Differential expression of DNA damage repair genes after chemoradiotherapy and inhibition rate in different bladder cancer cells

BACKGROUND: To investigate the potential mechanisms of chemoradiotherapy resistance in patients with bladder cancer. METHODS: We assessed three bladder cancer cell lines (5637, J82, and TCCSUP) for their sensitivity to chemoradiotherapy. Reverse transcription quantitative PCR (RT-qPCR) was used to detect the expression of specific genes after chemoradiotherapy or combined with olaparib. The Genome Cancer Atlas (TGCA) database was used to analyze possible radioresistance-related genes and the relationship between their expression and bladder cancer survival and prognostic indicators. RESULTS: The 5637 cell line showed the most significant sensitivity to chemoradiotherapy. The expression levels of DNA damage repair genes in 5637 cells did not significantly change after chemoradiotherapy. In contrast, the expression levels of BRCA1 and RBBP8 genes significantly increased in J82 and TCCSUP cells after chemoradiotherapy. After combination with olaparib, which is a poly (ADP-ribose) polymerase inhibitor that initiates DNA repair, 5637 cells were significantly inhibited by chemoradiotherapy. However, chemoradiotherapy inhibition on J82 cells was weakened when combined with olaparib. A high reactive expression of BRCA1 and RBBP8 after combination with olaparib suggested that olaparib was ineffective because it did not induce synthetic lethality in which inhibiting PARP by olaparib coincided with suppression of BRCA1/2 expression result in cancer cell death. CONCLUSIONS: The expression levels of RBBP8 and BRCA1 genes were associated with sensitivity to radiotherapy and chemotherapy in bladder cancer, and an increase in reactive expression after treatment led to worse sensitivity. Therefore, the reactive expression levels of BRCA1 and RBBP8 after chemoradiotherapy may be useful in evaluating the efficacy of olaparib combination therapy.