Star-Shaped Polylactide Dipyridamole Conjugated to 5-Fluorouracil and 4-Piperidinopiperidine Nanocarriers for Bioimaging and Dual Drug Delivery in Cancer Cells

Star-shaped polylactide (SSPLA) nanoparticles (NPs) with dipyridamole (DIP) core conjugated with 5-fluorouracil (5FU) and 4-piperidinopiperidine (4PIP) were designed and synthesized to achieve apoptosis by synergistic dose-dependent delivery than using free drugs. In our current investigation, DIP was employed as the initiator in ring-opening polymerization reaction to make SSPLADIP. We then described the synthesis of tailor-made, self-assembled, carboxyl group-substituted fluorescent SSPLADIP conjugated with a secondary amine group of 5FU anticancer drug to form a dual prodrug complex (SSPLADIP5FU). To compare the efficacy of this combination, another anticancer drug 4PIP was also covalently conjugated with a hydroxyl-end terminal by nucleophilic substitution on SSPLADIP to form SSPLADIP4PIP. 4PIP inhibits the topoisomerase enzyme in DNA replication. Synthesized star-shaped drug constructs were characterized by atomic force microscopy, scanning electron microscopy, NMR, fluorescence spectroscopy, gel permeation chromatography, and MALDI-TOF. This is the first report on these drug combinations (DIP–5FU and DIP–4PIP) fabricated on the polylactic acid biopolymer to form NPs of size <150 nm with excellent encapsulation and loading efficiency with time-dependent release in acidic pH (5.4). The release patterns of NPs were accordant with zero-order and Korsmeyer–Peppas models. The glial (G1), pancreatic (MIAPaCa2), colon (DLD1) cancer cells and normal fibroblast cell line (L929 cells) were used to study the NP uptake in lysosomes and nucleus after 48 h by confocal microscopy. The cytotoxicity of SSPLADIP5FUNPs showed an IC50 of 20 μg/mL in colon cancer cells and remained nontoxic to L929 cells even at 1000 μg/mL. To mimic the colonic environment, we placed free DIP in a simulated colonic fluid with our SSPLADIP5FU NPs. It was observed that our NPs were stable without binding with constituents in the colonic fluid, whereas free DIP bounded with Ca2+, protein, and phosphatidylcholine, resulting in quenching of its fluorescence. Apoptosis by tunability ratios of dual drugs was confirmed by fluorescence activated cell sorting and fluorescence resonance energy transfer assay in flow cytometry.