In the Spotlight
Overview of Scientific Roadmap for the Future of Animal-free Systemic Toxicity Testing Workshop, May 30-31, 2013
Published: June 28, 2013
Following a welcome and orientation from Donald Zink (FDA), CAAT’s Thomas Hartung began the morning session with a summary of CAAT’s recent “roadmap” activities. He urged presenters to move beyond critiquing 20th century toxicology, to focus on what still needs to be done to advance alternative methods in the 21st century. He then outlined what he sees as especially promising directions: the delineation of toxicity pathways, the development and use of Integrated Testing Strategies, and the expansion of human-on-a-chip technologies. Hartung also noted the growing research funding opportunities introduced by the US government’s attention to countering bioterrorism.
Michael Schwartz (University of Tuebingen) provided an update on the seven current SEURAT-1 projects (see also this AltTox “Spotlight” article). While several SEURAT-1 projects begun in an earlier round of funding are ending this year, they hope to develop Adverse Outcome Pathways (AOPs) describing liver, heart, and neurotoxicity in the remaining years of the SEURAT program. Schwartz also mentioned related efforts of the AXLR8 EU program, a coordinating activity of leading European and global research teams working to develop advanced tools for safety testing and risk assessment. The next AXLR8 annual report will be published later this year.
David Dix [previous Acting Director of EPA’s National Center for Computational Toxicology (NCCT), now Director of Office of Science Coordination and Policy (OSCP)] provided an update on the EPA’s ToxCast program. ToxCast Phase II (covering approximately 800 chemicals from a wide range of consumer and industrial sources) was recently completed, and they are very pleased with how well the assays performed. Phase II-derived predictive models are being constructed. To demonstrate the necessity/utility of multiple assays, Dix outlined how a suite of them can be used to characterize an estrogen receptor pathway.
James McKim (CeeTox) led off the Thursday afternoon session with an assessment of the current prospects for animal-free, repeated dose testing. There are in vitro replacements for acute and subacute systemic toxicity testing, but none yet for subchronic and chronic systemic toxicity. The technical challenges are considerable, but new cell culture models hold promise: 3-D culture systems such as InSphero’s liver model, and microfluidics systems such as developed by RealBio. McKim urged the use of integrated and tiered testing strategies in a systems biology approach, to capitalize on existing models and data.
Thomas Knudsen (EPA’s Center for Computational Toxicology) described progress on the EPA’s “Virtual Embryo” project, which is creating computer models of developmental processes and using them to predict reproductive toxicity. He presented an AOP describing embryonic vascular development and disruption caused by the introduction of 5HPP-33, a thalidomide analogue, which illustrated the AOP’s utility for organizing and integrating existing in vitro data.
David Basketter (DABMEB Consulting) reviewed the state of animal-free skin sensitization testing. At least 7 tests have been submitted to the European Union Reference Laboratory for alternatives to animal testing (EURL ECVAM) for approval. Three of these tests, covering protein, keratinocyte and dendritic cell reactivity, are nearly ready to submit to the Test Guidelines Program of the Organization Economic Cooperation and Development (OECD) for formal development as an integrated testing strategy (ITS) for skin sensitization.
Thomas Hartung moderated the end-of-day discussion, and highlighted lingering issues: for one, there is much yet to be learned about what drives the potency of reactivity. He stressed the need for a more “dispassionate” approach on the part of test developers so that the focus is on the best and most relevant science. Hartung also noted that Cosmetics Europe has funded a preliminary comparison of available sensitization methods using a small number of reference chemicals that have been characterized according to human potency; a paper has been submitted to Dermatitis.
Harvey Clewell (Hamner Institutes) began the Friday morning session with a discussion of the biokinetic limitations of in vitro methods. He emphasized the difficulty – and necessity – of reproducing fluctuations in bioavailability caused by physiochemical properties such as lipophilicity, volatility, and solubility. He stressed the importance of measuring actual available concentrations of substances in vitro, and accounting for losses to evaporation, binding (to plastic wells, proteins, and other structures), and metabolism (reduction due to renal clearance, ventilator clearance, poor absorption) in order to improve in vitro-in vivo extrapolations.
Thomas Hartung followed with an overview of shortcomings in existing cancer bioassays, and options for replacement. The way forward in carcinogenicity testing will depend on such strategies as improving the metabolic capacity of in vitro systems, further developing 3-D co-culture with improved physiologic culture conditions, using human cells, and employing better and more appropriate statistical analyses. Hartung also argued that Integrated Testing Strategies will be essential to future toxicity testing, but the success of ITS, as well as of weight-of-evidence evaluations and Evidence-Based Toxicology, are all contingent on the quality and integrity of the data.
Grace Patlewicz (DuPont) opened the afternoon session on “Drawing the Future Roadmap for Animal-Free Toxicity Testing.” Patlewicz described the OECD’s AOP project template and guidance, discussed the definition of AOP vs Mechanism of Action (MOA), and cautioned that AOP’s should not necessarily focus on Molecular Initiating Events (MIEs), and of course are not actually linear. AOPs facilitate organizing and integrating information in a meaningful way, and will have a significant impact in informing test guidelines, exploiting the OECD Toolbox, and devising Integrated Testing Strategies.
Alan Goldberg (CAAT) celebrated the significant advances that have been made toward animal-free toxicity testing in a relatively short time, noting that there are now in vitro tests for acute toxicity, repeat dose testing, and eye and skin irritation. He went on to predict that within the next two decades, risk assessment decisions will be made in a regulatory context entirely from in vitro screens. Goldberg likened the constructs of Pathways of Toxicity and AOPs to such “disruptive technologies” as the iPhone – developments that will completely change the field.
Presentations on Thursday afternoon and Friday were followed by one hour of lively, moderated discussion – including questions submitted by webinar participants.
Wrapping up the two-day Roadmap summit, Thomas Hartung noted that transatlantic dialogue has been essential to advancing the science, and urged that the dialogue continue. He also reiterated a point raised several times in discussions over the two-day session: the practical and even ethical necessity – in the interest of advancing the science – for sharing data more freely and enthusiastically.