Assessment of the Carcinogenic Potential of Pretomanid in Transgenic Tg.rasH2 Mice.

Pretomanid is a nitroimidazooxazine antimycobacterial drug that was approved as part of a three-drug oral regimen, consisting of bedaquiline, pretomanid, and linezolid, for 6-months treatment of adults with pulmonary extensively drug-resistant tuberculosis or with complicated forms of multidrug-resistant tuberculosis by the food and drug administration in the United States and regulatory bodies in over 10 other countries. Nitroaromatic compounds as a class carry a risk of genotoxicity and potential carcinogenicity based on reactive metabolite formation. A battery of good laboratory practice genotoxicity studies on pretomanid indicated that the compound was not genotoxic, however its hydroxy imidazole metabolite (M50) was genotoxic in the Ames assay. To assess the in vivo carcinogenic potential of pretomanid, hemizygous Tg.rasH2 mice were administered pretomanid once daily by oral gavage for 26 weeks. Male mice were given pretomanid in vehicle at doses of 0, 5, 15 and 40 mg/kg/day and female mice were given pretomanid in vehicle at doses of 0, 10, 30 and 80 mg/kg/day. Positive control mice of both sexes received intraperitoneal injections of urethane at 1000 mg/kg on Days 1, 3 and 5. There were no pretomanid-related early deaths, tumors, non-neoplastic microscopic findings, or gross necropsy findings at any dose level. The positive control gave the anticipated response of lung tumors. Oral administration of pretomanid to mice produced plasma exposure to the parent compound (high dose AUC of pretomanid 3 times the clinical AUC at the maximum recommended human dose) and exposure to the M50 metabolite (less than 10% of pretomanid) at all dose levels in both sexes. These data show that pretomanid was not carcinogenic in a transgenic mouse model at systemic exposures greater than human therapeutic exposures.

Preclinical strategy to reduce clinical hepatotoxicity using in vitro bioactivation data for >200 compounds.

Drug-induced liver injury is the most common cause of market withdrawal of pharmaceuticals, and thus, there is considerable need for better prediction models for DILI early in drug discovery. We present a study involving 223 marketed drugs (51% associated with clinical hepatotoxicity; 49% non-hepatotoxic) to assess the concordance of in vitro bioactivation data with clinical hepatotoxicity and have used these data to develop a decision tree to help reduce late-stage candidate attrition. Data to assess P450 metabolism-dependent inhibition (MDI) for all common drug-metabolizing P450 enzymes were generated for 179 of these compounds, GSH adduct data generated for 190 compounds, covalent binding data obtained for 53 compounds, and clinical dose data obtained for all compounds. Individual data for all 223 compounds are presented here and interrogated to determine what level of an alert to consider termination of a compound. The analysis showed that 76% of drugs with a daily dose of <100 mg were non-hepatotoxic (p < 0.0001). Drugs with a daily dose of ≥100 mg or with GSH adduct formation, marked P450 MDI, or covalent binding ≥200 pmol eq/mg protein tended to be hepatotoxic (∼ 65% in each case). Combining dose with each bioactivation assay increased this association significantly (80-100%, p < 0.0001). These analyses were then used to develop the decision tree and the tree tested using 196 of the compounds with sufficient data (49% hepatotoxic; 51% non-hepatotoxic). The results of these outcome analyses demonstrated the utility of the tree in selectively terminating hepatotoxic compounds early; 45% of the hepatotoxic compounds evaluated using the tree were recommended for termination before candidate selection, whereas only 10% of the non-hepatotoxic compounds were recommended for termination. An independent set of 10 GSK compounds with known clinical hepatotoxicity status were also assessed using the tree, with similar results.

Toxicity and toxicokinetic assessment of an anti-tubercular drug pretomanid in cynomolgus monkeys.

Pretomanid is a nitroimidazooxazine antimycobacterial drug that was approved in more than 10 countries as part of a three-drug, all oral regimen, consisting of bedaquiline, pretomanid, and linezolid (BPaL) for 6-months treatment of adults with pulmonary extensively drug-resistant tuberculosis (XDR-TB) or with complicated forms of multidrug-resistant tuberculosis (MDR-TB). The toxicological profile of pretomanid was thoroughly evaluated in repeat-dose oral toxicity studies up to 39 weeks long in cynomolgus monkeys. Exposures up to 10-fold higher than in humans at the approved pretomanid dose (200 mg) were achieved in acute studies allowing for characterization of dose-limiting toxicity. Target organs and processes identified in acute and chronic toxicity studies included QT prolongation, nervous system effects, and liver effects (minimal hepatocellular hypertrophy without elevations in liver enzymes). In a 13-week study, no cataracts were present at the end of dosing, but 2 of 12 monkeys had cataracts at the end of a 13-week recovery period. No cataracts related to pretomanid administration were observed in subsequent 13-week or 39-week studies. No male reproductive toxicity was observed in these studies. No-observed-adverse-effect levels (NOAELs) were identified in all studies. Exposures at the NOAELs equaled, or exceeded, human exposure at the approved pretomanid dose with the exception of female monkeys in a 39-week chronic toxicity study. These data support the use of pretomanid as part of the 6-month BPaL regimen for treating XDR-TB and MDR-TB.

Biological interactions between nanomaterials and placental development and function following oral exposure.

We summarize the literature involving the deposition of nanomaterials within the placenta following oral exposure and the biological interactions between nanomaterials and placental development and function. The review focuses on the oral exposure of metal and metal oxide engineered nanomaterials (ENMs), carbon-based ENMs, and nanoplastics in animal models, with a minor discussion of intravenous injections. Although the literature suggests that the placenta is an efficient barrier in preventing nanomaterials from reaching the fetus, nanomaterials that accumulate in the placenta may interfere with its development and function. Furthermore, some studies have demonstrated a decrease in placental weight and association with adverse fetal health outcomes following oral exposure to nanomaterials. Since nanomaterials are increasingly used in food, food packaging, and have been discovered in drinking water, the risk for adverse impacts on placental development and functions, with secondary effects on embryo-fetal development, following unintentional maternal ingestion of nanomaterials requires further investigation.

Lymphocyte loss and immunosuppression following acetaminophen-induced hepatotoxicity in mice as a potential mechanism of tolerance.

Current evidence suggests that drug-induced liver disease can be caused by an allergic response (drug-induced allergic hepatitis, DIAH) induced by hepatic drug-protein adducts. The relatively low incidence of these reactions has led us to hypothesize that tolerogenic mechanisms prevent DIAH from occurring in most people. Here, we present evidence for the existence of one of these regulatory pathways. Following a hepatotoxic dose of acetaminophen in C57Bl/6 mice, lymphocyte loss that appeared to be due at least in part to apoptosis was noted in the spleen, thymus, and draining lymph nodes of the liver. There was no observable lymphocyte loss in the absence of hepatotoxicity. Acetaminophen-induced liver injury (AILI) also led to a functional suppression of the immune system as determined by the inhibition of a delayed-type hypersensitivity response to dinitrochlorobenzene. Further studies with adrenalectomized mice suggested a role for corticosterone in the depletion of lymphocytes following APAP-induced liver injury. In conclusion, these findings suggest that lymphocyte loss and immunosuppression following AILI may prevent subsequent occurrences of allergic hepatitis and possibly other forms of APAP-induced allergies induced by hepatic drug-protein adducts. Similar regulatory pathways may inhibit other hepatotoxic drugs from causing allergic reactions.