Imaging tumor folate receptors using 111In-DTPA-methotrexate

Area of Science:

• Nuclear Medicine
• Oncology
• Radiochemistry

Background:

• Membrane folic acid receptors are crucial for cellular folate uptake.
• These receptors are overexpressed on various tumor cells, making them potential diagnostic targets.
• Methotrexate (MTX) and its analogs interact with folate receptors.

Purpose of the Study:

• To develop and evaluate an Indium-111 labeled diethylenetriaminepentaacetic acid-methotrexate (DTPA-MTX) conjugate for in vivo imaging of tumor folate receptors.
• To assess the receptor-mediated uptake of the developed radiotracer in tumor-bearing animal models.

Main Methods:

• Synthesis of DTPA-MTX by reacting ethylenediamine with MTX, followed by conjugation with DTPA dianhydride.
• Radiolabeling of DTPA-MTX with Indium-111 (111In).
• In vivo tissue distribution studies in breast tumor-bearing rats, including co-administration with cold folate to confirm receptor-mediated uptake, planar imaging, and whole-body autoradiography.

Main Results:

• 111In-DTPA-MTX demonstrated increasing tumor-to-blood count density ratios over 48 hours in tumor-bearing rats.
• In contrast, 111In-DTPA showed decreasing tumor-to-blood ratios over the same period.
• Co-administration with folic acid significantly reduced tumor uptake, confirming folate receptor-mediated targeting.
• Planar imaging and autoradiograms visualized tumors acceptably using 111In-DTPA-MTX.

Conclusions:

• 111In-DTPA-MTX is a feasible radiotracer for imaging tumors via folate receptor-mediated processes.
• This agent shows promise for diagnostic applications in oncology.
• Targeting folate receptors with radiolabeled methotrexate analogs is a viable strategy for tumor imaging.