CD38-Driven Mitochondrial Trafficking Promotes Bioenergetic Plasticity in Multiple Myeloma

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.See related commentary by Boise and Shanmugam, p. 2102.

Abstract 4970: Mitochondrial trafficking in the bone marrow microenvironment promotes bioenergetic flexibility in multiple myeloma

Multiple myeloma (MM) is an incurable malignancy of terminally differentiated plasma cells which is highly dependent on the bone marrow microenvironment (BMM). MM tumor survival, proliferation and drug resistance is reliant on ATP production however the mechanisms by which the malignant cells generate ATP are poorly defined. In this study, we investigate the contributions of oxidative phosphorylation and aerobic glycolysis to tumor cell ATP generation within BMM. Furthermore, we address whether ATP generation within tumor cells is enabled by the transfer of mitochondria from the non-malignant stromal cells of the BMM to the malignant plasma cell.

Bone marrow was obtained from patients under approval from the UK Health Research Authority. In-vivo experiments were performed with local Animal Welfare and Ethical Review Board approval and under license from the UK Home Office.

Using Seahorse extracellular flux analysis we show that primary MM cells have high baseline rates of mitochondrial respiration compared to MM cell lines. Furthermore, mitochondrial respiration rates increased ex-vivo after co-culture with non-malignant bone marrow stromal cells (BMSC). We engrafted the malignant MM1S cell line into NSG mice and examined the mitochondrial respiration rate from isolated tumor cells compared to MM1S cells cultured in-vitro. We found increased rates of mitochondrial respiration in MM1S cells isolated from mouse BM. To determine whether the increase in tumor oxidative phosphorylation observed in the presence of micro-environment cells was a result of mitochondrial transfer from BMSC to MM, we used three methods. Firstly we stained BMSC with the mitochondrial stain MitoTracker Green and cultured these with primary MM cells. Using a combination of flow cytometry and confocal microscopy we detected MitoTracker fluorescence in the MM cells after co-culture, showing that the stained mitochondria are transferred from BMSC to MM cells in-vitro. Secondly, mitochondrial transfer was directly observed between BMSC and MM cells, visualized by the acquisition of a mCherry labeled mitochondrial protein we transfected into BMSC. Finally, using a human MM cell line engrafted into an NSG mouse xenograft model, we detected murine mitochondrial DNA in sorted human MM1S and U266 tumor cells post-transplant. Through fixed cell confocal microscopy we found that mitochondria move through tunnelling nanotubes (TNTs), and inhibition of TNT formation by treatment with cytochalasin B resulted in reduced mitochondrial transfer and tumor cell oxidative phosphorylation.

Here we show that MM cellular metabolism favors oxidative phosphorylation over glycolysis, in the setting of the BMM. This is due to mitochondrial transfer occurring between non-malignant BMSC and malignant plasma cells. This process is necessary for optimum tumor growth in-vivo and forms part of the malignant phenotype of MM.

Citation Format: Christopher R. Marlein, Rachel E. Piddock, Charlotte Hellmich, Lyubov Zaitseva, Martin J. Auger, Kristian M. Bowles, Stuart A. Rushworth. Mitochondrial trafficking in the bone marrow microenvironment promotes bioenergetic flexibility in multiple myeloma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4970.

Abstract 2123: Myeloma derived macrophage inhibitory factor regulates BMSC IL6/8 via cMYC

Background

Multiple Myeloma (MM) is a plasma cell malignancy dependent on the bone marrow microenvironment. Macrophage inhibitory factor (MIF) acts directly on malignant plasma cells affecting homing and chemotherapy resistance, however the adaptive effect that MM derived MIF has on the tumor microenvironment is not yet defined. Here we investigate the function of MM derived MIF in the MM microenvironment by examining its effects on bone marrow mesenchymal stromal cells (BMSC).

Methods

Primary MM and BMSC were obtained from patient bone marrow. Proteome Profiler Human XL Cytokine Array was used. Inhibitors including JQ1 were

purchased from Merck. In-vivo experiments were performed using 8-10 week old NSG mice.

Results

First we injected 1 x 106 MM.1S MIF-knock down (KD) cells or MM.1S control-KD cells (containing the pCDH-luciferase-T2A-mCherry construct) into the tail vein of 6-8 week old NSG mice. MIF-KD in MM cells resulted in animals with significantly reduced tumor burden and improved overall survival. To further investigate the role of MIF in regulating the BM microenvironment we stimulated primary human BMSC with biologically appropriate doses of recombinant MIF and then used Human XL Cytokine Array and cytokine specific ELISA to assay the supernatant from these MIF stimulated BMSC. Results show that MIF induces IL-6 and IL-8 protein secretion from primary BMSC. To examine the mechanism of action of these observations we used a panel of inhibitors to screen for potential pathways responsible for MIF induced BMSC derived IL-6 and IL-8 expression. The c-Myc inhibitor JQ1 inhibited MIF induced IL-6 and IL-8 expression. Next, we looked at whether c-Myc regulates BMSC pro-tumoral interleukin production in-vivo. We injected NSG mice via the tail vein with human myeloma cell line U266 and then randomized animals to two groups; treating with either JQ1 (50mg/kg, IP) or alternatively vehicle control for 5 days, after which bloods were taken

to assess murine IL-6 levels (IL-8 is deleted from the mouse genome). Results show that murine IL-6 was significantly reduced in the JQ1 treated animals (carrying human MM) compared to vehicle control treated animals.

Summary

MM derived MIF is pro-tumoral through induction of c-Myc and downstream IL-6 and IL-8 in the BMSC of the tumor micro-environment. Identification of this novel pro-tumoral crosstalk mechanism which exists between MM and the bone marrow stroma provides scientific rationale for the clinical evaluation of new therapeutic targets in MM.

Citation Format: Rachel E. Piddock, Christopher R. Marlein, Amina Abdul-Aziz, Martin J. Auger, Kristian M. Bowles, Stuart A. Rushworth. Myeloma derived macrophage inhibitory factor regulates BMSC IL6/8 via cMYC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2123.

Myeloma-derived macrophage inhibitory factor regulates bone marrow stromal cell-derived IL-6 via c-MYC

Abstract

Multiple myeloma (MM) remains an incurable malignancy despite the recent advancements in its treatment. The protective effects of the niche in which it develops has been well documented; however, little has been done to investigate the MM cell’s ability to ‘re-program’ cells within its environment to benefit disease progression. Here, we show that MM-derived macrophage migratory inhibitory factor (MIF) stimulates bone marrow stromal cells to produce the disease critical cytokines IL-6 and IL-8, prior to any cell-cell contact. Furthermore, we provide evidence that this IL-6/8 production is mediated by the transcription factor cMYC. Pharmacological inhibition of cMYC in vivo using JQ1 led to significantly decreased levels of serum IL-6—a highly positive prognostic marker in MM patients.

Conclusions

Our presented findings show that MM-derived MIF causes BMSC secretion of IL-6 and IL-8 via BMSC cMYC. Furthermore, we show that the cMYC inhibitor JQ1 can reduce BMSC secreted IL-6 in vivo, irrespective of tumor burden. These data provide evidence for the clinical evaluation of both MIF and cMYC inhibitors in the treatment of MM.

Electronic supplementary material

The online version of this article (10.1186/s13045-018-0614-4) contains supplementary material, which is available to authorized users.

HIF1α drives chemokine factor pro-tumoral signaling pathways in acute myeloid leukemia

Approximately 80% of patients diagnosed with acute myeloid leukemia (AML) die as a consequence of failure to eradicate the tumor from the bone marrow microenvironment. We have recently shown that stroma-derived interleukin-8 (IL-8) promotes AML growth and survival in the bone marrow in response to AML-derived macrophage migration inhibitory factor (MIF). In the present study we show that high constitutive expression of MIF in AML blasts in the bone marrow is hypoxia-driven and, through knockdown of MIF, HIF1α and HIF2α, establish that hypoxia supports AML tumor proliferation through HIF1α signaling. In vivo targeting of leukemic cell HIF1α inhibits AML proliferation in the tumor microenvironment through transcriptional regulation of MIF, but inhibition of HIF2α had no measurable effect on AML blast survival. Functionally, targeted inhibition of MIF in vivo improves survival in models of AML. Here we present a mechanism linking HIF1α to a pro-tumoral chemokine factor signaling pathway and in doing so, we establish a potential strategy to target AML.

Targeting PI3Kδ and PI3Kγ signalling disrupts human AML survival and bone marrow stromal cell mediated protection

Phosphoinositide-3-kinase (PI3K) is an enzyme group, known to regulate key survival pathways in acute myeloid leukaemia (AML). It generates phosphatidylinositol-3,4,5-triphosphate, which provides a membrane docking site for protein kinaseB activation. PI3K catalytic p110 subunits are divided into 4 isoforms; α,β,δ and γ. The PI3Kδ isoform is always expressed in AML cells, whereas the frequency of PI3Kγ expression is highly variable. The functions of these individual catalytic enzymes have not been fully resolved in AML, therefore using the PI3K p110δ and p110γ-targeted inhibitor IPI-145 (duvelisib) and specific p110δ and p110γ shRNA, we analysed the role of these two p110 subunits in human AML blast survival. The results show that PI3Kδ and PI3Kγ inhibition with IPI-145 has anti-proliferative activity in primary AML cells by inhibiting the activity of AKT and MAPK. Pre-treatment of AML cells with IPI-145 inhibits both adhesion and migration of AML blasts to bone marrow stromal cells. Using shRNA targeted to the individual isoforms we demonstrated that p110δ-knockdown had a more significant anti-proliferative effect on AML cells, whereas targeting p110γ-knockdown significantly inhibited AML migration. The results demonstrate that targeting both PI3Kδ and PI3Kγ to inhibit AML-BMSC interactions provides a biologic rationale for the pre-clinical evaluation of IPI-145 in AML.

PI3Kδ and PI3Kγ isoforms have distinct functions in regulating pro-tumoural signalling in the multiple myeloma microenvironment

Phosphoinositide-3-kinase and protein kinase B (PI3K-AKT) is upregulated in multiple myeloma (MM). Using a combination of short hairpin RNA (shRNA) lentivirus-mediated knockdown and pharmacologic isoform-specific inhibition we investigated the role of the PI3K p110γ (PI3Kγ) subunit in regulating MM proliferation and bone marrow microenvironment-induced MM interactions. We compared this with inhibition of the PI3K p110δ (PI3kδ) subunit and with combined PI3kδ/γ dual inhibition. We found that MM cell adhesion and migration were PI3Kγ-specific functions, with PI3kδ inhibition having no effect in MM adhesion or migration assays. At concentration of the dual PI3Kδ/γ inhibitor duvelisib, which can be achieved in vivo we saw a decrease in AKT phosphorylation at s473 after tumour activation by bone marrow stromal cells (BMSC) and interleukin-6. Moreover, after drug treatment of BMSC/tumour co-culture activation assays only dual PI3kδ/γ inhibition was able to induce MM apoptosis. shRNA lentiviral-mediated targeting of either PI3Kδ or PI3Kγ alone, or both in combination, increased survival of NSG mice xeno-transplanted with MM cells. Moreover, treatment with duvelisib reduced MM tumour burden in vivo. We report that PI3Kδ and PI3Kγ isoforms have distinct functions in MM and that combined PI3kδ/γ isoform inhibition has anti-MM activity. Here we provide a scientific rationale for trials of dual PI3kδ/γ inhibition in patients with MM.