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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.

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 multi-day single dose drug delivery are evident in the success and patient adoption of injected or 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 one day. Areas covered: Reviews of systems to extend gastric residence reveals that one-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 hours 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.

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