Word count for text: 2779; abstract: 145, figure 7; reference count: 30 2 Key points• Functional mitochondria are transferred in-vivo from BMSC to the leukemic blast.• AML derived NOX-2 drives transfer of mitochondria via the generation of superoxide. AbstractImprovements in the understanding of the metabolic cross-talk between cancer and its micro-environment is expected to lead to novel therapeutic approaches. Acute myeloid leukemia (AML) cells have increased mitochondria compared to nonmalignant CD34+ hematopoietic progenitor cells. Furthermore, contrary to the Warburg hypothesis, (AML) relies on oxidative phosphorylation to generate ATP.Here we report that in human AML NOX2 generates superoxide, which stimulates bone marrow stromal cells (BMSC) to AML blast transfer of mitochondria through AML derived tunnelling nanotubes. Moreover, inhibition of NOX2 was able to prevent mitochondrial transfer, dramatically increase AML apoptosis and increase NSG mouse survival. Conversely, mitochondrial transfer could only be stimulated from BMSC to non-malignant CD34+ cells in response to oxidative stress. However, NOX2 inhibition had no detectable effect on non-malignant CD34+ cell survival.Taken together we identify tumor-specific dependence on NOX2 driven mitochondrial transfer as a novel therapeutic strategy in AML. 3Acute myeloid leukemia (AML) is an aggressive disease that originates in the bone marrow from malignant transformation of a myeloid progenitor cell. AML can occur at any age but primarily affects the elderly, with the average age at diagnosis of 72 years and three quarters of patients diagnosed after the age of sixty 1 . Despite existing cytotoxic treatments directly targeting the leukemic cell two-thirds of younger adults and 90% of older adults will die of their disease 2 . Moreover, current aggressive chemotherapy regimens are often poorly tolerated by the older less fit patients. Improved outcomes are expected to be achieved through novel therapies which are developed from an improved understanding of the biology of the disease.AML blasts cultured in vitro undergo high levels of apoptosis, however the tumor rapidly proliferates in vivo demonstrating that the tissue microenvironment plays a fundamental role in the development of AML disease 3,4 . . It is also established that AML cells have higher mitochondria levels compared to non-malignant haematopoietic stem cells 10,11 , which is entirely consistent with the observations that the tumor is dependent on a mitochondrial ATP production pathway. This proposes a key question; are the additional mitochondria in the AML blasts generated within the tumor cell or have they been acquired?For a long time mitochondria were thought to be retained in their somatic cell for their Monitoring Primer Set and the rLV.EF1.mCherry-mito-9 Lentivirus were purchased from Clontech Takara Bio Europe (Saint-Germain-en-Laye, France). Murine mitochondrial to nuclear DNA ratio kit was purchased from Detroit R&D (Detroit, MI, USA). All other reagents were obtained from Sigma-Aldr...

Key Points• Bone marrow adipocytes support AML survival.• AML induces adipocyte lipolysis of triglyceride to free fatty acids and subsequent transport by FABP4. Abstract

Metabolic adjustments are necessary for the initiation, proliferation, and spread of cancer cells. Although mitochondria have been shown to move to cancer cells from their microenvironment, the metabolic consequences of this phenomenon have yet to be fully elucidated. Here, we report that multiple myeloma cells use mitochondrial-based metabolism as well as glycolysis when located within the bone marrow microenvironment. The reliance of multiple myeloma cells on oxidative phosphorylation was caused by intercellular mitochondrial transfer to multiple myeloma cells from neighboring nonmalignant bone marrow stromal cells. This mitochondrial transfer occurred 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 study 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 tumor metabolism.Significance: Multiple myeloma relies on both oxidative phosphorylation and glycolysis following acquisition of mitochondria from its bone marrow microenvironment.