Gastrin-releasing Peptide Receptor Research Articles

68Ga-PSMA and 68Ga-DOTA-RM2 PET/MRI in Recurrent Prostate Cancer: Diagnostic Performance and Association with Clinical and Histopathological Data.

Simple SummaryProstate cancer (PCa) relapse occurs in up to 50% of patients after radical treatment. Once PCa recurrence is detected, a precise identification of the number and sites of recurrence is necessary to tailor the treatment on the patient’s needs. Positron emission tomography (PET) plays a pivotal role in this clinical setting and new radiotracers have been developed to improve its performance. While 68Ga-PSMA is a well-established radiotracer for PCa recurrence detection, 68Ga-DOTA-RM2 is a recently proposed tracer that targets the gastrin-releasing peptide receptors that are overexpressed in prostate cancer. In this work, the performance of 68Ga-PSMA and 68Ga-DOTA-RM2 PET/MRI in identifying recurrent disease were compared on the same cohort, using the same study protocol, as this is the only way to assess whether one outperforms the other and therefore should be preferred in clinical practice. Furthermore, the association between PET findings and clinical and histopathological characteristics was investigated to find potential biomarkers.The aim of the present study is to investigate and compare the performances of 68Ga-PSMA and 68Ga-DOTA-RM2 PET/MRI in identifying recurrent prostate cancer (PCa) after primary treatment and to explore the association of dual-tracer PET findings with clinical and histopathological characteristics. Thirty-five patients with biochemical relapse (BCR) of PCa underwent 68Ga PSMA PET/MRI for restaging purpose, with 31/35 also undergoing 68Ga-DOTA-RM2 PET/MRI scan within 16 days (mean: 3 days, range: 2–16 days). Qualitative and quantitative image analysis has been performed by comparing 68Ga-PSMA and 68Ga-DOTA-RM2 PET/MRI findings both on a patient and lesion basis. Clinical and instrumental follow-up was used to validate PET findings. Fisher’s exact test and Mann-Whitney U test were used to investigate the association between dual-tracer PET findings, clinical and histopathological data. p-value significance was defined below the 0.05 level. Patients’ mean age was 70 years (range: 49–84) and mean PSA at time of PET/MR scans was 1.88 ng/mL (range: 0.21–14.4). A higher detection rate was observed for 68Ga-PSMA PET/MRI, with more lesions being detected compared to 68Ga-DOTA-RM2 PET/MRI (26/35 patients, 95 lesions vs. 15/31 patients, 41 lesions; p = 0.016 and 0.002). 68Ga-PSMA and 68Ga-DOTA-RM2 PET/MRI findings were discordant in 11/31 patients; among these, 10 were 68Ga-PSMA positive (9/10 confirmed as true positive and 1/10 as false positive by follow-up examination). Patients with higher levels of PSA and shorter PSA doubling time (DT) presented more lesions on 68Ga-PSMA PET/MRI (p = 0.006 and 0.044), while no association was found between PET findings and Gleason score. 68Ga-PSMA has a higher detection rate than 68Ga-DOTA-RM2 in detecting PCa recurrence. The number of 68Ga-PSMA PET positive lesions is associated with higher levels of PSA and shorter PSA DT, thus representing potential prognostic factors.

Radiosynthesis and biological evaluation of 18F-labeled bispecific heterodimer targeted dual gastrin-releasing peptide receptor and prostate-specific membrane antigen for prostate cancer imaging.

Approximately 5% of prostatic primary tumors and 15% of metastatic tumors were found to be prostate-specific membrane antigen (PSMA)-negative. Targeting gastrin-releasing peptide receptor (GRPR) has been shown to complement patients with PSMA-negative prostate cancer (PCa). Based on previous findings, simultaneously targeting PSMA and GRPR imaging may improve the diagnosis of PCa. In this study, we report the radiosynthesis and biological evaluation of a bispecific heterodimer of NOTA-GRPR-PSMA that targeted both PSMA and GRPR for extended PCa imaging. NOTA-GRPR-PSMA was labeled using the Al18F-chelating one-step method. The competitive combination experiment and specific binding assay were performed in vitro using 22Rv1 (PSMA+) and PC-3 (GRPR+) cells. To determine the distribution and specificity in vivo, biodistribution and micro-PET/computed tomography of [18F]AlF-GRPR-PSMA were performed on mice bearing 22Rv1 or PC-3 tumors. [18F]AlF-GRPR-PSMA had a radiochemical purity of over 98% and demonstrated high stability in vivo and in vitro, with a LogD of -1.2 ± 0.05. Cell uptake and inhibition studies of [18F]AlF-GRPR-PSMA in 22Rv1 and PC-3 cells revealed bispecific GRPR and PSMA bindings. According to the biodistribution study and PET imaging, [18F]AlF-GRPR-PSMA was mainly excreted through the kidney. Tumor uptake was high in 22Rv1 tumor (10.1 ± 0.4 %ID/g) and moderate in PC-3 tumor (2.1 ± 0.6 %ID/g) 2 h p.i., whereas blocking studies significantly decreased the tumor uptake of 22Rv1 and PC-3. [18F]AlF-GRPR-PSMA has the potential to simultaneously target PSMA and GRPR for PCa imaging.

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

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. 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. 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). 68Ga-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. 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.

Gastrin-Releasing Peptide Receptor Antagonist [68Ga]RM2 PET/CT for Staging of Pre-Treated, Metastasized Breast Cancer.

Simple Summary[68Ga]RM2 positron emission tomography (PET)/computed tomography (CT) has shown to be a promising imaging method for primary breast cancer (BC) with positive estrogen receptor (ER) status, but it has not been tested for visualization of metastasized recurrent or progressive BC. The aim of this pilot study was to assess tumor visualization using [68Ga]RM2 PET/CT in patients with pre-treated ER-positive BC and suspected metastases. Eight female patients with initial ER-positive, pre-treated BC were included in this retrospective study. Strong RM2 binding was found in all metastatic lesions of six patients, whereas two patients were rated RM2-negative. Our data suggest that RM2 binding is maintained in the majority of patients with advanced disease stage of pre-treated ER-positive BC. Thus, [68Ga]RM2 PET/CT could support treatment decision in these patients, radiotherapy planning in oligometastatic patients or selection of patients for RM2 radioligand therapy.Background: Positron emission tomography (PET)/computed tomography (CT) using the gastrin-releasing peptide receptor antagonist [68Ga]RM2 has shown to be a promising imaging method for primary breast cancer (BC) with positive estrogen receptor (ER) status. This study assessed tumor visualization by [68Ga]RM2 PET/CT in patients with pre-treated ER-positive BC and suspected metastases. Methods: This retrospective pilot study included eight female patients with initial ER-positive, pre-treated BC who underwent [68Ga]RM2 PET/CT. Most of these patients (seven out of eight; 88%) were still being treated with or had received endocrine therapy. [68Ga]RM2 PET/CTs were visually analyzed by two nuclear medicine specialists in consensus. Tumor manifestations were rated qualitatively (i.e., RM2-positive or RM2-negative) and quantitatively using the maximum standardized uptake value (SUVmax). SUVmax values were compared between the two subgroups (RM2-positive vs. RM2-negative). Results: Strong RM2 binding was found in all metastatic lesions of six patients (75%), whereas tracer uptake in all metastases of two patients (25%) was rated negative. Mean SUVmax of RM2-positive metastases with the highest SUVmax per patient (in lymph node and bone metastases; 15.8 ± 15.1 range: 3.7–47.8) was higher than mean SUVmax of the RM2-negative metastases with the highest SUVmax per patient (in bone metastases; 1.6 ± 0.1, range 1.5–1.7). Conclusions: Our data suggest that RM2 binding is maintained in the majority of patients with advanced disease stage of pre-treated ER-positive BC. Thus, [68Ga]RM2 PET/CT could support treatment decision in these patients, radiotherapy planning in oligometastatic patients or selection of patients for RM2 radioligand therapy. Further studies with larger patient cohorts are warranted to confirm these findings.

Regulation of Gastric Acid Secretion of Liriope platyphylla Extract in Gastroesophageal Reflux Disease

Objectives: The purpose of this study was to confirm the effects of Liriope platyphylla extract on relieving Gastroesophageal reflux disease (GERD) through regulation of acid secretion.Methods: 8-week-old ICR mice were divided into untreated control group (Ctrl), GERD elecitation group (GERDE), Omeprazole administrate group before GERD elicitation (OMA), and Liriope platyphylla extract administrate group before GERD elicitation (LPA). After inducing GERD, gross observation and histological examination were performed and ATP6V1B1 (ATPase H+ Transporting V1 Subunit B1), GRPR (Gastrin-releasing peptide receptor), COX-1 (Cyclooxygenase 1), 8-OHdG (8-hydroxy-2’-deoxyguanosine), Cathelicidin, p-JNK (phospho c-Jun N-terminal kinase) were observed to confirm the damage defense effect of the esophageal mucosa, acid secretion regulation, antioxidant, anti-inflammatory, mucosal protection, and apoptosis regulationResults: OMA and LPA showed lower levels of damage compared to GERDE in gross observation and histological examination. ATP6V1B1, GRPR, and 8-OHdG showed lower positive reactions in OMA and LPA than in GERDE. COX-1 were less positive in GERDE and OMA than in Ctrl, but showed higher secretion in LPA than in Ctrl. Cathelicidin showed a decreased positive reaction in GERDE, OMA and LPA compared to Ctrl, but the decrease in positive reaction was smaller in OMA and LPA compared to GERDE. p-JNK showed increased positive reaction in GERDE, OMA and LPA than in Ctrl, but the increase in the positive reaction was smaller in the OMA and LPA compared to GERDE.Conclusions: The effects of Liriope platyphylla extract on esophageal mucosal damage protection, acid secretion regulation, antioxidant, anti-inflammatory, mucosal protection and apoptosis regulation were confirmed.

Exploring the signaling space of a GPCR using bivalent ligands with a rigid oligoproline backbone

G protein-coupled receptors (GPCRs) are one of the most important drug-target classes in pharmaceutical industry. Their diversity in signaling, which can be modulated with drugs, permits the design of more effective and better-tolerated therapeutics. In this work, we have used rigid oligoproline backbones to generate bivalent ligands for the gastrin-releasing peptide receptor (GRPR) with a fixed distance between their recognition motifs. This allows the stabilization of GPCR dimers irrespective of their physiological occurrence and relevance, thus expanding the space for medicinal chemistry. Specifically, we observed that compounds presenting agonists or antagonists at 20- and 30-Å distance induce GRPR dimerization. Furthermore, we found that 1) compounds with two agonists at 20- and 30-Å distance that induce dimer formation show bias toward Gq efficacy, 2) dimers with 20- and 30-Å distance have different potencies toward β-arrestin-1 and β-arrestin-2, and 3) the divalent agonistic ligand with 10-Å distance specifically reduces Gq potency without affecting β-arrestin recruitment, pointing toward an allosteric effect. In summary, we show that rigid oligoproline backbones represent a tool to develop ligands with biased GPCR signaling.

Radiolabeled Bombesin Analogs

Simple SummaryRecent 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.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.

Radionuclide-Based Imaging of Breast Cancer: State of the Art.

Simple SummaryBreast cancer is one of the most commonly diagnosed malignant tumors, possessing high incidence and mortality rates that threaten women’s health. Thus, early and effective breast cancer diagnosis is crucial for enhancing the survival rate. Radionuclide molecular imaging displays its advantages for detecting breast cancer from a functional perspective. Noninvasive visualization of biological processes with radionuclide-labeled small metabolic compounds helps elucidate the metabolic state of breast cancer, while radionuclide-labeled ligands/antibodies for receptor-targeted radionuclide molecular imaging is sensitive and specific for visualization of the overexpressed molecular markers in breast cancer. This review focuses on the most recent developments of novel radiotracers as promising tools for early breast cancer diagnosis.Breast cancer is a malignant tumor that can affect women worldwide and endanger their health and wellbeing. Early detection of breast cancer can significantly improve the prognosis and survival rate of patients, but with traditional anatomical imagine methods, it is difficult to detect lesions before morphological changes occur. Radionuclide-based molecular imaging based on positron emission tomography (PET) and single-photon emission computed tomography (SPECT) displays its advantages for detecting breast cancer from a functional perspective. Radionuclide labeling of small metabolic compounds can be used for imaging biological processes, while radionuclide labeling of ligands/antibodies can be used for imaging receptors. Noninvasive visualization of biological processes helps elucidate the metabolic state of breast cancer, while receptor-targeted radionuclide molecular imaging is sensitive and specific for visualization of the overexpressed molecular markers in breast cancer, contributing to early diagnosis and better management of cancer patients. The rapid development of radionuclide probes aids the diagnosis of breast cancer in various aspects. These probes target metabolism, amino acid transporters, cell proliferation, hypoxia, estrogen receptor (ER), progesterone receptor (PR), human epidermal growth factor receptor 2 (HER2), gastrin-releasing peptide receptor (GRPR) and so on. This article provides an overview of the development of radionuclide molecular imaging techniques present in preclinical or clinical studies, which are used as tools for early breast cancer diagnosis.

Refeeding activates neurons in the dorsomedial hypothalamus to inhibit food intake and promote positive valence

ObjectiveThe regulation of food intake is a major research area in the study of obesity, which plays a key role in the development of metabolic syndrome. Gene targeting studies have clarified the roles of hypothalamic neurons in feeding behavior, but the deletion of a gene has a long-term effect on neurophysiology. Our understanding of short-term changes such as appetite under physiological conditions is therefore still limited. MethodsTargeted recombination in active populations (TRAP) is a newly developed method for labeling active neurons by using tamoxifen-inducible Cre recombination controlled by the promoter of activity-regulated cytoskeleton-associated protein (Arc/Arg3.1), a member of immediate early genes. Transgenic mice for TRAP were fasted overnight, re-fed with normal diet, and injected with 4-hydroxytamoxifen 1 h after the refeeding to label the active neurons. The role of labeled neurons was examined by expressing excitatory or inhibitory designer receptors exclusively activated by designer drugs (DREADDs). The labeled neurons were extracted and RNA sequencing was performed to identify genes that are specifically expressed in these neurons. ResultsFasting-refeeding activated and labeled neurons in the compact part of the dorsomedial hypothalamus (DMH) that project to the paraventricular hypothalamic nucleus. Chemogenetic activation of the labeled DMH neurons decreased food intake and developed place preference, an indicator of positive valence. Chemogenetic activation or inhibition of these neurons had no influence on the whole-body glucose metabolism. The labeled DMH neurons expressed prodynorphin (pdyn), gastrin-releasing peptide (GRP), cholecystokinin (CCK), and thyrotropin-releasing hormone receptor (Trhr) genes. ConclusionsWe identified a novel cell type of DMH neurons that can inhibit food intake and promote feeding-induced positive valence. Our study provides insight into the role of DMH and its molecular mechanism in the regulation of appetite and emotion.

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.

A neuropeptide code for itch.

Itch is one of the most primal sensations, being both ubiquitous and important for the well-being of animals. For more than a century, a desire to understand how itch is encoded by the nervous system has prompted the advancement of many theories. Within the past 15 years, our understanding of the molecular and neural mechanisms of itch has undergone a major transformation, and this remarkable progress continues today without any sign of abating. Here I describe accumulating evidence that indicates that itch is distinguished from pain through the actions of itch-specific neuropeptides that relay itch information to the spinal cord. According to this model, classical neurotransmitters transmit, inhibit and modulate itch information in a context-, space- and time-dependent manner but do not encode itch specificity. Gastrin-releasing peptide (GRP) is proposed to be a key itch-specific neuropeptide, with spinal neurons expressing GRP receptor (GRPR) functioning as a key part of a convergent circuit for the conveyance of peripheral itch information to the brain.

99mTc]Tc-DB15 in GRPR-Targeted Tumor Imaging with SPECT: From Preclinical Evaluation to the First Clinical Outcomes.

Simple SummaryRadiolabeled gastrin-releasing peptide receptor (GRPR)-antagonists have been proposed for diagnostic imaging and radionuclide therapy—theranostics—of human tumors, including prostate (PC) and breast cancer (BC). We herein present [99mTc]Tc-DB15, a SPECT radiotracer based on the potent GRPR-antagonist [DPhe6,LeuNHEt13]BBN(6-13). After Sar11/Gly11-replacement an acyclic tetraamine was coupled at the N-terminus via a spacer allowing for stable binding of the diagnostic radiometal Tc-99m. The forming [99mTc]Tc-DB15 radiotracer displayed high in vitro uptake in GRPR-expressing mammary (T-47D) and prostate cancer (PC-3) cells. Furthermore, it showed an attractive biodistribution profile in mice bearing T-47D or PC-3 xenografts. A pilot proof-of-principle study of [99mTc]Tc-DB15 in PC and BC patients applying SPECT is currently under way. Promising results from the first two BC patients are presented herein.Diagnostic imaging and radionuclide therapy of prostate (PC) and breast cancer (BC) using radiolabeled gastrin-releasing peptide receptor (GRPR)-antagonists represents a promising approach. We herein propose the GRPR-antagonist based radiotracer [99mTc]Tc-DB15 ([99mTc]Tc-N4-AMA-DGA-DPhe6,Sar11,LeuNHEt13]BBN(6-13); N4: 6-carboxy-1,4,8,11-tetraazaundecane, AMA: aminomethyl-aniline, DGA: diglycolic acid) as a new diagnostic tool for GRPR-positive tumors applying SPECT/CT. The uptake of [99mTc]Tc-DB15 was tested in vitro in mammary (T-47D) and prostate cancer (PC-3) cells and in vivo in T-47D or PC-3 xenograft-bearing mice as well as in BC patients. DB15 showed high GRPR-affinity (IC50 = 0.37 ± 0.03 nM) and [99mTc]Tc-DB15 strongly bound to the cell-membrane of T-47D and PC-3 cells, according to a radiolabeled antagonist profile. In mice, the radiotracer showed high and prolonged GRPR-specific uptake in PC-3 (e.g., 25.56 ± 2.78 %IA/g vs. 0.72 ± 0.12 %IA/g in block; 4 h pi) and T-47D (e.g., 15.82 ± 3.20 %IA/g vs. 3.82 ± 0.30 %IA/g in block; 4 h pi) tumors, while rapidly clearing from background. In patients with advanced BC, the tracer could reveal several bone and soft tissue metastases on SPECT/CT. The attractive pharmacokinetic profile of [99mTc]DB15 in mice and its capability to target GRPR-positive BC lesions in patients highlight its prospects for a broader clinical use, an option currently being explored by ongoing clinical studies.

Bombesin-like peptide recruits disinhibitory cortical circuits and enhances fear memories

Disinhibitory neurons throughout the mammalian cortex are powerful enhancers of circuit excitability and plasticity. The differential expression of neuropeptide receptors in disinhibitory, inhibitory, and excitatory neurons suggests that each circuit motif may be controlled by distinct neuropeptidergic systems. Here, we reveal that a bombesin-like neuropeptide, gastrin-releasing peptide (GRP), recruits disinhibitory cortical microcircuits through selective targeting and activation of vasoactive intestinal peptide (VIP)-expressing cells. Using a genetically encoded GRP sensor, optogenetic anterograde stimulation, and trans-synaptic tracing, we reveal that GRP regulates VIP cells most likely via extrasynaptic diffusion from several local and long-range sources. Invivo photometry and CRISPR-Cas9-mediated knockout of the GRP receptor (GRPR) in auditory cortex indicate that VIP cells are strongly recruited by novel sounds and aversive shocks, and GRP-GRPR signaling enhances auditory fear memories. Our data establish peptidergic recruitment of selective disinhibitory cortical microcircuits as a mechanism to regulate fear memories.

Synthesis, Characterization and In Vitro Evaluation of Hybrid Monomeric Peptides Suited for Multimodal Imaging by PET/OI: Extending the Concept of Charge-Cell Binding Correlation.

In the context of hybrid multimodal imaging agents for gastrin releasing peptide receptor (GRPR) targeting, a correlation between the net charge and the receptor affinity of the agents was recently found. In particular, a decrease in in vitro GRPR binding affinity was observed in case of an increasing number of negative charges for dually labeled GRPR-specific peptide dimers suited for positron emission tomography and optical imaging (PET/OI). This adverse influence of anionic charges could be in part compensated by a higher valency of peptide multimerization. However, it remains unknown whether this adverse effect of anionic charges is limited to peptide multimers or if it is also found or even more pronounced when GRPR-specific peptide monomers are dually labeled with fluorescent dye and chelating agent/radionuclide. Moreover, it would be important to know if this effect is limited to GRPR-specific agents only or if these observations also apply to other dually labeled peptides binding to other receptor types. To address these questions, we synthesized hybrid labels, comprising a chelator, different fluorescent dyes carrying different net charges and a functional group for bioconjugation and introduced them into different peptides, specifically targeting the GRPR, the melanocortin-1 receptor (MC1R) and integrin αvβ3. The synthesized conjugates were evaluated with regard to their chemical, radiochemical, photophysical and receptor affinity properties. It was found that neither the 68Ga-radiolabeling nor the fluorescence characteristics of the dyes were altered by the conjugation of the MIUs to the peptides. Further, it was confirmed that the net number of anionic charges has a negative effect on the GRPR-binding affinity of the GRPR-targeting MIU-peptide monomer conjugates and that this same effect was also found to the same extent for the other receptor systems studied.

Sexual Experience Induces the Expression of Gastrin-Releasing Peptide and Oxytocin Receptors in the Spinal Ejaculation Generator in Rats.

Male sexual function in mammals is controlled by the brain neural circuits and the spinal cord centers located in the lamina X of the lumbar spinal cord (L3–L4). Recently, we reported that hypothalamic oxytocin neurons project to the lumbar spinal cord to activate the neurons located in the dorsal lamina X of the lumbar spinal cord (dXL) via oxytocin receptors, thereby facilitating male sexual activity. Sexual experiences can influence male sexual activity in rats. However, how this experience affects the brain–spinal cord neural circuits underlying male sexual activity remains unknown. Focusing on dXL neurons that are innervated by hypothalamic oxytocinergic neurons controlling male sexual function, we examined whether sexual experience affects such neural circuits. We found that >50% of dXL neurons were activated in the first ejaculation group and ~30% in the control and intromission groups in sexually naïve males. In contrast, in sexually experienced males, ~50% of dXL neurons were activated in both the intromission and ejaculation groups, compared to ~30% in the control group. Furthermore, sexual experience induced expressions of gastrin-releasing peptide and oxytocin receptors in the lumbar spinal cord. This is the first demonstration of the effects of sexual experience on molecular expressions in the neural circuits controlling male sexual activity in the spinal cord.

Structure–activity relationship studies on Pd176252 derivatives leading to discovery of novel GRP receptor antagonist with potent anticancer activity

Structure–activity relationship studies on Pd176252 derivatives leading to discovery of novel GRP receptor antagonist with potent anticancer activity

Engineering of 177Lu-labeled gold encapsulated into dendrimeric nanomaterials for the treatment of lung cancer

As a novel type of theranostic radioactive agents, 177Lu-labeled nanomaterials conjugated to macromolecules have been described. The study aimed to fabricate PAMAM-G4–(177Lu–dendrimer)–bombesin–folate in the dendrimeric cavity, assess the radiopharmaceutical ability for specifically targeted radiotherapy and simultaneously detects gastrin-releasing peptide receptors (GRPR) and folate receptors (FRs) overexpressed in lung carcinoma cells, respectively. In an aqueous-basic media, p-SCN-benzyl-DOTA was conjugated to the dendrimer. This dendrimer was formed by activating the carboxylic acid groups of DOTA–folic acid and bombesin with HATU and conjugating them to develop the dendrimer. As part of this process, the conjugate was combined with 1% HAuCl4, added NaBH4 and filtered by ultrafiltration. Infrared, UV–Vis, TEM analysis, dynamic light scattering (DLS), and fluorescence spectroscopy were employed to observe the composition of the fabricated sample. Radio-labeled 177LuCl3 was used to label the conjugate, which was then evaluated using the radio-HPLC method. Findings demonstrated dendrimeric functionalization with remarkable radiochemical composition purity up to >96%. Because of fluorescence studies, it was determined that the occurrence of AuNMs in the dendrimeric cavities gives beneficial photo-physical characteristics to the radiopharmaceutical for bio-imaging. HEL-299 lung cancer cells exhibited a selective absorption of the drug (%). It might be helpful as nuclear and optical imaging agents for lung cancers that overexpress FRs and GRPR and as a specific target for radiation therapy if combined with folate–bombesin.

LBA02-07 PROSPECTIVE STUDY OF 68 GA-RM2 PET/MRI IN PATIENTS WITH BIOCHEMICALLY RECURRENT PROSTATE CANCER AND NEGATIVE CONVENTIONAL IMAGING

You have accessJournal of UrologyLate-breaking Abstract II - Malignant1 Sep 2021LBA02-07 PROSPECTIVE STUDY OF 68GA-RM2 PET/MRI IN PATIENTS WITH BIOCHEMICALLY RECURRENT PROSTATE CANCER AND NEGATIVE CONVENTIONAL IMAGING Lucia Baratto, Hong Song, Heying Duan, Farshad Moradi, Guido Davidzon, and Andrei Iagaru Lucia BarattoLucia Baratto More articles by this author , Hong SongHong Song More articles by this author , Heying DuanHeying Duan More articles by this author , Farshad MoradiFarshad Moradi More articles by this author , Guido DavidzonGuido Davidzon More articles by this author , and Andrei IagaruAndrei Iagaru More articles by this author View All Author Informationhttps://doi.org/10.1097/JU.0000000000002149.07AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookLinked InTwitterEmail Abstract INTRODUCTION AND OBJECTIVE: 68Ga-RM2 is a synthetic bombesin receptor antagonist targeting gastrin-releasing peptide receptors (GRPr) that are overexpressed in several human tumors, including prostate cancer (PC). Men with biochemical recurrence (BCR) and negative CT/MRI and bone scintigraphy were evaluated for the presence of prostate cancer. METHODS: We enrolled 127 men with BCR PC, 45-83-year-old (mean±SD: 68.3±6.9). Imaging started at 40-89 minutes (mean±SD: 51.0±8.9) after injection of 113.8-152.6 MBq (mean±SD: 140.5±6.4) of 68Ga-RM2 using a time-of-flight (TOF)-enabled simultaneous positron emission tomography (PET) / magnetic resonance imaging (MRI) scanner. RESULTS: All patients had rising PSA and negative conventional imaging prior to enrollment. 68Ga-RM2 PET identified recurrent PC in 85 of the 127 participants. Positivity rate of 68Ga-RM2 PET was: 37.9% for PSA <0.5 ng/dl (n=29), 61.1% for PSA 0.5 – 1.0 ng/dl (n=18), 64.7% for PSA 1.0 – 2.0 ng/dl (n=17), 82.6% for PSA 2.0 – 5.0 ng/dl (n=23) and 87.5% for PSA >5.0 ng/dl (n=40). PSA velocity values were 1.9±2.7 ng/ml/year (range: 0-9.1) in patients with negative PET scans and 5.8±9 ng/ml/year (range: 0.2-45.4) in patients with positive PET scans (P: 0.01). CONCLUSIONS: 68Ga-RM2 PET identifies GRPr expression in BCR PC lesions despite negative conventional imaging, indicating it is a promising PET radiopharmaceutical in this clinical scenario. 68Ga-RM2 may identify higher risk patients given the highly statistically significant difference PSA velocity values between patients with negative and positive scans and may be a complementary radiopharmaceutical to the PSMA-targeting tracers to ultimately allow for personalized medicine. Source of Funding: DoD © 2021 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 206Issue Supplement 3September 2021Page: e1178-e1178 Advertisement Copyright & Permissions© 2021 by American Urological Association Education and Research, Inc.MetricsAuthor Information Lucia Baratto More articles by this author Hong Song More articles by this author Heying Duan More articles by this author Farshad Moradi More articles by this author Guido Davidzon More articles by this author Andrei Iagaru More articles by this author Expand All Advertisement Loading ...

68Ga-Radiolabeling and Pharmacological Characterization of a Kit-Based Formulation of the Gastrin-Releasing Peptide Receptor (GRP-R) Antagonist RM2 for Convenient Preparation of [68Ga]Ga-RM2.

Background: [68Ga]Ga-RM2 is a potent Gastrin-Releasing Peptide-receptor (GRP-R) antagonist for imaging prostate cancer and breast cancer, currently under clinical evaluation in several specialized centers around the world. Targeted radionuclide therapy of GRP-R-expressing tumors is also being investigated. We here report the characteristics of a kit-based formulation of RM2 that should ease the development of GRP-R imaging and make it available to more institutions and patients. Methods: Stability of the investigated kits over one year was determined using LC/MS/MS and UV-HPLC. Direct 68Ga-radiolabeling was optimized with respect to buffer (pH), temperature, reaction time and shaking time. Conventionally prepared [68Ga]Ga-RM2 using an automated synthesizer was used as a comparator. Finally, the [68Ga]Ga-RM2 product was assessed with regards to hydrophilicity, affinity, internalization, membrane bound fraction, calcium mobilization assay and efflux, which is a valuable addition to the in vivo literature. Results: The kit-based formulation, kept between 2 °C and 8 °C, was stable for over one year. Using acetate buffer pH 3.0 in 2.5–5.1 mL total volume, heating at 100 °C during 10 min and cooling down for 5 min, the [68Ga]Ga-RM2 produced by kit complies with the requirements of the European Pharmacopoeia. Compared with the module production route, the [68Ga]Ga-RM2 produced by kit was faster, displayed higher yields, higher volumetric activity and was devoid of ethanol. In in vitro evaluations, the [68Ga]Ga-RM2 displayed sub-nanomolar affinity (Kd = 0.25 ± 0.19 nM), receptor specific and time dependent membrane-bound fraction of 42.0 ± 5.1% at 60 min and GRP-R mediated internalization of 24.4 ± 4.3% at 30 min. The [natGa]Ga-RM2 was ineffective in stimulating intracellular calcium mobilization. Finally, the efflux of the internalized activity was 64.3 ± 6.5% at 5 min. Conclusion: The kit-based formulation of RM2 is suitable to disseminate GRP-R imaging and therapy to distant hospitals without complex radiochemistry equipment.

Estrogens influence female itch sensitivity via the spinal gastrin-releasing peptide receptor neurons

There are sex differences in somatosensory sensitivity. Circulating estrogens appear to have a pronociceptive effect that explains why females are reported to be more sensitive to pain than males. Although itch symptoms develop during pregnancy in many women, the underlying mechanism of female-specific pruritus is unknown. Here, we demonstrate that estradiol, but not progesterone, enhances histamine-evoked scratching behavior indicative of itch in female rats. Estradiol increased the expression of the spinal itch mediator, gastrin-releasing peptide (GRP), and increased the histamine-evoked activity of itch-processing neurons that express the GRP receptor (GRPR) in the spinal dorsal horn. The enhancement of itch behavior by estradiol was suppressed by intrathecal administration of a GRPR blocker. In vivo electrophysiological analysis showed that estradiol increased the histamine-evoked firing frequency and prolonged the response of spinal GRP-sensitive neurons in female rats. On the other hand, estradiol did not affect the threshold of noxious thermal pain and decreased touch sensitivity, indicating that estradiol separately affects itch, pain, and touch modalities. Thus, estrogens selectively enhance histamine-evoked itch in females via the spinal GRP/GRPR system. This may explain why itch sensation varies with estrogen levels and provides a basis for treating itch in females by targeting GRPR.