Abstract :
[en] Biological barriers to drug delivery are obstacles in the human body that prevent drugs from reaching their intended site of action at the rate and extent required for therapeutic effectiveness. These barriers include a diverse range of structures and components of the human body, such as the intestinal barrier, the pulmonary barrier, the skin barrier, the blood-brain barrier, the intravascular barrier, the tumor microenvironment, the plasma membrane of target cells, the intracellular barriers, etc. The current understanding of these biological barriers at the molecular level, their functional mechanisms, and the possibility of their modulation has opened up new avenues for various nanotechnology-based drug delivery approaches with the ultimate goal of getting enough control over where the drug goes in the body (biodistribution) and how much gets delivered at the target site (bioavailability).
This work explores this concept through the design, characterization, and in vitro evaluation of two categories of nanocarriers, namely pH-sensitive liposomes and polymeric nanoparticles (drug-polymer complexes), as drug delivery strategies to navigate respectively the cellular barriers (including the endosomal membrane) and intestinal barriers for bioavailability enhancement of therapeutic peptides and poorly water-soluble drugs, respectively.
It has been recently demonstrated that the modulation of one isoform of the native tetrameric lactate dehydrogenase (LDHB) could inspire new openings toward developing novel therapeutics for cancer treatment. Therefore, in the first part of this work, pH-sensitive liposomes combining the protective properties of polyethylene glycol (stealth liposomes) with the transfection ability of some functional pH-sensitive lipids (fusogenic and ionizable lipids) were investigated as a delivery platform that could efficiently deliver novel anticancer peptide inhibitors of lactate dehydrogenase B (LDHB) into selected tumor cell lines (SiHa) without disrupting the physiological function of healthy cells. This strategy utilizes the acidic pH environment of the endosomal network to trigger nanoparticle disassembly, endosomal membrane disruption, and cargo release, thereby knocking out LDHB activity in the cytosol. The formulated anticancer peptide-loaded liposomes exhibited acceptable encapsulation efficiency and attractive particle size for achieving selective accumulation into tumors through passive targeting. Some insights into their behavior in endosomal pH have been provided, and results evidenced distinct structural and release profiles for each class of pH-sensitive lipids (fusogenic and ionizable lipids) involved in liposome formulation. The ability of liposomes to disrupt the endosomal membrane (endosomolytic power) and release cargo in the cytosol compartment was studied by means of fluorescently labeled liposomes and cargo molecules. The biocompatibility studies confirm the safety and suitability of these formulated liposomal systems for intravenous administration.
The second part of the work deals with the evaluation of a new PDMAEMA-based polymeric platform tailored to improve the oral bioavailability of hydrophobic active pharmaceutical ingredients through solubility and permeability enhancement. The results of physicochemical investigations clearly demonstrate that 10kD-PDMAEMA has the ability to solubilize hydrophobic compounds through the formation of molecular complexes. More importantly, conditions at which this polymeric platform can be safely used to modulate the transfer of poorly soluble and permeable drugs across the Caco-2 monolayer have been identified. The permeability of fluorescein, used as a model drug to establish the proof of concept, was shown to increase by 6.1 without causing major toxicity signs, as confirmed by ultrastructure analysis of the Caco-2 cell monolayer subjected to the transport study. Preliminary information about the mechanism of transport of PMDAEMA-drug complexes across the Caco-2 cell monolayer has been comprehensively suggested.
Overall, the pH-responsive nanocarrier platforms developed in this work hold the promise for new openings towards the diversity of delivery technologies needed to navigate through a plethora of dynamic biological barriers in order to efficiently reach the tissue or disease target targets with drugs.
