Karissa Adkins

Begacestat (GSI-953): A Novel, Selective Thiophene Sulfonamide Inhibitor of Amyloid Precursor Protein γ-Secretase for the Treatment of Alzheimer's Disease

The presenilin containing γ-secretase complex is responsible for the regulated intramembraneous proteolysis of the amyloid precursor protein (APP), the Notch receptor, and a multitude of other substrates. γ-Secretase catalyzes the final step in the generation of Aβ40 and Aβ42 peptides from APP. Amyloid β-peptides (Aβ peptides) aggregate to form neurotoxic oligomers, senile plaques, and congophilic angiopathy, some of the cardinal pathologies associated with Alzheimers disease. Although inhibition of this protease acting on APP may result in potentially therapeutic reductions of neurotoxic Aβ peptides, nonselective inhibition of the enzyme may cause severe adverse events as a result of impaired Notch receptor processing. Here, we report the preclinical pharmacological profile of GSI-953 (begacestat), a novel thiophene sulfonamide γ-secretase inhibitor (GSI) that selectively inhibits cleavage of APP over Notch. This GSI inhibits Aβ production with low nanomolar potency in cellular and cell-free assays of γ-secretase function, and displaces a tritiated analog of GSI-953 from enriched γ-secretase enzyme complexes with similar potency. Cellular assays of Notch cleavage reveal that this compound is approximately 16-fold selective for the inhibition of APP cleavage. In the human APP-overexpressing Tg2576 transgenic mouse, treatment with this orally active compound results in a robust reduction in brain, plasma, and cerebral spinal fluid Aβ levels, and a reversal of contextual fear-conditioning deficits that are correlated with Aβ load. In healthy human volunteers, oral administration of a single dose of GSI-953 produces dose-dependent changes in plasma Aβ levels, confirming pharmacodynamic activity of GSI-953 in humans.

A Systems Biology Approach Utilizing a Mouse Diversity Panel Identifies Genetic Differences Influencing Isoniazid-Induced Microvesicular Steatosis

Isoniazid (INH), the mainstay therapeutic for tuberculosis infection, has been associated with rare but serious hepatotoxicity in the clinic. However, the mechanisms underlying inter-individual variability in the response to this drug have remained elusive. A genetically diverse mouse population model in combination with a systems biology approach was utilized to identify transcriptional changes, INH-responsive metabolites, and gene variants that contribute to the liver response in genetically sensitive individuals. Sensitive mouse strains developed severe microvesicular steatosis compared with corresponding vehicle control mice following 3 days of oral treatment with INH. Genes involved in mitochondrial dysfunction were enriched among liver transcripts altered with INH treatment. Those associated with INH treatment and susceptibility to INH-induced steatosis in the liver included apolipoprotein A-IV, lysosomal-associated membrane protein 1, and choline phosphotransferase 1. These alterations were accompanied by metabolomic changes including reduced levels of glutathione and the choline metabolites betaine and phosphocholine, suggesting that oxidative stress and reduced lipid export may additionally contribute to INH-induced steatosis. Finally, genome-wide association mapping revealed that polymorphisms in perilipin 2 were linked to increased triglyceride levels following INH treatment, implicating a role for inter-individual differences in lipid packaging in the susceptibility to INH-induced steatosis. Taken together, our data suggest that INH-induced steatosis is caused by not one, but multiple events involving lipid retention in the livers of genetically sensitive individuals. This work also highlights the value of using a mouse diversity panel to investigate drug-induced responses across a diverse population.

Correlation of pharmacodynamic activity, pharmacokinetics, and anti-product antibody responses to anti-IL-21R antibody therapeutics following IV administration to cynomolgus monkeys.

BackgroundAnti-IL-21R antibodies are potential therapeutics for the treatment of autoimmune diseases. This study evaluated correlations between the pharmacodynamic (PD) activity, pharmacokinetics, and anti-product antibody responses of human anti-IL-21R antibodies Ab-01 and Ab-02 following IV administration to cynomolgus monkeys.MethodsThe PD assay was based on the ability of recombinant human IL-21 (rhuIL-21) to induce expression of the IL-2RA gene in cynomolgus monkey whole blood samples ex vivo. Monkeys screened for responsiveness to rhuIL-21 stimulation using the PD assay, were given a single 10 mg/kg IV dosage of Ab-01, Ab-02, or a control antibody (3/group), and blood samples were evaluated for PD activity (inhibition of IL-2RA expression) for up to 148 days. Anti-IL-21R antibody concentrations and anti-product antibody responses were measured in serum using immunoassays and flow cytometry.ResultsFollowing IV administration of Ab-01 and Ab-02 to cynomolgus monkeys, PD activity was observed as early as 5 minutes (first time point sampled). This PD activity had good correlation with the serum concentrations and anti-product antibody responses throughout the study. The mean terminal half-life (t1/2) was ~10.6 and 2.3 days for Ab-01 and Ab-02, respectively. PD activity was lost at ~5-13 weeks for Ab-01 and at ~2 weeks for Ab-02, when serum concentrations were relatively low. The estimated minimum concentrations needed to maintain PD activity were ~4-6 nM for Ab-01 and ~2.5 nM for Ab-02, and were consistent with the respective KD values for binding to human IL-21R. For Ab-01, there was noticeable inter-animal variability in t1/2 values (~6-14 days) and the resulting PD profiles, which correlated with the onset of anti-product antibody formation. While all three Ab-01-dosed animals were positive for anti-Ab-01 antibodies, only one monkey (with the shortest t1/2 and the earliest loss of PD activity) had evidence of neutralizing anti-Ab-01 antibodies. All three Ab-02-dosed monkeys developed neutralizing anti-Ab-02 antibodies.ConclusionsFor anti-IL-21R antibodies Ab-01 and Ab-02, there was good correlation between PD activity and PK profiles following IV administration to cynomolgus monkeys. Compared with Ab-01, Ab-02 was eliminated markedly faster from the circulation, which correlated with a shorter duration of PD activity.

Development and application of a biomarker assay for determining the pharmacodynamic activity of an antagonist candidate biotherapeutic antibody to IL21R in whole blood.

BackgroundIn preparation for potential clinical development of Ab-01, an antagonistic antibody directed against the IL21R, studies were undertaken to address translational medicine needs that fall into four categories: 1) development of a pharmacodynamic biomarker assay suitable for use in the clinic, 2) demonstration that Ab-01 has the desired biological activity in vitro and in vivo in cynomolgus monkeys, the preferred safety study species, 3) pre-clinical in vivo proof-of-concept that the assay can be used to detect Ab-01 pharmacodynamic (PD) activity in treated subjects, and 4) comprehensive assessment of the agonistic potential of Ab-01 when cross-linked. This report and a recently published companion report address the first three of these needs. The fourth has been addressed in a separate study.MethodsGenes that change RNA expression upon ex vivo rhIL21 stimulation of whole blood were identified in human and cynomolgus monkey. The inhibitory effects of exogenously added Ab-01 were measured ex vivo in human and monkey, and the in vivo inhibitory effects of Ab-01 treatment were measured in monkey.ResultsStimulation of whole human blood for 2 hours with rhIL21 induced robust increases in RNA expression of 6 genes. This response was blocked by Ab-01, indicating that the assay is suitable for measuring Ab-01 activity in blood. rhIL21 induced expression of a similar set of genes in cynomolgus monkey blood. This response was blocked with Ab-01, thus demonstrating that Ab-01 has the desired activity in the species, and that safety studies done in cynomolgus monkeys are relevant. Proof -of-concept for using this assay system to detect PD activity in vivo was generated by measuring the response in monkey blood to ex vivo rhIL21 stimulation before and 5 minutes following in vivo Ab-01 administration.ConclusionsA robust PD biomarker assay suitable for clinical use has been developed in human whole blood. The successful adaptation of the assay to cynomolgus monkeys has enabled the demonstration of Ab-01 activity both in vitro and in vivo in monkey, thus validating the use of this species in safety studies and establishing proof-of-concept for using this PD assay system to aid in dose selection in clinical studies.

Dysregulation of protein degradation pathways may mediate the liver injury and phospholipidosis associated with a cationic amphiphilic antibiotic drug

A large number of antibiotics are known to cause drug-induced liver injury in the clinic; however, interpreting clinical risk is not straightforward owing to a lack of predictivity of the toxicity by standard preclinical species and a poor understanding of the mechanisms of toxicity. An example is PF-04287881, a novel ketolide antibiotic that caused elevations in liver function tests in Phase I clinical studies. In this study, a mouse diversity panel (MDP), comprised of 34 genetically diverse, inbred mouse strains, was utilized to model the toxicity observed with PF-04287881 treatment and investigate potential mechanisms that may mediate the liver response. Significant elevations in serum alanine aminotransferase (ALT) levels in PF-04287881-treated animals relative to vehicle-treated controls were observed in the majority (88%) of strains tested following a seven day exposure. The average fold elevation in ALT varied by genetic background and correlated with microscopic findings of hepatocellular hypertrophy, hepatocellular single cell necrosis, and Kupffer cell vacuolation (confirmed as phospholipidosis) in the liver. Global liver mRNA expression was evaluated in a subset of four strains to identify transcript and pathway differences that distinguish susceptible mice from resistant mice in the context of PF-04287881 treatment. The protein ubiquitination pathway was highly enriched among genes associated with PF-04287881-induced hepatocellular necrosis. Expression changes associated with PF-04287881-induced phospholipidosis included genes involved in drug transport, phospholipid metabolism, and lysosomal function. The findings suggest that perturbations in genes involved in protein degradation leading to accumulation of oxidized proteins may mediate the liver injury induced by this drug.

Utilization of iPSC-derived human neurons for high-throughput drug-induced peripheral neuropathy screening

As the number of cancer survivors continues to grow, awareness of long-term toxicities and impact on quality of life after chemotherapy treatment in cancer survivors has intensified. Chemotherapy-induced peripheral neuropathy (CIPN) is one of the most common side effects of modern chemotherapy. Animal models are used to study peripheral neuropathy and predict human risk; however, such models are labor-intensive and limited translatability between species has become a major challenge. Moreover, the mechanisms underlying CIPN have not been precisely determined and few human neuronal models to study CIPN exist. Here, we have developed a high-throughput drug-induced neurotoxicity screening model using human iPSC-derived peripheral-like neurons to study the effect of chemotherapy agents on neuronal health and morphology using high content imaging measurements (neurite length and neuronal cell viability). We utilized this model to test various classes of chemotherapeutic agents with known clinical liability to cause peripheral neuropathy such as platinum agents, taxanes, vinca alkaloids, proteasome inhibitors, and anti-angiogenic compounds. The model was sensitive to compounds that cause interference in microtubule dynamics, especially the taxane, epothilone, and vinca alkaloids. Conversely, the model was not sensitive to platinum and anti-angiogenic chemotherapeutics; compounds that are not reported to act directly on neuronal processes. In summary, we believe this model has utility for high-throughput screening and prediction of human risk for CIPN for novel chemotherapeutics.

Reproductive performance and early postnatal development in interleukin (IL)-13-deficient mice.

OBJECTIVE The purpose of this study was to assess the effect of interleukin (IL)-13 deficiency on fertility and reproductive performance of adult mice and on morphological and behavioral development of the offspring. METHODS Wild-type and homozygous IL-13-deficient (KO) mice were grouped by genotype, and male and female mice were mated within each group. Adult (F(0) ) mice were evaluated for reproductive performance, and development was assessed in F(1) fetuses on gestation day 18, and in F(1) pups to postnatal day 35. RESULTS In F(0) males, there were no differences in the number of males that mated or impregnated females, or in total sperm count or sperm motility, between the wild-type and KO groups. In F(0) females, there were no observed genotype-related differences in fertility, length of gestation, number of viable fetuses per litter, or viability of offspring. There were no differences in embryo-fetal development (external/palate, skeletal, visceral) of the F(1) fetuses between genotypes. Similarly, IL-13 deficiency had no impact on any postnatal parameters assessed including reflex, sexual maturation, learning, and memory. CONCLUSIONS IL-13 deficiency had no observed effect on reproductive performance or morphological and behavioral development in mice.

Identification of MHC Haplotypes Associated with Drug-induced Hypersensitivity Reactions in Cynomolgus Monkeys

Drug-induced hypersensitivity reactions can significantly impact drug development and use. Studies to understand risk factors for drug-induced hypersensitivity reactions have identified genetic association with specific human leukocyte antigen (HLA) alleles. Interestingly, drug-induced hypersensitivity reactions can occur in nonhuman primates; however, association between drug-induced hypersensitivity reactions and major histocompatibility complex (MHC) alleles has not been described. In this study, tissue samples were collected from 62 cynomolgus monkeys from preclinical studies in which 9 animals had evidence of drug-induced hypersensitivity reactions. Microsatellite analysis was used to determine MHC haplotypes for each animal. A total of 7 haplotypes and recombinant MHC haplotypes were observed, with distribution frequency comparable to known MHC I allele frequency in cynomolgus monkeys. Genetic association analysis identified alleles from the M3 haplotype of the MHC I B region (B*011:01, B*075:01, B*079:01, B*070:02, B*098:05, and B*165:01) to be significantly associated (χ2 test for trend, p < 0.05) with occurrence of drug-induced hypersensitivity reactions. Sequence similarity from alignment of alleles in the M3 haplotype B region and HLA alleles associated with drug-induced hypersensitivity reactions in humans was 86% to 93%. These data demonstrate that MHC alleles in cynomolgus monkeys are associated with drug-induced hypersensitivity reactions, similar to HLA alleles in humans.

Optimization of experimental conditions for functional in vitro characterization of humanized antibodies specific for staphylococcal enterotoxin B.

Staphylococcus aureus is a common nosocomial infection and its resistance to penicillin and methicillin antibiotics is a growing clinical problem. We previously described the development of a humanized anti-Staphylococcus enterotoxin B (SEB) antibody derived from the mouse antibody made by the 20B1 hybridoma. This antibody was humanized and characterized kinetically by surface plasmon resonance demonstrating that the humanized clones retained binding to SEB. Clones were then functionally characterized in an in vitro assay demonstrating that the murine 20B1, chimeric and humanized antibodies potently inhibited SEB-induced murine splenocyte proliferation assay. Here, we describe a human cell-based screening assay, optimized by varying multiple experimental parameters that resulted in an assay that was used to demonstrate full and potent neutralization by the parental, chimeric and humanized antibodies. The replacement of fetal bovine serum (FBS) with normal human serum (NHS) was found to be a crucial factor in the performance of the human cell based screening assay that enabled the calculation of mAb efficacy and potency. In addition, we found that anti-SEB antibodies showed similar efficacy and potency with a triple mutant Fc region (designed to be effector function null) or a wild-type Fc region, which is in contrast to previously described studies.

Principles of precision medicine and its application in toxicology

Precision medicine is an approach to developing drugs that focuses on employing biomarkers to stratify patients in clinical trials with the goal of improving efficacy and/or safety outcomes, ultimately increasing the odds of clinical success and drug approval. Precision medicine is an important tool for toxicologists to utilize, because its principles can be used to decide whether to pursue a drug target, to understand interindividual differences in response to drugs in both nonclinical and clinical settings, to aid in selecting doses that optimize efficacy or reduce adverse events, and to facilitate understanding of a drugs mode-of-action. Nonclinical models such as the mouse and non-human primate can be used to understand genetic variation and its potential translation to humans, and are available for toxicologists to employ in advance of drugs moving into clinical development. Understanding interindividual differences in response to drugs and how these differences can influence the drugs risk-benefit profile and lead to the identification of biomarkers that enhance patient efficacy and safety is of critical importance for toxicologists today, and in the future, as the fields of pharmacogenomics and genetics continue to advance.