A novel biomarker termed prostate-specific membrane (PSMA) antigen is the target for three new MRI agents that bind to the protein in a range of tumor types, including prostate cancer. These findings were presented at the 2015 Annual Meeting of the Society of Nuclear Medicine and Molecular Imaging (6–10 June, Baltimore, MD, USA).
“We have shown in this proof-of-concept study that PSMA could serve as a biomarker for MR-based molecular imaging due to its high concentration within target cells, limited expression within nontargeted tissues and accessibility on the cell surface,” commented Sangeeta Ray from the Johns Hopkins Medical Institutions (MD, USA), lead investigator of the study.
PSMA is present in primary and metastatic prostate tumors, and newly developing blood vessels of many nonprostate cancers. An investigational imaging agent could contribute to patient management by helping clinicians direct biopsies and cancer therapies.
For this research, PSMA binding affinities were analyzed for three different MR contrast agents, which were subsequently imaged in living cells utilizing a 9.4 tesla magnet MR system. Findings of the study revealed that the three synthesized gadolinium-based contrast agents (Gd-1, Gd-2, and Gd-3) were able to assess parameters of PSMA in the experimental cell lines and mouse models of prostate cancer. Gd-3 was associated with the most MR contrast enhancement, approximately 36%, and demonstrated PSMA-mediated uptake on MR images of mice.
The results of the study are promising, but further investigation is necessary as these agents are still in preliminary stages of study. “With adequate funding, we estimate that a lead compound could be tested in human patients within the next two to three years,” commented Ray.