Cancer treatments are becoming increasingly personalised, informed by both the genotypic and phenotypic characteristics of a patient’s tumour. In order to screen and validate therapeutics in a relevant clinical setting, the use of patient-derived xenograft (PDX) mouse models has increased. Patient tumour tissue is typically isolated and subcutaneously implanted into an immunodeficient mouse, where it can be expanded and maintained by serially passaging cells from mouse to mouse. These models recapitulate tumour heterogeneity as well as retaining molecular profiling specific to the patient but human stromal cells supporting the tumour are replaced with murine stromal cells after implantation. Success rate of implantation is also low favouring particular mutations and aggressive tumours. Better representation of a tumour at a preclinical setting increases the predictivity of the model a response to cancer therapeutics.
Why we funded it
This PhD Studentship aims to replace the need for PDX mice in the long-term expansion of primary breast cancer cells with an in vitro hydrogel-based model.
Publications involving PDX mice are increasing, with the number of publications approximately doubling every two years. In 2014/2015 Google Scholar indicated 6,860 papers were published using PDX models. A standard efficacy study typically requires an average of 20 animals with a further five required to generate the donor cells needed for the study. This gives an estimate of 17,500 animals used for PDX studies per year globally. With the continued increase in publications this will likely increase further, with an estimated 70,000 animals needed for PDX studies in 2020. This estimate is solely based on published studies and excludes animals used in industry.
The hydrogel for this model is formed from a self-assembling peptide creating a bespoke matrix environment with similar physical properties to the extracellular matrix (ECM). Further improvements to the model can be made by adding ECM components, such as collagens, glycoproteins and proteoglycans, as it is known differential expression of these molecules contributes to tumour progression. One of the current issues of in vitro culture is the ability of cancer cells to adapt to in vitro conditions, which can result in alterations to both genetic information and biological properties. To ensure genotypic and phenotypic stability after time in culture and passaging, the in vitro hydrogel-based model will be verified by comparison with the original patient tissues.
There is growing use of patient-derived xenograft (PDX) models, whereby patient tumours are implanted subcutaneously in immunodeficient animals. Such models are more refined than standard cancer models due to better representation of the heterogeneity of disease and drug response observed in the clinic. However, such close-to-patient cells cannot be grown in standard culture and are maintained in vivo via regular passage, using large numbers of animals. At a conservative estimate, 1000 PDX models are being derived and passaged at any one time. We intend to investigate an in vitro 3D peptide hydrogel system to replace use of animals for passaging these cells; if only 2 animals are being used to maintain each model currently being passaged, and passage takes place once every 6 weeks, this equates to 16,000 animals per year which would no longer be used, thus reducing the numbers of animals used for this purpose. The peptide hydrogel system allows formation of a fully defined, stable, bespoke nanofiber matrix, with dimensionality similar to native ECM and relevant bioactive ECM motifs/glycans. In ongoing NC3Rs-funded research it is being used to develop a human breast tissue model. Our main objectives are to extend this research by investigating this novel culture system’s ability to support the growth of PDX-derived primary breast cancer cells outside of animals; determine the influence of modifications to the systems associated with the breast cancer microenvironment e.g. addition of specific extracellular matrix components or stromal cells such as cancer-associated fibroblasts; and verify maintenance of genotype and phenotype of the cancer cells over passage. In addition, to ensure widespread adoption and maximise impact, we will investigate the ability of the system to be scaled-up for generating larger numbers of cells for downstream applications and for cells within the hydrogel to be cryopreserved for shipment to other laboratories.