Possible mechanism responsible for the acquisition of resistance to cis-diamminedichloroplatinum (II) by cultured human testicular seminoma cells

Purpose: We established a cis-diamminedichloroplatinum (II) (CDDP) resistant cell line and determined the mechanisms of CDDP resistance. Materials and Methods: The CDDP resistant cell line JKT/DDP was established from the highly metastatic human testicular seminoma cell line JKT-HM by long-term intermittent administration of low dose CDDP. Growth curves, CDDP sensitivity and intracellular CDDP concentrations were compared in JKT/DDP, the seminoma cell line JKT-1 and JKT-HM cells. Expression of the mRNA of MDR1, MRP, LRP and GST-pi was also compared. Results: The growth curve and doubling time of JKT/DDP were similar to those of JKT-1 and JKT-HM in culture without CDDP but different with CDDP added to the culture. Morphologically cytoplasm segmentation and chromatin aggregation in JKT-1 and JKT-HM were observed when CDDP was present, while JKT/DDP cells were spindle-shaped and showed cobblestone growth. The IC50 for CDDP determined by the collagen gel drop embedded drug sensitivity test showed that JKT/DDP was more resistant to CDDP than the other 2 cell lines. The expression of MDR1, MRP and GST-pi was higher than in JKT-1 or JKT-HM cells and the intracellular CDDP concentration was lower in JKT/DDP. Conclusions: The JKT/DDP cell line acquired CDDP resistance by increased cytoplasmic CDDP metabolism.