BACKGROUND: The alpha emitter astatine-211 (211At) is garnering attention as a novel targeted alpha therapy for patients with refractory thyroid cancer resistant to conventional therapy using beta emitter radioiodine (131I). Herein, we aimed to establish a robust method for the manufacturing and quality control of [211At]NaAt solution for intravenous administration under the good manufacturing practice guidelines for investigational products to conduct an investigator-initiated clinical trial.
RESULTS: 211At was separated and purified via dry distillation using irradiated Bi plates containing 211At obtained by the nuclear reaction of 209Bi(4He, 2n)211At. After purification, the 211At trapped in the cold trap was collected in a reaction vessel using 15 mL recovery solution (1% ascorbic acid and 2.3% sodium hydrogen carbonate). After stirring the 211At solution for 1 h inside a closed system, the reaction solution was passed through a sterile 0.22 μm filter placed in a Grade A controlled area and collected in a product vial to prepare the [211At]NaAt solution. According to the 3-lot tests, decay collected radioactivity and radiochemical yield of [211At]NaAt were 78.8 ± 6.0 MBq and 40 ± 3%, respectively. The radiochemical purity of [211At]At- obtained via ion-pair chromatography at the end of synthesis (EOS) was 97 ± 1%, and remained > 96% 6 h after EOS; it was detected at a retention time (RT) 3.2-3.3 min + RT of I-. LC-MS analysis indicated that this principal peak corresponded with an astatide ion (m/z = 210.988046). In gamma-ray spectrometry, the 211At-related peaks were identified (X-ray: 76.9, 79.3, 89.3, 89.8, and 92.3 keV; γ-ray: 569.7 and 687.0 keV), whereas the peak at 245.31 keV derived from 210At was not detected during the 22 h continuous measurement. The target material, Bi, was below the 9 ng/mL detection limit in all lots of the finished product. The pH of the [211At]NaAt solution was 7.9-8.6; the concentration of ascorbic acid was 9-10 mg/mL. Other quality control tests, including endotoxin and sterility tests, confirmed that the [211At]NaAt solution met all quality standards.
CONCLUSIONS: We successfully established a stable method of [211At]NaAt solution that can be administered to humans intravenously as an investigational product.

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.
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.
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.

Astatine-211 (211At) has physical properties that make it one of the top candidates for use as a radiation source for alpha particle-based radionuclide therapy, also referred to as targeted alpha therapy (TAT). Here, we summarize the main results of the completed clinical trials, further describe ongoing trials, and discuss future prospects.

In this study, we aim to evaluate the efficacy and safety of 225AC-DOTATATE targeted alpha therapy in advanced-stage paragangliomas (PGLs).
Nine (6 males and 3 females) consecutive patients with histologically proven PGLs were treated with 225Ac-DOTATATE targeted alpha therapy (TAT) and concomitant radiosensitizer, capecitabine, at 8-weekly intervals up to a cumulative activity of ~ 74 MBq. The primary endpoint included evaluating therapy response and disease control rate (DCR) using the RECIST 1.1 criteria. Additional secondary endpoints comprised clinical response assessment using EORTC QLQ-H&N35 questionnaire, Karnofsky Performance Scale (KPS), Eastern Cooperative Oncology Group performance status (ECOG), analgesic score (AS), dose alterations of anti-hypertensive drugs (anti-HTN), and the safety and side-effect profile evaluation as per CTCAE criteria version 5.0.
Following 225Ac-DOTATATE treatment, morphological response revealed partial response in 50%, stable disease in 37.5%, and disease progression in 12.5%, with a DCR of 87.5%. Similarly, the symptomatic response was remarkable, and anti-HTN drugs were stopped in 25% and reduced in 37.5%. Another significant finding in our study revealed a morphologic DCR of 66.6% (2/3) in patients who failed previous lutetium-177 peptide receptor radionuclide therapy (177Lu-PRRT). Regarding the KPS, ECOG, and AS performance scores, a notable improvement was observed post-225Ac-DOTATATE treatment. The QLQ-H&N35 symptom scores evaluated in seven H&N PGL patients showed significant improvement in all aspects. No improvement in sexual function was noted (P = 0.3559). Despite the significant reduction in the analgesic score post-treatment (P = 0.0031), the QLQ-H&N35 revealed only marginal significance concerning the intake of pain killers (P = 0.1723). No grade III/IV hematological, renal, and hepatological toxicities were noted.
The evidence from this study suggests 225Ac-DOTATATE therapy is effective and safe in the treatment of advanced-stage PGLs and also reports a clear benefit even in patient\'s refractory to the previous 177Lu-PRRT.

Actinium-225 (225Ac) is a promising radionuclide used in targeted alpha therapy (TAT). Although 225Ac labeling of bifunctional chelating ligands is effective, previous in vivo studies reported that free 225Ac can be released from the drugs and that such free 225Ac is predominantly accumulated in the liver and could cause unexpected toxicity. To accelerate the clinical development of 225Ac TAT with a variety of drugs, preparing methods to deal with any unexpected toxicity would be valuable. The aim of this study was to evaluate the feasibility of various chelators for reducing and excreting free 225Ac and compare their chemical structures. Nine candidate chelators (D-penicillamine, dimercaprol, Ca-DTPA, Ca-EDTA, CyDTA, GEDTA TTHA, Ca-TTHA, and DO3A) were evaluated in vitro and in vivo. The biodistribution and dosimetry of free 225Ac were examined in mice before an in vivo chelating study. The liver exhibited pronounced 225Ac uptake, with an estimated human absorbed dose of 4.76 SvRBE5/MBq. Aminopolycarboxylate chelators with five and six carboxylic groups, Ca-DTPA and Ca-TTHA, significantly reduced 225Ac retention in the liver (22% and 30%, respectively). Significant 225Ac reductions were observed in the heart and remainder of the body with both Ca-DTPA and Ca-TTHA, and in the lung, kidney, and spleen with Ca-TTHA. In vitro interaction analysis supported the in vivo reduction ability of Ca-DTPA and Ca-TTHA. In conclusion, aminopolycarboxylate chelators with five and six carboxylic groups, Ca-DTPA and Ca-TTHA, were effective for whole-body clearance of free 225Ac. This feasibility study provides useful information for reducing undesirable radiation exposure from free 225Ac.

Currently, targeted alpha therapy is one of the most investigated topics in radiopharmaceutical cancer management. Especially, the alpha emitter 225Ac has excellent nuclear properties and is gaining increasing popularity for the treatment of various tumor entities. We herein report on the synthesis of two universal 225Ac-chelators for mild condition radiolabeling and binding to conjugate molecules of pharmacological interest via the copper-mediated click chemistry. A convenient radiolabeling procedure was investigated as well as the complex stability proved for both chelators and two PSMA (prostate-specific membrane antigen)-targeting model radioconjugates. Studies regarding affinity and cell survival were performed on LNCaP cells followed by biodistribution studies, which were performed using LNCaP tumor-bearing mice. High efficiency radiolabeling for all conjugates was demonstrated. Cell binding studies revealed a fourfold lower cell affinity for the PSMA radioconjugate with one targeting motif compared to the radioconjugate owing two targeting motifs. Additionally, these differences were verified by in vitro cell survival evaluation and biodistribution studies, both showing a higher cell killing efficiency for the same dose, a higher tumor uptake (15%ID/g) and a rapid whole body clearance after 24 h. The synthesized chelators will overcome obstacles of lacking stability and worse labeling needs regarding 225Ac complexation using the DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrayl)tetraacetic acid) chelator. Moreover, the universal functionalization expands the coverage of these chelators in combination with any sensitive bio(macro)molecule, thus improving treatment of any addressable tumor target.

Background: BAY 1862864 is an α-particle emitting 227Th-labeled CD22-targeting antibody. This first-in-human dose-escalation phase I study evaluated BAY 1862864 in patients with CD22-positive relapsed/refractory B cell non-Hodgkin lymphoma (R/R-NHL). Materials and Methods: BAY 1862864 intravenous injections were administered at the starting 227Th radioactivity dose of 1.5 MBq (2 or 10 mg antibody), and the radioactivity dose escalated in ∼1.5 MBq increments (10 mg antibody) until the maximum tolerated dose (MTD) was reported. The primary objective was to determine the safety, tolerability, and MTD. Results: Twenty-one patients received BAY 1862864. Two dose-limiting toxicities (grade 3 febrile neutropenia and grade 4 thrombocytopenia) were reported in one patient in the 4.6 MBq (10 mg antibody) cohort. The MTD was not reached. Ten (48%) patients reported grade ≥3 treatment-emergent adverse events, with the most common being neutropenia, thrombocytopenia, and leukopenia, each occurring in 3 (14%) patients. Pharmacokinetics demonstrated the dose proportionality and stability of BAY 1862864 in the blood. The objective response rate (ORR) was 25% (5/21 patients) according to the LUGANO 2014 criteria, including 1 complete and 4 partial responses. The ORR was 11% (1/9) and 30% (3/10) in patients with relapsed high- and low-grade lymphomas, respectively. Conclusions: BAY 1862864 was safe and tolerated in patients with R/R-NHL. Clinical Trial Registration numbers: NCT02581878 and EudraCT 2014-004140-36.

OBJECTIVE: Radium-223, a targeted alpha therapy, is approved widely for the treatment of patients with metastatic castrate-resistant prostate cancer, based on a pivotal phase 3 study in predominantly white patients. We investigated the efficacy and safety of radium-223 in Asian patients with castrate-resistant prostate cancer and metastatic bone disease.
METHODS: This multicenter, prospective, single-arm, open-label phase 3 trial evaluated the efficacy and safety of the standard radium-223 regimen (55 kBq/kg every 4 weeks for six cycles) in patients from Asian countries. The primary endpoints were the safety and overall survival.
RESULTS: A total of 226 patients were enrolled and received at least one dose of radium-223. Median overall survival was 14.0 months (95% confidence interval [CI], 11.2-17.4). Median time to total alkaline phosphatase and prostate-specific antigen progression were 7.5 (95% CI, 6.8-7.7) and 3.6 (95% CI, 3.1-3.7) months, respectively. Median skeletal-related event-free survival was 26.0 months (95% CI, 12.6-not reached). Grade ≥3 treatment-emergent adverse events were reported in 103 (46%) of 226 patients, with anemia being the most common event (34 [15%] patients). Grade ≥3 drug-related treatment-emergent adverse events occurred in 39 (17%) of 226 patients. Serious treatment-emergent adverse events were reported in 65 (29%) of 226 patients. Seven (3%) patients had an adverse event leading to death; none were considered to be related to radium-223.
CONCLUSIONS: The results of this study support the use of the standard radium-223 regimen for the treatment of Asian patients with castrate-resistant prostate cancer and symptomatic bone metastases.

225Ac-PSMA-617 targeted-therapy has demonstrated efficacy in 75-85% of patients; however, responses are not durable. We aimed to establish translatable mouse models of disseminated prostate cancer (PCa) to evaluate effectiveness of 225Ac-PSMA-617 at various disease stages. Methods: C4-2, C4-2B, or 22Rv1 cells were injected into the left ventricle of male NSG mice. Disease progression was monitored using bioluminescence imaging (BLI). For treatment, mice were injected with 40 kBq 225Ac-PSMA-617 at one (early treatment cohort) or three weeks (late treatment cohort) post-inoculation. Treatment efficacy was monitored by BLI of whole-body tumor burden. Mice were sacrificed based on body conditioning score. Results: C4-2 cells yielded metastases in liver, lungs, spleen, stomach, bones, and brain - achieving a clinically relevant model of widespread metastatic disease. The disease burden in the early treatment cohort was stable over 27 weeks in 5/9 mice and progressive in 4/9 mice. These mice were sacrificed due to brain metastases. Median survival of the late treatment cohort was superior to controls (13 vs. 7 weeks; p<0.0001) but inferior to that in the early treatment cohort (13 vs. 27 weeks; p<0.001). Late cohort mice succumbed to extensive liver involvement. The 22Rv1 and C4-2B systemic models were not used for treatment due to high kidney metastatic burden or low take rate, respectively. Conclusion: C4-2 cells reproduced metastatic cancer spread most relevantly. Early treatment with 225Ac-PSMA-617 prevented liver metastases and led to significant survival benefit. Late treatment improved survival without reducing tumor burden in the liver, the main site of metastasis. The current findings suggest that early 225Ac-PSMA-617 intervention is more efficacious in the setting of widespread metastatic PCa.