Design, Synthesis, and Cytotoxicity Assessment of [(64)Cu]Cu-NOTA-Terpyridine Platinum Conjugate: A Novel Chemoradiotherapeutic Agent with Flexible Linker

Maximum benefits of chemoradiation therapy with platinum-based compounds are expected if the radiation and the drug are localized simultaneously in cancer cells. To optimize this concomitant effect, we developed the novel chemoradiotherapeutic agent [(64)Cu]Cu-NOTA-C3-TP by conjugating, via a short flexible alkyl chain spacer (C3), a terpyridine platinum (TP) moiety to a NOTA chelator complexed with copper-64 ((64)Cu). The decay of (64)Cu produces numerous low-energy electrons, enabling the (64)Cu-conjugate to deliver radiation energy close to TP, which intercalates into G-quadruplex DNA. Accordingly, the in vitro internalization kinetic and the cytotoxic activity of [(64)Cu]Cu-NOTA-C3-TP and its derivatives were investigated with colorectal cancer (HCT116) and normal human fibroblast (GM05757) cells. Radiolabeling by (64)Cu results in a >55,000-fold increase of cytotoxic potential relative to [(Nat)Cu]Cu-NOTA-C3-TP at 72 h post administration, indicating a large additive effect between (64)Cu and the TP drug. The internalization and nucleus accumulation of [(64)Cu]Cu-NOTA-C3-TP in the HCT116 cells were, respectively, 3.1 and 6.0 times higher than that for GM05757 normal human fibroblasts, which is supportive of the higher efficiency of the [(64)Cu]Cu-NOTA-C3-TP for HCT116 cancer cells. This work presents the first proof-of-concept study showing the potential use of the [(64)Cu]Cu-NOTA-C3-TP conjugate as a targeted chemoradiotherapeutic agent to treat colorectal cancer.