Contemporary therapeutic approaches targeting bone complications in prostate cancer

Skeletal complications are major causes of morbidity in patients with prostate cancer. Despite the osteoblastic appearance of prostate cancer bone metastases, elevated serum and urinary markers of bone resorption are indicative of high osteoclast activity. Increased osteoclast activity is independently associated with subsequent skeletal complications, disease progression, and death. Osteoclast-targeted therapies aim to reduce the risk for disease-related skeletal complications, bone metastases, and treatment-related fractures. This review focuses on recent advances in osteoclast-targeted therapies in the treatment and prevention of bone complications in prostate cancer. Osteoclast-targeted therapies have been extensively studied in men with prostate cancer. The potent bisphosphonate zoledronic acid significantly decreased the risk of skeletal complications in men with castration-resistant prostate cancer and bone metastases, and is Federal Drug Administration approved for this indication. Denosumab is a human monoclonal antibody that inhibits receptor activator of nuclear factor-κB (RANK) ligand, a critical mediator of osteoclast differentiation, activation, and survival. Data from recent phase III clinic trials demonstrate the emerging role for denosumab in the treatment of prostate cancer bone metastases and prevention of fractures associated with androgen deprivation therapy.     

Treatment strategy for advanced prostate cancer with bone metastases

The introduction of PSA screening has led to confirming a shift towards an earlier pathological stage in the diagnosis of prostate cancer. Consequently, the proportion of detecting early stage prostate cancer has clearly been increasing. On the other hand, progressive cancers in the form of distant metastases and locally advanced ones that have been confirmed at the initial diagnosis exhibit a constant rate. In addition, there have been a lot of cases where hormonal resistance was acquired during hormonal therapy which resulted in advanced metastases of the prostate. Prostate cancer has a tendency to be metastatic to bones. Combining the fact that the survival period of patients undergoing treatment is prolonged after metastases, the length of suffering caused by complications, such as ostealgia, pathological fracture and myelopathy, becomes an issue in which QOL and ADL of the patient are sacrificed for a long time. As for treatment of prostate cancer with metastases, a palliative treatment is common in the clinical scene. However, we can extend a life prognosis with use of radiotherapy and surgical treatment in addition to the palliative treatment at an appropriate time. It appears that a combination of new chemotherapy and hormonal therapy will be promising. In the future, we believe that the appearance of new anticancer drugs, endocrine therapies, bisphosphonates and strontium treatment could be used as a part of the treatment strategy for prostate cancer with bone metastases.     

Locally advanced prostate cancer

Opinion statement Standard therapy for clinically localized prostate cancer includes radical prostatectomy, external beam radiotherapy, or transperineal interstitial brachytherapy. Patients eligible for standard therapy are those with low risk features as defined by various risk group classifications, which generally include clinical stage T1 or T2a, serum prostate-specific antigen (PSA) less than 10 ng/mL, and biopsy Gleason sum of 6 or less. Although there has been important evolution in the performance of these techniques, particularly with respect to functional outcomes, these approaches for low-risk disease are relatively mature, and the cure rates with each of these therapies are similar in this patient population; locally advanced disease is more difficult to cure, however. Biochemical disease-free survival rates in men undergoing radical prostatectomy are clearly related to the pathologic stage. Prognostic groups can be defined based on pathologic stage with increasingly worse outcomes based on extracapsular extension (ECE), margin status, and the status of the lymph nodes and seminal vesicles. In patients with low risk features, the positive margin rate is generally low, making the presence or absence of ECE the dominant variable in predicting the likelihood of treatment failure. These observations suggest that more aggressive therapy is needed to cure those who are likely to have ECE or other adverse histologic features. Several nomograms predicting the likelihood of ECE or 5-year biochemical failure rates are now in routine clinical use, and can be used to select men at high risk of failure with single modality therapy for more aggressive treatment strategies. However, the optimal form of aggressive therapy for these patients is unknown.     

Psychological complications of prostate cancer

Over the past decade, interest has been growing in the quality of life of men with prostate cancer. Traditionally considered a group with few psychological complications, 10% to 20% of men with prostate cancer are found to have clinically significant levels of psychological distress. This article reviews the prevalence of psychiatric symptomatology among prostate cancer patients, the psychological challenges of coping with the disease, and general guidelines for treatment.     

Common complications of advanced cancer

Complications due to cancer and its treatment are common and increase in incidence and severity as the disease progresses. Central nervous system complications affect 15% to 20% of patients, and up to 75% have bone metastases at some point during the disease process. Endocrine abnormalities include hypercalcemia, adrenal insufficiency, and inappropriate antidiuretic syndrome. Hematologic disorders, malignant effusions, and gastrointestinal (GI) problems may cause significant morbidity.     

Predictive factors for skeletal complications in hormone-refractory prostate cancer patients with metastatic bone disease

Factors predictive of skeletal-related events (SREs) in bone metastatic prostate cancer patients with hormone-refractory disease were investigated. We evaluated the frequency of SREs in 200 hormone-refractory patients consecutively observed at our Institution and followed until death or the last follow-up. Baseline parameters were evaluated in univariate and multivariate analysis as potential predictive factors of SREs. Skeletal-related events were observed in 86 patients (43.0%), 10 of which (5.0%) occurred before the onset of hormone-refractory disease. In univariate analysis, patient performance status (P=0.002), disease extent (DE) in bone (P=0.0001), bone pain (P=0.0001), serum alkaline phosphatase (P=0.0001) and urinary N-telopeptide of type one collagen (P=0.0001) directly correlated with a greater risk to develop SREs, whereas Gleason score at diagnosis, serum PSA, Hb, serum albumin, serum calcium, types of bone lesions and duration of androgen deprivation therapy did not. Both DE in bone (hazard ratio (HR): 1.16, 95% confidence interval (CI): 1.07-1.25, P=0.000) and pain score (HR: 1.13, 95% CI: 1.06-1.20, P=0.000) were independent variables predicting for the onset of SREs in multivariate analysis. In patients with heavy tumour load in bone and great bone pain, the percentage of SREs was almost twice as high as (26 vs 52%, P<0.02) and occurred significantly earlier (P=0.000) than SREs in patients with limited DE in bone and low pain. Bone pain and DE in bone independently predict the occurrence of SREs in bone metastatic prostate cancer patients with hormone-refractory disease. These findings could help physicians in tailoring the skeletal follow-up most appropriate to individual patients and may prove useful for stratifying patients enrolled in bisphosphonate clinical trials.     

Clinical benefit of zoledronic acid for the prevention of skeletal complications in advanced prostate cancer

Men with prostate cancer are at high risk of developing bone metastases that can lead to clinically significant skeletal morbidity. Recently, a randomized, placebo-controlled, phase III trial in 422 men with hormone-refractory prostate cancer and bone metastases demonstrated that zoledronic acid (4 mg every 3 weeks) significantly reduced the incidence and onset of skeletal complications and provided significant long-term reductions in bone pain compared with placebo. Patients received zoledronic acid for a 15-month core phase, with the option to continue therapy for 9 more months on the extension phase. To evaluate the continuing benefit of long-term zoledronic acid therapy, retrospective exploratory analyses were conducted based on the incidence of skeletal-related events (SREs; defined as pathologic bone fracture, spinal cord compression, surgery or radiation therapy to bone, or change in antineoplastic therapy for bone pain) occurring only during the extension phase of this trial. Quality of life parameters included assessment with the Brief Pain Inventory. Similar to results reported for the 15-month core phase and the entire 24-month study, the 9-month extension phase demonstrated that zoledronic acid significantly reduced the percentage of patients with an SRE (P = 0.017), prolonged the median time to first SRE (P = 0.036), reduced the annual incidence of SREs by 52% (P = 0.016), and reduced the risk of SREs by 53% (P = 0.022) compared with placebo. Furthermore, zoledronic acid was safe and well tolerated. Therefore, zoledronic acid provides long-term continuing clinical benefit for men with prostate cancer and bone metastases and represents a new therapeutic option for this population.     

Newer therapies in advanced prostate cancer

Prostate cancer is a leading cause of morbidity and mortality among males. Androgen ablation as initial therapy for advanced prostate cancer provides high response rates but does not cure disease, as nearly all men with metastases will eventually progress to hormone-refractory prostate cancer (HRPC). Present chemotherapy regimens for HRPC can provide palliation and have recently demonstrated an increase in overall survival. Over the past 2 decades, these regimens represent clear advances in the treatment of metastatic prostate cancer but also demonstrate that newer therapies are needed. Studies are ongoing to provide viable alternatives among traditional cytotoxic therapies as well as among novel agents targeting specific molecular pathways. This article reviews some of the newer therapies being developed and evaluated, including the epothilone analogues, human epidermal growth factor receptor pathway inhibitors, angiogenesis inhibitors, and endothelin receptor antagonists.     

Chemotherapy in advanced prostate cancer.

In the United States, prostate cancer is the most commonly diagnosed cancer and the second leading cause of cancer death in men. Prostate cancer is a rare disease before age 40; however, the prevalence increases quickly to 80% by the age of 80, and with increasing life expectancy, hormone-refractory prostate cancer (HRPC) will soon represent the most common cancer in the male population in the United States and other Western countries. The evolution of early prostate cancer is variable and extends over many years; some tumors progress slowly or not at all, whereas others may progress more rapidly and be fatal after a few years. A widely held view is that chemotherapy has no role in HRPC because no single agent or combination has been shown to prolong survival in a randomized trial. This concept may be obsolete, as preliminary results for a number of approaches, mostly derived from laboratory observations, show that prostate cancers are not as resistant to chemotherapy as traditionally believed. The population of early "geriatric" HRPC patients is rapidly increasing, posing an even greater challenge to oncologists in coping with this difficult-to-manage patient population. In this article, we analyze the most novel chemotherapeutic combinations for the treatment of HRPC in otherwise healthy elderly men.     

Management of advanced prostate cancer

Most cases of advanced carcinoma of the prostate are hormonosensitive. The use of combined androgen blockade (CAB) seems to improve survival and quality of life, but only when combined with chemical castration by luteinizing-hormone-releasing hormone analog and without the use of steroidal antiandrogens. After CAB, further hormonal treatments remain efficacious, such as antiandrogen withdrawal followed by estrogens, aromatase inhibitors, and hormone-refractory prostate cancer multiple cytotoxic agents. For painful bone lesions, external beam radiotherapy, biphosphonates, and strontium 89 or samarium 153 provide pain relief. The use of new methods for the evaluation of response and quality of life will allow the rapid identification of effective treatments and permit powered phase III trials.     

Palliative prostate radiotherapy for symptomatic advanced prostate cancer

Background and purpose

To report the results for the use of short-course palliative radiotherapy to the prostate for localised symptoms.

Materials and methods

Fifty-eight patients were identified from radiotherapy records between 2003 and 2007. Data were collected retrospectively on patients’ demographics, radiotherapy details and response. Symptoms and toxicity were scored, retrospectively, according to the following scale: 0 = no symptoms, 1 = mild symptoms, 2 = moderate symptoms, and 3 = severe symptoms.

Results

All the 58 patients had advanced prostate carcinoma. The median age at radiotherapy was 76.6 years (range 54-91). Fifty-six patients (97%) had hormone refractory disease. Twenty-seven patients (47%) had evidence of metastatic disease. 20Gy in 5 fractions was the most commonly used fractionation. The most frequent baseline symptom was haematuria (54%). Eighty-nine percent (31/35) of the patients had a complete or partial resolution of symptoms at 4 months. Response rates for individual symptoms (including unknown responses) were: rectal symptoms (75%), pelvic pain (69%), urinary obstruction (54%) and haematuria (42%). A >50% reduction in PSA occurred in five patients. Toxicity was mild to moderate only and was self-limiting.

Conclusion

Palliative radiotherapy to the prostate gland for local symptoms appears to be an effective means of palliation with minimal toxic side effects. Prospective studies are now required to assess its benefits in more detail.     

New molecular targets in advanced prostate cancer

Classically, advanced prostate cancer has been treated with hormonal therapy and, most recently, chemotherapy. This treatment clearly demonstrated a survival benefit, but never a cure. With the ever-expanding understanding of the pathophysiology of prostate cancer, there has been a recent explosion in the potential molecular targets and novel therapeutic approaches to both advanced and potentially localized prostate cancer. This review will focus on what the author perceives to be the most promising of these new strategies. The endothelin pathway has been identified as pivotal in the viscous cycle of tumorigenesis in bone, leading to the development of endothelial receptor antagonists. Vaccine therapy using autologous granulocyte-macrophage colony-stimulating factor-producing prostate cancer cells has been effective in producing both immune and clinical responses. Randomized clinical trials of the immunotherapy cell product APC8015 (Provenge) have demonstrated improved survival in the hormone-refractory setting. The development of antisense oligonucleotides to segments of mRNA critical to the progression to androgen-independent disease has emerged as one further tool in the expanding armamentarium of potential therapies being tested. Clearly, headway is being made in improving outcomes in this most prevalent health problem.     

New molecular targets in advanced prostate cancer

Classically, advanced prostate cancer has been treated with hormonal therapy and, most recently, chemotherapy. This treatment clearly demonstrated a survival benefit, but never a cure. With the ever-expanding understanding of the pathophysiology of prostate cancer, there has been a recent explosion in the potential molecular targets and novel therapeutic approaches to both advanced and potentially localized prostate cancer. This review will focus on what the author perceives to be the most promising of these new strategies. The endothelin pathway has been identified as pivotal in the viscous cycle of tumorigenesis in bone, leading to the development of endothelial receptor antagonists. Vaccine therapy using autologous granulocyte–macrophage colony-stimulating factor-producing prostate cancer cells has been effective in producing both immune and clinical responses. Randomized clinical trials of the immunotherapy cell product APC8015 (Provenge^®) have demonstrated improved survival in the hormone-refractory setting. The development of antisense oligonucleotides to segments of mRNA critical to the progression to androgen-independent disease has emerged as one further tool in the expanding armamentarium of potential therapies being tested. Clearly, headway is being made in improving outcomes in this most prevalent health problem.     

Osteoprotegerin in prostate cancer bone metastasis

Osteoprotegerin (OPG), a critical regulator of osteoclastogenesis, is expressed by prostate cancer cells, and OPG levels are increased in patients with prostate cancer bone metastases. The objective of this study was to investigate the effects of OPG overexpression on prostate cancer cells and prostate cancer/bone cell interactions in vitro and in vivo. OPG-transfected C4-2 cells expressed 8.0 ng OPG per mL per 10(6) cells, whereas no OPG was detected in the media of C4-2 cells transfected with a control plasmid. OPG overexpressed by C4-2 cells protected these cells from tumor necrosis factor-related apoptosis-inducing ligand-induced apoptosis and decreased osteoclast formation. Subcutaneous OPG-C4-2 and pcDNA-C4-2 tumors exhibited similar growth and take-rate characteristics. However, when grown in bone, tumor volume was decreased in OPG-C4-2 versus pcDNA-C4-2 (P=0.0017). OPG expressed by C4-2 cells caused increases in bone mineral density (P=0.0074) and percentage of trabecular bone volume (P=0.007), and decreases in numbers of osteoblasts and osteoclasts when compared with intratibial pcDNA-C4-2 tumors (P=0.003 and P=0.019, respectively). In summary, our data show that increased expression of OPG in C4-2 cells does not directly affect proliferation of prostate cancer cells but indirectly decreases growth of C4-2 tumors in the bone environment. Our data also show that OPG expressed by C4-2 cells inhibits bone lysis associated with C4-2 bone metastasis, which results in net increases in bone volume. We therefore hypothesize that OPG expressed in prostate cancer patient bone metastases may be at least partially responsible for the osteoblastic character of most prostate cancer bone lesions.