Differential response of prostate specific antigen to testosterone surge after luteinizing hormone-releasing hormone analogue in prostate cancer and benign prostatic hyperplasia

Agonists of luteinizing hormone-releasing hormone in prostate cancer

INTRODUCTION

Androgen deprivation therapy (ADT) has been the first-line standard of care for treating patients with hormone-sensitive advanced prostate cancer (PCa) for many decades. The agonists of luteinizing hormone-releasing hormone (LHRH), also called gonadotropin-releasing hormone, are still the most frequently used form of medical ADT.

AREAS COVERED

This article reviews the available data and most recent information concerning the use of LHRH agonists in advanced PCa. This article also reviews the discovery and development of LHRH agonists and summarizes the clinical evidence for their efficacy in PCa.

EXPERT OPINION

The introduction and application of agonists of LHRH has modernized and improved the treatment of advanced PCa. The life-saving benefits of LHRH agonists are well established, yet underestimated. Despite their efficacy, agonists of LHRH have several disadvantages or drawbacks including disease flare. The approach to ADT has been recently further refined with the development of the LHRH antagonist degarelix. Degarelix, a highly clinically effective third-generation LHRH antagonist, is currently available in most countries for therapy of advanced PCa. This new drug offers attractive alternatives to LHRH agonists for treatment of advanced PCa. A therapy for castration-resistant PCa based on a targeted cytotoxic analog of LHRH, AEZS-108, is also emerging.

Higher percentage of positive biopsy cores and Gleason score are associated with a greater degree of prostate gland shrinkage after neoadjuvant cytoreductive therapy

PURPOSE

To determine whether adverse pathologic features, including tumor grade and percent positive biopsy (PPB) cores, predict for prostate size reduction after neoadjuvant cytoreductive therapy.

METHODS AND MATERIALS

Eighty-two consecutive patients who were diagnosed with prostate cancer by transperineal template-guided mapping biopsy (TTMB) received neoadjuvant cytoreductive therapy. The median number of biopsy cores was 59. Thirty patients received a leutinizing hormone-releasing hormone agonist and bicalutamide, whereas 52 patients received bicalutamide (50mg daily) and dutasteride (0.5mg daily). A transrectal ultrasound volumetric study of the prostate gland and ellipsoid volume determinations of the prostate gland and transition zone (TZ) were obtained immediately before TTMB and at 90 days (±7 days) after the initiation of neoadjuvant medical therapy. Univariate and multivariate regression analyses were performed to identify predictors of prostate gland and TZ volume reduction.

RESULTS

At TTMB, the mean prostate volumetric and ellipsoid volumes were 55.4 cm(3) and 49.0 cm(3), respectively. After neoadjuvant medical therapy, the mean volumetric and ellipsoid prostate volumes were 30.8 cm(3) and 28.5 cm(3), respectively. On average, the prostate volume decreased by 43.9% and 41.0% on volumetric and ellipsoid measurements, respectively. The TZ volume decreased from 19.8 cm(3) to 10.1 cm(3) (mean volume reduction of 47.7%). In multivariate analysis, prostate volume cytoreduction was most closely associated with PPB (p=0.014), TTMB prostate volume (p=0.01), and drug regimen (p=0.001).

CONCLUSIONS

The degree of prostate volume cytoreduction was positively associated with higher Gleason score and PPBs. Greater reductions in prostate volume may be an indicator of more aggressive cancer.

Luteinizing hormone-releasing hormone agonists in the treatment of prostate cancer: A review of their discovery, development, and place in therapy

BACKGROUND

Early identification of the biological activity of luteinizing hormone-releasing hormone (LHRH) paved the way for the synthesis of analogues with enhanced potency and biological properties. Early testing in animal models and humans provided insight into the potential clinical uses of these substances, and, within 10 years, LHRH-agonist therapy had become available for use in patients with advanced prostate cancer (PC). Over time, the role of LHRH-agonist therapy has expanded to include use as part of multimodal treatment regimens throughout the course of the disease.

OBJECTIVES

This article reviews the discovery and development of LHRH agonists and summarizes the clinical evidence for their efficacy in PC.

METHODS

Relevant clinical studies were identified through searches of the English-language literature indexed on MEDLINE through May 2006. The main search terms were prostate cancer and LHRH agonist.

RESULTS

Results of the initial therapeutic trials of sustained-release depot formulations of LHRH agonists in patients with PC were reported in the mid-1980s, indicating that these agents were effective and well tolerated in improving clinical symptoms and producing medical castration. Longer-term studies and subsequent meta-analyses of randomized controlled trials in patients with advanced PC found no significant differences in overall survival when single-therapy androgen suppression was achieved through the use of LHRH-agonist therapy or orchiectomy. Randomized trials have reported significant improvements in disease-free and overall survival in patients with locally advanced or high-grade PC treated with LHRH agonists in addition to radiotherapy. Several prospective randomized trials have reported decreases in rates of positive surgical margins with short-term (6 weeks to 4 months) neoadjuvant LHRH-agonist therapy in patients with stage T1 to T3a PC undergoing prostatectomy. Definitive comparisons of immediate and delayed treatment in patients with biochemical relapse have not been reported. However, the results of several studies suggest that immediate LHRH-agonist therapy (or orchiectomy) may improve the course of disease progression and survival. The risks of long-term treatment (eg, osteoporosis; fracture; anabolic loss of muscle mass, with a tendency toward weight gain) must be considered carefully in patients who are likely to receive chronic LHRH-agonist therapy. Intermittent schedules have been developed to reduce the adverse effects associated with LHRH-agonist therapy; some reports support sparing effects on bone and muscle mass and relative improvements in toxicities during off-therapy periods, whereas others have documented continuing decreases in bone mineral density (BMD), with the rate of bone loss highest during the early cycles of therapy. Bisphosphonate therapy has been shown to increase BMD in patients with PC and may therefore be beneficial when overt symptoms of osteopenia or osteoporosis are present.

CONCLUSIONS

LHRH-agonist therapy has been the mainstay of treatment for advanced PC for >20 years. Clinical evidence supports expanding use of these agents at an earlier stage of disease and as part of multimodal regimens that include radiotherapy. There is a need for further study of the efficacy of adjuvant LHRH-agonist therapy along with prostatectomy, in patients with biochemical failure, in intermittent regimens, and in conjunction with cytotoxic therapies in late-stage disease.

In vivo characterization of a novel GnRH (gonadotropin-releasing hormone) antagonist, LXT-101, in normal male rats

LXT-101 is a newly developed GnRH (gonadotropin-releasing hormone) analogue. In this study, the in vivo pharmacological profile in intact male rats and binding characters of LXT-101 were illustrated, and regulation of mRNA of hormone receptors related to the pituitary-gonadal axis during and after administration was observed to reveal its molecular mechanism of potent effect and reversibility. After single subcutaneous injections, LXT-101 produced a dose- and time-dependent suppression of serum testosterone level. Multiple administrations and osmotic pump implantation revealed that the time of onset and dose needed to maintain the effect of chemical castration decreased as the frequency of injection increased and gave direct proof that depot formulation could significantly improve the duration of antagonist delivery and pharmacological activities compared to the injectable formulation. And LXT-101 showed excellent character of regulating the pituitary-gonadal axis quickly and reversibly. Competitive binding assay showed that LXT-101 could specifically bind a pituitary GnRH receptor with high affinity. These results indicated that LXT-101 is fit for sustained-release formulation and it might possibly be developed as an ideal candidate for treating sex hormone-sensitive tumors and other disorders.

Is the flare phenomenon clinically significant?

OBJECTIVES

The existing luteinizing hormone-releasing hormone (LHRH) analogs have been the preferred method of inducing androgen deprivation for prostate cancer for over a decade. These agents are well known to cause a surge in serum testosterone levels during the first week of therapy. However, there are wide discrepancies in reports of the frequency and severity of acute clinical progression or clinical flare that might result from the testosterone surge. Also, there is not a clear consensus as to whether antiandrogens should be routinely given to all patients during the first month of LHRH therapy to prevent flare responses.

METHODS

Clinical trials involving LHRH analog therapy for prostate cancer were reviewed, and the frequency of clinical flare responses noted. Particular attention was given to the kinds of clinical problems associated with the flare response. The use of LHRH analog therapy in treatment of patients with prostate cancer for indications other than overt metastatic disease is discussed, because this is becoming a much more common use of these agents. This article analyzes 2 placebo-controlled, double-blind trials testing the effectiveness of existing antiandrogens in ameliorating flare responses.

RESULTS

The use of LHRH analogs for patients with stage D2 disease can be associated with clinical flare in approximately 10% of D2 patients. In addition to bone pain, cord compression, and bladder outlet obstruction, another potentially severe side effect is cardiovascular risk arising presumably from hypercoagulability associated with a rapid increase in tumor burden. In clinical series involving D2 patients, the frequency of clinical flare greatly varies, probably because of the level of scrutiny of the investigator and/or the prostate-cancer tumor burden present at the initiation of therapy. Concomitant antiandrogen therapy reduces, but does not totally eliminate, the flare responses in patients at high risk for flare. Treating prostate cancer in the D0 stage or in the neoadjuvant setting will result in biochemical evidence of testosterone surge, but these patients are at very little risk for clinical flare responses.

CONCLUSIONS

There is a wide variation in the reported frequency of clinical flare responses from LHRH analogs during the initial treatment of patients with stage D2 disease. The risk-to-benefit ratio, especially in patients with symptomatic bone metastasis, would dictate routine use of antiandrogen therapy for the first month of LHRH analog treatment. For patients at risk for cord compression, other means of ablating testosterone might be considered, such as ketoconazole, orchiectomy, or LHRH antagonists. Clinical flare responses, as opposed to biochemical flare responses, are very rare during LHRH analog therapy for stage D0 disease and/or in the setting of neoadjuvant hormonal therapy.