Stem cell-derived models to improve mechanistic understanding and prediction of human drug-induced liver injury

Current preclinical drug testing does not predict some forms of adverse drug reactions in humans. Efforts at improving predictability of drug-induced tissue injury in humans include using stem cell technology to generate human cells for screening for adverse effects of drugs in humans. The advent of induced pluripotent stem cells means that it may ultimately be possible to develop personalized toxicology to determine interindividual susceptibility to adverse drug reactions. However, the complexity of idiosyncratic drug-induced liver injury means that no current single-cell model, whether of primary liver tissue origin, from liver cell lines, or derived from stem cells, adequately emulates what is believed to occur during human drug-induced liver injury. Nevertheless, a single-cell model of a human hepatocyte which emulates key features of a hepatocyte is likely to be valuable in assessing potential chemical risk; furthermore, understanding how to generate a relevant hepatocyte will also be critical to efforts to build complex multicellular models of the liver. Currently, hepatocyte-like cells differentiated from stem cells still fall short of recapitulating the full mature hepatocellular phenotype. Therefore, we convened a number of experts from the areas of preclinical and clinical hepatotoxicity and safety assessment, from industry, academia, and regulatory bodies, to specifically explore the application of stem cells in hepatotoxicity safety assessment and to make recommendations for the way forward. In this short review, we particularly discuss the importance of benchmarking stem cell-derived hepatocyte-like cells to their terminally differentiated human counterparts using defined phenotyping, to make sure the cells are relevant and comparable between labs, and outline why this process is essential before the cells are introduced into chemical safety assessment. (Hepatology 2017;65:710-721).

Analysis of the interaction of phytoestrogens and synthetic chemicals: an in vitro/in vivo comparison

In the evaluation of chemical mixture toxicity, it is desirable to develop an evaluation paradigm which incorporates some critical attributes of real world exposures, particularly low dose levels, larger numbers of chemicals, and chemicals from synthetic and natural sources. This study evaluated the impact of low level exposure to a mixture of six synthetic chemicals (SC) under conditions of co-exposure to various levels of plant-derived phytoestrogen (PE) compounds. Estrogenic activity was evaluated using an in vitro human estrogen receptor (ER) transcriptional activation assay and an in vivo immature rat uterotrophic assay. Initially, dose-response curves were characterized for each of the six SCs (methoxyclor, o,p-DDT, octylphenol, bisphenol A, beta-hexachlorocyclohexane, 2,3-bis(4-hydroxyphenyl)-propionitrile) in each of the assays. The six SCs were then combined at equipotent ratios and tested at 5-6 dose levels spanning from very low, sub-threshold levels, to a dose in which every chemical in the mixture was at its individual estrogenic response threshold. The SC mixtures also were tested in the absence or presence of 5-6 different levels of PEs, for a total of 36 (in vitro) or 25 (in vivo) treatment groups. Both in vitro and in vivo, low concentrations of the SC mixture failed to increase estrogenic responses relative to those induced by PEs alone. However, significant increases in response occurred when each chemical in the SC mixture was near or above its individual response threshold. In vitro, interactions between high-doses of SCs and PEs were greater than additive, whereas mixtures of SCs in the absence of PEs interacted in a less than additive fashion. In vivo, the SC and PE mixture responses were consistent with additivity. These data illustrate a novel approach for incorporating key attributes of real world exposures in chemical mixture toxicity assessments, and suggest that chemical mixture toxicity is likely to be of concern only when the mixture components are near or above their individual response thresholds. However, these data suggest that extrapolation from in vitro assays to in vivo mixture effects should be approached with caution.

Refinement of a morphological scoring system for postimplantation rabbit conceptuses

BACKGROUND

The rabbit is used extensively in developmental toxicity testing, yet basic information on rabbit embryo development is lacking. The goals of this study were to refine a rabbit embryo morphology scoring system, and use it to evaluate rabbit whole embryo cultures (WEC).

METHODS

A total of 265 conceptuses were harvested between GD 8.0 and 12.0 (coitus = GD 0) at 6-hr intervals and examined in detail. Discreet developmental landmarks were then established for 18 morphological features and assigned scores ranging from 0 up to 6. The scoring system was then validated on a subset of randomly selected in vivo conceptuses, and was used to evaluate conceptuses grown for 12, 24, 36, or 48 hr in WEC beginning from GD 9.0 or 10.0. A few embryos also were examined using microscopic computed tomography (microCT)-based virtual histologytrade mark to assess the utility of this technology.

RESULTS

Morphology scores of in vivo developed conceptuses increased linearly (r2 = 0.98) with advancing gestational age, from means of 0.0 on GD 8.0 to 67.9 on GD 12.0. Application of the scoring system, supplemented with evidence from Virtual histologytrade mark, indicated that the WEC system supported normal morphological development of rabbit conceptuses. However, when explanted at GD 9, the rate of development was about 20% slower than in vivo, whereas the rate of development in WEC from GD 10 was indistinguishable from in vivo.

CONCLUSIONS

This work enhances the evaluation tools available to study mechanisms of normal and abnormal development in this widely used animal testing species.

A multi-institutional study benchmarking the zebrafish developmental assay for prediction of embryotoxic plasma concentrations from rat embryo-fetal development studies

Predicting embryotoxicity of pharmaceutical compounds or industrial chemicals is crucial for public safety. Conventional studies which monitor embryo-fetal development in rats and rabbits are costly and time consuming. Alternative assays which are simpler and less costly are being pursued. The purpose of this research was to assess the capacity for the zebrafish development assay to predict mammalian plasma levels that are embryotoxic. Previously published data on rat plasma levels associated with embryotoxicity were used to guide concentration ranges for each of 25 chemicals dissolved in the media bathing developing zebrafish embryos. Embryotoxic media concentrations were compared to embryotoxic rat plasma concentrations. Assays were conducted in parallel at multiple sites as a consortium effort through the Health and Environmental Sciences Institute (HESI). Considering results from all sites, the zebrafish embryo development assay predicted (within 1-log) the rat maternal exposure levels associated with embryotoxicity 75% of the time.

Species-specificity of ethylene glycol-induced developmental toxicity: toxicokinetic and whole embryo culture studies in the rabbit

High-dose gavage exposure to ethylene glycol (EG) is teratogenic in rats, but not rabbits. To investigate the reason for this species difference, toxicokinetic and whole embryo culture (WEC) studies were conducted in gestation day 9 New Zealand White rabbits, and the data compared to very similar data previously generated in pregnant rats. In the toxicokinetic study, maximal levels of unchanged EG in rabbits were comparable to those reported for rats. However, maximal levels of EG's teratogenic metabolite, glycolic acid (GA), in rabbit maternal blood and embryo were only 46% and 10% of the respective levels in rats. The toxicokinetic profile suggested that the lower GA levels in rabbits were due to a slower rate of maternal metabolism of EG to GA, slow uptake of GA into the yolk sac cavity fluid which surrounds the embryo, and negligible transfer via the visceral yolk sac (VYS) placenta. In the WEC study, exposure of rabbit conceptuses to high concentrations (< or = 12.5 mM) of GA was without effect, which contrasts with reported effects in rat WEC at > or = 3 mM. Overall, these data implicate toxicokinetics as an important factor underlying the species difference, although intrinsic insensitivity of the rabbit embryo might also be involved. Integration of these findings with published human data suggest that the rabbit is the more relevant model for human EG exposure, based on the negligible role of the rabbit VYS in placental transfer (humans lack a VYS) and similar rates of EG metabolism and extraembryonic fluid turnover.

Comparison of rat and rabbit embryo-fetal developmental toxicity data for 379 pharmaceuticals: on the nature and severity of developmental effects

Regulatory non-clinical safety testing of human pharmaceuticals typically requires embryo-fetal developmental toxicity (EFDT) testing in two species (one rodent and one non-rodent). The question has been raised whether under some conditions EFDT testing could be limited to one species, or whether the testing in a second species could be decided on a case-by-case basis. As part of a consortium initiative, we built and queried a database of 379 compounds with EFDT studies (in both rat and rabbit animal models) conducted for marketed and non-marketed pharmaceuticals for their potential for adverse developmental and maternal outcomes, including EFDT incidence and the nature and severity of adverse findings. Manifestation of EFDT in either one or both species was demonstrated for 282 compounds (74%). EFDT was detected in only one species (rat or rabbit) in almost a third (31%, 118 compounds), with 58% (68 compounds) of rat studies and 42% (50 compounds) of rabbit studies identifying an EFDT signal. For 24 compounds (6%), fetal malformations were observed in one species (rat or rabbit) in the absence of any EFDT in the second species. In general, growth retardation, fetal variations, and malformations were more prominent in the rat, whereas embryo-fetal death was observed more often in the rabbit. Discordance across species may be attributed to factors such as maternal toxicity, study design differences, pharmacokinetic differences, and pharmacologic relevance of species. The current analysis suggests that in general both species are equally sensitive on the basis of an overall EFDT LOAEL comparison, but selective EFDT toxicity in one species is not uncommon. Also, there appear to be species differences in the prevalence of various EFDT manifestations (i.e. embryo-fetal death, growth retardation, and dysmorphogenesis) between rat and rabbit, suggesting that the use of both species has a higher probability of detecting developmental toxicants than either one alone.

An in vitro screening paradigm for extracts of whole foods for detection of potential toxicants

The application of organic, conventional and biotechnology techniques can alter the intrinsic levels of natural toxicants in crop foods and methods are needed to screen for unexpected changes in toxicant levels. We evaluated crude, aqueous preparations of 37 foods purchased from a local market in a battery of four in vitro mammalian toxicity screens. The foods were evaluated in one or more of the following tests: (1) cytotoxicity (37 foods) and (2) chromosomal aberration test (nine foods), both in Chinese hamster ovary cells, (3) limb bud micromass assay (nine foods) using 11-day old CD-1 mouse embryos and (4) estrogenicity (MCF-7 cells transfected with estrogen receptor and lucerifase reporter constructs, 12 foods). IC50s for cellular proliferation ranged from < 1% (v/v, garlic) to > 10% (v/v, 18 foods), the maximal concentration tested. Five of nine preparations (soybeans, broccoli, garlic, snow peas and corn) were clastogenic and two (soybeans and snow peas) inhibited chrondrogenesis in the limb bud micromass assay. Five of nine preparations (soybeans, snow peas, cumin, asparagus and bean sprouts) produced significant estrogenic responses. Overall, the 12 foods evaluated in two or more of the tests showed different patterns of response. These preliminary data indicate that screening for potential toxicants is possible with fast, relatively inexpensive in vitro tests. These in vitro tests, while potentially useful to detect unexpected toxicants in plants that may signal the need for further evaluation, are not directly useful to predict human or animal risk from eating these plants.

Significance of 2-methoxypropionic acid formed from beta-propylene glycol monomethyl ether: integration of pharmacokinetic and developmental toxicity assessments in rabbits

Commercial grade propylene glycol monomethyl ether (PGME), which is composed of > 99.5% alpha-isomer and < 0.5% beta-isomer, has been shown in several studies to have a low potential for developmental toxicity. Nonetheless, questions have been raised about potential human developmental toxicity due to beta-PGME, because it can be metabolized to 2-methoxypropionic acid (MPA), a compound bearing structural similarity to the teratogen, methoxyacetic acid (MAA). Accordingly, a series of in vivo developmental toxicity, whole embryo culture, and in vivo pharmacokinetic experiments were conducted in New Zealand White rabbits (highly sensitive to these compounds) to better understand the developmental toxicity potential of MPA and the kinetics of its formation from beta-PGME. For the in vivo developmental toxicity studies, groups of 20 inseminated rabbits were gavaged with 0, 10, 26, or 78 mg/kg/day of MPA on gestation day (GD) 7-19, followed by fetal evaluation on GD 28. Results with MPA were compared with those of rabbits similarly dosed with 0, 2.5, 7.5, or 15 mg/kg/day of MAA. Developmental toxicity no-observable-effect levels (NOEL) were approximately 10-fold higher for MPA (26 mg/kg/day) than for MAA (2.5 mg/kg/day). Also, the severity of effects caused by MPA was less than that of MAA, and unlike MAA, MPA was not selectively toxic to the fetus. This differential toxicity was also seen in whole embryo cultures of GD 9 rabbit embryos, in which there were no adverse effects of MPA (1.0, 5.0 mM) or its parent compound, beta-PGME (0.5, 2.0 mM), but severe dysmorphogenesis in 100% of embryos cultured in 5.0 mM MAA. The pharmacokinetics study showed rapid and complete conversion of beta-PGME to MPA, with a relatively long elimination half-life (33-44 h) for MPA. However, peak and AUC concentrations of MPA in blood associated with the MPA LOEL dose of 78 mg/kg/day were 1.3 mM and 52.9 mM-h/l, respectively, suggesting a relatively high threshold based on internal dosimetry. Taken together, these data indicate a negligible risk of developmental toxicity due to MPA formation from the small amounts of beta-isomer present in commercial PGME.

Birth Control in Clinical Trials: Industry Survey of Current Use Practices, Governance, and Monitoring

The Health and Environmental Sciences Institute (HESI) Developmental and Reproductive Toxicology Technical Committee sponsored a pharmaceutical industry survey on current industry practices for contraception use during clinical trials. The objectives of the survey were to improve our understanding of the current industry practices for contraception requirements in clinical trials, the governance processes set up to promote consistency and/or compliance with contraception requirements, and the effectiveness of current contraception practices in preventing pregnancies during clinical trials. Opportunities for improvements in current practices were also considered. The survey results from 12 pharmaceutical companies identified significant variability among companies with regard to contraception practices and governance during clinical trials. This variability was due primarily to differences in definitions, areas of scientific uncertainty or misunderstanding, and differences in company approaches to enrollment in clinical trials. The survey also revealed that few companies collected data in a manner that would allow a retrospective understanding of the reasons for failure of birth control during clinical trials. In this article, suggestions are made for topics where regulatory guidance or scientific publications could facilitate best practice. These include provisions for a pragmatic definition of women of childbearing potential, guidance on how animal data can influence the requirements for male and female birth control, evidence-based guidance on birth control and pregnancy testing regimes suitable for low- and high-risk situations, plus practical methods to ascertain the risk of drug-drug interactions with hormonal contraceptives.

Comparing rat and rabbit embryo-fetal developmental toxicity data for 379 pharmaceuticals: on systemic dose and developmental effects

A database of embryo-fetal developmental toxicity (EFDT) studies of 379 pharmaceutical compounds in rat and rabbit was analyzed for species differences based on toxicokinetic parameters of area under the curve (AUC) and maximum concentration (C_max) at the developmental lowest adverse effect level (dLOAEL). For the vast majority of cases (83% based on AUC of n = 283), dLOAELs in rats and rabbits were within the same order of magnitude (less than 10-fold different) when compared based on available data on AUC and C_max exposures. For 13.5% of the compounds the rabbit was more sensitive and for 3.5% of compounds the rat was more sensitive when compared based on AUC exposures. For 12% of the compounds the rabbit was more sensitive and for 1.3% of compounds the rat was more sensitive based on C_max exposures. When evaluated based on human equivalent dose (HED) conversion using standard factors, the rat and rabbit were equally sensitive. The relative extent of embryo-fetal toxicity in the presence of maternal toxicity was not different between species. Overall effect severity incidences were distributed similarly in rat and rabbit studies. Individual rat and rabbit strains did not show a different general distribution of systemic exposure LOAELs as compared to all strains combined for each species. There were no apparent species differences in the occurrence of embryo-fetal variations. Based on power of detection and given differences in the nature of developmental effects between rat and rabbit study outcomes for individual compounds, EFDT studies in two species have added value over single studies.

The impact of dose rate on ethylene glycol developmental toxicity and pharmacokinetics in pregnant CD rats

High-dose bolus exposure of rats to ethylene glycol (EG) causes developmental toxicity mediated by a metabolite, glycolic acid (GA), whose levels increase disproportionately when its metabolism is saturated. However, low-level exposures that do not saturate GA metabolism have a low potential for developmental effects. Toward the goal of developing EG risk assessments based on internal dose metrics, this study examined the differences between fast (bolus) and slow (continuous infusion) dose-rate exposures to EG on developmental outcome and pharmacokinetics. Time-mated female CD rats received sc bolus injections of 0, 1000, or 2000 mg/kg/day of EG on gestation day (GD) 6-15 once daily, whereas three corresponding groups were given the same daily doses as an infusion administered continuously from GD 6-15 via an sc implantable pump. In the sc bolus groups, increases in 11 fetal malformations (major defects) and 12 variations (minor alterations) were seen at the 2000 mg/kg/day dose level, whereas increases in 2 malformations and 2 variations occurred at 1000 mg/kg/day. In contrast, equivalent daily doses of EG given slowly via infusion did not cause any developmental effects. A pharmacokinetics time course was then conducted to compare GD 11-12 kinetics from oral bolus (gavage) exposure versus sc infusion of EG. Although dose rate had a modest impact (8- to 11-fold difference) on peak EG levels, peak levels of GA in maternal blood, kidney, embryo, and exocoelomic fluid were 59, 100, 49, and 56 times higher, respectively, following gavage versus the same dose given by infusion. These data illustrate how high-dose bolus exposure to EG causes a dramatic shift to nonlinear GA kinetics, an event which is highly unlikely to occur following exposures to humans associated with consumer and worker uses.

Developmental sensitivity to the induction of great vessel malformations by N-(2-aminoethyl)ethanolamine

N-(2-Aminoethyl)ethanolamine (AEEA) induced malformations of the great vessels in the offspring of rats treated during gestation and early lactation (Schneider et al., 2012. Birth Defects Res B Dev Reprod Toxicol [in press]). The aim of this study was to determine if in utero exposure alone was sufficient to induce these malformations or whether a peri-postnatal exposure or physiological component was required. Three groups of five time-mated female Wistar Han rats were administered AEEA (250 mg/kg/day) by gavage from gestation day (GD) 6 to GD 19 (groups 1 and 2) or from GD 6 to postnatal day 3 (group 3). Animals were euthanized on GD 21 (group 1) or postnatal day 4 (groups 2 and 3), and the hearts of the offspring were examined for changes to the great vessels. The incidence of malformations in group 1 was 91.1%, and primarily consisted of high aortic arch and abnormal carotid course. One fetus had an aortic aneurysm. All fetuses in groups 2 and 3 were malformed, primarily exhibiting abnormal carotid course and aneurysms, which mainly affected the aorta, ductus arteriosus, and pulmonary trunk. The incidence of high aortic arch was lower relative to group 1. Aneurysms were more prevalent in group 3 compared to group 2. These findings indicate that exposure to AEEA during gestation alone was sufficient to induce malformations of the great vessels and aneurysms, which may be triggered by physiological changes that occur during or after birth, but that the critical period of susceptibility to AEEA-induced aneurysms in the rat extends beyond gestation into the early postnatal period.

Pre- and postnatal development in the cynomolgus monkey following administration of ABT-874, a human anti-IL-12/23p40 monoclonal antibody

BACKGROUND

ABT-874 is an anti-IL-12/23 monoclonal antibody that binds to the p40 subunit of human IL-12 and IL-23. As part of its preclinical safety assessment, studies were conducted to assess its potential effects on pre- and postnatal development in cynomolgus monkeys.

METHODS

In the embryo-fetal development studies, ABT-874 was administered once weekly subcutaneously to adult female cynomolgus monkeys at doses of 0, 5, 25, or 100 mg/kg during gestation days (GD) 20 to 48. Fetuses were examined for external, visceral, and skeletal development on GD 100 or 150. In the pre- and postnatal study, ABT-874 was administered once weekly subcutaneously to adult female cynomolgus monkeys at doses of 10, 50, or 200 mg/kg from GD 20 through postpartum day 182. Infants were examined from birth up to 9 months of age for morphological and functional development. Potential effects on the infant immune system were evaluated by immunophenotyping of peripheral blood lymphocytes and by T-dependent antibody response to KLH.

RESULTS

There was no ABT-874-related maternal toxicity or adverse effects on fetuses or infants. ABT-874 was present in maternal and fetal serum at GD 100 and 150, and in infant serum through day 63 postbirth. ABT-874 was also present at low levels in breast milk through postpartum day 175.

CONCLUSIONS

Exposure of cynomolgus monkey fetuses and infants to ABT-874 had no adverse effects on embryo-fetal or postnatal development.

Repeated dose toxicity and developmental toxicity of diisopropanolamine to rats

The repeated dose oral and dermal toxicity of diisopropanolamine (DIPA) was evaluated in rats and compared to the reported toxicity of the related secondary alcohol amine, diethanolamine (DEA). Fischer 344/DuCrl rats were given up to 750 mg/kg/day by dermal application, 5 days/week, for 4 weeks; or up to 1,000 mg DIPA/kg/day by drinking water for 13 weeks to evaluate potential toxic effects. Time-mated female CRL:CD(SD) rats were given up to 1,000 mg/kg/day by gavage on gestation days (GD) 6-20 for evaluation of maternal and fetal effects. In the dermal toxicity study, no adverse treatment-related in-life effects other than mild irritation at the site of dermal application at >or= 500 mg/kg/day were observed. There were no systemic effects in rats given up to 750 mg/kg/day. In the subchronic oral toxicity study, the most significant effects were an increase in absolute and relative kidney weights, unaccompanied by histopathologic changes, at >or= 500 mg/kg/day DIPA. The latter effect was ameliorated following a 4-week recovery period. In the developmental toxicity study, there were no maternal or developmental effects at any dose level evaluated. The toxicity of DIPA contrasts with that of DEA which has been shown to affect a number of organ systems when repeatedly administered orally or dermally at similar or lower dosages.

Male and female fertility assessment in the cynomolgus monkey following administration of ABT-874, a human Anti-IL-12/23p40 monoclonal antibody

BACKGROUND

ABT-874 is an anti-IL-12/23 monoclonal antibody that binds to the p40 subunit of human IL-12 and IL-23. As part of its preclinical safety assessment, studies were conducted to asses its potential effects on the reproductive system in male and female cynomolgus monkeys.

METHODS

Sexually mature male cynomolgus monkeys (n = 6/group) were administered once weekly subcutaneous doses of 0, 5, 25, or 100 mg/kg ABT-874 for 13 weeks. Four monkeys/group were necropsied at the end of the 13-week dosing period and two monkeys/group were necropsied following an 8-week recovery period. Endpoints assessed in these males included sperm parameters such as sperm count and morphology, male reproductive hormones, and testes histopathology. Sexually mature female cynomolgus monkeys (n = 6/group) were administered subcutaneous doses of 0, 5, 25, or 100 mg/kg/week ABT-874 for two menstrual cycles, and recovery was subsequently assessed in each of these animals over two menstrual cycles. Endpoints assessed in these females included menses and reproductive hormone levels.

RESULTS

In both the male and female fertility studies, there were no unscheduled deaths and there was no evidence of toxicity. In male monkeys, there were no ABT-874-related effects on sperm count or motility, histopathology of the testes or effects on testosterone and inhibin B levels. In addition, menstrual cycle length, progesterone, 17ß-estradiol, and luteinizing hormone levels in female monkeys were comparable among control and ABT-874-treated groups.

CONCLUSIONS

These results demonstrate that ABT-874 had no adverse effects on reproductive hormones or fertility parameters in male or female cynomolgus monkeys.

In vitro culture of preimplantation mouse embryos and day 12 limb-buds: effects of serum and albumin

The effects of three different protein sources at different concentrations on the growth and development of preimplantation mouse embryos and day 12 mouse limb-buds in culture were studied. Mouse embryos and forelimb-buds were cultured with a range of concentrations (5.5 to 42%) of either donor bovine serum (DBS) or fetal bovine serum (FBS), or (0.2 to 0.8%) bovine serum albumin (BSA). After 48 h in culture, the rate of embryo development was significantly higher in 5.5% DBS than in all other groups (P < 0.05). The embryo hatching rate was higher in 21% FBS, 42% FBS, and all DBS groups than in serum-free medium, and all BSA groups (P < 0.05). Morphologic analysis of cultured limb-buds at 72 h revealed that total, paw, and cartilage area were greater (P < 0.05) in the serum-free medium than in all other groups. Shape factor analysis suggested that 5.5% DBS was most beneficial to mouse limb-bud development. No differences were seen in DNA or protein content of limb-buds among groups. Results suggest that mouse forelimb-buds can be successfully cultured in serum-free medium and that high concentrations of FBS and DBS may be detrimental for preimplantation embryo and/or limb-bud growth and development.

Malarial PI4K inhibitor induced diaphragmatic hernias in rat: Potential link with mammalian kinase inhibition

Background

MMV390048 is an aminopyridine plasmodial PI4K inhibitor, selected as a Plasmodium blood‐stage schizonticide for a next generation of malaria treatments to overcome resistance to current therapies. MMV390048 showed an acceptable preclinical safety profile and progressed up to Phase 2a clinical trials. However, embryofetal studies revealed adverse developmental toxicity signals, including diaphragmatic hernias and cardiovascular malformations in rats but not rabbits.

Methods

In vivo exposures of free plasma concentrations of compound in rats were assessed in relation to in vitro human kinase inhibition by MMV390048, using the ADP‐Glo™ Kinase Assay.

Results

We demonstrate a potential link between the malformations seen in the embryofetal developmental (EFD) studies and inhibition of the mammalian PI4Kβ paralogue, as well as inhibition of the off‐target kinases MAP4K4 and MINK1. PI3Kγ may also play a role in the embryofetal toxicity as its in vitro inhibition is covered by in vivo exposure. The exposures in the rabbit embryofetal development studies did not reach concentrations likely to cause PI4K inhibition. Overall, we hypothesize that the in vivo malformations observed could be due to inhibition of the PI4K target in combination with the off‐targets, MAP4K4 and MINK1. However, these relationships are by association and not mechanistically proven.

Conclusions

Deciphering if the EFD effects are dependent on PI4K inhibition, and/or via inhibition of other off‐target kinases will require the generation of novel, more potent, and more specific PI4K inhibitors.

The inhibin B response to testicular toxicants ethylene glycol monomethyl ether or dibromoacetic acid in male rats

BACKGROUND

This study was conducted as part of an ILSI-HESIconsortium effort to assess the utility of circulating inhibin B as an early biomarker of testicular toxicity in rats.

METHODS

Two known testicular toxicants were selected for use in this study: ethylene glycol monomethyl ether (EGME) and dibromoacetic acid (DBAA). EGME (200 mg/kg/day), DBAA (250 mg/kg/day), or vehicle control (0.2% hydroxypropyl methylcellulose [HPMC]) was administered orally to male rats for 3, 6, or 14 consecutive days. On study days 4, 7, and 15, serum was collected for evaluation of inhibin B levels from all surviving animals and a subset of animals was necropsied from each of the control, EGME, and DBAAgroups.

RESULTS

Administration of EGMEresulted in spermatocyte degeneration in late stage tubules and spermatocyte depletion to stage III on day 4, progressing to loss of spermatocytes and round spermatids to stage VI by day 7 and continued germ cell loss and degeneration of elongating spermatids by day 15. Inhibin B levels among EGME-treated animals progressively decreased relative to their respective controls at all time points. Administration of DBAA was associated with spermatid retention at all three time points and abnormal residual bodies at days 7 and 15. Inhibin B levels among DBAA-treated animals decreased progressively relative to their respective controls on days 7 and 15.

CONCLUSIONS

Serum inhibin B levels in rats provided a signal of testicular toxicity for each of these known testicular toxicants administered at high levels; however, histopathology provided the earliest evidence of toxic effects.

Predicting Optimal Antimalarial Drug Combinations from a Standardized Plasmodium falciparum Humanized Mouse Model

The development of new combinations of antimalarial drugs is urgently needed to prevent the spread of parasites resistant to drugs in clinical use and contribute to the control and eradication of malaria. In this work, we evaluated a standardized humanized mouse model of erythrocyte asexual stages of Plasmodium falciparum (PfalcHuMouse) for the selection of optimal drug combinations. First, we showed that the replication of P. falciparum was robust and highly reproducible in the PfalcHuMouse model by retrospective analysis of historical data. Second, we compared the relative value of parasite clearance from blood, parasite regrowth after suboptimal treatment (recrudescence), and cure as variables of therapeutic response to measure the contributions of partner drugs to combinations in vivo. To address the comparison, we first formalized and validated the day of recrudescence (DoR) as a new variable and found that there was a log-linear relationship with the number of viable parasites per mouse. Then, using historical data on monotherapy and two small cohorts of PfalcHuMice evaluated with ferroquine plus artefenomel or piperaquine plus artefenomel, we found that only measurements of parasite killing (i.e., cure of mice) as a function of drug exposure in blood allowed direct estimation of the individual drug contribution to efficacy by using multivariate statistical modeling and intuitive graphic displays. Overall, the analysis of parasite killing in the PfalcHuMouse model is a unique and robust experimental in vivo tool to inform the selection of optimal combinations by pharmacometric pharmacokinetic and pharmacodynamic (PK/PD) modeling.

Development of a biomarker to monitor target engagement after treatment with dihydroorotate dehydrogenase inhibitors

Dihydroorotate dehydrogenase (DHODH) catalyzes a key step in pyrimidine biosynthesis and has recently been validated as a therapeutic target for malaria through clinical studies on the triazolopyrimidine-based Plasmodium DHODH inhibitor DSM265. Selective toxicity towards Plasmodium species could be achieved because malaria parasites lack pyrimidine salvage pathways, and DSM265 selectively inhibits Plasmodium DHODH over the human enzyme. However, while DSM265 does not inhibit human DHODH, it inhibits DHODH from several preclinical species, including mice, suggesting that toxicity could result from on-target DHODH inhibition in those species. We describe here the use of dihydroorotate (DHO) as a biomarker of DHODH inhibition. Treatment of mammalian cells with DSM265 or the mammalian DHODH inhibitor teriflunomide led to increases in DHO where the extent of biomarker buildup correlated with both dose and inhibitor potency on DHODH. Treatment of mice with leflunomide (teriflunomide prodrug) caused a large dose-dependent buildup of DHO in blood (up to 16-fold) and urine (up to 5,400-fold) that was not observed for mice treated with DSM265. Unbound plasma teriflunomide levels reached 20-85-fold above the mouse DHODH IC50, while free DSM265 levels were only 1.6-4.2-fold above, barely achieving ∼ IC90 concentrations, suggesting that unbound DSM265 plasma levels are not sufficient to block the pathway in vivo. Thus, any toxicity associated with DSM265 treatment in mice is likely caused by off-target mechanisms. The identification of a robust biomarker for mammalian DHODH inhibition represents an important advance to generally monitor for on-target effects in preclinical and clinical applications of DHODH inhibitors used to treat human disease.

Importance of tailored non-clinical safety testing of novel antimalarial drugs: Industry best-practice

Malaria is an acute, debilitating parasitic illness. There were 249 million cases of malaria in 2022, resulting in 608,000 deaths globally, 76% of which were children ≤5 years. The unique nature of this disease (recurrences leading to re-treatments and numerous organ systems affected), specific clinical treatment regimens, poor compliance, and diversity of affected populations (predominantly pediatrics, women of childbearing potential, pregnant and lactating women), often makes standard testing approaches inadequate, and tailor-made safety assessments are more appropriate. We provide best practice recommendations based on company experience for the non-clinical safety assessment of antimalarial drugs, with a focus on small molecules since they represent the majority of drug candidates for this illness. We focus on specific testing considerations for repeat dose toxicity studies, including combination toxicity assessments, since new drug treatment regimens typically foresee short treatment durations to improve compliance (i.e., 1 day) with combinations of compounds to improve efficacy and limit potential resistance. Due to the target population, the timing of reproductive, developmental, and juvenile toxicity studies may be earlier than general testing roadmaps for other small molecule drugs. In conclusion, key recommendations presented should enable a more effective and efficient development path whilst protecting clinical trial participants and patients.

Absence of developmental and reproductive toxicity in rats, rabbits, and zebrafish embryos exposed to antimalarial drug cabamiquine

BACKGROUND

When developing new antimalarial drugs, considering their potential use during pregnancy as preventive or curative therapy is crucial. This prevents the parasite from affecting embryonic development and reduces maternal and fetal death risks. Consequently, understanding the exposure and safety of antimalarial drugs during pregnancy is crucial, with well-designed animal studies playing a key role in this assessment.

METHODS

As part of the drug development program for cabamiquine, a series of developmental and reproductive toxicity studies were conducted in rats and rabbits. Additionally, the zebrafish embryo model was used to further improve embryo exposure, minimize confounding factors related to maternal toxicity, and assess developmental risks of cabamiquine.

RESULTS

In these studies, although maternal toxicity was observed, there were no cabamiquine-related adverse effects on fertility, embryonic, or fetal development at maternal exposures representing significant multiples (up to five and 10 times higher in rabbit and rats, respectively) than the exposure at the anticipated efficacious human dose. Similarly, no adverse effects were observed on ZF embryonic development, even though cabamiquine concentrations in the embryos were 10-fold higher than nominal concentrations.

CONCLUSIONS

The results obtained in a full set of reproductive toxicity studies did not provide evidence of detrimental effects on the conceptuses and progeny at maternally nontoxic doses and exposures, still representing a multiple of the anticipated systemic exposures in women of childbearing potential (WOCBP). Cabamiquine can therefore be considered a suitable therapeutic option for WOCBP and pregnant women living in malaria-endemic regions by significantly reducing maternal and infant malaria death rates.