Targeting PSMA by radioligands in non-prostate disease—current status and future perspectives

Robustness of apparent diffusion coefficient-based lymph node classification for diagnosis of prostate cancer metastasis

OBJECTIVES

The aim of this proof-of-principle study combining data analysis and computer simulation was to evaluate the robustness of apparent diffusion coefficient (ADC) values for lymph node classification in prostate cancer under conditions comparable to clinical practice.

MATERIALS AND METHODS

To assess differences in ADC and inter-rater variability, ADC values of 359 lymph nodes in 101 patients undergoing simultaneous prostate-specific membrane antigen (PSMA)-PET/MRI were retrospectively measured by two blinded readers and compared in a node-by-node analysis with respect to lymph node status. In addition, a phantom and 13 patients with 86 lymph nodes were prospectively measured on two different MRI scanners to analyze inter-scanner agreement. To estimate the diagnostic quality of the ADC in real-world application, a computer simulation was used to emulate the blurring caused by scanner and reader variability. To account for intra-individual correlation, the statistical analyses and simulations were based on linear mixed models.

RESULTS

The mean ADC of lymph nodes showing PSMA signals in PET was markedly lower (0.77 × 10-3 mm2/s) compared to inconspicuous nodes (1.46 × 10-3 mm2/s, p < 0.001). High inter-reader agreement was observed for ADC measurements (ICC 0.93, 95%CI [0.92, 0.95]). Good inter-scanner agreement was observed in the phantom study and confirmed in vivo (ICC 0.89, 95%CI [0.84, 0.93]). With a median AUC of 0.95 (95%CI [0.92, 0.97]), the simulation study confirmed the diagnostic potential of ADC for lymph node classification in prostate cancer.

CONCLUSION

Our model-based simulation approach implicates a high potential of ADC for lymph node classification in prostate cancer, even when inter-rater and inter-scanner variability are considered.

CLINICAL RELEVANCE STATEMENT

The ADC value shows a high diagnostic potential for lymph node classification in prostate cancer. The robustness to scanner and reader variability implicates that this easy to measure and widely available method could be readily integrated into clinical routine.

KEY POINTS

• The diagnostic value of the apparent diffusion coefficient (ADC) for lymph node classification in prostate cancer is unclear in the light of inter-rater and inter-scanner variability. • Metastatic and inconspicuous lymph nodes differ significantly in ADC, resulting in a high diagnostic potential that is robust to inter-scanner and inter-rater variability. • ADC has a high potential for lymph node classification in prostate cancer that is maintained under conditions comparable to clinical practice.

Prostate-Specific Membrane Antigen: Gateway to Management of Advanced Prostate Cancer

Prostate-specific membrane antigen (PSMA) as a transmembrane protein is overexpressed by prostate cancer (PC) cells and is accessible for binding antibodies or low-molecular-weight radioligands due to its extracellular portion. Successful targeting of PSMA began with the development of humanized J591 antibody. Due to their faster clearance compared to antibodies, small-molecule radioligands for targeted imaging and therapy of PC have been favored in recent development efforts. PSMA positron emission tomography (PET) imaging has higher diagnostic performance than conventional imaging for initial staging of high-risk PC and biochemical recurrence detection/localization. However, it remains to be demonstrated how to integrate PSMA PET imaging for therapy response assessment and as an outcome endpoint measure in clinical trials. With the recent approval of 177Lu-PSMA-617 by the US Food and Drug Administration for metastatic castration-resistant PC progressing after chemotherapy, the high value of PSMA-targeted therapy was confirmed. Compared to standard of care, PSMA-based radioligand therapy led to a better outcome and a higher quality of life. This review, focusing on the advanced PC setting, provides an overview of different approved and nonapproved PSMA-targeted imaging and therapeutic modalities and discusses the future of PSMA-targeted theranostics, also with an outlook on non-radiopharmaceutical-based PSMA-targeted therapies.

A Review of Clinical Trials of Cancer and Its Treatment as a Vaccine

BACKGROUND

Cancer and infectious diseases are one of the greatest challenges of modern medicine. An unhealthy lifestyle, poor drug use, or drug misuse contribute to the rise in morbidity and mortality brought on by these illnesses. The inadequacies of the medications now being used to treat these disorders, along with the growing issue of drug resistance, have compelled researchers to look for novel compounds with therapeutic promise. The number of infections and diseases has significantly abated due to vaccine development and use over time, which is described in detail. Several novel vaccines can now be produced by manipulating Deoxyribonucleic acid (DNA), Ribonucleic acid (RNA), Messenger Ribonucleic acid (mRNA), proteins, viral vector Recombinant, and other molecules due to advances in genetic engineering and our understanding of the immune defense.

OBJECTIVE

The main topic of discussion is cancer-based vaccinations, which were developed less than a decade ago but have already been used to treat a wide range of both life-threatening and deadly diseases. It contains clinical studies for cancer vaccines against kidney, liver, prostate, cervix, and certain RNA-based cancer vaccines against breast and bladder cancer.

RESULTS

Numerous studies using various DNA and RNA-based methods have been conducted on the basis of cancer, with 9-10 diseases related to DNA and 8-9 diseases associated with RNA. Some of these studies have been completed, while others have been eliminated due to a lack of research; further studies are ongoing regarding the same.

CONCLUSION

This brief discussion of vaccines and their varieties with examples also discusses vaccine clinical trials in relation to cancer diseases in this DNA and RNA-based cancer vaccine that has had successful clinical trials like the cervical cancer drug VGX-3100, the kidney cancer drug Pembrolizumab, MGN-1601, the prostate cancer drug pTVG-HP with rhGM-CSF, the melanoma cancer drug proteasome siRNA, and the lung cancer drug FRAME-001.

[18F]-PSMA-1007-PET for evaluation of kidney function

PURPOSE

Prostate-specific membrane antigen (PSMA) is present in the proximal tubule cells of the kidneys. This results in high renal tracer uptake in PSMA-PET, which may contain useful information on renal function. As part of the evaluation for [177Lu]-PSMA therapies, patients undergo PSMA-PET and additional [99mTc]-mercapto-acetyltriglycine (MAG3) scintigraphy to assess renal function. Aim of this study was to evaluate estimation of renal function with [18F]-PSMA-1007-PET/CT (PSMA-PET) by comparison to timely MAG3-scintigraphies.

MATERIALS AND METHODS

We retrospectively investigated 73 prostate cancer patients with 93 timely available PSMA-PET/CT, MAG3-scintigraphies and serum creatinine. For determination of split renal function in PSMA-PET/CT, we evaluated the relative unilateral total renal PSMA uptake, i.e. SUVmean multiplied by the renal volume (SRFPSMA-TOTAL) and relative unilateral maximal standardized uptake value (SRFSUV). These were compared to MAG3 split renal function (SRFMAG3) using Pearson correlation and receiver operating characteristics analysis. For determination of global renal function, correlation of bilateral total renal PSMA uptake with MAG3 tubular excretion rate and serum creatinine was assessed.

RESULTS

SRFMAG3 was strongly correlated with SRFPSMA-TOTAL (r= 0.872, p<0.001) and with SRFSUV (r=0.815, p<0.001). Relevant abnormalities of SRFMAG3 (unilateral renal function < 25 %) could be detected with sensitivities and specificities of 90% and 92% for SRFPSMA-TOTAL, and 80% and 95% for SRFSUV. Measures of absolute renal function were only weakly correlated with bilateral total renal PSMA uptake.

CONCLUSION

Renal [18F]-PSMA-1007 uptake allowed to quantify renal split function with good accuracy based on SRFPSMA-TOTAL or SRFSUV.

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.

Identification of incidental brain tumors in prostate cancer patients via PSMA PET/CT

PURPOSE

Brain metastases are rare in patients with prostate cancer and portend poor outcome. Prostate-specific membrane antigen positron emission tomography (PSMA PET)/CT scans including the brain have identified incidental tumors. We sought to identify the incidental brain tumor detection rate of PSMA PET/CT performed at initial diagnosis or in the setting of biochemical recurrence.

METHODS

An institutional database was queried for patients who underwent 68Ga-PSMA-11 or 18F-DCFPyL (18F-piflufolastat) PET/CT imaging at an NCI-designated Comprehensive Cancer Center from 1/2018 to 12/2022. Imaging reports and clinical courses were reviewed to identify brain lesions and describe clinical and pathologic features.

RESULTS

Two-thousand seven hundred and sixty-three patients underwent 3363 PSMA PET/CT scans in the absence of neurologic symptoms. Forty-four brain lesions were identified, including 33 PSMA-avid lesions: 10 intraparenchymal metastases (30%), 4 dural-based metastases (12%), 16 meningiomas (48%), 2 pituitary macroadenomas (6%), and 1 epidermal inclusion cyst (3%) (incidences of 0.36, 0.14, 0.58, 0.07, and 0.04%). The mean parenchymal metastasis diameter and mean SUVmax were 1.99 cm (95%CI:1.25-2.73) and 4.49 (95%CI:2.41-6.57), respectively. At the time of parenchymal brain metastasis detection, 57% of patients had no concurrent extracranial disease, 14% had localized prostate disease only, and 29% had extracranial metastases. Seven of 8 patients with parenchymal brain metastases remain alive at a median 8.8 months follow-up.

CONCLUSION

Prostate cancer brain metastases are rare, especially in the absence of widespread metastatic disease. Nevertheless, incidentally detected brain foci of PSMA uptake may represent previously unknown prostate cancer metastases, even in small lesions and in the absence of systemic disease.

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.

68 Ga-PSMA-Avid Intranasal Solitary Fibrous Tumor

ABSTRACT

The utility of molecular imaging in solitary fibrous tumors has not been fully established. We present a rare case of recurrent intranasal solitary fibrous tumor incidentally localized on 68 Ga-PSMA PET/CT scan, which turned out to be metabolically inactive on 18 F-FDG PET/CT.

A Tale of 3 Tracers: Contrasting Uptake Patterns of 18F-Fluciclovine, 68Ga-PSMA, and 18F-FDG in the Uterus and Adnexa

ABSTRACT

A 41-year-old woman with invasive lobular carcinoma of the breast underwent sequential 68Ga-PSMA-11 PET/CT and 18F-fluciclovine PET/CT as part of an ongoing clinical trial (NCT04750473). 68Ga-PSMA PET/CT showed increased radiotracer uptake in the uterine endometrium and left adnexa. 18F-fluciclovine PET/CT showed increased radiotracer uptake in a leiomyomatous uterus. A clinical 18F-FDG PET/CT demonstrated radiotracer uptake in the endometrium and a circumferential area of uptake in the left adnexa, a pattern more similar to the 68Ga-PSMA uptake pattern. This case highlights the discordance in the uptake pattern of 2 radiotracers approved for prostate cancer imaging but increasingly used in non-prostate malignancies imaging.

The Importance of Prostate-Specific Membrane Antigen Expression in Salivary Gland Tumors

Objective

Prostate-specific membrane antigen (PSMA) is a cell membrane protein expressed by prostate tissues. It is not prostate specific and is also expressed by some non-prostatic solid neoplasms. Our study aimed to investigate the potential role of PSMA in salivary gland tumors.

Methods

The present study was designed to retrospectively analyze our cases that presented with salivary gland tumors. The files of 105 patients were reviewed and their paraffin embedded blocks were retrieved from the pathology department. Immunohistochemical examination and staining were done using PSMA antibody. Tumor tissue PSMA immunohistochemical staining was scored semi-quantitatively with the modified quartile approach. Negative staining was scored 0, >0% and ≤25% tissue expression was considered weak (score 1), >25% and ≤50% tissue expression was considered mild (score 2), >50% and ≤75% tissue expression was considered moderate (score 3), and >75% tissue expression was considered strong (score 4).

Results

Eighty-eight patients (55 males, 33 females) were included in the study. Forty-eight patients had pleomorphic adenoma (PA), 35 had Warthin's tumor (WT), two had mucoepidermoid carcinoma, two had adenoid cystic carcinoma, and one had squamous cell carcinoma. There was statistically significant difference in terms of PSMA expression between PA and WT (p=0.003). PSMA expression was high in PA and absent in WT.

Conclusion

PSMA is a potential source of inspiration for future studies on the development of novel diagnostic and theranostic investigations of salivary gland tumors. Prospective studies targeting intratumoral PSMA in salivary gland tumors should be planned.

Late-Term Findings of Pancreatitis on 68 Ga-PSMA PET/CT in a Patient With Prostate Cancer

ABSTRACT

The 68 Ga-PSMA PET/CT imaging modality is used to evaluate biochemical recurrence, response to treatment, and staging in prostate cancer. Prostate-specific membrane antigen (PSMA) receptor activation can be seen in benign and malignant diseases as well as in many physiological tissues. Many pitfalls and artifacts have been reported when reporting 68 Ga-PSMA PET/CT. In this case, diffuse moderate PSMA receptor activation in pancreatic tissue due to the previous pancreatitis is presented in 68 Ga-PSMA PET/CT imaging modality that was performed for restaging of prostate cancer.

Functional Imaging of Liver Cancer (FLIC): Study protocol of a phase 2 trial of 18F-DCFPyL PET/CT imaging for patients with hepatocellular carcinoma

Background

While prostate specific membrane antigen (PSMA) is overexpressed in high-grade prostate cancers, it is also expressed in tumor neovasculature and other malignancies, including hepatocellular carcinoma (HCC). Importantly, no functional imaging for HCC is clinically available, making diagnosis and surveillance following local therapies particularly challenging. 18F-DCFPyL binds with high affinity to PSMA yet clears rapidly from the blood pool. PET imaging with 18F-DCFPyL may represent a new tool for staging, surveillance and assessment of treatment response in HCC. The purpose of this Functional Imaging Liver Cancer (FLIC) trial is to assess the ability of 18F-DCFPyL-PET/CT to detect sites of HCC.

Methods

This is a phase II multi-site prospective imaging trial with a plan to enroll 50 subjects with suspected HCC on standard of care CT or MRI and eligible for standard local treatment. Participants will undergo a baseline 18F-DCFPyL-PET/CT, prior to therapy. Subjects will also be scanned with 18F-FDG-PET/CT within 2 weeks of 18F-DCFPyL-PET/CT. Participants will undergo histopathologic assessment and standard of care local treatment for HCC within a multidisciplinary team context. Participants with histopathologic confirmation of HCC and a positive baseline 18F-DCFPyL-PET/CT will undergo a post-treatment 18F-DCFPyL-PET/CT during the first routine follow-up, typically within 4–8 weeks. Subjects with negative baseline 18F-DCFPyL-PET/CT will not be re-scanned after treatment but will remain in follow-up. Participants will be followed for 5-years to assess for progression-free-survival. The primary endpoint is the positive predictive value of 18F-DCFPyL-PET for HCC as confirmed by histopathology. Secondary endpoints include comparison of 18F-DCFPyL-PET/CT with CT, MRI, and 18F-FDG-PET/CT, and evaluation of the value of 18F-DCFPyL-PET/CT in assessing treatment response following local treatment. Exploratory endpoints include next generation sequencing of tumors, and analysis of extracellular vesicles to identify biomarkers associated with response to therapy.

Discussion

This is a prospective imaging trial designed to evaluate whether PSMA-PET/CT imaging with 18F-DCFPyL can detect tumor sites, assess local treatment response in HCC patients, and to eventually determine whether PSMA-PET/CT could improve outcomes of patients with HCC receiving standard of care local therapy. Importantly, this trial may help determine whether PSMA-selective radiopharmaceutical therapies may be beneficial for patients with HCC.

Clinical trial registration

NIH IND#133631. Submission date: 04-07-2021. Safe-to-proceed letter issued by FDA: 05.07.2021. NIH IRB #00080. ClinicalTrials.gov Identifier NCT05009979. Date of Registry: 08-18-2021. Protocol version date: 01-07-2022.

Time after Synthesis and Time after Injection Do Not Affect Diagnostic Quality of [18F]F-PSMA 1007 PET

Simple Summary

The total number of PSMA-PET-CT examinations for the staging of prostate cancer patients has increased in recent years, following its superior imaging properties. Fluorinated PSMA ligands can be produced in larger amounts, facilitating higher patient throughput compared to the initially developed gallium labelled PSMA-tracers; allowing PET in only a few patients per synthesis. This results in a longer time after, typically early morning, radiochemical synthesis (TaS) of [¹⁸]F-PSMA when the PSMA-PET scan is performed. Moreover, novel fluorinated-PSMA compounds are injected around two hours before PET-CT and the time after injection (TaI) might show significant deviation. [18F]-PSMA PET offers improved detection rates in the proximity of the urinary tract; however, it has the disadvantage of more unspecific uptake, e.g., in the skeleton. This article focusses on the question whether TaS or TaI have an influence on uptake patterns in malignant lesions and healthy tissue.

Abstract

PET imaging using PSMA ligands is increasingly used for staging in prostate cancer patients in different clinical indications. Unlike [⁶⁸Ga]Ga-labeled PSMA ligands, fluorinated compounds can be produced in large amounts; thus, they can be used for a higher number of patients. One concern is that in patients studied a long time after synthesis (TaS) or time after injection (TaI), the specific activity may decline; thus, the signal may be lower in these patients. In this study, we investigated a potential effect of TaS and TaI on image quality. In total, 134 consecutive patients were included in this retrospective analysis on the effect of TaS and TaI on uptake in prostate cancer lesions. All the patients underwent [¹⁸F]F-PSMA-1007 PET-CT from 99 min up to 549 min after tracer quality control. TaS and TaI were compared to the quantitative tumoral uptake parameters SUVmax and SUVpeak. In a second exploratory part of the analysis, TaS and TaI were correlated to a physiological tracer uptake in different organs. TaS and TaI did not affect the SUVmax and SUVpeak in tumor lesions in [¹⁸F]F-PSMA-1007 PET. The physiological uptake in salivary glands, lacrimal glands and the ganglia, spleen and urine was not significantly correlated to TaS or TaI; in contrast to the mean liver uptake, showing a weak, but significant correlation to TaS. The [¹⁸F]F-PSMA-1007 uptake in prostate cancer lesions is not significantly dependent on the TaS and TaI. These results are extremely reassuring when performing [¹⁸F]F-PSMA-1007 PET a considerable time after synthesis.

Ga-68 Prostate-Specific Membrane Antigen-HBED-CC Positron Emission Tomography/Computed Tomography in Anaplastic Thyroid Carcinoma

Purpose

Anaplastic thyroid carcinoma (ATC) is the most aggressive thyroid cancer and there is no established treatment that works well. The study was conducted to see prostate-specific membrane antigen (PSMA) expression in ATC as a stepping stone to study its role in potential theranostics.

Materials and Methods

Pathologically proven ATC patients were prospectively included in this study. Ga-68-PSMA positron emission tomography/computed tomography (PET/CT) was done to look for PSMA expression in local and distant sites 45-60 mins after injecting 2-3mCi of tracer.

Results

Twenty patients were enrolled in this study. Nodal metastases were seen in all patients, while distant metastases were seen in 17/20. The mean SUVmax of primary lesion was 6.72 ± 4.6. Mean SUVmax of node and lung lesions was 5.7 ± 5.6 and 2.9 ± 1.98, respectively. Mean SUVmax of liver, mediastinum, and parotid gland was 5.95 ± 3.03, 1.54 ± 0.68, and 9.03 ± 3.75, respectively. Mean Tumor to background ratio (liver = TBRl; mediastinum = TBRm; parotid = TBRp) were 1.21, 4.49 and 0.78, respectively.

Conclusion

ATC showed variable PSMA expression on Ga-68-PSMA-PET/CT and this attribute may be potentially useful in ATC theranostics.

Super Early Scan of PSMA PET/CT in Evaluating Primary and Metastatic Lesions of Prostate Cancer

68Ga-prostate specific membrane antigen (PSMA)-11 PET/CT has been widely used in the diagnosis of prostate cancer (PCa); however, the urine lead shielding resulting from the urinary metabolism of tracers may obstruct the detection of surrounding metastasis. In this research, the additive value of super early scanning in diagnosing primary lesions and metastasis in the pelvic cavity was evaluated. Firstly, the differentiation efficiency of 68Ga-PSMA-11 PET scanned at 3 min post-injection (min P.I.) was measured in PSMA-positive (22rv1 cells) and PSMA-negative (PC3 cells) model mice. Secondly, 106 patients were scanned at 3 min P.I. for the pelvic cavity and then scanned as a standard protocol at 45 min P.I. In the results, the differential diagnosis of PSMA expression was completely reflected as early as 3 min P.I. for mice models. For patients, when correlated with the Gleason score, the quantitative results of the super early scan displayed a comparable correlation coefficient with the routine scan. The target to bladder ratios increased from 1.44 ± 2.40 at 45 min to 10.10 ± 19.10 at 3 min (p < 0.001) for the primary lesions, and it increased from 0.99 ± 1.88 to 9.27 ± 23.03 for metastasis. Meanwhile, the target to background ratios increased from 2.21 ± 2.44 at 3 min to 19.13 ± 23.93 at 45 min (p < 0.001) for the primary lesions, and it increased from 1.68 ± 2.71 to 12.04 ± 18.73 (p < 0.001) for metastasis. In conclusion, super early scanning of 68Ga-PSMA-11 PET/CT added referable information for metastasis detection in order to avoid disturbing tracer activity in the urinary system.

18F-FDG Versus Non-FDG PET Tracers in Multiple Myeloma

Multiple myeloma (MM) accounts for 0.9% of cancer diagnoses, and incidence and mortality rate have increased in previous years. 18F-fluorodeoxyglucose (FDG) PET-computed tomography (CT) is an established modality for MM evaluation. MR imaging is helpful where 18F-FDG PET-CT is lacking. To standardize PET reporting, methods like Italian Myeloma Criteria for PET Use and Deauville criteria have been studied. Tracers like 11C-acetate and 11C-choline/18F-fluoromethylcholine (FCH) have shown higher sensitivity and detected more focal lesions and diffuse involvement than 18F-FDG PET-CT. 18F-FCH showed higher maximum standardized uptake value than 18FDG. 11C-methionine appears to be the best radiopharmaceutical, apart from 18F-FDG, for evaluating MM.

Advances in PSMA theranostics

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PSMA is an appealing target for theranostic because it is a transmembrane protein with a known substrate that is overexpessed on prostate cancer cells and internalizes upon ligand binding.

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There are a number of PSMA theranostic ligands in clinical evaluation, clinical trial, or clinically approved.

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PSMA theranostic ligands increase progression-free survival, overall survival, and pain in patients with metastatic castration resistant prostate cancer.

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A major obstacle to PSMA-targeted radioligand therapy is off-target toxicity in salivary glands.

The validation of prostate specific membrane antigen (PSMA) as a molecular target in metastatic castration-resistant prostate cancer has stimulated the development of multiple classes of theranostic ligands that specifically target PSMA. Theranostic ligands are used to image disease or selectively deliver cytotoxic radioactivity to cells expressing PSMA according to the radioisotope conjugated to the ligand. PSMA theranostics is a rapidly advancing field that is now integrating into clinical management of prostate cancer patients. In this review we summarize published research describing the biological role(s) and activity of PSMA, highlight the most clinically advanced PSMA targeting molecules and biomacromolecules, and identify next generation PSMA ligands that aim to further improve treatment efficacy. The goal of this review is to provide a comprehensive assessment of the current state-of-play and a roadmap to achieving further advances in PSMA theranostics.

Immunohistochemical Expression Pattern of Theragnostic Targets SSTR2 and PSMA in Endolymphatic Sac Tumors: A Single Institution Case Series

BACKGROUND

Endolymphatic sac tumors are rare neoplasia characterized by slow growth. However, their clinical impact should not be underestimated, considering their potential for local aggressive behavior and strong association with von Hippel-Lindau syndrome. Therefore, early detection with emerging theragnostic examinations such as ⁶⁸Ga-DOTATATE-PET/CT might improve patient management and reduce morbidity.

METHODS

We report the clinicopathological features of seven endolymphatic sac tumors. In this cohort, we performed immunohistochemical analysis of somatostatin receptor 2A (SSTR2A) and prostate specific membrane antigen (PSMA) protein expression patterns; two targets providing rationale for novel imaging modalities such as PSMA- or SSTR-targeted PET.

RESULTS

The tumor cells of all cases were negative for prostate specific membrane antigen and somatostatin receptor 2A, however immunolabeling was consistently detected in intratumoral endothelial cells of endolymphatic sac tumors for PSMA (7/7 cases, 100%), and for SSTR2A (5/7 cases, 71%).

CONCLUSIONS

Our results show a high rate of PSMA and SSTR2A expression in the tumor vasculature of endolymphatic sac tumors. PSMA and SSTR2A can be targeted with appropriate radioligands for diagnostic and therapeutic purposes. This finding provides a rationale for prospective clinical studies to test this approach as a sensitive screening tool for patients with suspected endolymphatic sac tumors including an improved management of von Hippel-Lindau syndrome.

68Ga-PSMA-11 PET/CT Parameter Correlates with Pathological VEGFR-2/PDGFR-β Expression in Renal Cell Carcinoma Patients

BACKGROUND

Response prediction is necessary for renal cell carcinoma (RCC) tumors. We aim to evaluate parameters derived from ⁶⁸ Ga-PSMA-11 PET/CT images for prediction of pathological VEGFR-2/PDGFR-β expression of primary RCC tumors.

METHODS

Forty-eight RCC patients were retrospectively enrolled with preoperative ⁶⁸ Ga-PSMA-11 PET/CT scan and surgical specimen. Radiological parameters including tumor diameter, mean CT value, and maximal standard uptake value (SUV_max) were derived from PET/CT images and pathological VEGFR-2/PDGFR-β/PSMA expression were identified with immunohistochemistry. Mann-Whitney U test was performed for continuous variables and the chi-square test for categorical variables. ROC was used for determining the effectiveness of preoperative parameters in differentiating VEGFR-2/PDGFR-β expression. Univariate and multivariate logistic regression analyses were performed for significant parameters to predict VEGFR-2 & PDGFR-β co-expression.

RESULTS

Of the 48 tumors, 25 (52.1%) harbored positive VEGFR-2 expression, 28 (58.3%) harbored positive PDGFR-β expression, and 24 (50%) were both VEGFR-2 positive and PDGFR-β positive. SUV_max significantly differed by subgroups of VEGFR-2/PDGFR-β expression (both P < 0.001). SUV_max demonstrated superior performance for differentiating VEGFR-2 & PDGFR-β co-expression (positive vs. negative), with area under the curve 0.87 (95% CI 0.78-0.96, P < 0.001), sensitivity 93% and specificity 78%. Moreover, SUV_max was identified as the significant predictor for VEGFR-2 & PDGFR-β co-expression (odds ratio 4.01, 95% CI 1.99-8.08, P < 0.001). Concordant with radiological findings with ⁶⁸ Ga-PSMA-11 PET/CT, pathological PSMA staining intensity was significantly higher in both VEGFR-2-positive tumor and PDGFR-β-positive tumor (P = 0.009 and P < 0.001, respectively).

CONCLUSION

⁶⁸ Ga-PSMA-11 PET/CT could effectively identify pathological VEGFR-2/PDGFR-β expression of primary RCC tumors, which may help with selection of mRCC patients suitable for TKIs treatment.

Prostate-Specific Membrane Antigen as Target for Neuroimaging of Central Nervous System Tumors

Introduction. Positron emission tomography (PET) imaging with prostate-specific membrane antigen- (PSMA-) binding tracers has been found incidentally to demonstrate uptake in CNS tumors. Following the encouraging findings of several such case reports, there is a growing interest in the potential application of PSMA-targeted PET imaging for diagnostics, theranostics, and monitoring of CNS tumors. This is a systematic literature review on PSMA-binding tracers in CNS tumors. Methods. A PubMed search was conducted, including preclinical and clinical reports. One hundred and twelve records were identified, and after screening, 56 were included in the final report. Results. Tissue studies demonstrated PSMA expression in tumor vascular endothelial cells, without expression in normal brain tissue, though the extent and intensity of staining varied by anti-PSMA antibody and methodology. Most included studies reported on gliomas, which showed strong PSMA ligand uptake and more favorable tumor to background ratios than other PET tracers. There are also case reports demonstrating PSMA ligand uptake in prostate cancer brain metastases, nonprostate cancer brain metastases, and meningiomas. We also review the properties of the various PSMA-binding radiotracers available. Therapeutic and theranostic applications of PSMA-binding tracers have been studied, including labeled alpha- and beta-ray emitting isotopes, as well as PSMA targeting in directing MRI-guided focused ultrasound. Conclusions. There is a potential application for PSMA-targeted PET in neuro-oncology as a combination of diagnostic and therapeutic use, as a theranostic modality for managing CNS tumors. Further research is needed regarding the mechanism(s) of PSMA expression in CNS tumors and its differential performance by tumor type.

Preliminary Clinical Application of RGD-Containing Peptides as PET Radiotracers for Imaging Tumors

Angiogenesis is a common feature of many physiological processes and pathological conditions. RGD-containing peptides can strongly bind to integrin αvβ3 expressed on endothelial cells in neovessels and several tumor cells with high specificity, making them promising molecular agents for imaging angiogenesis. Although studies of RGD-containing peptides combined with radionuclides, namely, ¹⁸F, ⁶⁴Cu, and ⁶⁸Ga for positron emission tomography (PET) imaging have shown high spatial resolution and accurate quantification of tracer uptake, only a few of these radiotracers have been successfully translated into clinical use. This review summarizes the RGD-based tracers in terms of accumulation in tumors and adjacent tissues, and comparison with traditional ¹⁸F-fluorodeoxyglucose (FDG) imaging. The value of RGD-based tracers for diagnosis, differential diagnosis, tumor subvolume delineation, and therapeutic response prediction is mainly discussed. Very low RGD accumulation, in contrast to high FDG metabolism, was found in normal brain tissue, indicating that RGD-based imaging provides an excellent tumor-to-background ratio for improved brain tumor imaging. However, the intensity of the RGD-based tracers is much higher than FDG in normal liver tissue, which could lead to underestimation of primary or metastatic lesions in liver. In multiple studies, RGD-based imaging successfully realized the diagnosis and differential diagnosis of solid tumors and also the prediction of chemoradiotherapy response, providing complementary rather than similar information relative to FDG imaging. Of most interest, baseline RGD uptake values can not only be used to predict the tumor efficacy of antiangiogenic therapy, but also to monitor the occurrence of adverse events in normal organs. This unique dual predictive value in antiangiogenic therapy may be better than that of FDG-based imaging.

Non-prostate cancer tumours: incidence on 18F-DCFPyL PSMA PET/CT and uptake characteristics in 1445 patients

Purpose

With increasing use of PSMA PET/CT in the staging and restaging of prostate cancer (PCa), the identification of non-prostate cancer tumours (NPCaT) has become an increasing clinical dilemma. Atypical presentations of PSMA expression in prostate cancer and expression in NPCaT are not well established. Understanding the normal and abnormal distribution of PSMA expression is essential in preparing clinically relevant reports and in guiding multidisciplinary discussion and decisions.

Methods

Retrospective review of 1445 consecutive ¹⁸F-DCFPyL PSMA PET/CT studies by experienced radiologists and nuclear medicine physicians. Lesions indeterminate for PCa were identified. Correlation was made with patient records, biopsy results, and dedicated imaging. Lesions were then categorized into four groups: 1. Confirmed prostate cancer, metastases, 2. NPCaT 3. Benign, and 4. Indeterminate lesions.

Results

68/1445 patients had lesions atypical for prostate cancer metastases. These comprised 8/68 (11.8%) atypical prostate cancer metastases, 17/68 (25.0%) NPCaT, 29/68 (42.6%) indeterminate, and 14/68 (20.6%) benign. In the context of the entire cohort, these are adjusted to 8/1445 (0.6%), 17/1445 (1.2%), 29/1445 (2.0%), and 14/1445 (1.0%) respectively. With the exception of Renal Cell Carcinoma (RCC), NPCaT demonstrated no or low PSMA expression. A similar trend was also observed for indeterminate and benign lesions. Conversely, most atypical PCa metastases demonstrated intermediate or high PSMA expression.

Conclusion

¹⁸F-DCFPyL PSMA PET/CT detection of NPCaT is low. Lesions demonstrating intermediate to high PSMA expression were exclusively prostate cancer metastases, aside from RCC, and lesions detected in organs with high background expression.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00259-022-05721-z.

First experiences with 177Lu-PSMA-617 therapy for recurrent or metastatic salivary gland cancer

Background

Advanced salivary gland cancers become difficult to treat when they are technically irresectable and radiotherapy limits are exceeded. There is also an unmet need to improve palliative systemic therapy. Salivary glands depict the Prostate-Specific Membrane Antigen (PSMA) on ⁶⁸Ga-PSMA-PET/CT, a transmembrane protein that is targeted for diagnosis and treatment of advanced prostate cancer. Some salivary gland carcinomas also express PSMA.

Methods

This study aimed to retrospectively evaluate the effectiveness of ¹⁷⁷Lu-PSMA-617 therapy for recurrent or metastatic salivary gland cancers, as a last resort treatment. Patients with serious tumour-related discomfort for whom no regular option was available were selected and critically re-assessed by the tumour board. Radionuclide therapy eligibility was confirmed when tumour targeting was greater than liver SUVmax on ⁶⁸Ga-PSMA-PET/CT. The protocol aimed at four cycles of 6.0–7.4 GBq ¹⁷⁷Lu-PSMA-617 every 6–8 weeks. Clinical response was evaluated by questionnaires and radiological response by ⁶⁸Ga-PSMA-PET/CT.

Results

Six patients were treated with ¹⁷⁷Lu-PSMA: four adenoid cystic carcinomas, one adenocarcinoma NOS and one acinic cell carcinoma. In two patients, radiological response was observed, showing either stable disease or a partial response, and four patients reported immediate relief of tumour-related symptoms. Most reported side effects were grade 1–2 fatigue, nausea, bone pain and xerostomia. Four patients prematurely discontinued therapy: three due to disease progression and one due to demotivating (grade 1) side-effects.

Conclusions

Palliative ¹⁷⁷Lu-PSMA therapy for salivary gland cancer may lead to rapid relief of tumour-associated discomfort and may even induce disease stabilization. It is safe, relatively well tolerated and can be considered when regular treatment options fail.

PSMA-targeted low-molecular double conjugates for diagnostics and therapy

This review presents data on dual conjugates of therapeutic and diagnostic action for targeted delivery to prostate cancer cells. The works of the last ten years on this topic were analyzed. The mail attention focuses on low-molecular-weight conjugates directed to the prostate-specific membrane antigen (PSMA); the comparison of high and low molecular weight PSMA-targeted conjugates was made. The considered conjugates were divided in the review into two main classes: diagnostic bimodal conjugates (which are containing two fragments for different types of diagnostics), theranostic conjugates (containing both therapeutic and diagnostic agents); also bimodal high molecular weight therapeutic conjugates containing two therapeutic agents are briefly discussed. The data of in vitro and in vivo studies for PSMA-targeted double conjugates available by the beginning of 2021 have been analyzed.

Glomangiopericytoma Uptake With 99mTc-MIBI, 18F-FDG, and 11C-Choline

ABSTRACT

The author presents 3 incidental cases of glomangiopericytoma exhibiting avidity of 99mTc-MIBI, 18F-FDG, and 11C-choline, respectively, during SPECT/CT evaluation of hyperparathyroidism, and PET/CT monitoring of metastatic melanoma and biochemical recurrence of prostate cancer. All the 3 cases show similar functional and anatomic features of tracer-avid lesion in the right nasal cavity from histologically proven glomangiopericytoma.

Prostate-Specific Membrane Antigen in Anaplastic and Poorly Differentiated Thyroid Cancer-A New Diagnostic and Therapeutic Target?

Several studies have demonstrated an expression of the prostate-specific membrane antigen (PSMA) in the cancer-related neovasculature of thyroid malignancies. Due to the poor prognosis and limited therapeutic options for patients with anaplastic (ATC) and poorly differentiated (PDTC) thyroid carcinoma, the aim of our study was to investigate the theranostic approach of PSMA expression in these patients. The PSMA uptake on Gallium-68 (⁶⁸Ga)-PSMA-positron emission tomography/computed tomography (PET/CT) and glucose uptake on F-18-Fluordeoxyglucose (¹⁸F-FDG)-PET/CTs were analysed in two ATC and six PDTC patients. The PSMA expression in corresponding patients' tissue samples was detected by immunohistochemistry. In addition, various tissue sections from 22 ATC and six PDTC patients were examined concerning PSMA expression. ⁶⁸Ga-PSMA-PET/CT showed heterogeneous PSMA expression among patients and lesions. Six of the eight analyzed patients (two ATC, four PDTC) showed increased glucose metabolism without increased PSMA uptake after PET/CT. In one patient (PDTC), ¹⁸F-FDG-PET/CT tracer uptake was positive and ⁶⁸Ga-PSMA-PET/CT showed heterogeneous results. Another patient (PDTC) evidenced only PSMA-positive lesions and received two cycles of Lutetium-177 (¹⁷⁷Lu)-PSMA therapy, which kept his disease stable for seven months. There was a correlation between immunohistochemical PSMA expression and uptake on ⁶⁸Ga-PMSA-PET/CT in three of the examined patients. Twenty-seven of the analyzed 39 ATC and 13 of the analyzed 22 PDTC tissue sections showed a strong PSMA expression. Considering the rarity of PDTC and ATC, which is the reason for the small patient population we studied, the findings of this study confirm the high diagnostic sensitivity and superiority of ¹⁸F-FDG-PET/CT in comparison to ⁶⁸Ga-PSMA-PET/CT in the diagnosis of ATC and PDTC. However, it can be suggested that ⁶⁸Ga-PMSA-PET/CT can be considered as a beneficial adjunct to the well-established ¹⁸F-FDG-PET/CT for a few individual selected patients with ATC and PDTC to detect lesions not discovered by ¹⁸F-FDG-PET/CT and to determine patients' eligibility for a radioligand therapy. Radiolabelled PSMA-ligands may, in the future, represent a theranostic approach with only minor side effects for a few individual selected patients with ATC and PDTC who need alternative treatment options in case of progression when established therapies are no longer effective. However, due to the small sample size of our collective, larger studies are needed to allow for a final evaluation on the significance of PSMA-targeted diagnostic and therapy for ATC and PDTC.

Pterygoid Base Pneumatization Simulating Residual Disease-A Pitfall of Structural Imaging in Juvenile Nasal Angiofibroma

ABSTRACT

As prostate-specific membrane antigen (PSMA) expression is universal in juvenile nasopharyngeal angiofibroma, it is commonly used for specifically differentiating recurrences from surgical site reparative tissues. Postoperative contrast-enhanced MRI revealed a residual disease in the left pterygoid base, but there was no PET/CT uptake with 68Ga-labeled PSMA at the same site. In retrospect, in comparison with preoperative PET/CT, it was found that the pterygoid base pneumatization was showing enhancement in contrast-enhanced MRI and not in functional PSMA. Postoperative 68Ga-PSMA PET/CT is a useful clinical tool in ambivalent diagnostic conditions avoiding morbidities.

11C-Choline PET/CT Depiction of Rectal Gastrointestinal Stromal Tumor

ABSTRACT

18F-FDG PET/CT is an established imaging modality for gastrointestinal stromal tumor evaluation and its posttherapeutic monitoring. 68Ga-PSMA has been recently reported with the incidental demonstration of this neoplasm on PET/CT. The author presents an uncommon case of this tumor detected by 11C-choline during the assessment of prostate cancer.

The potential of CAR T cell therapy for prostate cancer

Chimeric antigen receptor (CAR) T cell immunotherapy involves the genetic modification of the patient's own T cells so that they specifically recognize and destroy tumour cells. Considerable clinical success has been achieved using this technique in patients with lymphoid malignancies, but clinical studies that investigated treating solid tumours using this emerging technology have been disappointing. A number of developments might be able to increase the efficacy of CAR T cell therapy for treatment of prostate cancer, including improved trafficking to the tumour, techniques to overcome the immunosuppressive tumour microenvironment, as well as methods to enhance CAR T cell persistence, specificity and safety. Furthermore, CAR T cell therapy has the potential to be combined with other treatment modalities, such as androgen deprivation therapy, radiotherapy or chemotherapy, and could be applied as focal CAR T cell therapy for prostate cancer.

68Ga-PSMA PET/CT Scan on Postoperative Assessment of Sinonasal Glomangiopericytoma

ABSTRACT

Prostate-specific membrane antigen (PSMA) is expressed on the endothelial cells of tumor-associated neovasculature of various nonprostatic benign and malignant neoplasms. Positive intense uptake on PET/CT imaging with 68Ga-labeled PSMA is noted in a patient with sinonasal glomangiopericytoma, and the same is noted to be absent following complete surgical excision. 68Ga-PSMA PET/CT may be a useful tool for early recurrence identification, differentiating recurrence from surgical site reparative tissues, and peptide receptor radionuclide therapy of residual lesions.

Physiological PSMA Uptake in the Tubarial Salivary Glands and Its Implications in the PARIS Protocol-A First Study of Its Kind!

OBJECTIVES

Because prostate-specific membrane antigen (PSMA) expression is universal in juvenile nasal angiofibroma (JNA), PSMA PET/CT is commonly used in the postoperative setting using the postoperative angiofibroma radionuclide imaging study protocol. Our study aims to illustrate physiological PSMA ligand uptake distribution characteristics in the salivary glands, specifically the tubarial glands with tumor, to aid in accurate PSMA PET/CT analysis.

STUDY DESIGN

Forty-three consecutive patients who underwent a dedicated head and neck spot PSMA PET/CT for JNA were evaluated retrospectively. PSMA SUVmax values in the tumor, tubarial, parotid, submandibular, and sublingual salivary glands were determined visually and quantitatively.

RESULTS

All the tumors and the salivary glands showed increased tracer uptake. The median SUVmax ± SD ratios of the tumor, right and left tubarial gland, right and left parotid gland, right and left submandibular gland, and right and left sublingual gland were 2.7 ± 0.8 (range, 0.5-7.5), 3.8 ± 1.9 (range, 0.9-8.1), 4.7 ± 2.1 (range, 0.8-7.4), 9.5 ± 4.8 (range, 3.2-21.9), 9.2 ± 4.7 (range, 2.9-18.9), 10.4 ± 5.7 (range, 3.5-25.4), 10.4 ± 5.5 (range, 3.7-26.4), 6 ± 4.1 (range, 1.3-20.6), and 6.5 ± 4.2 (range, 1.8-19.7), respectively. The uptake in the tubarial glands was comparable with that of the tumor but less compared with other major salivary glands.

CONCLUSIONS

Ours is the first study demonstrating the quantitative uptake of tubarial salivary glands in detail. Because the tubarial glands uptake and the anatomical location are similar to that of the tumor, these physiological uptakes must be borne in mind to circumvent false-positive interpretations and care must be given during the planning of stereotactic radiotherapy for JNAs.

PSMA: a game changer in the diagnosis and treatment of advanced prostate cancer

Although management of advanced prostate cancer is evolving, a lot of work remains to be done for patients who have exhausted all options. Molecular targeting of prostate specific membrane antigen (PSMA) is valuable not only for diagnostic but also for therapeutic reasons. PSMA is thus considered to be useful in a theranostic approach. PSMA scans are upcoming diagnostic modalities which detect metastatic lesions that are missed by conventional imaging modalities. PSMA ligand therapy is also an upcoming treatment modality that has been proven to be beneficial with minimal toxicity in patients with advanced prostate cancer that have progressed on prior therapy. In this review article, we summarize the current knowledge regarding PSMA diagnostics and PSMA ligand therapies and discuss their implication in the treatment of advanced prostate cancer.

Molecular Imaging of Angiogenesis in Oncology: Current Preclinical and Clinical Status

Angiogenesis is an active process, regulating new vessel growth, and is crucial for the survival and growth of tumours next to other complex factors in the tumour microenvironment. We present possible molecular imaging approaches for tumour vascularisation and vitality, focusing on radiopharmaceuticals (tracers). Molecular imaging in general has become an integrated part of cancer therapy, by bringing relevant insights on tumour angiogenic status. After a structured PubMed search, the resulting publication list was screened for oncology related publications in animals and humans, disregarding any cardiovascular findings. The tracers identified can be subdivided into direct targeting of angiogenesis (i.e., vascular endothelial growth factor, laminin, and fibronectin) and indirect targeting (i.e., glucose metabolism, hypoxia, and matrix metallo-proteases, PSMA). Presenting pre-clinical and clinical data of most tracers proposed in the literature, the indirect targeting agents are not 1:1 correlated with angiogenesis factors but do have a strong prognostic power in a clinical setting, while direct targeting agents show most potential and specificity for assessing tumour vascularisation and vitality. Within the direct agents, the combination of multiple targeting tracers into one agent (multimers) seems most promising. This review demonstrates the present clinical applicability of indirect agents, but also the need for more extensive research in the field of direct targeting of angiogenesis in oncology. Although there is currently no direct tracer that can be singled out, the RGD tracer family seems to show the highest potential therefore we expect one of them to enter the clinical routine.

Safety, Biodistribution, and Radiation Dosimetry of 18F-rhPSMA-7.3 in Healthy Adult Volunteers

This first-in-humans study investigated the safety, biodistribution, and radiation dosimetry of a novel ¹⁸F-labeled radiohybrid prostate-specific membrane antigen (rhPSMA) PET imaging agent, ¹⁸F-rhPSMA-7.3. Methods: Six healthy volunteers (3 men, 3 women) underwent multiple whole-body PET acquisitions at scheduled time points up to 248 min after the administration of ¹⁸F-rhPSMA-7.3 (mean activity, 220; range, 210–228 MBq). PET scans were conducted in 3 separate sessions, and subjects were encouraged to void between sessions. Blood and urine samples were collected for up to 4 h after injection to assess metabolite-corrected radioactivity in whole blood, plasma, and urine. Quantitative measurements of ¹⁸F radioactivity in volumes of interest over target organs were determined directly from the PET images at 8 time points, and normalized time–activity concentration curves were generated. These normalized cumulated activities were then inputted into the OLINDA/EXM package to calculate the internal radiation dosimetry and the subjects’ effective dose. Results:¹⁸F-rhPSMA-7.3 was well tolerated. One adverse event (mild headache, not requiring medication) was considered possibly related to ¹⁸F-rhPSMA-7.3. The calculated effective dose was 0.0141 mSv/MBq when using a 3.5-h voiding interval. The organs with the highest mean absorbed dose per unit of administered radioactivity were the adrenals (0.1835 mSv/MBq), the kidneys (0.1722 mSv/MBq), the submandibular glands (0.1479 mSv), and the parotid glands (0.1137 mSv/MBq). At the end of the first scanning session (mean time, 111 min after injection), an average of 7.2% (range, 4.4%–9.0%) of the injected radioactivity of ¹⁸F-rhPSMA-7.3 was excreted into urine. Conclusion: The safety, biodistribution, and internal radiation dosimetry of ¹⁸F-rhPSMA-7.3 are considered favorable for PET imaging.

Protein analysis of extracellular vesicles to monitor and predict therapeutic response in metastatic breast cancer

Molecular profiling of circulating extracellular vesicles (EVs) provides a promising noninvasive means to diagnose, monitor, and predict the course of metastatic breast cancer (MBC). However, the analysis of EV protein markers has been confounded by the presence of soluble protein counterparts in peripheral blood. Here we use a rapid, sensitive, and low-cost thermophoretic aptasensor (TAS) to profile cancer-associated protein profiles of plasma EVs without the interference of soluble proteins. We show that the EV signature (a weighted sum of eight EV protein markers) has a high accuracy (91.1 %) for discrimination of MBC, non-metastatic breast cancer (NMBC), and healthy donors (HD). For MBC patients undergoing therapies, the EV signature can accurately monitor the treatment response across the training, validation, and prospective cohorts, and serve as an independent prognostic factor for progression free survival in MBC patients. Together, this work highlights the potential clinical utility of EVs in management of MBC.

A thermophoretic aptasensor can be used to profile cancer-associated proteins of extracellular vesicles (EVs) in patients’ plasma. Here, the authors use this technique to develop an EV-signature able to discriminate metastatic breast cancer, monitor treatment response, and predict patients’ progression-free survival.

Validation of Postoperative Angiofibroma Radionuclide Imaging Study (PARIS) Protocol Using PSMA PET/CT-A Proof of Concept Study

OBJECTIVES

Juvenile nasopharyngeal angiofibroma (JNA) expresses prostate-specific membrane antigen (PSMA), and PSMA PET/CT scan may be used for its imaging. Also, the precise diagnosis of residual/recurrent JNA after surgical treatment remains difficult with conventional contrast MRI and/or CT; functional imaging with PSMA PET/CT promises greater accuracy in the detection or exclusion of recurrent/residual JNA.

PATIENTS AND METHODS

In this prospective study, 22 postoperative JNA patients who underwent a PSMA PET/CT scan both preoperatively and postoperatively from January 2018 to September 2020 were included. All patients underwent a low-dose head and neck spot PET/CT imaging. Abnormal postcontrast enhancement of a definite lesion was considered residual/recurrent tumor in contrast-enhanced MRI (CEMRI). In PSMA PET/CT, any abnormal uptake apart from physiological sites in the head and neck was considered as residual lesions. Radiological results were categorized as negative, suspicious for residual lesions, or definite residual/recurrent tumors. PSMA PET/CT findings were considered as the radiological standard, and patients were managed accordingly. The sensitivity, specificity, positive predictive value, and negative predictive value were separately calculated for CEMRI and PSMA PET/CT for diagnosing residual lesions.

RESULTS

On postoperative CEMRI evaluation, 12 patients had residual tumors, 2 had normal suspicious scans, and 8 had normal postoperative scans. On PSMA PET/CT, only 7 patients had residual tumors and 15 had normal postoperative scans. In 1 patient with a residual tumor on both scans, a discrepancy was noted concerning tumor extent, and PSMA PET/CT accurately mapped the tumor. The sensitivity, specificity, positive predictive value, and negative predictive value of CEMRI were 100%, 53.33%, 41.67%, and 100%, respectively. The sensitivity, specificity, positive predictive value, and negative predictive value of PSMA PET/CT were 100% for all parameters.

CONCLUSIONS

Because CEMRI is oversensitive and less specific compared with PSMA PET/CT, Postoperative Angiofibroma Radionuclide Imaging Study (PARIS) protocol should be used always. In residual tumors, PSMA PET/CT has an outright advantage over CEMRI in the diagnosis, tumor mapping, decision making, planning stereotactic radiation, and aiding in future follow-ups.

Extensive preclinical evaluation of lutetium-177-labeled PSMA-specific tracers for prostate cancer radionuclide therapy

PURPOSE

Various radiolabeled prostate-specific membrane antigen (PSMA)-targeting tracers are clinically applied for prostate cancer (PCa) imaging and targeted radionuclide therapy. The PSMA binding affinities, biodistribution, and DNA-damaging capacities of these radiotracers have not yet been compared in detail. A major concern of PSMA-targeting radiotracers is the toxicity in other PSMA-expressing organs, such as the salivary glands, thus demanding careful evaluation of the most optimal and safest radiotracer. In this extensive preclinical study, we evaluated the clinically applied PSMA-targeting small molecule inhibitors DOTA-PSMA-617 (PSMA-617) and DOTAGA-PSMA-I&T (PSMA-I&T) and the PSMA nanobody DOTA-JVZ-007 (JVZ-007) using PSMA-expressing cell lines, a unique set of PCa patient-derived xenografts (PDX) and healthy human tissues.

METHODS AND RESULTS

In vitro displacement studies on PSMA-expressing cells and cryosections of a PSMA-positive PDX revealed high and specific binding affinity for all three tracers labeled with lutetium-177 with IC50 values in the nanomolar range. Interestingly, [177Lu]Lu-JVZ-007 could not be displaced by PSMA-617 or PSMA-I&T, suggesting that this tracer targets an alternative binding site. Autoradiography assays on cryosections of human salivary and renal tissues revealed [177Lu]Lu-PSMA-617 to have the lowest binding to these healthy organs compared with [177Lu]Lu-PSMA-I&T. In vivo biodistribution assays confirmed the in vitro results with comparable tumor uptake of [177Lu]Lu-PSMA-617 and [177Lu]Lu-PSMA-I&T at all timepoints, resulting in induction of similar levels of DNA double-strand breaks in the tumors. However, [177Lu]Lu-PSMA-I&T demonstrated approximately 40× higher renal uptake at 4 and 8 h post injection resulting in an unfavorable tumor-to-kidney ratio.

CONCLUSION

[177Lu]Lu-PSMA-617 has the most favorable biodistribution in mice as well as more favorable binding characteristics in vitro in PSMA-positive cells and human kidney and salivary gland specimens compared with [177Lu]Lu-PSMA-I&T and [177Lu]Lu-JVZ-007. Based on our preclinical evaluation, [177Lu]Lu-PSMA-617 is the best performing tracer to be taken further into clinical evaluation for PSMA-targeted radiotherapeutic development although with careful evaluation of the tracer binding to PSMA-expressing organs.

68Ga-Prostate-Specific Membrane Antigen PET/CT in Sinonasal Glomangiopericytoma-Exploring Theranostic Avenues!

ABSTRACT

Prostate-specific membrane antigen (PSMA) is expressed in the tumor-associated endothelial neovasculature of various nonprostatic benign and malignant neoplasms. A 25-year-old man with recurrent sinonasal glomangiopericytoma underwent whole-body 68Ga PSMA PET/CT to explore its theranostic role. There was intense PSMA uptake (SUVmax = 23.9) noted in the tumor. The uptake was more than that of the salivary glands, lacrimal glands, aorta, spleen, and the liver. Performance of PSMA PET/CT in sinonasal glomangiopericytoma opens up new frontiers concerning radiological imaging, early recurrence identification, and perhaps even radioligand therapy of residual/recurrent tumors.

PSMA Expression in Glioblastoma as a Basis for Theranostic Approaches: A Retrospective, Correlational Panel Study Including Immunohistochemistry, Clinical Parameters and PET Imaging

Aim

The aim of the current study was to enlighten the evolution of prostate-specific membrane antigen (PSMA) expression in glioblastoma between initial diagnosis and recurrence in order to provide preliminary insight for further clinical investigations into innovative PSMA-directed treatment concepts in neuro-oncology.

Methods

Patients who underwent resection for de-novo glioblastoma (GBM) and had a re-resection in case of a recurrent tumor following radiochemotherapy and subsequent chemotherapy were included (n = 16). Histological and immunohistochemical stainings were performed at initial diagnosis and at recurrence (n = 96 tissue specimens). Levels of PSMA expression both in endothelial and non-endothelial cells as well as vascular density (CD34) were quantified via immunohistochemistry and changes between initial diagnosis and recurrence were determined. Immunohistochemical findings were correlated with survival and established clinical parameters.

Results

PSMA expression was found to be present in all GBM tissue samples at initial diagnosis as well as in all but one case of recurrent tumor samples. The level of PSMA expression in glioblastoma varied inter-individually both in endothelial and non-endothelial cells. Likewise, the temporal evolution of PSMA expression highly varied in between patients. The level of vascular PSMA expression at recurrence and its change between initial diagnosis and recurrence was associated with post recurrence survival time: Patients with high vascular PSMA expression at recurrence as well as patients with increasing PSMA expression throughout the disease course survived shorter than patients with low vascular PSMA expression or decreasing vascular PSMA expression. There was no significant correlation of PSMA expression with MGMT promoter methylation status or Ki-67 labelling index.

Conclusion

PSMA is expressed in glioblastoma both at initial diagnosis and at recurrence. High vascular PSMA expression at recurrence seems to be a negative prognostic marker. Thus, PSMA expression in GBM might present a promising target for theranostic approaches in recurrent glioblastoma. Especially PSMA PET imaging and PSMA-directed radioligand therapy warrant further studies in brain tumor patients.

Co-delivery of PSMA antigen epitope and mGM-CSF with a cholera toxin-like chimeric protein suppressed prostate tumor growth via activating dendritic cells and promoting CTL responses

Subunit vaccines derived from tumor antigens play a role in tumor therapy because of their unique advantages. However, because of the weak immunogenicity of peptides in subunit vaccines, it is difficult to trigger an effective cytotoxic T lymphocyte (CTL) response, which is critical for cancer therapy. A requirement for the activation of CTL cells by exogenous antigens is the stimulation of antigen presenting cells (APC) with the help of adjuvants and cross-presentation to T lymphocytes. Standard nonconjugated adjuvant-peptide mixtures do not ensure co-targeting of the antigen and the adjuvant to the same APC, which limits the effects of adjuvants. In this study, a fusion protein consisting of murine granulocyte-macrophage colony stimulating factor (mGM-CSF) fused with CTA2 (A2 subunit of cholera toxin) was generated and assembled with CTB-PSMA624-632 (prostate specific membrane antigen (PSMA) peptide 624-632 fused to CTB) to obtain a cholera toxin-like protein. The chimeric protein retained the biological activity of mGM-CSF and had stronger GM1 binding activity than (CTB-PSMA624-632)5. C57BL/6J mice immunized with the CT-like chimeric protein exhibited delayed tumor growth following challenge with human PSMA-EGFP-expressing RM-1 cells. Experiment results showed that the CT-like chimeric protein could induce the maturation of DC cells and improve CTL responses. Overall, these results indicate that the nasal administration of a CT-like chimeric protein vaccine results in the development of effective immunity against prostate tumor cells and might be useful for future clinical anti-tumoral applications.

Advantage of 68Ga-PSMA PET/CT on Postradiotherapy Response Assessment of Juvenile Nasal Angiofibroma

ABSTRACT

Prostate-specific membrane antigen (PSMA) is universally expressed in the endothelial cells of tumor-associated neovasculature of juvenile nasopharyngeal angiofibroma. Functional 68Ga-PSMA PET/CT also enables easier differentiation of the residual tumor from postoperative changes. An 18-year-old man with the residual intracranial disease received radiotherapy after surgery. In PSMA PET/CT imaging, uptake was noted initially only in the residual disease, and the same was absent after successful response to radiotherapy, unlike contrast MRI, which showed persistent enhancement. Functional 68Ga-PSMA PET/CT may be a very useful tool clinically for identifying early responses to radiotherapy compared with conventional structural imaging.

Comparison of Prostate-Specific Membrane Antigen PET/CT and Contrast-Enhanced Magnetic Resonance Imaging in Follow-up Assessment of Juvenile Nasal Angiofibroma-A Novel Pilot Study

PURPOSE/BACKGROUND

The specific identification of residual/recurrent juvenile nasal angiofibroma (JNA) following surgical treatment remains difficult. Contrast MRI and CT may not enable the differentiation of tumor from postsurgical reparative tissue. Functional imaging with prostate-specific membrane antigen (PSMA) PET/CT targeting tumor-associated neovasculature has recently demonstrated universal positive uptake in primary JNA and offers promise of greater accuracy in the detection or exclusion of recurrent/residual JNA.

METHODS

In this prospective study, 18 postsurgical JNA patients with high suspicion for residual disease evinced by follow-up MR scan, or nasal endoscopy, or recent epistaxis during September 2018-November 2019 were included. All patients underwent head and neck spot PSMA PET/CT imaging. Postcontrast enhancement of a definite lesion was considered as a criterion for residual/recurrent tumor in contrast-enhanced MRI (CEMRI). In PSMA PET/CT, any abnormal uptake apart from physiological sites in the head and neck was considered as residual lesions. Radiological results were categorized as negative, suspicious, and residual/recurrent tumors. Any discrepancy between CEMRI and PSMA was resolved by surgical biopsies. The sensitivity, specificity, and positive and negative predictive values were separately calculated for CEMRI and PSMA PET/CT for diagnosing residual lesions. The interrater agreement κ value was also calculated.

RESULTS

On CEMRI evaluation, 14 of 18 patients had residual tumors, 2 had suspicious residual lesions, and 2 had normal postoperative scans. On PSMA PET/CT, 12 of 18 patients had residual tumors, and 6 had normal negative scans. Surgical biopsy in all 4 discordant cases was negative for tumors and revealed only fibrosis. In 1 patient with residual tumor on both scans, discrepancy was noted with regard to tumor extent demonstrated by the 2 scans, and further surgical excision confirmed the imaging findings of PSMA PET/CT as accurate. The sensitivity, specificity, and positive and negative predictive values of CEMRI were 100%, 33.33%, and 75% and 100%, respectively. The sensitivity, specificity, and positive and negative predictive values of PSMA PET/CT were 100% for all parameters. The interrater agreement between the 2 tests (κ) is 0.5 (95% confidence interval, 0.19-0.81).

CONCLUSIONS

The Ga-PSMA PET/CT is noted as more specific than the current standard of CEMRI in the identification of residual/recurrent JNA. It is the first radionuclide imaging scan that has found application in postoperative assessment of JNA.

TRIAL REGISTRATION

Clinical Trials Registry of India (CTRI/2018/08/015479).

Diagnostic performance of 18F-DCFPyL positron emission tomography/computed tomography for biochemically recurrent prostate cancer and change-of-management analysis

INTRODUCTION

Conventional imaging (CI) performs poorly to identify sites of disease in biochemically recurrent prostate cancer. ⁶⁸Ga-PSMA-11 positron emission tomography/computed tomography (PET/CT) is most studied but has a very short half-life. This study reports the diagnostic performance of the novel prostate-specific membrane antigen (PSMA) radiotracer ¹⁸F-DCFPyL using real-life data and tumor board simulation to estimate the impact of ¹⁸F-DCFPyL PET on patient management.

METHODS

Ninety-three ¹⁸F-DCFPyL PET/CT scans performed for patients previously treated for prostate cancer with a rising prostate-specific antigen (PSA) were retrospectively compared to contemporary CI and clinical imaging and PSA followups. A chart review was performed to document prior imaging, pathology results, serial serum PSA measurements, and other pertinent clinical data. Clinical utility of ¹⁸F-DCFPyL PET was measured using a simulated tumor board formed by three physicians with extensive prostate cancer experience deciding on management with and without knowledge of PET/CT results.

RESULTS

At median PSA 2.27 (interquartile rage [IQR] 5.27], 82% of ¹⁸F-DCFPyL PET/CT demonstrated at least one site of disease: non-regional lymph nodes (37% of scans), regional lymph node metastases (28%), local recurrence (27%), and bone metastases (20%), with higher PET positivity at higher PSA. Compared to ¹⁸F-DCFPyL PET/CT, CI showed overall poor performance, with accuracy below 20% for all extent of disease. PET/CT changed management in 44% of cases. The most frequent scenario was a radical change from initiating androgen deprivation therapy (ADT) to stereotactic body radiotherapy (SBRT) of oligo-lesional disease. In univariate and multivariate analysis, no patient characteristic could predict change of management by PET/CT results.

CONCLUSIONS

¹⁸F-DCFPyL significantly outperforms CI in recurring prostate cancer and is likely to impact management.

Current status of radioligand therapy and positron-emission tomography with prostate-specific membrane antigen

Prostate-specific membrane antigen (PSMA) is a transmembrane glycoprotein highly expressed by prostate cancer cells. PSMA-based radioligand therapy (RLT) emerged as a promising therapeutic option for prostate cancer in the early 2000s, and has been clinically validated with great enthusiasm during these past two decades. Last year, the European Association of Nuclear Medicine (EANM) published the procedure guidelines for the safe clinical practice of Lutetium-177 (¹⁷⁷Lu)-labelled PSMA RLT. In addition, PSMA RLT with alpha-ray-emitting radioisotopes has been also developed recently. Following the clinical use of ¹⁷⁷Lu-PSMA RLT, PSMA-targeted positron-emission tomography (PET) with Gallium-68 (⁶⁸Ga) has been performed inevitably for “theranostics” for the last decade; prostate cancer is going to be treated with PSMA-RLT based on the diagnosis by PSMA-PET. Furthermore, the diagnostic usefulness of ⁶⁸Ga-PSMA PET has been documented in various diseases beyond prostate cancer more recently. Regrettably, Japan is behind European countries and the United States in this field, and has just made a belated start of their clinical trials. In this review article, we briefly overviewed the current status of PSMA RLT and PSMA PET. We hope that this topic will be a particular focus of attention for most ANM readers in Japan, and that our efforts will help to facilitate the early approval of PSMA RLT and PSMA PET by the Japanese government even if only slightly.