Gastrin-releasing peptide receptor-based targeting using bombesin analogues is superior to metabolism-based targeting using choline for in vivo imaging of human prostate cancer xenografts

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.

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.

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.

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.

Nano-Theranostics for the Sensing, Imaging and Therapy of Prostate Cancers

We highlight hereby recent developments in the emerging field of theranostics, which encompasses the combination of therapeutics and diagnostics in a single entity aimed for an early-stage diagnosis, image-guided therapy as well as evaluation of therapeutic outcomes of relevance to prostate cancer (PCa). Prostate cancer is one of the most common malignancies in men and a frequent cause of male cancer death. As such, this overview is concerned with recent developments in imaging and sensing of relevance to prostate cancer diagnosis and therapeutic monitoring. A major advantage for the effective treatment of PCa is an early diagnosis that would provide information for an appropriate treatment. Several imaging techniques are being developed to diagnose and monitor different stages of cancer in general, and patient stratification is particularly relevant for PCa. Hybrid imaging techniques applicable for diagnosis combine complementary structural and morphological information to enhance resolution and sensitivity of imaging. The focus of this review is to sum up some of the most recent advances in the nanotechnological approaches to the sensing and treatment of prostate cancer (PCa). Targeted imaging using nanoparticles, radiotracers and biomarkers could result to a more specialised and personalised diagnosis and treatment of PCa. A myriad of reports has been published literature proposing methods to detect and treat PCa using nanoparticles but the number of techniques approved for clinical use is relatively small. Another facet of this report is on reviewing aspects of the role of functional nanoparticles in multimodality imaging therapy considering recent developments in simultaneous PET-MRI (Positron Emission Tomography-Magnetic Resonance Imaging) coupled with optical imaging in vitro and in vivo, whilst highlighting feasible case studies that hold promise for the next generation of dual modality medical imaging of PCa. It is envisaged that progress in the field of imaging and sensing domains, taken together, could benefit from the biomedical implementation of new synthetic platforms such as metal complexes and functional materials supported on organic molecular species, which can be conjugated to targeting biomolecules and encompass adaptable and versatile molecular architectures. Furthermore, we include hereby an overview of aspects of biosensing methods aimed to tackle PCa: prostate biomarkers such as Prostate Specific Antigen (PSA) have been incorporated into synthetic platforms and explored in the context of sensing and imaging applications in preclinical investigations for the early detection of PCa. Finally, some of the societal concerns around nanotechnology being used for the detection of PCa are considered and addressed together with the concerns about the toxicity of nanoparticles–these were aspects of recent lively debates that currently hamper the clinical advancements of nano-theranostics. The publications survey conducted for this review includes, to the best of our knowledge, some of the most recent relevant literature examples from the state-of-the-art. Highlighting these advances would be of interest to the biomedical research community aiming to advance the application of theranostics particularly in PCa diagnosis and treatment, but also to those interested in the development of new probes and methodologies for the simultaneous imaging and therapy monitoring employed for PCa targeting.

Evaluation of fine particulate matter on vascular endothelial function in vivo and in vitro

Ambient fine particulate matter (PM_2.5) and high-fat diet (HFD) are linked to the development of atherosclerosis. However, there is still unknown about the PM_2.5-induced atherosclerosis formation on vascular endothelial injury after co-exposed to PM_2.5 and HFD. Thus, the aim of this study was to evaluate the effects of PM_2.5 on atherogenesis in C57BL/6 mice and endothelial cells, as well as the co-exposure effect of PM_2.5 and HFD. In vivo study, C57BL/6 mice exposed to PM_2.5 and fed with standard chow diet (STD) or HFD for 1 month. PM_2.5 could increase vascular stiffness accessed by Doppler ultrasound, and more serious in co-exposure group. PM_2.5 impaired vascular endothelial layer integrity, exfoliated endothelial cells, and inflammatory cells infiltration through H&E staining. PM_2.5 reduced the expression of platelet/endothelial cell adhesion molecule-1 (PECAM-1) in vessel. Moreover, PM_2.5 could induce systemic inflammation detected by Mouse Inflammation Array. In vitro study, PM_2.5 triggered markedly mitochondrial damage by transmission electron microscope (TEM) and flow cytometer. Inflammatory cytokines were significantly increased in PM_2.5-exposed group. The cell viability and migration of endothelial cells were significantly suppressed. In addition, PM_2.5 remarkably declined the expression of vascular endothelial growth factor receptor 2 (VEGFR2) and increased the expression of somatostatin (SST) and its receptor. In conclusion, co-exposure of PM_2.5 and HFD might induce systemic inflammation and endothelial dysfunction in normal mice. Moreover, PM_2.5 could reduce vascular endothelial repair capacity through inhibiting the proliferation and migration of endothelial cells.

Iodinated Choline Transport-Targeted Tracers

We present a novel series of radioiodinated tracers and potential theranostics for diseases accompanied by pathological function of proteins involved in choline transport. Unlike choline analogues labeled with ¹¹C or ¹⁸F that are currently used in the clinic, the iodinated compounds described herein are applicable in positron emission tomography, single-photon emission computed tomography, and potentially in therapy, depending on the iodine isotope selection. Moreover, favorable half-lives of iodine isotopes result in much less challenging synthesis by isotope exchange reaction. Six of the described compounds were nanomolar ligands, and the best compound possessed an affinity 100-fold greater than that of choline. Biodistribution data of ¹²⁵I-labeled ligands in human prostate carcinoma bearing (PC-3) mice revealed two compounds with a biodistribution profile superior to that of [¹⁸F]fluorocholine.

A comparative PET imaging study of 44gSc- and 68Ga-labeled bombesin antagonist BBN2 derivatives in breast and prostate cancer models

INTRODUCTION

Radiolabeled peptides play a central role in nuclear medicine as radiotheranostics for targeted imaging and therapy of cancer. We have recently proposed the use of metabolically stabilized GRPR antagonist BBN2 for radiolabeling with 18F and 68Ga and subsequent PET imaging of GRPRs in prostate cancer. The present work studied the impact of 44gSc- and 68Ga-labeled DOTA complexes attached to GRPR antagonist BBN2 on the in vitro GRPR binding affinity, and their biodistribution and tumor uptake profiles in MCF7 breast and PC3 prostate cancer models.

METHODS

DOTA-Ava-BBN2 was radiolabeled with radiometals 68Ga and 44gSc. Gastrin-releasing peptide receptor (GRPR) affinities of peptides were assessed in PC3 prostate cancer cells. GRPR expression profiles were studied in human breast cancer tissue samples and MCF7 breast cancer cells. PET imaging of 68Ga- and 44gSc-labeled peptides was performed in MCF7 and PC3 xenografts as breast and prostate cancer models.

RESULTS

Radiopeptides [68Ga]Ga-DOTA-Ava-BBN2 and [44gSc]Sc-DOTA-Ava BBN2 were prepared in radiochemical yields of 70-80% (decay-corrected), respectively. High binding affinities were found for both peptides (IC50 = 15 nM (natGa) and 5 nM (natSc)). Gene expression microarray analysis revealed high GRPR mRNA expression levels in estrogen receptor (ER)-positive breast cancer, which was further confirmed with Western blot and immunohistochemistry. However, PET imaging showed only low tumor uptake of both radiotracers in MCF7 xenografts ([68Ga]Ga-DOTA-BBN2 (SUV60min 0.27 ± 0.06); [44gSc]Sc-DOTA-BBN2 (SUV60min 0.20 ± 0.03)). In contrast, high tumor uptake and retention were found for both radiopeptides in PC3 tumors ([68Ga]Ga-DOTA-BBN2 (SUV60min 0.46 ± 0.07); [44gSc]Sc-DOTA-BBN2 (SUV60min 0.51 ± 0.11)).

CONCLUSIONS

Comparison of 68Ga- and 44gSc-labeled DOTA-Ava-BBN2 peptides revealed slight but noticeable differences of the radiometal with an impact on the in vitro GRPR receptor binding properties in PC3 cells. No differences were found in their in vivo biodistribution profiles in MCF7 and PC3 xenografts. Radiopeptides [68Ga]Ga-DOTA-Ava-BBN2 and [44gSc]Sc-DOTA-Ava-BBN2 displayed comparable tumor uptake and retention profiles with rapid blood and renal clearance profiles in both tumor models.

ADVANCES IN KNOWLEDGE AND IMPLICATIONS FOR PATIENT CARE

The favorable PET imaging performance of [44gSc]Sc-DOTA-Ava-BBN2 in prostate cancer should warrant the development of an [43Sc]Sc-DOTA-Ava-BBN2 analog for clinical translation which comes with a main γ-line of much lower energy and intensity compared to 44gSc.

A comparative study of peptide-based imaging agents [68Ga]Ga-PSMA-11, [68Ga]Ga-AMBA, [68Ga]Ga-NODAGA-RGD and [68Ga]Ga-DOTA-NT-20.3 in preclinical prostate tumour models

INTRODUCTION

Peptide-based imaging agents targeting prostate-specific membrane antigen (PSMA) have revolutionized the evaluation of biochemical recurrence of prostate cancer (PCa) but lacks sensitivity at very low serum prostate specific antigen (PSA) levels. Once recurrence is suspected, other positron emission tomography (PET) radiotracers could be of interest to discriminate between local and distant relapse. We studied [¹⁸F]fluorodeoxyglucose ([¹⁸F]FDG) targeting glucose metabolism, [¹⁸F]fluorocholine ([¹⁸F]FCH) targeting membrane metabolism and peptide-based imaging agents [⁶⁸Ga]Ga-PSMA-11, [⁶⁸Ga]Ga-AMBA, [⁶⁸Ga]Ga-NODAGA-RGD and [⁶⁸Ga]Ga-DOTA-NT-20.3 targeting PSMA, gastrin releasing peptide receptor (GRPr), αvβ3 integrin and neurotensin type 1 receptor (NTSR1) respectively, in different PCa tumour models.

METHODS

Mice were xenografted with 22Rv1, an androgen-receptor (AR)-positive, PCa cell line that expresses PSMA and PC3, an AR-negative one that does not express PSMA. PET imaging using the different radiotracers was performed sequentially and the uptake characteristics compared to one other. NTSR1 and PSMA expression levels were analysed in tumours by immunohistochemistry.

RESULTS

[¹⁸F]FDG displayed low but sufficient uptake to visualize PC3 and 22Rv1 derived tumours. We also observed a low efficacy of [¹⁸F]FCH PET imaging and a low [⁶⁸Ga]Ga-NODAGA-RGD tumour uptake in those tumours. As expected, an elevated tumour uptake was obtained for [⁶⁸Ga]Ga-PSMA-11 in 22Rv1 derived tumour although no uptake was measured in the androgen independent cell line PC3, derived from a bone metastasis of a high-grade PCa. Moreover, in PC3 cell line, we obtained good tumour uptake, high tumour-to-background contrast using [⁶⁸Ga]Ga-AMBA and [⁶⁸Ga]Ga-DOTA-NT-20.3. Immunohistochemistry analysis confirmed high NTSR1 expression in PC3 derived tumours and conversely high PSMA expression in 22Rv1 derived tumours.

CONCLUSION

PET imaging using [⁶⁸Ga]Ga-AMBA and [⁶⁸Ga]Ga-DOTA-NT-20.3 demonstrates that GRPr and NTSR1 could represent viable alternative targets for diagnostic or therapeutic applications in PCa with limited PSMA expression levels. More preclinical and clinical studies will follow to explore this potential.

ADVANCES IN KNOWLEDGE AND IMPLICATIONS FOR PATIENT

Peptide-based imaging agents targeting PSMA represent a major progress in the evaluation of biochemical recurrence of PCa but sometimes yield false negative results in some lesions. Continuing efforts have thus been made to evaluate other radiotracers. Our preclinical results suggest that [⁶⁸Ga]labelled bombesin and neurotensin analogues could serve as alternative PET radiopharmaceuticals for diagnostic or therapy in cases of PSMA-negative PCa.

Dual Anti-cancer and Anti-Itch Activity of PD176252 Analogues: Design, Synthesis and Biological Evaluation

Background:

Cancer patients treated with targeted anti-cancer drug suffer from itch or pruritus. Itch or pruritus is an unpleasant sensation that brings about a negative impact on quality of life, and serious itch may lead to dose reduction and even discontinuation. Gastrin releasing peptide receptor (GRPR) plays a critical role in itch, inflammation and cancer, and GRPR antagonist has obvious effect on cancer, inflammation and itch. The aim of this paper is to develop a new agent with anti-cancer and anti-itch activity.

Methods:

A series of GRPR antagonist PD176252 analogues (3a-3l) were designed and synthesized. Both anticancer and anti-itch activities were evaluated. Anti-cancer activity was evaluated in three human cancer cell lines in vitro, the anti-itch activity in evaluated with Kunming mice by intrathecal injection of chloroquine phosphate as a modeling medium. And the cytotoxicity on normal cells was evaluated.

Results:

Of the tested compounds, compound 3i showed potently anti-cancer activity to all cancer cell lines tested with IC50 values of 10.5µM (lung), 11.6µM (breast) and 12.8µM (liver) respectively and it also showed significant inhibition of the scratching behavior. Comparing with PD17625, compound 3i and 3g gave better inhibition activities against all cancer cell lines, compound 3b, 3c and 3i showed better anti-itch activity. The compound 3i is safe for normal breast and liver normal cells, but it has high cytotoxicity on normal lung cell.

Conclusion:

The synthesized compounds have dual anti-cancer and anti-itch activity, so the development of drug with dual anti-tumor and anti-itch property is possible.

68Ga-PSMA-11 PET/MR Detects Local Recurrence Occult on mpMRI in Prostate Cancer Patients After HIFU

High-intensity focused ultrasound (HIFU) is a promising new modality for the treatment of localized prostate cancer (PCa). Follow-up of patients is recommended with biopsies and multiparametric MRI (mpMRI). However, mpMRI in the postinterventional setting is often false-negative. It was our aim to investigate if the new tracer targeting the prostate-specific membrane antigen (⁶⁸Ga-PSMA-11) could be used to localize recurrent disease with PET/MR in patients with discrepant findings between mpMRI and template biopsies. Methods: Interim analysis was performed of the first 10 patients scanned between September 2016 and May 2018 with positive template biopsy and negative mpMRI after HIFU from an ongoing clinical trial (NCT02265159). All patients underwent ⁶⁸Ga-PSMA-11 PET/MRI within 3 mo. Four prostatic quadrants were defined, and for every quadrant suspicion for recurrence was rated on a 5-point Likert scale from definitely no recurrence (1) to highly suspected of recurrence (5), with 4 used as a cutoff for suspected disease based on PET/MRI by a masked reader. ⁶⁸Ga-PSMA-11 uptake of suspected lesions and background areas was measured with the SUV_max The apparent diffusion coefficient values of lesions and background were given for each segment. PET/MRI scans were compared with the template biopsy results, including corresponding Gleason scores (GS), number of positive cores, and tumor length. Results: The quadrant-based sensitivity, specificity, and positive and negative predictive values for PET/MRI were 55%, 100%, 100%, and 85%, respectively. Patient-based PET/MRI was negative in 4 cases with GS 3 + 4 and a tumor length between 0.1 and 3 mm. All tumor lesions with GS 4 + 3 or higher were detected on PET/MRI. Conclusion: Our preliminary results indicate that ⁶⁸Ga-PSMA-11-PET/MR has the potential to localize PCa recurrence after HIFU occult on mpMRI.

Imaging of pancreatic neuroendocrine tumors: recent advances, current status, and controversies

Recently, there have been a number of advances in imaging pancreatic neuroendocrine tumors (panNETs), as well as other neuroendocrine tumors (NETs), which have had a profound effect on the management and treatment of these patients, but in some cases are also associated with controversies. Areas covered: These advances are the result of numerous studies attempting to better define the roles of both cross-sectional imaging, endoscopic ultrasound, with or without fine-needle aspiration, and molecular imaging in both sporadic and inherited panNET syndromes; the increased attempt to develop imaging parameters that correlate with tumor classification or have prognostic value; the rapidly increasing use of molecular imaging in these tumors and the attempt to develop imaging parameters that correlate with treatment/outcome results. Each of these areas and the associated controversies are reviewed. Expert commentary: There have been numerous advances in all aspects of the imaging of panNETs, as well as other NETs, in the last few years. The advances are leading to expanded roles of imaging in the management of these patients and the results being seen in panNETs/GI-NETs with these newer techniques are already being used in more common tumors.

Bombesin functionalized 64Cu-copper sulfide nanoparticles for targeted imaging of orthotopic prostate cancer

Aim: To synthesize and evaluate the imaging potential of Bom-PEG-[64Cu]CuS nanoparticles (NPs) in orothotopic prostate tumor. Materials & methods: [64Cu]CuS NPs were synthesized in aqueous solution by 64CuCl2 and Na2S reaction. Then PEG linker with or without bombesin peptide were conjugated to the surface of [64Cu]CuS NPs to produce Bom-PEG-[64Cu]CuS and PEG-[64Cu]CuS NPs. These two kinds of NPs were used for testing specific uptake in prostate cancer cells in vitro and imaging of orthotopic prostate tumor in vivo. Results: Bom-PEG-[64Cu]CuS and PEG-[64Cu]CuS NPs were successfully synthesized with core diameter of approximately 5 nm. Radioactive cellular uptake revealed that Bom-PEG-[64Cu]CuS was able to specifically bind to prostate cancer cells, and the microPET-CT imaging indicated clear visualization of orthotopic prostate tumors. Conclusion: Radiolabeled Bom-PEG-[64Cu]CuS NPs have potential as an ideal agent for orthotopic prostate tumor imaging by microPET-CT.

In Vivo Evaluation of a Bombesin Analogue Labeled with Ga-68 and Co-55/57

PURPOSE

The purpose of this study was to apply an analogue of bombesin, NOTA-AMBA, labeled with Co-55 or Ga-68, for preclinical imaging of prostate cancer.

PROCEDURES

The peptide NOTA-AMBA was labeled with Ga-68 or Co-55 by microwave irradiation. Biodistribution in xenograft mice (PC3) was performed at 1, 4, and 24 h (only cobalt at 24 h) using a fixed amount of peptide. Four weeks post-inoculation, xenograft mice were positron emission tomography/X-ray computed tomography scanned after tail vein injection of [(68)Ga]NOTA-AMBA or [(55)Co]NOTA-AMBA.

RESULTS

Labeling with Ga-68 and Co-55/57 was achieved in yields greater than 90 %. A radiochemical purity (RCP) of 95 and 90 % were obtained for Ga-68 and Co-55, respectively. Both radiopeptides showed high uptake in the intestines, stomach, pancreas, and in the tumor ([(68)Ga]NOTA-AMBA, 10.3 %ID/g at 1 h to 6.4 %ID/g at 4 h; [(57)Co]NOTA-AMBA, 8.2 %ID/g at 1 h to 5.3%ID/g at 24 h). Normal tissue cleared over time improving tumor-to-background ratios.

CONCLUSIONS

NOTA-AMBA was labeled in high yields and RCP with Ga-68 and Co-55/57. High tumor uptake in a subcutaneous mouse prostate cancer model was observed. At 24 h, [(55/57)Co]NOTA-AMBA showed better tumor-to-organ ratios than [(68)Ga]NOTA-AMBA at both 1 and 4 h post-injection. Hence, for imaging, [(55)Co]NOTA-AMBA was found to be superior compared to [(68)Ga]NOTA-AMBA.

Comparison of [(11)C]Choline ([(11)C]CHO) and [(18)F]Bombesin (BAY 86-4367) as Imaging Probes for Prostate Cancer in a PC-3 Prostate Cancer Xenograft Model

PURPOSE

Carbon-11- and fluorine-18-labeled choline derivatives are commonly used in prostate cancer imaging in the clinical setting for staging and re-staging of prostate cancer. Due to a limited detection rate of established positron emission tomography (PET) tracers, there is a clinical need for innovative tumor-specific PET compounds addressing new imaging targets. The aim of this study was to compare the properties of [(18)F]Bombesin (BAY 86-4367) as an innovative biomarker for prostate cancer imaging targeting the gastrin-releasing peptide receptor and [(11)C]Choline ([(11)C]CHO) in a human prostate tumor mouse xenograft model by small animal PET/X-ray computed tomography (CT).

PROCEDURES

We carried out a dual-tracer small animal PET/CT study comparing [(18)F]Bombesin and [(11)C]CHO. The androgen-independent human prostate tumor cell line PC-3 was implanted subcutaneously in the flanks of nu/nu NMRI mice (n = 10) (PET/CT measurements of two [(11)C]Choline mice could not be analyzed due to technical reasons). [(18)F]Bombesin and [(11)C]CHO PET/CT imaging was performed about 3-4 weeks after the implantation of PC-3 cells on two separate days. After the intravenous tail vein injection of 14 MBq [(18)F]Bombesin and 37 MBq [(11)C]CHO, respectively, a dynamic study over 60 min was acquired in list mode using an Inveon animal PET/CT scanner (Siemens Medical Solutions). The sequence of [(18)F]Bombesin and [(11)C]CHO was randomized. Image analysis was performed using summed images as well as dynamic data. To calculate static and dynamic tumor-to-muscle (T/M), tumor-to-blood (T/B), liver-to-blood (L/B), and kidney-to-blood (K/B) ratios, 4 × 4 × 4 mm(3) volumes of interest (VOIs) of tumor, muscle (thigh), liver, kidney, and blood derived from transversal slices were used.

RESULTS

The mean T/M ratio of [(18)F]Bombesin and [(11)C]CHO was 6.54 ± 2.49 and 1.35 ± 0.30, respectively. The mean T/B ratio was 1.83 ± 0.79 for [(18)F]Bombesin and 0.55 ± 0.10 for [(11)C]CHO. The T/M ratio as well as the T/B ratio for [(18)F]Bombesin were significantly higher compared to those for [(11)C]CHO (p < 0.001, respectively). Kidney and liver uptake was statistically significantly lower for [(18)F]Bombesin (K/B 3.41 ± 0.81, L/B 1.99 ± 0.38) compared to [(11)C]CHO [K/B 7.91 ± 1.85 (p < 0.001), L/B 6.27 ± 1.99 (p < 0.001)]. The magnitudes of the time course of T/M and T/B ratios (T/M and T/Bdyn ratios) were statistically significantly different (showing a higher uptake of [(18)F]Bombesin compared to [(11)C]CHO); additionally, also the change of the T/M and T/B ratios over time was significantly different between both tracers in the dynamic analysis (p < 0.001, respectively). Furthermore, there was a statistically significantly different change of the K/B and L/B ratios over time between the two tracers in the dynamic analysis (p = 0.026 and p < 0.001, respectively).

CONCLUSIONS

[(18)F]Bombesin (BAY 86-4367) visually and semi-quantitatively outperforms [(11)C]CHO in the PC-3 prostate cancer xenograft model. [(18)F]Bombesin tumor uptake was significantly higher compared to [(11)C]CHO. [(18)F]Bombesin showed better imaging properties compared to the clinically utilized [(11)C]CHO due to a higher tumor uptake as well as a lower liver and kidney uptake.

Fluorescence imaging of bombesin and transferrin receptor expression is comparable to 18F-FDG PET in early detection of sorafenib-induced changes in tumor metabolism

Physical measurement of tumor volume reduction is the most commonly used approach to assess tumor progression and treatment efficacy in mouse tumor models. However, it is relatively insensitive, and often requires long treatment courses to achieve gross physical tumor destruction. As alternatives, several non-invasive imaging methods such as bioluminescence imaging (BLI), fluorescence imaging (FLI) and positron emission tomography (PET) have been developed for more accurate measurement. As tumors have elevated glucose metabolism, 18F-fludeoxyglucose (18F-FDG) has become a sensitive PET imaging tracer for cancer detection, diagnosis, and efficacy assessment by measuring alterations in glucose metabolism. In particular, the ability of 18F-FDG imaging to detect drug-induced effects on tumor metabolism at a very early phase has dramatically improved the speed of decision-making regarding treatment efficacy. Here we demonstrated an approach with FLI that offers not only comparable performance to PET imaging, but also provides additional benefits, including ease of use, imaging throughput, probe stability, and the potential for multiplex imaging. In this report, we used sorafenib, a tyrosine kinase inhibitor clinically approved for cancer therapy, for treatment of a mouse tumor xenograft model. The drug is known to block several key signaling pathways involved in tumor metabolism. We first identified an appropriate sorafenib dose, 40 mg/kg (daily on days 0-4 and 7-10), that retained ultimate therapeutic efficacy yet provided a 2-3 day window post-treatment for imaging early, subtle metabolic changes prior to gross tumor regression. We then used 18F-FDG PET as the gold standard for assessing the effects of sorafenib treatment on tumor metabolism and compared this to results obtained by measurement of tumor size, tumor BLI, and tumor FLI changes. PET imaging showed ~55-60% inhibition of tumor uptake of 18F-FDG as early as days 2 and 3 post-treatment, without noticeable changes in tumor size. For comparison, two FLI probes, BombesinRSense™ 680 (BRS-680) and Transferrin-Vivo™ 750 (TfV-750), were assessed for their potential in metabolic imaging. Metabolically active cancer cells are known to have elevated bombesin and transferrin receptor levels on the surface. In excellent agreement with PET imaging, the BRS-680 imaging showed 40% and 79% inhibition on days 2 and 3, respectively, and the TfV-750 imaging showed 65% inhibition on day 3. In both cases, no significant reduction in tumor volume or BLI signal was observed during the first 3 days of treatment. These results suggest that metabolic FLI has potential preclinical application as an additional method for detecting drug-induced metabolic changes in tumors.

Bombesin related peptides/receptors and their promising therapeutic roles in cancer imaging, targeting and treatment

INTRODUCTION

Despite remarkable advances in tumor treatment, many patients still die from common tumors (breast, prostate, lung, CNS, colon, and pancreas), and thus, new approaches are needed. Many of these tumors synthesize bombesin (Bn)-related peptides and over-express their receptors (BnRs), hence functioning as autocrine-growth-factors. Recent studies support the conclusion that Bn-peptides/BnRs are well-positioned for numerous novel antitumor treatments, including interrupting autocrine-growth and the use of over-expressed receptors for imaging and targeting cytotoxic-compounds, either by direct-coupling or combined with nanoparticle-technology.

AREAS COVERED

The unique ability of common neoplasms to synthesize, secrete, and show a growth/proliferative/differentiating response due to BnR over-expression, is reviewed, both in general and with regard to the most frequently investigated neoplasms (breast, prostate, lung, and CNS). Particular attention is paid to advances in the recent years. Also considered are the possible therapeutic approaches to the growth/differentiation effect of Bn-peptides, as well as the therapeutic implication of the frequent BnR over-expression for tumor-imaging and/or targeted-delivery.

EXPERT OPINION

Given that Bn-related-peptides/BnRs are so frequently ectopically-expressed by common tumors, which are often malignant and become refractory to conventional treatments, therapeutic interventions using novel approaches to Bn-peptides and receptors are being explored. Of particular interest is the potential of reproducing with BnRs in common tumors the recent success of utilizing overexpression of somatostatin-receptors by neuroendocrine-tumors to provide the most sensitive imaging methods and targeted delivery of cytotoxic-compounds.

Metabolically Stabilized (68)Ga-NOTA-Bombesin for PET Imaging of Prostate Cancer and Influence of Protease Inhibitor Phosphoramidon

Peptide receptor-based targeted molecular imaging and therapy of cancer is on the current forefront of nuclear medicine preclinical research and clinical practice. The frequent overexpression of gastrin-releasing peptide (GRP) receptors in prostate cancer stimulated the development of radiolabeled bombesin derivatives as high affinity peptide ligands for selective targeting of the GRP receptor. In this study, we have evaluated a novel (68)Ga-labeled bombesin derivative for PET imaging of prostate cancer in vivo. In addition, we were interested in testing the recently proposed "serve-and-protect" strategy to improve metabolic stability of radiolabeled peptides in vivo and to enhance tumor uptake. GRP receptor targeting peptides NOTA-BBN2 and (nat)Ga-NOTA-BBN2 demonstrated a characteristic antagonistic profile and high binding affinity toward the GRP receptor in PC3 cells (IC50 4.6-8.2 nM). Radiolabeled peptide (68)Ga-NOTA-BBN2 was obtained from NOTA-BBN2 in radiochemical yields greater than 62% (decay-corrected). Total synthesis time was 35 min, including purification using solid-phase extraction. (68)Ga-NOTA-BBN2 exhibited favorable resistance against metabolic degradation by peptidases in vivo within the investigated time frame of 60 min. Interestingly, metabolic stability was not further enhanced in the presence of protease inhibitor phosphoramidon. Dynamic PET studies showed high tumor uptake in both PC3- and LNCaP-bearing BALB/c nude mice (SUV5min > 0.6; SUV60min > 0.5). Radiotracer (68)Ga-NOTA-BBN2 represents a novel radiometal-based bombesin derivative suitable for GRP receptor targeting in PC3 and LNCaP mouse xenografts. Further increase of metabolic stability in vivo and enhanced tumor uptake were not observed upon administration of protease inhibitor phosphoramidon. This led to the conclusion that the recently proposed "serve-and-protect" strategy may not be valid for peptides exhibiting favorable intrinsic metabolic stability in vivo.

(68)Ga-AMBA and (18)F-FDG for preclinical PET imaging of breast cancer: effect of tamoxifen treatment on tracer uptake by tumor

INTRODUCTION

AMBA is a bombesin analogue that binds to GRPr. In a mouse model of estrogen-dependent human breast cancer, we tested whether (68)Ga-AMBA can be used for PET detection of GRPr-expressing tumors and could be more accurate than (18)F-FDG to monitor tumor response to hormone therapy.

METHODS

The radiolabeling of (68)Ga-AMBA was automated using a R&D Synchrom module. ZR75-1, a breast cancer cell line, was xenografted in nude mice. (68)Ga-AMBA tumor uptake was compared with that of (18)F-FDG before and after treatment with tamoxifen.

RESULTS

AMBA was (68)Ga-radiolabelled in 30min with 95.3% yield and purity≥98%. Prior to treatment, (68)Ga-AMBA was highly concentrated into tumors (tumor to non-tumor ratio=2.4 vs. 1.3 with (18)F-FDG). With tamoxifen treatment (n=6) (68)Ga-AMBA uptake plateaued after 1week and decreased after 2weeks, with a significant reduction compared to controls (n=4). In contrast the effect of tamoxifen treatment could not be appreciated using (18)F-FDG.

CONCLUSIONS

(68)Ga-AMBA appeared better than (18)F-FDG to visualize and monitor the response to hormone treatment in this breast cancer model.

Characterization and evaluation of DOTA-conjugated Bombesin/RGD-antagonists for prostate cancer tumor imaging and therapy

INTRODUCTION

Here we present the metallation, characterization, in vivo and in vitro evaluations of dual-targeting, peptide-based radiopharmaceuticals with utility for imaging and potentially treating prostate tumors by virtue of their ability to target the αVβ3 integrin or the gastrin releasing peptide receptor (GRPr).

METHODS

[RGD-Glu-6Ahx-RM2] (RGD: Arg-Gly-Asp; Glu: glutamic acid; 6-Ahx: 6-amino hexanoic acid; RM2: (D-Phe-Gln-Trp-Ala-Val-Gly-His-Sta-Leu-NH2)) was conjugated to a DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) bifunctional chelator (BFCA) purified via reversed-phase high-performance liquid chromatography (RP-HPLC), characterized by electrospray ionization-mass spectrometry (ESI-MS), and radiolabeled with (111)In or (177)Lu. Natural-metallated compounds were assessed for binding affinity for the αVβ3 integrin or GRPr in human glioblastoma U87-MG and prostate PC-3 cell lines and stability prior to in vivo evaluation in normal CF-1 mice and SCID mice xenografted with PC-3 cells.

RESULTS

Competitive displacement binding assays with PC-3 and U87-MG cells revealed high to moderate binding affinity for the GRPr or the αVβ3 integrin (IC50 range of 5.39±1.37 nM to 9.26±0.00 nM in PC-3 cells, and a range of 255±47 nM to 321±85 nM in U87-MG cells). Biodistribution studies indicated high tumor uptake in PC-3 tumor-bearing mice (average of 7.40±0.53% ID/g at 1h post-intravenous injection) and prolonged retention of tracer (mean of 4.41±0.91% ID/g at 24h post-intravenous injection). Blocking assays corroborated the specificity of radioconjugates for each target. Micro-single photon emission computed tomography (microSPECT) confirmed favorable radiouptake profiles in xenografted mice at 20h post-injection.

CONCLUSIONS

[RGD-Glu-[(111)In-DO3A]-6-Ahx-RM2] and [RGD-Glu-[(177)Lu- DO3A]-6-Ahx-RM2] show favorable pharmacokinetic and radiouptake profiles, meriting continued evaluation for molecular imaging in murine U87-MG/PC-3 xenograft models and radiotherapy studies with (177)Lu and (90)Y conjugates.

ADVANCES IN KNOWLEDGE AND IMPLICATIONS FOR PATIENT CARE

These heterovalent, peptide-targeting ligands perform comparably with many mono- and multivalent conjugates with the potential benefit of increased sensitivity for detecting cancer cells exhibiting differential expression of target receptors.

⁸⁹Zr-huJ591 immuno-PET imaging in patients with advanced metastatic prostate cancer

PURPOSE

Given the bone tropism of prostate cancer, conventional imaging modalities poorly identify or quantify metastatic disease. (89)Zr-huJ591 positron emission tomography (PET) imaging was performed in patients with metastatic prostate cancer to analyze and validate this as an imaging biomarker for metastatic disease. The purpose of this initial study was to assess safety, biodistribution, normal organ dosimetry, and optimal imaging time post-injection for lesion detection.

METHODS

Ten patients with metastatic prostate cancer received 5 mCi of (89)Zr-huJ591. Four whole-body scans with multiple whole-body count rate measurements and serum activity concentration measurements were obtained in all patients. Biodistribution, clearance, and lesion uptake by (89)Zr-huJ591 immuno-PET imaging was analyzed and dosimetry was estimated using MIRD techniques. Initial assessment of lesion targeting of (89)Zr-huJ591 was done. Optimal time for imaging post-injection was determined.

RESULTS

The dose was well tolerated with mild chills and rigors seen in two patients. The clearance of (89)Zr-huJ591 from serum was bi-exponential with biological half-lives of 7 ± 4.5 h (range 1.1-14 h) and 62 ± 13 h (range 51-89 h) for initial rapid and later slow phase. Whole-body biological clearance was 219 ± 48 h (range 153-317 h). The mean whole-body and liver residence time was 78.7 and 25.6 h, respectively. Dosimetric estimates to critical organs included liver 7.7 ± 1.5 cGy/mCi, renal cortex 3.5 ± 0.4 cGy/mCi, and bone marrow 1.2 ± 0.2 cGy/mCi. Optimal time for patient imaging after injection was 7 ± 1 days. Lesion targeting of bone or soft tissue was seen in all patients. Biopsies were performed in 8 patients for a total 12 lesions, all of which were histologically confirmed as metastatic prostate cancer. One biopsy-proven lesion was not positive on (89)Zr-huJ591, while the remaining 11 lesions were (89)Zr-huJ591 positive. Two biopsy-positive nodal lesions were noted only on (89)Zr-huJ591 study, while the conventional imaging modality was negative.

CONCLUSION

(89)Zr-huJ591 PET imaging of prostate-specific membrane antigen expression is safe and shows good localization of disease in prostate cancer patients. Liver is the critical organ for dosimetry, and 7 ± 1 days is the optimal imaging time. A larger study is underway to determine lesion detection in an expanded cohort of patients with metastatic prostate cancer.

PET imaging of prostate tumors with 18F-Al-NOTA-MATBBN

Overexpression of the gastrin-releasing peptide receptor (GRPR) in prostate cancer provides a promising target for detection the disease. MATBBN is a new bombesin analog originating from the GRPR antagonists with a hydrophilic linker. In this study NOTA-conjugated MATBBN was labeled by the Al(18)F method and the potential of (18)F-Al-NOTA-MATBBN for prostate tumor PET imaging was also evaluated. NOTA-MATBBN was radiolabeled with (18) F using Al(18)F complexes. Partition coefficient, in vitro stability and GRPR binding affinity were also determined. PET studies were performed with (18)F-Al-NOTA-MATBBN in PC-3 tumor-bearing mice. (18)F-Al-NOTA-MATBBN can be produced within 30 min with a decay-corrected yield of 62.5 ± 2.1% and a radiochemical purity of >98%. The logP octanol-water value for the Al(18)F-labeled BBN analog was -2.40 ± 0.07 and the radiotracer was stable in phosphate-buffered saline and human serum for 2 h. The IC50 values of displacement for the (18)F-Al-NOTA-MATBBN with MATBBN was 126.9 ± 2.75 nm. The PC-3 tumors were clearly visible with high contrast after injection of the labeled peptide. At 60 min post-injection, the tumor uptakes for (18)F-Al-NOTA-MATBBN and (18)F-FDG were 4.59 ± 0.43 and 1.98 ± 0.35% injected dose/g, and tumor to muscle uptake radios for two tracers were 6.77 ± 1.10 and 1.78 ± 0.32, respectively. Dynamic PET revealed that (18) F-Al-NOTA-MATBBN was excreted mainly through the kidneys. GRPR-binding specificity was also demonstrated by reduced tumor uptake of (18)F-Al-NOTA-MATBBN after coinjection with excess unlabeled MATBBN peptide at 1 h post-injection. NOTA- MATBBN could be labeled rapidly with (18)F using one step method. (18)F-Al-NOTA-MATBBN may be a promising PET imaging agent for prostate cancer.

Design, synthesis, and in vitro evaluation of a binary targeting MRI contrast agent for imaging tumor cells

A binary targeting vector that consists of peptide sequences of Arg-Gly-Asp (RGD) and Asn-Gly-Arg (NGR) motifs has been designed and synthesized using solid-phase peptide synthesis procedure. The vector is then coupled with Gd-DOTA to work as a targeting contrast agent (CA1) for magnetic resonance imaging of human lung adenocarcinoma cells A549. Its longitudinal relaxivity is measured to be 7.55 mM(-1) s(-1) in aqueous solution at a magnetic field of 11.7 T, which is higher than that of Magnevist (4.25 mM(-1) s(-1)) in the same conditions. The cell experiment shows, at the same concentration, uptake quantity of CA1 by A549 is much more than Magnevist and also superior over CA2 (a single targeting contrast agent contains only RGD). The uptake can be blocked by the targetable peptide containing RGD or NGR without coupling Gd. To summarize, CA1 has very good ability to target A549 and higher relaxivity than that of Magnevist. So CA1 is promising MRI contrast agent for high-resolution MR molecular imaging of human lung adenocarcinoma A549 cells.

Prospective of ⁶⁸Ga-radiopharmaceutical development

Positron Emission Tomography (PET) experienced accelerated development and has become an established method for medical research and clinical routine diagnostics on patient individualized basis. Development and availability of new radiopharmaceuticals specific for particular diseases is one of the driving forces of the expansion of clinical PET. The future development of the ⁶⁸Ga-radiopharmaceuticals must be put in the context of several aspects such as role of PET in nuclear medicine, unmet medical needs, identification of new biomarkers, targets and corresponding ligands, production and availability of ⁶⁸Ga, automation of the radiopharmaceutical production, progress of positron emission tomography technologies and image analysis methodologies for improved quantitation accuracy, PET radiopharmaceutical regulations as well as advances in radiopharmaceutical chemistry. The review presents the prospects of the ⁶⁸Ga-based radiopharmaceutical development on the basis of the current status of these aspects as well as wide range and variety of imaging agents.

A comparative study of radiolabeled bombesin analogs for the PET imaging of prostate cancer

Radiolabeled bombesin (BBN) analogs that bind to the gastrin-releasing peptide receptor (GRPR) represent a topic of active investigation for the development of molecular probes for PET or SPECT of prostate cancer (PCa). RM1 and AMBA have been identified as the 2 most promising BBN peptides for GRPR-targeted cancer imaging and therapy. In this study, to develop a clinically translatable BBN-based PET probe, we synthesized and evaluated (18)F-AlF- (aluminum-fluoride) and (64)Cu-radiolabeled RM1 and AMBA analogs for their potential application in PET imaging of PCa.

METHODS

1,4,7-triazacyclononane, 1-glutaric acid-4,7 acetic acid (NODAGA)-conjugated RM1 and AMBA were synthesized and tested for their GRPR-binding affinities. The NODAGA-RM1 and NODAGA-AMBA probes were further radiolabeled with (64)Cu or (18)F-AlF and then evaluated in a subcutaneous PCa xenograft model (PC3) by small-animal PET imaging and biodistribution studies.

RESULTS

NODAGA-RM1 and NODAGA-AMBA can be successfully synthesized and radiolabeled with (64)Cu and (18)F-AlF. (64)Cu- and (18)F-AlF-labeled NODAGA-RM1 demonstrated excellent serum stability and tumor-imaging properties in the in vitro stability assays and in vivo imaging studies. (64)Cu-NODAGA-RM1 exhibited tumor uptake values of 3.3 ± 0.38, 3.0 ± 0.76, and 3.5 ± 1.0 percentage injected dose per gram of tissue (%ID/g) at 0.5, 1.5, and 4 h after injection, respectively. (18)F-AlF-NODAGA-RM1 exhibited tumor uptake values of 4.6 ± 1.5, 4.0 ± 0.87, and 3.9 ± 0.48 %ID/g at 0.5, 1, and 2 h, respectively.

CONCLUSION

The high-stability, efficient tumor uptake and optimal pharmacokinetic properties highlight (18)F-AlF-NODAGA-RM1 as a probe with great potential and clinical application for the PET imaging of prostate cancer.

(68)Ga-labeled bombesin analogs for receptor-mediated imaging

Targeted receptor-mediated imaging techniques have become crucial tools in present targeted diagnosis and radiotherapy as they provide accurate and specific diagnosis of disease information. Peptide-based pharmaceuticals are gaining popularity, and there has been vast interest in developing (68)Ga-labeled bombesin (Bn) analogs. The gastrin-releasing peptide (GRP) family and its Bn analog have been implicated in the biology of several human cancers. The three bombesin receptors GRP, NMB, and BRS-3 receptor are most frequently ectopically expressed by common, important malignancies. The low expression of Bn/GRP receptors in normal tissue and relatively high expression in a variety of human tumors can be of biological importance and form a molecular basis for Bn/GRP receptor-mediated imaging. To develop a Bn-like peptide with favorable tumor targeting and pharmacokinetic characteristics for possible clinical use, several modifications in the Bn-like peptides, such as the use of a variety of chelating agents, i.e., acyclic and macrocyclic agents with different spacer groups and with different metal ions (gallium), have been performed in recent years without significant disturbance of the vital binding scaffold. The favorable physical properties of (68)Ga, i.e., short half-life, and the fast localization of small peptides make this an ideal combination to study receptor-mediated imaging in patients.

The untapped potential of Gallium 68-PET: the next wave of ⁶⁸Ga-agents

(68)Gallium-PET ((68)Ga-PET) agents have significant clinical promise. The radionuclide can be produced from a (68)Ge/(68)Ga generator on site and is a convenient alternative to cyclotron-based PET isotopes. The short half-life of (68)Ga permits imaging applications with sufficient radioactivity while maintaining patient dose to an acceptable level. Furthermore, due to superior resolution, (68)Ga-PET agents have the ability to replace current SPECT agents in many applications. This article outlines the upcoming agents and challenges faced during the translational development of (68)Ga agents.

Molecular imaging of prostate cancer: PET radiotracers

OBJECTIVE

Recent advances in the fundamental understanding of the complex biology of prostate cancer have provided an increasing number of potential targets for imaging and treatment. The imaging evaluation of prostate cancer needs to be tailored to the various phases of this remarkably heterogeneous disease.

CONCLUSION

In this article, I review the current state of affairs on a range of PET radiotracers for potential use in the imaging evaluation of men with prostate cancer.

Radiolabelled peptides for oncological diagnosis

Radiolabelled receptor-binding peptides targeting receptors (over)expressed on tumour cells are widely under investigation for tumour diagnosis and therapy. The concept of using radiolabelled receptor-binding peptides to target receptor-expressing tissues in vivo has stimulated a large body of research in nuclear medicine. The ¹¹¹In-labelled somatostatin analogue octreotide (OctreoScan™) is the most successful radiopeptide for tumour imaging, and was the first to be approved for diagnostic use. Based on the success of these studies, other receptor-targeting peptides such as cholecystokinin/gastrin analogues, glucagon-like peptide-1, bombesin (BN), chemokine receptor CXCR4 targeting peptides, and RGD peptides are currently under development or undergoing clinical trials. In this review, we discuss some of these peptides and their analogues, with regard to their potential for radionuclide imaging of tumours.

Radiolabeled peptides: valuable tools for the detection and treatment of cancer

Human cancer cells overexpress many peptide receptors as molecular targets. Radiolabeled peptides that bind with high affinity and specificity to the receptors on tumor cells hold great potential for both diagnostic imaging and targeted radionuclide therapy. The advantage of solid-phase peptide synthesis, the availability of different chelating agents and prosthetic groups and bioconjugation techniques permit the facile preparation of a wide variety of peptide-based targeting molecules with diverse biological and tumor targeting properties. Some of these peptides, including somatostatin, bombesin, vasoactive intestinal peptide, gastrin, neurotensin, exendin and RGD are currently under investigation. It is anticipated that in the near future many of these peptides may find applications in nuclear oncology. This article presents recent developments in the field of small peptides, and their applications in the diagnosis and treatment of cancer.

Current research in nuclear medicine and molecular imaging: highlights of the 23rd Annual EANM Congress

The most recent research developments in nuclear medicine and molecular imaging were presented at the 2010 Annual Congress of the EANM. This review summarizes some of the most relevant contributions made in the fields of oncology, cardiovascular science, neurology and psychiatry, technological innovation and novel tracers. Presentations covered basic and clinical research in nuclear medicine and molecular imaging, and diagnostic and therapeutic applications of radioisotopes and radiopharmaceuticals on a global scale. The results reported demonstrate that investigative strategies using nuclear medicine techniques facilitate effective diagnosis and management of patients with most prevalent disease states. At the same time novel tracers and technologies are being explored, which hold promise for future new applications of nuclear medicine and molecular imaging in research and clinical practice.