Identification of an endogenous inhibitor of prostatic carcinoma cell growth.

The rate of expansion of primary prostatic carcinoma is comparatively slow, with tumours frequently taking years or decades to reach clinically relevant size. We now report the presence of an endogenous inhibitor, derived from aqueous extracts of human prostate tissue, which blocks prostatic carcinoma cell proliferation in vitro and prevents subcutaneous tumour expansion in vivo. Purification and characterization revealed the inhibitor to be spermine, a polyamine known to be locally abundant in the prostate. These results suggest that endogenous polyamine can negatively regulate the growth of prostatic carcinoma cells at their primary site in vivo and may explain the slow rate of primary tumour expansion in the prostate.