Bone Marrow Microenvironment Niche Research Articles

A closer look at the bone marrow microenvironment in multiple myeloma

Multiple myeloma, a plasma cell (PC) neoplasm accounting for nearly 10% of hematologic malignancies, remains an incurable disease of the bone marrow (BM) with a fascinating pathophysiology. The maladaptive nature of myeloma PCs and the BM microenvironment niche has been recognized to play a crucial role in the pathogenesis and progression of the disease which behaves in a manner similar to solid tumors in their growth and dissemination. A complex interaction between osteoclasts, endothelial cells, BM matrix, myeloid as well as the lymphoid elements and the malignant PCs occurs at the level of the microenvironment favoring the expansion of latter cells and their spread. A better understanding of the diseased PC and their milieu will enable the development of novel therapeutic tools capable of improving the outcome of this incurable blood cancer.

Bone Marrow Microenvironment Niche Regulates miR-221/222 in Acute Lymphoblastic Leukemia.

Niche-influenced miR-221/222 may define a novel therapeutic target in ALL to be combined with existing cytotoxic agents to more effectively eradicate refractory disease that contributes to relapse. Mol Cancer Res; 14(10); 909-19. ©2016 AACR.

Abstract 1114: Combination of a novel CXCR4 antagonist with chemotherapy reduces breast cancer bone metastatic tumor burden

Abstract Background: Bone is the most common site of metastasis for patients with breast cancer. Tumor cells migrate to and reside in the protective bone marrow microenvironment niche through adhesive interaction between tumor CXCR4 and stromal CXCL12 (SDF1). CXCL12 is produced by activated osteoblasts, bone marrow and lung stromal cells, and endothelial cells. Nearly 60% of breast cancers express CXCR4 and this is associated with decreased survival. We hypothesized that a Protein Epitope Mimetic (PEM) POL5551, a novel CXCR4 antagonist, will limit the extent of tumor metastasis by disrupting stromal-mediated protection from cytotoxic chemotherapy and in turn may prolong survival. Approach: In vitro, POL5551 had no direct cytotoxic activity and did not reduce proliferation of CXCR4+ MDA-MB-231 or 4T1 osteolytic breast cancer cell lines. However, in an in vitro scratch-wound assay POL5551 inhibited migration of MDA-MB-231 cells. In a Gaussia luciferase (GLuc) complementation model in MDA-MB-231 cells, the interaction of CXCL12 with CXCR4, but not CXCR7, was blocked by low nanomolar concentrations of POL5551. At 20 mg/kg administered from day 10 post inoculation, POL5551 displayed no single agent activity on primary tumor xenografts, and in combination with eribulin there was no synergistic effect on primary tumor xenografts. However, continuation of treatment with POL5551 after surgical tumor removal decreased tumor metastasis and prolonged survival to 58 days compared to control at 45 days and eribulin alone at 51 days. Also, POL5551 showed effects on immune infiltration to the primary tumor. To test the hypothesis that CXCR4 antagonism disrupts the protective bone marrow niche in which tumor cells reside and sensitizes them to cytotoxic chemotherapy, we employed a “framing dosing strategy”. In a second model of metastasis produced by intracardiac injection of MDA-MB-231 cells, POL5551 (20 mg/kg, s.c.) was administered to mice with bone metastases 4 hours before and 4 & 18 hours after eribulin chemotherapy (0.2 mg/kg, i.v.). While bone is the predominant site of metastasis with these cell lines, lung and liver metastasis also occurs. POL5551 in combination with eribulin decreased bone tumor burden more than eribulin alone (reduction in leg bone & liver tumor burden, versus control respectively: eribulin alone 58% & 75%, n.s.; POL5551+eribulin: 89% & 86%, P<0.05; n=4-5 mice per group). Conclusion: These preclinical data support a synergism of CXCR4 antagonism during chemotherapy for the treatment of metastatic breast cancer. These and additional data support initiation of a Phase I clinical trial to evaluate a related PEM CXCR4 antagonist in combination with eribulin chemotherapy in patients with metastatic breast cancer who have failed at least 2 lines of therapy. Note: This abstract was not presented at the meeting. Citation Format: Jingyu Xiang, Michelle A. Hurchla, Kathryn Luker, Garry Douglas, Barbara Romagnoli, Eric Chevalier, Michael Bauer, Johann Zimmermann, Klaus Dembowsky, Gary Luker, Katherine N. Weilbaecher. Combination of a novel CXCR4 antagonist with chemotherapy reduces breast cancer bone metastatic tumor burden. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1114. doi:10.1158/1538-7445.AM2014-1114

Bone and Stem Cells. Bone marrow microenvironment niches for hematopoietic stem and progenitor cells

In bone marrow, the special microenvironments known as niches control proliferation and differentiation of hematopoietic stem and progenitor cells (HSPCs) . However, the identity and functions of the niches has been a subject of longstanding debate. Although it has been reported previously that osteoblasts lining the bone surface act as HSC niches, their precise role in HSC maintenance remains unclear. On the other hand, the adipo-osteogenic progenitors with long processes, termed CXCL12-abundant reticular (CAR) cells, which preferentially express the chemokine CXCL12, stem cell factor (SCF) , leptin receptor and PDGF receptor-β were identified in the bone marrow. Recent studies revealed that endothelial cells of bone marrow vascular sinuses and CAR cells provided niches for HSCs. The identity and functions of various other candidate HSC niche cells, including nestin-expressing cells and Schwann cells would also be discussed in this review.

CXCR4 Inhibitors Selectively Eliminate CXCR4 Expressing Human Acute Myeloid Leukemia Cells in NOG Mouse Model

AbstractAbstract 1881The chemokine receptor CXCR4 favors the interaction of acute myeloid leukemia (AML) cells with their niche but the extent to which it participates to pathogenesis is unclear. Here we show that CXCR4 expression at the surface of leukemic cells allowed distinguishing CXCR4high (25/47; 53%) from CXCR4neg/low (22/47, 47%) AML patients. Leukemic engraftment in NOD/Shi-scid/IL-2Rnull (NOG) mice was observed for both the CXCR4high and CXCR4neg/low groups. When high levels of CXCR4 are expressed at the surface of AML cells, blocking the receptor function with small molecule inhibitors could promote leukemic cell death and reduce NOG leukemia-initiating cells (LICs). Conversely, these drugs had no efficacy when AML cells do not express CXCR4 or when they do not respond to CXCL12. Mechanisms of this anti-leukemic effect included interference with the retention of LICs with their supportive bone marrow microenvironment niches, as indicated by a mobilization of LICs in response to drugs, and increased apoptosis of leukemic cells in vitro and in vivo. CXCR4 expression level on AML blast cells and their migratory response to CXCL12 are therefore predictive of the response to the inhibitors and could be used as biomarkers to select patients that could potentially benefit from the drugs. Disclosures:No relevant conflicts of interest to declare.

Disruption of Leukemia/Stroma Cell Interactions by CXCR4 Antagonist CTCE-9908 Enhances Chemotherapy-Induced Apoptosis in AML

The chemokine receptor CXCR4 is critically involved in the migration of hematopoietic cells towards the stromal derived factor (SDF-1α)-producing bone marrow microenvironment. We and others have previously demonstrated that stroma/leukemia interactions mediate protection of leukemic cells from chemotherapy-induced apoptosis (Konopleva, Leukemia 2002). Using a peptide analog of SDF-1α designated CTCE-9908, we tested the hypothesis that CXCR4 inhibition interferes with stromal/leukemia cell interactions resulting in increased sensitivity to chemotherapy. Our results showed that CTCE-9908 significantly inhibits SDF-1α-induced migration of U937 (43% inhibition) and OCI-AML3 cells (40% inhibition) in a dose-dependent manner. In three of the four primary AML samples which expressed CXCR4 on cell surface and migrated in response to SDF-1α, 50 μg/ml CTCE-9908 reduced SDF-1α-induced migration of leukemic blasts (60%, 19% and 50% inhibition respectively). In in vitro co-culture systems, stromal cells significantly protected OCI-AML3 cells from chemotherapy induced apoptosis [no MS-5, 75.2±5.2% annexinV(+); with MS-5, 59±1.1% annexinV(+)]. Western blot analysis revealed that CTCE-9908 inhibits Akt and Erk phosphorylation in a dose-dependent manner in the OCI-AML3 cell line stimulated by SDF-1α. Blockade of CXCR4 expression with CTCE-9908 markedly abrogated the protective effects of stromal cells on OCI-AML3 [Ara-C, 59±1.1% annexinV(+); Ara-C + CTCE-9908, 76.9±1.35 annexinV(+)]. Most importantly, it decreased stroma-mediated protection from AraC-induced apoptosis in four out of five primary AML samples with surface expression of functional CXCR4 (mean increase, 25.1±9.3% compared to chemotherapy alone). In vivo, subcutaneous administration of 1.25mg CTCE-9908 induced mobilization of leukemic cells from primary AML patient transplanted into NOD/Scid-IL2Rγ-KO mice (from 15% to 27% circulating leukemic cells 1 hour post CTCE-9908 injection). Taken together, our data suggest that SDF-1α/CXCR4 interactions contribute to the resistance of leukemic cells to chemotherapy-induced apoptosis via retention of leukemic cells in the bone marrow microenvironment niches. Disruption of these interactions by the potent CXCR4 inhibitor CTCE-9908 represents a novel strategy for targeting leukemia cell/bone marrow microenvironment interaction. Based on these observations, in vivo experiments are ongoing to characterize the efficacy of chemotherapy combined with CTCE-9908.

CXCR4 up-regulation by imatinib induces chronic myelogenous leukemia (CML) cell migration to bone marrow stroma and promotes survival of quiescent CML cells

Chronic myelogenous leukemia (CML) is driven by constitutively activated Bcr-Abl tyrosine kinase, which causes the defective adhesion of CML cells to bone marrow stroma. The overexpression of p210Bcr-Abl was reported to down-regulate CXCR4 expression, and this is associated with the cell migration defects in CML. We proposed that tyrosine kinase inhibitors, imatinib or INNO-406, may restore CXCR4 expression and cause the migration of CML cells to bone marrow microenvironment niches, which in turn results in acquisition of stroma-mediated chemoresistance of CML progenitor cells. In KBM5 and K562 cells, imatinib, INNO-406, or IFN-alpha increased CXCR4 expression and migration. This increase in CXCR4 levels on CML progenitor cells was likewise found in samples from CML patients treated with imatinib or IFN-alpha. Imatinib induced G0-G1 cell cycle block in CML cells, which was further enhanced in a mesenchymal stem cell (MSC) coculture system. MSC coculture protected KBM-5 cells from imatinib-induced cell death. These antiapoptotic effects were abrogated by the CXCR4 antagonist AMD3465 or by inhibitor of integrin-linked kinase QLT0267. Altogether, these findings suggest that the up-regulation of CXCR4 by imatinib promotes migration of CML cells to bone marrow stroma, causing the G0-G1 cell cycle arrest and hence ensuring the survival of quiescent CML progenitor cells.