EVIDENCE FOR A NOVEL MECHANISM OF ANDROGEN RESISTANCE IN THE HUMAN PROSTATE-CANCER CELL-LINE, PC-3

Progression to hormone-refractory disease is a common outcome of human prostate cancer. In this study, we have investigated the basis of and rogen insensitivity in the human prostate cancer cell line, PC-3, whic h was derived from a bone metastasis of a hormone-refractory prostate cancer. PC-3 cells with virtually undetectable (PC-3(AR-)) or low (PC- 3(AR+)) levels of androgen receptor (AR) RNA expression were examined. RNase protection assays demonstrated that the level of AR RNA in PC-3 (AR+) cells was similar to that in a normal androgen-responsive genita l skin fibroblast cell strain. Quantitative immunocytochemical stainin g of AR in PC-3(AR+) cells using antibodies directed against the amino and carboxyl termini of the receptor revealed staining in 30% of cell s with either antibody. Furthermore, the level of AR staining in PC-3( AR+) cells was higher than in the androgen-responsive breast cancer ce ll lines ZR-75-1, T47-D, and MCF-7. Despite the expression of AR RNA a nd protein, PC-3(AR+) cell proliferation was unaffected by the presenc e of 0.1-10 nM mibolerone. Scatchard analysis demonstrated a complete absence of specific [H-3]dihydrotestosterone ([H-3]DHT) binding to PC- 3(AR+) cytosolic extracts, which could not be explained by structural alterations in the AR gene. The sizes of individual AR exons amplified from genomic DNA derived from PC-3(AR+) cells were identical to those amplified from normal human cells. Furthermore, sequence analysis did not reveal a mutation in the DNA- or hormone-binding domains of the A R gene in PC-3(AR+) cells. These data demonstrate that PC-3(AR+) cells express AR RNA and protein of apparently normal structure and, in vie w of the inability to detect specific ligand binding to the AR, imply the existence of a novel mechanism for the androgen insensitivity of t his prostate cancer cell line.