Immunologic effects of chronic administration of tofacitinib, a Janus kinase inhibitor, in cynomolgus monkeys and rats - Comparison of juvenile and adult responses.

Tofacitinib, an oral Janus kinase (JAK) inhibitor for treatment of rheumatoid arthritis, targets JAK1, JAK3, and to a lesser extent JAK2 and TYK2. JAK1/3 inhibition impairs gamma common chain cytokine receptor signaling, important in lymphocyte development, homeostasis and function. Adult and juvenile cynomolgus monkey and rat studies were conducted and the impact of tofacitinib on immune parameters (lymphoid tissues and lymphocyte subsets) and function (T-dependent antibody response (TDAR), mitogen-induced T cell proliferation) assessed. Tofacitinib administration decreased circulating T cells and NK cells in juvenile and adult animals of both species. B cell decreases were observed only in rats. These changes and decreased lymphoid tissue cellularity are consistent with the expected pharmacology of tofacitinib. No differences were observed between juvenile and adult animals, either in terms of doses at which effects were observed or differential effects on immune endpoints. Lymphomas were observed in three adult monkeys. Tofacitinib impaired the primary TDAR in juvenile monkeys, although a recall response was generated. Complete or partial reversal of the effects on the immune system was observed.

Renal and Hematologic Comparative Effects of Dissociated Agonist of the Glucocorticoid Receptor and Prednisone in Dogs With and Without Food Restriction.

Glomerulopathy and body weight gain were noted after chronic oral administration of a novel nonsteroidal dissociated agonist of the glucocorticoid receptor compound, fosdagrocorat, to beagle dogs fed an ad libitum diet. To further investigate the role of diet and treatment with either fosdagrocorat or the glucocorticoid comparator, prednisone, on renal safety, a 13-week investigative study was conducted in beagle dogs. Renal histopathology, clinical chemistry, urinalysis, glomerular filtration rate (GFR), body weight, heart rate, blood pressure (BP), and hematology were investigated in restricted- and ad libitum-fed dogs administered prednisone (2.2 mg/kg/d), fosdagrocorat (5 mg/kg/d), or vehicle for 13 weeks. Glomerulopathy was primarily observed in fosdagrocorat- and prednisone-treated ad libitum but not in feed-restricted or ad libitum vehicle-treated dogs. Kidneys in dogs from the prednisone-treated ad libitum had the greatest incidence and severity of tubular degenerative changes. Increased urine volume and decreased urine-specific gravity were present in prednisone- and fosdagrocorat-treated dogs, regardless of diet. These changes were not associated with consistent changes in GFR. Fosdagrocorat or prednisone treatment ad libitum dogs had the greatest increase in body weight gain. Sporadic changes in systolic and diastolic BP were noted in fosdagrocorat- and prednisone-treated groups. Significant reductions in serum cortisol and absolute eosinophils were noted in both ad libitum- and restriction-fed prednisone- and fosdagrocorat-treated dogs. In conclusion, prednisone-treated dogs fed ad libitum had greater glucocorticoid-induced renal effects than those dosed with fosdagrocorat.

Cellular and functional actions of tofacitinib related to the pathophysiology of hibernoma development.

Tofacitinib is an oral JAK inhibitor for the treatment of rheumatoid arthritis. In the 2-year carcinogenicity study with tofacitinib, increased incidence of hibernoma (a neoplasm of brown adipose tissue [BAT]) was noted in female rats at ≥30 mg/kg/day (≥41x human exposure multiples). Thus, signaling pathways within BAT were investigated by measuring BAT: weight, cell proliferation biomarkers, content of basal and prolactin-induced phosphorylated Signal Transducer and Activator of Transcription (STAT), and uncoupling protein 1 (UCP-1). The relationship between cardiovascular hemodynamics and plasma norepinephrine (NE) levels was also investigated. Tofacitinib administered to female rats at doses of 10, 30, or 75 mg/kg/day for 14 days increased BAT weight at 75 mg/kg/day and cell proliferation at ≥30 mg/kg/day. JAK inhibition, observed as lower pSTAT3 and pSTAT5 in BAT, was noted at ≥10 mg/kg/day, while lower activity of BAT was observed as lower UCP-1 protein at ≥30 mg/kg/day. In cultured brown adipocytes, prolactin-induced increase in pSTAT5 and pSTAT3 were inhibited by tofacitinib in a concentration-dependent manner. Tofacitinib lowered blood pressure, increased heart rate, and resulted in dose-dependent increases in circulating NE. Thus, JAK/STAT inhibition in BAT and sympathetic stimulation are two factors which might contribute to the genesis of hibernomas by tofacitinib in rats.

Mechanistic investigations of test article-induced pancreatic toxicity at the endocrine-exocrine interface in the rat.

Pancreatic toxicity commonly affects the endocrine or exocrine pancreas. However, it can also occur at the endocrine-exocrine interface (EEI), where the capillary network of the islet merges with the capillaries of the surrounding acinar tissue, that is, the insulo-acinar portal system. The goal of this article is to describe a novel, test article-induced pancreatic toxicity that originated at the EEI and to summarize investigations into the mechanistic basis of the injury. This injury was initially characterized by light microscopy in 7/14 day-toxicity studies in Sprague-Dawley (Crl: CD®[SD]) rats with undisclosed test articles. Microvascular injury at the interface resulted in peri-islet serum exudation, fibrin deposition, hemorrhage, inflammation, and secondary degeneration/necrosis of surrounding exocrine tissue. More chronic injury presented as islet fibrosis and lobular atrophy. Direct cytotoxicity affecting the capillary endothelium at the EEI was confirmed ultrastructurally on day 4. Endothelial microparticle and blood flow studies further confirmed endothelial involvement. Similar lesions occurred less frequently in 2 other rat strains and not in the mouse, dog, or cynomolgus macaque. In summary, in vivo and investigative study data confirmed primary endothelial cytotoxicity in the pathogenesis of this lesion and suggested that the lesion may be rat/rat strain-specific and of uncertain relevance for human safety risk assessment.

Comparative pathophysiology, toxicology, and human cancer risk assessment of pharmaceutical-induced hibernoma.

In humans, hibernoma is a very rare, benign neoplasm of brown adipose tissue (BAT) that typically occurs at subcutaneous locations and is successfully treated by surgical excision. No single cause has been accepted to explain these very rare human tumors. In contrast, spontaneous hibernoma in rats is rare, often malignant, usually occurs in the thoracic or abdominal cavity, and metastases are common. In recent years, there has been an increased incidence of spontaneous hibernomas in rat carcinogenicity studies, but overall the occurrence remains relatively low and highly variable across studies. There have only been four reported examples of pharmaceutical-induced hibernoma in rat carcinogenicity studies. These include phentolamine, an alpha-adrenergic antagonist; varenicline, a nicotine partial agonist; tofacitinib, a Janus kinase (JAK) inhibitor; and hydromorphone, an opiod analgesic. Potential non-genotoxic mechanisms that may contribute to the pathogenesis of BAT activation/proliferation and/or subsequent hibernoma development in rats include: (1) physiological stimuli, (2) sympathetic stimulation, (3) peroxisome proliferator-activated receptor (PPAR) agonism, and/or (4) interference or inhibition of JAK/Signal Transducer and Activator of Transcription (JAK/STAT) signaling. The evaluation of an apparent increase of hibernoma in rats from 2-year carcinogenicity studies of novel pharmaceutical therapeutics and its relevance to human safety risk assessment is complex. One should consider: the genotoxicity of the test article, dose/exposure and safety margins, and pathophysiologic and morphologic differences and similarities of hibernoma between rats and humans. Hibernomas observed to date in carcinogenicity studies of pharmaceutical agents do not appear to be relevant for human risk at therapeutic dosages.

Evaluation of the effects of subchronic oral administration of n-butyl maleate in Sprague-Dawley rats.

n-Butyl maleate, also referred to as monobutyl maleate, is an ester of maleic acid, which is used as a counterion in the pharmaceutical industry. While substantial published data exist on short-term treatment, maleic acid-induced renal toxicity in the rat, no toxicity data are available on the monobutyl ester. This study evaluated the oral subchronic nephrotoxicity potential of n-butyl maleate administered to Sprague-Dawley rats (10/males and females/group) at doses of 0 (vehicle control), 10, 30, or 60 mg/kg/d for 2 wk. Statistically significant elevations in organ weights were noted in males at 60 mg/kg/d and included: (a) increases in absolute heart, kidney, and liver weights; (b) increased liver to body weight ratios; and (c) increased heart, kidney, liver, spleen, and epididymides to brain weight ratios. In females, statistically significant increases in organ weights were limited to increases in adrenal to brain weights at > or = 10 mg/kg/d, kidney to brain weights at > or = 30 mg/kg/d, and kidney to body weight and liver to brain weight ratios at 60 mg/kg/d. There were no macroscopic or microscopic pathology changes observed in any of the tissues examined. Importantly, light microscopic examination of the kidney was unremarkable at the end of the 2-wk dosing period with n-butyl maleate. Although lacking a histopathological correlate, resultant increases in organ weights at 60 mg/kg/d might be considered indicative of an adverse effect. However, renal perturbation induced by n-butyl maleate was mild in comparison to maleic acid-induced renal toxicity, which manifested as impaired tubular resorption and necrosis of the proximal tubules at doses > or = 60 mg/kg/d. The no-observed-adverse-effect level (NOAEL) for the study was 30 mg/kg/d.