FAP inflammation imaging narrows in on osteoarthritis

SPECT and PET can detect the pathology of chronic joint pain due to rheumatoid arthritis when performed with agents that target antifibroblast activation protein (FAP) antibodies, according to a study presented last week during the 2014 Annual Meeting of the Society of Nuclear Medicine and Molecular Imaging (SNMMI) in St. Louis.

The agents used in this preclinical study combined the FAP biomarker 28H1 with In-111 for SPECT and Zr-89 for PET. Inflammation in the joints caused significant uptake—three to four times that of a control agent—for both SPECT and PET scans.

“Antibodies targeting [FAP] have been widely studied in oncology, because of the abundant expression of FAP in tumor stroma,” explained Peter Laverman, PhD, co-author of the study and assistant professor of nuclear medicine from the department of radiology and nuclear medicine at Radboud University Medical Center in Nijmegen, The Netherlands. “However, FAP is also expressed on activated fibroblasts in arthritic joints and therefore is an attractive target.”

FDG inflammation imaging was also conducted as a control, but unlike the other two agents, FDG uptake did not correlate with severity of disease. Results of the study also indicated that In-111 SPECT was better than Zr-89 PET due to some non-specific uptake in bone in the latter. The next step is to find out if SPECT imaging can be used for treatment monitoring.

“This is still early-stage preclinical data, so this is somewhat speculative, but SPECT imaging of RA patients using In-111-labeled anti-FAP antibody 28H1 might be going to play a role in the management of [arthritic] patients with regard to treatment regimens,” said Laverman, who suggested at least another two years of study will be required before this technique could be made available for clinical use.