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.

Mechanisms of Skin Toxicity Associated with Metabotropic Glutamate Receptor 5 Negative Allosteric Modulators.

Cutaneous reactions represent one of the most common adverse drug effects observed in clinical trials leading to substantial compound attrition. Three negative allosteric modulators (NAMs) of metabotropic glutamate receptors (mGluRs), which represent an important target for neurological diseases, developed by Pfizer, were recently failed in preclinical development due to delayed type IV skin hypersensitivity observed in non-human primates (NHPs). Here we employed large-scale phenotypic profiling in standardized panels of human primary cell/co-culture systems to characterize the skin toxicity mechanism(s) of mGluR5 NAMs from two different series. Investigation of a database of chemicals tested in these systems and transcriptional profiling suggested that the mechanism of toxicity may involve modulation of nuclear receptor targets RAR/RXR, and/or VDR with AhR antagonism. The studies reported here demonstrate how phenotypic profiling of preclinical drug candidates using human primary cells can provide insights into the mechanisms of toxicity and inform early drug discovery and development campaigns.

Anti-NGF monoclonal antibody muMab 911 does not deplete neurons in the superior cervical ganglia of young or old adult rats.

Nerve growth factor (NGF) blocking therapies are an emerging and effective approach to pain management. However, concerns about the potential for adverse effects on the structure and function of the peripheral nervous system have slowed their development. Early studies using NGF antisera in adult rats reported effects on the size and number of neurons in the sympathetic chain ganglia. In the work described here, both young adult (6-8 week) and fully mature (7-8 month) rats were treated with muMab 911, a selective, murine, anti-NGF monoclonal antibody, to determine if systemic exposures to pharmacologically active levels of antibody for 1 month cause loss of neurons in the sympathetic superior cervical ganglia (SCG). State-of-the-art, unbiased stereology performed by two independent laboratories was used to determine the effects of muMab 911 on SCG neuronal number and size, as well as ganglion size. Following muMab 911 treatment, non-statistically significant trends toward smaller ganglia, and smaller and fewer neurons, were seen when routine, nonspecific stains were used in stereologic assessments. However, when noradrenergic neurons were identified using tyrosine hydroxylase (TH) immunoreactivity, trends toward fewer neurons observed with routine stains were not apparent. The only statistically significant effects detected were lower SCG weights in muMab 911-treated rats, and a smaller volume of TH immunoreactivity in neurons from younger rats treated with muMab 911. These results indicate that therapeutically relevant exposures to the anti-NGF monoclonal antibody muMab 911 for 1 month have no effect on neuron numbers within the SCG from young or old adult rats.

Drug-induced Skin Lesions in Cynomolgus Macaques Treated with Metabotropic Glutamate Receptor 5 (mGluR5) Negative Allosteric Modulators.

Three orally administered metabotropic glutamate receptor 5 (mGluR5) negative allosteric modulators caused skin lesions consistent with delayed type-IV hypersensitivity in cynomolgus macaques in 2- and 12-week toxicity studies. Several monkeys developed macroscopic skin lesions in multiple locations after 8 to 9 days of dosing; the most prominent effects involved the genital region of males and generalized erythema occurred in both sexes. Microscopic lesions occurred in both clinically affected and unaffected areas and were characterized by lymphocytic interface inflammation, subepidermal bullae, and individual keratinocyte vacuolation/necrosis. In the 12-week study, clinical effects in 2 animals resolved with continued dosing, whereas in others the inflammatory process progressed with 1 female exhibiting systemic lymphocytic inflammation in multiple tissues. The inflammatory infiltrate consisted of CD3 and CD4 positive T lymphocytes with minimal CD68 positive macrophages and only rare CD8 positive T lymphocytes. A subset of animals given a dosing holiday was subsequently rechallenged with similar lesions developing but with a more rapid clinical onset. These skin lesions were consistent with type-IV delayed hypersensitivity with some features comparable to bullous drug eruptions in humans. A relationship between these findings and the intended mode of action for these compounds could not be ruled out, given the occurrence across different chemotypes.

Age-related testicular toxicity of mGluR5 negative allosteric modulators appears to be unrelated to testis drug transporter maturity.

Testicular degeneration was observed in exploratory toxicity studies in Wistar rats treated with several mGluR5 negative allosteric modulators. To determine if these testis effects were influenced by animal age, these compounds were administered to male Wistar rats of different ages (8, 10, and 12 weeks old) for 2 weeks followed by evaluation of male reproductive organ weights, testis histopathology, and inhibin B levels. Overall, seminiferous tubule degeneration was observed in 2/15, 5/15, and 0/15 compound treated rats from the 8, 10, and 12 week old cohorts and inhibin B was decreased in 8 and 10 week old animals, but not in 12 week old rats, suggesting that there is an age-related component to this testis toxicity. The gene expression profiles of drug transporters in the testis of rats aged PND 38 through PND 91 were very similar, indicating that immaturity of these transporters is an unlikely factor contributing to the age-related toxicity.

Toxicity of hydroxyurea in rats and dogs.

The toxicity of hydroxyurea, a treatment for specific neoplasms, sickle-cell disease, polycythemia, and thrombocytosis that kills cells in mitosis, was assessed in repeat-dose, oral gavage studies in rats and dogs and a cardiovascular study in telemetered dogs. Hydroxyurea produced hematopoietic, lymphoid, cardiovascular, and gastrointestinal toxicity with steep dose response curves. In rats dosed for 10 days, 50 mg/kg/day was tolerated; 500 mg/kg/day produced decreased body weight gain; decreased circulating leukocytes, erythrocytes, and platelets; decreased cellularity of thymus, lymph nodes, and bone marrow; and epithelial degeneration and/or dysplasia of the stomach and small intestine; 1,500 mg/kg/day resulted in deaths on day 5. In dogs, a single dose at ≥ 250 mg/kg caused prostration leading to unscheduled euthanasia. Dogs administered 50 mg/kg/day for 1 month had decreased circulating leukocytes, erythrocytes, and platelets; increased bone marrow cellularity with decreased maturing granulocytes; increased creatinine kinase activity; and increased iron pigment in bone marrow and hepatic sinusoidal cells. In telemetered dogs, doses ≥ 15 mg/kg decreased systolic blood pressure (BP); 50 mg/kg increased diastolic BP, heart rate, and change in blood pressure over time (+dP/dt), and decreased QT and PR intervals and maximum left ventricular systolic and end diastolic pressures with measures returning to control levels within 24 hr.

Preclinical studies of PF-04849285, an interferon-α8 fusion protein for the treatment of HCV.

BACKGROUND: This study presents preclinical data of a novel interferon (IFN)-α8 fusion protein, PF-04849285, and compares it with IFN-α2 and pegylated IFN-α2; the latter being the current standard of care for HCV. METHODS: The antiviral properties were evaluated in vitro using the HCV replication assay (replicon) and the general encephalomyocarditis virus assay. The binding affinity to both IFNR-subunits was assessed using surface plasmon resonance. Ex vivo experiments using cynomolgus monkey and human blood were used for the evaluation of induction of IFN-inducible biomarkers (interferon inducible protein 10 [IP-10], 2'-5'-oligoadenylate synthetase [OAS2] and interleukin-6 [IL-6]). The molecule was tested intravenously and subcutaneously in cynomolgus monkey in a single dose study for two weeks at 0.01, 1, 5 and 20 mg/kg. Each route and dose combination was given to a single male animal, blood samples were collected for evaluation of biomarkers and pharmacokinetics. The compound was also tested in cynomolgus monkey in a multiple dose study for four weeks, with a twice-a-week dosing prior to a three-week wash-out period for toxicokinetics, pharmacokinetics, and biomarker evaluation at 20, 50 or 100 mg/kg subcutaneously and 20 mg/kg intravenously. RESULTS: The molecule is 10× more potent than the pegylated IFN-α2a, with potency similar to the unmodified IFN-α2a. No unanticipated findings were observed in cynomolgus monkey when dosed up to 20 mg/kg, >10,000-fold margin over the anticipated efficacious human dose. CONCLUSIONS: The biomarker and toxicological findings were consistent with a potent IFN molecule. The potency and pharmacokinetic properties of the molecule are consistent with dosing at least every two weeks with the potential for monthly dosing' and not 'at least twice daily' as presented in the original [corrected].

Discovery of two clinical histamine H(3) receptor antagonists: trans-N-ethyl-3-fluoro-3-[3-fluoro-4-(pyrrolidinylmethyl)phenyl]cyclobutanecarboxamide (PF-03654746) and trans-3-fluoro-3-[3-fluoro-4-(pyrrolidin-1-ylmethyl)phenyl]-N-(2-methylpropyl)cyclobutanecarboxamide (PF-03654764).

The discovery of two histamine H(3) antagonist clinical candidates is disclosed. The pathway to identification of the two clinical candidates, 6 (PF-03654746) and 7 (PF-03654764) required five hypothesis driven design cycles. The key to success in identifying these clinical candidates was the development of a compound design strategy that leveraged medicinal chemistry knowledge and traditional assays in conjunction with computational and in vitro safety tools. Overall, clinical compounds 6 and 7 exceeded conservative safety margins and possessed optimal pharmacological and pharmacokinetic profiles, thus achieving our initial goal of identifying compounds with fully aligned oral drug attributes, "best-in-class" molecules.