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

To determine whether oestrogen enhances platinum sensitivity, and if promoter CpG methylation of the oestrogen receptor-alpha (ER-alpha) 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. 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-alpha was analysed by methylation-specific PCR using bisulphite DNA as a template or bisulphite DNA sequencing. 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-beta was expressed in both LNCaP and PC-3, ER-alpha was expressed only in LNCaP. Bisulphite DNA sequencing of the ER-alpha promoter showed partial methylation in LNCaP but complete methylation in PC-3. ER-alpha AS transfection diminished the cisplatin-induced apoptosis in oestrogen-treated LNCaP cells. In clinical samples there was ER-alpha hypermethylation in 40% of prostate cancers this correlated with Gleason score (GS, 31% for GS < 7, 50% for GS = 7 and 56% for GS > 7). In addition, five of eight HRPC samples showed ER-alpha hypermethylation. These findings suggest that HMG1 induction as an enhancer of platinum sensitivity is mediated through interaction between oestrogen and ER-alpha. As CpG hypermethylation of the ER-alpha promoter is a frequent event in aggressive prostate cancer, negative conversion of ER-alpha methylation is essential to achieve the most beneficial effect when combined chemotherapy of cisplatin with oestrogen is used in patients with prostate cancer.