Contemporary therapeutic approaches targeting bone complications in prostate cancer

Diagnostic imaging to detect and evaluate response to therapy in bone metastases from prostate cancer: current modalities and new horizons

Different therapeutic options for the management of prostate cancer (PC) have been developed, and some are successful in providing crucial improvement in both survival and quality of life, especially in patients with metastatic castration-resistant PC. In this scenario, diverse combinations of radiopharmaceuticals (for targeting bone, cancer cells and receptors) and nuclear medicine modalities (e.g. bone scan, SPECT, SPECT/CT, PET and PET/CT) are now available for imaging bone metastases. Some radiopharmaceuticals are approved, currently available and used in the routine clinical setting, while others are not registered and are still under evaluation, and should therefore be considered experimental. On the other hand, radiologists have other tools, in addition to CT, that can better visualize bone localization and medullary involvement, such as multimodal MRI. In this review, the authors provide an overview of current management of advanced PC and discuss the choice of diagnostic modality for the detection of metastatic skeletal lesions in different phases of the disease. In addition to detection of bone metastases, the evaluation of response to therapy is another critical issue, since it remains one of the most important open questions that a multidisciplinary team faces when optimizing the management of PC. The authors emphasize the role of nuclear modalities that can presently be used in clinical practice, and also look at future perspectives based on relevant clinical data with novel radiopharmaceuticals.

Prostate Cancer for the Internist

In the United States, approximately 240,000 men are diagnosed annually with prostate cancer. Although effective treatment options are available for clinically localized cancer, the potential burdensome co-morbidities and attendant healthcare costs from over diagnosis and over treatment have escalated the discussion and controversy regarding appropriate screening, diagnosis, and optimal management of prostate cancer. Although the lifetime risk of developing prostate cancer is approximately 1 in 6 (~16%), the risk of dying from the disease is only ~2%. The discrepancy between the cancer incidence and lethality has led to widespread scrutiny of prostate cancer patient management, particularly for low-grade, low-stage (indolent) disease. The vast majority of men diagnosed with clinically localized prostate cancer are treated with interventional therapies despite studies demonstrating that even without treatment, prostate cancer-specific mortality is low.

A MedLine/PubMed search was performed using PICO format (Patient, Intervention, Comparison and Outcome) identifying all relevant articles. No restrictions were used for publication dates. The terms “Prostate Cancer”, “Screening”, “Mortality”, “Morbidity” yielded 307 results. “Diagnosis”, “Prognosis” and “Survival” yielded 1504 results. Further filters were applied to narrow down the results using keywords “Prostate cancer screening guidelines 2014”, “Beyond PSA”, “NCCN Guidelines prostate”, “MRI guided Prostate biopsy” yielding 72, 274, 54 and 568 results respectively. Of these, approximately 137 articles were found relevant and were reviewed. References from the reviewed articles were included in the final article.

The use of dietary supplements to alleviate androgen deprivation therapy side effects during prostate cancer treatment

Prostate cancer (PCa), the most commonly diagnosed cancer and second leading cause of male cancer death in Western societies, is typically androgen-dependent, a characteristic that underlies the rationale of androgen deprivation therapy (ADT). Approximately 90% of patients initially respond to ADT strategies, however many experience side effects including hot flashes, cardiotoxicity, metabolic and musculoskeletal alterations. This review summarizes pre-clinical and clinical studies investigating the ability of dietary supplements to alleviate adverse effects arising from ADT. In particular, we focus on herbal compounds, phytoestrogens, selenium (Se), fatty acids (FA), calcium, and Vitamins D and E. Indeed, there is some evidence that calcium and Vitamin D can prevent the development of osteoporosis during ADT. On the other hand, caution should be taken with the antioxidants Se and Vitamin E until the basis underlying their respective association with type 2 diabetes mellitus and PCa tumor development has been clarified. However, many other promising supplements have not yet been subjected large-scale clinical trials making it difficult to assess their efficacy. Given the demographic trend of increased PCa diagnoses and dependence on ADT as a major therapeutic strategy, further studies are required to objectively evaluate these supplements as adjuvant for PCa patients receiving ADT.

Novel agents in the management of castration resistant prostate cancer

Prostate cancer (PCa) is a leading cause of cancer mortality in men and despite high cure rates with surgery and/or radiation, 30-40% of patients will eventually develop advanced disease. Androgen deprivation is the first line therapy for standard of care for men with advanced disease. Eventually however all men will progress to castration-resistant prostate cancer (CRPC). Insight into the molecular mechanisms of androgen resistance has led to the development of alternative novel hormonal agents. Newer hormonal agents such as abiraterone, enzalutamide and TOK-001; and the first cancer vaccine, Sipuleucel T have been approved for use in men with CRPC. The recognition of the importance of bone health and morbidity associated with skeletal related events has led to the introduction of the receptor activator of nuclear factor kappa-B-ligand inhibitor denosumab. Other molecularly targeted therapies have shown promise in pre-clinical studies, but this has not consistently translated into clinical efficacy. It is increasingly evident that CRPC is a heterogeneous disease and an individualized approach directed at identifying primary involvement of specific pathways could maximize the benefit from targeted therapies. This review focuses on targeted therapy for PCa with special emphasis on therapies that have been Food and Drug Administration approved for use in men with CRPC.

Optimizing bone health and minimizing skeletal morbidity in men with prostate cancer

Maintaining bone health is important in the management of men with prostate cancer. Patients receiving androgen deprivation therapy are at increased risk for treatment-related osteoporosis, and patients with bone metastases are at increased risk for skeletal morbidity related to debilitating skeletal-related events (SREs). Optimizing bone health in these patients includes lifestyle modifications, calcium/vitamin D supplementation, and osteoclast-targeted agents in select high-risk patients. No agent is approved for the prevention of bone metastases. Novel systemic agents have shown a beneficial effect bone by directly affecting tumor growth. Integration of these anticancer agents with osteoclast-targeted agents warrants further investigation.

Efficacy, patient-reported outcomes (PROs), and tolerability of the changing therapeutic landscape in patients with metastatic prostate cancer (MPC): a systematic literature review

OBJECTIVE

New therapies have attempted to improve on efficacy outcomes observed with docetaxel in patients with metastatic prostate cancer (MPC) who are hormone-therapy refractory or castration-resistant. In addition to the efficacy, patient-reported outcomes (PROs) and tolerability need to be assessed to define treatment benefit, as PROs measure the patient's subjective experience and can be correlated with hard outcomes. The main objective of this study was to evaluate the survival benefit of new therapies and secondary efficacy-related outcomes. Assessment of the number of studies reporting PROs and tolerability was also conducted.

METHODS

A predefined search strategy was conducted on major academic/governmental databases and conference proceedings (2007-2011). Exclusion criteria were applied.

RESULTS

Of 77 studies identified, 26 (34%) evaluated survival as an end point; 14 (18%) assessed PROs/tolerability. In chemotherapy-naive patients (no/minimal symptoms), median overall survival (OS) was 26 months for sipuleucel-T. In relapsed patients, the survival benefit of cabazitaxel/abiraterone was 15 months and that of enzalutamide was 18 months. Denosumab prolonged time to first on-study skeletal-related event (20.7 months denosumab, 17.1 months zoledronic acid; P = 0.0002, noninferiority; P = 0.008, superiority). Similar benefit was documented with radium-223, a new bone-targeted α-particle-emitting radiopharmaceutical. Radium-223 also significantly improved the OS (two-sided P = 0.00185). Specific to PROs, they were incorporated primarily as secondary end points, and improvements in pain response (most commonly evaluated) were variable among the agents. Last, the therapies were associated with unique toxicities requiring careful consideration.

CONCLUSIONS

The results of this review demonstrate that the therapeutic landscape of MPC has changed dramatically and many therapies in MPC now show OS improvements of about 4 months in the postdocetaxel setting.

Phase I pharmacokinetic and biodistribution study with escalating doses of ²²³Ra-dichloride in men with castration-resistant metastatic prostate cancer

PURPOSE

²²³Ra-Dichloride (²²³Ra) is a novel bone-seeking alpha-emitter that prolongs survival in patients with castration-resistant metastatic prostate cancer. We conducted a study to better profile the pharmacokinetics, pharmacodynamics, and biodistribution of this agent.

METHODS

Ten patients received either 50, 100, or 200 kBq of ²²³Ra per kilogram of body weight. Subsequently, six of these ten patients received a second dose of 50 kBq/kg. Pharmacokinetics and biodistribution were assessed by serial blood sampling, planar imaging, and whole-body counting. Pharmacodynamic assessment was based on measurements of prostate-specific antigen, bone alkaline phosphatase, and serum N-telopeptide. Safety was also assessed.

RESULTS

Pharmacokinetic studies showed rapid clearance of ²²³Ra from the vasculature, with a median of 14% (range 9-34%), 2% (range 1.6-3.9%), and 0.5% (range 0.4-1.0%) remaining in plasma at the end of infusion, after 4 h, and after 24 h, respectively. Biodistribution studies showed early passage into the small bowel and subsequent fecal excretion with a median of 52% of administered ²²³Ra in the bowel at 24 h. Urinary excretion was relatively minor (median of 4% of administered ²²³Ra). Bone retention was prolonged. No dose-limiting toxicity was observed. Pharmacodynamic effects were observed (alkaline phosphatase and serum N-telopeptides) in a significant fraction of patients.

CONCLUSION

²²³Ra cleared rapidly from plasma and rapidly transited into small bowel, with fecal excretion the major route of elimination. Administered activities up to 200 kBq/kg were associated with few side effects and appeared to induce a decline in serum indicators of bone turnover.

Current management of prostate cancer: dilemmas and trials

The past decade has witnessed significant advances in our understanding of the biology of prostate cancer. Androgen ablation/androgen receptor inhibition remains as the mainstay of treatment for advanced prostate cancer. Our understanding of the biology of prostate cancer has increased exponentially owing to advances in molecular biology. With this knowledge many intriguing issues have come to light, which clinicians and scientists alike strive to answer. These include why prostate cancer is so common, what drives the development of prostate cancer at a molecular level, why prostate cancer appears refractory to many families of cytotoxic chemotherapeutics, and why prostate cancer preferentially metastasizes to bone. Two clinical forms of prostate cancer have been identified: indolent organ confined disease, which elderly men often die of, and aggressive metastatic disease. A method of distinguishing between these two forms of the disease at an organ-confined stage remains elusive. Understanding the mechanisms of castrate resistance is a further issue of clinical importance. New trials of treatments, including molecular agents that target prostate cancer from a range of angles, have been instituted over the past 10-15 years. We can look at these trials not only as a chance to investigate the effectiveness of new treatments but also as an opportunity to further understand the complex biology of this disease.

Bone-targeted agents: preventing skeletal complications in prostate cancer

In men, prostate cancer is the most common non-cutaneous malignancy and the second most common cause of cancer death. Skeletal complications occur at various points during the disease course, either due to bone metastases directly, or as an unintended consequence of androgen deprivation therapy (ADT). Bone metastases are associated with pathologic fractures, spinal cord compression, and bone pain and can require narcotics or palliative radiation for pain relief. ADT results in bone loss and fragility fractures. This review describes the biology of bone metastases, skeletal morbidity, and recent advances in bone-targeted therapies to prevent skeletal complications of prostate cancer.

Targeted therapy in prostate cancer

The therapeutic approach to advanced prostate cancer has seen greater changes in the last 7 years than it did in the preceding 70. Although only one of the newly approved agents that improve overall survival is a targeted agent, it is a validation of the method of pathway analysis and drug design in delivering novel, clinically usable agents. As our knowledge of the molecular circuitry of tumour invasion, metastases and treatment resistance has become more refined, the number of new, potentially useful, targets has grown exponentially. This is reflected in the vast array of diverse targeted agents that are currently being evaluated in human trials. In this review, we briefly describe some of the key pathways that are involved in the evolution of the prostate cancer 'lethal phenotype', and review the clinical activity of some of the newly approved targeted therapies or those in advanced phases of clinical development.

Macrophage cathepsin K promotes prostate tumor progression in bone

Bone marrow macrophages (BMMs) share common progenitors with osteoclasts and are critical components of bone-tumor microenvironment; however, their function in prostate tumor growth in the skeleton has not been explored. BMMs are the major source of inflammatory factors and proteases, including cysteine protease cathepsin K (CTSK). In this study, utilizing mice deficient in CTSK, we demonstrate the critical involvement of this potent collagenase in tumor progression in bone. We present the evidence that tumor growth and progression in the bone are impaired in the absence of CTSK. Most importantly, we show for the first time that BMM-supplied CTSK may be involved in CCL2- and COX-2-driven pathways that contribute to tumor progression in bone. Together, our data unravel novel roles for CTSK in macrophage-regulated processes, and provide evidence for close interplay between inflammatory, osteolytic and tumor cell-driven events in the bone-tumor microenvironment.

RANKL-Targeted Therapies: The Next Frontier in the Treatment of Male Osteoporosis

Male osteoporosis is an increasingly recognized problem in aging men. A common cause of male osteoporosis is hypogonadism. Thousands of men with prostate cancer are treated with androgen deprivation therapy, a treatment that dramatically reduces serum testosterone and causes severe hypogonadism. Men treated with androgen deprivation therapy experience a decline in bone mineral density and have an increased rate of fracture. This paper describes prostate cancer survivors as a model of hypogonadal osteoporosis and discusses the use of RANKL-targeted therapies in osteoporosis. Denosumab, the only RANKL-targeted therapy currently available, increases bone mineral density and decreases fracture rate in men with prostate cancer. Denosumab is also associated with delayed time to first skeletal-related event and an increase in bone metastasis-free survival in these men. It is reasonable to investigate the use of RANKL-targeted therapy in male osteoporosis in the general population.