The development of therapy-induced drug resistance is still one of the most important
therapeutic limitations. Nevertheless, an integrating view of the molecular mechanisms
underlying resistance development in general is missing. In order to shed some light
on the network of this resistance development, we established drug-resistant (doxorubicin
(DX), methotrexate (MTX), cisplatin (cisPt), vincristine (Vin)) derivatives of six
tumour cell lines (Jurkat, U937, HL60, DoHH-2, K562 and ARH77) of haematopoetic origin.
Differential gene expression of drug-sensitive parental cell lines and the drug-resistant
derivatives thereof was analysed by suppressive subtractive hybridisation. After dot
blot screening for differential expression and sequencing of the cloned PCR fragments,
differential expression was confirmed by Northern blot analysis. In an attempt to
discriminate for differentially expressed genes only related to one or the other of
the investigated drugs, the cDNAs of various resistant sublines (doxorubicin-, methotrexate-,
cisplatin-resistant Jurkat cells) were pooled and compared with the sensitive parental
cell line. In addition, cDNAs of the resistant derivatives of the different haematopoetic
tumour cell lines were pooled and compared with the pooled cDNAs of the corresponding
sensitive haematopoetic cell lines to eliminate cell line to cell line variations
that were not related to drug resistance. As a result of this screening, the following
genes showed a higher (at least 2-fold) or exclusive expression in the drug-resistant
variants: serglycin, sorcin, BMPG (bone marrow proteoglycan gene) and PTI-1 (prostate-tumour-inducing
gene 1). In addition, elevated expression of hsp90, previously found by our group
to be upregulated in the drug-resistant colon carcinoma cell line LoVo H67P was found
to be overexpressed in drug-resistant HL60 cells.