A NOTCH3-CXCL12-driven myeloma-tumor niche signaling axis promotes chemoresistance in multiple myeloma

Multiple myeloma (MM) remains incurable due to disease relapse and drug resistance. Notch signals from the tumor microenvironment (TME) confer chemoresistance, but the cellular and molecular mechanisms are not entirely understood. Using clinical and transcriptomic datasets, we found that NOTCH3 is upregulated in CD138+ cells from newly diagnosed MM (NDMM) patients compared to healthy individuals and increased in progression/relapsed MM (PRMM) patients. Further, NDMM patients with high NOTCH3 expression exhibited worse responses to Bortezomib (BOR)-based therapies. Cells of the TME, including osteocytes, upregulated NOTCH3 in MM cells and protected them from apoptosis induced by BOR. NOTCH3 activation (NOTCH3OE) in MM cells decreased BOR anti-MM efficacy and its ability to improve survival in in vivo myeloma models. Molecular analyses revealed that NDMM and PRMM patients with high NOTCH3 exhibit CXCL12 upregulation. TME cells upregulated CXCL12 and activated the CXCR4 pathway in MM cells in a NOTCH3-dependent manner. Moreover, genetic or pharmacologic inhibition of CXCL12 in NOTCH3OE MM cells restored sensitivity to BOR regimes in vitro and in human bones bearing NOTCH3OE MM tumors cultured ex vivo. Our clinical and preclinical data unravel a novel NOTCH3-CXCL12 pro-survival signaling axis in the TME and suggest that osteocytes transmit chemoresistance signals to MM cells

Pharmacologic targeting of the p62 ZZ domain enhances both anti-tumor and bone-anabolic effects of bortezomib in multiple myeloma

Multiple myeloma (MM) is a malignancy of plasma cells whose antibody secretion creates proteotoxic stress relieved by the N-end rule pathway, a proteolytic system that degrades N-arginylated proteins in the proteasome. When the proteasome is inhibited, protein cargo is alternatively targeted for autophagic degradation by binding to the ZZ-domain of p62/ sequestosome-1. Here, we demonstrate that XRK3F2, a selective ligand for the ZZ-domain, dramatically improved two major responses to the proteasome inhibitor bortezomib (Btz) by increasing: i) killing of human MM cells by stimulating both Btz-mediated apoptosis and necroptosis, a process regulated by p62; and ii) preservation of bone mass by stimulating osteoblast differentiation and inhibiting osteoclastic bone destruction. Co-administration of Btz and XRK3F2 inhibited both branches of the bimodal N-end rule pathway exhibited synergistic anti-MM effects on MM cell lines and CD138+ cells from MM patients, and prevented stromal-mediated MM cell survival. In mice with established human MM, co-administration of Btz and XRK3F2 decreased tumor burden and prevented the progression of MM-induced osteolytic disease by inducing new bone formation more effectively than either single agent alone. The results suggest that p62-ZZ ligands enhance the anti- MM efficacy of proteasome inhibitors and can reduce MM morbidity and mortality by improving bone health

The multifunctional role of Notch signaling in multiple myeloma

Multiple myeloma (MM) is a hematologic cancer characterized by uncontrolled growth of malignant plasma cells in the bone marrow and currently is incurable. The bone marrow microenvironment plays a critical role in MM. MM cells reside in specialized niches where they interact with multiple marrow cell types, transforming the bone/bone marrow compartment into an ideal microenvironment for the migration, proliferation, and survival of MM cells. In addition, MM cells interact with bone cells to stimulate bone destruction and promote the development of bone lesions that rarely heal. In this review, we discuss how Notch signals facilitate the communication between adjacent MM cells and between MM cells and bone/bone marrow cells and shape the microenvironment to favor MM progression and bone disease. We also address the potential and therapeutic approaches used to target Notch signaling in MM

Bone-derived Sclerostin has endocrine actions in adipocyte precursors and pancreatic beta-cells

Osteocyte (Ot)-derived Sclerostin (Scl) has local actions in bone mediated by Lrp 4/5/6 receptors, inhibiting bone formation and stimulating bone resorption by antagonizing Wnt signaling. Emerging evidence suggests that Scl also exerts functions in distant tissues. We report here that mice with activated β-catenin in Ots (daβcatOt) and mice lacking Lrp4 in Ots (Lrp4Ot), two different genetic mouse models that exhibit high se-rum Scl, display a 2-fold increase in whole-body fat and peripheral white (WAT) and brown (BAT) adipose tissue mass. The goal of this study was to determine the contribution of Ot-derived Scl to the regulation of peripheral fat mass and glucose metabolism. To determine Scl’s contribution to the high fat phenotype, daβcatOt mice were crossed with SOST knockout mice. Deletion of SOST restored to control levels the elevated body-fat mass and WAT mass, but not BAT, in daβcatOt mice. In contrast, blockade of Scl signaling in bone via genetic deletion of Lrp4 in Ots, did not alter the elevated body fat displayed by daβcatOt mice, demonstrating that Scl actions on adi-pose tissue were not mediated by Scl actions on Ots. Consistent with direct effects of Scl on adipose tissue, treatment with recombinant Scl enhanced by 20% adipogenic differentiation of murine adipocyte precursors (preAd) in vitro, and increased the expression of mitochondrial related genes Pgc1a, Ucp1, and Prdm16 in preAds as well as in ex vivo fat organ cultures established from WAT. Further, Scl augmented mitochondrial respiration in preAds by inducing a 15% increase in maximal respiration and spare capacity, suggesting that Scl promotes adipogenesis in preAds by regulating mitochondrial oxidative phosphorylation. Both models of high serum Scl, daβcatOt and LRP4Ot mice, also were hypoglycemic and exhibited impaired glucose tolerance com-pared to control littermates. Genetic deletion of SOST restored to control values the glucose levels in blood and glucose tolerance, showing that serum Scl regulates glucose metabolism. Further, Scl fully prevented the increase in insulin mRNA expression induced by Wnt3a in rat pancreatic β-cells and decreased by 45% insulin secretion induced by high-glucose media, demonstrating that Scl acts directly on pancreatic β-cells to impair insulin production. In concert, these findings demonstrate that Scl exerts endocrine actions in fat tissues and the pancreas to regulate body composition and glucose metabolism, respectively. Further, our results provide new evidence supporting that endocrine actions of Scl mediate the crosstalk between bone and fat and the pancreas

Targeting Notch Inhibitors to the Myeloma Bone Marrow Niche Decreases Tumor Growth and Bone Destruction without Gut Toxicity

Systemic inhibition of Notch with γ-secretase inhibitors (GSI) decreases multiple myeloma tumor growth, but the clinical use of GSI is limited due to its severe gastrointestinal toxicity. In this study, we generated a GSI Notch inhibitor specifically directed to the bone (BT-GSI). BT-GSI administration decreased Notch target gene expression in the bone marrow, but it did not alter Notch signaling in intestinal tissue or induce gut toxicity. In mice with established human or murine multiple myeloma, treatment with BT-GSI decreased tumor burden and prevented the progression of multiple myeloma-induced osteolytic disease by inhibiting bone resorption more effectively than unconjugated GSI at equimolar doses. These findings show that BT-GSI has dual anti-myeloma and anti-resorptive properties, supporting the therapeutic approach of bone-targeted Notch inhibition for the treatment of multiple myeloma and associated bone disease. SIGNIFICANCE: Development of a bone-targeted Notch inhibitor reduces multiple myeloma growth and mitigates cancer-induced bone destruction without inducing the gastrointestinal toxicity typically associated with inhibition of Notch