PSMA radioligand therapy for solid tumors other than prostate cancer: background, opportunities, challenges, and first clinical reports

Global Research Output of Lutetium-177 PSMA in Prostate Cancer: Bibliometric and Altmetric Analyses

AIM

The integration of innovative radio-pharmaceutical agents targeting prostate-specific membrane antigen (PSMA) within nuclear medicine has transformed prostate cancer detection and management. This study aims to investigate the present landscape of [177Lu]Lu-PSMA in prostate cancer, elucidating trends, global contributions, scholarly outlets, institutions, and thematic concentrations with an aim to inform forthcoming research endeavors.

METHODS

We systematically probed the Scopus repository for relevant [177Lu]Lu-PSMA literature. An assessment of bibliometric and altmetric data was carried out. Finally, we assessed the correlation between the altmetric attention scores and the number of citations for the retrieved data.

RESULTS

Spanning January 2015 to July 2023, the study encompassed 466 articles concerning [177Lu]Lu-PSMA therapy for prostate cancer. Predominant citation accolades gravitated towards metastatic castration-resistant prostate cancer investigations and assessments of [177Lu]Lu-PSMA therapy's safety and efficacy. Further research encompassed adverse effects linked to [177Lu]Lu-PSMA intervention, including xerostomia, thrombocytopenia, anemia, and fatigue. Germany emerged as the primary academic contributor, with The Journal of Nuclear Medicine dominating publications (n = 55). A moderate significant correlation was detected between the number of citations and altmetric attention scores .

CONCLUSION

The findings highlight the growing interest and advancements in the utilization of [177Lu]Lu-PSMA therapy in prostate cancer and offer a comprehensive global perspective on future research directions.

Prostate Specific Membrane Antigen Expression in a Syngeneic Breast Cancer Mouse Model

PURPOSE

Prostate specific membrane antigen (PSMA) has been studied in human breast cancer (BCa) biopsies, however, lack of data on PSMA expression in mouse models impedes development of PSMA-targeted therapies, particularly in improving breast conserving surgery (BCS) margins. This study aimed to validate and characterize the expression of PSMA in murine BCa models, demonstrating that PSMA can be utilized to improve therapies and imaging techniques.

METHODS

Murine triple negative breast cancer 4T1 cells, and human cell lines, MDA-MB-231, MDA-MB-468, implanted into the mammary fat pads of BALB/c mice, were imaged by our PSMA targeted theranostic agent, PSMA-1-Pc413, and tumor to background ratios (TBR) were calculated to validate selective uptake. Immunohistochemistry was used to correlate PSMA expression in relation to CD31, an endothelial cell biomarker highlighting neovasculature. PSMA expression was also quantified by Reverse Transcriptase Polymerase Chain Reaction (RT-PCR).

RESULTS

Accumulation of PSMA-1-Pc413 was observed in 4T1 primary tumors and associated metastases. Average TBR of 4T1 tumors were calculated to be greater than 1.5-ratio at which tumor tissues can be distinguished from normal structures-at peak accumulation with the signal intensity in 4T1 tumors comparable to that in high PSMA expressing PC3-pip tumors. Extraction of 4T1 tumors and lung metastases followed by RT-PCR analysis and PSMA-CD31 co-staining shows that PSMA is consistently localized on tumor neovasculature with no expression in tumor cells and surrounding normal tissues.

CONCLUSION

The selective uptake of PSMA-1-Pc413 in these cancer tissues as well as the characterization and validation of PSMA expression on neovasculature in this syngeneic 4T1 model emphasizes their potential for advancements in targeted therapies and imaging techniques for BCa. PSMA holds great promise as an oncogenic target for BCa and its associated metastases.

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.

Advances in Radioligand Theranostics in Oncology

Theranostics with radioligands (radiotheranostics) has played a pivotal role in oncology. Radiotheranostics explores the molecular targets expressed on tumor cells to target them for imaging and therapy. In this way, radiotheranostics entails non-invasive demonstration of the in vivo expression of a molecular target of interest through imaging followed by the administration of therapeutic radioligand targeting the tumor-expressed molecular target. Therefore, radiotheranostics ensures that only patients with a high likelihood of response are treated with a particular radiotheranostic agent, ensuring the delivery of personalized care to cancer patients. Within the last decades, a couple of radiotheranostics agents, including Lutetium-177 DOTATATE (177Lu-DOTATATE) and Lutetium-177 prostate-specific membrane antigen (177Lu-PSMA), were shown to prolong the survival of cancer patients compared to the current standard of care leading to the regulatory approval of these agents for routine use in oncology care. This recent string of successful approvals has broadened the interest in the development of different radiotheranostic agents and their investigation for clinical translation. In this work, we present an updated appraisal of the literature, reviewing the recent advances in the use of established radiotheranostic agents such as radioiodine for differentiated thyroid carcinoma and Iodine-131-labeled meta-iodobenzylguanidine therapy of tumors of the sympathoadrenal axis as well as the recently approved 177Lu-DOTATATE and 177Lu-PSMA for differentiated neuroendocrine tumors and advanced prostate cancer, respectively. We also discuss the radiotheranostic agents that have been comprehensively characterized in preclinical studies and have shown some clinical evidence supporting their safety and efficacy, especially those targeting fibroblast activation protein (FAP) and chemokine receptor 4 (CXCR4) and those still being investigated in preclinical studies such as those targeting poly (ADP-ribose) polymerase (PARP) and epidermal growth factor receptor 2.

PSMA and FDG PET/CT Findings in Patient With Dedifferentiated Liposarcoma and Prostate Cancer Metastases

ABSTRACT

Dedifferentiated liposarcoma is an extremely rare and highly malignant tumor. We demonstrated a case of a 75-year-old man with significantly PSMA-avid and mildly FDG uptake-dedifferentiated liposarcoma in the retroperitoneal area. The double-tracer (PSMA and FDG) PET scans could further contribute to differential diagnosis and the following treatment strategy for patients who were suspected with prostate cancer metastases and other malignant tumors simultaneously.

Monitoring Dual-Cancer Treatment in a Patient With Prostate and Hepatocellular Carcinoma Using Prostate-Specific Membrane Antigen-Directed PET/CT

ABSTRACT

We report on a 70-year-old man affected with prostate carcinoma (PC) scheduled for prostate-specific membrane antigen (PSMA) PET/CT using 18 F-PSMA1007. Because of uptake in the liver and corresponding findings on magnetic resonance, diagnosis of hepatocellular carcinoma (HCC, G1) was established. The patient was then scheduled for antihormonal treatment for PC and locoregional therapy due to HCC. On follow-up PSMA-targeted PET/CT, we observed durable response to PC-associated therapy, whereas hepatic lesions showed progressive disease. As such, we herein report on a dual-cancer targeting molecular imaging strategy to determine disease extent in a patient affected with both PC and HCC, along with potential of monitoring both systemic and locoregional treatment.

Current clinical application of lutetium‑177 in solid tumors (Review)

Radionuclide-based therapy represents a novel treatment regimen for tumors. Among these therapies, lutetium-177 (177Lu) has gained significant attention due to its stability and safety, as well as its ability to emit both γ and β rays, allowing for both imaging with single photon emission computed tomography and tumor treatment. As a result, 177Lu can be used for both diagnosis and treatment for diseases such as prostatic and gastric cancer. Therefore, based on the available data, the present review provides a brief overview of the clinical applications of 177Lu-targeted radionuclide therapy in metastatic prostate cancer, neuroendocrine tumors and other types of solid tumors, and highlights the current therapeutic effect, reduction in damage to normal tissues and future research directions, including the development of new nuclides and the application of more nuclides in different tumors. In the future, such treatments could be used in more tumors.

Iridium-based Polymeric Multifunctional Imaging Tools for Biochemistry

Herein, we report the development of a macromolecular multifunctional imaging tool for biological investigations, which is comprised of an N-(2-hydroxypropyl)methacrylamide backbone, iridium-based luminescent probe, glutamate carboxypeptidase II (GCPII) targeting ligand, and biotin affinity tag. The iridium luminophore is a tris-cyclometalated complex based on [Ir(ppy)3] with one of its 2-phenylpyridine ligands functionalized to allow conjugation. Synthesized macromolecular probes differed in the structure of the polymer and content of the iridium complex. The applicability of the developed imaging tools has been tested in flow cytometry (FACS) based assay, laser confocal microscopy, and fluorescence lifetime imaging microscopy (FLIM). The FACS analysis has shown that the targeted iBodies containing the iridium luminophore exhibit selective labelling of GCPII expressing cells. This observation was also confirmed in the imaging experiments with laser confocal microscopy. The FLIM experiment has shown that the iBodies with the iridium label exhibit a lifetime greater than 100 ns, which distinguishes them from typically used systems labelled with organic fluorophores exhibiting short fluorescence lifetimes. The results of this investigation indicate that the system exhibits interesting properties, which supports the development of additional biological tools utilizing the key components (iridium complexes, iBody concept), primarily focusing on the longer lifetime of the iridium emitter.

The Utility of Prostate-Specific Membrane Antigen-11 PET in Detection and Management of Central Nervous System Neoplasms

ABSTRACT

We present a case series of 5 patients diagnosed with schwannoma and 1 patient diagnosed with astrocytoma who underwent PSMA PET imaging for tumor detection. We retrospectively analyzed the records of 4 male and 2 female patients (mean age, 53.2 ± 13.2) who underwent PSMA PET imaging between March and September 2023. PET interpretation showed increased Ga-PSMA-11 accumulation in all patients with a mean SUVmax of 3.11 ± 1.8. This series underscores PSMA PET's potential for CNS neoplasm detection.

Current diagnosis and treatment of salivary gland-type tumors of the lung

Salivary gland-type tumors of the lung are thought to originate from the submucosal exocrine glands of the large airways. Due to their rare occurrence, reports of their study are limited to small-scale or case reports. Therefore, daily clinical practices often require a search for previous reports. In the last 20 years, several genetic rearrangements have been identified, such as MYB::NF1B rearrangements in adenoid cystic carcinoma, CRTC1::MAML2 rearrangements in mucoepidermoid carcinoma, EWSR1::ATF1 rearrangements in hyalinizing clear cell carcinoma and rearrangements of the EWSR1 locus or FUS (TLS) locus in myoepithelioma and myoepithelial carcinoma. These molecular alterations have been useful in diagnosing these tumors, although they have not yet been linked to molecularly targeted therapies. The morphologic, immunophenotypic, and molecular characteristics of these tumors are similar to those of their counterparts of extrapulmonary origin, so clinical and radiologic differential diagnosis is required to distinguish between primary and metastatic disease of other primary sites. However, these molecular alterations can be useful in differentiating them from other primary lung cancer histologic types. The management of these tumors requires broad knowledge of the latest diagnostics, surgery, radiotherapy, bronchoscopic interventions, chemotherapy, immunotherapy as well as therapeutic agents in development, including molecularly targeted agents. This review provides a comprehensive overview of the current diagnosis and treatment of pulmonary salivary gland tumors, with a focus on adenoid cystic carcinoma and mucoepidermoid carcinoma, which are the two most common subtypes.

68Ga Prostate-specific Membrane Antigen Uptake in Metastatic Medullary Thyroid Carcinoma

We present the case of a 58-year-old man with advanced medullary thyroid carcinoma who had a treatment history with different types of modalities. In the follow-up, the patient had rising calcitonin and CEA levels. Metastatic lymph nodes, liver, and bone metastases with varying degrees of uptake were detected on 18F-fluorodeoxyglucose (FDG) and 68Ga-DOTATATE positron emission tomography/computed tomography (PET/CT). 68Ga prostate-specific membrane antigen (PSMA) PET/CT was performed to explore whether the patient might have a chance for PSMA-targeted radionuclide therapy, and increased PSMA expression was noted in most of the metastatic lesions, even some of which have higher PSMA uptake than 18F-FDG and 68Ga-DOTATATE.

Imaging Molecular Targets and Metabolic Pathways in Breast Cancer for Improved Clinical Management: Current Practice and Future Perspectives

Breast cancer is the most frequently diagnosed cancer and leading cause of cancer-related deaths worldwide. Timely decision-making that enables implementation of the most appropriate therapy or therapies is essential for achieving the best clinical outcomes in breast cancer. While clinicopathologic characteristics and immunohistochemistry have traditionally been used in decision-making, these clinical and laboratory parameters may be difficult to ascertain or be equivocal due to tumor heterogeneity. Tumor heterogeneity is described as a phenomenon characterized by spatial or temporal phenotypic variations in tumor characteristics. Spatial variations occur within tumor lesions or between lesions at a single time point while temporal variations are seen as tumor lesions evolve with time. Due to limitations associated with immunohistochemistry (which requires invasive biopsies), whole-body molecular imaging tools such as standard-of-care [18F]FDG and [18F]FES PET/CT are indispensable in addressing this conundrum. Despite their proven utility, these standard-of-care imaging methods are often unable to image a myriad of other molecular pathways associated with breast cancer. This has stimulated interest in the development of novel radiopharmaceuticals targeting other molecular pathways and processes. In this review, we discuss validated and potential roles of these standard-of-care and novel molecular approaches. These approaches' relationships with patient clinicopathologic and immunohistochemical characteristics as well as their influence on patient management will be discussed in greater detail. This paper will also introduce and discuss the potential utility of novel PARP inhibitor-based radiopharmaceuticals as non-invasive biomarkers of PARP expression/upregulation.

Head-to-head comparisons of enhanced CT, 68Ga-PSMA-11 PET/CT and 18F-FDG PET/CT in identifying adverse pathology of clear-cell renal cell carcinoma: a prospective study

OBJECTIVES

Accurate preoperative prediction of adverse pathology is crucial for treatment planning of renal cell carcinoma (RCC). Previous studies have emphasized the potential of prostate-specific membrane antigen positron emission tomography / computed tomography (PSMA PET/CT) in differentiating between benign and malignant localized renal tumors. However, there is a scarcity of case reports elucidating the identification of aggressive pathological features using PET/CT. Our study was designed to prospectively compare the diagnostic value of enhanced CT, 68Ga-PSMA-11 and 18F-fluorodeoxyglucose (18F-FDG) PET/CT in clear-cell renal cell carcinoma (ccRCC) with necrosis or sarcomatoid or rhabdoid differentiation.

MATERIALS AND METHODS

A prospective case series of patients with a newly diagnosed renal mass who underwent enhanced CT, 68Ga-PSMA-11 and 18F-FDG PET/CT within 30 days prior to nephrectomy was included. Complete preoperative and postoperative clinicopathological data were recorded. Patients who received neoadjuvant targeted therapy, declined enhanced CT or PET/CT scanning, refused surgical treatment or had non-ccRCC pathological indications were excluded. Radiological parameters were compared within subgroups of pathological characteristics. Bonferroni corrections were used to adjust for multiple testing and statistical significance was set at a p-value less than 0.017.

RESULTS

Seventy-two patients were available for the final analysis. Enhanced CT demonstrated poor performance in identifying necrosis, sarcomatoid or rhabdoid differentiation and adverse pathology (all P > 0.05). The maximum standardized uptake value (SUVmax) of 68Ga-PSMA-11 PET/CT was more effective than 18F-FDG PET/CT in identifying tumor necrosis and adverse pathology, with an area under the curve (AUC) of 0.85 (cutoff value=25.26, p<0.001; Delong test z=2.709, p=0.007) for tumor necrosis and AUC of 0.90 (cutoff value=25.26, p<0.001; Delong test z=3.433, p<0.001) for adverse pathology. However, no significant statistical difference was found between 68Ga-PSMA-11 and 18F-FDG PET/CT in predicting sarcomatoid or rhabdoid feature (AUC of 0.91 vs.0.75, Delong test z=1.998, p=0.046). Subgroup analyses based on age, sex, tumor location, maximal diameter, stage and WHO/ISUP grade demonstrated that 68Ga-PSMA-11 PET/CT SUVmax had a significant predictive value for adverse pathology. Enhanced CT value and SUVmax demonstrated strong reliability [intraclass correlation coefficient (ICC) > 0.80], indicating a robust correlation.

CONCLUSIONS

68Ga-PSMA-11 PET/CT demonstrates distinct advantages in identifying aggressive pathological features of primary ccRCC when compared to enhanced CT and 18F-FDG PET/CT. Further research and assessment are warranted to fully establish the clinical utility of 68Ga-PSMA-11 PET/CT in ccRCC.

68Ga-PSMA PET/CT for Response Evaluation of 223Ra Treatment in Metastatic Prostate Cancer

CT and bone scintigraphy are not useful for response evaluation of bone metastases to 223Ra treatment in metastatic castration-resistant prostate cancer (mCRPC). PET using 68Ga prostate-specific membrane antigen 11 (68Ga-PSMA) is a promising tool for response evaluation of mCRPC. The aim of this study was to determine the utility of 68Ga-PSMA PET/CT for response evaluation of 223Ra treatment in patients with mCRPC. Methods: Within this prospective, multicenter, imaging discovery study, 28 patients with mCRPC, eligible for 223Ra treatment, were included between 2019 and 2022. Patients received 223Ra according to the standard of care. Study procedures included CT, bone scintigraphy, and 68Ga-PSMA PET/CT at baseline, after 3 and 6 cycles of 223Ra treatment, and on treatment failure. Response to 223Ra treatment was visually assessed on all 3 imaging modalities. Total tumor volume within bone (TTVbone) was determined on 68Ga-PSMA PET/CT. Intrapatient heterogeneity in response was studied using a newly developed image-registration tool for sequential images of PET/CT. Results were compared with failure-free survival (good responders vs. poor responders; cutoff, 24 wk) and alkaline phosphatase (ALP) response after 3 cycles. Results: Visual response assessment criteria could not distinguish good responders from poor responders on 68Ga-PSMA PET/CT and bone scintigraphy. For 68Ga-PSMA PET/CT, TTVbone at baseline was lower in good responders than in poor responders, whereas TTVbone increased in both groups during treatment. TTVbone was higher in patients with new extraosseous metastases during 223Ra treatment. Although TTVbone and ALP correlated at baseline, changes in TTVbone and ALP on treatment did not. 68Ga-PSMA response of TTVbone showed intrapatient heterogeneity in most patients. Conclusion: mCRPC patients with lower TTVbone on 68Ga-PSMA PET/CT have the best clinical outcome after 223Ra treatment. Response is highly heterogeneous in most patients. A decrease in ALP, which occurred in most patients, was not correlated with a decrease in TTVbone, which might make one question the value of ALP for disease monitoring during 223Ra treatment in clinical practice.

Vascular Expression of Prostate-specific Membrane Antigen (PSMA) in MiTF Family Translocation Renal Cell Carcinoma and Related Neoplasms

Multiple studies have demonstrated prostate-specific membrane antigen (PSMA) expression in the neo-vasculature of non-prostate tumors including clear cell renal cell carcinoma (ccRCC). However, PSMA expression in rare renal tumors including MiTF family translocation renal cell carcinoma has not been previously characterized. We examined PSMA expression by immunohistochemistry in a series of MiTF family translocation renal cell carcinomas as well as in several genetically related tumors including alveolar soft part sarcoma and PEComas with TFE3 rearrangements. PSMA expression was also studied in several cases of ccRCC and papillary RCC. Overall, PSMA immunohistochemistry was performed in 61 samples from 58 patients. Vascular PSMA expression was seen with the highest frequency in ccRCC [88% (14/16)] (38% focal, 50% diffuse). Translocation RCC (tRCC) demonstrated the second highest frequency of PSMA expression [71% (22/28)] (57% focal, 14% diffuse), followed by alveolar soft part sarcoma [50% (4/8)] (38% focal, 12% diffuse). No PSMA expression was seen in PEComas with TFE3 rearrangement (0/3) or papillary RCC (0/6). PSMA expression was only present in tumor-associated neo-vasculature. A patient with oligometastatic tRCC underwent 68 Ga-PSMA-11 PET imaging which detected multiple putative metastatic lesions not detected on conventional computed tomography imaging performed 2 weeks prior, supporting the potential utility of PSMA imaging in tRCC. These findings have potential implications for the utility of PSMA guided diagnostic and therapeutic agents in both common and uncommon renal cell carcinoma subtypes as well as genetically related mesenchymal neoplasms.

Meta-analysis of 18 F-PSMA-1007 PET/CT, 18 F-FDG PET/CT, and 68Ga-PSMA PET/CT in diagnostic efficacy of prostate Cancer

OBJECTIVE

To compare 18 F-PSMA-1007 PET/CT, 18 F-FDG PET/CT and 68Ga-PSMA PET/CT in the diagnostic value of prostate cancer.

METHOD

The Chinese and foreign databases, such as Pubmed, Cochrane Library, Embase, CNKI, VIP, Wanfang, etc., were systematically searched within the period from the establishment of the database to June 1, 2022. Clinical studies related to the diagnosis of prostate cancer by methods such as 18 F-PSMA-1007 PET/CT, 18 F-FDG PET/CTCT, 68Ga-PSMA PET/CT, were researched. Two (2) investigators independently screened literatures, extracted data, and assessed the risk of bias when these data were included in the studies with the Quality Assessment of Diagnostic Accuracy Studies (QUADAS-2). Review Manager5.4, Stata 14.0, and Meta-disc 1.4 software were used for meta-analysis to compare the efficacy of different methods in the diagnose of prostate cancer.

RESULTS

Twenty-seven (27) studies, including 2891 subjects were included in our study. Meta-analysis results showed that the pooled sensitivities of 18 F-PSMA-1007 PET/CT, 18 F-FDG PET/CT, and 68Ga-PSMA PET/CT were 0.912 (95%CI: 0.883-0.936), 0.748 (95%CI: 0.698-0.795), and 0.916 (95%CI: 0.896-0.934), respectively; the pooled specification were 0.878 (0.844-0.907), 0.639 (95%CI: 0.589-0.687), and 0.734 (95%CI: 0.685-0.779), respectively; the positive likelihood ratios were 6.335 (95%CI: 4.288-9.357), 2.282 (95%CI: 1.497-3.477), and 3.593 (95%CI: 2.986-4.323), respectively; the negative likelihood ratios were 0.878 (95%CI: 0.844-0.907), 0.374 (95%CI: 0.280-0.499), and 0.110 (95%CI: 0.083-0.144), respectively; the diagnostic odds ratios were 65.125 (95%CI: 34.059-124.53), 7.094 (95%CI: 4.091-12.301), and 29.722 (95%CI: 20.141-43.863), respectively; the positive posterior probability was 64%, 38%, and 62%, respectively; the area under the SPOC curve was 0.95 (95%CI: 0.93-0.97), 0.81 (95%CI: 0.78-0.84), and 0.96 (95%CI: 0.92-0.98), respectively. The funnel plots indicated that there was no significant publication bias in the included literatures.

CONCLUSION

The current evidences showed that 18 F-PSMA-1007 PET/CT and 68Ga-PSMA PET/CT had higher diagnostic efficacy of prostate cancer compared with 18 F-FDG PET/CT, among which 68Ga-PSMA PET/CT was slightly higher in the sensitivity of the diagnosis of prostate cancer, while 18 F-PSMA-1007 PET/CT may have higher efficacy in specificity and confirmed positive rate. Due to the limitations of the quality of the included samples and literatures, the above conclusions should be further validated by expanding the sample size and improving the quality.

PSMA-targeted therapy for non-prostate cancers

Radioligand therapy (RLT) agents are demonstrating a crucial role in the clinical approach to aggressive malignancies such as metastatic castrate-resistant prostate cancer (m-CRPC). With the recent FDA approval of prostate-specific membrane antigen (PSMA)-targeted RLT for m-CRPC, the field has broadened its gaze to explore other cancers that express PSMA in the tumor parenchyma or tumor neovasculature. In this review article, we discuss current progress in the clinical use of PSMA RLTs in non-prostate cancers such salivary gland cancers, renal cell carcinoma, high grade glioma, and soft tissue sarcoma. We highlight early reports in small case series and clinical trials indicating promise for PSMA-targeted RLT and highlighting the importance of identifying patient cohorts who may most benefit from these interventions. Further study is indicated in non-prostate cancers investigating PSMA RLT dosimetry, PSMA PET/CT imaging as a biomarker, and assessing PSMA RLT safety and efficacy in these cancers.

Druggability of Targets for Diagnostic Radiopharmaceuticals

Targets play an indispensable and pivotal role in the development of radiopharmaceuticals. However, the initial stages of drug discovery projects are often plagued by frequent failures due to inadequate information on druggability and suboptimal target selection. In this context, we aim to present a comprehensive review of the factors that influence target druggability for diagnostic radiopharmaceuticals. Specifically, we explore the crucial determinants of target specificity, abundance, localization, and positivity rate and their respective implications. Through a detailed analysis of existing protein targets, we elucidate the significance of each factor. By carefully considering and balancing these factors during the selection of targets, more efficacious and targeted radiopharmaceuticals are expected to be designed for the diagnosis of a wide range of diseases in the future.

Incidental Detection of Papillary Thyroid Carcinoma in Tc-99 m PSMA Imaging in a Case with Negative FNA Result

Prostate-specific membrane antigen (PSMA) is a type II transmembrane glycoprotein and is expressed in multiple solid malignant neoplasms. We presented a case of a prostate cancer patient who went through Tc-99 m PSMA SPECT, and multifocal increased radiotracer uptake in the thyroid gland was demonstrated. Despite negative FNA results for malignancy, post-operative histopathologic examination illustrated papillary thyroid carcinoma.

A Review of Theranostics: Perspectives on Emerging Approaches and Clinical Advancements

Theranostics is the combination of two approaches-diagnostics and therapeutics-applied for decades in cancer imaging using radiopharmaceuticals or paired radiopharmaceuticals to image and selectively treat various cancers. The clinical use of theranostics has increased in recent years, with U.S. Food and Drug Administration (FDA) approval of lutetium 177 (177Lu) tetraazacyclododecane tetraacetic acid octreotate (DOTATATE) and 177Lu-prostate-specific membrane antigen vector-based radionuclide therapies. The field of theranostics has imminent potential for emerging clinical applications. This article reviews critical areas of active clinical advancement in theranostics, including forthcoming clinical trials advancing FDA-approved and emerging radiopharmaceuticals, approaches to dosimetry calculations, imaging of different radionuclide therapies, expanded indications for currently used theranostic agents to treat a broader array of cancers, and emerging ideas in the field. Keywords: Molecular Imaging, Molecular Imaging-Cancer, Molecular Imaging-Clinical Translation, Molecular Imaging-Target Development, PET/CT, SPECT/CT, Radionuclide Therapy, Dosimetry, Oncology, Radiobiology © RSNA, 2023.

Clinical Advances and Perspectives in Targeted Radionuclide Therapy

Targeted radionuclide therapy has become increasingly prominent as a nuclear medicine subspecialty. For many decades, treatment with radionuclides has been mainly restricted to the use of iodine-131 in thyroid disorders. Currently, radiopharmaceuticals, consisting of a radionuclide coupled to a vector that binds to a desired biological target with high specificity, are being developed. The objective is to be as selective as possible at the tumor level, while limiting the dose received at the healthy tissue level. In recent years, a better understanding of molecular mechanisms of cancer, as well as the appearance of innovative targeting agents (antibodies, peptides, and small molecules) and the availability of new radioisotopes, have enabled considerable advances in the field of vectorized internal radiotherapy with a better therapeutic efficacy, radiation safety and personalized treatments. For instance, targeting the tumor microenvironment, instead of the cancer cells, now appears particularly attractive. Several radiopharmaceuticals for therapeutic targeting have shown clinical value in several types of tumors and have been or will soon be approved and authorized for clinical use. Following their clinical and commercial success, research in that domain is particularly growing, with the clinical pipeline appearing as a promising target. This review aims to provide an overview of current research on targeting radionuclide therapy.

Innovation in Radionuclide Therapy for the Treatment of Prostate Cancers: Radiochemical Perspective and Recent Therapeutic Practices

Prostate cancer represents the second cause of death by cancer in males in western countries. While early-stage diseases are accessible to surgery and/or external radiotherapy, advanced metastatic prostate cancers are primarily treated with androgen deprivation therapy, to which new generation androgen receptor antagonists or taxane-based chemotherapies are added in the case of tumor relapse. Nevertheless, patients become invariably resistant to castration with a median survival that rarely exceeds 3 years. This fostered the search for alternative strategies, independent of the androgen receptor signaling pathway. In this line, radionuclide therapies may represent an interesting option as they could target either the microenvironment of sclerotic bone metastases with the use of radiopharmaceuticals containing samarium-153, strontium-89 or radium-223 or tumor cells expressing the prostate-specific membrane antigen (PSMA), a protein found at the surface of prostate cancer cells. This review gives highlights the chemical properties of radioligands targeting prostate cancer cells and recapitulates the clinical trials evaluating the efficacy of radionuclide therapies, alone or in combination with other approved treatments, in patients with castration-resistant prostate tumors. It discusses some of the encouraging results obtained, especially the benefit on overall survival that was reported with [¹⁷⁷Lu]-PSMA-617. It also addresses the specific requirements for the use of this particular class of drugs, both in terms of medical staff coordination and adapted infrastructures for efficient radioprotection.

Rapid Tumor Washout of 177Lu-PSMA Radioligand in Renal Cell Carcinoma

ABSTRACT

The role of prostate-specific membrane antigen (PSMA) targeted molecular imaging and radionuclide therapy in prostate cancer is well known. PSMA is also overexpressed in the neovasculature of a number of solid tumors, including renal cell carcinoma (RCC). Several studies have demonstrated the diagnostic utility of PSMA PET imaging in the setting of RCC. To date, no PSMA radioligand therapy of RCC patient has been reported according to literature. Here, we report our experience treating a patient with metastatic RCC with 177Lu-PSMA I&T radioligand therapy, but unexpected imaging findings with rapid washout of 177Lu-PSMA from the tumor.

Discriminating Inflammatory Radiation-Related Changes From Early Recurrence in Patients With Glioblastomas: A Preliminary Analysis of 68Ga-PSMA-11 PET/CT Compared With 18F-FDOPA PET/CT

PURPOSE OF THE REPORT

Using morphological and functional imaging to discriminate recurrence from postradiation-related modifications in patients with glioblastomas remains challenging. This pilot study aimed to assess the feasibility of using 68Ga-prostate-specific membrane antigen (PSMA) 11 PET/CT compared with 18F-FDOPA PET/CT to detect early recurrence.

METHODS

Nine patients followed up for glioblastomas who received MRI during 12 months of follow-up were referred for both 68Ga-PSMA-11 and 18F-FDOPA PET/CT. The SUVmax, lesion-to-striatum ratio, lesion-to-normal parenchyma ratio, and lesion-to-salivary gland ratio were calculated.

RESULTS

Good correlation between 18F-FDOPA and 68Ga-PSMA PET/CT findings was seen in 5 patients. In 4 patients, the findings of both examinations were consistent with recurrence but were better visualized with the PSMA PET/CT. Examinations of the fifth patient were suggestive of postradiation-related changes and were better analyzed with the PSMA PET/CT, which displayed relatively low uptake compared with DOPA PET/CT. Conversely, 4 patients showed conflicting results: recurrence was not detected on the PSMA PET/CT because of previously introduced bevacizumab treatment; in another patient, both examinations were consistent with recurrence, but there was an uptake mismatch at the suspected lesion sites, and 2 patients presented with inconsistent findings.

CONCLUSIONS

Despite a few discrepancies, this study highlights the potential role of 68Ga-PSMA-11 PET/CT for discriminating postradiation inflammation from recurrence. 68Ga-PSMA-11 PET/CT has an excellent lesion-to-background ratio, and false-positive and false-negative results could be minimized through implementing certain protocols before performing the examination. More powerful prospective studies are required to validate our results.

Advances in PET imaging of cancer

Molecular imaging has experienced enormous advancements in the areas of imaging technology, imaging probe and contrast development, and data quality, as well as machine learning-based data analysis. Positron emission tomography (PET) and its combination with computed tomography (CT) or magnetic resonance imaging (MRI) as a multimodality PET-CT or PET-MRI system offer a wealth of molecular, functional and morphological data with a single patient scan. Despite the recent technical advances and the availability of dozens of disease-specific contrast and imaging probes, only a few parameters, such as tumour size or the mean tracer uptake, are used for the evaluation of images in clinical practice. Multiparametric in vivo imaging data not only are highly quantitative but also can provide invaluable information about pathophysiology, receptor expression, metabolism, or morphological and functional features of tumours, such as pH, oxygenation or tissue density, as well as pharmacodynamic properties of drugs, to measure drug response with a contrast agent. It can further quantitatively map and spatially resolve the intertumoural and intratumoural heterogeneity, providing insights into tumour vulnerabilities for target-specific therapeutic interventions. Failure to exploit and integrate the full potential of such powerful imaging data may lead to a lost opportunity in which patients do not receive the best possible care. With the desire to implement personalized medicine in the cancer clinic, the full comprehensive diagnostic power of multiplexed imaging should be utilized.

RadioLigand Therapy with [177Lu]Lu-PSMA-617 for Salivary Gland Cancers: Literature Review and First Compassionate Use in France

Salivary gland cancers are rare tumors comprising a large group of heterogeneous tumors with variable prognosis. Their therapeutic management at a metastatic stage is challenging due to the lack of therapeutic lines and the toxicity of treatments. [¹⁷⁷Lu]Lu-PSMA-617 (prostate-specific membrane antigen) is a vectored radioligand therapy (RLT) initially developed to treat castration-resistant metastatic prostate cancer with encouraging results in terms of efficacy and toxicity. Many malignant cells could be treated with [¹⁷⁷Lu]Lu-PSMA-617 as long as they express PSMA as a consequence of androgenic pathway activation. RLT may be used when anti-androgen hormonal treatment has failed, particularly in prostate cancer. [¹⁷⁷Lu]Lu-PSMA-617 has been proposed in certain salivary gland cancers, though the expression of PSMA is demonstrated by a significant uptake using [⁶⁸Ga]Ga-PSMA-11 PET scan. This theranostic approach could be a new therapeutic option, warranting prospective investigation in a larger cohort. We review the literature on this subject and offer a clinical illustration of compassionate use in France as a perspective for administering [¹⁷⁷Lu]Lu-PSMA-617 in salivary gland cancer.

Integrating Theranostics Into Patient Care Pathways: AJR Expert Panel Narrative Review

Theranostics describes the coupling of a diagnostic biomarker and a therapeutic agent (i.e., a theranostic pair) that have a common target in tumor cells or their microenvironment. The term is increasingly associated with in vivo nuclear medicine oncologic applications that couple diagnostic imaging by means of gamma radiation with concomitant localized high-energy particulate radiation to a tissue expressing the common target. Several theranostic pairs have been translated into clinical practice in the United States and are poised to become a mainstay of cancer treatment. The purposes of this article are to review experience with theranostics for solid-organ malignancies and to address the practical integration into care pathways of β-emitting therapies that include somatostatin analogue radioligands for neuroendocrine tumors, PSMA-directed therapy for prostate cancer, and 131I-MIBG therapy for tumors of neural crest origin. Toxicities related to theranostics administration and indications for cessation of therapy in patients who experience adverse events are also discussed. A multidisciplinary team-based approach for identifying patients most likely to respond to these agents, determining the optimal time for therapy delivery, and managing patient care throughout the therapeutic course is critical to the success of a radiotheranostic program.

Up-Regulation of PSMA Expression In Vitro as Potential Application in Prostate Cancer Therapy

Possibilities to improve the therapeutic efficacy of Lu-177-PSMA-617 radionuclide therapy by modulation of target expression are being investigated. Knowledge on regulatory factors that promote prostate cancer (PCa) progression may contribute to targeting prostate cancer more effectively. We aimed at the stimulation of PCa cell lines using the substances 5-aza-2'-deoxycitidine (5-aza-dC) and valproic acid (VPA) to achieve increased prostate-specific membrane antigen (PSMA) expression. PC3, PC3-PSMA, and LNCaP cells were incubated with varying concentrations of 5-aza-dC and VPA to investigate the cell-bound activity of Lu-177-PSMA-617. Stimulation effects on both the genetically modified cell line PC3-PSMA and the endogenously PSMA-expressing LNCaP cells were demonstrated by increased cellular uptake of the radioligand. For PC3-PSMA cells, the fraction of cell-bound radioactivity was enhanced by about 20-fold compared to that of the unstimulated cells. Our study reveals an increased radioligand uptake mediated by stimulation for both PC3-PSMA and LNCaP cell lines. In perspective of an enhanced PSMA expression, the present study might contribute to advanced radionuclide therapy approaches that improve the therapeutic efficacy, as well as combined treatment options.

Kidney absorbed radiation doses for [ 177 Lu]Lu-PSMA-617 and [ 177 Lu]Lu-PSMA-I&T determined by 3D clinical dosimetry

PURPOSE

For prostate-specific membrane antigen-directed radioligand therapy (PSMA-RLT), [ 177 Lu]Lu-PSMA-617 and [ 177 Lu]Lu-PSMA-I&T are the currently preferred compounds. Recent preclinical studies suggested ~30x higher kidney absorbed dose for [ 177 Lu]Lu-PSMA-I&T compared to [ 177 Lu]Lu-PSMA-617, which may lead to an increased risk of kidney toxicity. We performed two single-centre, prospective dosimetry studies with either [ 177 Lu]Lu-PSMA-617 or [ 177 Lu]Lu-PSMA-I&T, using an identical dosimetry protocol. We evaluated the absorbed doses of both 177 Lu-labelled radioligands in human kidneys.

METHODS

3D SPECT/computed tomography (CT) imaging of the kidneys was performed after PSMA-RLT in cancer patients with PSMA-positive disease and an adequate glomerular filtration rate (≥50 mL/min). Ten metastatic hormone-sensitive prostate cancer patients (mHSPC) were treated with [ 177 Lu]Lu-PSMA-617 and 10 advanced salivary gland cancer (SGC) patients were treated with [ 177 Lu]Lu-PSMA-I&T. SPECT/CT imaging was performed at five timepoints (1 h, 24 h, 48 h, 72 h, and 168 h post-injection). In mHSPC patients, SPECT/CT imaging was performed after cycles 1 and 2 (cumulative activity: 9 GBq) and in SGC patients only after cycle 1 (activity: 7.4 GBq). Kidney absorbed dose was calculated using organ-based dosimetry.

RESULTS

The median kidney absorbed dose was 0.49 Gy/GBq (range: 0.34-0.66) and 0.73 Gy/GBq (range: 0.42-1.31) for [ 177 Lu]Lu-PSMA-617 and [ 177 Lu]Lu-PSMA-I&T, respectively (independent samples t test; P  = 0.010).

CONCLUSION

This study shows that the kidney absorbed dose for [ 177 Lu]Lu-PSMA-617 and [ 177 Lu]Lu-PSMA-I&T differs, with a ~1.5x higher median kidney absorbed dose for [ 177 Lu]Lu-PSMA-I&T. This difference in the clinical setting is considerably smaller than observed in preclinical studies and may not hamper treatments with [ 177 Lu]Lu-PSMA-I&T.

PSMA-Directed Imaging and Therapy of Salivary Gland Tumors: A Single-Center Retrospective Study

We analyzed the diagnostic performance of prostate-specific membrane antigen (PSMA) PET/CT and the dosimetry, efficacy, and safety of 177Lu-PSMA-617 radioligand therapy (RLT) in salivary gland malignancies (SGMs). Methods: We identified 28 SGM patients with PSMA PET/CT from our database. CT and PSMA PET/CT images were evaluated separately by 3 masked readers in joint reading sessions. Pathologic findings were grouped into 6 TNM regions, and lesion-based disease extent was classified as no disease (n = 1, 4%), unifocal (n = 2, 7%), oligometastatic (n = 9, 32%), multifocal (n = 3, 11%), or disseminated (n = 13, 47%). For each region, the SUVmax of the lesion with the highest uptake was measured and the visual PSMA expression score was evaluated on a per-patient basis using PROMISE criteria. The association between PSMA expression and clinical and histopathologic markers was tested using the Student t test. Five patients underwent PSMA RLT with intratherapeutic dosimetry. Response was assessed using RECIST 1.1, and adverse events were graded according to version 5.0 of the Common Terminology Criteria for Adverse Events. Results: Compared with CT, PSMA PET/CT demonstrated additional metastatic lesions in 11 of 28 (39%) patients, leading to upstaging of TNM and lesion-based disease extent in 3 (11%) and 6 (21%) patients, respectively. PSMA PET/CT detected CT-occult local tumor, regional lymph nodes, nonregional lymph nodes, and bone metastases in 1 (4%), 4 (14%), 2 (7%), and 4 (14%) patients, respectively; no additional lesions were detected in the other predefined regions. PSMA expression level was higher than liver in 6 patients (25%). A significantly higher SUVmax was observed in male than female patients (15.8 vs. 8.5, P = 0.007) and in bone than lung lesions (14.2 vs. 6.4, P = 0.006). PSMA RLT was discontinued after 1 cycle in 3 of 5 patients because of insufficient tumor doses. No adverse events of grade 4 or higher occurred. Conclusion: In SGMs, PSMA PET/CT demonstrated a superior detection rate and led to upstaging in about one third of patients when compared with CT. The male sex and the presence of bone metastases were associated with significantly higher PSMA expression. PSMA RLT was well tolerated, but most patients did not have more than 1 cycle because of insufficient tumor doses.

Underlying Features of Prostate Cancer-Statistics, Risk Factors, and Emerging Methods for Its Diagnosis

Prostate cancer (PCa) is the most frequently occurring type of malignant tumor and a leading cause of oncological death in men. PCa is very heterogeneous in terms of grade, phenotypes, and genetics, displaying complex features. This tumor often has indolent growth, not compromising the patient's quality of life, while its more aggressive forms can manifest rapid growth with progression to adjacent organs and spread to lymph nodes and bones. Nevertheless, the overtreatment of PCa patients leads to important physical, mental, and economic burdens, which can be avoided with careful monitoring. Early detection, even in the cases of locally advanced and metastatic tumors, provides a higher chance of cure, and patients can thus go through less aggressive treatments with fewer side effects. Furthermore, it is important to offer knowledge about how modifiable risk factors can be an effective method for reducing cancer risk. Innovations in PCa diagnostics and therapy are still required to overcome some of the limitations of the current screening techniques, in terms of specificity and sensitivity. In this context, this review provides a brief overview of PCa statistics, reporting its incidence and mortality rates worldwide, risk factors, and emerging screening strategies.

The Potential of PSMA as a Vascular Target in TNBC

Recent studies proving prostate-specific membrane antigen (PSMA) expression on triple-negative breast cancer (TNBC) cells and adjacent endothelial cells suggest PSMA as a promising target for therapy of until now not-targetable cancer entities. In this study, PSMA and its isoform expression were analyzed in different TNBC cells, breast cancer stem cells (BCSCs), and tumor-associated endothelial cells. PSMA expression was detected in 91% of the investigated TNBC cell lines. The PSMA splice isoforms were predominantly found in the BCSCs. Tumor-conditioned media from two TNBC cell lines, BT-20 (high full-length PSMA expression, PSMAΔ18 expression) and Hs578T (low full-length PSMA expression, no isoform expression), showed significant pro-angiogenic effect with induction of tube formation in endothelial cells. All TNBC cell lines induced PSMA expression in human umbilical vein endothelial cells (HUVEC). Significant uptake of radiolabeled ligand [⁶⁸Ga]Ga-PSMA was detected in BCSC1 (4.2%), corresponding to the high PSMA expression. Moreover, hypoxic conditions increased the uptake of radiolabeled ligand [¹⁷⁷Lu]Lu-PSMA in MDA-MB-231 (0.4% vs. 3.4%, under hypoxia and normoxia, respectively) and MCF-10A (0.3% vs. 3.0%, under normoxia and hypoxia, respectively) significantly (p < 0.001). [¹⁷⁷Lu]Lu-PSMA-induced apoptosis rates were highest in BT-20 and MDA-MB-231 associated endothelial cells. Together, these findings demonstrate the potential of PSMA-targeted therapy in TNBC.

Clinical Pharmacology of Radiotheranostics in Oncology

The combined use of diagnostic and therapeutic radioligands with the same molecular target, also known as theranostics, enables accurate patient selection, targeted therapy, and prediction of treatment response. Radioiodine, bone-seeking radioligands and norepinephrine analogs have been used for many years for diagnostic imaging and radioligand therapy of thyroid carcinoma, bone metastases, pheochromocytoma, paraganglioma, and neuroblastoma, respectively. In recent years, radiolabeled somatostatin analogs and prostate-specific membrane antigen ligands have shown clinical efficacy in the treatment of neuroendocrine tumors and prostate cancer, respectively. Several candidate compounds are targeting novel theranostic targets such as fibroblast activation protein, C-X-C chemokine receptor 4, and gastrin-releasing peptide receptor. In addition, several strategies to improve efficacy of radioligand therapy are being evaluated, including dosimetry-based dose optimization, multireceptor targeting, upregulation of target receptors, radiosensitization, pharmacogenomics, and radiation genomics. Design and evaluation of novel radioligands and optimization of dose and dose schedules, within the complex context of individualized multimodal cancer treatment, requires a multidisciplinary approach that includes clinical pharmacology. Significant increases in the use of these radiopharmaceuticals in routine oncological practice can be expected, which will have major impact on patient care as well as (radio)pharmacy utilization.

The clinical application of 68Ga-PSMA PET/CT and regulating mechanism of PSMA expression in patients with brain metastases of lung cancer

Brain metastases (BMs) of lung cancer are common malignant intracranial tumours associated with severe neurological symptoms and an abysmal prognosis. Prostate-specific membrane antigen (PSMA) has been reported to express significantly in a variety of solid tumours. However, the clinical applications of ⁶⁸Ga-PSMA PET/CT and the mechanism of PSMA expression in patients with BMs of lung cancer have rarely been reported. Experiments with ⁶⁸Ga-PSMA PET/CT and immunohistochemical staining were conducted to evaluate the expression of PSMA from seven patients with BMs of lung cancer who accepted surgical treatment in Fudan University Shanghai Cancer Center between October 2020 and October 2021. The mechanism of PSMA expression in BMs of lung cancer was explored by using single-cell RNA sequencing. The median maximum standardized uptake value (SUVmax) in BMs was higher than that in primary lung cancer (8.6 ± 2.8 vs. 3.6 ± 1.3, P < 0.01). The mean SUVmax in BMs was 1.76-fold higher than that in the liver, which indicated the potential of PSMA radioligand therapy (PSMA-RLT) for BMs. BMs showed intense PSMA staining, while normal lung tissue had no PSMA staining and there was only faint primary lung cancer staining by immunohistochemistry (IHC). Single-cell RNA sequencing (scRNA-seq) analysis found that PSMA was mainly expressed in oligodendrocytes of BMs, whereas it was expressed at lower levels in solid cells of lung cancer. PSMA expression in oligodendrocytes might be regulated by the factors ATF3 and NR4A1, which were associated with ER stress.

Glioblastoma PET/MRI: kinetic investigation of [18F]rhPSMA-7.3, [18F]FET and [18F]fluciclovine in an orthotopic mouse model of cancer

PURPOSE

Glioblastoma multiforme (GBM) is the most common glioma and standard therapies can only slightly prolong the survival. Neo-vascularization is a potential target to image tumor microenvironment, as it defines its brain invasion. We investigate [¹⁸F]rhPSMA-7.3 with PET/MRI for quantitative imaging of neo-vascularization in GBM bearing mice and human tumor tissue and compare it to [¹⁸F]FET and [¹⁸F]fluciclovine using PET pharmacokinetic modeling (PKM).

METHODS

[¹⁸F]rhPSMA-7.3, [¹⁸F]FET, and [¹⁸F]fluciclovine were i.v. injected with 10.5 ± 3.1 MBq, 8.0 ± 2.2 MBq, 11.5 ± 1.9 MBq (n = 28, GL261-luc2) and up to 90 min PET/MR imaged 21/28 days after surgery. Regions of interest were delineated on T2-weighted MRI for (i) tumor, (ii) brain, and (iii) the inferior vena cava. Time-activity curves were expressed as SUV mean, SUVR and PKM performed using 1-/2-tissue-compartment models (1TCM, 2TCM), Patlak and Logan analysis (LA). Immunofluorescent staining (IFS), western blotting, and autoradiography of tumor tissue were performed for result validation.

RESULTS

[¹⁸F]rhPSMA-7.3 showed a tumor uptake with a tumor-to-background-ratio (TBR) = 2.1-2.5, in 15-60 min. PKM (2TCM) confirmed higher K1 (0.34/0.08, p = 0.0012) and volume of distribution V_T (0.24/0.1, p = 0.0017) in the tumor region compared to the brain. Linearity in LA and similar k3 = 0.6 and k4 = 0.47 (2TCM, tumor, p = ns) indicated reversible binding. K1, an indicator for vascularization, increased (0.1/0.34, 21 to 28 days, p < 0.005). IFS confirmed co-expression of PSMA and tumor vascularization. [¹⁸F]fluciclovine showed higher TBR (2.5/1.8, p < 0.001, 60 min) and V_S (1.3/0.7, p < 0.05, tumor) compared to [¹⁸F]FET and LA indicated reversible binding. V_T increased (p < 0.001, tumor, 21 to 28 days) for [¹⁸F]FET (0.5-1.4) and [¹⁸F]fluciclovine (0.84-1.5).

CONCLUSION

[¹⁸F]rhPSMA-7.3 showed to be a potential candidate to investigate the tumor microenvironment of GBM. Following PKM, this uptake was associated with tumor vascularization. In contrast to what is known from PSMA-PET in prostate cancer, reversible binding was found for [¹⁸F]rhPSMA-7.3 in GBM, contradicting cellular trapping. Finally, [¹⁸F]fluciclovine was superior to [¹⁸F]FET rendering it more suitable for PET imaging of GBM.

Can PSMA-Targeting Radiopharmaceuticals Be Useful for Detecting Hepatocellular Carcinoma Using Positron Emission Tomography? An Updated Systematic Review and Meta-Analysis

BACKGROUND

Several studies proposed the use of positron emission tomography (PET) with Prostate-Specific Membrane Antigen (PSMA)-targeting radiopharmaceuticals in hepatocellular carcinoma (HCC). Our aim is to calculate the detection rate (DR) of this examination in HCC with a meta-analysis.

METHODS

A comprehensive literature search of studies on the DR of PET/CT or PET/MRI with PSMA-targeting radiopharmaceuticals in HCC was performed. Original articles evaluating these imaging examinations both in newly diagnosed HCC patients and HCC patients with disease relapse were included. Pooled DR including 95% confidence intervals (95% CI) was calculated. Statistical heterogeneity was also assessed using the I2 test.

RESULTS

The meta-analysis of six selected studies (126 patients) provided a DR of 85.9% for PET imaging with PSMA-targeting radiopharmaceuticals in the diagnosis of HCC. Moderate statistical heterogeneity among the included studies was found (I2 = 56%).

CONCLUSIONS

The quantitative data provided demonstrate the high DR of PET/CT or PET/MRI with PSMA-targeting radiopharmaceuticals for HCC lesion detection. However, more studies are needed to confirm the promising role of PSMA-targeted PET in HCC.

PSMA Expression in Solid Tumors beyond the Prostate Gland: Ready for Theranostic Applications?

In the past decades, the expanding use of prostate-specific membrane antigen (PSMA) imaging for prostate cancer has led to the incidental detection of a lot of extra-prostatic malignancies showing an increased uptake of PSMA. Due to these incidental findings, the increasing amount of immunohistochemistry studies and the deeper knowledge of the mechanisms of expression of this antigen, it is now clear that “PSMA” is a misnomer, since it is not specific to the prostate gland. Nevertheless, this lack of specificity could represent an interesting opportunity to bring new insights on the biology of PSMA and its sites of expression to image and treat new conditions, particularly several cancers. In this review, we will describe the main extra-prostatic cancers that exhibit PSMA expression and that can be studied with PSMA-based positron emission tomography–computed tomography (PET/CT) as an additional or alternative tool to conventional imaging. In particular, we will focus on cancers in which a radioligand therapy with ¹⁷⁷lutetium has been attempted, aiming to provide an overview of the possible future theragnostic applications of PSMA.

First communication on the efficacy of combined ¹⁷⁷Lutetium-PSMA with immunotherapy outside prostate cancer

Prostate-specific membrane antigen (PSMA)-targeted radioligand therapy is a validated treatment option for patients with advanced prostate cancer. Although PSMA expression is not limited to prostate tissue, little is known about its relevance to other types of cancer. Here, we present a case report of a patient with uterine leiomyosarcoma that is progressing while on immunotherapy and treated with ¹⁷⁷Lu-PSMA radionuclide therapy. We report for the first time that ¹⁷⁷Lu-PSMA radionuclide therapy combined with immunotherapy outside of prostate cancer. We did observe post-treatment reduction of tumor growth rate, although we did not notice disease response based on RECIST criteria. We suggest that ¹⁷⁷Lu-PSMA treatment especially combined with immunotherapy may be an option for patients with cancer without other therapeutic options. Insights: ¹⁷⁷Lu-PSMA radionuclide therapy should be considered for any tumor stained positive for PSMA.

[177Lu]Lu-PSMA-617 (PluvictoTM): The First FDA-Approved Radiotherapeutical for Treatment of Prostate Cancer

In March 2022, [¹⁷⁷Lu]Lu-PSMA-617 (Pluvicto^TM) was approved by the FDA for the treatment of prostate cancer patients. Until now, the approval has been limited to patients with PSMA-positive metastatic castration-resistant prostate cancer who have previously received other therapy options (such as inhibition of the androgen receptor pathway and taxane-based chemotherapy). [¹⁷⁷Lu]Lu-PSMA-617, which combines a PSMA-specific peptidomimetic with a therapeutical radionuclide, is used in a radioligand therapy that selectively delivers ionizing radiation to tumor cells, causing their death, while sparing the surrounding healthy tissue. In numerous clinical trials, the efficacy of [¹⁷⁷Lu]Lu-PSMA-617 was demonstrated.

Impact of Prostate-specific Membrane Antigen Positron Emission Tomography/Computed Tomography in the Management of Oligometastatic Renal Cell Carcinoma

Background

Prostate-specific membrane antigen (PSMA) is overexpressed in the neovasculature of renal cell carcinoma (RCC). However, there remains limited evidence regarding the use of PSMA positron emission tomography/computed tomography (PET/CT) in RCC.

Objective

To assess the impact of PSMA PET/CT in the management of metastatic RCC.

Design, setting, and participants

This was a retrospective review of patients who underwent PSMA PET/CT from 2014 to 2020 for restaging or suspected metastatic RCC in a tertiary academic setting.

Outcome measurements and statistical analysis

Management plans before and after PSMA PET/CT were recorded. Impact was classified as high (change of treatment intent, modality, or site), medium (change in treatment method), or low. Secondary outcomes included the patient-level detection rate, PSMA PET/CT parameters, sensitivity, and comparison to CT and, if available, fluorodeoxyglucose (FDG) PET/CT.

Results and limitations

Sixty-one patients met the inclusion criteria, of whom 54 (89%) had clear cell RCC. PSMA-positive disease was detected in 51 patients (84%). For 30 patients (49%) there was a change in management due to PSMA PET/CT (high impact, 29 patients, 48%). In 15 patients (25%), more metastases were detected on PSMA PET/CT than on CT. The sensitivity of combined PSMA PET/CT and diagnostic CT was 91% (95% confidence interval 77–98%). In a subcohort of 40 patients, the detection rate was 88% for PSMA and 75% for FDG PET/CT (p = 0.17). The maximum standardised uptake value (SUV_max) was higher for PSMA than for FDG PET/CT (15.2 vs 8.0; p = 0.02). Limitations include selection bias due to the retrospective design, and a lack of corresponding histopathology for all patients.

Conclusions

PSMA PET/CT is a promising imaging modality in metastatic RCC and led to a change in management in 49% of patients. PSMA PET/CT detected additional metastases compared to CT in 25% of patients and registered a significantly higher SUV_max than FDG PET/CT. Prospective studies are required to further define its role.

Patient summary

We report on a group of patients undergoing a new type of imaging for suspected advanced kidney cancer, called PSMA PET/CT. This imaging changed the management plan in 49% of the patients. PSMA PET/CT detected metastases in 84% of our patients and detected more metastases than computed tomography imaging in 25%.

Photodynamic therapy for prostate cancer: Recent advances, challenges and opportunities

Over the past two decades, there has been a tendency toward early diagnosis of prostate cancer due to raised awareness among the general public and professionals, as well as the promotion of prostate-specific antigen (PSA) screening. As a result, patients with prostate cancer are detected at an earlier stage. Due to the risks of urine incontinence, erectile dysfunction, etc., surgery is not advised because the tumor is so small at this early stage. Doctors typically only advise active surveillance. However, it will bring negative psychological effects on patients, such as anxiety. And there is a higher chance of cancer progression. Focal therapy has received increasing attention as an alternative option between active monitoring and radical therapy. Due to its minimally invasive, oncological safety, low toxicity, minimal effects on functional outcomes and support by level 1 evidence from the only RCT within the focal therapy literature, photodynamic treatment (PDT) holds significant promise as the focal therapy of choice over other modalities for men with localized prostate cancer. However, there are still numerous obstacles that prevent further advancement. The review that follows provides an overview of the preclinical and clinical published research on PDT for prostate cancer from 1999 to the present. It focuses on clinical applications of PDT and innovative techniques and technologies that address current problems, especially the use of nanoparticle photosensitizers in PDT of prostate cancer.

PSMA Radioligand Uptake as a Biomarker of Neoangiogenesis in Solid Tumours: Diagnostic or Theragnostic Factor?

Due to its overexpression on the surface of prostate cancer cells, prostate-specific membrane antigen (PSMA) is a relatively novel effective target for molecular imaging and radioligand therapy (RLT) in prostate cancer. Recent studies reported that PSMA is expressed in the neovasculature of various types of cancer and regulates tumour cell invasion as well as tumour angiogenesis. Several authors explored the role of diagnostic and therapeutic PSMA radioligands in various malignancies. In this narrative review, we describe the current status of the literature on PSMA radioligands' application in solid tumours other than prostate cancer to explore their potential role as diagnostic or therapeutic agents, with particular regard to the relevance of PSMA radioligand uptake as neoangiogenetic biomarker. Hence, a comprehensive review of the literature was performed to find relevant articles on the applications of PSMA radioligands in non-prostate solid tumours. Data on the general, methodological and clinical aspects of all included studies were collected. Forty full-text papers were selected for final review, 8 of which explored PSMA radioligand PET/CT performances in gliomas, 3 in salivary gland malignancies, 6 in thyroid cancer, 2 in breast cancer, 16 in renal cell carcinoma and 5 in hepatocellular carcinoma. In the included studies, PSMA radioligand PET showed promising performance in patients with non-prostate solid tumours. Further studies are needed to better define its potential role in oncological patients management, especially in those undergoing antineoangiogenic therapies, and to assess the efficacy of PSMA-RLT in this clinical context.

A pilot study of 68 Ga-PSMA-617 PET/CT imaging and 177Lu-EB-PSMA-617 radioligand therapy in patients with adenoid cystic carcinoma

Background

This pilot study was designed to evaluate the diagnostic value of ⁶⁸ Ga-PSMA-617 and ¹⁸F-FDG PET/CT in adenoid cystic carcinoma (ACC) and to assess the safety and therapeutic response to PSMA radioligand therapy (RLT) in ACC patients.

Methods

Thirty patients pathologically diagnosed with ACC were recruited into the cohort. Each patient underwent ⁶⁸ Ga-PSMA-617 and ¹⁸F-FDG PET/CT within 1 week. The number and SUVmax of PET-positive lesions were recorded and compared. Four patients accepted RLT using ¹⁷⁷Lu-EB-PSMA-617, in a dosage of approximately 1.85 GBq (50 mCi) per cycle for up to 3 cycles.

Results

Compared with ¹⁸F-FDG, ⁶⁸ Ga-PSMA-617 revealed more PET-positive extrapulmonary tumors (157 vs. 141, P = 0.016) and higher SUVmax (8.8 ± 3.6 vs. 6.4 ± 4.2, P = 0.027). However, ⁶⁸ Ga-PSMA-617 revealed less PET-positive pulmonary lesions (202 vs. 301, P < 0.001) and lower SUVmax of tumors (3.1 ± 3.0 vs. 4.2 ± 3.9, P < 0.001) than ¹⁸F-FDG. The combination of ⁶⁸ Ga-PSMA-617 and ¹⁸F-FDG can detect 469 PET-positive lesions, which was superior to each alone (469 vs. 359 vs. 442, P < 0.001). Two patients achieved remarkable response after PSMA RLT, while the other two patients showed reduced tumor uptake of recurrent foci, lung and liver metastases, whereas increased SUVmax of bone metastases.

Conclusions

⁶⁸ Ga-PSMA-617 PET/CT is a valuable imaging modality for the detection of ACC and combining with ¹⁸F-FDG PET/CT will achieve a higher detection efficiency. PSMA RLT may be a promising treatment for ACC and is worth of further investigation.

Trial registration: Diagnosis of Adenoid Cystic Carcinoma on ⁶⁸ Ga-PSMA-617 PET-CT and Therapy With ¹⁷⁷Lu-EB-PSMA-617 (NCT04801264, Registered 16 March 2021, retrospectively registered).

URL of registry: https://clinicaltrials.gov/ct2/show/NCT04801264.

Hetero-bivalent agents targeting FAP and PSMA

PURPOSE

We developed a theranostic radiopharmaceutical that engages two key cell surface proteases, fibroblast activation protein alpha (FAP) and prostate-specific membrane antigen (PSMA), each frequently overexpressed within the tumor microenvironment (TME). The latter is also expressed in most prostate tumor epithelium. To engage a broader spectrum of cancers for imaging and therapy, we conjugated small-molecule FAP and PSMA-targeting moieties using an optimized linker to provide ⁶⁴Cu-labeled compounds.

METHODS

We synthesized FP-L1 and FP-L2 using two linker constructs attaching the FAP and PSMA-binding pharmacophores. We determined in vitro inhibition constants (K_i) for FAP and PSMA. Cell uptake assays and flow cytometry were conducted in human glioma (U87), melanoma (SK-MEL-24), prostate cancer (PSMA + PC3 PIP and PSMA - PC3 flu), and clear cell renal cell carcinoma lines (PSMA + /PSMA - 786-O). Quantitative positron emission tomography/computed tomography (PET/CT) and tissue biodistribution studies were performed using U87, SK-MEL-24, PSMA + PC3 PIP, and PSMA + 786-O experimental xenograft models and the KPC genetically engineered mouse model of pancreatic cancer.

RESULTS

⁶⁴Cu-FP-L1 and ⁶⁴Cu-FP-L2 were produced in high radiochemical yields (> 98%) and molar activities (> 19 MBq/nmol). K_i values were in the nanomolar range for both FAP and PSMA. PET imaging and biodistribution studies revealed high and specific targeting of ⁶⁴Cu-FP-L1 and ⁶⁴Cu-FP-L2 for FAP and PSMA. ⁶⁴Cu-FP-L1 displayed more favorable pharmacokinetics than ⁶⁴Cu-FP-L2. In the U87 tumor model at 2 h post-injection, tumor uptake of ⁶⁴Cu-FP-L1 (10.83 ± 1.02%ID/g) was comparable to ⁶⁴Cu-FAPI-04 (9.53 ± 2.55%ID/g). ⁶⁴Cu-FP-L1 demonstrated high retention 5.34 ± 0.29%ID/g at 48 h in U87 tumor. Additionally, ⁶⁴Cu-FP-L1 showed high retention in PSMA + PC3 PIP tumor (12.06 ± 0.78%ID/g at 2 h and 10.51 ± 1.82%ID/g at 24 h).

CONCLUSIONS

⁶⁴Cu-FP-L1 demonstrated high and specific tumor targeting of FAP and PSMA. This compound should enable imaging of lesions expressing FAP, PSMA, or both on the tumor cell surface or within the TME. FP-L1 can readily be converted into a theranostic for the management of heterogeneous tumors.

Diagnostic Accuracy of PET/CT or PET/MRI Using PSMA-Targeting Radiopharmaceuticals in High-Grade Gliomas: A Systematic Review and a Bivariate Meta-Analysis

Background: Several studies proposed the use of positron emission tomography (PET) with Prostate Specific Membrane Antigen (PSMA)-targeting radiopharmaceuticals in brain tumors. Our aim is to calculate the diagnostic accuracy of these methods in high-grade gliomas (HGG) with a bivariate meta-analysis. Methods: A comprehensive literature search of studies on the diagnostic accuracy of PET/CT or PET/MRI with PSMA-targeting radiopharmaceuticals in HGG was performed. Original articles evaluating these imaging methods both in the differential diagnosis between HGG and low-grade gliomas (LGG) and in the assessment of suspicious HGG recurrence were included. Pooled sensitivity, specificity, positive and negative likelihood ratios (LR+ and LR-), and diagnostic odds ratio (DOR) including 95% confidence intervals (95% CI) were calculated. Statistical heterogeneity was also assessed using the I² test. Results: The meta-analysis of six selected studies (157 patients) provided the following results about PET/CT or PET/MRI with PSMA-targeting radiopharmaceuticals in the diagnosis of HGG: sensitivity 98.2% (95% CI: 75.3–99.9%), specificity 91.2% (95% CI: 68.4–98.1%), LR+ 4.5 (95% CI: 2.2–9.3), LR− 0.07 (95% CI: 0.04–0.15), and DOR 70.1 (95% CI: 19.6–250.9). No significant statistical heterogeneity among the included studies was found (I² = 0%). Conclusions: the quantitative data provided demonstrate the high diagnostic accuracy of PET/CT or PET/MRI with PSMA-targeting radiopharmaceuticals for HGG detection. However, more studies are needed to confirm the promising role of PSMA-targeted PET in this clinical setting.