A stable neurotensin-based radiopharmaceutical for targeted imaging and therapy of neurotensin receptor-positive tumours

Purpose: Neurotensin (NT) and its high affinity receptor (NTR1) are involved in several neoplastic processes. Thus, NT-based radiopharmaceuticals are potential tracers for targeted diagnosis and therapy of NTR-positive tumours. A new analogue based on NT(8-13), NT-XIX, with the three enzymatic cleavage sites stabilised, was synthesised and tested. Methods: The synthesis was performed by Boc strategy. Labelling with 99mTc/188Re was performed using the tricarbonyl technique. Metabolic stability was tested in vitro and in vivo. NT-XIX was further characterised in vitro in HT-29 cells and in vivo in nude mice with HT-29 xenografts. Results: NT-XIX showed much longer half-lives than non-stabilised analogues. Binding to NTR1 was highly specific, although the affinity was lower than that of natural NT. Bound activity rapidly internalised into HT-29 cells and 50% remained trapped after 24h. In the time-course biodistribution, the highest uptake was found in the tumour at all p.i. times. In vivo uptake was specific, and accumulation of activity in the kidneys was low. Radioactivity clearance from healthy organs was faster than that from the tumour, resulting in improved tumour-to-tissue ratios and good SPECT/CT imaging. Treatment with 188Re-NT-XIX (30MBq, in three or four fractions) decreased tumour growth by 50% after 3weeks. Conclusion: The high in vivo stability and the favourable in vivo behaviour makes NT-XIX an excellent candidate for the imaging and therapy of NTR1-positive tumour

Radiation dosimetry and biodistribution of 11C-ABP688 measured in healthy volunteers

Introduction: In this study, we assessed the whole-body biodistribution and radiation dosimetry of the new glutamatergic ligand 11C-ABP688. This ligand binds specifically to the metabotropic glutamatergic receptor of subtype 5 (mGluR5). Materials and methods: The study included five healthy male volunteers aged 20-29years. After intravenous injection of 240-260MBq, a series of four to ten whole-body positron emission tomography/computed tomography scans were initiated, yielding 60-80min of data. Residence times were then calculated in the relevant organs, and the software packages Mirdose and Olinda were used to calculate the absorbed radiation dose and the effective dose equivalent. Results: Of the excreted 11C activity at 1hour, approximately 80% were eliminated via the hepato-biliary pathway and 20% through the urinary tract. The absorbed dose (mGy/MBq) was highest in the liver (1.64 E -2 ± 5.08 E -3), gallbladder (8.13 E -3 ± 5.6 E -3), and kidneys (7.27 E -3 ± 2.79 E -3). The effective dose equivalent was 3.68 ± 0.84microSv/MBq. Brain uptake in the areas with high mGluR5 density was 2-3 (SUV). The agreement between the values obtained from Mirdose and the Olinda was excellent. Conclusion: 11C-ABP688 is a very promising ligand for the investigation of mGluR5 receptors in humans. Brain uptake is high and the effective dose equivalent so low that serial examinations in the same subject seem feasibl

The biodistribution of self-assembling protein nanoparticles shows they are promising vaccine platforms

Background Because of the need to limit side-effects, nanoparticles are increasingly being studied as drug-carrying and targeting tools. We have previously reported on a scheme to produce protein-based self-assembling nanoparticles that can act as antigen display platforms. Here we attempted to use the same system for cancer-targeting, making use of a C-terminal bombesin peptide that has high affinity for a receptor known to be overexpressed in certain tumors, as well as an N-terminal polyhistidine tag that can be used for radiolabeling with technetium tricarbonyl. Results In order to increase circulation time, we experimented with PEGylated and unPEGylated varities typo particle. We also tested the effect of incorporating different numbers of bombesins per nanoparticle. Biophysical characterization determined that all configurations assemble into regular particles with relatively monodisperse size distributions, having peaks of about 33 – 36 nm. The carbonyl method used for labeling produced approximately 80% labeled nanoparticles. In vitro, the nanoparticles showed high binding, both specific and non-specific, to PC-3 prostate cancer cells. In vivo, high uptake was observed for all nanoparticle types in the spleens of CD-1 nu/nu mice, decreasing significantly over the course of 24 hours. High uptake was also observed in the liver, while only low uptake was seen in both the pancreas and a tumor xenograft. Conclusions The data suggest that the nanoparticles are non-specifically taken up by the reticuloendothelial system. Low uptake in the pancreas and tumor indicate that there is little or no specific targeting. PEGylation or increasing the amount of bombesins per nanoparticle did not significantly improve targeting. In particular, the uptake in the spleen, which is a primary organ of the immune system, highlights the potential of the nanoparticles as vaccine carriers. Also, the decrease in liver and spleen radioactivity with time implies that the nanoparticles are broken down and cleared. This is an important finding, as it shows that the nanoparticles can be safely used as a vaccine platform without the risk of prolonged side effects. Furthermore, it demonstrates that technetium carbonyl radiolabeling of our protein-based nanoparticles can be used to evaluate their pharmacokinetic properties in vivo.ISSN:1477-315

A stable neurotensin-based radiopharmaceutical for targeted imaging and therapy of neurotensin receptor-positive tumors

ISSN:1619-7070ISSN:1619-708

Improving the tumor uptake of 99mTc-labeled neuropeptides using stabilized peptide analogues

Two neuropeptides, bombesin (BBS) and neurotensin (NT) and their radiolabeled analogues, have great potential for tumour targeting, either for diagnosis (e.g. with 99mTc) or therapy (e.g. with 90Y or 188Re). In this study, we investigated NT(8-13) and BBS(7-14) analogues with Na-histidinyl acetate linked to the N-terminus of the peptide. This His-derivative forms a stable and inert tridentate complex with the 99mTc(CO)3 and the 188Re(CO)3 moieties. The stability of 99mTc-labeled neurotensin and bombesin analogues was tested in human plasma samples and in tumour cell cultures in the presence and absence of specific enzyme inhibitors. The inhibitor of ACE (angiotensin converting enzyme) was the most effective in inhibiting the peptide cleavage of both NT(8-13) and BBS(7-14). In agreement with this finding, the replacement of Ile12 by tert-leucine (NT) and Leu13 by cyclohexylalanin (BBS) brought about a better stability. With NT(8-13) analogues, higher tumour to nontarget (t/nt) ratios and the same affinity to the receptor was observed, but with BBS(7-14) derivatives the affinity was lower and the t/nt ratio was not significantly improved. Toxicity tests showed no effect in mice of up to a five-hundred-fold higher dose than planned for patient application, which started successfully with NT(8-13) analogues.SCOPUS: cp.jinfo:eu-repo/semantics/publishe

PEGylation, increasing specific activity and multiple dosing as strategies to improve the risk-benefit profile of targeted radionuclide therapy with 177Lu-DOTA-bombesin analogues

Background Radiolabelled bombesin (BN) conjugates are promising radiotracers for imaging and therapy of breast and prostate tumours, in which BN2/gastrin-releasing peptide receptors are overexpressed. We describe the influence of the specific activity of a 177Lu-DOTA-PEG5k-Lys-B analogue on its therapeutic efficacy and compare it with its non-PEGylated counterpart. Methods Derivatisation of a stabilised DOTA-BN(7–14)[Cha13,Nle14] analogue with a linear PEG molecule of 5 kDa (PEG5k) was performed by PEGylation of the ϵ-amino group of a β3hLys-βAla-βAla spacer between the BN sequence and the DOTA chelator. The non-PEGylated and the PEGylated analogues were radiolabelled with 177Lu. In vitro evaluation was performed in human prostate carcinoma PC-3 cells, and in vivo studies were carried out in nude mice bearing PC-3 tumour xenografts. Different specific activities of the PEGylated BN analogue and various dose regimens were evaluated concerning their therapeutic efficacy. Results The specificity and the binding affinity of the BN analogue for BN2/GRP receptors were only slightly reduced by PEGylation. In vitro binding kinetics of the PEGylated analogue was slower since steady-state condition was reached after 4 h. PEGylation improved the stability of BN conjugate in vitro in human plasma by a factor of 5.6. The non-PEGylated BN analogue showed favourable pharmacokinetics already, i.e. fast blood clearance and renal excretion, but PEGylation improved the in vivo behaviour further. One hour after injection, the tumour uptake of the PEG5k-BN derivative was higher compared with that of the non-PEGylated analogue (3.43 ± 0.63% vs. 1.88 ± 0.4% ID/g). Moreover, the increased tumour retention resulted in a twofold higher tumour accumulation at 24 h p.i., and increased tumour-to-non-target ratios (tumour-to-kidney, 0.6 vs. 0.4; tumour-to-liver, 8.8 vs. 5.9, 24 h p.i.). In the therapy study, both 177Lu-labelled BN analogues significantly inhibited tumour growth. The therapeutic efficacy was highest for the PEGylated derivative of high specific activity administered in two fractions (2 × 20 MBq = 40 MBq) at day 0 and day 7 (73% tumour growth inhibition, 3 weeks after therapy). Conclusions PEGylation and increasing the specific activity enhance the pharmacokinetic properties of a 177Lu-labelled BN-based radiopharmaceutical and provide a protocol for targeted radionuclide therapy with a beneficial anti-tumour effectiveness and a favourable risk-profile at the same time.ISSN:2191-219

Radiopharmaceuticals: From Molecular Imaging to Targeted Radionuclide Therapy

The research and development of smart radiodrugs is the goal of the Center of Radiopharmaceutical Science of ETH, PSI, and USZ. Positron Emission Tomography (PET) allows the non-invasive visualization of biochemical processes within the body. Radiolabeled PET-tracers allow the study of neurophysiological diseases like Alzheimer, Parkinson's disease or the imaging of metastatic tumors. PET-techniques are nowadays an important part of routine nuclear medicine diagnosis. Tumor-cell targeting biomolecules (e.g. antibodies or peptides) coupled to therapeutic radionuclides can sterilize the malignant cells while sparing healthy tissue. This so-called targeted radionuclide therapy has made tremendous progress in the recent years and the first approved radiotherapeutics are available for clinical use

Radiation dosimetry and biodistribution of 11C-ABP688 measured in healthy volunteers

ISSN:1619-7070ISSN:1619-708