Although osteolysis is a common complication in patients with multiple myeloma (MM), the biologic mechanisms involved in the pathogenesis of MM-induced bone disease are poorly understood. Two factors produced by stromal-osteoblastic cells seem critical to the regulation of bone resorption: osteoprotegerin (OPG) and its ligand (OPGL). OPGL stimulates osteoclast differentiation and activity, whereas OPG inhibits these processes. The present study investigated whether myeloma cells affect physiologic OPG/OPGL balance in the bone marrow (BM) environment. Ten human myeloma cell lines and myeloma cells isolated from 26 consecutive patients with MM failed to express OPGL and only rarely produced a low amount of OPG. In a coculture system, human myeloma cells up-regulated OPGL expression but strongly down-regulated OPG production in preosteoblastic (preOB) or stromal cells (BMSCs) of primary human BM at the mRNA and protein levels. This effect, which was dependent on cell-to-cell contact between myeloma cells and BMSCs or preOB, partially involved the integrin VLA-4. In addition, overexpression of OPGL mRNA occurred in ex vivo BM cultures obtained from MM patients as compared with healthy donors, and immunohistochemical staining performed on BM biopsy specimens showed an increase of OPGL and a reduction of OPG expression in MM patients as compared with healthy subjects. In summary, these data indicate that myeloma cells affect the OPG/OPGL ratio in the BM environment and tend to confirm that the OPG/OPGL system is involved in the pathogenesis of MM-induced bone disease.

The biologic mechanisms involved in the pathogenesis of multiple myeloma (MM) bone disease are not completely understood. Recent evidence suggests that T cells may regulate bone resorption through the cross-talk between the critical osteoclastogenetic factor, receptor activator of nuclear factor-κB ligand (RANKL), and interferon γ (IFN-γ) that strongly suppresses osteoclastogenesis. Using a coculture transwell system we found that human myeloma cell lines (HMCLs) increased the expression and secretion of RANKL in activated T lymphocytes and similarly purified MM cells stimulated RANKL production in autologous T lymphocytes. In addition, either anti–interleukin 6 (anti–IL-6) or anti–IL-7 antibody inhibited HMCL-induced RANKL overexpression. Consistently, we demonstrated that HMCLs and fresh MM cells express IL-7 mRNA and secrete IL-7 in the presence of IL-6 and that bone marrow (BM) IL-7 levels were significantly higher in patients with MM. Moreover, we found that the release of IFN-γ by T lymphocytes was reduced in presence of both HMCLs and purified MM cells. Furthermore, in a stromal cell–free system, osteoclastogenesis was stimulated by conditioned medium of T cells cocultured with HMCLs and inhibited by recombinant human osteoprotegerin (OPG; 100 ng/mL to 1 μg/mL). Finally, RANKL mRNA was up-regulated in BM T lymphocytes of MM patients with severe osteolytic lesions, suggesting that T cells could be involved at least in part in MM-induced osteolysis through the RANKL overexpression.

Bisphosphonates have recently been introduced in the therapeutic armamentarium for the long-term treatment of patients with multiple myeloma (MM). These pyrophosphate analogs not only reduce the occurrence of skeletal-related events but also provide patients with a clinical benefit and improve the survival of some of them. We investigated the effects of two bisphosphonates, pamidronate and zoledronate, on both myeloma cells and bone marrow stromal cells (BMSCs). We show here that both bisphosphonates induce both myeloma cell and BMSC apoptosis. Furthermore, at lower concentrations, they induce a significant inhibition (40% and 60%, respectively) of the constitutive production of interleukin-6 (IL-6) by BMSCs. We have recently shown that BMSCs produce MMP-1, the major metalloproteinase involved in the initiation of bone resorption, production up-regulated by IL-1β. Here, we demonstrate that zoledronate significantly inhibits MMP-1 production by BMSCs stimulated with IL-1β more efficiently than pamidronate. However, zoledronate and to a lesser extent pamidronate are responsible for an up-regulation of MMP-2 secretion by BMSCs. MMP-2 is involved both in bone resorption and in the metastatic process. In conclusion, the apoptosis of myeloma cells and BMSCs and the inhibition of both IL-6 and MMP-1 production induced by bisphosphonates, mainly zoledronate, could have antitumoral effects in patients with MM. However, the up-regulation of MMP-2 secretion observed in vitro suggests a putative risk of tumor cell dissemination in vivo when using these new potent bisphosphonates. This potentially deleterious effect could be abolished by combining bisphosphonates with metalloproteinase inhibitors.

A fascinating but uncharacterized action of antimitotic chemotherapy is to collectively prime cancer cells to apoptotic mitochondrial outer membrane permeabilization (MOMP), while impacting only on cycling cell subsets. Here, we show that a proapoptotic secretory phenotype is induced by activation of cGAS/STING in cancer cells that are hit by antimitotic treatment, accumulate micronuclei and maintain mitochondrial integrity despite intrinsic apoptotic pressure. Organotypic cultures of primary human breast tumors and patient-derived xenografts sensitive to paclitaxel exhibit gene expression signatures typical of type I IFN and TNFα exposure. These cytokines induced by cGAS/STING activation trigger NOXA expression in neighboring cells and render them acutely sensitive to BCL-xL inhibition. cGAS/STING-dependent apoptotic effects are required for paclitaxel response in vivo, and they are amplified by sequential, but not synchronous, administration of BH3 mimetics. Thus anti-mitotic agents propagate apoptotic priming across heterogeneously sensitive cancer cells through cytosolic DNA sensing pathway-dependent extracellular signals, exploitable by delayed MOMP targeting.

The transmembrane metalloprotease‐disintegrin ADAM8 mediates cell adhesion and shedding of ligands, receptors and extracellular matrix components. Here, we report that ADAM8 is abundantly expressed in breast tumors and derived metastases compared to normal tissue, especially in triple‐negative breast cancers (TNBCs). Furthermore, high ADAM8 levels predicted poor patient outcome. Consistently, ADAM8 promoted an aggressive phenotype of TNBC cells in culture. In a mouse orthotopic model, tumors derived from TNBC cells with ADAM8 knockdown failed to grow beyond a palpable size and displayed poor vascularization. Circulating tumor cells and brain metastases were also significantly reduced. Mechanistically, ADAM8 stimulated both angiogenesis through release of VEGF‐A and transendothelial cell migration via β1‐integrin activation. In vivo , treatment with an anti‐ADAM8 antibody from the time of cell inoculation reduced primary tumor burden and metastases. Furthermore, antibody treatment of established tumors profoundly decreased metastases in a resection model. As a non‐essential protein under physiological conditions, ADAM8 represents a promising novel target for treatment of TNBCs, which currently lack targeted therapies and frequently progress with fatal dissemination.