All-trans retinoic acid regulates adhesion mechanism and transmigration of the acute promyelocytic leukaemia cell line NB-4 under physiologic flow

A case report of acute promyelocytic leukemia with myeloid sarcoma of the lumbar spine and literature review

Acute promyelocytic leukemia (APL) presenting solely as myeloid sarcoma (MS) is extremely rare. This report describes a 53-year-old male who presented with low back pain and a movement disorder in his lower limbs. MRI and PET/CT scans of the lumbar spine revealed an intraspinal mass. Pathological analysis of the surgically resected mass identified it as myeloid in origin. Routine blood tests were unremarkable, and bone marrow smears and immunophenotyping showed no evidence of abnormal myeloblasts or promyelocytes. However, bone marrow aspirates testing for acute leukemia fusion genes by qPCR revealed the presence of the PML::RARA fusion. Further investigation via FISH confirmed the fusion in both the bone marrow and the extramedullary mass. The patient was ultimately diagnosed with isolated promyelocytic extramedullary sarcoma (MS/APL). Treatment with all-trans retinoic acid and arsenic trioxide alleviated the back pain and restored the patient's mobility. After 1 year of consolidation therapy, bone marrow smears confirmed sustained remission, and the PML::RARA fusion gene was undetectable. In addition to this case, we review 41 other APL patients with extramedullary sarcoma as their first symptom (MS/APL) at the time of diagnosis and provide an analysis of these cases.

Diagnosis and management of acute promyelocytic leukemia: Brazilian consensus guidelines 2024 on behalf of the Brazilian Association of Hematology, Hemotherapy and Cellular Therapy

Improvements in clinical assessment have occurred since the last published recommendations on the diagnosis and treatment of acute promyelocytic leukemia in 2013. Here, a committee of specialists of the Brazilian Association of Hematology, Hemotherapy and Cellular Therapy presents a comprehensive review on the current knowledge, focusing on the advances in diagnosis, risk assessment, and frontline and salvage therapy. The concept of urgent diagnosis is explored as well as the management of critical situations such as coagulopathy and differentiation syndrome. Recent adjustments in risk stratification based on white blood cell counts only are presented together with the incorporation of chemo-free regimens for non-high-risk patients. Special conditions such as acute promyelocytic leukemia in children, the elderly and pregnant women are discussed. Finally, acute promyelocytic leukemia is presented as a highly curable disease because of the real possibility of targeted therapy towards differentiation, and, paradoxically, as a serious and urgent condition that deserves prompt recognition and management to avoid early mortality.

Differentiation Syndrome in Acute Leukemia: APL and Beyond

Differentiation syndrome (DS) is a frequent and potentially life-threatening clinical syndrome first recognized with the advent of targeted therapeutics for acute promyelocytic leukemia (APL). DS was subsequently observed more broadly with targeted therapeutics for acute myeloid leukemia (AML). DS is typically characterized by fever, dyspnea, hypotension, weight gain, pleural or pericardial effusions, and acute renal failure. The incidence in patients with APL ranges from 2 to 37%, with the wide variation likely attributed to different diagnostic criteria, use of prophylactic treatment, and different treatment regimens. Treatment with corticosteroids +/- cytoreductive therapy should commence as soon as DS is suspected to reduce DS-related morbidity and mortality. The targeted anti-leukemic therapy should be discontinued in patients with severe DS. Here, we discuss the pathogenesis of DS, clinical presentations, diagnostic criteria, management strategies, and implementation of prospective tracking on clinical trials.

ATRA treatment slowed P-selectin-mediated rolling of flowing HL60 cells in a mechano-chemical-dependent manner

All-trans retinoic acid (ATRA)-induced differentiation of acute promyelocytic leukemia (APL) toward granulocytes may trigger APL differentiation syndrome (DS), but there is less knowledge about the mechano-chemical regulation mechanism of APL DS under the mechano-microenvironment. We found that ATRA-induced changes in proliferation, morphology, and adhesive molecule expression levels were either dose or stimulus time dependent. An optimal ATRA stimulus condition for differentiating HL60 cells toward neutrophils consisted of 1 × 10^-6 M dose and 120 h of stimulus time. Under wall shear stresses, catch-slip bond transition governs P-selectin-mediated rolling for neutrophils and untreated or ATRA-treated (1 × 10^-6 M, 120 h) HL60 cells. The ATRA stimuli slowed down the rolling of HL60 cells on immobilized P-selectin no matter whether ICAM-1 was engaged. The β2 integrin near the PSGL-1/P-selectin axis would be activated within sub-seconds for each cell group mentioned above, thus contributing to slow rolling. A faster β2 integrin activation rate and the higher expression levels of PSGL-1 and LFA-1 were assigned to induce the over-enhancement of ATRA-treated HL60 adhesion in flow, causing APL DS development. These findings provided an insight into the mechanical-chemical regulation for APL DS development via ATRA treatment of leukemia and a novel therapeutic strategy for APL DS through targeting the relevant adhesion molecules.

Functional association of NR4A3 downregulation with impaired differentiation in myeloid leukemogenesis

The coincident downregulation of NR4A1 and NR4A3 has been implicated in myeloid leukemogenesis, but it remains unknown how these two genes function in myeloid cells and how their combined downregulation promotes myeloid leukemogenesis. Since NR4A1 abrogation is thought to confer a survival and proliferation advantage to myeloid cells, we hypothesized that downregulation of NR4A3 may have a complementary effect on myeloid cell differentiation. First, we tested the association between differentiation status of leukemic cells and NR4A3 expression using two large clinical datasets from patients with different acute myeloid leukemia (AML) subtypes. The analysis revealed a close association between differentiation status and different subtypes of AML Then, we probed the effects of differentiation-inducing treatments on NR4A3 expression and NR4A3 knockdown on cell differentiation using two myeloid leukemia cell lines. Differentiation-inducing treatments caused upregulation of NR4A3, while NR4A3 knockdown prevented differentiation in both cell lines. The cell culture findings were validated using samples from chronic myeloid leukemia (CML) patients at chronic, accelerated and blastic phases, and in acute promyelocytic leukemia (APL) patients before and after all trans-retinoic acid (ATRA)-based differentiation therapy. Progressive NR4A3 downregulation was coincident with impairments in differentiation in patients during progression to blastic phase of CML, and NR4A3 expression was increased in APL patients treated with ATRA-based differentiating therapy. Together, our findings demonstrate a tight association between impaired differentiation status and NR4A3 downregulation in myeloid leukemias, providing a plausible mechanistic explanation of how myeloid leukemogenesis might occur upon concurrent downregulation of NR4A1 and NR4A3.

Interleukin-8 is not a predictive biomarker for the development of the acute promyelocytic leukemia differentiation syndrome

Background

Differentiation syndrome (DS) is the main life-threatening adverse event that occurs in acute promyelocytic leukemia (APL) patients treated with all-trans retinoic acid (ATRA). Cytokine imbalances have been reported to play role during the developing of acute promyelocytic leukemia differentiation syndrome (APL-DS). However, the relationship between the plasma cytokine levels and their prognostic value for the prediction of DS developing in patients with APL during the treatment with ATRA and anthracyclines has not been previously reported.

Methods

In this study, we followed an APL cohort (n = 17) over 7 days of ATRA therapy in DS (n = 6) and non-DS groups (n = 11). Interleukin (IL)-1β, IL-6, IL-8, IL-10, IL-12p70 and TNF-α were measured in the peripheral blood plasma from 17 patients with APL and 11 healthy adult controls by using the cytometric bead array method.

Results

In non-DS patients, IL-8 plasma levels were significantly reduced in the seventh day of ATRA treatment (34.16; 6.99 to 147.11 pg mL^− 1 in D0 vs. 10.9; 0 to 26.81 pg mL^− 1 in D7; p = 0.02) whereas their levels did not discriminate between DS and non-DS development during the entire induction period (all p > 0.05 in D0, D3, and D7). No significant differences were found in IL-6 levels between groups (p > 0.05 in D0-D7). Other cytokines tested were all undetectable in patients with APL or healthy controls.

Conclusions

We demonstrated that the modulation of IL-8 following ATRA treatment may occur regardless of the development of DS and, therefore, does not appear to be a predictive biomarker to monitor the APL-DS.

Empagliflozin restores the integrity of the endothelial glycocalyx in vitro

The antihyperglycemic agent empagliflozin not only improves glycemic control but has also been associated with clinically meaningful reductions in cardiovascular events. Studies have shown that empagliflozin significantly reduces cardiovascular death and heart failure-associated hospitalizations. Given that endothelial dysfunction is closely linked with the pathogenesis of atherosclerotic cardiovascular disease, we hypothesized that the cardiovascular benefits observed with empagliflozin may be a result of its positive impact on the health of the endothelial glycocalyx (GCX), a critical component for the endothelium homeostasis. Human abdominal aortic endothelial cells (HAAECs) were either statically cultured or subjected to a steady wall shear stress of 10 dyne/cm². Empagliflozin (50 µM, 24 h) restored heparinase III-mediated GCX disruption and the normal mechanotransduction responses in GCX-compromised HAAECs while reducing the attachment of all-trans retinoic acid-transformed NB4 cells to HAAECs. The current body of work suggests that the cardioprotective properties previously reported for empagliflozin may in part be due to the ability of empagliflozin to preserve and restore the structural integrity of the GCX, which in turn helps to maintain vascular health by promoting an anti-inflammatory endothelium, in the presence of a pro-inflammatory environment. Further studies are needed to fully understand the mechanisms underlying the cardiovascular benefits of empagliflozin.

All-Trans Retinoic Acid Enhances Matrix Metalloproteinase 2 Expression and Secretion in Human Myeloid Leukemia THP-1 Cells

All-trans retinoic acid (ATRA) is an effective drug for the induction therapy of acute promyelocytic leukemia. However, the treatment is associated with adverse events such as retinoic acid syndrome (RAS) in some patients, whose histologic characteristics included organ infiltration by leukemic cells. Matrix metalloproteinase 2 (MMP-2) is often upregulated in tumor cells and plays a role in tumor cell migration and invasion by degrading the extracellular matrix. In this study, we examined the possible modulatory effects of ATRA on MMP-2 expression and secretion in human myeloid leukemia cell line THP-1. The cells were treated with various concentrations of ATRA, and MMP-2 expression and secretion were examined. MMP-2 expression and secretion started to increase with ATRA concentration as low as 0.1 nM and gradually increased thereafter. Agonists of retinoic acid receptor (RAR) or retinoid X receptor (RXR) alone could enhance MMP-2 secretion, and RAR or RXR antagonists alone could reverse ATRA-induced MMP-2 secretion. ATRA increased intracellular calcium ion levels, and a calcium-channel blocker inhibited ATRA-induced MMP-2 secretion. Dexamethasone suppressed ATRA-induced MMP-2 secretion. Our results suggest that ATRA enhances MMP-2 expression and secretion in human myeloid leukemia THP-1 cells in a calcium ion dependent manner through RAR/RXR signaling pathways, and this enhanced expression and secretion may be associated with the possible mechanisms of RAS.

Integrating microRNA and mRNA expression profiles of acute promyelocytic leukemia cells to explore the occurrence mechanisms of differentiation syndrome

The pathogenesis of therapy-induced differentiation syndrome (DS) in patients with acute promyelocytic leukemia (APL) remains unclear. In this study, mRNA and microRNA (miRNA) expression profiling of peripheral blood APL cells from patients complicated with vs. without DS were integratively analyzed to explore the mechanisms underlying arsenic trioxide treatment-associated DS. By integrating the differentially expressed data with the data of differentially expressed microRNAs and their computationally predicted target genes, as well as the data of transcription factors and differentially expressed target microRNAs obtained from a literature search, a DS-related genetic regulatory network was constructed. Then using an EAGLE algorithm in clusterViz, the network was subdivided into 10 modules. Using the Kyoto Encyclopedia of Genes and Genomes (KEGG) database the modules were annotated functionally, and three functionally active modules were recognized. The further in-depth analyses on the annotated functions of the three modules and the expression and roles of the related genes revealed that proliferation, differentiation, apoptosis and infiltration capability of APL cells might play important roles in the DS pathogenesis. The results could improve our understanding of DS pathogenesis from a more overall perspective, and could provide new clues for future research.

HMGB1 promotes differentiation syndrome by inducing hyperinflammation via MEK/ERK signaling in acute promyelocytic leukemia cells

Differentiation therapy based on all-trans-retinoic acid (ATRA) and arsenic trioxide (ATO) for the treatment of acute promyelocytic leukemia (APL) is complicated by the development of differentiation syndrome (DS), which can be fatal. We examined the role of HMGB1 (high-mobility group box 1) in DS using both in vitro and in vivo models. HMGB1 and the pro-inflammatory cytokines IL-1β and TNF-α were gradually released from NB4 and HL-60 cells treated with ATRA and/or ATO. Similarly, higher serum HMGB1 levels positively correlated with the clinical status of DS patients. Exogenous HMGB1 promoted rapid release of IL-1β and TNF-α as well as elevated expression of ICAM-1, without altering cell differentiation. Exogenous HMGB1 also enhanced pulmonary infiltration and up-regulated ICAM-1 expression in the ATRA-treated DS mouse. Pharmacological inhibition or depletion of MEK1/2 reduced the cytokine levels and suppressed expression of ICAM-1 and the adhesion of HMGB1-treated NB4 cells to endothelial cells, implicating MEK/ERK signaling in the response to HMGB1 during DS. Treatment with a HMGB1-neutralizing antibody reduced secretion of TNF-α and IL-1β, arrested the elevation of ICAM-1 and blunted the activation of ERK1/2 in ATRA-induced NB4 cells. The HMGB1-neutralizing antibody also decreased ICAM-1 expression and reduced mortality in ATRA-treated DS model mice. These findings demonstrate that released HMGB1 is central to DS, and that targeting HMGB1 may be of therapeutic value in the treatment of DS.

In vitro studies on the role of recombinant human soluble thrombomodulin in the context of retinoic acid mediated APL differentiation syndrome

Recombinant human soluble thrombomodulin (rTM) is a newly developed anti-coagulant approved for treatment of disseminated intravascular coagulation (DIC) in Japan. rTM exerts anti-inflammatory and cytoprotective functions via its lectin-like and epidermal growth factor-like domains, respectively. In this study, we retrospectively reviewed the treatment of 21 consecutive patients with coagulopathy, complicated by acute promyelocytic leukemia (APL), with all-trans retinoic acid (ATRA) with or without combination with rTM. Surprisingly, none of the 14 rTM-treated patients developed retinoic acid (RA)-related differentiation syndrome (DS). The co-culture of vascular endothelial cell-derived EA.hy926 and APL-derived NB4 cells in the presence of RA increased production of tumor necrosis factor alpha (TNF-α) in culture media, in parallel with activation of p38 mitogen-activated protein kinase and increased levels of intracellular adhesion molecule 1 (ICAM1) in EA.hy926 cells. This was also associated with increased levels of the phosphorylated forms of VE-cadherin and enhanced vascular permeability of EA.hy926 monolayers. Importantly, addition of rTM to this co-culture system inhibited the RA-induced phosphorylation of p38 and VE-cadherin and decreased ICAM1 and vascular permeability in EA.hy926 cells, without a decrease inthe levels of TNF-α. Taken together, use of rTM may be a promising treatment strategy to prevent DS in APL patients who receive ATRA.

Retinoic acid receptor gamma impacts cellular adhesion, Alpha5Beta1 integrin expression and proliferation in K562 cells

The interplay between cellular adhesion and proliferation is complex; however, integrins, particularly the α5β1 subset, play a pivotal role in orchestrating critical cellular signals that culminate in cellular adhesion and growth. Retinoids modify the expression of a variety of adhesive/proliferative signaling proteins including α5β1 integrins; however, the role of specific retinoic acid receptors involved in these processes has not been elucidated. In this study, the effect of all-trans-retinoic acid receptor (RAR) agonists on K562 cellular adhesion, proliferation, and α5β1 integrin cell surface expression was investigated. RARγ agonist exposure increased K562 cellular adhesion to RGD containing extracellular matrix proteins fibronectin and FN-120 in a time- and concentration dependent manner, while RARα or RARβ agonist treatment had no effect on cellular adhesion. Due to the novel RARγ- dependent cellular adhesion response exhibited by K562 cells, we examined α5 and β1 integrin subunit expression when K562 cells were exposed to retinoid agonists or vehicle for 24, 48, 72 or 96 hours. Our data demonstrates no differences in K562 cell surface expression of the α5 integrin subunit when cells were exposed to RARα, RARβ, or RARγ agonists for all time points tested. In contrast, RARγ agonist exposure resulted in an increase in cell surface β1 integrin subunit expression within 48 hours that was sustained at 72 and 96 hours. Finally, we demonstrate that while exposure to RARα or RARβ agonists have no effect on K562 cellular proliferation, the RARγ agonist significantly dampens K562 cellular proliferation levels in a time- and concentration- dependent manner. Our study is the first to report that treatment with a RARγ specific agonist augments cellular adhesion to α5β1 integrin substrates, increases cell surface levels of the β1 integrin subunit, and dampens cellular proliferation in a time and concentration dependent manner in a human erythroleukemia cell line.

Stenosis Hemodynamics Disrupt the Endothelial Cell Glycocalyx by MMP Activity Creating a Proinflammatory Environment

Hemodynamic forces are known to be able to induce an inflammatory phenotype in endothelial cells (ECs). The EC glycocalyx (GCX) is a dynamic structure which is regulated in response to different stimuli and hypothesized as an important contributor to the mechanotransduction of wall shear stresses (WSS). In this work, we used a three dimensional in vitro EC culture model with a 50% asymmetric stenosis to investigate degradation of the GCX by increased matrix metalloproteinase (MMP) activity in regions of WSS gradients and how this degradation might create a proinflammatory environment. Experiments showed GCX degradation was observed in regions of WSSGs created by a 50% asymmetric stenosis. Furthermore, inhibition of MMP activity abolished this regional degradation. The integrity of the GCX altered EC morphological elongation to flow and leukocyte adhesion patterns. These results help strengthen the hypothesis that the EC GCX is involved in the mechanotransduction of hemodynamic forces and that the GCX is regulated by MMP activity in regions of WSSGs.

MDI 301 suppresses myeloid leukemia cell growth in vitro and in vivo without the toxicity associated with all-trans retinoic acid therapy

MDI 301 is a novel 9-cis retinoic acid derivative in which the terminal carboxylic acid group has been replaced by a picolinate ester. MDI 301, a retinoic acid receptor-α - agonist, suppressed the growth of several human myeloid leukemia cell lines (HL60, NB4, OCI-M2, and K562) in vitro and induced cell-substrate adhesion in conjunction with upregulation of CD11b. Tumor growth in HL60-injected athymic nude mice was reduced. In vitro, MDI 301 was comparable to all-trans retinoic acid (ATRA) whereas in vivo, MDI 301 was slightly more efficacious than ATRA. Most importantly, unlike what was found with ATRA treatment, MDI 301 did not induce a cytokine response in the treated animals and the severe inflammatory changes and systemic toxicity seen with ATRA did not occur. A retinoid with these characteristics might be valuable in the treatment of promyelocytic leukemia, or, perhaps, other forms of myeloid leukemia.

Retinoids induce integrin-independent lymphocyte adhesion through RAR-α nuclear receptor activity

Oxidative metabolites of vitamin A, in particular all-trans-retinoic acid (atRA), have emerged as key factors in immunity by specifying the localization of immune cells to the gut. Although it is appreciated that isomers of retinoic acid activate the retinoic acid receptor (RAR) and retinoid X receptor (RXR) family of nuclear receptors to elicit cellular changes, the molecular details of retinoic acid action remain poorly defined in immune processes. Here we employ a battery of agonists and antagonists to delineate the specific nuclear receptors utilized by retinoids to evoke lymphocyte cell adhesion to ADAM (adisintegrin and metalloprotease) protein family members. We report that RAR agonism is sufficient to promote immune cell adhesion in both immortal and primary immune cells. Interestingly, adhesion occurs independent of integrin function, and mutant studies demonstrate that atRA-induced adhesion to ADAM members required a distinct binding interface(s) as compared to integrin recognition. Anti-inflammatory corticosteroids as well as 1,25-(OH)2D3, a vitamin D metabolite that prompts immune cell trafficking to the skin, potently inhibited the observed adhesion. Finally, our data establish that induced adhesion was specifically attributable to the RAR-α receptor isotype. The current study provides novel molecular resolution as to which nuclear receptors transduce retinoid exposure into immune cell adhesion.

9-cis-retinoic Acid and troglitazone impacts cellular adhesion, proliferation, and integrin expression in K562 cells

Retinoids are established pleiotropic regulators of both adaptive and innate immune responses. Recently, troglitazone, a PPAR gamma agonist, has been demonstrated to have anti-inflammatory effects. Separately, retinoids and troglitazone are implicated in immune related processes; however, their combinatory role in cellular adhesion and proliferation has not been well established. In this study, the effect of 9-cis-retinoic acid (9-cis-RA) and troglitazone on K562 cellular adhesion and proliferation was investigated. Troglitazone exposure decreased K562 cellular adhesion to RGD containing extracellular matrix proteins fibronectin, FN-120, and vitronectin in a concentration and time-dependent manner. In the presence of troglitazone, 9-cis-retinoic acid restores cellular adhesion to levels comparable to vehicle treatment alone on fibronectin, FN-120, and vitronectin substrates within 72 hours. Due to the prominent role of integrins in attachment to extracellular matrix proteins, we evaluated the level of integrin α5 subunit expression. Troglitazone treatment results in decrease in α5 subunit expression on the cell surface. In the presence of both agonists, cell surface α5 subunit expression was restored to levels comparable to vehicle treatment alone. Additionally, troglitazone and 9-cis-RA mediated cell adhesion was decreased in the presence of a function blocking integrin alpha 5 inhibitor. Further, through retinoid metabolic profiling and HPLC analysis, our study demonstrates that troglitazone augments retinoid availability in K562 cells. Finally, we demonstrate that troglitazone and 9-cis-retinoic acid synergistically dampen cellular proliferation in K562 cells. Our study is the first to report that the combination of troglitazone and 9-cis-retinoic acid restores cellular adhesion, alters retinoid availability, impacts integrin expression, and dampens cellular proliferation in K562 cells.

9-cis-retinoic acid promotes cell adhesion through integrin dependent and independent mechanisms across immune lineages

Retinoids are essential in the proper establishment and maintenance of immunity. Although retinoids are implicated in immune related processes, their role in immune cell adhesion has not been well established. In this study, the effect of 9-cis-retinoic acid (9-cis-RA) on human hematopoietic cell adhesion was investigated. 9-cis-RA treatment specifically induced cell adhesion of the human immune cell lines HuT-78, NB4, RPMI 8866 and U937. Due to the prominent role of integrin receptors in mediating immune cell adhesion, we sought to evaluate if cell adhesion was integrin-dependent. By employing a variety of integrin antagonist including function-blocking antibodies and EDTA, we establish that 9-cis-RA prompts immune cell adhesion through established integrin receptors in addition to a novel integrin-independent process. The novel integrin-independent adhesion required the presence of retinoid and was attenuated by treatment with synthetic corticosteroids. Finally, we demonstrate that 9-cis-RA treatment of primary murine B-cells induces ex vivo adhesion that persists in the absence of integrin function. Our study is the first to demonstrate that 9-cis-RA influences immune cell adhesion through at least two functionally distinct mechanisms.

Advances in understanding the pulmonary infiltration in acute promyelocytic leukaemia

In acute promyelocytic leukaemia (APL), differentiation therapy can be complicated by the development of a differentiation syndrome (DS). Pulmonary infiltration of differentiating leukaemic cells is a key event in the development of DS. Several mediators have been identified that may promote migration and extravasation of differentiating APL cells from the bloodstream into the tissue. Adhesion of APL cells to each other and to the endothelium is induced by upregulation of the expression of adhesion molecules and constitutively active β2-integrins during differentiation therapy. The expression of chemokines and their receptors is significantly upregulated as well. Pulmonary chemokine production can trigger transendothelial migration of differentiating APL cells from the bloodstream into the underlying tissue (initiation phase of DS). Massive production of chemokines by infiltrated APL cells can further enhance transendothelial migration of differentiating APL cells, causing an uncontrollable hyperinflammatory reaction in the lung (aggravation phase), which is not efficiently switched-off by corticosteroids.

Interaction of SDF-1alpha and CXCR4 plays an important role in pulmonary cellular infiltration in differentiation syndrome

This study aims to investigate the role of stromal cell-derived factor 1alpha (SDF-1alpha) and its receptor CXCR4 in cellular infiltration of the lung in differentiation syndrome (DS). The acute promyelocytic leukemia (APL) NB4 cells and freshly prepared APL cells from the patients were differentiated by all-trans retinoic acid (ATRA). The expression of SDF-1alpha in human lung tissues was examined by RT-PCR and Western blot analysis. The cells were subjected to adhesion, migration or invasion assays, and co-cultured with human lung tissues in a microgravity rotary cell culture system to examine cellular infiltration in situ. ATRA-differentiated cells expressed high levels of CXCR4, and adhered more strongly to matrigel. Their ability to migrate and invade was enhanced by SDF-1alpha and lung homogenate, and diminished by pre-treatment with an anti-CXCR4 blocking antibody. SDF-1alpha was expressed in the lung tissues of all seven human donors. ATRA-differentiated NB4 cells infiltrated into lung tissues, and this was reduced by pre-treatment with an anti-CXCR4 blocking antibody. The interaction of SDF-1alpha and CXCR4 plays an important role in pulmonary cellular infiltration during DS, suggesting that targeting SDF-1alpha and CXCR4 may provide the basis for potential treatments in the management of DS.

[Tripterine inhibits all-trans retinoic acid-caused adhesion between leukemia cells and endothelial cells]

OBJECTIVE

Increasing of adhesion between leukemia cells and endothelial cells during all-trans retinoic acid (ATRA) treatment plays an important role in retinoic acid syndrome. This work observed the effects of tripterine on this ATRA-caused increasing in adhesion.

METHODS

The effects of tripterine on ATRA-induced expressions of adhesive molecules in acute promyelocytic leukemia cell line NB4 and human umbilical vascular endothelial cells (HUVEC) were detected by flow cytometry. The effects of tripterine on adhesion between ATRA-treated NB4 and HUVEC were determined by adhesive assays.

RESULTS

ATRA caused remarkable elevation of intercellular adhesion molecule-1 (ICAM-1) in NB4 cells, which could be significantly reduced by tripterine (P<0.01). The expressions of E-selectin, vascular cell adhesion molecule-1 (VCAM-1) and ICAM-1 in HUVEC were elevated by conditioned medium from ATRA-induced NB4 (ATRA-NB4-CM) (P<0.01), and inhibited by tripterine with inhibition rates being 25.3%, 42.4% and 61.0% respectively. ATRA increased the adhesion between NB4 and HUVEC, which was reversed completely by tripterine.

CONCLUSION

Tripterine can inhibit ATRA-caused adhesion between leukemia cells and endothelial cells, and it might be a potential agent for treating retinoic acid syndrome.

All-transRetinoic Acid Enhances Murine Dendritic Cell Migration to Draining Lymph Nodes via the Balance of Matrix Metalloproteinases and Their Inhibitors

Cancers escape immune surveillance through the manipulation of the host's immune system. Sequestration of dendritic cells (DCs) within tumor tissues and the subsequent inhibition of their migration is one of the several mechanisms by which tumors induce immunosuppression. In view of recent findings depicting the improvement of tumor immune responses in cancer patients following all-trans retinoic acid (ATRA) treatment, we sought to identify the effects of ATRA on DC mobility in the context of tumor immunotherapy. Our results demonstrate that ATRA, added to differentiating murine bone marrow progenitor cells, enhances the invasive capacity of the resulting DCs. Immature DCs injected intratumorally in mice show increased accumulation in draining lymph nodes, but not in nondraining lymph nodes and spleens, when differentiated in the presence of ATRA. The in vitro migration of mature DCs through the basement membrane matrix toward the lymphoid chemokines CCL19 and CCL21 is enhanced in these cells, albeit not in the presence of a matrix metalloproteinase (MMP) inhibitor. An increase in MMP production with a simultaneous decrease in the production of their inhibitors (tissue inhibitors of matrix metalloproteinase or TIMPs) is provoked by ATRA. This affects the MMP/TIMP balance in DCs, in particular that of MMP-9 and TIMP-1, favoring protease activity and thus allowing for enhanced DC mobilization. In conclusion, this study demonstrates that ATRA is capable of improving DC trafficking in a tumor milieu and, in view of the encouraging results obtained in the clinic, further supports the notion that ATRA might be a valuable chemical adjuvant to current immunotherapeutic strategies for cancer.

All-trans retinoic acid induces different immunophenotypic changes on human HL60 and NB4 myeloid leukaemias

All-trans retinoic acid (ATRA) is used to treat patients with acute promyelocytic leukaemia (APL), inducing APL cells to differentiate into abnormal neutrophils. To investigate the possible relationship between the chromosome translocation t(15;17) found in APL and ATRA treatment, the human myeloid leukaemia cell lines HL60 and NB4, that are PML-RARalpha negative and positive, respectively, were treated with ATRA and immunophenotyped using a CD antibody microarray. For HL60 cells, ATRA induced major increases in descending order of CD38, CD11b, CD45RO, CD11c, CD54 and CD36 with repression of CD117 and CD44. For NB4 cells, ATRA induced major increases in descending order of CD11c, CD54, CD11a, CD11b, CD53, CD65, CD138, CD66c and T-cell receptor alpha/beta (TCRalpha/beta), with repression of CD38 and CD9. The induction of a number of these CD antigens is consistent with the known differentiation of these leukaemias to abnormal neutrophils. Approximately half of the antigens up-regulated by ATRA on NB4 cells were adhesion molecules, including CD11a, CD11b, CD11c, CD54, CD66c and CD138, consistent with the increased adhesiveness of leukaemia cells observed for APL patients treated with ATRA. On HL60 cells, ATRA induced expression of CD38, CD43 and CD45RO and repressed CD117, while the converse was true on NB4 cells that contain chimeric PML-RARalpha. For NB4 cells, ATRA induced some remarkable increases in CD antigens not seen for HL60: CD14 (16.6-fold), CD32 (27.8), CD53 (20.5), CD65 (139), CD66c (79.7), CD126 (15.1), and CD138 (57.6). The expression of these antigens may be regulated by PML-RARalpha in the presence of ATRA. Such CD antigens could be targets for synergistic treatment of APL with therapeutic antibodies following ATRA treatment.

Role of interleukin-8 and growth-regulated oncogene-α in the chemotactic migration of all-trans retinoic acid-treated promyelocytic leukemic cells toward alveolar epithelial cells*

OBJECTIVE

Although all-trans retinoic acid (ATRA) can treat acute promyelocytic leukemia (APL), it also causes retinoic acid syndrome with presentations similar to acute respiratory distress syndrome. We investigated the role of interleukin (IL)-8 and growth-regulated oncogene (GRO)-alpha in the chemotactic transmigration of ATRA-treated NB4 (ATRA-NB4) APL cells toward A549 alveolar epithelial cells.

DESIGN

An in vitro human cell culture study.

SETTING

University hospital research laboratories.

SUBJECTS

NB4 and A549 cells.

INTERVENTIONS

NB4 and A549 cells were separately cultured with ATRA and/or dexamethasone for 1-3 days. NB4 or ATRA-NB4 cells were then placed in an upper insert and co-incubated with A549 cells or their conditioned medium located in a lower plate.

MEASUREMENTS AND MAIN RESULTS

ATRA stimulated NB4 cells to transmigrate toward the A549 cells in a time- and dose-dependent manner. Replacement of A459 condition medium by its original medium abrogated this transmigration. Only A549 cells constitutively secreted GRO-alpha, and both A549 and NB4 cells constitutively secreted IL-8, which was enhanced by ATRA. Exogenous administration of IL-8 or GRO-alpha also promoted the ATRA-NB4 transmigration. The binding assay demonstrated that ATRA-NB4 cells bound IL-8, but not GRO-alpha, more avidly. Pretreatment with antibodies directed against IL-8 and GRO-alpha receptors reduced ATRA-NB4 transmigration by about 60%. Dexamethasone did not suppress their IL-8 secretion and transmigration in ATRA-NB4 cells, but when applied to A549 cells, IL-8 secretion was suppressed but not GRO-alpha secretion, and there was attenuation of ATRA-NB4 transmigration.

CONCLUSIONS

IL-8 and GRO-alpha secreted from alveolar epithelial cells play an important role in the cell-cell interaction involved in the chemotactic transmigration of ATRA-treated APL cells toward alveolar epithelial cells.

Therapeutic effect of all-trans-retinoic acid (at-RA) on an autoimmune nephritis experimental model: role of the VLA-4 integrin

Background

Mercuric chloride (HgCl₂) induces an autoimmune nephritis in the Brown Norway (BN) rats characterized by anti-glomerular basement membrane antibodies (anti-GBM Ab) deposition, proteinuria and a severe interstitial nephritis, all evident at day 13 of the disease. We assessed the effects of all-trans retinoic acid (at-RA) in this experimental model. At-RA is a vitamin A metabolite which has shown beneficial effects on several nephropathies, even though no clear targets for at-RA were provided.

Methods

We separated animals in four different experimental groups (HgCl₂, HgCl₂+at-RA, at-RA and vehicle). From each animal we collected, at days 0 and 13, numerous biological samples: urine, to measure proteinuria by colorimetry; blood to determine VLA-4 expression by flow citometry; renal tissue to study the expression of VCAM-1 by Western blot, the presence of cellular infiltrates by immunohistochemistry, the IgG deposition by immunofluorescence, and the cytokines expression by RT-PCR. Additionally, adhesion assays to VCAM-1 were performed using K562 α4 transfectant cells. ANOVA tests were used for statistical significance estimation.

Results

We found that at-RA significantly decreased the serum levels of anti-GBM and consequently its deposition along the glomerular membrane. At-RA markedly reduced proteinuria as well as the number of cellular infiltrates in the renal interstitium, the levels of TNF-α and IL-1β cytokines and VCAM-1 expression in renal tissue. Moreover, we reported here for the first time in an in vivo model that at-RA reduced, to basal levels, the expression of VLA-4 (α4β1) integrin induced by mercury on peripheral blood leukocytes (PBLs). In addition, using K562 α4 stable transfectant cells, we found that at-RA inhibited VLA-4 dependent cell adhesion to VCAM-1.

Conclusion

Here we demonstrate a therapeutic effect of at-RA on an autoimmune experimental nephritis model in rats. We report a significant reduction of the VLA-4 integrin expression on PBLs as well as the inhibition of the VLA4/VCAM1-dependent leukocyte adhesion by at-RA treatment. Thereby we point out the VLA-4 integrin as a target for at-RA in vivo.

Differential engagement of modules 1 and 4 of vascular cell adhesion molecule-1 (CD106) by integrins alpha4beta1 (CD49d/29) and alphaMbeta2 (CD11b/18) of eosinophils

We have studied adhesion of eosinophils to various forms of vascular cell adhesion molecule 1 (VCAM-1, CD106), an integrin counter-receptor implicated in eosinophil recruitment to the airway in asthma. Full-length 7d-VCAM-1, with seven immunoglobulin-like modules, contains integrin-binding sites in modules 1 and 4. The alternatively spliced six-module protein, 6d-VCAM-1, lacks module 4. In static assays, unactivated purified human blood eosinophils adhered similarly to recombinant soluble human 6d-VCAM-1 and 7d-VCAM-1 coated onto polystyrene microtiter wells. Further experiments, however, revealed differences in recognition of modules 1 and 4. Antibody blocking indicated that eosinophil adhesion to 6d-VCAM-1 or a VCAM-1 construct containing only modules 1-3, 1-3VCAM-1, is mediated by alpha4beta1 (CD49d/29), whereas adhesion to a construct containing modules 4-7, 4-7VCAM-1, is mediated by bothalpha4beta1 andalphaMbeta2 (CD11b/18). Inhibitors of phosphoinositide 3-kinase, which block adhesion of eosinophils mediated by alphaMbeta2, blocked adhesion to 4-7VCAM-1 but had no effect on adhesion to 6d-VCAM-1. Consistent with the antibody and pharmacological blocking experiments, eosinophilic leukemic cell lines lacking alphaMbeta2 did not adhere to 4-7VCAM-1 but did adhere to 6d-VCAM-1 or 1-3VCAM-1. Activation of eosinophils by interleukin (IL)-5 enhanced static adhesion to 6d-VCAM-1, 7d-VCAM-1, or 4-7VCAM-1; IL-5-enhanced adhesion to all 3 constructs was blocked by anti-alphaMbeta2. Adhesion of unstimulated eosinophils to 7d-VCAM-1 under flow conditions was inhibited by anti-alpha4 or anti-alphaM. IL-5 treatment decreased eosinophil adhesion to 7d-VCAM-1 under flow, and anti-alphaM had the paradoxical effect of increasing adhesion. These results demonstrate that alphaMbeta2 modulatesalpha4beta1-mediated eosinophil adhesion to VCAM-1 under both static and flow conditions.

Retinoic acid-induced CD38 antigen promotes leukemia cells attachment and interferon-gamma/interleukin-1beta-dependent apoptosis of endothelial cells: implications in the etiology of retinoic acid syndrome

All-trans retinoic acid (RA) treatment of patients with acute promyelocytic leukemia (APL) induces complete remission in more than 90% of the cases. Although RA therapy is well tolerated, about 25% of APL patients develop a potentially fatal condition called retinoic acid syndrome (RAS). Molecular mechanisms underlying the development of RAS pathogenesis, especially those that result in the damage of endothelial cells remain elusive. In the present study, we found that RA treatment induces the expression of interferon-gamma (IFN-gamma) and interleukin-1beta (IL-1beta) in peripheral blast cells from APL patients. IFN-gamma and IL-1beta also exerted synergistic effect in driving human umbilical cord endothelial cells (HUVECs) and human lung microvascular endothelial cells (HLMVECs) into apoptosis. RA also upregulated the expression of CD38, an ectoenzyme responsible for the generation of the calcium messenger cyclic ADP-ribose. Importantly, RA-induced CD38 expression promoted strong attachment of leukemia cells to endothelial cells, and incubation of endothelial cells with either high concentration (100 ng/ml) of IFN-gamma alone or low concentration of IL-1beta and IFN-gamma (10 ng/ml, each) induced strong apoptotic responses as revealed by caspase-8 activation and DNA fragmentation. Our results suggest that these RA-induced events could contribute to the development of RAS pathogenesis in patients with APL.

Treatment concepts of acute promyelocytic leukemia

In the past, acute promyelocytic leukemia (APL) was associated with a high risk of early mortality resulting from severe coagulopathy, frequently inducing fatal cerebral hemorrhage. With the introduction of the differentiating agent all-trans retinioc acid (ATRA) APL has changed to the best curable subtype of acute myeloid leukemia (AML). With ATRA and chemotherapy approximately 70-80% of patients with newly diagnosed APL achieve long-term remission and are probably cured. PML/RARalpha, the molecular fusion transcript of the specific translocation t(15;17) represents not only the target for ATRA but also permits a precise diagnosis and provides a marker for the identification of minimal residual or recurrent disease (MRD). During the last decade, substantial progress has been made with regard to the recognition of prognostic factors and the optimization of the combination of ATRA and chemotherapy. Remaining questions are the role of arsenic and of ara-C in first line therapy of APL as well as the indication of maintenance therapy in the individual patient. Several treatment options exist for patients with APL who have relapsed after ATRA and chemotherapy. Approximately 50% of the patients in first relapse can achieve long-lasting second remission and might be cured with salvage regimens. Currently, arsenic compounds and transplantation procedures seem to be the most promising options in relapsed disease. The role of CD33 antibodies has to be determined in future studies. Refining the molecular monitoring of MRD by quantitative RT-PCR, better elucidation of the biologic mechanisms, and the identification of prognostic factors might be helpful to make further progress in the treatment of APL.

Retinoic acid syndrome in NOD/scid mice induced by injecting an acute promyelocytic leukemia cell line

All-trans retinoic acid (ATRA) induces complete remission in patients with acute promyelocytic leukemia (APL). However, ATRA sometimes causes retinoic acid syndrome (RAS) characterized by respiratory distress, pleural effusions, fever and weight gain. To investigate the pathophysiology of RAS, we generated an animal model by injecting an APL cell line, NB4, into immunodeficient mice. When NOD/scid mice were injected intravenously with fully differentiated NB4 cells (1 x 10(7)) and then given a daily administration of ATRA, three of 12 mice died of pulmonary edema within 14 days. Pathologically, dilated lung capillary vessels and alveolar effusions were observed. After the injection, NB4 cells were detected in the lung within 2 days and in the pleural effusion later on. The gene expression levels of CXC chemokines (MIP-2 and KC) and ICAM-1 were increased in the lung and heart by the ATRA administration. In immunohistochemical analyses, MIP-2 was clearly detected in alveolar macrophages of the lung in mice with RAS. Dexamethasone treatment prevented the development of RAS and decreased the CXC chemokine mRNA expression in the lung. These findings suggested that the activation of adhesion molecules for leukocytes and expression of CXC chemokines in the lung are closely involved in triggering RAS.

Retinoic acid syndrome: manifestations, pathogenesis, and treatment

All-trans retinoic acid (ATRA) is a potent differentiation agent that is effective therapy in acute promyelocytic leukaemia. Although ATRA is generally well tolerated, some patients develop retinoic acid syndrome. This syndrome is manifested by unexplained fever, weight gain, respiratory distress, interstitial pulmonary infiltrates, pleural and pericardial effusion, episodic hypotension, and acute renal failure. However, if identified early enough, effective therapy can be administered. This chapter discusses the clinical aspects and pathogenesis of retinoic acid syndrome.

Acute promyelocytic leukaemia:a review

Acute promyelocytic leukaemia (APL) is characterised by the fusion gene transcript PML-RAR-alpha and is now the most frequently curable acute leukaemia in adults if promptly diagnosed and adequately treated. The clinical presentation is associated with a haemorrhagic diathesis and the blasts almost always have Auer rods. Poor prognostic factors include older age, elevated white blood cell count, low platelet count, and CD56 expression. The introduction of all-trans retinoic acid (ATRA), which leads to the differentiation of leukaemic blasts into mature granulocytes has been the major breakthrough in the treatment of APL. Induction treatment with concurrent ATRA and chemotherapy leads to a rapid resolution of the characteristic life-threatening coagulopathy, high complete remission rates and excellent survival rates, compared to chemotherapy alone. However, treatment with ATRA is associated with the retinoic acid syndrome (RAS), which is a major toxicity and may lead to mortality. The role of cytarabine as a part of initial induction regimen remains unclear. After achievement of complete remission (CR), there is a definitive role of maintenance therapy with ATRA with or without low-dose chemotherapy. In relapsed patients, arsenic trioxide is considered the treatment of choice. However, the best postremission treatment for patients with second CR remains unknown. With the continued improvement in the field of stem cell transplantation, it may play an important role in the few patients with relapsed/refractory disease or those in second CR.

Early onset of chemotherapy can reduce the incidence of ATRA syndrome in newly diagnosed acute promyelocytic leukemia (APL) with low white blood cell counts: results from APL 93 trial

Treatment combining ATRA and chemotherapy (CT) has improved the outcome of APL patients, by comparison with CT alone. ATRA syndrome is a life-threatening complication of ATRA treatment whose prophylaxis remains somewhat controversial. In APL93 trial, newly diagnosed APL patients </=65 years and with initial WBC counts below 5000/mm(3) were randomized between ATRA until CR achievement followed by CT (ATRA --> CT) and ATRA with early addition of CT, on day 3 of ATRA treatment (ATRA + CT). The incidence of ATRA syndrome in the ATRA --> CT arm was 18% (22/122) as compared to 9.2% (17/184) in the ATRA + CT arm (P = 0.035). In the ATRA --> CT arm, three (2.5%) patients died from ATRA syndrome, as compared to one (0.5%) in the ATRA + CT group. Early addition of chemotherapy to ATRA in newly diagnosed APL with low WBC counts significantly reduced the incidence of ATRA syndrome.

Acute Myeloid Leukemia and Acute Promyelocytic Leukemia

The therapeutic approach to the patient with acute myeloid leukemia (AML) currently evolves toward new frontiers. This is particularly apparent from the entree of high-throughput diagnostic technologies and the identification of prognostic and therapeutic targets, the introduction of therapies in genetically defined subgroups of AML, as well as the influx of investigational approaches and novel drugs into the pipeline of clinical trials that target pathogenetic mechanisms of the disease.

In Section I, Dr. Bob Löwenberg reviews current issues in the clinical practice of the management of adults with AML, including those of older age. Dr. Löwenberg describes upcoming possibilities for predicting prognosis in defined subsets by molecular markers and reviews experimental strategies to improve remission induction and postinduction treatment.

In Section II, Dr. James Griffin reviews the mechanisms that lead to activation of tyrosine kinases by mutations in AML, the consequences of that activation for the cell, and the opportunities for targeted therapy and discusses some examples of developing novel drugs (tyrosine kinase inhibitors) and their effectiveness in AML (FLT3).

In Section III, Dr. Martin Tallman describes the evaluation and management of patients with acute promyelocytic leukemia, a notable example of therapeutic progress in a molecularly defined entity of leukemia. Dr. Tallman focuses on the molecular genetics of APL, current curative treatment strategies and approaches for patients with relapsed and refractory disease. In addition, areas of controversy regarding treatment are addressed.

Regulation of human basophil adhesion to endothelium under flow conditions: Different very late antigen 4 regulation on umbilical cord blood-derived and peripheral blood basophils

BACKGROUND

Although soluble mediators released by basophils in tissue sites contribute to the chronic injury that occurs in hypersensitivity diseases, only limited information is available about how circulating basophils are recruited to tissues. In particular, the interaction of basophils with endothelium under conditions that mimic physiologic flow has not been explored.

OBJECTIVE

We sought to identify adhesion molecules regulating the attachment of human basophils to IL-4-activated human umbilical vein endothelial cells (HUVECs) under flow conditions.

METHODS

A parallel-plate flow chamber and blocking mAbs were used to define the adhesion molecules involved in the interactions of peripheral blood basophils (PBBs) and cord blood-derived basophils (CBDBs) with IL-4-activated HUVECs and with Chinese hamster ovary (CHO) cell transfectants expressing specific adhesion molecules. A fluorescent ligand specific for very late antigen 4 (VLA-4) was used to directly examine the VLA-4 affinity state of basophils.

RESULTS

Flowing PBBs and CBDBs attached to activated HUVECs and to CHO cells expressing P- or E-selectin. However, only CBDBs attached to vascular cell adhesion molecule 1 (VCAM-1)-transfected CHO cells under flow conditions. The attachment of CBDBs to CHO cells was blocked by mAbs directed against E-selectin, P-selectin, and VCAM-1, whereas attachment of PBBs was blocked by E-selectin and P-selectin mAbs. Activating VLA-4 with Mn(2+) on PBBs resulted in adhesion to the VCAM-1-transfected CHO cells, indicating that VLA-4 activity on PBBs can be regulated, at least in part, through affinity changes. The Mn(2+)-induced upregulation of basophil VLA-4 affinity was demonstrated directly by using a fluorescent ligand for VLA-4 and flow cytometry.

CONCLUSIONS

The interaction of human CBDBs and PBBs with endothelium under flow conditions is mediated in part by both P- and E-selectin. VLA-4 additionally contributes to the adhesion of flowing CBDBs. However, the affinity of VLA-4 is too low to support the adhesion under flow conditions of unstimulated PBBs.

Arsenic trioxide in the treatment of newly diagnosed acute promyelocytic leukemia: a single center experience

Arsenic trioxide (As(2)O(3)) has been found effective in the treatment in the treatment of acute promyelocytic leukemia (APML). Most studies with As(2)O(3) involve patients with APML who have relapsed following standard therapy. Between January 1998 and July 2000, 14 patients were recruited for an ongoing trial of As(2)O(3) in the treatment of newly diagnosed APML. Arsenic trioxide was administered at a dose of 10 mg/day until complete remission (CR) was achieved. Afterward, a consolidation course and a maintenance schedule consisting of As(2)O(3) as a single agent were administered over 6 months. There were 3 early deaths related to intra-cerebral hemorrhage: two on day 3 and one on day 4. Of the 11 evaluable patients, one died on day 21 secondary to uncontrolled sepsis, while the remaining 10 (91%) have attained CR. The average time to CR was 52.3 days (range: 34-70 days). One patient developed an isolated central nervous system (CNS) relapse and subsequently went into a second CR following therapy with triple intrathecal chemotherapy, cranial irradiation, and an additional 4-week course of systemic As(2)O(3). This patient, as well as the remaining nine, has continued to remain in CR at a median follow up of 15 months (range: 2-33 months). Eight out of 10 patients achieved molecular remission at variable periods during their consolidation and maintenance schedules. One patient developed an ATRA syndrome and was administered daunorubicin (40 mg/day) for 2 days. The side effects with this therapy were minimal and did not require cessation of therapy in any patient. There was no significant hepatic toxicity. In our experience, arsenic trioxide is effective in inducing and maintaining remission in patients with APML with minimal side effects. The optimal regimen and total dose required need to be defined.

Ear involvement in acute promyelocytic leukemia at relapse: a disease-associated 'sanctuary'?

Extramedullary (EM) involvement occurs infrequently in acute promyelocytic leukemia (APL) and usually involves skin and CNS. We describe seven patients (four observed at a single institution) who relapsed in various sites of the auditory apparatus, including the external canal and middle ear (temporal bone). Front-line treatment included ATRA and chemotherapy (six patients) or chemotherapy alone (one patient). Three patients had concomitant hematologic relapse, two had molecular relapse and two were in hematologic and molecular remission when ear localization was documented. Local symptoms that stimulated further diagnostic studies included ear bleeding/discharge in the first patient, but were mild in the others (hypoacusia, five patients; earache, two patients). Ear involvement by leukemia was documented by histological and/or molecular studies after local surgery in five cases, and by CT scan or NMR in the remaining patients. We suggest that the ear might represent a specific sanctuary for disease involvement in APL.

Acute promyelocytic leukemia: evolving therapeutic strategies

Acute promyelocytic leukemia (APL) is now the most curable subtype of acute myeloid leukemia in adults. All-trans retinoic acid (ATRA), which induces differentiation of the leukemic cells into mature granulocytes, represents the important advance. The incorporation of ATRA in induction results in a high complete remission rate, leads to rapid resolution of the characteristic life-threatening coagulopathy, and, most importantly, decreases the relapse rate compared with treatment with chemotherapy alone. However, ATRA is associated with unique toxicities not observed with conventional cytotoxic chemotherapy. A number of clinical trials have been performed to define the optimal role of ATRA in the treatment of patients. The therapeutic strategies have rapidly evolved as a result of both single institution and large cooperative group trials. Arsenic trioxide and stem cell transplantation are effective treatments for patients with APL who relapse after or are refractory to ATRA-based therapy. As experience with ATRA and arsenic trioxide in patients with APL accumulates, a number of important questions arise that need to be addressed.

Enhanced T-lineage acute lymphoblastic leukaemia cell survival on bone marrow stroma requires involvement of LFA-1 and ICAM-1

The bone marrow (BM) microenvironment supports leukaemia cell survival and proliferation. The roles played by adhesive receptor interactions in the survival of T-lineage acute lymphoblastic leukaemia (T-ALL) cells on BM stromal cells are not well understood. Recently, we have developed an assay that partially recapitulates the BM microenvironment using HS-5 BM stromal cells. In this assay, the magnitude of ex vivo T-ALL lymphoblast survival predicts patient outcome. We examined the molecular basis for cell-cell adhesive events leading to T-ALL lymphoblast survival on HS-5 and on donor-derived BM stroma. Lympho cyte function-associated antigen-1 (LFA-1) on T-ALL cell lines bound intercellular adhesion molecule-1 (ICAM-1) on HS-5 monolayers, and survival was inhibited 85-98% with monoclonal antibodies directed against LFA-1 or ICAM-1. We compared these results with patient-derived T-ALL lymphoblasts co-cultured on either HS-5 BM or normal BM monolayers and found that LFA-1 and ICAM-1 were required, but not alone sufficient for ex vivo leukaemic cell survival. On normal BM stroma, but not HS-5 monolayers, two additional adhesion molecules, vascular cell adhesion molecule-1 (VCAM-1) and E-selectin, were highly expressed and contributed to T-ALL cell survival. This is the first report to demonstrate the importance of LFA-1/ICAM-1-mediated adhesion as a critical event in a cascade of cell surface receptor-ligand interactions that regulate T-ALL survival in the BM microenvironment.

Orchestration of multiple arrays of signal cross-talk and combinatorial interactions for maturation and cell death: another vision of t(15;17) preleukemic blast and APL-cell maturation

Despite intensive molecular biology investigations over the past 10 years, and an important breakthrough on how PML-RARalpha, the fusion protein resulting from t(15;17), can alter RARalpha and PML functions, no definitive views on how leukemia is generated and by what mechanism(s) the normal phenotype is restored, are yet available. 'Resistances' to pharmacological levels of all-trans-retinoic acid (ATRA) have been observed in experimental in vivo and in vitro models. In this review, we emphasize the key role played by signal cross-talk for both normal and neoplastic hemopoiesis. After an overview of reported experimental data on APL-cell maturation and apoptosis, we apply our current knowledge on signaling pathways to underline those which might generate signal cross-talks. The design of biological models suitable to decipher the integration of signal cross-talks at the transcriptional level should be our first priority today, to generate some realistic therapeutic approaches After 'Ten Years of Molecular APL', we still know very little about how the disease develops and how effective medicines work.

Improvements to parallel plate flow chambers to reduce reagent and cellular requirements

BACKGROUND

The parallel plate flow chamber has become a mainstay for examination of leukocytes under physiologic flow conditions. Several design modifications have occurred over the years, yet a comparison of these different designs has not been performed. In addition, the reagent requirements of many designs prohibit the study of rare leukocyte populations and require large amounts of reagents.

RESULTS

In this study, we evaluate modifications to a newer parallel plate flow chamber design in comparison to the original parallel plate flow chamber described by Lawrence et al. We show that modifications in the chamber size, internal tubing diameters, injection valves, and a recirculation design may dramatically reduce the cellular and reagent requirements without altering measurements.

CONCLUSIONS

These modifications are simple and easily implemented so that study of rare leukocyte subsets using scarce or expensive reagents can occur.

Novel cyclic peptide inhibits intercellular adhesion molecule-1-mediated cell aggregation

Leukocyte adherence mediated by intercellular adhesion molecule-1 (ICAM-1) binding to leukocyte function-associated antigen (LFA-1) is required for proper inflammatory and immune function. Inhibition of ICAM-1\LFA-1 binding using monoclonal antibodies (mAb) has been shown to be efficacious at inhibiting lymphoma metastasis as well as leukocyte emigration into tissue in a number of inflammatory diseases such as ischemia-reperfusion injury, septic shock and rheumatoid arthritis. In this report, we describe the development and characterization of a small peptide antagonist of ICAM-1-dependent cell aggregation. By using repeated selection of a cyclic nonapeptide phage display library on purified ICAM-1, we identified phage that were competitively eluted with anti-ICAM-1 mAb. The peptide sequences were determined by nucleotide sequencing, and the peptide sequence (C*LLRMRSIC*) (IP01) that occurred most frequently was chosen for further study. Phage expressing this peptide sequence specifically bound ICAM-1 over a range of 5 x 10(6) to 1 x 10(8) phage/microL. A cyclic IP01 peptide, linear IP01 peptide, a cyclic nonapeptide with a scrambled IP01 sequence, and a random, cyclic nonapeptide were synthesized. The cyclic and linear IP01 peptides were able to inhibit ICAM-1-mediated cell aggregation at a concentration of 1 mM, whereas the random and scrambled peptide sequences did not alter aggregation. Cyclic IP01 had a half-maximal inhibitory concentration of approximately 970 microM. Cyclic IP01 did not inhibit cellular aggregation that was dependent on ICAM-2 or ICAM-3. Alanine substitutions in the cyclic IP01 identified at least four amino acids necessary for inhibition of ICAM-1 dependent cell aggregation; leucine 2, leucine 3, methionine 5, and arginine 6. Finally, we showed that cyclic IP01 can inhibit firm adhesion of neutrophils to endothelium, a critical event in inflammatory diseases, in an assay that recapitulates physiologic flow conditions. Homology of IP01 with the primary amino acid sequences of the alpha or beta subunit of LFA-1 was not identified. Thus, we identified a unique molecule that inhibits ICAM-1 dependent cell adhesion, but is not related to the primary sequence of the ICAM-1 ligand LFA-1. Due to the small size and ability to block cell-cell adhesion, IP01 may serve as a useful tool for study of ICAM-1 and LFA-1 biology as well as for the development of small molecule therapeutics.

Expression of P-selectin at low site density promotes selective attachment of eosinophils over neutrophils

The selective interaction of neutrophils with E-selectin and eosinophils with P-selectin has been previously reported, but the relevance of selectin site density and fluid shear has not been studied in detail. We have developed a new approach to examine these interactions in cell suspensions that integrates an on-line cone-plate viscometer with a flow cytometer. We find that eosinophils and neutrophils both use P-selectin glycoprotein ligand-1 to form stable conjugates with P-selectin Chinese hamster ovary cell transfectants, with a preferential adhesion of eosinophils. Further, the difference in cell adhesion between neutrophils and eosinophils is magnified at P-selectin expression levels below approximately 20 sites/microm2, a range likely to be relevant to endothelial cell expression levels in conditions associated with eosinophilia. The unique behavior is retained over shear rates ranging from 100 to 1500/s but is magnified at low shear. Results from parallel-plate flow chamber assays suggest that preferential eosinophil adhesion reflects an enhanced efficiency of initial PSGL-1 bond formation with P-selectin rather than a unique ability of eosinophils to mediate rolling interactions of longer duration on low-density P-selectin substrates. These differences may account in part for the increase in eosinophil accumulation in allergic diseases.