Development and validation of 3D in vitro dormant myeloma cell models to reduce and replace animal studies

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Scientific importance: Multiple myeloma (MM) is a B cell cancer caused by the growth of malignant plasma cells in the bone marrow (BM). It remains incurable, despite the development of therapies that target myeloma cell (MC)-intrinsic pathways. Disease relapse is thought to originate from dormant MCs, localised in specialised endosteal niches, which resist chemotherapy and repopulate the tumour [1, 2]. We have previously tracked individual MC's in vivo by multi-photon imaging as they colonise the endosteal niche, enter a dormant state and subsequently become activated to form colonies [1]. MC dormancy has been demonstrated to be a reversible state that is switched 'on' by engagement with osteoblasts (in the endosteal niche) and 'off' by osteoclastic bone resorption. We have determined dormant MCs are resistant to the chemotherapy melphalan that targets dividing cells. The demonstration that the endosteal niche is pivotal in controlling MC dormancy highlights the potential for targeting cell-extrinsic mechanisms to overcome cell-intrinsic drug resistance and prevent disease relapse. To recapitulate the BM microenvironment in an in vitro setting is highly challenging because of the cellular complexity, vasculature and 3-dimensional (3D) bone structure. However, since we know osteoblasts play a key role in MC dormancy and they reside on bone surfaces in close proximity to the extracellular matrix (ECM), this will provide a platform to mimic this in vivo aspect in vitro. Therefore, the aim of this 3Rs-focussed PhD studentship is to develop several in vitro 3D models of MC dormancy and then validate them by comparing them to new data and our existing data from established clinically relevant murine models of MC dormancy and drug resistance.Research plan and objectives: We aim to develop and validate several 3D in vitro models of MC dormancy which recapitulates the interaction of MC-osteoblastic cells in the BM microenvironment in vivo i.e. induces MC dormancy. We will do this by assessing and characterising dormant MCs in these newly established 3D in vitro models so they can be used reliability as effective alternatives to murine models of myeloma to assess new and novel anti-myeloma therapies and their mechanisms of action. We hypothesise that in vitro 3D models of MC dormancy will mimic the dormant MC's observed in the endosteal niche in the BM of currently established in vivo pre-clinical models of myeloma.