Expression of LHRH receptors in prostate cancer cells prior to therapy, following castration, or following treatment with LHRH agonists

Abstract

5163 Background: In the treatment of advanced prostate cancer, the effects of luteinizing hormone releasing hormone (LHRH) agonists are mediated through the down-regulation of pituitary LHRH receptors, inhibiting the pituitary-gonadal axis. Several groups have demonstrated LHRH receptor expression on prostate cancer cells. These tumoral receptors have been shown to mediate direct inhibitory effects in vitro. That expression of LHRH receptors persists in the castrate resistant state. To date, there is no information on LHRH receptor expression on the prostate after LHRH agonist therapy. This study investigates the expression of LHRH receptors following prolonged exposure to LHRH agonists. Methods: Expression of LHRH receptors was determined using immunohistochemistry and the intensity was graded on a scale from zero to 3. The expression was analyzed in three cohorts of patients: (1) 47 men with localized prostate cancer treated with radical prostatectomy with no hormone therapy, (2) 61 men with localized prostate cancer treated with neoadjuvant LHRH agonists for varying duration prior to prostatectomy, and (3) 22 men with metastatic prostate cancer who received a palliative transurethral resection of the prostate after clinical progression. In the final cohort, 15 men were treated with castration and 7 were treated with LHRH agonists. Results: 45 of 47 hormone naïve samples (95.7%) demonstrated LHRH receptor expression. Statistical analysis revealed a correlation between strong receptor expression and higher pathologic tumor stage as well as shorter overall survival. 60 of 61 samples treated with neoadjuvant LHRH agonist therapy (98.4%) demonstrated LHRH receptor expression. All 22 samples from patients with metastatic disease demonstrated LHRH receptor expression. The majority of these samples demonstrated moderate to strong intensity. Conclusions: LHRH receptors are expressed on prostate cancers cells of hormone naïve and castrated patients. The expression of these receptors appears to persist despite prolonged treatment with LHRH agonists. The continued expression of these receptors supports the concept of targeting prostatic LHRH receptors to deliver cytotoxic therapy based on LHRH analogs, such as AN-152. [Table: see text]