Computational science in drug metabolism and toxicology

In vitro and in silico genetic toxicity screening of flavor compounds and other ingredients in tobacco products with emphasis on ENDS

Electronic nicotine delivery systems (ENDS) are regulated tobacco products and often contain flavor compounds. Given the concern of increased use and the appeal of ENDS by young people, evaluating the potential of flavors to induce DNA damage is important for health hazard identification. In this study, alternative methods were used as prioritization tools to study the genotoxic mode of action (MoA) of 150 flavor compounds. In particular, clastogen-sensitive (γH2AX and p53) and aneugen-sensitive (p-H3 and polyploidy) biomarkers of DNA damage in human TK6 cells were aggregated through a supervised three-pronged ensemble machine learning prediction model to prioritize chemicals based on genotoxicity. In addition, in silico quantitative structure-activity relationship (QSAR) models were used to predict genotoxicity and carcinogenic potential. The in vitro assay identified 25 flavors as positive for genotoxicity: 15 clastogenic, eight aneugenic and two with a mixed MoA (clastogenic and aneugenic). Twenty-three of these 25 flavors predicted to induce DNA damage in vitro are documented in public literature to be in e-liquid or in the aerosols produced by ENDS products with youth-appealing flavors and names. QSAR models predicted 46 (31%) of 150 compounds having at least one positive call for mutagenicity, clastogenicity or rodent carcinogenicity, 49 (33%) compounds were predicted negative for all three endpoints, and remaining compounds had no prediction call. The parallel use of these predictive technologies to elucidate MoAs for potential genetic damage, hold utility as a screening strategy. This study is the first high-content and high-throughput genotoxicity screening study with an emphasis on flavors in ENDS products.

Current toxicological aspects on drug and chemical transport and metabolism across the human placental barrier

INTRODUCTION

Placenta plays an obligatory role in fetal growth and development by performing a multitude of functions, including embryo implantation, transport of nutrients and elimination of metabolic waste products and endocrine activity. Drugs and chemicals can transfer across the placental barrier from mother to fetus either by passive diffusion mechanisms and/or via a network of active transporters, which may lead to potential fetotoxicity effects. Placenta also expresses a wide variety of enzymes, being capable of metabolizing a large diversity of drugs and chemicals to metabolites of lower or even higher toxicity than parent compounds.

AREAS COVERED

The present review aims to summarize the current toxicological aspects in the emerging topic of drug transport and metabolism across the human placental barrier.

EXPERT OPINION

There is an emerging demand for accurate assessment of drug transport and metabolism across the human placental barrier, on the basis of a high throughput screening process in the early stages of drug design, to avoid drug candidates from potential fetotoxicity effects. In this aspect, combined studies, which take into account in vivo and in vitro investigations, as well as the ex vivo perfusion method and the recently developed computer-aided technologies, may significantly contribute to this direction.

In silico toxicology models and databases as FDA Critical Path Initiative toolkits

In silico toxicology methods are practical, evidence-based and high throughput, with varying accuracy. In silico approaches are of keen interest, not only to scientists in the private sector and to academic researchers worldwide, but also to the public. They are being increasingly evaluated and applied by regulators. Although there are foreseeable beneficial aspects--including maximising use of prior test data and the potential for minimising animal use for future toxicity testing--the primary use of in silico toxicology methods in the pharmaceutical sciences are as decision support information. It is possible for in silico toxicology methods to complement and strengthen the evidence for certain regulatory review processes, and to enhance risk management by supporting a more informed decision regarding priority setting for additional toxicological testing in research and product development. There are also several challenges with these continually evolving methods which clearly must be considered. This mini-review describes in silico methods that have been researched as Critical Path Initiative toolkits for predicting toxicities early in drug development based on prior knowledge derived from preclinical and clinical data at the US Food and Drug Administration, Center for Drug Evaluation and Research.

Highlights of the XII International Congress on Toxicology, 19 - 23 July 2010, Barcelona, Spain

IMPORTANCE OF THE FIELD

There are few true international meetings dedicated to covering multiple areas of toxicology. The XII International Congress of Toxicology (IUTOX) held from 19 to 23 July 2010 in Barcelona, Spain is one such meeting. The IUTOX is important as its emphasis is on chemical safety and integrating approaches and alternative possibilities to protecting public health. The meeting was an important forum with professional interactions in different subspecialties of toxicology addressing these current topics.

AREAS COVERED IN THIS REVIEW

The basis of toxic effects including mechanistic, effects testing, monitoring and alternative methods are covered in this meeting highlights article. Coverage of industry, clinical toxicologists, environmentalists, regulators and technological developers is provided.

WHAT THE READER WILL GAIN

Insight into the coverage of topics discussed at the XII IUTOX meeting.

TAKE HOME MESSAGE

Current topics in toxicology with international impact are presently centered on new testing strategies, biomarkers and understanding mechanisms of toxicity to help address the safety and risk of substances relevant to public health.