Discovery of Clinical Candidate PF-06648671: A Potent γ-Secretase Modulator for the Treatment of Alzheimer's Disease.

Herein, we describe the design and synthesis of γ-secretase modulator (GSM) clinical candidate PF-06648671 (22) for the treatment of Alzheimer's disease. A key component of the design involved a 2,5-cis-tetrahydrofuran (THF) linker to impart conformational rigidity and lock the compound into a putative bioactive conformation. This effort was guided using a pharmacophore model since crystallographic information was not available for the membrane-bound γ-secretase protein complex at the time of this work. PF-06648671 achieved excellent alignment of whole cell in vitro potency (Aß42 IC50 = 9.8 nM) and absorption, distribution, metabolism, and excretion (ADME) parameters. This resulted in favorable in vivo pharmacokinetic (PK) profile in preclinical species, and PF-06648671 achieved a human PK profile suitable for once-a-day dosing. Furthermore, PF-06648671 was found to have favorable brain availability in rodent, which translated into excellent central exposure in human and robust reduction of amyloid ß (Aß) 42 in cerebrospinal fluid (CSF).

The Discovery of 7-Isopropoxy-2-(1-methyl-2-oxabicyclo[2.1.1]hexan-4-yl)-N-(6-methylpyrazolo[1,5-a]pyrimidin-3-yl)imidazo[1,2-a]pyrimidine-6-carboxamide (BIO-7488), a Potent, Selective, and CNS-Penetrant IRAK4 Inhibitor for the Treatment of Ischemic Stroke.

Interleukin receptor-associated kinase 4 (IRAK4) is a key node of signaling within the innate immune system that regulates the production of inflammatory cytokines and chemokines. The presence of damage-associated molecular patterns (DAMPs) after tissue damage such as stroke or traumatic brain injury (TBI) initiates signaling through the IRAK4 pathway that can lead to a feed-forward inflammatory loop that can ultimately hinder patient recovery. Herein, we describe the first potent, selective, and CNS-penetrant IRAK4 inhibitors for the treatment of neuroinflammation. Lead compounds from the series were evaluated in CNS PK/PD models of inflammation, as well as a mouse model of ischemic stroke. The SAR optimization detailed within culminates in the discovery of BIO-7488, a highly selective and potent IRAK4 inhibitor that is CNS penetrant and has excellent ADME properties.

Adeno-Associated Virus-Mediated Dorsal Root Ganglion Toxicity in the New Zealand White Rabbit.

Recombinant adeno-associated virus (AAV)-mediated degeneration of sensory neurons in the dorsal root ganglia (DRG) and trigeminal ganglia (TG) has been observed in non-human primates (NHPs) following intravenous (IV) and intrathecal (IT) delivery. Administration of recombinant AAV encoding a human protein transgene via a single intra-cisterna magna (ICM) injection in New Zealand white rabbits resulted in histopathology changes very similar to NHPs: mononuclear cell infiltration, degeneration/necrosis of sensory neurons, and nerve fiber degeneration of sensory tracts in the spinal cord and of multiple nerves. AAV-associated clinical signs and incidence/severity of histologic findings indicated that rabbits were equally or more sensitive than NHPs to sensory neuron damage. Another study using human and rabbit transgene constructs of the same protein demonstrated comparable changes suggesting that the effects are not an immune response to the non-self protein transgene. Rabbit has not been characterized as a species for general toxicity testing of AAV gene therapies, but these studies suggest that it may be an alternative model to investigate mechanisms of AAV-mediated neurotoxicity and test novel AAV designs mitigating these adverse effects.

Prospective Validation of Machine Learning Algorithms for Absorption, Distribution, Metabolism, and Excretion Prediction: An Industrial Perspective.

Absorption, distribution, metabolism, and excretion (ADME), which collectively define the concentration profile of a drug at the site of action, are of critical importance to the success of a drug candidate. Recent advances in machine learning algorithms and the availability of larger proprietary as well as public ADME data sets have generated renewed interest within the academic and pharmaceutical science communities in predicting pharmacokinetic and physicochemical endpoints in early drug discovery. In this study, we collected 120 internal prospective data sets over 20 months across six ADME in vitro endpoints: human and rat liver microsomal stability, MDR1-MDCK efflux ratio, solubility, and human and rat plasma protein binding. A variety of machine learning algorithms in combination with different molecular representations were evaluated. Our results suggest that gradient boosting decision tree and deep learning models consistently outperformed random forest over time. We also observed better performance when models were retrained on a fixed schedule, and the more frequent retraining generally resulted in increased accuracy, while hyperparameters tuning only improved the prospective predictions marginally.

Target occupancy study and whole-body dosimetry with a MAGL PET ligand [11C]PF-06809247 in non-human primates.

BACKGROUND: Monoacylglycerol lipase (MAGL) is a key serine hydrolase which terminates endocannabinoid signaling and regulates arachidonic acid driven inflammatory responses within the central nervous system. To develop [11C]PF-06809247 into a clinically usable MAGL positron emission tomography (PET) radioligand, we assessed the occupancy of MAGL by an inhibitor in the non-human primate (NHP) brain. Additionally, we measured the whole-body distribution of [11C]PF-06809247 in NHP and estimated human effective radiation doses. METHODS: Seven cynomolgus monkeys were enrolled for brain PET measurements. Two PET measurements along with arterial blood sampling were performed in each NHP: one baseline and one pretreatment condition with intravenous administration of PF-06818883, a pro-drug of a selective MAGL inhibitor (total of seven doses between 0.01 and 1.27 mg/kg). Kinetic parameters K1, k2 and k3 were estimated by a two tissue compartment (2TC) model using metabolite corrected plasma radioactivity as the input function. k4 was set as 0 according to the irreversible binding of [11C]PF-06809247. Ki by 2TC and Patlak analysis were calculated as the influx constant. The target occupancy was calculated using Ki at baseline and pretreatment conditions. Two cynomolgus monkeys were enrolled for whole-body PET measurements. Estimates of the absorbed radiation dose in humans were calculated with OLINDA/EXM 1.1 using the adult male reference model. RESULTS: Radioactivity retention was decreased in all brain regions following pretreatment with PF-06818883. Occupancy was measured as 25.4-100.5% in a dose dependent manner. Whole-body PET showed high radioactivity uptake values in the liver, small intestine, kidney, and brain. The effective dose of [11C]PF-06809247 was calculated as 4.3 µSv/MBq. CONCLUSIONS: [11C]PF-06809247 is a promising PET ligand for further studies of MAGL in the human brain.

Development of a one-step RT-ddPCR method to determine the expression and potency of AAV vectors.

Robust assays to quantify adeno-associated virus (AAV) vector expression and potency are essential for gene therapy development. These assays inform the efficacy, safety, and pharmacodynamic profiles of AAV development candidates. Additionally, for gene downregulation strategies such as RNAi, knockdown of endogenous genes reflects the mechanism of action of such development candidates. Therefore, a method to quantify target mRNA repression is necessary for measuring vector potency both in vitro and in vivo. Here, we report the development of a one-step reverse-transcription droplet digital PCR (RT-ddPCR) method to analyze expression of AAV vectors and the potency of AAV-RNAi vectors. This one-step RT-ddPCR method simplifies the workflow, allows for duplexing reactions, and enables absolute quantification of transcripts without standard materials. With a gene augmentation vector, we demonstrate the application of RT-ddPCR in quantifying vector expression in vitro and in non-human primate (NHP) samples. This novel method is demonstrated to be precise and linear within the range of 0.05-25 ng of RNA input. Using an AAV-RNAi vector, we further demonstrate the utility of this RT-ddPCR method in quantifying potency. Orthogonal potency assays, including ELISA and functional readout, correlate well with RT-ddPCR results. Therefore, one-step RT-ddPCR can be implemented in the analytical and pharmacological characterization of AAV vectors.

Next-generation Bruton's tyrosine kinase inhibitor BIIB091 selectively and potently inhibits B cell and Fc receptor signaling and downstream functions in B cells and myeloid cells.

OBJECTIVES: Bruton's tyrosine kinase (BTK) plays a non-redundant signaling role downstream of the B-cell receptor (BCR) in B cells and the receptors for the Fc region of immunoglobulins (FcR) in myeloid cells. Here, we characterise BIIB091, a novel, potent, selective and reversible small-molecule inhibitor of BTK. METHODS: BIIB091 was evaluated in vitro and in vivo in preclinical models and in phase 1 clinical trial. RESULTS: In vitro, BIIB091 potently inhibited BTK-dependent proximal signaling and distal functional responses in both B cells and myeloid cells with IC50s ranging from 3 to 106 nm, including antigen presentation to T cells, a key mechanism of action thought to be underlying the efficacy of B cell-targeted therapeutics in multiple sclerosis. BIIB091 effectively sequestered tyrosine 551 in the kinase pocket by forming long-lived complexes with BTK with t 1/2 of more than 40 min, thereby preventing its phosphorylation by upstream kinases. As a key differentiating feature of BIIB091, this property explains the very potent whole blood IC50s of 87 and 106 nm observed with stimulated B cells and myeloid cells, respectively. In vivo, BIIB091 blocked B-cell activation, antibody production and germinal center differentiation. In phase 1 healthy volunteer trial, BIIB091 inhibited naïve and unswitched memory B-cell activation, with an in vivo IC50 of 55 nm and without significant impact on lymphoid or myeloid cell survival after 14 days of dosing. CONCLUSION: Pharmacodynamic results obtained in preclinical and early clinical settings support the advancement of BIIB091 in phase 2 clinical trials.

Optimization of dose and route of administration of the P-glycoprotein inhibitor, valspodar (PSC-833) and the P-glycoprotein and breast cancer resistance protein dual-inhibitor, elacridar (GF120918) as dual infusion in rats.

Transporters can play a key role in the absorption, distribution, metabolism, and excretion of drugs. Understanding these contributions early in drug discovery allows for more accurate projection of the clinical pharmacokinetics. One method to assess the impact of transporters in vivo involves co-dosing specific inhibitors. The objective of the present study was to optimize the dose and route of administration of a P-glycoprotein (P-gp) inhibitor, valspodar (PSC833), and a dual P-gp/breast cancer resistance protein (BCRP) inhibitor, elacridar (GF120918), by assessing the transporters' impact on brain penetration and absorption. A dual-infusion strategy was implemented to allow for flexibility with dose formulation. The chemical inhibitor was dosed intravenously via the femoral artery, and a cassette of known substrates was infused via the jugular vein. Valspodar or elacridar was administered as 4.5-hour constant infusions over a range of doses. To assess the degree of inhibition, the resulting ratios of brain and plasma concentrations, Kp's, of the known substrates were compared to the vehicle control. These data demonstrated that doses greater than 0.9 mg/hr/kg valspodar and 8.9 mg/hr/kg elacridar were sufficient to inhibit P-gp- and BCRP-mediated efflux at the blood-brain barrier in rats without any tolerability issues. Confirmation of BBB restriction by efflux transporters in preclinical species allows for subsequent prediction in humans based upon the proteomic expression at rodent and human BBB. Overall, the approach can also be applied to inhibition of efflux at other tissues (gut absorption, liver clearance) or can be extended to other transporters of interest using alternate inhibitors.

Harnessing Preclinical Data as a Predictive Tool for Human Brain Tissue Targeting.

One of the objectives within the medicinal chemistry discipline is to design tissue targeting molecules. The objective of tissue specificity can be either to gain drug access to the compartment of interest (e.g., the CNS) for Neuroscience targets or to restrict drug access to the CNS for all other therapeutic areas. Both neuroscience and non-neuroscience therapeutic areas have struggled to quantitatively estimate brain penetration or the lack thereof with compounds that are substrates of efflux transport proteins such as P-glycoprotein (P-gp) and breast cancer resistant protein (BCRP) that are key components of the blood-brain barrier (BBB). It has been well established that drug candidates with high efflux ratios (ER) of these transporters have poor penetration into brain tissue. In the current work, we outline a parallel analysis to previously published models for the prediction of brain penetration that utilize an alternate MDR1-MDCK cell line as a better predictor of brain penetration and whether a correlation between in vitro, rodent data, non-human primate (NHP), and human in vivo brain penetration data could be established. Analysis of structural and physicochemical properties in conjunction with in vitro parameters and preclinical in vivo data has been highlighted in this manuscript as a continuation of the previously published work.

D1 Agonist Improved Movement of Parkinsonian Nonhuman Primates with Limited Dyskinesia Side Effects.

Parkinson's disease is a progressive neurodegenerative disease characterized by striatal dopaminergic loss. L-DOPA treatment replaces lost dopamine and enables motor function; however, eventually, fluctuating efficacy and side effects associated with its use become challenging for many patients. Here, we demonstrate, in a clinically translatable nonhuman primate model of parkinsonian motor symptoms, that treatment with the partial D1 receptor agonist CVL-751, formerly known as PF-06649751, is just as effective as L-DOPA in enabling movement and reducing disability. Importantly, CVL-751 efficacy is observed with less of the concomitant dyskinesia side effect associated with L-DOPA treatment. Data presented suggest that partial D1 agonists may be an effective and important treatment strategy for the management of Parkinson's patients.

Identification and Development of an Irreversible Monoacylglycerol Lipase (MAGL) Positron Emission Tomography (PET) Radioligand with High Specificity.

Monoacylglycerol lipase (MAGL), a serine hydrolase extensively expressed throughout the brain, serves as a key gatekeeper regulating the tone of endocannabinoid signaling. Preclinically, inhibition of MAGL is known to provide therapeutic benefits for a number of neurological disorders. The availability of a MAGL-specific positron emission tomography (PET) ligand would considerably facilitate the development and clinical characterization of MAGL inhibitors via noninvasive and quantitative PET imaging. Herein, we report the identification of the potent and selective irreversible MAGL inhibitor 7 (PF-06809247) as a suitable radioligand lead, which upon radiolabeling was found to exhibit a high level of MAGL specificity; this enabled cross-species measurement of MAGL brain expression (Bmax), assessment of in vivo binding in the rat, and nonhuman primate PET imaging.

In Vitro-In Vivo Extrapolation of Key Transporter Activity at the Blood-Brain Barrier.

Understanding the quantitative implications of P-glycoprotein and breast cancer resistance protein efflux is a key hurdle in the design of effective, centrally acting or centrally restricted therapeutics. Previously, a comprehensive physiologically based pharmacokinetic model was developed to describe the in vivo unbound brain-to-plasma concentration ratio as a function of efflux activity measured in vitro. In the present work, the predictive utility of this framework was examined through application to in vitro and in vivo data generated on 133 unique compounds across three preclinical species. Two approaches were examined for the scaling of efflux activity to in vivo, namely relative expression as determined by independent proteomics measurements and relative activity as determined via fitting the in vivo neuropharmacokinetic data. The results with both approaches indicate that in vitro efflux data can be used to accurately predict the degree of brain penetration across species within the context of the proposed physiologically based pharmacokinetic framework.

Discovery and Characterization of (R)-6-Neopentyl-2-(pyridin-2-ylmethoxy)-6,7-dihydropyrimido[2,1-c][1,4]oxazin-4(9H)-one (PF-06462894), an Alkyne-Lacking Metabotropic Glutamate Receptor 5 Negative Allosteric Modulator Profiled in both Rat and Nonhuman Primates.

We previously observed a cutaneous type IV immune response in nonhuman primates (NHP) with the mGlu5 negative allosteric modulator (NAM) 7. To determine if this adverse event was chemotype- or mechanism-based, we evaluated a distinct series of mGlu5 NAMs. Increasing the sp3 character of high-throughput screening hit 40 afforded a novel morpholinopyrimidone mGlu5 NAM series. Its prototype, (R)-6-neopentyl-2-(pyridin-2-ylmethoxy)-6,7-dihydropyrimido[2,1-c][1,4]oxazin-4(9H)-one (PF-06462894, 8), possessed favorable properties and a predicted low clinical dose (2 mg twice daily). Compound 8 did not show any evidence of immune activation in a mouse drug allergy model. Additionally, plasma samples from toxicology studies confirmed that 8 did not form any reactive metabolites. However, 8 caused the identical microscopic skin lesions in NHPs found with 7, albeit with lower severity. Holistically, this work supports the hypothesis that this unique toxicity may be mechanism-based although additional work is required to confirm this and determine clinical relevance.

Insights from mathematical modeling for convection-enhanced intraputamenal delivery of GDNF.

Glial cell line-derived neurotrophic factor (GDNF) is a potential therapy for Parkinson's disease (PD) promoting survival and functional recovery of dopaminergic neurons when delivered to the degenerated striatum. To study the aspects of intraputamenal delivery of GDNF, a mathematical model of recombinant methionyl human GDNF (r-metHuGDNF) convection in the human putamen has been developed. The convection-enhanced delivery infusions of r-metHuGDNF were simulated at rates up to 5 µL/min. The high-rate infusions (≥1 µL/min) permit rapid and uniform distribution of drug with up to 75% of the distribution volume having a concentration within 5% of the infusate concentration. No relevant differences in distribution at infusion rates of 3 and 5 µL/min were found. The patterns of GDNF distribution were analyzed in relation to the anatomy of the posterior dorsal putamen, and a cylindrical shape was found to be preferable considering risks of target overflow. A magnetic resonance (MR) tracer Gd-DTPA (Magnevist®) was evaluated as a surrogate in clinical studies, and the most accurate prediction of GDNF distribution was calculated immediately after infusion. The clearance of GDNF from the striatum is confirmed to be slow, with a half-life of ca. 19 h.

Translational pharmacokinetic-pharmacodynamic analysis in the pharmaceutical industry: an IQ Consortium PK-PD Discussion Group perspective.

With inadequate efficacy being the primary cause for the attrition of drug candidates in clinical development, the need to better predict clinical efficacy earlier in the drug development process has increased in importance in the pharmaceutical industry. Here, we review current applications of translational pharmacokinetic-pharmacodynamic (PK-PD) modeling of preclinical data in the pharmaceutical industry, including best practices. Preclinical translational PK-PD modeling has been used in many therapeutic areas and has been impactful to drug development. The role of preclinical translational PK-PD modeling in drug discovery and development will continue to evolve and broaden, given that its broad implementation in the pharmaceutical industry is relatively recent and many opportunities still exist for its further application.

In Vitro-In Vivo Extrapolation of Intestinal Availability for Carboxylesterase Substrates Using Portal Vein-Cannulated Monkey.

Prediction of intestinal availability (FaFg) of carboxylesterase (CES) substrates is of critical importance in designing oral prodrugs with optimal properties, projecting human pharmacokinetics and dose, and estimating drug-drug interaction potentials. A set of ester prodrugs were evaluated using in vitro permeability (parallel artificial membrane permeability assay and Madin-Darby canine kidney cell line-low efflux) and intestinal stability (intestine S9) assays, as well as in vivo portal vein-cannulated cynomolgus monkey. In vitro-in vivo extrapolation (IVIVE) of FaFg was developed with a number of modeling approaches, including a full physiologically based pharmacokinetic (PBPK) model as well as a simplified competitive-rate analytical solution. Both methods converged as in the PBPK simulations enterocyte blood flow behaved as a sink, a key assumption in the competitive-rate analysis. For this specific compound set, the straightforward analytical solution therefore can be used to generate in vivo predictions. Strong IVIVE of FaFg was observed for cynomolgus monkey with R2 of 0.71-0.93. The results suggested in vitro assays can be used to predict in vivo FaFg for CES substrates with high confidence.

Discovery of a Highly Selective Glycogen Synthase Kinase-3 Inhibitor (PF-04802367) That Modulates Tau Phosphorylation in the Brain: Translation for PET Neuroimaging.

Glycogen synthase kinase-3 (GSK-3) regulates multiple cellular processes in diabetes, oncology, and neurology. N-(3-(1H-1,2,4-triazol-1-yl)propyl)-5-(3-chloro-4-methoxyphenyl)oxazole-4-carboxamide (PF-04802367 or PF-367) has been identified as a highly potent inhibitor, which is among the most selective antagonists of GSK-3 to date. Its efficacy was demonstrated in modulation of tau phosphorylation in vitro and in vivo. Whereas the kinetics of PF-367 binding in brain tissues are too fast for an effective therapeutic agent, the pharmacokinetic profile of PF-367 is ideal for discovery of radiopharmaceuticals for GSK-3 in the central nervous system. A (11) C-isotopologue of PF-367 was synthesized and preliminary PET imaging studies in non-human primates confirmed that we have overcome the two major obstacles for imaging GSK-3, namely, reasonable brain permeability and displaceable binding.

Insights From an Integrated Physiologically Based Pharmacokinetic Model for Brain Penetration.

Central-nervous-system, physiologically based pharmacokinetic (PBPK) models predict exposure profiles in the brain, that is, the rate and extent of distribution. The current work develops one such model and presents improved methods for determining key input parameters. A simple linear regression statistical model estimates the passive permeability at the blood-brain barrier from brain uptake index data and descriptors, and a novel analysis extracts the relative active transport parameter from in vitro assays taking into consideration both paracellular transport and unstirred water layers. The integrated PBPK model captures the concentration profiles of both rate-restricted and effluxed compounds with high passive permeability. In many cases, compounds distribute rapidly into the brain and are, therefore, not rate limited. The PBPK model is then simplified to a straightforward equation to describe brain-to-plasma ratios at steady state. The equation can estimate brain penetration either from in vitro efflux data or from in vivo results from another species and, therefore, is a valuable tool in the discovery setting.

Preclinical pharmacokinetic/pharmacodynamic modeling and simulation in the pharmaceutical industry: an IQ consortium survey examining the current landscape.

The application of modeling and simulation techniques is increasingly common in preclinical stages of the drug discovery and development process. A survey focusing on preclinical pharmacokinetic/pharmacodynamics (PK/PD) analysis was conducted across pharmaceutical companies that are members of the International Consortium for Quality and Innovation in Pharmaceutical Development. Based on survey responses, ~68% of companies use preclinical PK/PD analysis in all therapeutic areas indicating its broad application. An important goal of preclinical PK/PD analysis in all pharmaceutical companies is for the selection/optimization of doses and/or dose regimens, including prediction of human efficacious doses. Oncology was the therapeutic area with the most PK/PD analysis support and where it showed the most impact. Consistent use of more complex systems pharmacology models and hybrid physiologically based pharmacokinetic models with PK/PD components was less common compared to traditional PK/PD models. Preclinical PK/PD analysis is increasingly being included in regulatory submissions with ~73% of companies including these data to some degree. Most companies (~86%) have seen impact of preclinical PK/PD analyses in drug development. Finally, ~59% of pharmaceutical companies have plans to expand their PK/PD modeling groups over the next 2 years indicating continued growth. The growth of preclinical PK/PD modeling groups in pharmaceutical industry is necessary to establish required resources and skills to further expand use of preclinical PK/PD modeling in a meaningful and impactful manner.

Enhancing ketamine translational pharmacology via receptor occupancy normalization.

Ketamine is used preclinically and clinically to study schizophrenia and depression. Accordingly, it is imperative to understand the temporal relationship between the central concentrations and N-methyl-d-aspartate receptor (NMDAR) interactions of both ketamine and norketamine, its primary active metabolite, across species to assess the translatability of animal models to humans and the back-translation of clinical observations to the preclinical realm. However, such an interspecies normalization of ketamine and norketamine exposures at different clinical and preclinical doses (and their different routes and regimens) is lacking. This work defines the NMDAR occupancy (RO) time course following single doses of ketamine in rats, nonhuman primates (nhp) and humans to allow direct interspecies comparisons of specific ketamine-mediated pharmacodynamics via RO normalization. Total plasma concentration (Cp)-time profiles of ketamine and norketamine were generated from rats and nhp following a single, memory-impairing dose of ketamine; neuropharmacokinetics were determined in rats. [(3)H]MK-801-displacement studies in rats determined estimated mean (95% confidence interval) unbound plasma concentrations (Cp,u) for ketamine and norketamine producing 50% RO (IC50) of 1420 (990, 2140) nM and 9110 (5870, 13700) nM, respectively. Together, these datasets transformed Cp,u-time data to predicted RO (ROpred)-time profiles for rats, nhp and humans at behaviorally relevant ketamine doses. Subsequently, this approach helped determine an infusion paradigm in rats producing a ROpred-time profile mirroring that for a clinically antidepressant infusion. The described indication-independent methodology allows normalization to RO at any time following any ketamine dose (regardless of route or regimen) in any species by simply quantifying the Cp of ketamine and norketamine. Matching temporal RO relationships in animals and humans should allow direct comparisons of specific ketamine-dependent NMDAR-based pharmacodynamics.