Jean-François Gestin

Radiolabeled Antibodies for Cancer Imaging and Therapy

Radiolabeled antibodies were studied first for tumor detection by single-photon imaging, but FDG PET stopped these developments. In the meantime, radiolabeled antibodies were shown to be effective in the treatment of lymphoma. Radiolabeling techniques are well established and radiolabeled antibodies are a clinical and commercial reality that deserves further studies to advance their application in earlier phase of the diseases and to test combination and adjuvant therapies including radiolabeled antibodies in hematological diseases. In solid tumors, more resistant to radiations and less accessible to large molecules such as antibodies, clinical efficacy remains limited. However, radiolabeled antibodies used in minimal or small-size metastatic disease have shown promising clinical efficacy. In the adjuvant setting, ongoing clinical trials show impressive increase in survival in otherwise unmanageable tumors. New technologies are being developed over the years: recombinant antibodies and pretargeting approaches have shown potential in increasing the therapeutic index of radiolabeled antibodies. In several cases, clinical trials have confirmed preclinical studies. Finally, new radionuclides, such as lutetium-177, with better physical properties will further improve the safety of radioimmunotherapy. Alpha particle and Auger electron emitters offer the theoretical possibility to kill isolated tumor cells and microscopic clusters of tumor cells, opening the perspective of killing the last tumor cell, which is the ultimate challenge in cancer therapy. Preliminary preclinical and preliminary clinical results confirm the feasibility of this approach.

213Bi Radioimmunotherapy with an Anti-mCD138 Monoclonal Antibody in a Murine Model of Multiple Myeloma

New multiple myeloma (MM) treatments—such as high-dose melphalan therapy plus autologous stem cell transplantation or regimens incorporating bortezomide, thalidomide, and lenalidomide—substantially increase the rate of complete response that is associated with longer patient survival. Thus, maintaining the complete response status by improving the minimal residual disease after induction therapy is a key goal for MM management. Here, we address the question of radioimmunotherapy efficacy in MM minimal residual disease treatment in mice with a low tumor burden. α-emitters are particularly well adapted to this approach because the short range of α-particles enables localized irradiation of tumor cells within the bone marrow and a cytotoxic effect on isolated cells due to the high LET (linear energy transfer) of α-particles. The CD138 antigen was used as a target because of its strong expression on myeloma cells in 100% of patients. Method: Intravenous injection of 106 5T33 mouse myeloma cells into the Syngeneic mouse strain C57BL/KaLwRij resulted in a rapid invasion of the marrow and limb paralysis, as illustrated by bioluminescence imaging with luciferase-transfected 5T33 cells. Radioimmunotherapy was performed 10 d after 5T33 cell engraftment with an intravenous injection of an antimouse CD138 antibody radiolabeled with 213Bi at activities of 1.85, 3.7, 7.4, and 11.1 MBq. A blood cell count was performed weekly to monitor hematologic toxicity. The levels of blood Flt3 ligand were also measured to evaluate the radioimmunotherapy-related myelotoxicity. Disease progression was monitored by titrating the monoclonal IgG2b antibody produced by 5T33 cells. Results: The groups treated with 3.7 and 7.4 MBq exhibited a median survival greater than 300 and 227 d, respectively, compared with 45.5 d in the control untreated group. The highest activity (11.1 MBq) showed short-term toxicity whereas the lowest activity (1.85 MBq) gave results similar to those of the controls. With activities of 3.7 and 7.4 MBq, mice exhibited a transient hematologic toxicity whereas only temporary and moderate myelotoxicity was observed with 7.4 MBq. Conclusion: This study demonstrates promising therapeutic efficacy of 213Bi-labeled anti-mCD138 for the treatment of residual disease in the case of MM, with only moderate and transient toxicity.

Radioimmunoconjugates for the treatment of cancer.

Radioimmunotherapy (RIT) has been developed for more than 30 years. Two products targeting the CD20 antigen are approved in the treatment of non-Hodgkin B-cell lymphoma (NHBL): iodine 131-tositumomab and yttrium 90-ibritumomab tiuxetan. RIT can be integrated in clinical practice for the treatment of patients with relapsed or refractory follicular lymphoma (FL) or as consolidation after induction chemotherapy. High-dose treatment, RIT in first-line treatment, fractionated RIT, and use of new humanized monoclonal antibodies (MAbs), in particular targeting CD22, showed promising results in NHBL. In other hemopathies, such as multiple myeloma, efficacy has been demonstrated in preclinical studies. In solid tumors, more resistant to radiation and less accessible to large molecules such as MAbs, clinical efficacy remains limited. However, pretargeting methods have shown clinical efficacy. Finally, new beta emitters such as lutetium 177, with better physical properties will further improve the safety of RIT and alpha emitters, such as bismuth 213 or astatine 211, offer the theoretical possibility to eradicate the last microscopic clusters of tumor cells, in the consolidation setting. Personalized treatments, based on quantitative positron emission tomography (PET), pre-therapeutic imaging, and dosimetry procedures, also could be applied to adapt injected activity to each patient.

Production of [211At]-Astatinated Radiopharmaceuticals and Applications in Targeted α-Particle Therapy

(211)At is a promising radionuclide for α-particle therapy of cancers. Its physical characteristics make this radionuclide particularly interesting to consider when bound to cancer-targeting biomolecules for the treatment of microscopic tumors. (211)At is produced by cyclotron irradiation of (209)Bi with α-particles accelerated at ~28 MeV and can be obtained in high radionuclidic purity after isolation from the target. Its chemistry resembles iodine, but there is also a tendency to behave as a metalloid. However, the chemical behavior of astatine has not yet been clearly established, primarily due to the lack of any stable isotopes of this element, which precludes the use of conventional analytical techniques for its characterization. There are also only a limited number of research centers that have been able to produce this element in sufficient amounts to carry out extensive investigations. Despite these difficulties, chemical reactions typically used with iodine can be performed, and a number of biomolecules of interest have been labeled with (211)At. However, most of these compounds exhibit unacceptable instability in vivo due to the weakness of the astatine-biomolecule bond. Nonetheless, several compounds have shown high potential for the treatment of cancers in vitro and in several animal models, thus providing a promising basis that has allowed initiation of the first two clinical studies.

Does immunoscintigraphy serve clinical needs effectively? Is there a future for radioimmunotherapy?

Since 1980, immunoscintigraphy has been performed in thousands of patients, and its clinical value has been demonstrated for selective indications in malignant (early detection of recurrences of colorectal and ovarian carcinomas) and non-malignant (cardiovascular and inflammatory) pathology. However, many clinicians are not yet very convinced of its efficiency. Opinions range between favourable interest and marked scepticism. The causes of this inconclusive verdict include an often moderate target-to-background ratio in images, the immunogenicity of injected murine antibodies and the fact that a true benefit for the patient has not yet been clearly demonstrated in large series of patients. Future prospects could significantly improve this and involve the reduction of non-specific activity in normal tissues (to improve disease target contrast and thus make image interpretation easier) and the decreased immunogenicity of injected immunoconjugates (to permit repetition of examinations). Radioimmunotherapy, an innovative and promising approach, is still limited by numerous problems. The results of clinical studies are still inconclusive, being encouraging only for specific indications. In the future, pre-targetting techniques should allow the rapid elimination of radioactivity from normal tissues, resulting in a significant increase in tumour-to-normal tissue ratios. Progress is also required in the choice of radionuclides and labelling techniques and in methods for dosimetric estimations. The clinical indications of radioimmunotherapy after systemic injection will concern mainly radiosensitive tumours such as lymphomas, small-cell lung cancers and neuroblastomas. After endocavitary injection, radioimmunotherapy could prove efficient in the treatment of micrometastases of ovarian carcinomas. For all indications, this new approach should be combined with other therapeutic modalities.

Synthesis of two stereoisomeric polydentate ligands, trans and cis cyclopentane-1,2-diaminotetraacetic acids, and complexation by 111In and 153Sm

Abstract Two polyaminocarboxylic acid chelating agents were synthesized. Complexation properties regarding 111In and 153Sm, two radionuclides suitable for applications in immunoscintigraphy and radioimmunotherapy were investigated. The synthesis of aminodiacetic acid derivatives 7a and 7b involved preliminary stereoselective synthesis of the corresponding amines, cis and trans cyclopentane-1,2-diamines. 111In labelling confirmed the complexation abilities of the two ligands. An additional comparative study to probe the relationship between ligand structure and metal complex was performed with 153Sm.

Radiolabeling of HTE1PA: A new monopicolinate cyclam derivative for Cu-64 phenotypic imaging. In vitro and in vivo stability studies in mice

INTRODUCTION HTE1PA, a monopicolinate-N-alkylated cyclam-based ligand has previously demonstrated fast complexation process, high kinetic inertness and important thermodynamic and electrochemical stability with respect to natural copper. In this work we first developed a new synthetic route to obtain HTE1PA in good yields. Then, we investigated HTE1PA chelation properties towards copper-64 and assessed in vitro and in vivo stability of the resulting compound. METHODS Radiolabeling of HTE1PA with copper-64 was tested at different ligand concentrations in ammonium acetate medium. In vitro stability study was carried out by incubating [(64)Cu]TE1PA complex in human serum at both 37°C and 4°C; chromatographic controls were performed over 24h. Biodistribution, pharmacokinetic and hepatic metabolism of [(64)Cu]TE1PA were conducted in BALC/c mice in comparison with [(64)Cu]acetate and [(64)Cu]DOTA, used as a reference ligand. RESULTS The promising results obtained for natural copper complexation were confirmed. HTE1PA was quantitatively radiolabeled in 15 min at room temperature. The resulting complex showed high serum stability. [(64)Cu]TE1PA induced a significant uptake in the liver and kidneys at early biodistribution time point. Nevertheless, a high speed wash out was observed at 24h leading to significantly lower uptake into the liver compared to [(64)Cu]DOTA. The metabolism study was consistent with a high resistance to transchelation as the initial uptake into liver matches with the intact form of [(64)Cu]TE1PA. CONCLUSION Despite the partial elimination of HTE1PA - as copper-64 complex - through the hepatic route, its high selectivity for copper and its resistance to transchelation make it a promising ligand for antibody radiolabeling with either copper-64 or copper-67.

Spectroscopic and electrochemical studies of new copper(II) and nickel(II) N2S2 tetradentate complexes of potential interest to nuclear medicine

The coupling of radionuclides such as copper (67Cu and 64Cu) to antibodies by bifunctional chelating agents (or BCA) requires extremely high stability to avoid in vivo release of metal. Six copper(II) and five nickel(II) complexes with N2S2 tetradentate ligands were synthesised for potential medical applications, and stability studies were conducted. I.r and u.v.-vis. spectra provided structural data on the geometry of the complexes. The redox potentials obtained from cyclic voltammetry allowed us to estimate the stability constants of each complex and then select the more suitable ligand for future applications in radioimmunotherapy.

Synthesis of a Novel Bifunctional Chelating Agent for Actinium Complexation.

Abstract A novel bifunctional chelating agent for actinium was synthesized in eight steps. Bimolecular cyclization between an iminodiester and a polyamine was achieved through the action of a molar equivalent of sodium methoxide.

Synthesis of new semi-rigid chelating agents for samarium-153

This study describes a simple, efficient synthesis pathway from trans-1,2-diaminocyclohexane that provides access to a new class of semi-rigid polyamine, polycarboxylic, and polyphosphonic ligands. The key steps in synthesis were the functionalisation (with an appropriate branching group) of a bisphosphonate diaminocyclohexane derivative and the introduction of methanephosphonic functions by a rarely used method.