Retinoic acid and arsenic trioxide sensitize acute promyelocytic leukemia cells to ER stress.

Retinoic acid (RA) in association with chemotherapy or with arsenic trioxide (ATO) results in high cure rates of acute promyelocytic leukemia (APL). We show that RA-induced differentiation of human leukemic cell lines and primary blasts dramatically increases their sensitivity to endoplasmic reticulum (ER) stress-inducing drugs at doses that are not toxic in the absence of RA. In addition, we demonstrate that the PERK pathway, triggered in response to ER stress, has a major protective role. Moreover, low amounts of pharmacologically induced ER stress are sufficient to strongly increase ATO toxicity. Indeed, in the presence of ER stress, ATO efficiently induced apoptosis in RA-sensitive and RA-resistant APL cell lines, at doses ineffective in the absence of ER stress. Our findings identify the ER stress-related pathways as potential targets in the search for novel therapeutic strategies in AML.

PML-RARA-associated cooperating mutations belong to a transcriptional network that is deregulated in myeloid leukemias.

It has been shown that individual acute myeloid leukemia (AML) patients are characterized by one of few initiating DNA mutations and 5-10 cooperating mutations not yet defined among hundreds identified by massive sequencing of AML genomes. We report an in vivo insertional-mutagenesis screen for genes cooperating with one AML initiating mutations (PML-RARA, oncogene of acute promyelocytic leukemia, APL), which allowed identification of hundreds of genetic cooperators. The cooperators are mutated at low frequency in APL or AML patients but are always abnormally expressed in a cohort of 182 APLs and AMLs analyzed. These deregulations appear non-randomly distributed and present in all samples, regardless of their associated genomic mutations. Reverse-engineering approaches showed that these cooperators belong to a single transcriptional gene network, enriched in genes mutated in AMLs, where perturbation of single genes modifies expression of others. Their gene-ontology analysis showed enrichment of genes directly involved in cell proliferation control. Therefore, the pool of PML-RARA cooperating mutations appears large and heterogeneous, but functionally equivalent and deregulated in the majority of APLs and AMLs. Our data suggest that the high heterogeneity of DNA mutations in APLs and AMLs can be reduced to patterns of gene expression deregulation of a single 'mutated' gene network.

PML nuclear body disruption impairs DNA double-strand break sensing and repair in APL.

Proteins involved in DNA double-strand break (DSB) repair localize within the promyelocytic leukemia nuclear bodies (PML-NBs), whose disruption is at the root of the acute promyelocytic leukemia (APL) pathogenesis. All-trans-retinoic acid (RA) treatment induces PML-RARα degradation, restores PML-NB functions, and causes terminal cell differentiation of APL blasts. However, the precise role of the APL-associated PML-RARα oncoprotein and PML-NB integrity in the DSB response in APL leukemogenesis and tumor suppression is still lacking. Primary leukemia blasts isolated from APL patients showed high phosphorylation levels of H2AX (γ-H2AX), an initial DSBs sensor. By addressing the consequences of ionizing radiation (IR)-induced DSB response in primary APL blasts and RA-responsive and -resistant myeloid cell lines carrying endogenous or ectopically expressed PML-RARα, before and after treatment with RA, we found that the disruption of PML-NBs is associated with delayed DSB response, as revealed by the impaired kinetic of disappearance of γ-H2AX and 53BP1 foci and activation of ATM and of its substrates H2AX, NBN, and CHK2. The disruption of PML-NB integrity by PML-RARα also affects the IR-induced DSB response in a preleukemic mouse model of APL in vivo. We propose the oncoprotein-dependent PML-NB disruption and DDR impairment as relevant early events in APL tumorigenesis.

PML-RARα kinetics and impact of FLT3-ITD mutations in newly diagnosed acute promyelocytic leukaemia treated with ATRA and ATO or ATRA and chemotherapy.

The APL0406 study showed that arsenic trioxide (ATO) and all-trans retinoic acid (ATRA) are not inferior to standard ATRA and chemotherapy (CHT) in newly diagnosed, low-intermediaterisk acute promyelocytic leukaemia (APL). We analysed the kinetics of promyelocytic leukaemia-retinoic acid receptor-α (PML-RARα) transcripts by real-time quantitative PCR (RQ-PCR) in bone marrow samples from 184 patients and assessed the prognostic impact of fms-related tyrosine kinase 3-internal tandem duplication (FLT3-ITD) in 159 patients enrolled in this trial in Italy. After induction therapy, the reduction of PML-RARα transcripts was significantly greater in patients receiving ATRA-CHT as compared with those treated with ATRA-ATO (3.4 vs 2.9 logs; P=0.0182). Conversely, at the end of consolidation, a greater log reduction of PML-RARα transcripts was detected in the ATRA-ATO as compared with the ATRA-CHT group (6.3 vs 5.3 logs; P=0.0024). FLT3-ITD mutations had no significant impact on either event-free survival (EFS) or cumulative incidence of relapse in patients receiving ATRA-ATO, whereas a trend for inferior EFS was observed in FLT3-ITD-positive patients receiving ATRA-CHT. Our study shows at the molecular level that ATRA-ATO exerts at least equal and probably superior antileukaemic efficacy compared with ATRA-CHT in low-intermediaterisk APL. The data also suggest that ATRA-ATO may abrogate the negative prognostic impact of FLT3-ITD.

Current management of newly diagnosed acute promyelocytic leukemia.

The management of acute promyelocytic leukemia (APL) has considerably evolved during the past two decades. The advent of all-trans retinoic acid (ATRA) and its inclusion in combinatorial regimens with anthracycline chemotherapy has provided cure rates exceeding 80%; however, this widely adopted approach also conveys significant toxicity including severe myelosuppression and rare occurrence of secondary leukemias. More recently, the advent of arsenic trioxide (ATO) and its use in association with ATRA with or without chemotherapy has further improved patient outcome by allowing to minimize the intensity of chemotherapy, thus reducing serious toxicity while maintaining high anti-leukemic efficacy. The advantage of ATRA-ATO over ATRA chemotherapy has been recently demonstrated in two large randomized trials and this option has now become the new standard of care in low-risk (i.e. non-hyperleukocytic) patients. In light of its rarity, abrupt onset and high risk of early death and due to specific treatment requirements, APL remains a challenging condition that needs to be managed in highly experienced centers. We review here the results of large clinical studies conducted in newly diagnosed APL as well as the recommendations for appropriate diagnosis, prevention and management of the main complications associated with modern treatment of the disease.

Minimal residual disease negativity in elderly patients with acute myeloid leukemia may indicate different postremission strategies than in younger patients.

In the present analysis, we evaluated whether in elderly acute myeloid leukemia (AML) patients (>60 years), minimal residual disease (MRD) assessed by flow cytometry may have a role in guiding choice of postremission strategies. We analyzed 149 young and 61 elderly adults who achieved morphological CR after induction course of EORTC/GIMEMA protocols. Elderly patients reached a postconsolidation MRD negative status less frequently than younger ones (11 vs 28 %, p = 0.009). MRD negativity resulted in a longer 5-year disease-free survival (DFS) both in elderly (57 vs 13 %, p = 0.0197) and in younger patients (56 vs 31 %, p = 0.0017). Accordingly, 5-year cumulative incidence of relapse (CIR) of both elderly (83 vs 42 %, p = 0.045) and younger patients (59 vs 24 % p = NS) who were MRD positive doubled that of MRD negative ones. Nevertheless, CIR of MRD negative elderly patients was twofold higher than that of younger MRD negative ones (42 vs 24 %, p = NS). In conclusion, elderly patients in whom chemotherapy yields a MRD negative CR have duration of DFS and rate of CIR significantly better than those who remain MRD positive. Nonetheless, the high CIR rate observed in the elderly suggests that MRD negativity might have different therapeutic implications in this population than in the younger counterpart.

Arsenic trioxide-based therapy of relapsed acute promyelocytic leukemia: registry results from the European LeukemiaNet.

In 2008, a European registry of relapsed acute promyelocytic leukemia was established by the European LeukemiaNet. Outcome data were available for 155 patients treated with arsenic trioxide in first relapse. In hematological relapse (n=104), 91% of the patients entered complete hematological remission (CR), 7% had induction death and 2% resistance, 27% developed differentiation syndrome and 39% leukocytosis, whereas no death or side effects occurred in patients treated in molecular relapse (n=40). The rate of molecular (m)CR was 74% in hematological and 62% in molecular relapse (P=0.3). All patients with extramedullary relapse (n=11) entered clinical and mCR. After 3.2 years median follow-up, the 3-year overall survival (OS) and cumulative incidence of second relapse were 68% and 41% in hematological relapse, 66% and 48% in molecular relapse and 90 and 11% in extramedullary relapse, respectively. After allogeneic or autologous transplantation in second CR (n=93), the 3-year OS was 80% compared with 59% without transplantation (n=55) (P=0.03). Multivariable analysis demonstrated the favorable prognostic impact of first remission duration ⩾1.5 years, achievement of mCR and allogeneic or autologous transplantation on OS of patients alive after induction (P=0.03, P=0.01, P=0.01) and on leukemia-free survival (P=0.006, P<0.0001, P=0.003), respectively.

A miRNA Signature in Human Cord Blood Stem and Progenitor Cells as Potential Biomarker of Specific Acute Myeloid Leukemia Subtypes.

MicroRNAs (miRNAs) are important regulators of several cellular processes. During hematopoiesis, specific expression signatures have been reported in different blood cell lineages and stages of hematopoietic stem cell (HSC) differentiation. Here we explored the expression of miRNAs in umbilical cord blood stem (HSC) and progenitor cells (HPC) and compared it to unilineage granulocyte and granulo-monocyte differentiation as well as to primary blasts from patients with acute myeloid leukemia (AML). CD34 + CD38- ad CD34 + CD38 + cells were profiled using a global array consisting of about 2000 miRNAs. An approach combining bioinformatic prediction of miRNA targets with mRNA expression profiling was used to search for putative biologically enriched functions and networks. At least 15 miRNAs to be differentially expressed between HSC and HPC cell population, a cluster of 7 miRNAs are located in the q32 region of human chromosome 14 (miR-377-3p, -136-5p, 376a-3p, 495-3p, 654-3p, 376c-3p and 381-3p) whose expression decreased during the early stages of normal myelopoiesis but were markedly increased in a small set of AML. Interestingly, miR-4739 and -4516, two novel microRNA whose function and targets are presently unknown, showed specific and peculiar expression profile during the hematopoietic stem cells differentiation into unilineages and resulted strongly upregulated in almost all AML subsets. miR-181, -126-5p, -29b-3p and -22-3p resulted dis-regulated in specific leukemias phenotypes. This study provides the first evidence of a miRNA signature in human cord blood stem and progenitor cells with a potential role in hematopoietic stemness properties and possibly in leukemogenesis of specific AML subtypes.

Argonaute 2 sustains the gene expression program driving human monocytic differentiation of acute myeloid leukemia cells.

MicroRNAs are key regulators of many biological processes, including cell differentiation. These small RNAs exert their function assembled in the RNA-induced silencing complexes (RISCs), where members of Argonaute (Ago) family of proteins provide a unique platform for target recognition and gene silencing. Here, by using myeloid cell lines and primary blasts, we show that Ago2 has a key role in human monocytic cell fate determination and in LPS-induced inflammatory response of 1,25-dihydroxyvitamin D3 (D3)-treated myeloid cells. The silencing of Ago2 impairs the D3-dependent miR-17-5p/20a/106a, miR-125b and miR-155 downregulation, the accumulation of their translational targets AML1, VDR and C/EBPß and monocytic cell differentiation. Moreover, we show that Ago2 is recruited on miR-155 host gene promoter and on the upstream region of an overlapping antisense lncRNA, determining their epigenetic silencing, and miR-155 downregulation. These findings highlight Ago2 as a new factor in myeloid cell fate determination in acute myeloid leukemia cells.

miRNA let-7c promotes granulocytic differentiation in acute myeloid leukemia.

MicroRNAs (miRNAs), small non-coding RNAs that regulate gene expression post-transcriptionally, are involved in many complex cellular processes. Several miRNAs are differentially expressed in hematopoietic tissues and play important roles in normal differentiation, but, when aberrantly regulated, contribute to the abnormal proliferation and differentiation of leukemic cells. Recently, we reported that a small subset of miRNAs is differentially expressed in acute promyelocytic leukemia (APL) blasts and is modulated by treatment with all-trans-retinoic acid (ATRA). In particular, PML/RARα-positive blasts from APL patients display lower levels of miRNA let-7c, a member of the let-7 family, than normal promyelocytes and its expression increases after ATRA treatment. In this study, we investigated the effects of let-7c in acute myeloid leukemia (AML) cells. We found that ectopic expression of let-7c promotes granulocytic differentiation of AML cell lines and primary blasts. Moreover, we identified PBX2, a well-known homeodomain protein whose aberrant expression enhances HoxA9-dependent leukemogenesis, as a novel let-7c target that may contribute to the AML phenotype. Together, these studies raise the possibility that perturbation of the let-7c-PBX2 pathway may have a therapeutic value in AML.

Nucleophosmin/B26 regulates PTEN through interaction with HAUSP in acute myeloid leukemia.

PTEN (phosphatase and tensin homolog deleted in chromosome 10) is a bona fide dual lipid and protein phosphatase with cytoplasmic (Cy) and nuclear localization. PTEN nuclear exclusion has been associated with tumorigenesis. Nucleophosmin (NPM1) is frequently mutated in acute myeloid leukemia (AML) and displays Cy localization in mutated nucleophosmin (NPMc+) AML. Here we show that NPM1 directly interacts with herpes virus-associated ubiquitin specific protease (HAUSP), which is known as a PTEN deubiquitinating enzyme. Strikingly, PTEN is aberrantly localized in AML carrying NPMc+. Mechanistically, NPM1 in the nucleus opposes HAUSP-mediated deubiquitination and this promotes the shuttle of PTEN to the cytoplasm. In the cytoplasm, NPMc+ prevents HAUSP from deubiquitinating PTEN, causing the latter to stay in the cytoplasm where it is polyubiquitinated and degraded. Our findings delineate a new NPM1-HAUSP molecular interaction controlling PTEN deubiquitination and trafficking.

Comparative molecular analysis of therapy-related and de novo acute promyelocytic leukemia.

Therapy-related acute promyelocytic leukemia (t-APL) has been reported as a late complication of exposure to radiotherapy and/or chemotherapeutic agents targeting DNA topoisomerase II. We have analyzed in t-APL novel gene mutations recently associated with myeloid disorders. Unlike previous reports in acute myeloid leukemia (AML), our results showed neither IDHs nor TET2 mutations in t-APL. However we found an R882H mutation in the DNMT3A gene in a patient with t-APL suggesting a possible role of this alteration in the pathogenesis of t-APL.

Novel strategies in treatment of acute promyelocytic leukemia.

Acute promyelocytic leukemia (APL) is a subtype of acute myeloid leukemia characterized by t(15;17) and a life-threatening coagulopathy. Once highly fatal, nowadays standard treatment approaches with all-trans retinoic acid (ATRA) along with chemotherapy allows curing up to 80-85% of cases. In the past decade, arsenic trioxide used alone or in combination with ATRA has demonstrated high efficacy in APL, and is currently regarded as the gold standard for treatment of relapsed cases. Chemotherapy-free approaches based on the combination of arsenic trioxide and ATRA are currently being tested against standard ATRA and chemotherapy in randomized clinical trials for frontline therapy of APL.