Inactivated Wild-Type Parainfluenza Virus 1

In the search for effective anti-paramyxovirus drugs, human parainfluenza virus type 1 hemagglutinin-neuraminidase (hPIV1-HN) inhibition kinetics offer a promising prospect. This study focuses on the potential of C5- and C4-modified 2,3-unsaturated sialic acid (DANA) inhibitors, with an emphasis on their interaction with the hPIV1-HN enzyme. It is shown that strategic substitution of the C5 isopropyl group in BCX 2798 with a trifluoroacetyl function increases the inhibitory potency by 3- to 4-fold. In parallel, the researchers explored the peculiar nature of the hPIV1-HN catalytic site, which contains only small substituents and prefers a C4 sulfonylamide function over a carbonyl function in contrast to the C4 pocket of Newcastle disease virus hemagglutinin-neuraminidase (NDV-HN). Based on these findings, the researchers propose a newly discovered class of potent inhibitors with preferred C5 trifluoroacetamide and C4 trifluorosulfonamide groups. The results of this study provide a foundation for a deeper understanding of the C4 and C5 binding sites of hPIV1-HN and facilitate the development of new, more selective inhibitors.

Here, the ability of azide derivatives to inhibit hPIV1 HN was investigated by performing a hemagglutinin inhibition assay (HI). Hemagglutinin activity inhibition (NI) assays were performed using chicken red blood cells (C-RBCs) according to the method of El-Deeb et al. Compounds were diluted in PBS and mixed with 4 hemagglutination units (HAU) of inactivated hPIV1 per well dilution. After incubation at room temperature for 20 minutes, the plates were transferred to ice, an equal volume of ice-cold 1% C-RBC was added to each well, and the hemagglutination results were read after incubation at room temperature for 1 hour and 30 minutes.

As shown in Figure 1, the IC₅₀ values of the two reference compounds DANA and BCX 2798 are consistent with those reported in the literature. Notably, the trend of the IC₅₀ values for the azide series was very similar to that observed in the NI assay. Compound 7 showed an IC₅₀ value of 2.0 μM, while its trifluorinated analogue 8 showed an IC₅₀ value of 0.25 μM, which is 8 times lower. Extension of the fluorinated chain resulted in a decrease in the inhibitory potency of compound 9 (IC₅₀ > 10 μM), while compound 10 partially restored the inhibitory potency (IC₅₀ = 7.5 μM). The study showed that a very potent hPIV1 inhibitor was found in compound 8, with neuraminidase inhibitory activity 3-4 times stronger than the current reference molecule BCX-2798. In addition, this molecule also inhibited hPIV hemagglutinin activity in the nanomolar range.

Figure 1. Hemagglutination and neuraminidase inhibition assays using hPIV1 (Sendai strain) to evaluate DANA, BCX 2798, and compounds 8–10 (azido series). (Rota P, et al., 2023)