Adoption of a long-term in vitro bone model to facilitate investigations into cancer dormancy and bone metastasis

Helen’s award will enable her team to adopt the 3D humanised self-structuring in vitro bone model developed in Dr Amy Naylor’s lab at the University of Birmingham, with an NC3Rs PhD studentship where it will be used to replace mouse models for some studies of cancer dormancy and bone metastasis, focusing on leukaemia and breast cancer. Commonly used mouse models do not accurately mimic these key cancer hallmarks or the severity of the disease. The in vitro bone model enables long-term monitoring, facilitating the identification of mechanisms, biomarkers, and therapeutic targets. The award will also support the wider adoption of the in vitro model by other labs at the Cancer Research UK Scotland Centre where technical support and practical training for researchers will be provided to enable its use for other cancer types including prostate, lung and multiple myeloma.

This project is highly multidisciplinary involving expertise in cancer biology, bone regeneration and bioengineering. This project will repurpose a fully developed and characterised in vitro humanised 3D self-structuring bone model ‘‘SSBM’’ as a relevant alternative to REPLACE and REDUCE the use of mouse models for studying myeloid leukaemia, leukaemic stem cell (LSC) persistence and breast cancer dormancy and bone metastasis. The SSBM form ‘’mini-bone’’ structures, which are created using fibrin hydrogels seeded with osteoblasts, casted between two calcium phosphate anchors points. Over time, the fibrin supports osteoblast maturation and differentiation to osteocytes, bone extracellular matrix (ECM) production and subsequent mineralisation forming a mineralising collagen-rich matrix that recapitulates in vivo native bone. The benefits of the SSBM include the ability to incorporate different cell types and to carry out prolonged cultures for >1 year. At present, no single model system exists, that accurately replicates human bone and its microenvironment. In the solid cancer field there is a real need to find an alternative to REPLACE and REDUCE reliance on mouse models to study cancer dormancy and bone metastasis. Currently no reliable models exist to investigate cancer dormancy in the bone. The current mouse models, used to study metastasis are limited, as most cancers preferentially metastasise to the lungs when transplanted. This often prevents a comprehensive or linear picture of bone metastasis, as visceral organ metastasis occurs quickly, usually within 3-4 weeks, and bone metastasis later, making these studies incomplete due to the necessity to cull animals early. These types of studies are often deemed ‘moderate to severe’, due to the pain associated with bone metastasis. In leukaemia, xenotransplantation of human leukaemic cells into highly immunocompromised mice are the gold standard in vivo models. However, these models are not ideal, with high variability observed between patient samples, low engraftment rates and often the leukaemia, which develops not accurately replicating the human disease. Even then, high numbers of LSCs are required resulting in low engraftment rates ~20% for chronic and 40-66% for acute myeloid leukaemia with <25% developing leukaemia. These assays also entail serial transplantation to assess the self-renewal of LSC, requiring multiple mice for prolonged periods of time. These models only provide a short window of 12-16 weeks to study the disease pathogenesis and carry out drug testing, they don’t facilitate the longer-term studies required to investigate LSC quiescence/dormancy. In breast cancer, bone mediated dormancy, can occur for several years, and is most prevalent in ER+ luminal tumours with approximately 20% of women undergoing late relapse. This inability to accurately recapitulate the cell-intrinsic and micro-environmental factors which maintain dormancy has prevented the development of therapeutic approaches to target the dormant cancer cells. Even for metastatic bone disease which is more widely studied, therapies are deficient and once cancer invades bone tissue the cancer is widely untreatable. Research focusing on dormancy and bone metastasis has therefore been limited by the lack of clinically relevant models. Adoption of this SSBM by the cancer field would lead to widespread benefits: it would enhance our scientific knowledge of the endosteal niche, cancer dormancy and bone metastasis; provide a system to identify potential biomarkers to predict patients who are likely to develop bone metastasis and relapse; enable researchers to identify underlying mechanisms and therapeutic targets for better treatments to prevent relapse, ultimately improving longer-term outcomes for patients.