Targeting and Selective Killing of T47D Breast Cancer Cells by Purpurin and 5-Fluorouracil Anchored to Magnetic CNTs: Nitrene-Based Functionalization versus Uptake, Cytotoxicity, and Intracellular Fate.

Fe-encapsulated multiwall carbon nanotubes (Fe@MWCNTs) are candidates for magnetically targeted Drug Delivery Systems (mt-DDSs) against breast cancer. However, their full potential as versatile and biosafe vectors has yet to be developed. Key challenges that remain are relating surface functionalization to cytotoxicity and inducing selective cytotoxicity to cancer cells. We have studied quantitative uptake of pristine and functionalized Fe@MWCNTs (f-Fe@MWCNTs) in correlation to their cytotoxicity. Human monocyte macrophages (HMMs) and T47D breast cancer cells were selected as models to test selective cytotoxicity. [2+1]-Cycloaddition of nitrenes to Fe@MWCNTs yielded both effective functionalization and drug "tethering". Hydrophilization of Fe@MWCNTs was critical for efficient active cell uptake. f-Fe@MWCNTs were considerably more toxic to T47D cells than HMMs, in spite of longer exposure times of the latter. Eventually, Fe@MWCNTs loaded with 5-fluorouracil in a β-cyclodextrin cage or with covalently linked purpurin emerged as the most cytotoxic and steerable in a magnetic field toward promising mt-DDSs.