Both in vitro and in vivo toxicology studies offer their own advantages and disadvantages.
Before a pharmaceutical developer can initiate the clinical trial phase of any drug, researchers must first determine whether that drug has the potential or likelihood to harm people in significant ways. These research programs, known as toxicology studies or “tox screenings,” examine the impacts of chemical drugs (or biologic pharmaceuticals) on biological tissues, then on living animal subjects, in order to assess their likelihood of causing harm to humans.
In other words, preclinical tox studies fall into two categories: in vitro studies, in which the actions of drugs are tested on biological tissues in test tubes, and in vivo studies, in which pharmaceuticals are tested on live mammals. While not every tox study includes both these phases, a minimum of successful in vitro testing is required in order to certify a drug for clinical trials.
All preclinical tox research must comply with the good laboratory practice (GLP) guidelines set out by the US Food and Drug Administration (FDA), and by other regulatory bodies such as the EPA and OECD. These guidelines set out specific rules for the overall conduct within a study, as well as for personnel, equipment and facilities, testing procedures and reports, and quality assurance (QA) oversight.
The following breakdown examines both types of preclinical tox studies.
In vitro tox studies analyze the effects of a drug on specific tissues and cells.
As has often been said, preclinical in vitro studies blend the processes of drug discovery and development. These studies provide clear data on the mechanism of the drug, enabling developers to refine the formulation. Meanwhile, they offer early indicators of potential toxic effects, giving developers a chance to redesign future studies, or even to pivot to an entirely different development program without wasting further resources.
For these exact reasons, many developers begin with in vitro tox studies, which are far less expensive than in vivo ones, and can also take place more rapidly. However, in vitro studies are rather less significant than in vivo ones, in terms of their ability to reliably predict a drug’s actual impact on living mammalian subjects. Thus, successful in vitro toxicology studies are often followed by in vivo ones before a drug is submitted for FDA approval.
A typical in vitro tox study introduces the drug to cells and tissues in test tubes and/or petri dishes. These cells may be taken from the liver or bloodstream of mammals, or they may be bacterial, funal or yeast cells. In addition to checking for obvious hazards such as cytotoxicity (toxicity to cells), in vitro screenings also analyze the drug’s protein binding behavior, membrane permeability, metabolic stability, cell reproduction, and a range of other structural and functional impacts.
In vivo tox studies determine drugs’ impact on mammalian development.
Of course, mammals’ bodies consist not of just one type of cell, but of a complex set of interrelated tissues and systems composed of many types of cells in varying proportions. Thus, an in vitro tox study’s ability to predict a drug’s impact on a whole living animal may be incomplete at best; outright inaccurate at worst. For this reason, most pharma developers follow up successful in vitro studies with in vivo studies on live mammals such as rodents and swine.
One of the most common initial in vivo studies is an analysis of a drug’s capacity to irritate ocular and/or dermal tissue. If the test subjects respond well to this analysis, studies on immunotixicity, reproductive toxicity, genotoxicity and adjuvant safety (interactions with other pharmaceuticals) may follow. While all these types of studies are far more expensive and time-consuming than in vitro tox screenings, they can still prevent the wasting of far greater amounts of resources over the long term, if a drug displays any toxic characteristics that could prevent its approval by the FDA (or, still worse, could invite a patient lawsuit).
To reduce testing costs somewhat, several companies now offer rough-equivalent tests in kit form. For example, an in vivo dermal or ocular toxicity test may be replaced with an in vitro test on a permeable polycarbonate membrane, which has been cultured into stratified and highly differentiated layers of metabolically and mitotically active cells, closely mimicking the structure and function of mammalian epidermis.
Whether a developer utilizes in vitro or in vivo tox studies, or a combination of both, the expertise of a contract manufacturing partner often proves crucial in ensuring that these studies are conducted cost-effectively, and in a GLP-compliant manner. As a growing number of pharma developers partner with contract manufacturing organizations (CMOs) earlier-on in the development process, these efficiencies can be increased further than ever before.
In addition to being a writer and speaker, Raymond E Peck is the Founder and CEO of VxP Pharma Services and VxP Biologics, both based in Indianapolis Indiana.