David M. Bender

Synthesis, Crystallization, and Biological Evaluation of an Orally Active Prodrug of Gemcitabine

The design, synthesis, and biological characterization of an orally active prodrug (3) of gemcitabine are described. Additionally, the identification of a novel co-crystal solid form of the compound is presented. Valproate amide 3 is orally bioavailable and releases gemcitabine into the systemic circulation after passing through the intestinal mucosa. The compound has entered clinical trials and is being evaluated as a potential new anticancer agent.

Mitsunobu Approach to the Synthesis of Optically Active α,α-Disubstituted Amino Acids

Chiral tertiary alpha-hydroxy esters of known stereochemical configuration were transformed to alpha-azido esters by Mitsunobu reaction with HN3. Optimization of this reaction was shown to proceed at room temperature with high chemical yield using 1,1-(azodicarbonyl)dipiperidine (ADDP) and trimethylphosphine (PMe3). Complete inversion of configuration was observed at the alpha-carbon. Several alpha,alpha-disubstituted amino acids were synthesized in high overall chemical yield and optical purity.

Characterization of the Expression and Activity of Carboxylesterases 1 and 2 from the Beagle Dog, Cynomolgus Monkey, and Human

The carboxylesterases (CESs) are a family of serine hydrolases that hydrolyze compounds containing an ester, amide, or thioester. In humans, two dominant forms, CES1 and CES2, are highly expressed in organs of first-pass metabolism and play an important role in xenobiotic metabolism. The current study was conducted to better understand species-related differences in substrate selectivity and tissue expression of these enzymes. To elucidate potential similarities and differences among these enzymes, a series of 4-nitrophenyl esters and a series of gemcitabine prodrugs were evaluated using enzyme kinetics as substrates of expressed and purified CESs from beagle dog, cynomolgus monkey, and human genes. For the substrates examined, human and monkey CES2 more efficiently catalyzed hydrolysis compared with CES1, whereas CES1 was the more efficient enzyme in dog. Quantitative real-time polymerase chain reaction and Western blot analyses indicate that the pattern of CES tissue expression in monkey is similar to that of human, but the CES expression in dog is unique, with no detectable expression of CES in the intestine. Loperamide, a selective human CES2 inhibitor, was also found to be a CES2-selective inhibitor in both dog and monkey. This is the first study to examine substrate specificity among dog, human, and monkey CESs.

Cyclopropanecarboxylic Acid Esters as Potential Prodrugs with Enhanced Hydrolytic Stability

Esters of cyclopropanecarboxylic acid demonstrate a substantial increase in stability under both acid- and base-catalyzed hydrolytic conditions. Comparison of the stability of valacyclovir 13 with the cyclopropane analogue 14 shows that at 40 degrees C and pH 6 the half-life of 14 is >300 h while the value for 13 is 69.7 h. CBS-QB3 calculations on isodesmic reactions for transfer of groups from an alkane to an ester show that a cyclopropyl group provides hyperconjugative stabilization.

Discovery Formulations: Approaches and Practices in Early Preclinical Development

Reduced portfolio attrition and faster development of high quality drugs that address unmet medical needs is an established imperative within the pharmaceutical industry. Given the complexity of modern drug discovery, this goal can only be achieved through well-designed pharmacology, pharmacokinetic, and toxicology studies resulting in the identification of exceptional development candidates. Pivotal to the success of these studies is the use of appropriate formulations designed to deliver the compound to the desired site via the desired route, in a consistent and acceptable manner. It is also essential that the formulations are developed with a clear understanding of the goals of the studies, future application of the formulations, and/or the data from the studies. However, the development of an appropriate discovery formulation can be challenging due to a myriad of factors that include suboptimal biopharmaceutical properties, dose, compound purity, compound availability, and aggressive timelines. This chapter will cover formulations used in the discovery setting from conventional vehicles to solubilizing systems and alternate delivery approaches. The application of the appropriate formulation approach to meet the study goals and efficient development timelines will also be discussed.

Pharmacokinetic and screening studies of the interaction between mononuclear phagocyte system and nanoparticle formulations and colloid forming drugs

Studies have shown that nanoparticles (NPs) are cleared through the mononuclear phagocyte system (MPS). Pharmacokinetic studies of Doxil, DaunoXome, micellar doxorubicin (SP1049C) and small molecule (SM) doxorubicin were performed in SCID mice, Sprague-Dawley rats, and beagle dogs. An ex vivo MPS profiling platform was used to evaluate the interaction between the same agents, as well as colloid-forming and non-colloid forming SM drugs. In all species, the systemic clearance was highest for SP1049C and lowest for Doxil. With the exception of dog blood, the MPS screening results of mouse and rat blood showed that the greatest reduction in phagocytosis occurred after the ex vivo addition of SM-doxorubicin>SP1049C>DaunoXome>Doxil. The MPS profiling platform in rats, but not dogs, could differentiate between colloid forming and non-colloid forming drugs. The results of the MPS profiling platform were generally consistent with in vivo clearance rates of NP and SM anticancer drugs in mice and rats. This study suggests the MPS profiling platform is an effective method to screen and differentiate the important characteristics of NPs and colloid-forming drugs that affect their in vivo clearance. Implications of these findings on preclinical prediction of human clearance are discussed.

Clinical Bioavailability of the Novel BACE1 Inhibitor Lanabecestat (AZD3293): Assessment of Tablet Formulations Versus an Oral Solution and the Impact of Gastric pH on Pharmacokinetics

The relative bioavailability of lanabecestat administered as 2 tablet formulations versus an oral solution was investigated. This phase 1 single‐center, open‐label, randomized, 3‐period crossover study involved healthy male and nonfertile female subjects aged 18–55 years (NCT02039180). Subjects received a single 50‐mg lanabecestat dose as solution, tablet A, or tablet B on day 1 of each crossover period; 14 of 16 subjects completed the study. Relative bioavailability based on plasma lanabecestat AUC0–∞ (area under the plasma drug concentration–time curve from zero to infinity) geometric mean ratio versus oral solution (primary variable) was: tablet A, 1.052 (90% confidence interval [CI], 1.001–1.106); tablet B, 1.040 (0.989–1.093). These 90%CIs for geometric mean ratios are within accepted standard bioequivalence boundaries for all other pharmacokinetic (PK) parameters for both lanabecestat and metabolite (AZ13569724). All 3 formulations had similar plasma lanabecestat concentration–time profiles. Six adverse events were reported by 6 subjects (37.5%, all mild). GastroPlus modeling predicted a negligible impact of gastric pH changes on systemic PK (up to pH 7.4). Both tablet formulations fall within standard accepted bioequivalence criteria versus the oral solution. A single 50‐mg lanabecestat dose was well tolerated as a solution or tablet formulation in this population.

Developability Assessment of Clinical Candidates

The role of the developability (aka preformulation) scientist at the discovery development interface has been extensively discussed in the literature. In response to shifting trends in discovery and the continued push to shorten timelines and reduce costs, the engagement of the developability scientist on discovery teams has steadily moved upstream over the past two decades. In this new and continually changing role, the developability scientist has the opportunity to influence the selection of chemistry scaffolds entering the lead optimization phase and subsequently the selection of developable compounds for clinical testing. In its current state, developability assessment of clinical candidates is an assessment of the physicochemical and biopharmaceutical properties of the compound, carried out with due consideration to the patient in question, the clinical testing plan, and the commercial landscape. This chapter describes the dynamic and integrated nature of this assessment, along with a description of the in silico, in vitro, and in vivo tools used, and illustrative case studies. Key areas of focus include: (a) Solid form design and selection. (b) Characterization of the physicochemical properties associated with the solid form, such as solubility, stability, and dissolution properties. (c) Absorption modeling, including the definition of clinical product performance criteria and the need (if any) for absorption enhancement. (d) Assessment of absorption enhancement potential using technology platforms that lend themselves to commercial development (including in vivo evaluation where relevant). (e) The assembly of a comprehensive data package that includes an assessment of potential risks to clinical and commercial development.