Effect of PLGA composition on nanoencapsulation, fluorescence stability and cellular internalization of R-phycoerythrin in colorectal cancer cells.

In Colorectal Cancer (CRC), precise tumor imaging is crucial for detection but remainschallenging. R-phycoerythrin (R-PE), a highly fluorescent protein from red algae, shows potential for this purpose but its instability in aqueous environments limits direct use.Thus, nanoencapsulationcould be a promising strategy to overcome this limitation. Herein, R-PE was encapsulated in nanoparticles (NPs) obtained from two different types of poly (lactic-co-glycolic acid) - PLGA to evaluate the effects ofcopolymer molecular weight, termination, and Lactic Acid (LA) content onthephysicochemical and biological performanceof the R-PE-loaded nanoparticlein a CRC cell line. The nanoparticles were produced by double emulsification/solvent evaporation usingRG 502 (7-17 kDa, ester-terminated, LA: 50 %)andRG 653 H (24-38 kDa, carboxy-terminated, LA: 65 %). Surfactant concentrations (0.5 % or 0.75 % w/v in the first emulsion; 1 % or 1.5 % w/v in the second one) and organic phase volumes (6 or 10 mL) were also tested to optimize nanoparticles characteristics. The selected RG 502 R-PE NP and RG 653 H R-PE NP, with higher surfactant concentrations and the lower organic phase volume, showed, respectively, nanometric size (183 ± 1 and 221 ± 8 nm), appropriate PdI (0.080 and 0.183), high encapsulation efficiencies (91.26 ± 6.87 % and 90.78 ± 0.34 %) and stability for 40 days. In in vitro release assay, RG 653 H showed superior stability and lower R-PE release under physiological conditions. In cytotoxicity and phototoxicity assays using HCT-116 and L929 cells, both nanoparticles demonstrated biocompatibility, and showed maximum internalization in HCT-116 cells 3 h after treatment. However, RG 653 H R-PE NP exhibited higher fluorescence intensities over 24 h, demonstrating potential for use as a cellular biomarker in CRC.