NECESSITY OF TRANSLOCATION DOMAIN FOR REALISATION OF CYTOSTATIC EFFECT OF NON-TOXIC DERIVATIVES OF DIPHTHERIA TOXIN

The aim of the work was to evaluate in vitro the cytostatic effect of recombinant fragments of the non-toxic point mutant of diphtheria toxin — CRM197, which was suggested as a potent medication for treatment of triple negative breast cancer. For this purpose, non-toxic recombinant derivatives of diphtheria toxin — CRM197, subunit B SbB and receptor domain Rd had been isolated by Ni-NTA agarose affinity chromatography and their effect on the growth of individual colonies of triple negative breast cancer MDA–MB–231 cells were characterized by such parameters as average colony area, perimeter and circularity index. According to the obtained results, CRM197 and SbB, whose molecules contain the translocation domain Td, exhibited the same cytostatic effect against MDA–MB–231 cells, reducing the area and perimeter of individual colonies. Rd protein did not affect the last two parameters that characterize the size of the colonies, but changed the form of the margin of colonies, as evidenced by an increase in the circularity index. It is supposed that Td may be involved in the implementation of cytostatic action due to its inherent pore-forming activity in relation to lipid membranes. It is concluded that Rd and Td, unlike the catalytic domain of diphtheria toxin, play important roles in the implementation of the cytotoxic properties of CRM197, while SbB consisting of Rd and Td is the structural DT fragment of smallest molecular weight that can be used as the analog of CRM197.