Effect of ionizing radiation exposure and combined effect of radiation and conjugates of dendritic polymers with doxorubicin on the population of MCF-7 breast cancer stem cells

It is known that cancer stem cells (CSCs) represent the radio- and chemoresistant fraction of many malignant tumors, including breast cancer. Therefore efforts of specialists in the fields of experimental oncology and radiobiology have been directed towards the development of means/methods for eliminating CSCs and (or) increasing its sensitivity to known anticancer agents, in particular nanoparticles-based compounds. Polyamidoamine dendrimers of the second generation (G2), covalently conjugated with doxorubicin (Dox) and vector protein (alpha-fetoprotein recombinant third domain - 3D) were used in the presented study. Effect of ionizing radiation and combined effect of radiation and anticancer agents, such as free Dox, second generation dendrimers loaded with Dox (G2-Dox), and conjugates of the same dendrimers with the vector protein and Dox (3D-G2-Dox), on intracellular Dox content and the changes in the number of stem and non-stem cancer cells of MCF-7 breast cancer line were compared. CSCs were identified with flow cytometry by their ability to pump the fluorescent dye Hoechst33342 into the extracellular medium and form slightly stained side population (SP). The use of all studied compounds resulted in relatively low intracellular content of Dox in CSCs (SP) compared to that in the other cells (NSP). These findings largely explained the different cytotoxic effects of these compounds on different cell populations. The absolute number of NSP cells decreased, while the number of SP cells tended to increase under the influence of all Dox compounds used in the study. As a result, the average number of SP cells increased by 13.1%, 4.2%, and 3.4% after incubation with free Dox, G2-Dox and 3D-G2-Dox, respectively (p