Abstract 2974: Targeting CD38 inhibits metabolic capacity of acute myeloid leukemia in the tumour microenvironment
Authors: Mistry Jayna J. , Moore Jamie A. , Marlein Christopher R. , Hellmich Charlotte , Pillinger Genevra , Di Palma Federica , Collins Angela , Bowles Kristian M. , Rushworth Stuart A. 
Published: September 2020

Abstract
Acute myeloid leukaemia (AML) causes 85,000 global deaths per year, which is estimated to double by 2040. AML has been shown to be highly dependent on the bone marrow (BM) microenvironment. Mesenchymal stromal cells (MSC) specifically, play an important pro-tumoral role. We previously demonstrated AML blasts rely on higher mitochondrial content and are more dependent on oxidative phosphorylation compared to non-malignant unstimulated CD34+ progenitor cells. To achieve this high metabolic demand, functional mitochondria are transferred from the MSC to the AML blasts. Mitochondrial transfer has also been demonstrated in myeloma in a pro-tumoral process regulated by CD38. Taken together, these data indicate that mitochondria are a biologically plausible and attractive drug target in the treatment of AML.We investigated the role mitochondrial transfer and the subsequent metabolic consequences of inhibiting CD38 using daratumumab on the AML BM microenvironment.Primary AML blasts and MSC were isolated from patient's BM. Mitochondrial transfer was assessed by coculture of AML and MSC in vitro using both qPCR DNA analysis and flow cytometry analysis. We used an NSG xenograft mouse model of AML, we transplanted OCI-AML3-luc, and treated the animals with either vehicle control (PBS) or daratumumab (5mg/kg) on day 9 and 16 followed by bioluminescence imaging. Post transplantation, AML mitochondrial transfer was assessed by murine mitochondrial DNA in human AML blasts by species specific PCR analysis. Post transplantation mitochondrial health and function was measured by TMRM and Seahorse analysis.Targeting CD38 using daratumumab inhibits the transfer of mitochondria from MSC to AML in vitro. In vivo, treatment with daratumumab significantly reduced tumor burden and improved survival compared to untreated controls. Additionally, we found two doses of daratumumab resulted in reduced mitochondrial potential, mitochondrial content and oxygen consumption rate in the AML cells sorted from the human xenograft mouse model. Finally, analysis of human AML cells sorted from NSG mouse BM showed reduced levels of mouse mitochondrial DNA in the human AML blasts from daratumumab treated mice compared to mice with AML treated with vehicle control.CD38 inhibition by daratumumab treatment inhibits mitochondrial transfer from MSC to AML blasts in the BM microenvironment. This results in a reduction in oxidative phosphorylation in AML blasts and subsequent reduced leukemia growth, which in turn results in improved NSG/AML animal survival. Whilst it is probable that daratumumab has a number of mechanisms of action, here we demonstrate inhibition of mitochondrial transfer is an addition to the list for this drug in AML. These data support the further clinical investigation of daratumumab based chemotherapeutic strategies as a therapeutic approach for the treatment AML.
Citation Format: Jayna J. Mistry, Jamie A. Moore, Christopher R. Marlein, Charlotte Hellmich, Genevra Pillinger, Federica Di Palma, Angela Collins, Kristian M. Bowles, Stuart A. Rushworth. Targeting CD38 inhibits metabolic capacity of acute myeloid leukemia in the tumour microenvironment [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2974.