Preclinical safety, toxicokinetics and metabolism of BIIB131, a novel prothrombolytic agent for acute stroke

BIIB131, a small molecule, is currently in Phase 2 for the treatment of acute ischemic stroke. Safety and metabolism of BIIB131 were evaluated following intravenous administration to rats and monkeys. Exposure increased dose-proportionally in rats up to 60 mg/kg and more than dose-proportionally in monkeys at greater than 10 mg/kg accompanied by prolonged half-life and safety findings. The BIIB131 was poorly metabolized in microsomes with no inhibition of CYPs. BIIB131-glucuronide, formed by UGT1A1, accounted for 21.5% metabolism in human hepatocytes and 28-40% in rat bile. In rats, excretion was primarily via the bile. BIIB131 inhibited the hERG and Nav1.5 cardiac channels by 39% but showed no effect on cardiovascular parameters in monkeys. Toxicology findings were limited to reversable hematuria, changes in urinary parameters and local effects. A MTD of 30 mg/kg was established in monkeys, the most sensitive species, at total plasma Cmax and AUC of 6- and 14-fold, respectively, greater than the NOAEL. The Phase 1 study started with intravenous 0.05 mg/kg and ascended to 6.0 mg/kg which corresponded to safety margins of 147- to 0.9-fold (for Cmax) within the linear drug exposure. Thus, the preclinical profile of BIIB131 has been appropriately characterized and supports its further clinical development.

Morphogenetic events in mixed cultures of rat hepatocytes and nonparenchymal cells maintained in biological matrices in the presence of hepatocyte growth factor and epidermal growth factor

Hepatocytes were grown in chemically defined hepatocyte growth medium (HGM) containing hepatocyte growth factor (HGF) and epidermal growth factor (EGF) on collagen-coated polystyrene beads in roller bottle cultures, forming clusters of beads, and proliferating hepatocytes and nonparenchymal cells, including fenestrated endothelium-forming vascular structures. Desmin-positive cells surrounded hepatocytes. Collagen types I and III were deposited in a diffuse manner whereas collagen type IV surrounded the clusters of the epithelial cells, forming a basement membrane. When the mixed cell clusters were implanted in Matrigel (Collaborative Research, Bedford, MA), hepatocytes grew in three dimensions, forming plates and ducts. Many single, long plates of hepatocytes were seen, suggesting progressive linear assembly guided by hepatocyte specific structural parameters. HGF, EGF, and transforming growth factor-alpha (TGF-alpha) enhance these phenomena. HGF plus EGF elicited maximal response. TGF-beta1 suppressed formation of the ducts and plates. Within three months in Matrigel, the cultures established monolayers composed of plates, ducts, and a well-delineated canalicular network. The mixed cultures expressed albumin, A1AT, AFP, transferrin, and CYPIIB1. Following implantation of the cell clusters in Matrigel, there was decreased expression of c-met, urokinase, urokinase receptor, and TGF-beta1. Electron microscopy showed differentiated hepatocytes with nearly normal ultrastructure. The proliferating cell nuclear antigen (PCNA) labeling index was high (more than 80%) whereas the Bromo-deoxyaridine labeling index of ongoing DNA synthesis varied from 10% to 15%. These results show that the mixed cultures of proliferating hepatocytes and nonparenchymal cells can reproduce the hallmark structures of hepatic histological architecture while maintaining differentiation and the capacity to proliferate. (HEPATOLOGY 1999;29:90-100.)

Alcohol-mediated increases in acetaminophen hepatotoxicity: role of CYP2E and CYP3A

This commentary focuses on the roles of CYP3A and CYP2E in alcohol-mediated increases in acetaminophen hepatotoxicity. CYP2E has been considered to be the main form of P450 responsible for such toxicity in animals and humans. However, CYP3A, which is also induced by alcohol, has been shown to have a greater affinity for acetaminophen than CYP2E. Previous experiments implicating CYP2E in alcohol-mediated increases in acetaminophen hepatotoxicity have used inhibitors of this form of P450 that are now proving to be non-specific. Triacetyloleandomycin (TAO) is a potent inhibitor of CYP3A that maintains specificity in vitro over a large concentration range. In rats treated with ethanol or the combination of ethanol and isopentanol, the major higher chain alcohol in alcoholic beverages, TAO protects animals from increases in acetaminophen hepatotoxicity, suggesting a major role of CYP3A. CYP2E may not have a major role due to the rapid loss of induced levels in the absence of continued exposure to ethanol. Knockout mice, which are being used to define the role of particular proteins in biological responses, have been developed for CYP2E1 and CYP1A2 but not CYP3A. Cyp2e1(-/-) and Cyp1a2(-/-) mice are more resistant to acetaminophen hepatotoxicity than wild-type strains, even though the amounts of the other forms of P450s are unaltered in the liver. These findings suggest that the relative amounts of P450s and not just kinetic characteristics determine their role in acetaminophen hepatotoxicity. The clinical implications of the findings that CYP3A can have a major role in acetaminophen-mediated hepatotoxicity are discussed.

Synergistic increases in rat hepatic cytochrome P450s by ethanol and isopentanol

The purpose of this study was to determine if isopentanol alone or in combination with ethanol increased CYP2B1/2, CYP2E or CYP3A in the livers of rats. Increasing doses of isopentanol (0.5, 1, 2 or 3%) were administered in combination with 5.6% ethanol in the Lieber-DeCarli liquid diet for 7 days. Doses of 0.5 or 3% isopentanol were also administered alone. Isopentanol alone caused small increases in CYP2B1/2 and CYP3A. However, when isopentanol (2 or 3%) was combined with ethanol a synergistic increase in P4502B1/2 was observed. The combined alcohol treatment also resulted in a greater increase in immunoreactive CYP3A than either alcohol alone. Ethanol alone increased CYP2E 5-fold. Inclusion of isopentanol with ethanol resulted in either small or no additional increases in CYP2E. These results confirm our previous findings in cultured hepatocytes that when isopentanol is combined with ethanol, there is a synergistic increase in CYP2B1/2. Increases in CYP2B1/2, CYP2E and CYP3A protein moieties by ethanol, and by ethanol in combination with isopentanol, were associated with increases in their mRNAs. Blood isopentanol levels were 10-fold greater in rats administered 3% isopentanol in combination with ethanol compared to rats administered 3% isopentanol alone. From these results we suggest that isopentanol, a higher chain alcohol in alcoholic beverages, can contribute to increases in hepatic cytochrome P450 observed following consumption of alcoholic beverages.