The thermotropic effects of two series of lipophilic conjugates of the anticancer drug methotrexate with glucosyl- or pentaacetyl-glucosyl-lipoamino acid residues (GL-MTX) on a biological membrane model made up of dimyristoylphosphatidylcholine (DMPC) were investigated. Changes in the alkyl chain length of the lipoamino acid residues and in the free or acetylated state of the sugar moiety modulated the overall lipophilic/hydrophilic balance of the compounds and their solubility in aqueous media, thus also affecting their biological activity profile. The calorimetric (DSC) analysis of their interaction with DMPC multilamellar vesicles showed that when GL-MTX conjugates were mixed with DMPC during vesicle preparation, they were able to affect the packing order of the phospholipid bilayers in a concentration-dependent way. On the contrary, by incubating the conjugates with pre-formed empty DMPC liposomes at 37 degreesC, these derivatives were unable to penetrate the bilayers, most probably because of the presence of the two sugar residues. This behavior was correlated with the low biological activity observed in vitro for these conjugates, with respect to a corresponding series of MTX-LAA conjugates. (C) 2004 Elsevier B.V. All rights reserved.