Cell-active carbazole derivatives as inhibitors of the zika virus protease

Abstract

Zika virus (ZIKV) infection recently resulted in an international health emergency in the Americas in 2015-16 and despite its high profile there is still no approved treatment for ZIKV infection with millions of people being at risk. ZIKV is a member of Flaviviridae family which includes prominent members such as dengue virus (DENV) and West Nile virus (WNV). One of the best validated targets for developing anti-flaviviral treatment for DENV and WNV infection is the NS2B/NS3 protease.However the inhibitors reported to date have shown limited promise for further clinical development largely due to poor cellular activity. Prompted by the conserved nature of the viral NS2B/NS3 protease across flaviviruses, we envisaged that small molecule inhibitors of the ZIKVpro may be developed by applying rational design on previously reported scaffolds with demonstrated activity against other flaviviral proteases. Starting with an earlier WNVpro hit we performed a scaffold hopping exercise and discovered that certain carbazole derivatives bearing amidine groups possessed improved potency and significant cellular activity against ZIKV. We successfully addressed various issues with the synthesis of novel N-substituted carbazole-based amidines thus permitting a targeted SAR campaign. The in vitro biochemical (ZIKVpro IC 50 0.5-0.8 µM) and cell-based (EC 50 1-2 µM) inhibitory profiles exhibited by the novel lead molecules described in this work, are among the best reported to date. Furthermore, these molecules possess capacity for further optimization of pharmacokinetics and may evolve to broad spectrum flaviviral protease inhibitors.

Antiviral Agents against Flavivirus Protease: Prospect and Future Direction

“…Initial efforts were made to develop peptide-based protease inhibitors with or without a serine trap moiety such as CF 3 -ketone, an aldehyde, or a boronic acid that may mimic the substrate to resemble the substrate binding mode of the viral polyprotein to the viral protease and block its activity by forming a stabilized inhibitor-protease intermediate. However, peptides are, in general, unstable in vivo and mostly non-permeable to cross cell membranes, so focus has now shifted to the development of small molecules against flavivirus protease [ 63 ].…”

Antiviral Agents Against Flavivirus Protease: Prospect and Future Direction

“…Initial efforts were made to develop peptides-based protease inhibitor with or without serine trap. However, peptides are in general unstable in vivo and mostly non-permeable to cross cell membranes, so focus now has changed to develop small molecule against flavivirus protease [57].…”

“…Rassias et al synthesized a series of novel N-substituted carbazole-based amidines as ZIKV protease inhibitors, and compound 4 (carbazole derivative) demonstrated its in vitro biochemical and cell-based inhibitory profiles against ZIKV with an IC50 of 0.52 μM and EC50 of 1.25 μM [57]. Using quantitative high throughput screenings (qHTS) for small-molecule protease inhibitors, Abrams et al [58] found that compounds 5 (MK-591) and 6 (JNJ-40418677) showed antiviral effects primarily through inhibition of the Zika viral protease with IC50 values of 3.0 µM and 3.9 µM, respectively.…”

Structure and Dynamics of Zika Virus Protease and Its Insights into Inhibitor Design

“…Several strategies, such as high throughput screening (HTS), computation-guided drug design, and fragment based drug discovery have been applied to develop protease in-hibitors [129][130][131][132][133]. The available inhibitors have been reviewed thoroughly [10,33,117,[134][135][136][137][138][139]. Inhibitors include substrate derived peptidic compounds, small molecules binding to the active site and allosteric inhibitors (Figure 5) [11].…”