The current strategy for the preclinical assessment of novel molecules for the treatment of solid tumours involves efficacy assessment in animal models. These models involve a xenograft tumour implanted subcutaneously in the animal, typically in mice. However, these models are not always good predictors of a molecule’s activity in humans and can require the use of large numbers of animals. In vitro methods can indicate whether a drug successfully interacts with the intended target but currently cannot accurately mimic pharmacokinetic or metabolic events.
Why we funded it
This Project Grant aims to reduce the numbers of xenograft mouse models required in preclinical cancer studies using a hollow fibre assay (HFA) for validation of target-drug interactions.
Use of the HFA allows for the reduction of mice required for preclinical assessment as several fibres can be transplanted into one animal. Approximately eight mice are needed per group in a xenograft study to generate appropriate statistical power. Preliminary evidence suggests the HFA assay requires three mice per group for a similar statistical power. The assays are short-term, seven to ten days, compared to xenograft studies which can take up to in excess of three weeks. The use of the fibre also means there is a reduction in tumour burden, which if excessive can cause pain and discomfort.
The HFA uses biocompatible PVDF hollow fibres designed to allow free passage of macromolecules and drugs but restricts the passage of cells. These fibres are loaded with human tumour cells, heat-sealed at both ends and surgically transplanted subcutaneously, or intraperitoneally, into anaesthetised mice. Animals are treated with the test agent from day three for four consecutive days, with studies terminated on day seven or day ten. The tumour cells from the fibre are then analysed for viability, with untreated cells compared to treated cells to determine the effect of the agent. One benefit of the HFA is the ability to use specifically engineered target-expressing tumour cell lines, which may not be tumourigenic in vivo but could grow in the fibre.
The current strategies employed for the preclinical assessment of novel therapeutics usually involve the assessment of efficacy in subcutaneous xenograft (and allograft) tumour models in mice. These models are often poorly predictive of activity in man. This is because unlike the original tumour, these subcutaneous tumours are usually encapsulated and have radically altered growth characteristics.
Modern drug discovery is target driven, i.e. molecules are designed to interact with clinically relevant targets expressed in human cancers, and thus a better system is sought where evidence of target interaction and efficacy of the compound is obtained.
Although in vitro assays can indicate if drug / target interactions have occurred, it is not possible to mimic pharmacokinetic or metabolic events, or ascertain therapeutic index, and thus it is necessary to use some sort of in vivo system to take these factors into account.
We propose utilisation of an in vivo hollow fibre assay (HFA), currently used by the NCI and ourselves as a general screening tool, as a basis of such a system. We believe adoption of this system would lead to significant reduction in the numbers of animals used world-wide for anti-tumour efficacy studies, with the important refinements of there being no ‘indigenous’ tumour burden and a shorter assay time leading to reduced exposure of the animal to procedures.
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