Insight into the Modification of Polymeric Micellar and Liposomal Nanocarriers by Fluorescein-Labeled Lipids and Uptake-Mediating Lipopeptides

Abstract

Encapsulation of diagnostic and therapeutic compounds in transporters improves their delivery to the point of need. An even more efficient treatment of diseases can be achieved using carriers with targeting or protecting moieties. In the present work, we investigated micellar and liposomal nanocarriers modified with fluorescein, peptides, and polymers that are covalently bound to fatty acids or phospholipids to ensure a self-driven incorporation into the micelles or liposomes. First, we characterized the photophysics of the fluorescent probes in the absence and in the presence of nanocarriers. Changes in the fluorescence decay time, quantum yield, and intensity of a fluorescein-labeled fatty acid (fluorescein-labeled palmitic acid [fPA]) and a fluorescein-labeled lipopeptide (P2fA2) were found. By exploiting these changes, we investigated a lipopeptide (P2A2 as an uptake-mediating unit) in combination with different nanocarriers (micelles and liposomes) and determined the corresponding association constant Kass values, which were found to be very high. In addition, the mobility of fPA was exploited using fluorescence correlation spectroscopy (FCS) and fluorescence depolarization (FD) experiments to characterize the nanocarriers. Cellular uptake experiments with mouse brain endothelial cells provided information on the uptake behavior of liposomes modified by uptake-mediating P2A2 and revealed differences in the uptake behavior between pH-sensitive and pH-insensitive liposomes.

Shining Light on Polymeric Drug Nanocarriers with Fluorescence Correlation Spectroscopy

“…Such studies are not limited to polymeric NCs, but can also be applied to other nanocarrier system. In particular, nanocarriers based on lipids [40,68,81,95,96,[152][153][154][155][156] and proteins [157][158][159][160] as well as on metal-organic framework, [86,161,162] calcium phosphate, [163,164] silica [165][166][167] or gold [168,169] nanoparticles, were often characterized with FCS. Furthermore, inherently fluorescent nanoparticles such as quantum dots, [101,104,109,[170][171][172] carbon dots [173][174][175] or nanodiamonds [176][177][178][179] have been extensively studied with respect to their interactions with plasma proteins and use for transfection or bioimaging.…”

“…In 2006, Rigler and Meier [32] studied the encapsulation of small dye molecules and fluorescently labeled Avidin in nanocontainers prepared from amphiphilic triblock copolymers and introduced the described above method to evaluate the drug loading efficiency using molecular/particle fluorescence brightness. In the last two decades, FCS has become a powerful tool to quantify the loading of therapeutic molecules in various polymeric nanocariers, including polymer nanoparticles, [30][31][32][33][34][35] amphiphilic copolymer micelles and aggregates, [36][37][38][39][40][41][42][43][44][45] polymerosomes, [46][47][48][49][50] nanogels, [29,[51][52][53][54] polymer brushes, [55,56] dendritic core-shell star polymers, [57] etc.…”

Self-assembled biodegradable polymeric micelles to improve dapoxetine delivery across the blood–brain barrier

“…42,43 The resulting prolonged circulation half-life allows diffusion in the tissues or micelles taken up by absorptive enterocytes that will be predominantly transported via the bloodstream. 44,45 Both M cells and enterocytes are assimilated into the blood and lymph vessels in addition to participating in mucoadhesion, which delays the drugs' residence time.…”

Fluorescence Correlation Spectroscopy Monitors the Fate of Degradable Nanocarriers in the Blood Stream

“…FCS is particularly well-suited to study drug NC systems in complex media because of its very high sensitivity and selectivity. During the last 2 decades, the technique has often been used to monitor the formation of NCs, their drug loading, , stability, − interactions with plasma proteins, ,,− and drug release . Furthermore, due to the fluorescence-based selectivity of FCS, such studies were performed not only in aqueous buffers but also in blood plasma and other biofluids. ,− …”