PET Using a GRPR Antagonist 68Ga-RM26 in Healthy Volunteers and Prostate Cancer Patients

Development of a PSMA and EphA2 dual-receptor-activated fluorescent probe for wash-free prostate cancer cell imaging

Prostate cancer (PCa) remains a leading cause of cancer-related mortality in men, underscoring the need for improved diagnostic tools. In this study, a novel dual-receptor-activated fluorescence probe (9) designed to simultaneously bind to prostate-specific membrane antigen (PSMA) and erythropoietin-producing hepatocellular receptor type A2 (EphA2), two key biomarkers in PCa, was developed and applied for wash-free cell imaging. The probe was synthesized by conjugating both PSMA- and EphA2-targeting ligands with a sulfonated benzothiazole environment-sensitive dye. 9 demonstrated good binding affinity (Kd = 34 nM for PSMA, 9.70 nM for EphA2) with significant fluorescence activation upon receptor binding (14.1-fold for PSMA; 8.6-fold for EphA2). Cell studies demonstrated 9 showed negligible cytotoxicity and good targeting specificity, which could enable convenient monitoring of the dynamic biological processes in PCa, such as ligand-receptor interactions. The study may also provide insights into the design and applications of multiple-receptor-activated fluorescence probes.

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.

Approaching Gallium-68 radiopharmaceuticals for tumor diagnosis: a Medicinal Chemist's perspective

Nuclear medicine has revolutionized disease diagnosis and treatment, particularly in oncology, by enabling precise imaging and targeted therapies using radiopharmaceuticals. Recently, Gallium-68 (68Ga) has emerged as a powerful positron emission tomography (PET) imaging agent, with a growing role in theranostics when paired with 177Lu for cancer treatment. The ability to obtain 68Ga from 68Ge/68Ga generators, along with its favorable radiochemical and pharmacokinetic properties, has driven an increasing number of clinical applications, which culminated with the approvals of 68Ga-DOTA-TOC and 68Ga-DOTA-TATE for the treatment of neuroendocrine tumors, and 68Ga-PSMA-11 for prostate cancer over the past decade. This review provides a comprehensive overview of 68Ga radiochemistry, chelators, and key compounds in clinical trials, highlighting the potential of this radionuclide in precision oncology.

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.

Gastrin-Releasing Peptide Receptor Targeting PET/CT With 68 Ga-NOTA-RM26 in the Assessment of Glioma and Combined Multiregional Biopsies

PURPOSE

The aim of this study was to investigate the value of 68 Ga-NOTA-RM26 ( 68 Ga-RM26), a gastrin-releasing peptide receptor-targeting antagonist labeled with the radionuclide 68 Ga, in the diagnosis of high-grade gliomas and in combination with multiregional biopsies using PET/CT.

PATIENTS AND METHODS

After institutional review board approval and informed consent, a total of 35 patients with suspected glioma lesions were enrolled in this study. All patients underwent 68 Ga-RM26 PET/CT scans within 2 weeks before surgery.

RESULTS

There were 8 grade II gliomas, 6 grade III gliomas, and 18 grade IV gliomas in a total of 32 glioma lesions. 68 Ga-RM26 PET/CT diagnosed 74.4% of lesions (27/32) of all glioma tumor types, and almost all high-grade gliomas were successfully diagnosed (23/24, 95.8%). Among the 9 negative glioma lesions, there were 8 low-grade gliomas (grade II). There was a significantly higher SUV max , SUV mean , and the lesion-to-background ratio (T/B ratio) in high-grade gliomas compared with low-grade gliomas ( P < 0.001). In addition, there was a high correlation between the immunohistochemical staining score of gliomas and parameters (SUV max , SUV mean , and T/B ratio) on 68 Ga-RM26 PET/CT ( P < 0.001), and verified by immunohistochemical staining on multiple-point samples of glioma lesions guided by 68 Ga-RM26 PET/CT.

CONCLUSIONS

68 Ga-RM26 could noninvasively diagnose high-grade gliomas and be a promising PET tracer for predicting glioma grading before surgery. This pilot study indicated that the uptake of 68 Ga-RM26 correlates with WHO grade in glioma, and preoperative 68 Ga-RM26 PET/CT may be helpful to guide multiple-point biopsy of gliomas.

Cancer Targeting Radiopeptidomimetics in Molecular Nuclear Medicine

Peptides are highly receptor-affine molecules exhibiting suitable pharmacokinetics. Additionally, low-cost production, simple protocols allowing easy modifications, and tolerance toward harsh reaction conditions make peptides ideal ligands for preparation of radiopharmaceuticals for cancer detection and treatment. However, natural peptides being substrates for enzymes are susceptible to proteolysis, which limits the in vivo lifetime and the target uptake. Therefore, the majority of peptides are not able to progress beyond preclinical research. Advancement of peptides for clinical analysis needs modification to instill improved features. Continuous increase and further expected rise in cancer cases in the next decade require development of more disease-directed and promising radiopharmaceuticals. Redesigned peptide, mimicking the original peptide with similar or improved affinity and high metabolic stability, shall have significant edge. This review outlines the design of peptidomimetics by incorporation of D-amino acids (inverso); reversal of D-amino acid sequence (retro-inverso), and reversal of L-amino acid sequence (retro). Clinically successful radiopeptidomimetics prepared using the three approaches have been elaborated to elucidate the important role of peptidomimetics in cancer management.

Head-to-Head Comparison of [68Ga]Ga-NOTA-RM26 and [18F]FDG PET/CT in Patients with Gastrointestinal Stromal Tumors: A Prospective Study

Gastrointestinal stromal tumors (GISTs) are the most common stromal tumors in the gastrointestinal tract. This study was designed to evaluate a gastrin-releasing peptide receptor antagonist PET tracer, [68Ga]Ga-NOTA-RM26, and compare it with [18F]FDG PET/CT in the assessment of patients with GISTs. Methods: With institutional review board approval and informed consent, 30 patients with suspected or proven GISTs based on abdominal CT or gastroscopy were recruited. All patients underwent [68Ga]Ga-NOTA-RM26 and [18F]FDG PET/CT scans. Pathology and other patient information were collected. Results: No radiopharmaceutical-related adverse events were observed in the patients. In total, 18 lesions in 16 patients were diagnosed as GIST, 3 patients were diagnosed with schwannoma, and 4 patients were diagnosed with leiomyoma. In 18 GISTs, the mean SUVmax of [68Ga]Ga-NOTA-RM26 PET was significantly higher than that of [18F]FDG PET (17.07 ± 19.57 vs. 2.28 ± 1.65; P < 0.01), and [68Ga]Ga-NOTA-RM26 PET/CT had a higher tumor detection rate than did [18F]FDG PET/CT (88.9% vs. 50%; P < 0.01). The uptake of [68Ga]Ga-NOTA-RM26 in GISTs was significantly higher than that in 2 other benign tumors (leiomyoma or schwannoma) (17.07 ± 19.57 vs. 4.23 ± 1.77; P = 0.014). With the SUVmax cutoff value of 6.0, the sensitivity of 68Ga-NOTA-RM26 PET/CT in diagnosing GISTs is 72% and the specificity is 85.7%. Conclusion: Compared with [18F]FDG PET/CT, [68Ga]Ga-NOTA-RM26 PET/CT is a promising and effective imaging modality for the detection of GISTs.

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.

68Ga-NOTA-RM26 PET/CT in the evaluation of glioma: a pilot prospective study

BACKGROUND

Gliomas are the most common malignant primary tumors of the central nervous system. There is an urgent need for new convenient, targeted and specific imaging agents for gliomas. This study aimed to firstly evaluate the feasibility of 68Ga-NOTA-RM26 PET/CT imaging in glioma and analyze the relationship between the imaging characteristics and glioma grade, classification and molecular alterations.

RESULTS

Twenty-two patients were confirmed as glioma by surgery or biopsy. All patients exhibited 68Ga-NOTA-RM26 uptake. SUVmax was chosen as the imaging marker for analysis. For all glioma patients, there were significant differences between grades (P = 0.047). For primary gliomas, SUVmax had good discrimination for both tumor classifications (P = 0.045) and grades (P = 0.03). There was a positive correlation (P < 0.01) between GRPR expression level and SUVmax. P53 mutations caused significant differences in SUVmax (P = 0.03).

CONCLUSIONS

This study is the first application of 68Ga-NOTA-RM26 in glioma patients and confirmed the safety and efficacy in glioma patients. 68Ga-NOTA-RM26 PET/CT has potential value in tumor grade, classification, and molecular alterations.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT06412952. Registered 26 April 2024, https://clinicaltrials.gov/study/NCT06412952.

Gastrin-releasing peptide receptor (GRPR) as a novel biomarker and therapeutic target in prostate cancer

Aim: This comprehensive review aims to explore the potential applications of Gastrin-releasing peptide receptor (GRPR) in the diagnosis and treatment of prostate cancer. Additionally, the study investigates the role of GRPR in prognostic assessment for individuals afflicted with prostate cancer.Methods: The review encompasses a thorough examination of existing literature and research studies related to the upregulation of GRPR in various tumor types, with a specific focus on prostate. The review also evaluates the utility of GRPR as a molecular target in prostate cancer research, comparing its significance to the well-established Prostate-specific membrane antigen (PSMA). The integration of radionuclide-targeted therapy with GRPR antagonists is explored as an innovative therapeutic approach for individuals with prostate cancer.Results: Research findings suggest that GRPR serves as a promising molecular target for visualizing low-grade prostate cancer. Furthermore, it is demonstrated to complement the detection of lesions that may be negative for PSMA. The integration of radionuclide-targeted therapy with GRPR antagonists presents a novel therapeutic paradigm, offering potential benefits for individuals undergoing treatment for prostate cancer.Conclusions: In conclusion, this review highlights the emerging role of GRPR in prostate cancer diagnosis and treatment. Moreover, the integration of radionuclide-targeted therapy with GRPR antagonists introduces an innovative therapeutic approach that holds promise for improving outcomes in individuals dealing with prostate cancer. The potential prognostic value of GRPR in assessing the disease's progression adds another dimension to its clinical significance in the realm of urology.

Engineering peptide drug therapeutics through chemical conjugation and implication in clinics

The development of peptide drugs has made tremendous progress in the past few decades because of the advancements in modification chemistry and analytical technologies. The novel-designed peptide drugs have been modified through various biochemical methods with improved diagnostic, therapeutic, and drug-delivery strategies. Researchers found it a helping hand to overcome the inherent limitations of peptides and bring continued advancements in their applications. Furthermore, the emergence of peptide-drug conjugates (PDCs)-utilizes target-oriented peptide moieties as a vehicle for cytotoxic payloads via conjugation with cleavable chemical agents, resulting in the key foundation of the new era of targeted peptide drugs. This review summarizes the various classifications of peptide drugs, suitable chemical modification strategies to improve the ADME (adsorption, distribution, metabolism, and excretion) features of peptide drugs, and recent (2015-early 2024) progress/achievements in peptide-based drug delivery systems as well as their fruitful implication in preclinical and clinical studies. Furthermore, we also summarized the brief description of other types of PDCs, including peptide-MOF conjugates and peptide-UCNP conjugates. The principal aim is to provide scattered and diversified knowledge in one place and to help researchers understand the pinching knots in the science of PDC development and progress toward a bright future of novel peptide drugs.

Gastrin-releasing peptide receptor as theranostic target in estrogen-receptor positive breast cancer: A preclinical study of the theranostic pair [55Co]Co- and [177Lu]Lu-DOTA-RM26

BACKGROUND

Patients with advanced metastatic estrogen receptor-positive breast cancer often develop resistance to standard treatments, leading to uncontrolled progression. Thus, innovative therapies are urgently needed. The gastrin-releasing peptide receptor (GRPR) is overexpressed in various cancers, including breast cancer, making it an interesting theranostic target. RM26, a GRPR-targeting antagonist, has demonstrated promising in vivo kinetics in prostate cancer models. This study evaluated the theranostic capabilities of [55Co]Co-/[177Lu]Lu-DOTA-RM26 in vitro in estrogen receptor-positive breast cancer cells and assessed the diagnostic potential of [55Co]Co-DOTA-RM26 in vivo in a breast cancer mouse model.

METHODS

We analyzed the binding specificity of [57Co]Co-/[177Lu]Lu-DOTA-RM26 in T47D breast cancer cells, using [57Co]Co-DOTA-RM26 as a surrogate for [55Co]Co-DOTA-RM26. The therapeutic efficacy of increasing [177Lu]Lu-DOTA-RM26 concentrations was determined via viability assay in vitro. Ex vivo biodistribution of [57Co]Co-DOTA-RM26 (17.2 ± 2.7 kBq, 33 ± 5.2 pmol/mouse) was investigated in 12 mice (n= 4/group) with orthotopic breast cancer tumors. The mice were sacrificed at 4 and 24 h post-injection (pi), including a blocking group (20 nmol of unlabeled [Tyr4]-Bombesin) at 4 h pi. For imaging, two tumor-bearing mice underwent [55Co]Co-DOTA-RM26 PET/CT, 4 and 24 h pi (2.8 ± 0.2 MBq, 167.5 ± 0.5 pmol/mouse), with or without GRPR blocking.

RESULTS

In vitro studies revealed high, specific binding of [57Co]Co-DOTA-RM26 (43 ± 1 % of total added activity per 106 cells (%IA/106)) and [177Lu]Lu-DOTA-RM26 (37 ± 4 %IA/106). The activity was predominantly localized at the cell surface: 71 ± 3 % and 80 ± 6 % for [57Co]Co-DOTA-RM26 and [177Lu]Lu-DOTA-RM26, respectively. [177Lu]Lu-DOTA-RM26 significantly reduced cell viability at all activity concentrations >0.625 MBq/mL (p < 0.0001), with cell viability below 1 % at concentrations ≥5 MBq/mL. Biodistribution data (n = 12) indicated a high, specific tumor uptake of [57Co]Co-DOTA-RM26, surpassing all other tissues significantly at both time points, 3.7 ± 0.6 % of the injected activity per gram (%IA/g) 4 h pi and 0.98 ± 0.05 %IA/g 24 h pi. The kidneys showed the second-highest uptake (2.0 ± 0.1 %IA/g 4 h pi), followed by the pancreas (1.4 ± 0.4 %IA/g 4 h pi). PET/CT imaging with [55Co]Co-DOTA-RM26 supported the biodistribution data and, distinctly visualized the tumor 24 h pi and showed an improved tumor-to-background compared to the earlier time points. Effective GRPR blocking significantly reduced tumor uptake in the PET images 24 h pi.

CONCLUSION

These findings suggest that the theranostic pair [55Co]Co-/[177Lu]Lu-DOTA-RM26 holds significant promise as a theranostic agent for estrogen receptor-positive breast cancer.

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.

Lipid-Based Nanocarriers: Bridging Diagnosis and Cancer Therapy

Theranostics is a growing field that matches diagnostics and therapeutics. In this approach, drugs and techniques are uniquely coupled to diagnose and treat medical conditions synergically or sequentially. By integrating diagnostic and treatment functions in a single platform, the aim of theranostics is to improve precision medicine by tailoring treatments based on real-time information. In this context, lipid-based nanocarriers have attracted great scientific attention due to their biodegradability, biocompatibility, and targeting capabilities. The present review highlights the latest research advances in the field of lipid-based nanocarriers for cancer theranostics, exploring several ways of improving in vivo performance and addressing associated challenges. These nanocarriers have significant potential to create new perspectives in the field of nanomedicine and offer promise for a significant step towards more personalized and precise medicine, reducing side effects and improving clinical outcomes for patients. This review also presents the actual barriers to and the possible challenges in the use of nanoparticles in the theranostic field, such as regulatory hurdles, high costs, and technological integration. Addressing these issues through a multidisciplinary and collaborative approach among institutions could be essential for advancing lipid nanocarriers in the theranostic field. Such collaborations can leverage diverse expertise and resources, fostering innovation and overcoming the complex challenges associated with clinical translation. This approach will be crucial for realizing the full potential of lipid-based nanocarriers in precision medicine.

Evaluation of ABD-Linked RM26 Conjugates for GRPR-Targeted Drug Delivery

Targeting the gastrin-releasing peptide receptor (GRPR) with the bombesin analogue RM26, a 9 aa peptide, has been a promising strategy for cancer theranostics, with recent success in radionuclide imaging of prostate cancer. However, therapeutic application of the short peptide RM26 would require a longer half-life to prevent fast clearance from the circulation. Conjugation to an albumin-binding domain (ABD) is a viable strategy to extend the in vivo half-life of peptides and proteins. We previously reported an ABD-fused RM26 peptide targeting GRPR (ABD-RM26 Gen 1) that showed prolonged and stable tumor uptake over 144 h; however, the observed high kidney uptake indicated that the conjugate's binding to albumin was reduced and that this could be an obstacle for its use as a delivery system for targeted therapy, especially for radiotherapy. Here, we have designed, produced, and preclinically evaluated a series of novel ABD-RM26 conjugates with the aim of improving the conjugate's binding to albumin and decreasing the kidney uptake. We developed three second-generation constructs with varying formats, differing in the relative positions of the targeting moieties and the radionuclide chelator. The produced conjugates were radiolabeled with indium-111 and evaluated in vitro and in vivo. All constructs displayed improved biophysical characteristics, biodistribution, and lower kidney uptake compared to previously reported first-generation molecules. The ABD-RM26 Gen 2A conjugate showed the best biodistribution profile with a nearly 6-fold reduction in kidney uptake. However, the ABD-RM26 Gen 2A conjugate's binding to GRPR was compromised. This conjugate's assembly of albumin- and GRPR-binding moieties might be used for further development of drug conjugates for targeted therapy/radiotherapy of GRPR-expressing cancers.

Synthesis, preclinical, and initial clinical evaluation of integrin αVβ3 and gastrin-releasing peptide receptor (GRPR) dual-targeting radiotracer [68Ga]Ga-RGD-RM26-03

Integrin receptor αvβ3 and gastrin-releasing peptide receptor (GRPR) expression of tumors could be detected using PET imaging with radiolabeled Arg-Gly-Asp (RGD) and the antagonistic bombesin analog RM26, respectively. The purpose of this study was to investigate the dual receptor-targeting property of the heterodimer RGD-RM26-03 (denoted as LNC1015), demonstrate the tumor diagnostic value of [68Ga]Ga-LNC1015 in preclinical experiments, and evaluate its preliminary clinical feasibility.

METHODS

LNC1015 was designed and synthesized by linking cyclic RGD and the RM26 peptide. Preclinical pharmacokinetics were detected in a PC3 xenograft model using microPET and biodistribution studies. The clinical feasibility of [68Ga]Ga-LNC1015 PET/CT was performed in patients with breast cancer, and the results were compared with those of 18F-fluorodeoxyglucose (FDG).

RESULTS

[68Ga]Ga-LNC1015 had good stability in saline for at least 2 h, and favorable binding affinity and specificity were demonstrated in vitro and in vivo. The tumor uptake and retention of [68Ga]Ga-LNC1015 during PET imaging were improved compared with its monomeric counterparts [68Ga]Ga-RGD and [68Ga]Ga-RM26 at all the time points examined. In our initial clinical studies, the tumor uptake and tumor-to-background ratio (TBR) of primary and metastatic lesions in [68Ga]Ga-LNC1015 PET/CT were significantly higher than those in [18F]FDG PET/CT, resulting in high lesion detection rate and tumor delineation.

CONCLUSION

The dual targeting radiotracer [68Ga]Ga-LNC1015 showed significantly improved tumor uptake and retention, as well as lower liver uptake than [68Ga]Ga-RGD and [68Ga]Ga-RM26 monomer. The first-in-human study showed high TBRs in patients, suggesting favorable pharmacokinetics and high clinical feasibility for PET/CT imaging of cancer.

Biodistribution and radiation dosimetry of [99mTc]Tc-N4-BTG in patients with biochemical recurrence of prostate cancer

BACKGROUND

In patients with prostate cancer (PCa), imaging with gastrin-releasing peptide receptor (GRPR) ligands is an alternative to PSMA-targeted tracers, particularly if PSMA expression is low or absent. [99mTc]Tc-N4-BTG is a newly developed GRPR-directed probe for conventional scintigraphy and single photon emission computed tomography (SPECT) imaging. The current study aims to investigate the safety, biodistribution and dosimetry of [99mTc]Tc-N4-BTG in patients with biochemical recurrence (BCR) of PCa.

RESULTS

No adverse pharmacologic effects were observed. Injection of [99mTc]Tc-N4-BTG resulted in an effective dose of 0.0027 ± 0.0002 mSv/MBq. The urinary bladder was the critical organ with the highest mean absorbed dose of 0.028 ± 0.001 mGy/MBq, followed by the pancreas with 0.0043 ± 0.0015 mGy/MBq, osteogenic cells with 0.0039 ± 0.0005 mGy/MBq, the kidneys with 0.0034 ± 0.0003 mGy/MBq, and the liver with 0.0019 ± 0.0004 mGy/MBq, respectively. No focal tracer uptake suggestive of PCa recurrence could be revealed for any of the patients.

CONCLUSION

[99mTc]Tc-N4-BTG appears to be a safe diagnostic agent. Compared to GRPR-targeted PET tracers, this 99mTc-labelled SPECT agent could contribute to a broader application and better availability of this novel approach. Further research to assess its clinical value is warranted.

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.

Peptide-Drug Conjugates: Design, Chemistry, and Drug Delivery System as a Novel Cancer Theranostic

The emergence of peptide-drug conjugates (PDCs) that utilize target-oriented peptide moieties as carriers of cytotoxic payloads, interconnected with various cleavable/noncleavable linkers, resulted in the key-foundation of the new era of targeted therapeutics. They are capable of retaining the integrity of conjugates in the blood circulatory system as well as releasing the drugs at the tumor microenvironment. Other valuable advantages are specificity and selectivity toward targeted-receptors, higher penetration ability, and drug-loading capacity, making them a suitable candidate to play their vital role as promising carrier agents. In this review, we summarized the types of cell-targeting (CTPs) and cell-penetrating peptides (CPPs) that have broad applications in the advancement of targeted drug-delivery systems (DDS). Moreover, the techniques to overcome the limitations of peptide-chemistry for their extensive implementation to construct the PDCs. Besides this, the diversified breakthrough of linker chemistry, and ample knowledge of various cytotoxic payloads used in PDCs in recent years, as well as the mechanism of action of PDCs was critically discussed. The principal aim is to provide scattered and diversified knowledge in one place and to help researchers understand the pinching knots in the science of PDC development, also their progression toward a bright future for PDCs as novel theranostics in clinical practice.

The Balance Between the Therapeutic Efficacy and Safety of [177Lu]Lu-NeoB in a Preclinical Prostate Cancer Model

PURPOSE

Radiolabeled NeoB is a promising gastrin-releasing peptide receptor (GRPR)-targeting radiopharmaceutical for theranostics of GRPR-expressing malignancies, e.g., prostate cancer (PCa). The aim of this study was to evaluate the effect of different doses of [177Lu]Lu-NeoB on the balance between therapeutic efficacy and safety in a preclinical PCa model.

PROCEDURES

To determine the efficacy of [177Lu]Lu-NeoB, PC-3 xenografted mice received 3 sham injections (control group) or 3 injections of 30 MBq/300 pmol, 40 MBq/400 pmol, or 60 MBq/600 pmol [177Lu]Lu-NeoB (groups 1, 2, and 3, respectively) 1 week apart. To quantify tumor uptake, single-photon emission computed tomography/computed tomography (SPECT/CT) imaging was performed 4 h after the first, second, and third injection on a separate group of animals. For safety evaluations, pancreatic and renal tissues of non-tumor-bearing mice treated with the abovementioned [177Lu]Lu-NeoB doses were evaluated 12 and 24 weeks post-treatment.

RESULTS

Treatment of PC-3 tumors with all three studied [177Lu]Lu-NeoB doses was effective. Median survival times were significantly (p < 0.0001) improved for treatment groups 1, 2, and 3 versus the control group (82 days, 89 days, 99 days versus 19 days, respectively). However, no significant differences were observed between treatment groups. Quantification of SPECT/CT images showed minimal differences in the average absolute radioactivity uptake, especially after the third injection. Histopathological analysis revealed no clear signs of treatment-related pancreatic toxicity. For the kidneys, atrophy and fibrosis were observed for one animal from group 1 and a chronic inflammatory response was observed for both animals from group 3 at 24 weeks post-treatment.

CONCLUSIONS

Treatment with [177Lu]Lu-NeoB is effective in a preclinical PCa model. Adjusting the administered dose could positively impact the risk-benefit balance as a higher dose might not lead to an increased therapeutic effect, but it may lead to an increase in toxicological effects in healthy organs such as the kidneys.

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.

Development of a 18F-Labeled Bicyclic Peptide Targeting EphA2 for Molecular Imaging of PSMA-Negative Prostate Cancer

Although PSMA PET/CT imaging has great potential for noninvasively detecting prostate cancer (PCa), limitations exist for patients with low PSMA expression, caused by androgen deprivation treatment or neuroendocrine differentiation. Analysis of The Cancer Genome Atlas Prostate Adenocarcinoma (TCGA-PRAD) data found that erythropoietin-producing hepatocellular receptor A2 (EphA2), a receptor overexpressed in most PCa could be a potential target for PSMA-negative PCa. A fluorescent ligand ETF and a radiolabeled ligand [18F]AlF-ETN derived from a EphA2-targeting bicyclic peptide were synthesized and investigated. ETF could selectively stain and visualize the EphA2-positive but PSMA-negative PC3 cells, in complementary to the PSMA-targeting probe. PET/CT imaging and biodistribution experiments demonstrated that [18F]AlF-ETN specifically accumulated in PC3 tumors with a high contrast (tumor-to-muscle ratio: 21.29 ± 6.55). In conclusion, we have demonstrated the potential for using EphA2 to detect PSMA-negative PCa and developed a radiolabeled ligand [18F]AlF-ETN to specifically image EphA2 expressing PCa with high contrast.

Side-by-side comparison of the two widely studied GRPR radiotracers, radiolabeled NeoB and RM2, in a preclinical setting

INTRODUCTION

NeoB and RM2 are the most investigated gastrin-releasing peptide receptor (GRPR)-targeting radiotracers in preclinical and clinical studies. Therefore, an extensive side-by-side comparison of the two radiotracers is valuable to demonstrate whether one has advantages over the other. Accordingly, this study aims to compare the in vitro and in vivo characteristics of radiolabeled NeoB and RM2 to guide future clinical studies.

METHOD

The stability of the radiolabeled GRPR analogs was determined in phosphate buffered saline (PBS), and commercially available mouse and human serum. Target affinity was determined by incubating human prostate cancer PC-3 cells with [177Lu]Lu-NeoB or [177Lu]Lu-RM2, + / - increasing concentrations of unlabeled NeoB, RM2, or Tyr4-bombesin (BBN). To determine uptake and specificity cells were incubated with [177Lu]Lu-NeoB or [177Lu]Lu-RM2 + / - Tyr4-BBN. Moreover, in vivo studies were performed to determine biodistribution and pharmacokinetics. Finally, radiotracer binding to various GRPR-expressing human cancer tissues was investigated.

RESULTS

Both radiotracers demonstrated high stability in PBS and human serum, but stability in mouse serum decreased substantially over time. Moreover, both radiotracers demonstrated high GRPR affinity and specificity, but a higher uptake of [177Lu]Lu-NeoB was observed in in vitro studies. In vivo, no difference in tumor uptake was seen. The most prominent difference in uptake in physiological organs was observed in the GRPR-expressing pancreas; [177Lu]Lu-RM2 had less pancreatic uptake and a shorter pancreatic half-life than [177Lu]Lu-NeoB. Furthermore, [177Lu]Lu-RM2 presented with a lower tumor-to-kidney ratio, while the tumor-to-blood ratio was lower for [177Lu]Lu-NeoB. The autoradiography studies revealed higher binding of radiolabeled NeoB to all human tumor tissues.

CONCLUSION

Based on these findings, we conclude that the in vivo tumor-targeting capability of radiolabeled NeoB and RM2 is similar. Additional studies are needed to determine whether the differences observed in physiological organ uptakes, i.e., the pancreas, kidneys, and blood, result in relevant differences in organ absorbed doses when the radiotracers are applied for therapeutic purposes.

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.

Peptide-Based Agents for Cancer Treatment: Current Applications and Future Directions

Peptide-based strategies have received an enormous amount of attention because of their specificity and applicability. Their specificity and tumor-targeting ability are applied to diagnosis and treatment for cancer patients. In this review, we will summarize recent advancements and future perspectives on peptide-based strategies for cancer treatment. The literature search was conducted to identify relevant articles for peptide-based strategies for cancer treatment. It was performed using PubMed for articles in English until June 2023. Information on clinical trials was also obtained from ClinicalTrial.gov. Given that peptide-based strategies have several advantages such as targeted delivery to the diseased area, personalized designs, relatively small sizes, and simple production process, bioactive peptides having anti-cancer activities (anti-cancer peptides or ACPs) have been tested in pre-clinical settings and clinical trials. The capability of peptides for tumor targeting is essentially useful for peptide-drug conjugates (PDCs), diagnosis, and image-guided surgery. Immunomodulation with peptide vaccines has been extensively tested in clinical trials. Despite such advantages, FDA-approved peptide agents for solid cancer are still limited. This review will provide a detailed overview of current approaches, design strategies, routes of administration, and new technological advancements. We will highlight the success and limitations of peptide-based therapies for cancer treatment.

Novel GRPR-Targeting Peptide for Pancreatic Cancer Molecular Imaging in Orthotopic and Liver Metastasis Mouse Models

Despite advancements in pancreatic cancer treatment, it remains one of the most lethal malignancies with extremely poor diagnosis and prognosis. Herein, we demonstrated the efficiency of a novel peptide GB-6 labeled with a near-infrared (NIR) fluorescent dye 3H-indolium, 2-[2-[2-[(2-carboxyethyl)thio]-3-[2-[1,3-dihydro-3,3-dimethyl-5-sulfo-1-(3-sulfopropyl)-2H-indol-2-ylidene]ethylidene]-1-cyclohexen-1-yl]ethenyl]-3,3-dimethyl-5-sulfo-1-(3-sulfopropyl)-, inner salt (MPA) and radionuclide technetium-99m (99mTc) as targeting probes using the gastrin-releasing peptide receptor (GRPR) that is overexpressed in pancreatic cancer as the target. A short linear peptide with excellent in vivo stability was identified, and its radiotracer [99mTc]Tc-HYNIC-PEG4-GB-6 and the NIR probe MPA-PEG4-GB-6 exhibited selective and specific uptake by tumors in an SW1990 pancreatic cancer xenograft mouse model. The favorable biodistribution of the tracer [99mTc]Tc-HYNIC-PEG4-GB-6 in vivo afforded tumor-specific accumulation with high tumor-to-muscle and -bone contrasts and renal body clearance at 1 h after injection. The biodistribution analysis revealed that the tumor-to-pancreas and -intestine fluorescence signal ratios were 5.2 ± 0.3 and 6.3 ± 1.5, respectively, in the SW1990 subcutaneous xenograft model. Furthermore, the high signal accumulation in the orthotopic pancreatic and liver metastasis tumor models with tumor-to-pancreas and -liver fluorescence signal ratios of 7.66 ± 0.48 and 3.94 ± 0.47, respectively, enabled clear tumor visualization for intraoperative navigation. The rapid tumor targeting, precise tumor boundary delineation, chemical versatility, and high potency of the novel GB-6 peptide established it as a high-contrast imaging probe for the clinical detection of GRPR, with compelling additional potential in molecular-targeted therapy.

Preclinical assessment of IRDye800CW-labeled gastrin-releasing peptide receptor-targeting peptide for near infrared-II imaging of brain malignancies

We aimed to develop a new biocompatible gastrin-releasing peptide receptor (GRPR) targeted optical probe, IRDye800-RM26, for fluorescence image-guided surgery (FGS) of brain malignancies in near-infrared window II (NIR-II) imaging. We developed a novel GRPR targeting probe using a nine-amino-acid bombesin antagonist analog RM26 combined with IRDye800CW, and explored the fluorescent probe according to optical properties. Fluorescence imaging characterization in NIR-I/II region was performed in vitro and in vivo. Following simulated NIR-II image-guided surgery, we obtained time-fluorescent intensity curves and time-signal and background ratio curves. Further, we used histological sections of brain from tumor-beating mice model to compare imaging specificity between 5-aminolevulinic acid (5-ALA) and IRDye800-RM26, and evaluated biodistribution and biocompatibility. IRDye800-RM26 had broad emission ranging from 800 to 1200 nm, showing considerable fluorescent intensity in NIR-II region. High-resolution NIR-II imaging of IRDye800-RM26 can enhance the advantages of NIR-I imaging. Dynamic and real time fluorescence imaging in NIR-II region showed that the probe can be used to treat brain malignancies in mice between 12 and 24 h post injection. Its specificity in targeting glioblastoma was superior to 5-ALA. Biodistribution analysis indicated IRDye800-RM26 excretion in the kidney and liver. Histological and blood test analyses did not reveal acute severe toxicities in mice treated with effective dose (40 μg) of the probe for NIR-II imaging. Because of the considerable fluorescent intensity in NIR-II region and high spatial resolution, biocompatible and excretable IRDye800-RM26 holds great potentials for FGS, and is essential for translation into human 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.

Evolving strategies and application of proteins and peptide therapeutics in cancer treatment

Several proteins and peptides have therapeutic potential and can be used for cancer therapy. By binding to cell surface receptors and other indicators uniquely linked with or overexpressed on tumors compared to healthy tissue, protein biologics enhance the active targeting of cancer cells, as opposed to the passive targeting of cells by conventional small-molecule chemotherapeutics. This study focuses on peptide medications that exist to slow or stop tumor growth and the spread of cancer, demonstrating the therapeutic potential of peptides in cancer treatment. As an alternative to standard chemotherapy, peptides that selectively kill cancer cells while sparing healthy tissue are developing. A mountain of clinical evidence supports the efficacy of peptide-based cancer vaccines. Since a single treatment technique may not be sufficient to produce favourable results in the fight against cancer, combination therapy is emerging as an effective option to generate synergistic benefits. One example of this new area is the use of anticancer peptides in combination with nonpeptidic cytotoxic drugs or the combination of immunotherapy with conventional therapies like radiation and chemotherapy. This review focuses on the different natural and synthetic peptides obtained and researched. Discoveries, manufacture, and modifications of peptide drugs, as well as their contemporary applications, are summarized in this review. We also discuss the benefits and difficulties of potential advances in therapeutic peptides.

Phase I Trial of [99mTc]Tc-maSSS-PEG2-RM26, a Bombesin Analogue Antagonistic to Gastrin-Releasing Peptide Receptors (GRPRs), for SPECT Imaging of GRPR Expression in Malignant Tumors

The gastrin-releasing peptide receptor (GRPR) is overexpressed in prostate cancer (PCa) and in hormone-driven breast cancer (BCa). The aim of this phase I clinical trial was to evaluate safety, biodistribution, and dosimetry after the administration of the recently developed GRPR-targeting antagonistic bombesin analogue [99mTc]Tc-maSSS-PEG2-RM26 in PCa and BCa patients. Planar and whole-body SPECT/CT imaging was performed in six PCa patients and seven BCa patients 2, 4, 6, and 24 h post the intravenous administration of 40 µg of [99mTc]Tc-maSSS-PEG2-RM26 (600–700 MBq). No adverse events or pathological changes were observed. The rapid blood clearance of [99mTc]Tc-maSSS-PEG2-RM26 was observed with predominantly hepatobiliary excretion. The effective doses were 0.0053 ± 0.0007 for male patients and 0.008 ± 0.003 mSv/MBq for female patients. The accumulation of [99mTc]Tc-maSSS-PEG2-RM26 in tumors was observed in four out of six PCa and in seven out of seven BCa patients. In four BCa patients, a high uptake of the agent into the axillary lymph nodes was detected. Immunohistochemistry revealed positive GRPR expression in 60% of primary PCa, 71.4% of BCa tumors, and 50% of examined BCa lymph nodes. In conclusion, a single administration of [99mTc]Tc-maSSS-PEG2-RM26 was safe and well tolerated. [99mTc]Tc-maSSS-PEG2-RM26 SPECT may be useful for tumor detection in PCa and BCa patients, pending further studies.

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

Considering the wide range of therapeutic options for localized prostate cancer (e.g., active surveillance, radiation-beam therapy, focal therapy, and radical prostatectomy), accurate assessment of the aggressiveness and localization of primary prostate cancer lesions is essential for treatment decision making. National Comprehensive Cancer Network guidelines recognize prostate-specific membrane antigen (PSMA) PET/CT for use in initial staging of high-risk primary prostate cancer. The gastrin-releasing peptide receptor (GRP-R) is a neuropeptide receptor overexpressed by low-risk prostate cancer cells. We aimed to perform the first (to our knowledge) prospective head-to-head comparison of PSMA- and GRP-R-targeted imaging at initial staging to understand how PSMA PET and GRP-R PET can be used or combined in clinical practice. Methods: This was a prospective, single-center, diagnostic cross-sectional imaging study using anonymized, masked, and independent interpretations of paired PET/CT studies in 22 patients with 68Ga-PSMA-617 (a radiolabeled PSMA inhibitor) and 68Ga-RM2 (68Ga-DOTA-4-amino-1-carboxymethylpiperidine-d-Phe-Gln-Trp-Ala-Val-Gly-His-Sta-Leu-NH2, a radiolabeled GRP-R antagonist). We enrolled patients with newly diagnosed, biopsy-proven prostate cancer. None had received neoadjuvant hormone therapy or chemotherapy, and all underwent extended pelvic lymph node dissection. Histologic findings served as a reference. Results: On a lesion-based analysis (including lesions < 0.1 cm3), 68Ga-PSMA-617 PET/CT detected 74.3% (26/35) of all tumor lesions and 68Ga-RM2 PET/CT detected 78.1% (25/32; 1 patient could not be offered 68Ga-RM2 PET/CT). Paired examinations showed positive uptake of the 2 tracers in 21 of 32 lesions (65.6%), negative uptake in 5 of 32 lesions (15.6%), and discordant uptake in 6 of 32 lesions (18.8%). Uptake of 68Ga-PSMA-617 was higher when the International Society of Urological Pathology (ISUP) score was at least 4 versus at least 1 (P < 0.0001) or 2 (P = 0.0002). There were no significant differences in uptake between ISUP scores for 68Ga-RM2. Median 68Ga-RM2 SUVmax was significantly higher than median 68Ga-PSMA-617 SUVmax in the ISUP-2 subgroup (P = 0.01). Conclusion: 68Ga-PSMA-617 PET/CT is useful to depict higher, more clinically significant ISUP score lesions, and 68Ga-RM2 PET/CT has a higher detection rate for low-ISUP tumors. Combining PSMA PET and GRP-R PET allows for better classification of intraprostatic lesions.

Clinical advancement of precision theranostics in prostate cancer

Theranostic approaches with positron emission tomography/computed tomography (PET/CT) or PET/magnetic resonance imaging (PET/MRI) molecular imaging probes are being implemented clinically in prostate cancer (PCa) diagnosis and imaging-guided precision surgery. This review article provides a comprehensive summary of the rapidly expanding list of molecular imaging probes in this field, including their applications in early diagnosis of primary prostate lesions; detection of lymph node, skeletal and visceral metastases in biochemical relapsed patients; and intraoperative guidance for tumor margin detection and nerve preservation. Although each imaging probe shows preferred efficacy in some applications and limitations in others, the exploration and research efforts in this field will eventually lead to improved precision theranostics of PCa.

Clinical Pharmacology of Radiotheranostics in Oncology

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

Preclinical Characterisation of PSMA/GRPR-Targeting Heterodimer [68Ga]Ga-BQ7812 for PET Diagnostic Imaging of Prostate Cancer: A Step towards Clinical Translation

The development of radioligands targeting prostate-specific membrane antigen (PSMA) and gastrin-releasing peptide receptor (GRPR) has shown promising results for the imaging and therapy of prostate cancer. However, studies have shown that tumors and metastases can express such targets heterogeneously. To overcome this issue and to improve protein binding, radioligands with the ability to bind both PSMA and GRPR have been developed. Herein, we present the preclinical characterization of [68Ga]Ga-BQ7812; a PSMA/GRPR-targeting radioligand for the diagnostic PET imaging of prostate cancer. This study aimed to evaluate [68Ga]Ga-BQ7812 to promote the translation of such imaging probes into the clinic. [68Ga]Ga-BQ7812 demonstrated rapid and specific binding to both targets in a PSMA/GRPR-expressing PC3-pip cell line. Results from the biodistribution study in PC3-pip xenografted mice showed specific binding to both targets, with the highest activity uptake at 1 h pi in tumor (PSMA+/GRPR+, 10.4 ± 1.0% IA/g), kidneys (PSMA+, 45 ± 16% IA/g), and pancreas (GRPR+, 5.6 ± 0.7% IA/g). At 3h pi, increased tumour-to-organ ratios could be seen due to higher retention in the tumor compared with other PSMA or GRPR-expressing organs. These results, together with low toxicity and an acceptable estimated dosimetry profile (total effective dose = 0.0083 mSv/MBq), support the clinical translation of [68Ga]Ga-BQ7812 and represent a step towards its first clinical trial.

Cortical abnormalities of synaptic vesicle protein 2A in focal cortical dysplasia type II identified in vivo with 18F-SynVesT-1 positron emission tomography imaging

PURPOSE

The loss of synaptic vesicle glycoprotein 2A (SV2A) is well established as the major correlate of epileptogenesis in focal cortical dysplasia type II (FCD II), but this has not been directly tested in vivo. In this positron emission tomography (PET) study with the new tracer ¹⁸F-SynVesT-1, we evaluated SV2A abnormalities in patients with FCD II and compared the pattern to ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG).

METHODS

Sixteen patients with proven FCD II and 16 healthy controls were recruited. All FCD II patients underwent magnetic resonance imaging (MRI) and static PET imaging with both ¹⁸F-SynVesT-1 and ¹⁸F-FDG, while the controls underwent MRI and PET with only ¹⁸F-SynVesT-1. Visual assessment of PET images was undertaken. The standardized uptake values (SUVs) of ¹⁸F-SynVesT-1 were computed for regions of interest (ROIs), along with SUV ratio (SUVr) between ROI and centrum semiovale (white matter). Asymmetry indices (AIs) were analyzed between the lesion and the contralateral hemisphere for intersubject comparisons.

RESULTS

Lesions in the brains of FCD II patients had significantly reduced ¹⁸F-SynVesT-1 uptake compared with contralateral regions, and brains of the controls. ¹⁸F-SynVesT-1 PET indicated low lesion uptake in 14 patients (87.5%), corresponding to hypometabolism detected by ¹⁸F-FDG PET, with higher accuracy for lesion localization than MRI (43.8%) (P < 0.05). AI analyses demonstrated that in the lesions, SUVr for each of the radiotracers were not significantly different (P > 0.05), and ¹⁸F-SynVesT-1 SUVr correlated with that of ¹⁸F-FDG across subjects (R² = 0.41, P = 0.008). Subsequent visual ratings indicated that ¹⁸F-SynVesT-1 uptake had a more restricted pattern of reduction than ¹⁸F-FDG uptake in FCD II lesions (P < 0.05).

CONCLUSION

SV2A PET with ¹⁸F-SynVesT-1 shows a higher accuracy for the localization of FCD II lesions than MRI and a more restricted pattern of abnormality than ¹⁸F-FDG PET.

GRPr Theranostics: Current Status of Imaging and Therapy using GRPr Targeting Radiopharmaceuticals

Addressing molecular targets, that are overexpressed by various tumor entities, using radiolabeled molecules for a combined diagnostic and therapeutic (theranostic) approach is of increasing interest in oncology. The gastrin-releasing peptide receptor (GRPr), which is part of the bombesin family, has shown to be overexpressed in a variety of tumors, therefore, serving as a promising target for those theranostic applications. A large amount of differently radiolabeled bombesin derivatives addressing the GRPr have been evaluated in the preclinical as well as clinical setting showing fast blood clearance and urinary excretion with selective GRPr-binding. Most of the available studies on GRPr-targeted imaging and therapy have evaluated the theranostic approach in prostate and breast cancer applying bombesin derivatives tagged with the predominantly used theranostic pair of ⁶⁸Ga/¹⁷⁷Lu which is the focus of this review.

Clinical Evaluation of Nuclear Imaging Agents in Breast Cancer

Precision medicine is the customization of therapy for specific groups of patients using genetic or molecular profiling. Noninvasive imaging is one strategy for molecular profiling and is the focus of this review. The combination of imaging and therapy for precision medicine gave rise to the field of theranostics. In breast cancer, the detection and quantification of therapeutic targets can help assess their heterogeneity, especially in metastatic disease, and may help guide clinical decisions for targeted treatments. Positron emission tomography (PET) or single-photon emission tomography (SPECT) imaging has the potential to play an important role in the molecular profiling of therapeutic targets in vivo for the selection of patients who are likely to respond to corresponding targeted therapy. In this review, we discuss the state-of-the-art nuclear imaging agents in clinical research for breast cancer. We reviewed 17 clinical studies on PET or SPECT agents that target 10 different receptors in breast cancer. We also discuss the limitations of the study designs and of the imaging agents in these studies. Finally, we offer our perspective on which imaging agents have the highest potential to be used in clinical practice in the future.

Towards Complete Tumor Resection: Novel Dual-Modality Probes for Improved Image-Guided Surgery of GRPR-Expressing Prostate Cancer

Nuclear and optical dual-modality probes can be of great assistance in prostate cancer localization, providing the means for both preoperative nuclear imaging and intraoperative surgical guidance. We developed a series of probes based on the backbone of the established GRPR-targeting radiotracer NeoB. The inverse electron demand of the Diels–Alder reaction was used to integrate the sulfo-cyanine 5 dye. Indium-111 radiolabeling, stability studies and a competition binding assay were carried out. Pilot biodistribution and imaging studies were performed in PC-3 tumor-bearing mice, using the best two dual-labeled probes. The dual-modality probes were radiolabeled with a high yield (>92%), were proven to be hydrophilic and demonstrated high stability in mouse serum (>94% intact labeled ligand at 4 h). The binding affinity for the GRPR was in the nanomolar range (21.9–118.7 nM). SPECT/CT images at 2 h p.i. clearly visualized the tumor xenograft and biodistribution studies, after scanning confirmed the high tumor uptake (8.47 ± 0.46%ID/g and 6.90 ± 0.81%ID/g for probe [111In]In-12 and [111In]In-15, respectively). Receptor specificity was illustrated with blocking studies, and co-localization of the radioactive and fluorescent signal was verified by ex vivo fluorescent imaging. Although optimal tumor-to-blood and tumor-to-kidney ratios might not yet have been reached due to the prolonged blood circulation, our probes are promising candidates for the preoperative and intraoperative visualization of GRPR-positive prostate cancer.

Dual-tracer PET/CT-targeted, mpMRI-targeted, systematic biopsy, and combined biopsy for the diagnosis of prostate cancer: a pilot study

PURPOSE

Growing evidence proved the efficacy of multi-parametric MRI (mpMRI) and prostate-specific membrane antigen (PSMA) positron emission tomography/computed tomography (PET/CT)-guided targeted biopsy (TB) in prostate cancer (PCa) diagnosis, but there is no direct comparison between mpMRI-TB and PSMA PET/CT-TB. Gastrin-releasing peptide receptor (GRPR) is highly expressed in PCa, which can compensate for the unstable expression of PSMA in PCa. Therefore, we designed a study to compare the efficiency of mpMRI-TB, dual-tracer (GRPR and PSMA) PET/CT-TB, systematic biopsy, and combined biopsy for the diagnosis of prostate cancer.

METHODS

One hundred twelve suspicious PCa patients were enrolled from September 2020 to June 2021. Patients with anyone of positive dual-tracer PET/CT or mpMRI underwent TB, and all enrolled patients underwent systematic biopsy (SB) after TB. The primary outcome was the detection rates of PCa in different biopsy strategies. Secondary outcomes were the performance of three imaging methods, omission diagnostic rates, and upgrading and downgrading of biopsy samples relative to those of prostatectomy specimens in different biopsy strategies. McNemar's tests and Bonferroni correction in multiple comparisons were used to compare the primary and secondary outcomes.

RESULTS

In 112 men, clinically significant PCa (grade group[GG] ≥ 2) accounted for 34.82% (39/112), and nonclinically significant PCa (GG = 1) accounted for 4.46% (5/112). ⁶⁸ Ga-PSMA PET/CT-TB achieved higher PCa detection rate (69.77%) and positive ratio of biopsy cores (0.44) compared with SB (39.29% and 0.12) and mpMRI-TB (36.14% and 0.23), respectively (P < 0.005). Dual-tracer PET/CT screen out patients for avoiding 52.67% (59/112) unnecessary biopsy, whereas dual-tracer PET/CT-TB plus SB achieved high detection rate (77.36%) without misdiagnosis of csPCa.

CONCLUSION

Dual-tracer PET/CT might screen patients for avoiding unnecessary biopsy. Dual-tracer PET/CT-TB plus SB might be a more effective and promising strategy for the definite diagnosis of clinically significant PCa than mpMRI-TB.

A new fluorescently labeled bisphosphonate for theranostics in tumor bone metastasis

Bone metastasis of malignant solid tumors has become one of the most serious complications, especially in breast cancer, which was particularly challenging for early detection and treatment in clinical practice. In this work, we reported a new fluorescently labeled bisphosphonate for bone metastasis detection of breast cancer. The designed probes were based on Rhodamine B and bisphosphonate as recognition group, which can specifically target hydroxyapatite (HA) existed in bone tissue. After the osteoclasts were adsorbed on the bone surface, the surrounding microenvironment was acidified, causing the HA to locally dissolve. The probe bound to the HA was then released, and realized the fluorescence turn on under acidic conditions. In vitro experiments showed that G0 was more excellent than G2 owing to shorter connecting arm. Subsequently, we proved that G0 could combine with HA rapidly and exhibit excellent response in solid state. More importantly, we established a model of bone metastasis with MDA-MB-231 cells which was similar to the clinical cases and evaluated the theranostics value of G0 prospectively, which provide the potential application prospect in clinical.

Radiolabeled Bombesin Analogs

Simple Summary

Recent medical advancements have strived for a personalized medicine approach to patients, aimed at optimizing therapy outcomes with minimum toxicity. In this respect, nuclear medicine methodologies have been playing increasingly important roles. For example, the overexpression of peptide receptors, such as the gastrin-releasing peptide receptor (GRPR), on tumor cells as opposed to their lack of expression in healthy surrounding tissues can be elegantly exploited with the aid of “smart” peptide carriers, such as the analogs of the amphibian 14-peptide bombesin (BBN). These molecules can bring clinically attractive radionuclides to malignant lesions in prostate, breast, and other human cancers, sparing healthy tissues. Depending upon the radionuclide in question, diagnostic imaging with single-photon emission computed tomography (SPECT) or positron emission tomography (PET) has been pursued, identifying patients who are eligible for peptide radionuclide receptor therapy (PRRT) in an integrated “theranostic” approach. In the present review, we (i) discuss the major steps taken in the development of anti-GRPR theranostic radioligands, with a focus on those selected for clinical testing; (ii) comment on the present status in this field of research; and (iii) reflect on the current limitations as well as on new opportunities for their broader and more successful clinical applications.

Abstract

The gastrin-releasing peptide receptor (GRPR) is expressed in high numbers in a variety of human tumors, including the frequently occurring prostate and breast cancers, and therefore provides the rationale for directing diagnostic or therapeutic radionuclides on cancer lesions after administration of anti-GRPR peptide analogs. This concept has been initially explored with analogs of the frog 14-peptide bombesin, suitably modified at the N-terminus with a number of radiometal chelates. Radiotracers that were selected for clinical testing revealed inherent problems associated with these GRPR agonists, related to low metabolic stability, unfavorable abdominal accumulation, and adverse effects. A shift toward GRPR antagonists soon followed, with safer analogs becoming available, whereby, metabolic stability and background clearance issues were gradually improved. Clinical testing of three main major antagonist types led to promising outcomes, but at the same time brought to light several limitations of this concept, partly related to the variation of GRPR expression levels across cancer types, stages, previous treatments, and other factors. Currently, these parameters are being rigorously addressed by cell biologists, chemists, nuclear medicine physicians, and other discipline practitioners in a common effort to make available more effective and safe state-of-the-art molecular tools to combat GRPR-positive tumors. In the present review, we present the background, current status, and future perspectives of this endeavor.

Molecular Imaging in Primary Staging of Prostate Cancer Patients: Current Aspects and Future Trends

Accurate primary staging is the cornerstone in all malignancies. Different morphological imaging modalities are employed in the evaluation of prostate cancer (PCa). Regardless of all developments in imaging, invasive histopathologic evaluation is still the standard method for the detection and staging of the primary PCa. Magnetic resonance imaging (MRI) and computed tomography (CT) play crucial roles; however, functional imaging provides additional valuable information, and it is gaining ever-growing acceptance in the management of PCa. Targeted imaging with different radiotracers has remarkably evolved in the past two decades. [111In]In-capromab pendetide scintigraphy was a new approach in the management of PCa. Afterwards, positron emission tomography (PET) tracers such as [11C/18F]choline and [11C]acetate were developed. Nevertheless, none found a role in the primary staging. By introduction of the highly sensitive small molecule prostate-specific membrane antigen (PSMA) PET/CT, as well as recent developments in MRI and hybrid PET/MRI systems, non-invasive staging of PCa is being contemplated. Several studies investigated the role of these sophisticated modalities in the primary staging of PCa, showing promising results. Here, we recapitulate the role of targeted functional imaging. We briefly mention the most popular radiotracers, their diagnostic accuracy in the primary staging of PCa, and impact on patient management.

Potential Targets Other Than PSMA for Prostate Cancer Theranostics: A Systematic Review

Background: Prostate-specific membrane antigen (PSMA) is not sufficiently overexpressed in a small proportion of prostate cancer (PCa) patients, who require other strategies for imaging and/or treatment. We reviewed potential targets other than PSMA for PCa theranostics in nuclear medicine that have already been tested in humans. Methods: We performed a systematic web search in the PubMed and Cochrane databases, with no time restrictions by pooling terms (“prostate cancer”, “prostatic neoplasms”) and (“radioligand”, “radiotracer”). Included articles were clinical studies. The results were synthetized by the target type. Results: We included 38 studies on six different targets: gastrin-releasing peptide receptors (GRPRs) (n = 23), androgen receptor (n = 11), somatostatin receptors (n = 6), urokinase plasminogen activator surface receptor (n = 4), fibroblast activation protein (n = 2 studies) and integrin receptors (n = 1). GRPRs, the most studied target, has a lower expression in high-grade PCa, CRPC and bone metastases. Its use might be of higher interest in treating earlier stages of PCa or low-grade PCa. Radiolabeled fibroblast activation protein inhibitors were the most recent and promising molecules, but specific studies reporting their interest in PCa are needed. Conclusion: Theranostics in nuclear medicine will continue to develop in the future, especially for PCa patients. Targets other than PSMA exist and deserve to be promoted.

Prostate cancer: Molecular imaging and MRI

The role of molecular imaging in initial evaluation of men with presumed or established diagnosis of prostate cancer and work up of biochemical recurrence and metastatic disease is rapidly evolving due to superior diagnostic performance compared to anatomic imaging. However, variable tumor biology and expression of transmembrane proteins or metabolic alterations poses a challenge. We review the evidence and controversies with emphasis on emerging PET radiopharmaceuticals and experience on clinical utility of PET/CT and PET/MRI in diagnosis and management of prostate cancer.

A New, Second Generation Trithiol Bifunctional Chelate for 72,77As: Trithiol(b)-(Ser)2-RM2

Trithiol chelates are suitable for labeling radioarsenic (72As: 2.49 MeV β+, 26 h; 77As: 0.683 MeV β-, 38.8 h) to form potential theranostic radiopharmaceuticals for positron emission tomography (PET) imaging and therapy. A trithiol(b)-(Ser)2-RM2 bioconjugate and its arsenic complex were synthesized and characterized. The trithiol(b)-(Ser)2-RM2 bioconjugate was radiolabeled with no-carrier-added 77As in over 95% radiochemical yield and was stable for over 48 h, and in vitro IC50 cell binding studies of [77As]As-trithiol(b)-(Ser)2-RM2 in PC-3 cells demonstrated high affinity for the gastrin-releasing peptide (GRP) receptor (low nanomolar range). Limited biodistribution studies in normal mice were performed with HPLC purified 77As-trithiol(b)-(Ser)2-RM2 demonstrating both pancreatic uptake and hepatobiliary clearance.