COLCEMID RESISTANCE IN MURINE SEWA CELLS - NON-PGY GENE AMPLIFICATIONAT LOW-LEVELS OF RESISTANCE AND PREFERENTIAL PGY2 GENE AMPLIFICATION AT HIGH-LEVELS OF RESISTANCE

Mammalian cell lines often become multidrug-resistant to cytotoxic dru gs by amplification and/or overexpression of the P-glycoprotein (Pgy) genes. However, several malignant cell lines seem to acquire low level s of drug resistance by non-P-glycoprotein mediated mechanisms. We rep ort here on cytogenetical signs of non-Pgy gene amplification in murin e SEWA cells during the early steps of selection in Colcemid (COL). In line TC13COL0.01, rare cells exhibited a homogeneously staining regio n (HSR) distally in chromosome 16. As the COL-concentration was raised the HSR-chromosome was retained and, in addition, the cells developed numerous double minutes (DMs). The DMs, but not the HSR, contained am plified Pgy genes. The HSR may correspond to amplified heat shock prot ein 70 (Hsp70) genes, detected by Southern analysis. A second low-leve l COL-resistant line, TC13D70.01, contained DMs but showed no amplific ation of Pgy, Hsp70, Hsp90, alpha- or beta-tubulin genes. In higher CO L-concentration, P-glycoprotein mediated drug resistance was induced. In contrast to actinomycin D-resistant SEWA cells, in which higher amp lification levels of Pgy1 than of Pgy2 are regularly present, the COL- resistant lines showed a preference for Pgy2 gene amplification. These results are in line with the suggestion that the murine Pgy1 and Pgy2 genes have overlapping but distinct drug specificities.