Characteristics of association of oleoyl derivatives of 5-fluorodeoxyuridine and methotrexate with low-density lipoproteins (LDL)

In order to prepare cytotoxic drug-low density lipoprotein (LDL) particles, we have synthesized lipophilic prodrugs of two broad-spectrum antineoplastic agents, methotrexate (MTX) and 5-fluorodeoxyuridine (FUdR), by coupling them to oleic acid. 3H-Labeled prodrugs were incorporated in 125I-LDL carriers, allowing the study of both drug and carrier simultaneously. Utilizing the dry film procedure, monooleoyl FUdR showed the highest incorporation efficiency with over 40% of the initial drug associated with LDL. The prepared prodrug-LDL solution was found to be a single complex of 30 molecules of prodrug per LDL particle when examined by agarose gel electrophoresis and density gradient ultracentrifugation. No unbound FUdROl1 could be recovered, indicating that all dissolved prodrug associates with LDL. After incubation of FUdROl1 with human serum, 22% of the compound associates with lipoproteins and 78% was recovered in the albumin-containing fraction. When human serum was pretreated with oleic acid in order to saturate albumin's fatty acids binding sites, a strong decrease (from 78 to 22%) in association to the albumin-containing fraction was observed, accompanied by a threefold increase (from 22 to 67%) in lipoprotein association. It is concluded that existing hydrophilic antineoplastic agents can be successfully modified in order to achieve association with LDL. This may ultimately lead to an increased delivery of cytotoxic drugs to tumor cells.