EJNM: RGD PET probe uptake reproducible in mouse model
Mouse tumor xenograft studies using PET probe-18F-labeled PEGylated arginine-glycine aspartic acid (RGD) dimer {[18F] FPP (RGD) 2} are reproducible with relatively low variability, according to a study published in the December issue of European Journal of Nuclear Medicine Molecular Imaging.

Serial PET studies may be useful for monitoring antiangiogenic therapy response or for drug screening; however, the reproducibility of serial scans has not been determined for [18F] FPP (RGD) 2 used to image tumor alpha 5 beta 3 integrin levels in preclinical and clinical studies.

The purpose of the study was to determine the reproducibility of [18F] FPP (RGD) 2, using small animal PET, according to Edwin Chang, PhD, a basic life science research associate in the molecular imaging program at Stanford, department of radiology at Stanford University in Stanford, Calif., and colleagues.

Human HCT116 colon cancer xenografts were implanted into nude mice in the breast and scapular region and grown for approximately two and half weeks.

A three-minute acquisition was performed on a small animal PET scanner approximately one hour after administration of [18F] FPP (RGD) 2 via the tail vein. A second small animal PET scan was performed approximately six hours later after reinjection of the probe to assess for reproducibility.

Percentage injected dose per gram (percentage ID/g) values were calculated from the mean or maximum activity in the region of interest around the tumor xenograft activity.

The researchers found the coefficient of variation for percentage IDmean/g and percentage IDmax/g values between [18F] FPP (RGD) 2 small animal PET scans performed six hours apart on the same day were 11.1 percent and 10.4 percent, respectively. Immunofluorescence studies revealed a direct relationship between extent of alpha 5 beta 3 integrin expression in tumors and tumor vasculature with level of tracer uptake.

“[18F] FPP (RGD) 2 small animal PET mouse tumor xenograft studies are reproducible with relatively low variability. Strict attention to consistent protocol parameters, in particular, uniform injection techniques, time of imaging after injection, and region of interest definition, can ensure accurate repeat scans,” concluded Chang and colleagues.