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Investigating CXCR4 expression of tumor cells and the vascular compartment: A multimodal approach
Marta Braga1, Chee Hau Leow2, Javier Hernandez Gil3
1Department of Surgery and Cancer, Faculty of Medicine, Imperial College London, London, United Kingdom.
Abstract:
The C-X-C chemokine receptor 4 (CXCR4) is G protein-coupled receptor that upon binding to its cognate ligand, can lead to tumor progression. Several CXCR4-targeted therapies are currently under investigation, and with it comes the need for imaging agents capable of accurate depiction of CXCR4 for therapeutic stratification and monitoring. PET agents enjoy the most success, but more cost-effective and radiation-free approaches such as ultrasound (US) imaging could represent an attractive alternative. In this work, we developed a targeted microbubble (MB) for imaging of vascular CXCR4 expression in cancer. A CXCR4-targeted MB was developed through incorporation of the T140 peptide into the MB shell. Binding properties of the T140-MB and control, non-targeted MB (NT-MB) were evaluated in MDA-MB-231 cells where CXCR4 expression was knocked-down (via shRNA) through optical imaging, and in the lymphoma tumor models U2932 and SuDHL8 (high and low CXCR4 expression, respectively) by US imaging. PET imaging of [18F]MCFB, a tumor-penetrating CXCR4-targeted small molecule, was used to provide whole-tumor CXCR4 readouts. CXCR4 expression and microvessel density were performed by immunohistochemistry analysis and western blot. T140-MB were formed with similar properties to NT-MB and accumulated sensitively and specifically in cells according to their CXCR4 expression. In NOD SCID mice, T140-MB persisted longer in tumors than NT-MB, indicative of target interaction, but showed no difference between U2932 and SuDHL8. In contrast, PET imaging with [18F]MCFB showed a marked difference in tumor uptake at 40-60 min post-injection between the two tumor models (p<0.05). Ex vivo analysis revealed that the large differences in CXCR4 expression between the two models are not reflected in the vascular compartment, where the MB are restricted; in fact, microvessel density and CXCR4 expression in the vasculature was comparable between U2932 and SuDHL8 tumors. In conclusion, we successfully developed a T140-MB that can be used for imaging CXCR4 expression in the tumor vasculature.
Insights
We developed targeted microbubbles (T140-MB) for ultrasound imaging of vascular C-X-C chemokine receptor 4 (CXCR4) in cancer. T140-MB specifically bind to CXCR4, offering a cost-effective alternative to PET imaging for therapeutic monitoring.
Area of Science:
- Biomedical Engineering
- Molecular Imaging
- Oncology
Background:
- C-X-C chemokine receptor 4 (CXCR4) plays a role in tumor progression.
- Accurate imaging of CXCR4 is crucial for cancer therapy stratification and monitoring.
- While PET agents are successful, cost-effective and radiation-free ultrasound (US) imaging is an attractive alternative.
Purpose of the Study:
- To develop a targeted microbubble (MB) for imaging vascular CXCR4 expression in cancer using ultrasound.
- To evaluate the binding properties and in vivo performance of CXCR4-targeted MBs.
Main Methods:
- Incorporation of the T140 peptide into MB shells to create CXCR4-targeted MBs (T140-MB).
- Evaluation of T140-MB binding in CXCR4-knockdown cells and in lymphoma tumor models (U2932 and SuDHL8) using optical and US imaging.
- Comparison with PET imaging ([18F]MCFB) and ex vivo analysis (immunohistochemistry, western blot).
Main Results:
- T140-MB exhibited specific accumulation in cells based on CXCR4 expression.
- T140-MB showed prolonged retention in tumors, indicating target interaction, but without differentiation between high and low CXCR4 models.
- PET imaging revealed significant differences in tumor uptake between models, contrasting with comparable vascular CXCR4 expression observed in ex vivo analysis.
Conclusions:
- A T140-peptide targeted microbubble (T140-MB) was successfully developed for imaging CXCR4 expression within the tumor vasculature.
- Ultrasound imaging with T140-MB offers a specific approach to visualize vascular CXCR4, complementing other imaging modalities.
