In Vitro's Growing Space in Safety Testing
An expert panel discusses the advances and challenges in moving toward animal-free toxicology. The fourth of a four-part series.
Twenty five years ago, Dr. Clive Roper, Charles River's Head of In Vitro Sciences in Edinburgh, delivered the first of many scientific presentations about what would become his life's work: in vitro skin penetration tests. When he finished the talk, an eminent professor stood up and remarked, rather pessimistically, that while he found Dr. Roper's material interesting he thought it would take at least another 50 years before the regulatory agencies would honor it in the literature. The man was wrong. By 2004, the Organisation for Economic Cooperation and Development (OECD) Guidelines had added the method to its chapter on the testing of chemicals (OECD 428) and papers from Dr. Ropers work were cited in OECD Guidance Document No. 28. The relative speed in which this method found its footing speaks volumes about an industry that, historically and understandably, has been cautious about altering a decades-long process of using animals to evaluate their drug products.
But with a global incentive to reduce, refine or replace the number of research animals, and the difficulties pharmaceutical companies have had in translating animal data, the field has begun investing more attention and money in developing less invasive ways of measuring toxicity. Their enthusiasm is being driven by advances in in vitro cell-based models, in chemico models and in silico models that now offer very different approaches for conducting preclinical safety studies. On Wednesday, a panel of experts at the Society of Toxicology's annual meeting in New Orleans gathered for a discussion about where the fields of in vitro toxicology and integrated toxicology have been, how they have evolved and where they are headed. Along with Dr. Roper, who helped organize the session, the panel included Dr. Natalie Burden, who oversees programs on toxicology and regulatory sciences that focus on environmental testing at the UK National Centre for the Replacement, Refinement and Reduction of Animals in Research (NC3RS), Dr Doug Learn, Director of Photobiology and Cellular Therapeutic Safety in Horsham, Pa., and Dr. Peter Gaskin, Associate Director, Scientific Program Management at Charles River, Edinburgh.
Here are some key points made during the standing-room-only discussion:
Paradigm shifts are already occurring in preclinical cardiac toxicity testing.
The US Food and Drug Administration and ChanTest are spearheading a new strategy entitled, "Comprehensive in vitro Proarrhythmia Assay" (CiPA) that shifts emphasis away from QT-interval prolongation (a weak surrogate marker for drug-induced cardiac arrhythmia) and focuses on predicting cardiac risk using two in vitro biological assays and one in silico computational analysis. Meanwhile, NC3Rs' CRACK It innovation fund, with sponsorship from GSK, is supporting the development of a physiologically-relevant contractility platform with cells that are phenotypically mature, possess a robust contractile apparatus, move calcium between intracellular and extracellular spaces and metabolically generate substantive amounts of energy. An international consortium of 39 partners that includes the NC3Rs and which is being funded by the European Commission is also developing two novel tools for screening cardiotoxicity. A glimpse of the scientific abstracts being presented at the Safety Pharmacology meeting reflects the creative partnering and large shifts in investment toward in silico and in vitro approaches, says Dr. Burden.
A good integrated toxicology strategy comes down to making good choices.
An integrated toxicology strategy or regime utilizes the best tests available in order to confirm the safety of the test article. These tests may be in silico, in chemico, in vitro or in vivo. Just make sure you use the right toolbox. For dermal IND, says Dr. Roper, you would likely collect early in vivo pharmacokinetic data to determine systemic exposure, conduct in vitro metabolic profiling of hepatocytes in minipigs or rats, and use an in vitro skin penetration assay for formulation selection. This would all be in support of running the main in vivo battery of GLP preclinical toxicology tests.
The regulatory landscape is slowly evolving to reflect the scientific advances in toxicology.
Changes in dermal irritation/corrosion tests offer a good example of how a decade of evolution in OECD guidance correlates with advances occurring in the field of skin testing. From 2002 to 2013 there have been four test guidelines added to the OECD—three of them simultaneously in 2013—that reflect refinements in these processes and the shift to in vitro testing methods, noted Dr. Learn. On the other hand, recommendations for the In Vitro 3T3 NRU phototoxicity test were published in 1994, yet took another 19 years before the International Conference on Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human Use (ICH) recommended its use and recognized skin constructs and the Reactive Oxygen Species (ROS) as a way to evaluate photosafety.
In vitro tests will one day replace animal safety testing.
This will happen but it's going to take many years, acknowledged Dr. Roper. Pound for pound, some of the in vitro tests are stronger than the animal tests, but equally, there are many tests for which there is no alternative in the offing. All GLP regulatory tests and systems need to be validated to be accepted by regulators and by industry. The science has to be good. We have to be as good, if not better than, the animal standard, panelists noted. In vitro toxicology has the advantage that it uses tissues from human, but gaining complexity between tissues is only just beginning, leaving the animal tests with advantages for complex toxicology. As we develop Adverse Outcome Pathways, i.e. identify the mechanisms involved in disease, only then can new tests be identified to further the pursuit towards animal free toxicology. Today, the integrated paradigm gives us by far the best of both worlds.