Determination of the zebrafish embryo developmental toxicity assessment (ZEDTA) as an alternative non-mammalian approach for the safety assessment of agrochemicals

With the US Environment Protection Agency reducing requests for (and funding of) mammalian studies alongside the proposed elimination of requests by 2035, there is an urgent need for fully validated New Approach Methods (NAMs) to fill the resultant gap for safety assessment of agrochemicals. One promising NAM for assessing the potential for human prenatal developmental toxicity potential is the Zebrafish Embryo Developmental Toxicity Assessment, a bioassay that has been used by the pharmaceutical industry for more than a decade in early-stage drug safety assessment. Despite its promise, little data has been generated to assess the validity of ZEDTA for assessing Developmental and Reproductive Toxicity of new agrochemical products. Addressing this knowledge gap, we tested 67 compounds (insecticides, herbicides and fungicides) spanning multiple different chemical groupings and mechanisms of action. ZEDTA assay results were compared with the European Chemicals Agency (ECHA) Classification and Labelling (C&L) for mammalian hazard classification and with publicly available data to determine the ZEDTA's translation power. Overall, the ZEDTA assay had an effective detection capability of 65 % for sensitivity and 64 % for specificity as compared with the ECHA-C&L classification and publicly available data. Comparing the ZEDTA data there were both strengths and weaknesses in alignments for across the different chemical classes and chemical mechanisms of action. Overall, the data generated, show the performance of the ZEDTA assay was comparable with other bioassays highlighted as alternatives for mammalian assessment and holds good promise as a NAM for screening agrochemical prenatal developmental toxicity during new product human safety assessment.

Assessing the impact and risk of immunomodulatory compounds on pregnancy

There have been remarkable advancements in understanding the complex and dynamic immune biological processes engaged during all stages of pregnancy. Exquisite control of immune processes is critical to successful outcome in all stages of pregnancy from ovulation to birth. There are many immunomodulatory therapeutics that may offer beneficial treatment options for a variety of diseases (e.g., inflammation/autoimmunity, cancer) to patients that are or desire to become pregnant. It is important to understand the potential for these immunomodulatory therapeutics to alter the critical immune processes in pregnancy to inform clinical risk relative to successful pregnancy. The Health and Environmental Sciences Institute-Developmental and Reproductive Toxicology/Immuno-safety Technical Committee (HESI DART/ITC) conducted a survey on approaches to assess adverse pregnancy outcomes with immunomodulators. HESI DART/ITC also organized a workshop for an extended discussion on immune mechanisms during pregnancy, the adequacy of current tools/methodologies to identify concerns for potential pregnancy hazards from immunomodulatory therapies, ways to identify and address scientific gaps, and global regulatory considerations across various immunomodulatory modalities and indications. In this manuscript we summarize learnings from these efforts to characterize risk within this patient population, promote more informed treatment decisions, and enable safer pharmacological interventions during pregnancy.

New approach methodologies to confirm developmental toxicity of pharmaceuticals based on weight of evidence

The aim of embryo-fetal developmental toxicity assessments for pharmaceuticals is to inform potential risk of adverse pregnancy outcome, which has traditionally relied on studies in pregnant animals. Recent updates to international safety guidelines (ICH S5R3) have incorporated information on how to use weight of evidence and alternative assays to reduce animal use while still informing risk of fetal harm. Uptake of these alternative approaches has been slow due to limitations in understanding how alternative assays translate to in vivo effects and then relevance to human exposure. To understand the predictivity of new approach methodologies for developmental toxicity (DevTox NAMs), we used two pharmaceutical examples (glasdegib and lorlatinib) to illustrate the value of DevTox NAMs to complement weight of evidence (WoE) assessments while considering the relationship of concentration-effect levels in NAMs to in vivo studies. The in vitro results generated in a battery of assays (mEST, rWEC, zebrafish, and human based stem cells) confirmed the WoE based on literature and further confirmed by preliminary embryo-fetal development data. The data generated for these two compounds supports integrating DevTox NAMs into the developmental toxicity assessment for advanced cancer indications.

A novel human stem cell-based biomarker assay for in vitro assessment of developmental toxicity

BACKGROUND

Testing for developmental toxicity according to the current regulatory guidelines requires large numbers of animals, making these tests very resource intensive, time-consuming, and ethically debatable. Over the past decades, several alternative in vitro assays have been developed, but these often suffered from low predictability and the inability to provide a mechanistic understanding of developmental toxicity.

METHODS

To identify embryotoxic compounds, we developed a human induced pluripotent stem cells (hiPSCs)-based biomarker assay. The assay is based on the differentiation of hiPSCs into functional cardiomyocytes and hepatocytes. Proper stem cell differentiation is investigated by morphological profiling and assessment of time-dependent expression patterns of cell-specific biomarkers. In this system, a decrease in the expression of the biomarker genes and morphology disruption of the differentiated cells following compound treatment indicated teratogenicity.

RESULTS

The hiPSCs-based biomarker assay was validated with 21 well-established in vivo animal teratogenic and non-teratogenic compounds during cardiomyocyte and hepatocyte differentiation. The in vivo teratogenic compounds (e.g., thalidomide and valproic acid) markedly disrupted morphology, functionality, and the expression pattern of the biomarker genes in either one or both cell types. Non-teratogenic chemicals generally had no effect on the morphology of differentiated cells, nor on the expression of the biomarker genes. Compared to the in vivo classification, the assay achieved high accuracy (91%), sensitivity (91%), and specificity (90%).

CONCLUSION

The assay, which we named ReproTracker®, is a state-of-the-art in vitro method that can identify the teratogenicity potential of new pharmaceuticals and chemicals and signify the outcome of in vivo test systems.

No developmental toxicity observed with dolutegravir in rat whole embryo culture

BACKGROUND

An in vitro rat whole embryo culture study investigated whether direct exposure to dolutegravir (Tivicay^TM ) during the critical period for neural tube development would result in abnormal development.

METHODS

Dolutegravir (DTG), and HIV integrase inhibitor, was administered at 0 (vehicle), 5.3 μg/mL and 9.3 μg/mL on Gestation Day (GD) 9 through 11 (approximate 40 hour exposure period) along with positive (Valproic Acid) and negative (Penicillin G) controls. The DTG concentrations tested were selected based on clinical exposure at the maximum human recommended dose and maximum feasible concentration that could be formulated under the experimental conditions.

RESULTS

Approximately 6% of DTG present in the culture media was absorbed into the embryos, demonstrating embryonic exposure at a similar level to that observed in a rat DTG placental transfer study. There was no effect in either the DTG or Penicillin G groups on visceral yolk sac size/morphology, embryo size, somite number and embryo morphology at any concentration tested. Valproic Acid, by contrast, produced statistically significant decreases in visceral yolk sac size, embryo size and somite number along with defects in visceral yolk sac and embryonic morphology, including neural tube defects (NTDs), in all embryos.

CONCLUSION

DTG at the maximum human recommended dose administered to rats in a whole embryo culture assay did not produce any abnormal effects, while the positive control Valproic Acid produced abnormal effects, including neural tube defects.

Establishment of an in vitro method of rabbit embryo toxicity with toxicokinetics study

This report introduces a novel method, rabbit whole embryo culture (WEC) combined with toxicokinetics (TK), for toxicity testing. Rodent WEC has been extensively used for in vitro screening of developmental toxicity. To improve the reliability of in vitro data, it is important to consider TK and species specificity. To test the utility and effectiveness of this method, we investigated the toxic effect of thalidomide on rabbit embryos and its behavior in test systems both in vitro and in vivo under the same experimental condition. The data showed that thalidomide induced embryo malformations such as embryonic brain hypoplasia, short limb buds, and declined embryonic growth both in vitro and in vivo. The toxic effect increased with the increasing exposure of the embryo to thalidomide. In addition, we observed similar toxic effects and exposure-effect relationships in vivo and in vitro. Therefore, we preliminarily conclude that this new method can effectively predict and explain thalidomide toxicity. Furthermore, we investigated the behavior of test compounds in the WEC system for the first time, and this method is expected to be an important technique for in vitro toxicity study after extensive verification.

Inhibition of ACC causes malformations in rats and rabbits: comparison of mammalian findings and alternative assays

Acetyl-CoA carboxylase (ACC) is an enzyme within the de novo lipogenesis (DNL) pathway and plays a role in regulating lipid metabolism. Pharmacologic ACC inhibition has been an area of interest for multiple potential indications including oncology, acne vulgaris, metabolic diseases such as type 2 diabetes mellitus, and non-alcoholic fatty liver disease/non-alcoholic steatohepatitis. A critical role for ACC in de novo synthesis of long-chain fatty acids during fetal development has been demonstrated in studies in mice lacking Acc1, where the absence of Acc1 results in early embryonic lethality. Following positive predictions of developmental toxicity in alternative in vitro assays (positive in murine embryonic stem cell [mESC] assay and rat whole embryo culture, but negative in zebrafish), developmental toxicity (growth retardation and dysmorphogenesis associated with disrupted midline fusion) was observed with the oral administration of the dual ACC1 and 2 inhibitor, PF-05175157, in Sprague Dawley rats and New Zealand White rabbits. The results of these studies are presented here to make comparisons across the assays, as well as mechanistic insights from the mESC assay demonstrating high ACC expression in the mESC and that ACC induced developmental toxicity can be rescued with palmitic acid providing supportive evidence for DNL pathway inhibition as the underlying mechanism. Ultimately, while the battery of alternative approaches and weight-of-evidence case were useful for hazard identification, the embryo-fetal development studies were necessary to inform the risk assessment on the adverse fetal response, as malformations and/or embryo fetal lethality were limited to doses that caused near complete inhibition of DNL.

Morphometric analysis of developing zebrafish embryos allows predicting teratogenicity modes of action in higher vertebrates

The early identification of teratogens in humans and animals is mandatory for drug discovery and development. Zebrafish has emerged as an alternative model to traditional preclinical models for predicting teratogenicity and other potential chemical-induced toxicity hazards. To prove its predictivity, we exposed zebrafish embryos from 0 to 96 h post fertilization to a battery of 31 compounds classified as teratogens or non-teratogens in mammals. The teratogenicity score was based on the measurement of 16 phenotypical parameters, namely heart edema, pigmentation, body length, eye size, yolk size, yolk sac edema, otic vesicle defects, otoliths defects, body axis defects, developmental delay, tail bending, scoliosis, lateral fins absence, hatching ratio, lower jaw malformations and tissue necrosis. Among the 31 compounds, 20 were detected as teratogens and 11 as non-teratogens, resulting in 94.44 % sensitivity, 90.91 % specificity and 87.10 % accuracy compared to rodents. These percentages decreased slightly when referred to humans, with 87.50 % sensitivity, 81.82 % specificity and 74.19 % accuracy, but allowed an increase in the prediction levels reported by rodents for the same compounds. Positive compounds showed a high correlation among teratogenic parameters, pointing out at general developmental delay as major cause to explain the physiological/morphological malformations. A more detailed analysis based on deviations from main trends revealed potential specific modes of action for some compounds such as retinoic acid, DEAB, ochratoxin A, haloperidol, warfarin, valproic acid, acetaminophen, dasatinib, imatinib, dexamethasone, 6-aminonicotinamide and bisphenol A. The high degree of predictivity and the possibility of applying mechanistic approaches makes zebrafish a powerful model for screening teratogenicity.

In Vitro Micropatterned Human Pluripotent Stem Cell Test (µP-hPST) for Morphometric-Based Teratogen Screening

Exposure to teratogenic chemicals during pregnancy may cause severe birth defects. Due to high inter-species variation of drug responses as well as financial and ethical burdens, despite the widely use of in vivo animal tests, it’s crucial to develop highly predictive human pluripotent stem cell (hPSC)-based in vitro assays to identify potential teratogens. Previously we have shown that the morphological disruption of mesoendoderm patterns formed by geometrically-confined cell differentiation and migration using hPSCs could potentially serve as a sensitive morphological marker in teratogen detection. Here, a micropatterned human pluripotent stem cell test (µP-hPST) assay was developed using 30 pharmaceutical compounds. A simplified morphometric readout was developed to quantify the mesoendoderm pattern changes and a two-step classification rule was generated to identify teratogens. The optimized µP-hPST could classify the 30 compounds with 97% accuracy, 100% specificity and 93% sensitivity. Compared with metabolic biomarker-based hPSC assay by Stemina, the µP-hPST could successfully identify misclassified drugs Bosentan, Diphenylhydantoin and Lovastatin, and show a higher accuracy and sensitivity. This scalable µP-hPST may serve as either an independent assay or a complement assay for existing assays to reduce animal use, accelerate early discovery-phase drug screening and help general chemical screening of human teratogens.

A Developmental Toxicology Assay Platform for Screening Teratogenic Liability of Pharmaceutical Compounds

Increasing need for proactive safety optimization of pharmaceutical compounds has led to generation and/or refinement of in vitro developmental toxicology assays. Our laboratory has developed three in vitro developmental toxicology assays to assess teratogenic liability of pharmaceutical compounds. These assays included a mouse molecular embryonic stem cell assay (MESCA), a dechorionated zebrafish embryo culture (ZEC) assay, and a streamlined rat whole embryo culture (rWEC) assay. Individually, the assays presented good (73-82%) predictivity. However, it remains to be determined whether combining or tiering the assays could enhance performance. Seventy-three compounds representing a broad spectrum of pharmaceutical targets and chemistry were evaluated across the assays to generate testing strategies that optimized performance. The MESCA and ZEC assays were found to have two limitations: compound solubility and frequent misclassification of compounds with H1 receptor or GABAnergic activity. The streamlined rWEC assay was found to be a cost-effective stand-alone assay for supporting poorly soluble compounds and/or ones with H1 or GABAnergic activity. For all other compounds, a tiering strategy using the MESCA and ZEC assays additionally optimized throughput, cost, and minimized animal use. The tiered strategy resulted in improved performance achieving 88% overall predictivity and was comparable with 89% overall predictivity achieved with frequency analysis (final teratogenic classification made from most frequent teratogenic classification from each individual assay). Furthermore there were 21 compounds in the test set characterized as definitive or suspect human teratogens and the multiassay approach achieved 95 and 91% correct classification using the tiered or frequency screening approach, respectively.

Establishment and assessment of a new human embryonic stem cell-based biomarker assay for developmental toxicity screening

A metabolic biomarker-based in vitro assay utilizing human embryonic stem (hES) cells was developed to identify the concentration of test compounds that perturbs cellular metabolism in a manner indicative of teratogenicity. This assay is designed to aid the early discovery-phase detection of potential human developmental toxicants. In this study, metabolomic data from hES cell culture media were used to assess potential biomarkers for development of a rapid in vitro teratogenicity assay. hES cells were treated with pharmaceuticals of known human teratogenicity at a concentration equivalent to their published human peak therapeutic plasma concentration. Two metabolite biomarkers (ornithine and cystine) were identified as indicators of developmental toxicity. A targeted exposure-based biomarker assay using these metabolites, along with a cytotoxicity endpoint, was then developed using a 9-point dose-response curve. The predictivity of the new assay was evaluated using a separate set of test compounds. To illustrate how the assay could be applied to compounds of unknown potential for developmental toxicity, an additional 10 compounds were evaluated that do not have data on human exposure during pregnancy, but have shown positive results in animal developmental toxicity studies. The new assay identified the potential developmental toxicants in the test set with 77% accuracy (57% sensitivity, 100% specificity). The assay had a high concordance (≥75%) with existing in vivo models, demonstrating that the new assay can predict the developmental toxicity potential of new compounds as part of discovery phase testing and provide a signal as to the likely outcome of required in vivo tests.

Establishment of a molecular embryonic stem cell developmental toxicity assay

The mouse embryonic stem cell test (EST) is a 10-day screen for teratogenic potential developed to reduce animal use for embryotoxicity testing of chemicals (Spielmann, 2005; Spielmann et al., 1997). In this study, we used the cytotoxicity IC(50) values and transcriptional expression changes as primary endpoints in a shorter 4-day version of the EST, the molecular embryonic stem cell assay. Mouse D3 embryonic stem cells were used for cytotoxicity assessment (monolayers) or grown as embryoid bodies in low attachment plates for transcriptional profiling. Sixty-five compounds with known in vivo teratogenicity (33 teratogens and 32 nonteratogens) were evaluated to develop a model for classifying compounds with teratogenic potential. The expression of 12 developmentally regulated gene targets (nanog, fgf5, gsc, cd34, axin2, apln, chst7, lhx1, fgf8, sox17, foxa2, and cxcr4) was measured following exposure of embryoid bodies to a single compound concentration (0.1 × the cytotoxicity IC(20)) for 4 days. In the decision-tree model, compounds with IC(50) values < 22 µM were categorized as teratogens, whereas compounds in the two groups with IC(50) values between 22-200 µM and > 200 µM were categorized as teratogens if ≥ 8 and 12 genes, respectively, were deregulated by at least 10%. Forty-seven of 65 compounds of the training set were correctly identified (72% total concordance). In a test set of 12 additional compounds (5 teratogens, 7 nonteratogens), 10 were correctly classified by this approach (83% concordance). The false positive rate in the training and test sets was 24 and 0%, respectively, indicating that this assay has potential to identify teratogens.