Recent Progress in Polymer Therapeutics as Nanomedicines - Harnessing Biomaterials in Nanomedicine: Preparation, Toxicity, and Applications - page 101

polymeric micelles as opposed to up to few nanometers for lipid
micelles).
There are several aggregates structures used for drug delivery.
Here we will briefly discuss the common ones (Figures 4.1C and D).
Frequently encountered structure is the micelle. Diblock and triblock
copolymers are commonly used to construct micellar assemblies,
where the hydrophilic block constitutes the shell of the micelle
that interacts with the aqueous surroundings and the hydrophobic
block forms the micellar core. The hydrophobic core can serve as
a depot for small non-soluble drugs. Usually PEG (also referred to
in this field as PEO, polyethyleneoxide) is used as the hydrophilic
block. Polycaprolactone (PCL) and polylactic acid (PLA) are typical
hydrophobic blocks, but other hydrophobic polymers, peptide
segments, or fatty acids are used as well. The incorporation of other
functions such as targeting and increased cellular uptake can be
achieved by attaching functional moieties to the hydrophilic block,
thus placing them in the solvent exposed shell of the micelle. For
example, Wu et al. [135] prepared targeted pH-responsive micelles
by mixing AP peptide, that has a specific affinity to IL-4 receptors
of atherosclerotic plaques and breast tumor tissue, conjugated to
PEG-PLA copolymer, with pH-responsive methyl ether poly(ethylene
glycol) (MPEG)-poly( β -amino ester) (PAE) block copolymer (MPEG-
PAE). The mixed block copolymers were self-assembled forming
150 nm-diameter micelles, which disassemble at pH below 6.8.
The micelles were loaded with doxorubicin. This system showed
efficient delivery and excellent anti-cancer therapeutic efficacy in
MDA-MB231 human breast tumor-bearing mice (compared with free
doxorubicin and doxorubicin encapsulated in equivalent micelles
without the AP targeting). There are many more studies in progress,
and some are viewed in recent reviews [133, 136]. Some polymeric
micellar systems are already in clinical trials (Table 4.6), such as
Genexol-PM, methoxypoly(ethylene glycol)-block-poly(D,L-lactide)
(mPEG-PDLLA) polymeric micelles used for the formulation of
paclitaxel. These micelles were successfully tested in phase II for the
treatment of metastatic breast cancer [137], advanced or metastatic
pancreatic cancer [138], and advanced non-small-cell lung cancer in
combination with cisplatin [139].
Another structure commonly in use is the vesicle. Polymeric
vesicles are termed polymersomes (similarly to lipid vesicles-
liposomes) and are composed of polymeric membrane closing on