Preparation and characterization of immunoconjugates as an initial step for targeted alpha therapy

The basic principle of targeted alpha therapy (TAT) is that the alpha-emitting radionuclide is attached to specifically designed biomolecules, formulated as conjugates from antibodies, peptides and other small molecules. The design and characterization of the immunoconjugates, stand as critical steps in ensuring the efficacy of treatment, especially when they are employed for labeling with radionuclides, encompassing both beta and alpha emitters. Astatine-211 as an alpha emitter that has been of great interest in recent years can significantly provide the combined success of its cytotoxic power and the specificity of the targeting agent (1). The preparation of the immunoconjugates involves several steps and procedures, starting with the purification of the antibody using methods such as ultracentrifugation or gel filtration. This antibody can be derived either from a commercially available product or produced in the laboratory. Different chelators or prosthetic groups are used for conjugation, with the choice depending on the selected target molecule. Characterization of the immunoconjugates is a crucial step to assess their quality and functionality. Various analytical techniques could be employed to determine structural integrity and purity, including mass, Raman and infrared spectrometry, size exclusion chromatography, or electrophoresis (2). To enhance the stability of the product, further freeze-drying processes can be conducted using established protocols (3). Ongoing research in this field aims to establish protocols for preparing immunoconjugates and defining minimum quality criteria for these preparations. This progress could represent a significant step forward for in-vivo examinations and holds promise for the future of cancer research treatment using alpha radiotherapy

Syndecan-1 antigen, a promising new target for triple-negative breast cancer immuno-PET and radioimmunotherapy. A preclinical study on MDA-MB-468 xenograft tumors

International audienceBackgroundOverexpression of syndecan-1 (CD138) in breast carcinoma correlates with a poor prognosis and an aggressive phenotype. The objective of this study was to evaluate the potential of targeting CD138 by immuno-PET imaging and radioimmunotherapy (RIT) using the antihuman syndecan-1 B-B4 mAb radiolabeled with either 124I or 131I in nude mice engrafted with the triple-negative MDA-MB-468 breast cancer cell line.MethodThe immunoreactivity of 125I-B-B4 (80%) was determined, and the affinity of 125I-B-B4 and the expression of CD138 on MDA-MB-468 was measured in vitro by Scatchard analysis. CD138 expression on established tumors was confirmed by immunohistochemistry. A biodistribution study was performed in mice with subcutaneous MDA-MB-468 and 125I-B-B4 at 4, 24, 48, 72, and 96 h after injection and compared with an isotype-matched control. Tumor uptake of B-B4 was evaluated in vivo by immuno-PET imaging using the 124I-B-B4 mAb. The maximum tolerated dose (MTD) was determined from mice treated with 131I-B-B4 and the RIT efficacy evaluated.Results 125I-B-B4 affinity was in the nanomolar range (Kd = 4.39 ± 1.10 nM). CD138 expression on MDA-MB-468 cells was quite low (Bmax = 1.19 × 104 ± 9.27 × 102 epitopes/cell) but all expressed CD138 in vivo as determined by immunohistochemistry. The tumor uptake of 125I-B-B4 peaked at 14% injected dose (ID) per gram at 24 h and was higher than that of the isotype-matched control mAb (5% ID per gram at 24 h). Immuno-PET performed with 124I-B-B4 on tumor-bearing mice confirmed the specificity of B-B4 uptake and its retention within the tumor. The MTD was reached at 22.2 MBq. All mice treated with RIT (n = 8) as a single treatment at the MTD experienced a partial (n = 3) or complete (n = 5) response, with three of them remaining tumor-free 95 days after treatment.ConclusionThese results demonstrate that RIT with 131I-B-B4 could be considered for the treatment of metastatic triple-negative breast cancer that cannot benefit from hormone therapy or anti-Her2/neu immunotherapy. Immuno-PET for visualizing CD138-expressing tumors with 124I-B-B4 reinforces the interest of this mAb for diagnosis and quantitative imaging

P-230 - Aryliodonium ylides as efficient precursors for astatine-211 labeling

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Targeted alpha-therapy with 211At-anti-mCD138 mAb in a syngeneic murine Multiple Myeloma model : can repeated doses or fractionation protocol overpass single dose efficiency?

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Alpha Particles Induce Autophagy in Multiple Myeloma Cells

International audienceOBJECTIVES: Radiation emitted by the radionuclides in radioimmunotherapy (RIT) approaches induce direct killing of the targeted cells as well as indirect killing through the bystander effect. Our research group is dedicated to the development of α-RIT, i.e., RIT using α-particles especially for the treatment of multiple myeloma (MM). γ-irradiation and β-irradiation have been shown to trigger apoptosis in tumor cells. Cell death mode induced by (213)Bi α-irradiation appears more controversial. We therefore decided to investigate the effects of (213)Bi on MM cell radiobiology, notably cell death mechanisms as well as tumor cell immunogenicity after irradiation.METHODS: Murine 5T33 and human LP-1 MM cell lines were used to study the effects of such α-particles. We first examined the effects of (213)Bi on proliferation rate, double-strand DNA breaks, cell cycle, and cell death. Then, we investigated autophagy after (213)Bi irradiation. Finally, a coculture of dendritic cells (DCs) with irradiated tumor cells or their culture media was performed to test whether it would induce DC activation.RESULTS: We showed that (213)Bi induces DNA double-strand breaks, cell cycle arrest, and autophagy in both cell lines, but we detected only slight levels of early apoptosis within the 120 h following irradiation in 5T33 and LP-1. Inhibition of autophagy prevented (213)Bi-induced inhibition of proliferation in LP-1 suggesting that this mechanism is involved in cell death after irradiation. We then assessed the immunogenicity of irradiated cells and found that irradiated LP-1 can activate DC through the secretion of soluble factor(s); however, no increase in membrane or extracellular expression of danger-associated molecular patterns was observed after irradiation.CONCLUSION: This study demonstrates that (213)Bi induces mainly necrosis in MM cells, low levels of apoptosis, and autophagy that might be involved in tumor cell death

Radio- immunothérapie alpha : Principes et intérêts en immunité antitumorale

International audience> La radioimmunothérapie alpha (RITα) est une thérapie anticancéreuse vectorisée utilisant généralement un anticorps monoclonal spécifique d'un antigène tumoral couplé à un émetteur de particules α. Les émetteurs α représentent un outil idéal pour éradiquer les tumeurs disséminées ou les métastases. De récentes données démontrent que les rayonnements ionisants, en plus de leur cytotoxicité directe, peuvent aussi induire une immunité antitumorale efficace. Les effets biologiques de l'irradiation pourraient donc être utilisés pour potentialiser la réponse à différents types d'immunothérapie, et ainsi ouvrir la voie au développement de nouvelles thérapies combinant RITα et immunothérapies. < radionucléide. Le choix du radionu-cléide repose sur des considérations pratiques (le coût, la disponibilité, le type de techniques de radiomar-quage et la facilité d'utilisation), le type d'émission du radioélément, le transfert d'énergie linéique (TEL : quantité d'énergie transférée au milieu par la particule incidente, par unité de longueur de la trajectoire en keV 1 /µm) et la demi-vie physique du radioisotope (durée nécessaire pour que la moitié des noyaux radioactifs d'une source se soient désintégrés) [2]. Cette dernière doit être, autant que possible, en adéquation avec la pharmacocinétique du vecteur utilisé, afin de délivrer la plus grande dose possible de radioactivité à la tumeur après l'injection. Une demi-vie trop courte entraînera un nombre élevé de désintégrations avant d'atteindre la cible. À l'inverse, une demi-vie trop longue engendrera un grand nombre de désintégrations du radionucléide pendant la phase d'éli-mination du vecteur, rendant le radioimmunoconjugué plus toxique. La demi-vie doit également être compatible avec les applications cliniques et la prise en charge du patient. Ainsi, le temps nécessaire au transfert du radionucléide du site de production jusqu'à l'hôpital, 1 1 keV (kiloélectronvolts) = 10 3 eV ; 1 MeV (megaélectonvolts) = 10 6 eV

T cell repertoire and Epstein-Barr virus-specific T cell response in chronic active Epstein-Barr virus infection: a case study.

International audienceIn a patient with chronic active Epstein-Barr virus infection associated with vasculitis and fulminant CD4+ T cell lymphoproliferative disorder, we probed the peripheral blood mononuclear cells (PBMC) for the presence of an EBV-specific T cell repertoire and tested the possible relationship between the lymphocytic infiltrate and the EBV-specific T cell response. Our results give credence to the presence of an apparently normal EBV-specific memory T cell response after in vitro reactivation of the patient's PBMC with autologous infected B lymphoblastoid cell lines. In keeping with the characterization of the vasculitis, certain T cell subsets were detected after expansion of skin lesion-infiltrating lymphocytes and were found to be infected with EBV. These particular T cell expansions were neither the effectors nor the targets of the in vitro reactivated EBV-specific T cells, thus excluding a simple relationship between EBV, the skin lesions, and the T cell expansions frequently observed in these patients