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Abstract
The review concentrates on the use of polymeric micelles as pharmaceutical carriers.
Micellization of biologically active substances is a general phenomenon that increases
the bioavailability of lipophilic drugs and nutrients. Currently used low-molecular-weight
pharmaceutical surfactants have low toxicity and high solubilization power towards
poorly soluble pharmaceuticals. However, micelles made of such surfactants usually
have relatively high critical micelle concentration (CMC) and are unstable upon strong
dilution (for example, with the blood volume upon intravenous administration). On
the other hand, amphiphilic block co-polymers are also known to form spherical micelles
in solution. These micelles have very high solubilization capacity and rather low
CMC value that makes them very stable in vivo. Amphiphilic block co-polymers suitable
for micelle preparation are described and various types of polymeric micelles are
considered as well as mechanisms of their formation, factors influencing their stability
and disintegration, their loading capacity towards various poorly soluble pharmaceuticals,
and their therapeutic potential. The basic mechanisms underlying micelle longevity
and steric protection in vivo are considered with a special emphasis on long circulating
drug delivery systems. Advantages and disadvantages of micelles when compared with
other drug delivery systems are considered. New polymer-lipid amphiphilic compounds
such as diacyillipid-polyethylene glycol, are described and discussed. These compounds
are very attractive from a practical point of view, since they easily micellize yielding
extremely stable micelles with very high loading capacity. Micelle passive accumulation
in the areas with leaky vasculature (tumors, infarct zones) is discussed as an important
physiology-based mechanism of drug delivery into certain target zones. Targeted polymeric
micelles prepared by using thermo- or pH-sensitive components or by attaching specific
targeted moieties (such as antibodies) to their outer surface are described as well
as their preparation and some in vivo properties. The fast growing field of diagnostic
micelles is analyzed. Polymeric micelles are considered loaded with various agents
for gamma, magnetic resonance, and computed tomography imaging. Their in vitro and
in vivo properties are discussed and the results of the initial animal experiments
are presented.