A new method for radiolabeling of human immunoglobulin-G and its biological evaluation

Radiolabeled human Immunoglobulin-G (hIgG) has demonstrated its utility in inflammation and infection imaging. However, the present method of radiolabeling hIgG is time-consuming and complex.

To develop a simplified method of radiolabeling hIgG with technetium-99m ((99m)Tc) via a nicotinyl hydrazine derivative ((99m)Tc-HYNIC-hIgG) and its biological evaluation.

In vitro and in vivo studies showed that (99m)Tc-hIgG prepared by this method was fairly stable in physiological saline and human serum till 24 h. Only 4.3% degradation of the radiolabeled drug was seen till 24 h. Blood clearance pattern of the radiopharmaceutical exhibited biphasic exponential pattern. Biodistribution of (99m)Tc-HYNIC-hIgG in mice was observed up to 24 h. Significant accumulation of the radiotracer was found in liver (4.93 %), kidney (3.67%) and intestine (2.12 %) at 4 h interval by 24 h interval, it was reduced to 1.99%, 2.18% and 1.93 % respectively. Significant amount of radioactivity in liver, kidney and intestine suggest hepatobilliary as well as renal route of clearance for (99m)Tc-HYNIC-hIgG. The anterior whole body and spot scintigraphy images showed increased uptake of 99mTc-HYNIC-hIgG, with the area seen as a focal hot spot, indicating good localization of the radiolabeled hIgG at the site of infection.

The present findings indicate that (99m)Tc-HYNIC-hIgG holds great potential for the scintigraphy localization of inflammation. The shelf life of the developed kit, when stored at (-) 20°C was found to be at least 3 months.