Nirmatrelvir

Krad DA, et al. Antiviral Research, 2025, 241, 106247.

Nirmatrelvir was experimentally applied as a selective SARS-CoV-2 main protease (MPro, 3CLPro) inhibitor to evaluate its antiviral efficacy in combination therapy. In vitro assays employed SARS-CoV-2-infected cell cultures treated with Nirmatrelvir alone or in combination with the GRP78 (HSPA5/BiP) inhibitor HA15. Antiviral activity was quantitatively assessed using multiple complementary methods, including cytopathic effect (CPE) observation, viral RNA quantification by RT-qPCR, TCID₅₀ infectious titer determination, and immunoblot analysis of viral non-structural proteins as well as Spike and N proteins. Both the ancestral SARS-CoV-2 strain and Omicron variants were tested to confirm strain-independent efficacy. To validate host-target involvement, additional experiments utilized alternative GRP78 inhibitors and siRNA-mediated GRP78 knockdown. In vivo efficacy was further examined in a hamster COVID-19 model, where pulmonary pathology was evaluated histologically. These experimental results demonstrate that Nirmatrelvir, when combined with GRP78 inhibition, achieves markedly enhanced suppression of viral replication through coordinated viral and host-directed mechanisms.