We summarize the development and evaluation of new type of phospholipid polymers as a solubilizer for poorly water-soluble compounds. That is, a water-soluble and amphiphilic poly(2-methacryloyloxyethyl phosphorylcholine-random-n-butyl methacrylate) contains 30 mol% hydrophilic 2-methacryloyloxyethyl phosphorylcholine units and its weight-averaged molecular weight is around 5.0 × 10 4 . When the polymer is dissolved in an aqueous medium, a large portion of hydrophobic n-butyl methacrylate units assemble, forming polymer aggregates. To avoid severe biological reactions caused by conventional solubilizers, the phospholipid polymer can be applied for the solubilization of poorly water-soluble bioactive compounds. The polarity inside these polymer aggregate is the same as that of ethanol and n-butanol. Therefore, bioactive compounds, whose solubility is poor in water but good in these alcohols, can be entrapped in the polymer aggregate. The phospholipid polymer can penetrate the cell membrane by molecular diffusion, carrying inside the cell the bioactive compound, without exhibiting significant cytotoxicity. Several animal experiments have revealed that the pharmacological performance of various bioactive compound/phospholipid polymer complexes is excellent. Furthermore, functionalization of the polymer aggregate with biomolecules, such as antibodies and oligonucleotides, can be done, leading to selective capturing of the target molecules. These examples clearly indicate that water-soluble and amphiphilic phospholipid polymer is a candidate for preparing safer formulations and more effective pharmaceutical treatment with several bioactive compounds.
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