From Characterization to Cellular Internalization: Nanostructured Lipid Carriers Containing Green Propolis in Tumor Cells

Nanostructured lipid carriers (NLCs) are drug delivery systems composed of lipid matrices capable of encapsulating a variety of molecules, in addition to exhibiting low toxicity, safe biodegradation, increased half-life, and controlled drug release, thereby attenuating side effects. Brazilian green propolis has attracted growing scientific interest due to its antitumor activity, acting through the inhibition of cell proliferation, induction of apoptosis, and inhibition of tumor growth. However, its therapeutic application is limited by low bioavailability and stability. In this context, the encapsulation of green propolis in NLCs emerges as a strategy to promote its controlled release and improve its bioavailability, thereby enhancing its antitumor activity. The objective of this study was to synthesize NLCs using the emulsification-ultrasonication method, aiming to encapsulate propolis, functionalize them through the addition of DPPE-CAP-Biotinyl, label them with the fluorescent probes Rhodamine B and TopFluor-PE, and analyze the potential for NLC internalization in two tumor cell lines: SCC9 (oral cell carcinoma) and A375 (melanoma). The formulations exhibited hydrodynamic diameters ranging from approximately 300 to 670 nm, with PDI values ranging from 0.02 to 0.43, reflecting different degrees of homogeneity among the samples. The zeta potential was negative for all formulations, ranging from -15 to -34 mV, indicating colloidal stability of the dispersions. In the internalization assay, all tested formulations were found to have been internalized by the cells after 4 hours of incubation, with vesicle formation at the membrane and cytoplasmic accumulation. Additionally, live-cell imaging assays revealed cellular internalization within the first few minutes of incubation, occurring at approximately 15 minutes in both cell lines, suggesting rapid and similar internalization kinetics between the tumor cell lines evaluated. The results obtained indicate that the developed NLCs exhibit physicochemical characteristics suitable for nanoparticle internalization into tumor cells, highlighting their potential as a carrier system for green propolis.