IDENTIFICATION OF GENETIC CHANGES ASSOCIATED WITH DRUG-RESISTANCE BY REVERSE IN-SITU HYBRIDIZATION

The molecular cytogenetic techniques of comparative genomic hybridizat ion (GGH) and reverse in situ hybridization (REVISH) allow the entire genomes of tumours to be screened for genetic changes without the requ irement for specific probes or markers. In order to define the ability of REVISH to detect and map regions of amplification associated with drug resistance, we investigated a panel of cell lines selected for re sistance to doxorubicin and intrinsic sensitivity to topoisomerase II- inhibitory drugs. We have defined a modified REVISH protocol, which in volves double hybridizations with genomic DNA from the test cell lines and chromosome-specific whole chromosome paints to identify the chrom osomes to which the amplicons localize. Sites of amplification are the n mapped by fractional length measurements (Flpter), using published g enome databases. Our findings show that amplification of the topoisome rase II alpha gene is readily detected and mapped, as is amplification of the MDR and MRP loci. Interestingly, REVISH detected a new amplico n in the doxorubicin-resistant lung cancer cell tine, GLC4-ADR, which mapped to chromosome 1q. REVISH is therefore ideally suited to charact erize genetic changes specific for drug resistance within a background of genetic anomalies associated with tumour progression.