Panayiotis P. Constantinides

Lipid Microemulsions for Improving Drug Dissolution and Oral Absorption: Physical and Biopharmaceutical Aspects

AbstractPurpose. This review highlights the state-of-the-art in pharmaceutical microemulsions with emphasis on self-emulsifying systems, from both a physical and biopharmaceutical perspective. Although these systems have several pharmaceutical applications, this review is primarily focused on their potential for oral drug delivery and intestinal absorption improvement. Methods. Physicochemical characteristics and formulation design based on drug solubility and membrane permeability are discussed. Results. Case studies in which lipid microemulsions have successfully been used to improve drug solubilization/dissolution and/or intestinal absorption of poorly absorbed drugs/peptides are presented. Conclusions. Drug development issues such as commercial viability, mechanisms involved, range of applicability, safety, scale-up and manufacture are outlined, and future research and development efforts to address these issues are discussed.

Formulation and Intestinal Absorption Enhancement Evaluation of Water-in-Oil Microemulsions Incorporating Medium-Chain Glycerides

We developed self-emulsifying water-in-oil (w/o) microemulsions incorporating medium-chain glycerides and measured their conductance, viscosity, refractive index and particle size. Formulation of Calcein (a water-soluble marker molecule, MW = 623), or SK&F 106760 (a water-soluble RGD peptide, MW = 634) in a w/o microemulsion having a composition of Captex 355/Capmul MCM/Tween 80/Aqueous (65/22/10/3, % w/w), resulted in significant bioavailabil-ity enhancement in rats relative to their aqueous formulations. Upon intraduodenal administration the bioavailability was enhanced from 2% for Calcein in isotonic Tris, pH 7.4 to 45% in the microemulsion and from 0.5% for SK&F 106760 in physiological saline to 27% in the microemulsion formulation. The microemulsion did not induce gross changes in GI mucosa at a dosing volume of 3.3 ml/kg. These results suggest that water-in-oil microemulsion systems may be utilized for enhancement of intestinal drug absorption.

Formulation and physical characterization of water-in-oil microemulsions containing long- versus medium-chain glycerides

Abstract Stable self-emulsifying water-in-oil (w/o) microemulsions of extremely small particle size (5–30 nm) and consisting of an oil, a blend of a low and high HLB surfactants and an aqueous phase, have been developed using commercially available and pharmaceutically acceptable components. Their formation was monitored by the corresponding pseudo-ternary phase diagram. The oil phase contained long- or medium-chain triglycerides, and mono-/diglycerides or sorbitan esters (low HLB surfactants). Polysorbate 80 (Tween 80) was used as a high HLB surfactant. Microemulsions were readily prepared by admixing appropriate quantities of the various components with gentle hand-mixing or stirring to ensure thorough mixing. In the case of microemulsions incorporating long-chain glycerides and/or sorbitan esters, high temperature (40–60°C) was used to reduce viscosity and solubilize all components during the formation of microemulsions. Limited levels of aqueous phase (

Formulation Development and Antitumor Activity of a Filter-Sterilizable Emulsion of Paclitaxel

AbstractPurpose. Paclitaxel is currently administered i.v. as a slow infusion of asolution of the drug in an ethanol:surfactant:saline admixture. However,poor solubilization and toxicity are associated with this drug therapy.Alternative drug delivery systems, including parenteral emulsions, areunder development in recent years to reduce drug toxicity, improveefficacy and eliminate premedication. Methods. Paclitaxel emulsions were prepared by high-shearhomogenization. The particle size of the emulsions was measured by dynamiclight scattering. Drug concentration was quantified by HPLC and invitro drug release was monitored by membrane dialysis. The physicalstability of emulsions was monitored by particle size changes in boththe mean droplet diameter and 99% cumulative distribution. Paclitaxelpotency and changes in the concentration of known degradants wereused as chemical stability indicators. Single dose acute toxicity studieswere conducted in healthy mice and efficacy studies in B16 melanomatumor-bearing mice. Results. QW8184, a physically and chemically stable sub-micronoil-in-water (o/w) emulsion of paclitaxel, can be prepared at high drugloading (8-10 mg/mL) having a mean droplet diameter of <100 nmand 99% cumulative particle size distribution of <200 nm. In vitro release studies demonstrated low and sustained drug release both inthe presence and absence of human serum albumin. Based on singledose acute toxicity studies, QW8184 is well tolerated both in miceand rats with about a 3-fold increase in the maximum-tolerated-dose(MTD) over the current marketed drug formulation. Using the B16mouse melanoma model, a significant improvement in drug efficacywas observed with QW8184 over Taxol®. Conclusions. QW8184, a stable sub-micron o/w emulsion of paclitaxelhas been developed that can be filter-sterilized and administered i.v.as a bolus dose. When compared to Taxol®, this emulsion exhibitedreduced toxicity and improved efficacy most likely due to thecomposition and dependent physicochemical characteristics of the emulsion.

Water-in-Oil Microemulsions Containing Medium-chain Fatty Acids/Salts: Formulation and Intestinal Absorption Enhancement Evaluation

AbstractPurpose. Water-in-oil (w/o) microemulsions have been developed which, in addition to non-ionic medium-chain glycerides, incorporate ionic lipids, primarily medium-chain fatty acids, such as caprylic (C8) capric (C10) and lauric (C12) acids and their corresponding sodium salts. The absorption enhancing activity of w/o microemulsions incorporating these lipids was evaluated in the rat using Calcein (MW = 623) a water-soluble and poorly absorbed marker molecule. Methods. Phase diagrams were constructed where C8/C10 or C12 fatty acids were treated as lipophilic surfactants and their sodium salts as hydrophilic ones. The anesthetised rat model was employed to evaluate Calcein absorption upon a single intraduodenal administration from a solution and the various w/o microemulsions. Results. A wide range of clear and transparent w/o microemulsions were obtained at ambient temperature either in liquid or solid form when a fixed blend of medium chain fatty acid/salt was titrated by a fixed ratio of the oil containing the oil-soluble mono- and diglycerides and deionized water or physiological saline. Upon intraduodenal administration in the anesthetised rat, the absorption of Calcein was improved from about 2% in aqueous solution up to about 37% in w/o microemulsions. Solid and liquid formulations were equally effective in improving bioavailability. The absorption enhancement activity of the fatty acids/salts followed the order C8 ≈ C10 > C12. Absorption enhancement of Calcein was significantly reduced in the absence or presence of low levels of C8/C10 mono-/diglycerides. Conclusions. These results further support the use of medium-chain glycerides and fatty acids/salts in microemulsion formulations to improve intestinal absorption of water-soluble compounds.

Enhanced intestinal absorption of an RGD peptide from water-in-oil microemulsions of different composition and particle size

Abstract The fibrinogen receptor antagonist SK&F 106760 is a water-soluble tetrapeptide (Mr634) with very low oil/water partitioning and membrane permeability. Thus, the intraduodenal bioavailability of this peptide in the rat from a saline formulation was found to be less than 1%. Upon formulation, however, in w/o microemulsions of different composition and particle size, the intraduodenal bioavailability of SK&F 106760 was increased up to 29% depending on the microemulsion composition. There was no apparent correlation between the particle size of microemulsions (mean droplet diameter of 0.010–1.0 μm) and enhanced absorption. None of the investigated microemulsions induced gross changes in gastrointestinal mucosa at a dosing volume of 3.3 ml/kg. Lipids containing medium-chain fatty acids play a major role on the observed absorption enhancement. These findings further support the use of microemulsion formulations for oral drug/peptide delivery, provided however, that development issues with these systems are properly addressed.

Nanodelivery strategies in cancer chemotherapy: biological rationale and pharmaceutical perspectives

Nanotechnology is revolutionizing our approach to drug delivery, a key determinant of drug efficacy. Here, we present cancer drug delivery strategies that exploit nanotechnology, providing first an overview of tumor biology aspects that critically affect the design of drug delivery carriers, namely the enhanced permeability and retention effect, the lower tumor extracellular pH and tumor-specific antigens. In general, nanoscience-based approaches have circumvented limitations in the delivery of cancer therapeutics, related to their poor aqueous solubility and toxicity issues with conventional vehicles and resulted in improved pharmacokinetics and biodistribution. Included in the discussion are promising examples and pharmaceutical perspectives on liposomes, nanoemulsions, solid lipid nanoparticles, polymeric nanoparticles, dendrimers, carbon nanotubes and magnetic nanoparticles. As the cardinal features of the ideal multifunctional cancer drug nanocarrier are becoming clear, and drug development challenges are proactively addressed, we anticipate that future advances will enhance therapeutic outcomes by refining the delivery and targeting of complex payloads.

Targeting Mitochondrial STAT3 with the Novel Phospho-Valproic Acid (MDC-1112) Inhibits Pancreatic Cancer Growth in Mice

New agents are needed to treat pancreatic cancer, one of the most lethal human malignancies. We synthesized phospho-valproic acid, a novel valproic acid derivative, (P-V; MDC-1112) and evaluated its efficacy in the control of pancreatic cancer. P-V inhibited the growth of human pancreatic cancer xenografts in mice by 60%–97%, and 100% when combined with cimetidine. The dominant molecular target of P-V was STAT3. P-V inhibited the phosphorylation of JAK2 and Src, and the Hsp90-STAT3 association, suppressing the activating phosphorylation of STAT3, which in turn reduced the expression of STAT3-dependent proteins Bcl-xL, Mcl-1 and survivin. P-V also reduced STAT3 levels in the mitochondria by preventing its translocation from the cytosol, and enhanced the mitochondrial levels of reactive oxygen species, which triggered apoptosis. Inhibition of mitochondrial STAT3 by P-V was required for its anticancer effect; mitochondrial STAT3 overexpression rescued animals from the tumor growth inhibition by P-V. Our results indicate that P-V is a promising candidate drug against pancreatic cancer and establish mitochondrial STAT3 as its key molecular target.

Carboxylesterases 1 and 2 Hydrolyze Phospho-Nonsteroidal Anti-Inflammatory Drugs: Relevance to Their Pharmacological Activity

Phospho-nonsteroidal anti-inflammatory drugs (phospho-NSAIDs) are novel NSAID derivatives with improved anticancer activity and reduced side effects in preclinical models. Here, we studied the metabolism of phospho-NSAIDs by carboxylesterases and assessed the impact of carboxylesterases on the anticancer activity of phospho-NSAIDs in vitro and in vivo. The expression of human liver carboxylesterase (CES1) and intestinal carboxylesterase (CES2) in human embryonic kidney 293 cells resulted in the rapid intracellular hydrolysis of phospho-NSAIDs. Kinetic analysis revealed that CES1 is more active in the hydrolysis of phospho-sulindac, phospho-ibuprofen, phospho-naproxen, phospho-indomethacin, and phospho-tyrosol-indomethacin that possessed a bulky acyl moiety, whereas the phospho-aspirins are preferentially hydrolyzed by CES2. Carboxylesterase expression leads to a significant attenuation of the in vitro cytotoxicity of phospho-NSAIDs, suggesting that the integrity of the drug is critical for anticancer activity. Benzil and bis-p-nitrophenyl phosphate (BNPP), two carboxylesterase inhibitors, abrogated the effect of carboxylesterases and resensitized carboxylesterase-expressing cells to the potent cytotoxic effects of phospho-NSAIDs. In mice, coadministration of phospho-sulindac and BNPP partially protected the former from esterase-mediated hydrolysis, and this combination more effectively inhibited the growth of AGS human gastric xenografts in nude mice (57%) compared with phospho-sulindac alone (28%) (p = 0.037). Our results show that carboxylesterase mediates that metabolic inactivation of phospho-NSAIDs, and the inhibition of carboxylesterases improves the efficacy of phospho-NSAIDs in vitro and in vivo.

Phosphosulindac (OXT‐328) Selectively Targets Breast Cancer Stem Cells In Vitro and in Human Breast Cancer Xenografts

Pharmacological targeting of breast cancer stem cells (CSCs) is highly promising for the treatment of breast cancer, as the small population of CSCs appears responsible for tumor initiation and progression and also for resistance to conventional treatment. Here we report that the novel phosphosulindac (OXT‐328, PS) selectively and effectively eliminates breast CSCs both in vitro and in vivo. PS reduced cell proliferation and induced apoptosis in various breast CSCs. Breast CSCs are resistant to conventional cancer drugs but are sensitive to PS. Long‐term treatment of mixtures of cultured breast CSCs and breast cancer cells with PS preferentially eliminated the CSCs. PS impaired the ability of CSCs to form mammospheres and markedly suppressed the expression of CSC‐related genes. More importantly, PS prevented by half (p =.06) the formation of tumors initiated by CSCs in immunodeficient mice, and inhibited by 83% (p <.05) the growth of already formed breast cancer xenografts, reducing the proportion of CSCs in them. PS suppressed the Wnt/β‐catenin pathway by stimulating the degradation of β‐catenin and its relocalization to the cell membrane and also blocked the epithelial–mesenchymal transition and the generation of breast CSCs. These results indicate that PS has a strong inhibitory effect against breast cancer, acting, at least in part, by targeting CSCs through a signaling mechanism involving Wnt signaling. STEM Cells2012;30:2065–2075