To evaluate the role of Her2/neu as a molecular marker predictive of the treatment response to bicalutamide in prostate cancer (PCa).

Four PCa cell lines with graded Her2/neu expression levels and 63 primary tumor cultures derived from men with PCa and selected according to Her2/neu tumor levels were used. Primary tumor cultures and PCa cell lines were treated with bicalutamide (0.1-10 μM) in the presence of dehydrotestosterone (10⁻¹² M) for 4 days. The presence of a significant correlation between Her2/nue expression and drug efficacy was used to define the role of Her2/neu as molecular predictor of bicalutamide effectiveness. As an indicator of drug effectiveness we used the concentration that inhibits 50% values determined after bicalutamide treatment.

After bicalutamide treatment, no significant differences in the concentration that inhibits 50% were found among the different tumor cell lines (P = .081). In this experimental model, the correlation analysis suggested that the effectiveness of this drug was not influenced by Her2/neu levels (r = 0.053, P = .823). In primary cultures with high Her2/neu levels (43 tumor cultures), the mean value of the concentration that inhibits 50% for bicalutamide was 0.43 ± 0.13 μM, and in cultures with low Her2/neu levels (20 tumor cultures), the same parameter was 0.5 ± 0.16 μM (P = .14). The correlation analysis suggested that the effectiveness of this drug was not influenced by Her2/neu levels (r = 0.33, P = .101).

Our biologic data seem to indicate that the antitumor effect of bicalutamide is independent of Her2/neu levels in preclinical models of PCa. Bicalutamide could be configured as a pharmacologic option to treat patients with high or low levels of Her2/neu.