Adeno-associated virus (AAV) delivery of lysosomal enzymes to the brain is currently being tested in several clinical trials. However, publicly available non-human primate (NHP) studies comprehensively reporting biodistribution, transgene expression, and safety across the central nervous system (CNS) remain limited. Here, we examined AAV9-GBA1 (encoding glucocerebrosidase [GCase]) delivery to mice and NHPs. Loss-of-function GBA1 mutations cause Gaucher's disease and are risk factors for Parkinson's disease and dementia with Lewy bodies. In mice, early postnatal intracerebroventricular administration produced appreciable transgene expression and increased GCase activity in the brain without adverse findings. Two independent adult NHP studies evaluated AAV9-GBA1 brain delivery via intracisterna magna (ICM) and intraparenchymal (IPa) administration. ICM delivery produced considerable transgene expression in the spinal cord and dorsal root ganglia (DRG) neurons along with adverse microscopic findings, but limited brain expression and activity. In contrast, IPa delivery into the thalamus and/or putamen produced substantial transgene expression and GCase activity in injected and connected brain regions, with limited effects in distal regions, including the spinal cord. While no AAV-related DRG toxicity was detected with IPa, procedure- and AAV9-GBA1-related adverse microscopic brain findings were observed and associated with clinical outcomes. Further technological advances are needed to achieve safe and therapeutic AAV transgene expression in NHP brain.

Adeno-associated virus (AAV) artificial microRNAs (amiRNAs) targeting superoxide dismutase 1 (SOD1) have been proposed as a therapeutic strategy for people living with amyotrophic lateral sclerosis (ALS) who harbor toxic gain-of-function variants in the SOD1 gene. Clinical efforts have primarily focused on AAV delivery via the cerebrospinal fluid (CSF), as blood-brain-barrier-crossing capsids are still being developed preclinically. However, intra-CSF delivery has been shown to be highly variable and increases the risk for AAV-related adverse events such as dorsal root ganglion (DRG) toxicity. Here, we show that immunosuppressants (IMS) following intra-CSF delivery of AAV9-amiR-SOD1 in non-human primates (NHPs) prevented AAV-related DRG toxicity, and this benefit was maintained for over 300 days even after immunotherapy stopped at 90 days post-AAV treatment. In line with prior literature, we found intra-CSF delivery of AAV9-amiR-SOD1 to be highly variable in adult mice and NHPs, requiring higher doses of virus to achieve efficacious endpoints. To address this concern, we developed a proof-of-principle study showing that AAV9-amiR-SOD1, in combination with a SOD1-targeting antisense oligonucleotide, provided an additive therapeutic benefit in SOD1-G93A mice compared with AAV9-amiR-SOD1 alone. This combinatorial approach lowered the viral load needed to reach efficacious endpoints, which could mitigate AAV-related adverse events alongside IMS.

Administration of adeno-associated virus (AAV) gene therapies via blood or cerebrospinal fluid (CSF) in non-human primates (NHPs) can lead to degeneration of dorsal root ganglion (DRG) neurons and nerve fibers in the spinal cord and peripheral nerves. AAV cargo expression is implicated in AAV DRG toxicity, but the underlying mechanism(s) is unknown. Here, we performed a time course study of intra-cisterna magna (ICM) administration of an AAV9 variant encoding human survival of motor neuron 1 (hSMN1) to identify molecular and cellular changes preceding pathology. Increases in inflammatory gene modules, cerebrospinal fluid (CSF) cytokines, and immune cell infiltrates as early as day 5 prior to neuron and nerve fiber degeneration on days 15 and 29 suggested a role for the immune response in AAV-mediated toxicity. Prophylactic treatment with a glucocorticoid steroid dexamethasone and a calcineurin inhibitor tacrolimus diminished pathology in NHPs following administration of three AAV gene therapy vectors. Collectively, these data demonstrate a causal role for the immune response to AAV in AAV-mediated DRG and nerve fiber toxicity. The efficacy of immunosuppression with three different AAV cargos suggests broad utility across AAV vectors and provides a clinically feasible approach to mitigating this potential toxicity in patients.

PET imaging allows the study of enzyme concentration and activity in vivo . The enzyme natural turnover α , relevant for drug development, can be estimated if a suicide inhibitor drug is used. The main aim of this study was to develop a model for estimating α by accounting for the presence of residual inhibitor. We analyzed nonhuman primate PET data with monoacyglycerol lipase (MAGL) tracer [ 11 C]PF-06809247, and suicide inhibitor PF-06818883 (0.03–1.27 mg/kg, active compound PF-06807893). As [ 11 C]PF-06809247 is an irreversible tracer, we used simulations to evaluate the impact of flow limitation on identifiability of kinetic parameters. Based on this, MAGL activity estimates were obtained from three outcome parameters: K i , k 3 , K ˜ 3 (= K 1 K i K 1 − K i ). A new model, which links enzyme activity to the inhibitor drug’s plasma concentration, was used to estimate α . Using a conservative statistical cut-off, MAGL turnover half-lives were estimated ( K i : 3.9 h; k 3 : 4.6 h; K ˜ 3 : 6.1 h) – with faster turnover for K i (flow-limited). Serial PET experiments and measuring the drug’s plasma concentration allowed to estimate α correcting for residual suicide inhibition. This approach can be extended to other PET enzyme targets, improving our understanding of enzyme pathological alterations and suicide inhibitor-based therapies.

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 (Aβ42 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 β (Aβ) 42 in cerebrospinal fluid (CSF).

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.

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.

Dorsal root ganglion (DRG) toxicity has been consistently reported as a potential safety concern after delivery of adenoassociated viruses (AAVs) containing gene-replacement vectors but has yet to be reported for RNAi-based vectors. Here, we report DRG toxicity after AAV intra-CSF delivery of an RNAi expression construct-artificial microRNA targeting superoxide dismutase 1 (SOD1)-in non-human primates (NHPs) and provide evidence that this can be recapitulated within mice. Histopathology evaluation showed that NHPs and mice develop DRG toxicity after AAV delivery, including DRG neuron degeneration and necrosis and nerve-fiber degeneration that were associated with increases in cerebrospinal fl uid (CSF) and serum phosphorylated neurofilament heavy chain (pNF-H). RNA-sequencing analysis of DRGs showed that dysregulated pathways were preserved between NHPs and mice, including increases in innate/adaptive immune responses and decreases in mitochondrial- and neuronal-related genes, following AAV treatment. Finally, endogenous miR-215p was upregulated in DRGs of AAV-treated NHPs and mice. Increases in miR-21-5p were also identified within the CSF of NHPs, which significantly correlated with pNF-H, implicating miR-21-5p as a potential biomarker of DRG toxicity in conjunction with other molecular analytes. This work highlights the importance of assessing safety concerns related to DRG toxicity when developing RNAi-based AAV vectors for therapeutic purposes.

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.

Abstract 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 K 1, k 2 and k 3 were estimated by a two tissue compartment (2TC) model using metabolite corrected plasma radioactivity as the input function. k 4 was set as 0 according to the irreversible binding of [11C]PF-06809247. K i by 2TC and Patlak analysis were calculated as the influx constant. The target occupancy was calculated using K i 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.

AbstractObjectivesBruton'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.MethodsBIIB091 was evaluated in vitro and in vivo in preclinical models and in phase 1 clinical trial.ResultsIn 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 t1/2 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.ConclusionPharmacodynamic results obtained in preclinical and early clinical settings support the advancement of BIIB091 in phase 2 clinical trials.

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.

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.

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.

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 (B-max), assessment of in vivo binding in the rat, and nonhuman primate PET imaging.

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.

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.