Biomedical Engineering Reference
In-Depth Information
1.1 Polymer Based Nanotheranostics
A wide range of FDA (Food and Drug Administration, U.S.) approved synthetic
and natural polymers have already entered in medical and pharmaceutical markets
(Mansour et al. 2010; Nair and Laurencin 2006). Polymers confer extensive flexibil-
ity in tuning their physiochemical properties on the basis of their monomer number
and functional groups present. Among the extensive number of biocompatible pol-
ymers being used for cancer theranostics, few deserve mention, like poly(ethylene
glycol) (PEG), poly(lactic-co-glycolic acid) (PLGA), poly(lactic acid) (PLA), chi-
tosan and polycaprolactone (PCL). The diversity in such polymer based systems has
now traversed to a new level with the surge of polymer conjugate systems.
In a characteristic construct of polymer-based nanotheranostics, the prime com-
plementary components include, contrast agent for detection and imaging, thera-
peutic agent, polymer matrix for carrying both of them, and an additional polymer
interface for improving stability and biodistribution which in special cases is also
used for integrating targeting molecule so as to sequester the complexes specifically
to the site of action. In this chapter, the authors make an attempt to consolidate upon
PEG, PLGA and chitosan based systems reported thus far for cancer therapy and
diagnosis. Their conjugate systems with other polymers are also be included in the
following discussion to provide a comprehensive prospect of each polymer.
1.1.1 PEG Based Nanotheranostics
PEG is a hydrophilic polymer which is invariably included in many theranostic
systems to prolong their residence time in the biological system and circumvent
enzymatic degradation of encapsulated moieties by the reticuloendothelial sys-
tem (RES) (Kwon et al. 1994). It also enables the system on the whole to stealth-
ily overcome host immune system by impersonating them as native molecules
(Richter and Akerblom 1984; Cheng et al. 1999; Goodson and Katre 1990). PEG
plays the role of carrier for therapeutic and diagnostic molecules by either directly
conjugating with them (covalently or electrostatically) or encapsulating them
within micelle systems with an additional polymer conjugated. The formation
and stability of such polymer conjugate based micelle system is mostly driven by
hydrophobic interaction between the blocks of conjugate polymer with the immi-
nent environment and drug molecules. Additionally these PEG micelles have high
chain mobility in aqueous environment which develops a large exclusion volume
around the polymer thus avoiding interaction with constituents of biological fluids.
PEG for Protein Delivery
PEG has been also used to modify protein and peptides for delivering them effi-
ciently to cancer cells. The PEG moiety is conjugated to proteins at specific sites
of -SH group in cysteine and amine group at the
N
terminus, such systems have
