Targeting Claudin 18.2 Using a Highly Specific Antibody Enables Cancer Diagnosis and Guided Surgery

Exploring various carbon nanomaterials-based electrodes modified with polymelamine for the reagentless electrochemical immunosensing of Claudin18.2

Claudin18.2 (CLDN18.2) is a tight junction protein often overexpressed in various solid tumors, including gastrointestinal and esophageal cancers, serving as a promising target and potential biomarker for tumor diagnosis, treatment assessment, and prognosis. Despite its significance, no biosensor has been reported to date for the detection of CLDN18.2. Here, we present the inaugural immunosensor for CLDN18.2. In this study, an amine-rich conducting polymer of polymelamine (PM) was electrografted onto different carbon nanomaterial-based screen-printed electrodes (SPEs), including carbon (C), graphene (Gr), graphene oxide (GO), carbon nanotube (CNT), and carbon nanofiber (CNF) via cyclic voltammetry. A comparative study was performed to explore the best material for the preparation of the PM-modified electrodes to be used as in-situ redox substrate for the immunosensor fabrication. The surface chemistry and structural features of pristine and PM-deposited electrodes were analyzed using Raman and scanning electron microscopy (SEM) techniques. Our results showed that the PM deposited on Gr and CNT/SPEs exhibited the most significant and stable redox behavior in PBS buffer. The terminal amine moieties on the PM-modified electrode surfaces were utilized for immobilizing anti-CLDN18.2 monoclonal antibodies via N-ethyl-N'-(3-(dimethylamino)propyl)carbodiimide/N-hydroxysuccinimide chemistry to construct the electrochemical immunosensor platform. Differential pulse voltammetry-based immunosensing of CLDN18.2 protein on BSA/anti-CLDN18.2/PM-Gr/SPE and BSA/anti-CLDN18.2/PM-CNT/SPE exhibited excellent selectivity against other proteins such as CD1, PDCD1, and ErBb2. The limits of detection of these two immunosensor platforms were calculated to be 7.9 pg/mL and 0.104 ng/mL for the CNT and Gr immunosensors, respectively. This study demonstrated that the PM-modified Gr and CNT electrodes offer promising platforms not only for the reagentless signaling but also for covalent immobilization of biomolecules. Moreover, these platforms offer excellent sensitivity and selectivity for the detection of CLDN18.2 due to its enhanced stable redox activity. The immunosensor demonstrated promising results for the sensitive detection of CLDN18.2 in biological samples, addressing the critical need for early gastric cancer diagnosis.

Claudin18.2-Targeted SPECT/CT Imaging for Gastric Cancer: Preclinical Evaluation and Clinical Translation of the 99mTc-Labeled Nanobody (PHG102) Radiotracer

Claudin18.2 (CLDN18.2) has emerged as a significant target in the treatment of advanced gastric cancer. The screening of patients positive for CLDN18.2 is crucial for the effective application of targeted therapies specific to CLND18.2. In this study, we developed a novel nanobody-based probe, [99mTc]Tc-PHG102, for use in nuclear medicine. We analyzed its radiochemical yield and stability to ensure accurate probe characterization. Additionally, we assessed the probe's affinity and specificity toward the CLDN18.2 target and evaluated its efficacy in the BGC82318.2 xenograft model for SPECT/CT imaging of gastric cancer. The binding of [99mTc]Tc-PHG102 to HEK-293T18.2 and BGC82318.2 cells was notably higher than its binding to HEK-293T18.1, HEK-293T, and BGC823 cells, with bound values of 12.87 ± 1.46%, 6.16 ± 0.34%, 1.25 ± 0.22%, 1.14 ± 0.26%, and 1.32 ± 0.07% AD, respectively. The binding ability of [99mTc]Tc-PHG102 was significantly different between CLDN18.2-positive and negative cells (P < 0.001). Imaging results demonstrated a time-dependent tumor accumulation of the radiotracer. Notably, at 0.5 h postinjection, rapid accumulation was observed with an average tumor uptake of 4.63 ± 0.81% ID/cc (n = 3), resulting in clear tumor visualization. By 1 h postinjection, as [99mTc]Tc-PHG102 was rapidly metabolized, a decrease in uptake by other organs was noted. Preliminary clinical imaging trials further confirmed the safety and effectiveness of the probe, indicating specificity for lesions expressing CLDN18.2 in gastric cancer and favorable in vivo metabolic properties. In conclusion, the nanobody-based probe [99mTc]Tc-PHG102 proves to be a safe and effective tool for detecting CLDN18.2 expression levels in gastric cancer tumors and for screening CLDN18.2-positive patients.

Preparation of Radiolabeled Zolbetuximab Targeting CLDN18.2 and Its Preliminary Evaluation for Potential Clinical Applications

Claudin18.2 (CLDN18.2), due to its high expression in various gastric cancer tissues, is considered an optimal target for antitumor drug molecules. In this study, we obtained the labeled compounds of [125I]I-zolbetuximab using the Iodogen method. Under the optimum labeling conditions, the molar activity of [125I]I-zolbetuximab was 1.75 × 102 GBq/μmol, and the labeling efficiency was more than 99%. The labeled compounds exhibited excellent in vitro stability in both phosphate buffer saline (PBS, pH = 7.4) and fetal bovine serum systems (FBS) (radiochemical purity >90% at 72 h). The uptake percentage of [125I]I-zolbetuximab in MKN45-CLDN18.2 cells is 24.69 ± 0.84% after 6 h. The saturation binding assay and specificity assay further demonstrated the high specificity of [125I]I-zolbetuximab for CLDN18.2. The long retention at the tumor site and rapid metabolic clearance at other organ sites of [125I]I-zolbetuximab were observed in small-animal SPECT-CT imaging. The same trend was also observed in the biodistribution study. Due to the excellent targeting ability of zolbetuximab for CLDN18.2, [125I]I-zolbetuximab exhibits strong specific binding and retention with cells and tumors highly expressing CLDN18.2. However, the balance between mAb's longer cycle time in vivo and targeting binding and retention ability should be intensively considered for using this kind of radiopharmaceutical in the diagnosis and treatment of CLDN18.2-positive gastric cancer.

Molecular SPECT/CT Profiling of Claudin18.2 Expression In Vivo: Implication for Patients with Gastric Cancer

Zolbetuximab (IMAB362), a monoclonal antibody targeting Claudin18.2 (CLDN 18.2), demonstrates a significant clinical benefit in patients with advanced gastroesophageal cancers. The noninvasive assessment of CLDN18.2 expression through molecular imaging offers a potential avenue for expedited monitoring and the stratification of patients into risk groups. This study elucidates that CLDN18.2 is expressed at a noteworthy frequency in primary gastric cancers and their metastases. The iodogen method was employed to label IMAB362 with 123I/131I. The results demonstrated the efficient and reproducible synthesis of 123I-IMAB362, with a specific binding affinity to CLDN18.2. Immuno-single-photon emission computed tomography (SPECT) imaging revealed the rapid accumulation of 123I-IMAB362 in gastric cancer xenografts at 12 h, remaining stable for 3 days in patient-derived tumor xenograft models. Additionally, tracer uptake of 123I-IMAB362 in MKN45 cells surpassed that in MKN28 cells at each time point, with tumor uptake correlating significantly with CLDN18.2 expression levels. Positron emission tomography/computed tomography imaging indicated that tumor uptake of 18F-FDG and the functional/viable tumor volume in the 131I-IMAB362 group were significantly lower than those in the 123I-IMAB362 group on day 7. In conclusion, 123I-IMAB362 immuno-SPECT imaging offers an effective method for direct, noninvasive, and whole-body quantitative assessment of tumor CLDN18.2 expression in vivo. This approach holds promise for accelerating the monitoring and stratification of patients with gastric cancer.

Progress of Clinical Studies Targeting Claudin18.2 for the Treatment of Gastric Cancer

Claudin18.2 is a tight junction protein, highly selective, generally expressed only in normal gastric mucosal epithelial cells, which can effectively maintain the polarity of epithelial and endothelial cells, thus effectively regulating the permeability and conductance of the paracellular pathway. Abnormal expression of Claudin18.2 can occur in various primary malignant tumors, especially gastrointestinal tumors, and even in metastatic foci. It regulates its expression by activating the aPKC/MAPK/AP-1 pathway, and therefore, the Claudin18.2 protein is a pan-cancer target expressed in primary and metastatic lesions in human cancer types. Zolbetuximab (IMAB362), an antibody specific for Claudin18.2, has been successfully tested in a phase III clinical trial, and the results of the study showed that combining Zolbetuximab with chemotherapy notably extends patients' survival and is expected to be a potential first-line treatment for patients with Claudin18.2(+)/HER-2(-) gastric cancer. Here, we systematically describe the biological properties and oncogenic effects of Claudin18.2, centering on its clinical-pathological aspects and the progress of drug studies in gastric cancer, which can help to further explore its clinical value.

Synthesis, preclinical evaluation and pilot clinical translation of [68Ga]Ga-PMD22, a novel nanobody PET probe targeting CLDN18.2 of gastrointestinal cancer

PURPOSE

Claudin18.2 (CLDN18.2) is a novel target for diagnosis and therapy of gastrointestinal cancer. This study aimed to evaluate the safety and feasibility of a novel CLDN18.2-targeted nanobody, PMD22, labeled with gallium-68 ([68Ga]Ga), for detecting CLDN18.2 expression in patients with gastrointestinal cancer using PET/CT imaging.

METHODS

[68Ga]Ga-PMD22 was synthesized based on the nanobody, and its cell binding properties were assayed. Preclinical pharmacokinetics were determined in CLDN18.2-positive xenografts using microPET/CT. Effective dosimetry of [68Ga]Ga-PMD22 was evaluated in 5 gastrointestinal cancer patients, and PET/CT imaging of [68Ga]Ga-PMD22 and [18F]FDG were performed head-to-head in 16 gastrointestinal cancer patients. Pathological tissues were obtained for CLDN18.2 immunohistochemical (IHC) staining and comparative analysis with PET/CT findings.

RESULTS

Cell binding assay showed that [68Ga]Ga-PMD22 had a higher binding ability to AGSCLDN18.2 and BGC823CLDN18.2 cells than to AGS and BGC823 cells (p < 0.001). MicroPET/CT images showed that [68Ga]Ga-PMD22 rapidly accumulated in AGSCLDN18.2 and BGC823CLDN18.2 tumors, and high contrast tumor to background imaging was clearly observed. In the pilot study, the effective dose of [68Ga]Ga-PMD22 was 1.68E-02 ± 1.45E-02 mSv/MBq, and the CLDN18.2 IHC staining result was highly correlated with the SUVmax/BKGstomach of [68Ga]Ga-PMD22 (rs = 0.848, p < 0.01).

CONCLUSION

A novel [68Ga]Ga-labeled nanobody probe targeting CLDN18.2, [68Ga]Ga-PMD22, was established and preliminarily proved to be safe and effective in revealing CLDN18.2-positive gastrointestinal cancer, providing a basis for the clinical translation of the agent.

CLINICAL TRIAL REGISTRATION

This study was registered on the ClinicalTrials.gov (NCT05937919).

Recent Advances in Radiotracers Targeting Novel Cancer-Specific Biomarkers in China: A Brief Overview

Radiopharmaceuticals play a critical role in nuclear medicine, providing novel tools for specifically delivering radioisotopes for the diagnosis and treatment of cancers. As the starting point for developing radiopharmaceuticals, cancer-specific biomarkers are important and receive worldwide attention. This field in China is currently experiencing a rapid expansion, with multiple radiotracers targeting novel targets being developed and translated into clinical studies. This review provides a brief overview of the exploration of novel imaging targets, preclinical evaluation of their targeting ligands, and translational research in China from 2020 to 2023, for detecting cancer, guiding targeted therapy, and visualizing the immune microenvironment. We believe that China will play an even more important role in the development of nuclear medicine in the world in the future.

Exploration of radionuclide labeling of a novel scFv-Fc fusion protein targeting CLDN18.2 for tumor diagnosis and treatment

PURPOSE

Claudin 18.2 (CLDN18.2), due to its highly selective expression in tumor cells, has made breakthrough progress in clinical research and is expected to be integrated into routine tumor diagnosis and treatment.

METHODS

In this research, we obtained an scFv-Fc fusion protein (SF106) targeting CLDN18.2 through hybridoma technology. The scFv-Fc fusion protein was labeled with radioactive isotopes (124I and 177Lu) to generate the radio-probes. The targeting and specificity of the radio-probes were tested in cellular models, and its diagnostic and therapeutic potential was further evaluated in tumor-bearing models.

RESULTS

The molecular probes [124I]I-SF106 and [177Lu]Lu-DOTA-SF106 possess high radiochemical purity (RCP, 98.18 ± 0.93 % and 97.05 ± 1.1 %) and exhibit good stability in phosphate buffer saline and 5 % human serum albumin (92.44 ± 4.68 % and 91.03 ± 2.42 % at 120 h). [124I]I-SF106 uptake in cells expressing CLDN18.2 was well targeted and specific, and the dissociation constant was 17.74 nM [124I]I-SF106 micro-PET imaging showed that the maximum standardized uptake value (SUVmax) was significantly higher than CLDN18.2-negative tumors (1.83 ± 0.02 vs. 1.23 ± 0.04, p < 0.001). The maximum uptake was attained in tumors expressing CLDN18.2 at 48 h after injection. [124I]I-SF106 and [177Lu]Lu-DOTA-SF106 dosimetric study showed that the effective dose in humans complies with the medical safety standards required for their clinical application. The results of treatment experiments showed that 3 MBq of [177Lu]Lu-DOTA-SF106 in CLDN18.2-expressing tumor-bearing mice could significantly inhibit tumor growth.

CONCLUSION

These results indicate that radionuclide-labeled scFv-Fc molecular probes ([124I]I-SF106 and [177Lu]Lu-DOTA-SF106) provide a new possibility for the diagnosis and treatment of CLDN18.2-positive cancer patients in clinical practice.

An iodine‑labelled Antibody-drug conjugate PET probe for noninvasive monitoring of Nectin-4 expression in urothelial carcinoma

BACKGROUND AND PURPOSE

Some kinds of antibody-drug conjugate (ADC) with high affinity to Nectin-4 have demonstrated breakthrough progress in the third-line setting for bladder cancer. However, many patients are still difficult to benefit from treatment based on the heterogeneity of tumour. As the most advanced auxiliary treatment technology, treatment visualization can most intuitively predict the effectiveness of drug treatment, and timely detect the occurrence of drug resistance. Among them, nuclear medicine molecular probes play an important role in this field.

METHODS

124/125I-EV was prepared by labelling Enfortumad Vedetin (EV), an ADC drugs widely used in clinic targeted Nectin-4, with Na124/125I using N-bromine succinimide as oxidant. The radiochemical purity was analyzed via radio-TLC and bioactivity was measured by enzyme-linked immunosorbent assay. Cell uptake assay and small-animal PET imaging were performed to verified the specificity and targeting.

KEY RESULTS

124/125I-EV was prepared with high labeling yield and radiochemical purity. ELISA assays demonstrated that 124I-EV maintained the same high bioactivity as EV with significantly higher uptake in SW780 cells (Nectin-4 positive, 4.05 ± 0.32 %IA/5 × 105 cells at 8 h) than that in T24 cells (Nectin-4 negative, 1.34 ± 0.18 %IA/5 × 105 cells, p < 0.001). In PET imaging, 124I-EV had a significantly higher accumulation in SW780 tumour than that in T24 tumour and the uptake in SW780 tumour could be specifically blocked when co-injected with cold EV. The signal-to-noise ratio at the tumour site gradually increased with time, and peaked at 72 h.

CONCLUSION AND IMPLICATIONS

124I-EV was successfully prepared with high specificity and binding affinity of Nectin-4. This radioactive probe completely simulates the internal circulation of ADC drugs and tumour uptake and retention, which will greatly improve the clinical application of ADC therapy.

Progress in research of tumor biomarkers and molecular imaging probes for gastric cancer

Gastric cancer is a malignant tumor still associated with high morbidity and mortality worldwide. Its onset is relatively insidious, and when detected, it is already at an advanced stage, lacks effective individualized treatments, and has a poor prognosis. If gastric cancer can be diagnosed at an early stage, the survival rate of patients can be greatly improved. However, traditional imaging modalities lack specificity and sensitivity. In recent years, molecular imaging technology is booming, which can non-invasively and dynamically monitor gastric cancer at the cellular and molecular levels, and provide more reference information for clinical selection of treatment options and assessment of efficacy and prognosis. This article reviews the biomarkers of gastric cancer and molecular probes in various imaging modalities.

Targeting CLDN18.2 in cancers of the gastrointestinal tract: New drugs and new indications

Cancers of the gastrointestinal (GI) tract greatly contribute to the global cancer burden and cancer-related death. Claudin-18.2(CLDN18.2), a transmembrane protein, is a major component of tight junctions and plays an important role in the maintenance of barrier function. Its characteristic widespread expression in tumour tissues and its exposed extracellular loops make it an ideal target for researchers to develop targeted strategies and immunotherapies for cancers of the GI tract. In the present review, we focus on the expression pattern of CLDN18.2 and its clinical significance in GI cancer. We also discuss the tumour-promoting and/or tumour-inhibiting functions of CLDN18.2, the mechanisms regulating its expression, and the current progress regarding the development of drugs targeting CLDN18.2 in clinical research.

Development of a CLDN18.2-targeting Immuno-PET Probe for Non-invasive Imaging in Gastrointestinal Tumors

Claudin18.2 (CLDN18.2) is a tight junction protein that is overexpressed in a variety of solid tumors such as gastrointestinal cancer and oesophageal cancer. It has been identified as a promising target and a potential biomarker to diagnose tumor, evaluate efficacy, and determine patient prognosis. TST001 is a recombinant humanized CLDN18.2 antibody that selectively binds to the extracellular loop of human Claudin18.2. In this study, we constructed a solid target radionuclide zirconium-89 (⁸⁹Zr) labled-TST001 to detect the expression of in the human stomach cancer BGC823^CLDN18.2 cell lines. The [⁸⁹Zr]Zr-desferrioxamine (DFO)-TST001 showed high radiochemical purity (RCP, >99%) and specific activity (24.15 ± 1.34 GBq/μmol), and was stable in 5% human serum albumin, and phosphate buffer saline (>85% RCP at 96 h). The EC₅₀ values of TST001 and DFO-TST001 were as high as 0.413 ± 0.055 and 0.361 ± 0.058 nM (P > 0.05), respectively. The radiotracer had a significantly higher average standard uptake values in CLDN18.2-positive tumors than in CLDN18.2-negative tumors (1.11 ± 0.02 vs. 0.49 ± 0.03, P = 0.0016) 2 days post injection (p.i.). BGC823^CLDN18.2 mice models showed high tumor/muscle ratios 96 h p.i. with [⁸⁹Zr]Zr-DFO-TST001 was much higher than those of the other imaging groups. Immunohistochemistry results showed that BGC823^CLDN18.2 tumors were highly positive (+++) for CLDN18.2, while those in the BGC823 group did not express CLDN18.2 (-). The results of ex vivo biodistribution studies showed that there was a higher distribution in the BGC823^CLDN18.2 tumor bearing mice (2.05 ± 0.16 %ID/g) than BGC823 mice (0.69 ± 0.02 %ID/g) and blocking group (0.72 ± 0.02 %ID/g). A dosimetry estimation study showed that the effective dose of [⁸⁹Zr]Zr-DFO-TST001 was 0.0705 mSv/MBq, which is within the range of acceptable doses for nuclear medicine research. Taken together, these results suggest that Good Manufacturing Practices produced by this immuno-positron emission tomography probe can detect CLDN18.2-overexpressing tumors.