Rapid Reduction of s1-Receptor Binding and 18F-FDG Uptake in Rat Gliomas After In Vivo Treatment with Doxorubicin

s-Receptors are strongly overexpressed in most rodent and human tumors and are proliferation markers. To evaluate the potential of a radiolabeled s1-ligand for therapy monitoring, we compared early changes of 11C-1-(3,4-dimethoxyphenethyl)-4-(3-phenylpropyl)piperazine (11C-SA4503) binding and 18F-FDG uptake in gliomas after in vivo chemotherapy.Methods:C6 cells (2.5 · 106) were subcutaneously injected into the right shoulder of maleWistar rats. After 7 d, the tumor volumewas 0.606 0.08 cm3. Animals then received either saline or doxorubicin (8 mg/kg, intraperitoneally). One control and 1 treated rat were imaged simultaneously, 24 or 48 h after treatment, under pentobarbital anesthesia. Rodents (n 5 20) were scanned first with 11C-SA4503 (25MBq, intravenously) followedmore than100min after-ward by 18F-FDG (20 MBq, intravenously), using a dedicated small-animal PET camera (60-min protocol, tumors in the field of view). Tumor homogenates were prepared and subjected to s-receptor assays. The biodistribution of 18F-FDG was assessed. Results: Tumors appeared 4–5 d after inoculation and grew exponentially. No significant reduction of tumor growth was visible within 48 h after doxorubicin treatment. Both PET tracers visualized the tumors and showed reduced uptake afte