It is our goal in this review not only to protect the array of ligand-targeted siRNA NPs, but also to indicate possible flaws in the particular study and alert the reader to the potential of the ligand, independent of the efficacy of the NP. tumors is due to the enhanced permeation and retention (EPR) effect. The EPR effect is usually thought to result from a combination of leakiness of tumor blood vessels resulting in flux of NPs from your blood into the tumor tissue and reduced numbers of lymphatic vessels in tumors associated with decreased drainage of NPs and occurs despite a higher interstitial pressure within the tumor. Notably, several rarely used therapies, such as nitroglycerin, may enhance the EPR effect and augment accumulation of NPs within tumors [2, 3]. When NPs Rifaximin (Xifaxan) have diameters less than ~10?nm, they are rapidly secreted by the kidneys and the effect of EPR is greatly reduced . Moreover, NPs with very short half-life and/or with their nonspecific binding may accumulate within the tumor to a greater extent, if the Rifaximin (Xifaxan) EPR effect is usually enhanced by pegylation of particles. By prolonging blood circulation (plasma half-life) of the NP and reducing nonspecific binding, pegylation may also enable accumulation of ligand-nanoparticle conjugates in tumors above the EPR effect. Building on accumulation of NPs in tumors from the EPR effect, researchers have sought to increase their tumor delivery by coating the particles with tumor-localizing ligands. The mechanism by which ligands increase the antitumor efficacy of their cargo (in our case siRNA) is usually somewhat controversial. Most investigators have decided that increased efficacy of targeted ligand-siRNA NPs is due to enhanced binding to the tumor surface marker and accumulation of NPs in the tumor compared to that in nontargeted tissues. Some investigators, however, have found that accumulation of targeted and nontargeted NPs within tumors was comparable and found that increased efficacy of the targeted NP was due to enhanced receptor-mediated endocytosis and increased intracellular localization of the siRNA therapeutic . Most likely, both mechanisms have important functions in ligand- targeted therapy, improving efficacy, and depend around Rabbit Polyclonal to SLC6A8 the delivery vehicle, the target of the ligand, and strategy used in making the ligand (i.e., aptamer, peptide, or antibody). In this review, we describe various strategies that have been developed for ligand-siRNA therapeutics to increase their selectivity toward tumors (Physique 1). Decorating the NP with Rifaximin (Xifaxan) the ligand together with PEG shell, however, does not adequately describe how ligand molecules may affect stability of the core particle. As investigators have reported, ligand molecules and their specific linkages to the NP may significantly influence release of siRNA and their efficacy . Open in a separate windows Physique 1 Schematic overview of the different ligands and core particles that target tumors. An array of core particles and ligands has been used to carry siRNA which inhibit oncogenes or induce apoptosis of tumor cells. In addition, the efficacy (or lack thereof) of the siRNA-NP may interfere with the impartial evaluation of ligand-directed therapies. It is our goal in this review not only to cover the array of ligand-targeted siRNA NPs, but also to indicate possible flaws in the particular study and alert the reader to the potential of the ligand, independent of the efficacy of the NP. This determination will be particularly important in cases in which there has been Rifaximin (Xifaxan) reduced antitumor efficacy with the nanoparticle. 2. Ligands Targeting Tumor Cells and Vessels Ligands targeting tumor cells and their angiogenic vessels have primarily been peptides isolated by the phage display method (Table 1) (Physique 2) Rifaximin (Xifaxan) [7C15] (see review by ). Since tumor cells and angiogenic blood vessels often have comparable cell surface receptors, ligands can have dual targeting capabilities for both tumor vasculature and tumor cells. When this is the case, siRNA therapeutic agents.
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