Efficacy and Safety of Actinium-225 Prostate-Specific Membrane Antigen Radioligand Therapy in Metastatic Prostate Cancer: A Systematic Review and Metanalysis

Current Status and Future Perspectives of Nuclear Medicine in Prostate Cancer from Imaging to Therapy: A Comprehensive Review

Nuclear medicine has emerged as a critical modality in the diagnostic and therapeutic management of urological malignancies, particularly prostate cancer. Advances in single-photon emission computed tomography/computed tomography (CT) and positron emission tomography/CT (PET/CT) have enhanced tumor assessment across staging, treatment response, and recurrence settings. Molecular imaging, which offers insights beyond traditional anatomical imaging, is increasingly integral in specific clinical scenarios. Theranostic nuclear medicine, which combines diagnostic imaging with targeted therapy, has become a well-established treatment option, particularly for patients with metastatic castration-resistant prostate cancer (mCRPC). The development of the prostate-specific membrane antigen (PSMA) radioligands has revolutionized clinical management by enabling precise disease staging and delivering effective radioligand therapy (RLT). Ongoing research aims to refine the role of PSMA PET imaging in staging and treatment monitoring, while optimizing PSMA-targeted RLT for broader clinical use. Given that prostate cancer remains highly prevalent, the anticipated increase in the demand for RLT presents both challenges and opportunities for nuclear medicine services globally. Theranostic approaches exemplify personalized medicine by enabling the tailoring of treatments to individual tumor biology, thereby improving survival outcomes and maintaining patients' quality of life with minimal toxicity. Although the current focus is on advanced disease, future research holds promise for expanding these strategies to earlier stages, potentially enhancing curative prospects. This evolving field not only signifies a paradigm shift in the care of prostate cancer patients but also underscores the growing importance of nuclear medicine in delivering precision oncology.

The Safety and Efficacy of Targeted Alpha Therapy, Ac-225 Prostate-Specific Membrane Antigen, in Patients With Metastatic Castration-Resistant Prostate Cancer: A Systematic Review and Meta-Analysis

BACKGROUND

Metastatic castration resistance prostate cancer (mCRPC) is a challenging disease with a significant burden of mortality and morbidity. Most of the patients attain resistance to the available treatments, necessitating further novel therapies in this clinical setting. Actinium 225 (225Ac) prostate-specific membrane antigen (PSMA) radioligand therapy has emerged as a promising option and has been utilized for the last decade. Although a few meta-analyses were performed on the efficacy and safety of 225Ac-PSMA RLT in mCRPC patients, several current studies have been added to the literature since the latest meta-analysis. We aimed to gather all individual studies to perform up-to-date meta-analyses.

METHODS

We searched the literature using Pubmed-Medline, Web of Science, Elsevier-Sceince Direct, and Cochrane-Central databases. The data for any PSA decline, over 50% PSA decline, overall survival (OS), progression-free survival (PFS), and toxicity profile were captured from the studies eligible for meta-analysis. We utilized the random effect model to generate pooled estimates.

RESULTS

The sixteen eligible studies contained 1102 patients. Sixty-three percent of patients achieved more than 50% PSA decline, while 82% had any PSA decline after the completion of therapy. The pooled mean OS and PFS were 12.72 months (9.52-15.91) and 11.02 months (6.88-15.15), respectively. The most common adverse event was xerostomia, with a pooled proportion of 84%. Grade ≥ 3 anemia, thrombocytopenia, leucopenia, and nephrotoxicity were encountered in 9%, 5%, 4%, and 4% of the patients.

CONCLUSIONS

225Ac-PSMA RLT is an efficacious and safe treatment for mCRPC. Future well-designed randomized controlled studies comparing 225Ac-PSMA RLT with other approved therapeutic options would better comprehend the exact role of this therapy in the treatment sequence of mCRPC.

A Meta-Analysis and Meta-Regression of the Efficacy, Toxicity, and Quality of Life Outcomes Following Prostate-Specific Membrane Antigen Radioligand Therapy Utilising Lutetium-177 and Actinium-225 in Metastatic Prostate Cancer

BACKGROUND AND OBJECTIVE

Management of metastatic prostate cancer (mPCa) presents significant challenges. In this systematic review, meta-analysis, and meta-regression, the efficacy, safety, and quality of life (QoL) outcomes of prostate-specific membrane antigen (PSMA)-targeted radioligand therapy (PRLT) utilising lutetium-177 ([177Lu]Lu-PSMA) and actinium-225 ([225Ac]Ac-PSMA) were assessed.

METHODS

A detailed literature search across PubMed/Medline, EMBASE, Web of Science, Scopus, and Cochrane Library was conducted, culminating in the inclusion of 100 studies involving 8711 patients. Data on prostate-specific antigen (PSA) responses, toxicity profiles, and QoL and survival outcomes were analysed. Proportional meta-analyses and meta-regression analyses were performed.

KEY FINDINGS AND LIMITATIONS

The estimated proportion of patients with PSA decline ≥50% was 0.49 for [177Lu]Lu-PSMA and 0.60 for [225Ac]Ac-PSMA in mPCa, particularly metastatic castration-resistant prostate cancer. A meta-regression analysis indicated an association between the cumulative amount of administered activity and the proportion of PSA ≥50% decline. Positive PSA responses were observed alongside improved overall survival across both therapies. Our analyses also identified the key factors associated with PSA responses and survival outcomes, including baseline haemoglobin level, and the presence of visceral metastases. Although anaemia was commonly observed, with [177Lu]Lu-PSMA, severe toxicities were infrequent. Improved QoL was observed following [177Lu]Lu-PSMA therapy, whereas it remained stable following the second cycle of [225Ac]Ac-PSMA treatment. Heterogeneity across studies for PSA responses and toxicity profiles is a limitation.

CONCLUSIONS AND CLINICAL IMPLICATIONS

Our findings suggest an association between PRLT and reductions in PSA levels, as well as associations with enhanced survival outcomes in mPCa. Furthermore, our analysis shows a low incidence of severe toxicity associated with this treatment. These observations highlight the important role of PRLT in the management of mPCa.

Radiation-Therapy Related Salivary Dysfunction

Radiation-induced xerostomia (RIX) is a common and debilitating side effect of head and neck cancer radiotherapy, significantly impacting patients' quality of life. This review comprehensively summarizes the current understanding of RIX, encompassing its clinical quantification, underlying pathophysiology, and established and emerging treatment modalities. We explore various objective and subjective measures used to quantify salivary flow and assess the severity of xerostomia in clinical settings. The pathophysiological mechanisms leading to RIX are elucidated, including radiation damage to salivary glands, alterations in saliva composition, and the role of inflammatory processes. Current treatment strategies, such as saliva substitutes and stimulants, are discussed alongside their limitations. Furthermore, we delve into novel investigational approaches, including gene therapy, stem cell transplantation, and pharmacologic interventions, offering promising avenues for future RIX management. This review provides clinicians and researchers with a comprehensive overview of RIX, highlighting the need for continued research to develop more effective preventative and therapeutic strategies to alleviate this burdensome condition.

The Emerging Potential of Lead-212 Theranostics

The field of theranostics uses radiopharmaceuticals to diagnose and treat disease, allowing for a personalized approach to treatment. Most theranostic therapies involve the use of beta-emitting radiopharmaceuticals. Because of their higher energies and decreased range, the use of alpha-emitting radiopharmaceuticals offers potential advantages over beta-emitting radiopharmaceuticals, including the potential for improved cell kill and decreased toxicity to normal tissues. This article focuses on the potential use of lead-212 as a theranostic treatment agent.

Evaluating Xerostomia as a side effect of [255Ac]Ac-PSMA therapy in prostate cancer: a systematic review and meta-analysis

PURPOSE

This systematic review and meta-analysis evaluates xerostomia occurrence in prostate cancer (PC) patients undergoing [225Ac]Ac-prostate-specific membrane antigen ([225Ac]Ac-PSMA) therapy.

METHODS

Following the Preferred Reporting Items for Systematic Review and Meta-Analysis Protocols (PRISMA-P) guidelines, comprehensive electronic searches were conducted across PubMed, Scopus, and Web of Science. The study included articles addressing xerostomia as a side effect of [225Ac]Ac-PSMA therapy in clinical settings, encompassing both tandem and monotherapy strategies. Methodological quality was assessed using the National Institutes of Health (NIH) Assessment Tool. Stata software was employed to perform pooled xerostomia rates, heterogeneity analysis, meta-regression, and publication bias analysis.

RESULTS

Twenty studies met inclusion criteria, comprising 2949 [225Ac]Ac-PSMA cycles administered to 1207 PC patients. For [225Ac]Ac-PSMA monotherapy, the pooled rate of any-grade xerostomia was 84% (95%CI: 69-94%). Grade 1-2 xerostomia had a pooled rate 83% (95%CI: 71-93%), while therapy discontinuation due to xerostomia was 5% (95%CI: 0-13%). Grade 3 xerostomia was evident in 13% (95%CI: 7-20%). [225Ac]Ac/[177Lu]Lu-PSMA tandem therapy resulted in lower pooled rate of 68% for grade 1-2 toxicity (95%CI: 17-100%). Indirect comparison revealed a two-fold decrease in xerostomia risk with tandem protocol compared to monotherapy. Significant heterogeneity was observed, primarily influenced by baseline median prostate-specific antigen values (p = 0.04). Publication bias was present in most xerostomia subgroups, with trim-and-fill analysis adjusting for effect size in specific categories.

CONCLUSION

Xerostomia is most pronounced in patients undergoing [225Ac]Ac-PSMA monotherapy. Tandem approach with [177Lu]Lu-PSMA could reduce xerostomia rates and improve compliance. Further large-scale, prospective studies are necessary for generalization and result consolidation.

Time for action: actinium-225 PSMA-targeted alpha therapy for metastatic prostate cancer - a systematic review and meta-analysis

Rationale: Metastatic prostate cancer in the castration-resistant (mCRPC) setting remains challenging to treat. Prostate-specific membrane antigen (PSMA)-targeted alpha therapy (TAT) is emerging as a promising option. We aimed to systematically review the efficacy and safety of PSMA-TAT in patients with prostate cancer. Methods: A comprehensive search of PubMed/MEDLINE and EMBASE databases was conducted up to October 2024, adhering to the PRISMA guidelines. Selected studies were original research articles evaluating the efficacy and/or safety of PSMA-TAT including at least 10 patients. The outcomes measured included any prostate-specific antigen (PSA) response, ≥50% PSA reduction (PSA50), progression-free survival (PFS), overall survival (OS), and adverse events. PSA50 was pooled using a random-effects model, incorporating individual patient data on PSA50 and previous lines of treatment. Results: Eighteen studies involving 1,155 patients met the inclusion criteria. The majority included heavily pre-treated patients. The most commonly employed radiopharmaceutical was [225Ac]Ac-PSMA-617, in 15 studies. The pooled PSA50 response rate was 65% [95% Confidence interval (CI), 57-72%] with a moderate level of heterogeneity (I² = 81.17%, p < 0.001). Pooled response rates in patients who received none, one, and more than one prior line of treatment were 82% (95% CI, 73-90%), 72% (95% CI, 56-85%), and 55% (95% CI, 48-63%), respectively. PFS varied from 3 to 15 months, and OS from 8 to 31 months. Adverse events were predominantly mild (grades 1-2); severe adverse events (≥ grade 3) included anaemia (11%) and thrombocytopenia (6%). Conclusion: PSMA-TAT holds promising efficacy and an acceptable safety profile for treating metastatic prostate cancer. Randomised controlled trials are needed to optimise treatment protocols toward the implementation of PSMA-TAT into clinical practice.

A Look to the Future: Potential Theranostic Applications in Head and Neck Tumors

Theranostics, the practice of using a diagnostic radiopharmaceutical to guide radiotherapy with a chemically identical (or nearly identical) therapeutic radiopharmaceutical, is an exciting new field under development within the auspices of nuclear medicine. We aim to provide a narrative review of the areas of theranostics use and development which are occurring specifically in the head and neck, with attention to the therapeutic use of existing diagnostically used radiotracers such as agents that target prostate-specific membrane antigen (PSMA) and somatostatin receptors (e.g., DOTATATE derivatives), as well as developing classes of radiotracers such as those targeting fibrinogen-activating protein (FAP) and carbonic anhydrase IX (CAIX), as well as new meta-iodo-benzylguanidine (MIBG) derivatives. Most of those agents are still at the preclinical or early clinical stages of development, but as this is an emerging field, we aim to both outline current progress and suggest future directions.

Local and systemic biodistribution of a small-molecule radiopharmaceutical probe after transcatheter embolization and intra-arterial delivery in a porcine orthotopic renal tumor model

BACKGROUND

Small-molecule biomacromolecules target tumor-specific antigens. They are employed as theranostic agents for imaging and treatment. Intravenous small-molecule radioligands exhibit rapid tumor uptake and excretion. However, systemic administration for peptide receptor radionuclide therapy still lacks the therapeutic index to completely treat solid tumors beyond palliation. We study intra-arterial delivery with tumor embolization of a small molecule as a means to deliver local intertumoral brachytherapy for curative internal ablation.

RESULTS

18F-fluorodeoxyglucose (FDG) was used as a surrogate for a small-molecule theranostic agent in a porcine renal tumor model, this tumor model is not known to specifically express human tumor antigens, but the model demonstrates similar vascularity. Angiography and micron particle embolization of the tumor arterioles were performed in a renal tumor model. Significantly more tumor uptake (2-4×), was observed for intra-arterial administration (IA) compared to intravenous (IV) (%ID/g = 44.41 ± 2.48 vs. 23.19 ± 4.65; P = 0.0342 at 1 min and 40.8 ± 2.43 vs. 10.94 ± 0.42; P = 0.018 at 10 min). At later time points, up to 120 min after injection, washout of the tracer from the tumor was observed, but the percent injected dose per gram remained elevated, with three times higher concentration of FDG with IA administration compared with IV, but the difference was not statistically significant. A trend towards diminished systemic percent injected dose per gram measured in the blood, liver, kidney, spleen, muscle, and urine for study IA compared to IV administration is observed.

CONCLUSION

Combining IA administration of a small-molecule radioprobe surrogate with embolization of the tumor's arterioles extending the time for interaction of the drug within the tumor by diminishing flow out of the tumor via the efferent capillaries significantly increases the first-pass uptake of the small-molecule drug within a tumor and decreases the radiation to normal nontumor tissues when compared with IV injection of the same drug. The minimally invasive drug delivery allows tumor-specific theranostic treatment of renal tumors with a brachytherapy-absorbed dose of radiation that is potentially curative.

The Role of Nuclear Medicine in Imaging and Therapy of Prostate Cancer: The State of the Art

Prostate cancer (PCa) is the second most diagnosed cancer in men. In recent years, nuclear medicine has played an expanding role in diagnosing, staging, monitoring, and treating PCa. Specifically, the introduction of prostate-specific membrane antigen PET/computed tomography has significantly contributed to detecting locoregional and distant disease. Radioligand therapy, with its capacity to induce highly selective cytotoxic effects, is progressively being integrated into PCa therapy. The advent of novel therapeutic agents, additional indications, and a more comprehensive integration between nuclear imaging and therapy, represent the forefront of nuclear medicine in PCa.

Cancer therapy-related salivary dysfunction

Salivary gland dysfunction is a common side effect of cancer treatments. Salivary function plays key roles in critical daily activities. Consequently, changes in salivary function can profoundly impair quality of life for cancer patients. We discuss salivary gland anatomy and physiology to understand how anticancer therapies such as chemotherapy, bone marrow transplantation, immunotherapy, and radiation therapy impair salivary function. We discuss approaches to quantify xerostomia in the clinic, including the advantages and limitations of validated quality-of-life instruments and approaches to directly measuring salivary function. Current and emerging approaches to treat cancer therapy-induced dry mouth are presented using radiation-induced salivary dysfunction as a model. Limitations of current sialagogues and salivary analogues are presented. Emerging approaches, including cellular and gene therapy and novel pharmacologic approaches, are described.

Review on the Increasing Role for PSMA-Based Radioligand Therapy in Prostate Cancer

In 2021, two randomized controlled trials (RCTs), TheraP and VISION, demonstrated that 177Lu-PSMA-617 as monotherapy was more effective for the decline of PSA than the comparator third-line treatments.

METHODS

Our review summarizes new RCTs that add to the use of radioligand therapy (RLT) for patients with high-risk prostate cancer (PCa).

RESULTS

Four past and present RCTs included 1081 patients. An RCT, ENZA-p, studied first-line treatment of patients with metastatic castration-resistant PCa (mCRPC). A combination of enzalutamide (ENZA) and 177Lu-PSMA-617 gave longer progression-free survival than ENZA as monotherapy. Other RCTs of patients with mCRPC, including the PSMAfore, and SPLASH trials, showed 177Lu-PSMA-617 as second-line treatment gave better progression-free survival than androgen receptor pathway inhibitors (combined p value < 6.9 × 10-6).

CONCLUSIONS

Patients with PCa gain if they are given PSMA-RLT early in the treatment of PCa and as part of combination therapies.

Advances in PSMA Alpha Theragnostics

Alpha theranostics offer an attractive alternative form of therapy, which has best been investigated and documented with 225Ac-PSMA in patients with prostate cancer. Advantages offered by targeted alpha therapy include overcoming radiation resistance, oxygen independence, effecting double-stranded DNA breakages within the tumors with anticipated improved clinical outcomes and an acceptable side effect profile. The previous Seminars article on this topic, published in 2020, had to rely mostly on published case reports and small observational studies. In the last few years, however, several meta-analyses have emerged that evaluate the safety and efficacy of 225Ac-PSMA in prostate cancer patients, followed most recently by a multi-center retrospective study initiated by WARMTH. The findings of these publications, together with the exploration of TAT offered in clinical conditions other than as a last resort, is the focus of this updated overview. Unresolved clinical issues that remain, include the appropriate selection of patients that would benefit most from treatment with 225Ac-PSMA, treatment timing within the disease landscape, optimal dosing schedule, dosimetry, when and how to best use combination therapies and minimization and treatment of side effects, particularly that of xerostomia.

Navigating The Prostate Cancer Frontier: A Bibliometric and Altmetric Analysis of [225Ac]Ac-PSMA Therapy

The main aim of this study was to evaluate the current state of bibliometric and altmetric research output of [225Ac]Ac-Prostate specific membrane antigen (PSMA) and its implications for prostate cancer (PC). Both PubMed and Scopus digital libraries were systematically explored to retrieve relevant data on the topic of interest. The study of various bibliometric and altmetric indices was facilitated through the use of Microsoft Excel, Stata (Version 17.0), and VOSviewer (Version 1.6) Softwares. The parameters included in this study comprised the examination of published articles, annual trends, countries, institutions, authors, journals, and co-occurring keywords. From 2014 to 2024, our study examined a total of 100 publications within the given domain. The studies that received the highest citations primarily centered on the crucial topic of metastatic castration-resistant prostate cancer, with a particular emphasis on evaluating the safety and effectiveness of [225Ac]Ac-PSMA therapy. Moreover, much scholarly inquiry has been devoted to examining the [225Ac]Ac-PSMA adverse effects. Three high prolific countries (namely, Germany, United States, and South Africa) dominated the research render in terms of publications and citations. Finally, A strong correlation was observed between altmetric score and citation number (P < 0.001). The observed surge in scholarly research output and altmetric indicators associated with [225Ac]Ac-PSMA signifies a shift in emphasis towards embracing alpha targeted therapy in PC.

Preclinical Evaluation of Biodistribution and Toxicity of [211At]PSMA-5 in Mice and Primates for the Targeted Alpha Therapy against Prostate Cancer

Astatine (211At) is a cyclotron-produced alpha emitter with a physical half-life of 7.2 h. In our previous study, the 211At-labeled prostate-specific membrane antigen (PSMA) compound ([211At]PSMA-5) exhibited excellent tumor growth suppression in a xenograft model. We conducted preclinical biodistribution and toxicity studies for the first-in-human clinical trial. [211At]PSMA-5 was administered to both normal male ICR mice (n = 85) and cynomolgus monkeys (n = 2). The mice were divided into four groups for the toxicity study: 5 MBq/kg, 12 MBq/kg, 35 MBq/kg, and vehicle control, with follow-ups at 1 day (n = 10 per group) and 14 days (n = 5 per group). Monkeys were observed 24 h post-administration of [211At]PSMA-5 (9 MBq/kg). Blood tests and histopathological examinations were performed at the end of the observation period. Blood tests in mice indicated no significant myelosuppression or renal dysfunction. However, the monkeys displayed mild leukopenia 24 h post-administration. Despite the high accumulation in the kidneys and thyroid, histological analysis revealed no abnormalities. On day 1, dose-dependent single-cell necrosis/apoptosis was observed in the salivary glands of mice and intestinal tracts of both mice and monkeys. Additionally, tingible body macrophages in the spleen and lymph nodes indicated phagocytosis of apoptotic B lymphocytes. Cortical lymphopenia (2/10) in the thymus and a decrease in the bone marrow cells (9/10) were observed in the 35 MBq/kg group in mice. These changes were transient, with no irreversible toxicity observed in mice 14 days post-administration. This study identified no severe toxicities associated with [211At]PSMA-5, highlighting its potential as a next-generation targeted alpha therapy for prostate cancer. The sustainable production of 211At using a cyclotron supports its applicability for clinical use.

PSMA-Targeted Radiopharmaceuticals for Prostate Cancer Diagnosis and Therapy

ABSTRACT

Prostate cancer (PCa) is the most common noncutaneous malignancy in men. Until recent years, accurate imaging of men with newly diagnosed PCa, or recurrent or low-volume metastatic disease, was limited. Further, therapeutic options for men with advanced, metastatic, castration-resistant disease were increasingly limited as a result of increasing numbers of systemic therapies being combined in the upfront metastatic setting. The advent of urea-based, small-molecule inhibitors of prostate-specific membrane antigen (PSMA) has partially addressed those shortcomings in diagnosis and therapy of PCa. On the diagnostic side, there are multiple pivotal phase III trials with several different agents having demonstrated utility in the initial staging setting, with generally modest sensitivity but very high specificity for determining otherwise-occult pelvic nodal involvement. That latter statistic drives the utility of the scan by allowing imaging interpreters to read with very high sensitivity while maintaining a robust specificity. Other pivotal phase III trials have demonstrated high detection efficiency in patients with biochemical failure, with high positive predictive value at the lesion level, opening up possible new avenues of therapy such as metastasis-directed therapy. Beyond the diagnostic aspects of PSMA-targeted radiotracers, the same urea-based chemical scaffolds can be altered to deliver therapeutic isotopes to PCa cells that express PSMA. To date, one such agent, when combined with best standard-of-care therapy, has demonstrated an ability to improve overall survival, progression-free survival, and freedom from skeletal events relative to best standard-of-care therapy alone in men with metastatic, castration-resistant PCa who are post chemotherapy. Within the current milieu, there are a number of important future directions including the use of artificial intelligence to better leverage diagnostic findings, further medicinal chemistry refinements to the urea-based structure that may allow improved tumor targeting and decreased toxicities, and the incorporation of new radionuclides that may better balance efficacy with toxicities than those nuclides that are available.

Implementing Ac-225 labelled radiopharmaceuticals: practical considerations and (pre-)clinical perspectives

BACKGROUND

In the past years, there has been a notable increase in interest regarding targeted alpha therapy using Ac-225, driven by the observed promising clinical anti-tumor effects. As the production and technology has advanced, the availability of Ac-225 is expected to increase in the near future, making the treatment available to patients worldwide.

MAIN BODY

Ac-225 can be labelled to different biological vectors, whereby the success of developing a radiopharmaceutical depends heavily on the labelling conditions, purity of the radionuclide source, chelator, and type of quenchers used to avoid radiolysis. Multiple (methodological) challenges need to be overcome when working with Ac-225; as alpha-emission detection is time consuming and highly geometry dependent, a gamma co-emission is used, but has to be in equilibrium with the mother-nuclide. Because of the high impact of alpha emitters in vivo it is highly recommended to cross-calibrate the Ac-225 measurements for used quality control (QC) techniques (radio-TLC, HPLC, HP-Ge detector, and gamma counter). More strict health physics regulations apply, as Ac-225 has a high toxicity, thereby limiting practical handling and quantities used for QC analysis.

CONCLUSION

This overview focuses specifically on the practical and methodological challenges when working with Ac-225 labelled radiopharmaceuticals, and underlines the required infrastructure and (detection) methods for the (pre-)clinical application.

Pb-214/Bi-214-TCMC-Trastuzumab inhibited growth of ovarian cancer in preclinical mouse models

Introduction: Better treatments for ovarian cancer are needed to eliminate residual peritoneal disease after initial debulking surgery. The present study evaluated Trastuzumab to deliver Pb-214/Bi-214 for targeted alpha therapy (TAT) for HER2-positive ovarian cancer in mouse models of residual disease. This study is the first report of TAT using a novel Radon-222 generator to produce short-lived Lead-214 (Pb-214, t1/2 = 26.8 min) in equilibrium with its daughter Bismuth-214 (Bi-214, t1/2 = 19.7 min); referred to as Pb-214/Bi-214. In this study, Pb-214/Bi-214-TCMC-Trastuzumab was tested. Methods: Trastuzumab and control IgG antibody were conjugated with TCMC chelator and radiolabeled with Pb-214/Bi-214 to yield Pb-214/Bi-214-TCMC-Trastuzumab and Pb-214/Bi-214-TCMC-IgG1. The decay of Pb-214/Bi-214 yielded α-particles for TAT. SKOV3 and OVAR3 human ovarian cancer cell lines were tested for HER2 levels. The effects of Pb-214/Bi-214-TCMC-Trastuzumab and appropriate controls were compared using clonogenic assays and in mice bearing peritoneal SKOV3 or OVCAR3 tumors. Mice control groups included untreated, Pb-214/Bi-214-TCMC-IgG1, and Trastuzumab only. Results and discussion: SKOV3 cells had 590,000 ± 5,500 HER2 receptors/cell compared with OVCAR3 cells at 7,900 ± 770. In vitro clonogenic assays with SKOV3 cells showed significantly reduced colony formation after Pb-214/Bi-214-TCMC-Trastuzumab treatment compared with controls. Nude mice bearing luciferase-positive SKOV3 or OVCAR3 tumors were treated with Pb-214/Bi-214-TCMC-Trastuzumab or appropriate controls. Two 0.74 MBq doses of Pb-214/Bi-214-TCMC-Trastuzumab significantly suppressed the growth of SKOV3 tumors for 60 days, without toxicity, compared with three control groups (untreated, Pb-214/Bi-214-TCMC-IgG1, or Trastuzumab only). Mice-bearing OVCAR3 tumors had effective therapy without toxicity with two 0.74 MBq doses of Pb-214/Bi-214-TCMC-trastuzumab or Pb-214/Bi-214-TCMC-IgG1. Together, these data indicated that Pb-214/Bi-214 from a Rn-222 generator system was successfully applied for TAT. Pb-214/Bi-214-TCMC-Trastuzumab was effective to treat mouse xenograft models. Advantages of Pb-214/Bi-214 from the novel generator systems include high purity, short half-life for fractioned therapy, and hourly availability from the Rn-222 generator system. This platform technology can be applied for a variety of cancer treatment strategies.

PSMA Radioligand Therapy in Prostate Cancer: Where Are We and Where Are We Heading?

ABSTRACT

Diagnosis and treatment of prostate cancer are complex and very challenging, being a major health care burden. The efficacy of radioligand therapy with prostate-specific membrane antigen agents has been proven beneficial in certain clinical indications. In this review, we describe management of prostate cancer patients according to current guidelines, especially focusing on the available clinical evidence for prostate-specific membrane antigen radioligand therapy.

Targeted Alpha Therapy: All We Need to Know about 225Ac's Physical Characteristics and Production as a Potential Theranostic Radionuclide

The high energy of α emitters, and the strong linear energy transfer that goes along with it, lead to very efficient cell killing through DNA damage. Moreover, the degree of oxygenation and the cell cycle state have no impact on these effects. Therefore, α radioisotopes can offer a treatment choice to individuals who are not responding to β- or gamma-radiation therapy or chemotherapy drugs. Only a few α-particle emitters are suitable for targeted alpha therapy (TAT) and clinical applications. The majority of available clinical research involves 225Ac and its daughter nuclide 213Bi. Additionally, the 225Ac disintegration cascade generates γ decays that can be used in single-photon emission computed tomography (SPECT) imaging, expanding the potential theranostic applications in nuclear medicine. Despite the growing interest in applying 225Ac, the restricted global accessibility of this radioisotope makes it difficult to conduct extensive clinical trials for many radiopharmaceutical candidates. To boost the availability of 225Ac, along with its clinical and potential theranostic applications, this review attempts to highlight the fundamental physical properties of this α-particle-emitting isotope, as well as its existing and possible production methods.