Wallac wizard 1480 automatic gamma counter

Whole-body clearance was derived from serial measurements of count-rate using a 12.7 cm (5 inch) thick sodium iodide NaI (Tl) scintillation detector at a fixed geometry (3 m from probe to patient). Probe measurements were made following MVT-2163 infusion before and after first voiding, and at the times of PET imaging. Background-corrected geometric mean count rates were normalized to the immediate post-infusion value to yield relative retained activities. To determine clearance from the circulation, blood samples were taken at 15, 30, and 90 minutes post-infusion and subsequently at the times of PET imaging. Serum activity concentration was measured with a NaI (Tl) gamma well-type detector (Wallac Wizard 1480 automatic gamma counter, PerkinElmer) and converted to percent injected activity/liter (% IA/L).

Tyrosine residues on ELP_Depot-FGF21 or FGF21 cleaved from ELP-tev-FGF21 were reacted with Na¹²⁵I radionuclide (Perkin Elmer) using Pierce Pre-Coated Iodination Tubes (Thermo Fisher Scientific) and the indirect method for iodination. Radiolabeled protein was purified with Zeba Spin Desalting Columns. Activities of radiolabeled constructs were measured with an Atomlab 400 Dose Calibrator (Biodex, Shirley, NY) and correlated to protein concentration.
7–9-week-old male ob/ob mice were injected i.v. with 1 mg/kg radiolabeled ELP_Depot-FGF21 or FGF21 cleaved from ELP-tev-FGF21. The fusion was injected at a dilute concentration (10 µM) to avoid LCST phase transition of the ELP within the blood vessel. 10 uL blood samples were collected at frequent time points from the tail vein, and sample counts were measured at the end of the study on a Wallac Wizard 1480 Automatic Gamma Counter (Perkin Elmer). An activity vs. count standard curve was used to convert sample counts to activities, and subsequently to moles of drug. For tracking serum drug levels following a therapeutic dose, 9-week-old male ob/ob mice were injected via s.c. with 20 mg/kg radiolabeled ELP_Depot-FGF21 or FGF21 cleaved from ELP-tev-FGF21. Blood was collected and counts were measured as previously described.