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.

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.

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.

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.

Comparing absorbed doses and radiation risk of the α-emitting bone-seekers [223Ra]RaCl2 and [224Ra]RaCl2

[²²³Ra]RaCl₂ and [²²⁴Ra]RaCl₂ are bone seekers, emitting high LET, and short range (< 100 μm) alpha-particles. Both radionuclides show similar decay properties; the total alpha energies are comparable (²²³Ra: ≈28 MeV, ²²⁴Ra: ≈26 MeV). [²²⁴Ra]RaCl₂ has been used from the mid-1940s until 1990 for treating different bone and joint diseases with activities of up to approximately 50 MBq [²²⁴Ra]RaCl₂. In 2013 [²²³Ra]RaCl₂ obtained marketing authorization by the FDA and by the European Union for the treatment of metastatic prostate cancer with an activity to administer of 0.055 MBq per kg body weight for six cycles. For intravenous injections in humans a model calculation using the biokinetic model of ICRP67 shows a ratio of organ absorbed dose coefficients (²²⁴Ra:²²³Ra) between 0.37 (liver) and 0.97 except for the kidneys (2.27) and blood (1.57). For the red marrow as primary organ-at-risk, the ratio is 0.57. The differences are mainly caused be the differing half-lives of the decay products of both radium isotopes. Both radionuclides show comparable DNA damage patterns in peripheral blood mononuclear cells after internal ex-vivo irradiation. Data on the long-term radiation-associated side effects are only available for treatment with [²²⁴Ra]RaCl₂. Two epidemiological studies followed two patient groups treated with [²²⁴Ra]RaCl₂ for more than 25 years. One of them was the "Spiess study", a cohort of 899 juvenile patients who received several injections of [²²⁴Ra]RaCl₂ with a mean specific activity of 0.66 MBq/kg. Another patient group of ankylosing spondylitis patients was treated with 10 repeated intravenous injections of [²²⁴Ra]RaCl₂, 1 MBq each, 1 week apart. In total 1,471 of these patients were followed-up in the "Wick study". In both studies, an increased cancer mortality by leukemia and solid cancers was observed. Similar considerations on long-term effects likely apply to [²²³Ra]RaCl₂ as well since the biokinetics are similar and the absorbed doses in the same range. However, this increased risk will most likely not be observed due to the much shorter life expectancy of prostate cancer patients treated with [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.

Enhancing 223Ra Treatment Efficacy by Anti-1 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. β1 integrin (β1I) interference has been shown to increase radiosensitivity and significantly enhance external-beam radiation efficiency. We hypothesized that targeting β1I would improve 223Ra outcome. Methods: We tested the effect of combining 223Ra and anti-β1I antibody treatment in PC3 and C4-2B PCa cell models expressing high and low β1I 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 β1I 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-β1I 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 β1I significantly improves 223Ra outcome and points toward combinatorial application in PCa tumors with high β1I expression.

The role of dosimetry and biological effects in metastatic castration-resistant prostate cancer (mCRPC) patients treated with 223Ra: first in human study

BACKGROUND

223Ra is currently used for treatment of metastatic castration resistant prostate cancer patients (mCRPC) bone metastases with fixed standard activity. Individualized treatments, based on adsorbed dose (AD) in target and non-target tissue, are absolutely needed to optimize efficacy while reducing toxicity of α-emitter targeted therapy. This is a pilot first in human clinical trial aimed to correlate dosimetry, clinical response and biological side effects to personalize 223Ra treatment.

METHODS

Out of 20 mCRPC patients who underwent standard 223Ra treatment and dosimetry, in a subset of 5 patients the AD to target and non-target tissues was correlated with clinical effects and radiation-induced chromosome damages. Before each 223Ra administrations, haematological parameters, PSA and ALP values were evaluated. Additional blood samples were obtained baseline (T0), at 7 days (T7), 30 days (T30) and 180 days (T180) to evaluate chromosome damage. After administration WB planar 223Ra images were obtained at 2-4 and 18-24 h. Treatment response and toxicity were monitored with clinical evaluation, bone scan, 18F-choline-PET/CT, PSA value and ALP while haematological parameters were evaluated weekly after 223Ra injection and 2 months after last cycle.

RESULTS

1. a correlation between AD to target and clinical response was evidenced with threshold of 20 Gy as a cut-off to obtain tumor control; 2. the AD to red marrow was lower than 2 Gy in all the patients with no apparently correlation between dosimetry and clinical toxicity. 3. a high dose dependent increase of the number of dicentrics and micronuclei during the course of 223Ra therapy was observed and a linear correlation has been found between blood AD (BAD) and number of dicentrics.

CONCLUSIONS

This study provides some interesting preliminary evidence to be further investigated: dosimetry may be useful to identify a more appropriate 223Ra administered activity predicting AD to target tissue; a dose dependent complex chromosome damage occurs during 223Ra administration and this injury is more evident in heavily pre-treated patients; dosimetry could be used for radioprotection purpose.

TRIAL REGISTRATION

The pilot study has been approved from the Ethics Committee of Regina Elena National Cancer Institute (N:RS1083/18-2111).

Radiopharmacokinetic modelling and radiation dose assessment of 223Ra used for treatment of metastatic castration-resistant prostate cancer

PURPOSE

Ra-223 dichloride (223Ra, Xofigo®) is used for treatment of patients suffering from castration-resistant metastatic prostate cancer. The objective of this work was to apply the most recent biokinetic model for radium and its progeny to show their radiopharmacokinetic behaviour. Organ absorbed doses after intravenous injection of 223Ra were estimated and compared to clinical data and data of an earlier modelling study.

METHODS

The most recent systemic biokinetic model of 223Ra and its progeny, developed by the International Commission on Radiological Protection (ICRP), as well as the ICRP human alimentary tract model were applied for the radiopharmacokinetic modelling of Xofigo® biodistribution in patients after bolus administration. Independent kinetics were assumed for the progeny of 223Ra. The time activity curves for 223Ra were modelled and the time integrated activity coefficients, [Formula: see text] in the source regions for each progeny were determined. For estimating the organ absorbed doses, the Specific Absorbed Fractions (SAF) and dosimetric framework of ICRP were used together with the aforementioned [Formula: see text] values.

RESULTS

The distribution of 223Ra after injection showed a rapid plasma clearance and a low urinary excretion. Main elimination was via faeces. Bone retention was found to be about 30% at 4 h post-injection. Similar tendencies were observed in clinical trials of other authors. The highest absorbed dose coefficients were found for bone endosteum, liver and red marrow, followed by kidneys and colon.

CONCLUSION

The biokinetic modelling of 223Ra and its progeny may help to predict their distributions in patients after administration of Xofigo®. The organ dose coefficients of this work showed some variation to the values reported from clinical studies and an earlier compartmental modelling study. The dose to the bone endosteum was found to be lower by a factor of ca. 3 than previously estimated.

Sequencing Life-Prolonging Agents in Castration-Resistant Prostate Cancer Patients: Comparison of Sequences With and Without 223Ra

Background: The retrospective studies that have so far described the outcomes of the sequential use of life-prolonging agents (LPAs) did not include metastatic castration-resistant prostate cancer (mCRPC) patients who received radium-223 (²²³Ra) as part of their treatment. Consequently, it is not known whether including ²²³Ra in the therapeutic sequence has an impact on cumulative survival. The aim of this study was to evaluate this impact by comparing the cumulative overall survival (OS) in two series of mCRPC patients sequentially treated with two or three LPAs after first-line docetaxel (DOC), including ²²³Ra and not. Materials and Methods: The authors retrospectively reviewed the records of mCRPC patients with bone involvement alone who received two or three LPAs (including ²²³Ra) after first-line DOC. The control group was a contemporary series of mCRPC patients with bone involvement alone treated with sequences of two or three LPAs other than ²²³Ra after first-line DOC. Results: Median cumulative OS was 40.6 months in the ²²³Ra group of 78 patients and 36.2 months in the non-²²³Ra group of 186 patients (p = 0.08). OS outcomes were significantly influenced by the number of treatment lines, and baseline Eastern Cooperative Oncology Group performance status (PS) and prostate-specific antigen levels. Conclusions: To the best of the authors' knowledge, this is the first study designed to evaluate the impact of introducing ²²³Ra in the treatment sequences for mCRPC patients, and the results show that its use does not negatively affect cumulative OS.

Hydroxyapatite and Titanium Dioxide Nanoparticles: Radiolabelling and In Vitro Stability of Prospective Theranostic Nanocarriers for 223Ra and 99mTc

Hydroxyapatite and titanium dioxide are widely used materials in a broad spectrum of branches. Due to their appropriate properties such as a large specific surface area, radiation stability or relatively low toxicity, they could be potentially used as nanocarriers for medicinal radionuclides for diagnostics and therapy. Two radiolabelling strategies of both nanomaterials were carried out by 99mTc for diagnostic purposes and by 223Ra for therapeutic purposes. The first one was the radionuclide sorption on ready-made nanoparticles and the second one was direct radionuclide incorporation into the structure of the nanoparticles. Achieved labelling yields were higher than 94% in all cases. Afterwards, in vitro stability tests were carried out in several solutions: physiological saline, bovine blood plasma, bovine blood serum, 1% and 5% human albumin solutions. In vitro stability studies were performed as short-term (59 h for 223Ra and 31 h for 99mTc) and long-term experiments (five half-lives of 223Ra, approx. 55 days). Both radiolabelled nanoparticles with 99mTc have shown similar released activities (about 20%) in all solutions. The best results were obtained for 223Ra radiolabelled titanium dioxide nanoparticles, where overall released activities were under 6% for 59 h study in all matrices and under 3% for 55 days in a long-term perspective.

The Prognostic Value of Quantitative Bone SPECT/CT Before 223Ra Treatment in Metastatic Castration-Resistant Prostate Cancer

Radiolabeled bisphosphonates such as ^99mTc-3,3-diphosphono-1,2-propanodicarboxylic acid (^99mTc-DPD) typically show intense uptake in skeletal metastases from metastatic castration-resistant prostate cancer (mCRPC). Extensive bone involvement is regarded as a risk factor for mCRPC patients treated with ²²³Ra-dichloride (²²³Ra). The aim of this study was to quantify ^99mTc-DPD uptake by means of SPECT/CT before ²²³Ra and compare the results with the feasibility of treatment and overall survival (OS). Methods: Sixty consecutive mCRPC patients were prospectively included in this study. SPECT/CT of the central skeleton covering the skull to the mid-femoral level was performed before the first cycle of ²²³Ra. The bone compartment was defined by means of low-dose CT. Emission data were corrected for scatter, attenuation, and decay supplemented by resolution recovery using dedicated software. The Kaplan-Meier estimator, U test, and Cox regression analysis were used for statistics. Results: Total ^99mTc-DPD uptake of the central skeleton varied between 11% and 56% of injected dose (%ID) or between 1.8 and 10.5 %ID/1,000 mL of bone volume (%ID/L). SUV_mean ranged from 1.9 to 7.4, whereas the SUV_max range was 18-248. Patients unable to complete ²²³Ra treatment because of progression and/or cytopenia (n = 23) showed significantly higher uptake (31.9 vs. 25.4 %ID and 6.0 vs. 4.7 %ID/L; P < 0.02). OS after ²²³Ra (median, 15.2 mo) was reduced to 7.3 mo in cases of skeletal uptake that was 26 %ID or higher, as compared with 30.8 mo if lower than 26 %ID (P = 0.008). Similar results were obtained for %ID/L and SUV_mean SUV_max did not correlate with survival. %ID/L was identified as an independent prognostic factor for OS (hazard ratio, 1.381 per unit), along with number of previous treatment lines. Conclusion: Quantitative SPECT/CT of bone scans performed at baseline is prognostic for survival in mCRPC patients treated with ²²³Ra.

Assessing Radiographic Response to 223Ra with an Automated Bone Scan Index in Metastatic Castration-Resistant Prostate Cancer Patients

For effective clinical management of patients being treated with ²²³Ra, there is a need for radiographic response biomarkers to minimize disease progression and to stratify patients for subsequent treatment options. The objective of this study was to evaluate an automated bone scan index (aBSI) as a quantitative assessment of bone scans for radiographic response in patients with metastatic castration-resistant prostate cancer (mCRPC). Methods: In a multicenter retrospective study, bone scans from patients with mCRPC treated with monthly injections of ²²³Ra were collected from 7 hospitals in Sweden. Patients with available bone scans before treatment with ²²³Ra and at treatment discontinuation were eligible for the study. The aBSI was generated at baseline and at treatment discontinuation. The Spearman rank correlation was used to correlate aBSI with the baseline covariates: alkaline phosphatase (ALP) and prostate-specific antigen (PSA). The Cox proportional-hazards model and Kaplan-Meier curve were used to evaluate the association of covariates at baseline and their change at treatment discontinuation with overall survival (OS). The concordance index (C-index) was used to evaluate the discriminating strength of covariates in predicting OS. Results: Bone scan images at baseline were available from 156 patients, and 67 patients had both a baseline and a treatment discontinuation bone scan (median, 5 doses; interquartile range, 3-6 doses). Baseline aBSI (median, 4.5; interquartile range, 2.4-6.5) was moderately correlated with ALP (r = 0.60, P < 0.0001) and with PSA (r = 0.38, P = 0.003). Among baseline covariates, aBSI (P = 0.01) and ALP (P = 0.001) were significantly associated with OS, whereas PSA values were not (P = 0.059). After treatment discontinuation, 36% (24/67), 80% (54/67), and 13% (9/67) of patients demonstrated a decline in aBSI, ALP, and PSA, respectively. As a continuous variable, the relative change in aBSI after treatment, compared with baseline, was significantly associated with OS (P < 0.0001), with a C-index of 0.67. Median OS in patients with both aBSI and ALP decline (median, 134 wk) was significantly longer than in patients with ALP decline only (median, 77 wk; P = 0.029). Conclusion: Both aBSI at baseline and its change at treatment discontinuation were significant parameters associated with OS. The study warrants prospective validation of aBSI as a quantitative imaging response biomarker to predict OS in patients with mCRPC treated with ²²³Ra.

Dose-Dependent Growth Delay of Breast Cancer Xenografts in the Bone Marrow of Mice Treated with 223Ra: The Role of Bystander Effects and Their Potential for Therapy

The role of radiation-induced bystander effects in radiation therapy remains unclear. With renewed interest in therapy with α-particle emitters, and their potential for sterilizing disseminated tumor cells (DTCs), it is critical to determine the contribution of bystander effects to the overall response so they can be leveraged for maximum clinical benefit. Methods: Female Foxn1_nu athymic nude mice were administered 0, 50, or 600 kBq/kg ²²³RaCl₂ to create bystander conditions. At 24 hours after administration, MDA-MB-231 or MCF-7 human breast cancer cells expressing luciferase were injected into the tibial marrow compartment. Tumor burden was tracked weekly via bioluminescence. Results: The MDA-MB-231 xenografts were observed to have a 10-day growth delay in the 600 kBq/kg treatment group only. In contrast, MCF-7 cells had 7- and 65-day growth delays in the 50 and 600 kBq/kg groups, respectively. Histologic imaging of the tibial marrow compartment, α-camera imaging, and Monte Carlo dosimetry modeling revealed DTCs both within and beyond the range of the α-particles emitted from ²²³Ra in bone for both MCF-7 and MDA-MB-231 cells. Conclusion: Taken together, these results support the participation of ²²³Ra-induced antiproliferative/cytotoxic bystander effects in delayed growth of DTC xenografts. They indicate that the delay depends on the injected activity and therefore is dose-dependent. They suggest using ²²³RaCl₂ as an adjuvant treatment for select patients at early stages of breast cancer.

Optimization of Cation Exchange for the Separation of Actinium-225 from Radioactive Thorium, Radium-223 and Other Metals

Actinium-225 (²²⁵Ac) can be produced with a linear accelerator by proton irradiation of a thorium (Th) target, but the Th also underdoes fission and produces 400 other radioisotopes. No research exists on optimization of the cation step for the purification. The research herein examines the optimization of the cation exchange step for the purification of ²²⁵Ac. The following variables were tested: pH of load solution (1.5–4.6); rinse steps with various concentrations of HCl, HNO₃, H₂SO₄, and combinations of HCl and HNO₃; various thorium chelators to block retention; MP50 and AG50 resins; and retention of 20–45 elements with different rinse sequences. The research indicated that HCl removes more isotopes earlier than HNO₃, but that some elements, such as barium and radium, could be eluted with ≥2.5 M HNO₃. The optimal pH of the load solution was 1.5–2.0, and the optimized rinse sequence was five bed volumes (BV) of 1 M citric acid pH 2.0, 3 BV of water, 3 BV of 2 M HNO₃, 6 BV of 2.5 M HNO₃ and 20 BV of 6 M HNO₃. The sequence recovered >90% of ²²⁵Ac with minimal ²²³Ra and thorium present.

223Ra-dichloride therapy of bone metastasis: optimization of SPECT images for quantification

BACKGROUND

223Ra imaging is crucial to evaluate the successfulness of the therapy of bone metastasis of castration-resistant prostate cancer (CRPC). The goals of this study were to establish a quantitative tomographic 223Ra imaging protocol with clinically achievable conditions, as well as to investigate its usefulness and limitations. We performed several experiments using the Infinia Hawkeye 4 gamma camera (GE) and physical phantoms in order to assess the optimal image acquisition and reconstruction parameters, such as the windows setting, as well as the iteration number and filter of the reconstruction algorithm. Then, based on the MIRD pamphlet 23, we used a NEMA phantom and an anthropomorphic TORSO® phantom to calibrate the gamma camera and investigate the accuracy of quantification.

RESULTS

Experiences showed that the 85 keV ± 20%, 154 keV ± 10%, and 270 keV ± 10% energy windows are the most suitable for 223Ra imaging. The study with the NEMA phantom showed that the OSEM algorithm with 2 iterations, 10 subsets, and the Butterworth filter offered the best compromise between contrast and noise. Moreover, the calibration factors for different sphere sizes (26.5 ml, 11.5 ml, and 5.6 ml) were constant for 223Ra concentrations ranging between 6.5 and 22.8 kBq/ml. The values found are 73.7 cts/s/MBq, 43.8 cts/s/MBq, and 43.4 cts/s/MBq for 26.5 ml, 11.5 ml, and 5.6 ml sphere, respectively. For concentration lower than 6.5 kBq/ml, the calibration factors exhibited greater variability pointing out the limitations of SPECT/CT imaging for quantification. By the use of a TORSO® phantom, we simulated several tumors to normal tissue ratios as close as possible to clinical conditions. Using the calibration factors obtained with the NEMA phantom, for 223Ra concentrations higher than 8 kBq/ml, we were able to quantify the activity with an error inferior to 18.8% in a 5.6 ml lesion.

CONCLUSIONS

Absolute quantitative 223Ra SPECT imaging appears feasible once the dimension of the target is determined. Further evaluation should be needed to apply the calibration factor-based quantitation to clinical 223Ra SPECT/CT imaging. This will open the possibility for patient-specific 223Ra treatment planning and therapeutic outcome prediction in patients.

A random walk approach to estimate the confinement of α-particle emitters in nanoparticles for targeted radionuclide therapy

BACKGROUND

Targeted radionuclide therapy is a highly efficient but still underused treatment modality for various types of cancers that uses so far mainly readily available β-emitting radionuclides. By using α-particle emitters several shortcomings due to hypoxia, cell proliferation and in the selected treatment of small volumes such as micrometastasis could be overcome. To enable efficient targeting longer-lived α-particle emitters are required. These are the starting point of decay chains emitting several α-particles delivering extremely high radiation doses into small treatment volumes. However, as a consequence of the α-decay the daughter nuclides receive high recoil energies that cannot be managed by chemical radiolabelling techniques. By safe encapsulation of all α-emitters in the decay chain in properly sized nanocarriers their release may be avoided.

RESULTS

The encapsulation of small core nanoparticles loaded with the radionuclide in a shell structure that safely confines the recoiling daughter nuclides promises good tumour targeting, penetration and uptake, provided these nanostructures can be kept small enough. A model for spherical nanoparticles is proposed that allows an estimate of the fraction of recoiling α-particle emitters that may escape from the nanoparticles as a function of their size. The model treats the recoil ranges of the daughter nuclides as approximately equidistant steps with arbitrary orientation in a three-dimensional random walk model.

CONCLUSIONS

The presented model allows an estimate of the fraction of α-particles that are emitted from outside the nanoparticle when its size is reduced below the radius that guarantees complete confinement of all radioactive daughter nuclides. Smaller nanoparticle size with reduced retention of daughter radionuclides might be tolerated when the effects can be compensated by fast internalisation of the nanoparticles by the target cells.

Progress in Targeted Alpha-Particle Therapy. What We Learned about Recoils Release from In Vivo Generators

This review summarizes recent progress and developments as well as the most important pitfalls in targeted alpha-particle therapy, covering single alpha-particle emitters as well as in vivo alpha-particle generators. It discusses the production of radionuclides like ²¹¹At, ²²³Ra, ²²⁵Ac/²¹³Bi, labelling and delivery employing various targeting vectors (small molecules, chelators for alpha-emitting nuclides and their biomolecular targets as well as nanocarriers), general radiopharmaceutical issues, preclinical studies, and clinical trials including the possibilities of therapy prognosis and follow-up imaging. Special attention is given to the nuclear recoil effect and its impacts on the possible use of alpha emitters for cancer treatment, proper dose estimation, and labelling chemistry. The most recent and important achievements in the development of alpha emitters carrying vectors for preclinical and clinical use are highlighted along with an outlook for future developments.

Present and Future Prospects of Radiation Therapy Using α-Emitting Nuclides

Therapy with α-radiation has issues associated with internal exposure; its clinical use has been avoided. However, phase III clinical tests of the α-emitting nuclide ²²³Ra on patients with cancer have been conducted, and results were reported in 2011 to 2012. Since then, research has being carried out on targeted internal therapy by introducing α-emitting nuclides directly into the cancers. For many decades, nontargeted radon therapy has been carried out and is controversial because its mechanism of action is stimulation. The low-level radiation sends powerful signals to upregulate many biological protection systems, which protect against the effects of radiogenic and nonradiogenic toxins. These vital systems prevent, repair, and remove DNA and other biomolecular damage being produced endogenously at a very high rate by the very abundant reactive oxygen species associated with aerobic metabolism. Stimulation of protection systems results in beneficial effects, including a lower risk of cancer. This article reports the results of treatments on 4 patients with cancer and reviews the clinical use of α-radiation from ²²³Ra and radon. It discusses the prospect of using the novel ²²⁵Ac-prostate-specific membrane antigen ligand-617 ligand as a therapeutic agent for prostate cancer. It presents a new treatment system that we developed, α-Radiorespiro-Rn, which seems to be extremely effective in treating cancer.

Molecular radiotheragnostics in prostate cancer

Two different molecular radio-theragnostic principles are applied in prostate cancer, providing a personalised management for those patients. Firstly, radiopharmaceuticals with the same or similar mechanism of action but different energy (gamma-γ, eg 99mTc-diphosphonates or positron-β+, eg 18F-NaF emitting isotopes) can be used to identify patients with osteoblastic metastases for a treatment with bone seeking beta (β-) or alpha (α-) emitting radionuclides to deliver targeted molecular radiotherapy. A number of such β- emitting molecules have been used for bone palliation. More recently, an alpha emitting 223Ra-dicholoride demonstrated not only symptomatic relief but also significantly improved overall survival in castration-resistant prostate cancer with predominant bone metastases. The second principle involves utilisation of the same prostatic specific membrane antigen (PSMA) or similar compound (eg PSMA-11, PSMA-617), but different label with either β+ (68Ga) or γ (99mTc) emitting radioisotope for imaging and subsequently β- (177Lu) or α (225Ac) emitting radionuclide for treatment.

The potential of 223Ra and 18F-fluoride imaging to predict bone lesion response to treatment with 223Ra-dichloride in castration-resistant prostate cancer

PURPOSE

The aims of this study were to calculate bone lesion absorbed doses resulting from a weight-based administration of 223Ra-dichloride, to assess the relationship between those doses and corresponding 18F-fluoride uptake and to assess the potential of quantitative 18F-fluoride imaging to predict response to treatment.

METHODS

Five patients received two intravenous injections of 223Ra-dichloride, 6 weeks apart, at 110 kBq/kg whole-body weight. The biodistribution of 223Ra in metastatic lesions as a function of time after administration as well as associated lesion dosimetry were determined from serial 223Ra scans. PET/CT imaging using 18F-fluoride was performed prior to the first treatment (baseline), and at week 6 immediately before the second treatment and at week 12 after baseline.

RESULTS

Absorbed doses to metastatic bone lesions ranged from 0.6 Gy to 44.1 Gy. For individual patients, there was an average factor difference of 5.3 (range 2.5-11.0) between the maximum and minimum lesion dose. A relationship between lesion-absorbed doses and serial changes in 18F-fluoride uptake was demonstrated (r2 = 0.52). A log-linear relationship was demonstrated (r2 = 0.77) between baseline measurements of 18F-fluoride uptake prior to 223Ra-dichloride therapy and changes in uptake 12 weeks after the first cycle of therapy. Correlations were also observed between both 223Ra and 18F-fluoride uptake in lesions (r = 0.75) as well as between 223Ra absorbed dose and 18F-fluoride uptake (r = 0.96).

CONCLUSIONS

There is both inter-patient and intra-patient heterogeneity of absorbed dose estimates to metastatic lesions. A relationship between 223Ra lesion absorbed dose and subsequent lesion response was observed. Analysis of this small group of patients suggests that baseline uptake of 18F-fluoride in bone metastases is significantly correlated with corresponding uptake of 223Ra, the associated 223Ra absorbed dose and subsequent lesion response to treatment.

Development of separation technology for the removal of radium-223 from targeted thorium conjugate formulations. Part II: purification of targeted thorium conjugates on cation exchange columns

Tumor targeting pharmaceuticals will play a crucial role in future pharma pipelines. The targeted thorium conjugate (TTC) therapeutic platform could provide real benefit to patients, whereby targeting moieties like monoclonal antibodies are radiolabelled with the alpha-emitting radionuclide thorium-227 (²²⁷Th, t_1/2 = 18.7 days). A potential problem could be the accumulation of the long-lived daughter nuclide radium-223 (²²³Ra, t_1/2 = 11.4 days) in the drug product during manufacturing and distribution. Therefore, the level of ²²³Ra must be standardized before administration to the patient. The focus in this study has been the removal of ²²³Ra, as the other progenies will have a very limited stay in the formulation. In this study, the purification of TTCs labeled with decayed ²²⁷Th has been explored. Columns packed with a strong cation exchange resin have been used to sequester ²²³Ra. The separation of TTC from ²²³Ra has been evaluated as influenced by both formulation and process parameters with a design of experiments (DOE) study; including citrate or acetate buffer, pH, buffer concentration, presence or absence of pABA + EDTA, resin amount and sodium chloride concentration. The aim was to achieve a separation with high sorption of ²²³Ra and accompanying low TTC sorption. The results were analyzed by multivariate analysis. Four regression models of TTC and ²²³Ra sorption from citrate and acetate buffered formulations were developed. The predictive accuracy of sorption in the four statistical models was given by standard deviations and confidence intervals. The TTC sorption in citrate and acetate buffered formulations was affected by the identical variables and the variation in TTC sorption was comparable for the two models. However, the DOE variables had a significantly stronger impact on the ²²³Ra sorption in citrate buffered formulations than the ²²³Ra sorption in acetate buffer. An optimal separation with a TTC sorption below 25% and ²²³Ra sorption above 90% can be achieved in both citrate and acetate buffered formulations. Stability studies of radiochemical purity (RCP) indicated that the measured ²²⁷Th values may be partly due to free ²²⁷Th and not TTC, but the results indicate that TTC stability may be controlled by optimizing formulation parameters. Hence, the sorption data and the regression models presented must be reviewed and further explored with regard to what is known about the stability of the TTC in the different buffered formulations.

Development of separation technology for the removal of radium-223 from targeted thorium conjugate formulations. Part I: purification of decayed thorium-227 on cation exchange columns

Targeted thorium conjugates (TTCs) are being explored as a potential future platform for specific tumor targeting pharmaceuticals. In TTCs, the alpha emitting radionuclide thorium-227 (²²⁷Th) with a half-life of 18.697 d is labeled to targeting moieties, such as monoclonal antibodies (mAbs). The amount of daughter nuclide radium-223 (²²³Ra, t_1/2=11.435 d) will increase during manufacture and distribution, and so a technology for purification is required to assure an acceptable level of ²²³Ra is administrated to the patient. Since ²²³Ra is the only progeny of ²²⁷Th with a long half-life (days), the progenies of ²²³Ra will have a very limited stay in the formulation once ²²³Ra is removed. The focus in this study has, therefore, been on the removal of ²²³Ra. In this study, the sorption and separation of ²²³Ra (radium(II)) and ²²⁷Th (thorium(IV)) on cation exchange columns has been evaluated as a purification method of decayed ²²⁷Th (i.e. prior to radiolabelling of a mAb and formation of TTC). The goal is to minimize the sorption of ²²⁷Th and maximize the sorption of ²²³Ra. Statistical experimental design with formulation and process parameters, including buffered formulations comprising citrate and acetate, at various concentrations and pH, presence of free radical scavenger and chelator, and resin amount have been evaluated for impact on the purification process. The studies have been interpreted by the aid of multivariate data analysis. The correlations between design of experimental variables and sorption are summarized by regression models. The predictive accuracy of radionuclide sorption was given by standard deviation and 95% confidence intervals originating from statistical cross validation. Experimental results and statistical models for citrate-buffered formulations verified reproducible and acceptable sorption levels of ²²³Ra and ²²⁷Th under selected conditions. For acetate-buffered formulations, prediction of ²²⁷Th sorption was influenced by complex variable relationships and hence a risk of obtaining irreproducibility. Fine-tuned variable levels showed, however, variable combinations predicting high sorption of ²²³Ra (>90%) and low sorption of ²²⁷Th (<3%) also for the acetate-buffered formulations. The optimal separation conditions should be decided based on tuning the variables levels for ²²³Ra in the citrate-buffered formulations, while for acetate, the optimal separation should be based on tuning variable levels for ²²⁷Th sorption. The ionic strength of the formulation also seemed to affect the radionuclide sorption. Labeling of an antibody-chelator conjugate with purified ²²⁷Th (i.e. preparation of TTC) was successful in the selected citrate-buffered formulations tested.

68Ga-PSMA-11 PET as a Gatekeeper for the Treatment of Metastatic Prostate Cancer with 223Ra: Proof of Concept

We retrospectively evaluated the utility of ⁶⁸Ga-PSMA-11 PET for planning ²²³RaCl₂ therapy of patients with metastatic prostate cancer and its impact on the therapeutic response as determined by prostate-specific antigen (PSA) and alkaline phosphatase (ALP), as well as the correlation of PSA changes with the results of prostate-specific membrane antigen (PSMA) PET follow-up scans. Methods: Sixty-three patients with a median age of 73 y who underwent 307 cycles of therapy with ²²³RaCl₂ were analyzed. In 31 patients, bone scanning and radiologic imaging were performed for pretherapeutic imaging (group 1). In 32 patients, bone scanning and PSMA PET were performed before therapy (group 2). Patients with small lymph node metastases and local recurrence were not excluded from treatment, consistent with current guidelines. PSA and ALP were measured before each treatment cycle and 4 wk after the final cycle. Thirteen patients from group 2, who underwent a second PSMA PET scan as a follow-up, were evaluated to determine the significance of PSA changes as a follow-up marker. Results: In group 1, 4 patients (12.9%) showed a PSA decline, of whom 2 patients and 1 patient showed a PSA decline of more than 30% and more than 50%, respectively. In contrast, in group 2, 14 patients (43.8%) showed a PSA decline, of whom 10 and 8 patients showed a decline of more than 30% and more than 50%, respectively (P = 0.007). Thirty-seven patients had a high ALP level (19 from group 1 and 18 from group 2). Twelve (63.2%) and 16 (88.9%) patients in groups 1 and 2, respectively, showed an ALP decline. This difference was not significant; however, 7 (36%) and 13 (72.2%) patients in groups 1 and 2, respectively, showed an ALP decline of more than 30% (P = 0.04). Considering any ALP decline as a response, no patient with increasing ALP showed a PSA response (P = 0.036). There was a significant correlation between the PSA changes and the therapeutic response according to follow-up PSMA PET. Conclusion: When PSMA PET is used as the gatekeeper in addition to bone scanning, radionuclide therapy with ²²³Ra may be more effective and have more success regarding changes in the PSA. An increase in PSA during therapy cycles occurs because of disease progression.

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.

Factors affecting (223)Ra therapy: clinical experience after 532 cycles from a single institution

PURPOSE

The aim of this study was to identify baseline features that predict outcome in (223)Ra therapy.

METHODS

We retrospectively reviewed 110 patients with metastatic castration-resistant prostate cancer treated with (223)Ra. End points were overall survival (OS), progression-free survival (PFS), bone event-free survival (BeFS), and bone marrow failure (BMF). The following parameters were evaluated prior to the first (223)Ra cycle: serum levels of hemoglobin (Hb), prostate-specific antigen (PSA), alkaline phosphatase (ALP), Eastern Cooperative Oncology Group (ECOG) status, pain score, use of chemotherapy, and external beam radiation therapy (EBRT). During/after (223)Ra we evaluated: the total number of radium cycles (RaTot), the PSA doubling time (PSADT), and the use of chemotherapy, EBRT, abiraterone, and enzalutamide.

RESULTS

A significant reduction of ALP (p < 0.001) and pain score (p = 0.041) occurred throughout the (223) Ra cycles. The risk of progression was associated with declining ECOG status [hazard ratio (HR) = 3.79; p < 0.001] and decrease in PSADT (HR = 8.22; p < 0.001). RaTot, ALP, initial ECOG status, initial pain score, and use of abiraterone were associated with OS (p ≤ 0.008), PFS (p ≤ 0.003), and BeFS (p ≤ 0.020). RaTot, ALP, initial ECOG status, and initial pain score were significantly associated with BMF (p ≤ 0.001) as well as Hb (p < 0.001) and EBRT (p = 0.009). On multivariable analysis, only RaTot and abiraterone remained significantly associated with OS (p < 0.001; p = 0.033, respectively), PFS (p < 0.001; p = 0.041, respectively), and BeFS (p < 0.001; p = 0.019, respectively). Additionally, RaTot (p = 0.027) and EBRT (p = 0.013) remained significantly associated with BMF.

CONCLUSION

Concomitant use of abiraterone and (223)Ra seems to have a beneficial effect, while the EBRT may increase the risk of BMF.

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.

Molecular targeted α-particle therapy for oncologic applications

OBJECTIVE

A significant challenge facing traditional cancer therapies is their propensity to significantly harm normal tissue. The recent clinical success of targeting therapies by attaching them to antibodies that are specific to tumor-restricted biomarkers marks a new era of cancer treatments.

CONCLUSION

In this article, we highlight the recent developments in α-particle therapy that have enabled investigators to exploit this highly potent form of therapy by targeting tumor-restricted molecular biomarkers.

Radium-223 chloride: a potential new treatment for castration-resistant prostate cancer patients with metastatic bone disease

Background

Radium-223 chloride (²²³Ra; Alpharadin) is an alpha-emitting radioisotope that targets areas of osteoblastic metastasis and is excreted by the small intestine. When compared with beta-emitters (eg, strontium-89, samarium-153), ²²³Ra delivers a high quantity of energy per track length with short tissue penetration.

Objective

This review describes the mechanism, radiobiology, and preclinical development of ²²³Ra and discusses the clinical data currently available regarding its safety and efficacy profile.

Methods

Data from clinical trials including abstracts were collected and reviewed using the PubMed Database, as well as the American Society of Clinical Oncology abstract database.

Conclusion

Current bone-targeted therapies fall into two main categories: antiresorptive agents (eg, zoledronic acid, denosumab), which have been shown to delay skeletal-related events, and radiopharmaceuticals (eg, samarium-153), which may have a role in pain palliation. Historically, neither antiresorptive agents nor radiopharmaceuticals have shown definitive evidence of improved overall survival or other antitumor effects in metastatic castrate-resistant prostate cancer (mCRPC). Radiopharmaceuticals are limited by myelosuppresion, thrombocytopenia, and renal excretion. In a recently reported randomized Phase III trial in men with symptomatic bone-metastatic CRPC who had received or were ineligible for docetaxel chemotherapy, ²²³Ra treatment resulted in improved overall survival and delayed skeletal-related events. Toxicity consisted of minor gastrointestinal side effects and mild neutropenia and thrombocytopenia that were rarely severe. Pending regulatory approval, ²²³Ra may represent a unique and distinct option for an important subgroup of patients with mCRPC; future trials should address its use in combination or in sequence with existing and novel agents.