Re-evaluation of the mechanism of cytotoxicity of dialkylated lariat ether compounds

Abstract

The cytotoxicity of dialkylated lariat ethers has been previously attributed to their ionophoric properties.

Acylated and alkylated benzo(crown-ethers) form ion-dependent ion channels in biological membranes

“…After 150 s (time point t 3 , 250 s), 10 mL of diaphorase (Worthington Biochemical Corporation, Lakewood, NJ) 10 mg/mL solution was added. The final step involved the addition of 0.62 mL of a 10 mM stock solution of dialkylated diaza lariat ether (LEC 10 ) (16,20,24) in TFE (time point t 4 , 400 s), for a final LEC 10 concentration of 2 mM; or 3.1 mL of a 2 mM stock solution of valinomycin (Sigma) in dimethyl sulfoxide, for a final valinomycin concentration of 2 mM; or 3.1 mL of a 20 mg/mL stock solution of lysozyme in lactate/NAD þ solution, for a final lysozyme concentration of 20 mg/mL; or 3.1 mL of 10 mM stock solution of each of the MABCE compounds in TFE, for final concentrations of 10 mM. Fluorescence intensity FIGURE 1 Synthesis of monoacylated and monoalkylated benzo crown-ether compounds.…”

“…Some bioactive lariat ether compounds can actually be membrane lytic agents instead of ionophores (20). The addition of these compounds to cells at concentrations corresponding to their normal working range effectively released the cytoplasmic enzyme lactate dehydrogenase (a 146 kDa (34,35) globular protein folds with 160 A ˚diameter [PDB: 3PQD]), indicating that the membrane integrity was compromised.…”

“…The initial motivation in biology for developing synthetic ionophores was to create a new class of antibiotics inspired by many naturally occurring ionophoric antibiotics (5,8,(11)(12)(13)(14)(15)(16)(17)(18). Unfortunately, many of the potent ionophores developed in this context also proved highly toxic to mammalian cells (19,20). More recently, research focused on new classes of synthetic ion channels has been spurred by a multitude of factors.…”

“…Such indirect assays can be miselading. For instance, we recently found that one family of crown ethers, dialkylated lariat ethers, which were previously assumed to form membrane channels (16,24) based on flux assays, are membrane lytic and do not exhibit channel activity in lipid bilayers (20).…”

Assessment of a host–guest interaction in a bilayer membrane model

“…Of course, some carrier function not detected in the planar bilayer experiment, cannot be excluded. 19 …”