Targeting Radioresistant Breast Cancer Cells By Single Agent CHK1 Inhibitor Via Enhancing Replication Stress

Objective:The goal of our study is to seek for a better regimen targeting radioresistant breast cancer cells(RBCC).Methods:Using biomedical basically methods like Western blot, colony formation,immunofluorescence, comet assay, DNA fiber and Xenograft model to do the experiments.We defined the differences of DNA damage response(DDR) between the parental cells and the RBCC developed via long-term exposures to fractionated ionizing radiation(IR), and determined how CHK1 inhibitor affects cell killing with or without combination with IR.Results:DDR proteins ATR/CHK1/BRCA1/Ct IP were induced in RBCC. Consistent with this result, enhanced G2/M arrest and increased homologous recombination(HR) activity were observed in RBCC. Surprisingly, CHK1 inhibitor AZD7762 failed to sensitize RBCC to IR although it impaired G2/M arrest and HR activity. Strikingly, AZD7762 alone significantly inhibited the growth of RBCC in in vitro and in vivo assays. We hypothesize that CHK1 inhibition leads to the specific killing for RBCC due to its abrogation in the suppression of oncogenic stress. In agreement, the expression of oncogenes c Myc/CDC25A/c-Src/H-ras/E2F1 was elevated in RBCC compared to parental cells.Correspondingly, AZD7762 exposure led to significantly higher levels of single strand DNA/DNA double strand breaks/replication initiation and resulted in remarkably lower levels of deoxynucleotide supply/replication fork speed in RBCC in comparison to parental cells.