SYNTHETIC POLYMERS AS NANOCARRIERS FOR CANCER THERAPY

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. Introduction
Nanotechnology is making a significant impact on drug delivery. There is a growing interest in integrating nanotechnology with medicine, creating so-called nanomedicine aiming for disease diagnosis and treatment with unprecedented precision and efficacy [1]. In drug delivery, nanomedicine is a recently developed term to describe nanometer sized (1–1000nm), multi-component drug or drug delivery systems for disease treatment [2].


Synthetic polymers as nano carriers
To reach the targeted tumor tissue, nanoparticles must be able to stay in the bloodstream for considerable lengths of time without being eliminated. Nanoparticles with no surface modification are usually caught by the MPS, primarily the liver and spleen, during circulation, depending on their size and surface characteristics [9]. To overcome this problem, nanoparticles can be coated with hydrophilic polymers. Coating can efficiently protect nanoparticles from capture by macrophages [10, 11-12]. The increased hydration also helps nanoparticles to be more water soluble and less sensitive to enzymatic degradation, therefore enhancing biocompatibility [12, 13].



Polyplexes: They are complexes of positively charge polymers that condense siRNAs by charge-to-charge interaction. Polyplexes have been studied as siRNA delivery system; however, their poor pharmacokinetics excludes them from being used systemically. Lately, RGD (Arg-Gly-Asp) peptide, which binds to αv integrin, highly expressed in certain cancers and tumor vasculature, was coupled to PEG and attached to Polyethyleneimine (PEI), a cationic polymer. Intravenous administration of VEGFR-siRNAs formulated in the RGD-PEG-PEI nanoplex given every 3 days significantly suppressed the growth of subcutaneously transplanted tumors in nude mice.