Standard Safety Procedure Before Therapeutic Administration of 223Ra-Dichloride.

223Ra-dichloride is an α-emitter therapy approved for the treatment of castration-resistant prostate cancer with symptomatic bone metastases. 223Ra-dichloride is the first targeted α-therapy for this indication with evidence of benefit in overall survival. The administration is intravenous, and extravasation can cause severe injuries such as tissue necrosis. To prevent this side effect, some procedures can be performed according to the guideline of the European Association of Nuclear Medicine. Ionizing radiation is a well-established risk factor for the development of cutaneous squamous cell carcinoma, but surprisingly there are few reports of local adverse effects related to extravasation of radiotherapies at the injection sites. Recently, a possible case of cutaneous cancer was observed after 223Ra-dichloride extravasation. Methods: To complement the prevention of extravasation, we developed a standardized technique to be performed before the injection of 223Ra. Results: Our technique was successfully applied to the study population, and no apparent extravasation was seen. Conclusion: Our study suggests that use of this standardized technique before administration of 223Ra is helpful in preventing extravasation during this treatment.

Design and in vitro evaluation of 223Ra/99mTc-loaded spherical nano-hydroxyapatite in bone tumor therapy.

Aim: Nano-hydroxyapatite (nHA) is a good nanocarrier to load 223Ra, but the low specific activity (sp.act.) of 223Ra@nHA limits its application in medicine. Methods: We proposed a method for preparing nHA using PEG as a template, which significantly increases the sp.act of 223Ra@nHA and a new method to loaded 99mTc for in vivo tracking. Results: The nHA synthesized using PEG as a template was associated with higher sp.act for 223Ra in comparison to nHA with identical particle size and without PEG. The nHA load 99mTc-MDP was associated with higher labeling rate and stability in comparison to 99mTc. Conclusion: All these findings suggest that using PEG as a template and 99mTc-MDP could be the most effective of synthetic 223Ra/99mTc@nHA.

[Box: see text].

Biodistribution study of 211Pb progeny released from intravenously applied 223Ra labelled TiO2 nanoparticles in a mouse model.

BACKGROUND: Targeted alpha therapy is one of the most powerful therapeutical modalities available in nuclear medicine. It's therapeutic potency is based on the nuclides that emit one or several alpha particles providing strong and highly localized therapeutic effects. However, some of these radionuclides, like e.g.223Ra or 225Ac decay in cascades, where the radioactive progeny originating from the consecutive alpha-decays may leave the original vector and cause unwanted irradiation of non-target organs. This progeny, even if partially retained in target tissues by internalization processes, typically do not follow the fate of originally targeted radiopharmaceutical and potentially spread over body following their own biodistribution. In this study we aimed to estimate 211Pb/211Bi progeny fate from the 223Ra surface-labelled TiO2 nanoparticles in vitro and the fate of 211Pb in vivo in a mice model. RESULTS: In vitro stability studies have shown significant differences between the release of the mother 223Ra and its progeny (211Pb, 211Bi) in all the biological matrices that have been tested. The lowest released activities were measured in saline, resulting in less than 5 % of released activity for all nuclides. Contrary to that, the highest released activity of 223Ra of up to 10 % within 48 h was observed in 5 % solution of albumin. The released activity of its progeny; the 211Pb and 211Bi was in the range of 20-40 % in this test medium. Significantly higher released activities of 211Pb and 211Bi compared to 223Ra by at least 10 % was observed in each biological medium, except saline, where no significant differences were observed. The in vivo biodistribution studies results in a mice model, show similar pattern, where it was found that even after accumulation of nanoparticles in target tissues, approximately 10 % of 211Pb is continuously released into the blood stream within 24 h, followed by its natural accumulation in kidneys. CONCLUSION: This study confirms our assumption that the progeny formed in a chain alpha decay of a certain nuclide, in this case the 223Ra, can be released from its original vector, leave the target tissue, relocate and could be deposited in non-target organs. We did not observe complete progeny wash-out from its original target tissues in our model. This indicates strong dependence of the progeny hot atom fate after its release from the original radiopharmaceutical preparation on multiple factors, like their internalization and retention in cells, cell membranes, extracellular matrices, protein binding, etc. We hypothesize, that also the primary tumour or metastasis size, their metabolic activity may significantly influence progeny fate in vivo, directly impacting the dose delivered to non-target tissues and organs. Therefore a bottom-up approach should be followed and detailed pre-/clinical studies on the release and biodistribution of radioactive progeny originating from the chain alpha emitters should be preferably performed.

The Impact of Baseline PSMA PET/CT Versus CT on Outcomes of 223Ra Therapy in Metastatic Castration-Resistant Prostate Cancer Patients.

Imaging before 223Ra-dichloride (223Ra) therapy is crucial for selecting metastatic castration-resistant prostate cancer (mCRPC) patients with bone-only disease. The purpose of this study was to evaluate if baseline prostate-specific membrane antigen (PSMA) PET/CT (bPSMA) versus CT is associated with outcomes of 223Ra therapy. Methods: A secondary analysis of the data of a prospective observational study (NCT04995614) was performed. Patients received a maximum of 6 223Ra cycles and were retrospectively divided into the bPSMA or baseline CT (bCT) groups. All patients received baseline bone scintigraphy. Primary endpoints were alkaline phosphatase and prostate-specific antigen response. Secondary endpoints were overall survival (OS) and radiologic response. Results: Between 2017 and 2020, 122 mCRPC patients were included: 18 (14.8%) in the bPSMA group and 104 (85.2%) in the bCT group. All baseline characteristics were comparable. No significant differences in alkaline phosphatase or prostate-specific antigen response were found. The bCT group showed an OS significantly shorter than that of the bPSMA group (12.4 vs. 19.9 mo, P = 0.038). In 31 of 76 patients (40.1%) in the bCT group who also received posttherapy CT, lymph node or visceral metastases (soft-tissue involvement [STI]) were detected after 223Ra therapy, compared with 0 of 15 patients in the bPSMA group who received posttherapy PSMA PET/CT or CT. No significant difference in OS was found between patients in the bCT or posttherapy CT subgroup without STI (46/76) and the bPSMA group. Conclusion: bPSMA versus CT does not seem to impact biochemical response during 223Ra therapy in mCRPC patients. Nevertheless, patients in the bCT group had a significantly shorter OS, most likely due to underdetection of STI in this group. Therefore, replacing bCT with PSMA PET/CT appears to be a valuable screening method for identifying patients who will benefit most from 223Ra therapy.

Beyond Average: α-Particle Distribution and Dose Heterogeneity in Bone Metastatic Prostate Cancer.

α-particle emitters are emerging as a potent modality for disseminated cancer therapy because of their high linear energy transfer and localized absorbed dose profile. Despite great interest and pharmaceutical development, there is scant information on the distribution of these agents at the scale of the α-particle pathlength. We sought to determine the distribution of clinically approved [223Ra]RaCl2 in bone metastatic castration-resistant prostate cancer at this resolution, for the first time to our knowledge, to inform activity distribution and dose at the near-cell scale. Methods: Biopsy specimens and blood were collected from 7 patients 24 h after administration. 223Ra activity in each sample was recorded, and the microstructure of biopsy specimens was analyzed by micro-CT. Quantitative autoradiography and histopathology were segmented and registered with an automated procedure. Activity distributions by tissue compartment and dosimetry calculations based on the MIRD formalism were performed. Results: We revealed the activity distribution differences across and within patient samples at the macro- and microscopic scales. Microdistribution analysis confirmed localized high-activity regions in a background of low-activity tissue. We evaluated heterogeneous α-particle emission distribution concentrated at bone-tissue interfaces and calculated spatially nonuniform absorbed-dose profiles. Conclusion: Primary patient data of radiopharmaceutical therapy distribution at the small scale revealed that 223Ra uptake is nonuniform. Dose estimates present both opportunities and challenges to enhance patient outcomes and are a first step toward personalized treatment approaches and improved understanding of α-particle radiopharmaceutical therapies.

Biomarcadores pronósticos en el uso del radio-223 en pacientes con cáncer de próstata metastásico resistente a la castración / Prognostic biomarkers in the use of radium-223 in patients with metastatic castration-resistant prostate cancer

Objetivos Establecer biomarcadores basales en pacientes con cáncer de próstata metastásico resistente a la castración (CPMRC) tratados con Ra-223 que predigan una mejor supervivencia global (SG), así como valorar la toxicidad hematológica y la respuesta. Materiales y métodos Estudio retrospectivo multicéntrico en 151 pacientes con CPMRC tratados con Ra-223 entre 2013 y 2020. Se valoró la SG de acuerdo a: los niveles basales de hemoglobina (Hb), el antígeno prostático específico (PSA), la fosfatasa alcalina (FA), la escala de dolor de la OMS, el Eastern Cooperative Oncology Group (ECOG), el número de lesiones en gammagrafía ósea (GO), el uso de agentes de protección ósea y las dosis recibidas. Se determinó el grado de toxicidad hematológica y la respuesta basada en los cambios de la FA y el dolor pre y postratamiento. Resultados Mediana de SG de 24meses (IC95%: 16,5-31). En el 70% que recibieron tratamiento completo (5-6dosis) la mediana de SG fue de 34,9meses, versus 5,8 en el tratamiento incompleto (1-4dosis). La SG fue mayor en los pacientes con menor PSA, FA, Hb>13g/dl, menor número de metástasis óseas y ECOG 0-1. 52/151pacientes (34%) fallecieron durante el seguimiento. Cerca del 70% de los pacientes presentaron disminución del dolor, y el 66%, reducción de la FA. La mitad de los pacientes presentaron eventos adversos hematológicos leves, y solo el 5%, severos. Conclusiones Los pacientes con CPMRC tratados con Ra-223 que presentan biomarcadores basales como Hb>13g/ml, ECOG 0-1, PSA<20ng/ml y menor número de lesiones en GO muestran mejor SG, con un adecuado perfil de seguridad (AU)

Objectives Establish basal biomarkers in patients with bone metastatic castration-resistant prostate cancer (mCRPC) treated with Ra-223 that predicted a better overall survival (OS), assess hematology toxicity and treatment response. Materials and methods Retrospective multicenter study in 151 patients with mCRPC between 2013 and 2020. OS was assessed according to basal hemoglobin (Hb), PSA, alkaline phosphatase (AP), WHO pain scale, Eastern Cooperative Oncology Group (ECOG), number of metastatic lesions on bone scan (BS), use of protective bone agents and received. Hematological toxicities were evaluated. Treatment response was based on changes in FA and pain. Results Median OS was 24months (95%CI: 16.5-31). OS in 70% of patients who received complete Ra-223 treatment (5-6 doses) was 34.9m vs. 5.8m in patients with incomplete treatment (1-4 doses). OS was longer in patients with lower PSA and AP, Hb>13g/dL, lesser bone metastasis on GO and ECOG 0-1. 52/151 patients (34%) died during follow-up. Nearly 70% of patients experienced decrease in pain and 66% reduction on AP. Half of patients had mild hematological adverse effects and only 5% had severe. Conclusions mCRPC patients treated with Ra-223 who had Hb>13g/mL, ECOG 0-1, low AP, PSA<20ng/ml and lesser bone metastasis on BS shown a better OS with adequate safety profile (AU)

177Lu-Prostate-Specific Membrane Antigen Therapy in Patients with Metastatic Castration-Resistant Prostate Cancer and Prior 223Ra (RALU Study).

223Ra-dichloride (223Ra) and 177Lu-prostate-specific membrane antigen (PSMA) are approved treatments for metastatic castration-resistant prostate cancer (mCRPC). The safety and effectiveness of sequential use of 223Ra and 177Lu-PSMA in patients with mCRPC are not well described. This study aimed to evaluate 177Lu-PSMA safety and efficacy in patients with mCRPC previously treated with 223Ra. Methods: The radium→lutetium (RALU) study was a multicenter, retrospective, medical chart review. Participants had received at least 1 223Ra dose and, in any subsequent therapy line, at least 1 177Lu-PSMA dose. Primary endpoints included the incidence of adverse events (AEs), serious AEs, grade 3-4 hematologic AEs, and abnormal laboratory values. Secondary endpoints included overall survival, time to next treatment/death, and change from baseline in serum prostate-specific antigen and alkaline phosphatase levels. Results: Data were from 133 patients. Before 177Lu-PSMA therapy, 56% (75/133) of patients received at least 4 life-prolonging therapies; all patients received 223Ra (73% received 5-6 injections). Overall, 27% (36/133) of patients received at least 5 177Lu-PSMA infusions. Any-grade treatment-emergent AEs were reported in 79% (105/133) of patients and serious AEs in 30% (40/133). The most frequent grade 3-4 laboratory abnormalities were anemia (30%, 40/133) and thrombocytopenia (13%, 17/133). Median overall survival was 13.2 mo (95% CI, 10.5-15.6 mo) from the start of 177Lu-PSMA. Conclusion: In this real-world setting, 223Ra followed by 177Lu-PSMA therapy in heavily pretreated patients with mCRPC was clinically feasible, with no indication of impairment of 177Lu-PSMA safety or effectiveness.

Performance evaluation of alpha-particle discrimination using ultra-thin plastic scintillation sheets and their application to alpha-emitters for targeted alpha therapy.

Alpha-particle discrimination using ultra-thin plastic scintillator sheets for measuring the activity of α-emitters under the existence of α- and ß-emitters was investigated. 241Am, 32P and 223Ra were also used to evaluate the applicability of the present technique to α-emitters for medicine, and the self-absorption effect due to additives was investigated for validation. The results demonstrated that ≥95% of detection efficiency for α-particles emitted from 241Am with ≤1% ß-contribution of 32P for the low carrier salt concentration solution. Regarding using 223Ra, ≥90% of α-efficiency was achievable with ≤1% ß-contribution through sufficient dilution and selection of scintillator sheets of appropriate thicknesses.

68Ga-PSMA PET/CT for Response Evaluation of 223Ra Treatment in Metastatic Prostate Cancer.

CT and bone scintigraphy are not useful for response evaluation of bone metastases to 223Ra treatment in metastatic castration-resistant prostate cancer (mCRPC). PET using 68Ga prostate-specific membrane antigen 11 (68Ga-PSMA) is a promising tool for response evaluation of mCRPC. The aim of this study was to determine the utility of 68Ga-PSMA PET/CT for response evaluation of 223Ra treatment in patients with mCRPC. Methods: Within this prospective, multicenter, imaging discovery study, 28 patients with mCRPC, eligible for 223Ra treatment, were included between 2019 and 2022. Patients received 223Ra according to the standard of care. Study procedures included CT, bone scintigraphy, and 68Ga-PSMA PET/CT at baseline, after 3 and 6 cycles of 223Ra treatment, and on treatment failure. Response to 223Ra treatment was visually assessed on all 3 imaging modalities. Total tumor volume within bone (TTVbone) was determined on 68Ga-PSMA PET/CT. Intrapatient heterogeneity in response was studied using a newly developed image-registration tool for sequential images of PET/CT. Results were compared with failure-free survival (good responders vs. poor responders; cutoff, 24 wk) and alkaline phosphatase (ALP) response after 3 cycles. Results: Visual response assessment criteria could not distinguish good responders from poor responders on 68Ga-PSMA PET/CT and bone scintigraphy. For 68Ga-PSMA PET/CT, TTVbone at baseline was lower in good responders than in poor responders, whereas TTVbone increased in both groups during treatment. TTVbone was higher in patients with new extraosseous metastases during 223Ra treatment. Although TTVbone and ALP correlated at baseline, changes in TTVbone and ALP on treatment did not. 68Ga-PSMA response of TTVbone showed intrapatient heterogeneity in most patients. Conclusion: mCRPC patients with lower TTVbone on 68Ga-PSMA PET/CT have the best clinical outcome after 223Ra treatment. Response is highly heterogeneous in most patients. A decrease in ALP, which occurred in most patients, was not correlated with a decrease in TTVbone, which might make one question the value of ALP for disease monitoring during 223Ra treatment in clinical practice.

Prognostic biomarkers in the use of radium-223 in patients with metastatic castration-resistent prostate cancer.

OBJECTIVES: This study aimed to establish basal biomarkers in patients with bone metastatic castration-resistant prostate cancer (mCRPC) treated with 223Ra to predict better overall survival (OS), and assess hematologic toxicity and treatment response. MATERIALS AND METHODS: This was a retrospective multicenter study including 151 patients with mCRPC between 2013 and 2020. OS was assessed according to basal hemoglobin (Hb), prostate-specific antigen (PSA), and alkaline phosphatase (AP) values, the World Health Organization pain scale, the Eastern Cooperative Oncology Group (ECOG) performance status scale, the number of metastatic lesions on bone scintigraphy (BS), and the use of protective bone agents and the dose received. The grade of hematological toxicities was evaluated as well as treatment response based on changes in AP and pre- and post-treatment pain. RESULTS: The median OS was 24 months (95% confidence interval 16.5-31). The OS in 70% of patients who received complete (5-6 doses) versus incomplete (1-4 doses) 223Ra treatment was 34.9 vs. 5.8 months, respectively, being longer in patients with lower PSA and AP values, Hb >13 g/dl, lesser bone metastasis on bone scan and with an ECOG 0-1. 52/151 patients (34%) died during follow-up. Pain reduced in nearly 70% of patients and 66% presented a reduction in AP values. Half of the patients presented mild and 5 % severe hematological adverse effects. CONCLUSIONS: mCRPC patients treated with 223Ra with Hb values >13 g/mL, an ECOG 0-1, low AP values, PSA < 20 ng/mL and lesser bone metastasis on BS presented a better OS with an adequate safety profile.

Pain Outcomes in Patients with Metastatic Castration-Resistant Prostate Cancer Treated with 223Ra: PARABO, a Prospective, Noninterventional Study.

223Ra, a targeted α-therapy, is approved for the treatment of patients with metastatic castration-resistant prostate cancer (mCRPC) who have bone metastases. In the phase 3 ALSYMPCA study, 223Ra prolonged survival and improved quality of life versus placebo. Our real-world study, PARABO, investigated pain and bone pain-related quality of life in patients with mCRPC and symptomatic bone metastases receiving 223Ra in clinical practice. Methods: PARABO was a prospective, observational, noninterventional single-arm study conducted in nuclear medicine centers across Germany (NCT02398526). The primary endpoint was a clinically meaningful pain response (≥2-point improvement from baseline for the worst-pain item score in the Brief Pain Inventory-Short Form). Results: The analysis included 354 patients, who received a median of 6 223Ra injections (range, 1-6). Sixty-seven percent (236/354) received 5-6 injections, and 33% (118/354) received 1-4 injections. Of 216 patients with a baseline worst-pain score of more than 1, 59% (128) had a clinically meaningful pain response during treatment. Corresponding rates were 67% (range, 98/146) with 5-6 223Ra injections versus 43% (range, 30/70) with 1-4 injections, 60% (range, 60/100) in patients with no more than 20 lesions versus 59% (range, 65/111) in those with more than 20 lesions, and 65% (range, 69/106) in patients without prior or concomitant opioid use versus 54% (range, 59/110) in those with prior or concomitant opioid use. Mean subscale scores (pain severity and pain interference) on the Brief Pain Inventory-Short Form improved during treatment. Conclusion: 223Ra reduced pain in patients with mCRPC and symptomatic bone metastases, particularly in patients who received 5-6 injections. The extent of metastatic disease did not impact pain response.

Quantification of groundwater discharge into a shallow coastal lagoon applying a multi-tracer approach.

In many cases, shallow coastal lagoons are, on the one hand, vulnerable habitats for birds and marine ecosystems and, on the other hand, threatened by discharging nutrient-laden surface waters and groundwater. In particular, the localization and quantification of submarine groundwater discharge (SGD) is of key concern in this regard. The presented study aimed at investigating SGD into a vulnerable coastal lagoon that is strongly impacted by evaporation applying a multi-tracer approach. The joint application of radionuclides (222Rn, 223Ra, 224Ra), stable water isotopes (δ18O, δ2H) and the water salinity as environmental water tracers allowed evaluating the suitability of the individual parameters in this specific type of environment. Whilst stable isotope and salinity data were difficult to construe in terms of SGD occurrence due to the intense impact of evaporation, a radon mass balance allowed localising SGD areas within the lagoon and quantifying the related SGD flux rates. In addition, a 224Ra/223Ra ratio analysis revealed information on the apparent age of the discharged groundwater, and hence on the flushing intensity of the lagoon. Besides these site-specific results, the study allowed the following general conclusions regarding the suitability of the applied tracers: (i) we verified the suitability of a radon mass balance approach for proving/disproving SGD occurrence and quantifying SGD fluxes in shallow coastal lagoons strongly impacted by evaporation; (ii) we showed that the impact of evaporation may impede the use of water stable isotope and salinity data as SGD indicators in such specific environments; (iii) we demonstrated that the tidal impact on a lagoon water body during a sampling campaign can be compensated by adapting sampling schedule and cruise track to the tidal cycle.

Safety and Survival Outcomes of 177Lu-Prostate-Specific Membrane Antigen Therapy in Patients with Metastatic Castration-Resistant Prostate Cancer with Prior 223Ra treatment: The RALU Study.

The radium lutetium (RALU) study evaluated the feasibility of sequential α- and ß-emitter use in patients with bone-predominant metastatic castration-resistant prostate cancer. Methods: This preplanned interim retrospective analysis investigated safety and survival outcomes with 177Lu-PSMA in patients treated with prior 223Ra. Results: Forty-nine patients were evaluated. Patients received a median of 6 223Ra injections; 59% of patients received at least 4 177Lu-PSMA cycles. Most (69%) patients received at least 4 life-prolonging therapies before 177Lu-PSMA. Common Terminology Criteria for Adverse Events grade 3-4 treatment-emergent adverse events during 177Lu-PSMA therapy and a 30-d follow-up period included anemia (18%) and thrombocytopenia (2%). Median overall survival was 12.6 mo (95% CI, 8.8-16.1 mo) and 31.4 mo (95% CI, 25.7-37.6 mo) from starting 177Lu-PSMA or 223Ra, respectively. Conclusion: 177Lu-PSMA treatment was well tolerated in patients who had received prior 223Ra. 223Ra use before 177Lu-PSMA is feasible and can be considered for future assessment of the optimal treatment sequence.

Combined Targeted Radiopharmaceutical Therapy and Immune Checkpoint Blockade: From Preclinical Advances to the Clinic.

Immune checkpoint inhibitors (ICIs) have revolutionized cancer care, but many patients with poorly immunogenic tumors fail to benefit. Preclinical studies have shown that external beam radiotherapy (EBRT) can synergize with ICI to prompt remarkable tumor regression and even eradication. However, EBRT is poorly suited to widely disseminated disease. Targeted radiopharmaceutical therapy (TRT) selectively delivers radiation to both the primary tumor and the metastatic sites, and promising results achieved with this approach have led to regulatory approval of certain agents (e.g., 177Lu-PSMA-617/Pluvicto for metastatic prostate cancer). To further improve therapeutic outcomes, combining TRT and ICI is a burgeoning research area, both preclinically and in clinical trials. Here we introduce basic TRT radiobiology and survey emerging and clinically translated TRT agents that have been combined with ICI.

Nuts and Bolts of 223Ra-dichoride Therapy.

Radionuclide therapy with 223Ra-dichloride can be helpful for patients with osteoblastic osseous metastatic disease in the setting of castration resistant prostate cancer without visceral metastases. This article reviews the indications, proper use and handling, patient work-up prior to therapy and many of the technical considerations including discussion of coding/billing along with pitfalls that have been identified.

[223Ra] RaCl2 nanomicelles showed potent effect against osteosarcoma: targeted alpha therapy in the nanotechnology era.

The treatment of bone metastatsis as primary bone cancer itself is still a challenge. The use od radium dichloride ([223Ra] RaCl2) has emerged in the last few years as one of the best treatment choice for bone cancer, with especial focus in bone metastasis. The alpha-emitter radiopharmaceutical has showed potent and efficient results in several clinical trials. In this study we have formulated radium dichloride ([223Ra] RaCl2) nanomicelles in order to evaluate and compare with pure radium dichloride ([223Ra] RaCl2). The results showed that nanomicelles at the same dose had a superior effect (20% higher efficient) when compared with pure radium dichloride ([223Ra] RaCl2). The results corroborated the effectiveness of the nanosystem validating the application of nanotechnology in alpha-radiotherapy with radium dichloride ([223Ra] RaCl2).

223Ra Induces Transient Functional Bone Marrow Toxicity.

223Ra is a bone-seeking, α-particle-emitting radionuclide approved for the treatment of patients with metastatic prostate cancer and is currently being tested in a variety of clinical trials for primary and metastatic cancers to bone. Clinical evaluation of 223Ra hematologic safety showed a significantly increased rate of neutropenia and thrombocytopenia in patients, hinting at myelosuppression as a side effect. Methods: In this study, we investigated the consequences of 223Ra treatment on bone marrow biology by combining flow cytometry, single-cell RNA sequencing, three-dimensional multiphoton microscopy and bone marrow transplantation analyses. Results: 223Ra accumulated in bones and induced zonal radiation damage confined to the bone interface, followed by replacement of the impaired areas with adipocyte infiltration, as monitored by 3-dimensional multiphoton microscopy ex vivo. Flow cytometry and single-cell transcriptomic analyses on bone marrow hematopoietic populations revealed transient, nonspecific 223Ra-mediated cytotoxicity on resident populations, including stem, progenitor, and mature leukocytes. This toxicity was paralleled by a significant decrease in white blood cells and platelets in peripheral blood-an effect that was overcome within 40 d after treatment. 223Ra exposure did not impair full hematopoietic reconstitution, suggesting that bone marrow function is not permanently hampered. Conclusion: Our results provide a comprehensive explanation of 223Ra reversible effects on bone marrow cells and exclude long-term myelotoxicity, supporting safety for patients.

177Lu-Prostate-Specific Membrane Antigen Ligand After 223Ra Treatment in Men with Bone-Metastatic Castration-Resistant Prostate Cancer: Real-World Clinical Experience.

We analyzed real-world clinical outcomes of sequential α-/ß-emitter therapy for metastatic castration-resistant prostate cancer (mCRPC). Methods: We assessed safety and overall survival in 26 patients who received 177Lu-prostate-specific membrane antigen ligand (177Lu-PSMA) after 223Ra in the ongoing noninterventional REASSURE study (223Ra α-Emitter Agent in Nonintervention Safety Study in mCRPC Population for Long-Term Evaluation; NCT02141438). Results: Patients received 223Ra for a median of 6 injections and subsequent 177Lu-PSMA for a median of 3.5 mo (≥ the fourth therapy in 69%). The median time between 223Ra and 177Lu-PSMA treatment was 8 mo (range, 1-31 mo). Grade 3 hematologic events occurred in 9 of 26 patients (during or after 177Lu-PSMA treatment in 5/9 patients; 8/9 patients had also received docetaxel). Median overall survival was 28.0 mo from the 223Ra start and 13.2 mo from the 177Lu-PSMA start. Conclusion: Although the small sample size precludes definitive conclusions, these preliminary data, especially the 177Lu-PSMA treatment duration, suggest that the use of 177Lu-PSMA after 223Ra is feasible in this real-world setting.

Enhancing 223Ra Treatment Efficacy by Anti-ß1 Integrin Targeting.

223Ra is an α-emitter approved for the treatment of bone metastatic prostate cancer (PCa), which exerts direct cytotoxicity toward PCa cells near the bone interface, whereas cells positioned in the core respond poorly because of short α-particle penetrance. ß1 integrin (ß1I) interference has been shown to increase radiosensitivity and significantly enhance external-beam radiation efficiency. We hypothesized that targeting ß1I would improve 223Ra outcome. Methods: We tested the effect of combining 223Ra and anti-ß1I antibody treatment in PC3 and C4-2B PCa cell models expressing high and low ß1I levels, respectively. In vivo tumor growth was evaluated through bioluminescence. Cellular and molecular determinants of response were analyzed by ex vivo 3-dimensional imaging of bone lesions and by proteomic analysis and were further confirmed by computational modeling and in vitro functional analysis in tissue-engineered bone mimetic systems. Results: Interference with ß1I combined with 223Ra reduced PC3 cell growth in bone and significantly improved overall mouse survival, whereas no change was achieved in C4-2B tumors. Anti-ß1I treatment decreased the PC3 tumor cell mitosis index and spatially expanded 223Ra lethal effects 2-fold, in vivo and in silico. Regression was paralleled by decreased expression of radioresistance mediators. Conclusion: Targeting ß1I significantly improves 223Ra outcome and points toward combinatorial application in PCa tumors with high ß1I expression.

The prognostic power of inflammatory indices and clinical factors in metastatic castration-resistant prostate cancer patients treated with radium-223 (BIO-Ra study).

PURPOSE: To combine peripheral blood indices and clinical factors in a prognostic score for metastatic castration-resistant prostate cancer (mCRPC) patients treated with radium-223 dichloride ([223Ra]RaCl2). PATIENTS AND METHODS: Baseline neutrophil-to-lymphocyte ratio (NLR), derived NLR (donor), lymphocyte-to-monocyte ratio (LMR), platelet-to-lymphocyte ratio (PLR), systemic inflammation index (SII), Eastern Cooperative Oncology Group performance status (ECOG PS), Gleason score (GS) group, number of bone metastases, prostate-specific antigen (PSA), alkaline phosphatase (ALP), line of therapy, previous chemotherapy, and the presence of lymphadenopathies were collected from seven Italian centers between 2013 and 2020. Lab and clinical data were assessed in correlation with the overall survival (OS). Inflammatory indices were then included separately in the multivariable analyses with the prognostic clinical factors. The model with the highest discriminative ability (c-index) was chosen to develop the BIO-Ra score. RESULTS: Five hundred and nineteen mCRPC patients (median OS: 19.9 months) were enrolled. Higher NLR, dNLR, PLR, and SII and lower LMR predicted worse OS (all with a p < 0.001). The multivariable model including NLR, ECOG PS, number of bone metastases, ALP, and PSA (c-index: 0.724) was chosen to develop the BIO-Ra score. Using the Schneeweiss scoring system, the BIO-Ra score identified three prognostic groups (36%, 27.3%, and 36.6% patients, respectively) with distinct median OS (31, 26.6, and 9.6 months, respectively; hazard ratio: 1.62, p = 0.008 for group 2 vs. 1 and 5.77, p < 0.001 for group 3 vs. 1). CONCLUSIONS: The BIO-Ra score represents an easy and widely applicable tool for the prognostic stratification of mCRPC patients treated with [223Ra]RaCl2 with no additional costs.