Design and characterization of monoacylglycerol lipid cubic phase systems for the effective delivery of small molecule pharmaceuticals

To be effective, a drug must be efficiently delivered in sufficient quantities over a period of time long enough for it to carry out its desired effect. A major challenge in this sense is poor retention and bioavailability of drugs, particularly those that display poor solubility. The number of newly discovered drugs is disproportionate to the number that make it to market because of less than desirable solubility and permeability profiles, but smart drug delivery systems, such as lipid-based systems, are capable of overcoming these challenges. One particular system, the amphiphilic, biocompatible, and biodegradable lipid cubic phase, has shown promise as an effective carrier system for the controlled release of drugs varying in solubility. This work explores the behaviour of a variety of industrially relevant small molecule pharmaceuticals in lipid cubic phases formulated with different host lipids for potential controlled delivery applications. An understanding of the molecular mechanisms underlying the process of dissolution/diffusion from these phases was elucidated to support the field of controlled drug delivery using in silico molecular dynamic modelling and empirical approaches. A comprehensive characterization approach was taken both macroscopically and microscopically using small-angle X-ray scattering and polarized light to ascertain the mesophase accessed upon incorporation of molecules of varying solubilities and size. In the first instance, the influence of environmental conditions on the release profile of four antihistamine molecules was studied to establish in vitro models that might assist in predicting the dissolution behaviour of a given pharmaceutical with known physicochemical properties. Two model first-generation and two model second-generation H1 antagonist antihistamine drugs were selected and formulated in two separate monoacyglycerol-derived matrices. The impact of encapsulating the molecules in the lipid cubic systems on their mucoadhesive properties was demonstrated using multi-parametric surface plasmon resonance (MP-SPR). With a potential application in developing therapies for the treatment of allergic reactions, the ability of the formulations to inhibit mediator release utilizing RBL-2H3 mast cells with the propensity to release histamine upon induction was presented. Lipid cubic formulations can enhance the intestinal solubility and subsequent bioavailability of notoriously hydrophobic drug entities by reducing drug precipitation and facilitating mass transport to the intestinal surface for absorption. In this context, the aims of the second study were twofold: to evaluate an approach to regulate the rate of degradation of lipid cubic phase drug delivery systems by targeting the enzyme interactions responsible for their demise; and to study the subsequent drug release profiles from bulk lipid cubic gels using model drugs of contrasting hydrophobicity. In a novel approach, monoacylglycerol cubic phases were formulated with a potent lipase inhibitor tetrahydrolipstatin displaying controlled degradation with at least a 4-fold longer release compared to the blank systems. Sustained release of a model hydrophobic pharmaceutical (a clofazimine salt) was studied over 30 days to highlight the advantage of incorporating an inhibitor into the cubic network to achieve tunable lipid release systems. The final aspect of this thesis deals with the interplay between the lipolysis rate and the interfacial interaction of porcine pancreatic lipase with lipid cubic substrates encapsulating the THL. In the final chapter, inhibitor-modified monoolein lipid cubic formulations designed to encapsulate and control the release of a model BCS class IV drug paclitaxel (PTX) were examined under simulated lipolysis in the presence of lipase and its cofactors colipase and calcium. We present a combination of thermodynamic and molecular dynamics simulations of the competitive inhibition with experimental dynamic digestion studies to reveal the role and mode of action of the studied lipase effectors in designing a degradation-controlled release system for the poorly soluble drug PTX. These studies facilitated a deeper understanding of the approach described in the previous chapter, expanding the study to open new important possibilities in the field of pharmaceutical transport especially where difficult-to-formulate drugs are concerned

Lipid cubic systems for sustained and controlled delivery of antihistamine drugs

Antihistamines are capable of blocking mediator responses in allergic reactions including allergic rhinitis and dermatological reactions. By incorporating various H1 receptor antagonists into a lipid cubic phase network, these active ingredients can be delivered locally over an extended period of time owing to the mucoadhesive nature of the system. Local delivery can avoid inducing unwanted side effects, often observed after systematic delivery. Lipid-based antihistamine delivery systems are shown here to exhibit prolonged release capabilities. In vitro drug dissolution studies investigated the extent and release rate of two model first generation and two model second-generation H1 antagonist antihistamine drugs from two monoacyglycerol-derived lipid models. To optimize the formulation approach, the systems were characterized macroscopically and microscopically by small-angle X-ray scattering and polarized light to ascertain the mesophase accessed upon an incorporation of antihistamines of varying solubilities and size. The impact of encapsulating the antihistamine molecules on the degree of mucoadhesivity of the lipid cubic systems was investigated using multiparametric surface plasmon resonance. With the ultimate goal of developing therapies for the treatment of allergic reactions, the ability of the formulations to inhibit mediator release utilizing RBL-2H3 mast cells with the propensity to release histamine upon induction was explored, demonstrating no interference from the lipid excipient on the effectiveness of the antihistamine molecules

Stent conditioned media for in vitro evaluation of hydrophobic stent coatings

In vitro cell studies of hydrophobic drugs face difficulties associated with their low aqueous solubility. To study poorly soluble drugs in bio-relevant media, solubilizing agents are frequently used to make stock solutions before final reconstitution in media. This results in drug concentrations that are not representative of in vivo conditions and may pose adverse effects on cells’ biological functions. This is especially true of typical hydrophobic stent coatings intended for vascular applications, where poor in vitro to in vivo correlation exists. To this end, a method for preparation of hydrophobic drug suspensions in bio-relevant media via stent conditioned media using paclitaxel (PTX) as a model drug is proposed. Since the drug is present as a suspension, this media was validated for its content uniformity and potency to induce formation of micronuclei, typical of cells undergoing prolonged mitotic arrest. Further, PTX uptake by endothelial cells was quantified and showed that the PTX stent conditioned media (at a theoretical concentration of 100 μM) suppressed cellular growth equivalent to the 0.1 μM DMSO dissolved PTX

Modulating the release of pharmaceuticals from lipid cubic phases using a lipase inhibitor

Lipid cubic phase formulations have gained recognition as potential controlled delivery systems for a range of active pharmaceutical and biological agents on account of their desirable physiochemical properties and ability to encapsulate both hydrophobic and hydrophilic molecules. The most widely studied lipid cubic systems are those of the monoacylglycerol lipid family. These formulations are susceptible to lipolysis by a variety of enzymes, including lipases and esterases, which attack the ester bond present on the lipid chain bridging the oleic acid component to the glycerol backbone. The release of poorly soluble molecules residing in the lipid membrane portions of the phase is limited by the breakdown of the matrix; thus, presenting a potential means for further controlling and sustaining the release of therapeutic agents by targeting the matrix stability and its rate of degradation. The aims of the present study were twofold: to evaluate an approach to regulate the rate of degradation of lipid cubic phase drug delivery systems by targeting the enzyme interactions responsible for their demise; and to study the subsequent drug release profiles from bulk lipid cubic gels using model drugs of contrasting hydrophobicity. Here, hybrid materials consisting of cubic phases with monoacylglycerol lipids of different chain lengths formulated with a potent lipase inhibitor tetrahydrolipstatin were designed. Modulation of the release ofa hydrophobic model pharmaceutical, a clofazimine salt, was obtained by exploiting the matrices’ enzyme-driven digestion. A stable cubic phase is described, displaying controlled degradation with at least a 4-fold improvement compared to the blank systems shown in inhibitor-containing cubic systems. Sustained release of the model hydrophobic pharmaceutical was studied over 30 days to highlight the advantage of incorporating an inhibitor into the cubic network to achieve tunable lipid release systems. This is done without negatively affecting the structure of the matrix itself, as shown by comprehensive small-angle x-ray scattering experiments

Long acting injectables for therapeutic proteins

Biotherapeutic development presents a myriad of challenges in relation to delivery, in particular for protein therapeutics. Protein delivery is complicated due to hydrophilicity, size, rate of degradation in vivo, low permeation through biological barriers, pH and temperature sensitivity, as well as the need to conserve its quaternary structure to retain function. To preserve therapeutic levels in vivo, proteins require frequent administration due to their short half-lives. Formulation strategies combining proteins with lipid carriers for parenteral administration show potential for improving bioavailability, while preserving protein activity and bypassing the mucosal barriers of the body. Encapsulating protein in long acting injectable delivery systems can improve therapeutic indices by prolonging and controlling protein release and reducing the need for repeat interventions. Two lyotropic crystal forming lipids, monoolein and phytantriol, have been formulated to produce lipidic cubic phases and assessed for their use as long acting protein eluting injectables. Three soluble proteins, cytochrome c, glyceraldehyde-3-phosphate dehydrogenase and aldehyde dehydrogenase and one membrane protein, cytochrome c oxidase, were incorporated into bulk cubic phase formulations of each lipid system to comparatively assess protein release kinetics. The activity of the soluble proteins was measured upon release from a phytantriol bulk cubic phase and phytantriol cubosomes, produced using a liquid precursor method. </p