scholarly journals Chemosensitization of acute myeloid leukemia (AML) following mobilization by the CXCR4 antagonist AMD3100

Blood ◽  
2009 ◽  
Vol 113 (24) ◽  
pp. 6206-6214 ◽  
Author(s):  
Bruno Nervi ◽  
Pablo Ramirez ◽  
Michael P. Rettig ◽  
Geoffrey L. Uy ◽  
Matthew S. Holt ◽  
...  

Abstract The CXCR4–SDF-1 axis plays a central role in the trafficking and retention of normal and malignant stem cells in the bone marrow (BM) microenvironment. Here, we used a mouse model of acute promyelocytic leukemia (APL) and a small molecule competitive antagonist of CXCR4, AMD3100, to examine the interaction of mouse APL cells with the BM microenvironment. APL cells from a murine cathepsin G-PML-RARα knockin mouse were genetically modified with firefly luciferase (APLluc) to allow tracking by bioluminescence imaging. Coculture of APLluc cells with M2-10B4 stromal cells protected the leukemia cells from chemotherapy-induced apoptosis in vitro. Upon injection into syngeneic recipients, APLluc cells rapidly migrated to the BM followed by egress to the spleen then to the peripheral blood with death due to leukostasis by day 15. Administration of AMD3100 to leukemic mice induced a 1.6-fold increase in total leukocytes and a 9-fold increase of circulating APL blast counts, which peak at 3 hours and return to baseline by 12 hours. Treatment of leukemic mice with chemotherapy plus AMD3100 resulted in decreased tumor burden and improved overall survival compared with mice treated with chemotherapy alone. These studies provide a proof-of-principle for directing therapy to the critical tethers that promote AML-niche interactions.

Blood ◽  
2007 ◽  
Vol 110 (11) ◽  
pp. 2377-2377
Author(s):  
Eleni D. Lagadinou ◽  
Panagiotis G. Ziros ◽  
Olga A. Tsopra ◽  
Kostas Dimas ◽  
Panagiotis Pantazis ◽  
...  

Abstract Chemotherapy resistance remains a major challenge in the treatment of acute myeloid leukemia (AML). Besides the P-glycoprotein efflux of chemotherapeutics, additional cellular factors may contribute to drug resistance in AML. c- Jun N-terminal Kinase (JNK) is a protein kinase activated after exposure of cells to chemotherapeutic agents. Recently, studies in solid tumours have associated chemoresistance with failure of cancer cells to activate JNK. We asked whether drug resistance in AML is also attributed to intrinsic failure of the AML blasts to activate JNK. In vitro treatment of U937 AML cell line with anthracyclines induced a rapid and robust JNK phosphorylation and apoptosis. In contrast, the anthracyline-resistant derivative U937R cells showed no JNK activation after exposure to anthracyclines, also at doses that resulted in high accumulation of the drug within the cells. Inhibition of JNK in drug-sensitive U937 cells made them resistant to anthracyclines. First, JNK1-siRNA transfected U937 cells exhibited a 50.4% and 61.3% reduced daunorubicin- (DNR, 1μM 24hr) and doxorubicin- (DOX, 1.5 μM 24hr) induced apoptosis respectively; as compared to empty vector or untransfected U937 cells (P< 0.001). Second, pretreatment of U937 cells with the 420116 cell-permeable JNK inhibitor (1 μM) reduced to a less but yet significant extent DNR-induced apoptosis as compared to cells treated with a negative control peptide (P = 0.013<0.05). On the other hand, selective restoration of the inactive JNK pathway in resistant U937R cells by transfection with a mutant form of the SEK1/MKK4 upstream activator of JNK sensitized U937R cells to anthracyclines, compared to empty vector transfected cells (3.3-fold increase in DNR-induced apoptosis, 1μM DNR, 24hr and 3.1-fold increase in DOX-induced apoptosis, 1.5μM DOX, 24hr). Furthermore, we assessed the activation of JNK pathway in 29 primary AML bone marrow samples after short term (30-60 min) in vitro exposure to DNR (1 μM) and correlated it with clinical data. We found a strong correlation between the in vitro pharmacodymanic changes of phospho-JNK levels in AML primary blasts and the response of the AML patients to standard induction chemotherapy (P = 0.012). In addition, the drug-induced JNK activation pattern correlated with AML evolving from antecedent MDS (P = 0.017) and patient age (P = 0.046). In summary, our in vitro and in vivo results suggest that JNK activation failure is another mechanism of anthracycline resistance in AML. Elucidating the ultimate mechanisms leading to JNK suppression in chemoresistant AML may be of major therapeutic value.


2008 ◽  
Vol 295 (6) ◽  
pp. E1307-E1314 ◽  
Author(s):  
Jonathan M. Peterson ◽  
Yan Wang ◽  
Randall W. Bryner ◽  
David L. Williamson ◽  
Stephen E. Alway

Insulin resistance is a primary characteristic of type 2 diabetes. Several lines of evidence suggest that accumulation of free fatty acids in skeletal muscle may at least in part contribute to insulin resistance and may be linked to mitochondrial dysfunction, leading to apoptosis. Palmitate treatment of several cell lines in vitro results in apoptosis and inhibits protein kinase B (Akt) activity in response to insulin. However, the role of Bax and Bcl-2 in regulating palmitate-induced apoptosis has not been well studied. Therefore, the purpose of this study was to determine whether palmitate-induced apoptosis in C2C12 myotubes is dependent on Bax to Bcl-2 binding. An additional purpose of this study was to determine whether the changes in Bax to Bcl-2 binding corresponded to decreases in Akt signaling in palmitate-treated myoblasts. Apoptotic signaling proteins were examined in C2C12 myotubes treated overnight with palmitate. Bax to Bcl-2 binding was determined through a coimmunoprecipitation assay that was performed in myotubes after 2 h of serum starvation, followed by 10 min of serum reintroduction. This experiment evaluated whether temporal Akt activity coincided with Bax to Bcl-2 binding. Last, the contribution of Bax to palmitate-induced apoptosis was determined by treatment with Bax siRNA. Palmitate treatment increased apoptosis in C2C12 myotubes as shown by a twofold increase in DNA fragmentation, an approximately fivefold increase in caspase-3 activity, and a 2.5-fold increase in caspase-9 activity. Palmitate treatment significantly reduced Akt protein expression and Akt activity. In addition, there was a fourfold reduction in Bax to Bcl-2 binding with palmitate treatment, which mirrored the reduction in AktSer473 phosphorylation. Furthermore, treatment of the C2C12 myotubes with Bax siRNA attenuated the apoptotic effects of palmitate treatment. These data show that palmitate induces Bax-mediated apoptosis in C2C12 myotubes and that this effect corresponds to reductions in AktSer473 phosphorylation.


Blood ◽  
2007 ◽  
Vol 110 (11) ◽  
pp. 867-867 ◽  
Author(s):  
Geoffrey L. Uy ◽  
Michael P. Rettig ◽  
Pablo Ramirez ◽  
Bruno Nervi ◽  
Camille N. Abboud ◽  
...  

The CXCR4-SDF-1 axis possesses a central role in the trafficking and retention of both normal and malignant stem cells in the bone marrow. Previous work from our laboratory established that in a murine model, a single dose of the CXCR4 antagonist, AMD3100, sensitizes AML blasts to chemotherapy supporting the premise that the interaction between AML blasts and the marrow microenvironment confers resistance to genotoxic stress (Nervi et al., ASH 2006). Here we examine the effects of repetitive dosing of AMD3100 on the kinetics of normal and leukemic mobilization. Following SQ injection of AMD3100 5mg/kg into B6/129 F1 mice daily for 5 days (n=8), we observed a 2.4 fold increase in total leukocyte counts with a 12.4 increase in CFU-GM when compared to 3 hours post injection (Fig 1A). No differences were seen in the degree of mobilization between d1 and d5 with WBC and CFU-GM counts returning to baseline after 24 hours. We next tested repetitive doses of AMD3100 in our mouse model of AML in which 106 blasts derived from leukemic mice carrying the PML-RARα fusion gene in the murine cathepsin G locus are adoptively transferred into genetically compatible secondary recipients. AMD3100 at 5mg/kg was then administered to these AML mice for 4 consecutive days. At 3 hrs post AMD3100 injection, we observed a 1.8 fold increase in peripheral leukocyte counts with a 4.5 fold increase in circulating blasts compared to baseline (n=3). Again, no significant differences are seen in the degree of mobilization from d1 to d4 (Fig 1B). Based on these preclinical data, we have initiated a phase I/II trial of AMD3100 plus mitoxantrone, etoposide and cytarabine (MEC) in relapsed or refractory AML in which AMD3100 is administered 4 hours prior to MEC daily for 5 consecutive days. To study the kinetics of human AML mobilization, we administered AMD3100 by SQ injection followed by 24hr observation period prior to chemotherapy. Two patients have been treated at the first dose level of AMD3100, 80 μg/kg. In pt #1 following AMD3100 mobilization, total WBC increased from 3 × 103/mm3 to a peak of 17 × 103/mm3 at 6 hours post-AMD3100 representing a 5.7 fold increase in total white count (Fig 2). In addition, the blasts (CD45dim, SSlow) increased by 7.3 fold. Similarly in pt #2, we observed a 2 fold increase in the total WBC from 2.5 to 5.1 × 103/mm3 with a 2.3 fold increase in blasts (CD45dim, SSlow). Mobilization of AML was confirmed in both patients through informative FISH for 11q23 (MLL). No adverse events have been observed during mobilization. These data provide the preclinical rationale for repetitive dosing of AMD3100 and direct clinical evidence that AMD3100 mobilizes human AML blasts into the peripheral circulation. Our trial of AMD3100 plus MEC in relapsed or refractory AML is ongoing. Figure 1. AMD3100 induced mobilization of (A) normal progenitors and (B) AML blasts Figure 1. AMD3100 induced mobilization of (A) normal progenitors and (B) AML blasts Figure 2. AMD3100 mobilization of human AML Figure 2. AMD3100 mobilization of human AML


Blood ◽  
2012 ◽  
Vol 120 (21) ◽  
pp. 780-780
Author(s):  
Edward Allan R. Sison ◽  
Daniel Magoon ◽  
Eric Chevalier ◽  
Klaus Dembowsky ◽  
Patrick Brown

Abstract Abstract 780 Background: The interaction between the cell surface receptor CXCR4 and the chemokine SDF-1 (CXCL12) is critical in signaling between leukemic blasts and the bone marrow microenvironment. We previously demonstrated that CXCR4 is an important mediator of chemotherapy resistance, as chemotherapy-induced upregulation of s-CXCR4 in acute myeloid leukemia (AML) cell lines and primary samples led to increased SDF-1-mediated chemotaxis and increased protection by normal human bone marrow stroma from chemotherapy-induced apoptosis. We also showed that stromal protection and chemotherapy resistance could be reversed by treatment with the FDA-approved CXCR4 inhibitor plerixafor, both in vitro in stromal co-cultures of pre-B cell ALL cell lines and in vivo in xenografts of primary samples of infant MLL-rearranged ALL. Therefore, disruption of the CXCR4/SDF-1 axis is a rational means to target extrinsic survival mechanisms in acute leukemia. The novel Protein Epitope Mimetic (PEM) POL5551 is a selective and potent antagonist of CXCR4. Treatment with POL5551 inhibits vascular accumulation of CXCR4+ smooth muscle cells but its effects on ALL have not been reported. We hypothesized that treatment of ALL cell lines with POL5551 would 1) decrease s-CXCR4 expression, 2) inhibit SDF-1-mediated chemotaxis, and 3) reverse stromal-mediated protection from chemotherapy-induced apoptosis. Methods/Results: Pre-B cell ALL (697, HB11;19, NALM-6, SEMK2) and T cell ALL cell lines (CCRF-CEM-1301, Jurkat, Molt-4) were treated with dose ranges of POL5551. Cells were harvested at multiple time points over 72 hours and s-CXCR4 was measured by FACS. S-CXCR4 was potently and markedly reduced in all cell lines, with IC50 levels of <5 nM at 1 hour and IC50 levels of <20 nM at 48 hours. In comparison, 3- to 30-fold higher doses of plerixafor were needed to achieve similar levels of reduction. Simultaneous measurement of cell proliferation using the WST-1 proliferation assay demonstrated that treatment with POL5551 neither increased nor decreased leukemia cell proliferation in a significant manner. To ascertain the functionality of s-CXCR4 inhibition, we performed chemotaxis assays. Leukemia cells were treated with 10 nM POL5551 or vehicle control and placed into hanging cell culture inserts. Migration through a permeable membrane toward an SDF-1 gradient was then measured after 24 hours. Compared to control-treated cells, POL5551-treated cells had significantly decreased SDF-1-induced chemotaxis (average 38% reduction in chemotaxis in pre-B cell lines, p<0.001; average 41% reduction in T cell lines, p=0.05). We also performed co-culture experiments with normal human bone marrow stroma in the presence and absence of POL5551 to further demonstrate the functional effects of s-CXCR4 inhibition. Specifically, we cultured leukemia cells off stroma (O), on stroma (S), or pretreated with POL5551 for 30 minutes prior to plating on stroma (P+S). Cells from each culture condition were then treated with dose ranges of chemotherapy. Following treatment, we measured apoptosis by staining with Annexin V/7-AAD. IC10 through IC90 values were obtained using Calcusyn. To quantify stromal protection, we calculated a Protective Index (PI), defined as the S IC values divided by the O IC values. Thus, PI >1 signified stromal protection, while PI ≤1 signified no stromal protection. To quantify the ability of POL5551 to reverse stromal protection, we calculated a Reversal Index (RI), defined as the P+S IC values divided by the O IC values. Therefore, PI > RI indicated a decrease in stromal protection, while RI ≤1 indicated a reversal of stromal protection. Overall, stroma protected leukemia cells from chemotherapy-induced apoptosis. Importantly, treatment with POL5551 abrogated stromal-mediated protection and restored chemosensitivity (eg, PI 1.182 vs. RI 0.956 for NALM-6 treated with daunorubicin +/− 20 nM POL5551, p<1×10e-9). Conclusions: The novel CXCR4 antagonist POL5551 is a potent inhibitor of CXCR4 in pre-B and T ALL cell lines with activity at nanomolar concentrations in decreasing s-CXCR4 expression, inhibiting SDF-1-induced chemotaxis, and reversing stromal-mediated protection from chemotherapy in vitro. Therefore, if our findings are confirmed in primary samples and in vivo, interruption of leukemia-microenvironment signaling with POL5551 may prove to be an effective strategy in the treatment of pre-B and T cell ALL. Disclosures: Chevalier: Polyphor Ltd: Employment. Dembowsky:Polyphor Ltd: Employment.


Blood ◽  
2000 ◽  
Vol 95 (3) ◽  
pp. 1014-1022 ◽  
Author(s):  
Charles Perkins ◽  
Caryn N. Kim ◽  
Guofu Fang ◽  
Kapil N. Bhalla

We investigated the in vitro growth inhibitory and apoptotic effects of clinically achievable concentrations of As2O3 (0.5 to 2.0 μmol/L) against human myeloid leukemia cells known to be resistant to a number of apoptotic stimuli. These included chronic myelocytic leukemia (CML) blast crisis K562 and HL-60/Bcr-Abl cells, which contain p210 and p185 Bcr-Abl, respectively, and HL-60 cell types that overexpress Bcl-2 (HL-60/Bcl-2), Bcl-xL(HL-60/Bcl-xL), MDR (HL-60/VCR), or MRP (HL-60/AR) protein. The growth-inhibitory IC50 values for As2O3 treatment for 7 days against all these cell types ranged from 0.8 to 1.5 μmol/L. Exposure to 2 μmol/L As2O3 for 7 days induced apoptosis of all cell types, including HL-60/Bcr-Abl and K562 cells. This was associated with the cytosolic accumulation of cyt c and preapoptotic mitochondrial events, such as the loss of inner membrane potential (▵Ψm) and the increase in reactive oxygen species (ROS). Treatment with As2O3 (2 μmol/L) generated the activities of caspases, which produced the cleavage of the BH3 domain containing proapoptotic Bid protein and poly (ADP-ribose) polymerase. Significantly, As2O3-induced apoptosis of HL-60/Bcr-Abl and K562 cells was associated with a decline in Bcr-Abl protein levels, without any significant alterations in the levels of Bcl-xL, Bax, Apaf-1, Fas, and FasL. Although As2O3 treatment caused a marked increase in the expression of the myeloid differentiation marker CD11b, it did not affect Hb levels in HL-60/Bcr-Abl, K562, or HL-60/neo cells. However, in these cells, As2O3 potently induced hyper-acetylation of the histones H3 and H4. These findings characterize As2O3 as a growth inhibiting and apoptosis-inducing agent against a variety of myeloid leukemia cells resistant to multiple apoptotic stimuli.


2016 ◽  
Vol 2016 ◽  
pp. 1-10 ◽  
Author(s):  
Hongyu Qiao ◽  
Ran Zhang ◽  
Lina Gao ◽  
Yanjie Guo ◽  
Jinda Wang ◽  
...  

Introduction. Bone marrow-derived mesenchymal stromal cells (BMSCs) have emerged as promising cell candidates but with poor survival after transplantation. This study was designed to investigate the efficacy of VEGF, bFGF, and IGF-1 on BMSCs’ viability and proliferation bothin vivoandin vitrousing bioluminescence imaging (BLI).Methods. BMSCs were isolated fromβ-actin-Fluc+transgenic FVB mice, which constitutively express firefly luciferase. Apoptosis was induced by hypoxia preconditioning for up to 24 h followed by flow cytometry and TUNEL assay. 106BMSCs with/without growth factors were injected subcutaneously into wild type FVB mice’s backs. Survival of BMSCs was longitudinally monitored using bioluminescence imaging (BLI) for 5 weeks. Protein expression of Akt, p-Akt, PARP, and caspase-3 was detected by Western blot.Results. Hypoxia-induced apoptosis was significantly attenuated by bFGF and IGF-1 compared with VEGF and control groupin vitro(P<0.05). When combined with matrigel, IGF-1 showed the most beneficial effects in protecting BMSCs from apoptosisin vivo.The phosphorylation of Akt had a higher ratio in the cells from IGF-1 group.Conclusion. IGF-1 could protect BMSCs from hypoxia-induced apoptosis through activation of p-Akt/Akt pathway.


Endocrinology ◽  
2010 ◽  
Vol 152 (2) ◽  
pp. 536-544 ◽  
Author(s):  
Jeong Mo Kim ◽  
Yong-ho Lee ◽  
Cheol Ryong Ku ◽  
Eun Jig Lee

Abstract The interaction between the chemokine stromal cell-derived factor 1 and its receptor CXCR4 plays an important role in GH production and cell proliferation in normal and tumorous pituitary somatotrope cells. Therefore, the chemokine receptor CXCR4 could be an attractive target for antitumor drugs in patients with acromegaly. A synthetic antagonist of CXCR4, cyclic pentapeptide d-Arg3FC131 (c[Gly1-d-Tyr2-d-Arg3-Arg4-Nal5]) significantly inhibited GH production and proliferation of GH3 somatotrope tumor cells in vitro. It also induced apoptosis of GH3 cells through activation of the caspase-3 pathway. Systemic administration of d-Arg3FC131 inhibited the growth of GH3 cell xenografts in immunodeficient nude mice by inducing apoptosis and suppressing the proliferation of tumor cells. These results indicate that d-Arg3FC131 might have potential for the treatment of pituitary tumors producing excess GH in patients with acromegaly.


Blood ◽  
2018 ◽  
Vol 132 (Supplement 1) ◽  
pp. 1361-1361 ◽  
Author(s):  
Daniel A Luedtke ◽  
Yongwei Su ◽  
Holly Edwards ◽  
Lisa Polin ◽  
Juiwanna Kushner ◽  
...  

Abstract Introduction: Patients with acute myeloid leukemia (AML) face overall 5-year survival rates of 65% and 27% for children and adults, respectively, leaving significant room for improvement. Relapse remains a major contributor to such low overall survival rates, and leukemic stem cells (LSCs) that survive treatment are believed to be responsible for AML relapse. The anti-apoptotic protein Bcl-2 is overexpressed in bulk AML cells and LSCs and is associated with poor clinical outcomes. Thus, Bcl-2 represents a promising therapeutic target for the treatment of AML. Venetoclax (ABT-199) is a selective Bcl-2 inhibitor that has shown great potential for treating a number of malignancies, including AML. Venetoclax inhibits Bcl-2, preventing it from sequestering pro-apoptotic Bcl-2 family protein Bim, leading to Bim activated Bax/Bak, resulting in apoptosis. However, Mcl-1 can also sequester Bim and prevent apoptosis. We previously showed that directly targeting Mcl-1 can enhance the antileukemic activity of venetoclax (Luedtke DA, et al. Signal Transduct Target Ther. Apr 2017). Alternatively, we proposed that indirect targeting of Mcl-1 may preserve or enhance the antileukemic activity of venetoclax, and prevent resistance resulting from Mcl-1. It has been reported that inhibition of CDK9 can downregulate cell survival genes regulated by superenhancers, including Mcl-1, MYC, and Cyclin D1. One CDK9 inhibitor in clinical development, flavopiridol (alvocidib), has progressed to phase II clinical trials in AML. However, off target effects and dose-limiting toxicities remain a concern. Voruciclib is an oral, selective CDK inhibitor differentiated by its potent inhibition of CDK9 as compared to other CDK inhibitors. This selectivity may potentially circumvent toxicities resulting from inhibition of non-CDK targets like MAK and ICK that are inhibited by flavopiridol. Voruciclib has been shown in vitro to promote apoptosis and decrease Mcl-1 expression levels in chronic lymphocytic leukemia (CLL) cells (Paiva C, et al. PLOS One. Nov 2015) and inhibit tumor growth in mouse xenograft models of diffuse large B-cell lymphoma (DLBCL) in combination with venetoclax (Dey J. et al Scientific Reports. Dec 2017). Based on these data, voruciclib may downregulate Mcl-1 in AML cells and therefore synergistically enhance the antileukemic activity of venetoclax. Methods/Results: Culturing AML cell lines (THP-1, U937, MOLM-13, MV4-11, and OCI-AML3) and primary patient samples with various concentrations of voruciclib resulted in a concentration-dependent increase in Annexin V+ cells (2 μM voruciclib induced 13.8-55.8% Annexin V+ cells) along with increased levels of cleaved caspase 3 and PARP, demonstrating that voruciclib induces apoptosis in AML cells. Next, we tested the combination of voruciclib and venetoclax in AML cell lines and primary AML patient samples at clinically achievable concentrations. Annexin V/PI staining, flow cytometry analysis, and combination index calculation (using CalcuSyn software) revealed synergistic induction of apoptosis by voruciclib and venetoclax combination (combination index values for MV4-11, U937, THP-1, and MOLM-13 cells were <0.73; treatment with 2 µM voruciclib and venetoclax for 24 h resulted in >80% apoptosis). Importantly, synergy was observed in both venetoclax sensitive and resistant cell lines. This was accompanied by increased cleavage of caspase 3 and PARP. Lentiviral shRNA knockdown of Bak and Bax partially rescued AML cells from voruciclib-induced apoptosis, showing that voruciclib induces apoptosis at least partially through the intrinsic apoptosis pathway. However, Bak and Bax knockdown had little to no effect on induction of apoptosis by the combination treatment, indicating that there might be other molecular mechanisms underlying the synergistic interaction between the two agents. Treatment with the pan-caspase inhibitor Z-VAD-FMK partially rescued cells from combination treatment induced-apoptosis. Discussion: Collectively, these results demonstrate that voruciclib and venetoclax synergistically induce apoptosis in AML cells in vitro and reverse venetoclax resistance. Further studies to determine the mechanism of action and in vivo efficacy of this promising combination in AML xenografts and PDX models are underway. Disclosures Ge: MEI Pharma: Research Funding.


Blood ◽  
2009 ◽  
Vol 114 (22) ◽  
pp. 1721-1721
Author(s):  
Ha-Yon Kim ◽  
Ji-Young Hwang ◽  
Seong-Woo Kim ◽  
Gak-Won Yun ◽  
Young-Joon Yang ◽  
...  

Abstract Abstract 1721 Poster Board I-747 AMD3100, a small bicyclam antagonist for chemokine receptor CXCR4, induces the peripheral mobilization of hematopoietic stem cells. It also induces the segregation of leukemia cells in the bone marrow microenvironment, which should enhance the chemosensitivity of the cells. Based on these observations, AMD3100 is being considered for clinical use. However, AMD3100 activates G-protein coupled with CXCR4 and acts as a partial CXCR4 agonist. In this study, we explored whether AMD3100 affects the proliferation and survival of myeloid leukemia cells. As demonstrated previously, both AMD3100 and T140, another CXCR4 antagonist, markedly inhibited stromal cell-derived factor-1 (SDF-1)-induced chemotaxis and induced the internalization of CXCR4 in myeloid leukemia cell lines (U937, HL-60, MO7e, KG1a, and K562 cells) and CD34+ primary human acute myeloid leukemia (AML) cells. SDF-1 alone did not stimulate the proliferation of these leukemia cells, nor did it rescue the cells from apoptosis induced by serum deprivation. By contrast, AMD3100, but not T140, stimulated the proliferation of all five leukemia cell lines and primary AML cells in a dose-dependent manner in serum-free conditions for up to 5 days (∼ 2-fold increases at a concentration of 10-5M), which was abrogated by pretreating the cells with pertussis toxin. AMD3100 binds to CXCR7, another SDF-1 receptor, and all of the cells examined in this study expressed CXCR4 on the cell surface to some extent. The proliferation-enhancing effects of AMD3100 were not changed by knocking-down CXCR7 using the siRNA technique, whereas knocking-down CXCR4 significantly delayed the enhanced proliferation induced by AMD3100. Neither AMD3100 nor T140 induced the phosphorylation of Akt, Stat3, MAPK p44/p42, or MAPK p38, which are involved in SDF-1 signaling. In extended cultures of these cells for up to 14 days, AMD3100, but not T140, induced a marked decrease in the number of cells, compared to the control, after incubation for 5-7 days. Adding SDF-1 at the beginning and middle of the incubation did not affect the early increase or later decrease in the number of cells. AMD3100 reduced the apoptosis of these cells to a modest degree over the first 5-7 days and then markedly increased it. Consistent with the proliferation assay, AMD3100 increased the number of leukemia cell colonies during the early period of the assay, while it markedly decreased the number and size of the colonies in the later period of the assay. In conclusion, AMD3100 exerts dual effects, initially enhancing and subsequently inhibiting the survival and proliferation, in myeloid leukemia cells in vitro. Disclosures No relevant conflicts of interest to declare.


Blood ◽  
2011 ◽  
Vol 118 (21) ◽  
pp. 3614-3614
Author(s):  
Metodi V. Stankov ◽  
Kirsten Heitmann ◽  
Zhe Li ◽  
Basant Kumar Thakur ◽  
Diana Panayotova-Dimitrova ◽  
...  

Abstract Abstract 3614 Despite well-described anti-cancer effects and promising results in clinical trials, little is known regarding the selectivity of histone deacetylase (HDAC) inhibitors in killing malignant and sparing normal cells. Using Down syndrome associated myeloid leukemia (DS-AMKL) as a model for an exceptionally sensitive form of acute myeloid leukemia (AML), we elucidated a role of HDAC inhibitors in blocking autophagy, which exploits a specific vulnerability of several types of cancer. We could show that HDAC1/2 inhibition efficiently inversed the DS-AMKL gene signature, resulting in p53-independent cell cycle arrest (BrdU incorporation and CFSE assay) and apoptosis (Annexin V/ 7-AAD and Nicoletti staining, caspase 3/7 activity assay) of DS-AMKL cell lines (CMK and CMY) and primary DS-AMKL leukemic blast. In contrast, control cell lines K562 and M07 were resistant to VPA-induced apoptosis. DS-AMKL is characterized by the high activation of the insulin-like growth factor (IGF) signaling cascade, which in turn results in the constitutive activation of mammalian target of rapamycin (mTOR). mTOR has been characterized as a major suppressor of autophagy, a lysosomal degradation process that takes place constitutively at a basal level and protects cells against damaged or unnecessary organelles and protein aggregates. Measuring endogenous LC3-I to LC3-II conversion levels by Western blot, a posttranslational modification during autophagy, we confirmed a lower basal autophagic activity in DS-AMKL cells compared to the control cell lines, K562 and M07 (LC3B-II/actin [RU]: 1.5 CMK, 1.0 CMY, 6.0 K562 and 3.0 M07). Studying the effect of HDAC inhibition on autophagy, we detected an initial, dose-dependent increase in LC3-II band formation, punctae formation and decrease in total LC3-GFP cellular abundance (i.e., autophagy activation) 12h after VPA treatment in all cell lines (CMK, CMY, K562 and M07), indicative for induction of autophagy. However, prolonged exposure to VPA for up to 24h led to a block of autophagic flux, as shown by a gradual accumulation of LC3-GFP (fold increase in LC3-GFP MFI compared to untreated control: 1.3 CMK**, 1.1 CMY*, 2.0 K562** and 2.0 M07** at 2mM VPA; **p<0.01; *p<0.05). Autophagy participates in the removal of damaged mitochondria, which prevents the initiation of intrinsic apoptotic pathway or DNA damage by increased ROS generation. Our results demonstrated a dose-dependent relationship between VPA-associated accumulation of mitochondrial mass and the intrinsic autophagic activity of the respective leukemic cell lines (fold increase in MitoTracker green MFI: 4.7 CMK**, 4.8 CMY**, 1.3 K562 and 1.2 M07 at 10mM VPA; **p<0.01). Likewise, the VPA-mediated mitochondrial mass accumulation correlated with ROS formation (fold increase in CM-H2DCFDA MFI: 3.3 CMK**, 2.7 CMY**, 1.5 K562** and 1.2 M07** at 10mM VPA; **p<0.01) and reflects the sensitivity to VPA induced apoptosis. In addition, we detected DNA-double strand breaks as indicated by an increase of phosphorylated H2AX. The effects of HDAC inhibitors on DS-AMKL cells could be recapitulated by pharmacologic (autophagosome-lysosome fusion using vinblastine and nocodazole; autophagolysosomal degradation using ammonium chloride, chloroquine and hydroxychloroquine) and genetic (shRNA-mediated knockdown of ATG5 or ATG7) inhibition of autophagy, underlining dependency on their low basal level of autophagy. Inversely, induction of autophagy by starvation reversed the effects of HDAC inhibition on cell lines and primary DS-AMKL cells (i.e. induction of apoptosis, accumulation of mitochondria and ROS-production). Thus, our study identified the role of HDAC inhibitors in blocking autophagy, exploiting the specific vulnerability of DS-AMKL cells with suppressed basic autophagy due to high mTOR activation. This was unexpected as previous studies proposed HDAC inhibitors as autophagy activators. VPA treatment of DS-AMKL cell lines and primary cells repressed autophagy below a critical threshold leading to accumulation of mitochondria, production of ROS, DNA-damage and apoptosis, which could be reverted upon autophagy activation. Our findings suggest repression of autophagy by HDAC inhibition as a novel treatment strategy in leukemic cells with highly active mTOR pathway. Disclosures: No relevant conflicts of interest to declare.


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