Background & objective: Developed from fluorescence in situ hybridization (FISH), comparative genomic hybridization (CGH) is a new molecular and cellular technique,used to examine the genomic imbalances,especially the loss and amplification of chromosomes,and to locate these alterations in certain chromosome regions. For a comprehensive understanding of the possible differences in genomic DNA between nasopharyngeal carcinoma drug-resistant and drug-sensitive cells, we analyzed the genomic DNA of a nasopharyngeal carcinoma drug-resistant cell line CNE2/DDP and its parent cell line CNE2 with CGH.
Methods: Genomic DNA was extracted from CNE2/DDP and CNE2 cells, as well as from normal placenta tissue. Fluorescent random primed labeling method was used to label the DNA probes (CNE2 and CNE2/DDP cells with green fluorescein-12-dUTP and normal placenta tissue with red tetramethylrhodamine-5-dUTP). The labeled DNA probes were then co-hybridized with normal lymphocyte metaphase chromosomes. Signals were taken by charge coupled device (CCD) and processed with Quips CGH Program after fluorescent hybridization. The green-to-red fluorescent ratio was calculated automatically and showed with graphs.
Results: There were extensive chromosome changes in CNE2, mainly the gain of 1q, 3q, 5p, 6p, 7p, 8q, 9q, 11p, 12q and 19q, and the loss of 4q, 12p, 13p, 14p, 15p, 18, 20q, 21p and 22. However, the CNE2/DDP cells, which come from the CNE2, showed a relatively normal karyotype except loss of 8p and gain of 8q and 19q. Consistent result was achieved after the CNE2/DDP cells were cultured in the medium free of any drugs for over one month. It appears that the CNE2/DDP cell has relative normal and much more stable chromosome constitution than its parent CNE2 cell.
Conclusion: The CNE2/DDP is a single drug-resistant clone selected from CNE2,which is a blend of sub-clones that have different sorts of chromosome number and structure. It strongly suggests that the appearance of tumor drug-resistance is mainly a select process in which the would-be drug-resistant cell clone be selected from unfavorable survival condition.