LDL-mediated drug targeting.

The possibilities and limitations in using the low-density lipoprotein (LDL) as a carrier for drugs are discussed. LDL, which may be regarded as the natural counterpart of liposomes, possesses a lipid core that may be utilized as a drug reservoir. Unlike most types of liposomes, the endogenous LDL particle is not avidly taken up by the reticuloendothelial system and may persist in the circulation for prolonged times after injection. A well-characterized membrane receptor recognizes LDL, and binding appears to be coupled to uptake and intracellular processing. Since many tumor tissues express a high amount of LDL receptors, there is a rationale for the design of a toxic LDL-cytostatic drug complex. The behavior of LDL in vivo will be discussed and the principles of LDL-mediated targeting to tumor cells will be evaluated. In addition, methods for drug incorporation into LDL will be critically assessed, while evaluation methods will be presented that may set the standards for future research.