Imaging of a
tumor with ESR was tried using two different types of spin probes, a low molecular weight spin probe,
CPROXYL, and a
polymer spin probe,
TEMPO-DX. Spin probes were administered to a mouse bearing a solid
tumor that was a transplanted Ehrlich's
ascites carcinoma in the back, using two methods, conventional
intraperitoneal injection and continuous
intravenous injection with a micro-feeder. First, the accumulation of the probe was examined by X-band ESR.
CPROXYL, which was administered to a mouse intraperitoneally, was exclusively retained in urine, showing that it was rapidly excreted into the bladder, while
TEMPO-DX was absorbed from the peritoneal cavity with difficulty to the vessel. Using continuous
intravenous injection,
CPROXYL was also rapidly excreted, but it was confirmed that
TEMPO-DX concentrated in
tumor tissue because it has a long half-life in vivo. In addition, measurement of ESR imaging was done to measure the distribution of spin probes with continuous
intravenous injection. The strongest spot of
CPROXYL was observed on ESR images, showing the accumulation at the bladder, while the spot of
TEMPO-DX was observed in the solid
tumor of the back of the mouse. These results suggest that
TEMPO-DX could stay much longer than a low molecular weight spin probe in vivo and concentrate at the
tumor.
TEMPO-DX may be useful for developing specific ESR imaging agents for
tumor.