Nature: toremifene is expected to be an anti-Ebola drug

Fatal infections caused by Ebola virus (EBOV) break out frequently in recent years, and Ebola outbreak in West Africa caused a large number of deaths. There are no approved effective drugs or vaccines against EBOV. Since 2013, scientists have adopted a large number of small molecules and marketed drugs in vitro mouse model tests and computer virtual screening to find compounds of anti EBOV. In 2013, Johansen, LM et al., conducted experiments on a series of selective estrogen receptor modulators including anticancer drug toremifene, finding that they have potential inhibitory effect on EBOV virus. But they did not clarify the mechanism.

Recently, David I. Stuart and other researchers from the University of Oxford took EBOV outer membrane glycoprotein (GP) as the study object and found that toremifene can combine GP and reduce its stability, thereby blocking viral fusion with the endosomal membrane and playing anti-viral effect. They also resolved the crystal structure of GP protein and the complex of GP protein, toremifene and ibuprofen, clarifying the action mechanism of toremifene.

EBOV outer membrane has a three-glycoproteins (GP, furin protein is cut into two subunits GP1 and GP2), which is solely responsible for host cell attachment, fusion kernel entry and film. Thus, GP is the primary target for the development of antiviral drugs. The researchers used recombinant protein - recombinant EBOV outer membrane glycoprotein (GP) to test whether the nine compounds would bind directly to proteins through the method of protein thermal transfer. Experimental results showed that when the dose of toremifene was 100 μM and pH value was 5.2, it can significantly reduce the melting temperature (Tm) of EBOV GP to 14 ℃. This is opposite to the previously-reported research result that inhibitors reducing the melting temperature of proteins will increase the stability of protein structure. In contrast, ibuprofen showed only a very critical effect (Tm decrease rate was less than 2 ℃), lacking for potential virus inhibition.

The researchers also first reported EBOV GP protein with no ligand and high-resolution crystal structure of the GP and toremifene and ibuprofen complex. Surprisingly, toremifene and ibuprofen all combined in a hole between the subunits GP1 and GP2. This hole is located in a huge tunnel entrance, and this big tunnel can be connected with other similar tunnels. The interactions of drug and GP1, GP2 are mainly hydrophobic effect. In filamentous virus, amino acid residues which combine with these drugs are highly conserved, excepting Marburg virus (MARV), indicating that the Marburg virus probably will not be combined with these drugs. This work illustrates the suppression mechanism of drugs on viruses, providing a viable direction for the development of more anti-EBOV drugs. Flarebio Biotech LLC is a National High-Tech Enterprise with research, production and sales as one. And high-quality recombinant proteins such as recombinant NRG3 are offered at competitive prices.