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Development of a tumor-targeting MR contrast agent using the high-affinity folate receptor: work in progress
S D Konda1, M Aref, M Brechbiel
1Biomedical Magnetic Resonance Laboratory, College of Medicine, and the Beckman Institute, University of Illinois, Urbana-Champaign, USA.
Rationale And Objectives:
Macromolecular contrast agents enhance tumors by means of active or passive targeting. Active targeting requires surface receptors. Many tumors of epithelial origin express the high-affinity folate receptor (hFR), including ovarian tumors. The objective of this research was to enhance tumors that express hFR using macromolecular contrast agents conjugated to folic acid.
Methods:
The authors prepared a folate-conjugated dendrimer polychelate by attaching folic acid to a fourth-generation ammonia-core polyamidoamine dendrimer. The remaining amines were reacted with 2-(4-isothiocyanatobenzyl)-6-methyldiethylenetriamine pentaacetic acid. Relaxivity measurements (r1 and r2) and MRI were conducted at 4.7 T.
Results:
The dendrimer r2 exceeded that of Gd-HP-DO3A by 8.2 times at 4.7 T. It increased the tumor percentage contrast enhancement, 24 hours after injection, of T2-weighted images by 33%.
Conclusions:
This new agent accumulates in tumors expressing hFR. These results do not differentiate between active and passive targeting mechanisms. Receptor-negative tumors suggest a mechanism other than a nonspecific blood pool effect.
Insights
Researchers developed a novel folate-conjugated dendrimer polychelate to enhance tumors expressing the folate receptor (hFR). This targeted contrast agent shows promise for improving tumor visualization in medical imaging.
Area of Science:
- Biomedical Imaging
- Nanotechnology
- Oncology
Background:
- Macromolecular contrast agents are crucial for tumor enhancement via active or passive targeting.
- The high-affinity folate receptor (hFR) is frequently expressed in epithelial tumors, including ovarian cancers.
Purpose of the Study:
- To develop and evaluate a macromolecular contrast agent conjugated with folic acid for enhancing tumors expressing hFR.
Main Methods:
- Synthesis of a folate-conjugated dendrimer polychelate using a fourth-generation ammonia-core polyamidoamine dendrimer.
- Conjugation with folic acid and subsequent reaction with a chelating agent.
- Relaxivity measurements (r1 and r2) and MRI at 4.7 T.
Main Results:
- The synthesized dendrimer exhibited an 8.2-fold higher r2 relaxivity compared to Gd-HP-DO3A at 4.7 T.
- A 33% increase in tumor contrast enhancement was observed on T2-weighted images 24 hours post-injection.
Conclusions:
- The folate-conjugated agent effectively accumulates in tumors expressing hFR.
- The study suggests targeting mechanisms beyond passive accumulation, as indicated by minimal enhancement in receptor-negative tumors.
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