Next-generation inhibitors of SARS-CoV-2 M<sup>pro</sup> overcome the deficiencies of Paxlovid.

Luo, Gan; Wang, Gang; Liao, Chongbing; Zhong, Baisen; Fan, Lianfeng; Zhang, Jue; Rao, Jie; Zhang, Junjie et al. · Nat Commun · 2026

basic_science · Level V

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Abstract

It remains elusive to design peptidomimetic inhibitors of SARS-CoV-2 main protease (M<sup>pro</sup>) refractory to multiple deficiencies of Paxlovid (ritonavir-boosted nirmatrelvir), pertaining mainly to E166X mutations-conferred drug resistance and inherent pharmacokinetic limitations to nirmatrelvir. We identify via virtual screening an iso-quinoline P1 moiety in place of the traditional γ-lactam and design iso-quinoline-containing inhibitors with high affinity for M<sup>pro</sup> and its nirmatrelvir-resistant E166X mutants. Further optimization at P4 cultivates distinctive peptidomimetic inhibitors with drastically improved pharmacokinetic properties and significantly enhanced antiviral efficacy independent of ritonavir. Two such inhibitors, FD3-32 and FD3-36, also potent against SARS-CoV-1 and MERS-CoV M<sup>pro</sup>, are more effective as a monotherapy regimen than Paxlovid in reducing viral loads in vivo and protecting infected male mice from acute lung injury. Here, we report the discovery of next-generation SARS-CoV-2 M<sup>pro</sup> inhibitors that overcome the deficiencies of Paxlovid, promising efficacious antivirals critical for mitigating the current and future pandemics of coronaviruses.