DTPA(DOTA)-Nimotuzumab Radiolabeling with Generator-produced Thorium for Radioimmunotherapy of EGFR-overexpressing Carcinomas

Introduction: The feasibility of preparing the “in-house” generators and the Th- DTPA(DOTA)-Nimotuzumab radioimmunoconjugate was evaluated. ²²⁶Th is perspective for TAT, however, due to short half-life it is preferable to apply this radionuclide for readily available epithelial malignancies. Nimotuzumab being specific for EGFR expressing cells as a targeting moiety is considered to be suitable for thorium delivery. Methods: TEVA extraction chromatographic resin and anion exchange resin AG 1x8 were used as sorbents for ²²⁶Th generator. In order to determine features of labeling by Th4⁺ we applied ²³⁴Th as a longer-lived analog of short-lived ²²⁶Th and the immunoconjugates DTPA(DOTA)-Nimotuzumab were used for radiolabeling. Results: The generator on the base of TEVA resin has shown higher volume activity of the product compared to the AG 1x8. The ²²⁶Th volume concentration was up to 80%/mL. The radiolabeling of BFCA by thorium radioisotopes reached 95% at the MR(Th:p-SCN-Bn-DTPA) = 1:100 and 86% for MR(Th:p-SCN-Bn-DOTA) = 1:5000 at 90°C. The procedure of Nimotuzumab labeling with Th4+ for radiotherapy of EGFR-overexpressing carcinomas was established. The overall labeling yield in both radioimmunoconjugates - DTPA and DOTA functionalized - was in the range of 45-50%. The immunoconjugate Nimotuzumab-p-SCN-Bn-DTPA was obtained with a molar ratio 1:25 (Nimotuzumab: BFCA), within 1 hour of conjugation at 25°C and labelled via postconjugation approach. Whereas Nimotuzumab-p-SCN-Bn-DOTA was obtained at the same conditions, but radiolabeled by the method of pre-conjugation. Conclusion: Thorium-234 incorporation into both radioimmunoconjugates reached 45-50%. It has been shown that Th-DTPA-Nimotuzumab radioimmunoconjugate specifically bound with EGFR overexpressing epidermoid carcinoma A431 cells.