The Route of the Malignant Plasma Cell in Its Survival Niche: Exploring “Multiple Myelomas”

Targeting of mitochondrial fission through natural flavanones elicits anti-myeloma activity

BACKGROUND

Mitochondrial alterations, often dependent on unbalanced mitochondrial dynamics, feature in the pathobiology of human cancers, including multiple myeloma (MM). Flavanones are natural flavonoids endowed with mitochondrial targeting activities. Herein, we investigated the capability of Hesperetin (Hes) and Naringenin (Nar), two aglycones of Hesperidin and Naringin flavanone glycosides, to selectively target Drp1, a pivotal regulator of mitochondrial dynamics, prompting anti-MM activity.

METHODS

Molecular docking analyses were performed on the crystallographic structure of Dynamin-1-like protein (Drp1), using Hes and Nar molecular structures. Cell viability and apoptosis were assessed in MM cell lines, or in co-culture systems with primary bone marrow stromal cells, using Cell Titer Glo and Annexin V-7AAD staining, respectively; clonogenicity was determined using methylcellulose colony assays. Transcriptomic analyses were carried out using the Ion AmpliSeq™ platform; mRNA and protein expression levels were determined by quantitative RT-PCR and western blotting, respectively. Mitochondrial architecture was assessed by transmission electron microscopy. Real time measurement of oxygen consumption was performed by high resolution respirometry in living cells. In vivo anti-tumor activity was evaluated in NOD-SCID mice subcutaneously engrafted with MM cells.

RESULTS

Hes and Nar were found to accommodate within the GTPase binding site of Drp1, and to inhibit Drp1 expression and activity, leading to hyperfused mitochondria with reduced OXPHOS. In vitro, Hes and Nar reduced MM clonogenicity and viability, even in the presence of patient-derived bone marrow stromal cells, triggering ER stress and apoptosis. Interestingly, Hes and Nar rewired MM cell metabolism through the down-regulation of master transcriptional activators (SREBF-1, c-MYC) of lipogenesis genes. An extract of Tacle, a Citrus variety rich in Hesperidin and Naringin, was capable to recapitulate the phenotypic and molecular perturbations of each flavanone, triggering anti-MM activity in vivo.

CONCLUSION

Hes and Nar inhibit proliferation, rewire the metabolism and induce apoptosis of MM cells via antagonism of the mitochondrial fission driver Drp1. These results provide a framework for the development of natural anti-MM therapeutics targeting aberrant mitochondrial dependencies.

Editorial: 'Engineering the Tumor Immune Microenvironment' Special Issue

Cancer immunotherapies, while promising and occasionally even curative, encounter numerous hurdles within the tumor microenvironment that hinder their efficacy [...].

Lactate trafficking inhibition restores sensitivity to proteasome inhibitors and orchestrates immuno-microenvironment in multiple myeloma

Metabolic changes of malignant plasma cells (PCs) and adaptation to tumour microenvironment represent one of the hallmarks of multiple myeloma (MM). We previously showed that MM mesenchymal stromal cells are more glycolytic and produce more lactate than healthy counterpart. Hence, we aimed to explore the impact of high lactate concentration on metabolism of tumour PCs and its impact on the efficacy of proteasome inhibitors (PIs). Lactate concentration was performed by colorimetric assay on MM patient's sera. The metabolism of MM cell treated with lactate was assessed by seahorse and real time Polymerase Chain Reaction (PCR). Cytometry was used to evaluate mitochondrial reactive oxygen species (mROS), apoptosis and mitochondrial depolarization. Lactate concentration resulted increased in MM patient's sera. Therefore, PCs were treated with lactate and we observed an increase of oxidative phosphorylation-related genes, mROS and oxygen consumption rate. Lactate supplementation exhibited a significant reduction in cell proliferation and less responsive to PIs. These data were confirmed by pharmacological inhibition of monocarboxylate transporter 1 (MCT1) by AZD3965 which was able to overcame metabolic protective effect of lactate against PIs. Consistently, high levels of circulating lactate caused expansion of Treg and monocytic myeloid derived suppressor cells and such effect was significantly reduced by AZD3965. Overall, these findings showed that targeting lactate trafficking in TME inhibits metabolic rewiring of tumour PCs, lactate-dependent immune evasion and thus improving therapy efficacy.

Drug resistance in multiple myeloma: Soldiers and weapons in the bone marrow niche

Multiple myeloma (MM) is still an incurable disease, despite considerable improvements in treatment strategies, as resistance to most currently available agents is not uncommon. In this study, data on drug resistance in MM were analyzed and led to the following conclusions: resistance occurs via intrinsic and extrinsic mechanisms, including intraclonal heterogeneity, drug efflux pumps, alterations of drug targets, the inhibition of apoptosis, increased DNA repair and interactions with the bone marrow (BM) microenvironment, cell adhesion, and the release of soluble factors. Since MM involves the BM, interactions in the MM-BM microenvironment were examined as well, with a focus on the cross-talk between BM stromal cells (BMSCs), adipocytes, osteoclasts, osteoblasts, endothelial cells, and immune cells. Given the complex mechanisms that drive MM, next-generation treatment strategies that avoid drug resistance must target both the neoplastic clone and its non-malignant environment. Possible approaches based on recent evidence include: (i) proteasome and histone deacetylases inhibitors that not only target MM but also act on BMSCs and osteoclasts; (ii) novel peptide drug conjugates that target both the MM malignant clone and angiogenesis to unleash an effective anti-MM immune response. Finally, the role of cancer stem cells in MM is unknown but given their roles in the development of solid and hematological malignancies, cancer relapse, and drug resistance, their identification and description are of paramount importance for MM management.

The Urgent Need for Precision Medicine in Cancer and Its Microenvironment: The Paradigmatic Case of Multiple Myeloma

Precision medicine is particularly relevant for cancer and microenvironment deconvolution for therapeutic purposes in hematological and non-hematological malignancies [...].