Envigo: 9 December 2015: The complexity of non-clinical safety studies has been increasing in recent years as researchers seek to obtain as much information as possible about the safety and pharmacology of their therapeutics prior to commencing clinical studies.
Toxicological testing of pharmaceuticals has been an important part of regulatory drug R&D for over half a century, and there is now an extensive library of regulations and guidance that researchers must take into account when developing new products or new formulations of existing products.
As each therapeutic is different, there is deliberate flexibility in much of the guidance to ensure that product-specific considerations are investigated. Navigating this guidance effectively forms a major part of a successful partnership between CROs and their customers.
Preclinical Objectives
Non-clinical therapeutic product development is not as straightforward as following a prescriptive list of investigations to satisfy regulators. Studies often contain product-specific measurements, loosely termed ‘biomarkers’, to assess both off-target effects on normal tissue, as well as on-target effects due to the mechanism of the product being taken forward. Both these on- and off-target effects can have dose-limiting implications on the effective use of a chosen therapeutic.
It should be noted that the objectives of this preclinical work are essentially the same, whether you are developing small or large molecule therapeutics. The goal is to understand the potential efficacy, bioavailability and safety of the product in a series of in silico, in vitro and in vivo studies before entering the clinic. However, there are critical differences in how the non-clinical safety testing of biologics has developed, and some of these approaches are now being incorporated into small molecule drug studies.
The term ‘biologics’ refers to newer classes of products that include a wide range of different therapeutic modalities, such as monoclonal antibodies, recombinant proteins, peptides, DNA and RNA oligonucleotides, cell and gene therapies, as well as vaccines. Of course, vaccines have been successfully used clinically for many years, and new approaches to vaccination are continually being implemented. With them comes a need to demonstrate both safety and clinically relevant pharmacology in non-clinical safety studies.
Molecules that make up most, but not all, biologics are amino and nucleic acids. The catabolism of proteins, peptides, DNA and RNA by enzymatic cleavage and subsequent clearance and recycling is well understood, and so the possibility of producing bioactive or toxic metabolites is limited. As a result, the general focus of safety studies for biologics is on on-target effects, and more occasionally on non-target tissue effects – in essence, pharmacology. The emphasis is different in small molecule safety assessment where xenobiotics introduced into the body are cleared by many different mechanisms, all of which can contribute to the toxicity of the product.
Non-Clinical Species
It is important to consider whether the exaggerated pharmacological effects of a biopharmaceutical can be dose-limiting. As a consequence, those studying these effects need to assess the pharmacological response within well-designed and executed safety studies. Researchers are therefore required to perform safety studies in pharmacologically relevant species – those non-clinical species in which the therapeutic has a comparable mode of action to that expected in the clinical setting. This means that species selection is essential, and that a series of in silico, in vitro and in vivo investigations are carried out to evaluate the drug pharmacology in a range of laboratory animals and thus identify the most relevant species.
Small molecule safety programmes typically use a rodent and non-rodent species; however, there is more flexibility in a biologics safety programme. The default position is still to identify a rodent and non-rodent species in which the therapeutic is active, but if this is not possible and only one species exists then a one-species safety programme can be conducted. There are also examples of where there is no relevant species as the therapeutic is only active in humans. In this instance, several other options may be explored, such as using a transgenic animal that expresses the human target, or a surrogate molecule (usually a murine version of the human therapeutic) to generate safety data.
Programme Design
With appropriate scientific justification, certain stand-alone studies that are relevant for small molecule drugs may be combined with other studies when developing biologics, while some may be excluded altogether. The essential safety data is still collected, but usually in conjunction with other investigations rather than in separate studies. This has the added benefit of reducing the total number of animals used in such investigations, but has the knock-on effect of making this research far more complex.
As with all generalities, there are exceptions. Not all biologics are made up of ‘naturally occurring’ molecules, some have been extensively chemically modified. This can mean that hybrid new chemical entity/biologics approaches are undertaken to assess the safety profile of those modified components. These challenges – including the need to demonstrate clinically relevant pharmacology on studies – underline that the designs of biologics safety programmes require a great deal of understanding of the therapeutics’ mode of action.
Expected Biology
So, while some differences exist in the approach taken to assess the non-clinical safety of small and large molecule therapeutics, there are greater similarities. As discussed, there are potential off-target toxicities that need to be investigated for xenobiotics, where the selection of a relevant species is just as critical. For example, some drugs produce specific metabolites, relevant in the clinical setting, that are not reproduced in all non-clinical species. In these cases, the toxicity of the therapeutic may need to be evaluated in species that produce a similar metabolic profile to that in human. If the metabolite is human-specific, it may be necessary to also test the safety of that human metabolite in a relevant safety testing species.
Equally, the importance of dose-limiting pharmacology can be a critical investigation, and this may be explored in non-clinical safety studies. In practice, this means that many product-specific biomarkers of drug intervention are now included on safety studies to measure the pharmacology of the drug, in addition to traditional safety endpoints. Also, specific safety markers may be included to assist in the selection of safe clinical doses. In all cases, the expected biology of the therapeutic must be well-understood in order to design product-specific packages that stand up to regulatory scrutiny and predict clinical safety.
Bioanalytical Support
With an increasing focus on including biomarkers to measure all manner of potential toxicities as well as pharmacodynamics on studies, one of the biggest barriers to being able to support non-clinical product development is the bioanalytical support required. Many of the complex biological responses measured are focused on specific therapeutic areas: CROs that operate in preclinical areas are building their knowledge and experience across a wide range of therapeutic areas and adapting their service offerings to provide customers with a better understanding of drug mechanism of action on safety studies.
A very translational approach to study design and execution can be offered – from early programme design and the identification of relevant biomarkers for use on the project, through to problem-solving in the review of findings from these complex biological systems –placing well-equipped CROs as an essential partner in the product R&D pathway.
