Rationale and clinical implication of combined chemotherapy with cisplatin and oestrogen in prostate cancer: primary evidence based on methylation analysis of oestrogen receptor‐α

OBJECTIVE To determine whether oestrogen enhances platinum sensitivity, and if promoter CpG methylation of the oestrogen receptor-α (ER-α) gene determines the potential of cisplatin-induced apoptosis in prostate cancer, as the high-mobility group 1 (HMG1) preferentially binds to cisplatin-modified DNA and is up-regulated after oestrogen treatment in breast cancer cell line MCF-7. MATERIALS AND METHODS The study comprised prostate cancer cell lines (LNCaP and PC-3), 156 pathologically confirmed 156 radical prostatectomy samples and eight hormone-refractory prostate cancer (HRPC) samples (from needle biopsy). Expression of HMG1 in cell lines was analysed by Western blotting or differential reverse-transcription-polymerase chain reaction (PCR). The methylation status of ER-α was analysed by methylation-specific PCR using bisulphite DNA as a template or bisulphite DNA sequencing. RESULTS In LNCaP cells, treatment with oestrogen increased HMG1 expression and co-treatment with cisplatin and oestrogen reduced cell viability by accelerating apoptosis, compared with cisplatin alone. However, in PC-3, oestrogen did not up-regulate HMG1 or accelerate the cisplatin-induced apoptosis. Although ER-β was expressed in both LNCaP and PC-3, ER-α was expressed only in LNCaP. Bisulphite DNA sequencing of the ER-α promoter showed partial methylation in LNCaP but complete methylation in PC-3. ER-α AS transfection diminished the cisplatin-induced apoptosis in oestrogen-treated LNCaP cells. In clinical samples there was ER-α hypermethylation in 40% of prostate cancers this correlated with Gleason score (GS, 31% for GS   7). In addition, five of eight HRPC samples showed ER-α hypermethylation. CONCLUSION These findings suggest that HMG1 induction as an enhancer of platinum sensitivity is mediated through interaction between oestrogen and ER-α. As CpG hypermethylation of the ER-α promoter is a frequent event in aggressive prostate cancer, negative conversion of ER-α methylation is essential to achieve the most beneficial effect when combined chemotherapy of cisplatin with oestrogen is used in patients with prostate cancer.