Irradiation and chemotherapy drug effects on cancer stem cells (SP) of melanoma B16 and breast adenocarcinoma MCF-7

The existence of cancer stem cells (CSC), resistant to radiation and chemical exposure is one of the possible causes of cancer recurrence. Since regularities of changes of mentioned cell fraction are not well understood, this study examined relative and absolute CSC number in melanoma B16 and breast cancer MCF-7 stable cultures after low-LET irradiation and anticancer drugs treatment. CSC were identified using side population (SP) technique by the ability to exclude fluorescent dye Hoechst 33342. A linear dependence of the relative number of SP cells on the dose of radiation was found (R=0.98 for B16 and R=0.96 for MCF-7). There was an increase of SP cells absolute number after the exposure; this effect was the most expressed at doses of 5-10 Gy (3 and 5 times in B16 and MCF-7 cultures, respectively, as compared to control, p