What is the Best Radionuclide for Immuno-PET of Multiple Myeloma? A Comparison Study Between 89Zr- and 64Cu-Labeled Anti-CD138 in a Preclinical Syngeneic Model

Zirconium 89 and Copper 64 for ImmunoPET: From Antibody Bioconjugation and Radiolabeling to Molecular Imaging

Immunotherapy has transformed cancer treatment. Nevertheless, given the heterogeneity of clinical efficacy, the multiplicity of treatment options available and the possibility of serious adverse effects, selecting the most effective treatment has become the greatest challenge. Molecular imaging offers an attractive way for this purpose. ImmunoPET provides specific imaging with positron emission tomography (PET) using monoclonal antibodies (mAb) or its fragments as vector. By combining the high targeting specificity of mAb and the sensitivity of PET technique, immunoPET could noninvasively and dynamically reveal tumor antigens expression and provide theranostic tools of several types of malignancies. Because of their slow kinetics, mAbs require radioelements defined by a consistent half-life. Zirconium 89 (89Zr) and Copper 64 (64Cu) are radiometals with half-lives suitable for mAb labeling. Radiolabeling with a radiometal requires the prior use of a bifunctional chelate agent (BFCA) to functionalize mAb for radiometal chelation, in a second step. There are a number of BFCA available and much research is focused on antibody functionalization techniques or on developing the optimum chelating agent depending the selected radiometal. In this manuscript, we present a critical account of radiochemical techniques with radionuclides 89Zr and 64Cu and their applications in preclinical and clinical immuno-PET imaging.

Imaging diagnosis and efficacy monitoring by [89Zr]Zr-DFO-KN035 immunoPET in patients with PD-L1-positive solid malignancies

Rationale: Although programmed death-ligand 1 (PD-L1) inhibitors have achieved efficacy in cancer therapy, their response rate is low. Differences in the prognosis of patients with cancer under anti-PD-L1 treatment are related to the PD-L1 level in tumors. Accurate PD-L1 detection can optimize the accuracy of tumor immunotherapy and avoid ineffective clinical diagnosis and treatments. Methods: We investigated the imaging efficiency and therapy monitoring capacity of [89Zr]Zr-DFO-KN035 immunoPET for tumors. We labeled the monodomain anti-PD-L1 antibody KN035 with the radionuclide zirconium-89 and used this tracer for PET imaging. [89Zr]Zr-DFO-KN035 uptakes in patients with PD-L1-positive tumors, including primary and metastatic tumors, as well as in normal tissues, were comparatively assessed by using positron emission tomography/computed tomography imaging. Results: In PD-L1-positive patients, [89Zr]Zr-DFO-KN035 was sensitive in tumor-targeting imaging and could detect multiple metastatic foci, including multiple bone metastases (tumor-to-muscle ratios of 7.102 and 6.118 at 55 and 120 h, respectively) and lymph-node metastases (tumor-to-muscle ratios of 11.346 and 6.542 at 55 and 120 h, respectively). The needed radioactive dose of [89Zr]Zr-DFO-KN035 (55.5-92.5 MBq) used in this study was considerably lower than that of [18F]FDG (370-555 MBq). [89Zr]Zr-DFO-KN035 monitored and predicted the site of adverse reactions in antitumor immunotherapy. Moreover, after antitumor treatment, [89Zr]Zr-DFO-KN035 enabled observational imaging for therapeutic efficacy evaluation, which can help predict patient prognosis. Conclusion: [89Zr]Zr-DFO-KN035 can be used for the diagnosis and therapy monitoring of PD-L1-positive tumors and provide noninvasive and comprehensive observations for tumor diagnostic imaging, prognosis prediction, and efficacy evaluation.

Methods for the Production of Radiolabeled Bioagents for ImmunoPET

Immunoglobulin-based positron emission tomography (ImmunoPET) is making increasingly significant contributions to the nuclear imaging toolbox. The exquisite specificity of antibodies combined with the high-resolution imaging of PET enables clinicians and researchers to localize diseases, especially cancer, with a high degree of spatial certainty. This review focuses on the radiopharmaceutical preparation necessary to obtain those images-the work behind the scenes, which occurs even before the patient or animal is injected with the radioimmunoconjugate. The focus of this methods review will be the chelation of four radioisotopes to their most common and clinically relevant chelators.

Neuronal Ndst1 depletion accelerates prion protein clearance and slows neurodegeneration in prion infection

Select prion diseases are characterized by widespread cerebral plaque-like deposits of amyloid fibrils enriched in heparan sulfate (HS), a abundant extracellular matrix component. HS facilitates fibril formation in vitro, yet how HS impacts fibrillar plaque growth within the brain is unclear. Here we found that prion-bound HS chains are highly sulfated, and that the sulfation is essential for accelerating prion conversion in vitro. Using conditional knockout mice to deplete the HS sulfation enzyme, Ndst1 (N-deacetylase / N-sulfotransferase) from neurons or astrocytes, we investigated how reducing HS sulfation impacts survival and prion aggregate distribution during a prion infection. Neuronal Ndst1-depleted mice survived longer and showed fewer and smaller parenchymal plaques, shorter fibrils, and increased vascular amyloid, consistent with enhanced aggregate transit toward perivascular drainage channels. The prolonged survival was strain-dependent, affecting mice infected with extracellular, plaque-forming, but not membrane bound, prions. Live PET imaging revealed rapid clearance of recombinant prion protein monomers into the CSF of neuronal Ndst1- deficient mice, neuronal, further suggesting that HS sulfate groups hinder transit of extracellular prion protein monomers. Our results directly show how a host cofactor slows the spread of prion protein through the extracellular space and identify an enzyme to target to facilitate aggregate clearance.

Current and Future PET Imaging for Multiple Myeloma

Positron emission tomography (PET) is an imaging modality used for the noninvasive assessment of tumor staging and response to therapy. PET with 18F labeled fluorodeoxyglucose (18F-FDG PET) is widely used to assess the active and inactive lesions in patients with multiple myeloma (MM). Despite the availability of 18F-FDG PET for the management of MM, PET imaging is less sensitive than next-generation flow cytometry and sequencing. Therefore, the novel PET radiotracers 64Cu-LLP2A, 68Ga-pentixafor, and 89Zr-daratumumab have been developed to target the cell surface antigens of MM cells. Furthermore, recent studies attempted to visualize the tumor-infiltrating lymphocytes using PET imaging in patients with cancer to investigate their prognostic effect; however, these studies have not yet been performed in MM patients. This review summarizes the recent studies on PET with 18F-FDG and novel radiotracers for the detection of MM and the resulting preclinical research using MM mouse models and clinical studies. Novel PET technologies may be useful for developing therapeutic strategies for MM in the future.

Preclinical Evaluation of a 64Cu-Based Theranostic Approach in a Murine Model of Multiple Myeloma

Although the concept of theranostics is neither new nor exclusive to nuclear medicine, it is a particularly promising approach for the future of nuclear oncology. This approach is based on the use of molecules targeting specific biomarkers in the tumour or its microenvironment, associated with optimal radionuclides which, depending on their emission properties, allow the combination of diagnosis by molecular imaging and targeted radionuclide therapy (TRT). Copper-64 has suitable decay properties (both β⁺ and β- decays) for PET imaging and potentially for TRT, making it both an imaging and therapy agent. We developed and evaluated a theranostic approach using a copper-64 radiolabelled anti-CD138 antibody, [⁶⁴Cu]Cu-TE1PA-9E7.4 in a MOPC315.BM mouse model of multiple myeloma. PET imaging using [⁶⁴Cu]Cu-TE1PA-9E7.4 allows for high-resolution PET images. Dosimetric estimation from ex vivo biodistribution data revealed acceptable delivered doses to healthy organs and tissues, and a very encouraging tumour absorbed dose for TRT applications. Therapeutic efficacy resulting in delayed tumour growth and increased survival without inducing major or irreversible toxicity has been observed with 2 doses of 35 MBq administered at a 2-week interval. Repeated injections of [⁶⁴Cu]Cu-TE1PA-9E7.4 are safe and can be effective for TRT application in this syngeneic preclinical model of MM.

An Overview of In Vitro Assays of 64Cu-, 68Ga-, 125I-, and 99mTc-Labelled Radiopharmaceuticals Using Radiometric Counters in the Era of Radiotheranostics

Radionuclides are unstable isotopes that mainly emit alpha (α), beta (β) or gamma (γ) radiation through radiation decay. Therefore, they are used in the biomedical field to label biomolecules or drugs for diagnostic imaging applications, such as positron emission tomography (PET) and/or single-photon emission computed tomography (SPECT). A growing field of research is the development of new radiopharmaceuticals for use in cancer treatments. Preclinical studies are the gold standard for translational research. Specifically, in vitro radiopharmaceutical studies are based on the use of radiopharmaceuticals directly on cells. To date, radiometric β- and γ-counters are the only tools able to assess a preclinical in vitro assay with the aim of estimating uptake, retention, and release parameters, including time- and dose-dependent cytotoxicity and kinetic parameters. This review has been designed for researchers, such as biologists and biotechnologists, who would like to approach the radiobiology field and conduct in vitro assays for cellular radioactivity evaluations using radiometric counters. To demonstrate the importance of in vitro radiopharmaceutical assays using radiometric counters with a view to radiogenomics, many studies based on ⁶⁴Cu-, ⁶⁸Ga-, ¹²⁵I-, and ^99mTc-labeled radiopharmaceuticals have been revised and summarized in this manuscript.

Sinomenine ameliorates adjuvant-induced arthritis by inhibiting the autophagy/NETosis/inflammation axis

Studies have found that neutrophil extracellular traps (NETs) which are the specific dying form of neutrophil upon activation have fundamental role in the rheumatoid arthritis onset and progression. The purpose of this study was to explore the therapeutic effect of Sinomenine on adjuvant-induced arthritis in mice, and the neutrophil activities regulated by Sinomenine. The rheumatoid arthritis model was established by local injection of adjuvant and the Sinomenine treatment was administered orally for 30 days, during which, arthritic scores were evaluated and the joint diameter was measured to determine disease progression. The joint tissues and serum were acquired for further tests after sacrifice. Cytometric beads assay was performed to measure the concentration of cytokines. For paraffin-embedded ankle tissues, hematoxylin and erosin staining and Safranin O-fast staining were adopted to monitor the tissue changes of joint. In order to analyze the inflammation, NETs and autophagy of neutrophils in vivo, immunohistochemistry assays were applied to detect the protein expression levels in the local joints. To describe the effect brought by Sinomenine on inflammation, autophagy and NETs in vitro, the western blotting and the immunofluorescence assays were performed. The joint symptoms of the adjuvant induced arthritis were alleviated by the Sinomenine treatment significantly in terms of the ankle diameter and scores. The improvement of local histopathology changes and decrease of inflammatory cytokines in the serum also confirmed the efficacy. The expression levels of interleukin-6, P65 and p-P65 in the ankle areas of mice were remarkably reduced by Sinomenine. Compared with the model group, the decreased expression levels of lymphocyte antigen 6 complex and myeloperoxidase in the Sinomenine treating group showed the inhibitory effect of Sinomenine on the neutrophil migration. The expression of protein arginine deiminase type 4 (PAD4), ctrullinated histone H3 (CitH3) and microtubule-associated protein 1 light chain 3B (LC3B) had the similar tendency. Upon activation of lipopolysaccharide (LPS) in vitro, Sinomenine suppressed the phosphorylation of P65, extracellular signal-regulated kinase (ERK) and P38 of neutrophil. Meanwhile, Sinomenine inhibited NETs formation induced by phorbol 12-myristate 13-acetate (PMA), which were demonstrated by the decreased expression of neutrophil elastase (NE), PAD4 and CitH3. Sinomenine also inhibited PMA-induced autophagy in vitro based on the changes of Beclin-1 and LC3B. Sinomenine has good efficacy in treating adjuvant induced arthritis via regulating neutrophil activities. Apart from inhibiting activation of nuclear factor kappa-B (NF-κB) and mitogen-activated protein kinase (MAPK) pathways, the mechanism includes suppression of NETs formation via autophagy inhibition.

Toward Optimized 89Zr-Immuno-PET: Side-by-Side Comparison of [89Zr]Zr-DFO-, [89Zr]Zr-3,4,3-(LI-1,2-HOPO)- and [89Zr]Zr-DFO*-Cetuximab for Tumor Imaging: Which Chelator Is the Most Suitable?

89Zr represents a highly favorable positron emitter for application in immuno-PET (Positron Emission Tomography) imaging. Clinically, the 89Zr4+ ion is introduced into antibodies by complexation with desferrioxamine B. However, producing complexes of limited kinetic inertness. Therefore, several new chelators for 89Zr introduction have been developed over the last years. Of these, the direct comparison of the most relevant ones for clinical translation, DFO* and 3,4,3-(LI-1,2-HOPO), is still missing. Thus, we directly compared DFO with DFO* and 3,4,3-(LI-1,2-HOPO) immunoconjugates to identify the most suitable agent stable 89Zr-complexation. The chelators were introduced into cetuximab, and an optical analysis method was developed, enabling the efficient quantification of derivatization sites per protein. The cetuximab conjugates were efficiently obtained and radiolabeled with 89Zr at 37 °C within 30 min, giving the [89Zr]Zr-cetuximab derivatives in high radiochemical yields and purities of >99% as well as specific activities of 50 MBq/mg. The immunoreactive fraction of all 89Zr-labeled cetuximab derivatives was determined to be in the range of 86.5−88.1%. In vivo PET imaging and ex vivo biodistribution studies in tumor-bearing animals revealed a comparable and significantly higher kinetic inertness for both [89Zr]Zr-3,4,3-(LI-1,2-HOPO)-cetuximab and [89Zr]Zr-DFO*-cetuximab, compared to [89Zr]Zr-DFO-cetuximab. Of these, [89Zr]Zr-DFO*-cetuximab showed a considerably more favorable pharmacokinetic profile with significantly lower liver and spleen retention than [89Zr]Zr-3,4,3-(LI-1,2-HOPO)-cetuximab. Since [89Zr]Zr-DFO* demonstrates a very high kinetic inertness, paired with a highly favorable pharmacokinetic profile of the resulting antibody conjugate, DFO* currently represents the most suitable chelator candidate for stable 89Zr-radiolabeling of antibodies and clinical translation.

Recent developments on the application of molecular probes in multiple myeloma: Beyond [18F]FDG

Multiple myeloma (MM) is a neoplastic plasma cell proliferative disorder characterized by various osteolytic bone destruction as a radiological morphological marker. Functional imaging, particularly nuclear medicine imaging, is a promising method to visualize disease processes before the appearance of structural changes by targeting specific biomarkers related to metabolism ability, tumor microenvironment as well as neoplastic receptors. In addition, by targeting particular antigens with therapeutic antibodies, immuno-PET imaging can support the development of personalized theranostics. At present, various imaging agents have been prepared and evaluated in MM at preclinical and clinical levels. A summary overview of molecular functional imaging in MM is provided, and commonly used radiotracers are characterized.

Anti-BCMA Immuno-NanoPET Radiotracers for Improved Detection of Multiple Myeloma

Current clinical imaging modalities for the sensitive and specific detection of multiple myeloma (MM) rely on nonspecific imaging contrast agents based on gadolinium chelates for magnetic resonance imaging (MRI) or for 18 F-FDG-directed and combined positron emission tomography (PET) and computed tomography (CT) scans. These tracers are not, however, able to detect minute plasma cell populations in the tumor niche, leading to false negative results. Here, a novel PET-based anti-BCMA nanoplatform labeled with 64 Cu is developed to improve the monitoring of these cells in both the spine and femur and to compare its sensitivity and specificity to more conventional immunoPET (64 Cu labeled anti-BCMA antibody) and passively targeted PET radiotracers (64 CuCl2 and 18 F-FDG). This proof-of-concept preclinical study confirmed that by conjugating up to four times more radioisotopes per antibody with the immuno-nanoPET platform, an improvement in the sensitivity and in the specificity of PET to detect tumor cells in an orthotopic model of MM is observed when compared to the traditional immunoPET approach. It is anticipated that when combined with tumor biopsy, this immuno-nanoPET platform may improve the management of patients with MM.

ImmunoPET imaging of hematological malignancies: From preclinical promise to clinical reality

Immuno-positron emission tomography (immunoPET) imaging is a paradigm-shifting imaging technique for whole-body and all-lesion tumor detection, based on the combined specificity of tumor-targeting vectors [e.g., monoclonal antibodies (mAbs), nanobodies, and bispecific antibodies] and the sensitivity of PET imaging. By noninvasively, comprehensively, and serially revealing heterogeneous tumor antigen expression, immunoPET imaging is gradually improving the theranostic prospects for hematological malignancies. In this review, we summarize the available literature regarding immunoPET in imaging hematological malignancies. We also highlight the pros and cons of current conjugation strategies, and modular chemistry that can be leveraged to develop novel immunoPET probes for hematological malignancies. Lastly, we discuss the use of immunoPET imaging in guiding antibody drug development.

Positron Emission Tomographic Imaging of Tumor Cell Death Using Zirconium-89-Labeled APOMAB® Following Cisplatin Chemotherapy in Lung and Ovarian Cancer Xenograft Models

PURPOSE

Early detection of tumor treatment responses represents an unmet clinical need with no approved noninvasive methods. DAB4, or its chimeric derivative, chDAB4 (APOMAB®) is an antibody that targets the Lupus associated antigen (La/SSB). La/SSB is over-expressed in malignancy and selectively targeted by chDAB4 in cancer cells dying from DNA-damaging treatment. Therefore, chDAB4 is a unique diagnostic tool that detects dead cancer cells and thus could distinguish between treatment responsive and nonresponsive patients.

PROCEDURES

In clinically relevant tumor models, mice bearing subcutaneous xenografts of human ovarian or lung cancer cell lines or intraperitoneal ovarian cancer xenografts were untreated or given chemotherapy followed 24h later by chDAB4 radiolabeled with [⁸⁹Zr]Zr^IV. Tumor responses were monitored using bioluminescence imaging and caliper measurements. [⁸⁹Zr]Zr-chDAB4 uptake in tumor and normal tissues was measured using an Albira SI Positron-Emission Tomography (PET) imager and its biodistribution was measured using a Hidex gamma-counter.

RESULTS

Tumor uptake of [⁸⁹Zr]Zr-chDAB4 was detected in untreated mice, and uptake significantly increased in both human lung and ovarian tumors after chemotherapy, but not in normal tissues.

CONCLUSION

Given that tumors, rather than normal tissues, were targeted after chemotherapy, these results support the clinical development of chDAB4 as a radiodiagnostic imaging agent and as a potential predictive marker of treatment response.

Theranostic Agents in Musculoskeletal Disorders

Theranostic-based strategies, combining therapeutic and diagnostic properties of a single agent, have gained enormous attention in the past few years. Today, various multifunctional theranostic modalities have been examined, using different bioactive targeting, for the detection, quantifying, and monitoring of therapy response in different pathologies. Herein we review the newly emerging approaches in theranostic nanomedicine for the detection and therapy for musculoskeletal disorders to provide valuable insights for developing more efficient agents for clinical use. Some potential preclinical applications of radionuclide nanotheranostic agents are described in rheumatoid arthritis, osteoarthrosis, multiple myeloma, and neoplastic diseases.

State of the Art in Radiolabeling of Antibodies with Common and Uncommon Radiometals for Preclinical and Clinical Immuno-PET

Inert and stable radiolabeling of monoclonal antibodies (mAb), antibody fragments, or antibody mimetics with radiometals is a prerequisite for immuno-PET. While radiolabeling is preferably fast, mild, efficient, and reproducible, especially when applied for human use in a current Good Manufacturing Practice compliant way, it is crucial that the obtained radioimmunoconjugate is stable and shows preserved immunoreactivity and in vivo behavior. Radiometals and chelators have extensively been evaluated to come to the most ideal radiometal–chelator pair for each type of antibody derivative. Although PET imaging of antibodies is a relatively recent tool, applications with ⁸⁹Zr, ⁶⁴Cu, and ⁶⁸Ga have greatly increased in recent years, especially in the clinical setting, while other less common radionuclides such as ⁵²Mn, ⁸⁶Y, ⁶⁶Ga, and ⁴⁴Sc, but also ¹⁸F as in [¹⁸F]AlF are emerging promising candidates for the radiolabeling of antibodies. This review presents a state of the art overview of the practical aspects of radiolabeling of antibodies, ranging from fast kinetic affibodies and nanobodies to slow kinetic intact mAbs. Herein, we focus on the most common approach which consists of first modification of the antibody with a chelator, and after eventual storage of the premodified molecule, radiolabeling as a second step. Other approaches are possible but have been excluded from this review. The review includes recent and representative examples from the literature highlighting which radiometal–chelator–antibody combinations are the most successful for in vivo application.

In Vivo Albumin-Binding of a C-Functionalized Cyclam Platform for 64 Cu-PET/CT Imaging in Breast Cancer Model

An improved glucose-chelator-albumin bioconjugate (GluCAB) derivative, GluCAB-2^Mal , has been synthesized and studied for in vivo ⁶⁴ Cu-PET/CT imaging in breast cancer mice models together with its first-generation analogue GluCAB-1^Mal . The radioligand works on the principle of tumor targeting through the enhanced permeability and retention (EPR) effect with a supportive role played by glucose metabolism. [⁶⁴ Cu]Cu-GluCAB-2^Mal (99 % RCP) exhibited high serum stability with immediate binding to serum proteins. In vivo experiments for comparison between tumor targeting of [⁶⁴ Cu]Cu-GluCAB-2^Mal and previous-generation [⁶⁴ Cu]Cu-GluCAB-1^Mal encompassed microPET/CT imaging and biodistribution analysis in an allograft E0771 breast cancer mouse model. Tumor uptake of [⁶⁴ Cu]Cu-GluCAB-2^Mal was clearly evident with twice as much accumulation as compared to its predecessor and a tumor/muscle ratio of up to 5 after 24 h. Further comparison indicated a decrease in liver accumulation for [⁶⁴ Cu]Cu-Glu-CAB-2^Mal .

Investigation on the reactivity of nucleophilic radiohalogens with arylboronic acids in water: access to an efficient single-step method for the radioiodination and astatination of antibodies

Easy access to radioiodinated and ²¹¹At-labelled bio(macro)molecules is essential to develop new strategies in nuclear imaging and targeted radionuclide therapy of cancers. Yet, the labelling of complex molecules with heavy radiohalogens is often poorly effective due to the multiple steps and intermediate purifications needed. Herein, we investigate the potential of arylboron chemistry as an alternative approach for the late stage labelling of antibodies. The reactivity of a model precursor, 4-chlorobenzeneboronic acid (1) with nucleophilic iodine-125 and astatine-211 was at first investigated in aqueous conditions. In the presence of a copper(ii) catalyst and 1,10-phenanthroline, quantitative radiochemical yields (RCYs) were achieved within 30 minutes at room temperature. The optimum conditions were then applied to a CD138 targeting monoclonal antibody (mAb) that has previously been validated for imaging and therapy in a preclinical model of multiple myeloma. RCYs remained high (>80% for ¹²⁵I-labelling and >95% for ²¹¹At-labelling), and the whole procedure led to increased specific activities within less time in comparison with previously reported methods. Biodistribution study in mice indicated that targeting properties of the radiolabelled mAb were well preserved, leading to a high tumour uptake in a CD138 expressing tumour model. The possibility of divergent synthesis from a common modified carrier protein demonstrated herein opens facilitated perspectives in radiotheranostic applications with the radioiodine/²¹¹At pairs. Overall, the possibility to develop radiolabelling kits offered by this procedure should facilitate its translation to clinical applications.

The high reactivity of astatine and iodine in water with arylboronic acids provides access to an efficient single-step antibody radiolabelling.

Targeted-Alpha-Therapy Combining Astatine-211 and anti-CD138 Antibody in A Preclinical Syngeneic Mouse Model of Multiple Myeloma Minimal Residual Disease

Simple Summary

Multiple myeloma is a cancer that remains incurable. Among the many therapies under evaluation, antibodies can be used as vehicles to target and deliver toxic radiation to the tumour cells. Our objective was therefore to investigate the potential of targeted alpha therapy, combining an anti-CD138 mAb with astatine-211, to destroy the residual cells responsible for relapse. We have shown in a mouse model that mimics human disease, that destroying multiple myeloma cells is feasible with low toxicity by injecting an anti-CD138 mAb coupled with astatine-211. This approach could eradicate residual cells after initial treatment and thus prevent recurrence.

Abstract

Despite therapeutic progress in recent years with the introduction of targeted therapies (daratumumab, elotuzumab), multiple myeloma remains an incurable cancer. The question is therefore to investigate the potential of targeted alpha therapy, combining an anti-CD138 antibody with astatine-211, to destroy the residual cells that cause relapses. A preclinical syngeneic mouse model, consisting of IV injection of 1 million of 5T33 cells in a KaLwRij C57/BL6 mouse, was treated 10 days later with an anti-mCD138 antibody, called 9E7.4, radiolabeled with astatine-211. Four activities of the ²¹¹At-9E7.4 radioimmunoconjugate were tested in two independent experiments: 370 kBq (n = 16), 555 kBq (n = 10), 740 kBq (n = 17) and 1100 kBq (n = 6). An isotype control was also tested at 555 kBq (n = 10). Biodistribution, survival rate, hematological parameters, enzymatic hepatic toxicity, histological examination and organ dosimetry were considered. The survival median of untreated mice was 45 days after engraftment. While the activity of 1100 kBq was highly toxic, the activity of 740 kBq offered the best efficacy with 65% of overall survival 150 days after the treatment with no evident sign of toxicity. This work demonstrates the pertinence of treating minimal residual disease of multiple myeloma with an anti-CD138 antibody coupled to astatine-211.

ImmunoPET in Multiple Myeloma-What? So What? Now What?

Despite constant progress over the past three decades, multiple myeloma (MM) is still an incurable disease, and the identification of new biomarkers to better select patients and adapt therapy is more relevant than ever. Recently, the introduction of therapeutic monoclonal antibodies (mAbs) (including direct-targeting mAbs and immune checkpoint inhibitors) appears to have changed the paradigm of MM management, emphasizing the opportunity to cure MM patients through an immunotherapeutic approach. In this context, immuno-positron emission tomography (immunoPET), combining the high sensitivity and resolution of a PET camera with the specificity of a radiolabelled mAb, holds the capability to cement this new treatment paradigm for MM patients. It has the potential to non-invasively monitor the distribution of therapeutic antibodies or directly monitor biomarkers on MM cells, and to allow direct observation of potential changes over time and in response to various therapeutic interventions. Tumor response could, in the future, be anticipated more effectively to provide individualized treatment plans tailored to patients according to their unique imaging signatures. This work explores the important role played by immunotherapeutics in the management of MM, and focuses on some of the challenges for this drug class and the significant interest of companion imaging agents such as immunoPET.

ImmunoPET: Concept, Design, and Applications

Immuno-positron emission tomography (immunoPET) is a paradigm-shifting molecular imaging modality combining the superior targeting specificity of monoclonal antibody (mAb) and the inherent sensitivity of PET technique. A variety of radionuclides and mAbs have been exploited to develop immunoPET probes, which has been driven by the development and optimization of radiochemistry and conjugation strategies. In addition, tumor-targeting vectors with a short circulation time (e.g., Nanobody) or with an enhanced binding affinity (e.g., bispecific antibody) are being used to design novel immunoPET probes. Accordingly, several immunoPET probes, such as 89Zr-Df-pertuzumab and 89Zr-atezolizumab, have been successfully translated for clinical use. By noninvasively and dynamically revealing the expression of heterogeneous tumor antigens, immunoPET imaging is gradually changing the theranostic landscape of several types of malignancies. ImmunoPET is the method of choice for imaging specific tumor markers, immune cells, immune checkpoints, and inflammatory processes. Furthermore, the integration of immunoPET imaging in antibody drug development is of substantial significance because it provides pivotal information regarding antibody targeting abilities and distribution profiles. Herein, we present the latest immunoPET imaging strategies and their preclinical and clinical applications. We also emphasize current conjugation strategies that can be leveraged to develop next-generation immunoPET probes. Lastly, we discuss practical considerations to tune the development and translation of immunoPET imaging strategies.

Proteomics-inspired precision medicine for treating and understanding multiple myeloma

Introduction

Remarkable progress in molecular characterization methods has led to significant improvements in how we manage multiple myeloma (MM). The introduction of novel therapies has led to significant improvements in overall survival over the past 10 years. However, MM remains incurable and treatment choice is largely based on outdated risk-adaptive strategies that do not factor in improved treatment outcomes in the context of modern therapies.

Areas covered

This review discusses current risk-adaptive strategies in MM and the clinical application of proteomics in the monitoring of treatment response, disease progression, and minimal residual disease (MRD). We also discuss promising biomarkers of disease progression, treatment response, and chemoresistance. Finally, we will discuss an immunomics-based approach to monoclonal antibody (mAb), vaccine, and CAR-T cell development.

Expert opinion

It is an exciting era in oncology with basic scientific knowledge translating in novel therapeutic approaches to improve patient outcomes. With the advent of effective immunotherapies and targeted therapies, it has become crucial to identify biomarkers to aid in the stratification of patients based on anticipated sensitivity to chemotherapy. As a paradigm of diseases highly dependent on protein homeostasis, multiple myeloma provides the perfect opportunity to investigate the use of proteomics to aid in precision medicine.