Michel Chérel

Cancer radioimmunotherapy with alpha-emitting nuclides

In lymphoid malignancies and in certain solid cancers such as medullary thyroid carcinoma, somewhat mixed success has been achieved when applying radioimmunotherapy (RIT) with β-emitters for the treatment of refractory cases. The development of novel RIT with α-emitters has created new opportunities and theoretical advantages due to the high linear energy transfer (LET) and the short path length in biological tissue of α-particles. These physical properties offer the prospect of achieving selective tumoural cell killing. Thus, RIT with α-emitters appears particularly suited for the elimination of circulating single cells or cell clusters or for the treatment of micrometastases at an early stage. However, to avoid non-specific irradiation of healthy tissues, it is necessary to identify accessible tumoural targets easily and rapidly. For this purpose, a small number of α-emitters have been investigated, among which only a few have been used for in vivo preclinical studies. Another problem is the availability and cost of these radionuclides; for instance, the low cost and the development of a reliable actinium-225/bismuth-213 generator were probably determining elements in the choice of bismuth-213 in the only human trial of RIT with an α-emitter. This article reviews the literature concerning monoclonal antibodies radiolabelled with α-emitters that have been developed for possible RIT in cancer patients. The principal radio-immunoconjugates are considered, starting with physical and chemical properties of α-emitters, their mode of production, the possibilities and difficulties of labelling, in vitro studies and finally, when available, in vivo preclinical and clinical studies.

Thoracic Staging in Lung Cancer: Prospective Comparison of 18F-FDG PET/MR Imaging and 18F-FDG PET/CT

Therapeutic decisions in non–small cell lung cancer (NSCLC) patients depend on the tumor stage. PET/CT with 18F-FDG is widely accepted as the diagnostic standard of care. The purpose of this study was to compare a dedicated pulmonary 18F-FDG PET/MR imaging protocol with 18F-FDG PET/CT for primary and locoregional lymph node staging in NSCLC patients using histopathology as the reference. Methods: Twenty-two patients (12 men, 10 women; mean age ± SD, 65.1 ± 9.1 y) with histopathologically confirmed NSCLC underwent 18F-FDG PET/CT, followed by 18F-FDG PET/MR imaging, including a dedicated pulmonary MR imaging protocol. T and N staging according to the seventh edition of the American Joint Committee on Cancer staging manual was performed by 2 readers in separate sessions for 18F-FDG PET/CT and PET/MR imaging, respectively. Results from histopathology were used as the standard of reference. The mean and maximum standardized uptake value (SUVmean and SUVmax, respectively) and maximum diameter of the primary tumor was measured and compared in 18F-FDG PET/CT and PET/MR imaging. Results: PET/MR imaging and 18F-FDG PET/CT agreed on T stages in 16 of 16 of patients (100%). All patients were correctly staged by 18F-FDG PET/CT and PET/MR (100%), compared with histopathology. There was no statistically significant difference between 18F-FDG PET/CT and 18F-FDG PET/MR imaging for lymph node metastases detection (P = 0.48). For definition of thoracic N stages, PET/MR imaging and 18F-FDG PET/CT were concordant in 20 of 22 patients (91%). PET/MR imaging determined the N stage correctly in 20 of 22 patients (91%). 18F-FDG PET/CT determined the N stage correctly in 18 of 22 patients (82%). The mean differences for SUVmean and SUVmax of NSCLC in 18F-FDG PET/MR imaging and 18F-FDG PET/CT were 0.21 and −5.06. These differences were not statistically significant (P > 0.05). The SUVmean and SUVmax measurements derived from 18F-FDG PET/CT and 18F-FDG PET/MR imaging exhibited a high correlation (R = 0.74 and 0.86, respectively; P < 0.0001). Size measurements showed an excellent correlation between 18F-FDG PET/MR imaging and 18F-FDG PET/CT (R = 0.99; P < 0.0001). The lower and upper limits of agreement between 18F-FDG PET/CT and 18F-FDG PET/MR imaging using Bland–Altman analysis were −2.34 to 3.89 for SUVmean, −7.42 to 4.40 for SUVmax, and −0.59 to 0.83 for the tumor size, respectively. Conclusion: 18F-FDG PET/MR imaging using a dedicated pulmonary MR imaging protocol, compared with 18F-FDG PET/CT, does not provide advantages in thoracic staging in NSCLC patients.

Comparison of the biologic effects of MA5 and B-B4 monoclonal antibody labeled with iodine-131 and bismuth-213 on multiple myeloma.

Using a specific monoclonal antibody (MAb), B‐B4, coupled to bismuth‐213 (213Bi) by a chelating agent (CITC‐DTPA), the feasibility of alpha‐radioimmunotherapy (RIT) for multiple myeloma (MM) has been demonstrated previously.

Mechanisms of cell sensitization to a radioimmunotherapy by doxorubicin or paclitaxel in multiple myeloma cell lines

Purpose: The purpose of this study was to analyze different mechanisms (cell cycle synchronization, DNA damage, and apoptosis) that might underlie potential synergy between chemotherapy (paclitaxel or doxorubicin) and radioimmunotherapy with α radionuclides. Experimental Design: Three multiple myeloma cell lines (LP1, RMI 8226, and U266) were treated with 213Bi-radiolabeled B-B4, a monoclonal antibody that recognizes syndecan-1 (CD138) 24 hours after paclitaxel (1 nmol/L) or doxorubicin (10 nmol/L) treatment. Cell survival was assessed using a clonogenic survival assay. Cell cycle modifications were assessed by propidium iodide staining and DNA strand breaks by the comet assay. Level of apoptosis was determined by Apo 2.7 staining. Results: Radiation enhancement ratio showed that paclitaxel and doxorubicin were synergistic with α radioimmunotherapy. After a 24-hour incubation, paclitaxel and doxorubicin arrested all cell lines in the G2-M phase of the cell cycle. Doxorubicin combined with α radioimmunotherapy increased tail DNA in the RPMI 8226 cell line but not the LP1 or U266 cell lines compared with doxorubicin alone or α radioimmunotherapy alone. Neither doxorubicin nor paclitaxel combined with α radioimmunotherapy increased the level of apoptosis induced by either drug alone or α radioimmunotherapy alone. Conclusion: Both cell cycle arrest in the G2-M phase and an increase in DNA double-strand breaks could lead to radiosensitization of cells by doxorubicin or paclitaxel, but apoptosis would not be involved in radiosensitization mechanisms.

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.

Contribution of (64Cu)-ATSM PET in molecular imaging of tumour hypoxia compared to classical (18F)-MISO — a selected review

During the carcinogenesis process, tumour cells often have a more rapid proliferation potential than cells that participate in blood capillary formation by neoangiogenesis. As a consequence of the poorly organized vasculature of various solid tumours, a limited oxygen delivery is observed. This hypoxic mechanism frequently occurs in solid cancers and can lead to therapeutic resistance. The present selected literature review is focused on the comparison of two positron emitting radiopharmaceuticals agents, which are currently leaders in tumour hypoxia imaging by PET. {18F}-fluoromisonidazole (=FMISO) is most commonly used as an investigational PET agent with an investigational new drug exemption from the FDA, while {64Cu}-diacetyl-bis(N4-methylthiosemicarbazone) (64Cu-ATSM) has been presented as an alternative radiopharmaceutical not yet readily available. The comparison of these two radiopharmaceutical agents is particularly focused on isotope properties, radiopharmaceutical labelling process, pharmacological mechanisms, dosimetry data in patients, and clinical results in terms of image contrast. PET imaging has demonstrated a good efficacy in tumour hypoxia imaging with both FMISO and Cu-ATSM, but FMISO has presented too slow an in vivo accumulation and a weak image contrast of the hypoxia area. Despite a less favourable dosimetry, 64Cu-ATSM appears superior in terms of imaging performance, calling for industrial and clinical development of this innovative radiopharmaceutical.

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.

Reconstitution of two isoforms of the human interleukin-11 receptor and comparison of their functional properties

Long‐term stable Ba/F3 transfectants (B13Rα1 and B13Rα2) expressing two isoforms of the human IL‐11Rα receptor (α1 full length or α2 lacking the cytoplasmic domain) in combination with human gp130 were established. IL‐11Rα1 and IL‐11Rα2 were each expressed and detected as three bands upon Western blot analysis, with apparent molecular masses in agreement with those of the polypeptide backbone (47 and 44 kDa, respectively) with no, one or two N‐linked sugars. B13Rα1 and B13Rα2 bound IL‐11–thioredoxin with similar efficiencies and proliferated with superimposable dose–response curves to IL‐11, demonstrating that the intracellular domain of IL‐11Rα has no significant contribution on ligand binding and signaling. Analysis of a set of anti‐human gp130 mAbs confirmed the similar responsiveness of B13Rα1 and B13Rα2 transfectants.

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.

BackgroundOverexpression 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.Results125I-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.