Accurate delivery
Siberian scientists have improved the delivery of systems against cancer and viruses
Alyona Litvinenko, "Science in Siberia"
Sometimes a gene does not work correctly in the body, which leads to the appearance of too large amounts of the protein encoded by it. In other cases, the wrong (mutant) protein is synthesized: all this affects health and can cause serious illness. To combat such "errors", so-called therapeutic nucleic acids are often used. The greatest difficulty in their application is delivery to the problem area (cells): Siberian scientists are trying to solve this question. An article about the study was published in the European Journal of Pharmaceuticals and Biopharmaceutics (Kabilova et al., Targeted delivery of nucleic acids into xenograft tumors mediated by novel folate-equipped liposomes).
Antisense oligonucleotides are one of the most developed classes of therapeutic nucleic acids. They got their name due to the fact that they are complementary (have opposite significance) to matrix RNA (mRNA), as well as viral RNA and bacterial mRNA encoding proteins, that is, molecules with a meaningful, semantic sequence.
Antisense oligonucleotides are capable of suppressing the expression of any gene at the level of matrix RNA, splitting it. Another mechanism of action is blocking translation (protein synthesis), when the ribosome simply cannot displace it when binding an oligonucleotide. As a result, the shortened protein with an irregular structure is disposed of and does not accumulate in the cell.
"There are a number of proteins whose overexpression is associated with cancer, inflammation, and so on. For example, during a viral infection, viral RNAs and proteins are synthesized in cells. Antisense nucleotide can suppress their synthesis, and therefore the spread of infection. At the moment, the main problem of using therapeutic nucleic acids is delivery to the right place: with intravenous administration, antisense oligonucleotides spread throughout the body and are quickly excreted by the kidneys, without having time to have the maximum effect," says Marina Arkadyevna Zenkova, Doctor of Biological Sciences, Head of the Laboratory of Nucleic Acid Biochemistry at the Institute of Chemical Biology and Fundamental Medicine SB RAS.
To solve this problem, the specialists of the IHBFM SB RAS are developing systems for the delivery of therapeutic nucleic acids that can not only send the drug to its destination, but also contribute to the preservation of its activity in cells, for example, in a tumor. As delivery systems, Siberian scientists use complexes based on cationic liposomes: particles up to 100 nanometers in size, constructed from cationic and neutral lipids (fat-soluble substances). Cationic liposomes bind to antisense oligonucleotides and protect them from the effects of adverse factors in the blood, as well as promote penetration into cells, since they resemble cell membranes in structure.
The most important component of the delivery system – cationic (positively charged) lipids of a unique structure – was developed by specialists of the Lomonosov Moscow Institute of Fine Chemical Technologies (now Moscow Technological University, Institute of Fine Chemical Technologies). Such lipids completely biodegrade in the human body, leaving only natural molecules that are not toxic. In addition, the substances do not cause the inclusion of a specific immune response and work equally actively with various therapeutic nucleic acids.
In addition, each cell has a set of receptors – complex protein structures capable of binding firmly to a specific molecule – ligand. If it is included in the complex, then such "addressed" liposomes, together with antisense oligonucleotides, will bind to cells on the surface of which there are receptors for this ligand.
"Usually tumor cells contain folic acid receptors on the surface. That is why it is often used as an addressing ligand in various drug delivery systems," explains Marina Zenkova. – In general, folic acid is necessary for the normal functioning of the cell. However, if the latter begins to overexpress folic acid receptors on the surface, most likely, the cell already acquires a malignant phenotype. Therefore, we have included this acid in the composition of liposomes so that it provides a specific, directed interaction with tumor cells."
The advantage of liposomal systems developed by scientists is that they can be prepared in advance. To do this, the chemically synthesized components of liposomes, including the folate-containing guide component, are mixed in an organic solvent and dried in a vacuum. Then the resulting lipid film is suspended in water, treated with ultrasound, packaged and stored in the refrigerator before use. If it is necessary to deliver nucleic acid, it is mixed with this solution in certain proportions and injected into the body – that is, such a treatment option is relatively inexpensive. Nucleic acid in combination with liposomes quickly reaches the tumor cells and remains in them in significant amounts even 24 hours after injection.
"Now we are trying to make even more complex addressing systems, looking for the possibility of attaching peptides, antibodies that can stimulate the capture of complexes by certain cells. The problem is that the most malignant tumors have few surface receptors – identification marks, so there is still a lot to work out," concludes Marina Zenkova.
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