Plastic antibodies

Antibodies from polymers will effectively mark and destroy cancer cells

Phys Tech blog on Naked Science website

An international group of researchers led by Nikolai Barlev, head of the MIPT Cell Signaling Laboratory, has shown the fundamental possibility of creating a new class of antitumor drugs based on nanoMIP – "plastic antibodies". This type of nanoparticles is a polymer synthetic analog of antibodies and is capable of specifically binding target proteins on the surface of cancer cells. In the future, the development of this approach may lead to a change in the existing paradigm in the development of new cancer treatments. The research was conducted by an international team of scientists from the University of Leicester (UK), University College London (UK), the Institute of Cytology of the Russian Academy of Sciences and MIPT. The work has been published on the pages of the magazine Nano Letters and was supported by an RNF grant.

Fig. 1. Scheme of binding of synthesized nanoMIPs to the cell surface. Polymer nanoparticles bind specifically to EGFR, while doxorubicin (shown in red) exits the nanoparticles and penetrates the cell membrane / MIPT Press Service

The synthesis of a polymer nanoparticle occurs in the presence of a target molecule, which leads to the formation of nanoMIP prints of the latter. This process can be compared to the removal of molds for casting, in which the final material retains the outlines of the model. It is called imprinting. At the same time, the resulting "forms" acquire the ability to specifically recognize and bind the "target" molecule. In the study, the tyrosine kinase receptor EGFR (epithelial growth factor receptor - epithelial growth factor receptor) was selected as a target. Its increased presence is observed in a wide range of tumors – from colorectal cancer, lung cancer, the most aggressive form of breast cancer, triple negative breast cancer, to brain tumors. It is because of these factors that EGFR became one of the first targets for anti-tumor drugs based on antibodies. In this work, nanoparticles were obtained by double imprinting against two target molecules – a linear epitope ("epitope" is a target site that is recognized by an antibody upon binding) EGFR and the cytotoxic drug doxorubicin. Thus, the final product can simultaneously bind to EGFR and have a therapeutic effect due to modification with doxorubicin.

Nikolay Barlev, Head of the MIPT Cell Signaling Regulation Laboratory: "Despite their effectiveness, antibody-based drugs are difficult to develop and expensive to manufacture. In the treatment of those forms of cancer in which EGFR overexpression is observed, specific monoclonal antibodies against this target (setuximab, or Erbitux®) are successfully used. However, due to the instability of this drug in the body, the patient regularly needs to inject a fresh portion of antibodies throughout the course of therapy. One such course for a patient costs about 100 thousand US dollars. Synthetic analogues of antibodies, such as nanoMIP, are devoid of these disadvantages, in addition, unlike biomolecules, in general, their stability does not depend on environmental conditions such as temperature and acidity, which means that the range of their possible use is wider. In the future, they can significantly expand the possibilities of diagnosis and treatment of a variety of diseases."

At the same time, for the synthesis of nanoMIPs capable of specifically recognizing and binding a certain protein, it is enough to create a "fingerprint" not of the entire molecule, but only of its small portion. This short oligopeptide is covalently (that is, with the formation of a chemical bond) "sewn" onto glass beads, which are then mixed with acrylamide monomers and doxorubicin. It is worth noting that polyacrylamide, unlike its own monomers, is a biologically safe material that is used, for example, in the production of soft contact lenses. As the temperature increases, polymerization of monomers occurs, and nanoparticles ranging in size from 100 to 200 nm with a molecular "fingerprint" of the target protein and doxorubicin included in them are formed. Unreacted monomers and non-specific nanoparticles are washed away, while synthesized "plastic antibodies" remain bound to glass beads (Fig. 2).

Fig. 2. nanoMIP synthesis scheme with an EGFR end fragment immobilized on glass beads / MIPT Press Service

Nikolay Barlev: "For the first time, we managed to obtain multifunctional nanoMIPs that combine the specificity of recognition of target proteins and the possibility of targeted delivery of various chemicals. Previously, this was impossible, since the synthesis technology did not allow to standardize the conditions for obtaining nanoMIP and the effectiveness of the resulting product was unpredictable. The use of solid-phase synthesis helped to solve this problem. The next step is the creation of ferromagnetic nanoMIPs, which allows us to further expand the functionality of "plastic antibodies" for both diagnosis and therapy of various diseases."

As part of the study, the scientists demonstrated moderate and specific toxicity of the obtained nanoparticles for cancer cells. Moreover, such toxicity was achieved exclusively due to the addition of doxorubicin during polymerization, since control nanoparticles that did not carry an antitumor drug did not affect the cells in any way. In addition, when therapeutic nanoMIPs were added, multiple DNA breaks were observed in the cells, characteristic of the effects of doxorubicin (this is the basis for its mechanism of action). Finally, the binding of "plastic antibodies" to EGFR additionally led to a decrease in the density of receptors on the cell surface.

Thus, the potential therapeutic effect of the developed nanoparticles for the treatment of EGFR-dependent tumors is due to three factors – the direct cytotoxic effect of the delivered antitumor drug, the masking of the receptor from its ligand and a decrease in the concentration of EGFR on the cell surface. The successful results of in vitro experiments indicate the prospects of using nanoMIP for specific drug delivery and are a good prerequisite for further research.

As part of the competition for the creation of academic laboratories with institutes of the Russian Academy of Sciences, a Laboratory for the Regulation of Cellular Signaling was opened on the basis of MIPT in June this year under the leadership of Nikolai Barlev. One of the areas of work of the new laboratory will be the further development of the technology of "plastic antibodies" for the treatment of tumors.

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