How Scientists Are Developing CLDN18.2-Targeting Probes to Transform Cancer Imaging
For the first patient, treatment follows a standard protocol—chemotherapy that brings difficult side effects with limited effectiveness.
For the second, doctors administer a targeted molecular therapy specifically designed for her cancer type, leading to better outcomes with fewer side effects.
This isn't a distant future scenario—it's the promise of precision medicine enabled by discoveries like CLDN18.2, a protein that has emerged as a crucial biomarker in gastric and other cancers 7 .
The challenge? Current detection methods require invasive tissue biopsies that provide limited information and cannot capture the full complexity of a patient's cancer.
To appreciate the significance of this research, we must first understand the target. CLDN18.2 belongs to the claudin family of proteins, which form tight junctions between cells—acting as biological gates that control what passes through cellular barriers 7 .
| Feature | Description | Clinical Significance |
|---|---|---|
| Normal Expression | Restricted to stomach lining cells | Limited expression reduces potential side effects of targeted therapies |
| Cancer Expression | Highly expressed in gastric, pancreatic, and other cancers | Makes it an ideal "marker" for cancerous cells |
| Accessibility | Becomes exposed on cell surface during cancer transformation | Allows therapies and imaging agents to reach it easily |
| Prevalence | Found in approximately 80% of gastric cancers | Potential benefit for majority of gastric cancer patients 9 |
Under normal conditions, CLDN18.2 remains tucked away between stomach cells. However, during cancer transformation, this protein becomes exposed on the surface of tumor cells, making it an ideal target for therapies and imaging agents 7 . This discovery has been so significant that the FDA recently approved zolbetuximab, the first CLDN18.2-targeted drug, for treating gastric and gastroesophageal junction cancers 9 .
Prevalence of CLDN18.2 expression across different cancer types 7
Traditional cancer imaging like CT and MRI scans primarily show anatomical structures—the size and shape of tumors. While valuable, these techniques reveal little about the biological characteristics of cancer cells. This limitation is particularly significant for targeted therapies, which work on specific molecular pathways rather than simply attacking rapidly dividing cells 6 .
Molecular imaging represents a paradigm shift. Instead of asking "How big is the tumor?", it enables us to ask "What unique molecules does this tumor possess?" and "How is it behaving at the cellular level?" 4
| Technique | How It Works | Advantages | Limitations |
|---|---|---|---|
| PET/CT | Uses radioactive tracers to track biological processes | High sensitivity, provides quantitative data | Requires radioactive materials, specialized equipment |
| Optical Imaging | Uses light-emitting probes for detection | Safe, can be used during surgery | Limited penetration depth |
| MRI | Uses magnetic fields and radio waves | Excellent soft tissue detail, no radiation | Lower sensitivity for molecular targets |
| Ultrasound | Uses sound waves | Real-time imaging, portable, inexpensive | Limited molecular imaging capabilities |
Among these techniques, PET/CT has emerged as particularly promising for CLDN18.2 detection because it combines the high sensitivity of radioactive tracer detection with precise anatomical localization 1 . The development of CLDN18.2-specific probes for PET/CT could allow clinicians to noninvasively assess CLDN18.2 expression across all tumor sites in the body, addressing a critical limitation of conventional biopsies 7 .
The central challenge in molecular imaging lies in creating agents that can specifically seek out and bind to targets like CLDN18.2. While antibodies have shown promise, they have limitations—particularly their large size, which means they take longer to reach tumors and clear from the body slowly.
This is where peptides enter the picture. These short chains of amino acids offer the perfect balance of specificity, small size, and customizability, making them ideal candidates for molecular imaging probes 1 .
In a groundbreaking 2023 study, researchers employed an ingenious method called phage display technology to identify CLDN18.2-specific peptides 1 . Their step-by-step approach exemplifies the creativity and precision of modern biological research:
Scientists began with a staggering collection of 100 billion different 7-amino acid peptides, each displayed on the surface of a bacteriophage (a virus that infects bacteria).
This diverse library was first exposed to cells expressing CLDN18.1 (the lung-specific cousin of CLDN18.2) to remove any peptides that might bind to similar but undesired targets.
The remaining phages were then introduced to cells expressing CLDN18.2, allowing the specific binders to attach.
The bound phages were collected, amplified, and put through additional rounds of this selection process to enrich the pool for the strongest and most specific binders.
After four rounds of screening, the researchers selected 54 monoclonal clones for further evaluation. Through DNA sequencing and binding assays, they identified four distinct peptide sequences with specificity for CLDN18.2 1 .
Among these, one standout performer emerged: the T37 peptide.
| Peptide Name | Binding Specificity | Selected for Further Study |
|---|---|---|
| T37 | CLDN18.2-specific | Yes (primary candidate) |
| T25 | CLDN18.2-specific | No |
| T9 | CLDN18.2-specific | No |
| T51 | CLDN18.2-specific | No |
The development of CLDN18.2-targeting imaging probes relies on a sophisticated array of research tools and techniques. Here are some key components of the CLDN18.2 researcher's toolkit:
| Tool Category | Specific Examples | Purpose in Research |
|---|---|---|
| Cell Lines | 293T-CLDN18.2, BGC823-CLDN18.2 | Engineered to express CLDN18.2 for binding experiments |
| Detection Antibodies | CLDN18 (43-14A) Rabbit Monoclonal 2 | Gold standard for detecting CLDN18.2 protein in tissues |
| IHC Kits | IHCeasy® Claudin 18 Ready-To-Use IHC Kit 3 | Complete solutions for detecting CLDN18.2 in tissue samples |
| Binding Assays | Flow cytometry, cell ELISA | Measure how strongly and specifically peptides bind to target |
| Radiolabeling | ⁶⁸Ga-DOTA conjugation | Creates radioactive versions of peptides for PET imaging |
| Animal Models | Mouse xenograft models | Test imaging probes in living organisms with CLDN18.2+ tumors |
These tools collectively enable the meticulous process of probe development, from initial screening through preclinical validation.
The successful development of CLDN18.2-specific imaging probes opens exciting possibilities for clinical cancer care. In the near future, we might witness:
A simple PET/CT scan with a CLDN18.2-targeted probe could identify patients most likely to benefit from CLDN18.2-targeted therapies like zolbetuximab 7 .
Doctors could use repeat scans to assess whether therapies are effectively engaging their targets, allowing rapid adjustment of treatment plans.
Since CLDN18.2 expression can vary within tumors 2 , whole-body imaging could identify regions with different expression patterns.
As research reveals CLDN18.2 expression in additional cancer types, these imaging approaches could help identify new patient populations for targeted therapies.
Nevertheless, the development of CLDN18.2-specific peptides for molecular imaging represents a remarkable convergence of molecular biology, imaging physics, and clinical oncology.
As this field advances, we move closer to a future where cancer imaging reveals not just where tumors are, but what makes them vulnerable—transforming our approach from anatomical warfare to precise molecular intervention. The ability to see the invisible biological details of cancer could ultimately make all the difference for patients facing this challenging disease.