Probing the Assembly of HDL Mimetic, Drug Carrying Nanoparticles Using Intrinsic Fluorescence.

Reconstituted high-density lipoprotein (HDL) containing apolipoprotein A-I (Apo A-I) mimics the structure and function of endogenous (human plasma) HDL due to its function and potential therapeutic utility in atherosclerosis, cancer, neurodegenerative diseases, and inflammatory diseases. Recently, a new class of HDL mimetics has emerged, involving peptides with amino acid sequences that simulate the the primary structure of the amphipathic alpha helices within the Apo A-I protein. The findings reported in this communication were obtained using a similar amphiphilic peptide (modified via conjugation of a myristic acid residue at the amino terminal aspartic acid) that self-assembles (by itself) into nanoparticles while retaining the key features of endogenous HDL. The studies presented here involve the macromolecular assembly of the myristic acid conjugated peptide (MYR-5A) into nanomicellar structures and its characterization via steady-state and time-resolved fluorescence spectroscopy. The structural differences between the free peptide (5A) and MYR-5A conjugate were also probed, using tryptophan fluorescence, FÓ§rster resonance energy transfer (FRET), dynamic light scattering, and gel exclusion chromatography. To our knowledge, this is the first report of a lipoprotein assembly generated from a single ingredient and without a separate lipid component. The therapeutic utility of these nanoparticles (due to their capablity to incorporate a wide range of drugs into their core region for targeted delivery) was also investigated by probing the role of the scavenger receptor type B1 in this process. SIGNIFICANCE STATEMENT: Although lipoproteins have been considered as effective drug delivery agents, none of these nanoformulations has entered clinical trials to date. A major challenge to advancing lipoprotein-based formulations to the clinic has been the availability of a cost-effective protein or peptide constituent, needed for the assembly of the drug/lipoprotein nanocomplexes. This report of a robust, spontaneously assembling drug transport system from a single component could provide the template for a superior, targeted drug delivery strategy for therapeutics of cancer and other diseases (Counsell and Pohland, 1982).

Reconstituted HDL: Drug Delivery Platform for Overcoming Biological Barriers to Cancer Therapy.

Drug delivery to malignant tumors is limited by several factors, including off-target toxicities and suboptimal benefits to cancer patient. Major research efforts have been directed toward developing novel technologies involving nanoparticles (NPs) to overcome these challenges. Major obstacles, however, including, opsonization, transport across cancer cell membranes, multidrug-resistant proteins, and endosomal sequestration of the therapeutic agent continue to limit the efficiency of cancer chemotherapy. Lipoprotein-based drug delivery technology, "nature's drug delivery system," while exhibits highly desirable characteristics, it still needs substantial investment from private/government stakeholders to promote its eventual advance to the bedside. Consequently, this review focuses specifically on the synthetic (reconstituted) high-density lipoprotein rHDL NPs, evaluating their potential to overcome specific biological barriers and the challenges of translation toward clinical utilization and commercialization. This highly robust drug transport system provides site-specific, tumor-selective delivery of anti-cancer agents while reducing harmful off-target effects. Utilizing rHDL NPs for anti-cancer therapeutics and tumor imaging revolutionizes the future strategy for the management of a broad range of cancers and other diseases.