Near-Infrared Fluorescence Imaging Contrast Agents for Clinical Research: Limitations and Alternatives ()
1. Introduction
Near-infrared fluorescence imaging is a technique that will establish itself in the short term in clinical practice at the international level because it is recognized for its potential to improve the performance of surgical interventions, its investment and operating costs moderate and its portability. Researchers continue to explore new applications for NIR imaging, whether in the field of neuroimaging, image-guided therapy, or other emerging areas. It is today a strategy aimed at reducing geographic inequalities in the face of cancer. For all these reasons, translational and clinical research work in fluorescence imaging arouses great interest for the development of new diagnostic and therapeutic strategies. It is in this sense that NIR-specific nanoparticles and contrast agents are being developed to target specific biomarkers, thereby improving the sensitivity and specificity of imaging.
However, the limited number of contrast agents authorized for use in humans is a major constraint. Hence the interest in proposing alternatives and strategies to overcome these difficulties.
2. Context
Although the technology is now mature, there is currently the problem of the availability of contrast agents to be injected intravenously. Only Indocyanine Green (ICG) [1] and Methylene Blue [2] currently have marketing authorization in most countries as illustrated in Figure 1 for the detection of the sentinel lymph node in breast cancer by fluorescence imaging using ICG. These are useful tracers for lymphatic and vascular identification but they do not allow specific molecular imaging which constitutes the main interest in oncology of this modality. However, near-infrared wavelengths allow better penetration through biological tissues, reducing light scattering and providing better depth resolution. Likewise, biological tissues absorb less light in the NIR range, thereby reducing unwanted auto-fluorescence.
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Figure 1. Fluorescence-guided SLNB Using Indocyanine Green. [5]
Currently, numerous multicenter clinical research studies are currently underway with some molecular probes manufactured in accordance with the principles and guidelines to be respected for medicinal products for human use [3] [4] .
3. Alternative and Methodological Approach
They consist of coupling a fluorescent marker in the form of an NHS derivative, such as IR DYE 800 CW [6] manufactured in compliance with GMPs, with therapeutic monoclonal antibodies having marketing authorization for molecular imaging [7] .
The marking is particularly simple since it involves, on an aliquot of the antibody and under sterile conditions, deprotonating the NH2 functions of the antibody by adding NaHCO3 QSP pH 8.6 to incubate for 12 hours at +4˚C with NHS fluorochrome in limiting quantities in Figure 2.
For a given antibody, the marking procedure must be the subject of a validation file on the final preparation filtered on a sterilizing membrane at 0.22 µm and covering:
- The quality of the marking and quantification of the free fraction of the fluorochrome (CCM or HPLC),
- Preservation of the immuno-reactivity of the fluorescent antibody, by FACS on tumor line cells Human expressing the antigen of interest,
- The absence of oligomerization of the fluorescent antibody (HPLC on a diffusion exclusion column),
- Control (if possible) by in vivo fluorescence imaging on mice xenografted subcutaneously with tumor cells of the line selected for the FACS immunoreactivity test,
- Sterility controls (culture) and absence of pyrogens (Limulus test).
Once the procedure has been validated, it would be unnecessary to repeat the tests before each clinical research examination. A check of the marking by TLC and the placing in the sample library at +4˚C for 1 month of each injected formulation would be sufficient for additional tests if necessary.
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Figure 2. Schematic representation of 89 Zr-mAb-IRDye800 CW. [8]
Note that monoclonal antibodies play a crucial role in tumor targeting imaging, a technique that aims to specifically visualize cancer cells or tumor tissues using contrast agents. They are designed to bind specifically to antigens on the surface of tumor cells. This gives high targeting specificity, allowing precise discrimination between cancer cells and healthy tissues. The use of monoclonal antibodies in molecular imaging allows visualization of specific biomarkers associated with malignancy. This may include antigens specific to certain tumors or proteins overexpressed in cancer cells.
4. Conclusion
Molecular near-infrared fluorescence imaging is experiencing development, the process of which could be accelerated by the process of which could be accelerated by obtaining more clinical contrast agents. Alternative solutions are therefore necessary to promote clinical research in this area. These methods must be shared to make it easier for researchers. Researchers continue to explore new applications for NIR imaging, whether in the field of neuroimaging, image-guided therapy, or other emerging areas.