Knowledge-Based Design of 5-Fluororacil Prodrug Liposomal Formulation: Molecular Packing and Interaction Revealed by Interfacial Isotherms and X-ray Scattering Techniques

Prodrugs and nanoformulations are two effective strategies for sustained drug release and targeting drug delivery. In this study, we combined the two strategies to judiciously design the liposome formulation incorporating an amphiphilic prodrug of 5-fouroracil (5-FU), named 5-FCPal, for sustained drug release and enhanced bioavailability. 5-FCPal is an analogue of capecitabine (N⁴-pentyloxycarbonyl-5'-deoxy-5-fluorocytidine, Xeloda) by substituting the pentyl group at the N⁴ position with the palmityl. The amphiphilic molecule of 5-FCPal can self-assemble with the phospholipids to form stable vesicle structures with high drug loading. Although lipid vesicles have been widely studied and commercially used for clinical applications, because of the enormous options of the lipids and the equitable balance of hydrophobicity and bioavailability, it is essential to fundamentally understand the molecular interactions when designing and optimizing the liposomal prodrug formulations. We report the study of using X-ray liquid surface scattering techniques integrated with a Langmuir trough to explicitly reveal the interfacial behavior of the monolayer membrane of 5-FCPal with various saturated and unsaturated lipids with positively charged, neutral, and negatively charged head groups. More specifically, interfacial packing of the molecules was quantified using interfacial isotherms, X-ray reflectivity (XR), and grazing-incidence diffraction (GIXD). The results indicate that the interactions between the prodrug and the cationic lipids are most favorable. The highest drug loading is quantified by increasing the molar ratio of the prodrug until stable monolayer structures were disrupted by the multiple-layer domain of prodrug aggregates. Stable liposomes of 100 nm with 50% drug loading of 5-FCPal were generated based on the findings from the X-ray studies.

Heterogeneous toroidal spiral particles for islet encapsulation

Transplantable cell encapsulation systems present a promising approach to deliver a therapeutic solution from hormone-producing cells for the treatment of endocrine diseases like type 1 diabetes. However, the development of a broadly effective and safe transplantation system has been challenging. While some current micro-sized capsules have been optimized for adequate nutrient and metabolic transport, they lack the robustness and retrievability for the clinical safety translation that macro-devices may offer. An existing challenge to be addressed in the current macro-devices is their configuration which may lead to unsatisfactory mass transfer. Here, we design and characterize a millimeter-size particle system of poly-ethylene glycol (PEG) featuring internal toroidal spiral channels, called toroidal spiral particles (TSPs). The characteristic internal structure of the TSPs allows for large encapsulation capacity and large surface area available to all the encapsulated cell mass for effective molecular diffusion. The polymeric matrix renders the particle flexible yet robust for safe transplantation and retrieval. We demonstrate the feasibility of fabricating these particles with various polymer compositions, while optimizing their mechanical properties as well as glucose and insulin permeability. Encapsulation of islets of Langerhans is achieved with high loading capacity (∼160 IEQ per TSP) and excellent cell viability. TSP-encapsulated islets showed similar glucose-stimulated insulin secretion to the naked islets. Preliminary biocompatibility of the TSPs on naïve C57BL/6 mice shows minimal inflammatory response after 4-week transplantation into the intraperitoneal (IP) space. Long-term therapeutic efficacy of encapsulated islets needs to be confirmed in diabetic rodent models in the future, while determining minimal mass required to reverse diabetes. However, we believe from the in vitro favorable results and the TSPs' unique design that TSPs may provide a safe, effective method to transplant and retrieve therapeutic cells for type 1 diabetes treatment and may also be applicable for other cell therapies.

High-loading Gα13-binding EXE peptide nanoparticles prevent thrombosis and protect mice from cardiac ischemia/reperfusion injury

Inefficient delivery is a major obstacle to the development of peptide-based drugs targeting the intracellular compartment. We recently showed that selectively inhibiting integrin outside-in signaling using a peptide (mP6) derived from the Gα13-binding ExE motif within the integrin β3 cytoplasmic domain had antithrombotic effects. Here, we engineered lipid-stabilized, high-loading peptide nanoparticles (HLPN), in which a redesigned ExE peptide (M3mP6) constituted up to 70% of the total nanoparticle molarity, allowing efficient in vivo delivery. We observed that M3mP6 HLPN inhibited occlusive thrombosis more potently than a clopidogrel/aspirin combination without adverse effects on hemostasis in rodents. Furthermore, M3mP6 HLPN synergized with P2Y12 receptor inhibitors or the clopidogrel/aspirin combination in preventing thrombosis, without exacerbating hemorrhage. M3mP6 HLPN also inhibited intravascular coagulation more potently than the P2Y12 inhibitor cangrelor. Postischemia injection of M3mP6 HLPN protected the heart from myocardial ischemia-reperfusion injury in a mouse model. This study demonstrates an efficient in vivo peptide delivery strategy for a therapeutic that not only efficaciously prevented thrombosis with minimal bleeding risk but also protected from myocardial ischemia-reperfusion injury in mice.

Impeded Molecular Reorganization by Polyethylene Glycol Conjugation Revealed by X-ray Reflectivity and Diffraction Measurements

Polyethylene glycol (PEG) coatings have been widely applied in pharmaceutical and biomedical systems to prevent nonspecific protein absorption, increase vesicle blood circulation time, and sustain drug release. This study systematically investigated the planar interfacial organization of phospholipid monolayers containing various amounts of PEG conjugations before and after enzyme-catalyzed degradation of the lipids using X-ray reflectivity and grazing incidence X-ray diffraction techniques. Results showed that attaching PEG to the headgroup of the lipids up to 15 mol % had limited effects on molecular packing of the lipid monolayers in the condensed phase at the gas-liquid interface and negligible effects on the enzyme adsorption to the interface. After enzyme-catalyzed degradation, equimolar fatty acids and lyso PC were generated. The fatty acids together with the subphase Ca²⁺ self-assembled into highly organized multilayer domains at the interface. The X-ray measurements unambiguously revealed that the densely packed PEG markedly hindered microphase separation and formation of the palmitic acid-Ca²⁺ complexes.

Spontaneous collapse of palmitic acid films on an alkaline buffer containing calcium ions

Understanding the interaction of ions with fatty acids is important to identify their roles in various bioprocesses and to build novel biomimetic systems. In this study, the molecular organization of palmitic acid (PA) films on alkaline buffer solutions (pH 7.4) with and without divalent Ca²⁺ was measured at a constant surface area using Langmuir troughs coupled with microscopy and X-ray interfacial techniques. Without Ca²⁺, PA molecules remained a monolayer organization; however, with Ca²⁺, formation of the inverted bilayers of PA-Ca²⁺ superstructures caused a spontaneous 2D to 3D transformation under no compression due to the strong interaction between PA and the divalent cation. Self-assembly of this highly-organized inverted bilayer superstructure involved a two-step process of nucleation and nuclei growth. During nucleation, densely packed PA and Ca²⁺ monolayer firstly corrugated and some of PA and Ca²⁺ molecules ejected out from the monolayer; the ejected molecules then reorganized and formed the inverted bilayer nuclei. Nucleation was followed by nuclei growth, during which PA and Ca²⁺ in the monolayer kept integrating into the inverted bilayer structure through molecule migration and PA rotation around Ca²⁺.