Autophagy prevents graft failure during murine graft-versus-host disease

ABSTRACT

Autophagy is an intracellular survival process that has established roles in the long-term survival and function of hematopoietic stem cells (HSC). We investigated the contribution of autophagy to HSC fitness during allogeneic transplantation and graft-versus-host disease (GVHD). We demonstrate in vitro that both tumor necrosis factor and IL-1β, major components of GVHD cytokine storm, synergistically promote autophagy in both HSC and their more mature hematopoietic progenitor cells (HPC). In vivo we demonstrate that autophagy is increased in donor HSC and HPC during GVHD. Competitive transplant experiments demonstrated that autophagy-deficient cells display reduced capacity to reconstitute the hematopoietic system compared to wild-type counterparts. In a major histocompatibility complex-mismatched model of GVHD and associated cytokine dysregulation, we demonstrate that autophagy-deficient HSC and progenitors fail to establish durable hematopoiesis, leading to primary graft failure and universal transplant related mortality. Using several different models, we confirm that autophagy activity is increased in early progenitor and HSC populations in the presence of T-cell-derived inflammatory cytokines and that these HSC populations require autophagy to survive. Thus, autophagy serves as a key survival mechanism in HSC and progenitor populations after allogeneic stem cell transplant and may represent a therapeutic target to prevent graft failure during GVHD.

Bacterial Lipopolysaccharides Suppress Erythroblastic Islands and Erythropoiesis in the Bone Marrow in an Extrinsic and G- CSF-, IL-1-, and TNF-Independent Manner

Anemia of inflammation (AI) is the second most prevalent anemia after iron deficiency anemia and results in persistent low blood erythrocytes and hemoglobin, fatigue, weakness, and early death. Anemia of inflammation is common in people with chronic inflammation, chronic infections, or sepsis. Although several studies have reported the effect of inflammation on stress erythropoiesis and iron homeostasis, the mechanisms by which inflammation suppresses erythropoiesis in the bone marrow (BM), where differentiation and maturation of erythroid cells from hematopoietic stem cells (HSCs) occurs, have not been extensively studied. Here we show that in a mouse model of acute sepsis, bacterial lipopolysaccharides (LPS) suppress medullary erythroblastic islands (EBIs) and erythropoiesis in a TLR-4- and MyD88-dependent manner with concomitant mobilization of HSCs. LPS suppressive effect on erythropoiesis is indirect as erythroid progenitors and erythroblasts do not express TLR-4 whereas EBI macrophages do. Using cytokine receptor gene knock-out mice LPS-induced mobilization of HSCs is G-CSF-dependent whereas LPS-induced suppression of medullary erythropoiesis does not require G- CSF-, IL- 1-, or TNF-mediated signaling. Therefore suppression of medullary erythropoiesis and mobilization of HSCs in response to LPS are mechanistically distinct. Our findings also suggest that EBI macrophages in the BM may sense innate immune stimuli in response to acute inflammation or infections to rapidly convert to a pro-inflammatory function at the expense of their erythropoietic function.

HIF prolyl hydroxylase inhibitor FG-4497 enhances mouse hematopoietic stem cell mobilization via VEGFR2/KDR

In normoxia, hypoxia-inducible transcription factors (HIFs) are rapidly degraded within the cytoplasm as a consequence of their prolyl hydroxylation by oxygen-dependent prolyl hydroxylase domain (PHD) enzymes. We have previously shown that hematopoietic stem and progenitor cells (HSPCs) require HIF-1 for effective mobilization in response to granulocyte colony-stimulating factor (G-CSF) and CXCR4 antagonist AMD3100/plerixafor. Conversely, HIF PHD inhibitors that stabilize HIF-1 protein in vivo enhance HSPC mobilization in response to G-CSF or AMD3100 in a cell-intrinsic manner. We now show that extrinsic mechanisms involving vascular endothelial growth factor receptor-2 (VEGFR2), via bone marrow (BM) endothelial cells, are also at play. PTK787/vatalanib, a tyrosine kinase inhibitor selective for VEGFR1 and VEGFR2, and neutralizing anti-VEGFR2 monoclonal antibody DC101 blocked enhancement of HSPC mobilization by FG-4497. VEGFR2 was absent on mesenchymal and hematopoietic cells and was detected only in Sca1+ endothelial cells in the BM. We propose that HIF PHD inhibitor FG-4497 enhances HSPC mobilization by stabilizing HIF-1α in HSPCs as previously demonstrated, as well as by activating VEGFR2 signaling in BM endothelial cells, which facilitates HSPC egress from the BM into the circulation.

MYB down-regulation enhances sensitivity of U937 myeloid leukemia cells to the histone deacetylase inhibitor LBH589 in vitro and in vivo

The effect of combining MYB suppression with the histone deacetylase inhibitor LBH589 was studied in human myeloid leukemia cell lines. MYB knockdown inhibited proliferation and induced apoptosis in U937 and K562 cells in vitro, and also sensitized both to the pro-apoptotic effect of LBH589. This was accompanied by enhanced expression of the pro-apoptotic BCL2 family members BOK and BIM. U937 cells carrying inducible MYB shRNA were also transplanted into NOD/SCID mice. The combination of MYB knockdown and LBH589 prolonged survival compared to either treatment alone, suggesting that further development of such combinations might lead to effective and safe leukemia therapies.

Abstract A17: The dual angiogenesis/heparanase inhibitor PG545 inhibits solid tumor progression in models of breast, prostate and liver cancer: A comparative assessment of once versus twice weekly administration schedules

PG545 is Progen's lead oncology candidate currently undergoing formal preclinical development. PG545 is a synthetic heparan sulfate (HS) mimetic that prevents neovascularization by inhibiting growth-factor heparan sulfate binding and metastasis through the inhibition of heparan sulfate cleavage by heparanase. PG545 was assessed for efficacy in a number of xenograft models, namely the MDA-MB-231 (breast), PC3 (prostate), HepG2 (liver) and the orthotopic model Hep3B (liver). In the Hep3B liver cancer model, a concurrent study dosed tumor-bearing mice with radiolabeled PG545 every 96 h for three doses in order to generate a pharmacokinetic (PK) profile of the compound in blood and tumor tissue. In the efficacy studies, once or twice weekly treatment was initiated once the tumors reached 100–200cm3 (depending on the study). Although not significantly different to twice weekly dosing, PG545 exhibited maximal antitumor efficacy when dosed once weekly in each of the four independent studies. Moreover, in the Hep3B liver cancer study, PG545 exhibited antitumor activity to a similar extent as the tyrosine kinase inhibitor sorafenib which is approved by the FDA for inoperable hepatocellular carcinoma. A preliminary pharmacokinetic profile using radiolabeled compound [3H]-PG545 was also obtained. Data generated using both compartmental and non-compartmental modeling indicate a favourable pharmacokinetic profile and significant uptake of [3H]-PG545 into the tumor from the bloodstream. Taken together, the tumor efficacy and pharmacokinetic data support the ongoing preclinical development of PG545 as a once weekly, subcutaneously administered injection for the treatment of cancer.

Citation Information: Mol Cancer Ther 2009;8(12 Suppl):A17.

Prediction of pre-eclampsia by abnormal uterine Doppler ultrasound and modification by aspirin

OBJECTIVE

To assess the effect of low dose aspirin on severe pre-eclampsia when given to women identified as high risk by abnormal uterine artery Doppler ultrasound.

DESIGN

Women with abnormal uterine artery flow velocity waveforms were recruited to the CLASP trial at 24 weeks. Abnormal uterine artery waveforms, with a high resistance index or an early diastolic notch, were identified at the 18-22 week anomaly scan and confirmed at 24 weeks. Of those women with persistently abnormal waveforms, 63 agreed to enter the CLASP trial. Three women were lost to follow up and five did not comply. Thus, 60 were randomised: 29 to placebo and 31 to low dose aspirin (60 mg daily) and analysis by intention to treat is reported.

RESULTS

There were nine cases (29%) of pre-eclampsia in the aspirin group and twelve (41%) in the placebo group (odds ratio (OR) 0-58, confidence interval (CI) 0.2-1.69, P = 0.32). Severe pre-eclampsia developed in four women in the aspirin group and eleven women in the placebo group (OR 0.24, CI 0.07-0.88, P = 0.03) and intrauterine growth retardation occurred in eight cases in the aspirin group and twelve in the placebo group (OR 0.49, CI 0.17-1.47). The mean birthweight and gestation at delivery were 2.69 kg and 38.5 weeks in the aspirin group and 2.38 kg and 37.4 weeks in the placebo group, neither of which were statistically significant using the unpaired t test; P = 0.09 and P = 0.23, respectively.

CONCLUSION

In high risk pregnancy low dose aspirin commenced at 24 weeks may reduce the incidence of severe pre-eclampsia.

Braxton-Hicks contractions can alter uteroplacental perfusion

Color flow imaging was used to study the effect of spontaneous low-amplitude uterine contractions (Braxton-Hicks) on flow velocity waveforms obtained from the main uterine artery in 13 women between 26 and 34 weeks' gestation. Eight women had abnormal waveforms, as defined by the presence of an early diastolic notch, and five women had normal waveforms. In the former group, three women with chronic hypertension were started on the calcium antagonist nifedipine during this study. Contractions, which were monitored by external tocography, occurred more frequently in the group with abnormal waveforms and were temporally associated with an increase in impedance to blood flow. This effect occurred to the same degree in both normal and abnormal groups, but in the abnormal group the already impaired blood flow to the intervillous space was further diminished, resulting in absence of forward flow in diastole. Such acute reductions of flow in response to frequent, impalpable uterine contractions may cause a prolonged and silent insult to uteroplacental perfusion, which could hasten fetal compromise. This effect appeared to be abolished in patients on nifedipine, suggesting a possible therapeutic role for this drug in uteroplacental insufficiency.