Phase I pharmacokinetic and biodistribution study with escalating doses of ²²³Ra-dichloride in men with castration-resistant metastatic prostate cancer. Eur J Nucl Med Mol Imaging. 2013;40:1384-1393. [PMID: 23653243 DOI: 10.1007/s00259-013-2427-6]

Development of separation technology for the removal of radium-223 from decayed thorium-227 in drug formulations. Material screening and method development

Targeted thorium conjugates are currently being investigated as a new class of alpha-radiopharmaceuticals. The natural decay of thorium-227 ((227)Th) results in the ingrowth of radium-223 ((223)Ra). Consideration must, therefore, be given to define acceptable limits of (223)Ra in the drug product at the time of dose administration. By effective sequestration of (223)Ra, we aim to improve the radiochemical purity and extend the effective user window of drug products containing (227)Th. (223)Ra is the first progeny of (227)Th and the only one with a long half-life (days). We have, therefore, focused on the removal of this specific species since the progenies of (223)Ra will have a very limited lifetime in the formulation once (223)Ra is removed. In this study, we investigated a multitude of materials for their ability to reduce the (223)Ra level by: (1) passive diffusion or (2) by cartridge filtration on gravity columns. In addition, we probe the compatibility of these materials in the presence of antibody trastuzumab to assess the level of protein binding and estimate the quenching of radiolysis by binding of radionuclides. A screening matrix of organic and inorganic materials was established, i.e. strontium and calcium alginate gel beads, distearoyl phosphatidylglycerol (DSPG) liposomes, ceramic hydroxyapatite, Zeolite UOP type 4A and cation exchange resins AG50W-X8 and SOURCE 30S. First, passive diffusional uptake of (223)Ra by suspended materials present in the formulation was measured as a decrease in sample radioactivity after separation. Second, selected materials were packed on gravity columns in order to evaluate the efficiency of column separation versus diffusional adsorption. The retention of (223)Ra and (227)Th were characterized by measuring the radioactivity in the eluate and on the columns. Finally, the compatibility between trastuzumab, as a selected model antibody, and suspensions of the binding materials was analyzed during storage of the drug product in the presence of adsorbent. The formation of H2O2 was evaluated to measure the influence of radionuclide binding material on radiolysis in the formulation. All the materials bound (223)Ra by passive diffusional uptake ranging from 31% to 95% with DSPG liposomes demonstrating superiority at 95% efficiency. All materials suitable for assessment by gravity column filtration bound (223)Ra almost quantitatively (∼100%) and with minimal variation (relative standard deviation  <1%). The uptake was significantly higher compared to passive diffusional uptake. Alginate gel beads, ceramic hydroxyapatite and SOURCE 30S reduced the antibody concentration in solution to 40-50% while the Zeolite UOP type 4A, AG50W-X8 resin and DSPG liposomes showed ≤10% reduction of antibody concentration. Ceramic hydroxyapatite significantly reduced H2O2 formed by radionuclide initiated radiolysis.

A Phase 1, Open-Label Study of the Biodistribution, Pharmacokinetics, and Dosimetry of 223Ra-Dichloride in Patients with Hormone-Refractory Prostate Cancer and Skeletal Metastases

The aim of this single-site, open-label clinical trial was to determine the biodistribution, pharmacokinetics, absorbed doses, and safety from 2 sequential weight-based administrations of (223)Ra-dichloride in patients with bone metastases due to castration-refractory prostate cancer.

METHODS

Six patients received 2 intravenous injections of (223)Ra-dichloride, 6 wk apart, at 100 kBq/kg of whole-body weight. The pharmacokinetics and biodistribution as a function of time were determined, and dosimetry was performed for a range of organs including bone surfaces, red marrow, kidneys, gut, and whole body using scintigraphic imaging; external counting; and blood, fecal, and urine collection. Safety was assessed from adverse events.

RESULTS

The injected activity cleared rapidly from blood, with 1.1% remaining at 24 h. The main route of excretion was via the gut, although no significant toxicity was reported. Most of the administered activity was taken up rapidly into bone (61% at 4 h). The range of absorbed doses delivered to the bone surfaces from α emissions was 2,331-13,118 mGy/MBq. The ranges of absorbed doses delivered to the red marrow were 177-994 and 1-5 mGy/MBq from activity on the bone surfaces and from activity in the blood, respectively. No activity-limiting toxicity was observed at these levels of administration. The absorbed doses from the second treatment were correlated significantly with the first for a combination of the whole body, bone surfaces, kidneys, and liver.

CONCLUSION

A wide range of interpatient absorbed doses was delivered to normal organs. Intrapatient absorbed doses were significantly correlated between the 2 administrations for any given patient. The lack of gastrointestinal toxicity is likely due to the low absorbed doses delivered to the gut wall from the gut contents. The lack of adverse myelotoxicity implies that the absorbed dose delivered from the circulating activity may be a more relevant guide to the potential for marrow toxicity than that due to activity on the bone surfaces.

Dosimetry of bone metastases in targeted radionuclide therapy with alpha-emitting (223)Ra-dichloride

PURPOSE

Ra-dichloride is an alpha-emitting radiopharmaceutical used in the treatment of bone metastases from castration-resistant prostate cancer. Image-based dosimetric studies remain challenging because the emitted photons are few. The aim of this study was to implement a methodology for in-vivo quantitative planar imaging, and to assess the absorbed dose to lesions using the MIRD approach.

METHODS

The study included nine Caucasian patients with 24 lesions (6 humeral head lesions, 4 iliac wing lesions, 2 scapular lesions, 5 trochanter lesions, 3 vertebral lesions, 3 glenoid lesions, 1 coxofemoral lesion). The treatment consisted of six injections (one every 4 weeks) of 50 kBq per kg body weight. Gamma-camera calibrations for (223)Ra included measurements of sensitivity and transmission curves. Patients were statically imaged for 30 min, using an MEGP collimator, double-peak acquisition, and filtering to improve the image quality. Lesions were delineated on (99m)Tc-MDP whole-body images, and the ROIs superimposed on the (223)Ra images after image coregistration. The activity was quantified with background, attenuation, and scatter correction. Absorbed doses were assessed deriving the S values from the S factors for soft-tissue spheres of OLINDA/EXM, evaluating the lesion volumes by delineation on the CT images.

RESULTS

In 12 lesions with a wash-in phase the biokinetics were assumed to be biexponential, and to be monoexponential in the remainder. The optimal timing for serial acquisitions was between 1 and 5 h, between 18 and 24 h, between 48 and 60 h, and between 7 and 15 days. The error in cumulated activity neglecting the wash-in phase was between 2 % and 12 %. The mean effective half-life (T 1/2eff) of (223)Ra was 8.2 days (range 5.5-11.4 days). The absorbed dose (D) after the first injection was 0.7 Gy (range 0.2-1.9 Gy. Considering the relative biological effectiveness (RBE) of alpha particles (RBE = 5), D RBE = 899 mGy/MBq (range 340-2,450 mGy/MBq). The percent uptake of (99m)Tc and (223)Ra (activity extrapolated to t = 0) were significantly correlated.

CONCLUSION

The feasibility of in vivo quantitative imaging in (223)Ra therapy was confirmed. The lesion uptake of (223)Ra-dichloride was significantly correlated with that of (99m)Tc-MDP. The D RBE to lesions per unit administered activity was much higher than that of other bone-seeking radiopharmaceuticals, but considering a standard administration of 21 MBq (six injections of 50 kBq/kg to a 70-kg patient), the mean cumulative value of D RBE was about 19 Gy, and was therefore in the range of those of other radiopharmaceuticals. The macrodosimetry of bone metastases in treatments with (223)Ra-dichloride is feasible, but more work is needed to demonstrate its helpfulness in predicting clinical outcomes.

Assessment of anticancer-treatment outcome in patients with metastatic castration-resistant prostate cancer-going beyond PSA and imaging, a systematic literature review

BACKGROUND

In the past years, there has been significant progress in anticancer drug development for patients with metastatic castration-resistant prostate cancer (CRPC). However, the current instruments to assess clinical treatment response have limitations and may not sufficiently reflect patient benefit. Our objective was to systematically identify tools to evaluate both patient benefit and clinical anticancer-treatment response as basis for an international consensus process and development of a specific pragmatic instrument for men with CRPC.

METHODS

PubMed, Embase and CINAHL were searched to identify currently available tools to assess anticancer-treatment benefit, other than standard imaging procedures and prostate-specific antigen measurements, namely quality of life (QoL), detailed pain assessment, physical function and objective measures of other complex cancer-related syndromes in patients with CRPC. Additionally, all CRPC phase III trials published in the last 5 years were reviewed as well as studies using physical function tools in a general cancer population. The PRIMSA statement was followed for the systematic review process.

RESULTS

The search generated 1096 hits, 185 full-text papers were screened and finally 73 publications were included. Additional 89 publications were included by hand-search. We identified a total of 98 tools used in CRPC trials and grouped these into three categories: 22 tools assessing QoL domains and subgroups, 47 tools for pain assessment and 29 tools for objective measures, mainly physical function and assessment of skeletal disease burden.

CONCLUSION

A wide variety of assessment tools and also efforts to standardize and harmonize patient-reported outcomes and pain assessment were identified. However, the specific needs of the increasing CRPC population living longer with their incurable cancer are insufficiently captured and objective physical outcome measures are under-represented. In the age of new anticancer drug targets and principles, new methods to monitor patient relevant outcomes of antineoplastic therapy are of utmost importance.

Radium-223 dichloride: a review of its use in patients with castration-resistant prostate cancer with symptomatic bone metastases

Radium-223 dichloride (Xofigo®; formerly Alpharadin™) [hereafter referred to as radium-223] is a first-in-class alpha particle-emitting radiopharmaceutical that has recently been approved for the treatment of patients with castration-resistant prostate cancer (CRPC) with symptomatic bone metastases and no known visceral metastatic disease. Radium-223 is a calcium mimetic, which targets bone, delivering cytotoxic radiation to the sites of bone metastases. In the recently reported Alpharadin™ in Symptomatic Prostate Cancer (ALSYMPCA) phase III study, radium-223 was associated with significantly improved overall survival compared with placebo, making it the first bone-targeted CRPC therapy for which an overall survival benefit has been demonstrated. The ALSYMPCA study also demonstrated the beneficial effects of radium-223 on disease-related symptomatic skeletal events, pain and health-related quality of life. Radium-223 was generally well tolerated, being associated with low rates of myelosuppression and generally mild gastrointestinal adverse events. Thus, radium-223 is a valuable addition to the treatment options for this poor-prognosis population.

223Ra α-Therapy in Patients with Bone Metastases from Castration-resistant Prostate Cancer

In developed countries such as Canada, the lifetime risk of prostate cancer is about one in six, with a 30% chance of relapse with bone metastases in each case. Bone involvement not only decreases prognosis, but also increases the likelihood of many other medical ailments. There currently exist numerous treatment options for pain palliation for these patients. Common options include chemotherapy, external beam radiotherapy, bisphosphonates, and radionuclide therapy with strontium 89. Each variation, however, shows clear drawbacks. A type of radionuclide therapy, newly approved in Canada, using alpha particles from radium 223 is showing promise. Unlike the previously mentioned therapies, radium 223 is the only one that excels in all desirable aspects for palliation therapy. Radium 223 not only decreases or eliminates metastases-related bone pain, but also has a great safety profile, increases the average length of survival, and exhibits areas of cost-effectiveness. Radium 223 also delays skeletal-related events and prostate-specific antigen elevation, representing a noteworthy breakthrough for bone-targeted radionuclide therapies.

Radium-223 dichloride for the treatment of bone metastatic castration-resistant prostate cancer: an evaluation of its safety

INTRODUCTION

Approximately 10 - 20% of prostate cancer cases ultimately progress to castration-resistant prostate cancer (CRPC), for which there is a poor prognosis and a therapeutic need. Radium-223 dichloride (radium-223 [Xofigo]) is a first-in-class α-emitting radiopharmaceutical shown to significantly prolong overall survival in patients with CRPC with symptomatic bone metastases and no visceral metastases. Current treatment guidelines recommended it in both pre- and post-docetaxel settings.

AREAS COVERED

Radium-223 mechanism of action, pharmacokinetics and key efficacy and safety data are reviewed. The evaluation of adverse events reported in the Phase III ALSYMPCA trial is summarized for the overall population and patient subpopulations (prior docetaxel, concomitant external beam radiation therapy and baseline opioid use). An evaluation of how radium-223 is being incorporated into the CRPC treatment paradigm and the implications of its safety profile for future use are provided.

EXPERT OPINION

The pronounced efficacy and safety profile of radium-223 positions it as a valuable new therapeutic tool in the CRPC armamentarium. Its novel mechanism of action underlies low rates of hematologic adverse events. Radium-223 treatment will become common in the majority of pre-docetaxel symptomatic CRPC cases, as it has proved to be highly efficient with few safety concerns earlier in the course of disease.

Radium-223 for the treatment of castration-resistant prostate cancer

The vast majority of patients with metastatic castration-resistant prostate cancer (mCRPC) develop bone metastases. Bone metastases are a source of significant morbidity and affect quality of life in these patients. Several bone-targeting agents are approved for the treatment of bone metastases in prostate cancer, including bisphosphonates, denosumab, and radiopharmaceuticals. Radium-223 is a novel first-in-class alpha-emitting radiopharmaceutical that has been approved for treatment of patients with mCRPC with bone metastases. Radium-223 delivers cytotoxic radiation to the sites of bone metastases and offers the advantage of minimal myelosuppression. The landmark Phase III ALSYMPCA trial demonstrated that, in addition to providing bone-related palliation, radium-223 can also prolong overall survival in patients with mCRPC with bone metastases in the absence of visceral metastases and in the absence of lymphadenopathy greater than 3 cm. Ongoing trials will further elucidate its use in sequence or combination with other available therapies for mCRPC.

Pain, PSA flare, and bone scan response in a patient with metastatic castration-resistant prostate cancer treated with radium-223, a case report

Background

Radium-223 has been shown to improve overall survival in men with metastatic castration-resistant prostate cancer with symptomatic bone metastases. The bone scan response to radium-223 has only been described in one single center trial of 14 patients, none of whom achieved the outstanding bone scan response presented in the current case.

Case presentation

In this case report, we describe a 75 year-old white man with extensively pre-treated metastatic castration-resistant prostate cancer and symptomatic bone metastases who experienced a flare in pain and prostate-specific antigen, followed by dramatic clinical (pain), biochemical (prostate-specific antigen), and imaging (bone scan) response.

Conclusion

The flare phenomena and bone scan response we observed have not previously been described with radium-223. This case suggests that the degree and duration of bone scan response may be predictive of overall survival benefit.

Targeting bone metastases in prostate cancer: improving clinical outcome

Bone metastases develop in most patients with metastatic castration-resistant prostate cancer (mCRPC). They affect the structural integrity of bone, manifesting as pain and skeletal-related events (SREs), and are the primary cause of patient disability, reduced quality of life (QOL) and death. Understanding the pathophysiology of bone metastases resulted in the development of agents that improve clinical outcome, suggesting that managing both the systemic disease and associated bone events is important. Historically, the treatment of CRPC bone metastases with early radiopharmaceuticals and external beam radiation therapy was largely supportive; however, now, zoledronic acid and denosumab are integral to the therapeutic strategy for mCRPC. These agents substantially reduce skeletal morbidity and improve patient QOL. Radium-223 dichloride is the first bone-targeting agent to show improved survival and reduced pain and symptomatic skeletal events in patients with mCRPC without visceral disease. Five other systemic agents are currently approved for use in mCRPC based on their ability to improve survival. These include the cytotoxic drugs docetaxel and cabazitaxel, the hormone-based therapies, abiraterone and enzalutamide, and the immunotherapeutic vaccine sipuleucel-T. Abiraterone and enzalutamide are able to reduce SREs and improve survival in this setting. Novel agents targeting tumour and bone cells are under clinical development.

Radium-223 in the treatment of osteoblastic metastases: a critical clinical review

The element radium (Ra) was discovered by the Curies in 1898 and within a decade was in broad scientific testing for the management of several forms of cancer. The compound was known to give rise to a series of both high-energy particulate and penetrating γ-emissions. The latter found an important role in early 20th century brachytherapy applications, but the short-range α-particles seemed much less useful. Although highly cytotoxic when released within a few cell diameters of critical cell nuclei, the dense double-strand break damage was poorly repaired, and concerns regarding treatment-related toxicities and secondary malignancies halted clinical development. Moreover, the most common isotope of Ra has an exceptionally long half-life (>1600 years for (226)Ra) that proved daunting when aiming for a systemic cancer therapy. Fortunately, other radium isotopes have more convenient half-lives while still producing cytotoxic α particles. Radium-223 dichloride has a half-life of 11.4 days, and this isotope was identified as an excellent candidate for radionuclide therapy of cancers metastatic to bone. The calcium-mimetic chemical properties of the radium allowed intravenous infusion with rapid uptake to sites of new bone formation. The highly efficient bone localization suggested a potential therapeutic role for osteoblastic bone metastases, and a series of phase 1, 2, and 3 clinical trials was undertaken to explore this possibility. This series of clinical explorations culminated in the ALSYMPCA trial, an international, placebo-controlled, phase 3 study that accrued 921 symptomatic men with bone-metastatic, castrate-resistant prostate cancer. Results of this trial demonstrated a prolongation of overall survival, and regulatory agencies around the world have now approved this product as a treatment for advanced prostate cancer.

One-Year Postapproval Clinical Experience with Radium-223 Dichloride in Patients with Metastatic Castrate-Resistant Prostate Cancer

OBJECTIVES

We report our 1-year postapproval clinical experience with Radium-223 dichloride for treatment of castrate-resistant prostate cancer with bone metastases.

METHODS

The clinical courses of the first 25 patients treated were reviewed retrospectively. Incidence of hematologic, gastrointestinal, and other adverse events were identified, including those events that led to cessation or delay in treatment. Alterations in bone pain and serum alkaline phosphatase and prostate-specific antigen (PSA) levels were evaluated.

RESULTS

Six patients received all 6 scheduled doses of Radium-223 dichloride, 2 completed 5 doses, 6 received 4 doses, 2 completed 3 doses, 6 patients had 2 doses, and 3 patients received one dose, for a total of 91 doses administered. Nine patients discontinued treatment after receiving at least one dose due to progressive disease, 5 required blood transfusions, 5 developed gastrointestinal symptoms, 4 reported worsening bone pain, and 1 developed dermatitis. Downward trends in serum alkaline phosphatase and PSA were seen in 11 and 5 patients, respectively.

CONCLUSIONS

About one-quarter of cohort completed the entire six-dose treatment. Advancing soft tissue disease was the primary reason for cessation of therapy. The adverse events were mild and manageable. A decline in serum alkaline phosphatase was more common than a decline in PSA.

Treatment of castration-resistant prostate cancer and bone metastases with radium-223 dichloride

Radium-223 dichloride (Ra-223) is the first α-particle emitting radiopharmaceutical to be approved for the treatment of patients with castration-resistant prostate cancer and associated bone metastases, and the first bone-targeting agent to significantly improve patient overall survival whilst reducing pain and the symptomatic skeletal events (SSEs) associated with bone metastases. Ra-223 exhibits a favourable safety profile, with low myelosuppression rates and fewer adverse events than placebo. Compared with other approved radiopharmaceuticals, the α-particle emitting Ra-223 has a high biological efficiency and a short penetration range, potentially sparing bone marrow toxicity and limiting unwanted exposure. Ra-223 has a short half-life and decays to a stable product, reducing the problem of storage and disposal associated with radiopharmaceuticals. Ra-223 offers a new treatment option with great potential in this setting. However, concerns remain amongst patients, their families and health care professionals over the use of radiopharmaceuticals. This article, which draws on the experiences of health care workers during the ALSYMPCA (ALpharadin in SYMtomatic Prostate CAncer) study, reviews the clinical development of Ra-223, highlighting the key issues for the uro-oncology nurse who has a pivotal role within the multi-disciplinary team (MDT) to ensure safe and effective treatment to the patient. The role of the uro-oncology nurse is multifaceted, including patient pre-assessment and post-treatment monitoring and coordination of the MDT. In addition, their role in communicating with and educating those involved with Ra-223 on what to expect from the agent can alleviate fears associated with its use.

Targeted alpha anticancer therapies: update and future prospects

Targeted alpha therapy (TAT) is an emerging option for local and systemic cancer treatment. Preclinical research and clinical trials show that alpha-emitting radionuclides can kill targeted cancer cells while sparing normal cells, thus reducing toxicity. (223)RaCl2 (Xofigo(®)) is the first alpha emitting radioisotope to gain registration in the US for palliative therapy of prostate cancer bone metastases by indirect physiological targeting. The alpha emitting radioisotopes (211)At, (213)Bi, (225)Ac and (227)Th are being used to label targeting vectors such as monoclonal antibodies for specific cancer therapy indications. In this review, safety and tolerance aspects are considered with respect to microdosimetry, specific energy, Monte Carlo model calculations, biodosimetry, equivalent dose and mutagenesis. The clinical efficacy of TAT for solid tumors may also be enhanced by its capacity for tumor anti-vascular (TAVAT) effects. This review emphasizes key aspects of TAT research with respect to the PAI2-uPAR complex and the monoclonal antibodies bevacizumab, C595 and J591. Clinical trial outcomes are reviewed for neuroendocrine tumors, leukemia, glioma, melanoma, non-Hodgkins lymphoma, and prostate bone metastases. Recommendations and future directions are proposed.

Clinical use of bone-targeting radiopharmaceuticals with focus on alpha-emitters

Various single or multi-modality therapeutic options are available to treat pain of bone metastasis in patients with prostate cancer. Different radionuclides that emit β-rays such as ¹⁵³Samarium and ⁸⁹Strontium and achieve palliation are commercially available. In contrast to β-emitters, ²²³Radium as a α-emitter has a short path-length. The advantage of the α-emitter is thus a highly localized biological effect that is caused by radiation induced DNA double-strand breaks and subsequent cell killing and/or limited effectiveness of cellular repair mechanisms. Due to the limited range of the α-particles the bone surface to red bone marrow dose ratio is also lower for ²²³Radium which is expressed in a lower myelotoxicity. The α emitter ²²³Radium dichloride is the first radiopharmaceutical that significantly prolongs life in castrate resistant prostate cancer patients with wide-spread bone metastatic disease. In a phase III, randomized, double-blind, placebo-controlled study 921 patients with castration-resistant prostate cancer and bone metastases were randomly assigned. The analysis confirmed the ²²³Radium survival benefit compared to the placebo (median, 14.9 mo vs 11.3 mo; P < 0.001). In addition, the treatment results in pain palliation and thus, improved quality of life and a delay of skeletal related events. At the same time the toxicity profile of ²²³Radium was favourable. Since May 2013, ²²³Radium dichloride (Xofigo^®) is approved by the US Food and Drug Administration.

Targeted α-particle therapy of bone metastases in prostate cancer

Medical oncology is moving toward personalized and precision treatments. This evolution is spearheaded by ongoing discoveries on the fundamental machinery that controls tumor and hosts microenvironment biological behavior. α-Particles with their high energy and short range had long been recognized as potentially useful in the treatment of cancer. More than a century after the discovery of radium by the Curies, 223Ra dichloride is now available in the expanding armamentarium of therapies for metastatic castration-resistant prostate cancer. This advance occurs in the context of several other novel therapeutics in advanced prostate cancer that include more effective androgen receptor pathway inhibition, better chemotherapy, and immunotherapy. We present a concise review on the therapeutic use of 223Ra dichloride in this clinically important setting including excerpts on the radium history, physical properties, the alpharadin in symptomatic prostate cancer clinical trial, and practical information on its use in the clinic. It is anticipated that, with the current emergence of 223Ra as a viable form of therapy, interest in and use of α-particle therapy in the management of cancer will grow.

Radiation safety considerations for the use of ²²³RaCl₂ DE in men with castration-resistant prostate cancer

The majority of patients with late stage castration-resistant prostate cancer (CRPC) develop bone metastases that often result in significant bone pain. Therapeutic palliation strategies can delay or prevent skeletal complications and may prolong survival. An alpha-particle based therapy, radium-223 dichloride (²²³RaCl₂), has been developed that delivers highly localized effects in target areas and likely reduces toxicity to adjacent healthy tissue, particularly bone marrow. Radiation safety aspects were evaluated for a single comprehensive cancer center clinical phase 1, open-label, single ascending-dose study for three cohorts at 50, 100, or 200 kBq kg⁻¹ body weight. Ten patients received administrations, and six patients completed the study with 1 y follow-up. Dose rates from patients administered ²²³Ra dichloride were typically less than 2 μSv h⁻¹ MBq⁻¹ on contact and averaged 0.02 μSv h⁻¹ MBq⁻¹ at 1 m immediately following administration. Removal was primarily by fecal excretion, and whole body effective half-lives were highly dependent upon fecal compartment transfer, ranging from 2.5-11.4 d. Radium-223 is safe and straightforward to administer using conventional nuclear medicine equipment. For this clinical study, few radiation protection limitations were recommended post-therapy based on facility evaluations. Specific precautions are dependent on local regulatory authority guidance. Subsequent studies have demonstrated significantly improved overall survival and very low toxicity, suggesting that ²²³Ra may provide a new standard of care for patients with CRPC and bone metastases.

Radioimmunotherapy with α-particle-emitting radionuclides

α-particle-emitting radionuclides are highly cytotoxic and are thus promising candidates for use in targeted radioimmunotherapy of cancer. Due to their high linear energy transfer (LET) combined with a short path length in tissue, α-particles cause severe DNA double-strand breaks that are repaired inaccurately and finally trigger cell death. For radioimmunotherapy, α-emitters such as 225Ac, 211At, 212Bi/212Pb, 213Bi and 227Th are coupled to antibodies via appropriate chelating agents. The α-emitter immunoconjugates preferably target proteins that are overexpressed or exclusively expressed on cancer cells. Application of α-emitter immunoconjugates seems particularly promising in treatment of disseminated cancer cells and small tumor cell clusters that are released during the resection of a primary tumor. α-emitter immunoconjugates have been successfully administered in numerous experimental studies for therapy of ovarian, colon, gastric, blood, breast and bladder cancer. Initial clinical trials evaluating α-emitter immunoconjugates in terms of toxicity and therapeutic efficacy have also shown positive results in patients with melanoma, ovarian cancer, acute myeloid lymphoma and glioma. The present problems in terms of availability of therapeutically effiective α-emitters will presumably be solved by use of alternative production routes and installation of additional production facilities in the near future. Therefore, clinical establishment of targeted α-emitter radioimmunotherapy as one part of a multimodal concept for therapy of cancer is a promising, middle-term concept.

Radium-223 chloride: Extending life in prostate cancer patients by treating bone metastases

The treatment scope for patients with metastatic castrate-resistant prostate cancer (mCRPC) is rapidly expanding. On May 15, 2013, the U.S. Food and Drug Administration (FDA) approved radium-223 chloride ((223)RaCl2) for the treatment of mCRPC patients whose metastases are limited to the bones. Radium-223 is an α-emitting alkaline earth metal ion, which, similar to calcium ions, accumulates in the bone. In a phase III study (ALSYMPCA), mCRPC patients with bone metastases received best standard-of-care treatment with placebo or (223)RaCl2. At a prespecified interim analysis, the primary endpoint of median overall survival was significantly extended by 3.6 months in patients treated with radium-223 compared with placebo (P < 0.001). The radioisotope was well tolerated and gave limited bone marrow suppression. (223)RaCl2 is the first bone-targeting antitumor therapy that received FDA approval based on a significant extended median overall survival. Further studies are required to optimize its dosing and to confirm its efficacy and safety in cancer patients.