EFFECT OF CISPLATIN EXPOSURE ON THE DEGREE OF N-MYC AMPLIFICATION IN SMALL-CELL LUNG-CARCINOMA CELL-LINES WITH N-MYC AMPLIFICATION

To know whether the degree of N-myc gene amplification would change or not by the treatment with chemotherapeutic agents, we studied the eff ect of cisplatin (CDDP) exposure on the degree of amplification of the N-myc gene in two small cell lung carcinoma (SCLC) cell lines with N- myc amplification (H-69, SBC-4). The N-myc gene was amplified around 6 0-fold in H-69 and 40-fold in SEC-4 cells compared with placenta tissu es, and these two cell Lines were more resistant to CDDP than the nine other SCLC cell lines without N-myc amplification. H-69/CP cells beca me 4.1 times and SBC-4/CP cells 2.1 times more resistant to CDDP compa red to their parent cells by continuous in vitro exposure to CDDP. How ever, there was no significant difference in the degree of amplificati on or overexpression of the N-myc gene between parent and CDDP-resista nt cells in both cell lines. Namely, the degree of N-myc amplification did not show a significant change by making these cells more resistan t to CDDP. These results suggest that (1) the amplification of the N-m yc gene may be unchangeable by chemotherapeutic agents, and (2) the de gree of CDDP resistance may not correlate with the degree of amplifica tion or overexpression of the N-myc gene, if activation of the N-myc g ene would be related to the drug resistance.