Ionic liquid versus prodrug strategy to address formulation challenges.

PURPOSE: A poorly water soluble acidic active pharmaceutical ingredient (API) was transformed into an ionic liquid (IL) aiming at faster and higher oral availability in comparison to a prodrug. METHODS: API preparations were characterized in solid state by single crystal and powder diffraction, NMR, DSC, IR and in solution by NMR and ESI-MS. Dissolution and precipitation kinetics were detailed as was the role of the counterion on API supersaturation. Transepithelial API transport through Caco-2 monolayers and counterion cytotoxicity were assessed. RESULTS: The mechanism leading to a 700 fold faster dissolution rate and longer duration of API supersaturation of the ionic liquid in comparison to the free acid was deciphered. Transepithelial transport was about three times higher for the IL in comparison to the prodrug when substances were applied as suspensions with the higher solubility of the IL outpacing the higher permeability of the prodrug. The counterion was nontoxic with IC50 values in the upper µM / lower mM range in cell lines of hepatic and renal origin as well as in macrophages. CONCLUSION: The IL approach was instrumental for tuning physico-chemical API properties, while avoiding the inherent need for structural changes as required for prodrugs.

Orally bioavailable Syk inhibitors with activity in a rat PK/PD model.

Design and optimization of benzo- and pyrido-thiazoles/isothiazoles are reported leading to the discovery of the potent, orally bioavailable Syk inhibitor 5, which was found to be active in a rat PK/PD model. Compound 5 showed acceptable overall kinase selectivity. However, in addition to Syk it also inhibited Aurora kinase in enzymatic and cellular settings leading to findings in the micronucleus assay. As a consequence, compound 5 was not further pursued.

Discovery of Roblitinib (FGF401) as a Reversible-Covalent Inhibitor of the Kinase Activity of Fibroblast Growth Factor Receptor 4.

FGF19 signaling through the FGFR4/ß-klotho receptor complex has been shown to be a key driver of growth and survival in a subset of hepatocellular carcinomas, making selective FGFR4 inhibition an attractive treatment opportunity. A kinome-wide sequence alignment highlighted a poorly conserved cysteine residue within the FGFR4 ATP-binding site at position 552, two positions beyond the gate-keeper residue. Several strategies for targeting this cysteine to identify FGFR4 selective inhibitor starting points are summarized which made use of both rational and unbiased screening approaches. The optimization of a 2-formylquinoline amide hit series is described in which the aldehyde makes a hemithioacetal reversible-covalent interaction with cysteine 552. Key challenges addressed during the optimization are improving the FGFR4 potency, metabolic stability, and solubility leading ultimately to the highly selective first-in-class clinical candidate roblitinib.

Pharmacokinetic Studies around the Mono- and Difunctionalization of a Bioavailable Cyclic Decapeptide Scaffold.

We previously reported the design of several cyclic decapeptides based on a generic scaffold that achieved favorable oral bioavailability and exposure. With the goal to further investigate the potential of this approach, we describe herein the effect of mono- and difunctionalization of this scaffold. A series of cyclic decapeptides were therefore subjected to a range of in vitro assays and pharmacokinetic (PK) studies to investigate whether the introduction of polar or charged groups could be tolerated by the "engineered" scaffold while maintaining good PK profiles. Whereas the introduction of charged amino acids proved-besides maintaining low clearance-to conceal the inherent PK properties of the scaffold, the introduction of polar amino acids (i.e., threonine and pyridyl alanine) led to several cyclic decapeptides exhibiting excellent PK profiles together with a solubility that was significantly improved relative to that of previously reported cyclic decapeptides.

Design and Development of a Cyclic Decapeptide Scaffold with Suitable Properties for Bioavailability and Oral Exposure.

Permeability and oral bioavailability of macrocyclic peptides still represent difficult challenges in drug discovery. Despite the recognized potential of macrocyclic peptides as therapeutics, their use is still restricted to extracellular targets and intravenous administration. Indeed, macrocyclic peptides generally suffer from limited proteolytic stability, high clearance, and poor membrane permeability, and this leads to the absence of systemic exposure after oral administration. To overcome these limitations, we started to investigate the development of a general cyclic decapeptide scaffold that possesses ideal features for cell permeability and oral exposure. On the basis of a rigid hairpin structure, the scaffold design aimed to decrease the overall polarity of the compound, thereby limiting the energetic cost of NH desolvation and the entropy penalty during cell penetration. The results of this study also demonstrate the importance of rigidity for the ß-turn design regarding clearance. To stabilize the scaffold in the desired ß-hairpin conformation, the introduction of d-proline at the i+1 turn position proved to be beneficial for both permeability and clearance. As a result, cyclopeptide decamers with unprecedented high values for oral bioavailability and exposure are reported herein. NMR spectroscopy conformation and dynamic analysis confirmed, for selected examples, the rigidity of the scaffold and the presence of transannular hydrogen bonds in polar and apolar environments. Furthermore, we showed, for one compound, that its transition from a polar environment to an apolar one was accompanied by an increased molecular motion, revealing an entropy contribution to membrane permeation.

The influence of aqueous content in small scale salt screening--improving hit rate for weakly basic, low solubility drugs.

Salt screening and selection is a well established approach for improving the properties of drug candidates, including dissolution rate and bioavailability. Typically during early development only small amounts of compound are available for solid state profiling, including salt screening. In order to probe large areas of experimental space, high-throughput screening is utilized and is often designed in a way to search for suitable crystallization parameters within hundreds or even thousands of conditions. However, the hit rate in these types of screens can be very low. In order to allow for selection of a salt form early within the drug development process whilst using smaller amounts of compounds, a screening procedure taking into account the compounds properties and the driving forces for salt formation is described. Experiments were carried out on the model compounds clotrimazole, cinnarizine itraconazole and atropine. We found an increase in crystalline hit rate for water-insoluble drugs crystallized from solutions that included at least 10% aqueous content. Conversely it was observed that compounds with greater water solubility did not benefit from aqueous content in salt screening, instead organic solvents lead to more crystalline screening hits. Results from four model compounds show that the inclusion of an aqueous component to the salt reaction can enhance the chance of salt formation and significantly improve the crystalline hit rate for low water soluble drugs.