Phase I study of concurrent weekly docetaxel and repeated samarium-153 lexidronam in patients with castration-resistant metastatic prostate cancer

Role of osteoclast inhibitors in prostate cancer bone metastasis; a narrative review

OBJECTIVE

To study the role of Osteoclast inhibitors in advanced prostate cancer metastasis treatment and their efficacy in reducing skeletal related events.

METHODS: DATA SOURCE

A comprehensive search was done using search terms as "osteoclast inhibitors" "Bisphosphonates" "Zoledronic acid" " pamidronate" " Alendronate" "Denosumab" " Prostate cancer metastasis" in pubmed and Google scholar. Relevant articles were screened and collected . The collected articles were used to frame the review and data showing use of Osteoclast inhibitors In prostate cancer bone metastasis was collected.

DATA SUMMARY

Prostate cancer metastasizes most commonly to the skeleton thus leading to significant morbidity ranging from pain, pathological fractures to spinal cord compression and are the primary cause of patient disability and reduced quality of life.Initially, radiation therapy and radiopharmaceuticals were the mainstay of treatment however the role of Bisphosphonates and denosumab has become an integral part of therapy to manage metastatic prostate cancer. These agents significantly decrease skeletal related events and enhance patients quality of life. Emerging therapies like Radium-223 have also shown promise in reducing skeletal related events and also improving survival rates in patients with bone metastasis. Other treatment options which are being used are systemic agents like Docetaxel, cabazitaxel, hormonal therapies like abiraterone and enzalutamide. Immunotherapy with sipuleucel-T has demonstrated a reduction in mortality among prostate cancer patients with metastasis, highlighting the need for further research in this area. Ongoing studies are investigating novel agents that target both tumor cells and the bone microenvironment.

CONCLUSION

Osteoclast inhibitors are effective in reducing skeletal related events in advanced bone metastasis and improve the quality of life of patients.

Targeted Radiopharmaceutical Therapy for Bone Metastases

Radiopharmaceutical approaches for targeting bone metastasis have traditionally focused on palliation of pain. Several agents have been clinically used over the last several decades and have proven value in pain palliation providing pain relief and improving quality of life. The role is well established across several malignancies, most commonly used in osteoblastic prostate cancer patients. These agents have primarily based on targeting and uptake in bone matrix and have mostly included beta emitting isotopes. The advent alpha emitter and FDA approval of 223Ra-dichloride has created a paradigm shift in clinical approach from application for pain palliation to treatment of bone metastasis. The approval of 223Ra-dichloride given the survival benefit in metastatic prostate cancer patients, led to predominant use of this alpha emitter in prostate cancer patients. With rapid development of radiopharmaceutical therapies and approval of other targeted agents such as 177Lu-PSMA the approach to treatment of bone metastasis has further evolved and combination treatments have increasingly been applied. Novel approaches are needed to improve and expand the use of such therapies for treatment of bone metastasis. Combination therapies with different targeting mechanisms, combining chemotherapies and cocktail of alpha and beta emitters need further exploration.

Bone-Targeting Radiopharmaceuticals as Monotherapy or Combined With Chemotherapy in Patients With Castration-Resistant Prostate Cancer Metastatic to Bone

In patients with metastatic castration-resistant prostate cancer, bone is the most common site for metastases. Because of their osteoblastic character, these lesions are very suitable for treatment with bone-seeking radiopharmaceuticals (RPs). Nowadays, radium-223-chloride is the only RP with a proven benefit in overall survival, whereas the β-emitting RPs are used for pain palliation. In the past, many trials that investigated RPs alone, or in combination with chemotherapy have been performed. Because of different designs, characteristics of included patients, and chemotherapeutical and RP regimens, interpretation of the promising data and positioning of RPs in the treatment of metastatic prostate cancer has become difficult. In this review, we provide an overview of the existing data per RP with a focus on the different RPs in combination with chemotherapy. Furthermore, we aim to clarify the benefits on pain response and quality of life. Finally, we focus on the optimal timing and use of biomarkers in the treatment of patients with castration-resistant prostate cancer with RPs.

Randomized phase III trial to evaluate radiopharmaceuticals and zoledronic acid in the palliation of osteoblastic metastases from lung, breast, and prostate cancer: report of the NRG Oncology RTOG 0517 trial

BACKGROUND

Skeletal-related events (SREs), common sequelae of metastatic cancer, are reduced by bisphosphonates. In this study, it was postulated that radiopharmaceuticals, added to bisphosphonates, could further decrease the incidence of SREs.

METHODS

NRG Oncology RTOG 0517 randomized patients with breast, lung, and prostate cancer and blastic bone metastases to either zoledronic acid (ZA) alone or ZA plus radiopharmaceuticals (Sr-89 or Sm-153). The primary endpoint was time to development of SREs. Secondary objectives included quality of life (QOL), pain control, overall survival (OS), and toxicity.

RESULTS

261 patients (median age 68; 62% male; 55% prostate, 35% breast, 10% lung) were accrued between July 2006 and February 2011. The study closed early due to a lower than expected rate of SREs. 52 (42%) patients in the ZA arm and 49 (40%) in the radiopharmaceutical arm experienced an SRE. Median time free of SREs was 29.9 and 27.4 months, respectively (p = 0.84). Median OS in the ZA arm and radiopharmaceutical arms was 32.1 and 26.9 months, respectively (p = 0.37). Cox proportional hazards regression model showed that primary disease site (lung) and number of bone metastases (> 2) had a negative impact on OS (p < 0.0001, p = 0.01, respectively). The addition of radiopharmaceuticals to ZA led to a significant reduction in pain at 1 month based on BPI worst score (p = 0.02). No other group differences were noted for QOL or toxicity.

CONCLUSION

The addition of radiopharmaceuticals to bisphosphonates did not alter time to SREs or OS for patients with breast, lung, prostate cancers and blastic bone metastases, although it was associated with significant pain reduction at 1 month.

CLINICAL TRIAL REGISTRY

This protocol (RTOG 0517) is registered with ClinicalTrials.gov (NCT00365105), and may be viewed online at http://www.clinicaltrials.gov/ct2/show/NCT00365105?term=RTOG+0517&rank=1 .

TRAPEZE: a randomised controlled trial of the clinical effectiveness and cost-effectiveness of chemotherapy with zoledronic acid, strontium-89, or both, in men with bony metastatic castration-refractory prostate cancer

BACKGROUND

Bony metastatic castration-refractory prostate cancer is associated with a poor prognosis and high morbidity. TRAPEZE was a two-by-two factorial randomised controlled trial of zoledronic acid (ZA) and strontium-89 (Sr-89), each combined with docetaxel. All have palliative benefits, are used to control bone symptoms and are used with docetaxel to prolong survival. ZA, approved on the basis of reducing skeletal-related events (SREs), is commonly combined with docetaxel in practice, although evidence of efficacy and cost-effectiveness is lacking. Sr-89, approved for controlling metastatic pain and reducing need for subsequent bone treatments, is generally palliatively used in patients unfit for chemotherapy. Phase II analysis confirmed the safety and feasibility of combining these agents. TRAPEZE aimed to determine the clinical effectiveness and cost-effectiveness of each agent.

METHODS

Patients were randomised to receive six cycles of docetaxel plus prednisolone: alone, with ZA, with a single Sr-89 dose after cycle 6, or with both. Primary outcomes were clinical progression-free survival (CPFS: time to pain progression, SRE or death) and cost-effectiveness. Secondary outcomes were SRE-free interval (SREFI), total SREs, overall survival (OS) and quality of life (QoL). Log-rank test and Cox regression modelling were used to determine clinical effectiveness. Cost-effectiveness was assessed from the NHS perspective and expressed as cost per additional quality-adjusted life-year (QALY). An additional analysis was carried out for ZA to reflect the availability of generic ZA.

RESULTS

PATIENTS

757 randomised (median age 68.7 years; Eastern Cooperative Oncology Group scale score 0, 40%; 1, 52%; 2, 8%; prior radiotherapy, 45%); median prostate-specific antigen 143.78 ng/ml (interquartile range 50.8-353.9 ng/ml). Stratified log-rank analysis of CPFS was statistically non-significant for either agent (Sr-89, p = 0.11; ZA, p = 0.45). Cox regression analysis adjusted for stratification variables showed CPFS benefit for Sr-89 [hazard ratio (HR) 0.845, 95% confidence interval (CI) 0.72 to 0.99; p = 0.036] and confirmed no effect of ZA (p = 0.46). ZA showed a significant SREFI effect (HR 0.76; 95% CI 0.63 to 0.93; p = 0.008). Neither agent affected OS (Sr-89, p = 0.74; ZA, p = 0.91), but both increased total cost (vs. no ZA and no Sr-89, respectively); decreased post-trial therapies partly offset costs [net difference: Sr-89 £1341; proprietary ZA (Zometa(®), East Hanover, NJ, USA) £1319; generic ZA £251]. QoL was maintained in all trial arms; Sr-89 (0.08 additional QALYs) and ZA (0.03 additional QALYs) showed slight improvements. The resulting incremental cost-effectiveness ratio (ICER) for Sr-89 was £16,590, with £42,047 per QALY for Zometa and £8005 per QALY for generic ZA.

CONCLUSION

Strontium-89 improved CPFS, but not OS. ZA did not improve CPFS or OS but significantly improved SREFI, mostly post progression, suggesting a role as post-chemotherapy maintenance therapy. QoL was well maintained in all treatment arms, with differing patterns of care resulting from the effects of Sr-89 on time to progression and ZA on SREFI and total SREs. The addition of Sr-89 resulted in additional cost and a small positive increase in QALYs, with an ICER below the £20,000 ceiling per QALY. The additional costs and small positive QALY changes in favour of ZA resulted in ICERs of £42,047 (Zometa) and £8005 for the generic alternative; thus, generic ZA represents a cost-effective option. Additional analyses on the basis of data from the Hospital Episode Statistics data set would allow corroborating the findings of this study. Further research into the use of ZA (and other bone-targeting therapies) with newer prostate cancer therapies would be desirable.

STUDY REGISTRATION

Current Controlled Trials ISRCTN12808747.

FUNDING

This project was funded by the NIHR Health Technology Assessment programme and will be published in full in Health Technology Assessment; Vol. 20, No. 53. See the NIHR Journals Library website for further project information.

A Phase 1 Trial of Cabazitaxel Combined With 188Re-Hydroxyethylidene Diphosphonate in Patients With Metastatic Castration-Resistant Prostate Cancer Who Progressed on or After a Docetaxel-Containing Treatment: The ReCab Trial

PURPOSE

In patients with metastatic castration-resistant prostate cancer (mCRPC), bone-seeking radiopharmaceuticals, such as Re-hydroxyethylidene diphosphonate (HEDP), are effective for pain palliation and have a marked antitumor effect. Cabazitaxel is the standard second-line chemotherapy for mCRPC patients. We performed a phase 1 study investigating the safety and feasibility of the combined treatment with Re-HEDP and cabazitaxel in mCRPC patients.

METHODS

Patients with mCRPC and documented disease progression on or after docetaxel were eligible for inclusion. In both dose levels, cabazitaxel (4 cycles of cabazitaxel 25 mg/m + 2 cycles of cabazitaxel 20 mg/m in level 1, and 6 cycles of cabazitaxel 25 mg/m in level 2) were combined with 2 cycles of Re-HEDP 40 MBq/kg (1.1 mCi/kg) (after the second and fourth cabazitaxel cycles). Three patients were planned for each dose level, expanding to 6 patients in case of a dose-limiting toxicity (DLT). A DLT is defined as any grade 4 toxicity, or grade 3 toxicity delaying the next treatment cycle.

RESULTS

Twelve patients were included, of whom 3 had progressive disease before the third cycle of cabazitaxel. In total, 1 DLT occurred (dose level 1) after treatment cycle 6 (Re-HEDP) (thrombopenia grade 3 delaying the next treatment cycle). The cohort was expanded to 6 patients, with no further DLTs. No DLT occurred in dose level 2. The most important adverse events were of hematologic origin, followed by mild fatigue and diarrhea.

CONCLUSIONS

Combination therapy with cabazitaxel and Re-HEDP is feasible and generally well tolerated with similar hematologic toxicity compared with cabazitaxel monotherapy.

Efficacy and safety of 153Sm-EDTMP as treatment of painful bone metastasis: a large single-center study

PURPOSE

The purpose of this study is to assess the efficacy of ¹⁵³Sm-EDTMP (Quadramet®) in a clinical setting.

METHODS

We have conducted a retrospective study of all consecutive patients (pts) treated with ¹⁵³Sm-EDTMP for painful bone metastases. At each visit (before and after treatment), four parameters were collected: (i) pain assessment according to the 10-step visual analogue scale (VAS), (ii) sleep disturbance related to pain, (iii) dose of analgesic medication, and (iv) answer to the following closed question "Do you think you obtained a benefit from treatment?" Success of treatment was defined by the combination of these four parameters.

RESULTS

Three hundred seventy consecutive ¹⁵³Sm-EDTMP treatments for painful bone metastases were given. Patients had the following primary tumors: breast carcinoma (153), prostate carcinoma (155), lung carcinoma (27), or other cancers (35). Fifty-eight percent of the patients had received previous external osseous radiotherapy. Ninety-seven percent of the patients were treated with concomitant analgesics and 61% were treated with diphosphonates. A clinical benefit was described in 55.0% of cases at D30. Treatment was more effective in cases of breast and prostate cancers compared with other types of primary cancers. Patients described a benefit at D30 in 62, 58, 6, and 38% of cases of breast, prostate, lung, and other cancers. The subjective efficacy was accompanied by a decrease in analgesic intake in 35.0% of cases.

CONCLUSION

¹⁵³Sm-EDTMP therapy is an effective supportive treatment in patients who suffer from bone metastases, especially in patients with breast or prostate cancer.

Phase I/II trials of 186Re-HEDP in metastatic castration-resistant prostate cancer: post-hoc analysis of the impact of administered activity and dosimetry on survival

PURPOSE

To investigate the role of patient-specific dosimetry as a predictive marker of survival and as a potential tool for individualised molecular radiotherapy treatment planning of bone metastases from castration-resistant prostate cancer, and to assess whether higher administered levels of activity are associated with a survival benefit.

METHODS

Clinical data from 57 patients who received 2.5-5.1 GBq of 186Re-HEDP as part of NIH-funded phase I/II clinical trials were analysed. Whole-body and SPECT-based absorbed doses to the whole body and bone lesions were calculated for 22 patients receiving 5 GBq. The patient mean absorbed dose was defined as the mean of all bone lesion-absorbed doses in any given patient. Kaplan-Meier curves, log-rank tests, Cox's proportional hazards model and Pearson's correlation coefficients were used for overall survival (OS) and correlation analyses.

RESULTS

A statistically significantly longer OS was associated with administered activities above 3.5 GBq in the 57 patients (20.1 vs 7.1 months, hazard ratio: 0.39, 95 % CI: 0.10-0.58, P = 0.002). A total of 379 bone lesions were identified in 22 patients. The mean of the patient mean absorbed dose was 19 (±6) Gy and the mean of the whole-body absorbed dose was 0.33 (±0.11) Gy for the 22 patients. The patient mean absorbed dose (r = 0.65, P = 0.001) and the whole-body absorbed dose (r = 0.63, P = 0.002) showed a positive correlation with disease volume. Significant differences in OS were observed for the univariate group analyses according to disease volume as measured from SPECT imaging of 186Re-HEDP (P = 0.03) and patient mean absorbed dose (P = 0.01), whilst only the disease volume remained significant in a multivariable analysis (P = 0.004).

CONCLUSION

This study demonstrated that higher administered activities led to prolonged survival and that for a fixed administered activity, the whole-body and patient mean absorbed doses correlated with the extent of disease, which, in turn, correlated with survival. This study shows the importance of patient stratification to establish absorbed dose-response correlations and indicates the potential to individualise treatment of bone metastases with radiopharmaceuticals according to patient-specific imaging and dosimetry.

The role of radiation therapy in the treatment of metastatic castrate-resistant prostate cancer

In the setting of castrate-resistant prostate cancer, patients present with a variety of symptoms, including bone metastases, spinal cord compression and advanced pelvic disease. Fortunately, a variety of radiotherapeutic options exist for palliation. This article focuses on these options, including both external beam radiotherapy and radiopharmaceuticals.

Targeting the interleukin-11 receptor α in metastatic prostate cancer: A first-in-man study

BACKGROUND

Receptors in tumor blood vessels are attractive targets for ligand-directed drug discovery and development. The authors have worked systematically to map human endothelial receptors (“vascular zip codes”) within tumors through direct peptide library selection in cancer patients. Previously, they selected a ligand-binding motif to the interleukin-11 receptor alpha (IL-11Rα) in the human vasculature.

METHODS

The authors generated a ligand-directed, peptidomimetic drug (bone metastasis-targeting peptidomimetic-11 [BMTP-11]) for IL-11Rα–based human tumor vascular targeting. Preclinical studies (efficacy/toxicity) included evaluating BMTP-11 in prostate cancer xenograft models, drug localization, targeted apoptotic effects, pharmacokinetic/pharmacodynamic analyses, and dose-range determination, including formal (good laboratory practice) toxicity across rodent and nonhuman primate species. The initial BMTP-11 clinical development also is reported based on a single-institution, open-label, first-in-class, first-in-man trial (National Clinical Trials number NCT00872157) in patients with metastatic, castrate-resistant prostate cancer.

RESULTS

BMTP-11 was preclinically promising and, thus, was chosen for clinical development in patients. Limited numbers of patients who had castrate-resistant prostate cancer with osteoblastic bone metastases were enrolled into a phase 0 trial with biology-driven endpoints. The authors demonstrated biopsy-verified localization of BMTP-11 to tumors in the bone marrow and drug-induced apoptosis in all patients. Moreover, the maximum tolerated dose was identified on a weekly schedule (20-30 mg/m²). Finally, a renal dose-limiting toxicity was determined, namely, dose-dependent, reversible nephrotoxicity with proteinuria and casts involving increased serum creatinine.

CONCLUSIONS

These biologic endpoints establish BMTP-11 as a targeted drug candidate in metastatic, castrate-resistant prostate cancer. Within a larger discovery context, the current findings indicate that functional tumor vascular ligand-receptor targeting systems may be identified through direct combinatorial selection of peptide libraries in cancer patients. Cancer 2015;121:2411–2421. © 2015 The Authors. Cancer published by Wiley Periodicals, Inc. on behalf of American Cancer Society.

The authors report on the development of a new ligand-directed peptidomimetic (termed bone metastasis-targeting peptidomimetic-11) for interleukin-11 receptor-based human vascular targeting, including the translation from preclinical studies to a first-in-class, first-in-man clinical trial in patients with metastatic, castrate-resistant prostate cancer.

Recent advances in bone-targeted therapies of metastatic prostate cancer

Prostate cancer is one of the most common malignancies affecting men worldwide, with bone being the most common site of metastasis in patients that progress beyond organ confinement. Bone metastases are virtually incurable and result in significant disease morbidity and mortality. Bone provides a unique microenvironment whose local interactions with tumor cells offer novel targets for therapeutic interventions. Several attractive molecules or pathways have been identified as new potential therapeutic targets for bone metastases caused by metastatic castration-resistant prostate cancer. In this review, we present the recent advances in molecular targeted therapies for prostate cancer bone metastasis focusing on therapies that target the bone cells and the bone microenvironment. The therapies covered in this review include agents that inhibit bone resorption, agents that stimulate bone formation, and agents that target the bone matrix. Suggestions to devise more effective molecular targeted therapies are proposed. Hopefully, with better understanding of the biology of the disease and the development of more robust targeted therapies, the survival and quality of life of the affected individuals could be significantly improved.

Bone-seeking radiopharmaceuticals as targeted agents of osteosarcoma: samarium-153-EDTMP and radium-223

Osteosarcoma is a cancer characterized by formation of bone by malignant cells. Routine bone scan imaging with Tc-99m-MDP is done at diagnosis to evaluate primary tumor uptake and check for bone metastases. At time of relapse the Tc-99m-MDP bone scan also provides a specific means to assess formation of bone by malignant osteosarcoma cells and the potential for bone-seeking radiopharmaceuticals to deliver radioactivity directly into osteoblastic osteosarcoma lesions. This chapter will review and compare a bone-seeking radiopharmaceutical that emits beta-particles, samarium-153-EDTMP, with an alpha-particle emitter, radium-223. The charged alpha particles from radium-223 have far more mass and energy than beta particles (electrons) from Sm-153-EDTMP. Because radium-223 has less marrow toxicity and more radiobiological effectiveness, especially if inside the bone forming cancer cell than samarium-153-EDTMP, radium-223 may have greater potential to become widely used against osteosarcoma as a targeted therapy. Radium-223 also has more potential to be used with chemotherapy against osteosarcoma and bone metastases. Because osteosarcoma makes bone and radium-223 acts like calcium, this radiopharmaceutical could possibly become a new targeted means to achieve safe and effective reduction of tumor burden as well as facilitate better surgery and/or radiotherapy for difficult to resect large, or metastatic tumors.

Bone-targeted therapies in metastatic castration-resistant prostate cancer: evolving paradigms

Majority of patients with metastatic castrate resistant prostate cancer (mCRPC) develop bone metastases which results in significant morbidity and mortality as a result of skeletal-related events (SREs). Several bone-targeted agents are either in clinical use or in development for prevention of SREs. Bisphosphonates were the first class of drugs investigated for prevention of SREs and zoledronic acid is the only bisphosphonate that is FDA-approved for this indication. Another bone-targeted agent is denosumab which is a fully humanized monoclonal antibody that binds to the RANK-L thereby inhibiting RANK-L mediated bone resorption. While several radiopharmaceuticals were approved for pain palliation in mCRPC including strontium and samarium, alpharadin is the first radiopharmaceutical to show significant overall survival benefit. Contemporary therapeutic options including enzalutamide and abiraterone have effects on pain palliation and SREs as well. Other novel bone-targeted agents are currently in development, including the receptor tyrosine kinase inhibitors cabozantinib and dasatinib. Emerging therapeutics in mCRPC has resulted in great strides in preventing one of the most significant sources of complications of bone metastases.

Optimal bone health management strategies in patients with prostate cancer

Bone health is affected in patients with prostate cancer, both by the disease and its treatment. Metastases to bone leads to pain, fractures, and spinal cord compression; bone loss due to androgen deprivation therapy (ADT) leads to osteoporosis and its complications. Both these scenarios are a major cause of morbidity and adversely affect the quality of life of these patients. Maintaining an optimum bone health throughout the natural course of prostate cancer is an important aspect in the management of this disease. An understanding of the complex interplay between osteoclasts, osteoblasts, receptor activator of nuclear factor κB (RANK), and various other tyrosine kinases involved in the pathophysiology of bone metastases is essential. Zoledronic acid (ZA), an intravenously administered bisphosphonate, and Denosumab, a subcutaneously administered inhibitor of nuclear factor B ligand (RANKL), have already been approved by Food and Drug Administration (FDA) for their use in treatment of bone metastases. This article discusses the pathophysiology of bone metastases and bone loss due to ADT in prostate cancer, role of biomarkers, newer modalities of imaging, World Health Organization (WHO)/FRAX nomogram in evaluation of these patients, utility of currently available drugs and evidence supporting their use, and newer therapeutic agents like alpha-emitting Radium-223, endothelin-A receptor antagonists (Atrasentan and Zibotentan) and the proto-oncogene tyrosine-protein kinase (SRC) inhibitor, Dasatinib.

Repetitively dosed docetaxel and ¹⁵³samarium-EDTMP as an antitumor strategy for metastatic castration-resistant prostate cancer

BACKGROUND

β-emitting bone-seeking radiopharmaceuticals have historically been administered for pain palliation whereas docetaxel prolongs life in patients with metastatic castration-resistant prostate cancer (mCRPC). In combination, these agents simultaneously target the bone stroma and cancer cell to optimize antitumor effects. The toxicity and efficacy when each agent is combined at full, recommended doses, in a repetitive fashion is not well established.

METHODS

Patients with progressive mCRPC and ≥ 3 bone lesions received (153) Sm-EDTMP (samarium-153 ethylene diamine tetramethylene phosphonate) at a dose of 1.0 mCi/kg every 9 weeks and docetaxel at a dose of 75 mg/m(2) every 3 weeks. In the absence of unacceptable toxicity, patients were allowed to continue additional cycles, defined by 9 weeks of treatment, until intolerance or biochemical/radiographic disease progression.

RESULTS

Of the 30 patients treated, approximately 50% were considered to be taxane-naive, 36.7% were taxane-refractory, and 13.3% had previously been exposed to taxanes but were not considered refractory. Patients received on average 2.5 cycles of treatment (6.5 doses of docetaxel and 2.5 doses of (153) Sm-EDTMP). Twelve patients (40%) demonstrated a decline in their prostate-specific antigen level of ≥ 50%. The median progression-free survival (biochemical or radiographic) was 7.0 months and the overall survival was 14.3 months. Nine patients (30%) did not recover platelet counts >100 K/mm(3) after a median of 3 cycles to allow for additional treatment, with 4 patients experiencing prolonged thrombocytopenia. The most common reasons for trial discontinuation were progressive disease and hematologic toxicity.

CONCLUSIONS

The results of the current study indicate that (153) Sm-EDTMP can be safely combined with docetaxel at full doses on an ongoing basis in patients with mCRPC. Although thrombocytopenia limited therapy for some patients, preliminary efficacy supports the strategy of combining a radiopharmaceutical with chemotherapy, which is an appealing strategy given the anticipated availability of α emitters that can prolong survival.

Targeting bone physiology for the treatment of metastatic prostate cancer

Metastatic prostate cancer has a unique predilection for bone that can lead to significant clinical sequelae, such as fracture and cord compression. This tropism for bone yields not only clinical challenges, but also opportunities to understand the tumor biology in bone and to develop relevant therapeutic strategies. The process by which tumor cells migrate to bone, remain dormant, and then colonize and expand is based on complex interactions between prostate cancer tumor cells and the host microenvironment. This review will provide an overview of these interactions as well as therapies targeting osseous metastases in castration-resistant prostate cancer.

Beyond Palliation: Therapeutic Applications of 153Samarium-EDTMP

Primary and metastatic malignant bone lesions result in significant pain and disability in oncology patients. Targeted bone-seeking radioisotopes including ¹⁵³Samarium ethylene-diamine-tetramethylene-phosphonic acid (¹⁵³Sm-EDTMP) have been shown to effectively palliate bone pain, often when external beam radiotherapy (EBRT) is not feasible. However, recent evidence also suggests ¹⁵³Sm-EDTMP has cytotoxic activity either alone or in combination with chemotherapy or EBRT. ¹⁵³Sm-EDTMP may be useful as anti-neoplastic therapy apart from pain palliation in a variety of malignancies. For prostate cancer patients, several phase I and II clinical trials have shown that combined ¹⁵³Sm-EDTMP and docetaxel-based chemotherapy can result in >50% decrease in prostate-specific antigen with manageable myelosuppression. In hematologic malignancies, ¹⁵³Sm-EDTMP produced clinical responses when combined with bortezomib in multiple myeloma. ¹⁵³Sm-EDTMP also can be used with myeloablative chemotherapy for marrow conditioning prior to stem cell transplant. In osteosarcoma, ¹⁵³Sm-EDTMP infusion delivers radiation to multiple unresectable lesions simultaneously and provides local cytotoxicity without soft tissue damage that can be combined with chemotherapy or radiation. Prior to routine incorporation of ¹⁵³Sm-EDTMP into therapeutic regimens, we must learn how to ensure optimal delivery to tumors, determine which patients are likely to benefit, improve our ability to assess clinical response in bone lesions and further evaluate the efficacy ¹⁵³Sm-EDTMP in combination with chemotherapy, radiation and novel targeted agents.

Therapeutic strategies for bone metastases and their clinical sequelae in prostate cancer

OPINION STATEMENT

Skeletal metastases threaten quality of life, functionality, and longevity in patients with metastatic castration-resistant prostate cancer (mCRPC). Therapeutic strategies for bone metastases in prostate cancer can palliate pain, delay/prevent skeletal complications, and prolong survival. Pharmacologic agents representing several drug classes have demonstrated the ability to achieve these treatment goals in men with mCRPC. Skeletal-related events such as fracture and the need for radiation can be delayed using drugs that target the osteoclast/osteoblast pathway. Cancer-related bone pain can be palliated using beta-emitting bone-seeking radiopharmaceuticals such as samarium-153 EDTMP and strontium-89. Also, prospective randomized studies have demonstrated that cytotoxic chemotherapy can palliate bone pain. For the first time, bone-directed therapy has been shown to prolong survival using the novel alpha-emitting radiopharmaceutical radium-223. Given these multifold clinical benefits, treatments targeting bone metabolism, tumor-bone stromal interactions, and bone metastases themselves are now central elements of routine clinical care. Decisions about which agents, alone or in combination, will best serve the patient's and clinician's clinical goals is contingent on the treatment history to date, present disease manifestations, and symptomatology. Clinical trials exploring novel agents such as those targeting c-Met and Src are under way, using endpoints that directly address how patients feel, function, and survive.

The Role of Bone-Seeking Radionuclides in the Palliative Treatment of Patients with Painful Osteoblastic Skeletal Metastases

Background

Pain from skeletal metastases represents a major burden of advanced disease from solid tumors. Analgesic medications, bisphosphonates, hormonal agents, cytotoxic chemotherapy, and external beam radiotherapy are all effective treatments. However, patients often suffer from diffuse painful metastases and respond poorly to these standard therapies. Bone-seeking radionuclides can specifically target osteoblastic lesions to offer palliation of pain.

Methods

This article offers a narrative review of bone-seeking radionuclides, examines the evidence of safety and efficacy for the treatment of painful skeletal metastases, and presents guidelines for their appropriate use in this patient population.

Results

Seven bone-seeking radionuclides have shown evidence of both safety and efficacy in reducing pain from diffuse skeletal metastases. 153Sm-EDTMP and 89Sr are most commonly used in the United States and have been safely utilized for both repeat dosing as well as concurrent dosing with cytotoxic chemotherapy.

Conclusions

Targeted bone-seeking radionuclides are underutilized in the treatment of painful diffuse osteoblastic metastases. Several new agents are in active clinical investigation, and the pending approval of the first alpha-emitting radionuclide (223Ra) may offer a new class of agents that provide greater efficacy and less toxicity than those currently available for routine clinical use.

Castration-resistant prostate cancer: new science and therapeutic prospects

There is a growing number of new therapies targeting different pathways that will revolutionize patient management strategies in castration-resistant prostate cancer (CRPC) patients. Today there are more clinical trial options for CRPC treatment than ever before, and there are many promising agents in late-stage clinical testing. The hypothesis that CRPC frequently remains driven by a ligand-activated androgen receptor (AR) and that CRPC tissues exhibit substantial residual androgen levels despite gonadotropin-releasing hormone therapy, has led to the evaluation of new oral compounds such as abiraterone and MDV 3100. Their results, coupled with promising recent findings in immunotherapy (eg sipuleucel-T) and with agents targeting angiogenesis (while awaiting the final results of the CALGB trial 90401) will most probably impact the management of patients with CRPC in the near future. Other new promising agents need further development. With our increased understanding of the biology of this disease, further trial design should incorporate improved patient selection so that patient populations are those who may be most likely to benefit from treatment.

Optimal management of bone metastases in prostate cancer

The biological basis of the selective outgrowth of disseminated prostate cancer cells within the hematopoietic bone microenvironment remains a compelling biological mystery. A major proportion of the morbidity and mortality related to prostate cancer can be traced to the burden of bone metastases. The optimal management of bone health in men with prostate cancer requires control of the underlying epithelial neoplasm, attenuation of the subverted bone remodeling process that accompanies disease progression, reduction in the bone complications of disease-directed therapy, and management of co-existing comorbidities that enhance bone fragility. While bone-homing radioisotopes, bisphosphonates, and RANK ligand inhibitors have demonstrated reduction in bone pain and/or other skeletal-related events, further advances into definitive improvements in survival and/or global quality of life are required. A deeper understanding of the biology of bone metastases will likely facilitate a bone-directed therapeutic approach toward a major impact on the survival of men with this important disease.

Multimodality therapy: bone-targeted radioisotope therapy of prostate cancer

Accumulating data suggest that bone-seeking radiopharmaceuticals can be used to treat prostate cancer bone metastasis and improve the clinical outcome of patients with advanced prostate cancer. It remains to be elucidated whether radiopharmaceuticals enhance the disruption of the onco-niche or the eradication of micrometastatic cells in the bone marrow. The purpose of this review is to investigate the role of bone-targeted radioisotope therapy in the setting of multimodality therapy for advanced prostate cancer. We examine available data and evaluate whether dose escalation, newer generations, or repeated dosing of radiopharmaceuticals enhance their antitumor effects and whether their combination with hormone ablative therapy, chemotherapy, or novel targeted therapy can improve clinical efficacy.

The role of docetaxel based therapy for prostate cancer in the era of targeted medicine

Docetaxel based chemotherapy has been shown to modestly extend life, relieve pain and improve the quality of life in patients with metastatic castration-resistant prostate cancer. Current trials are attempting to build on the backbone of docetaxel by combining it with novel biological agents. Trials are also investigating the role of docetaxel for earlier stages of prostate cancer. No standard second-line systemic therapy exists and such patients are candidates for clinical trials. The increased understanding of the mechanisms of progressive castration-resistant prostate cancer is being translated into an increasing pipeline of novel therapies.

Phase I trial with a combination of docetaxel and ¹⁵³Sm-lexidronam in patients with castration-resistant metastatic prostate cancer

BACKGROUND

This study was designed to evaluate toxicity and preliminary efficacy of 2 cycles of concomitant standard dose/schedule of (153)Sm-lexidronam plus Q 3 weeks schedule escalating doses of docetaxel in metastatic castration-resistant prostate cancer (mCRPC).

METHODS

mCRPC patients with progressive bone metastases were treated in 4 cohorts. Docetaxel doses were escalated from 50, 50, 0 mg/m(2) (on days 1, 22, 43, per 12-week cycle) to 75, 75, 75 mg/m(2). (153)Sm-lexidronam was administered on days 2 (Q 12 weeks) at dose of 1 mCi/kg/cycle (maximum of 2 cycles).

RESULTS

Thirteen patients received an average of 3.6 doses of docetaxel (range, 2-6 doses, median 4) and 1.5 doses of (153)Sm-lexidronam (range, 1-2, median 2). Toxicity was primarily hematologic. There were total 35 episodes grade 3/4 neutropenia with a median 7 (range 7-14) days to recovery to ≤grade 1. One dose limiting grade 3 thrombocytopenia occurred on cohorts 3 and 4. Eight of 13 (62%) patients had PSA > 50% decrease as best response during the treatment. Median time to bone disease progression was 5.2 months (range 91 days-10 months+); 6/13 (46%) patients had stable/improved bone scans at 6 months and 6/6 (100%) symptomatic patients had improvement in pain.

CONCLUSIONS

Concurrent 6-month administration of 4 doses (75 mg/m(2)) of standard Q 3 weeks schedule of docetaxel with 2 Q 3 months infusions of 1 mCi/Kg (153)Sm-lexidronam is feasible with reversible bone marrow suppression, and deserves further testing in mCRPC patients with extensive bone metastasis.