Dendritic Molecular Baskets for Selective Binding of Toxic Methotrexate

We describe the preparation, assembly, recognition characteristics, and bioactivity of dendritic basket 612−. This novel cavitand has a deep aromatic pocket with three (S)-glutamic acid dendrons at the rim to amplify water solubility and prevent self-association. 1H NMR spectroscopy, calorimetry (ITC), and mass spectrometry (ESI-MS) measurements validate the formation of an inclusion complex between 612− and anticancer drug methotrexate (MTX2−) in water (Kd=9.2 μM). To identify the docking pose, a comparison of computed (DFT and MM) and experimental 1H NMR chemical shifts suggests that MTX2− folds inside 612− (π⋅⋅⋅π), forming HBs with the peptidic dendrons while anchoring (C−H⋅⋅⋅π) to the aromatic pocket through its N-methyl group. In consequence, 612− selectively binds MTX2− in competition with structurally similar folic acid and leucovorin (reversal poisoning agent). While the host is biocompatible (HEK293; IC50>150 μM) and produces inclusion complex [MTX⊂6]14− in cell media, it experiences limitation in pharmacokinetic sequestration of MTX2− as dihydrofolate reductase's affinity to the drug is suggested to prevail over that of 612−. Nonetheless, considering the basket's biocompatibility, tunability, and chemoselectivity, it stands as the leading candidate in the pursuit of an effective abiotic antidote for methotrexate poisoning.