The unlabeled analogue 8 was shown to be a good inhibitor of both STS and CA, and biodistribution studies in rats, mice-bearing tumor xenografts, and piglets with [18F]8 demonstrated that the radioactive signal came primarily from blood.66 Persistent signal in the blood is presumably a consequence of reaction between [18F]8 and CA found in red blood cells, which is known to be highly expressed in erythrocytes.65 The related 11C-labeled compound [11C]9 was also prepared to test whether introduction of an ortho-methoxy group would confer selectivity for STS over CA. The gene discussed is STS; the disease is neoplasm.