Targeted delivery of α-Mangostin to Prostate Cancer Cells Utilizing Reconstituted High-Density Lipoprotein Nanoparticles

Purpose: Androgen deprivation therapy remains the primary treatment for inhibiting the progression of prostate cancer (PCa). However, depletion of systemic androgens enhances the development of androgen independence resulting in the highly malignant castration-resistant phenotype. Interest has grown in utilizing cell cycle checkpoint inhibitors to induce cellular arrest and apoptosis. A natural compound, α-Mangostin, possesses selective anti-cancer effects against PCa by inhibiting CDK4-CyclinD complex activity, thus restricting the progression of the cell cycle. However, the employment of α-Mangostin as a chemotherapeutic is limited due to its poor oral bioavailability and hydrophobicity, making delivery difficult. Reconstituted High-Density Lipoproteins nanoparticles (rHDL-NPs) are biocompatible targeted nanoparticles capable of encapsulating various compounds. Drug delivery is mediated through a non-endocytic mechanism via the Scavenger Receptor Class B Type-1 (SR-B1). Significant overexpression of SR-B1 has been documented in PCa, which enhances cholesterol accumulation thus fuels growth, proliferation, and intertumoral androgen synthesis. This increased expression of the SR-B1 makes it a primary target for the rHDL-NPs. Because of its lipophilic characteristics, we hypothesize that the α-Mangostin can be successfully encapsulated in the rHDL-NPs, retain its biological effects, and be delivered via the SR-B1. Methods: The rHDL formulations were prepared using a modified protocol utilizing sodium cholate and sonication. The physical characteristics of the rHDL were determined using Dynamic Light Scattering (DLS), which include the polydispersity index (PDI) Zeta Potential particle diameter. The absorbance of the samples was measured using a spectrophotometer for the concentration of α-Mangostin and used to calculate the encapsulation efficiency. The anisotropy was calculated to compare the degree of molecular rotation between the free and encapsulated drug. The fluorescence lifetime (FLT) was used to detect changes in the local environment of the drug. Cytotoxicity studies were conducted using three cell lines: PZ-HPV as the normal cell line, DU145, and 22RV1 as the PCa cell lines. Different concentrations of free and rHDL encapsulated α-Mangostin were administered to 2D cell cultures to determine if there was a difference in cytotoxicity. Vehicle and empty particles were used as controls. A CCK-8 assay was used to determine the cell viability after administering the treatments. Results: The rHDL nanoparticles were produced to meet the standards of the NIH criteria for lipid-based nanoparticles. The drug was found in the same fraction as the rHDL, with an average encapsulation efficiency of 55%. There was a significant increase in anisotropy when compared to the free drug. The FLT decreased by more than half. The drug loading study found the maximum amount of drug encapsulated without decreasing the particle quality. Finally, the α-Mangostin rHDL-NPs continued to produce a cytotoxic effect comparable to the free drug. Conclusion: This study produced and characterized a stable α-Mangostin rHDL-NP formulation. The changes in the anisotropy and FLT suggest that encapsulation of the α-Mangostin has occurred. Furthermore, the encapsulation of the α-Mangostin did not block the cytotoxic effects against the PCa cell lines and decreased cell viability.