Abstract Patient derived xenograft (PDX) models are regarded as gold standard preclinical models in leukaemia research, especially in testing new drug combinations where typically 45-50 animals are used per assay. 9000 animal experiments are performed annually in leukaemia research with these expensive procedures being described as moderate severity, meaning they cause significant pain, suffering and visible distress to animal’s state. Furthermore, not all clinical leukaemia samples engraft and when they do data turnaround time can be between 6-12 months. Heavy dependence on animal models is because clinical leukaemia samples do not proliferate in vitro. Alternative cell line models though popular for drug testing are not biomimetic – they are not dependent on the microenvironment for survival, growth and treatment response and being derived from relapse samples they do not capture the molecular complexity observed at disease presentation. Here we have developed an in vitro platform to rapidly establish co-cultures of patient-derived leukaemia cells with 3D bone marrow mesenchyme spheroids, BM-MSC-spheroids. We optimise protocols for developing MSC-spheroid leukaemia co-culture using clinical samples and deliver drug response data within a week. Using three patient samples representing distinct cytogenetics we show that patient-derived-leukaemia cells show enhanced proliferation when co-cultured with MSC-spheroids. In addition, MSC-spheroids provided improved protection against treatment. This makes our spheroids suitable to model treatment resistance – a major hurdle in current day cancer management Given this 3Rs approach is 12 months faster (in delivering clinical data), is a human cell-based biomimetic model and 45-50 animals/drug-response assay cheaper the anticipated target end-users would include academia and pharmaceutical industry. This animal replacement prototype would facilitate clinically translatable research to be performed with greater ethical, social and financial sustainability. Research Highlights Scientific Benefit A 3D spheroid-based approach for ex vivo co-culture of clinical leukaemia samples for further investigation into cancer biology such as blast-niche interactions, blast proliferation and treatment resistance 3Rs Benefit To replace moderate severity animal procedures in leukaemia research and drug testing Practical Benefit 3Rs approach that yields drug response data quickly and is more ethically, socially and financially sustainable than its in vivo counterparts Current applications Exploration of leukaemia biology such as blasts proliferation, blast-niche interactions, niche-impacted treatment resistance and obtain drug response data Potential applications Extend the approach to include other haematological cancers as well as bone cancers.

A human mesenchymal spheroid prototype to replace moderate severity animal procedures in leukaemia drug testing