Chemotherapy is usually the subsequent treatment for
non-small cell lung cancer patients with acquired radioresistance after long-term fractionated
radiotherapy. However, few studies have focused on the selection of chemotherapeutic drugs to treat
lung adenocarcinoma patients with radioresistance. Our study compared the sensitivity changes of
lung adenocarcinoma cells to conventional chemotherapeutic drugs under radioresistant circumstances by using three
lung adenocarcinoma cell models, which were irradiated with fractionated X-rays at a total dose of 60 Gy. The results showed that the toxicities of
paclitaxel,
docetaxel and
SN-38 were increased in radioresistant cells. The IC50 values of
docetaxel and
SN-38 decreased 0 ~ 3 times and 3 ~ 36 times in radioresistant cells, respectively. Notably, the A549 radioresistant cells were approximately 36 times more sensitive to
SN-38 than the parental cells. Further results revealed that the downregulation of the efflux transporter BCRP by long-term fractionated irradiation was an important factor contributing to the increased cytotoxicity of
SN-38. In addition, the reported
miRNAs and transcriptional factors that regulate BCRP did not participate in the downregulation. In conclusion, these results presented important data on the sensitivity changes of
lung adenocarcinoma cells to chemotherapeutic drugs after acquiring radioresistance and suggested that
irinotecan (the
prodrug of
SN-38) might be a promising drug candidate for
lung adenocarcinoma patients with acquired radioresistance.