The Inhibition of NS2B/NS3 Protease: A New Therapeutic Opportunity to Treat Dengue and Zika Virus Infection

Abstract

In the global pandemic scenario, dengue and zika viruses (DENV and ZIKV, respectively), both mosquito-borne members of the flaviviridae family, represent a serious health problem, and considering the absence of specific antiviral drugs and available vaccines, there is a dire need to identify new targets to treat these types of viral infections. Within this drug discovery process, the protease NS2B/NS3 is considered the primary target for the development of novel anti-flavivirus drugs. The NS2B/NS3 is a serine protease that has a dual function both in the viral replication process and in the elusion of the innate immunity. To date, two main classes of NS2B/NS3 of DENV and ZIKV protease inhibitors have been discovered: those that bind to the orthosteric site and those that act at the allosteric site. Therefore, this perspective article aims to discuss the main features of the use of the most potent NS2B/NS3 inhibitors and their impact at the social level.

Keywords: NS2B/NS3 serine protease; antiviral agents; dengue virus; orthosteric and allosteric inhibitors; zika virus.

Figure 1

Catalytic cycle of the serine protease NS3pro has a functional catalytic triad comprising the His51, Asp 75, and Ser135 amino acid residues. Then, the cleavage of peptidic substrates begins by a Ser135 -nucleophilic attack to the carbonyl group at the P1 position. Due to the inherent poor nucleophilicity of the hydroxyl group from the Ser135, it should be previously activated by the action of an adjacent His51 residue, generating the Ser135–O− nucleophile (I). Subsequently, the stabilization of this complex into the oxyanion hole via H-bond interactions with Gly 153 residue favors the formation of a tetrahedral intermediary (II). This tetrahedral state is decomposed and results in the C-terminal cleavage, releasing an amine fragment. The N-terminal fragment remains covalently connected to the protease via an ester bond, which is posteriorly hydrolyzed by the action of a water molecule. In this step, His 51 acts as a base in order to increase the nucleophilic character of this water molecule (III). Finally, the N-terminal fragment is released by reprotonation of the carboxylic acid, beginning a new catalytic cycle (IV).

Figure 2

Structure of the lead compound 1.

Figure 3

Structure and activity against ZIKV and DENV2 proteases of proline-based allosteric inhibitors 2–8.

Figure 4

Structure of allosteric inhibitors without proline 9–10.

Figure 5

Structure and activity against ZIKV and DENV2 proteases of allosteric inhibitors 11–14.

Figure 6

Allosteric inhibitors of the DENV and ZIKV NS2B/NS3 proteases.

Figure 7

Allosteric inhibitors of the DENV and ZIKV NS2B/NS3 proteases 17–22.

Figure 8

Structure and activity against ZIKV and DENV2 proteases of the pyrazine-based allosteric inhibitor 23.

Figure 9

Retro-tripeptide inhibitor 24.

Figure 10

Met-Pro dipeptide inhibitor 25 and its fused-bicyclic derivate 26.

Figure 11

Peptidomimetics against DENV 1-4 NS2B/NS3 protease 27–30.

Figure 12

Structure of inhibitors 31–35.

Figure 13

Structure of inhibitors 36 and 37.

Figure 14

Peptide-hybrid inhibitor 38 of DENV2.

Figure 15

Peptidomimetics 39 and 40 containing a boronic acid as a warhead.

Figure 16

Inhibitors endowed with an aldehyde warhead 41 and 42.

Figure 17

Inhibitor 43 endowed with an aldehyde warhead.

Figure 18

Structure of polypeptide 44 and of the cyclic peptide 45.

Figure 19

Cyclic peptide 46.

Figure 20

Structure of inhibitor 47.

Figure 21

Peptide aldehyde inhibitor 48 of NS2B/NS3 protease from ZIKV.

Figure 22

Inhibitors against NS2B/NS3 protease from ZIKV.

Figure 23

Macrocyclic inhibitors 52 and 53 of NS2B/NS3 protease from ZIKV.