Use of the dTAG system in vivo to degrade CDK2 and CDK5 in adult mice and explore potential safety liabilities.

The degradation tag (dTAG) system for target protein degradation can remove proteins from biological systems without the drawbacks of some genetic methods, such as slow kinetics, lack of reversibility, low specificity, and the inability to titrate dosage. These drawbacks can make it difficult to compare toxicity resulting from genetic and pharmacological interventions, especially in vivo. Because the dTAG system has not been studied extensively in vivo, we explored the use of this system to study the physiological sequalae resulting from CDK2 or CDK5 degradation in adult mice.

Comprehensive Nonclinical Safety Assessment of Nirmatrelvir Supporting Timely Development of the SARS-COV-2 Antiviral Therapeutic, Paxlovid™.

COVID-19 is a potentially fatal infection caused by the SARS-CoV-2 virus. The SARS-CoV-2 3CL protease (Mpro) is a viral enzyme essential for replication and is the target for nirmatrelvir. Paxlovid (nirmatrelvir co-administered with the pharmacokinetic enhancer ritonavir) showed efficacy in COVID-19 patients at high risk of progressing to hospitalization and/or death.

Gastric Neuroendocrine Tumors With Parietal Cell Atrophy in a Long-term Carcinogenicity Study in Rats.

Malignant neuroendocrine tumors were diagnosed in the stomach of two out of sixty female Sprague-Dawley rats treated for 89 weeks with a high dose of a novel, small molecule, cannabinoid-1 antagonist. The tumors were associated with parietal cell atrophy accompanied by foveolar hyperplasia of the glandular stomach mucosa. Parietal cell atrophy/foveolar hyperplasia was considered test article related at the high dose, given the higher incidence and severity relative to untreated controls, although the precise mechanism of the parietal cell atrophy was undetermined.

Preclinical characterization of an intravenous coronavirus 3CL protease inhibitor for the potential treatment of COVID19.

COVID-19 caused by the SARS-CoV-2 virus has become a global pandemic. 3CL protease is a virally encoded protein that is essential across a broad spectrum of coronaviruses with no close human analogs. PF-00835231, a 3CL protease inhibitor, has exhibited potent in vitro antiviral activity against SARS-CoV-2 as a single agent.

Discovery of a Novel Inhibitor of Coronavirus 3CL Protease for the Potential Treatment of COVID-19.

COVID-19 caused by the SARS-CoV-2 virus has become a global pandemic. 3CL protease is a virally encoded protein that is essential across a broad spectrum of coronaviruses with no close human analogs. The designed phosphate prodrug PF-07304814 is metabolized to PF-00835321 which is a potent inhibitor of the coronavirus family 3CL pro, with selectivity over human host protease targets.

De novo lipogenesis is essential for platelet production in humans.

Acetyl-CoA carboxylase (ACC) catalyses the first step of de novo lipogenesis (DNL). Pharmacologic inhibition of ACC has been of interest for therapeutic intervention in a wide range of diseases. We demonstrate here that ACC and DNL are essential for platelet production in humans and monkeys, but in not rodents or dogs.

Optimizing the Benefit/Risk of Acetyl-CoA Carboxylase Inhibitors through Liver Targeting.

Preclinical and clinical data suggest that acetyl-CoA carboxylase (ACC) inhibitors have the potential to rebalance disordered lipid metabolism, leading to improvements in nonalcoholic steatohepatitis (NASH). Consistent with these observations, first-in-human clinical trials with our ACC inhibitor PF-05175157 led to robust reduction of de novo lipogenesis (DNL), albeit with concomitant reductions in platelet count, which were attributed to the inhibition of fatty acid synthesis within bone marrow. Herein, we describe the design, synthesis, and evaluation of carboxylic acid-based ACC inhibitors with organic anion transporting polypeptide (OATP) substrate properties, which facilitated selective distribution of the compounds at the therapeutic site of action (liver) relative to the periphery.

Testicular microlithiasis in a clinically healthy cynomolgus monkey ().

The present article describes an occurrence of testicular microlithiasis in a cynomolgus monkey from a routine regulatory toxicology study. The monkey was from a negative control group. Microscopically, the lesion was characterized by multiple extracellular mineralized calculi within seminiferous tubular epithelia of both testes without any tissue reaction or abnormal condition such as cryptorchidism, testicular neoplasm, or hypogonadism.

Activation of Liver AMPK with PF-06409577 Corrects NAFLD and Lowers Cholesterol in Rodent and Primate Preclinical Models.

Dysregulation of hepatic lipid and cholesterol metabolism is a significant contributor to cardiometabolic health, resulting in excessive liver lipid accumulation and ultimately non-alcoholic steatohepatitis (NASH). Therapeutic activators of the AMP-Activated Protein Kinase (AMPK) have been proposed as a treatment for metabolic diseases; we show that the AMPK β1-biased activator PF-06409577 is capable of lowering hepatic and systemic lipid and cholesterol levels in both rodent and monkey preclinical models. PF-06409577 is able to inhibit de novo lipid and cholesterol synthesis pathways, and causes a reduction in hepatic lipids and mRNA expression of markers of hepatic fibrosis.

Characterization of ectopic myelinated nerve fibers in the retina of a cynomolgus monkey (Macaca fascicularis).

We report histopathology of retinal myelination discovered in a cynomolgus monkey. It consisted of a uniform population of spindle cells arranged in fascicles within the retina at the optic disk. The present case is remarkable in that there is a paucity of reports describing myelinated retinal nerve fibers in monkeys.

The Application of Paraphenylenediamine Staining for Assessment of Phospholipidosis.

Drug-induced phospholipidosis is characterized by intracellular accumulation of phospholipids with lamellar bodies in cells exposed to xenobiotics. Demonstration of the lamellar bodies by transmission electron microscopy (TEM) is the hallmark for a definitive diagnosis of phospholipidosis. However, the preparation of tissue samples for TEM and their ultrastructural evaluation are technically challenging and time consuming.

Using Histopathologic Evidence to Differentiate Reproductive Senescence from Xenobiotic Effects in Middle-aged Female Sprague-Dawley Rats.

The female reproductive cycle is orchestrated by cyclical and coordinated hormonal changes under the direction of the hypothalamic-pituitary-gonadal (HPG) axis. Any disruption of the HPG axis may lead to functional and structural alterations in the female reproductive system. Test article-related disturbances in the estrous cycle can be recognized in nonclinical toxicity studies by staging the cycle based on microscopic evaluation of female reproductive organs.

Polycystic kidney disease in Sprague-Dawley rats.

Polycystic kidney disease (PKD) is a cystic genetic disorder of the kidneys which is typically associated with cystic bile duct dilatation in the liver in humans, and domestic and laboratory animals. In humans, there are two types of PKD, autosomal dominant polycystic kidney disease (ADPKD) and autosomal recessive polycystic kidney disease (ARPKD). ADPKD is caused by mutations in PKD1 or PKD2 gene while ARPKD is caused by mutation or loss of the PKHD1 (polycystic kidney and hepatic disease 1) gene.

Spontaneous unilateral renal dysplasia in a clinically healthy cynomolgus monkey (Macaca fascicularis).

Renal dysplasia is a congenital renal malformation characterized by disruption of normal renal development with asynchronous differentiation of nephrons, collecting ducts, and parenchyma and abnormal patterning of cortical and medullary tissues. The present article describes unilateral renal dysplasia discovered in a cynomolgus monkey from a routine toxicology study. The affected kidney was small and characterized by extensive interstitial fibrosis with the formation of fibromuscular collars around glomeruli and tubules, immature nephrons, and persistent mesenchyme encompassing few collecting ducts.

The relationship of glucokinase activator-induced hypoglycemia with arteriopathy, neuronal necrosis, and peripheral neuropathy in nonclinical studies.

Glucokinase activators (GKAs) are being developed for the treatment of type 2 diabetes. The toxicity of 4 GKAs (PF-04279405, PF-04651887, piragliatin, and PF-04937319) was assessed in mice, rats, dogs, and/or monkeys. GKAs were administered for 2 to 8 weeks.

Comparative nonclinical assessments of the proposed biosimilar PF-05280586 and rituximab (MabThera®).

Comparative nonclinical studies were conducted with the proposed biosimilar PF-05280586 and rituximab-EU (MabThera®). In side-by-side analyses, peptide maps and complement-dependent cytotoxicity assay results were similar. Sexually-mature cynomolgus monkeys were administered PF-05280586 or rituximab-EU as a single dose of 0, 2, 10, or 20 mg/kg on day 1 and observed for 92 days (single-dose study) or as 5 weekly injections of 0 or 20 mg/kg and necropsied on day 30, the day after the 5th dose, or on day 121 (repeat-dose study).

An atypical case of islet cell hyperplasia in a Wistar rat.

The present article describes an unusual proliferative islet finding observed incidentally in a young male Wistar rat in a 2-week toxicity study. Histologically, the islet lesion was characterized by diffuse enlargement of the islets, which consisted of peripheral proliferation of non-insulin-containing islet cells surrounding normal-appearing insulin-containing cells in the center. To the authors' knowledge, this is the first report of spontaneous proliferative islet lesion composed of non-insulin-containing cells in young rats.

Renal dysplasia in Beagle dogs: four cases.

Anomalies of renal development comprise abnormalities in the amount of renal tissue (agenesis and hypoplasia); anomalies of renal position, form, and orientation; and renal dysplasia. There are previous reports of canine renal dysplasia in different breeds but none in the Beagle breed. This is the first report of renal dysplasia in this breed of dog.

Correlation among clinicopathological parameters of myocardial damage in rats treated with isoproterenol.

The correlation among clinicopathological parameters of myocardial damage was investigated in rats administered a single subcutaneous dose of isoproterenol at 0 (saline), 0.04, 0.4 and 4 mg/kg.

Lack of elevated liver carcinogenicity of aminophenylnorharman in p53-deficient mice.

The hepatocarcinogenic potential of 9-(4'-aminophenyl)-9H-pyrido[3,4-b]indole (aminophenylnorharman, APNH) was investigated using male and female p53 deficient mice. Incidence of oval cell hyperplasia was 2/14 (14.3%), 14/23 (60.

High susceptibility of nullizygous p53 knockout mice to colorectal tumor induction by 1,2-dimethylhydrazine.

Purpose: The susceptibility of male p53 nullizygote (-/-), heterozygote (+/-), and wild-type (+/+) mice to 1,2-dimethylhydrazine (DMH) induction of colon carcinogenesis was investigated.

Methods: In a preliminary short-term experiment, male mice of three genotypes were given s.c.

Elevated susceptibility of the p53 knockout mouse esophagus to methyl-N-amylnitrosamine carcinogenesis.

Mutations of the p53 tumor suppressor gene constitute one of the most frequent molecular changes in a wide variety of human cancers, including those in the esophagus. Mice deficient in p53 have recently attracted attention for their potential to identify chemical genotoxins. In this study we investigated the susceptibility of p53 nullizygous (-/-), heterozygous (+/-) and wild-type (+/+) mice to methyl-N-amylnitrosamine (MNAN), which specifically induces esophageal tumors in mice and rats.

Summation of initiation activities in the liver after partial hepatectomy.

Summation of initiation activities of different carcinogens in the liver after partial hepatectomy (PH) was investigated with reference to induction of glutathione S-transferase placental form (GST-P) positive foci. Firstly, effects of repeated administration of 1,2-dimethylhydradine (DMH) were compared with the results of a single administration of the same total dose (Expt. I).