Acute Promyelocytic Leukemia Differentiation Research Articles

All-trans retinoic acid (ATRA)-induced TFEB expression is required for myeloid differentiation in acute promyelocytic leukemia (APL).

In acute promyelocytic leukemia (APL), normal retinoid signaling is disrupted by an abnormal PML-RARα fusion oncoprotein, leading to a block in cell differentiation. Therapeutic concentrations of all-trans-retinoic acid (ATRA) can restore retinoid-induced transcription and promote degradation of the PML-RARα protein. Autophagy is a catabolic pathway that utilizes lysosomal machinery to degrade intracellular material and facilitate cellular re-modeling. Recent studies have identified autophagy as an integral component of ATRA-induced myeloid differentiation. As the molecular communication between retinoid signaling and the autophagy pathway is not defined, we performed RNA sequencing of NB4 APL cells treated with ATRA and examined autophagy-related transcripts. ATRA altered the expression of >80 known autophagy-related transcripts, including the key transcriptional regulator of autophagy and lysosomal biogenesis, TFEB (11.5-fold increase). Induction of TFEB and its transcriptional target, sequestosome 1 (SQSTM1, p62), is reduced in ATRA-resistant NB4R cells compared to NB4 cells. TFEB knockdown in NB4 cells alters the expression of transcriptional targets of TFEB and reduces CD11b transcript levels in response to ATRA. We show for the first time that TFEB plays an important role in ATRA-induced autophagy during myeloid differentiation and that autophagy induction potentiates leukemic cell differentiation (Note: this study includes data obtained from NCT00195156, https://clinicaltrials.gov/show/NCT00195156).

Neutrophil elastase-mediated proteolysis of the tumor suppressor p200 CUX1 promotes cell proliferation and inhibits cell differentiation in APL

AimsNeutrophil elastase (NE) is a critical proteolytic enzyme that is involved in cancer. We previously reported high NE expression in peripheral blood neutrophils from acute promyelocytic leukemia (APL) patients. The present study aimed to elucidate the specific role and mechanisms of NE in APL development. Materials and methodsNE expression was detected in APL bone marrow samples and analyzed in the BloodSpot database. CCK-8 assay and flow cytometry were used to assess cell proliferation and cell cycle distribution, respectively. The expression levels of proliferation and differentiation markers were measured by Western blotting and quantitative real-time PCR. The co-expression and interaction of NE and p200 cut-like homeobox 1 (CUX1) were evaluated by indirect immunofluorescence, co-immunoprecipitation, and in situ proximity ligation assay. Key findingsNE was highly expressed in APL bone marrow and blood neutrophils. NE overexpression promoted the proliferation and inhibited the differentiation of NB4 cells, whereas NE downregulation achieved the opposite results in U937 cells. Mechanistically, NE interacted with and effectively hydrolyzed the tumor suppressor p200 CUX1. Rescue experiments revealed that p200 CUX1 upregulation reversed the functional influence of NE on APL cells. SignificanceNE-mediated proteolysis of the tumor suppressor p200 CUX1 promotes APL progression. NE/p200 CUX1 axis is a novel and promising therapeutic target for APL treatment.

Clinical and Functional Studies Reveal That TP73 Isoforms Levels Are Associated with Prognosis and RA-Resistance in Acute Promyelocytic Leukemia

Clinical and Functional Studies Reveal That TP73 Isoforms Levels Are Associated with Prognosis and RA-Resistance in Acute Promyelocytic Leukemia

Efficacy and Safety of Daily All-Trans Retinoic Acid Monotherapy As Maintenance Therapy for Acute Promyelocytic Leukemia

Introduction Acute promyelocytic leukemia (APL) is a distinct subtype of acute myeloid leukemia with a unique chromosomal translocation t(15;17), causing promyelocytic leukemia gene fusion with the retinoic acid receptor α gene (PML-RARα). Therapeutic All-trans retinoic acid (ATRA) converts PML-RARα into transcriptional activator, induces APL differentiation. ATRA added during all treatment period have been reported to improve the outcomes of newly diagnosed APL. However, the benefits of maintenance therapy for patients with acute promyelocytic leukemia (APL) who achieved molecular complete remission (CRmol) are uncertain. In this study, we evaluated the efficacy and toxicity of daily ATRA monotherapy comparing with ATRA for 15 days with or without additional chemotherapy. Materials and Methods A retrospective data on 129 patients with newly diagnosed APL was conducted between February 2007 and August 2014. Induction and consolidation therapy were based on PETHEMA protocol. Among 113 patients (87.6%) who achieved CRmol following induction and 3 cycles of consolidation chemotherapy, 35 patients were treated daily with ATRA monotherapy (ATRAdaily), 39 with intermittent ATRA monotherapy for 15 days every 3 months (ATRA15), and 39 with ATRA plus continuous low-dose 6 mercaptopurine and methotrexate chemotherapy (ATRA/CT) for 2 years as a maintenance therapy. Event-free survival was defined as the time of CRmol to the development of events, which were defined by relapse, death, and toxicity that required hospitalization or dose reduction. Results The median age of patients was 46 years (range, 18-80 years). There was no significant difference among the three groups (ATRAdaily, ATRA15, and ATRA/CT) in terms of age, sex, ECOG PS, WBC count, platelet count, fibrinogen, prothrombin time, and Sanz risk score. Among the 12 relapsed patients during maintenance therapy, 3 presented molecular relapse and 9 hematologic relapse. Six (15.4%) relapses were observed in the ATRA15 group, whereas 2 (5.7%) and 4 (10.3%) relapses were observed in the ATRAdaily and ATRA/CT groups, respectively. At a median follow-up of 75.3 months (range: 9.0-140.4 months) from CRmol, the 5-year relapse free survival (RFS) for patients receiving maintenance therapy with ATRAdaily was higher than that of the patients in the ATRA15 or ATRA/CT groups without a statistically significant difference, 93.0 ± 4.8%, 84.6 ± 5.8%, and 88.0 ± 5.7%, respectively (P = 0.447). The 5-year overall survival (OS) rate was 92.7 ± 5.1%, 94.6 ± 3.7%, and 91.2 ± 5.0% for the ATRAdaily, ATRA15, and ATRA/CT groups, respectively (P = 0.601). However, ATRA/CT group frequently had myelosuppression (n = 11, 28.2%). The 5-year EFS rate was 81.5 ± 7.6%, 86.4 ± 5.7%, and 51.7 ± 8.2% for the ATRAdaily, ATRA15, and ATRA/CT groups, respectively (P < 0.001). In the multivariate analysis, maintenance therapy in the ATRA/CT group compared to ATRAdaily showed a significantly lower EFS (HR = 2.14, 95% CI = 1.06-4.31, P = 0.023). ECOG PS ≥ 2 was also associated with lower EFS (P = 0.033). Sanz risk score was the only adverse prognostic factor for RFS, and OS (HR = 6.20, 95% CI = 1.29-29.90, P = 0.023; HR=5.30, 95% CI = 1.10-25.63, P = 0.038). Conclusions In conclusion, in the present study, ATRAdaily as a maintenance therapy for patients with newly diagnosed APL who achieved CRmol showed non-inferiority compared with ATRA/CT in terms of RFS and OS. In addition, ATRAdaily maintenance therapy can be a feasible and effective choice in terms of myelosuppression or hepatotoxicity. In the future, well-conducted systematic studies of long term survivorship, quality of life, and treatment-related complications are needed to confirm these observations. Figure Disclosures No relevant conflicts of interest to declare.

Adenanthin Induces Differentiation of Acute Promyelocytic Leukemia Cells by Targeting Peroxiredoxin III

To investigate the differentiation of acute promyelocytic leukemia (APL) cells induced by adenosine targeting Prx III. HL-60 cells were divided into four groups: control group, all-trans retinoic acid (ATRA) group, adenanthin group and ATRA+adenanthin group. Cell morphologic changes were observed under optical microscope. The influence of adenanthin on the differentiation of HL-60 was observed by nitro blue tetrazolium chloride (NBT) test. Cell surface differentiation antigens CD11b expression was measured by flow cytometry. The protein expression of Prx III was detected by immunohistochemical assay. Adenanthin could induce the differentiation of HL-60 cells; the NBT reduction positive rate in ATRA+adenanthin group was significantly higher than that in ATRA group and adenanthin group (P＜0.05). The percentage of CD11b positive cells in ATRA+adenanthin group (43.62％±1.38％) was higher than that in adenanthin group (28.15％±1.78％), ATRA group (36.72％±1.33％) and control group (7.99％±1.78％) (P＜0. 05). The content of Prx Ⅲ protein in adenanthin group was significantly higher than that in control group and ATRA group (P＜0.05). Adenanthin and ATRA have a synergistic effect on the differentiation and maturation of HL-60 cells, and its mechanism may be related with regulation of Prx III expression.

Abstract 2991: Targeting glutamine metabolism leads to terminal differentiation in acute myeloid leukemia (AML)

Abstract The ability of All Trans Retinoic Acid (ATRA) to induce terminal differentiation in Acute Promyelocytic Leukemia (APL) has revolutionized treatment for this deadly subset of AML. Unfortunately, identifying targets that induce differentiation in non-APL cases of AML has met with limited success. Our lab has been interested in the role of glutamine metabolism in cellular differentiation programs. As such, we have investigated the degree to which glutamine contributes to the maintenance of an undifferentiated state in AML. Herein, we report that in vitro incubation with the glutamine blocking agent, 6-diazo-5-oxo-L-norleucine (DON) robustly induces differentiation in the human AML cell line, U937. DON treatment induces phenotypic and molecular changes indicative of differentiation, including increased granularity and vacuolization, and upregulation of differentiation markers CD11b and CD14. The differentiation of these cells was confirmed by their highly abrogated growth in methylcellulose-based colony-forming assays. Differentiated AML cells were not exposed to DON during colony-forming assays, suggesting an irreversible change in cellular differentiation triggered by short-term pretreatment. We have demonstrated that DON-induced cellular differentiation is active in other AML cell lines as well. Importantly, the differentiating effect of DON can be abrogated by the addition of a cell permeable form of α-ketoglutarate (αKG), dimethyl-2-ketoglutarate (DMK). αKG is a key metabolite in glutamine metabolism and is also a critical cofactor for a range of demethylase enzymes involved in epigenetic remodeling. Indeed, we have noted a robust increase in histone methylation marks, such as H3K27Me3, during DON-induced differentiation. Further, we have observed a dramatic increase in the transcription of critical transcription factors (CEBPA, FLT3, MYB, SOX4) twenty-four hours after DON treatment, a time point immediately preceding observed phenotypic differentiation changes. In light of these findings, experiments are currently underway to use DON differentiation therapy as a means of treating mouse models of AML. Taken as a whole, these data support the use of glutamine blockade as a novel differentiating therapy in AML. Given the remarkable curative potential of differentiation therapy and the poor survival rates of adults with AML (particularly older patients), our findings represent a particularly novel approach to treating this deadly disease. Citation Format: Robert Leone, Im-Meng Sun, Roshan Chikarmane, Radhika Viswanathan, Sanjeda Patwari, Matthew Arwood, Gabriel Ghiaur, Jonathan Powell. Targeting glutamine metabolism leads to terminal differentiation in acute myeloid leukemia (AML) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2991.

PB1705 CBC PARAMETERS BASED DERIVED PREDICTIVE FACTOR FOR ACUTE PROMYELOCYTE LEUKEMIA

Background:Acute promyelocytic leukemia (APML) due to coagulopathies drives hematological distress in clinical practices. A targeted and timely offered treatment can be a benefitting tool for patients.Aims:Present study was conducted to introduce pre‐microscopic screening of patients with acute promyelocytic leukemia (APML) through research potential parameters generated by routine hematology analyzers during CBC analysis.Methods:Blood samples of controls and patients (APML and other hematological neoplasms) were analyzed on Sysmex XN‐1000. Peripheral blood film was examined for morphological diagnosis. CBC parameters and values for intensities of white blood cell's side, forward, and side florescence light scatter were recorded from analyzer software. Statistical and machine learning (unsupervised) tools were used to evaluate the predictive power of routine and research CBC parameters. Novel APML factor was derived from white blood cell and platelet count along mean value of neutrophil side fluorescence light (NE‐SFL) through logistic regression. At proposed cutoff value (‐2.011), APML factor was challenged for prediction of APML among present study cases.Results:Values for white blood cell (WBC), platelet, and NE‐SFL were exceptionally discriminative for APML 5.65, 29.5, and 54.4 respectively in comparison to non‐APML 7.96, 219, and 47.00 respectively cases. In combination, WBC and platelet count increased the predictive power of NE‐SFL when utilized in derivation of our proposed “APML factor”: ‐4.5070 + (0.049213 x NE‐SFL) + (‐0.017431 x PLT) + (‐0.0058366 x WBC). This factor gave robust impact in differentiation of APML with high values 0.935 and 0.985 for sensitivity and negative predictive power (NPP) respectively at cutoff of ‐2.011.Summary/Conclusion:Our proposed APML factor has strong potential to be incorporate/calculate and examine as part of CBC report for early prediction of APML.

Autophagy is Required to Regulate Mitochondria Renewal, Cell Attachment, and All-trans–Retinoic Acid–Induced Differentiation in NB4 Acute Promyelocytic Leukemia Cells

All-trans-retinoic acid (ATRA) is a potent inducer of cellular differentiation, growth arrest, and apoptosis as well as a front-line therapy for acute promyelocytic leukemia (APL). The present study provides evidence that induction of autophagy is required for ATRA to induce differentiation of APL (NB4) cells into granulocytes. ATRA treatment causes ~12-fold increase in the number of acidic vesicular organelles and induces marked up-regulation of LC3-II, autophagy-related 5 (ATG5), and Beclin-1. Transmission electron microscopy (TEM) revealed a decrease in mitochondria and ATRA-induced differentiation. To determine the role of autophagy in the differentiation of APL, we knocked down ATG5 in NB4 cells to find that ATRA-induced differentiation is significantly inhibited during ATG5 knock down in cells, indicating the role of autophagy in differentiation of APL. Further experiments revealed restriction of autophagy during ATRA-induced differentiation and inhibition of tissue transglutaminase 2 (TG2) and phospho-focal adhesion kinase (p-FAK), which are known to have roles in differentiation and cell attachment. We examinedexpression of Beclin-1 and B-cell lymphoma-2 (Bcl-2) and levels of mechanistic target of rapamycin (mTOR) after ATRA treatment. ATRA inhibits Bcl-2, up-regulates Beclin-1 expression, and reduces induction of mTOR activation/phosphorylation in NB4 cells. Our results reveal that autophagy has roles in regulation of differentiation, mitochondria elimination, and cell attachment during ATRA-induced APL differentiation.

Insulin-like Growth Factor Binding Protein 7 Activates the Retinoid Acid Differentiation Pathway in Acute Myeloid Leukemia Cells

Acute myeloid leukemia (AML) is characterized by the accumulation of malignant blasts with impaired transcriptional differentiation programs. Despite important advances in AML therapy, the five-year overall survival rate of AML patients remains a disappointing 30-40%. This poor prognosis is mainly caused by survival of chemotherapy resistant leukemic cells, named leukemic stem cells (LSC), re-initiating relapse. However, for AML patients with PML-RARA positive acute promyelocytic leukemia (APL), treatment with all trans retinoic acid (ATRA) results in cure rates of >90%. Upon ATRA treatment, APL cells can restore transcription leading to granulocytic differentiation, and in combination with arsenic trioxide APL cells go into apoptosis. While the success of ATRA treatment has been demonstrated for APL patients, so far it has not proved effective for non-APL AML patients.Previously, we demonstrated that insulin-like growth factor binding protein 7 (IGFBP7), a negative regulator of IGF1 receptor (IGF1R) activity, induces apoptosis of AML cells and sensitizes AML cells to chemotherapy-induced cell death. Since it has been shown that IGF1R inhibitors can eliminate therapy-resistant cells by modifying their chromatin state, we hypothesized that IGFBP7 may also have the capacity to modify an epigenetic state and unlock the ATRA-driven differentiation response. To this end, we generated APL cell lines with down- or upregulated IGFBP7 levels and demonstrated that knockdown of IGFBP7 in NB4 cells blocked ATRA-induced differentiation, whereas overexpression of IGFBP7 led to an 8-fold increase in differentiation in the presence of low concentrations of ATRA, together suggesting a role for IGFBP7 in ATRA-induced differentiation in APL cells.Strategies to increase efficacy of ATRA-based therapy might also improve treatment outcomes for non-APL AML, and therefore we investigated the potential of IGFBP7 to induce susceptibility for ATRA-driven differentiation in this group. ATRA and IGFBP7 treatment of non-APL AML cell lines and primary AML cells derived from patients at diagnosis demonstrated an enhanced efficiency of the combination therapy to induce differentiation of myeloid CD45dimCD33+ AML cells (2.5-fold increase in CD11b-expression) and/or to reduce viability of AML CD45dim cells as compared to single treatments (from 30-39% to 70% reduction upon IGFBP7, ATRA or combination therapy, respectively), in 50% of tested primary AML samples, while this combination therapy did not influence normal hematopoietic cell survival. Remarkably, ATRA-IGFBP7 treatment diminished the in vivo engraftment potential of primary AML cells as compared to treatment with either drug alone in NSG mice (from 28% and 52% to 17% engraftment upon ATRA, IGFBP7 or combination therapy, respectively). Re-transplantation of human AML derived from first transplanted mice into secondary recipients demonstrated that the ATRA-IGFBP7 combination treatment also eliminated LSC more effectively (1.4-fold reduction). Together these data suggest that IGFBP7 enhances sensitivity of AML (stem) cells to ATRA, and is able to induce a transcriptional program sensitizing AML cells for ATRA-induced differentiation and cell death.To identify factors responsible for IGFBP7-induced ATRA sensitivity, we performed gene expression profiling of primary AML samples treated with IGFBP7, and identified growth factor independent protein 1 (GFI1) as one of the top down-regulated genes upon IGFBP7 stimulation. As overexpression of GFI1 in non-APL AML patient samples resulted in a >2.5-fold reduction in IGFBP7-induced susceptibility to ATRA-driven differentiation, low GFI1 expression is suggested to be associated with susceptibility to ATRA in AML cells.In conclusion, our results indicate that treatment of AML patient with a combination of ATRA and IGFBP7 might be successful in preventing relapse and improving AML patient survival, which has to be confirmed in further clinical studies. DisclosuresOssenkoppele:Karyopharm: Consultancy, Research Funding; Novartis: Consultancy, Honoraria, Research Funding; Jazz: Consultancy, Honoraria; Genentech: Consultancy, Honoraria; Roche: Consultancy, Honoraria; BMS: Consultancy, Honoraria; Pfizer: Consultancy, Honoraria; Genmab: Research Funding; Celgene: Honoraria, Research Funding; Johnson & Johnson: Consultancy, Honoraria, Research Funding.

Elucidating the Non-Catalytic Function of Fatty Acid Synthase and Its Autophagy-Dependent Degradation in Acute Myelocytic Leukemia Differentiation Therapy

Acute myeloid leukemia (AML) is characterized by a block in myeloid differentiation and an aberrant cell proliferation of leukemia blasts. While other AML therapies cure only 30% of the patients, acute promyelocytic leukemia (APL) is successfully treated by differentiation therapy using all-trans retinoic acid (ATRA) in combination with chemotherapy or arsenic trioxide. A better understanding of the molecular mechanisms underlying ATRA therapy in APL may offer new perspectives in the treatment of additional AML subtypes.Fatty acid synthase (FASN) is the only human lipogenic enzyme able of de novo fatty acid synthesis. Its expression is very low in healthy adult tissues, whereas increased expression is commonly found in a variety of cancerous tissues. Therefore, FASN represents an attractive potential drug target.To investigate if a similar expression pattern is found in normal versus malignant myeloid cells, we determined FASN expression in fresh leukemic blast cells from untreated AML patients obtained at the Inselspital Bern (Switzerland) (n=68) and expression data available online from the Bloodspot server (n=203). In both AML cohorts, we found that FASN expression is significantly higher in AML patients than in healthy granulocytes (p<0.05). Accordingly, FASN protein levels are reduced in NB4 and HT93 APL cells upon ATRA-induced granulocyte differentiation. Additionally, silencing FASN in NB4 cells led to an acceleration of differentiation upon ATRA treatment. Surprisingly, solely inhibiting the catalytic function of FASN using C75 or Orlistat did not affect granulocyte differentiation nor FASN expression. To validate that FASN levels and not activity attenuate granulocyte differentiation, we took advantage of the green tea polyphenol epigallocatechin-3-gallate (EGCG) that reduces FASN protein expression. Indeed, similar to knocking down FASN, EGCG treatment of NB4 cells resulted in increased differentiation paralleled by decreased FASN protein levels.We and others demonstrated the importance of autophagy for successful ATRA-induced APL differentiation. Autophagy is an intracellular degradation system that ensures a dynamic recycling of cytoplasmic contents. This process is regulated by the so-called autophagy related genes or ATGs. ATG1, or ULK1, is a key autophagy gene of the initiation complex that is inhibited by mTOR-mediated phosphorylation leading to reduced autophagy activity.FASN expression correlates with mTOR activity in several solid cancers, therefore we hypothesized that FASN activates mTOR resulting in decreased autophagy in AML cells. Indeed, lowering FASN protein expression by either shRNA or EGCG resulted in increased autophagy together with a decreased mTOR-mediated phosphorylation of ULK1.Next, we aimed at understanding how FASN expression is regulated during ATRA treatment. We found a negative correlation between KLF5 and FASN expression in both AML patient cohorts (r=-0.3) and 4 potential KLF binding sites on the FASN promoter, suggesting that KLF5 inhibits FASN transcription.However, since the protein half-life of FASN is around 24 hours, transcriptional inhibition is not sufficient to fully explain the reduced protein levels upon ATRA treatment. We therefore tested if FASN protein itself is degraded via autophagy. Co-treatment of NB4 cells with ATRA and the lysosome inhibitor Bafilomycin A1 led to a dose dependent accumulation of FASN protein suggesting that FASN is an autophagy substrate during ATRA treatment. Furthermore, using mCherry-LC3B expressing NB4 cells, we were able to show FASN and LC3B co-localization by fluorescence microscopy.Finally, we asked whether inhibiting FASN expression levels would increase ATRA sensitivity in non-APL AML cells. To this end, we treated KG-1, OCI-AML2 and MOLM-13 AML cells with EGCG in combination with ATRA. Importantly, combining ATRA with EGCG resulted in increased differentiation of these non-APL cells paralleled by reduced FASN levels, decreased mTOR activity and ULK1 phosphorylation.Together, our data suggest that EGCG treatment is beneficial for differentiation therapy of non-APL AML cells by activating autophagy via degradation of FASN and thereby inactivating mTOR. Furthermore, high FASN expression in AML is likely due to low expression of its positive transcriptional regulator KLF5 and low autophagy activity. DisclosuresNo relevant conflicts of interest to declare.

MiR-382-5p modulates the ATRA-induced differentiation of acute promyelocytic leukemia by targeting tumor suppressor PTEN

In acute promyelocytic leukemia (APL), all-trans retinoic acid (ATRA) treatment induces granulocytic differentiation and maturation. MicroRNAs play pivotal roles in formation of the leukemic phenotype. Previously, microRNA-382-5p (miR-382-5p) was upregulated in acute myeloid leukemia (AML) with t(15;17). In the present study, we found that miR-382-5p expression was elevated with ATRA-induced differentiation of APL. To investigate the potential functional role of miR-382-5p in APL differentiation, an APL cell line was transfected with miR-382-5p mimics, inhibitors, or negative control (NC). The results showed in APL cell line NB4 that miR-382-5p downregulation upon ATRA treatment was a key event in the drug response. Mechanistic investigations revealed that miR-382-5p targeted the ATRA-regulated tumor suppressor gene PTEN through direct binding to its 3′ UTR. Enforced expression of miR-382-5p or specific PTEN inhibitors inhibited ATRA-induced granulocytic differentiation via regulation of the cell cycle regulator cyclinD1. Conversely, PTEN overexpression promoted differentiation and enhanced sensitivity of NB4 cell line to physiological levels of ATRA. Finally, we found that PTEN overexpression restored PML nuclear bodies (NBs). Taken together, these results demonstrated that up-regulated miR-382-5p in NB4 cell line inhibited granulocytic differentiation through the miR-382-5p/PTEN axis, uncovering PTEN as a critical element in the granulocytic differentiation program induced by ATRA in APL.

Adenylate cyclase 7 regulated by miR-192 promotes ATRA-induced differentiation of acute promyelocytic leukemia cells

Adenylate cyclase 7 (AC7) has been reported to participate in various biological processes during cancer progression. However, the roles of AC7 in all-trans retinoic acid (ATRA)-induced differentiation of acute promyelocytic leukemia (APL) cells are still unknown. In this study, firstly, our results showed that AC7 affected intracellular cAMP level and influenced ATRA-induced differentiation of APL cells. Secondly, we revealed that miR-192 could directly target AC7 expression and knockdown of miR-192 promoted ATRA-induced APL cell differentiation by regulating AC7 expression. Furthermore, we found that AC7 expression was lower in patients with relapsed APL than that in patients with newly diagnosed APL, while miR-192 expression was relatively higher in patients with relapsed APL. Taken together, our results show that miR-192-mediated AC7 could play important roles in differentiation of APL cells, AC7 and miR-192 might be new biomarkers and therapeutic targets for patients with relapsed APL.

Genome‑wide profiling of lncRNA expression patterns in patients with acute promyelocytic leukemia with differentiation therapy.

Long non‑coding RNAs (lncRNAs) are crucial factors in acute promyelocytic leukemia (APL) cell differentiation. However, their expression patterns and regulatory functions during all‑trans‑retinoic acid (ATRA)‑induced APL differentiation remain to be fully elucidated. The profile of dysregulated lncRNAs between three bone marrow (BM) samples from patients with APL post‑induction and three BM samples from untreated matched controls was examined with the Human Transcriptome Array2.0. The dysregulated lncRNA expression of an additional 27APL BM samples was validated by reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR) analysis. The lncRNA functions were predicted through co‑expressed messenger RNA (mRNA) annotations. Co‑expressed lncRNA‑mRNA networks were constructed to analyze the functional pathways. In total, 825lncRNAs and 1,218mRNAs were dysregulated in the treated APL BM group, compared with the untreated APL BM group. The expression of 10 selected lncRNAs was verified by RT‑qPCR analysis. During APL differentiation, NONHSAT076891 was the most upregulated lncRNA, whereas TCONS_00022632‑XLOC_010933 was the most downregulated. Functional analysis revealed that several lncRNAs may exert activities in biological pathways associated with ATRA‑induced APL differentiation through cis and/or trans regulation of mRNAs. The findings of the present study assist in explaining the contributions of lncRNAs in APL myeloid differentiation and improve current knowledge on the potential mechanisms regarding dysregulated lncRNA expression in ATRA‑induced APL differentiation.

Rhein augments ATRA-induced differentiation of acute promyelocytic leukemia cells

BackgroundRhein (4, 5-dihydroxyanthraquinone-2-carboxylic acid), a natural anthraquinone derivative, is a traditional Chinese herb that has been used as a medication in many Asian countries. It has been used as a laxative and stomach drug for a long time in both China and Korea. It is well-known to have many pharmacological activities, such as anti-cancer, anti-bacterial, anti-fungal, anti-oxidant, anti-atherogenic, anti-angiogenic, anti-fibrosis, anti-inflammatory, hepatoprotective, and nephroprotective properties. However, little is known about how rhein may affect the differentiation activities in acute promyelocytic leukemia (APL) cells. PurposeThe present study was designed to examine the anti-leukemic effects of rhein against APL cells and to explore the underlying mechanism. MethodsCell viability was investigated by MTS assay. To examine the differentiation activities in APL cells, the cell surface molecules (CD11b, CD14, CCR1 and CCR2), phagocytosis, reactive oxygen species (ROS) were determined by flow cytometry. Also, induction of caspase-3 activity and reduction of mitochondrial membrane potential (MMP) were determined by flow cytometry. RNA and protein expressions were determined by qRT-PCR and western blotting, respectively. ResultsIn this study we assessed the role of rhein in treating APL. Interestingly, rhein potentiated all-trans retinoic acid (ATRA)-induced macrophage differentiation in NB4 cells by inducing changes in morphology, expression of the differentiation markers CD11b and CD14, ROS production, phagocytic activity, and expression of CCR1 and CCR2. Signaling through CD11b was found to be dependent on ERK activation. Additionally, rhein induced APL cell death by activating apoptosis and suppressing the mTOR pathway. ConclusionTherefore, we suggest that a combination of rhein and ATRA carries strong therapeutic potential through the beneficial differentiation of APL cells. Moreover, rhein causes cell death via the activation of apoptosis and suppression of survival signals in APL cells. In combination with the ability of rhein to promote functional macrophage differentiation in APL, these properties suggest that a combined treatment of rhein and ATRA has great potential as an anti-leukemic therapy for APL.

Upregulation of ID2 antagonizes arsenic trioxide-induced antitumor effects in cancer cells.

Arsenic trioxide (ATO) strongly induces apoptosis and differentiation in acute promyelocytic leukemia, and induces cell cycle arrest in most solid tumors. Although many signaling pathways are involved in its antitumor mechanism, a detailed investigation of the transforming growth factor beta-bone morphogenetic protein signaling pathway has not been performed. A microarray containing 113 genes associated with the pathway was used to screen important molecules that participate in the antitumor effects of ATO. The expression levels of the inhibitors of DNA binding-2 (ID2) in 4 different types of cancer cells were determined by quantitative reverse transcription PCR and Western blotting. Human esophageal squamous cell carcinoma cell line Eca109 and pancreatic carcinoma cell line BxPC3 cells were transfected with siRNAs targeting ID2 and scrambled control siRNA. Cell proliferation was evaluated by methyl thiazolyl tetrazolium assay. Eighteen upregulated and 12 downregulated genes were identified. After verification at the transcriptional and translational levels in 4 different cancer cells, ID2 was identified as an ATO antitumor-associated protein. In addition, specific silencing of ID2 could enhance ATO-induced cell proliferation inhibition in cancer cells. A combination of ATO and ID2-targeted agents may have considerable therapeutic benefits in cancers.

Acute promyelocytic leukemia: state-of-the-art management

Acute promyelocytic leukemia (APL) is driven by the promyelocytic leukemia (PML) -retinoic acid receptor (RAR) α fusion protein generated by the chromosomal translocation t (15;17) which affects both nuclear receptor signaling and PML nuclear body (NB) assembly. The advent of all-trans retinoic acid (ATRA) and arsenic trioxide (ATO) as molecular targeted therapies directed against PML-RARα has been a major breakthrough in APL treatment. ATRA and ATO target RARα and PML, respectively, and elicit PML-RARα degradation, leading to the reformation of normal NBs and cell differentiation. In several multicenter trials, more than 90% of newly diagnosed APL patients treated with ATRA and chemotherapy achieved complete remission, of whom 20%-30% subsequently relapsed; the overall survival was approximately 80% in these studies. However, several major clinical problems continue to account for treatment failure including early death due to hemorrhage, infection during consolidation, disease relapse, and secondary malignancies. These issues are associated mainly with anticancer agents used in combination with ATRA. Combination therapy using ATRA and ATO is the current standard therapy for untreated patients with APL in Western countries. The current problems in patients with APL treated with ATRA and ATO are APL differentiation syndrome and high risk of relapse in patients with an initial leukocyte count of more than 10×109/l.

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.

The autophagy scaffold protein ALFY is critical for the granulocytic differentiation of AML cells

Acute myeloid leukemia (AML) is a malignancy of myeloid progenitor cells that are blocked in differentiation. Acute promyelocytic leukemia (APL) is a rare form of AML, which generally presents with a t(15;17) translocation causing expression of the fusion protein PML-RARA. Pharmacological doses of all-trans retinoic acid (ATRA) induce granulocytic differentiation of APL cells leading to cure rates of >80% if combined with conventional chemotherapy. Autophagy is a lysosomal degradation pathway for the removal of cytoplasmic content and recycling of macromolecules. ATRA induces autophagy in ATRA-sensitive AML and APL cells and autophagy inhibition attenuates ATRA-triggered differentiation. In this study, we aimed at identifying if the autophagy-linked FYVE-domain containing protein (ALFY/WDFY3) is involved in autophagic degradation of protein aggregates contributes to ATRA therapy-induced autophagy. We found that ALFY mRNA levels increase significantly during the course of ATRA-induced differentiation of APL and AML cell lines. Importantly ALFY depletion impairs ATRA-triggered granulocytic differentiation of these cells. In agreement with its function in aggrephagy, knockdown of ALFY results in reduced ATRA-induced proteolysis. Our data further suggest that PML-RARα is an autophagy substrate degraded with the help of ALFY. In summary, we present a crucial role for ALFY in retinoid triggered maturation of AML cells.

Reprogramming acute myeloid leukemia into sensitivity for retinoic-acid-driven differentiation.

The success of all-trans retinoic acid (ATRA) therapy for acute promyelocytic leukemia (APL) provides a rationale for using retinoic acid (RA)-based therapy for other subtypes of acute myeloid leukemia (AML). Recently, several studies showed that ATRA may drive leukemic cells efficiently into differentiation and/or apoptosis in a subset of AML patients with an NPM1 mutation, a FLT3-ITD, an IDH1 mutation, and patients overexpressing EVI-1. Because not all patients within these molecular subgroups respond to ATRA and clinical trials that tested ATRA response in non-APL AML patients have had disappointing results, the identification of additional biomarkers may help to identify patients who strongly respond to ATRA-based therapy. Searching for response biomarkers might also reveal novel RA-based combination therapies with an efficient differentiation/apoptosis-inducing effect in non-APL AML patients. Preliminary studies suggest that the epigenetic or transcriptional state of leukemia cells determines their susceptibility to ATRA. We hypothesize that reprogramming by inhibitors of epigenetic-modifying enzymes or by modulation of microRNA expression might sensitize non-APL AML cells for RA-based therapy. AML relapse is caused by a subpopulation of leukemia cells, named leukemic stem cells (LSCs), which are in a different epigenetic state than the total bulk of the AML. The survival of LSCs after therapy is the main cause ofthe poor prognosis of AML patients, and novel differentiation therapies should drive these LSCs into maturity. In this review, we summarize the current knowledge on the epigenetic aspects of susceptibility to RA-induced differentiation in APL and non-APL AML.

Ex Vivo High-Throughput Flow Cytometry Screening Identifies Subsets of Responders to Differentiation Agents in Individual AML Patient Samples

Background:Prognoses for acute promyelocytic leukemia (APL) patients improved drastically upon the introduction of differentiation therapy with all-trans-retinoic acid (ATRA) in combination with conventional chemotherapy. Unfortunately, this therapeutic approach has not translated to other genetic subtypes of acute myeloid leukemia (AML) where patients demonstrate marked heterogeneity to differentiating agents. To provide improved detection of drug-induced differentiation in AML patients, we have developed a high-throughput, flow cytometry-based personalized medicine platform.Methods:Total white blood cells were isolated from each patient sample by red cell lysis, plated in serum-free media in 384-well format and incubated with drugs for 3 days. Viable cells remaining after each drug treatment were identified and quantified using cell surface marker expression, cell membrane integrity, and morphology (FSC/SSC) to determine the compound's efficacy and specificity against the blast population. Changes in cell surface marker expression and shifts in morphology indicative of blast differentiation were also evaluated with each compound. As a control for ex vivo differentiation, two APL patient samples were treated ex vivo with ATRA and we observed the blasts gaining CD66b expression indicating granulocytic differentiation.Results:A refractory AML patient was identified whose leukemic blasts exhibited a strong differentiating response to dexamethasone treatment ex vivo. This resulted in loss of CD34 expression (a marker of immature blast cells), gain of CD163 expression (a marker of monocytic/macrophage maturation) and a significant change in cellular size and granularity. After being enrolled in a clinical trial (REB: 13-6962-C) the patient was treated based on the assay for 1 week (40 mg/day) with dexamethasone. Post-treatment samples from the peripheral blood and bone marrow of the patient exhibited the same morphological and cell surface marker changes predicted by the ex vivo assay. The CD163+ cells in the patient also gained additional markers of myeloid differentiation (CD11b, CD14, CD16). After additional cytarabine and fludarabine treatment, the patient remains in remission 4 months post-treatment.Conclusions:Following this initial study, we have continued to identify subgroups of both AML and Myelodysplastic Syndrome patients where blasts differentiate in response to dexamethasone, calcitriol, ATRA or other known differentiating agents using unique cell surface markers of monocytic and myeloid maturation. Flow cytometry expression changes correlated with changes in morphology as observed by May-Grunwald Giemsa staining. In the patient described above this included an increase in cytoplasm and vacuoles consistent with monocytic/macrophage differentiation, which positively correlates with CD163 expression. We aim to apply our assay towards the identification of subgroups of AML patients who respond to differentiation therapies and develop clinical trials to combine differentiating agents with chemotherapy. This approach has the potential to extend the clinical success of APL differentiation therapy to AML patients. DisclosuresPrashad:Notable Labs: Employment, Equity Ownership. Western:Notable Labs: Consultancy. Biondi:Notable Labs: Employment. Shah:Notable Labs: Employment. Liu:Notable Labs: Employment, Equity Ownership. Nguyen:Notable Labs: Employment, Equity Ownership. Warnock:Notable Labs: Employment, Equity Ownership. Quinzio:Notable Labs: Employment, Equity Ownership. De Silva:Notable Labs: Employment, Equity Ownership. Schimmer:Novartis: Honoraria. Heiser:Notable Labs: Employment, Equity Ownership.