Physicochemical behavior of cytotoxic ether lipids

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Abstract
The physicochemical properties of four biologically active alkyllysophosphatidylcholine analogs have been investigated using differential scanning calorimetry (DSC), 31P NMR, and fluorescence spectroscopy. Each of the alkyl ether lipids, suspended in a buffer/ethylene glycol matrix, undergo a thermotropic structural rearrangement at temperatures near 0 degree C. The axially asymmetric 31P NMR spectra obtained for all four lipids, after prolonged incubation at -20 degrees C, are consistent with the notion that these amphiphiles are able to form extended lamellar structures at temperatures below the main phase transition temperature (Tm). We have attributed the sharp, isotropic 31P resonance, observed for each derivative at temperatures above the Tm, to the presence of a micellar state. This has been confirmed via 31P NMR experiments employing the lanthanide shift reagent PrCl3. The critical micelle concentrations (cmc) of these lysolipids have been determined via the fluorescence titration of [6-palmitoyl-2-[[(2-trimethylammonium)ethyl]methyl]amino] naphthalene (PATMAN). The low values obtained for both the lamellar to micellar phase transition temperature (-7.88 +/- 0.19 degree C) and the cmc (0.15 +/- 0.02 microM) for the 2-benzyloxylysolipid (1) indicate that this analog exhibits a marked preference for the micellar state relative to the 2-methoxy (2), 2-deoxy (3), and 2-hydroxy (4) substituted compounds.

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