[The Questionnaire Survey of Japanese Practice and Environment for Targeted Radionuclide Therapy in 2021]

PURPOSE

Recently, the targeted radionuclide therapy (TRT) was urgently required to adapt the practice and environment because of the implementation of novel therapeutic radiopharmaceuticals such as alpha- and beta- radionuclides therapy. The present study aimed to clarify the questionnaire survey with the current situation (safety controls for workers and patients) at Japanese TRT facilities.

METHODS

The massive questionnaire survey, 2 months from October to November 2021, was conducted among nationwide 251 facilities that have performed TRT in the past two years. The alpha- and beta- therapeutic radiopharmaceuticals were categorized and answered by one representative of the facility under anonymity. We analyzed the actual situation of each facility related to occupational exposure, radiation protection, contamination inspection, patient release criteria, and dosimetry for TRT.

RESULTS

The survey response rate was 69.1% (174 facilities). About 75% of these facilities reported that they either follow the guidelines or take their own measures to reduce occupational exposure. The confirmed means of patient release criteria were 68.0% with the administered radioactivity and 87.2% with the ambient dose rate. The cold run was not performed for the first time at 15.0% and 10.0% of the facilities for β- and α-emitting radionuclides, respectively. The facilities without attachment syringe shields were 39.2% for alpha-radionuclides therapy and 20.3% for beta-radionuclides therapy.

CONCLUSION

We clarified the Japanese problem for TRT practice and environment by the questionnaire survey. Our findings indicated that the Japanese guidelines and manuals for TRT were not partly followed in the nationwide facilities.

Dual targeting with 224Ra/212Pb-conjugates for targeted alpha therapy of disseminated cancers: A conceptual approach

Metastases are the primary cause of death among cancer patients and efficacious new treatments are sorely needed. Targeted alpha-emitting radiopharmaceuticals that are highly cytotoxic may fulfill this critical need. The focus of this paper is to describe and explore a novel technology that may improve the therapeutic effect of targeted alpha therapy by combining two radionuclides from the same decay chain in the same solution. We hypothesize that the dual targeting solution containing bone-seeking 224Ra and cell-directed complexes of progeny 212Pb is a promising approach to treat metastatic cancers with bone and soft tissue lesions as well as skeletal metastases of mixed lytic/osteoblastic nature. A novel liquid 224Ra/212Pb-generator for rapid preparation of a dual targeting solution is described. Cancer cell targeting monoclonal antibodies, their fragments, synthetic proteins or peptides can all be radiolabeled with 212Pb in the 224Ra-solution in transient equilibrium with daughter nuclides. Thus, 224Ra targets stromal elements in sclerotic bone metastases and 212Pb-chelated-conjugate targets tumor cells of metastatic prostate cancer or osteosarcoma. The dual targeting solution may also be explored to treat metastatic breast cancer or multiple myeloma after manipulation of bone metastases to a more osteoblastic phenotype by the use of bisphosphonates, denosumab, bortezomib or hormone therapy prior to treatment. This may improve targeting of bone-seeking 224Ra and render an augmented radiation dose deposited within metastases. Our preliminary preclinical studies provide conceptual evidence that the dual 224Ra-solution with bone or tumor-targeted delivery of 212Pb has potential to inhibit cancer metastases without significant toxicity. In some settings, the use of a booster dose of purified 212Pb-conjugate alone could be required to elevate the effect of this tumor cell directed component, if needed, e.g., in a fractionated treatment regimen, where the dual targeting solution will act as maintenance treatment.

Developments in Combining Targeted Radionuclide Therapies and Immunotherapies for Cancer Treatment

Targeted radionuclide therapy (TRT) and immunotherapy are rapidly growing classes of cancer treatments. Basic, translational, and clinical research are now investigating therapeutic combinations of these agents. In comparison to external beam radiation therapy (EBRT), TRT has the unique advantage of treating all disease sites following intravenous injection and selective tumor uptake and retention-a particularly beneficial property in metastatic disease settings. The therapeutic value of combining radiation therapy with immune checkpoint blockade to treat metastases has been demonstrated in preclinical studies, whereas results of clinical studies have been mixed. Several clinical trials combining TRT and immune checkpoint blockade have been initiated based on preclinical studies combining these with EBRT and/or TRT. Despite the interest in translation of TRT and immunotherapy combinations, many questions remain surrounding the mechanisms of interaction and the optimal approach to clinical implementation of these combinations. This review highlights the mechanisms of interaction between anti-tumor immunity and radiation therapy and the status of basic and translational research and clinical trials investigating combinations of TRT and immunotherapies.

The evolution of PRRT for the treatment of neuroendocrine tumors; What comes next?

Lu-177 has been developed for the treatment of patients with peptide receptor radionuclide therapy (PRRT). A second generation pure no-carrier-added Lu-177 has a high specific activity and has waste disposal advantages over the first generation carrier-added Lu-177. PRRT has recently been developed for the treatment of neuroendocrine tumors (NETs). The majority of pancreatic and gastroenteric NETs (GEP-NETs) express the somatostatin receptors (SSTRs) 2 and 5. These receptors can be specifically targeted with a somatostatin peptide analogue (DOTATOC/DOTATATE) which can be chelated to a positron emission tomography (PET) emitting radioisotope such as Ga-68 for imaging or to a β-emitting radioisotope Lu-177 for therapy. A key advantage of this approach is that the receptor expression can be demonstrated by PET imaging before the patient is treated. Clinical studies in G1 and G2 GEP-NETS have demonstrated that PRRT is extremely effective in terms of progression free survival (PFS), symptom control and quality of life, with a well-established safety profile. A beneficial effect on outcome survival awaits to be confirmed. The first commercially available product Lu-177-DOTATATE was approved following the NETTER-1 trial in G1 and G2 GE-NETS. Lu-177-DOTATATE 7,4 GBq every 8 weeks for 4 cycles, together with octreotide LAR 30 mg monthly, demonstrated a median PFS of 28,4 months compared to 8,5 months for octreotide LAR 60 mg monthly. A second pivotal study COMPETE is currently in progress, comparing no carrier-added (n.c.a.) Lu-177-DOTATOC to the m-TOR inhibitor Everolimus in both GE-NETs and PNETs. Two studies, NETTER-2 and COMPOSE are currently underway in patients with high grade G2 and G3 NETs. Novel SSTR antagonists are being developed as next generation targeting molecules for SSTR2-expressing tumors. Antagonists have a higher tumor binding to receptors than agonists, opening up the potential indications for SSTR2 targeting to tumors which have a relatively lower expression of SSTR2 compared to NET such as small cell lung cancer, hepatocellular carcinoma and breast cancer. In addition to Lu-177, radioisotopes with different radiation properties such as Tb-161 and the α-emitter Ac-225 are being developed which have the potential to improve treatment efficacy across the range of G1 to G3 NETs.

Synthesis and Biological Evaluation of 99mTc(I) Tricarbonyl Complexes Dual-Targeted at Tumoral Mitochondria

For effective Auger therapy of cancer, the Auger-electron emitters must be delivered to the tumor cells in close proximity to a radiosensitive cellular target. Nuclear DNA is considered the most relevant target of Auger electrons to have augmented radiotoxic effects and significant cell death. However, there is a growing body of evidence that other targets, such as the mitochondria, could be relevant subcellular targets in Auger therapy. Thus, we developed dual-targeted 99mTc(I) tricarbonyl complexes containing a triphenylphosphonium (TPP) moiety to promote accumulation of 99mTc in the mitochondria, and a bombesin peptide to provide specificity towards the gastrin releasing peptide receptor (GRPr) overexpressed in prostate cancer cells. The designed dual-targeted complex, 99mTc-TPP-BBN, is efficiently internalized by human prostate cancer PC3 cells through a specific GRPr-mediated mechanism of uptake. Moreover, the radioconjugate provided an augmented accumulation of 99mTc in the mitochondria of the target tumor cells, most probably following its intracellular cleavage by cathepsin B. In addition, 99mTc-TPP-BBN showed an enhanced ability to reduce the survival of PC3 cells, in a dose-dependent manner.

131I-IITM and 211At-AITM: Two Novel Small-Molecule Radiopharmaceuticals Targeting Oncoprotein Metabotropic Glutamate Receptor 1

Targeted radionuclide therapy (TRT) targeting oncoproteins facilitates the delivery of therapeutic radionuclides to tumor tissues with high precision. Herein, we developed 2 new radiopharmaceuticals, 4-¹³¹I-iodo- and 4-²¹¹At-astato-N-[4-(6-(isopropylamino)pyridine-4-yl)-1,3-thiazol-2-yl]-N-methylbenzamide (¹³¹I-IITM and ²¹¹At-AITM), targeting the ectopic metabotropic glutamate receptor 1 (mGluR1) in melanomas for TRT studies. Methods: ¹³¹I-IITM and ²¹¹At-AITM were synthesized by reacting a stannyl precursor with ¹³¹I-NaI and ²¹¹At in the presence of an oxidizing agent. The therapeutic efficacy and safety of the 2 radiopharmaceuticals were investigated using mGluR1-expressing B16F10 melanoma cells and melanoma-bearing mice. Results: ¹³¹I-IITM and ²¹¹At-AITM were obtained with a radiochemical purity of greater than 99% and radiochemical yields of 42.7% ± 10.4% and 45.7% ± 6.5%, respectively, based on the total radioactivity of used radionuclides. ¹³¹I-IITM and ²¹¹At-AITM exhibited a maximum uptake of 4.66% ± 0.70 and 7.68% ± 0.71 percentage injected dose per gram (%ID/g) in the targeted melanomas, respectively, and were rapidly cleared from nontarget organs after intravenous injection. Both agents markedly inhibited melanoma growth compared with the controls (61.00% and 95.68%, respectively). In the melanoma model, considerably greater therapeutic efficacy with negligible toxicity was observed using ²¹¹At-AITM. Conclusion: The nontoxic radiopharmaceuticals ¹³¹I-IITM and ²¹¹At-AITM are useful high-precision TRT agents that can be used to target the oncoprotein mGluR1 for melanoma therapy.