Targeting of renal carcinoma with 67/64Cu-labeled anti-L1-CAM antibody chCE7: selection of copper ligands and PET imaging

67Cu Production Capabilities: A Mini Review

Is the ⁶⁷Cu production worldwide feasible for expanding preclinical and clinical studies? How can we face the ingrowing demands of this emerging and promising theranostic radionuclide for personalized therapies? This review looks at the different production routes, including the accelerator- and reactor-based ones, providing a comprehensive overview of the actual ⁶⁷Cu supply, with brief insight into its use in non-clinical and clinical studies. In addition to the most often explored nuclear reactions, this work focuses on the ⁶⁷Cu separation and purification techniques, as well as the target material recovery procedures that are mandatory for the economic sustainability of the production cycle. The quality aspects, such as radiochemical, chemical, and radionuclidic purity, with particular attention to the coproduction of the counterpart ⁶⁴Cu, are also taken into account, with detailed comparisons among the different production routes. Future possibilities related to new infrastructures are included in this work, as well as new developments on the radiopharmaceuticals aspects.

Evaluation of production cross-sections for theranostic 67Cu radionuclide via proton-induced nuclear reaction on 68Zn target

Copper-67 (T_1/2 = 61.83 h, E_β-^mean=141 keV, I_β-^total=100%; E_γ = 184.577 keV, I_γ = 48.7%) is a promising radionuclide for theranostic applications especially in radio immunotherapy. However, one of the main drawbacks for its application is related to its limited availability. Various nuclear reaction routes investigated in the last years can result in ⁶⁷Cu production, although the use of proton beams is the method of choice taken into account in this work. The goal of this work is a revision of the cross-sections aimed at ⁶⁷Cu yield, which were evaluated for the ⁶⁸Zn(p,2p)⁶⁷Cu reaction route up to 80 MeV proton energy. A well-defined statistical procedure, i.e., the Simultaneous Evaluation on KALMAN (SOK), combined with the least-squares concept, was used to obtain the evaluated data together with the covariance matrix. The obtained evaluated data were also compared to predictions provided by the nuclear reaction model codes TALYS and EMPIRE, and a partial agreement among them has been found. These data may be useful for both existing and potential applications in nuclear medicine, to achieve an improvement and validation of the various nuclear reaction models, and may also find applications in other fields (e.g., activation analysis and thin layer activation).

Anti-HER2 monoclonal antibody based-radioimmunoconjugates: Assessment of the chelating agent influence

In the present work, the radioimmunoconjugates ¹¹¹In-DTPA-trastuzumab and ¹⁷⁷Lu-DOTA-trastuzumab were evaluated regarding the influence of the chelating agents on the physical-chemical parameters and human epidermal growth factor receptor 2 (HER2) tumor cell binding. Data showed that both chelating agents, at predetermined molar ratios (antibody:chelator - 1:10 and 1:20), did not influence the immunoconjugates integrity, the radiolabeling process and the radiolabeled antibodies stability. However, differences were observed in the lipophilic feature between DOTA and DTPA radioimmunoconjugates and in the specific binding to SK-BR-3 tumor cells (HER2 positive). Therefore, this study showed the importance of assessing the influence of chelating agents and their molar ratios in the development process of radioimmunoconjugates.

Different Shades of L1CAM in the Pathophysiology of Cancer Stem Cells

L1 cell adhesion molecule (L1CAM) is aberrantly expressed in several tumor types where it is causally linked to malignancy and therapy resistance, acting also as a poor prognosis factor. Accordingly, several approaches have been developed to interfere with L1CAM function or to deliver cytotoxic agents to L1CAM-expressing tumors. Metastatic dissemination, tumor relapse and drug resistance can be fueled by a subpopulation of neoplastic cells endowed with peculiar biological properties that include self-renewal, efficient DNA repair, drug efflux machineries, quiescence, and immune evasion. These cells, known as cancer stem cells (CSC) or tumor-initiating cells, represent, therefore, an ideal target for tumor eradication. However, the molecular and functional traits of CSC have been unveiled only to a limited extent. In this context, it appears that L1CAM is expressed in the CSC compartment of certain tumors, where it plays a causal role in stemness itself and/or in biological processes intimately associated with CSC (e.g., epithelial-mesenchymal transition (EMT) and chemoresistance). This review summarizes the role of L1CAM in cancer focusing on its functional contribution to CSC pathophysiology. We also discuss the clinical usefulness of therapeutic strategies aimed at targeting L1CAM in the context of anti-CSC treatments.

A novel approach to medical radioisotope production using inverse kinematics: A successful production test of the theranostic radionuclide 67Cu

A novel method for the production of important medical radioisotopes has been developed. The approach is based on performing the nuclear reaction in inverse kinematics, namely sending a heavy-ion beam of appropriate energy on a light target (e.g. H, d, He) and collecting the isotope of interest. In this work, as a proof-of-concept, we studied the production of the theranostic radionuclide ⁶⁷Cu (T_1/2 = 62 h) via the reaction of a ⁷⁰Zn beam at 15 MeV/nucleon with a hydrogen gas target. The ⁶⁷Cu radionuclide alongside other coproduced isotopes, was collected after the gas target on an aluminum catcher foil and their radioactivity was measured by off-line γ-ray analysis. After 36 h post irradiation, apart from the product of interest ⁶⁷Cu, the main radioimpurity coming from the ⁷⁰Zn + p reaction was ^69mZn (T_1/2 = 13.8 h), which can be reduced by further radio-cooling. Moreover, along with the radionuclide of interest produced in inverse kinematics, the production of additional radioisotopes is possible by making use of the forward-focused neutrons from the reaction and allowing them to interact with a secondary target. A preliminary successful test of this concept was realized in the present study. The main requirement to obtain activities appropriate for preclinical studies is the development of high-intensity heavy-ion primary beams.

A High-Affinity Repebody for Molecular Imaging of EGFR-Expressing Malignant Tumors

The accurate detection of disease-related biomarkers is crucial for the early diagnosis and management of disease in personalized medicine. Here, we present a molecular imaging of human epidermal growth factor receptor (EGFR)-expressing malignant tumors using an EGFR-specific repebody composed of leucine-rich repeat (LRR) modules. The repebody was labeled with either a fluorescent dye or radioisotope, and used for imaging of EGFR-expressing malignant tumors using an optical method and positron emission tomography. Our approach enabled visualization of the status of EGFR expression, allowing quantitative evaluation in whole tumors, which correlated well with the EGFR expression levels in mouse or patients-derived colon cancers. The present approach can be effectively used for the accurate detection of EGFR-expressing cancers, assisting in the development of a tool for detecting other disease biomarkers.

Evaluation of (177)Lu-CHX-A''-DTPA-Bevacizumab as a radioimmunotherapy agent targeting VEGF expressing cancers

This study aimed at the preparation and evaluation of (177)Lu-CHX-A''-DTPA-Bevacizumab for targeting VEGF over-expressing cancers. Bevacizumab conjugated to p-NCS-Bn-CHX-A''-DTPA was radiolabeled with (177)Lu. The radioimmunoconjugate characterized by SE-HPLC exhibited radiochemical purity of 98.0±0.6%. In vitro stability was retained upto 4 days at 37°C. In vitro cell binding studies showed good uptake by VEGF expressing U937 tumor cells. Biodistribution studies in melanoma model showed significant uptake and retention of (177)Lu-CHX-A''-DTPA-Bevacizumab in tumor with reduction in uptake in presence of cold Bevacizumab confirming its specificity to VEGF.

Bifunctional (64)Cu-labelled macrobicyclic cage amine isothiocyanates for immuno-positron emission tomography

New macrobicyclic cage amine or "sarcophagine" (sar) bifunctional chelators have been synthesised that form copper complexes of exceptional in vivo stability and incorporate isothiocyanate (-NCS) functional groups for conjugation to an antibody. The chelators were synthesised from the methyl-capped complex [Mg(II)(CH3)(NH2)sar](2+). Coordination of Mg(II) within the cavity of the cage amine ligand protects the secondary amine atoms from reacting with the -NCS functional groups. Two different [Mg(II)(NCS-sar)](2+) derivatives were conjugated to the HER2/neu-targeting antibody trastuzumab and the progress of the reaction monitored by electrospray mass spectrometry. The Mg(II) ion was removed from the immunoconjugates under mild conditions (0.1 M citrate buffer, pH 6). Labelling of the (CH3)(p-NCS-Ph)sar-trastuzumab conjugate with (64)Cu(II), a radioisotope suitable for positron emission tomography (PET), was fast (∼5 min) and easily performed at room temperature with high radiochemical purity (>95%). Biodistribution and PET imaging studies in vivo showed that (64)Cu-labelled (CH3)(p-NCS-Ph)sar-trastuzumab maintained high stability under physiological conditions with high and selective uptake in a HER2-positive cancer cell line. The stability of the copper complex and the 12.7 h half-life of the radioisotope allows clear visualisation of tumours out to 48 h.

Development of [⁶⁴Cu]-DOTA-PR81 radioimmunoconjugate for MUC-1 positive PET imaging

OBJECTIVE

Breast cancer radioimmunoscintigraphy targeting MUC1 expression is a growing field of work in nuclear medicine research. PR81 is a monoclonal antibody that binds with high affinity to MUC1, which is over expressed on breast tumors. In this study, we report production, quality control and preclinical qualifications of a copper-64 labeled PR81 for PET imaging of breast cancer.

METHODS

PR81 was conjugated with DOTA-NHS-ester and purified by molecular filtration followed by chelate:mAb ratio determination by spectrophotometric method. DOTA-PR81 was labeled with (64)Cu followed by radiochemical purity, in vitro stability, in vitro internalization and immunoreactivity determination. The tissue biodistribution of the (64)Cu-DOTA-PR81 and (64)Cu-DOTA-hIgG was evaluated in BALB/c mice with breast carcinoma tumors using tissue counting and imaging.

RESULTS

The radiochemical purity of radioimmunoconjugate was >95±1.9% (ITLC) (specific activity; 4.6 μCi/μg). The average number of chelators per antibody was 3.4±0.3:1. The (64)Cu-DOTA-PR81 showed immunoreactivity towards MUC1 antigen and MCF7 cell line with significant in vitro stability (>89% in PBS and 78±0.5% in human serum) over 48 h. Maximum internalized activity of radiolabeled PR81 in 4-8 h was 81.5%. The biodistribution and scintigraphy studies showed the accumulation of the complex at the site of tumors with high sensitivity and specificity compared to control probes.

CONCLUSION

The results showed that (64)Cu-DOTA-PR81 may be considered as a potential PET tracer for diagnosis and follow-up of MUC1 expression in oncology.

New bifunctional chelator for 64Cu-immuno-positron emission tomography

A new tetraazamacrocyclic bifunctional chelator, TE2A-Bn-NCS, was synthesized in high overall yield from cyclam. An extra functional group (NCS) was introduced to the N-atom of TE2A for specific conjugation with antibody. The Cu complex of TE2A-Bn-NCS showed high kinetic stability in acidic decomplexation and cyclic voltammetry studies. X-ray structure determination of the Cu-TE2A-Bn-NH2 complex confirmed octahedral geometry, in which copper atom is strongly coordinated by four macrocyclic nitrogens in equatorial positions and two carboxylate oxygen atoms occupy the elongated axial positions. Trastuzumab was conjugated with TE2A-Bn-NCS and then radiolabeled with 64Cu quantitatively at room temperature within 10 min. Biodistribution studies showed that the 64Cu-labeled TE2A-Bn-NCS-trastuzumab conjugates maintain high stability in physiological conditions, and NIH3T6.7 tumors were clearly visualized up to 3 days by 64Cu-immuno-positron emission tomography imaging in animal models.

Feasibility of isotope harvesting at a projectile fragmentation facility: ⁶⁷Cu

The work presented here describes a proof-of-principle experiment for the chemical extraction of (67)Cu from an aqueous beam stop at the National Superconducting Cyclotron Laboratory (NSCL). A 76 MeV/A (67)Cu beam was stopped in water, successfully isolated from the aqueous solution through a series of chemical separations involving a chelating disk and anion exchange chromatography, then bound to NOTA-conjugated Herceptin antibodies, and the bound activity was validated using instant thin-layer chromatography (ITLC). The chemical extraction efficiency was found to be 88 ± 3% and the radiochemical yield was ≥95%. These results show that extraction of radioisotopes from an aqueous projectile-fragment beam dump is a feasible method for obtaining radiochemically pure isotopes.

Future prospects for SPECT imaging using the radiolanthanide terbium-155 - production and preclinical evaluation in tumor-bearing mice

INTRODUCTION

We assessed the suitability of the radiolanthanide (155)Tb (t1/2=5.32 days, Eγ=87 keV (32%), 105keV (25%)) in combination with variable tumor targeted biomolecules using preclinical SPECT imaging.

METHODS

(155)Tb was produced at ISOLDE (CERN, Geneva, Switzerland) by high-energy (~1.4 GeV) proton irradiation of a tantalum target followed by ionization and on-line mass separation. (155)Tb was separated from isobar and pseudo-isobar impurities by cation exchange chromatography. Four tumor targeting molecules - a somatostatin analog (DOTATATE), a minigastrin analog (MD), a folate derivative (cm09) and an anti-L1-CAM antibody (chCE7) - were radiolabeled with (155)Tb. Imaging studies were performed in nude mice bearing AR42J, cholecystokinin-2 receptor expressing A431, KB, IGROV-1 and SKOV-3ip tumor xenografts using a dedicated small-animal SPECT/CT scanner.

RESULTS

The total yield of the two-step separation process of (155)Tb was 86%. (155)Tb was obtained in a physiological l-lactate solution suitable for direct labeling processes. The (155)Tb-labeled tumor targeted biomolecules were obtained at a reasonable specific activity and high purity (>95%). (155)Tb gave high quality, high resolution tomographic images. SPECT/CT experiments allowed excellent visualization of AR42J and CCK-2 receptor-expressing A431 tumors xenografts in mice after injection of (155)Tb-DOTATATE and (155)Tb-MD, respectively. The relatively long physical half-life of (155)Tb matched in particular the biological half-lives of (155)Tb-cm09 and (155)Tb-DTPA-chCE7 allowing SPECT imaging of KB tumors, IGROV-1 and SKOV-3ip tumors even several days after administration.

CONCLUSIONS

The radiolanthanide (155)Tb may be of particular interest for low-dose SPECT prior to therapy with a therapeutic match such as the β(-)-emitting radiolanthanides (177)Lu, (161)Tb, (166)Ho, and the pseudo-radiolanthanide (90)Y.

Positron emission tomography of 64Cu-DOTA-Rituximab in a transgenic mouse model expressing human CD20 for clinical translation to image NHL

PURPOSE

This study aims to evaluate (64)Cu-DOTA-rituximab (PETRIT) in a preclinical transgenic mouse model expressing human CD20 for potential clinical translation.

PROCEDURES

(64)Cu was chelated to DOTA-rituximab. Multiple radiolabeling, quality assurance, and imaging experiments were performed. The human CD20 antigen was expressed in B cells of transgenic mice (CD20TM). The mice groups studied were: (a) control (nude mice, n = 3) that received 7.4 MBq/dose, (b) with pre-dose (CD20TM, n = 6) received 2 mg/kg pre-dose of cold rituximab prior to PETRIT of 7.4 MBq/dose, and (c) without pre-dose (CD20TM, n = 6) PETRIT alone received 7.4 MBq/dose. Small animal PET was used to image mice at various time points (0, 1, 2, 4, 24, 48, and 72 h). The OLINDA/EXM software was used to determine the human equivalent dose for individual organs.

RESULTS

PETRIT was obtained with a specific activity of 545 ± 38.91 MBq/nmole, radiochemical purity >95%, and immunoreactivity >75%. At 24 h, spleenic uptake of PETRIT%ID/g (mean ± STD) with and without pre-dose was 1.76 ± 0.43% and 16.5 ± 0.45%, respectively (P value = 0.01). Liver uptake with and without pre-dose was 0.41 ± 0.51% and 0.52 ± 0.17% (P value = 0.86), respectively. The human equivalents of highest dose organs with and without pre-dose are osteogenic cells at 30.8 ± 0.4 μSv/MBq and the spleen at 99 ± 4 μSv/MBq, respectively.

CONCLUSIONS

PET imaging with PETRIT in huCD20 transgenic mice provided human dosimetry data for eventual applications in non-Hodgkins lymphoma patients.

Development of copper based drugs, radiopharmaceuticals and medical materials

Copper is one of the most interesting elements for various biomedical applications. Copper compounds show vast array of biological actions, including anti-inflammatory, anti-proliferative, biocidal and other. It also offers a selection of radioisotopes, suitable for nuclear imaging and radiotherapy. Quick progress in nanotechnology opened new possibilities for design of copper based drugs and medical materials. To date, copper has not found many uses in medicine, but number of ongoing research, as well as preclinical and clinical studies, will most likely lead to many novel applications of copper in the near future.

H(2)azapa: a versatile acyclic multifunctional chelator for (67)Ga, (64)Cu, (111)In, and (177)Lu

Preliminary experiments with the novel acyclic triazole-containing bifunctional chelator H2azapa and the radiometals (64)Cu, (67)Ga, (111)In, and (177)Lu have established its significant versatile potential as an alternative to 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) for metal-based radiopharmaceuticals. Unlike DOTA, H2azapa radiolabels quantitatively with (64)Cu, (67)Ga, (111)In, and (177)Lu in 10 min at room temperature. In vitro competition experiments with human blood serum show that (64)Cu remained predominantly chelate-bound, with only 2% transchelated to serum proteins after 20 h. Biodistribution experiments with [(64)Cu(azapa)] in mice reveal uptake in various organs, particularly in the liver, lungs, heart, intestines, and kidneys. When compared to [(64)Cu(DOTA)](2-), the lipophilic neutral [(64)Cu(azapa)] was cleared through the gastrointestinal tract and accumulated in the liver, which is common for lipophilic compounds or free (64)Cu. The chelator H2azapa is a model complex for a click-based bifunctional chelating agent, and the lipophilic benzyl "place-holders" will be replaced by hydrophilic peptides to modulate the pharmacokinetics and direct activity away from the liver and gut. The solid-state molecular structure of [In(azapa)(H2O)][ClO4] reveals a very rare eight-coordinate distorted square antiprismatic geometry with one triazole arm bound, and the structure of [(64)Cu(azapa)] shows a distorted octahedral geometry. The present study demonstrates significant potential for bioconjugates of H2azapa as alternatives to DOTA in copper-based radiopharmaceuticals, with the highly modular and "clickable" molecular scaffold of H2azapa easily modified into a variety of bioconjugates. H2azapa is a versatile addition to the "pa" family, joining the previously published H2dedpa ((67/68)Ga and (64)Cu), H4octapa ((111)In, (177)Lu, and (90)Y), and H5decapa ((225)Ac) to cover a wide range of important nuclides.

Comparison of (64)Cu-complexing bifunctional chelators for radioimmunoconjugation: labeling efficiency, specific activity, and in vitro/in vivo stability

High radiolabeling efficiency, preferably to high specific activity, and good stability of the radioimmunoconjugate are essential features for a successful immunoconjugate for imaging or therapy. In this study, the radiolabeling efficiency, in vitro stability, and biodistribution of immunoconjugates with eight different bifunctional chelators labeled with (64)Cu were compared. The anti-CD20 antibody, rituximab, was conjugated to four macrocyclic bifunctional chelators (p-SCN-Bn-DOTA, p-SCN-Bn-Oxo-DO3A, p-SCN-NOTA, and p-SCN-PCTA), three DTPA derivatives (p-SCN-Bn-DTPA, p-SCN-CHX-A″-DTPA, and ITC-2B3M-DTPA), and a macrobicyclic hexamine (sarcophagine) chelator (sar-CO2H) = (1-NH2-8-NHCO(CH2)3CO2H)sar where sar = sarcophagine = 3,6,10,13,16,19-hexaazabicyclo[6.6.6]icosane). Radiolabeling efficiency under various conditions, in vitro stability in serum at 37 °C, and in vivo biodistribution and imaging in normal mice over 48 h were studied. All chelators except sar-CO2H were conjugated to rituximab by thiourea bond formation with an average of 4.9 ± 0.9 chelators per antibody molecule. Sar-CO2H was conjugated to rituximab by amide bond formation with 0.5 chelators per antibody molecule. Efficiencies of (64)Cu radiolabeling were dependent on the concentration of immunoconjugate. Notably, the (64)Cu-NOTA-rituximab conjugate demonstrated the highest radiochemical yield (95%) under very dilute conditions (31 nM NOTA-rituximab conjugate). Similarly, sar-CO-rituximab, containing 1/10th the number of chelators per antibody compared to that of other conjugates, retained high labeling efficiency (98%) at an antibody concentration of 250 nM. In contrast to the radioimmunoconjugates containing DTPA derivatives, which demonstrated poor serum stability, all macrocyclic radioimmunoconjugates were very stable in serum with <6% dissociation of (64)Cu over 48 h. In vivo biodistribution profiles in normal female Balb/C mice were similar for all the macrocyclic radioimmunoconjugates with most of the activity remaining in the blood pool up to 48 h. While all the macrocyclic bifunctional chelators are suitable for molecular imaging using (64)Cu-labeled antibody conjugates, NOTA and sar-CO2H show significant advantages over the others in that they can be radiolabeled rapidly at room temperature, under dilute conditions, resulting in high specific activity.

Development of a large scale production of 67Cu from 68Zn at the high energy proton accelerator: closing the 68Zn cycle

A number of research irradiations of (68)Zn was carried out at Brookhaven Linac Isotope Producer aiming to develop a practical approach to produce the radioisotope (67)Cu through the high energy (68)Zn(p,2p)(67)Cu reaction. Disks of enriched zinc were prepared by electrodeposition of (68)Zn on aluminum or titanium substrate and isolated in the aluminum capsule for irradition. Irradiations were carried out with 128, 105 and 92 MeV protons for at least 24h. After irradiation the disk was chemically processed to measure production yield and specific activity of (67)Cu and to reclaim the target material. The recovered (68)Zn was irradiated and processed again. The chemical procedure comprised BioRad cation exchange, Chelex-100 and anion exchange columns. Reduction of the oxidation degree of copper allowed for more efficient Cu/Co/Zn separation on the anion exchange column. No radionuclides other than copper isotopes were detected in the final product. The chemical yield of (67)Cu reached 92-95% under remote handling conditions in a hot box. Production yield of (67)Cu averaged 29.2 μCi/[μA-h×g (68)Zn] (1.08MBq/[μA-h×g (68)Zn]) in 24h irradiations. The best specific activity achieved was 18.6 mCi/μg (688.2 MBq/μg).

The development of copper radiopharmaceuticals for imaging and therapy

The increasing use of positron emission tomography in preclinical and clinical settings has widened the demand for radiopharmaceuticals with high specificity that can image biological phenomena in vivo. While many PET tracers have been developed from small organic molecules labeled with carbon-11 or fluorine-18, the short half-lives of these radionuclides preclude their incorporation into radiotracers, which can be used to image biological processes that are not induced immediately after system perturbation. Additionally, the continuing development of targeted agents, such as antibodies and nanoparticles, which undergo extended circulation, require that radionuclides with half-lives that are complimentary to the biological half-lives of these molecules be developed. Copper radionuclides have received considerable attention since they offer a variety of half-lives and decay energies and because the coordination chemistry of cooper and its role in biology is well understood. However, in addition to the radiometal chelate, a successful copper based radiopharmaceutical depends upon the chemical structure of the entire radiotracer, which may include a biologically important molecule and a chemical linker that can be used to deliver the copper radionuclide to a specific target and modulate its in vivo properties, respectively. This review discusses the development of copper radiopharmaceuticals and the importance of factors such as chemical structure on their pharmacokinetics in vivo.

L1-CAM-targeted antibody therapy and (177)Lu-radioimmunotherapy of disseminated ovarian cancer

The L1-cell adhesion molecule (L1-CAM) is highly expressed in various cancer types including ovarian carcinoma but is absent from most normal tissue. A chimeric monoclonal antibody, chCE7, specifically binds to human L1-CAM and exhibits anti-proliferative effects on L1-CAM-expressing tumor cells. The goal of this study was to evaluate the efficacy of a novel (177)Lu-chCE7 radioimmunotherapeutic agent and to compare it to a treatment protocol with unlabeled, growth-inhibiting chCE7 in a mouse xenograft model of disseminated ovarian cancer. chCE7agl, an aglycosylated IgG1 variant with improved pharmacokinetics, was conjugated with 1,4,7,10-tetraazacyclododecane-N-N'-N'-N‴-tetraacetic acid (DOTA) and labeled with the low-energy β-emitter (177)Lu. Tumor growth and survival were assessed after a single i.v. dose of 8 MBq (60 μg) radioimmunoconjugate in nude mice bearing either subcutaneous or intraperitoneal SKOV3.ip1 human ovarian cancer tumors. Therapeutic efficacy was compared with three times weekly i.p. administration of 10 mg/kg unconjugated chCE7. In vivo analysis of (177)Lu-chCE7agl biodistribution demonstrated high and specific accumulation of radioactivity at the tumor site with maximal tumor uptake of up to 48.0 ± 8.1% ID/g at 168 h postinjection. A single treatment with (177)Lu-DOTA-chCE7agl caused significant retardation of tumor growth and prolonged median survival from 33 to 71 days, while administration of a nontargeted (177)Lu-immunoconjugate had no beneficial effect. Three times weekly i.p. application of unlabeled chCE7 10 mg/kg similarly increased survival from 44 to 72 days. We conclude that a single dose of (177)Lu-DOTA-chCE7agl is as effective as repeated administration of nonradioactive chCE7 for treatment of small intraperitoneal tumors expressing L1-CAM.

Development and validation of the 57Co assay for determining the ligand to antibody ratio in bifunctional chelate/antibody conjugates for use in radioimmunotherapy

INTRODUCTION

The ligand to antibody ratio is an important characteristic of a chelate/antibody conjugate. It has been widely reported that if the ratio is too high, there will be detrimental effects on immunoreactivity and biodistribution; conversely, if the ratio is too low, the radionuclide may not bind efficiently, and the stability and the specific activity will be reduced. There are little published data on the accuracy or precision of the (57)Co assay. The UK Clinical Trials Regulations state that "systems with procedures that assure the quality of every aspect of the trial should be implemented". The aims of this study were to assess the reliability and accuracy of the (57)Co binding assay and validate it against defined criteria.

METHOD

Thirty-two serial assays were assessed for reliability. Two batches of conjugated antibody were also analysed by matrix-assisted laser desorption/ionisation time of flight (MALDI-TOF) mass spectrometry (MS) to allow the comparison of the functional test with a physical method.

RESULTS

Reliability: The coefficient of variation was 0.13. Accuracy: There was 9% variation between the (57)Co binding assay and MALDI-TOF MS results.

CONCLUSION

A detailed method for the (57)Co ligand to antibody test is described that allows a discrete value to be obtained. The assay was validated as fit for purpose against target values of coefficient of variation <0.20, accuracy±10%, over a permissive range of 0.5-3.0 ligand to antibody ratio.

Preclinical evaluation of (177)lu-nimotuzumab: a potential tool for radioimmunotherapy of epidermal growth factor receptor-overexpressing tumors

BACKGROUND

The humanized monoclonal antibody Nimotuzumab (h-R3) has demonstrated an exceptional and better clinical profile than other monoclonal antibodies for immunotherapy of epidermal growth factor receptor-overexpressing tumors. This work deals with the preparation and radiolabeling optimization of (177)Lu-Nimotuzumab and their preclinical evaluation.

METHODS

Nimotuzumab was conjugated with S-2-(4-isothiocyanatobenzyl)-1,4,7,10-tetraazacyclododecane tetraacetic acid (p-SCN-Bn-DOTA), testing different molar ratios. The immunoconjugates were characterized. The radiolabeling with (177)Lu was optimized. Radioimmunoconjugates stability was tested in 2-[bis[2-[bis(carboxymethyl)amino]ethyl]amino]acetic acid (DTPA) excess and human serum. In vitro studies were performed in tumor model cell lines. Receptor-specific binding was tested by competitive inhibition. (177)Lu-Nimotuzumab in vivo studies were conducted in healthy and xenograft animals.

RESULTS

Nimotuzumab conjugates were obtained with high purity. Radiolabeling yield and specific activities ranged from 63.6% to 94.5% and from 748 to 1142 MBq/mg, respectively. The stability in DTPA excess and human serum was 95.9% and 93.2% after 10 days, respectively. The radioimmunoconjugate showed specific receptor binding in tumor cell lines. Biodistribution in healthy animals showed the typical behavior of the immunoconjugates based on monoclonal antibodies. The study in xenografts mice demonstrated uptake of (177)Lu-Nimotuzumab in the tumor and reticuloendothelial organs.

CONCLUSIONS

(177)Lu-Nimotuzumab was obtained with high purity and specific activities under optimal conditions without significant loss in immunoreactivity and might be a potential radioimmunoconjugate for radioimmunotherapy of tumors with epidermal growth factor receptor overexpression.

A practical guide to the construction of radiometallated bioconjugates for positron emission tomography

Positron emission tomography (PET) has become a vital imaging modality in the diagnosis and treatment of disease, most notably cancer. A wide array of small molecule PET radiotracers have been developed that employ the short half-life radionuclides (11)C, (13)N, (15)O, and (18)F. However, PET radiopharmaceuticals based on biomolecular targeting vectors have been the subject of dramatically increased research in both the laboratory and the clinic. Typically based on antibodies, oligopeptides, or oligonucleotides, these tracers have longer biological half-lives than their small molecule counterparts and thus require labeling with radionuclides with longer, complementary radioactive half-lives, such as the metallic isotopes (64)Cu, (68)Ga, (86)Y, and (89)Zr. Each bioconjugate radiopharmaceutical has four component parts: biomolecular vector, radiometal, chelator, and covalent link between chelator and biomolecule. With the exception of the radiometal, a tremendous variety of choices exists for each of these pieces, and a plethora of different chelation, conjugation, and radiometallation strategies have been utilized to create agents ranging from (68)Ga-labeled pentapeptides to (89)Zr-labeled monoclonal antibodies. Herein, the authors present a practical guide to the construction of radiometal-based PET bioconjugates, in which the design choices and synthetic details of a wide range of biomolecular tracers from the literature are collected in a single reference. In assembling this information, the authors hope both to illuminate the diverse methods employed in the synthesis of these agents and also to create a useful reference for molecular imaging researchers both experienced and new to the field.

One step purification process for no-carrier-added 64Cu produced using enriched nickel target

Copper-64 has found many applications in positron emission tomography (PET). Its half-life allows to use it for dosimetric studies associated to copper-67 targeted radiotherapy in cancer treatment. The use of 64Ni(p,n)64Cu nuclear reaction is known to produce 64Cu in large amount and with a high specific activity. In this study, targets were obtained by electroplating onto a gold backing and a typical target irradiation uses 200ߙnA, 17ߙMeV protons during 30ߙmin. After irradiation, pure copper-64 is obtained using only one chromatographic column. Nickel-64 is removed in a first elution step and cobalt isotopes in a second one. The extraction yield for copper-64 is 9±23% and nickel and cobalt impurities are under the detection limit. A recovery process of nickel-64 has also been developed.

Imaging cancer using PET--the effect of the bifunctional chelator on the biodistribution of a (64)Cu-labeled antibody

INTRODUCTION

Use of copper radioisotopes in antibody radiolabeling is challenged by reported loss of the radionuclide from the bifunctional chelator used to label the protein. The objective of this study was to investigate the relationship between the thermodynamic stability of the (64)Cu-complexes of five commonly used bifunctional chelators (BFCs) and the biodistribution of an antibody labeled with (64)Cu using these chelators in tumor-bearing mice.

METHODS

The chelators [S-2-(aminobenzyl)1,4,7-triazacyclononane-1,4,7-triacetic acid (p-NH(2)-Bn-NOTA): 6-[p-(bromoacetamido)benzyl]-1, 4, 8, 11-tetraazacyclotetradecane-N, N', N'', N'''-tetraacetic acid (BAT-6): S-2-(4-aminobenzyl)-1,4,7,10-tetraazacyclododocane tetraacetic acid (p-NH(2)-Bn-DOTA): 1,4,7,10-tetraazacyclododocane-N, N', N", N"'-tetraacetic acid (DOTA): and 1-N-(4-aminobenzyl)-3,6,10,13,16,19-hexaazabicyclo[6.6.6]eicosane-1,8-diamine (SarAr)] were conjugated to the anti-GD2 antibody ch14.18, and the modified antibody was labeled with (64)Cu and injected into mice bearing subcutaneous human melanoma tumors (M21) (n = 3-5 for each study). Biodistribution data were obtained from positron emission tomography images acquired at 1, 24 and 48 hours post-injection, and at 48 hours post-injection a full ex vivo biodistribution study was carried out.

RESULTS

The biodistribution, including tumor targeting, was similar for all the radioimmunoconjugates. At 48 h post-injection, the only statistically significant differences in radionuclide uptake (p < 0.05) were between blood, liver, spleen and kidney. For example, liver uptake of [(64)Cu]ch14.18-p-NH(2)-Bn-NOTA was 4.74 ± 0.77 per cent of the injected dose per gram of tissue (%ID/g), and for [(64)Cu]ch14.18-SarAr was 8.06 ± 0.77 %ID/g. Differences in tumor targeting correlated with variations in tumor size rather than which BFC was used.

CONCLUSIONS

The results of this study indicate that differences in the thermodynamic stability of these chelator-Cu(II) complexes were not associated with significant differences in uptake of the tracer by the tumor. However, there were significant differences in tracer concentration in other tissues, including those involved in clearance of the radioimmunoconjugate (e.g., liver and spleen).

Investigation of novel bis- and tris-tetraazamacrocycles for use in the copper-64 ((64)Cu) radiolabeling of antibodies with potential to increase the therapeutic index for drug targeting

The (64)Cu complexes of a series of mono-, bis-, and tris-tetraazamacrocycles have been prepared, and their stability in human sera has been assessed. The ligands forming the most stable Cu(2+) complexes were then conjugated to the B72.3 antibody (mAb). Conditions for conjugation of the ligands to the mAb were optimized for the concentration of protein, ligand, pH, temperature, and time. The optimum moles of Cu(2+) attached to the mAb were as high as 3.5 for L2 and 5.5 or 2.7 for L5, and the immunoreactivity was > or =80%. Biodistribution of the radioimmunoconjugates showed good tumor localization and target-to-background ratios that were significantly enhanced compared to those achieved with monotetraazamacrocyclic derivatives.

High-resolution animal PET imaging of prostate cancer xenografts with three different 64Cu-labeled antibodies against native cell-adherent PSMA

BACKGROUND

The prostate specific membrane antigen (PSMA) is expressed by virtually all prostate cancers and represents an ideal target for diagnostic and therapeutic strategies. This article compares the in vivo behavior and tumor uptake of three different radiolabeled anti-PSMA monoclonal antibodies (mAbs) and corresponding F(ab)(2) and Fab fragments thereof.

METHODS

The mAbs 3/A12, 3/F11, and 3/E7 and fragments of 3/A12 were conjugated with the chelating agent DOTA and radiolabeled with 64Cu. For the microPET imaging studies, SCID mice bearing PSMA-positive C4-2 and PSMA-negative DU 145 prostate cancer xenografts were used. Each animal received 20-30 microg radiolabeled mAb or fragment corresponding to an activity of 8-14 MBq. Imaging was performed 3, 24, and 48 hr post-injection. After the last scan, mice were sacrificed and tracer in vivo biodistribution was measured by gamma-counting.

RESULTS

Static microPET images of mice with PSMA-positive tumors revealed a high uptake of the mAbs in the C4-2 tumors at 24 and 48 hr after tracer injection and only a minimal distribution in the DU 145 tumors and other organs. In contrast, the F(ab)(2) and Fab fragments of 3/A12 were detected at a high extend in the kidney but not in the C4-2 tumors. These results were confirmed by gamma counting of dissected organs after the final imaging.

CONCLUSIONS

Due to the high and specific uptake of the 64Cu-labeled mAbs in PSMA-positive tumors, these antibodies represent excellent tools for prostate cancer imaging.

Molecular imaging of vessels in mouse models of disease

Vascular imaging of angiogenesis in mouse models of disease requires multi modal imaging hardware capable of targeting both structure and function at different physical scales. The three dimensional (3D) structure and function vascular information allows for accurate differentiation between biological processes. For example, image analysis of vessel development in angiogenesis vs. arteriogenesis enables more accurate detection of biological variation between subjects and more robust and reliable diagnosis of disease. In the recent years a number of micro imaging modalities have emerged in the field as preferred means for this purpose. They provide 3D volumetric data suitable for analysis, quantification, validation, and visualization of results in animal models. This review highlights the capabilities of microCT, ultrasound and microPET for multimodal imaging of angiogenesis and molecular vascular targets in a mouse model of tumor angiogenesis. The basic principles of the imaging modalities are described and experimental results are presented.

PET imaging of prostate cancer xenografts with a highly specific antibody against the prostate-specific membrane antigen

Prostate-specific membrane antigen (PSMA), a transmembrane glycoprotein, is highly expressed by virtually all prostate cancers and is currently the focus of several diagnostic and therapeutic strategies. We have previously reported on the generation of several monoclonal antibodies (mAb) and antibody fragments that recognize and bind with high affinity to the extracellular domain of cell-adherent PSMA. This article reports the in vivo behavior and tumor uptake of the radiolabeled anti-PSMA mAb 3/A12 and its potential as a tracer for PET.

METHODS

The mAb 3/A12 was conjugated with the chelating agent 1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetraacetic acid (DOTA) and radiolabeled with (64)Cu. Severe combined immunodeficient mice bearing PSMA-positive C4-2 prostate carcinoma xenografts were used for small-animal PET imaging. Mice with PSMA-negative DU 145 tumors served as controls. For PET studies, each animal received 20-30 microg of radiolabeled mAb corresponding to an activity of 7.6-11.5 MBq. Imaging was performed 3, 24, and 48 h after injection. After the last scan, the mice were sacrificed and tracer in vivo biodistribution was measured by gamma-counting.

RESULTS

Binding of the mAb 3/A12 on PSMA-expressing C4-2 cells was only minimally influenced by DOTA conjugation. The labeling efficiency using (64)Cu and DOTA-3/A12 was 95.3% +/- 0.3%. The specific activity after (64)Cu labeling was between 327 and 567 MBq/mg. After tracer injection, static small-animal PET images of mice with PSMA-positive tumors revealed a tumor-to-background ratio of 3.3 +/- 1.3 at 3 h, 7.8 +/- 1.4 at 24 h, and 9.6 +/- 2.7 at 48 h. In contrast, no significant tracer uptake occurred in the PSMA-negative DU 145 tumors. These results were confirmed by direct counting of tissues after the final imaging.

CONCLUSION

Because of the high and specific uptake of (64)Cu-labeled mAb 3/A12 in PSMA-positive tumors, this ligand represents an excellent candidate for prostate cancer imaging and potentially for radioimmunotherapy.

ARRONAX, a high-energy and high-intensity cyclotron for nuclear medicine

PURPOSE

This study was aimed at establishing a list of radionuclides of interest for nuclear medicine that can be produced in a high-intensity and high-energy cyclotron.

METHODS

We have considered both therapeutic and positron emission tomography radionuclides that can be produced using a high-energy and a high-intensity cyclotron such as ARRONAX, which will be operating in Nantes (France) by the end of 2008. Novel radionuclides or radionuclides of current limited availability have been selected according to the following criteria: emission of positrons, low-energy beta or alpha particles, stable or short half-life daughters, half-life between 3 h and 10 days or generator-produced, favourable dosimetry, production from stable isotopes with reasonable cross sections.

RESULTS

Three radionuclides appear well suited to targeted radionuclide therapy using beta ((67)Cu, (47)Sc) or alpha ((211)At) particles. Positron emitters allowing dosimetry studies prior to radionuclide therapy ((64)Cu, (124)I, (44)Sc), or that can be generator-produced ((82)Rb, (68)Ga) or providing the opportunity of a new imaging modality ((44)Sc) are considered to have a great interest at short term whereas (86)Y, (52)Fe, (55)Co, (76)Br or (89)Zr are considered to have a potential interest at middle term.

CONCLUSIONS

Several radionuclides not currently used in routine nuclear medicine or not available in sufficient amount for clinical research have been selected for future production. High-energy, high-intensity cyclotrons are necessary to produce some of the selected radionuclides and make possible future clinical developments in nuclear medicine. Associated with appropriate carriers, these radionuclides will respond to a maximum of unmet clinical needs.

Quantitative radioimmunoPET imaging of EphA2 in tumor-bearing mice

PURPOSE

EphA2 receptor tyrosine kinase is significantly overexpressed in a wide variety of cancer types. High EphA2 expression has been correlated with increased metastatic potential and poor patient survival. Although many recent reports have focused on blocking the EphA2 signaling pathway in cancer, the in vivo imaging of EphA2 has not yet been investigated.

METHODS

We labeled 1C1, a humanized monoclonal antibody against both human and murine EphA2, with (64)Cu through the chelating agent 1,4,7,10-tetraazacyclododecane N,N',N'',N'''-tetraacetic acid (DOTA) and carried out positron emission tomography (PET) imaging of eight tumor models with different EphA2 expression levels. Western blotting of tumor tissue lysate was performed to correlate the EphA2 expression level with (64)Cu-DOTA-1C1 uptake in the tumors. Immunofluorescence staining and biodistribution studies were also carried out to validate the in vivo results.

RESULTS

The radiolabeling yield was 88.9 +/- 9.5% (n = 7) and the specific activity of (64)Cu-DOTA-1C1 was 1.32 +/- 0.14 GBq/mg of 1C1 mAb. The antibody retained antigen-binding affinity/specificity after DOTA conjugation as measured by FACS analysis. The uptake of (64)Cu-DOTA-1C1 in CT-26 tumors was as high as 25.1 +/- 2.5 %ID/g (n = 3) at 18 h post injection. (64)Cu-DOTA-IgG, an isotype-matched control, exhibited minimal non-specific uptake in all eight tumor models. In vivo EphA2 specificity of (64)Cu-DOTA-1C1 was confirmed by successful blocking of CT-26 tumor uptake by unlabeled 1C1. Most importantly, the tumor uptake value obtained from PET imaging had excellent linear correlation with the relative tumor tissue EphA2 expression level measured by Western blot, where r (2) equals 0.90 and 0.92 at 18 h and 42 h post injection, respectively.

CONCLUSION

The tumor uptake of (64)Cu-DOTA-1C1 measured by microPET imaging reflects tumor EphA2 expression level in vivo. This is, to our knowledge, the first report of quantitative radioimmunoPET imaging of EphA2 in living subjects. Future clinical investigation of (64)Cu-DOTA-1C1 is warranted.

Synthesis, characterization and in vivo studies of Cu(II)-64-labeled cross-bridged tetraazamacrocycle-amide complexes as models of peptide conjugate imaging agents

Copper-64, a positron emitter suitable for positron emission tomography (PET), demonstrates improved in vivo clearance when chelated by the cross-bridged tetraazamacrocycle CB-TE2A compared to TETA. Good in vivo clearance was also observed for 64Cu-CB-TE2A conjugated to a peptide, which converts one coordinating carboxylate pendant arm to an amide. To better understand the in vivo stability of peptide- conjugated CB-TE2A, cross-bridged monoamides were synthesized. Crystal structures of natCu(II)-CB-TEAMA and natCu(II)-CB-PhTEAMA revealed hexadentate, distorted octahedral coordination geometry. In vivo biodistribution showed clearance of all 64Cu-radiolabeled cross-bridged monoamides from liver and bone marrow such that uptake at 24 h was <10% of uptake at 30 min. In contrast, >60% of 30 min uptake from 64Cu-TETA was retained in these tissues at 24 h. Clearance of 64Cu-cross-bridged monoamides from nontarget organs suggests good in vivo stability, thus supporting the use of CB-TE2A as a bifunctional chelator without modifications to the macrocycle backbone.

Copper-67 radioimmunotherapy and growth inhibition by anti-L1-cell adhesion molecule monoclonal antibodies in a therapy model of ovarian cancer metastasis

PURPOSE

We examined the tumor-targeting and therapeutic effects of (67)Cu-labeled single amino acid mutant forms of anti-L1 monoclonal antibody chCE7 in nude mice with orthotopically implanted SKOV3ip human ovarian carcinoma cells.

EXPERIMENTAL DESIGN

For radioimmunotherapy, chCE7 antibodies with a mutation of histidine 310 to alanine (chCE7H310A) and a mutation of asparagine 297 to glutamine (chCE7agl) were generated to achieve more rapid blood clearance. Biodistributions of (67)Cu-4-(1,4,8,11-tetraazacyclotetradec-1-yl)-methyl benzoic acid tetrachloride (CPTA)-labeled mutant antibodies were measured in nude mice bearing SKOV3ip human ovarian cancer metastases. The effects of single i.v. injections of (67)Cu-chCE7agl alone on tumor reduction and survival were investigated. In addition, a combination of low-dose (67)Cu-radioimmunotherapy with unlabeled anti-L1 antibody L1-11A on survival was investigated.

RESULTS

(67)Cu-CPTA-chCE7agl showed high (up to 49% ID/g) and persistent (up to 168 h) uptake in SKOV3ip metastases, with low levels in normal tissues. (67)Cu-CPTA-chCE7H310A revealed a shorter half-life in the blood and a lower tumor uptake and retention. A single low dose of 4 MBq of (67)Cu-chCE7agl reduced tumor growth but did not prolong survival significantly, whereas a single 10.5 MBq dose of (67)Cu-chCE7agl reduced tumor growth and prolonged survival significantly. The combination of unlabeled monoclonal antibody L1-11A with a subtherapeutic dose of (67)Cu-radioimmunotherapy also prolonged survival significantly.

CONCLUSION

The results show improved pharmacokinetics and biodistributions as well as the therapeutic effect of the (67)Cu-labeled single amino acid mutant chCE7agl. Therapeutic data indicate, for the first time, the feasibility of combining anti-L1-directed growth inhibition and (67)Cu-radioimmunotherapy, thereby increasing the efficiency of antibody treatment of metastatic ovarian carcinoma.

Evaluation of 177Lu-DOTA-labeled aglycosylated monoclonal anti-L1-CAM antibody chCE7: influence of the number of chelators on the in vitro and in vivo properties

INTRODUCTION

In this study, we optimized the 1,4,7,10-tetraazacyclododecane-N-N'-N"-N"'-tetraacetic acid (DOTA) chelator-to-antibody (c/a) ratio for the aglycosylated variant of the anti-L1-CAM antibody chCE7 (chCE7agl), providing high specific activity and low liver uptake in 177Lu-labeled form.

METHODS

chCE7agl was substituted with increasing molar excess of DOTA-NCS. The number of chelators coupled to the antibody and the binding affinities to target tumor cells (IC50 values) of the resulting immunoconjugates were determined. The different immunoconjugates were labeled with 177Lu; specific activity was measured, and metabolic stability was analyzed in human plasma. The effect of different c/a ratios on blood clearance and liver uptake was tested in nude mice. Changes of the protein backbone structure were analyzed by circular dichroism spectroscopy.

RESULTS

chCE7agl was substituted with 7, 12 or 15 DOTA ligands. The IC50 concentrations displacing radioiodinated chCE7 antibody increased with the number of chelators (1.5-fold with 7 ligands, 2.5-fold with 12 ligands and a 5-fold increase with 15 ligands). The highest specific activity for 177Lu-DOTA-chCE7agl was obtained with a c/a ratio of 12 (106 MBq/mg). Radioimmunoconjugates were stable in human plasma for at least 24 h. Blood clearance and liver uptake were measured after 24 h (c/a ratios of 12 and 15) or 48 h (c/a ratio of 7). The liver-to-blood ratios were 0.35+/-0.14 (7 ligands), 0.77+/-0.19 (12 ligands) and 17.85+/-3.44 (15 ligands).

CONCLUSIONS

DOTA-chCE7agl conjugates with a c/a ratio of 12 combined high specific activity with good in vitro and in vivo properties. The rapid elimination rate from the blood and the high uptake in the liver of chCE7agl substituted with 15 DOTA ligands were found not to be due to conformational changes of the antibody backbone structure.

Efficient inhibition of intra-peritoneal tumor growth and dissemination of human ovarian carcinoma cells in nude mice by anti-L1-cell adhesion molecule monoclonal antibody treatment

The L1 cell adhesion molecule is implicated in the control of proliferation, migration, and invasion of several tumor cell types in vitro. Recently, L1 overexpression was found to correlate with tumor progression of ovarian carcinoma, one of the most common causes of cancer-related deaths in gynecologic malignant diseases. To evaluate L1 as a potential target for ovarian cancer therapy, we investigated the effects of anti-L1 monoclonal antibodies (chCE7 and L1-11A) on proliferation and migration of L1-positive human SKOV3ip ovarian carcinoma cells in vitro and the therapeutic efficacy of L1-11A against i.p. SKOV3ip tumor growth in nude mice. In vitro, both anti-L1 antibodies efficiently inhibited the proliferation of SKOV3ip cells as well as other L1-expressing tumor cell lines (renal carcinoma, neuroblastoma, and colon carcinoma). On two cell lines, hyper-cross-linking of L1-11A with a secondary antibody was necessary for significant inhibition of proliferation, indicating that cross-linking of L1 is required for the antiproliferative effect. L1-negative prostate carcinoma cells were not influenced by antibody treatment. Biweekly treatment of ovarian carcinoma-bearing mice with L1-11A led to a dose-dependent and significant reduction of tumor burden (up to -63.5%) and ascites formation (up to -75%). This effect was associated with reduced proliferation within the tumors. L1-directed antibody-based inhibition of peritoneal growth and dissemination of human ovarian carcinoma cells represents important proof-of-principle for the development of a new therapy against one of the leading gynecologic malignant diseases.

In vivo evaluation of 177Lu- and 67/64Cu-labeled recombinant fragments of antibody chCE7 for radioimmunotherapy and PET imaging of L1-CAM-positive tumors

PURPOSE

The L1 cell adhesion protein is overexpressed in tumors, such as neuroblastomas, renal cell carcinomas, ovarian carcinomas, and endometrial carcinomas, and represents a target for tumor diagnosis and therapy with anti-L1-CAM antibody chCE7. Divalent fragments of this internalizing antibody labeled with 67/64Cu and 177Lu were evaluated to establish a chCE7 antibody fragment for radioimmunotherapy and positron emission tomography imaging, which combines high-yield production with improved clearance and biodistribution properties.

EXPERIMENTAL DESIGN

chCE7F(ab')2 fragments were produced in high amounts (0.2 g/L) in HEK-293 cells, substituted with the peptide-linked tetraazamacrocycle 3-(p-nitrobenzyl)-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate-triglycyl-L-p-isothiocyanato-phenylalanine, and labeled with 67Cu and 177Lu. In vivo bioevaluation involved measuring kinetics of tumor and tissue uptake in nude mice with SK-N-BE2c xenografts and NanoPET (Oxford Positron Systems, Oxford, United Kingdom) imaging with 64Cu-3-(p-nitrobenzyl)-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate-triglycine-chCE7F(ab')2.

RESULTS

The 177Lu- and 67Cu-labeled immunoconjugates reached maximal tumor accumulation at 24 hours after injection with similar levels of 12%ID/g to 14%ID/g. Blood levels dropped to 1.0%ID/g for the 177Lu fragment and 2.3%ID/g for the 67Cu fragment at 24 hours. The most striking difference concerned radioactivity present in the kidneys, being 34.5%ID/g for the 177Lu fragment and 16.0%ID/g for the 67Cu fragment at 24 hours. Positron emission tomography imaging allowed clear visualization of s.c. xenografts and peritoneal metastases and a detailed assessment of whole-body tracer distribution.

CONCLUSIONS

67/64Cu- and 177Lu-labeled recombinant chCE7F(ab')2 revealed suitable in vivo characteristics for tumor imaging and therapy but displayed higher kidney uptake than the intact monoclonal antibody. The 67Cu- and 177Lu-labeled immunoconjugates showed different in vivo behavior, with 67/64Cu-3-(p-nitrobenzyl)-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate-triglycine-F(ab')2 appearing as the more favorable conjugate due to superior tumor/kidney ratios.

Preparation and biological evaluation of copper-64-labeled tyr3-octreotate using a cross-bridged macrocyclic chelator

PURPOSE

Somatostatin receptors (SSTr) are expressed on many neuroendocrine tumors, and several radiotracers have been developed for imaging these types of tumors. For this reason, peptide analogues of somatostatin have been well characterized. Copper-64 (t(1/2) = 12.7 hours), a positron emitter suitable for positron emission tomography (PET) imaging, was shown recently to have improved in vivo clearance properties when chelated by the cross-bridged tetraazamacrocycle 4,11-bis(carboxymethyl)-1,4,8,11-tetraazabicyclo(6.6.2)hexadecane (CB-TE2A) compared with 1,4,8,11-tetraazacyclotetradecane-1,4,8,11-tetraacetic acid (TETA).

EXPERIMENTAL DESIGN

CB-TE2A and TETA were conjugated to the somatostatin analogue tyrosine-3-octreotate (Y3-TATE) for evaluation of CB-TE2A as a bifunctional chelator of 64Cu. The in vitro affinity of each compound for SSTr was determined using a homologous competitive binding assay. In vivo characteristics of both radiolabeled compounds were examined in biodistribution and microPET studies of AR42J tumor-bearing rats.

RESULTS

Cu-CB-TE2A-Y3-TATE (Kd = 1.7 nmol/L) and Cu-TETA-Y3-TATE (Kd = 0.7 nmol/L) showed similar affinities for AR42J derived SSTr. In biodistribution studies, nonspecific uptake in blood and liver was lower for 64Cu-CB-TE2A-Y3-TATE. Differences increased with time such that, at 4 hours, blood uptake was 4.3-fold higher and liver uptake was 2.4-fold higher for 64Cu-TETA-Y3-TATE than for 64Cu-CB-TE2A-Y3-TATE. In addition, 4.4-times greater tumor uptake was detected with 64Cu-CB-TE2A-Y3-TATE than with 64Cu-TETA-Y3-TATE at 4 hours postinjection. MicroPET imaging yielded similar results.

CONCLUSIONS

CB-TE2A appears to be a superior in vivo bifunctional chelator of 64Cu for use in molecular imaging by PET or targeted radiotherapy due to both improved nontarget organ clearance and higher target organ uptake of 64Cu-CB-TE2A-Y3-TATE compared with 64Cu-TETA-Y3-TATE.

An assessment of the effects of shell cross-linked nanoparticle size, core composition, and surface PEGylation on in vivo biodistribution

Amphiphilic core-shell nanoparticles have drawn considerable interest in biomedical applications. The precise control over their physicochemical parameters and the ability to attach various ligands within specific domains suggest shell cross-linked (SCK) nanoparticles may be used as multi-/polyvalent scaffolds for drug delivery. In this study, the biodistribution of four SCKs, differing in size, core composition, and surface PEGylation, was evaluated. To facilitate in-vivo tracking of the SCKs, the positron-emitting radionuclide copper-64 was used. By using biodistribution and microPET imaging approaches, we found that small diameter (18 nm) SCKs possessing a polystyrene core showed the most favorable biological behavior in terms of prolonged blood retention and low liver accumulation. The data demonstrated that both core composition, which influenced the SCK flexibility and shape adaptability, and hydrodynamic diameter of the nanoparticle play important roles in the respective biodistributions. Surface modification with poly(ethylene glycol) (PEG) had no noticeable effects on SCK behavior.

Molecular imaging with copper-64

Molecular imaging is expected to change the face of drug discovery and development. The ability to link imaging to biology for guiding therapy should improve the rate at which novel imaging technologies, probes, contrast agents, drugs and drug delivery systems can be transferred into clinical practice. Nuclear medicine imaging, in particular, positron emission tomography (PET) allows the detection and monitoring of a variety of biological and pathophysiological processes, at tracer quantities of the radiolabelled target agents, and at doses free from pharmacological effects. In the field of drug discovery and development, the use of radiotracers for radiolabelling target agents has now become one of the essential tools in identifying, screening and development of new target agents. In this regard, (64)Cu (t(1/2)=12.7 h) has been identified as an emerging PET isotope. Its half-life is sufficiently long for radiolabelling a range of target agents and its ease of production and adaptable chemistry make it an excellent radioisotope for use in molecular imaging. This review describes recent advances, in the routes of (64)Cu production, design and application of bi-functional ligands for use in radiolabelling with (64/67)Cu(2+), and their significance and anticipated impact on the field of molecular imaging and drug development.

In vivo evaluation of copper-64-labeled monooxo-tetraazamacrocyclic ligands

Copper-64 (T(1/2)=12.7 h; beta(+): 0.653 MeV, 17.4%; beta(-): 0.578 MeV, 39%) has applications in positron emission tomography (PET) imaging and radiotherapy, and is conveniently produced on a biomedical cyclotron. Tetraazamacrocyclic ligands are the most widely used bifunctional chelators (BFCs) for attaching copper radionuclides to antibodies and peptides due to their relatively high kinetic stability. In this paper, we evaluated three monooxo-tetraazamacrocyclic ligands with different ring sizes and oxo group positions. H1 [1,4,7,10-tetraazacyclotridecan-11-one], H2 [1,4,8,11-tetraazacyclotetradecan-5-one] and H3 [1,4,7,10-tetraazacyclotridecan-2-one] were radiolabeled with (64)Cu in high radiochemical yields under mild conditions. The three (64)Cu-labeled complexes are all +1 charged, as determined by their electrophoretic mobility. While they demonstrated >95% stability in rat serum out to 24 h, both biodistribution and microPET imaging studies revealed high uptake and long retention of the compounds in major clearance organs (e.g., blood, liver and kidney), which suggests that (64)Cu dissociated from the complexes in vivo. Of the three complexes, (64)Cu-2(+), which has a cyclam backbone (1,4,8,11-tetraazacyclotetradecane), exhibited the lowest nontarget organ accumulation. The data from these studies may invalidate the candidacy of the monooxo-tetraazamacrocyclics as BFCs for copper radiopharmaceuticals. However, the data presented here suggest that neutral or negatively charged Cu(II) complexes of tetraazamacrocyclic ligands with a cyclam backbone (tetradecane) are optimal for copper radiopharmaceutical applications.