Comparison of 68Ga-PSMA-617 PET/CT and 68Ga-RM2 PET/CT in Patients with Localized Prostate Cancer Who Are Candidates for Radical Prostatectomy: A Prospective, Single-Arm, Single-Center, Phase II Study

A Vision for Gastrin-Releasing Peptide Receptor Targeting for Imaging and Therapy: Perspective from Academia and Industry

The gastrin-releasing peptide receptor (GRPR) is overexpressed in various cancers, including prostate cancer, breast cancer, small cell and non-small cell lung cancer, uterine and ovarian cancer, colon cancer, and gastrointestinal stromal tumors. This makes GRPR a multicancer target for theranostics, that is, molecular imaging and therapy. Here, we explore the current state of GRPR-targeted theranostics from bench to bedside, highlighting the preclinical development of various GRPR-targeting compounds and clinical applications. We review the role of GRPR-targeted molecular imaging for all stages of prostate cancer, breast cancer, and other tumors and provide a quo vadis GRPR. We aimed to offer a comprehensive overview of GRPR-targeted theranostics to inform researchers, clinicians, pharma, and regulators of the potential benefits and emerging opportunities in the pursuit of personalized precision cancer care.

Development of Novel Gastrin-Releasing Peptide Receptor-Targeted Radioligand with Albumin Binder to Improve Accumulation in Tumor

Gastrin-releasing peptide receptor (GRPR) is a promising target for cancer radiotheranostics combining nuclear imaging with targeted radionuclide therapy. Improving the accumulation of radioligands in tumors by introducing an albumin binder (ALB) is useful to promote the efficacy of radiotheranostics. In this study, we designed and synthesized a novel GRPR-targeted radioligand [111In]In-AMTG-DA1 containing an ALB moiety to improve tumor accumulation. [111In]In-AMTG-DA1 showed marked binding ability to albumin, high affinity for GRPR, and high-level stability in vitro. In biodistribution studies, the tumor accumulation of [111In]In-AMTG-DA1 was much higher than that of the control ligand without an ALB moiety. The introduction of ALB increased the tumor area under the curve (AUC) value of [111In]In-AMTG-DA1 by 3.5 times. In a single-photon emission computed tomography (SPECT) study, [111In]In-AMTG-DA1 visualized a GRPR-expressing tumor clearly at 24 h postinjection. Our findings suggest the favorable pharmacokinetics of [111In]In-AMTG-DA1 as a GRPR-targeted radioligand exhibiting a high-level accumulation in tumors.

Design and Synthesis of 68Ga-Labeled Peptide-Based Heterodimers for Dual Targeting of NTS1 and GRPR

Tumor heterogeneity remains one of the main obstacles for cancer diagnosis and treatment. The simultaneous targeting of several cancer biomarkers is an appealing approach for improved diagnostic procedures. Neurotensin receptor 1 (NTS1) and Gastrin-Releasing Peptide Receptor (GRPR) are both G-protein coupled receptors with complementary profile of expression in several cancer types. This work proposes the design, the synthesis and the in vitro radiopharmaceutical characterization of three heterodimers, based on GRP/NT modified peptides, radiolabeled with gallium-68. Two NTS1/GRPR targeting pharmacophores containing linear hybrids that differ in the C-terminus were synthesized (i. e., JMV 7110 and JMV 7253). The branched analogue of the silicon-containing heterodimer JMV 7110, namely JMV 7266, was also synthesized. After radiolabeling with 68Ga, saturation binding studies performed on HT29 (NTS1 +/GRPR-) and PC3 (NTS1 +/GRPR+) cells demonstrated a significant loss in NTS1 and GRPR affinity compared to the reference monomers with the exception of the NTS1 affinity of [68Ga]Ga-JMV 7266 which was preserved. Considering cellular processing, NTS1-internalization at 1 h was the highest with [68Ga]Ga-JMV 7266 and was similar to the reference compound. Interestingly [68Ga]Ga-JMV 7266 demonstrated lower efflux than the other linear heterodimers but also than its NT reference compound. The branched structure of [68Ga]Ga-JMV 7266 seems beneficial for dual NTS1/GRPR targeting.

Using mpMRI, PSMA, and GRPR PET to Assess Focal Therapy Eligibility and Plan Treatment in Biopsy-proven Low-/Intermediate-risk Prostate Cancer: A Whole-mount Pathology-based Study

PURPOSE

Focal therapy (FT) is an emerging strategy for selectively ablating prostate cancer (PCa). However, existing challenges comprise conventional techniques inadequately identifying appropriate candidates and insufficient characterization of multifocality and sampling-biases in the biopsy-based trials. We evaluated the value of adding prostate-specific membrane antigen (PSMA) and gastrin-releasing peptide receptors (GRPR) PET to multiparametric MRI (PET/mpMRI) in preoperative assessments for FT, with whole-mount pathology as a comprehensive reference.

METHODS

A total of 38 men with biopsy-proven low-risk/intermediate-risk PCa underwent mpMRI, 68Ga-PSMA, and 68Ga-RM26 PET. Any focal lesion uptake (PETFL) was considered for positive PET results, while PI-RADS for mpMRI interpretation. Index lesion was defined with the highest Gleason score or largest diameter. Detection rates for clinically significant (cs) PCa (lesion-level) and diagnostic performances for localization (segment-level) were assessed. Correct identification of FT-ineligible men (index lesion Grade Group>3 or contralateral csPCa) was documented.

RESULTS

For detecting the overall 73 csPCa, both 68Ga-PSMA and 68Ga-RM26 PET/mpMRI demonstrated significantly higher detection rates (87.7% and 94.5% vs. 72.6%, P<0.005), as well as higher accuracies for localization (0.87 and 0.90 vs. 0.81, P<0.001) than mpMRI alone. Twenty of 38 (53%) men were confirmed FT-ineligible, of which mpMRI, 68Ga-PSMA, and 68Ga-RM26 PET/mpMRI identified 12 (60%), 20 (100%) and 17 (85%), respectively. Finally, 68Ga-PSMA and 68Ga-RM26 PET/mpMRI identified csPCa lesions in 88.5% and 100% of FT-eligible men, respectively.

CONCLUSIONS

Combining PSMA/GRPR PET and mpMRI facilitates enhanced detection rates as well as higher accuracies for localization in localized PCa. 68Ga-PSMA and 68Ga-RM26 PET/mpMRI may serve as promising imaging tools to improve the preoperative assessments in FT candidates with low-risk/intermediate-risk PCa.

Additive Value of [68Ga]Ga-RM26 PET/CT to [68Ga]Ga-PSMA-617 PET/CT in Detecting Pelvic Lymph Node Metastasis in Prostate Cancer: A Prospective, Single-Center, Phase II Study

Lymph node staging in prostate cancer is crucial for treatment and prognosis, yet [68Ga]Ga-PSMA-617 PET/CT has limited sensitivity in detecting pelvic lymph node metastasis (PLNM). [68Ga]Ga-RM26 PET/CT, targeting the gastrin-releasing peptide receptor, complements [68Ga]Ga-PSMA-617 PET/CT in assessing primary tumor extension and aggressiveness. However, its role in detecting PLNM and complementing [68Ga]Ga-PSMA-617 PET/CT remains underexplored. Methods: This prospective study enrolled newly diagnosed yet untreated prostate cancer patients who underwent [68Ga]Ga-RM26 PET/CT and [68Ga]Ga-PSMA-617 PET/CT, followed by radical prostatectomy and extended pelvic lymph node dissection. The primary objective was to evaluate the diagnostic performance of both PET/CT modalities in detecting PLNM. Results: In total, 68 patients were enrolled, with a 30.9% (21/68) pathologic PLNM rate. In patient-based analysis, [68Ga]Ga-RM26 PET/CT had sensitivity and specificity of 0.43 and 0.94, respectively, compared with 0.52 and 0.89 for [68Ga]Ga-PSMA-617 PET/CT. [68Ga]Ga-RM26 PET/CT detected additional PLNMs in 50% (5/10) of patients that were missed by [68Ga]Ga-PSMA-617 PET/CT. The combined use of [68Ga]Ga-RM26 PET/CT and [68Ga]Ga-PSMA-617 PET/CT resulted in sensitivity of 0.76 and specificity of 0.85. In total, 1,049 lymph nodes were dissected, including 991 normal and 58 positive nodes. In lesion-based analysis, [68Ga]Ga-RM26 PET/CT had sensitivity and specificity of 0.38 and 0.99, respectively, compared with 0.5 and 0.99 for [68Ga]Ga-PSMA-617 PET/CT. [68Ga]Ga-RM26 PET/CT identified 41.4% (12/29) of pathologic positive nodes missed by [68Ga]Ga-PSMA-617 PET/CT. The combined [68Ga]Ga-RM26 and [68Ga]Ga-PSMA-617 PET/CT demonstrated sensitivity of 0.71 and specificity of 0.99. Conclusion: In dual-target imaging, [68Ga]Ga-RM26 PET/CT identified additional PLNMs. The combination of [68Ga]Ga-RM26 PET/CT and [68Ga]Ga-PSMA-617 PET/CT achieved higher diagnostic sensitivity with minimal loss of specificity.

The evolving role of positron emission tomography in precision prostate cancer biopsy

Prostate cancer is one of the most common cancers among men, and accurate detection and diagnosis are crucial for effective treatment planning. Diagnostic prostate biopsy plays a pivotal role in the detection and characterization of prostate cancer. Recent advancements in molecular imaging, particularly with Positron Emission Tomography (PET) using radiolabelled Prostate-Specific Membrane Antigen (PSMA) tracers, have shown significant improvements in enhancing prostate cancer detection. PSMA PET, when combined with magnetic resonance imaging (MRI) in hybrid PET/MRI systems, provides improved sensitivity and specificity, enabling more precise localization of clinically significant prostate cancer (csPCa) lesions. This narrative review explores the evolving role of PET/CT and PET/MRI-guided prostate biopsy. We examine the integration of PET with MRI for the detection of prostate cancer, highlighting key studies that have demonstrated improved diagnostic outcomes. Additionally, we discuss the current limitations, including the high costs and longer scan times associated with PET/MRI, as well as the challenges in data interpretation. The review also considers emerging technologies, such as promising molecular probes for prostate PET imaging, such as gastrin-releasing peptide receptor (GRPR) and fibroblast activation protein inhibitor (FAPI). Finally, the present work provides the clinician with a comprehensive yet concise up-to-date review of the literature to easily evaluate the possibilities currently offered by hybrid imaging technologies of personalized imaging-guided biopsy for prostate cancer patients.

Prostate-specific membrane antigen (PSMA) expression in primary and metastatic renal cell cancer (UroCCR-65 study)

BACKGROUND

Prostate-specific membrane antigen (PSMA) has been shown to be overexpressed in the neo-vasculature of renal cancers. However, studies investigating the pattern of PSMA expression in primary RCC and RCC metastases according to metastatic sites are rare. 44 frozen samples of RCC, 19 primaries (9 clear cell (cc) RCC, 7 papillary (pap) RCC, and 3 chromophobe (ch) RCC) and 25 (24 samples have ccRCC histology and one is unclassified) unpaired metastases (8 from adrenals, 8 from bones, 2 from lungs, 2 from liver and 5 others (1 lymph node, 1 pancreas, 1 brain, 1 gallbladder and 1 muscle)), were available from the UroCCR project (NCT03293563). PSMA expression was assessed by autoradiography using [177Lu]Lu-PSMA-617 as binding agent and the specific binding (total binding-non-specific binding) was calculated and expressed as a percentage of total binding. A patient suffering from metastatic ccRCC was also administered [68Ga]Ga-PSMA-11 to evaluate PSMA expression.

RESULTS

The mean specific binding was 28.9 ± 40.4% for primary renal cancer and 65.0 ± 38.9% for metastasis. Regarding histology, high PSMA expression was depicted in 33.3% of ccRCC, 33.3% of chRCC and 57.1% of papRCC. PSMA was more frequently expressed in primary samples of papRCC histology with renal capsule invasion (p = 0.0286). A higher PSMA-specific binding and a higher number of samples with high PSMA-expression were depicted in metastatic samples. Bone metastasis showed lower binding than other metastatic sites combined (p = 0.0005). The patient suffering from metastatic ccRCC showed high [68Ga]Ga-PSMA-11 uptake on known distant metastases and additional site uncovered.

CONCLUSION

PSMA showed high expression in metastases of ccRCC.

CLINICAL TRIAL REGISTRATION

NCT, NCT03293563, prospectively registered September 20, 2017, http://www.

CLINICALTRIALS

gov .

A Comprehensive Systematic Review and Meta-analysis of the Role of Prostate-specific Membrane Antigen Positron Emission Tomography for Prostate Cancer Diagnosis and Primary Staging before Definitive Treatment

BACKGROUND AND OBJECTIVE

Positron emission tomography (PET) with prostate-specific membrane antigen (PSMA) in the diagnosis and primary staging of patients with prostate cancer (PCa) has an established role, but recent summative evidence on its actual diagnostic and staging value is still missing. We aimed to collect and analyze published studies reporting the accuracy of PSMA PET for the diagnosis of clinically significant prostate cancer (csPCa) and detection of distant metastases at primary staging before definitive treatment.

METHODS

We performed a systematic review of the literature, by searching the PubMed/MEDLINE, Cochrane library's CENTRAL, EMBASE, and Scopus databases, from inception to April 2024. Two coprimary outcomes were assessed: first, to evaluate the sensitivity, specificity, positive (PPV) and negative (NPV) predictive values of PSMA PET in detecting intraprostatic csPCa on a per-patient level, and second, to assess the positivity rates of metastatic disease in the primary staging, prior to definitive therapy. As a secondary outcome, the diagnostic accuracy of PET PSMA for the detection of lymph nodal invasion (LNI) was tested in a per-patient-level analysis of studies where pelvic lymph node dissection (PLND) was available as the reference standard. Positivity and detection rates were pooled using random-effect models. Preplanned subgroup analyses tested the diagnostic accuracy of PET PSMA across different study cohorts. Variation in PPV and NPV over csPCa and LNI prevalence was evaluated.

KEY FINDINGS AND LIMITATIONS

In total, 12 and 99 studies, with a total of 1533 and 18 649 participants, respectively, were included in the quantitative synthesis for intraprostatic diagnosis and staging. For intraprostatic disease, the sensitivity, specificity, PPV, and NPV of PSMA PET for csPCa were 82% (95% confidence interval [CI] 73-90%), 67% (95% CI 46-85%), 77% (95% CI 63-88%), and 73% (95% CI 56-87%), respectively. At a bivariate analysis, the diagnostic accuracy of PSMA PET estimated through a summary receiver operating characteristic curve-derived area under the curve was 84%, increasing up to 88% when combined with magnetic resonance imaging (MRI). On staging level, PSMA PET results were positive outside the prostate in 23% of the patients, with substantial variation in positivity rates between high-risk (31%) and intermediate-risk (12%) subcohorts. When using PLND as the reference standard (51 studies, 7713 patients), the sensitivity, specificity, PPV, and NPV of PSMA PET were, respectively, 54%, 94%, 77%, and 86%. With higher csPCa and LNI prevalence, a similar increase in PPV and a decrease in NPV were observed.

CONCLUSIONS AND CLINICAL IMPLICATIONS

The current updated systematic review and meta-analysis provides updated evidence on the diagnostic and staging accuracy of PSMA PET in PCa. We reported good accuracy of PSMA PET to discriminate csPCa, particularly when added to MRI, but NPV alone is insufficient to omit a biopsy. Regarding staging, PSMA PET cannot be used alone to determine the need for lymph node dissection (LND) and should be combined with additional clinical information within predictive tools. As such, further research should develop and validate models that incorporate PSMA PET to reliably inform biopsy or LND.

Is Copper-61 the New Gallium-68? Automation and Preclinical Proof-of-Concept of 61Cu-Based Radiopharmaceuticals for Prostate Cancer Imaging

Background: While gallium-68 has traditionally dominated PET imaging in oncology, copper radionuclides have sparked interest for their potential applications in nuclear medicine and theranostics. Considering the advantageous physical decay properties of copper-61 compared to those of gallium-68, we describe a fully automated GMP-compliant synthesis process for 61Cu-based radiopharmaceuticals and demonstrate their in vivo application for targeting the overexpressed PSMA by PET/MR imaging. Methods: Copper-61 was obtained through the irradiation of natural zinc liquid targets in a biomedical cyclotron. [61Cu]Cu-DOTAGA-PSMA-I&T and [61Cu]Cu-NODAGA-PSMA-I&T were produced without manual intervention in two Synthera® Extension modules. Radiochemical purity was analyzed by radio-HPLC and iTLC. Cellular uptake was evaluated in LNCaP and DU145 cells. In vivo PET/MRI was performed in control mice to evaluate the biodistribution of both radiopharmaceuticals, and in tumor-bearing mice to assess the targeting ability towards PSMA. Results: The fully automated process developed proved to be effective for the synthesis of 61Cu-based radiopharmaceuticals, with appropriate molar activities. The final products exhibited high radiochemical purity (>98%) and remained stable for up to 6 h after the EOS. A time-dependent increase in cellular uptake was observed in LNCaP cells, but not in DU145 cells. As opposed to [61Cu]Cu-NODAGA-PSMA-I&T, [61Cu]Cu-DOTAGA-PSMA-I&T exhibited poor kinetic stability in vivo. Subsequent PET/MR imaging with [61Cu]Cu-NODAGA-PSMA-I&T showed tumor uptake lasting up to 4 h post-injection, predominant renal clearance, and no detectable accumulation in non-targeted organs. Conclusions: These results demonstrate the feasibility of the implemented process, which yields adequate amounts of high-quality radiopharmaceuticals and can be adapted to any standard production facility. This streamlined approach enhances reproducibility and scalability, bringing copper-61 closer to widespread clinical use, to the detriment of the conventionally accepted gallium-68.

99mTc-MIP-1404 SPECT/CT Companion Diagnostic for 177Lu-PSMA Therapy in Metastatic Castration-Resistant Prostate Cancer

Our objective was to determine the feasibility, diagnostic performance, and predictive value of 99mTc-MIP-1404 SPECT in patients undergoing baseline staging and assessment of eligibility for prostate-specific membrane antigen (PSMA)-targeted radiopharmaceutical therapy (RPT) for metastatic castration-resistant prostate cancer. Methods: Data of 46 patients undergoing 99mTc-MIP-1404 planar scintigraphy and SPECT/CT for staging and assessment of eligibility for 177Lu-PSMA RPT were retrospectively analyzed. Overall image quality was assessed, and images were visually analyzed for the presence and localization of pathologic uptake. Metastatic uptake was visually scored using a 3-point scale. 99mTc-MIP-1404 findings were compared with the results of posttherapeutic 177Lu-PSMA scans in patients subsequently commencing RPT (n = 35). The predictive and prognostic significance of uptake intensity in 99mTc-MIP-1404 scans was evaluated. Results: The image quality of 99mTc-MIP-1404 scans was rated as excellent in 98% of cases. Imaging results were concordant in 206 of 210 localizations, demonstrating almost perfect agreement with 177Lu-PSMA scans (κ = 0.957 [95% CI, 0.916-0.999]). Uptake intensity higher than liver uptake identified responders (P = 0.0115) and was associated with prolonged progression-free survival (median, 146 vs. 96 d; hazard ratio for progression, 0.3838 [95% CI, 0.1721-0.8556]; P = 0.0192). In multivariable analysis, 99mTc-MIP-1404 uptake higher than in liver emerged as an independent predictor of treatment response (odds ratio, 12.37 [95% CI, 1.613-203.3]; P = 0.0319). Nevertheless, 27% of responders demonstrated uptake no higher than that in the liver. Conclusion: 99mTc-MIP-1404 imaging is suitable for assessment of eligibility for RPT in patients with advanced metastatic castration-resistant prostate cancer. In particular, pretherapeutic uptake intensity is predictive of response to 177Lu-PSMA RPT.

Novel Radiopharmaceuticals and Future of Theranostics in Genitourinary Cancers

BACKGROUND AND OBJECTIVE

This review aims to provide an overview of novel diagnostic and therapeutic radiopharmaceuticals tested recently or used currently in genitourinary cancers within prospective phase 1-2 clinical trials, summarizing progresses and future directions.

METHODS

A systematic search was conducted using the PubMed/MEDLINE and ClinicalTrials.gov databases for original prospective research studies following the Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines.

KEY FINDINGS AND LIMITATIONS

Forty-six papers were systematically reviewed; 74 ongoing clinical trials were identified. The results of 27 novel radiopharmaceuticals (ie, not approved by the Food and Drug Administration/European Medicines Agency and not listed in the Pharmacopeia) prospectively investigated in genitourinary cancers, mostly prostate, for diagnostic, theranostic, or therapeutic purposes (21, one, and five of the 27 radiopharmaceuticals, respectively) over the past 5 yr were presented. Most were prostate-specific membrane antigen-targeting agents (17/27); other targets included gastrin-releasing peptide receptor, carbonic anhydrase IX, Cu, six transmembrane epithelial antigen of the prostate 1, tumor-associated glycoprotein 42, and urokinase-type plasminogen activator receptor. Ongoing research confirms the same trend. Fibroblast activation protein inhibitor, PD-L1, CD8, nectin-4, and HER2 are other targets under investigation. Among the 22 ongoing therapeutic trials (out of the 74 ongoing clinical trials), targeted alpha therapy is being explored in 12, and five are evaluating combinations of radioligand therapy with other treatments. We confirmed the safety of radiopharmaceuticals (regardless of the diagnostic/therapeutic purpose) and showed promising results in terms of diagnostic accuracy and therapeutic efficacy in genitourinary cancers.

CONCLUSIONS AND CLINICAL IMPLICATIONS

There continues to be expansion in radiopharmaceutical approaches to genitourinary cancers, reflecting a strong emphasis on improving tumor detection and treatment, which will likely impact future management across the disease spectrum, with the potential for improved patient care and outcomes.

Diagnostic Value of Gastrin-Releasing Peptide Receptor-Targeted PET Imaging in Oncology: A Systematic Review

Gastrin-releasing peptide receptor (GRPR), overexpressed in various cancers, is a promising target for positron emission tomography (PET). This systematic review investigated the diagnostic value of GRPR-targeted PET imaging in oncology. A systematic search was conducted on major medical databases until May 23, 2024. Keywords were modified to include clinical original studies on GRPR-targeted PET in cancer patients. Out of 1624 searched studies initially, 107 were eligible for the full-text review. Overall, data from 38 studies met inclusion criteria, investigating GRPR-targeting radiotracers in breast cancer, prostate cancer, gastrointestinal stromal tumours (GIST) and gliomas (including optic pathway glioma and glioblastoma multiforme). In breast cancer, GRPR-targeted PET effectively detected primary tumours and metastases, particularly in estrogen receptor (ER)-positive patients, and predicted treatment response. In prostate cancer, high sensitivity (up to 88%) and specificity (up to 90%) for detecting primary tumours were observed, providing added value when combined with magnetic resonance imaging (MRI). In biochemical recurrence, sites of prostate cancer were identified even at PSA levels below 0.5ng/dL. Compared with PSMA PET, GRPR-targeted PET showed comparable or superior detection rates. Considering GIST, GRPR-targeted PET imaging proved to be a valuable diagnostic tool, particularly when [18F] FDG PET results were inconclusive. Regarding gliomas, GRPR-targeted PET achieved a 100% detection rate (MRI reference), aiding localization, preoperative planning, and differentiation between recurrence and malignant transformation. GRPR-targeted PET shows promise in improving cancer diagnostics, particularly in ER-positive breast cancer, prostate cancer, and gliomas, and may enhance clinical decision-making.

Advancements in molecular imaging probes for precision diagnosis and treatment of prostate cancer

Prostate cancer is the second most common cancer in men, accounting for 14.1% of new cancer cases in 2020. The aggressiveness of prostate cancer is highly variable, depending on its grade and stage at the time of diagnosis. Despite recent advances in prostate cancer treatment, some patients still experience recurrence or even progression after undergoing radical treatment. Accurate initial staging and monitoring for recurrence determine patient management, which in turn affect patient prognosis and survival. Classical imaging has limitations in the diagnosis and treatment of prostate cancer, but the use of novel molecular probes has improved the detection rate, specificity, and accuracy of prostate cancer detection. Molecular probe-based imaging modalities allow the visualization and quantitative measurement of biological processes at the molecular and cellular levels in living systems. An increased understanding of tumor biology of prostate cancer and the discovery of new tumor biomarkers have allowed the exploration of additional molecular probe targets. The development of novel ligands and advances in nano-based delivery technologies have accelerated the research and development of molecular probes. Here, we summarize the use of molecular probes in positron emission tomography (PET), single-photon emission computed tomography (SPECT), magnetic resonance imaging (MRI), optical imaging, and ultrasound imaging, and provide a brief overview of important target molecules in prostate cancer.

PSMA-Targeted Intracellular Self-Assembled Probe for Enhanced PET Imaging

Positron-emission tomography (PET) offers high sensitivity for cancer diagnosis. However, small-molecule-based probes often exhibit insufficient accumulation in tumor sites, while nanoparticle-based agents typically have limited delivery efficiency. To address this challenge, this study proposes a novel PET imaging probe, 68Ga-CBT-PSMA, designed for prostate cancer. This probe integrates an intracellular self-assembly strategy to enhance PET imaging signals and significantly improve the signal-to-noise ratio. The glutamate-urea-based prostate-specific membrane antigen (PSMA)-targeting motif enables specific recognition of prostate cancer cells and enhances cellular uptake; then the self-assembly process induced by glutathione reduction effectively accumulates the probe within tumor cells, thereby amplifying PET imaging signals. This approach not only enhances signal intensity and resolution but also facilitates precise cancer localization and diagnosis, offering new avenues for advancing cancer diagnostic techniques.

Detection rate of gastrin-releasing peptide receptor (GRPr) targeted tracers for positron emission tomography (PET) imaging in primary prostate cancer: a systematic review and meta-analysis

The gastrin-releasing peptide receptor (GRPr) has gained recognition as a promising target for both diagnostic and therapeutic applications in a variety of human cancers. This study aims to explore the primary tumor detection capabilities of [68Ga] Ga-GRPr PET imaging, specifically in newly diagnosed intra-prostatic prostate cancer lesions (PCa). Following PRISMA-DTA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses of Diagnostic Test Accuracy Studies) guidelines, a systematic literature search was conducted using the Medline, Embase, Scopus, and Web of Science databases. Data regarding patient characteristics and imaging procedure details-including the type of radiotracer used, administered activity, image acquisition time, scanner modality, criteria, and detection rate of index test-were extracted from the included studies. The pooled patient-and lesion-based detection rates, along with their corresponding 95% confidence intervals (CI), were calculated using a random effects model. The final analysis included 9 studies involving 291 patients and 350 intra-prostatic lesions with [68Ga] Ga-GRPr PET imaging in primary PCa. In per-patient-based analysis of [68Ga] Ga-GRPr PET imaging, the pooled detection rates of overall and patients with Gleason score ≥ 7 were 87.09% (95% CI 74.98-93.82) and 89.01% (95% CI 68.17-96.84), respectively. In per-lesion-based analysis, the pooled detection rate [68Ga] Ga-GRPr PET imaging was 78.54% (95% CI 69.8-85.29). The pooled detection rate mpMRI (multiparametric magnetic resonance imaging) in patient-based analysis was 91.85% (95% CI 80.12-96.92). The difference between the detection rates of the mpMRI and [68Ga] Ga-GRPr PET imaging was not statistically significant (OR 0.90, 95% CI 0.23-3.51). Our findings suggest that [68Ga] Ga-GRPr PET imaging has the potential as a diagnostic target for primary PCa. Future research is needed to determine the effectiveness of [68Ga] Ga-GRPr PET in delivering additional imaging data and guiding therapeutic decisions.

Radiopharmaceuticals Targeting Gastrin-Releasing Peptide Receptor for Diagnosis and Therapy of Prostate Cancer

The high incidence and heavy disease burden of prostate cancer (PC) require accurate and comprehensive assessment for appropriate disease management. Prostate-specific membrane antigen (PSMA) positron emission tomography (PET) cannot detect PSMA-negative lesions, despite its key role in PC disease management. The overexpression of gastrin-releasing peptide receptor (GRPR) in PC lesions reportedly performs as a complementary target for the diagnosis and therapy of PC. Radiopharmaceuticals derived from the natural ligands of GRPR have been developed. These radiopharmaceuticals enable the visualization and quantification of GRPR within the body, which can be used for disease assessment and therapeutic guidance. Recently developed radiopharmaceuticals exhibit improved pharmacokinetic parameters without deterioration in affinity. Several heterodimers targeting GRPR have been constructed as alternatives because of their potential to detect tumor lesions with a low diagnostic efficiency of single target detection. Moreover, some GRPR-targeted radiopharmaceuticals have entered clinical trials for the initial staging or biochemical recurrence detection of PC to guide disease stratification and therapy, indicating considerable potential in PC disease management. Herein, we comprehensively summarize the progress of radiopharmaceuticals targeting GRPR. In particular, we discuss the impact of ligands, chelators, and linkers on the distribution of radiopharmaceuticals. Furthermore, we summarize a potential design scheme to facilitate the advancement of radiopharmaceuticals and, thus, prompt clinical translation.

Gastrin Releasing Peptide Receptors-targeted PET Diagnostics and Radionuclide Therapy for Prostate Cancer Management: Preclinical and Clinical Developments of the Past 5 Years

Each tumor has its own distinctive molecular identity. Treatment, therefore, should be tailored to this unique cancer phenotype. Theragnostics uses the same compound for targeted imaging and treatment, radiolabeled to an appropriate radionuclide, respectively. Gastrin-releasing peptide receptors (GRPRs) are overexpressed in prostate cancer, and radiolabeled GRPR antagonists have shown high diagnostic performance at staging and biochemical recurrence. Several GRPR-targeting theragnostic compounds have been developed preclinically. Their translation into clinics is underway with 4 clinical trials recruiting participants with GRPR-expressing tumors.

Evaluation of gastrin-releasing peptide receptor, prostate-specific membrane antigen, and neurotensin receptor 1 as potential biomarkers for accurate prostate cancer stratified diagnosis

BACKGROUND

Studies on single-target PET imaging of gastrin-releasing peptide receptor (GRPR), prostate-specific membrane antigen (PSMA), or neurotensin receptor 1(NTR1) have been reported. However, the performance of these three targets in the progression of PCa remains unclear. Our study aims to compare the expression of GRPR, PSMA, and NTR1 in patients with prostatic intraepithelial neoplasia (PIN), prostate cancer (PCa), and lymph node metastasis. We synthesized molecular probes targeting the markers to achieve a non-invasive precise detection of PCa patients with PET/CT imaging.

METHODS

In this study, the expression of GRPR, PSMA, and NTR1 was evaluated by immunohistochemistry in 34 PIN, 171 PCa, and 22 lymph node metastasis tissues of patients. The correlation between their expression and the clinicopathological parameters of PCa patients was assessed. Sixteen PCa patients with different Gleason scores (GS) underwent dual-tracer (68Ga-NOTA-RM26 and 68Ga-NOTA-PSMA617) PET/CT.

RESULTS

In the PIN stage, the expression of GRPR was significantly higher than that of PSMA and NTR1 (P < 0.001), while NTR1 expression was significantly higher than PSMA and GRPR expression in primary PCa (P = 0.001). High PSMA expression in PCa patients was associated with shorter progression-free survival (P = 0.037) and overall survival (P = 0.035). PCa patients with high GS had higher tumor uptake of 68Ga-NOTA-PSMA617 than those with low GS (P = 0.001), while PCa patients with low GS had higher tumor uptake of 68Ga-NOTA-RM26 than those with high GS (P = 0.001).

CONCLUSIONS

This study presents three novel biomarkers (PSMA, GRPR, and NTR1) as imaging agents for PET/CT, and may offer a promising approach for non-invasive precise detection and Gleason grade prediction of PCa patients.

Prostate-specific membrane antigen-targeted surgery in prostate cancer: Accurate identification, real-time diagnosis, and precise resection

Radical prostatectomy (RP) combined with pelvic lymph node dissection (PLND) is the first step in multimodal treatment of prostate cancer (PCa) without distant metastases. For a long time, the surgical resection range has been highly dependent on the surgeon's visualization and experience with preoperative imaging. With the rapid development of prostate-specific membrane antigen positron emission tomography and single-photon emission computed tomography (PSMA-PET and PSMA-SPECT), PSMA-targeted surgery has been introduced for a more accurate pathological diagnosis and complete resection of positive surgical margins (PSMs) and micro-lymph node metastases (LNMs). We reviewed PSMA-targeted surgeries, including PSMA-PET-guided prostatic biopsy (PSMA-TB), PSMA-targeted radio-guided surgery (PSMA-RGS), PSMA-targeted fluorescence-guided surgery (PSMA-FGS), and multi-modality/multi-targeted PSMA-targeted surgery. We also discuss the strengths and challenges of PSMA-targeted surgery, and propose that PSMA-targeted surgery could be a great addition to existing surgery protocols, thereby improving the accuracy and convenience of surgery for primary and recurrent PCa in the near future.

Advances of radiolabeled GRPR ligands for PET/CT imaging of cancers

GRPR is a type of seven-transmembrane G-protein coupled receptor that belongs to the bombesin protein receptor family. It is highly expressed in various cancers, including prostate cancer, breast cancer, lung cancer, gastrointestinal cancer, and so on. As a result, molecular imaging studies have been conducted using radiolabeled GRPR ligands for tumor diagnosis, as well as monitoring of recurrence and metastasis. In this paper, we provided a comprehensive overview of relevant literature from the past two decades, with a specific focus on the advancements made in radiolabeled GRPR ligands for imaging prostate cancer and breast cancer.

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

BACKGROUND

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

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

Introduction

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

Methods

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

Results

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

Conclusion

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

The Impact of PSMA PET/CT on Modern Prostate Cancer Management and Decision Making-The Urological Perspective

Prostate-specific membrane antigen (PSMA) PET use in prostate cancer treatment has recently become a routinely used imaging modality by urologists. New, established data regarding its performance in different stages of prostate cancer, as well as gaining clinical knowledge with new tracers, drives the need for urologists and other clinicians to improve the utilization of this tool. While the use of PSMA PET/CT is more common in metastatic disease, in which it outperforms classical imaging modalities and drives treatment decisions and adjustments, recently, it gained ground in localized prostate cancer as well, especially in high-risk disease. Still, PSMA PET/CT might reveal lesions within the prostate or possibly locoregional or metastatic disease, not always representing true cancer when utilized in earlier stages of the disease, potentially adding diagnostic burden and changing treatment decisions. As urological treatment options advance toward focal treatments in localized organ-confined prostate cancer, recent reports suggest the utilization of PSMA PET/CT in treatment planning and follow-up and even when choosing active surveillance. This review aims to reveal the current perspective of urologists regarding its daily use.

A prospective comparative study of [68Ga]Ga-RM26 and [68Ga]Ga-PSMA-617 PET/CT imaging in suspicious prostate cancer

PURPOSE

Prostate-specific membrane antigen (PSMA)-based PET/CT imaging has limitations in the diagnosis of prostate cancer (PCa). We recruited 207 participants with suspicious PCa to perform PET/CT imaging with radiolabeled gastrin-releasing peptide receptor (GRPR) antagonist, [68Ga]Ga-RM26, and compare with [68Ga]Ga-PSMA-617 and histopathology.

METHODS

Every participant with suspicious PCa was scanned with both [68Ga]Ga-RM26 and [68Ga]Ga-PSMA-617 PET/CT. PET/CT imaging was compared using pathologic specimens as a reference standard.

RESULTS

Of the 207 participants analyzed, 125 had cancer, and 82 were diagnosed with benign prostatic hyperplasia (BPH). The sensitivity and specificity of [68Ga]Ga-RM26 and [68Ga]Ga-PSMA-617 PET/CT imaging differed significantly for detecting clinically significant PCa. The area under the ROC curve (AUC) was 0.54 for [68Ga]Ga-RM26 PET/CT and 0.91 for [68Ga]Ga-PSMA-617 PET/CT in detecting PCa. For clinically significant PCa imaging, the AUCs were 0.51 vs. 0.93, respectively. [68Ga]Ga-RM26 PET/CT imaging had higher sensitivity for PCa with Gleason score (GS) = 6 (p = 0.03) than [68Ga]Ga-PSMA-617 PET/CT but poor specificity (20.73%). In the group with PSA < 10 ng/mL, the sensitivity, specificity, and AUC of [68Ga]Ga-RM26 PET/CT were lower than [68Ga]Ga-PSMA-617 PET/CT (60.00% vs. 80.30%, p = 0.12, 23.26% vs. 88.37%, p = 0.000, and 0.524 vs. 0.822, p = 0.000, respectively). [68Ga]Ga-RM26 PET/CT exhibited significantly higher SUVmax in specimens with GS = 6 (p = 0.04) and in the low-risk group (p = 0.01), and its uptake did not increase with PSA level, GS, or clinical stage.

CONCLUSION

This prospective study provided evidence for the superior accuracy of [68Ga]Ga-PSMA-617 PET/CT over [68Ga]Ga-RM26 PET/CT in detecting more clinically significant PCa. [68Ga]Ga-RM26 PET/CT showed an advantage for imaging low-risk PCa.

Modular One-Pot Strategy for the Synthesis of Heterobivalent Tracers

Bivalent ligands, i.e., molecules having two ligands covalently connected by a linker, have been gathering attention since the first description of their pharmacological potential in the early 80s. However, their synthesis, particularly of labeled heterobivalent ligands, can still be cumbersome and time-consuming. We herein report a straightforward procedure for the modular synthesis of labeled heterobivalent ligands (HBLs) using dual reactive 3,6-dichloro-1,2,4,5-tetrazine as a starting material and suitable partners for sequential S_NAr and inverse electron-demand Diels-Alder (IEDDA) reactions. This assembly method conducted in a stepwise or in a sequential one-pot manner provides quick access to multiple HBLs. A conjugate combining ligands toward the prostate-specific membrane antigen (PSMA) and the gastrin-releasing peptide receptor (GRPR) was radiolabeled, and its biological activity was assessed in vitro and in vivo (receptor binding affinity, biodistribution, imaging) as an illustration that the assembly methodology preserves the tumor targeting properties of the ligands.

Theranostics of Primary Prostate Cancer: Beyond PSMA and GRP-R

The imaging of Prostate-Specific Membrane Antigen (PSMA) is now widely used at the initial staging of prostate cancers in patients with a high metastatic risk. However, its ability to detect low-grade tumor lesions is not optimal.

METHODS

First, we prospectively performed neurotensin receptor-1 (NTS₁) IHC in a series of patients receiving both [⁶⁸Ga]Ga-PSMA-617 and [⁶⁸Ga]Ga-RM2 before prostatectomy. In this series, PSMA and GRP-R IHC were also available (n = 16). Next, we aimed at confirming the PSMA/GRP-R/NTS₁ expression profile by retrospective autoradiography (n = 46) using a specific radiopharmaceuticals study and also aimed to decipher the expression of less-investigated targets such as NTS₂, SST₂ and CXCR4.

RESULTS

In the IHC study, all samples with negative PSMA staining (two patients with ISUP 2 and one with ISUP 3) were strongly positive for NTS₁ staining. No samples were negative for all three stains-for PSMA, GRP-R or NTS₁. In the autoradiography study, binding of [¹¹¹In]In-PSMA-617 was high in all ISUP groups. However, some samples did not bind or bound weakly to [¹¹¹In]In-PSMA-617 (9%). In these cases, binding of [¹¹¹n]In-JMV 6659 and [¹¹¹In]In-JMV 7488 towards NTS₁ and NTS₂ was high.

CONCLUSIONS

Targeting PSMA and NTS₁/NTS₂ could allow for the detection of all intraprostatic lesions.