*4.7. RNA Extraction and Real-Time Quantitative PCR*

Total RNA was extracted from cancer cells according to the standard protocol as described elsewhere [41]. PCR reaction mix for real-time quantitative PCR (qPCR) has consisted of the following components: 1 µL synthesized cDNA, 5x qPCRmix-HS SYBR (PB025, Evrogen, Moscow, Russia), 10 mM each forward and reverse PCR primers for *RAD51* or control genes. Real-time qPCR was carried according to the manufacturer's protocol by the CFX96 Real-Time detection system (Bio-Rad, Hercules, CA, USA). The absolute levels of each mRNA were normalized relative to *GAPDH* as a control gene. The production of quantitative data based on the number of cycles required for the fluorescent detection amplifying of target genes (the Ct value). The relative level of expression of the target genes was based on the following formula 2−∆∆Ct .
