CD38-targeted Immuno-PET of Multiple Myeloma: From Xenograft Models to First-in-Human Imaging

Trends in cancer imaging

Molecular imaging of cancer is a collaborative endeavor, uniting scientists and physicians from diverse fields. Such collaboration is actively developing and translating cutting-edge molecular imaging approaches to enhance the diagnostic landscape of human malignancies. The advent of positron emission tomography (PET) and PET imaging tracers has realized non-invasive target annotation and tumor characterization at the molecular level. In surgical procedures, novel imaging techniques, such as fluorescence or Cherenkov luminescence, help identify tumors and enhance surgical precision. Simultaneously, progress in imaging equipment, innovative algorithms, and artificial intelligence has opened avenues for next-generation cancer screening and imaging, augmenting the efficiency and accuracy of cancer diagnosis. In this review, we provide a panorama of molecular cancer imaging and ongoing developments in the field.

Expanding horizons in cancer therapy by immunoconjugates targeting tumor microenvironments

Immunoconjugates are promising molecules combining antibodies with different agents, such as toxins, drugs, radionuclides, or cytokines that primarily aim to target tumor cells. However, tumor microenvironment (TME), which comprises a complex network of various cells and molecular cues guiding tumor growth and progression, remains a major challenge for effective cancer therapy. Our review underscores the pivotal role of TME in cancer therapy with immunoconjugates, examining the intricate interactions with TME and recent advancements in TME-targeted immunoconjugates. We explore strategies for targeting TME components, utilizing diverse antibodies such as neutralizing, immunomodulatory, immune checkpoint inhibitors, immunostimulatory, and bispecific antibodies. Additionally, we discuss different immunoconjugates, elucidating their mechanisms of action, advantages, limitations, and applications in cancer immunotherapy. Furthermore, we highlight emerging technologies enhancing the safety and efficacy of immunoconjugates, such as antibody engineering, combination therapies, and nanotechnology. Finally, we summarize current advancements, perspectives, and future developments of TME-targeted immunoconjugates.

EANM guidelines on the use of [18F]FDG PET/CT in diagnosis, staging, prognostication, therapy assessment, and restaging of plasma cell disorders

We provide updated guidance and standards for the indication, acquisition, and interpretation of [18F]FDG PET/CT for plasma cell disorders. Procedures and characteristics are reported and different scenarios for the clinical use of [18F]FDG PET/CT are discussed. This document provides clinicians and technicians with the best available evidence to support the implementation of [18F]FDG PET/CT imaging in routine practice and future research.

Development of New CD38 Targeted Peptides for Cancer Imaging

PURPOSE

Multiple myeloma (MM) affects over 35,000 patients each year in the US. There remains a need for versatile Positron Emission Tomography (PET) tracers for the detection, accurate staging, and monitoring of treatment response of MM that have optimal specificity and translational attributes. CD38 is uniformly overexpressed in MM and thus represents an ideal target to develop CD38-targeted small molecule PET radiopharmaceuticals to address these challenges.

PROCEDURES

Using phage display peptide libraries and pioneering algorithms, we identified novel CD38 specific peptides. Imaging bioconjugates were synthesized using solid phase peptide chemistry, and systematically analyzed in vitro and in vivo in relevant MM systems.

RESULTS

The CD38-targeted bioconjugates were radiolabeled with copper-64 (64Cu) with100% radiochemical purity and an average specific activity of 3.3 - 6.6 MBq/nmol. The analog NODAGA-PEG4-SL022-GGS (SL022: Thr-His-Tyr-Pro-Ile-Val-Ile) had a Kd of 7.55 ± 0.291 nM and was chosen as the lead candidate. 64Cu-NODAGA-PEG4-SL022-GGS demonstrated high binding affinity to CD38 expressing human myeloma MM.1S-CBR-GFP-WT cells, which was blocked by the non-radiolabeled version of the peptide analog and anti-CD38 clinical antibodies, daratumumab and isatuximab, by 58%, 73%, and 78%, respectively. The CD38 positive MM.1S-CBR-GFP-WT cells had > 68% enhanced cellular binding when compared to MM.1S-CBR-GFP-KO cells devoid of CD38. Furthermore, our new CD38-targeted radiopharmaceutical allowed visualization of tumors located in marrow rich bones, remaining there for up to 4 h. Clearance from non-target organs occurred within 60 min. Quantitative PET data from a murine disseminated tumor model showed significantly higher accumulation in the bones of tumor-bearing animals compared to tumor-naïve animals (SUVmax 2.06 ± 0.4 versus 1.24 ± 0.4, P = 0.02). Independently, tumor uptake of the target compound was significantly higher (P = 0.003) compared to the scrambled peptide, 64Cu-NODAGA-PEG4-SL041-GGS (SL041: Thr-Tyr-His-Ile-Pro-Ile-Val). The subcutaneous MM model demonstrated significantly higher accumulation in tumors compared to muscle at 1 and 4 h after tracer administration (SUVmax 0.8 ± 0.2 and 0.14 ± 0.04, P = 0.04 at 1 h; SUVmax 0.89 ± 0.01 and 0.09 ± 0.01, P = 0.0002 at 4 h).

CONCLUSIONS

The novel CD38-targeted, radiolabeled bioconjugates were specific and allowed visualization of MM, providing a starting point for the clinical translation of such tracers for the detection of MM.

Role of minimal residual disease assessment in multiple myeloma

Multiple myeloma (MM) is a hematologic malignancy characterized by clonal proliferation of plasma cells. MM is a heterogeneous disease, featured by various molecular subtypes with different outcomes. With the advent of very efficient therapies including monoclonal antibodies, bispecific T-cell engagers and chimeric antigen receptor T cells (CAR T cells), most MM patients now have a prolonged survival. However, the disease remains incurable, and a subgroup of high-risk patients continue to have early relapse and short survival. Novel and highly sensitive methods have been developed allowing the detection of minimal residual disease (MRD) during or after treatment. Achievement of MRD negativity is a strong and independent prognostic factor in both prospective randomized clinical trials and in the real-world setting. While MRD assessment is now a validated endpoint in clinical trials, its incorporation in clinical practice is not yet established and its potential impact on guiding therapy remains under in-depth evaluation. Here we discuss the different methods available for MRD assessment and the role of MRD evaluation in MM management.

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.

CD38-Specific Gallium-68 Labeled Peptide Radiotracer Enables Pharmacodynamic Monitoring in Multiple Myeloma with PET

The limited availability of molecularly targeted low-molecular-weight imaging agents for monitoring multiple myeloma (MM)-targeted therapies has been a significant challenge in the field. In response, a first-in-class peptide-based radiotracer, [68Ga]Ga-AJ206, is developed that can be seamlessly integrated into the standard clinical workflow and is specifically designed to noninvasively quantify CD38 levels and pharmacodynamics by positron emission tomography (PET). A bicyclic peptide, AJ206, is synthesized and exhibits high affinity to CD38 (KD: 19.1 ± 0.99 × 10-9 m) by surface plasmon resonance. Further, [68Ga]Ga-AJ206-PET shows high contrast within 60 min and suitable absorbed dose estimates for clinical use. Additionally, [68Ga]Ga-AJ206 detects CD38 expression in cell line-derived xenografts, patient-derived xenografts (PDXs), and disseminated disease models in a manner consistent with flow cytometry and immunohistochemistry findings. Moreover, [68Ga]Ga-AJ206-PET successfully quantifies CD38 pharmacodynamics in PDXs, revealing increased CD38 expression in the tumor following all-trans retinoic acid (ATRA) therapy. In conclusion, [68Ga]Ga-AJ206 exhibits the salient features required for clinical translation, providing CD38-specific high-contrast images in multiple models of MM. [68Ga]Ga-AJ206-PET could be useful for quantifying total CD38 levels and pharmacodynamics during therapy to evaluate approved and new therapies in MM and other diseases with CD38 involvement.

CD46-Targeted Theranostics for PET and 225Ac-Radiopharmaceutical Therapy of Multiple Myeloma

PURPOSE

Multiple myeloma is a plasma cell malignancy with an unmet clinical need for improved imaging methods and therapeutics. Recently, we identified CD46 as an overexpressed therapeutic target in multiple myeloma and developed the antibody YS5, which targets a cancer-specific epitope on this protein. We further developed the CD46-targeting PET probe [89Zr]Zr-DFO-YS5 for imaging and [225Ac]Ac-DOTA-YS5 for radiopharmaceutical therapy of prostate cancer. These prior studies suggested the feasibility of the CD46 antigen as a theranostic target in multiple myeloma. Herein, we validate [89Zr]Zr-DFO-YS5 for immunoPET imaging and [225Ac]Ac-DOTA-YS5 for radiopharmaceutical therapy of multiple myeloma in murine models.

EXPERIMENTAL DESIGN

In vitro saturation binding was performed using the CD46 expressing MM.1S multiple myeloma cell line. ImmunoPET imaging using [89Zr]Zr-DFO-YS5 was performed in immunodeficient (NSG) mice bearing subcutaneous and systemic multiple myeloma xenografts. For radioligand therapy, [225Ac]Ac-DOTA-YS5 was prepared, and both dose escalation and fractionated dose treatment studies were performed in mice bearing MM1.S-Luc systemic xenografts. Tumor burden was analyzed using BLI, and body weight and overall survival were recorded to assess antitumor effect and toxicity.

RESULTS

[89Zr]Zr-DFO-YS5 demonstrated high affinity for CD46 expressing MM.1S multiple myeloma cells (Kd = 16.3 nmol/L). In vitro assays in multiple myeloma cell lines demonstrated high binding, and bioinformatics analysis of human multiple myeloma samples revealed high CD46 expression. [89Zr]Zr-DFO-YS5 PET/CT specifically detected multiple myeloma lesions in a variety of models, with low uptake in controls, including CD46 knockout (KO) mice or multiple myeloma mice using a nontargeted antibody. In the MM.1S systemic model, localization of uptake on PET imaging correlated well with the luciferase expression from tumor cells. A treatment study using [225Ac]Ac-DOTA-YS5 in the MM.1S systemic model demonstrated a clear tumor volume and survival benefit in the treated groups.

CONCLUSIONS

Our study showed that the CD46-targeted probe [89Zr]Zr-DFO-YS5 can successfully image CD46-expressing multiple myeloma xenografts in murine models, and [225Ac]Ac-DOTA-YS5 can effectively inhibit the growth of multiple myeloma. These results demonstrate that CD46 is a promising theranostic target for multiple myeloma, with the potential for clinical translation.

The role of conventional and novel PET radiotracers in assessment of myeloma bone disease

Over 80 % of patients with multiple myeloma (MM) experience osteolytic bone lesions, primarily due to an imbalanced interaction between osteoclasts and osteoblasts. This imbalance can lead to several adverse outcomes such as pain, fractures, limited mobility, and neurological impairments. Myeloma bone disease (MBD) raises the expense of management in addition to being a major source of disability and morbidity in myeloma patients. Whole-body x-ray radiography was the gold standard imaging modality for detecting lytic lesions. Osteolytic lesions are difficult to identify at an earlier stage on X-ray since the lesions do not manifest themselves on conventional radiographs until at least 30 % to 50 % of the bone mass has been destroyed. Hence, early diagnosis of osteolytic lesions necessitates the utilization of more complex and advanced imaging modalities, such as PET. One of the PET radiotracers that has been frequently investigated in MM is 18F-FDG, which has demonstrated a high level of sensitivity and specificity in detecting myeloma lesions. However, 18F-FDG PET/CT has several restrictions, and therefore the novel PET tracers that can overcome the limitations of 18F-FDG PET/CT should be further examined in assessment of MBD. The objective of this review article is to thoroughly examine the significance of both conventional and novel PET radiotracers in the assessment of MBD. The intention is to present the information in a manner that would be easily understood by healthcare professionals from diverse backgrounds, while minimizing the use of complex nuclear medicine terminology.

Microarray-Based CD38 Peptide Probe Screening for Multiple Myeloma Imaging

Assessing CD38 expression in vivo has become a significant element in multiple myeloma (MM) therapy, as it can be used to detect lesions and forecast the effectiveness of treatment. Accurate diagnosis requires a multifunctional, high-throughput probe screening platform to develop molecular probes for tumor-targeted multimodal imaging and treatment. Here, we investigated a microarray chip-based strategy for high-throughput screening of peptide probes for CD38. We obtained two new target peptides, CA-1 and CA-2, from a 105 peptide library with a dissociation constant (KD) of 10-7 M. The specificity and affinity of the target peptides were confirmed at the molecular and cellular levels. Peptide probes were labeled with indocyanine green (ICG) dye and 68Ga-DOTA, which were injected into a CD38-positive Ramos tumor-bearing mouse via its tail vein, and small animal fluorescence and positron emission tomography (PET) imaging showed that the peptide probes could show specific enrichment in the tumor tissue. Our study shows that a microchip-based screening of peptide probes can be used as a promising imaging tool for MM diagnosis.

A Gallium-68-Labeled Peptide Radiotracer For CD38-Targeted Imaging In Multiple Myeloma With PET

PURPOSE

The limited availability of molecularly targeted low-molecular-weight imaging agents for monitoring multiple myeloma (MM)-targeted therapies has been a significant challenge in the field. In response, we developed [68Ga]Ga-AJ206, a peptide-based radiotracer that can be seamlessly integrated into the standard clinical workflow and is specifically designed to non-invasively quantify CD38 levels and pharmacodynamics by positron emission tomography (PET).

EXPERIMENTAL DESIGN

We synthesized a high-affinity binder for quantification of CD38 levels. Affinity was tested using surface plasmon resonance, and In vitro specificity was evaluated using a gallium-68-labeled analog. Distribution, pharmacokinetics, and CD38 specificity of the radiotracer were assessed in MM cell lines and in primary patient-derived myeloma cells and xenografts (PDX) with cross-validation by flow cytometry and immunohistochemistry. Furthermore, we investigated the radiotracer's potential to quantify CD38 pharmacodynamics induced by all-trans retinoic acid therapy (ATRA).

RESULTS

[68Ga]Ga-AJ206 exhibited high CD38 binding specificity (KD: 19.1±0.99 nM) and CD38-dependent In vitro binding. [68Ga]Ga-AJ206-PET showed high contrast within 60 minutes and suitable absorbed dose estimates for clinical use. Additionally, [68Ga]Ga-AJ206 detected CD38 expression in xenografts, PDXs and disseminated disease models in a manner consistent with flow cytometry and immunohistochemistry findings. Moreover, [68Ga]Ga-AJ206-PET successfully quantified CD38 pharmacodynamics in PDXs, revealing increased CD38 expression in the tumor following ATRA therapy.

CONCLUSIONS

[68Ga]Ga-AJ206 exhibited the salient features required for clinical translation, providing CD38-specific high contrast images in multiple models of MM. [68Ga]Ga-AJ206-PET could be useful for quantifying total CD38 levels and pharmacodynamics during therapy to evaluate approved and new therapies in MM and other diseases with CD38 involvement.

Current and Future Use of Long Axial Field-of-View Positron Emission Tomography/Computed Tomography Scanners in Clinical Oncology

The latest technical development in the field of positron emission tomography/computed tomography (PET/CT) imaging has been the extension of the PET axial field-of-view. As a result of the increased number of detectors, the long axial field-of-view (LAFOV) PET systems are not only characterized by a larger anatomical coverage but also by a substantially improved sensitivity, compared with conventional short axial field-of-view PET systems. In clinical practice, this innovation has led to the following optimization: (1) improved overall image quality, (2) decreased duration of PET examinations, (3) decreased amount of radioactivity administered to the patient, or (4) a combination of any of the above. In this review, novel applications of LAFOV PET in oncology are highlighted and future directions are discussed.

New Developments in Myeloma Treatment and Response Assessment

Recent innovative strategies have dramatically redefined the therapeutic landscape for treating multiple myeloma patients. In particular, the development and application of immunotherapy and high-dose therapy have demonstrated high response rates and have prolonged remission duration. Over the past decade, new morphologic or hybrid imaging techniques have gradually replaced conventional skeletal surveys. PET/CT using 18F-FDG is a powerful imaging tool for the workup at diagnosis and for therapeutic evaluation allowing medullary and extramedullary assessment. The independent negative prognostic value for progression-free and overall survival derived from baseline PET-derived parameters such as the presence of extramedullary disease or paramedullary disease, as well as the number of focal bone lesions and SUVmax, has been reported in several large prospective studies. During therapeutic evaluation, 18F-FDG PET/CT is considered the reference imaging technique because it can be performed much earlier than MRI, which lacks specificity. Persistence of significant abnormal 18F-FDG uptake after therapy is an independent negative prognostic factor, and 18F-FDG PET/CT and medullary flow cytometry are complementary tools for detecting minimal residual disease before maintenance therapy. The definition of a PET metabolic complete response has recently been standardized and the interpretation criteria harmonized. The development of advanced PET analysis and radiomics using machine learning, as well as hybrid imaging with PET/MRI, offers new perspectives for multiple myeloma imaging. Most recently, innovative radiopharmaceuticals such as C-X-C chemokine receptor type 4-targeted small molecules and anti-CD38 radiolabeled antibodies have shown promising results for tumor phenotype imaging and as potential theranostics.

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.

89Zr-DFO-Isatuximab for CD38-Targeted ImmunoPET Imaging of Multiple Myeloma and Lymphomas

Multiple myeloma (MM) is the second most prevalent hematological malignancy. It remains incurable despite the availability of novel therapeutic approaches, marking an urgent need for new agents for noninvasive targeted imaging of MM lesions. CD38 has proven to be an excellent biomarker due to its high expression in aberrant lymphoid and myeloid cells relative to normal cell populations. Using isatuximab (Sanofi), the latest FDA-approved CD38-targeting antibody, we have developed Zirconium-89(89Zr)-labeled isatuximab as a novel immunoPET tracer for the in vivo delineation of MM and evaluated the extension of its applicability to lymphomas. In vitro studies validated the high binding affinity and specificity of 89Zr-DFO-isatuximab for CD38. PET imaging demonstrated the high performance of 89Zr-DFO-isatuximab as a targeted imaging agent to delineate tumor burden in disseminated models of MM and Burkitt's lymphoma. Ex vivo biodistribution studies confirmed that high accumulations of the tracer in bone marrow and bone skeleton correspond to specific disease lesions as they are reduced to background in blocking and healthy controls. This work demonstrates the promise of 89Zr-DFO-isatuximab as an immunoPET tracer for CD38-targeted imaging of MM and certain lymphomas. More importantly, its potential as an alternative to 89Zr-DFO-daratumumab holds great clinical relevance.

Clinical Value of FDG-PET/CT in Multiple Myeloma: An Update

FDG-PET/CT is a standardized imaging technique that has reached a great importance in the management of patients affected by Multiple Myeloma. It is proved, in fact, that it allows a deep evaluation of therapy efficacy and provides several prognostic indexes both at staging and after therapy. For this reason, it is now recognised as a gold standard for therapy assessment. Beside this, in reacent years FDG-PET/CT contribution to the understanding of Multiple Myeloma has progressively grown. Papers have been published analyzing the prognostic value of active disease volume measurement and standardization issues, the meaning of FDG positive paramedullary and extrameduallary disease, the prognostic impact of FDG positive minimal residual disease, the relation between focal lesions and clonal eterogenity of this disease and the comparison with whole body DWI-MR in terms of detection and therapy assessment. These newer aspects not of clinical impact yet, of FDG-PET/CT in Multiple Myeloma will be presented and discussed in this review.

Multitracer PET/CT with [18F]Fluorodeoxiglucose and [18F]Fluorocholine in the Initial Staging of Multiple Myeloma Patients Applying the IMPeTus Criteria: A Pilot Study

Initial staging of patients diagnosed with multiple myeloma (MM) can lead to negative results using conventional diagnostic imaging workup, including [¹⁸F]Fluorodesoxiglucose ([¹⁸F]FDG) PET/CT. The aim of this prospective pilot study was to evaluate the diagnostic efficacy of [¹⁸F]Fluorocholine ([¹⁸F]FCH) PET/CT in the initial staging of MM patients who were candidates for autologous bone marrow transplant. Materials and Methods: The inclusion criteria of our study were: (a) patients diagnosed with MM; (b) candidates for autologous bone marrow transplant (AT); and (c) studied with [¹⁸F]FCH PET/CT and [¹⁸F]FDG PET/CT for initial staging less than 4 weeks apart. Imaging analysis included the presence of: bone marrow infiltration, focal bone lesions, and para-medullary or extra-medullary disease, according to the proposed IMPeTus criteria. The analysis was performed per lesion, per patient, and per location. Results: The study population included ten patients. Globally, [¹⁸F]FCH PET/CT showed bone marrow uptake in all the patients and visualised 16 more focal lesions than [¹⁸F]FDG PET/CT. One patient presented a plasmacytoma, detected by both tracers. Extra-medullary and para-medullary disease was identified with different degrees of uptake by both tracers. In summary, [¹⁸F]FCH PET seemed to be superior to [¹⁸F]FDG PET/CT in detecting focal bone lesions. SUVmax values were slightly higher in [¹⁸F]FCH PET/CT than in [¹⁸F]FDG PET/CT. Conclusions: Taking into account the small study population, according to our results, [¹⁸F]FCH PET/CT could be a useful tool for staging MM patients.

First-In-Human Pilot PET Immunoimaging Study of 64Cu-Anti-Carcinoembryonic Antigen Monoclonal Antibody (hT84.66-M5A) in Patients with Carcinoembryonic Antigen-Producing Cancers

Background: PET imaging using radiolabeled immunoconstructs shows promise in cancer detection and in assessing tumor response to therapies. The authors report the first-in-human pilot study evaluating M5A, a humanized anti-carcinoembryonic antigen (CEA) monoclonal antibody (mAb), radiolabeled with ⁶⁴Cu in patients with CEA-expressing malignancies. The purpose of this pilot study was to identify the preferred patient population for further evaluation of this agent in an expanded trial. Methods: Patients with CEA-expressing primary or metastatic cancer received ⁶⁴Cu-DOTA-hT84.66-M5A with imaging performed at 1 and 2 days postinfusion. ⁶⁴Cu-DOTA-hT84.66-M5A PET scan findings were correlated with CT, MRI, and/or FDG PET scans and with histopathologic findings from planned surgery or biopsy performed postscan. Results: Twenty patients received ⁶⁴Cu-DOTA-hT84.66-M5A. Twelve patients demonstrated positive images, which were confirmed in 10 patients as tumor by standard-of-care (SOC) imaging, biopsy, or surgical findings. Four of the 8 patients with negative imaging were confirmed as true negative, with the remaining 4 patients having disease demonstrated by SOC imaging or surgery. All 5 patients with locally advanced rectal cancer underwent planned biopsy or surgery after ⁶⁴Cu-DOTA-hT84.66-M5A imaging (4 patients imaged 6-8 weeks after completing neoadjuvant chemotherapy and radiation therapy) and demonstrated a high concordance between biopsy findings and ⁶⁴Cu-DOTA-hT84.66-M5A PET scan results. Three patients demonstrated positive uptake at the primary site later confirmed by biopsy and at surgery as residual disease. Two patients with negative scans each demonstrated complete pathologic response. In 5 patients with medullary thyroid cancer, ⁶⁴Cu-DOTA-hT84.66-M5A identified disease not seen on initial CT scans in 3 patients, later confirmed to be disease by subsequent surgery or MRI. Conclusions: ⁶⁴Cu-DOTA-hT84.66-M5A demonstrates promise in tumor detection, particularly in patients with locally advanced rectal cancer and medullary thyroid cancer. A successor trial in locally advanced rectal cancer has been initiated to further evaluate this agent's ability to define tumor extent before and assess disease response after neoadjuvant chemotherapy and radiotherapy. clinical trial.gov (NCT02293954).

First-in-Humans Evaluation of Safety and Dosimetry of 64Cu-LLP2A for PET Imaging

There remains an unmet need for molecularly targeted imaging agents for multiple myeloma (MM). The integrin very late antigen 4 (VLA4), is differentially expressed in malignant MM cells and in pathogenic inflammatory microenvironmental cells. [64Cu]Cu-CB-TE1A1P-LLP2A (64Cu-LLP2A) is a VLA4-targeted, high-affinity radiopharmaceutical with promising utility for managing patients diagnosed with MM. Here, we evaluated the safety and human radiation dosimetry of 64Cu-LLP2A for potential use in MM patients. Methods: A single-dose [natCu]Cu-LLP2A (Cu-LLP2A) tolerability and toxicity study was performed on CD-1 (Hsd:ICR) male and female mice. 64Cu-LLP2A was synthesized in accordance with good-manufacturing-practice-compliant procedures. Three MM patients and six healthy participants underwent 64Cu-LLP2A-PET/CT or PET/MRI at up to 3 time points to help determine tracer biodistribution, pharmacokinetics, and radiation dosimetry. Time-activity curves were plotted for each participant. Mean organ-absorbed doses and effective doses were calculated using the OLINDA software. Tracer bioactivity was evaluated via cell-binding assays, and metabolites from human blood samples were analyzed with analytic radio-high-performance liquid chromatography. When feasible, VLA4 expression was evaluated in the biopsy tissues using 14-color flow cytometry. Results: A 150-fold mass excess of the desired imaging dose was tolerated well in male and female CD-1 mice (no observed adverse effect level). Time-activity curves from human imaging data showed rapid tracer clearance from blood via the kidneys and bladder. The effective dose of 64Cu-LLP2A in humans was 0.036 ± 0.006 mSv/MBq, and the spleen had the highest organ uptake, 0.142 ± 0.034 mSv/MBq. Among all tissues, the red marrow demonstrated the highest residence time. Image quality analysis supports an early imaging time (4-5 h after injection of the radiotracer) as optimal. Cell studies showed statistically significant blocking for the tracer produced for all human studies (82.42% ± 13.47%). Blood metabolism studies confirmed a stable product peak (>90%) up to 1 h after injection of the radiopharmaceutical. No clinical or laboratory adverse events related to 64Cu-LLP2A were observed in the human participants. Conclusion: 64Cu-LLP2A exhibited a favorable dosimetry and safety profile for use in humans.

Functional Imaging in the Evaluation of Treatment Response in Multiple Myeloma: The Role of PET-CT and MRI

Bone disease is among the defining characteristics of symptomatic Multiple Myeloma (MM). Imaging techniques such as fluorodeoxyglucose positron emission tomography-computed tomography (FDG PET/CT) and magnetic resonance imaging (MRI) can identify plasma cell proliferation and quantify disease activity. This function renders these imaging tools as suitable not only for diagnosis, but also for the assessment of bone disease after treatment of MM patients. The aim of this article is to review FDG PET/CT and MRI and their applications, with a focus on their role in treatment response evaluation. MRI emerges as the technique with the highest sensitivity in lesions' detection and PET/CT as the technique with a major impact on prognosis. Their comparison yields different results concerning the best tool to evaluate treatment response. The inhomogeneity of the data suggests the need to address limitations related to these tools with the employment of new techniques and the potential for a complementary use of both PET/CT and MRI to refine the sensitivity and achieve the standards for minimal residual disease (MRD) evaluation.

CD38-specific nanobodies allow in vivo imaging of multiple myeloma under daratumumab therapy

RATIONALE

Recent studies have demonstrated the feasibility of CD38-specific antibody constructs for in vivo imaging of multiple myeloma. However, detecting multiple myeloma in daratumumab-pretreated patients remains difficult due to overlapping binding epitopes of the CD38-specific imaging antibody constructs and daratumumab. Therefore, the development of an alternative antibody construct targeting an epitope of CD38 distinct from that of daratumumab is needed. We report the generation of a fluorochrome-conjugated nanobody recognizing such an epitope of CD38 to detect myeloma cells under daratumumab therapy in vitro, ex vivo, and in vivo.

METHODS

We conjugated the CD38-specific nanobody JK36 to the near-infrared fluorescent dye Alexa Fluor 680. The capacity of JK36AF680 to bind and detect CD38-expressing cells pretreated with daratumumab was evaluated on CD38-expressing tumor cell lines in vitro, on primary myeloma cells from human bone marrow biopsies ex vivo, and in a mouse tumor model in vivo.

RESULTS

Fluorochrome-labeled nanobody JK36AF680 showed specific binding to CD38-expressing myeloma cells pretreated with daratumumab in vitro and ex vivo and allowed for specific imaging of CD38-expressing xenografts in daratumumab-pretreated mice in vivo.

CONCLUSIONS

Our study demonstrates that a nanobody recognizing a distinct, non-overlapping epitope of CD38 allows the specific detection of myeloma cells under daratumumab therapy in vitro, ex vivo, and in vivo.

Immuno-PET: Design options and clinical proof-of-concept

Radioimmunoconjugates have been used for over 30 years in nuclear medicine applications. In the last few years, advances in cancer biology knowledge have led to the identification of new molecular targets specific to certain patient subgroups. The use of these targets in targeted therapies approaches has allowed the developments of specifically tailored therapeutics for patients. As consequence of the PET-imaging progresses, nuclear medicine has developed powerful imaging tools, based on monoclonal antibodies, to in vivo characterization of these tumor biomarkers. This imaging modality known as immuno-positron emission tomography (immuno-PET) is currently in fastest-growing and its medical value lies in its ability to give a non-invasive method to assess the in vivo target expression and distribution and provide key-information on the tumor targeting. Currently, immuno-PET presents promising probes for different nuclear medicine topics as staging/stratification tool, theranostic approaches or predictive/prognostic biomarkers. To develop a radiopharmaceutical drug that can be used in immuno-PET approach, it is necessary to find the best compromise between the isotope choice and the immunologic structure (full monoclonal antibody or derivatives). Through some clinical applications, this paper review aims to discuss the most important aspects of the isotope choice and the usable proteic structure that can be used to meet the clinical needs.

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.

The spatio-temporal evolution of multiple myeloma from baseline to relapse-refractory states

Deciphering Multiple Myeloma evolution in the whole bone marrow is key to inform curative strategies. Here, we perform spatial-longitudinal whole-exome sequencing, including 140 samples collected from 24 Multiple Myeloma patients during up to 14 years. Applying imaging-guided sampling we observe three evolutionary patterns, including relapse driven by a single-cell expansion, competing/co-existing sub-clones, and unique sub-clones at distinct locations. While we do not find the unique relapse sub-clone in the baseline focal lesion(s), we show a close phylogenetic relationship between baseline focal lesions and relapse disease, highlighting focal lesions as hotspots of tumor evolution. In patients with ≥3 focal lesions on positron-emission-tomography at diagnosis, relapse is driven by multiple distinct sub-clones, whereas in other patients, a single-cell expansion is typically seen (p < 0.01). Notably, we observe resistant sub-clones that can be hidden over years, suggesting that a prerequisite for curative therapies would be to overcome not only tumor heterogeneity but also dormancy.

Proceedings from the Blood and Marrow Transplant Clinical Trials Network Myeloma Intergroup Workshop on Immune and Cellular Therapy in Multiple Myeloma

The Blood and Marrow Transplant Clinical Trials Network (BMT CTN) Myeloma Intergroup conducted a workshop on Immune and Cellular Therapy in Multiple Myeloma on January 7, 2022. This workshop included presentations by basic, translational, and clinical researchers with expertise in plasma cell dyscrasias. Four main topics were discussed: platforms for myeloma disease evaluation, insights into pathophysiology, therapeutic target and resistance mechanisms, and cellular therapy for multiple myeloma. Here we provide a comprehensive summary of these workshop presentations.

HER2-targeted dual radiotracer approach with clinical potential for noninvasive imaging of trastuzumab-resistance caused by epitope masking

Rationale: The decreased HER2-accessibility by epitope masking is a primary trastuzumab-resistance mechanism. In this study, we developed a HER2-targeted dual radiotracer approach to predict the HER2-trastuzumab engagement noninvasively. Methods: Two novel HER2-specific VHHs, MIRC208 and MIRC213, were acquired by immunizing alpaca with human HER2 protein, and were site-specifically labeled with ^99mTc. Biodistribution and SPECT/CT imaging studies were performed in mice bearing HER2-positive and HER2-negative tumors. The HER2 binding sites of ^99mTc-MIRC208 and ^99mTc-MIRC213 were investigated by cell binding and SPECT/CT imaging studies. We evaluated the therapeutic predictive ability of our dual-radiotracer imaging approach for trastuzumab treatment in mice bearing MUC4-positive tumors (trastuzumab-resistant JIMT-1 and 87MUC4) and MUC4-negative tumors (trastuzumab-sensitive 7HER2 and NCI-N87). The preliminary clinical studies of ^99mTc-MIRC208 were performed in two patients with HER2-positive breast tumors. Results:^99mTc-MIRC208 and ^99mTc-MIRC213 clearly visualized HER2-positive tumors, but not HER2-negative tumors. ^99mTc-MIRC208 competes with trastuzumab for HER2-binding while ^99mTc-MIRC213 recognizes HER2 on an epitope that is not masked by MUC4. The SPECT/CT studies with ^99mTc-MIRC208 and ^99mTc-MIRC213 clearly showed that the MUC4-negative and trastuzumab-sensitive 7HER2 and NCI-N87 tumors had very similar tumor uptake with the SUV₂₀₈/SUV₂₁₃ (2 h) ratios of 1.11 ± 0.17 in 7HER2 and 1.25 ± 0.22 in NCI-N87. However, the MUC4-positive JIMT-1 tumors showed the decreased SUV₂₀₈/SUV₂₁₃ (2 h) ratio (0.63 ± 0.07), which correlated well with the low response rate to trastuzumab therapy. The SUV₂₀₈/SUV₂₁₃ (2 h) ratio was reduced to 0.72 ± 0.02 in MUC4-expressing NCI-N87 cells, and resulting in the decreased trastuzumab sensitivity, further supporting the correlation between the SUV₂₀₈/SUV₂₁₃ (2 h) ratio and trastuzumab-sensitivity. The primary and metastatic HER2-positive lesions of patients were clearly visualized by ^99mTc-MIRC208 SPECT at 2 h post injection. Conclusion: Overall, we demonstrated that the dual radiotracer imaging strategy is a valid noninvasive approach for the cancer patient selection before trastuzumab therapy. ^99mTc-MIRC213 SPECT is utilized to quantify the tumor HER2 expression and screen HER2-positive cancer patients, while ^99mTc-MIRC208 SPECT is used to determine the HER2-accessibility of trastuzumab. The SUV₂₀₈/SUV₂₁₃ (2 h) ratio is an important biomarker to determine the responsiveness of trastuzumab therapy.

Radiotheranostic Agents in Hematological Malignancies

Radioimmunotherapy (RIT) is a cancer treatment that combines radiation therapy with tumor-directed monoclonal antibodies (Abs). Although RIT had been introduced for the treatment of CD20 positive non-Hodgkin lymphoma decades ago, it never found a broad clinical application. In recent years, researchers have developed theranostic agents based on Ab fragments or small Ab mimetics such as peptides, affibodies or single-chain Abs with improved tumor-targeting capacities. Theranostics combine diagnostic and therapeutic capabilities into a single pharmaceutical agent; this dual application can be easily achieved after conjugation to radionuclides. The past decade has seen a trend to increased specificity, fastened pharmacokinetics, and personalized medicine. In this review, we discuss the different strategies introduced for the noninvasive detection and treatment of hematological malignancies by radiopharmaceuticals. We also discuss the future applications of these radiotheranostic agents.

99mTc-CD3813: A Nanobody-Based Single Photon Emission Computed Tomography Radiotracer with Clinical Potential for Myeloma Imaging and Evaluation of CD38 Expression

Daratumumab (DARA) is an anti-CD38 monoclonal antibody for the treatment of multiple myeloma (MM). The tumor CD38 expression level is one of the important factors in determining the efficacy of DARA treatment. Therefore, there is an urgent clinical need for a noninvasive tool to evaluate the CD38 levels in cancer patients before, during, and after DARA treatment. In this study, we prepared a new molecular imaging probe ^99mTc-CD3813, the ^99mTc-labeled nanobody CD3813, for noninvasive imaging of CD38 expression by single photon emission computed tomography (SPECT). We evaluated ^99mTc-CD3813 for its CD38 affinity and specificity and its capacity to image the CD38 expression in the MM and lymphoma xenografts models. ^99mTc-CD3813 SPECT/CT is able to visualize subcutaneous/orthotopic myeloma lesions in animal models and has advantages over ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography. Excess DARA has less impact on its tumor uptake (3.14 ± 0.83 vs 2.29 ± 0.91 %ID/g, n.s.), strongly suggesting that there is no competition between ^99mTc-CD3813 and DARA in binding to CD38. ^99mTc-CD3813 SPECT/CT revealed significant reduction in CD38 expression in the Ramos-bearing mice under DARA treatment, as evidenced by their reduced tumor uptake (3.04 ± 0.70 vs 1.07 ± 0.28 %ID/cc, P < 0.001). ^99mTc-CD3813 SPECT/CT was also able to detect the increased tumor uptake (0.79 ± 0.29 vs 2.12 ± 0.12 %ID/cc, P < 0.001) due to the upregulation of CD38 levels caused by all-trans retinoic acid infection. ^99mTc-CD3813 is a promising SPECT radiotracer for imaging the CD38-positive tumors and has clinical potential as a molecular imaging tool for evaluation of the CD38 expression level in patients before, during, and after DARA treatment.

Multi-Modal Optical Imaging and Combined Phototherapy of Nasopharyngeal Carcinoma Based on a Nanoplatform

Nasopharyngeal carcinoma (NPC) is a common malignant tumor of the head and neck with a high incidence rate worldwide, especially in southern China. Phototheranostics in combination with nanoparticles is an integrated strategy for enabling simultaneous diagnosis, real-time monitoring, and administration of precision therapy for nasopharyngeal carcinoma (NPC). It has shown great potential in the field of cancer diagnosis and treatment owing to its unique noninvasive advantages. Many Chinese and international research teams have applied nano-targeted drugs to optical diagnosis and treatment technology to conduct multimodal imaging and collaborative treatment of NPC, which has become a hot research topic. In this review, we aimed to introduce the recent developments in phototheranostics of NPC based on a nanoplatform. This study aimed to elaborate on the applications of nanoplatform-based optical imaging strategies and treatment modalities, including fluorescence imaging, photoacoustic imaging, Raman spectroscopy imaging, photodynamic therapy, and photothermal therapy. This study is expected to provide a scientific basis for further research and development of NPC diagnosis and treatment.

Influence of Fc Modifications and IgG Subclass on Biodistribution of Humanized Antibodies Targeting L1CAM

Immuno-PET is a powerful tool to noninvasively characterize the in vivo biodistribution of engineered antibodies. Methods: L1 cell adhesion molecule-targeting humanized (HuE71) IgG1 and IgG4 antibodies bearing identical variable heavy- and light-chain sequences but different fragment crystallizable (Fc) portions were radiolabeled with 89Zr, and the in vivo biodistribution was studied in SKOV3 ovarian cancer xenografted nude mice. Results: In addition to showing uptake in L1 cell adhesion molecule-expressing SKOV3 tumors, as does its parental counterpart HuE71 IgG1, the afucosylated variant having enhanced Fc-receptor affinity showed high nonspecific uptake in lymph nodes. On the other hand, aglycosylated HuE71 IgG1 with abrogated Fc-receptor binding did not show lymphoid uptake. The use of the IgG4 subclass showed high nonspecific uptake in the kidneys, which was prevented by mutating serine at position 228 to proline in the hinge region of the IgG4 antibody to mitigate in vivo fragment antigen-binding arm exchange. Conclusion: Our findings highlight the influence of Fc modifications and the choice of IgG subclass on the in vivo biodistribution of antibodies and the potential outcomes thereof.

ImmunoPET: harnessing antibodies for imaging immune cells

Dramatic, but uneven, progress in the development of immunotherapies for cancer has created a need for better diagnostic technologies including innovative non-invasive imaging approaches. This review discusses challenges and opportunities for molecular imaging in immuno-oncology and focuses on the unique role that antibodies can fill. ImmunoPET has been implemented for detection of immune cell subsets, activation and inhibitory biomarkers, tracking adoptively transferred cellular therapeutics, and many additional applications in preclinical models. Parallel progress in radionuclide availability and infrastructure supporting biopharmaceutical manufacturing has accelerated clinical translation. ImmunoPET is poised to provide key information on prognosis, patient selection, and monitoring immune responses to therapy in cancer and beyond.

Teaching cancer imaging in the era of precision medicine: Looking at the big picture

The role of imaging in cancer diagnosis and treatment has evolved at the same rapid pace as cancer management. Over the last twenty years, with the advancement of technology, oncology has become a multidisciplinary field that allows for researchers and clinicians not only to create individualized treatment options for cancer patients, but also to evaluate patients’ response to therapy with increasing precision. Familiarity with these concepts is a requisite for current and future radiologists, as cancer imaging studies represent a significant and growing component of any radiology practice, from tertiary cancer centers to community hospitals.

In this review we provide the framework to teach cancer imaging in the era of genomic oncology. After reading this article, readers should be able to illustrate the basics cancer genomics, modern cancer genomics, to summarize the types of systemic oncologic therapies available, their patterns of response and their adverse events, to discuss the role of imaging in oncologic clinical trials and the role of tumor response criteria and to display the future directions of oncologic imaging.

Engineering nanobodies for next-generation molecular imaging

In recent years, nanobodies have emerged as ideal imaging agents for molecular imaging. Molecular nanobody imaging combines the specificity of nanobodies with the sensitivity of state-of-the-art molecular imaging modalities, such as positron emission tomography (PET). Given that modifications of nanobodies alter their pharmacokinetics (PK), the engineering strategies that combine nanobodies with radionuclides determine the effectiveness, reliability, and safety of the molecular imaging probes. In this review, we introduce conjugation strategies that have been applied to nanobodies, including random conjugation, ^99mTc tricarbonyl chemistry, sortase A-mediated site-specific conjugation, maleimide-cysteine chemistry, and click chemistries. We also summarize the latest advances in nanobody tracers, emphasizing their preclinical and clinical use. In addition, we elaborate on nanobody-based near-infrared fluorescence (NIRF) imaging and image-guided surgery.

Modern radiographic imaging in multiple myeloma, what is the minimum requirement?

Imaging innovations offer useful techniques applicable to many oncology specialties. Treatment advances in the field of multiple myeloma (MM) have increased the need for accurate diagnosis, particularly in the bone marrow, which is an essential component in myeloma-defining criteria. Modern imaging identifies osteolytic lesions, distinguishes solitary plasmacytoma from MM, and evaluates the presence of extramedullary disease. Furthermore, imaging is increasingly valuable in post-treatment response assessment. Detection of minimal residual disease after therapy carries prognostic implications and influences subsequent treatment planning. Whole-body low-dose Computed Tomography is now recommended over the conventional skeletal survey, and more sophisticated functional imaging methods, such as ¹⁸F-Fluorodeoxyglucose Positron Emission Tomography , and diffusion-weighted Magnetic Resonance Imaging are proving effective in the assessment and monitoring of MM disease. This review focuses on understanding indications and advantages of these imaging modalities for diagnosing and managing myeloma.

Imaging of treatment response and minimal residual disease in multiple myeloma: state of the art WB-MRI and PET/CT

Bone imaging has been intimately associated with the diagnosis and staging of multiple myeloma (MM) for more than 5 decades, as the presence of bone lesions indicates advanced disease and dictates treatment initiation. The methods used have been evolving, and the historical radiographic skeletal survey has been replaced by whole body CT, whole body MRI (WB-MRI) and [¹⁸F]FDG-PET/CT for the detection of bone marrow lesions and less frequent extramedullary plasmacytomas.Beyond diagnosis, imaging methods are expected to provide the clinician with evaluation of the response to treatment. Imaging techniques are consistently challenged as treatments become more and more efficient, inducing profound response, with more subtle residual disease. WB-MRI and FDG-PET/CT are the methods of choice to address these challenges, being able to assess disease progression or response and to detect "minimal" residual disease, providing key prognostic information and guiding necessary change of treatment.This paper provides an up-to-date overview of the WB-MRI and PET/CT techniques, their observations in responsive and progressive disease and their role and limitations in capturing minimal residual disease. It reviews trials assessing these techniques for response evaluation, points out the limited comparisons between both methods and highlights their complementarity with most recent molecular methods (next-generation flow cytometry, next-generation sequencing) to detect minimal residual disease. It underlines the important role of PET/MRI technology as a research tool to compare the effectiveness and complementarity of both methods to address the key clinical questions.

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.

Theranostics – present and future

Theragnostics in nuclear medicine constitute an essential element of precision medicine. This notion integrates radionuclide diagnostics procedures and radionuclide therapies using appropriate radiopharmaceutics and treatment targeting specific biological pathways or receptors. The term theragnostics should also include another aspect of treatment: not only whether a given radioisotopic drug can be used, but also in what dose it ought to be used. Theragnostic procedures also allow predicting the effects of treatment based on the assessment of specific receptor density or the metabolic profile of neoplastic cells. The future of theragnostics depends not only on the use of new radiopharmaceuticals, but also on new gamma cameras. Modern theragnostics already require unambiguous pharmacokinetic and pharmacodynamic measurements based on absolute values. Only dynamic studies provide such a possibility. The introduction of the dynamic total-body PET-CT will enable this type of measurements characterizing metabolic processes and receptor expression on the basis of Patlak plot.

Metabolic Volume Measurements in Multiple Myeloma

Multiple myeloma (MM) accounts for 10-15% of all hematologic malignancies, as well as 20% of deaths related to hematologic malignant tumors, predominantly affecting bone and bone marrow. Positron emission tomography/computed tomography with 18F-fluorodeoxyglucose (FDG-PET/CT) is an important method to assess the tumor burden of these patients. It is often challenging to classify the extent of disease involvement in the PET scans for many of these patients because both focal and diffuse bone lesions may coexist, with varying degrees of FDG uptake. Different metrics involving volumetric parameters and texture features have been proposed to objectively assess these images. Here, we review some metabolic parameters that can be extracted from FDG-PET/CT images of MM patients, including technical aspects and predicting MM outcome impact. Metabolic tumor volume (MTV) and total lesion glycolysis (TLG) are volumetric parameters known to be independent predictors of MM outcome. However, they have not been adopted in clinical practice due to the lack of measuring standards. CT-based segmentation allows automated, and therefore reproducible, calculation of bone metabolic metrics in patients with MM, such as maximum, mean and standard deviation of the standardized uptake values (SUV) for the entire skeleton. Intensity of bone involvement (IBI) is a new parameter that also takes advantage of this approach with promising results. Other indirect parameters obtained from FDG-PET/CT images, such as visceral adipose tissue glucose uptake and subcutaneous adipose tissue radiodensity, may also be useful to evaluate the prognosis of MM patients. Furthermore, the use and quantification of new radiotracers can address different metabolic aspects of MM and may have important prognostic implications.

Annotating CD38 Expression in Multiple Myeloma with [18F]F-Nb1053

Noninvasive diagnosis of multiple myeloma (MM) is a clinical challenge. CD38 is an established biomarker for MM, and the development of CD38-targeted radiotracers may improve the management of MM. By taking the advantages of bioorthogonal click chemistry, a nanobody (i.e., Nb1053-LLQS) specific for CD38 was successfully labeled with ¹⁸F. The diagnostic efficacy and specificity of the developed tracer (i.e., [¹⁸F]F-Nb1053) were evaluated by immuno-positron emission tomography (immunoPET) imaging in disseminated MM.1S-bearing models. [¹⁸F]F-Nb1053 was developed with high radiochemical purity (>98%) and excellent immunoreactivity. [¹⁸F]F-Nb1053 immunoPET successfully delineated disseminated MM lesions in preclinical MM models. The uptake in the humerus, femur, and tibia was 1.42 ± 0.50%ID/g, 1.35 ± 0.53%ID/g, and 1.48 ± 0.67%ID/g (n = 6), respectively. Tumor uptake of [¹⁸F]F-Nb1053 decreased after daratumumab premedication, indicating the superior specificity of the reported probe. This work successfully developed a novel CD38-specific probe [¹⁸F]F-Nb1053 that may potentially optimize the management of MM upon clinical translation.

Annotating BCMA Expression in Multiple Myelomas

B cell maturation antigen (BCMA) is a promising theranostic target for multiple myeloma (MM). BCMA-targeted therapeutics, such as antibody-drug conjugates and chimeric antigen receptor T-cell immunotherapies, are rapidly reshaping the treatment landscape of MM. Along with the progress, a critical challenge is to noninvasively visualize the dynamic change of BCMA for a better-personalized prescription of the above-mentioned therapeutics. We aim to develop immuno-positron emission tomography (immunoPET) imaging strategies to visualize BCMA expression and realize target-specific diagnosis of MM in the work. A series of BCMA-targeting nanobodies were produced and two of them were successfully labeled with gallium-68 (⁶⁸Ga). MM models were established using MM.1S cell line and NOD-Prkdc^em26Cd52Il2rg^em26Cd22/Nju mice. The diagnostic efficacies of the developed probes (i.e., [⁶⁸Ga]Ga-NOTA-MMBC2 and [⁶⁸Ga]Ga-NOTA-MMBC3) were investigated in disseminated MM models by immunoPET imaging, region of interest analysis on PET images, biodistribution study, and histopathological staining study. [⁶⁸Ga]Ga-NOTA-MMBC2 and [⁶⁸Ga]Ga-NOTA-MMBC3 were developed with radiochemical purities of >99%. ImmunoPET imaging with either [⁶⁸Ga]Ga-NOTA-MMBC2 or [⁶⁸Ga]Ga-NOTA-MMBC3 precisely visualized BCMA expression and delineated MM lesions throughout the bone marrows. Moreover, [⁶⁸Ga]Ga-NOTA-MMBC3 immunoPET successfully detected remnant MM after treatment with daratumumab, a prescription medicine used to treat MM. The immunoPET imaging data correlated well with the biodistribution and immunohistochemistry staining results. The work successfully developed two state-of-the-art BCMA-targeted radiotracers for annotating BCMA expression and diagnosing MM. Translational studies interpreting the diagnostic efficacies of the immunoPET radiotracers are warranted.

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.

A non-internalised CD38-binding radiolabelled single-domain antibody fragment to monitor and treat multiple myeloma

Background

Antibody-based therapies targeting CD38 are currently used as single agents as well as in combination regimens for multiple myeloma, a malignant plasma cell disorder. In this study, we aimed to develop anti-CD38 single-domain antibodies (sdAbs) that can be used to trace CD38⁺ tumour cells and subsequently used for targeted radionuclide therapy. SdAbs are derived from Camelidae heavy-chain antibodies and have emerged as promising theranostic agents due to their favourable pharmacological properties.

Methods

Four different anti-CD38 sdAbs were produced, and their binding affinities and potential competition with the monoclonal antibody daratumumab were tested using biolayer interferometry. Their binding kinetics and potential cell internalisation were further studied after radiolabelling with the diagnostic radioisotope Indium-111. The resulting radiotracers were evaluated in vivo for their tumour-targeting potential and biodistribution through single-photon emission computed tomography (SPECT/CT) imaging and serial dissections. Finally, therapeutic efficacy of a lead anti-CD38 sdAb, radiolabelled with the therapeutic radioisotope Lutetium-177, was evaluated in a CD38⁺ MM xenograft model.

Results 

We retained anti-CD38 sdAb #2F8 as lead based on its excellent affinity and superior stability, the absence of competition with daratumumab and the lack of receptor-mediated internalisation. When intravenously administered to tumour-xenografted mice, radiolabelled sdAb #2F8 revealed specific and sustained tumour retention with low accumulation in other tissues, except kidneys, resulting in high tumour-to-normal tissue ratios. In a therapeutic setting, myeloma-bearing mice received three consecutive intravenous administrations of a high (18.5 MBq) or a low radioactive dose (9.3 MBq) of ¹⁷⁷Lu-DTPA-2F8 or an equal volume of vehicle solution. A dose-dependent tumour regression was observed, which translated into a prolonged median survival from 43 days for vehicle-treated mice, to 62 days (p = 0.027) in mice receiving the low and 65 days in mice receiving the high (p = 0.0007) radioactive dose regimen, respectively.

Conclusions

These results highlight the theranostic potential of radiolabelled anti-CD38 sdAbs for the monitoring and treatment of multiple myeloma.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13045-021-01171-6.

64Cu-labeled daratumumab F(ab')2 fragment enables early visualization of CD38-positive lymphoma

PURPOSE

Abnormal CD38 expression in some hematologic malignancies, including lymphoma, has made it a biomarker for targeted therapies. Daratumumab (Dara) is the first FDA-approved CD38-specific monoclonal antibody, enabling successfully immunoPET imaging over the past years. Radiolabeled Dara however has a long blood circulation and delayed tumor uptake which can limit its applications. The focus of this study is to develop ⁶⁴Cu-labeled Dara-F(ab')₂ for the visualization of CD38 in lymphoma models.

METHODS

F(ab')₂ fragment was prepared from Dara using an IdeS enzyme and purified with Protein A beads. Western blotting, flow cytometry, and surface plasmon resonance (SPR) were performed for in vitro assay. Probes were labeled with ⁶⁴Cu after the chelation of 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA). Small animal PET imaging and quantitative analysis were performed after injection of ⁶⁴Cu-labeled Dara-F(ab')₂, IgG-F(ab')₂, and Dara for evaluation in lymphoma models.

RESULTS

Flow cytometry and SPR assay proved the specific binding ability of Dara-F(ab')₂ and NOTA-Dara-F(ab')₂ in vitro. Radiolabeling yield of [⁶⁴Cu]Cu-NOTA-Dara-F(ab')₂ was over 90% and with a specific activity of 4.0 ± 0.6 × 10³ MBq/μmol (n = 5). PET imaging showed [⁶⁴Cu]Cu-NOTA-Dara-F(ab')₂ had a rapid and high tumor uptake as early as 2 h (6.9 ± 1.2%ID/g) and peaked (9.5 ± 0.7%ID/g) at 12 h, whereas [⁶⁴Cu]Cu-NOTA-Dara reached its tumor uptake peaked at 48 h (8.3 ± 1.4%ID/g, n = 4). In comparison, IgG-F(ab')₂ and HBL-1 control groups found no noticeable tumor uptake. [⁶⁴Cu]Cu-NOTA-Dara-F(ab')₂ had significantly lower uptake in blood pool, bone, and muscle than [⁶⁴Cu]Cu-NOTA-Dara and its tumor-to-blood and tumor-to-muscle ratios were significantly higher than controls.

CONCLUSIONS

[⁶⁴Cu]Cu-NOTA-Dara-F(ab')₂ showed a rapid and high tumor uptake in CD38-positive lymphoma models with favorable imaging contrast, showing its promise as a potential PET imaging agent for future clinical applications.

Imaging of Cancer Immunotherapy: Response Assessment Methods, Atypical Response Patterns, and Immune-Related Adverse Events, From the AJR Special Series on Imaging of Inflammation

The introduction of immunotherapy with immune-checkpoint inhibitors (ICIs) has revolutionized cancer treatment paradigms. Since the FDA approval of the first ICI in 2011, multiple additional ICIs have been approved and granted marketing authorization, and many promising agents are in early clinical adoption. Due to the distinctive biologic mechanisms of ICIs, the patterns of tumor response and progression differ for immunotherapy from those observed with cytotoxic chemotherapies. With increasing clinical adoption of immunotherapy, it is critical for radiologists to recognize different response patterns and common pitfalls to avoid misinterpretation of imaging studies or prompt premature cessation of potentially effective treatment. This article provides an overview of ICIs and their mechanisms of action and reviews the anatomic and metabolic immune-related response assessment methods, typical and atypical patterns of immunotherapy response (including pseudoprogression, hyper-progression, dissociated response, and durable response), and common imaging features of immune-related adverse events. Future multicenter trials are needed to validate the proposed immune-related response criteria and identify the functional imaging markers of early treatment response and survival.

Minimal Residual Disease in Myeloma: Application for Clinical Care and New Drug Registration

The development of novel agents has transformed the treatment paradigm for multiple myeloma, with minimal residual disease (MRD) negativity now achievable across the entire disease spectrum. Bone marrow-based technologies to assess MRD, including approaches using next-generation flow and next-generation sequencing, have provided real-time clinical tools for the sensitive detection and monitoring of MRD in patients with multiple myeloma. Complementary liquid biopsy-based assays are now quickly progressing with some, such as mass spectrometry methods, being very close to clinical use, while others utilizing nucleic acid-based technologies are still developing and will prove important to further our understanding of the biology of MRD. On the regulatory front, multiple retrospective individual patient and clinical trial level meta-analyses have already shown and will continue to assess the potential of MRD as a surrogate for patient outcome. Given all this progress, it is not surprising that a number of clinicians are now considering using MRD to inform real-world clinical care of patients across the spectrum from smoldering myeloma to relapsed refractory multiple myeloma, with each disease setting presenting key challenges and questions that will need to be addressed through clinical trials. The pace of advances in targeted and immune therapies in multiple myeloma is unprecedented, and novel MRD-driven biomarker strategies are essential to accelerate innovative clinical trials leading to regulatory approval of novel treatments and continued improvement in patient outcomes.

In vivo quantitative assessment of therapeutic response to bortezomib therapy in disseminated animal models of multiple myeloma with [18F]FDG and [64Cu]Cu-LLP2A PET

Background

Multiple myeloma (MM) is a disease of cancerous plasma cells in the bone marrow. Imaging-based timely determination of therapeutic response is critical for improving outcomes in MM patients. Very late antigen-4 (VLA4, CD49d/CD29) is overexpressed in MM cells. Here, we evaluated [¹⁸F]FDG and VLA4 targeted [⁶⁴Cu]Cu-LLP2A for quantitative PET imaging in disseminated MM models of variable VLA4 expression, following bortezomib therapy.

Methods

In vitro and ex vivo VLA4 expression was evaluated by flow cytometry. Human MM cells, MM.1S-CG and U266-CG (C: luciferase and G: green fluorescent protein), were injected intravenously in NOD-SCID gamma mice. Tumor progression was monitored by bioluminescence imaging (BLI). Treatment group received bortezomib (1 mg/kg, twice/week) intraperitoneally. All cohorts (treated, untreated and no tumor) were longitudinally imaged with [¹⁸F]FDG (7.4–8.0 MBq) and [⁶⁴Cu]Cu-LLP2A (2–3 MBq; Molar Activity: 44.14 ± 1.40 MBq/nmol) PET, respectively.

Results

Flow cytometry confirmed high expression of CD49d in U266 cells (> 99%) and moderate expression in MM.1S cells (~ 52%). BLI showed decrease in total body flux in treated mice. In MM.1S-CG untreated versus treated mice, [⁶⁴Cu]Cu-LLP2A localized with a significantly higher SUV_mean in spine (0.58 versus 0.31, p < 0.01) and femur (0.72 versus 0.39, p < 0.05) at week 4 post-tumor inoculation. There was a four-fold higher uptake of [⁶⁴Cu]Cu-LLP2A (SUV_mean) in untreated U266-CG mice compared to treated mice at 3 weeks post-treatment. Compared to [⁶⁴Cu]Cu-LLP2A, [¹⁸F]FDG PET detected treatment-related changes at later time points.

Conclusion

[⁶⁴Cu]Cu-LLP2A is a promising tracer for timely in vivo assessment of therapeutic response in disseminated models of MM.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13550-021-00840-4.

89Zr-PET imaging in humans: a systematic review

Purpose

The remarkable amount of preclinical data achieved on 89Zr-PET imaging led to a significant clinical translation, concerning mainly immuno-PET applications. The aim of this systematic review is to provide a complete overview on clinical applications of 89Zr-PET imaging, using a systematic approach to identify and collect published studies performed in humans, sorted by field of application and specific disease subsections.

Methods

A systematic literature search of articles suiting the inclusion criteria was conducted on Pubmed, Scopus, Central, and Web Of Science databases, including papers published from January 1967 to November 2020. Eligible studies had to be performed on humans through PET imaging with 89Zr-labeled compounds. The methodological quality was assessed through the Quality Assessment of Diagnostic accuracy Studies-2 tool.

Results

A total of 821 articles were screened. 74 studies performed on humans were assessed for eligibility with the exclusion of further 18, thus 56 articles were ultimately selected for the qualitative analysis.

Conclusions

89Zr has shown to be a powerful PET-imaging tool, in particular for radiolabeling antibodies in order to study antigen expression, biodistribution, anticancer treatment planning and follow-up. Other than oncologic applications, 89Zr-radiolabeled antibodies have been proposed for use in inflammatory and autoimmune disorders with interesting results. 89Zr-labeled nanoparticles represent groundbreaking radiopharmaceuticals with potential huge fields of application. To evaluate the clinical usefulness of 89Zr PET-imaging in different conditions and in real-world settings, and to widen its use in clinical practice, further translation of preclinical to clinical data is needed.