I-124 codrituzumab imaging and biodistribution in patients with hepatocellular carcinoma

Glypican-3 deficiency in liver cancer upregulates MAPK/ERK pathway but decreases cell proliferation

Glypican-3 (GPC3) is overexpressed in hepatocellular carcinomas and hepatoblastomas and represents an important therapeutic target but the biologic importance of GPC3 in liver cancer is unclear. To date, there are limited data characterizing the biological implications of GPC3 knockout (KO) in liver cancers that intrinsically express this target. Here, we report on the development and characterization of GPC3-KO liver cancer cell lines and compare to them to parental lines. GPC3-KO variants were established in HepG2 and Hep3B liver cancer cell lines using a lentivirus-mediated CRISPR/Cas9 system. We assessed the effects of GPC3 deficiency on oncogenic properties in vitro and in murine xenograft models. Downstream cellular signaling pathway changes induced by GPC3 deficiency were examined by RNAseq and western blot. To confirm the usefulness of the models for GPC3-targeted drug development, we evaluated the target engagement of a GPC3-selective antibody, GC33, conjugated to the positron-emitting zirconium-89 (89Zr) in subcutaneous murine xenografts of wild type (WT) and KO liver cancer cell lines. Deletion of GPC3 significantly reduced liver cancer cell proliferation, migration, and invasion compared to the parental cell lines. Additionally, the tumor growth of GPC3-KO liver cancer xenografts was significantly slower compared with control xenografts. RNA sequencing analysis also showed GPC3-KO resulted in a reduction in the expression of genes associated with cell cycle regulation, invasion, and migration. Specifically, we observed the downregulation of components in the AKT/NFκB/WNT signaling pathways and of molecules related to cell cycle regulation with GPC3-KO. In contrast, pMAPK/ERK1/2 was upregulated, suggesting an adaptive compensatory response. KO lines demonstrated increased sensitivity to ERK (GDC09994), while AKT (MK2206) inhibition was more effective in WT lines. Using antibody-based positron emission tomography (immunoPET) imaging, we confirmed that 89Zr-GC33 accumulated exclusively in GPC3-expression xenografts but not in GPC3-KO xenografts with high tumor uptake and tumor-to-liver signal ratio. We show that GPC3-KO liver cancer cell lines exhibit decreased tumorigenicity and altered signaling pathways, including upregulated pMAPK/ERK1/2, compared to parental lines. Furthermore, we successfully distinguished between GPC3+ and GPC3- tumors using the GPC3-targeted immunoPET imaging agent, demonstrating the potential utility of these cell lines in facilitating GPC3-selective drug development.

Pilot study of humanized glypican-3-targeted zirconium-89 immuno-positron emission tomography for hepatocellular carcinoma

Purpose

Glypican-3 (GPC3)-targeted radioisotope immuno-positron emission tomography (immunoPET) may lead to earlier and more accurate diagnosis of hepatocellular carcinoma (HCC), thus facilitating curative treatment, decreasing early recurrence, and enhancing patient survival. We previously demonstrated reliable HCC detection using a zirconium-89-labeled murine anti-GPC3 antibody (89Zr-αGPC3M) for immunoPET. This study evaluated the efficacy of the humanized antibody successor (αGPC3H) to further clinical translation of a GPC3-based theranostic for HCC.

Methods

In vitro αGPC3 binding to HepG2 cells was assessed by flow cytometry. In vivo 89Zr-αGPC3H and 89Zr-αGPC3M tumor uptake was evaluated by PET/CT and biodistribution studies in an orthotopic xenograft mouse model of HCC.

Results

αGPC3H maintained binding to GPC3 in vitro and 89Zr-αGPC3H immunoPET identified liver tumors in vivo. PET/CT and biodistribution analyses demonstrated high 89Zr-αGPC3H tumor uptake and tumor-to-liver ratios, with no difference between groups.

Conclusion

Humanized αGPC3 successfully targeted GPC3 in vitro and in vivo. 89Zr-αGPC3H immunoPET had comparable tumor detection to 89Zr-αGPC3M, with highly specific tumor uptake, making it a promising strategy to improve HCC detection.

Peptide Binder to Glypican-3 as a Theranostic Agent for Hepatocellular Carcinoma

Glypican-3 (GPC3) is a membrane-associated glycoprotein that is significantly upregulated in hepatocellular carcinomas (HCC) with minimal to no expression in normal tissues. The differential expression of GPC3 between tumor and normal tissues provides an opportunity for targeted radiopharmaceutical therapy to treat HCC, a leading cause of cancer-related deaths worldwide. Methods: DOTA-RYZ-GPC3 (RAYZ-8009) comprises a novel macrocyclic peptide binder to GPC3, a linker, and a chelator that can be complexed with different radioisotopes. The binding affinity was determined by surface plasma resonance and radioligand binding assays. Target-mediated cellular internalization was radiometrically measured at multiple time points. In vivo biodistribution, monotherapy, and combination treatments with 177Lu or 225Ac were performed on HCC xenografts. Results: RAYZ-8009 showed high binding affinity to GPC3 protein of human, mouse, canine, and cynomolgus monkey origins and no binding to other glypican family members. Potent cellular binding was confirmed in GPC3-positive HepG2 cells and was not affected by isotope switching. RAYZ-8009 achieved efficient internalization on binding to HepG2 cells. Biodistribution study of 177Lu-RAYZ-8009 showed sustained tumor uptake and fast renal clearance, with minimal or no uptake in other normal tissues. Tumor-specific uptake was also demonstrated in orthotopic HCC tumors, with no uptake in surrounding liver tissue. Therapeutically, significant and durable tumor regression and survival benefit were achieved with 177Lu- and 225Ac-labeled RAYZ-8009, as single agents and in combination with lenvatinib, in GPC3-positive HCC xenografts. Conclusion: Preclinical in vitro and in vivo data demonstrate the potential of RAYZ-8009 as a theranostic agent for the treatment of patients with GPC3-positive HCC.

A review of recent advancements in Actinium-225 labeled compounds and biomolecules for therapeutic purposes

In nuclear medicine, cancers that cannot be cured or can only be treated partially by traditional techniques like surgery or chemotherapy are killed by ionizing radiation as a form of therapeutic treatment. Actinium-225 is an alpha-emitting radionuclide that is highly encouraging as a therapeutic approach and more promising for targeted alpha therapy (TAT). Actinium-225 is the best candidate for tumor cells treatment and has physical characteristics such as high (LET) linear energy transfer (150 keV per μm), half-life (t1/2  = 9.92d), and short ranges (400-100 μm) which prevent the damage of normal healthy tissues. The introduction of various new radiopharmaceuticals and radioisotopes has significantly assisted the advancement of nuclear medicine. Ac-225 radiopharmaceuticals continuously demonstrate their potential as targeted alpha therapeutics. 225 Ac-labeled radiopharmaceuticals have confirmed their importance in medical and clinical areas by introducing [225 Ac]Ac-PSMA-617, [225 Ac]Ac-DOTATOC, [225 Ac]Ac-DOTA-substance-P, reported significantly improved response in patients with prostate cancer, neuroendocrine, and glioma, respectively. The development of these radiopharmaceuticals required a suitable buffer, incubation time, optimal pH, and reaction temperature. There is a growing need to standardize quality control (QC) testing techniques such as radiochemical purity (RCP). This review aims to summarize the development of the Ac-225 labeled compounds and biomolecules. The current state of their reported resulting clinical applications is also summarized as well.

Site-Specifically Conjugated Single-Domain Antibody Successfully Identifies Glypican-3-Expressing Liver Cancer by Immuno-PET

Primary liver cancer is the third leading cause of cancer-related deaths, and its incidence and mortality are increasing worldwide. Hepatocellular carcinoma (HCC) accounts for 80% of primary liver cancer cases. Glypican-3 (GPC3) is a heparan sulfate proteoglycan that histopathologically defines HCC and represents an attractive tumor-selective marker for radiopharmaceutical imaging and therapy for this disease. Single-domain antibodies are a promising scaffold for imaging because of their favorable pharmacokinetic properties, good tumor penetration, and renal clearance. Although conventional lysine-directed bioconjugation can be used to yield conjugates for radiolabeling full-length antibodies, this stochastic approach risks negatively affecting target binding of the smaller single-domain antibodies. To address this challenge, site-specific approaches have been explored. Here, we used conventional and sortase-based site-specific conjugation methods to engineer GPC3-specific human single-domain antibody (HN3) PET probes. Methods: Bifunctional deferoxamine (DFO) isothiocyanate was used to synthesize native HN3 (nHN3)-DFO. Site-specifically modified HN3 (ssHN3)-DFO was engineered using sortase-mediated conjugation of triglycine-DFO chelator and HN3 containing an LPETG C-terminal tag. Both conjugates were radiolabeled with 89Zr, and their binding affinity in vitro and target engagement of GPC3-positive (GPC3+) tumors in vivo were determined. Results: Both 89Zr-ssHN3 and 89Zr-nHN3 displayed nanomolar affinity for GPC3 in vitro. Biodistribution and PET/CT image analysis in mice bearing isogenic A431 and A431-GPC3+ xenografts, as well as in HepG2 liver cancer xenografts, showed that both conjugates specifically identify GPC3+ tumors. 89Zr-ssHN3 exhibited more favorable biodistribution and pharmacokinetic properties, including higher tumor uptake and lower liver accumulation. Comparative PET/CT studies on mice imaged with both 18F-FDG and 89Zr-ssHN3 showed more consistent tumor accumulation for the single-domain antibody conjugate, further establishing its potential for PET imaging. Conclusion: 89Zr-ssHN3 showed clear advantages in tumor uptake and tumor-to-liver signal ratio over the conventionally modified 89Zr-nHN3 in xenograft models. Our results establish the potential of HN3-based single-domain antibody probes for GPC3-directed PET imaging of liver cancers.

Molecular and immune landscape of hepatocellular carcinoma to guide therapeutic decision-making

Liver cancer, primarily HCC, exhibits highly heterogeneous histological and molecular aberrations across tumors and within individual tumor nodules. Such intertumor and intratumor heterogeneities may lead to diversity in the natural history of disease progression and various clinical disparities across the patients. Recently developed multimodality, single-cell, and spatial omics profiling technologies have enabled interrogation of the intertumor/intratumor heterogeneity in the cancer cells and the tumor immune microenvironment. These features may influence the natural history and efficacy of emerging therapies targeting novel molecular and immune pathways, some of which had been deemed undruggable. Thus, comprehensive characterization of the heterogeneities at various levels may facilitate the discovery of biomarkers that enable personalized and rational treatment decisions, and optimize treatment efficacy while minimizing the risk of adverse effects. Such companion biomarkers will also refine HCC treatment algorithms across disease stages for cost-effective patient management by optimizing the allocation of limited medical resources. Despite this promise, the complexity of the intertumor/intratumor heterogeneity and ever-expanding inventory of therapeutic agents and regimens have made clinical evaluation and translation of biomarkers increasingly challenging. To address this issue, novel clinical trial designs have been proposed and incorporated into recent studies. In this review, we discuss the latest findings in the molecular and immune landscape of HCC for their potential and utility as biomarkers, the framework of evaluation and clinical application of predictive/prognostic biomarkers, and ongoing biomarker-guided therapeutic clinical trials. These new developments may revolutionize patient care and substantially impact the still dismal HCC mortality.

Imaging ligands targeting glypican-3 receptor expression in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the third leading cause of cancer mortality. Early detection of HCC is important since potentially curative therapies exist in the initial stages of HCC; no curative therapies exist for late-stage HCC. However, the initial detection of HCC remains challenging due to the lack of symptoms during the early stage of the disease. Other methods of screening and detecting HCC, including blood serum tests and conventional imaging methods, remain inadequate due to genetic differences between patients and the high background activity of liver tissues. Thus, there is a need for an accurate imaging agent for the diagnosis, staging, and prognosis of HCC. Glypican-3 (GPC3) is an oncofetal receptor responsible for regulating cell division, growth, and survival. GPC3 is a clinically relevant biomarker for imaging and therapeutics, as its expression is HCC tumor-specific and absent from normal and other pathological liver tissues. The development of novel GPC3-targeting imaging agents has encompassed three classes of biomolecules: peptides, antibodies, and aptamers. These biomolecules serve as constructs for diagnostic imaging (demonstrating potential as positron emission tomography [PET], single-photon emission tomography [SPECT], and optical imaging agents) and HCC treatment delivery. More than 20 unique ligands have been identified in the literature as showing specificity for the GPC3 receptor. Although several ligands are currently under clinical investigation as therapies for HCC, clinical translation of GPC3-targeting ligands as imaging agents is lacking. This review highlights the current landscape of ligands targeting GPC3 and describes their promising possibilities as imaging agents for HCC.

Radiopharmaceuticals for PET and SPECT Imaging: A Literature Review over the Last Decade

Positron emission tomography (PET) uses radioactive tracers and enables the functional imaging of several metabolic processes, blood flow measurements, regional chemical composition, and/or chemical absorption. Depending on the targeted processes within the living organism, different tracers are used for various medical conditions, such as cancer, particular brain pathologies, cardiac events, and bone lesions, where the most commonly used tracers are radiolabeled with 18F (e.g., [18F]-FDG and NA [18F]). Oxygen-15 isotope is mostly involved in blood flow measurements, whereas a wide array of 11C-based compounds have also been developed for neuronal disorders according to the affected neuroreceptors, prostate cancer, and lung carcinomas. In contrast, the single-photon emission computed tomography (SPECT) technique uses gamma-emitting radioisotopes and can be used to diagnose strokes, seizures, bone illnesses, and infections by gauging the blood flow and radio distribution within tissues and organs. The radioisotopes typically used in SPECT imaging are iodine-123, technetium-99m, xenon-133, thallium-201, and indium-111. This systematic review article aims to clarify and disseminate the available scientific literature focused on PET/SPECT radiotracers and to provide an overview of the conducted research within the past decade, with an additional focus on the novel radiopharmaceuticals developed for medical imaging.

Theragnostics in primary and secondary liver tumors: the need for a personalized approach

Primary and secondary hepatic tumors have a dramatic impact in oncology. Despite many advances in diagnosis and therapy, the management of hepatic malignancies is still challenging, ranging from various loco-regional approaches to system therapies. In this scenario, theragnostic approaches, based on the administration of a radiopharmaceuticals' pair, the first labeled with a radionuclide suitable for the diagnostic phase and the second one bound to radionuclide emitting particles for therapy, is gaining more and more importance. Selective internal radiation therapy (SIRT) with microspheres labeled with ⁹⁰Y or ¹⁶⁶Ho is widely used as a loco-regional treatment for primary and secondary hepatic tumors. While ¹⁶⁶Ho presents both gamma and beta emission and can be therefore considered a real "theragnostic" agent, for ⁹⁰Y-microspheres theragnostic approach is realized at the diagnostic phase through the utilization of macroaggregates of human albumin, labeled with ^99mTc as "biosimilar" agent respect to microspheres. The aim of the present review was to cover theragnostic applications of ⁹⁰Y/¹⁶⁶Ho-labeled microspheres in clinical practice. Furthermore, we report the preliminary data concerning the potential role of some emerging theragnostic biomarkers for hepatocellular carcinoma, such as glypican-3 (GPC3) and prostate specific membrane antigen (PSMA).

Radiomics, Radiogenomics, and Next-Generation Molecular Imaging to Augment Diagnosis of Hepatocellular Carcinoma

Ultrasound, computed tomography, magnetic resonance imaging, and [F]F-fluorodeoxyglucose positron emission tomography are invaluable in the clinical evaluation of human cancers. Radiomics and radiogenomics tools may allow clinicians to standardize interpretation of these conventional imaging modalities, while better linking radiographic hallmarks to disease biology and prognosis. These advances, coupled with next-generation positron emission tomography imaging tracers capable of providing biologically relevant tumor information, may further expand the tools available in our armamentarium against human cancers. We present current imaging methods and explore emerging research that may improve diagnosis and monitoring of local, oligometastatic, and disseminated cancers exhibiting heterogeneous uptake of [F]F-fluorodeoxyglucose, using hepatocellular carcinoma as an example.

Radiochemistry, Production Processes, Labeling Methods, and ImmunoPET Imaging Pharmaceuticals of Iodine-124

Target-specific biomolecules, monoclonal antibodies (mAb), proteins, and protein fragments are known to have high specificity and affinity for receptors associated with tumors and other pathological conditions. However, the large biomolecules have relatively intermediate to long circulation half-lives (>day) and tumor localization times. Combining superior target specificity of mAbs and high sensitivity and resolution of the PET (Positron Emission Tomography) imaging technique has created a paradigm-shifting imaging modality, ImmunoPET. In addition to metallic PET radionuclides, 124I is an attractive radionuclide for radiolabeling of mAbs as potential immunoPET imaging pharmaceuticals due to its physical properties (decay characteristics and half-life), easy and routine production by cyclotrons, and well-established methodologies for radioiodination. The objective of this report is to provide a comprehensive review of the physical properties of iodine and iodine radionuclides, production processes of 124I, various 124I-labeling methodologies for large biomolecules, mAbs, and the development of 124I-labeled immunoPET imaging pharmaceuticals for various cancer targets in preclinical and clinical environments. A summary of several production processes, including 123Te(d,n)124I, 124Te(d,2n)124I, 121Sb(α,n)124I, 123Sb(α,3n)124I, 123Sb(3He,2n)124I, natSb(α, xn)124I, natSb(3He,n)124I reactions, a detailed overview of the 124Te(p,n)124I reaction (including target selection, preparation, processing, and recovery of 124I), and a fully automated process that can be scaled up for GMP (Good Manufacturing Practices) production of large quantities of 124I is provided. Direct, using inorganic and organic oxidizing agents and enzyme catalysis, and indirect, using prosthetic groups, 124I-labeling techniques have been discussed. Significant research has been conducted, in more than the last two decades, in the development of 124I-labeled immunoPET imaging pharmaceuticals for target-specific cancer detection. Details of preclinical and clinical evaluations of the potential 124I-labeled immunoPET imaging pharmaceuticals are described here.

Glypican-3-Targeted Alpha Particle Therapy for Hepatocellular Carcinoma

Glypican-3 (GPC3) is expressed in 75% of hepatocellular carcinoma (HCC), but not normal liver, making it a promising HCC therapeutic target. GC33 is a full-length humanized monoclonal IgG1 specific to GPC3 that can localize to HCC in vivo. GC33 alone failed to demonstrate therapeutic efficacy when evaluated in patients with HCC; however, we posit that cytotoxic functionalization of the antibody with therapeutic radionuclides, may be warranted. Alpha particles, which are emitted by radioisotopes such as Actinium-225 (Ac-225) exhibit high linear energy transfer and short pathlength that, when targeted to tumors, can effectively kill cancer and limit bystander cytotoxicity. Macropa, an 18-member heterocyclic crown ether, can stably chelate Ac-225 at room temperature. Here, we synthesized and evaluated the efficacy of [²²⁵Ac]Ac–Macropa–GC33 in mice engrafted with the GPC3-expressing human liver cancer cell line HepG2. Following a pilot dose-finding study, mice (n = 10 per group) were treated with (1) PBS, (2) mass-equivalent unmodified GC33, (3) 18.5 kBq [²²⁵Ac]Ac–Macropa–IgG1 (isotype control), (4) 9.25 kBq [²²⁵Ac]Ac–Macropa–GC33, and (5) 18.5 kBq [²²⁵Ac]Ac–Macropa–GC33. While significant toxicity was observed in all groups receiving radioconjugates, the 9.25 kBq [²²⁵Ac]Ac–Macropa–GC33 group demonstrated a modest survival advantage compared to PBS (p = 0.0012) and 18.5 kBq [²²⁵Ac]Ac–IgG1 (p = 0.0412). Hematological analysis demonstrated a marked, rapid reduction in white blood cells in all radioconjugate-treated groups compared to the PBS and unmodified GC33 control groups. Our studies highlight a significant disadvantage of using directly-labeled biomolecules with long blood circulation times for TAT. Strategies to mitigate such treatment toxicity include dose fractionation, pretargeting, and using smaller targeting ligands.

Insight into the Development of PET Radiopharmaceuticals for Oncology

While the development of positron emission tomography (PET) radiopharmaceuticals closely follows that of traditional drug development, there are several key considerations in the chemical and radiochemical synthesis, preclinical assessment, and clinical translation of PET radiotracers. As such, we outline the fundamentals of radiotracer design, with respect to the selection of an appropriate pharmacophore. These concepts will be reinforced by exemplary cases of PET radiotracer development, both with respect to their preclinical and clinical evaluation. We also provide a guideline for the proper selection of a radionuclide and the appropriate labeling strategy to access a tracer with optimal imaging qualities. Finally, we summarize the methodology of their evaluation in in vitro and animal models and the road to clinical translation. This review is intended to be a primer for newcomers to the field and give insight into the workflow of developing radiopharmaceuticals.

ImmunoPET: Concept, Design, and Applications

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

Glypican 3-Targeted Therapy in Hepatocellular Carcinoma

Glypican-3 (GPC3) is an oncofetal glycoprotein attached to the cell membrane by a glycophosphatidylinositol anchor. GPC3 is overexpressed in some kinds of tumors, particularly hepatocellular carcinoma (HCC). The prognostic significance of serum GPC3 levels and GPC3 immunoreactivity in tumor cells has been defined in patients with HCC. In addition to its usefulness as a biomarker, GPC3 has attracted attention as a novel therapeutic target molecule, and clinical trials targeting GPC3 are in progress. The major mechanism of anti-GPC3 antibody (GPC3Ab) against cancer cells is antibody-dependent cellular cytotoxicity and/or complement-dependent cytotoxicity. Since GPC3Ab is associated with immune responses, a combination of protocols with immune checkpoint inhibitors has also been investigated. Moreover, some innovative approaches for GPC3-targeting therapy have emerged in recent years. This review introduces the results of recent clinical trials targeting GPC3 in HCC and summarizes the latest knowledge regarding the role of GPC3 in HCC progression and clinical application targeting GPC3.