Acute Myeloid Leukaemia
Since 2008, we have developed a program of work studying the pathways and processes which underpin the initiation, progression and drug resistance of Acute Myeloid Leukaemia (AML). Early work initially looked at intra-cellular pro-survival responses to cytotoxic stress and identified pro-tumoral roles for HO-1 (Rushworth et al, 2010), FLIP1 (Rushworth et al, 2010), NRF-2 (Rushworth et al, 2011; Rushworth et al, 2012) and BTK (Rushworth et al, 2014) in AML proliferation. We extended our studies to identify cell surface SDF1/CXCR4 (Zaitseva et al, 2014), CD117 (Rushworth et al, 2015) and FLT3-ITD (Pillinger et al, 2015) as receptors which signal through BTK in AML cells. This work subsequently led to clinical trials of ibrutinib in AML patients.
During this time we were the first to report the anti-platelet effect of ibrutinib as the cause for the bleeding observed in the early phase clinical trials of patients with leukaemia and lymphoma (Rushworth et al, 2013).
As we developed our understanding of AML we increasingly came to recognise the disease as a 'tissue' rather than a 'cell'. We developed our studies to look at the fundamental role of the 'non-malignant' cells in the bone marrow microenvironment in supporting tumour growth. We found that hypoxia drives AML blasts to secrete macrophage migratory inhibitory factor (MIF) (Abdul-Aziz et al, 2017) which in turn up-regulates pro-tumoral IL-6 and IL-8 release from the bone marrow stromal cells (BMSC) in the leukaemia micro-environment (Abdul-Aziz AM et al, 2018). In addition we have identified novel AML regulated changes in tumour metabolism. AML induces bone marrow adipocytes to breakdown triglyceride and release free fatty acid which then promotes leukaemia growth (Shafat et al, 2017) and AML blasts steal mitochondria from neighbouring bone marrow mesenchymal stromal cells (BMSC) to support ATP production via oxidative phosphorylation in the blast cells (Marlein et al, 2017). In human AML we discovered that it is AML derived NOX2 which generates superoxide, which in turn stimulates BMSC to AML blast transfer of mitochondria through AML-derived tunneling nanotubes (Marlein et al, 2017). Furthermore we have found that a prerequisite for BMSC to AML mitochondrial transfer is tumour driven up-regulation of mitochondrial biogenesis in the BMSC (Marlein et al, 2018).
We continue to investigate the functions of the 'non-malignant' cells of the AML tumour with a view to improving the understanding of the biology of leukaemia and the identification of new targets for treating patients.
Since 2011, we have extended our work to studies on another type of bone marrow/ blood cancer, Multiple Myeloma (MM). Initially we concentrated on intra-cellular pro-survival signalling in response to cytotoxic stress and chemotherapy drugs. We identified roles pro-tumoral roles for HO-1 (Barrera et al, 2012) and BTK (Rushworth et al, 2013) as well as microRNA125b (Murray et al, 2013) in MM proliferation. Moreover we found that in MM, BTK inhibition acts synergistically with proteasome inhibitors (e.g. bortezomib) and IMIDs (e.g. lenalidomide) (Rushworth et al, 2013) to kill malignant plasma cells. In relapsed disease, we identified the BTK pathway as important in bortezomib resistance and that BTK inhibition appeared to re-sensitise MM cells to proteasome inhibitor treatment (Murray et al, 2015). These studies have subsequently resulted in a number of clinical trials of the BTK inhibitor ibrutinib in MM patients.
In parallel with our work in AML we increasingly came to appreciate that MM functioned more as a 'tissue' rather than a 'cell'. As in the AML work (above) we shifted our focus in MM to look at the part the 'non-malignant' cells in the bone marrow microenvironment played in supporting tumour growth. We have identified isoform specific functions of PI3Kγ and PI3Kδ in the MM micro-environment (Piddock et al, 2017). We have also found a pro-tumoral interaction between MM cells and the BMSC, whereby MM-derived macrophage migratory inhibitory factor (MIF) causes BMSC secretion of IL-6 and IL-8 via BMSC cMYC (Piddock et al, 2018). Furthermore, we show that the cMYC inhibitor JQ1 can reduce BMSC secreted IL-6 in vivo, irrespective of tumour burden (Sun et al, 2017). These data provide evidence for the clinical evaluation of both MIF and cMYC inhibitors in the treatment of MM.
More recently we have expanded our studies to investigate some of the metabolic processes involved in myeloma disease progression and chemotherapy resistance. We have identified that MM cells use mitochondrial-based metabolism as well as glycolysis when located within the bone marrow microenvironment. The reliance of MM cells on oxidative phosphorylation was mediated by intercellular mitochondrial transfer to MM cells from neighbouring non-malignant BMSC. This mitochondrial transfer occurs through tumor-derived tunneling nanotubes (TNT). Moreover, shRNA mediated knockdown of CD38 inhibits mitochondrial transfer and TNT formation in-vitro and blocks mitochondrial transfer and improves animal survival in vivo. This work describes a potential treatment strategy to inhibit mitochondrial transfer for clinical benefit and scientifically expands the understanding of the functional effects of mitochondrial transfer on tumour metabolism (Marlein et al, 2019).
We continue to investigate tumour metabolism and the functions of the 'non-malignant' cells in MM, with a view to improving the understanding of the biology of MM and the identification of new targets for treating patients.
Bone marrow microenvironment: ageing, senescence and infection
Our studies on the tumour microenvironment have developed into our latest stream of work investigating the effects of infection, senescence and ageing on the bone marrow.
We have found that AML cells induce a senescent associated secretory phenotype (SASP) in the BM microenvironment, which supports the survival and proliferation of the leukaemic blasts. The senescence response and SASP is driven by superoxide generated locally by the tumour and targeting these senescent p16INK4a-expressing stromal cells slows leukaemia growth (Abdul-Aziz*, Sun*, Hellmich* et al. 2019).
Under the stress of acute bacterial infection, hematopoietic stem cells (HSCs) within the bone marrow undergo rapid expansion in order to rapidly facilitate the hosts immune response. We have shown that infection by Gram-negative bacteria drives an increase in mitochondrial mass in mammalian HSCs, which results in a metabolic transition from glycolysis toward oxidative phosphorylation. We discovered that mitochondria are transferred from the BMSCs into HSCs under the regulation of superoxide and importantly, that mitochondrial transfer occurs before an increase in mitochondrial biogenesis, in a system which has evolved in mammals to generate the intracellular energy necessary to drive the required rapid granulocytic response to bacterial infection (Mistry*, Marlein* et al, 2019). Moreover, we think it likely that these mechanisms, which support bone marrow cell metabolism and which are hi-jacked by AML (Marlein et al, 2017; Marlein et al, 2018) and myeloma (Marlein et al, 2019) to support tumor growth, are a fundamental reason why blood cancers arising in the bone marrow microenvironment are presently so difficult to treat.
Work is ongoing to further develop our understanding of stress, age and senescence on bone marrow function in the benign and malignant setting, with a view to developing improved treatments for cancer and age-related diseases.