Towards Cancer Nanoradiopharmaceuticals-Radioisotope Nanocarrier System for Prostate Cancer Theranostics Based on Radiation-Synthesized Polymer Nanogels.

Despite the tremendous development of oncology, prostate cancer remains a debilitating malignancy. One of the most promising approaches to addressing this issue is to exploit the advancements of nanomedicine in combination with well-established nuclear medicine and radiotherapy. Following this idea, we have developed a radioisotope nanocarrier platform of electron-beam-synthesized nanogels based on poly(acrylic acid). We have developed a functionalization protocol, showing the very high (>97%) efficiency of the conjugation in targeting a ligand-bombesin derivative. This engineered peptide can bind gastrin-releasing peptide receptors overexpressed in prostate cancer cells; moreover, it bears a radioisotope-chelating moiety. Our nanoplatform exhibits very promising performance in vitro; the radiolabeled nanocarriers maintained high radiochemical purity of >90% in both the labeling buffer and human serum for up to 14 days. The application of the targeted nanocarrier allowed also effective and specific uptake in PC-3 prostate cancer cells, up to almost 30% after 4 h, which is a statistically significant improvement in comparison to carrier-free radiolabeled peptides. Although our system requires further studies for more promising results in vivo, our study represents a vital advancement in radionanomedicine-one of many steps that will lead to effective therapy for castration-resistant prostate cancer.

[99mTc]Tc-PSMA-T4-Novel SPECT Tracer for Metastatic PCa: From Bench to Clinic.

Despite significant advances in nuclear medicine for diagnosing and treating prostate cancer (PCa), research into new ligands with increasingly better biological properties is still ongoing. Prostate-specific membrane antigen (PSMA) ligands show great potential as radioisotope carriers for the diagnosis and therapy of patients with metastatic PCa. PSMA is expressed in most types of prostate cancer, and its expression is increased in poorly differentiated, metastatic, and hormone-refractory cancers; therefore, it may be a valuable target for the development of radiopharmaceuticals and radioligands, such as urea PSMA inhibitors, for the precise diagnosis, staging, and treatment of prostate cancer. Four developed PSMA-HYNIC inhibitors for technetium-99m labeling and subsequent diagnosis were subjected to preclinical in vitro and in vivo studies to evaluate and compare their diagnostic properties. Among the studied compounds, the PSMA-T4 (Glu-CO-Lys-L-Trp-4-Amc-HYNIC) inhibitor showed the best biological properties for the diagnosis of PCa metastases. [99mTc]Tc-PSMA-T4 also showed effectiveness in single-photon emission computed tomography (SPECT) studies in humans, and soon, its usefulness will be extensively evaluated in phase 2/3 clinical trials.

IAEA Contribution to Nanosized Targeted Radiopharmaceuticals for Drug Delivery.

The rapidly growing interest in the application of nanoscience in the future design of radiopharmaceuticals and the development of nanosized radiopharmaceuticals in the late 2000's, resulted in the creation of a Coordinated Research Project (CRP) by the International Atomic Energy Agency (IAEA) in 2014. This CRP entitled 'Nanosized delivery systems for radiopharmaceuticals' involved a team of expert scientist from various member states. This team of scientists worked on a number of cutting-edge areas of nanoscience with a focus on developing well-defined, highly effective and site-specific delivery systems of radiopharmaceuticals. Specifically, focus areas of various teams of scientists comprised of the development of nanoparticles (NPs) based on metals, polymers, and gels, and their conjugation/encapsulation or decoration with various tumor avid ligands such as peptides, folates, and small molecule phytochemicals. The research and development efforts also comprised of developing optimum radiolabeling methods of various nano vectors using diagnostic and therapeutic radionuclides including Tc-99m, Ga-68, Lu-177 and Au-198. Concerted efforts of teams of scientists within this CRP has resulted in the development of various protocols and guidelines on delivery systems of nanoradiopharmaceuticals, training of numerous graduate students/post-doctoral fellows and publications in peer reviewed journals while establishing numerous productive scientific networks in various participating member states. Some of the innovative nanoconstructs were chosen for further preclinical applications-all aimed at ultimate clinical translation for treating human cancer patients. This review article summarizes outcomes of this major international scientific endeavor.

Does the Number of Bifunctional Chelators Conjugated to a mAb Affect the Biological Activity of Its Radio-Labeled Counterpart? Discussion Using the Example of mAb against CD-20 Labeled with 90Y or 177Lu.

There has been considerable interest in developing a monoclonal antibody (mAb) against-CD-20 (for example, Rituximab) modified by bifunctional chelating agents (BCA) for non-Hodgkin's lymphoma radioimmunotherapy. Therefore, many researchers have modified this monoclonal antibody by attaching different BCA moieties and evaluated their biological activities in terms of in vitro study and in vivo study in healthy and tumor xenografted rodents. This mini-perspective reviews the in vitro studies, the immunoreactivity and physiological distribution studies: organ-to-blood and the tumor-to-organ ratio of conjugates with different numbers of chelators per mAb. We set up a null hypothesis that states there is no statistical significance between the biological activity of monoclonal antibody (Rituximab) and the number of conjugated bifunctional chelators. Overall, we have concluded that there is no strong evidence for this hypothesis. However, the literature data should be questioned due to the potential lack of uniform study methodology.

Initial Experience of Clinical Use of [99mTc]Tc-PSMA-T4 in Patients with Prostate Cancer. A Pilot Study.

Numerous different molecules of prostate-specific membrane antigen (PSMA) ligands are used to detect prostate cancer (PCa); most approaches utilize gallium PET and a few reports describe the role of SPECT/CT. [99mTc]Tc-PSMA-T4 is a new radiopharmaceutical designed for the diagnosis of patients with PCa. We conducted a single site, prospective, preliminary case series study that included 31 patients with PCa; all had undergone clinical, biochemical or imaging examination and exhibited clear or suspicious active disease or clinical/biochemical recurrence of PCa. Whole-body (WB) SPECT/CT after i.v. administration of [99mTc]Tc-PSMA-T4 was utilized; acquisition images were obtained at three time points. The clinical value of the images was assessed in regard to the evaluation of tumor extent in patients with confirmed PC that qualified for initial therapy and the evaluation of tumor recurrence; both provided encouraging results. The late acquisition of WB-SPECT resulted in better lesions delineation. The results of the analysis of the sensitivity/specificity were: 92%/100% in cases of primary cancer, 83%/100% in terms of pelvic lymph nodes disease, 100%/95% in other lymph nodes and soft tissue involvement, respectively, and bone mets were both 100%. An oncotropic SPECT [99mTc]Tc-PSMA-T4 can help in selecting a rational therapeutic strategy for a patient with an initial diagnosis of PCa by assessing the extent of cancer and also after complex radical or palliative therapy in case of biochemical recurrence for re-staging.

Synthesis and Properties of Targeted Radioisotope Carriers Based on Poly(Acrylic Acid) Nanogels.

Radiation crosslinking was employed to obtain nanocarriers based on poly(acrylic acid)-PAA-for targeted delivery of radioactive isotopes. These nanocarriers are internally crosslinked hydrophilic macromolecules-nanogels-bearing carboxylic groups to facilitate functionalization. PAA nanogels were conjugated with an engineered bombesin-derivative-oligopeptide combined with 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate chelating moiety, aimed to provide selective radioligand transport. 4-(4,6-Dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium (DMTMM) toluene-4-sulfonate was used as the coupling agent. After tests on a model amine-p-toluidine-both commercial and home-synthesized DOTA-bombesin were successfully coupled to the nanogels and the obtained products were characterized. The radiolabeling efficiency of nanocarriers with 177Lu, was chromatographically tested. The results provide a proof of concept for the synthesis of radiation-synthesized nanogel-based radioisotope nanocarriers for theranostic applications.

PSMA-D4 Radioligand for Targeted Therapy of Prostate Cancer: Synthesis, Characteristics and Preliminary Assessment of Biological Properties.

A new PSMA ligand (PSMA-D4) containing the Glu-CO-Lys pharmacophore connected with a new linker system (L-Trp-4-Amc) and chelator DOTA was developed for radiolabeling with therapeutic radionuclides. Herein we describe the synthesis, radiolabeling, and preliminary biological evaluation of the novel PSMA-D4 ligand. Synthesized PSMA-D4 was characterized using TOF-ESI-MS, NMR, and HPLC methods. The novel compound was subject to molecular modeling with GCP-II to compare its binding mode to analogous reference compounds. The radiolabeling efficiency of PSMA-D4 with 177Lu, 90Y, 47Sc, and 225Ac was chromatographically tested. In vitro studies were carried out in PSMA-positive LNCaP tumor cells membranes. The ex vivo tissue distribution profile of the radioligands and Cerenkov luminescence imaging (CLI) was studied in LNCaP tumor-bearing mice. PSMA-D4 was synthesized in 24% yield and purity >97%. The radio complexes were obtained with high yields (>97%) and molar activity ranging from 0.11 to 17.2 GBq mcmol-1, depending on the radionuclide. In vitro assays confirmed high specific binding and affinity for all radiocomplexes. Biodistribution and imaging studies revealed high accumulation in LNCaP tumor xenografts and rapid clearance of radiocomplexes from blood and non-target tissues. These render PSMA-D4 a promising ligand for targeted therapy of prostate cancer (PCa) metastases.

Development and validation of the HPLC method for quality control of radiolabelled DOTA-TATE and DOTA-TOC preparations.

INTRODUCTION: The information on the presence of cold metal complexes in radiolabeled DOTA-TATE or DOTA-TOC is important in assessing the cause of the radiolabeling failure, poor radiolabeling yield and/or low effective molar activity. DOTA-peptide complexes are detectable using UV-Vis detector. The main limitation in the quantitative analysis is the limited availability of standard substances and the lack of data on their molar absorption coefficients. The aim of our study was development and validation of HPLC method enabling RCP analysis and identification and quantification of metal complexes impurities in the radiopharmaceutical preparations of DOTA-chelated peptides. METHODS: Complexes of DOTA-TATE and DOTA-TOC with several metals, were prepared. Their molar absorption coefficients at 220 nm were determined. The developed HPLC method has been validated in terms of quantitative determination of non-complexed DOTA-TATE and DOTA-TOC and their respective complexes with metallic individuals. RESULTS: Good chromatographic separation of the individual metal-DOTA-peptide complexes was achieved. The resolution between peaks of interest in radioactive preparations (complexes with: yttrium-90, lutetium-177, gallium-68) and metallic impurities was well above 1.5 (except gallium-68 DOTA-TOC preparations). Limits of detection and quantification were determined based on the parameters of the calibration curves. Based on the spectrophotometric and HPLC-DAD studies and statistical analysis of the results obtained, the average molar absorption coefficient was determined for studied DOTA-TATE and DOTA-TOC complexes, εHPLC-DAD = 48 × 103M-1 cm-1. With the use of the determined molar absorption coefficient the method enabled quantitative determination of non-labelled peptide in the radioactive preparation in the linearity range of 0.5-100 µg/mL for DOTA-TATE(net) and 0.5-100 µg/mL for DOTA-TOC(net). CONCLUSION: The developed HPLC method is suitable for RCP determination of radiolabelled DOTA-TATE and DOTA-TOC preparations. Determination of the average molar absorption coefficient for DOTA-TATE and DOTA-TOC complexes allows assessment of the total content of the peptide in radiopharmaceutical preparation regardless of its chemical form (free ligand, associated with radionuclide, in the form of a complex with metal ions being the impurity) using the HPLC method with UV detection.

Influence of DOTA Chelators on Radiochemical Purity and Biodistribution of 177Lu- and 90Y-Rituximab in Xenografted Mice.

This work presents a comparative biological evaluation of 90Y- and 177Lu- labelled DOTA-SCN and DOTA-NHS conjugated to Rituximab in tumour-bearing mice. Two DOTA derivatives, p-SCN-Bn-DOTA and DOTA-NHS-ester were conjugated to Rituximab and then freeze-dried kit formulations were prepared, as previously described (1). Tissue distribution was investigated in tumour-bearing (Raji s.c.) male Rj: NMRI-Foxn1nu/Foxn1nu mice at different time points after administration of 177Lu-DOTA-Rituximab or 90Y-DOTA-Rituximab (6 MBq/10 µg per mouse). In addition, tumour images were acquired with a PhotonIMAGERTM after injection of 90Y-DOTA (SCN)-Rituximab. All radioimmunoconjugates were obtained with high radiolabelling yield (RCP > 98%) and specific activity of ca. 0.6 GBq/mg. The conjugates were stable in human serum and in 0.9% NaCl; however, progressive aggregation was observed with time, in particular for DOTA -(SCN) conjugates. Both 177Lu- and 90Y-DOTA -(SCN)-Rituximab revealed slow blood clearance. The maximum tumour uptake was found 72 h after injection of 177Lu-DOTA -(SCN)-Rituximab (9.3 ID/g). A high radioactivity uptake was observed in liver and spleen, confirming the hepatobiliary excretion route. The results obtained by the radioactive optical imaging harmonize with those from the biodistribution study.

Structural studies on radiopharmaceutical DOTA-minigastrin analogue (CP04) complexes and their interaction with CCK2 receptor.

BACKGROUND: The cholecystokinin receptor subtype 2 (CCK-2R) is an important target for diagnostic imaging and targeted radionuclide therapy (TRNT) due to its overexpression in certain cancers (e.g., medullary thyroid carcinoma (MTC)), thus matching with a theranostic principle. Several peptide conjugates suitable for the TRNT of MTC have been synthesized, including a very promising minigastrin analogue DOTA-(DGlu)6-Ala-Tyr-Gly-Trp-Met-Asp-Phe-NH2 (CP04). In this contribution, we wanted to see whether CP04 binding affinity for CCK-2R is sensitive to the type of the complexed radiometal, as well as to get insights into the structure of CP04-CCK2R complex by molecular modeling. RESULTS: In vitro studies demonstrated that there is no significant difference in CCK-2R binding affinity and specific cellular uptake between the CP04 conjugates complexed with [68Ga]Ga3+ or [177Lu]Lu3+. In order to investigate the background of this observation, we proposed a binding model of CP04 with CCK-2R based on homology modeling and molecular docking. In this model, the C-terminal part of the molecule enters the cavity formed between the receptor helices, while the N-terminus (including DOTA and the metal) is located at the binding site outlet, exposed in large extent to the solvent. The radiometals do not influence the conformation of the molecule except for the direct neighborhood of the chelating moiety. CONCLUSIONS: The model seems to be in agreement with much of structure-activity relationship (SAR) studies reported for cholecystokinin and for CCK-2R-targeting radiopharmaceuticals. It also explains relative insensitivity of CCK-2R affinity for the change of the metal. The proposed model partially fits the reported site-directed mutagenesis data.

From preclinical development to clinical application: Kit formulation for radiolabelling the minigastrin analogue CP04 with In-111 for a first-in-human clinical trial.

INTRODUCTION: A variety of radiolabelled minigastrin analogues targeting the cholecystokinin 2 (CCK2) receptor were developed and compared in a concerted preclinical testing to select the most promising radiotracer for diagnosis and treatment of medullary thyroid carcinoma (MTC). DOTA-DGlu-DGlu-DGlu-DGlu-DGlu-DGlu-Ala-Tyr-Gly-Trp-Met-Asp-Phe-NH2 (CP04) after labelling with (111)In displayed excellent characteristics, such as high stability, receptor affinity, specific and persistent tumour uptake and low kidney retention in animal models. Therefore, it was selected for further clinical evaluation within the ERA-NET project GRAN-T-MTC. Here we report on the development of a pharmaceutical freeze-dried formulation of the precursor CP04 for a first multi-centre clinical trial with (111)In-CP04 in MTC patients. MATERIALS AND METHODS: The kit formulation was optimised by adjustment of buffer, additives and radiolabelling conditions. Three clinical grade batches of a final kit formulation with two different amounts of peptide (10 or 50 µg) were prepared and radiolabelled with (111)In. Quality control and stability assays of both the kits and the resulting radiolabelled compound were performed by HPLC analysis. RESULTS: Use of ascorbic acid buffer (pH4.5) allowed freeze-drying of the kit formulation with satisfactory pellet-formation. Addition of methionine and gentisic acid as well as careful selection of radiolabelling temperature was required to avoid extensive oxidation of the Met(11)-residue. Trace metal contamination, in particular Zn, was found to be a major challenge during the pharmaceutical filling process in particular for the 10 µg formulation. The final formulations contained 10 or 50 µg CP04, 25mg ascorbic acid, 0.5mg gentisic acid and 5mg L-methionine. The radiolabelling performed by incubation of 200-250 MBq (111)InCl3 at 90 °C for 15 min resulted in reproducible radiochemical purity (RCP) >94%. Kit-stability was proven for >6 months at +5 °C and at +25 °C. The radiolabelled product was stable for >4h at +25 °C. CONCLUSION: A kit formulation to prepare (111)In-CP04 for clinical application was developed, showing high stability of the kit as well as high RCP of the final product.

The radiometal makes a difference. Synthesis and preliminary characterisation of DOTA-minigastrin analogue complexes with Ga, Lu and Y.

BACKGROUND: The minigastrin analogue - CP04: DOTA-(DGlu)6-Ala-Tyr-Gly-Trp-Met-Asp-Phe-NH2 has been developed for CCK2R targeting. This analogue can be radiolabelled with 111In or 68Ga for imaging, or with 90Y and 177Lu for therapy. However, affinity of the chelator-peptide conjugates to the cell membrane receptors may vary depending on the metal incorporated into the complex. So far, there are no such studies for the ligands of gastrin/cholecystokinin receptor CCK2R. It is supposed that the reason for the differentiation of receptor affinity to the respective receptors is in the changes of structure of chelating system and their influence on the bioactive conformations of the metal conjugated peptides. Herein, we report on the radiolabeling of CP04 with 90Y, 177Lu and 68Ga and synthesis of cold CP04 complexes with respective stable metals for further structural and physico-chemical and biological studies. MATERIALS AND METHODS: From 200 to 600 MBq of 90Y, 177Lu or 68Ga were used for radiolabelling of 20 µg of CP04 dissolved in ascorbic acid solution (50 mg/mL, pH 4.5). Non-radioactive complexes with Lu and Ga were synthesized in milligram amounts starting from 0.5 mg up to 5 mg of CP04 dissolved in ascorbic acid solution (50 mg/mL, pH 4.5) when using 2-molar excess of the metal ions. Complex formation needed 5 min in microwave oven or 12 min in thermo-block at 95°C. RP-HPLC isocratic method (Kinetex 150/4.6 mm; 25% AcN/0.1% TFA, 1 mL/min) with UV/Vis and radiometric detection was developed for investigation of the radiolabelled and "cold" complexes. For LC-MS investigations, HPLC method was modified replacing TFA by formic acid. RESULTS AND DISCUSSION: Yields of CP04 radiolabelling were greater than 90% for all three radionuclides. The HPLC method enabled identification of these radio-complexes based on comparison to their non-radioactive equivalents. In all cases, chromatograms revealed peaks that could be attributed to the metal-CP04 complexes and to impurities (including methionine oxidation). LC-MS analysis of Ga and Lu complexes revealed conformity of the observed molecular ions to the predicted formulas (m/z 2116 and 2220 Da for Ga and Lu, respectively). Different chromatographic behaviour observed for Ga-CP04 complex comparing to Lu- and Y- labelled peptide (relative retention to CP04: 1.08, 0.86 and 0.85, respectively) suggest different coordination of the metal ions. Therefore, further studies are planned using the non-radioactive complexes in order to assess their structural conformations.

Standardization of Procedures for the Preparation of (177)Lu- and (90)Y-labeled DOTA-Rituximab Based on the Freeze-dried Kit Formulation.

Rituximab when radiolabelled with (177)Lu or (90)Y has been investigated for the treatment of patients with Non-Hodgkin's Lymphoma. In this study, we optimized the preparation of antibody conjugates with chelating agent in the freeze-dried kit. It shortens procedures needed for the successful radiolabeling with lutetium-177 and yttrium-90 and assures reproducible labelling yields. Various molar ratios of Rituximab:DOTA (from 1:5 to 1:100) were used at the conjugation step and different purification method to remove unbound DOTA were investigated (size-exclusion chromatography, dialysis, ultrafiltration). The final monoclonal antibody concentration was quantified by Bradford method, and the number of DOTA molecules was determined by radiolabeling assay using (64)Cu. The specific activity of (177)Lu-DOTA-Rituximab and (90)Y-DOTA-Rituximab were optimized using various amounts of radiometal. Quality control (SE-HPLC, ITLC) and stability study were performed. An average of 4.2 ± 0.8 p-SCN-Bz-DOTA molecules could be randomly conjugated to a single molecule of Rituximab. The ultrafiltration system was the most efficient for purification and resulted in the highest recovery efficiency (77.2%). At optimized conditions the (177)Lu-DOTARituximab and (90)Y-DOTA-Rituximab were obtained with radiochemical purity >99% and specific activity ca. 600 MBq/mg. The radioimmunoconjugates were stable in human serum and 0.9% NaCl. After 72 h of incubation the radiochemical purity of (177)Lu-DOTA-Rituximab decreased to 94% but it was still more than 88% for (90)Y-DOTA-Rituximab. The radioimmunoconjugate showed stability after six months storage at 2 - 8(0)C, as a lyophilized formulation. Our study shows that Rituximab-DOTA can be efficiently radiolabeled with (177)Lu and (90)Y via p-SCN-Bn-DOTA using a freezedried kit.

Comparison of chromatographic methods for quality control of DMSA complexes with 99mTc and 188Re at (III) and (V) oxidation states.

BACKGROUND: The reliable method for determination of identity and radiochemical purity (RCP) is of great importance in radiopharmaceutical development. This is especially relevant when more than one form of radiometal/ligand complex can be formed during radiolabelling, such as complexes of 99mTc or 188Re with meso-2,3-dimercaptosuccinic acid (DMSA), where depending on the pH, metal can occur either at +3 or +5 oxidation state. The aim of our study was to evaluate possibilities for optimization of chromatographic systems leading to specific and reliable analytical method for determination of the identity and RCP of DMSA complexes with 99mTc or 188Re. MATERIAL AND METHODS: The commercial DMSA kits (POLATOM) were used for preparation of technetium-99m (III) and (V) complexes with DMSA. 99mTc(V)-DMSA complexes were prepared by addition of NaHCO3 to the kit vial prior to 99mTc-eluate to obtain pH ~8. 188Re(V)-DMSA was prepared either directly or using intermediate 188Re(III)-EDTA complex added to DMSA. RCP was evaluated by TLC using: ITLC-SG developed in methylethylketon, SG60 coated plates developed in: n-BuOH/H2O/CH3COOH and n-PrOH/H2O/CH3COOH systems, and in H2O. Comparative biodistribution studies were performed in normal Wistar rats. RESULTS: Using silica gel plates and n-PrOH, H2O and acetic acid in the developing solution, we observed that 99mTc/188Re(III)-DMSA and 99mTc/188Re(V)-DMSA complexes could be well separated from each other and from the impurities in the form of free pertechnetate/perrhenate. In vivo studies showed quite different biodistribution of 99mTc(III)- and 99mTc(V)-DMSA. The trivalent complex accumulated mainly in kidneys (>40%ID), while 99mTc(V)-DMSA revealed high excretion with urine and relatively high concentration in osseous tissue (ca. 2 %ID/g). Accumulation of this complex in kidneys was very low (ca. 2.5 %ID). Biodistribution pattern of 188Re(V)-DMSA prepared directly was almost identical to that of 99mTc(V)-DMSA. Biodistribution results of the 188Re preparation obtained using 188Re(III)-EDTA intermediate indicated that the preparation contained the mixture of penta- and trivalent 188Re complexes. The quite high accumulation of radioactivity in kidneys (23 %ID) gave evidence of the presence of 188Re(III)-DMSA in this preparation, what was also confirmed by the results of TLC analysis performed using silica gel plate and n-propanol/water/acetic acid as developing system. CONCLUSIONS: Based on our study, we have made recommendation on the suitable methods for investigations of RCP of DMSA complexes, i.e.: SG60 plates developed in the mixture of n-propanol/water/acetic acid, which enable determination of the tri- and pentavalent DMSA complexes, as well as, the pertechnetate/perrhenate impurity, and developed in water for determination of the colloidal residue.

Imaging of inflamed carotid artery atherosclerotic plaques with the use of 99mTc-HYNIC-IL-2 scintigraphy in end-stage renal disease patients.

PURPOSE: Identification of vulnerable plaques remains crucial for better cardiovascular risk assessment. At least 20% of inflammatory cells within unstable (vulnerable) plaques comprise T lymphocytes, which contain receptors for interleukin-2 (IL-2); those receptors can be identified by scintigraphy with radiolabelled IL-2.The aim of this study was to identify the "inflamed" (vulnerable) plaques by scintigraphy using IL-2 labelled with (99m)Tc in the selected, high cardiovascular risk group of end-stage renal disease (ESRD) patients. METHODS: A total of 28 patients (18 men, 10 women, aged 55.2 ± 9.6 years, 17 on peritoneal dialysis, 11 on haemodialysis) underwent common carotid artery (CCA) scintigraphy with the use of (99m)Tc-hydrazinonicotinamide (HYNIC)-IL-2. In all cases, ultrasound examination of the CCA was performed and levels of selected proinflammatory factors, atherogenic markers and calcium-phosphate balance parameters were measured. Finally, the target to non-target (T/nT) ratio of IL-2 uptake in atherosclerotic plaques with intima-media thickness (IMT), classic cardiovascular risk factors and concentrations of the measured factors were compared. RESULTS: Increased (99m)Tc-HYNIC-IL-2 uptake in atherosclerotic plaques in 38/41 (91%) cases was detected. The median T/nT ratio of focal (99m)Tc-HYNIC-IL-2 uptake in atherosclerotic plaques was 2.35 (range 1.23-3.63). The mean IMT value on the side of plaques assessed by scintigraphy was 0.79 ± 0.18 mm (median 0.8, range 0.5-1.275). Correlations between T/nT ratio and homocysteine (R = 0.22, p = 0.037), apolipoprotein B (apoB) (R = 0.31, p = 0.008), apoB to apoA-I ratio (R = 0.29, p = 0.012) and triglyceride concentration (R = 0.26, p = 0.021) were detected. A lower T/nT ratio in patients with better parameters of nutritional status (haemoglobin, albumin, adiponectin) in comparison with patients with worse nutritional parameters (3.20 ± 0.5 vs 2.16 ± 0.68, p = 0.025) was revealed as well as a difference between values of T/nT ratio in groups of patients with values of apoB, soluble CD40 ligand and asymmetric dimethylarginine above and below median (3.18 ± 0.52 vs 2.16 ± 0.68, p = 0.031). No statistically significant association was found between T/nT ratio and mean value of either IMT or classic cardiovascular risk factors. CONCLUSION: Scintigraphy with the use of (99m)Tc-HYNIC-IL-2 can be a tool for inflamed atherosclerotic (vulnerable) plaque visualization within CCA in ESRD patients. Quantitative results of carotid artery scintigraphy with (99m)Tc-HYNIC-IL-2 correlate with serum concentration of selected cardiovascular risk markers.

Investigation of 99mTc-labelling of recombinant human interleukin-2 via hydrazinonicotinamide.

INTRODUCTION: Interleukin-2 (IL-2) when radiolabelled with (99m)Tc has been proved useful in imaging the side of lymphocytic infiltration in patients with autoimmune disorders and plays a significant role as a T-cell imaging agent. However, the labelling procedures used so far appeared to be rather complex and laborious. The aim of present study was to develop an efficient procedure of (99m)Tc-labelling of recombinant human interleukin-2 (rhIL-2) via hydrazinonicotinamide (HYNIC) to develop a dry kit formulation. METHODS: Various molar ratios of rhIL-2/HYNIC (from 1:2 to 1:12) were used at the conjugation step. The conjugates were purified on a PD-10 column to remove the excess of unbound HYNIC, as well as of any aggregates. The final peptide concentration was quantified by the BCA method, and the number of HYNIC molecules incorporated into a rhIL-2 molecule was determined based on the reaction with 2-sulfobenzaldehyde. The (99m)Tc-labelling was optimized using various amounts of HYNIC-rhIL-2, (99m)Tc, SnCl(2), tricine and nicotinic acid (NA). Quality control included GF-HPLC, ITLC, SDS-PAGE and biological assay. Biodistribution studies were performed in Swiss mice and Wistar rats. RESULTS: Generally, the highest radiolabelling yields were achieved when the HYNIC-rhIL-2 conjugates of ca. 2-4 HYNIC molecule substitution ratios were used. The optimal pH of the reaction medium was found to be in the range of 6.5 to 7.0. GF-HPLC analysis indicated that monomer and aggregates of (99m)Tc-HYNIC-rhIL-2 are formed during radiolabelling. At optimized conditions of wet radiolabelling, the (99m)Tc-HYNIC-rhIL-2 monomer was obtained with radiochemical purity >99%, specific activity of ca. 4 GBq/mg rhIL-2 and overall yield of ca. 65%. The two-vial freeze-dried kit was prepared: the first vial contained 30 µg HYNIC-rhIL-2, co-ligands, buffer and antioxidant; the second vial contained tricine and SnCl(2). The monomer of (99m)Tc-HYNIC-rhIL-2 was obtained by gel chromatography on a PD-10 column. No differences between labelled and unlabelled IL2 in terms of biological activity were observed. CONCLUSIONS: Our study shows that rhIL-2 can be efficiently radiolabelled with (99m)Tc via HYNIC, with tricine and NA as co-ligands using a two-vial freeze-dried kit. This enables the preparation of sterile and ready-to-use (99m)Tc-HYNIC(tricine,NA)-rhIL-2 within 1 h.

Radiochemical synthesis and preliminary in vivo evaluation of new radioactive platinum complexes with carnosine.

Application of cross-linking agents such as SATA and 2-iminothiolane (2-IT) for radiochemical synthesis of new radioactive Pt(II) and Pt(IV) complexes with carnosine was investigated. The mixed-ligand Pt(II)([(125)I]Hist)(Carnosine) complex has been synthesized in a multi-step reaction. First, carnosine was modified by the attachment of SATA. After chromatographic purification, the conjugate was unprotected to form a reactive sulfhydryl functional group, and then the modified carnosine was substituted to PtCl(2)[(125)I]Hist complex. The Pt(II)(IT-[(125)I]Carnosine) and Pt(IV)(IT-[(131)I]Carnosine) complexes were synthesized in a three-step reaction. First, carnosine was labeled with iodine radionuclide ((125)I or (131)I), followed by conjugation with 2-IT. The modified IT-[*I]Carnosine was complexed with tetrachloroplatinate or hexachloroplatinate. Comparative biodistribution studies were performed in normal Wistar rats and in Lewis rats with implanted (s.c.) rat pancreatic tumor cells (AR42J). The HPLC analysis showed a relatively fast formation of the new mixed-ligand Pt([(125)I]Hist)(Carnosine) complex (yield ca. 50% after 20h). Reaction of K(2)PtCl(4) with [(125)I]Carnosine modified by 2-IT proceeded rapidly and with a high yield (>95% after 2h). The synthesis of the Pt(IV)IT-[*I]Carnosine complex was the slower reaction in comparison to the analogous synthesis of the Pt(II) complex (yield ca. 70% after 12h), thus a purification step was necessary. The biodistribution study proved the in vivo stability of the newly synthesized complexes (a low accumulation in thyroid gland and in GIT) and showed that the conjugation of the modified carnosine changes significantly biodistribution scheme of the Pt complexes comparing to the reference Pt(II)[*I]Hist and Pt(IV)([*I]Hist)(2) complexes. The mixed-ligand complex was rapidly excreted in urine and revealed the highest accumulation in kidneys (>5%ID/g). A very high concentration in blood and in liver was observed for the Pt(II)(IT-[(125)I]Carnosine) complex; however, at the same time the lowest concentration in kidneys was noted. Preliminary studies in the rat's tumor model indicated for this complex a favorable tumor to muscle ratio. In the case of Pt(IV)(IT-[*I]Carnosine) apart from ca. 12-times decrease of the liver accumulation, additional 4-times decrease of an accumulation in kidneys was observed in comparison to the Pt(IV)([*I]Hist)(2) complex. Our study showed that the short peptides can be efficiently substituted to the platinum core via the reactive sulfhydryl group introduced by SATA or 2-IT. The new radioactive platinum complexes with carnosine possess favorable biodistribution schemes, which make them potential candidates for radio-chemotherapeutical agents.

Comparative study on DOTA-derivatized bombesin analog labeled with 90Y and 177Lu: in vitro and in vivo evaluation.

INTRODUCTION: The aim of the study was to compare in vitro and in vivo a novel DOTA-chelated bombesin (BN) analog of the amino acid sequence, QRLGNQWAVGHLM-CONH(2) (BN[2-14]NH(2)), labeled with (90)Y and (177)Lu, for its potential use in targeted radiotherapy of tumors expressing gastrin releasing peptide (GRP) receptors. The same amino acid sequence, but with different chelator, referred as BN1.1 (Gly-Gly-Cys-Aca-QRLGNQWAVGHLM-CONH(2)), has already been studied and reported; however, the DOTA-chelated one, suitable for labeling with M(+3) type radiometals, was not yet described. METHODS: The conditions for labeling of DOTA-BN[2-14]NH(2) with noncarrier added (90)Y and with (177)Lu [specific activity (SA), 15 Ci/mg Lu] were investigated and optimized to provide (90)Y-DOTA-BN[2-14]NH(2) and (177)Lu-DOTA-BN[2-14]NH(2) of high SA. The stability of the radiolabeled compounds in human serum was evaluated over a period of 24 h. The human prostate cancer cell line PC-3, known to express GRP receptors, was used for in vitro evaluation of radiolabeled peptide affinity to GRP receptors and for assessment of cytotoxicity of both nonlabeled and radiolabeled peptide. Biodistribution accompanied by receptor blocking was studied in normal Swiss mice. RESULTS: (90)Y-DOTA-BN[2-14]NH(2) and (177)Lu-DOTA-BN[2-14]NH(2) were obtained with radiochemical yield >98% and high SA (67.3 GBq (90)Y/mumol and 33.6 GBq (177)Lu/mumol, respectively). They were stable when incubated in human serum for up to 24 h. The binding affinities of DOTA-BN[2-14]NH(2) and both (nat)Y- and (nat)Lu-labeled analogs to GRP receptors were high (IC(50)=1.78, 1.99, and 1.34 nM, respectively), especially for the (nat)Lu-DOTA-BN[2-14]NH(2) complex. The cytotoxicity study of DOTA-BN[2-14]NH(2) to PC-3 cells revealed an IC(50)=6300 nM after 72 h of exposition, while the labeled derivatives showed no significant cytotoxic effect. The internalization rate to PC-3 cells was more rapid for (177)Lu-labeled peptide (84.87%) than for the (90)Y-labeled one (80.79%), while the efflux rate was slower for (177)Lu-DOTA-BN[2-14]NH(2) (46.8% vs. 61.74%). The biodistribution study of both derivatives in normal mice revealed a specific binding to GRP receptor-positive tissues, which could be blocked by coinjection of cold peptide. The effect of receptor blockage in vivo was also more pronounced for the (177)Lu-labeled peptide than that for the (90)Y-labeled (81% vs. 42%, respectively). CONCLUSIONS: Our studies demonstrated that DOTA-BN[2-14]NH(2) can be labeled with (90)Y (NCA) and (177)Lu (CA) with high radiochemical yields. The in vitro and in vivo comparison between (90)Y-DOTA-BN[2-14]NH(2) and (177)Lu-DOTA-BN[2-14]NH(2) indicated that the change of radiometal in the complex from Y to Lu influence the binding affinity to the GRP receptors with preference to the (177)Lu-labeled derivative.

Antitumor activity of platinum(II) complexes with histamine and radioiodinated histamine in a transplantable murine adenocarcinoma model.

PURPOSE: Antitumor activity of the dichloroplatinum(II)-histamine complexes labeled with I-125 or I-131 was investigated in a transplantable murine adenocarcinoma (MA) model. METHODS: The tumor model was obtained in C3H/W female mice after subcutaneous inoculation of the tumor cells derived from the mice bearing a mammary tumor of spontaneous origin. Antitumor activities of the platinum-histamine complexes were investigated in three independent experiments, which differed in applied doses of preparations (PtCl(2)Hist, PtCl(2)[(125)I]Hist, PtCl(2)[(131)I]Hist, PtCl(2)Hist/PtCl(2)[(125)I]Hist and PtCl(2)Hist/PtCl(2)[(131)I]Hist), treatment schedules as well as stages of the disease progress in the animals used. Experiment 1 included long-term, multidose treatment with low single doses (treatment duration 31-32 days; 8-10 doses of ca. 0.25.MTD(Pt) each). Experiment 2 included short-term, multidose treatment with higher single doses (4 x ca. 0.5.MTD(Pt) up to Day 13 of the treatment). Experiment 3 included long-term concomitant multidose treatment with higher single doses (9x0.9-0.4.MTD(Pt) up to Day 33). RESULTS: The long-term treatment with the platinum-histamine preparations revealed inhibiting activity on the tumor growth and size in comparison to control groups. The most intensive and significant antitumor effects were observed for the radioactive complexes. The tumor growth delay factors (GDFs) observed in Experiment 1 were 0.4, 0.7, and 1.2 for PtCl(2)Hist, PtCl(2)Hist/PtCl(2)[(131)I]Hist, and PtCl(2)Hist/PtCl(2)[(125)I]Hist, respectively. Significant (P<.05) prolongations of median survivals (MS) were found in Experiment 2 following the treatment with higher single doses of PtCl(2)Hist and PtCl(2)His/PtCl(2)[(125)I]Hist (Ratio MS(tr)/MS(con) ca. 1.4). A slightly less potent activity was observed for PtCl(2)Hist/PtCl(2)[(131)I]Hist, and no survival improvement was found for the groups treated mostly with the radiation (PtCl(2)[(125)I]Hist and PtCl(2)[(131)I]Hist). The intensive and long-term concomitant scheduling of the radioactive platinum-histamine complexes labeled with I-125 and I-131 (Experiment 3) resulted in a significant inhibition of the tumor growth (GDF=1.9) and survival prolongation of the tumor-bearing mice (MS(tr)/MS(con)=1.5, P=.023). The treatment-related toxicity was mild. CONCLUSION: An enhancement of the antitumor activity due to the multidose concomitant treatment with a combination of cytotoxic/cytostatic dichloroplatinum(II)-histamine and the attached iodine radionuclides was shown in the murine model of experimental neoplasm.