Interaction between leukaemic cells and the bone marrow stroma

Mesenchymal stromal cells (MSC) enhance growth and protect leukaemic cells from drug-induced toxicity in the bone marrow microenvironment (BMM), however, these interactions are not fully understood and less is known about the impact of leukaemic cells on supportive MSC. The nucleoside-analogue, cytarabine (ara-C), has for several decades been the mainstay of chemotherapy regimens for acute myeloid leukaemia (AML), despite poor efficacy. Despite research efforts, chemoresistance mechanisms are heterogeneous between patients or remain unknown. Additionally, DNA damage following chemotherapy treatment can persist in patient bone marrow (BM)-MSC. This genotoxicity hinders functionality and may be implicated in long-term complications including hematopoietic failure and secondary malignancies. This study aimed to further elucidate the mechanisms by which BM stromal cells interact with leukaemic cells, leading to changes in chemosensitivity and implicated in poor response/relapse in leukaemia.This study utilised an in vitro trans-well co-culture model for assessment of leukaemic-stromal interactions, both with the leukaemic cell lines HL-60 and K562, combine with the BM stromal cell line HS-5 or primary patient MSC. Protection of leukaemic cells by stromal cells from ara-C cytotoxicity in this study confirmed evidence in the literature, both by unidirectional and bidirectional interactions. Altered ara-C genotoxicity by leukaemic-stromal crosstalk was shown for the first time in this work; stromal cells were sensitised to genotoxicity, while leukaemic cells were themselves protected in co-culture. Expression of hENT1 was not altered by co-culture, however bidirectional interactions did cause differential cytokine secretion, with macrophage migration-inhibitory factor (MIF) secretion decreased in co-culture. Separation of cells uncovered opposing MIF secretion profiles with high (HL-60) and low (K562) ara-C sensitive cells, but this was not correlated to chemosensitivity when MIF was enhanced or inhibited.Overall, this thesis contributes evidence that the BMM is remodelled to benefit haematological malignancies, with evidence of altered cytokine secretion and drug handling by leukaemic-stromal interactions. Chemoresistance involves a network of interlinking mechanisms which are compounded by patient heterogeneity. This study shows for the first time that leukaemic-stromal interactions alter ara-C genotoxicity and provides a basis for future research to fully understand how cells in the BMM can be targeted. This could potentially improve patient outcomes and reduce the long-term complications of current therapies in AML