Targeted delivery of ^99mTc-folic acid to folate receptor expressing tumors

To optimise ^99mTc labeling of Folic acid and use ^99mTc-Folic acid as a diagnostic agent for Folate receptor expressing tumors in mouse model. Folic acid was radiolabeled with ^99mTc using Stannous Tartarate as a reducing agent. Radiolabeling was optimised by varying concentration of Folic acid, Stannous Tartarate, pH and incubation time. The RCP of ^99m Tc-Folic acid was checked by paper chromatography. The stability of ^99mTc- Folic acid was checked in human serum and with DTPA challenge test and was found to be stable. In-vitro uptake studies were done by incubating ^99mTc-Folic acid with Folate receptor expressing B16F10 murine Melanoma cells (1x10⁵). In-vivo biodistribution studies of ^99mTc- Folic acid were done in B16F10 Melanoma tumor model developed in-house in C57BL/6 mice. Gamma imaging studies were done post injection of ^99mTc- Folic acid in B16F10 Melanoma tumor model. The RCP of ^99m Tc-Folic was ≥90% which was stable in human serum and when subjected to DTPA challenge test. In-vitro uptake of ^99m Tc-Folic acid was 30 % at two hours when incubated with B16F10 murine Melanoma cells (1x10⁵) which decreased to 7% when cold Folic acid was added. In vivo biodistribution studies in B16F10 Melanoma tumor model showed tumor uptake of 8% at two hours post injection. Gamma imaging studies showed localisation of ^99m Tc-Folic acid in B16F10 Melanoma tumour developed in C57BL/6 mice. Folic acid was optimally radiolabeled with ^99mTc having RCP > 90%. Preliminary in-vivo studies in Folate receptor expressing tumor model showed tumor uptake of 8%, hence may be used in future as a diagnostic agent for detecting Folate receptor expressing tumors. In-vitro studies showed that cold Folic acid bound to the folate receptors competitively and inhibited the cell binding of radiolabelled folate in the cells. This shows that ^99mTc-FA is not interfering with the cell binding efficiency of Folic acid to the folate receptors. (author)