Travis T. Wager

Physiochemical drug properties associated with in vivo toxicological outcomes

Relationships between physicochemical drug properties and toxicity were inferred from a data set consisting of animal in vivo toleration (IVT) studies on 245 preclinical Pfizer compounds; an increased likelihood of toxic events was found for less polar, more lipophilic compounds. This trend held across a wide range of types of toxicity and across a broad swath of chemical space.

Moving beyond Rules: The Development of a Central Nervous System Multiparameter Optimization (CNS MPO) Approach To Enable Alignment of Druglike Properties

The interplay among commonly used physicochemical properties in drug design was examined and utilized to create a prospective design tool focused on the alignment of key druglike attributes. Using a set of six physicochemical parameters ((a) lipophilicity, calculated partition coefficient (ClogP); (b) calculated distribution coefficient at pH = 7.4 (ClogD); (c) molecular weight (MW); (d) topological polar surface area (TPSA); (e) number of hydrogen bond donors (HBD); (f) most basic center (pK(a))), a druglikeness central nervous system multiparameter optimization (CNS MPO) algorithm was built and applied to a set of marketed CNS drugs (N = 119) and Pfizer CNS candidates (N = 108), as well as to a large diversity set of Pfizer proprietary compounds (N = 11 303). The novel CNS MPO algorithm showed that 74% of marketed CNS drugs displayed a high CNS MPO score (MPO desirability score ≥ 4, using a scale of 0-6), in comparison to 60% of the Pfizer CNS candidates. This analysis suggests that this algorithm could potentially be used to identify compounds with a higher probability of successfully testing hypotheses in the clinic. In addition, a relationship between an increasing CNS MPO score and alignment of key in vitro attributes of drug discovery (favorable permeability, P-glycoprotein (P-gp) efflux, metabolic stability, and safety) was seen in the marketed CNS drug set, the Pfizer candidate set, and the Pfizer proprietary diversity set. The CNS MPO scoring function offers advantages over hard cutoffs or utilization of single parameters to optimize structure-activity relationships (SAR) by expanding medicinal chemistry design space through a holistic assessment approach. Based on six physicochemical properties commonly used by medicinal chemists, the CNS MPO function may be used prospectively at the design stage to accelerate the identification of compounds with increased probability of success.

Defining Desirable Central Nervous System Drug Space through the Alignment of Molecular Properties, in Vitro ADME, and Safety Attributes

As part of our effort to increase survival of drug candidates and to move our medicinal chemistry design to higher probability space for success in the Neuroscience therapeutic area, we embarked on a detailed study of the property space for a collection of central nervous system (CNS) molecules. We carried out a thorough analysis of properties for 119 marketed CNS drugs and a set of 108 Pfizer CNS candidates. In particular, we focused on understanding the relationships between physicochemical properties, in vitro ADME (absorption, distribution, metabolism, and elimination) attributes, primary pharmacology binding efficiencies, and in vitro safety data for these two sets of compounds. This scholarship provides guidance for the design of CNS molecules in a property space with increased probability of success and may lead to the identification of druglike candidates with favorable safety profiles that can successfully test hypotheses in the clinic.

Entrainment of disrupted circadian behavior through inhibition of casein kinase 1 (CK1) enzymes

Circadian pacemaking requires the orderly synthesis, posttranslational modification, and degradation of clock proteins. In mammals, mutations in casein kinase 1 (CK1) ε or δ can alter the circadian period, but the particular functions of the WT isoforms within the pacemaker remain unclear. We selectively targeted WT CK1ε and CK1δ using pharmacological inhibitors (PF-4800567 and PF-670462, respectively) alongside genetic knockout and knockdown to reveal that CK1 activity is essential to molecular pacemaking. Moreover, CK1δ is the principal regulator of the clock period: pharmacological inhibition of CK1δ, but not CK1ε, significantly lengthened circadian rhythms in locomotor activity in vivo and molecular oscillations in the suprachiasmatic nucleus (SCN) and peripheral tissue slices in vitro. Period lengthening mediated by CK1δ inhibition was accompanied by nuclear retention of PER2 protein both in vitro and in vivo. Furthermore, phase mapping of the molecular clockwork in vitro showed that PF-670462 treatment lengthened the period in a phase-specific manner, selectively extending the duration of PER2-mediated transcriptional feedback. These findings suggested that CK1δ inhibition might be effective in increasing the amplitude and synchronization of disrupted circadian oscillators. This was tested using arrhythmic SCN slices derived from Vipr2−/− mice, in which PF-670462 treatment transiently restored robust circadian rhythms of PER2::Luc bioluminescence. Moreover, in mice rendered behaviorally arrhythmic by the Vipr2−/− mutation or by constant light, daily treatment with PF-670462 elicited robust 24-h activity cycles that persisted throughout treatment. Accordingly, selective pharmacological targeting of the endogenous circadian regulator CK1δ offers an avenue for therapeutic modulation of perturbed circadian behavior.

Selective inhibition of casein kinase 1 epsilon minimally alters circadian clock period.

The circadian clock links our daily cycles of sleep and activity to the external environment. Deregulation of the clock is implicated in a number of human disorders, including depression, seasonal affective disorder, and metabolic disorders. Casein kinase 1 epsilon (CK1ϵ) and casein kinase 1 delta (CK1δ) are closely related Ser-Thr protein kinases that serve as key clock regulators as demonstrated by mammalian mutations in each that dramatically alter the circadian period. Therefore, inhibitors of CK1δ/ϵ may have utility in treating circadian disorders. Although we previously demonstrated that a pan-CK1δ/ϵ inhibitor, 4-[3-cyclohexyl-5-(4-fluoro-phenyl)-3H-imidazol-4-yl]-pyrimidin-2-ylamine (PF-670462), causes a significant phase delay in animal models of circadian rhythm, it remains unclear whether one of the kinases has a predominant role in regulating the circadian clock. To test this, we have characterized 3-(3-chloro-phenoxymethyl)-1-(tetrahydro-pyran-4-yl)-1H-pyrazolo[3,4-d]pyrimidin-4-ylamine (PF-4800567), a novel and potent inhibitor of CK1ϵ (IC50 = 32 nM) with greater than 20-fold selectivity over CK1δ. PF-4800567 completely blocks CK1ϵ-mediated PER3 nuclear localization and PER2 degradation. In cycling Rat1 fibroblasts and a mouse model of circadian rhythm, however, PF-4800567 has only a minimal effect on the circadian clock at concentrations substantially over its CK1ϵ IC50. This is in contrast to the pan-CK1δ/ϵ inhibitor PF-670462 that robustly alters the circadian clock under similar conditions. These data indicate that CK1ϵ is not the predominant mediator of circadian timing relative to CK1δ. PF-4800567 should prove useful in probing unique roles between these two kinases in multiple signaling pathways.

Physicochemical drug properties associated with in vivo toxicological outcomes: a review

The genesis of any toxicological or safety outcome is multifactorial and complex; for this reason, it can be difficult for drug discovery projects to factor the avoidance of toxicity outcomes into their target design. A focus on readily measurable parameters from high-throughput in vitro assays (e.g., primary potency, clearance) is easier to handle and have become the mainstays of drug discovery projects. However, the fundamental origins of adverse safety or toxicity findings can be considered as deriving from four parameters, all of which are in the control of the drug designer. These can be described as primary pharmacology, off target pharmacology, the presence of a defined structural fragment that can be associated with adverse outcomes and the overall physicochemical properties of the molecule that may predispose it to adverse outcomes. In the drug discovery community, there has been recognition for many years of the influence of physicochemical drug properties (in particular lipophilicity) on the toxicology profile of compounds, and recent research is now beginning to quantify that risk in a probabilistic sense. This review focuses on the overall properties of classes of molecules that are associated with an increased probability of adverse outcomes in in vivo studies.

Design and selection parameters to accelerate the discovery of novel central nervous system positron emission tomography (PET) ligands and their application in the development of a novel phosphodiesterase 2A PET ligand.

To accelerate the discovery of novel small molecule central nervous system (CNS) positron emission tomography (PET) ligands, we aimed to define a property space that would facilitate ligand design and prioritization, thereby providing a higher probability of success for novel PET ligand development. Toward this end, we built a database consisting of 62 PET ligands that have successfully reached the clinic and 15 radioligands that failed in late-stage development as negative controls. A systematic analysis of these ligands identified a set of preferred parameters for physicochemical properties, brain permeability, and nonspecific binding (NSB). These preferred parameters have subsequently been applied to several programs and have led to the successful development of novel PET ligands with reduced resources and timelines. This strategy is illustrated here by the discovery of the novel phosphodiesterase 2A (PDE2A) PET ligand 4-(3-[(18)F]fluoroazetidin-1-yl)-7-methyl-5-{1-methyl-5-[4-(trifluoromethyl)phenyl]-1H-pyrazol-4-yl}imidazo[5,1-f][1,2,4]triazine, [(18)F]PF-05270430 (5).

Discovery and preclinical profiling of 3-[4-(morpholin-4-yl)-7H-pyrrolo[2,3-d]pyrimidin-5-yl]benzonitrile (PF-06447475), a highly potent, selective, brain penetrant, and in vivo active LRRK2 kinase inhibitor.

Leucine rich repeat kinase 2 (LRRK2) has been genetically linked to Parkinsons disease (PD) by genome-wide association studies (GWAS). The most common LRRK2 mutation, G2019S, which is relatively rare in the total population, gives rise to increased kinase activity. As such, LRRK2 kinase inhibitors are potentially useful in the treatment of PD. We herein disclose the discovery and optimization of a novel series of potent LRRK2 inhibitors, focusing on improving kinome selectivity using a surrogate crystallography approach. This resulted in the identification of 14 (PF-06447475), a highly potent, brain penetrant and selective LRRK2 inhibitor which has been further profiled in in vivo safety and pharmacodynamic studies.

Strategies to optimize the brain availability of central nervous system drug candidates

Introduction: Access to the CNS is essential for most neurotherapeutics to elicit their effects. Leveraging design strategies incorporating physicochemical properties, in vitro and in vivo assays to predict and measure brain penetration, and brain delivery approaches may enable the drug discovery community to improve access of drug candidates into the CNS compartment. Areas covered: This article reviews aspects of the most recent molecular design, in vitro and in vivo strategies, and delivery technologies to optimize the unbound brain concentrations (C b,u) of CNS molecules. Through this, the article provides insight into recent ideas and concepts in CNS drug molecule design, methods for evaluating CNS drug exposures and alternative approaches to maximize drug access to neurocompartments. Expert opinion: The most pharmacologically relevant measure in assessing a compounds pharmacodynamic response in the CNS is its C b,u. The utilization of emerging design strategies, together with in vitro and in vivo assays, may enable the design of molecules with optimal C b,u:C p,u (C p,u, unbound plasma concentration) and appropriate C b,u, to elicit a biological response from the neurotherapeutic target. Where drug properties intrinsically render a compound CNS impaired, using novel CNS delivery approaches may result in sufficient C b,u to furnish a biological response.

Central Nervous System Multiparameter Optimization Desirability: Application in Drug Discovery

Significant progress has been made in prospectively designing molecules using the central nervous system multiparameter optimization (CNS MPO) desirability tool, as evidenced by the analysis reported herein of a second wave of drug candidates that originated after the development and implementation of this tool. This simple-to-use design algorithm has expanded design space for CNS candidates and has further demonstrated the advantages of utilizing a flexible, multiparameter approach in drug discovery rather than individual parameters and hard cutoffs of physicochemical properties. The CNS MPO tool has helped to increase the percentage of compounds nominated for clinical development that exhibit alignment of ADME attributes, cross the blood-brain barrier, and reside in lower-risk safety space (low ClogP and high TPSA). The use of this tool has played a role in reducing the number of compounds submitted to exploratory toxicity studies and increasing the survival of our drug candidates through regulatory toxicology into First in Human studies. Overall, the CNS MPO algorithm has helped to improve the prioritization of design ideas and the quality of the compounds nominated for clinical development.