Growth-inhibitory effect of prostasomes on prostatic cancer cell lines in culture

Objectives: Prostasomes, small corpuscular organelles derived from the prostate gland, were isolated from human seminal plasma for incubation with three human prostatic cancer cell lines: DU145, PC3, and LNCaP. The aim of this study was to establish any possible growth-inhibitory effect of prostasomes on prostatic cancer cell lines. Methods: Prostasomes were isolated from human seminal plasma. We determined their growth-inhibitory effect on the prostatic cancer cell lines by a fluorimetric cytotoxic assay technique. The results obtained were presented as survival index, defined as a percentage of control cultures, after compensation for blank values. Results: The prostasomes exhibited a dose-dependent growth-inhibitory effect on the cells, cell line DU145 being the most sensitive one displaying a survival index (mean I SD) of 46+/-10% at 200 mu g prostasomes (protein)/ml while the other two cell lines displayed survival indices of 93+/-6 and 93+/-9%. Heat treatment of the prostasomes abolished their growth-inhibitory effect on the cell lines, whereas 24-hour dialysis of the prostasomes did not affect their activity in this regard. Seminal plasma devoid of prostasomes exhibited less effect on the growth of these cancer cell lines, and heat treatment of the plasma did not influence the result. However, dialysis of the seminal plasma for 24 h abrogated its growth-inhibitory effect. Conclusion: The prostasomal growth-inhibitory effect on the cancer cell lines was different from that of the prostasome-free seminal plasma. The former effect was most probably of a proteinaceous nature while the latter effect was most likely due to the divalent cation composition of seminal plasma. In this regard, the zinc ion content seemed to be decisive. Copyright (C) 2000 S. Karger AG, Basel.