Expression of Receptors for Luteinizing Hormone-Releasing Hormone (LH-RH) in Prostate Cancers following Therapy with LH-RH Agonists

Abstract

In addition to their expression on pituitary cells, receptors for luteinizing hormone-releasing hormone (LH-RH) are found on most prostate cancer cells. These tumoral LH-RH receptors mediate the direct cytotoxic effects of LH-RH analogs and are potential therapeutic targets. Although pituitary LH-RH receptors are downregulated following prolonged exposure to LH-RH agonists, there is no evidence that tumoral receptors behave in a similar manner. To better characterize expression of tumoral LH-RH receptors, specimens of prostate cancer from various cohorts of patients were analyzed. Surgical specimens were obtained from untreated patients with prostate cancer and from patients with metastatic castration-resistant prostate cancer previously treated with bilateral orchiectomy. To address the possibility of receptor downregulation, two additional cohorts of patients who had been previously treated with LH-RH agonists were included. One group received neoadjuvant therapy prior to prostatectomy, and the other group was treated for metastatic disease with LH-RH agonists and, at progression, required palliative resection of the prostate. Lymph node metastases from previously untreated patients were subjected to similar analysis. Expression of LH-RH receptors was found in most specimens. The relative expression of LH-RH receptor mRNA in untreated patients was greater in patients whose tumor had received a Gleason score <8. LH-RH receptor expression persisted despite prolonged exposure to LH-RH agonists. These findings support the concept of targeting cytotoxic LH-RH analogs to prostatic LH-RH receptors, using these receptors to gain entry into cancer cells to deliver a hybridized cytotoxic moiety for the treatment of prostate cancer.