Determination of the proliferative fraction of a transplantable, hormone-dependent, human prostatic carcinoma (PC-82) by monoclonal antibody Ki-67: potential application for hormone therapy monitoring.

The transplantable, hormone-dependent, human prostatic carcinoma PC-82 was used as an in vivo model for monitoring the proliferative fraction of tumor cells under the influence of androgen withdrawal and resubstitution. The number of cycling cells was assessed by means of an immunoperoxidase method and monoclonal antibody Ki-67. The number of Ki-67-positive tumor cells dropped from an average of 17% in androgen-supplemented, tumor-bearing female BALB/c mice to approximately 1.0% within 10 days after removal of the testosterone (T) implant. A similar effect was noted after castration of tumor-bearing male BALB/c mice. Androgen resubstitution after a 10-day period of T deprivation resulted in a rise in the tumor cell proliferation index to 20% within 4 days. The same pattern of response to androgen depletion and resubstitution also was found when the number of cycling cells in S phase was assessed by the 5-bromo-2'-deoxyuridine incorporation technique. Administration of supraphysiologic doses of T in intact male mice did not lead to an increase in the number of Ki-67-stained nuclei. Androgen manipulation did not influence the immunohistochemically assessed expression of prostatic acid phosphatase and prostate-specific antigen. The rapid effect of hormone deprivation and resubstitution in the tumor cell proliferation fraction suggests that monoclonal antibody Ki-67 can be used for monitoring the short-term effects of hormonal treatment of prostatic cancer.