Advances in 177Lu-PSMA and 225Ac-PSMA Radionuclide Therapy for Metastatic Castration-Resistant Prostate Cancer

First real-world clinical experience with [177Lu]Lu-PSMA-I&T in patients with metastatic castration-resistant prostate cancer beyond VISION and TheraP criteria

PURPOSE

To report real-world clinical experience with [177Lu]Lu-PSMA-I&T targeted radionuclide therapy (TRT) in patients with metastatic castration-resistant prostate cancer (mCRPC) in a single tertiary referral university hospital.

METHODS

Patients with mCRPC who were treated with [177Lu]Lu-PSMA-I&T TRT as standard of care between February 2022 and August 2023 were included in this retrospective study. Patients were treated with a maximum of six cycles with a fixed activity of 7.4 GBq/100µg [177Lu]Lu-PSMA-I&T per cycle.

RESULTS

50 patients with mCRPC were included, of them 84% had prior therapy with two lines of taxane-based chemotherapy treated and at least one line of androgen receptor signaling inhibitor. A total of 126 cycles with a median of 2 cycles (IQR 1-6) [ 177Lu]Lu-PSMA-I&T were administered per patient. PSA declines of ≥ 50% and ≥ 70% were achieved in 16% and 10% of the patients, respectively. Radiological response was achieved in 11% of the patients. In total, 68 treatment-related Adverse Events (TRAEs) were observed, mainly grade 1-2 in 88% of cases. Grade 3/4 TRAEs were observed in 12% of cases. No grade 3 or higher xerostomia was reported. Median progression-free survival was 7.7 months (95% CI 4.0-11.3) and median overall survival was 8.1 months (95% CI 5.0-11.3).

CONCLUSION

In heavily pretreated patients with mCRPC, treatment of [177Lu]Lu-PSMA-I&T TRT is well tolerated and safe, but real-world efficacy of [177Lu]Lu-PSMA appears lower compared to data from recent phase-3 clinical trials using a different radioligand [177Lu]Lu-PSMA-617. Further studies may show whether patients with mCRPC benefit more from [177Lu]Lu-PSMA when initiated at an earlier stage of treatment.

JHU-2545 preferentially shields salivary glands and kidneys during PSMA-targeted imaging

PURPOSE

Prostate-specific membrane antigen (PSMA) radioligand therapy is a promising treatment for metastatic castration-resistant prostate cancer (mCRPC). Several beta or alpha particle-emitting radionuclide-conjugated small molecules have shown efficacy in late-stage mCRPC and one, [[177Lu]Lu]Lu-PSMA-617, is FDA approved. In addition to tumor upregulation, PSMA is also expressed in kidneys and salivary glands where specific uptake can cause dose-limiting xerostomia and potential for nephrotoxicity. The PSMA inhibitor 2-(phosphonomethyl)pentanedioic acid (2-PMPA) can prevent kidney uptake in mice, but also blocks tumor uptake, precluding its clinical utility. Preferential delivery of 2-PMPA to non-malignant tissues could improve the therapeutic window of PSMA radioligand therapy.

METHODS

A tris(isopropoxycarbonyloxymethyl) (TrisPOC) prodrug of 2-PMPA, JHU-2545, was synthesized to enhance 2-PMPA delivery to non-malignant tissues. Mouse pharmacokinetic experiments were conducted to compare JHU-2545-mediated delivery of 2-PMPA to plasma, kidney, salivary glands, and C4-2 prostate tumor xenograft. Imaging studies were conducted in rats and mice to measure uptake of PSMA PET tracers in kidney, salivary glands, and prostate tumor xenografts with and without JHU-2545 pre-treatment.

RESULTS

JHU-2545 resulted in approximately 3- and 53-fold greater exposure of 2-PMPA in rodent salivary glands (18.0 ± 0.97 h*nmol/g) and kidneys (359 ± 4.16 h*nmol/g) versus prostate tumor xenograft (6.79 ± 0.19 h*nmol/g). JHU-2545 also blocked rodent kidneys and salivary glands uptake of the PSMA PET tracers [68Ga]Ga-PSMA-11 and [18 F]F-DCFPyL by up to 85% with little effect on tumor.

CONCLUSIONS

JHU-2545 pre-treatment may enable greater cumulative administered doses of PSMA radioligand therapy, possibly improving safety and efficacy.

A Comparative Analysis of Alpha and Beta Therapy in Prostate Cancer Using a 3D Image-Based Spatiotemporal Model

PURPOSE

In treating prostate cancer, distinguishing alpha and beta therapies is vital for efficient radiopharmaceutical delivery. Our study introduces a 3D image-based spatiotemporal computational model that utilizes MRI-derived images to evaluate the efficacy of 225Ac-PSMA and 177Lu-PSMA therapies. We examine the impact of tumor size, diffusion, interstitial fluid pressure (IFP), and interstitial fluid velocity (IFV) on the absorbed doses.

METHODS

An MRI-based geometric model of the tumor and its surrounding environment is initially developed. Subsequently, COMSOL Multiphysics software is utilized to solve convection-diffusion-reaction equations and conduct numerical analyses of blood pressure distribution. This computational methodology provides valuable insights into interstitial fluid patterns and the spatiotemporal distribution of extracellular and intracellular concentrations of 225Ac-PSMA and 177Lu-PSMA. In addition, our study investigates the impacts of increasing tumor size on absorbed doses and mechanisms involved in radiopharmaceutical transport and delivery.

RESULTS

Larger tumors have diminished absorbed doses, highlighting the need for customized treatments according to tumor size. Diffusion significantly influences the transport and delivery of radiopharmaceuticals. Additionally, alpha therapy was observed to consistently yield higher absorbed doses within the tumor than beta therapy.

CONCLUSIONS

This study reveals the complex interplay between radiopharmaceutical properties, the tumor microenvironment, and treatment outcomes. It highlights the potential of 225Ac-PSMA in prostate cancer treatment, advocating for personalized treatment strategies tailored to the specific characteristics of each patient and their tumor.

Potential of Technetium and Rhenium Theranostics

While theranostics has transformed the precision medicine landscape over the last decade, there is scope for the development of true theranostic pairs, e.g. diagnostic and therapeutic partners in which any physical, chemical, and biological differences are negligible to in vivo application. Although simple to state in theory, there are, in fact, limited options exhibiting optimal physical characteristics and wholly shared elements. Further compounding real-world application of the traditional theranostic method are additional barriers. The use of PET/CT as the cornerstone of the diagnostic pair in theranostics creates inequity of access and opportunity based on socioeconomic and geographic factors, and the growing demand for both 68Ga and 177Lu is straining production capabilities globally. Improving access to theranostics globally will require novel thinking and infrastructure investment to ensure that patients of all economic and social backgrounds have access to this transformative technology. An approach which is underdeveloped, but which may address gaps in health inequities and improve outcomes, is the application of the widely available generator-produced 99mTc for imaging and 188Re for therapy. Despite favourable and near identical radiochemistry, the search for the next generation of theranostic radionuclide pairs seldom references technetium or rhenium radionuclides. Advances in SPECT/CT instrumentation and radiochemistry provide an opportunity to deliver theranostics to communities not serviced by PET-based theranostics. The 188Re and 99mTc supply by daily elution of a generator affords significant convenience, flexibility and delayed biomolecule imaging. Low abundance gamma emissions of 188Re allow serial imaging and dosimetry calculations. 99mTc / 188Re theranostics could address inequity in access and opportunity to cutting edge theranostics.

Ac-225 radiochemistry through the lens of [225Ac]Ac-DOTA-TATE

BACKGROUND

Targeted alpha therapy with Ac-225 showed to be effective in treating metastatic cancers. However, the complex decay chain requires optimized radiolabeling and quality control. This study aims to determine critical parameters and establish optimal labeling and accurate measuring techniques for radiochemical yield and purity with DOTA-TATE as a model molecule. Ac-225 sources were analyzed for metals (ΣFe, Zn, Cu) and quantified by UPLC. Optimization of radiolabeling kinetics for clinical conditions was performed in regards to temperature (20-90 °C), heating time (5-60 min), pH (2.5-10, with/without excess of metal ions), buffers, quenchers, volume (0.1-10 mL) and molar activity (90-540 kBq/nmol). The quality control was investigated using radio-TLC/HPLC by changing gradient to evaluate peak separation, radiolysed peptide and impurity separation.

RESULTS

Metal ingrowth was observed in Ac-225 stocks (n = 3), (time of arrival: 17.9, 36.8 and 101.4 nmol per 10 MBq). Optimal radiochemical yields were achieved with > 80 °C (20 min) at pH 8.5 (15 mM TRIS) up to 270 kBq. Labeling at a high pH showed a higher RCY, even in presence of an excess of metals. High stability (RCP > 90%) was achieved after addition of quenchers (cysteine, methionine, ascorbate, histidine, or gentisic acid (35 mM)) up to 24 h. For optimal determination of the radiochemical purity (indirect HPLC) fifty fractions are required.

CONCLUSION

The quality of Ac-225 labeled DOTA-radiopharmaceuticals is highly dependent on the pH and stabilization (buffer/quencher). Within this research it is demonstrated that optimized quality control methods and accurate measurement of the radiolabeling kinetics are crucial to ensure safe implementation for patient treatment.

Assessment of the therapeutic efficacy of [177Lu]Lu-PSMA-X compared to taxane chemotherapy in taxane-chemo-naïve patients with metastatic castration-resistant prostate cancer: A systematic review and meta-analysis

INTRODUCTION AND AIM

Radioligand therapy (RLT) with 177Lu-labelled prostate specific membrane antigen ([177Lu]Lu-PSMA-X, referring with "PSMA-X" to a generic PSMA chemical compound) inhibitors has emerged as a viable treatment option in metastatic castration resistant prostate cancer patients having previously progressed on taxane and androgen receptor inhibitors. The aim of this study was to perform a systematic review and meta-analysis to assess the therapeutic efficacy of [177Lu]Lu-PSMA-X compared to taxane chemotherapy in taxane-chemo-naïve patients with metastatic castration-resistant prostate cancer.

MATERIALS AND METHODS

Searches in several bibliographic databases were made using relevant key words, and articles published up to March 2024 were included. The endpoints included prostate specific antigen (PSA) response rate (RR), progression-free survival, and overall survival. Individual patient data were pooled when feasible. PSA50 was defined as the median proportion of patients achieving at least a 50% decline in serum PSA from baseline. A meta-analysis of the PSA50 response rate (proportion meta-analysis) was performed, generating pooled estimates and 95% confidence intervals (95% CI).

RESULTS

From the initially selected 8,414 studies published between 2019 and 2023, 24 were included in the [177Lu]Lu-PSMA-X treated group and 17 in the taxane treated group. Our findings show that [177Lu]Lu-PSMA-X RLT yielded comparable PSA50 responses in taxane-naïve patients versus those receiving taxane chemotherapy, despite considerable study heterogeneity. Notably, the taxane-naïve group had more extensive pretreatment.

CONCLUSIONS

This meta-analysis combines the largest cohorts of taxane-naïve mCRPC patients treated with [177Lu]Lu-PSMA-X RLT and taxane-treated mCRPC. It underscores similar PSA50 response rates in both groups, suggesting a potential role for [177Lu]Lu-PSMA-X RLT in taxane-naïve patients who cannot or choose not to undergo chemotherapy.

Long-Term Safety and Survival Outcomes of [225Ac]Ac-PSMA (Prostate-Specific Membrane Antigen) and [225Ac]Ac-/[177Lu]Lu-PSMA (TANDEM) Radioligand Therapy (PRLT) in Metastatic Castration-Resistant Prostate Cancer

This study aims to retrospectively assess the safety of [225Ac]Ac-PSMA-PRLT, both as monotherapy and in combination (TANDEM) with Lutetium-177, concerning tolerance after the radiopharmaceutical administration and long-term safety, its impact on salivary glands' function, overall survival (OS), and follow-up duration. Between December 2020 and September 2024, 89 patients received a total of 151 cycles of [225Ac]Ac-PSMA-PRLT. Patients with at least one follow-up (n = 71) were included in the analysis to evaluate xerostomia, as well as long-term hematological, renal, and hepatic toxicities, graded according to CTCAE v5.0. The most common adverse event after the radiopharmaceutical administration was flare pain (n = 16). As of the time of analysis, 68 patients had passed away (76.4%; range of survival 5 days to 39 months, median 7 months), while 21 patients were still alive (23.6%; follow-up duration: 1-33 months). Severe (G3/G4) long-term adverse events were rare, with 15 cases of G3 anemia (21.1%), 6 cases of G3 leukocytopenia (8.4%), and 14 cases of G3/G4 thrombocytopenia (19.7%). Hematological toxicity was primarily associated with severe bone marrow involvement or prior chemotherapy. Additionally, one case of G3 nephrotoxicity (1.4%) and six cases of G3 hepatotoxicity (8.4%) were observed. Only nine patients (12.7%) reported de novo xerostomia (G1/G2). In conclusion, this study demonstrates that [225Ac]Ac-PSMA PRLT, both as monotherapy and combined with [177Lu]Lu-PSMA as TANDEM PRLT, is generally safe in terms of both tolerance after the radiopharmaceutical administration and long-term toxicity.

Androgen Signaling in Prostate Cancer: When a Friend Turns Foe

Androgen (AR) signaling is the main signaling for the development of the prostate and its normal functioning. AR is highly specific for testosterone and dihydrotestosterone, significantly contributing to prostate development, physiology, and cancer. All these receptors have emerged as crucial therapeutic targets for PCa. In the year 1966, the Noble prize was awarded to Huggins and Hodge for their groundbreaking discovery of AR. As it is a pioneer transcription factor, it belongs to the steroid hormone receptor family and consists of domains, including DNA binding domain (DBD), hormone response elements (HRE), C-terminal ligand binding domain (LBD), and N-terminal regulatory domains. Structural variations in AR, such as AR gene amplification, LBD mutations, alternative splicing of exons, hypermethylation of AR, and co- regulators, are major contributors to PCa. It's signaling is crucial for the development and functioning of the prostate gland, with the AR being the key player. The specificity of AR for testosterone and dihydrotestosterone is important in prostate physiology. However, when it is dysregulated, AR contributes significantly to PCa. However, the structural variations in AR, such as gene amplification, mutations, alternative splicing, and epigenetic modifications, drive the PCa progression. Therefore, understanding AR function and dysregulation is essential for developing effective therapeutic strategies. Thus, the aim of this review was to examine how AR was initially pivotal for prostate development and how it turned out to show both positive and detrimental implications for the prostate.

Improvement of End-of-Synthesis Radiochemical Purity of 177Lu-DOTA-PSMA-Ligands with Alternative Synthesis Approaches: Conversion Upswing and Side-Products Minimization

BACKGROUND

Radiochemical purity is a key criterion for the quality of radiopharmaceuticals used in clinical practice. The joint improvement of analytical methods capable of identifying related radiochemical impurities and determining the actual radiochemical purity, as well as the improvement of synthesis methods to minimize the formation of possible radiochemical impurities, is integral to the implementation of high-tech nuclear medicine procedures. PSMA-targeted radionuclide therapy with lutetium-177 has emerged as an effective treatment option for prostate cancer, and [177Lu]Lu-PSMA-617 and [177Lu]Lu-PSMAI&T have achieved global recognition as viable radiopharmaceuticals. Recently, it was shown that specific radiochemical impurities can form during the synthesis of [177Lu]Lu-PSMA-617 because of a spontaneous, thermally mediated condensation of the Glu-C(O)-Lys fragment, resulting in the formation of three different cyclic forms (with no affinity for PSMA). During this study, we identified another impurity, a product of detachment of the Glu-CO fragment from PSMA-617, caused by heating. The total content of all four thermally mediated degradation products may reach 9-11% during classical incubation for 30 min at 95 °C, reducing the radiochemical purity to an unacceptable level (albeit with high levels of radiochemical conversion). It is reasonable to assume that the formation of similar impurities is characteristic of all PSMA-specific vectors that contain Glu-C(O)-Lys pharmacophores. Because the formation of these impurities directly depends on the temperature and incubation time, to reduce their content in the reaction mixture at the end of the synthesis, it is necessary to select conditions to achieve a high level of radiochemical conversion for the minimum possible time and/or at the minimum sufficient temperature.

METHODS

In this study, using [177Lu]Lu-PSMA-617 as an example, we evaluated the efficiency of alternative methods of synthesis with microwave heating and co-solvent (ethanol) addition to ensure radiochemical yield and radiochemical purity in the shortest possible time and at the minimum necessary and sufficient synthesis temperature.

RESULTS

Both approaches achieved a significant reduction in the impurities content, while achieving satisfactory synthesis yields in a short time. In addition to improving the synthesis parameters and radiochemical purity, the use of microwave heating and the addition of ethanol reduces the negative influence of other auxiliaries on labeling kinetics. Notably, the addition of ethanol under certain conditions allowed [177Lu]Lu-PSMA-617 to be synthesized at room temperature for only 10 min. This makes it possible to achieve exceptionally high real radiochemical purity of the preparations, determined only by the quality of the original precursor. The approaches considered in this study can be successfully applied to improve the synthesis process and quality parameters of the finished product, both for known radiopharmaceuticals and for those under development.

Tubarial salivary glands show a low relative contribution to functional salivary gland tissue mass

BACKGROUND

In 2021, the tubarial salivary glands (TSGs) were newly identified on prostate-specific membrane antigen (PSMA) positron emission tomography/computed tomography (PET/CT) as macroscopic glands in the nasopharyngeal wall. However, the relative contribution of the TSGs to the total salivary gland function, and consequently on the development of xerostomia after external beam radiotherapy (EBRT) or PSMA-targeted radionuclide therapy (RNT) is not known. Therefore, we aimed to determine the presence of the TSGs and to quantify uptake in the TSGs on PSMA PET.

METHODS

Qualitative and quantitative analyses were performed on 68Ga-PSMA-11 PET/CT scans of 100 patients with prostate cancer. The mean and maximum standardized uptake value (SUVmean and SUVmax) in the TSGs were measured and compared to the parotid, submandibular and sublingual salivary glands (PSGs, SMSGs and SLSGs, respectively). Furthermore, proportional function of the TSGs was compared to the PSGs, SMSGs and SLSGs based on the total organ PSMA (TO-PSMA).

RESULTS

The TSGs were visible on 95% of the 68Ga-PSMA-11 PET/CT scans. The normalized median SUVmean and SUVmax was significantly higher for the PSGs (p < 0.001) and SMSGs (p < 0.001) compared to the TSGs, but not for the SLSGs (p = 0.242 and p = 0.300, respectively). The normalized median TO-PSMA was significantly higher for the PSGs (p < 0.001) and SMSGs (p < 0.001), and significant lower for the SLSGs (p < 0.001) compared the TSGs.

CONCLUSIONS

The SUVmean, SUVmax and TO-PSMA of the TSGs were most comparable to the SLSGs. However, the measured PSMA uptake may be disproportional towards the saliva production. Therefore, future studies should focus on the relation between PSMA uptake and salivary function before and after PSMA therapy.

Deciphering the effects of radiopharmaceutical therapy in the tumor microenvironment of prostate cancer: an in-silico exploration with spatial transcriptomics

Radiopharmaceutical therapy (RPT) is an emerging prostate cancer treatment that delivers radiation to specific molecules within the tumor microenvironment (TME), causing DNA damage and cell death. Given TME heterogeneity, it's crucial to explore RPT dosimetry and biological impacts at the cellular level. We integrated spatial transcriptomics (ST) with computational modeling to investigate the effects of RPT targeting prostate-specific membrane antigen (PSMA), fibroblast activation protein (FAP), and gastrin-releasing peptide receptor (GRPR) each labelled with beta-emitting lutetium-177 (177Lu) and alpha-emitting actinium-225 (225Ac). Methods: Three ST datasets from primary tissue samples of two prostate cancer patients were obtained. From these datasets, we extracted gene expressions, including FOLH1, GRPR, FAP, and Harris Hypoxia, and estimated the proportions of different cell types-epithelial, endothelial, and prostate cancer (PC) cells-in the corresponding ST spots. We computed the spatiotemporal distribution of each RPT targeting PSMA, FAP, and GRPR at each ST spot by solving the partial differential equation (PDE) using a convection-reaction-diffusion (CRD) model, assuming similar pharmacokinetic parameters across all ligands. A well-established physiologically based pharmacokinetic (PBPK) model was used to simulate the input function in the prostate, carefully calibrated to deliver 10 Gy to the prostate tumor over 20 days. Dosimetry was estimated using the Medical Internal Radiation Dose (MIRD) formalism, applying the dose point kernels (DVK) method. The survival probability was estimated using the linear quadratic model, applied to both beta-emitting RPT labeled with 177Lu and 225Ac. A modified linear quadratic model was used to estimate the bioeffect of the alpha-emitting RPT. Results: The results demonstrate distinct dose-response and efficacy patterns across ST samples, with FAP-targeted RPT exhibiting limited effectiveness in tumor cell-rich areas compared to PSMA- and GRPR-targeted therapies. GRPR-targeted RPT showed higher resistance in hypoxic regions relative to the other therapies. Additionally, 225Ac-labeled RPT was more effective overall than 177Lu-labeled RPT, especially in areas with low cancer-cell fraction or high hypoxia. The findings suggest that a combination of 225Ac-labeled FAP- and PSMA-targeted RPT offers the best therapeutic strategy. Conclusion: The proposed method, which combines ST and computational modeling to determine the dosimetry and cell survival probability of RPT in the TME, holds promise for identifying optimal personalized RPT strategies.

Prostate-Specific Membrane Antigen-Targeted NIR Phototheranostics for Prostate Cancer

The evolution of targeted cancer theranostics has revolutionized personalized medicine by integrating diagnostic and therapeutic capabilities. Prostate-specific membrane antigen (PSMA) has emerged as a key theranostic target in the context of prostate cancer, paving the way for the clinical approval of multiple drugs. However, the persistent challenge of off-target toxicity, which plagues both conventional and advanced treatment modalities such as targeted chemotherapy and radiotherapy, thus demands further innovation. Considering this critical issue, this review discusses the recent advances in the binary treatment techniques, i.e., phototherapies, that have the potential to circumvent the key concern of off-target toxicity associated with personalized chemotherapy and radiotherapy. Precisely, an up-to-date overview of the latest developments in the near-infrared (NIR)-based phototheranostic strategies for prostate cancer by targeting PSMA has been presented. Furthermore, we have discussed the associated particulars that require specific attention in enhancing the translational potential of phototheranostic techniques.

Developments in radionanotheranostic strategies for precision diagnosis and treatment of prostate cancer

BACKGROUND

Prostate Cancer (PCa) is the second most diagnosed urological cancer among men worldwide. Conventional methods used for diagnosis of PCa have several pitfalls which include lack of sensitivity and specificity. On the other hand, traditional treatment of PCa poses challenges such as long-term side effects and the development of multidrug resistance (MDR).

MAIN BODY

Hence, there is a need for novel PCa agents with the potential to lessen the burden of these adverse effects on patients. Nanotechnology has emerged as a promising approach to support both early diagnosis and effective treatment of tumours by ensuring precise delivery of the drug to the targeted site of the disease. Most cancer-related biological processes occur on the nanoscale hence application of nanotechnology has been greatly appreciated and implemented in the management and therapeutics of cancer. Nuclear medicine plays a significant role in the non-invasive diagnosis and treatment of PCa using appropriate radiopharmaceuticals. This review aims to explore the different radiolabelled nanomaterials to enhance the specific delivery of imaging and therapeutic agents to cancer cells. Thereafter, the review appraises the advantages and disadvantages of these modalities and then discusses and outlines the benefits of radiolabelled nanomaterials in targeting cancerous prostatic tumours. Moreover, the nanoradiotheranostic approaches currently developed for PCa are discussed and finally the prospects of combining radiopharmaceuticals with nanotechnology in improving PCa outcomes will be highlighted.

CONCLUSION

Nanomaterials have great potential, but safety and biocompatibility issues remain. Notwithstanding, the combination of nanomaterials with radiotherapeutics may improve patient outcomes and quality of life.

Imaging and therapy in prostate cancer using prostate specific membrane antigen radioligands

Prostate specific membrane antigen (PSMA) directed PET imaging has rapidly transformed prostate cancer workup over the past decade and paved the way for a theranostic approach using 177Lu-labelled PSMA radioligand therapy (RLT). This review gives an overview of the underlying principles behind PSMA as a target; the current use of PSMA PET in prostate cancer imaging and benefits compared to conventional imaging; and therapeutic applications including optimisation of patient selection. It also explores the evidence base of PSMA PET for other indications not in routine clinical use and the future of PSMA-directed RLT.

Role of Lutetium Radioligand Therapy in Prostate Cancer

Theranostics utilize ligands that chelate radionuclides and selectively bind with cancer-specific membrane antigens. In the case of prostate cancer (PCa), the state-of-the-art lutetium-177-PSMA combines the radioactive β-emitter 177Lu with Vipivotide Tetraxetan, a prostate-specific membrane antigen (PSMA)-binding ligand. Several studies have been conducted, and the therapy is not without adverse effects (e.g., xerostomia, nausea, and fatigue); however, few events are reported as severe. The available evidence supports the use of 177Lu-PSMA in selected metastatic castration-resistant prostate cancer patients, and the treatment is considered a standard of care in several clinical scenarios. Emerging research shows promising results in the setting of hormone-sensitive prostate cancer; however, evidence from high-quality controlled trials is still missing. In this review, we discuss the available evidence for the application of 177Lu-PSMA in the management of PCa patients.

[68Ga]PSMA-11 for positron emission tomography (PET) imaging of prostate-specific membrane antigen (PSMA)-positive lesions in men with prostate cancer

INTRODUCTION

Theranostics targeting prostate-specific membrane antigen (PSMA) represent a new targeted approach for prostate cancer care that combines diagnostic and therapeutic radiopharmaceuticals to diagnose and treat the disease. Positron emission tomography (PET) is the imaging method of choice and several diagnostic radiopharmaceuticals for quantifying PSMA have received FDA approval and are in clinical use. [68Ga]Ga-PSMA-11 is one such imaging agent and the focus of this article. One beta-emitting radioligand therapy ([177Lu]Lu-PSMA-617) has also received FDA approval for prostate cancer treatment, and several other alpha- and beta-emitting radioligand therapies are in clinical trials.

AREAS COVERED

Theranostics targeting PSMA in men with prostate cancer are discussed with a focus on use of [68Ga]Ga-PSMA-11 for imaging PSMA-positive lesions in men with prostate cancer. The review covers [68Ga]Ga-PSMA-11 manufacture, current regulatory status, comparison of [68Ga]Ga-PSMA-11 to other imaging techniques, clinical updates, and emerging applications of artificial intelligence for [68Ga]Ga-PSMA-11 PET.

EXPERT OPINION

[68Ga]Ga-PSMA-11 is used in conjunction with a PET/CT scan to image PSMA positive lesions in men with prostate cancer. It is manufactured by chelating precursor with68Ga, either from a generator or cyclotron, and has regulatory approval around the world. It is widely used clinically in conjunction with radioligand therapies like [177Lu]Lu-PSMA-617.

Gene Abnormalities and Modulated Gene Expression Associated with Radionuclide Treatment: Towards Predictive Biomarkers of Response

Molecular radiotherapy (MRT), also known as radioimmunotherapy or targeted radiotherapy, is the delivery of radionuclides to tumours by targeting receptors overexpressed on the cancer cell. Currently it is used in the treatment of a few cancer types including lymphoma, neuroendocrine, and prostate cancer. Recently reported outcomes demonstrating improvements in patient survival have led to an upsurge in interest in MRT particularly for the treatment of prostate cancer. Unfortunately, between 30% and 40% of patients do not respond. Further normal tissue exposure, especially kidney and salivary gland due to receptor expression, result in toxicity, including dry mouth. Predictive biomarkers to select patients who will benefit from MRT are crucial. Whilst pre-treatment imaging with imaging versions of the therapeutic agents is useful in demonstrating tumour binding and potentially organ toxicity, they do not necessarily predict patient benefit, which is dependent on tumour radiosensitivity. Transcript-based biomarkers have proven useful in tailoring external beam radiotherapy and adjuvant treatment. However, few studies have attempted to derive signatures for MRT response prediction. Here, transcriptomic studies that have identified genes associated with clinical radionuclide exposure have been reviewed. These studies will provide potential features for seeding multi-component biomarkers of MRT response.

PSMA-targeted radiotheranostics in modern nuclear medicine: then, now, and what of the future?

In 1853, the perception of prostate cancer (PCa) as a rare ailment prevailed, was described by the eminent Londoner surgeon John Adams. Rapidly forward to 2018, the landscape dramatically altered. Currently, men face a one-in-nine lifetime risk of PCa, accentuated by improved diagnostic methods and an ageing population. With more than three million men in the United States alone grappling with this disease, the overall risk of succumbing to stands at one in 39. The intricate clinical and biological diversity of PCa poses serious challenges in terms of imaging, ongoing monitoring, and disease management. In the field of theranostics, diagnostic and therapeutic approaches that harmoniously merge targeted imaging with treatments are integrated. A pivotal player in this arena is radiotheranostics, employing radionuclides for both imaging and therapy, with prostate-specific membrane antigen (PSMA) at the forefront. Clinical milestones have been reached, including FDA- and/or EMA-approved PSMA-targeted radiodiagnostic agents, such as [18F]DCFPyL (PYLARIFY®, Lantheus Holdings), [18F]rhPSMA-7.3 (POSLUMA®, Blue Earth Diagnostics) and [68Ga]Ga-PSMA-11 (Locametz®, Novartis/ ILLUCCIX®, Telix Pharmaceuticals), as well as PSMA-targeted radiotherapeutic agents, such as [177Lu]Lu-PSMA-617 (Pluvicto®, Novartis). Concurrently, ligand-drug and immune therapies designed to target PSMA are being advanced through rigorous preclinical research and clinical trials. This review delves into the annals of PSMA-targeted radiotheranostics, exploring its historical evolution as a signature molecule in PCa management. We scrutinise its clinical ramifications, acknowledge its limitations, and peer into the avenues that need further exploration. In the crucible of scientific inquiry, we aim to illuminate the path toward a future where the enigma of PCa is deciphered and where its menace is met with precise and effective countermeasures. In the following sections, we discuss the intriguing terrain of PCa radiotheranostics through the lens of PSMA, with the fervent hope of advancing our understanding and enhancing clinical practice.

Comparison of a 3D CZT and conventional SPECT/CT system for quantitative Lu-177 SPECT imaging

PURPOSE

Next-generation SPECT/CT systems with CdZnTe (CZT) digital detectors in a ring-like setup are emerging to perform quantitative Lu-177 SPECT imaging in clinical routine. It is essential to assess how the shorter acquisition time might affect the image quality and uncertainty on the mean absorbed dose of the tumors and organs at risk compared to a conventional system.

METHODS

A NEMA Image Quality phantom was scanned with a 3D CZT SPECT/CT system (Veriton, by Spectrum Dynamics) using 6 min per bed position and with a conventional SPECT/CT system (Symbia T16, by Siemens) using 16 min per bed position. The sphere-to-background ratio was 12:1 and the background activity concentration ranged from 0.52 to 0.06 MBq/mL. A clinical reconstruction protocol for dosimetry purposes was determined for both systems by maximizing the sphere-to-background ratio while keeping the coefficient of variation of the background as low as possible. The corresponding image resolution was determined by the matching filter method and used for a dose uncertainty assessment of both systems following an established uncertainty model..

RESULTS

The optimized iterative reconstruction protocol included scatter and attenuation correction for both systems and detector response modeling for the Siemens system. For the 3D CZT system, 6 iterations and 8 subsets were combined with a Gaussian post-filter of 3 mm Full Width Half Maximum (FWHM) for post-smoothing. For the conventional system, 16 iterations and 16 subsets were applied with a Gaussian post-smoothing filter of 1 mm FWHM. For these protocols, the sphere-to-background ratio was 18.5% closer to the true ratio for the conventional system compared to the 3D CZT system when considering the four largest spheres. Meanwhile, the background coefficient of variation was very similar for both systems. These protocols resulted in SPECT image resolution of 14.8 mm and 13.6 mm for the 3D CZT and conventional system respectively. Based on these resolution estimates, a 50% dose uncertainty corresponded to a lesion volume of 28 mL for the conventional system and a lesion volume of 33 mL for the 3D CZT system.

CONCLUSIONS

An optimized reconstruction protocol for a Veriton system with 6 min of acquisition time per bed position resulted in slightly higher dose uncertainties than a conventional Symbia system using 16 min of acquisition time per bed position. Therefore, a 3D CZT SPECT/CT allows to significantly reduce the acquisition times with only a very limited impact on dose uncertainties such that quantitative Lu-177 SPECT/CT imaging becomes much more accessible for treatment concurrent dosimetry. Nevertheless, the uncertainty of SPECT-based dose estimates remains high.

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.

Evaluation of the tolerability and safety of [225Ac]Ac-PSMA-I&T in patients with metastatic prostate cancer: a phase I dose escalation study

BACKGROUND

Life expectancy of patients with metastatic castration-resistant prostate cancer (mCRPC) is still limited despite several systemic treatments. Within five years after diagnosis of primary prostate cancer, 10-20% of the patients have mCRPC and curation is not an option. Radionuclide therapy (RNT) targeted against prostate-specific membrane antigen (PSMA) emerged as a new treatment option and showed effective results in patients with mCRPC. Survival benefit after [177Lu]Lu-PSMA RNT has already been demonstrated in several clinical trials. However, [225Ac]Ac-PSMA (225Ac-PSMA) appears to be an even more promising radiopharmaceutical for the treatment of mCRPC. The use of alpha emitting radionuclides offers advantages over beta emitting radionuclides due to the high linear energy transfer effective for killing tumor cells and the limited range to reduce the radiation effects on the healthy tissue. However, these results are based on retrospective data and safety data of 225Ac-PSMA are still limited. Therefore, a prospective trial is needed to determine the optimal amount of activity that can be administered.

METHODS

The 225Ac-PSMA-Imaging & Therapy (I&T) trial is an investigator-initiated phase I, single-center, open label, repeated dose-escalation and expansion trial. Patient with PSMA-positive mCRPC after at least one line of chemotherapy and/or one line of nonsteroidal antiandrogen will be treated with 225Ac-PSMA-I&T in increasing amount of activity per cycle. Dose-escalation following an accelerated 3 + 3 design which allows to open the next dose-level cohort in the absence of dose limiting toxicity while the previous one is still ongoing. Up to 4 treatment cohorts will be explored including up to 3 dose-escalation cohorts and one expansion cohort where patients will be administered with the recommended dose. A total of up to 30 patients will be enrolled in this trial. All patients will be evaluated for safety. Additionally, dosimetry was performed for the patients in the dose-escalation cohorts after the first 225Ac-PSMA-I&T administration.

DISCUSSION

This trial will assess the safety and tolerability of 225Ac-PSMA-I&T in patients with mCRPC to recommend the optimal dose for the phase II trial.

TRIAL REGISTRATION

ClinicalTrials.gov, (NCT05902247). Retrospectively registered 13 June 2023.

Implementation of dosimetry for molecular radiotherapy; results from a European survey

PURPOSE

The use of molecular radiotherapy (MRT) has been rapidly evolving over the last years. The aim of this study was to assess the current implementation of dosimetry for MRTs in Europe.

METHODS

A web-based questionnaire was open for treating centres between April and June 2022, and focused on 2020-2022. Questions addressed the application of 16 different MRTs, the availability and involvement of medical physicists, software used, quality assurance, as well as the target regions for dosimetry, whether treatment planning and/or verification were performed, and the dosimetric methods used.

RESULTS

A total of 173 responses suitable for analysis was received from centres performing MRT, geographically distributed over 27 European countries. Of these, 146 centres (84 %) indicated to perform some form of dosimetry, and 97 % of these centres had a medical physicist available and almost always involved in dosimetry. The most common MRTs were 131I-based treatments for thyroid diseases and thyroid cancer, and [223Ra]RaCl2 for bone metastases. The implementation of dosimetry varied widely between therapies, from almost all centres performing dosimetry-based planning for microsphere treatments to none for some of the less common treatments (like 32P sodium-phosphate for myeloproliferative disease and [89Sr]SrCl2 for bone metastases).

CONCLUSIONS

Over the last years, implementation of dosimetry, both for pre-therapeutic treatment planning and post-therapy absorbed dose verification, increased for several treatments, especially for microsphere treatments. For other treatments that have moved from research to clinical routine, the use of dosimetry decreased in recent years. However, there are still large differences both across and within countries.

"One Method to Label Them All": A Single Fully Automated Protocol for GMP-Compliant 68Ga Radiolabeling of PSMA-11, Transposable to PSMA-I&T and PSMA-617

BACKGROUND

Prostate-specific membrane antigen (PSMA) is an ideal target for molecular imaging and targeted radionuclide therapy in prostate cancer. Consequently, various PSMA ligands were developed. Some of these molecules are functionalized with a chelator that can host radiometals, such as 68Ga for PET imaging. The 68Ga radiolabeling step benefits from process automation, making it more robust and reducing radiation exposure.

OBJECTIVE

To design a single automated radiolabeling protocol for the GMP-compliant preparation of [68Ga]Ga-PSMA-11, transposable to the production of [68Ga]Ga-PSMA-617 and [68Ga]Ga-PSMA-I&T.

METHODS

A GAIA® synthesis module and a GALLIAD® generator were used. Radio-TLC and radio-HPLC methods were validated for radiochemical purity (RCP) determination. Three [68Ga]Ga-PSMA-11 validation batches were produced and thoroughly tested for appearance and pH, radionuclide identity and purity, RCP, stability, residual solvent and sterility. Minimal modifications were made to the reagents and disposables for optimal application to other PSMA ligands.

RESULTS

[68Ga]Ga-PSMA-11 for clinical application was produced in 27 min. The 3 validation batches met the quality criteria expected by the European Pharmacopoeia to allow routine production. For optimal transposition to PSMA-617, the solid phase extraction cartridge was changed to improve purification of the radiolabeled product. For application to PSMA-I&T, the buffer solution initially used was replaced by HEPES 2.7 M to achieve good radiochemical yields. Residual HEPES content was checked in the final product and was below the Ph. Eur. threshold.

CONCLUSION

A single automated radiolabeling method on the GAIA® module was developed and implemented for 68Ga radiolabeling of 3 PSMA ligands, with slight adjustments for each molecule.

Radiometals in Imaging and Therapy: Highlighting Two Decades of Research

The present article highlights the important progress made in the last two decades in the fields of molecular imaging and radionuclide therapy. Advancements in radiometal-based positron emission tomography, single photon emission computerized tomography, and radionuclide therapy are illustrated in terms of their production routes and ease of radiolabeling. Applications in clinical diagnostic and radionuclide therapy are considered, including human studies under clinical trials; their current stages of clinical translations and findings are summarized. Because the metalloid astatine is used for imaging and radionuclide therapy, it is included in this review. In regard to radionuclide therapy, both beta-minus (β-) and alpha (α)-emitting radionuclides are discussed by highlighting their production routes, targeted radiopharmaceuticals, and current clinical translation stage.

Clinical Experience with [225Ac]Ac-PSMA Treatment in Patients with [177Lu]Lu-PSMA-Refractory Metastatic Castration-Resistant Prostate Cancer

For patients with advanced-stage metastatic castration-resistant prostate cancer (mCRPC) who do not respond to [177Lu]Lu-PSMA therapy, there are limited treatment options. Clinical results obtained with [225Ac]Ac-PSMA are promising. We retrospectively analyzed the outcomes of patients treated with [225Ac]Ac-PSMA between December 2018 and October 2022. Methods: We evaluated the treatment results of 23 patients (mean age, 70.3 ± 8.8 y) with mCRPC who were refractory to treatment with [177Lu]Lu-PSMA (2-9 cycles). The safety profile was assessed according to Common Technology Criteria for Adverse Events version 5.0. Treatment efficacy was assessed using prostate-specific membrane antigen PET progression criteria and prostate-specific antigen (PSA) response according to Prostate Cancer Working Group 2 criteria after the first cycle of [225Ac]Ac-PSMA treatment. Results: All patients received androgen-deprivation therapy, whereas 22 (96%) and 19 (83%) patients received chemotherapy and second-generation antiandrogen therapy, respectively. One patient received 4 cycles, 2 received 3 cycles, 8 received 2 cycles, and 12 received 1 cycle of [225Ac]Ac-PSMA. The median interval between cycles was 13 wk (range, 8-28 wk). [225Ac]Ac-PSMA was administered with a mean activity of 7.6 MBq (range, 6.2-10.0 MBq) in each cycle. Patients were at an advanced stage of disease, and tumor burden was very high. Although the best PSA response was observed in 5 patients (26%) after [225Ac]Ac-PSMA treatment, there was at least some level of decline in PSA observed in 11 patients (58%; n = 19). Treatment response was assessed in patients who underwent [68Ga]Ga-PSMA PET/CT imaging. After the first cycle of treatment (n = 18), 50% of patients (n = 9) showed disease progression according to prostate-specific membrane antigen PET progression criteria, and the disease control rate was calculated to be 50%. Median progression-free survival was 3.1 mo, and median overall survival was 7.7 mo. Grade 3 hematologic toxicity occurred in 1 patient, and grade 3 nephrotoxicity was observed in another patient. Parotid SUVmax decreased by 33%, although all patients complained of dry mouth before treatment. Conclusion: We observed that [225Ac]Ac-PSMA therapy was safe and showed potential even in cases with advanced-stage mCRPC in which all other treatment options were completed.

Cancer Care by Committee to be Superseded by Personal Physician-Patient Partnership Informed by Artificial Intelligence

Multidisciplinary tumor boards (MTBs) have become the reference standard of cancer management, founded upon randomized controlled trial (RCT) evidence-based guidelines. The inordinate delays inherent in awaiting formal regulatory agency approvals of novel therapeutic agents, and the rigidities and nongeneralizability of this regimented approach, often deny cancer patients timely access to effective innovative treatment. Reluctance of MTBs to accept theranostic care of patients with advanced neuroendocrine tumors (NETs) and metastatic castrate-resistant prostate cancer resulted in decades of delay in the incorporation of 177Lu-octreotate and 177Lu-prostate-specific membrane antigen (PSMA) into routine clinical oncology practice. Recent developments in immunotherapy and molecular targeted precision therapy, based on N-of-One individual multifactorial genome analyses, have greatly increased the complexity of decision-making. Burgeoning specialist workload and tight time frames now threaten to overwhelm the logistically, and emotionally, demanding MTB system. It is hypothesized that the advent of advanced artificial intelligence technology and Chatbot natural language algorithms will shift the cancer care paradigm from a MTB management model toward a personal physician-patient shared-care partnership for real-world practice of precision individualized holistic oncology.

Emerging Role of Nuclear Medicine in Prostate Cancer: Current State and Future Perspectives

Prostate cancer is the most frequent epithelial neoplasia after skin cancer in men starting from 50 years and prostate-specific antigen (PSA) dosage can be used as an early screening tool. Prostate cancer imaging includes several radiological modalities, ranging from ultrasonography, computed tomography (CT), and magnetic resonance to nuclear medicine hybrid techniques such as single-photon emission computed tomography (SPECT)/CT and positron emission tomography (PET)/CT. Innovation in radiopharmaceutical compounds has introduced specific tracers with diagnostic and therapeutic indications, opening the horizons to targeted and very effective clinical care for patients with prostate cancer. The aim of the present review is to illustrate the current knowledge and future perspectives of nuclear medicine, including stand-alone diagnostic techniques and theragnostic approaches, in the clinical management of patients with prostate cancer from initial staging to advanced disease.

GRPR versus PSMA: expression profiles during prostate cancer progression demonstrate the added value of GRPR-targeting theranostic approaches

Introduction

Central to targeted radionuclide imaging and therapy of prostate cancer (PCa) are prostate-specific membrane antigen (PSMA)-targeting radiopharmaceuticals. Gastrin-releasing peptide receptor (GRPR) targeting has been proposed as a potential additional approach for PCa theranostics. The aim of this study was to investigate to what extent and at what stage of the disease GRPR-targeting applications can complement PSMA-targeting theranostics in the management of PCa.

Methods

Binding of the GRPR- and PSMA-targeting radiopharmaceuticals [177Lu]Lu-NeoB and [177Lu]Lu-PSMA-617, respectively, was evaluated and compared on tissue sections of 20 benign prostatic hyperplasia (BPH), 16 primary PCa and 17 progressive castration-resistant PCa (CRPC) fresh frozen tissue specimens. Hematoxylin-eosin and alpha-methylacyl-CoA racemase stains were performed to identify regions of prostatic adenocarcinoma and potentially high-grade prostatic intraepithelial neoplasia. For a subset of primary PCa samples, RNA in situ hybridization (ISH) was used to identify target mRNA expression in defined tumor regions.

Results

The highest median [177Lu]Lu-NeoB binding was observed in primary PCa samples, while median and overall [177Lu]Lu-PSMA-617 binding was highest in CRPC samples. The highest [177Lu]Lu-NeoB binding was observed in 3/17 CRPC samples of which one sample showed no [177Lu]Lu-PSMA-617 binding. RNA ISH analyses showed a trend between mRNA expression and radiopharmaceutical binding, and confirmed the distinct GRPR and PSMA expression patterns in primary PCa observed with radiopharmaceutical binding.

Conclusion

Our study emphasizes that GRPR-targeting approaches can contribute to improved PCa management and complement currently applied PSMA-targeting strategies in both early and late stage PCa.

PSMA Targeted Molecular Imaging and Radioligand Therapy for Prostate Cancer: Optimal Patient and Treatment Issues

Theranostics (therapy + diagnosis) targeting prostate-specific membrane antigen (PSMA) is an emerging therapeutic modality that could alter treatment strategies for prostate cancer. Although PSMA-targeted radioligand therapy (PSMA-RLT) has a highly therapeutic effect on PSMA-positive tumor tissue, the efficacy of PSMA-RLT depends on PSMA expression. Moreover, predictors of treatment response other than PSMA expression are under investigation. Therefore, the optimal patient population for PSMA-RLT remains unclear. This review provides an overview of the current status of theranostics for prostate cancer, focusing on PSMA ligands. In addition, we summarize various findings regarding the efficacy and problems of PSMA-RLT and discuss the optimal patient for PSMA-RLT.

PSMA-targeted radioligand therapy in prostate cancer: current status and future prospects

INTRODUCTION

The prostate-specific membrane antigen (PSMA) targeted radioligand therapy (PRLT) for the treatment of metastatic castration-resistant prostate cancer (mCRPC) patients has generated significant interest among the oncologic community, with several publications documenting good response rates and survival benefits with low toxicity profiles.

AREAS COVERED

Indications, patient preparation, dose administration, post-treatment imaging, dosimetry, and side effect profiles of 177Lu-PSMA-617 are discussed in this article. We also discuss results from prospective studies, major retrospective studies, meta-analyses, clinical trials, and mentioned major ongoing clinical trials on PRLT. We have also portrayed our own experiences and future perspectives on PRLT.

EXPERT OPINION

For PRLT, PSMA-617 and PSMA-I&T molecules have revolutionized the theranostic approach in the management of advanced prostate cancer, with solid backing from several published articles showing favorable outcomes and an excellent safety profile of 177Lu-PSMA-617. Improvement in quality of life and survival was seen in the majority of mCRPC patients after 177Lu-PSMA-617 PRLT. Patients with good performance status, asymptomatic, only lymph node metastases, high PSMA expressing lesions, and no discordant FDG avid lesions have a longer survival after 177Lu-PSMA-617 PRLT than patients with poor performance status, symptomatic, hepatic, brain, and skeletal metastases, discordant PSMA, and FDG-avid lesions. Docetaxel and cabazitaxel are approved treatments for mCRPC patients. 177Lu-PSMA-617 is approved as a third-line systemic treatment for mCRPC patients with failure to respond to androgen receptor pathway inhibitors and docetaxel therapy. PRLT is a safe and effective alternative to cabazitaxel (third-line systemic treatment), but it has a higher cost. 177Lu-PSMA-617 could be a more efficient therapeutic option for mCRPC patients as first-line or combined therapy, and it may be a useful therapeutic option for the treatment of metastatic hormone-sensitive prostate cancer (mHSPC) patients. Several clinical studies and clinical trials on PRLT are currently underway. In the future, the results of these trials will be helpful in evolving treatment strategies for prostate cancer patients.

What's to come in PSMA therapies and diagnostics: A summary of clinical trials involving PSMA radioligand-based therapeutic and/or diagnostic approaches with active recruitment

INTRODUCTION

Prostate-Specific Membrane Antigen (PSMA)-based diagnostics and therapeutics are proving highly valuable in identifying disease sites and providing targeted radioligand therapy (RLT) for disseminated disease in prostate cancer (PC). With successful integration of these tools in limited PC presentations, there is a real need and excitement for trials testing PSMA-based approaches more broadly.

AREAS COVERED

We review the ongoing trials registered on ClinicalTrials.gov which aim to evaluate PSMA-PET or PSMA-RLT applications. We outline clinical contexts which have significant ongoing study and therefore may see imminent change, as well as contexts which are lacking in study in the hopes of guiding future research.

EXPERT OPINION

Trials examining intensification strategies through targeted radiotherapy, combination systemic therapies, and RLTs have the potential to demonstrate improved clinical outcomes using PSMA-PET CT for guidance. We expect that PSMA-PET will become fundamental in the work-up of patients before targeted radiotherapy or surgery. The results of ongoing trials will likely clarify the benefits of PSMA-RLT in metastatic PC including in oligometastatic and hormone-sensitive disease; however, there is a sparsity of trials evaluating PSMA-RLT outside of metastatic PC. Clinical trials with PSMA PET/CT as an endpoint for disease control are emerging and standardized reporting and metrics for PSMA staging and response will facilitate the inclusion of PSMA PET endpoints into therapeutic trials.

225Ac-PSMA-617 radioligand therapy of de novo metastatic hormone-sensitive prostate carcinoma (mHSPC): preliminary clinical findings

PURPOSE

225Ac-PSMA-617 has demonstrated good anti-tumor effect as a treatment option for metastatic castration-resistant prostate cancer (mCRPC) patients. No study has previously assessed treatment outcome and survival following 225Ac-PSMA-617 treatment of de novo metastatic hormone-sensitive prostate carcinoma (mHSPC) patients. Based on the potential side effects that are known and explained to the patients by the oncologist, some of the patients refused the standard treatment and are seeking alternative therapies. Thus, we report our preliminary findings in a retrospective series of 21 mHSPC patients that refused standard treatment options and were treated with 225Ac-PSMA-617.

METHODS

We retrospectively reviewed patients with histologically confirmed de novo treatment-naïve bone ± visceral mHSPC that were treated with 225Ac-PSMA-617 radioligand therapy (RLT). Inclusion criteria included an Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 2, treatment-naive bone ± visceral mHSPC, and patients refusal for ADT ± docetaxel, abiraterone acetate, or enzalutamide. We evaluated the response to treatment using prostate-specific antigen (PSA) response and the progression-free survival (PFS) and overall survival (OS) as well as the toxicities.

RESULTS

Twenty-one mHSPC patients were included in this preliminary work. Following treatment, twenty patients (95%) had any decline in PSA and eighteen patients (86%) presented with a PSA decline of ≥ 50% including 4 patients in whom PSA became undetectable. A lower percentage decrease in PSA following treatment was associated with increased mortality and shorter progression-free survival. Overall, administration of 225Ac-PSMA-617 was well tolerated. The commonest toxicity seen was grade I/II dry mouth observed in 94% of patients.

CONCLUSIONS

Given these favorable results, randomized prospective multicenter trials assessing the clinical value of 225Ac-PSMA-617 as a therapeutic agent for mHSPC administered either as monotherapy or administered concomitant with ADT are of interest.

[177Lu]Lu-PSMA-Radioligand Therapy Efficacy Outcomes in Taxane-Naïve Versus Taxane-Treated Patients with Metastatic Castration-Resistant Prostate Cancer: A Systematic Review and Metaanalysis

Radioligand therapy (RLT) with ¹⁷⁷Lu-prostate-specific membrane antigen (PSMA) inhibitors ([¹⁷⁷Lu]Lu-PSMA) is currently approved for patients with metastatic castration-resistant prostate cancer (mCRPC) after progression with at least 1 taxane and 1 androgen-receptor-pathway inhibitor. However, the impact of prior chemotherapy on [¹⁷⁷Lu]Lu-PSMA-RLT outcomes is debatable, with various studies showing inconsistent results. This study was conducted to precisely evaluate the impact of prior taxane chemotherapy on response and survival outcomes in mCRPC patients after [¹⁷⁷Lu]Lu-PSMA-RLT. Methods: This review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Searches in PubMed, Scopus, and Embase were made using relevant key words, and articles up to December 2022 were included. The endpoints included prostate-specific antigen (PSA) response rate (RR), progression-free survival, and overall survival (OS). Individual patient data were pooled when feasible. Univariate odds ratios (ORs) and hazard ratios (HRs) were extracted from the individual articles, and pooled estimates and 95% CIs were generated using metaanalysis. Results: Thirteen articles comprising 2,068 patients were included. In 6 articles (553 patients), taxane-naïve patients had significantly better odds of biochemical response after [¹⁷⁷Lu]Lu-PSMA-RLT (pooled OR, 1.82; 95% CI, 1.21-2.71). Individual patient data metaanalysis for PSA RRs in 3 articles revealed a significantly higher PSA RR in the taxane-naïve versus taxane-treated patients (57.1% vs. 39.5%; difference, 17.6%; 95% CI, 5.6%-28.9%). Further, taxane-naïve status was also a predictor of significantly better progression-free survival (5 articles; 1,027 patients; pooled HR, 0.60; 95% CI, 0.51-0.69) and OS (8 articles; 1,594 patients; pooled HR, 0.54; 95% CI, 0.43-0.68) after [¹⁷⁷Lu]Lu-PSMA-RLT. There was no evidence of publication bias. Conclusion: mCRPC patients with no prior taxanes had significantly better outcomes after [¹⁷⁷Lu]Lu-PSMA-RLT than did taxane-treated patients. Further trials evaluating [¹⁷⁷Lu]Lu-PSMA-RLT in the taxane-naïve setting are now required.

Safety and Therapeutic Optimization of Lutetium-177 Based Radiopharmaceuticals

Peptide receptor radionuclide therapy (PRRT) using Lutetium-177 (¹⁷⁷Lu) based radiopharmaceuticals has emerged as a therapeutic area in the field of nuclear medicine and oncology, allowing for personalized medicine. Since the first market authorization in 2018 of [¹⁷⁷Lu]Lu-DOTATATE (Lutathera®) targeting somatostatin receptor type 2 in the treatment of gastroenteropancreatic neuroendocrine tumors, intensive research has led to transfer innovative ¹⁷⁷Lu containing pharmaceuticals to the clinic. Recently, a second market authorization in the field was obtained for [¹⁷⁷Lu]Lu-PSMA-617 (Pluvicto®) in the treatment of prostate cancer. The efficacy of ¹⁷⁷Lu radiopharmaceuticals are now quite well-reported and data on the safety and management of patients are needed. This review will focus on several clinically tested and reported tailored approaches to enhance the risk-benefit trade-off of radioligand therapy. The aim is to help clinicians and nuclear medicine staff set up safe and optimized procedures using the approved ¹⁷⁷Lu based radiopharmaceuticals.

Advances in Radionuclides and Radiolabelled Peptides for Cancer Therapeutics

Radiopharmaceutical therapy, which can detect and treat tumours simultaneously, was introduced more than 80 years ago, and it has changed medical strategies with respect to cancer. Many radioactive radionuclides have been developed, and functional, molecularly modified radiolabelled peptides have been used to produce biomolecules and therapeutics that are vastly utilised in the field of radio medicine. Since the 1990s, they have smoothly transitioned into clinical application, and as of today, a wide variety of radiolabelled radionuclide derivatives have been examined and evaluated in various studies. Advanced technologies, such as conjugation of functional peptides or incorporation of radionuclides into chelating ligands, have been developed for advanced radiopharmaceutical cancer therapy. New radiolabelled conjugates for targeted radiotherapy have been designed to deliver radiation directly to cancer cells with improved specificity and minimal damage to the surrounding normal tissue. The development of new theragnostic radionuclides, which can be used for both imaging and therapy purposes, allows for more precise targeting and monitoring of the treatment response. The increased use of peptide receptor radionuclide therapy (PRRT) is also important in the targeting of specific receptors which are overexpressed in cancer cells. In this review, we provide insights into the development of radionuclides and functional radiolabelled peptides, give a brief background, and describe their transition into clinical application.

The Emerging Role of PET/CT with PSMA-Targeting Radiopharmaceuticals in Clear Cell Renal Cancer: An Updated Systematic Review

BACKGROUND

Recent articles proposed the employment of positron emission tomography/computed tomography (PET/CT) with prostate-specific membrane antigen (PSMA)-targeting radiopharmaceuticals in clear cell renal cell carcinoma (ccRCC).

METHODS

The authors performed a comprehensive literature search of studies on the performance of PET/CT with PSMA-targeting radiopharmaceuticals in ccRCC. Original articles concerning this imaging examination were included in newly diagnosed ccRCC patients and ccRCC patients with disease recurrence.

RESULTS

A total of sixteen papers concerning the diagnostic performance of PSMA-targeted PET/CT in ccRCC (331 patients) were included in this systematic review. The included articles demonstrated an excellent detection rate of PSMA-targeting PET/CT in ccRCC.

CONCLUSIONS

PSMA-targeted PET/CT seems promising in detecting ccRCC lesions as well as in discriminating the presence of aggressive phenotypes. Prospective multicentric studies are warranted to strengthen the role of PSMA-targeting PET/CT in ccRCC.