GC376 is a 3CLpro inhibitor; inhibits the replication of viruses TGEV, FIPV and PTV with IC₅₀ values of 0.15, 0.2 and 0.15 μM.

IC50: 0.15 μM (TGEV), 0.2 μM (FIPV), 0.15 μM (PTV), 0.15 μM (229E), 1.1 μM (MHV), 5.3 μM (MNV-1), 0.6 μM (BCV)^[1]

GC376 covalently binds to Cys 139, Cys 147, and Cys 144 of NV 3CLpro, PV 3Cpro, and TGEV 3CLpro, respectively. GC376 is significantly effective against caliciviruses (NV and MNV-1), coronaviruses (TGEV, FIPV, MHV, 229E, and BCV), and picornaviruses (HRVs 18, 51, and 68, EV71, and PTV), with nanomolar or low micromolar IC₅₀s, except for FCV and HAV. Interestingly, FCV is less sensitive to GC376, with IC₅₀ of 35 μM. GC376 shows no or weak effectiveness against the replication of HAV in cells^[1]. Proteases from NV, MD145 or MNV-1 are inhibited by GC376 with a similar potency. The IC₅₀ values of GC376 against 3CLpro from NV, MD145, and MNV-1 are comparable among tested viruses^[2]. GC376 effectively inhibits the replication of NPI52-resistant viruses in cell culture as wild-type viruses, indicating that the mutation does not confer cross-resistance to GC376^[3].

GC376 exhibits favorable bioavailability and safety in cats. GC376 is rapidly absorbed after s.c. administration and the peak plasma level is reached within 2 hr after injection. The mean plasma drug concentrations remains above the 50% effective concentration (EC₅₀) value of the aldehyde form of GC376 (8 ng/mL) for 18 hrs post injection. Virus infected cats shows improvement in attitude and resolution of fever. The profound absolute lymphopenia observed in all cats prior to antiviral treatment also returns to normal before the next blood testing one week later^[3].

• [1]. Kim Y, et al. Broad-spectrum antivirals against 3C or 3C-like proteases of picornaviruses, noroviruses, and coronaviruses. J Virol. 2012 Nov;86(21):11754-62.

  [2]. Takahashi D, et al. Structural and inhibitor studies of norovirus 3C-like proteases. Virus Res. 2013 Dec 26;178(2):437-44.

  [3]. Yunjeong Kim, et al. Reversal of the Progression of Fatal Coronavirus Infection in Cats by a Broad-Spectrum Coronavirus Protease Inhibitor. PLoS Pathog. 2016 Mar 30;12(3):e1005531.

The stock solution (10 mM) of GC376 is prepared in DMSO and further diluted in assay buffer. The final concentrations of DMSO in the assay did not exceed 1.5% (vol/vol). The 3CLpro from NV, MD145 or MNV-1 are incubated with various concentrations (0.01 to 50 µM) of GC376 in 25 µL of assay buffer for 30 min at 37 °C. Following incubation, 25 µL of assay buffer containing substrate is added, and the mixtures are incubated in a 96-well black plate at 37 °C for 60 min. The fluorescence signals are detected using an excitation and emission wavelength of 490 and 520 nm on a fluorescence microplate reader. The RFU are calculated for each well, and the dose-dependent FRET inhibition curves are fitted with variable slope (four parameters) using GraphPad Prism software in order to determine the IC₅₀ values of GC376^[2]. MCE has not independently confirmed the accuracy of these methods. They are for reference only.

• [1]. Kim Y, et al. Broad-spectrum antivirals against 3C or 3C-like proteases of picornaviruses, noroviruses, and coronaviruses. J Virol. 2012 Nov;86(21):11754-62.

  [2]. Takahashi D, et al. Structural and inhibitor studies of norovirus 3C-like proteases. Virus Res. 2013 Dec 26;178(2):437-44.

  [3]. Yunjeong Kim, et al. Reversal of the Progression of Fatal Coronavirus Infection in Cats by a Broad-Spectrum Coronavirus Protease Inhibitor. PLoS Pathog. 2016 Mar 30;12(3):e1005531.

507.53

C₂₁H₃₀N₃NaO₈S

1416992-39-6

Room temperature in continental US; may vary elsewhere

DMSO; In Vivo: GC376 is dissolved in 10% ethanol and 90% PEG-400.

* "<1 mg/ml"="" means="" slightly="" soluble="" or="" insoluble.="" "≥"="" means="" soluble,="" but="" saturation="">