David H. Altreuter

Current membrane-based bioartificial organs consist of three basic components: (1) a synthetic membrane, (2) cells that secrete the product of interest, and (3) an encapsulated matrix material. Alginate and agarose have been widely used to encapsulate cells for artificial organ applications. It is important to understand the degree of transport resistance imparted by these matrices in cell encapsulation to determine if adequate nutrient and product fluxes can be obtained. For artificial organs in xenogeneic applications, it may also be important to determine the extent of immunoprotection offered by the matrix material. In this study, diffusion coefficients were measured for relevant solutes [ranging in size from oxygen to immunoglobulin G (IgG)] into and out of agarose and alginate gels. Alginate gels were produced by an extrusion/ionic crosslinking process using calcium while agarose gels were thermally gelled. The effect of varying crosslinking condition, polymer concentration, and direction of diffusion on transport was investigated. In general, 2-4% agarose gels offered little transport resistance for solutes up to 150 kD, while 1.5-3% alginate gels offered significant transport resistance for solutes in the molecular weight range 44-155 kD-lowering their diffusion rates from 10- to 100-fold as compared to their diffusion in water. Doubling the alginate concentration had a more significant effect on hindering diffusion of larger molecular weight species than did doubling the agarose concentration. Average pore diameters of approximately 170 and 147 A for 1.5 and 3% alginate gels, respectively, and 480 and 360 A for 2 and 4% agarose gels, respectively, were estimated using a semiempirical correlation based on diffusional transport of different-size solutes. The method developed for measuring diffusion in these gels is highly reproducible and useful for gels crosslinked in the cylindrical geometry, relevant for studying transport through matrices used in cell immobilization in the hollow fiber configuration. (c) 1996 John Wiley & Sons, Inc.

INTRODUCTION: The development of oral sustained release dosage forms has been a longstanding goal due to the potential for ease of administration, improved pharmacokinetics, reduced dosing frequency, and improved adherence. The benefits of multiday single-dose drug delivery are evident in the success and patient adoption of injected and implanted dosage forms. However, in the space of oral medications, all current commercially available gastric resident dosage forms, and most in development, are limited to gastric residence of less than 1 day. AREAS COVERED: Reviews of systems to extend gastric residence reveal that 1 day or more residence has been an unmet challenge. New dosage forms are in development that seek to address many of the key physiological and design challenges of long-term gastric retention beyond 24 h and up to a week or longer. The present analysis highlights the design, material considerations and implications of unfolding dosage form systems with ultra-long-term gastric residence. EXPERT OPINION: The development of oral dosage forms providing sustained release of high potency medications over days or weeks could transform care, significantly decrease patient burden in chronic disease management and improve outcomes.

Two enzymes, Mucor javanicus lipase and subtilisin Carlsberg (SC), catalyzed the nonaqueous acylation of doxorubicin (DOX). Compared to the untreated enzyme the rate of DOX acylation at the C-14 position with vinyl butyrate in toluene was 25-fold higher by lipase ion-paired with Aerosol OT (AOT) and 5-fold higher by lipase activated by 98% (w/w) KCl co-lyophilization (3.21 and 0.67 mumol/min g-lipase, respectively, vs 0.13 mumol/min g-lipase). Particulate subtilisin Carlsberg (SC) was nearly incapable of DOX acylation, but ion-paired SC (AOT-SC) catalyzed acylation at a rate of 2.85 mumol/min g-protease. The M. javanicus formulations, AOT-SC, and SC exclusively acylated the C14 primary hydroxyl group of DOX. Co-lyophilization of SC with 98% (w/w) KCl expanded the enzyme's regiospecificity such that KCl-SC additionally acylated the C4' hydroxyl and C3' amine groups. The total rate of DOX conversion with KCl-SC was 56.7 mumol/min g-protease. The altered specificity of KCl-SC is a new property of the enzyme imparted by the salt activation, and represents the first report of unnatural regioselectivity exhibited by a salt-activated enzyme. Using AOT-SC catalysis, four unique selectively acylated DOX analogues were generated, and KCl-SC was used to prepare DOX derivatives acylated at the alternative sites. Cytotoxicities of select derivatives were evaluated against the MCF7 breast cancer cell line (DOX IC50 = 27 nM) and its multidrug-resistant sub-line, MCF7-ADR (DOX IC50 = 27 muM). The novel derivative 14-(2-thiophene acetate) DOX was relatively potent against both cell lines (IC50 of 65 nM and 8 muM, respectively) and the 14-(benzyl carbonate) DOX analogue was as potent as DOX against the MCF7 line (25 nM). Activated biocatalysts and their novel regioselectivity differences thus enabled single-step reaction pathways to an effective collection of doxorubicin analogues.

Abstract Lipase‐catalyzed esterification has been performed in hexane to generate novel mixtures of fatty acid esters from specially chosen combinations of fatty acids and alcohols. By varying the alcohol and enzyme compositions in the enzymatic reactions, different ester mixtures were produced, which were further purified and analyzed for ester composition by gas chromatography‐mass spectrometry. Depending on the combination of alcohols and enzymes used, the final ester mixture exhibited significant compositional variation. These mixtures could be manipulated at the synthesis step, thereby enabling a high degree of product control. Such manipulation over enzyme‐catalyzed ester synthesis in mixtures may be useful in the preparation of ester flavors for use in the food industry.