Advanced Drug Carriers Targeting Bone Marrow

The progression of nanotechnology has produced engineered fine nanoparticles for use in biomedical applications. Drug delivery systems are in a particularly promising field for the use of the unique properties of nanoparticles in biomedical applications. The pharmacokinetics of nanoparticles differs considerably from that of small drug molecules. Therefore, a drug delivery system based on nanoparticles offers a novel direction of drug discovery as well as an improved delivery system for use with conventional drugs. It has been demonstrated that drug delivery systems using nanoparticles are advantageous for stable solubilization of lipophilic drugs, reduced toxicity, inhibition of enzymatic degradation of the drugs, and so on (Moghimi et al., 2001; Papahadjopoulos et al., 1991; Torchilin, 2005). Nanoparticulate drugs show longer circulation time by avoiding renal excretion compared to drugs with small molecules. Moreover, one important technology termed "PEGylation", surface modification of nanoparticles by polyethylene glycol (PEG) chains, prolonged the circulation time (Klibanov et al., 1990; Owens & Peppas, 2006). These long-circulating nanoparticles are effective to increase the passive delivery of anticancer drugs into tumor tissues having leaky blood capillaries with wide fenestrations (Matsumura & Maeda, 1986; Gabizon et al., 1994).