Synthesis and Characterization of Poly(RGD) Proteinoid Polymers and NIR Fluorescent Nanoparticles of Optimal d,l-Configuration for Drug-Delivery Applications—In Vitro Study

Abstract

RGD sequence is a tripeptide composed of three amino acids: arginine (R), glycine (G), and aspartic acid (D). The RGD peptide has a high affinity to the integrin alpha v beta 3, which is overexpressed on the membrane of many cancer cells and is attracted to areas of angiogenesis. Proteinoids are biodegradable polymers based on amino acids which are formed by bulk thermal step-growth polymerization mechanism. Hollow proteinoid nanoparticles (NPs) may be formed via self-assembly process of the proteinoid polymers. We propose using novel RGD-based proteinoid polymers to manufacture NPs in which the RGD motif is self-incorporated in the proteinoid backbone. Such P(RGD) NPs can act both as a drug carrier (by encapsulation of a desired drug) and as a targeting delivery system. This article presents the synthesis of four RGD proteinoids with different RGD optical configurations, ( d ) or ( l ) arginine, glycine, and ( d ) or ( l ) aspartic acid, in order to determine which configuration is optimal as a drug-targeting carrier. These new RGD proteinoid polymers possess high molecular weights and molecular weight monodispersity. Homonuclear nuclear magnetic resonance methods were employed to predict the expected concentration of RGD tripeptide sequence in the polymer. Near infrared fluorescent NPs have been prepared by the encapsulation of indocyanine green (ICG) dye within the different P(RGD) NPs. The dry diameters of the hollow P(R d GD d ), P(R d GD), P(RGD), and P(RGD d ) NPs are 55 ± 13, 48 ± 9, 45 ± 11, and 42 ± 9 nm, respectively, whereas those of the ICG-encapsulated NPs were significantly higher, 141 ± 24, 95 ± 13, 86 ± 11, and 87 ± 12 nm, respectively. The ICG-encapsulated P(R d GD) NPs exhibited higher selectivity toward epithelial injury, as demonstrated using an in vitro scratch assay, because the P(R d GD) NPs accumulated in the injured area at higher concentrations when compared to other P(RGD) NPs with different chiralities. Therefore, the P(R d GD) polymer configuration is the polymer of choice for use as a targeted drug carrier to areas of angiogenesis, such as in tumors, wounds, or cuts.

Engineering of Doxorubicin-Encapsulating and TRAIL-Conjugated Poly(RGD) Proteinoid Nanocapsules for Drug Delivery Applications

“…The dry diameter and size distribution of the hollow P(RGD), Dox/P(RGD), TRAIL-P(RGD), and PEGylated Dox/P(RGD) and TRAIL-P(RGD) NCs were measured with high resolution scanning electron microscopy (HR-SEM) and analyzed by ImageJ software, an open source Java image processing program, as described previously [ 33 ].…”

“…Previous work illustrated encapsulation of various amphiphiles, e.g., dyes, [ 28 , 29 , 30 ] vitamin A [ 31 ], and Ouxin [ 32 ], for diagnostic imaging, reduction-responsive vehicle, cosmetics, and agriculture. P(R D GD) nanocapsules (NCs) exhibit higher selectivity toward angiogenesis sites compared to other configurations of amino acids such as P(R D GD D ), which includes D-aspartic acid [ 33 ].…”

“…This initiates polymerization with the other amino acids, forming a proteinoid polymer [ 20 ]. Previous study in our lab demonstrated via NMR that the RGD content in P(RGD) is about 11% [ 33 ].…”

Tumor-Targeted Fluorescent Proteinoid Nanocapsules Encapsulating Synergistic Drugs for Personalized Cancer Therapy

“…D-arginine (R), glycine (G) and L-aspartic acid (D) were used for randomly achieving the RGD sequence within the proteinoid backbone; previous studies showed that 13% of the established proteinoids contain the RGD sequence [ 26 , 28 ]. The R D GD polymer configuration denoted here as P(RGD) is the polymer of choice for targeted drug delivery to areas of angiogenesis such as a tumor microenvironment [ 28 ].…”

“…D-arginine (R), glycine (G) and L-aspartic acid (D) were used for randomly achieving the RGD sequence within the proteinoid backbone; previous studies showed that 13% of the established proteinoids contain the RGD sequence [ 26 , 28 ]. The R D GD polymer configuration denoted here as P(RGD) is the polymer of choice for targeted drug delivery to areas of angiogenesis such as a tumor microenvironment [ 28 ]. The RGD sequence is known for its specific attraction to αvβ3 integrin, an endothelial cell receptor for the extracellular matrix, which is highly expressed on neovascular endothelial cells that support tumor growth [ 29 , 30 ].…”