined patient groups. This review compares the efficacy and clinical performance of different antivirals, including emerging drugs such as obeldesivir and alternative protease inhibitors (lopinavir, simnotrelvir). It further examines their roles in prophylaxis, treatment of long covid symptoms, pharmacological considerations and antiviral resistance. Particular attention is given to factors underlying variable outcome of the trials, including viral variant evolution, population immunity increases, disease severity changes and timing of therapy initiation.

PMID 41914684
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PubMedAnnals of internal medicine2026-02-09

Outpatient Treatment of Confirmed COVID-19: A Living, Rapid Review for the American College of Physicians (Version 3).

Sommer Isolde I, Dobrescu Andreea A, Gadinger Arianna A, Sharifan Amin A et al.

Clinicians and patients need updated information on antiviral treatments for COVID-19. To provide a final update on the benefits and harms of COVID-19 antiviral treatments in adult outpatients. Ovid/MEDLINE, Epistemonikos COVID-19 L·OVE platform, and iSearch COVID-19 portfolio (22 January 2025); Ovid/MEDLINE (24 September 2025). Two reviewers screened 20% of abstracts and full texts, then single screening. Randomized controlled trials were included for benefits and harms, and cohort studies were included for harms. One reviewer extracted data and assessed risk of bias and certainty of evidence (CoE); a second reviewer verified. Seven studies from the Omicron period were included. 125 mg of ensitrelvir may not reduce time to recovery and may result in no difference in serious adverse events (both low CoE) but may increase adverse events (44.2% vs. 24.8%; low CoE). Molnupiravir probably improves recovery (31.8% vs. 22.6%) and reduces time to recovery (9 vs. 15 median days) and persistent symptoms from 3 to 6 months (8.5% vs. 11.0%), with no effect on mortality, hospitalization, serious adverse events, and adverse events (all moderate CoE). Nirmatrelvir-ritonavir may increase recovery (70.7% vs. 53.6%; low CoE) and reduce time to recovery (no data, P = 0.011; low CoE) but probably increases adverse events (1.3% vs. 1.0%; moderate CoE). Simnotrelvir-ritonavir reduces time to recovery (-35.8 median hours; high CoE) and probably increases adverse events (28.9% vs. 21.6%; moderate CoE). There was no difference in recovery between molnupiravir and favipiravir (high CoE) and nirmatrelvir-ritonavir and molnupiravir (low CoE). Evidence for many outcomes is limited. Three COVID-19 antivirals improved or accelerated recovery, with varying adverse event profiles. Molnupiravir probably offers long-term benefits. American College of Physicians. (PROSPERO: CRD420251029146; OSF: https://osf.io/ywp6u).

PMID 41662710
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PubMedAdvanced science (Weinheim, Baden-Wurttemberg, Germany)2025-12-13

Structure-Based Development of Ultra-Broad-Spectrum 3C-Like Protease Inhibitors.

Su Haixia H, Nie Tianqing T, Chen Guofeng G, Xiong Muya M et al.

Recurrence of coronavirus outbreaks and zoonotic origins of human coronaviruses underscore the importance of developing pan-coronavirus antivirals. The highly conserved 3C-like protease (3CLpro) in coronaviruses, together with the well-established druggability, makes it an ideal target for broad-spectrum antiviral therapeutics. Here, the inhibitory activity of approved 3CLpro inhibitors, including nirmatrelvir, ensitrelvir, and simnotrelvir, against fifteen 3CLpros is first reported by enzymatic assays. Despite their potent inhibition toward 3CLpros of β-CoVs, these inhibitors show reduced potency against 3CLpros from the other three genera, particularly against two newly identified human coronaviruses (α-CCoV-HuPn-2018 and δ-PDCoV). In this context, continued efforts in structure-based optimization of nirmatrelvir lead to the identification of compound 8 that potently inhibits a panel of 32 3CLpros across all subgenera (IC50s: 19-146 nm), with an IC50 value of 61 and 81 nm against α-CCoV-HuPn-2018 and δ-PDCoV 3CLpros, respectively. Moreover, it effectively inhibits nirmatrelvir-resistant 3CLpro mutants and demonstrates broad-spectrum antiviral efficacy in cells. These findings suggest an important rule that a small, non-cyclic P2 segment and a P4 segment with a suitable size are preferred by the design of ultra-broad-spectrum 3CLpro inhibitors, and provide a proof-of-concept guide for developing broad-spectrum antivirals as potential pan-CoV therapeutics.

PMID 41388583
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