p21-activated kinase 1 (PAK1) has an important role in transducing signals in several oncogenic pathways. The concept of inhibiting this kinase has garnered significant interest over the past decade, particularly for targeting cancers associated with PAK1 amplification. Animal studies with the selective group I PAK (pan-PAK1, 2, 3) inhibitor G-5555 from the pyrido[2,3-d]pyrimidin-7-one class uncovered acute toxicity with a narrow therapeutic window. To attempt mitigating the toxicity, we introduced significant structural changes, culminating in the discovery of the potent pyridone side chain analogue G-9791. Mouse tolerability studies with this compound, other members of this series, and compounds from two structurally distinct classes revealed persistent toxicity and a correlation of minimum toxic concentrations and PAK1/2 mediated cellular potencies. Broad screening of selected PAK inhibitors revealed PAK1, 2, and 3 as the only overlapping targets. Our data suggest acute cardiovascular toxicity resulting from the inhibition of PAK2, which may be enhanced by PAK1 inhibition, and cautions against continued pursuit of pan-group I PAK inhibitors in drug discovery.
Variable-hydrate
active pharmaceutical ingredients (APIs) are known
to form thermodynamically and kinetically stabilized solid phases
over a continuous range of nonstoichiometric hydration levels. Some
of these forms can be problematic in the production of solid dosage
forms (e.g., tablets and capsules), where manufacturing processes
can induce changes in the hydration level of the API, resulting in
transformations to undesirable solid phases that may affect product
quality. In order to improve the development of variable-hydrate APIs
for commercial use, reliable methods must be developed to not only
measure the hydration levels, but also to probe the influences of
water molecules on the molecular-level structures of APIs within dosage
formulations. In this study, we examine a Genentech development compound, GNE-A, which is a hydrochloride (HCl) salt of an API that
exhibits variable-hydrate behavior. Using a combination of 35Cl solid-state NMR (SSNMR), variable-relative humidity (RH) powder
X-ray diffraction (PXRD), thermogravimetric analysis, and dispersion-corrected
plane-wave density functional theory (DFT-D2*) calculations, we reveal
the local and long-range structural effects of water under different
storage and processing conditions. 35Cl SSNMR spectra are
particularly sensitive to the presence of water and reveal distinct
anionic Cl– environments in the hydrated and dehydrated
forms of the HCl API. Our data demonstrate that complete dehydration
of the material is surprisingly difficult, even with repeated drying
cycles. Finally, 35Cl SSSNMR is shown to be very useful
for probing the local structural environments of Cl– ions in tablets processed using either wet or dry granulation, since
there are no interfering signals from the complex array of excipient
molecules present in the formulation.
Micro- and nano-carrier formulations have been developed as drug delivery systems for active pharmaceutical ingredients (APIs) that suffer from poor physico-chemical, pharmacokinetic, and pharmacodynamic properties. Encapsulating the APIs in such systems can help improve their stability by protecting them from harsh conditions such as light, oxygen, temperature, pH, enzymes, and others. Consequently, the API’s dissolution rate and bioavailability are tremendously improved. Conventional techniques used in the production of these drug carrier formulations have several drawbacks, including thermal and chemical stability of the APIs, excessive use of organic solvents, high residual solvent levels, difficult particle size control and distributions, drug loading-related challenges, and time and energy consumption. This review illustrates how supercritical fluid (SCF) technologies can be superior in controlling the morphology of API particles and in the production of drug carriers due to SCF’s non-toxic, inert, economical, and environmentally friendly properties. The SCF’s advantages, benefits, and various preparation methods are discussed. Drug carrier formulations discussed in this review include microparticles, nanoparticles, polymeric membranes, aerogels, microporous foams, solid lipid nanoparticles, and liposomes.
Multicomponent solids such as cocrystals have emerged as a way to control and engineer the stability, solubility, and manufacturability of solid active pharmaceutical ingredients (APIs). Cocrystals are typically formed by solution-or solid-phase reactions of APIs with suitable cocrystal coformers, which are often weak acids. One key structural question about a given multicomponent solid is whether it should be classified as a salt, where the basic API is protonated by the acid, or as a cocrystal, where the API and coformer remain neutral and engage in hydrogen bonding interactions. It has previously been demonstrated that solid-state NMR spectroscopy is a powerful probe of structure in cocrystals and salts of APIs; however, the poor sensitivity of solid-state NMR spectroscopy usually restricts the types of experiments that can be performed. Here, relayed dynamic nuclear polarization (DNP) was applied to reduce solid-state NMR experiment times by 1-2 orders of magnitude for salts and cocrystals of a complex API. The large sensitivity gains from DNP facilitates rapid acquisition of natural isotopic abundance 13C and 15N solid-state NMR spectra. Critically, DNP enables double resonance 1H-15N solid-state NMR experiments such as 2D 1H-15N HETCOR, 1H-15N CP-build up, 15N{1H} J-resolved/attached proton tests, 1H-15N DIPSHIFT, and 1H-15N PRESTO. The latter two experiments allow 1H-15N dipolar coupling constants and H-N bond lengths to be accurately measured, providing an unambiguous assignment of nitrogen protonation state and definitive classification of the multicomponent solids as cocrystals or salts. These types of measurements should also be extremely useful in the context of polymorph discrimination, NMR crystallography structure determination, and for probing hydrogen bonding in a variety of organic materials.
Herein we report on the structure-based discovery of a C-2 hydroxyethyl moiety which provided consistently high levels of selectivity for JAK1 over JAK2 to the imidazopyrrolopyridine series of JAK1 inhibitors. X-ray structures of a C-2 hydroxyethyl analogue in complex with both JAK1 and JAK2 revealed differential ligand/protein interactions between the two isoforms and offered an explanation for the observed selectivity. Analysis of historical data from related molecules was used to develop a set of physicochemical compound design parameters to impart desirable properties such as acceptable membrane permeability, potent whole blood activity, and a high degree of metabolic stability. This work culminated in the identification of a highly JAK1 selective compound (31) exhibiting favorable oral bioavailability across a range of preclinical species and robust efficacy in a rat CIA model.
Cold
crystallization of amorphous pharmaceuticals is an important
aspect in the search to stabilize amorphous or glassy compounds used
as amorphous pharmaceutical ingredients (APIs). In the present work,
we report results for the isothermal crystallization of the compound
GDC-0276 based on differential scanning calorimetric and rheometric
measurements. The kinetics of isothermal crystallization from the
induction time to the completion of crystallization can be described
by the classic Johnson–Mehl–Avrami (JMA) equation. The
time–temperature-transformation (TTT) diagrams were constructed
for two time pointsthat of induction and that of completion
of crystallization. The results show that the rheological measurement
for GDC-0276 has a better overall sensitivity in detection of the
early stage nucleation and, consequently, detects the onset of crystallization
sooner than does the differential scanning calorimetry. Rheological
measurements were also used to obtain the temperature dependence of
the viscosity of GDC-0276 and the relevant parameters were used in
a modified form of the JMA model to describe the temperature dependence
of the crystal induction and completion times, that is, the TTT diagram
for the material. In the modification, we assumed that the kinetics
followed the viscosity to the 0.75 power as suggested by the recent
work of Huang et al. (Huang, C., et al., J. Chem. Phys.
2018,
149, 054503). The relationship
and the possible impact on crystallization kinetics of the break-down
of the Stokes–Einstein relation in glass-forming liquids are
discussed. From the crystallization kinetics modeling, the solid–liquid
interfacial surface tension σSL was obtained for
GDC-0276 and was compared with that obtained from the melting point
depression measurements of the material confined in nanoporous glasses.
The differences between the values from the two methods are discussed.
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