CCND1 overexpression and cisplatin resistance in testicular germ cell tumors and other human cancers

Development of resistance to cisplatin is a major issue leading to chemotherapeutic failure. Although many resistance mechanisms have been demonstrated, they are only responsible for a small proportion of clinically resistant cases. The genetic/molecular alterations responsible for drug resistance in the majority of clinical cases have not been identified. The aim of this study was to investigate the mechanisms leading to the resistance to platinum based therapy in testicular germ cell tumours (TGCTs), as well as in ovarian and prostate cancer. We analysed three pairs of cisplatin resistant and parental TGCT cell lines using Affymetrix expression microarrays (Human Genome U133 plus 2.0 arrays) and revealed a limited number of differentially expressed genes between the parental and resistant cells across all three cell lines. Among them, CCND1 was the most significantly differentially expressed gene. We confirmed that overall expression of CCND1 was significantly higher in resistant cases compared to sensitive samples in both fresh frozen and formalin-fixed, paraffin-embedded TGCT clinical samples by quantitative reverse transcription PCR analysis. Although CCND1 protein was not expressed or only expressed in a very small proportion of tumour cells in each TGCT sample, the resistant samples had a much higher proportion of cells expressing CCND1 than the sensitive cases. We also found that CCND1 was dramatically overexpressed both in induced and intrinsically resistant samples of ovarian and prostate cancers. Finally we knocked down CCND1 using siRNA and found that combined CCND1 knockdown and cisplatin treatment inhibited cell growth, decreased cell viability, and induced apoptosis in vitro significantly more effectively than any of these single treatments. In conclusion, we have demonstrated that deregulation of CCND1 is a major cause of cisplatin resistance in TGCTs and it may also be implicated in other human cancers. CCND1 could be used as a marker for treatment stratification and combined CCND1 inhibition and cisplatin chemotherapy may be valuable in treating the large number of CCND1 deregulated resistant tumours.