ImmunoPET imaging of human CD8+ T cells with novel 68Ga-labeled nanobody companion diagnostic agents

ImmunoPET imaging of Trop2 expression in solid tumors with nanobody tracers

PURPOSE

The high expression of the transmembrane glycoprotein trophoblast cell-surface antigen 2 (Trop2) was strongly associated with the progression of solid tumors, including pancreatic and gastric cancers. Our study aimed to construct Trop2-specific immuno-positron emission tomography (immunoPET) probes and assess the diagnostic abilities in preclinical pancreatic and gastric cancer models.

METHODS

The expression of Trop2 in pancreatic cancer was determined by single-cell sequencing and immunohistochemistry on tissue microarray (TMA). Flow cytometry was used to screen the expression of Trop2 in pancreatic cancer cell lines. Two nanobodies (i.e., RTD98 and RTD01) targeting Trop2 were developed and labeled with gallium-68 (68Ga, T1/2 = 1.1 h) to construct immunoPET imaging probes. The agents were researched in cell-derived pancreatic and patient-derived gastric cancer models expressing varying Trop2.

RESULTS

Single-cell sequencing results showed high expression of Trop2 in pancreatic ductal cells as well as acinar cells and immunohistochemical staining of TMA from pancreatic cancers showed significantly higher expression of Trop2 in cancerous than in paracancerous tissues. ImmunoPET utilizing [68Ga]Ga-NOTA-RTD98 could clearly delineate subcutaneous tumors, both in cell-derived pancreatic cancer models and patient-derived gastric cancer models, superior to imaging using [18F]-FDG or a non-specific probe [68Ga]Ga-NOTA-RTD161. Another probe with improved pharmacokinetics targeting Trop2, [68Ga]Ga-NOTA-RTD01, was further prepared and showed advantageous diagnostic capabilities in preclinical pancreatic cancer models.

CONCLUSION

In the work, we reported two nanobody tracers targeting human Trop2 which may facilitate better use of Trop2-targeted therapeutics by noninvasively displaying expression dynamics of the target.

Tailoring biomaterials for monitoring and evoking tertiary lymphoid structures

Despite the remarkable clinical success of immune checkpoint blockade (ICB) in the treatment of cancer, the response rate to ICB therapy remains suboptimal. Recent studies have strongly demonstrated that intratumoral tertiary lymphoid structures (TLSs) are associated with a good prognosis and a successful clinical response to immunotherapy. However, there is still a shortage of efficient and wieldy approaches to image and induce intratumoral TLSs in vivo. Biomaterials have made great strides in overcoming the deficiencies of conventional diagnosis and therapies for cancer, and antitumor therapy has also benefited from biomaterial-based drug delivery models. In this review, we summarize the reported methods for TLS imaging and induction based on biomaterials and provide potential strategies that can further enhance the effectiveness of imaging and stimulating intratumoral TLSs to predict and promote the response rates of ICB therapies for patients. STATEMENT OF SIGNIFICANCE: In this review, we focused on the promising of biomaterials for imaging and induction of TLSs. We reviewed the applications of biomaterials in molecular imaging and immunotherapy, identified the biomaterials that may be suitable for TLS imaging and induction, and provided outlooks for further research. Accurate imaging and effective induction of TLSs are of great significance for understanding the mechanism and clinical application. We highlighted the need for multidisciplinary coordination and cooperation in this field, and proposed the possible future direction of noninvasive imaging and artificial induction of TLSs based on biomaterials. We believe that it can facilitate collaboration and galvanize a broader effort.

Emerging biomedical imaging-based companion diagnostics for precision medicine

The tumor heterogeneity, which leads to individual variations in tumor microenvironments, causes poor prognoses and limits therapeutic response. Emerging technology such as companion diagnostics (CDx) detects biomarkers and monitors therapeutic responses, allowing identification of patients who would benefit most from treatment. However, currently, most US Food and Drug Administration-approved CDx tests are designed to detect biomarkers in vitro and ex vivo, making it difficult to dynamically report variations of targets in vivo. Various medical imaging techniques offer dynamic measurement of tumor heterogeneity and treatment response, complementing CDx tests. Imaging-based companion diagnostics allow for patient stratification for targeted medicines and identification of patient populations benefiting from alternative therapeutic methods. This review summarizes recent developments in molecular imaging for predicting and assessing responses to cancer therapies, as well as the various biomarkers used in imaging-based CDx tests. We hope this review provides informative insights into imaging-based companion diagnostics and advances precision medicine.

The NR_109/FUBP1/c-Myc axis regulates TAM polarization and remodels the tumor microenvironment to promote cancer development

BACKGROUND

Tumor-associated macrophages (TAMs) are a major component of the tumor microenvironment (TME) and exert an important role in tumor progression. Due to the heterogeneity and plasticity of TAMs, modulating the polarization states of TAMs is considered as a potential therapeutic strategy for tumors. Long noncoding RNAs (lncRNAs) have been implicated in various physiological and pathological processes, yet the underlying mechanism on how lncRNAs manipulate the polarization states of TAMs is still unclear and remains to be further investigated.

METHODS

Microarray analyses were employed to characterize the lncRNA profile involved in THP-1-induced M0, M1 and M2-like macrophage. Among those differentially expressed lncRNAs, NR_109 was further studied, for its function in M2-like macrophage polarization and the effects of the condition medium or macrophages mediated by NR_109 on tumor proliferation, metastasis and TME remodeling both in vitro and in vivo. Moreover, we revealed how NR_109 interacted with far upstream element-binding protein 1 (FUBP1) to regulate the protein stability through hindering ubiquitination modification by competitively binding with JVT-1. Finally, we examined sections of tumor patients to probe the correlation among the expression of NR_109 and related proteins, showing the clinical significance of NR_109.

RESULTS

We found that lncRNA NR_109 was highly expressed in M2-like macrophages. Knockdown NR_109 impeded IL-4 induced M2-like macrophage polarization and significantly reduced the activity of M2-like macrophages to support the proliferation and metastasis of tumor cells in vitro and in vivo. Mechanistically, NR_109 competed with JVT-1 to bind FUBP1 at its C-terminus domain, impeded the ubiquitin-mediated degradation of FUBP1, activated c-Myc transcription and thus promoted M2-like macrophages polarization. Meanwhile, as a transcription factor, c-Myc could bind to the promoter of NR_109 and enhance the transcription of NR_109. Clinically, high NR_109 expression was found in CD163⁺ TAMs from tumor tissues and was positively correlated with poor clinical stages of patients with gastric cancer and breast cancer.

CONCLUSIONS

Our work revealed for the first time that NR_109 exerted a crucial role in regulating the phenotype-remodeling and function of M2-like macrophages via a NR_109/FUBP1/c-Myc positive feedback loop. Thus, NR_109 has great translational potentials in the diagnosis, prognosis and immunotherapy of cancer.

Application Progress of the Single Domain Antibody in Medicine

The camelid-derived single chain antibody (sdAb), also termed VHH or nanobody, is a unique, functional heavy (H)-chain antibody (HCAb). In contrast to conventional antibodies, sdAb is a unique antibody fragment consisting of a heavy-chain variable domain. It lacks light chains and a first constant domain (CH1). With a small molecular weight of only 12~15 kDa, sdAb has a similar antigen-binding affinity to conventional Abs but a higher solubility, which exerts unique advantages for the recognition and binding of functional, versatile, target-specific antigen fragments. In recent decades, with their unique structural and functional features, nanobodies have been considered promising agents and alternatives to traditional monoclonal antibodies. As a new generation of nano-biological tools, natural and synthetic nanobodies have been used in many fields of biomedicine, including biomolecular materials, biological research, medical diagnosis and immune therapies. This article briefly overviews the biomolecular structure, biochemical properties, immune acquisition and phage library construction of nanobodies and comprehensively reviews their applications in medical research. It is expected that this review will provide a reference for the further exploration and unveiling of nanobody properties and function, as well as a bright future for the development of drugs and therapeutic methods based on nanobodies.

Mannosylated-serum albumin nanoparticle imaging to monitor tumor-associated macrophages under anti-PD1 treatment

BACKGROUND

Immune checkpoint inhibitors such as anti-programmed cell death protein 1 (PD1) block tumor growth by reinvigorating the immune system; however, determining their efficacy only by the changes in tumor size may prove inaccurate. As the immune cells including macrophages in the tumor microenvironment (TME) are associated with the response to anti-PD1 therapy, tumor-associated macrophages (TAMs) imaging using nanoparticles can noninvasively provide the immune enrichment status of TME. Herein, the mannosylated-serum albumin (MSA) nanoparticle was labeled with radioactive isotope ⁶⁸Ga to target the mannose receptors on macrophages for noninvasive monitoring of the TME according to anti-PD1 therapy.

RESULTS

B16F10-Luc and MC38-Luc tumor-bearing mice were treated with anti-PD1, and the response to anti-PD1 was determined by the tumor volume. According to the flow cytometry, the responders to anti-PD1 showed an increased proportion of TAMs, as well as lymphocytes, and the most enriched immune cell population in the TME was also TAMs. For noninvasive imaging of TAMs as a surrogate of immune cell augmentation in the TME via anti-PD1, we acquired [⁶⁸Ga] Ga-MSA positron emission tomography. According to the imaging study, an increased number of TAMs in responders at the early phase of anti-PD1 treatment was observed in both B16F10-Luc and MC38-Luc tumor-bearing mice models.

CONCLUSION

As representative immune cells in the TME, non-invasive imaging of TAMs using MSA nanoparticles can reflect the immune cell enrichment status in the TME closely associated with the response to anti-PD1. As non-invasive imaging using MSA nanoparticles, this approach shows a potential to monitor and evaluate anti-tumor response to immune checkpoint inhibitors.

Development and Characterization of Nanobody-Derived CD47 Theranostic Pairs in Solid Tumors

Overexpression of CD47 is frequently observed in various types of human malignancies, inhibiting myeloid-mediated elimination of tumor cells and affecting the prognosis of cancer patients. By mapping biomarker expression, immuno-positron emission tomography has been increasingly used for patient screening and response monitoring. By immunization alpacas with recombinant human CD47, we prepared a CD47-targeting nanobody C2 and developed [⁶⁸Ga]Ga-NOTA-C2, followed by an exploration of the diagnostic value in CD47-expressing tumor models including gastric-cancer patient-derived xenograft models. By fusing C2 to an albumin binding domain (ABD), we synthesized ABDC2, which had increased in vivo half-life and improved targeting properties. We further labeled ABDC2 with ⁶⁸Ga/⁸⁹Zr/¹⁷⁷Lu to develop radionuclide theranostic pairs and evaluated the pharmacokinetics and theranostic efficacies of the agents in cell- and patient-derived models. Both C2 and ABDC2 specifically reacted with human CD47 with a high K _D value of 23.50 and 84.57 pM, respectively. [⁶⁸Ga]Ga-NOTA-C2 was developed with high radiochemical purity (99 >%, n = 4) and visualized CD47 expression in the tumors. In comparison to the rapid renal clearance and short half-life of [⁶⁸Ga]Ga-NOTA-C2, both [⁶⁸Ga]Ga-NOTA-ABDC2 and [⁸⁹Zr]Zr-DFO-ABDC2 showed prolonged circulation and increased tumor uptake, with the highest uptake of [⁸⁹Zr]Zr-DFO-ABDC2 occurring at 72 h post-injection. Moreover, [¹⁷⁷Lu]Lu-DOTA-ABDC2 radioimmunotherapy suppressed the tumor growth but was associated with toxicity, warranting further optimization of the treatment schedules. Taken together, we reported a series of nanobody-derived CD47-targeted agents, of which [⁶⁸Ga]Ga-NOTA-C2 and [⁸⁹Zr]Zr-DFO-ABDC2 are readily translatable. Optimization and translation of CD47-targeted theranostic pair may provide new prospects for CD47-targeted management of solid tumors.

Development and comparison of 68Ga/18F/64Cu-labeled nanobody tracers probing Claudin18.2

Claudin 18.2 (CLDN18.2) is an emerging target for the treatment of gastric cancers. We aim to develop tracers to image the expression of CLDN18.2. A humanized nanobody targeting CLDN18.2 (clone hu19V3) was produced and labeled with ⁶⁸Ga, ⁶⁴Cu, and ¹⁸F. The tracers were investigated in subcutaneous and metastatic models established using two different mouse types (nude and Balb/c mice) and two different cell lines (CHO-CLDN18.2 and CT26-CLDN18.2). Gastric cancer patient-derived xenograft (PDX) models were further established for validation experiments. Three novel CLDN18.2-targeted tracers (i.e., [⁶⁸Ga]Ga-NOTA-hu19V3, [⁶⁴Cu]Cu-NOTA-hu19V3, and [¹⁸F]F-hu19V3) were developed with good radiochemical yields and excellent radiochemical purities. [⁶⁸Ga]Ga-NOTA-hu19V3 immuno-positron emission tomography (immunoPET) rapidly delineated subcutaneous CHO-CLDN18.2 lesions and CT26-CLDN18.2 tumors, as well as showing excellent diagnostic value in PDX models naturally expressing CLDN18.2. While [⁶⁸Ga]Ga-NOTA-hu19V3 had high kidney accumulation, [⁶⁴Cu]Cu-NOTA-hu19V3 showed reduced kidney accumulation and improved image contrast at late time points. Moreover, [¹⁸F]F-hu19V3 was developed via click chemistry reaction under mild conditions and precisely disseminated CHO-CLDN18.2 lesions in the lungs. Furthermore, region of interest analysis, biodistribution study, and histopathological staining results correlated well with the in vivo imaging results. Taken together, immunoPET imaging with the three tracers can reliably visualize CLDN18.2 expression.

Emerging Biomaterials Imaging Antitumor Immune Response

Immunotherapy is one of the most promising clinical modalities for the treatment of malignant tumors and has shown excellent therapeutic outcomes in clinical settings. However, it continues to face several challenges, including long treatment cycles, high costs, immune-related adverse events, and low response rates. Thus, it is critical to predict the response rate to immunotherapy by using imaging technology in the preoperative and intraoperative. Here, the latest advances in nanosystem-based biomaterials used for predicting responses to immunotherapy via the imaging of immune cells and signaling molecules in the immune microenvironment are comprehensively summarized. Several imaging methods, such as fluorescence imaging, magnetic resonance imaging, positron emission tomography imaging, ultrasound imaging, and photoacoustic imaging, used in immune predictive imaging, are discussed to show the potential of nanosystems for distinguishing immunotherapy responders from nonresponders. Nanosystem-based biomaterials aided by various imaging technologies are expected to enable the effective prediction and diagnosis in cases of tumors, inflammation, and other public diseases.

Positron Emission Tomography Probes for Imaging Cytotoxic Immune Cells

Non-invasive positron emission tomography (PET) imaging of immune cells is a powerful approach for monitoring the dynamics of immune cells in response to immunotherapy. Despite the clinical success of many immunotherapeutic agents, their clinical efficacy is limited to a subgroup of patients. Conventional imaging, as well as analysis of tissue biopsies and blood samples do not reflect the complex interaction between tumour and immune cells. Consequently, PET probes are being developed to capture the dynamics of such interactions, which may improve patient stratification and treatment evaluation. The clinical efficacy of cancer immunotherapy relies on both the infiltration and function of cytotoxic immune cells at the tumour site. Thus, various immune biomarkers have been investigated as potential targets for PET imaging of immune response. Herein, we provide an overview of the most recent developments in PET imaging of immune response, including the radiosynthesis approaches employed in their development.

Pilot study of a novel nanobody 68 Ga-NODAGA-SNA006 for instant PET imaging of CD8+ T cells

PURPOSE

Positron emission tomography (PET) with specific diagnostic probes for quantifying CD8⁺ T cells has emerged as a powerful technique for monitoring the immune response. However, most CD8⁺ T cell radiotracers are based on antibodies or antibody fragments, which are slowly cleared from circulation. Herein, we aimed to develop and assess ⁶⁸ Ga-NODAGA-SNA006 for instant PET (iPET) imaging of CD8⁺ T cells.

METHODS

A novel nanobody without a hexahistidine (His₆) tag, SNA006-GSC, was designed, site-specifically conjugated with NODAGA-maleimide and radiolabelled with ⁶⁸ Ga. The PET imaging profiles of ⁶⁸ Ga-NODAGA-SNA006 were evaluated in BALB/c MC38-CD8⁺/CD8^- tumour models and cynomolgus monkeys. Three volunteers with lung cancer underwent whole-body PET/CT imaging after ⁶⁸ Ga-NODAGA-SNA006 administration. The biodistribution, pharmacokinetics and dosimetry of patients were also investigated. In addition, combined with immunohistochemistry (IHC), the quantitative performance of the tracer for monitoring CD8 expression was evaluated in BALB/c MC38-CD8⁺/CD8^- and human subjects.

RESULTS

⁶⁸ Ga-NODAGA-SNA006 was prepared with RCP > 98% and SA > 100 GBq/μmol. ⁶⁸ Ga-NODAGA-SNA006 exhibited specific uptake in MC38-CD8⁺ xenografts tumours, CD8-rich tissues (such as the spleen) in monkeys and CD8⁺ tumour lesions in patients within 1 h. Fast washout from circulation was observed in three volunteers (t_1/2 < 20 min). A preliminary quantitative linear relationship (R² = 0.9668, p < 0.0001 for xenografts and R² = 0.7924, p = 0.0013 for lung patients) appeared between ⁶⁸ Ga-NODAGA-SNA006 uptake and CD8 expression. ⁶⁸ Ga-NODAGA-SNA006 was well tolerated by all patients.

CONCLUSION

⁶⁸ Ga-NODAGA-SNA006 PET imaging can instantly quantify CD8 expression with an ideal safety profile and is expected to be important for dynamically tracking CD8⁺ T cells and monitoring immune responses for individualised cancer immunotherapy.

TRIAL REGISTRATION

NCT05126927 (19 November 2021, retrospectively registered).

Radiopharmaceuticals as Novel Immune System Tracers

Immune checkpoint inhibitors (ICIs) have transformed the treatment paradigms for multiple cancers. However, ICI therapy often fails to generate measurable and sustained antitumor responses, and clinically meaningful benefits remain limited to a small proportion of overall patients. A major obstacle to development and effective application of novel therapeutic regimens is optimized patient selection and response assessment. Noninvasive imaging using novel immunoconjugate radiopharmaceuticals (immuno–positron emission tomography and immuno-single-photon emission computed tomography) can assess for expression of cell surface immune markers, such as programmed cell death protein ligand-1 (PD-L1), akin to a virtual biopsy. This emerging technology has the potential to provide clinicians with a quantitative, specific, real-time evaluation of immunologic responses relative to cancer burden in the body. We discuss the rationale for using noninvasive molecular imaging of the programmed cell death protein-1 and PD-L1 axis as a biomarker for immunotherapy and summarize the current status of preclinical and clinical studies examining PD-L1 immuno–positron emission tomography. The strategies described in this review provide insight for future clinical trials exploring the use of immune checkpoint imaging as a biomarker for both ICI and radiation therapy, and for the rational design of combinatorial therapeutic regimens.

Imaging and therapeutic targeting of the tumor immune microenvironment with biologics

The important role of tumor microenvironmental elements in determining tumor progression and metastasis has been firmly established. In particular, the presence and activity profile of tumor-infiltrating immune cells may be associated with the outcome of the disease and may predict responsiveness to (immuno)therapy. Indeed, while some immune cell types, such as macrophages, support cancer cell outgrowth and mediate therapy resistance, the presence of activated CD8⁺ T cells is usually indicative of a better prognosis. It is therefore of the utmost interest to obtain a full picture of the immune infiltrate in tumors, either as a prognostic test, as a way to stratify patients to maximize therapeutic success, or as therapy follow-up. Hence, the non-invasive imaging of these cells is highly warranted, with biologics being prime candidates to achieve this goal.

Noninvasive Imaging of CD4+ T Cells in Humanized Mice

Antibody-based PET (immunoPET) with radiotracers that recognize specific cells of the immune system provides an opportunity to monitor immune cell trafficking at the organismal scale. We previously reported the visualization of human CD8+ T cells, including CD8+ tumor-infiltrating lymphocytes (TIL), in mice using a humanized CD8-targeted minibody. Given the important role of CD4+ T cells in adaptive immune responses of health and disease including infections, tumors, and autoimmunity, we explored immunoPET using an anti-human-CD4 minibody. We assessed the ability of [64Cu]Cu-NOTA-IAB41 to bind to various CD4+ T-cell subsets in vitro. We also determined the effect of the CD4-targeted minibody on CD4+ T-cell abundance, proliferation, and activation state in vitro. We subsequently evaluated the ability of the radiotracer to visualize CD4+ T cells in T-cell rich organs and orthotopic brain tumors in vivo. For the latter, we injected the [64Cu]Cu-NOTA-IAB41 radiotracer into humanized mice that harbored intracranial patient-derived glioblastoma (GBM) xenografts and performed in vivo PET, ex vivo autoradiography, and anti-CD4 IHC on serial brain sections. [64Cu]Cu-NOTA-IAB41 specifically detects human CD4+ T cells without impacting their abundance, proliferation, and activation. In humanized mice, [64Cu]Cu-NOTA-IAB41 can visualize various peripheral tissues in addition to orthotopically implanted GBM tumors. [64Cu]Cu-NOTA-IAB41 is able to visualize human CD4+ T cells in humanized mice and can provide noninvasive quantification of CD4+ T-cell distribution on the organismal scale.

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.

Probing immune infiltration dynamics in cancer by in vivo imaging

Cancer immunotherapies typically aim to stimulate the accumulation and activity of cytotoxic T-cells or pro-inflammatory antigen-presenting cells, reduce immunosuppressive myeloid cells or regulatory T-cells, or elicit some combination of effects thereof. Notwithstanding the encouraging results, immunotherapies such as PD-1/PD-L1-targeted immune checkpoint blockade act heterogeneously across individual patients. It remains challenging to predict and monitor individual responses, especially across multiple sites of metastasis or sites of potential toxicity. To address this need, in vivo imaging of both adaptive and innate immune cell populations has emerged as a tool to quantify spatial leukocyte accumulation in tumors non-invasively. Here we review recent progress in the translational development of probes for in vivo leukocyte imaging, focusing on complementary perspectives provided by imaging of T-cells, phagocytic macrophages, and their responses to therapy.

GPC3-targeted immunoPET imaging of hepatocellular carcinomas

PURPOSE

Early detection of hepatocellular carcinoma (HCC) remains a clinical challenge. Glypican 3 (GPC3) is a proteoglycan highly specific for HCC and is a potential diagnostic and therapeutic target for HCC. This work aims to develop GPC3-targeted immuno-positron emission tomography (immunoPET) imaging strategies and to assess the diagnostic values in preclinical HCC models.

METHODS

Flow cytometry was used to screen GPC3-positive HCC cell lines. The expression of GPC3 in HCCs was detected by immunohistochemistry on tissue microarray. A novel GPC3-specific single domain antibody (sdAb) was produced and labeled with gallium-68 (⁶⁸Ga, T_1/2 = 1.1 h) and fluorine-18 (¹⁸F, T_1/2 = 1.8 h) to develop radiotracers with different half-lives. The diagnostic efficacies of the developed probes (i.e., [⁶⁸Ga]Ga-NOTA-G2, [¹⁸F]F-G2, and [⁶⁸Ga]Ga-NOTA-ABDG2) were interrogated in preclinical HCC models bearing varying GPC3 levels.

RESULTS

GPC3 was strongly expressed on HCC cell lines and patients with poorly differentiated HCC. [⁶⁸Ga]Ga-NOTA-G2 immunoPET imaging specifically delineated the subcutaneous HCC lesions, outperforming the traditional ¹⁸F-fluorodeoxyglucose PET and the nonspecific [⁶⁸Ga]Ga-NOTA-NbGFP immunoPET. ImmunoPET imaging with [¹⁸F]F-G2 also efficiently diagnosed the tumors with clarity. Moreover, the fusion of G2 to an albumin-binding domain (ABD) significantly increased the tumor uptake and decreased kidney accumulation of the radiotracer when compared to [⁶⁸Ga]Ga-NOTA-G2.

CONCLUSIONS

In the work, we successfully developed sdAb-derived GPC3-targeted immunoPET imaging strategies and characterized the superior diagnostic accuracies in preclinical HCC models. Furthermore, we synthesized a fusion protein ABDG2 with improved targeting and pharmacokinetic properties, serving as a promising candidate for developing radioimmunotherapy agents.

Promise and challenges of clinical non-invasive T-cell tracking in the era of cancer immunotherapy

In the last decades, our understanding of the role of the immune system in cancer has significantly improved and led to the discovery of new immunotherapeutic targets and tools, which boosted the advances in cancer immunotherapy to fight a growing number of malignancies. Approved immunotherapeutic approaches are currently mainly based on immune checkpoint inhibitors, antibody-derived targeted therapies, or cell-based immunotherapies. In essence, these therapies induce or enhance the infiltration and function of tumor-reactive T cells within the tumors, ideally resulting in complete tumor eradication. While the clinical application of immunotherapies has shown great promise, these therapies are often accompanied either by a variety of side effects as well as partial or complete unresponsiveness of a number of patients. Since different stages of disease progression elicit different local and systemic immune responses, the ability to longitudinally interrogate the migration and expansion of immune cells, especially T cells, throughout the whole body might greatly facilitate disease characterization and understanding. Furthermore, it can serve as a tool to guide development as well as selection of appropriate treatment regiments. This review provides an overview about a variety of immune-imaging tools available to characterize and study T-cell responses induced by anti-cancer immunotherapy. Moreover, challenges are discussed that must be taken into account and overcome to use immune-imaging tools as predictive and surrogate markers to enhance assessment and successful application of immunotherapies.

Evaluation of SARS-CoV-2-Neutralizing Nanobody Using Virus Receptor Binding Domain-Administered Model Mice

Due to the rapid spread of coronavirus disease 2019 (COVID-19), there is an urgent requirement for the development of additional diagnostic tools for further analysis of the disease. The isolated nanobody Nb11-59 binds to the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) receptor-binding domain (RBD) with high affinity to neutralize the virus and block the angiotensin-converting enzyme 2- (ACE2-) RBD interaction. Here, we introduce a novel nanobody-based radiotracer named ⁶⁸Ga-Nb1159. The radiotracer retained high affinity for the RBD and showed reliable radiochemical characteristics both in vitro and in vivo. Preclinical positron emission tomography (PET) studies of ⁶⁸Ga-Nb1159 in mice revealed its rapid clearance from circulation and robust uptake into the renal and urinary systems. Fortunately, ⁶⁸Ga-Nb1159 could specifically reveal the distribution of the RBD in mice. This study also helped to evaluate the pharmacodynamic effects of the neutralizing nanobody. Moreover, ⁶⁸Ga-Nb1159 may be a promising tool to explore the distribution of the RBD and improve the understanding of the virus. In particular, this study identified a novel molecular radioagent and established a reliable evaluation method for specifically investigating the RBD through noninvasive and visual PET technology.

Visualizing T cell responses: The T cell PET imaging toolbox

T lymphocytes are key mediators of the adaptive immune response. Inappropriate or imbalanced T cell responses are underlying factors in cancer progression, allergy and other immune disorders. Monitoring the spatiotemporal dynamics of T cells and their functional status has the potential to provide unique biological insights in health and disease. Non-invasive positron emission tomography (PET) imaging represents an ideal whole-body modality for achieving this goal. With the appropriate PET imaging probes, T cell dynamics can be monitored in vivo, with high specificity and sensitivity. Herein, we provide a comprehensive overview of the applications of this state-of-the-art T cell PET imaging toolbox, and the potential it has to improve the clinical management of cancer immunotherapy and T cell- driven diseases. We also discuss future directions and prospects for 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: 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.

Radiolabeling Strategies of Nanobodies for Imaging Applications

Nanobodies are small recombinant antigen-binding fragments derived from camelid heavy-chain only antibodies. Due to their compact structure, pharmacokinetics of nanobodies are favorable compared to full-size antibodies, allowing rapid accumulation to their targets after intravenous administration, while unbound molecules are quickly cleared from the circulation. In consequence, high signal-to-background ratios can be achieved, rendering radiolabeled nanobodies high-potential candidates for imaging applications in oncology, immunology and specific diseases, for instance in the cardiovascular system. In this review, a comprehensive overview of central aspects of nanobody functionalization and radiolabeling strategies is provided.

Nanobodies for Medical Imaging: About Ready for Prime Time?

Recent advances in medical treatments have been revolutionary in shaping the management and treatment landscape of patients, notably cancer patients. Over the last decade, patients with diverse forms of locally advanced or metastatic cancer, such as melanoma, lung cancers, and many blood-borne malignancies, have seen their life expectancies increasing significantly. Notwithstanding these encouraging results, the present-day struggle with these treatments concerns patients who remain largely unresponsive, as well as those who experience severely toxic side effects. Gaining deeper insight into the cellular and molecular mechanisms underlying these variable responses will bring us closer to developing more effective therapeutics. To assess these mechanisms, non-invasive imaging techniques provide valuable whole-body information with precise targeting. An example of such is immuno-PET (Positron Emission Tomography), which employs radiolabeled antibodies to detect specific molecules of interest. Nanobodies, as the smallest derived antibody fragments, boast ideal characteristics for this purpose and have thus been used extensively in preclinical models and, more recently, in clinical early-stage studies as well. Their merit stems from their high affinity and specificity towards a target, among other factors. Furthermore, their small size (~14 kDa) allows them to easily disperse through the bloodstream and reach tissues in a reliable and uniform manner. In this review, we will discuss the powerful imaging potential of nanobodies, primarily through the lens of imaging malignant tumors but also touching upon their capability to image a broader variety of nonmalignant diseases.