Bombesin-like receptor 3 expression induced by bisphenol A is likely associated with reduced cell proliferation by inhibiting DNA synthesis and inducing inflammation in liver cells.

BACKGROUND: Bisphenol A (BPA) is an exogenous endocrine disruptor mimicking hormones closely associated with health complications, such as cancer progression. BPA is also related to an increase in the prevalence of obesity-related diseases due to its obesogenic action. Bombesin-like receptor 3 (BRS3) is an important factor that should be considered in the adipogenic gene network, as depletion of this gene alters adiposity. METHODS: Therefore, the present study aimed to investigate the messenger ribonucleic acid (mRNA) expression of BRS3 in human liver THLE-2 cells post-BPA treatment by real-time polymerase chain reaction. The effects of BPA on the levels of pro-inflammatory proteins, interleukin 6 (IL6) and CC motif chemokine ligand 2 (CCL2), in conditioned media of BPA-treated THLE-2 cells and deoxyribonucleic acid (DNA) synthesis in replicating BPA-treated THLE-2 cells during the cell cycle were also examined by enzyme-linked immunosorbent assay (ELISA) and flow cytometry, respectively. RESULTS: The study found that the mRNA expression of BRS3 was increased in THLE-2 cells treated with BPA. The study also showed that the expression levels of IL6 and CCL2 reached an optimum level in the conditioned media of BPA-treated THLE-2 cells after 48 h of treatment. Subsequently, the DNA synthesis analysis showed that bromodeoxyuridine/propidium iodide (BrdU/PI) stained positive cells were decreased in BPA-treated THLE-2 cells at 72 h of treatment. CONCLUSION: The study demonstrates that BRS3 expression induced by BPA is likely associated with reduced cell proliferation by inhibiting DNA synthesis and inducing cellular inflammation in liver cells.

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.

Assessment of the bound conformation of bombesin to the BB1 and BB2 receptors.

Bombesin is an endogenous peptide involved in a wide spectrum of physiological activities ranging from satiety, control of circadian rhythm and thermoregulation in the central nervous system, to stimulation of gastrointestinal hormone release, activation of macrophages and effects on development in peripheral tissues. Actions of the peptide are mediated through the two high affinity G-protein coupled receptors BB1R and BB2R. Under pathophysiological conditions, these receptors are overexpressed in many different types of tumors, such as prostate cancer, breast cancer, small and non-small cell lung cancer and pancreatic cancer. This observation has been used for designing cell markers, but it has not been yet exploited for therapeutical purposes. Despite the enormous biological interest of the peptide, little is known about the stereochemical features that contribute to their activity. On the one hand, mutagenesis studies identified a few receptor residues important for high bombesin affinity and on the other, a few studies focused on the relevance of diverse residues of the peptide for receptor activation. Models of the peptide bound to BB1R and BB2R can be helpful to improve our understanding of the stereochemical features granting bombesin activity. Accordingly, the present study describes the computational process followed to construct such models by means of Steered Molecular Dynamics, using models of the peptide and its receptors. Present results provide new insights into the structure-activity relationships of bombesin and its receptors, as well as render an explanation for the differential binding affinity observed towards BB1R and BB2R. Finally, these models can be further exploited to help for designing novel small molecule peptidomimetics with improved pharmacokinetics profile.

Radiometal Complexes as Pharmacokinetic Modifiers: A Potent 68Ga-Labeled Gastrin-Releasing Peptide Receptor Antagonist Based on the Macrocyclic Metal Chelator NODIA-Me.

The gastrin-releasing peptide receptor (GRPr) is overexpressed in various cancer types including prostate and breast carcinomas, making it an attractive target for molecular imaging and therapy. In this work, we designed a novel GRPr antagonistic probe comprising metal chelator NODIA-Me. This 1,4,7-triazacyclononane-based chelator forms positively charged metal complexes due to its neutral methylimidazole arms. Because a positive charge at the N-terminus of GRPr conjugates is responsible for high receptor affinity as exemplified by the current gold standard DOTA-RM2, we investigated if a positively charged radiometal complex can be used as a pharmacokinetic modifier to also produce high-affinity GRPr conjugates. In this respect, the bioconjugate NODIA-Me-Ahx-JMV594 was prepared by a combination of solid-phase peptide synthesis and solution-based reactions in a 94% yield. Radiolabeling provided the 68Ga-labeled conjugate in radiochemical yields of >95% and radiochemical purities of >98% with mean molar activities of Am ∼17 MBq nmol-1. The competitive GRPr affinity of the metal-free and 69/71Ga-labeled conjugate was determined to be IC50 = 0.41 ± 0.06 and 1.45 ± 0.06 nM, respectively. The metal-free GRPr antagonist DOTA-RM2 and its corresponding 69/71Ga complex had IC50 values of 1.42 ± 0.07 and 0.98 ± 0.19 nM, respectively. Small-animal PET imaging of mice bearing GRPr(+) PC-3 tumors revealed high radioactivity accumulation in the tumors and in the pancreas as an organ with high levels of GRPr expression. These findings were corroborated by the corresponding ex vivo biodistribution data, in which the tumors and the pancreas exhibited the highest radioactivity accumulation. By coinjection of an excess of NODIA-Me-Ahx-JMV594, uptake in the tumors and GRPr(+) organs was significantly reduced, confirming specific receptor-mediated uptake. The estrogen receptor-positive tumor of a female breast cancer patient was clearly visualized by PET imaging using 68Ga-labeled NODIA-Me-Ahx-JMV594. To summarize, the positive charge at the N-terminus of the conjugate induced by the Ga(NODIA-Me) complex resulted in high GRPr affinity comparable to that of the potent antagonist DOTA-RM2. The conjugate NODIA-Me-Ahx-JMV594 is a promising probe for imaging of GRPr tumors that warrants further evaluation in larger patient cohorts as well as in combination with other radiometals.

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.

NEUROENDOCRINE PEPTIDES IN THE PATHOGENESIS OF COLORECTAL CARCINOMA.

Colorectal carcinoma (CRC) is the third most frequent neoplasm worldwide and the second leading cause of mortality. Neuroendocrine peptides such as glucagon, bombesin, somatostatin, cholecystokinin, and gastrin as well as growth factors such as platelet-derived growth factor, epidermal growth factor, insulin-like growth factor, and fibroblast growth factor have been postulated as being involved in carcinogenesis. The fact that these neuroendocrine peptides are involved in the development of CRC through the activation of growth factors that stimulate a series of molecular pathways that activate oncogenic signaling mechanisms is emphasized in this review. Peptides such as CCK1, serotonin, and bombesin have been found to be over-expressed in human tumor tissues. Meanwhile, the expression of peptides such as GLP2 has been seen mainly in murine models. The information contained in this review provides a better understanding of the role these peptides play in the pathogenesis of CRC for basic and clinical science studies.

Neuromedin B excites central lateral amygdala neurons and reduces cardiovascular output and fear-potentiated startle.

Neuromedin B (NMB) and gastrin-releasing peptide (GRP) are the two mammalian analogs in the bombesin peptide family that exert a variety of actions including emotional processing, appetitive behaviors, cognition, and tumor growth. The bombesin-like peptides interact with three receptors: the NMB-preferring bombesin 1 (BB1) receptors, the GRP-preferring bombesin 2 (BB2) receptors and the orphan bombesin 3 (BB3) receptors. Whereas, injection of bombesin into the central amygdala reduces satiety and modulates blood pressure, the underlying cellular and molecular mechanisms have not been determined. As administration of bombesin induces the expression of Fos in the lateral nucleus of the central amygdala (CeL) which expresses BB1 receptors, we probed the effects of NMB on CeL neurons using in vitro and in vivo approaches. We showed that activation of the BB1 receptors increased action potential firing frequency recorded from CeL neurons via inhibition of the inwardly rectifying K+ (Kir) channels. Activities of phospholipase Cß and protein kinase C were required, whereas intracellular Ca2+ release was unnecessary for BB1 receptor-elicited potentiation of neuronal excitability. Application of NMB directly into the CeA reduced blood pressure and heart rate and significantly reduced fear-potentiated startle. We may provide a cellular and molecular mechanism whereby bombesin-like peptides modulate anxiety and fear responses in the amygdala.

Scandium-44: Diagnostic Feasibility in Tumor-Related Angiogenesis.

Angiogenesis-related cell-surface molecules, including integrins, aminopeptidase N, vascular endothelial growth factor, and gastrin-releasing peptide receptor (GRPR), play a crucial role in tumour formation. Radiolabelled imaging probes targeting angiogenic biomarkers serve as valuable vectors in tumour identification. Nowadays, there is a growing interest in novel radionuclides other than gallium-68 (68Ga) or copper-64 (64Cu) to establish selective radiotracers for the imaging of tumour-associated neo-angiogenesis. Given its ideal decay characteristics (Eß+average: 632 KeV) and a half-life (T1/2 = 3.97 h) that is well matched to the pharmacokinetic profile of small molecules targeting angiogenesis, scandium-44 (44Sc) has gained meaningful attention as a promising radiometal for positron emission tomography (PET) imaging. More recently, intensive research has been centered around the investigation of 44Sc-labelled angiogenesis-directed radiopharmaceuticals. Previous studies dealt with the evaluation of 44Sc-appended avb3 integrin-affine Arg-Gly-Asp (RGD) tripeptides, GRPR-selective aminobenzoyl-bombesin analogue (AMBA), and hypoxia-associated nitroimidazole derivatives in the identification of various cancers using experimental tumour models. Given the tumour-related hypoxia- and angiogenesis-targeting capability of these PET probes, 44Sc seems to be a strong competitor of the currently used positron emitters in radiotracer development. In this review, we summarize the preliminary preclinical achievements with 44Sc-labelled angiogenesis-specific molecular probes.

68Ga-Labeled [Thz14]Bombesin(7-14) Analogs: Promising GRPR-Targeting Agonist PET Tracers with Low Pancreas Uptake.

With overexpression in various cancers, the gastrin-releasing peptide receptor (GRPR) is a promising target for cancer imaging and therapy. However, the high pancreas uptake of reported GRPR-targeting radioligands limits their clinical application. Our goal was to develop 68Ga-labeled agonist tracers for detecting GRPR-expressing tumors with positron emission tomography (PET), and compare them with the clinically validated agonist PET tracer, [68Ga]Ga-AMBA. Ga-TacBOMB2, TacBOMB3, and TacBOMB4, derived from [Thz14]Bombesin(7-14), were confirmed to be GRPR agonists by a calcium mobilization study, and their binding affinities (Ki(GRPR)) were determined to be 7.62 ± 0.19, 6.02 ± 0.59, and 590 ± 36.5 nM, respectively, via in vitro competition binding assays. [68Ga]Ga-TacBOMB2, [68Ga]Ga-TacBOMB3, and [68Ga]Ga-AMBA clearly visualized PC-3 tumor xenografts in a PET imaging study. [68Ga]Ga-TacBOMB2 showed comparable tumor uptake but superior tumor-to-background contrast ratios when compared to [68Ga]Ga-AMBA. Moreover, [68Ga]Ga-TacBOMB2 and [68Ga]Ga-TacBOMB3 showed a much lower rate of uptake in the pancreas (1.30 ± 0.14 and 2.41 ± 0.72%ID/g, respectively) than [68Ga]Ga-AMBA (62.4 ± 4.26%ID/g). In conclusion, replacing Met14 in the GRPR-targeting sequence with Thz14 retains high GRPR-binding affinity and agonist properties. With good tumor uptake and tumor-to-background uptake ratios, [68Ga]Ga-TacBOMB2 is promising for detecting GRPR-expressing tumors. The much lower pancreas uptake of [68Ga]Ga-TacBOMB2 and [68Ga]Ga-TacBOMB3 suggests that [Thz14]Bombesin(7-14) is a promising targeting vector for the design of GRPR-targeting radiopharmaceuticals, especially for radioligand therapy application.

Structures of human gastrin-releasing peptide receptors bound to antagonist and agonist for cancer and itch therapy.

Gastrin releasing peptide receptor (GRPR), a member of the bombesin (BBN) G protein-coupled receptors, is aberrantly overexpressed in several malignant tumors, including those of the breast, prostate, pancreas, lung, and central nervous system. Additionally, it also mediates non-histaminergic itch and pathological itch conditions in mice. Thus, GRPR could be an attractive target for cancer and itch therapy. Here, we report the inactive state crystal structure of human GRPR in complex with the non-peptide antagonist PD176252, as well as two active state cryo-electron microscopy (cryo-EM) structures of GRPR bound to the endogenous peptide agonist gastrin-releasing peptide and the synthetic BBN analog [D-Phe6, ß-Ala11, Phe13, Nle14] Bn (6-14), in complex with Gq heterotrimers. These structures revealed the molecular mechanisms for the ligand binding, receptor activation, and Gq proteins signaling of GRPR, which are expected to accelerate the structure-based design of GRPR antagonists and agonists for the treatments of cancer and pruritus.

Intraluminal chloride regulates lung branching morphogenesis: involvement of PIEZO1/PIEZO2.

BACKGROUND: Clinical and experimental evidence shows lung fluid volume as a modulator of fetal lung growth with important value in treating fetal lung hypoplasia. Thus, understanding the mechanisms underlying these morphological dynamics has been the topic of multiple investigations with, however, limited results, partially due to the difficulty of capturing or recapitulating these movements in the lab. In this sense, this study aims to establish an ex vivo model allowing the study of lung fluid function in branching morphogenesis and identify the subsequent molecular/ cellular mechanisms. METHODS: Ex vivo lung explant culture was selected as a model to study branching morphogenesis, and intraluminal injections were performed to change the composition of lung fluid. Distinct chloride (Cl-) concentrations (5.8, 29, 143, and 715 mM) or Cl- channels inhibitors [antracene-9-carboxylic acid (A9C), cystic fibrosis transmembrane conductance regulator inhibitor172 (CFTRinh), and calcium-dependent Cl- channel inhibitorA01 (CaCCinh)] were injected into lung lumen at two timepoints, day0 (D0) and D2. At D4, morphological and molecular analyses were performed in terms of branching morphogenesis, spatial distribution (immunofluorescence), and protein quantification (western blot) of mechanoreceptors (PIEZO1 and PIEZO2), neuroendocrine (bombesin, ghrelin, and PGP9.5) and smooth muscle [alpha-smooth muscle actin (α-SMA) and myosin light chain 2 (MLC2)] markers. RESULTS: For the first time, we described effective intraluminal injections at D0 and D2 and demonstrated intraluminal movements at D4 in ex vivo lung explant cultures. Through immunofluorescence assay in in vivo and ex vivo branching morphogenesis, we show that PGP9.5 colocalizes with PIEZO1 and PIEZO2 receptors. Fetal lung growth is increased at higher [Cl-], 715 mM Cl-, through the overexpression of PIEZO1, PIEZO2, ghrelin, bombesin, MLC2, and α-SMA. In contrast, intraluminal injection of CFTRinh or CaCCinh decreases fetal lung growth and the expression of PIEZO1, PIEZO2, ghrelin, bombesin, MLC2, and α-SMA. Finally, the inhibition of PIEZO1/PIEZO2 by GsMTx4 decreases branching morphogenesis and ghrelin, bombesin, MLC2, and α-SMA expression in an intraluminal injection-independent manner. CONCLUSIONS: Our results identify PIEZO1/PIEZO2 expressed in neuroendocrine cells as a regulator of fetal lung growth induced by lung fluid.

Targeting the Gastrin-Releasing Peptide Receptor (GRP-R) in Cancer Therapy: Development of Bombesin-Based Peptide-Drug Conjugates.

Targeted tumour therapy has proved to be an efficient alternative to overcome the limitations of conventional chemotherapy. Among several receptors upregulated in cancer cells, the gastrin-releasing peptide receptor (GRP-R) has recently emerged as a promising target for cancer imaging, diagnosing and treatment due to its overexpression on cancerous tissues such as breast, prostate, pancreatic and small-cell lung cancer. Herein, we report on the in vitro and in vivo selective delivery of the cytotoxic drug daunorubicin to prostate and breast cancer, by targeting GRP-R. Exploiting many bombesin analogues as homing peptides, including a newly developed peptide, we produced eleven daunorubicin-containing peptide-drug conjugates (PDCs), acting as drug delivery systems to safely reach the tumour environment. Two of our bioconjugates revealed remarkable anti-proliferative activity, an efficient uptake by all three tested human breast and prostate cancer cell lines, high stability in plasma and a prompt release of the drug-containing metabolite by lysosomal enzymes. Moreover, they revealed a safe profile and a consistent reduction of the tumour volume in vivo. In conclusion, we highlight the importance of GRP-R binding PDCs in targeted cancer therapy, with the possibility of further tailoring and optimisation.

Nanostrategies for Therapeutic and Diagnostic Targeting of Gastrin-Releasing Peptide Receptor.

Advances in nanomedicine bring the attention of researchers to the molecular targets that can play a major role in the development of novel therapeutic and diagnostic modalities for cancer management. The choice of a proper molecular target can decide the efficacy of the treatment and endorse the personalized medicine approach. Gastrin-releasing peptide receptor (GRPR) is a G-protein-coupled membrane receptor, well known to be overexpressed in numerous malignancies including pancreatic, prostate, breast, lung, colon, cervical, and gastrointestinal cancers. Therefore, many research groups express a deep interest in targeting GRPR with their nanoformulations. A broad spectrum of the GRPR ligands has been described in the literature, which allows tuning of the properties of the final formulation, particularly in the field of the ligand affinity to the receptor and internalization possibilities. Hereby, the recent advances in the field of applications of various nanoplatforms that are able to reach the GRPR-expressing cells are reviewed.

Early Prediction of Radiation-Induced Pulmonary Fibrosis Using Gastrin-Releasing Peptide Receptor-Targeted PET Imaging.

Early diagnosis of radiation-induced pulmonary fibrosis (RIPF) in lung cancer patients after radiation therapy is important. A gastrin-releasing peptide receptor (GRPR) mediates the inflammation and fibrosis after irradiation in mice lungs. Previously, our group synthesized a GRPR-targeted positron emission tomography (PET) imaging probe, [64Cu]Cu-NODAGA-galacto-bombesin (BBN), an analogue peptide of GRP. In this study, we evaluated the usefulness of [64Cu]Cu-NODAGA-galacto-BBN for the early prediction of RIPF. We prepared RIPF mice and acquired PET/CT images of [18F]F-FDG and [64Cu]Cu-NODAGA-galacto-BBN at 0, 2, 5, and 11 weeks after irradiation (n = 3-10). We confirmed that [64Cu]Cu-NODAGA-galacto-BBN targets GRPR in irradiated RAW 264.7 cells. In addition, we examined whether [64Cu]Cu-NODAGA-galacto-BBN monitors the therapeutic efficacy in RIPF mice (n = 4). As a result, the lung uptake ratio (irradiated-to-normal) of [64Cu]Cu-NODAGA-galacto-BBN was the highest at 2 weeks, followed by its decrease at 5 and 11 weeks after irradiation, which matched with the expression of GRPR and was more accurately predicted than [18F]F-FDG. These uptake results were also confirmed by the cell uptake assay. Furthermore, [64Cu]Cu-NODAGA-galacto-BBN could monitor the therapeutic efficacy of pirfenidone in RIPF mice. We conclude that [64Cu]Cu-NODAGA-galacto-BBN is a novel PET imaging probe for the early prediction of RIPF-targeting GRPR expressed during the inflammatory response.

Towards Selective Delivery of a Ruthenium(II) Polypyridyl Complex-Containing Bombesin Conjugate into Cancer Cells.

An increasing number of novel Ru(II) polypyridyl complexes have been successfully applied as photosensitizers (PSs) for photodynamic therapy (PDT). Despite recent advances in optimized PSs with refined photophysical properties, the lack of tumoral selectivity is often a major hurdle for their clinical development. Here, classical maleimide and versatile NHS-activated acrylamide strategies were employed to site-selectively conjugate a promising Ru(II) polypyridyl complex to the N-terminally Cys-modified Bombesin (BBN) targeting unit. Surprisingly, the decreased cell uptake of these novel Ru-BBN conjugates in cancer cells did not hamper the high phototoxic activity of the Ru-containing bioconjugates and even decreased the toxicity of the constructs in the absence of light irradiation. Overall, although deceiving in terms of selectivity, our new bioconjugates could still be useful for advanced cancer treatment due to their nontoxicity in the dark.

Value of 68Ga-labeled bombesin antagonist (RM2) in the detection of primary prostate cancer comparing with [18F]fluoromethylcholine PET-CT and multiparametric MRI-a phase I/II study.

OBJECTIVES: The bombesin derivative RM2 is a GRPr antagonist with strong binding affinity to prostate cancer (PCa). In this study, the impact of [68Ga]Ga-RM2 positron emission tomography-computed tomography (PET-CT) for the detection of primary PCa was compared with that of [18F]FCH PET-CT and multiparametric magnetic resonance imaging (mpMRI). METHODS: This phase I/II study was conducted in 30 biopsy-positive PCa subjects. The patients were stratified into high (10 patients), intermediate (10 patients), and low risk (10 patients) for extraglandular metastases as defined by National Comprehensive Cancer Network (NCCN) criteria (NCCN Clinical Practice Guidelines in Oncology, 2016). The prostate gland was classified in 12 anatomic segments for data analysis of the imaging modalities as well as histopathologic findings. The segment with the highest radiotracer uptake was defined as the "index lesion." All cases were scheduled to undergo prostatectomy with pelvic lymph node (LN) dissection in intermediate- and high-risk patients. Intraprostatic and pelvic nodal [68Ga]Ga-RM2 and [18F]FCH PET-CT findings were correlated with mpMRI and histopathologic results. RESULTS: Of the 312 analyzed regions, 120 regions (4 to 8 lesions per patient) showed abnormal findings in the prostate gland. In a region-based analysis, overall sensitivity and specificity of [68Ga]Ga-RM2 PET-CT in the detection of primary tumor were 74% and 90%, respectively, while it was 60% and 80% for [18F]FCH PET-CT and 72% and 89% for mpMRI. Although the overall sensitivity of [68Ga]Ga-RM2 PET-CT was higher compared to that of [18F]FCH PET-CT and mpMRI, the statistical analysis showed only significant difference between [68Ga]Ga-RM2 PET-CT and [18F]FCH PET-CT in the intermediate-risk group (p = 0.01) and [68Ga]Ga-RM2 PET-CT and mpMRT in the high-risk group (p = 0.03). In the lesion-based analysis, there was no significant difference between SUVmax of [68Ga]Ga-RM2 and [18F]FCH PET-CT in the intraprostatic malignant lesions ([68Ga]Ga-RM2: mean SUVmax: 5.98 ± 4.13, median: 4.75; [18F]FCH: mean SUVmax: 6.08 ± 2.74, median: 5.5; p = 0.13). CONCLUSIONS: [68Ga]Ga-RM2 showed promising PET tracer for the detection of intraprostatic PCa in a cohort of patients with different risk stratifications. However, significant differences were only found between [68Ga]Ga-RM2 PET-CT and [18F]FCH PET-CT in the intermediate-risk group and [68Ga]Ga-RM2 PET-CT and mpMRT in the high-risk group. In addition, GRP-R-based imaging seems to play a complementary role to choline-based imaging for full characterization of PCa extent and biopsy guidance in low- and intermediate-metastatic-risk PCa patients and has the potential to discriminate them from those at higher risks. KEY POINTS: • [68Ga]Ga-RM2 is a promising PET tracer with a high detection rate for intraprostatic PCa especially in intermediate-risk prostate cancer patients. • GRPr-based imaging seems to play a complementary role to choline-based or PSMA-based PET/CT imaging in selected low- and intermediate-risk PCa patients for better characterization and eventually biopsy guidance of prostate cancer disease.

Estimation of Human Absorbed Dose of 188Re-Hynic-Bombesin Based on Biodistribution Data in Rats.

BACKGROUND: HYNIC-Bombesin (BBN) is a potential peptide for targeted radionuclide therapy in gastrin-releasing peptide receptor (GRPr)-positive malignancies. The 188Re-HYNICBBN is a promising radiopharmaceutical for use in prostate cancer therapy. OBJECTIVE: The aim of this study was to estimate the absorbed dose due to 188Re-HYNIC-BBN radio-complex in human organs based on bio-distribution data of rats. METHODS: In this research, using bio-distribution data of 188Re-HYNIC-BBN in rats, its radiation absorbed dose of the adult human was calculated for different organs based on the MIRD dose calculation method. RESULTS: A considerable equivalent dose amount of 188Re-Hynic-BBN (0.093 mGy/MBq) was accumulated in the prostate. Moreover, all other tissues except for the kidneys and pancreas approximately received insignificant absorbed doses. CONCLUSION: Since the acceptable absorbed dose for the complex was observed in the prostate, 188Re-Hynic-Bombesin can be regarded as a new potential agent for prostate cancer therapy.

PET Imaging Using Gallium-68 (68Ga) RM2.

Molecular imaging is advancing rapidly with promising new molecular targets emerging for theragnostic, ie, imaging and treatment with the same compound, to provide targeted, personalized medicine. Gastrin-releasing peptide receptors (GRPR) are overexpressed in prostate cancer. Gallium-68 (68Ga) RM2 is a GRPR antagonist and shows high sensitivity and specificity for the detection of primary prostate cancer and recurrent disease. However, compared with the widely used 68Ga-PSMA11 and 18F-DCFPyL, a discordance in uptake pattern is seen reflecting the heterogeneity in tumor biology of prostate cancer. In this review, we present the background, current status, and future perspectives of PET imaging using 68Ga-RM2.

PET Probes for Preclinical Imaging of GRPR-Positive Prostate Cancer: Comparative Preclinical Study of [68Ga]Ga-NODAGA-AMBA and [44Sc]Sc-NODAGA-AMBA.

Gastrin-releasing peptide receptors (GRPR) are overexpressed in prostate cancer (PCa). Since bombesin analogue aminobenzoic-acid (AMBA) binds to GRPR with high affinity, scandium-44 conjugated AMBA is a promising radiotracer in the PET diagnostics of GRPR positive tumors. Herein, the GRPR specificity of the newly synthetized [44Sc]Sc-NODAGA-AMBA was investigated in vitro and in vivo applying PCa PC-3 xenograft. After the in-vitro assessment of receptor binding, PC-3 tumor-bearing mice were injected with [44Sc]Sc/[68Ga]Ga-NODAGA-AMBA (in blocking studies with bombesin) and in-vivo PET examinations were performed to determine the radiotracer uptake in standardized uptake values (SUV). 44Sc/68Ga-labelled NODAGA-AMBA was produced with high molar activity (approx. 20 GBq/µmoL) and excellent radiochemical purity. The in-vitro accumulation of [44Sc]Sc-NODAGA-AMBA in PC-3 cells was approximately 25-fold higher than that of the control HaCaT cells. Relatively higher uptake was found in vitro, ex vivo, and in vivo in the same tumor with the 44Sc-labelled probe compared to [68Ga]Ga-NODAGA-AMBA. The GRPR specificity of [44Sc]Sc-NODAGA-AMBA was confirmed by significantly (p ≤ 0.01) decreased %ID and SUV values in PC-3 tumors after bombesin pretreatment. The outstanding binding properties of the novel [44Sc]Sc-NODAGA-AMBA to GRPR outlines its potential to be a valuable radiotracer in the imaging of GRPR-positive PCa.

68Ga-Labeled [Leu13ψThz14]Bombesin(7-14) Derivatives: Promising GRPR-Targeting PET Tracers with Low Pancreas Uptake.

The gastrin-releasing peptide receptor (GRPR) is a G-protein-coupled receptor that is overexpressed in many solid cancers and is a promising target for cancer imaging and therapy. However, high pancreas uptake is a major concern in the application of reported GRPR-targeting radiopharmaceuticals, particularly for targeted radioligand therapy. To lower pancreas uptake, we explored Ga-complexed TacsBOMB2, TacsBOMB3, TacsBOMB4, TacsBOMB5, and TacsBOMB6 derived from a potent GRPR antagonist sequence, [Leu13ψThz14]Bombesin(7-14), and compared their potential for cancer imaging with [68Ga]Ga-RM2. The Ki(GRPR) values of Ga-TacsBOMB2, Ga-TacsBOMB3, Ga-TacsBOMB4, Ga-TacsBOMB5, Ga-TacsBOMB6, and Ga-RM2 were 7.08 ± 0.65, 4.29 ± 0.46, 458 ± 38.6, 6.09 ± 0.95, 5.12 ± 0.57, and 1.51 ± 0.24 nM, respectively. [68Ga]Ga-TacsBOMB2, [68Ga]Ga-TacsBOMB3, [68Ga]Ga-TacsBOMB5, [68Ga]Ga-TacsBOMB6, and [68Ga]Ga-RM2 clearly show PC-3 tumor xenografts in positron emission tomography (PET) images, while [68Ga]Ga-TacsBOMB5 shows the highest tumor uptake (15.7 ± 2.17 %ID/g) among them. Most importantly, the pancreas uptake values of [68Ga]Ga-TacsBOMB2 (2.81 ± 0.78 %ID/g), [68Ga]Ga-TacsBOMB3 (7.26 ± 1.00 %ID/g), [68Ga]Ga-TacsBOMB5 (1.98 ± 0.10 %ID/g), and [68Ga]Ga-TacsBOMB6 (6.50 ± 0.36 %ID/g) were much lower than the value of [68Ga]Ga-RM2 (41.9 ± 10.1 %ID/g). Among the tested [Leu13ψThz14]Bombesin(7-14) derivatives, [68Ga]Ga-TacsBOMB5 has the highest tumor uptake and tumor-to-background contrast ratios, which is promising for clinical translation to detect GRPR-expressing tumors. Due to the low pancreas uptake of its derivatives, [Leu13ψThz14]Bombesin(7-14) represents a promising pharmacophore for the design of GRPR-targeting radiopharmaceuticals, especially for targeted radioligand therapy application.