Comparison of the malignant phenotype and genotype of the human androgen-independent cell line DU 145 and a subline derived from metastasis after orthotopic implantation in nude mice

To investigate the potential genetic changes underlying the progression of human hormone-resistant prostate cancer, we related chromosomal alterations of the DU 145 cell line and a subline isolated form a metastasis in an orthotopic model to tumorigenicity, metastasis and chemoresistance. In 15 mice 1 × 105 DU 145 cells were injected into the dorsal prostate. From a resulting paraaortic lymphnode metastasis, we isolated a subline (DU 145 MN1), which was injected into 15 nude mice. The sulforhodamine B (SRB) assay was used to analyze cell doubling time and the IC50 of cisplatin and 5-fluorouracil for both cell lines. Cytogenetic characterization was performed with conventional karyotype analysis and fluorescence in situ hybridization (FISH). After orthotopic implantation of DU 145 cells tumorigenicity was 100% whereas only 2 mice revealed lymphnode metastases. In contrast, the take rate after implantation of DU 145 MN1 was 100%, with lymphnode metastases in 7 mice. The SRB assay revealed a 8-fold increased IC50 for cisplatin and a 2.5-fold increase for 5-FU in DU 145 MN1 as compared to DU 145 cells. There was gain of a chromosome 8 and only two copies of chromosome 17 in the DU 145 MN1 cells as compared to the parental cell line. The emergence of an i(9)(q10) in addition to two normal chromosome 9 homologues in the DU 145 MN1 cell line was confirmed by FISH using a chromosome 9-specific painting probe. In summary, clonal evolution of the chromosomal changes following repeated orthotopic implantation, may assist in locating the genes involved in the progression and chemoresistance of human hormone-resistant prostate cancer.