Encemab is ready for clinical trials

Siberian scientists have developed a unique drug for tick-borne encephalitis

Diana Khomyakova, "Science in Siberia" Photo by Yulia Pozdnyakova

Preclinical studies of the drug "Encemab", created at the Institute of Chemical Biology and Fundamental Medicine of the SB RAS on the basis of a humanized antibody against tick-borne encephalitis virus, have shown that this drug acts hundreds of times more effectively than human serum immunoglobulin, is completely non-toxic and safe for patients.

"We can get encephalitis from three different types of ticks – not only taiga (Ixodes persuicatus), but also Pavlovsky (Ixodes pavlovsky) and even pasture (Dermacentor reticulatus). By the way, in some regions of Altai, in pasture ticks, which are not considered dangerous at all, this virus occurs several times more often than in taiga ones," says Nina Viktorovna Tikunova, Doctor of Biological Sciences, Head of the Laboratory of Molecular Microbiology of the IHBFM SB RAS.

For emergency prevention of the disease, the victim is usually injected with human serum immunoglobulin specific against tick-borne encephalitis in the next two days after the bite. People who have already contracted the virus can be treated with this remedy. Moreover, the effect is most noticeable in severe clinical forms of the disease. However, the problem is that a modern drug is made from the blood plasma of donors living in foci of tick-borne encephalitis, which is why the patient receives, in addition to the necessary antibodies, a huge range of others that may be undesirable. In addition, in order for serum immunoglobulin to be effective, it has to be administered in fairly significant doses, and the body may react badly to a large amount of foreign protein. The question arises of replacing such a drug with an alternative one.

Scientists of the Institute of Chemical Biology and Fundamental Medicine SB RAS have developed the drug "Encemab" from a chimeric antibody against tick-borne encephalitis virus. It is based on monoclonal antibodies, a large panel of which was obtained in the IHBFM several decades ago.

A chimeric antibody is an antibody created from parts of protein molecules from two different sources (for example, a mouse and a human). Its molecule contains two fundamentally different parts. One of them, the smaller one, binds the antigen, and the other, the larger one, triggers all the necessary reactions in the body. It is necessary that the second part be exactly human, otherwise the answer will be unpredictable and the treatment will not take place. Monoclonal antibodies are antibodies produced by immune cells belonging to the same clone, that is, originating from the same plasma progenitor cell.

"We have checked how the drug works in emergency prevention. To begin with, the mice were injected with lethal doses of tick–borne encephalitis virus, and a day later - an antibody in dosages of 1 and 10 micrograms per kilogram of weight, and in all cases 100% of the mice survived. Serum immunoglobulin ensured the salvation of mice only in 10% of cases, and in order for at least 70% of them not to die, it was necessary to inject one milligram of a commercial drug per kilogram of weight," says Nina Tikunova. – The question arose in conducting a full range of preclinical studies with subsequent access to clinical trials."

The experimental part of the work consisted in confirming the specific antiviral activity of the drug, the study of pharmacokinetics, acute and subchronic toxicity and immunological safety and was carried out jointly with colleagues from the Tomsk branch of the NGO "Microgen" of the Ministry of Health of Russia and the branch of the Institute of Bioorganic Chemistry named after M.M. Shemyakin and Yu.A. Ovchinnikov of the Russian Academy of Sciences (Pushchino).

It is believed that a tick with its bite can transmit to a person from five to eight lethal doses for mice.

"At the stage of testing antiviral activity, it turned out: on the one hand, the created chimeric antibody can work as a drug for emergency prevention, and on the other – as a therapeutic. Because of this, the volume of necessary preclinical studies has increased. It was necessary to assess chronic toxicity with a single administration, and with multiple (during treatment, the drug is administered several times). Thus, the work on toxicology was doubled," Nina Viktorovna reports. In addition, in both these cases, it was necessary to do pharmacokinetics for intravenous and intramuscular administration, which completely divided the preclinical trials into four parts.

Toxicity studies were conducted at the branch of the Institute of Bioorganic Chemistry of the Russian Academy of Sciences in Pushchino. The provided drug was tested against a comparison drug – human immunoglobulin against tick-borne encephalitis (solution for injection manufactured by FSUE NPO Microgen of the Ministry of Health of the Russian Federation). Encemab was tested in two doses, 10 and 20 times higher than therapeutic. And then an amazing thing was discovered: he showed absolutely no acute and chronic toxicity. When scientists submitted a report to the Ministry of Industry and Trade, they were told that this does not happen, the Ministry of Health simply will not give the go-ahead for further research. Then I had to redo the testing. They took a tenfold and a hundredfold dose. And here the drug turned out to be safe, while serum immunoglobulin, taken at a dose only 1.5 times higher than the therapeutic one, showed much worse results: some of the mice died, and the other suffered from fur spreading. In terms of pharmacokinetic behavior, Encemab did not differ from antibody-based drugs available on the market, nor did it affect the immune response.

"It is especially important that our drug did not have an antibody–dependent increase in infection," the researcher notes. The fact is that tick-borne encephalitis virus refers to flavivirus, which have one unpleasant effect found on Dengue fever: if a person has had an infection caused by the Dengue virus of one genotype, and has contracted another, then the severity of the disease was much higher, up to a fatal outcome. Accordingly, this makes vaccination dangerous. It was especially important for scientists to prove that the created drug does not have such an effect.

"Now we can compare Encemab with human immunoglobulin against tick-borne encephalitis. First, one dose of the first (what needs to be administered to a person based on 10 kg of weight) it is only 2 mg of protein, while the other has 100-160 mg. Secondly, our drug contains a single specific antibody, and the commercial one contains the entire spectrum of antibodies from the blood plasma of donors living in epidemic foci. Thirdly, Encemab has much higher specific activity, – says Nina Tikunova. – We also noticed that different batches of commercial antibodies differ in the ratio of protein-antiviral activity. And finally, donor blood is required for the production of immunoglobulin, and neither human nor animal blood is needed to create an Encemab," says Nina Tikunova.

To date, preclinical studies of the drug have been fully completed. Anticipating possible questions about the absence of toxicity, scientists are redoing the work on the study of chronic toxicity with large doses. But the developed drug can already be registered with the Ministry of Health in order to obtain permission for the first phase of clinical trials.

Portal "Eternal youth" http://vechnayamolodost.ru  06.07.2016