title: Chemosensitivity of radioresistant cells in the multicellular spheroids of A549 lung adenocarcinoma.
abstract: BACKGROUND
  The relapse of cancer after radiotherapy is a clinical knotty problem. Previous studies have demonstrated that the elevation of several factors is likely in some way to lead to the development of treatment tolerance, so it is necessary to further explore the problem of re-proliferated radioresistant cells to chemotherapeutic agents. In the present study, we aimed to investigate the chemosensitivity of radioresistant cells originated from the multicellular spheroids of A549 lung adenocarcinoma.
  
  
  METHODS
  After irradiated with 25 Gy of 6 MV X-ray to A549 multicellular spheroids, whose 10th re-proliferated generations were employed as radioresistant cells, and the control groups were A549 parental cells and MCF7/VCR resistant cells. The chemo-sensitivity test was made by six kinds of chemotherapeutic drugs which were DDP, VDS, 5-Fu, HCP, MMC and ADM respectively, while verapamil (VPL) was used as the reversal agent. Then the treatment effect was evaluated by MTT assay, and the multidrug resistant gene expressions of mdr1 and MRP were measured by RT-PCR.
  
  
  RESULTS
  Both A549 parental cells and A549 derived radioresistant cells were resistant to DDP, but sensitive to VDS, 5-Fu, HCP, MMC and ADM. The inhibitory rates of VPL to these two types of cell were 98% and 25% respectively (P < 0.001). In addition, without drugs added, the absorbance value (A value) of A549 parental cells was 2-folds higher than that of their radioresistant cells (P < 0.001). As to the MCF7/VCR cells, they were resistant to DDP and VDS, but slight sensitive to MMC, ADM, 5-Fu, and HCP with 80% of inhibitory rate to VPL. The subsequent RT-PCR demonstrated that the Mdr1/beta2-MG and MRP/beta2-MG of all A549 cells were about 0 and 0.7 respectively, and those of MCF7/VCR cells were 35 and 4.36.
  
  
  CONCLUSIONS
  The chemosensitivity of A549 radioresistant cells had not changed markedly, and the decreased sensitivity to VPL could not be explained by the gene expression of mdr1 and MRP. It is possible that the changes in the cell membrane and decreased proliferate ability might be attributed to the resistance. Unlike multidrug resistance induced by chemotherapy, VPL may be not an ideal reverser to radioresistant cells. Therefore, the new biological strategy needs to be developed to treat recurring radioresistant tumor in combination with chemotherapy.
authors.affiliation: Cancer Center, Zhujiang Hospital, Southern Medical University, Guangzhou 510282, PR China. shidegang@tom.com
authors.forename: Degang
authors.initials: D
authors.lastname: Shi
authors.forename: Genming
authors.initials: G
authors.lastname: Shi
authors.forename: Gang
authors.initials: G
authors.lastname: Huang
authors.forename: Jiren
authors.initials: J
authors.lastname: Zhang
authors.forename: Eric
authors.initials: E
authors.lastname: Lartigau
mesh_terms: D018435:ATP Binding Cassette Transporter, Subfamily B; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism; D000230:Adenocarcinoma / Q000188:drug therapy* / Q000473:pathology / Q000532:radiotherapy; D000970:Antineoplastic Agents / Q000494:pharmacology*; D001943:Breast Neoplasms / Q000188:drug therapy / Q000473:pathology / Q000532:radiotherapy; D002121:Calcium Channel Blockers / Q000494:pharmacology; D049109:Cell Proliferation; D002945:Cisplatin / Q000494:pharmacology; D019583:Dose Fractionation, Radiation; D004317:Doxorubicin / Q000494:pharmacology; D019008:Drug Resistance, Neoplasm; D005472:Fluorouracil / Q000494:pharmacology; D006801:Humans; D008175:Lung Neoplasms / Q000188:drug therapy* / Q000473:pathology / Q000532:radiotherapy; D016685:Mitomycin / Q000494:pharmacology; D011836:Radiation Tolerance / Q000187:drug effects*; D018874:Spheroids, Cellular / Q000187:drug effects* / Q000528:radiation effects*; D014407:Tumor Cells, Cultured; D014700:Verapamil / Q000494:pharmacology; D014751:Vindesine / Q000494:pharmacology; D014965:X-Rays
chemical_list: C513055:ABCB1 protein, human; D018435:ATP Binding Cassette Transporter, Subfamily B; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000970:Antineoplastic Agents; D002121:Calcium Channel Blockers; D016685:Mitomycin; D004317:Doxorubicin; D014700:Verapamil; D002945:Cisplatin; D014751:Vindesine; D005472:Fluorouracil