Rebecca Nofsinger

Chemistry-enabled drug delivery (prodrugs): recent progress and challenges.

Prodrugs can be used to enhance the properties of an active pharmaceutical ingredient or drug, generally by improving solubility and/or permeability of the compound. However, discovery teams duly spend considerable time and resources on structure-activity optimization and formulation-enabled drug delivery technologies to achieve the target exposures and biopharmaceutical properties, when early implementation of prodrugs could lead to an improved drug molecule. The goal of this review is to provide an overview of the achievements during the past few years in developing prodrugs and highlighting the challenges of following this approach.

Discovery of MK‐8970: An Acetal Carbonate Prodrug of Raltegravir with Enhanced Colonic Absorption

Developing new antiretroviral therapies for HIV‐1 infection with potential for less frequent dosing represents an important goal within drug discovery. Herein, we present the discovery of ethyl (1‐((4‐((4‐fluorobenzyl)carbamoyl)‐1‐methyl‐2‐(2‐(5‐methyl‐ 1,3,4‐oxadiazole‐2‐carboxamido)propan‐2‐yl)‐6‐oxo‐1,6‐dihydropyrimidin‐5‐yl)oxy)ethyl) carbonate (MK‐8970), a highly optimized prodrug of raltegravir (Isentress). Raltegravir is a small molecule HIV integrase strand‐transfer inhibitor approved for the treatment of HIV infection with twice‐daily administration. Two classes of prodrugs were designed to have enhanced colonic absorption, and derivatives were evaluated in pharmacokinetic studies, both in vitro and in vivo in different species, ultimately leading to the identification of MK‐8970 as a suitable candidate for development as an HIV therapeutic with the potential to require less frequent administration while maintaining the favorable efficacy, tolerability, and minimal drug–drug interaction profile of raltegravir.

Design of Prodrugs to Enhance Colonic Absorption by Increasing Lipophilicity and Blocking Ionization

Prodrugs are chemistry-enabled drug delivery modifications of active molecules designed to enhance their pharmacokinetic, pharmacodynamic and/or biopharmaceutical properties. Ideally, prodrugs are efficiently converted in vivo, through chemical or enzymatic transformations, to the active parent molecule. The goal of this work is to enhance the colonic absorption of a drug molecule with a short half-life via a prodrug approach to deliver sustained plasma exposure and enable once daily (QD) dosing. The compound has poor absorption in the colon and by the addition of a promoiety to block the ionization of the molecule as well as increase lipophilicity, the relative colonic absorption increased from 9% to 40% in the retrograde dog colonic model. A combination of acceptable solubility and stability in the gastrointestinal tract (GI) as well as permeability was used to select suitable prodrugs to optimize colonic absorption.

Comparing Dog and Human Intestinal Fluids: Implications on Solubility and Biopharmaceutical Risk Assessment

Despite many documented differences in gut physiology compared to humans, the beagle dog has been successfully used as a preclinical model for assessing the relative bioavailability of dosage forms during formulation development. However, differences in pH and bile salt concentration and micellar structure between dog and human intestinal fluids may influence the solubility and dissolution behavior of especially BCS II/IV compounds. Recently, a canine fasted simulated intestinal fluid (FaSSIFc) mimicking the composition in the lumen of the beagle dog under the fasted state has been proposed. In this manuscript, we present the utilization of FaSSIFc to compare solubility of several preclinical candidates against human FaSSIF. While solubility of free bases and neutral compounds was easily predicted by the relative amounts of sodium taurocholate in the fluids, free acids were shown to be much more soluble in FaSSIFc owing to both the solubility at higher pH as well as the increased bile salt concentration. For one of the model compounds, we demonstrate that the high solubility necessitates the need for a formulation comparison at a relatively higher dose in the dog to mimic the outcome of a human relative bioavailability study. Finally, we show how using the solubility value in FaSSIFc for the same compound results in better predictability of the plasma concentration profiles in dogs from a physiologically based absorption model. The collective data indicate that caution and more detailed measurements are required if the dog is used as the preclinical model for the development of formulations of weak acids.

3D printed capsules for quantitative regional absorption studies in the GI tract

Graphical abstract Figure. No Caption available. Abstract Drug development is a long process which requires careful evaluation of the drug substance (active pharmaceutical ingredient, API), drug product (tablet, capsule etc.) and the bioperformance (both pre‐clinical and clinical) before testing the efficacy of the final dosage form. The earliest assessment of a new drug substance requires an understanding of the safety and clinical performance (Phase 1) wherein faster processes (like on‐site formulation strategy) have been set in place for quick clinical read‐outs. One key gap that exists in this early assessment is the ability to evaluate modified release drug products. Here, an additive manufacturing approach is used to prepare polyvinyl alcohol (PVA) capsule shells using 3D printing (3DP), where the shells can be filled with either a solid or a liquid vehicle containing the API. In this work we demonstrate how we can delay the release of the API from the printed capsules allowing us to evaluate regional absorption in pre‐clinical studies. By using 3DP, a new method to provide a series of release profiles is demonstrated, where the induction time of a delayed burst release is controlled by the wall thicknesses of printed capsules. New hanging baskets were also designed and 3D printed for the dissolution tests to better understand the rupturing of these capsules in an USP 2 dissolution apparatus. By controlling the wall thickness of the capsule, the induction time of drug release can be controlled from 12 to 198 min. This wide range of induction times demonstrated with this 3DP strategy is not currently available in a commercially available oral drug product form. Varying the induction times to the drug release to interrogate different regions of the GI tract is exhibited in vivo (beagle dogs) and initial analysis suggested a good in vitro/in vivo relationship (IVIVR).