Molecular analysis of the t(15;17) translocation in acute promyelocytic leukaemia

Autophagy Inhibition-induced Cytosolic DNA Sensing Combined with Differentiation Therapy Induces Irreversible Myeloid Differentiation in Leukemia Cells

Accumulating evidence indicates that various oncogenic mutations interfere with normal myeloid differentiation of leukemogenic cells during the early process of acute myeloid leukemia (AML) development. Differentiation therapy is a therapeutic strategy capable of terminating leukemic expansion by reactivating the differentiation potential; however, the plasticity and instability of leukemia cells counteract the establishment of treatments aimed at irreversibly inducing and maintaining their differentiation states. On the basis of our previous observation that autophagy inhibitor treatment induces the accumulation of cytosolic DNA and activation of cytosolic DNA-sensor signaling selectively in leukemia cells, we herein examined the synergistic effect of cytosolic DNA-sensor signaling activation with conventional differentiation therapy on AML. The combined treatment succeeded in inducing irreversible differentiation in AML cell lines. Mechanistically, cytosolic DNA was sensed by absent in melanoma 2 (AIM2), a cytosolic DNA sensor. Activation of the AIM2 inflammasome resulted in the accumulation of p21 through the inhibition of its proteasomal degradation, thereby facilitating the myeloid differentiation. Importantly, the combined therapy dramatically reduced the total leukemia cell counts and proportion of blast cells in the spleens of AML mice. Collectively, these findings indicate that the autophagy inhibition-cytosolic DNA-sensor signaling axis can potentiate AML differentiation therapy.

SIGNIFICANCE

Clinical effects on AML therapy are closely associated with reactivating the normal myeloid differentiation potential in leukemia cells. This study shows that autophagosome formation inhibitors activate the cytosolic DNA-sensor signaling, thereby augmenting conventional differentiation therapy to induce irreversible differentiation and cell growth arrest in several types of AML cell lines.

Interdisciplinary Quality Improvement Led by the Molecular Pathology Laboratory Expedites Diagnosis of Acute Promyelocytic Leukemia

OBJECTIVES

Acute promyelocytic leukemia (APL) requires emergent treatment while definitive laboratory results are pending. Following the death of a patient whose diagnosis was delayed, we sought to improve our institution's workflow by using the EPIDEM (Exploration, Promotion, Implementation, Documentation, Evaluation, Modification) quality improvement model.

METHODS

APL is confirmed by identifying translocation t(15;17)(q24;q21) PML-RARA by using either molecular or cytogenetic methods on peripheral blood or bone marrow specimens. We used the EPIDEM model to decrease the turnaround time (TAT) of molecular diagnosis by improving communication and developing reflex testing. We additionally compared 32 APL cases against a control group of 18 suspected APL cases.

RESULTS

Our review of 687 multiplex polymerase chain reaction orders and 33 PML-RARA orders (January 2012 to April 2021) showed an initial TAT decrease from 4.48 days to 2.71 days (P < .0001), which further decreased to 0.64 days (P < .0001) after implementation of the PML-RARA qualitative assay. Compared with patients suspected of having APL, patients with confirmed APL had higher dimerized plasmin fragment D (P = .0145), lower fibrinogen (P ≤ .0001), and lower WBC (P ≤ .0001).

CONCLUSIONS

By using the EPIDEM model, with its emphasis on local context, culture, and resources, improved communication and workflow changes enabled us to reduce the time needed to diagnose APL to 0.64 days and identify potential locally derived screening cutoffs.

When Poisons Cure: The Case of Arsenic in Acute Promyelocytic Leukemia

Arsenic has been known for centuries for its double-edged potential: a poison and at the same time a therapeutic agent. The name "arsenikon," meaning "potent," speaks itself for the pharmaceutical properties of this compound, questioned and analyzed for at least 2000 years. In the last decades, acute promyelocytic leukemia (APL) has evolved from a highly fatal to a curable disease, due to the use of all-trans-retinoic acid and, more recently, arsenic trioxide combinations. The success of these entirely chemo-free regimens increased the awareness of APL and reduced the prevalence of early deaths, which was an impending issue in this disease. Further improvements are expected with the next use of oral arsenic formulations, which will allow a complete outpatient approach, at least in the post-induction settings, further improving patients' quality of life. The wide use of standardized approaches in APL will also help unravel long-standing open questions, including the pathogenesis, prevention, and treatment of the differentiation syndrome and of short-term organ toxicities. In the long term, the study of survivorship issues, such as fertility and organ-related and psychological damages, in the increasing number of survivors will help further improve their life after APL.

Verteporfin Inhibits Cell Proliferation and Induces Apoptosis in Human Leukemia NB4 Cells without Light Activation

Background and Aims: Verteporfin (VP), clinically used in photodynamic therapy for neovascular macular degeneration, has recently been proven a suppressor of yes-associated protein (YAP) and has shown potential in anticancer treatment. However, its anti-human leukemia effects in NB4 cells remain unclear. In this study, we investigated the effects of VP on proliferation and apoptosis in human leukemia NB4 cells. Methods: NB4 cells were treated with VP for 24 h. The effects of VP on cell proliferation were determined using a Cell-Counting Kit-8 assay (CCK-8) assay and colony forming assay. Apoptosis and cell cycle were evaluated by flow cytometry (FCM). The protein levels were detected by western blot. Results: We found that VP inhibited the proliferation of NB4 cells in a concentration and time-dependent manner. FCM analysis showed that VP induced apoptosis in a concentration dependent manner and that VP treatment led to cell cycle arrest at G0/G1 phase. Moreover, VP significantly decreased the protein expression of YAP, p-YAP, Survivin, c-Myc, cyclinD1, p-ERK, and p-AKT. In addition, VP increased the protein expression of cleaved caspase3, cleaved PARP, Bax, and p-p38 MAPK. Conclusions: VP inhibited the proliferation and induced apoptosis in NB4 cells.

Pim2 cooperates with PML-RARalpha to induce acute myeloid leukemia in a bone marrow transplantation model

Although the potential role of Pim2 as a cooperative oncogene has been well described in lymphoma, its role in leukemia has remained largely unexplored. Here we show that high expression of Pim2 is observed in patients with acute promyelocytic leukemia (APL). To further characterize the cooperative role of Pim2 with promyelocytic leukemia/retinoic acid receptor alpha (PML/RARalpha), we used a well-established PML-RARalpha (PRalpha) mouse model. Pim2 coexpression in PRalpha-positive hematopoietic progenitor cells (HPCs) induces leukemia in recipient mice after a short latency. Pim2-PRalpha cells were able to repopulate mice in serial transplantations and to induce disease in all recipients. Neither Pim2 nor PRalpha alone was sufficient to induce leukemia upon transplantation in this model. The disease induced by Pim2 overexpression in PRalpha cells contained a slightly higher fraction of immature myeloid cells, compared with the previously described APL disease induced by PRalpha. However, it also clearly resembled an APL-like phenotype and showed signs of differentiation upon all-trans retinoic acid (ATRA) treatment in vitro. These results support the hypothesis that Pim2, which is also a known target of Flt3-ITD (another gene that cooperates with PML-RARalpha), cooperates with PRalpha to induce APL-like disease.

The molecular pathogenesis of acute promyelocytic leukaemia: implications for the clinical management of the disease

Acute promyelocytic leukaemia (APL) is characterised by chromosomal rearrangements of 17q21, leading to fusion of the gene encoding retinoic acid receptor alpha (RARalpha) to a number of alternative partner genes (X), the most frequent of which are PML (>95%), PLZF (0.8%) and NPM (0.5%). Over the last few years, it has been established that the X-RARalpha fusion proteins play a key role in the pathogenesis of APL through recruitment of co-repressors and the histone deacetylase (HDAC)-complex to repress genes implicated in myeloid differentiation. Paradoxically, the X-RARalpha fusion protein has the potential to mediate myeloid differentiation at pharmacological doses of its ligand (all trans-retinoic acid (ATRA)), which is dependent on the dissociation of the HDAC/co-repressor complex. Arsenic compounds have also been shown to be promising therapeutic agents, leading to differentiation and apoptosis of APL blasts. It is now apparent that the nature of the RARalpha-fusion partner is a critical determinant of response to ATRA and arsenic, underlining the importance of cytogenetic and molecular characterisation of patients with suspected APL to determine the most appropriate treatment approach. Standard protocols involving ATRA combined with anthracycline-based chemotherapy, lead to cure of approximately 70% patients with PML-RARalpha-associated APL. Patients at high risk of relapse can be identified by minimal residual disease monitoring. The challenge for future studies is to improve complete remission rates through reduction of induction deaths, particularly due to haemorrhage, identification of patients at high risk of relapse who would benefit from additional therapy, and identification of a favourable-risk group, for which treatment intensity could be reduced, thereby reducing risks of treatment toxicity and development of secondary leukaemia/myelodysplasia. With the advent of ATRA and arsenic, APL has already provided the first example of successful molecularly targeted therapy; it is hoped that with further understanding of the pathogenesis of the disease, the next decade will yield further improvements in the outlook for these patients.

Retinoid therapy of childhood cancer

In vitro studies that showed RA could cause growth arrest and differentiation of myelogenous leukemia and neuroblastoma led to clinical trials of retinoids in APL and neuroblastoma that increased survival for both of those diseases. In the case of APL, ATRA has been the drug of choice, and preclinical and clinical data support direct combinations of ATRA with cytotoxic chemotherapy. For neuroblastoma, a phase I study defined a dose of 13-cis-RA, which was tolerable in patients after myeloablative therapy, and a phase III trial that showed postconsolidation therapy with 13-cis-RA improved EFS for patients with high-risk neuroblastoma. Preclinical studies in neuroblastoma indicate that ATRA or 13-cis-RA can antagonize cytotoxic chemotherapy and radiation, so use of 13-cis-RA in neuroblastoma is limited to maintenance after completion of cytotoxic chemotherapy and radiation. A limitation on the antitumor benefit of ATRA in APL is the marked decrease in drug levels that occurs during therapy as a result of induction of drug metabolism, resulting in a shorter drug half-life and decreased plasma levels. Although early studies sought to overcome the pharmacologic limitations of ATRA therapy in APL, the demonstration that ATO is active against APL in RA-refractory patients has led to a focus on studies employing ATO. Use of 13-cis-RA in neuroblastoma has avoided the decreased plasma levels seen with ATRA. It is likely that recurrent disease seen during or after 13-cis-RA therapy in neuroblastoma is due to tumor cell resistance to retinoid-mediated differentiation induction. Studies in neuroblastoma cell lines resistant to 13-cis-RA and ATRA have shown that they can be sensitive, and in some cases collaterally hypersensitive, to the cytotoxic retinoid fenretinide. Fenretinide induces tumor cell cytotoxicity rather than differentiation, acts independently from RA receptors, and in initial phase I trials has been well tolerated. Clinical trials of fenretinide, alone and in combination with ceramide modulators, are in development.

Rapid diagnosis of acute promyelocytic leukemia by analyzing the immunocytochemical pattern of the PML protein with the monoclonal antibody PG-M3

The fusion protein, promyelocytic leukemia-retinoic acid receptor (PML-RAR)alpha, generated by the t(15;17) translocation has an abnormal cellular distribution with colocalization of RARalpha and PML proteins. We analyzed the immunostaining pattern of PML protein using the PG-M3 monoclonal antibody directed against the amino terminal portion of PML (retained in wild-type PML and PML-RARalpha fusion protein) in the diagnosis of acute promyelocytic leukemia (APL). In addition, we compared this test with other methods for detecting the PML-RARalpha fusion gene. A normal immunostaining pattern was observed in nonmyeloid disorders and in 78 of 111 acute myeloid leukemias (AMLs). A microgranular pattern was observed in 25 AMLs, all corresponding to APL. These results were concordant with the reverse transcriptase-polymerase chain reaction results for PML-RARalpha fusion gene. Only 1 case positive for the PML-RARalpha transcript showed a normal protein pattern by immunocytochemistry. PML immunostaining was helpful to rapidly differentiate 7 cases with borderline characteristics and to obtain the diagnosis in 2 cases with scarce material. The effectiveness and low cost of this technique support its routine use as a first-line procedure in the differential diagnosis of AML.

Characterisation of the PML/RAR alpha rearrangement associated with t(15;17) acute promyelocytic leukaemia

The vast majority of cases of APL are associated with t(15; 17) leading to the formation of PML-RAR alpha, RAR alpha-PML and aberrant PML fusion products. PML-RAR alpha is invariably transcribed and is believed to mediate leukaemogenesis. PML was initially considered to be a transcription factor. However, characterisation of other RING finger containing proteins shows no direct evidence for DNA binding. The RING, B-box, and coiled-coil domains are more likely to represent sites of protein-protein interaction and may be critical for the stability of the multiprotein nuclear domains of which PML is an integral part. In APL the nuclear bodies become disrupted, presumably as a consequence of the presence of PML-RAR alpha and aberrant PML proteins that might render the structure unstable. PML-RAR alpha is capable of binding RXR and sequestering it into the disrupted nuclear domains. Sequestration of RXR would be expected to limit high affinity binding of VDR, TR and residual RARs to DNA response elements and might account for the block in myeloid differentiation at the promyelocyte stage that characterizes APL. Recently PML has been found to have growth suppressor/anti-oncogenic activity. It is unclear whether this is a property of PML itself or reflects a nonspecific function of the PML-associated nuclear domains. Hence the PML/RAR alpha rearrangement alone may be sufficient to cause APL. Abnormal PML function may prevent its growth-suppressor activity, leading to leukaemic transformation; concomitant disruption of retinoid pathways due to sequestration of RXR and/or an abnormal repertoire and character of response element activation mediated by the fusion protein, causing the block in myeloid differentiation (Fig. 3). Disruption of RAR alpha would be expected to account for the similar leukaemic phenotype associated with the t(5;17) and t(11;17) APL cytogenetic variants. Further characterisation of NPM and PLZF at the structural and functional level will determine whether PML and other proteins disrupted in APL associated translocations play an active or purely permissive role in leukaemogenesis and will help dissect the events leading to transformation from those causing blockade of myeloid differentiation and mediating the response to ATRA.

Relapse of acute promyelocytic leukemia follows serial negative RT-PCR assays: a cautionary tale

Six patients with acute promyelocytic leukaemia (APL) and t(15;17) were investigated by cytogenetics and by reverse transcriptase polymerase chain reaction (RT-PCR) for the fusion transcript PML-RARA. The clone was detected in remission following all-trans retinoic acid and chemotherapy by cytogenetics and/or by RT-PCR up to 2 months from diagnosis. Thereafter the PML-RARA transcript was not seen in 20/21 first remission samples in five cases studied. Remission was maintained in two patients, one following bone marrow transplantation (BMT). Despite serial negative RT-PCR results, PML-RARA reemerged at or prior to relapse following BMT in the remaining three cases. Frequent molecular monitoring and caution in the interpretation of negative RT-PCR results are indicated in APL.

Tretinoin. A review of its pharmacodynamic and pharmacokinetic properties and use in the management of acute promyelocytic leukaemia

Tretinoin (all-trans retinoic acid), a vitamin A derivative, induces cellular differentiation in several haematological precursor cell lines and cells from patients with acute promyelocytic leukaemia. Drug treatment with tretinoin is associated with morphological and functional maturation of leukaemic promyelocytes and a progressive reduction in the occurrence of the characteristic t(15;17) chromosomal translocation. Recent therapeutic trials indicate that tretinoin induces remission in 64 to 100% of patients with acute promyelocytic leukaemia. In newly diagnosed patients, remission induction treatment with tretinoin followed by intensive chemotherapy resulted in a significant reduction in relapse rate and prolongation of event-free and overall survival compared with chemotherapy alone in 1 comparative trial. Tretinoin alone does not totally eradicate the leukaemic clone and consolidation chemotherapy is recommended as follow-up. The use of reverse transcription polymerase chain reaction (RT-PCR) provides a sensitive and specific technique to assist in prediction and monitoring of a patient's response to treatment and to help detect the presence of residual or recurrent disease. The use of tretinoin is potentially limited by the rapid and almost universal development of drug resistance and occurrence of the often severe retinoic acid syndrome. Useful strategies have been described to manage these effects but current and future efforts must be directed at elucidating the mechanisms involved and determining the optimum therapeutic management. In summary, results to date indicate that the combination of tretinoin and intensive chemotherapy is more effective than chemotherapy alone and appears to improve the prognosis of newly diagnosed patients with acute promyelocytic leukaemia. Further information on the relative efficacy of various induction and post-remission strategies in subsets of patients will help determine optimum use of this promising agent in the management of acute promyelocytic leukaemia.

Cytogenetics in acute myeloid leukaemia

A wealth of literature spanning 20 years describing cytogenetic abnormalities in acute myeloid leukaemia (AML) already exists. It ranges from single case reports of unusual abnormalities to large multicentre studies of hundreds of cases. A landmark publication was the Fourth International Workshop on Chromosomes in Acute Leukaemia which established a base line for diagnosis, prognosis and frequency of chromosome abnormalities in AML. Two large sources of information are a book, 'The Chromosomes in Human Cancer and Leukemia' and a catalogue of chromosome abnormalities, which aims to list all chromosome abnormalities described in the scientific and medical literature from 1973, when the widespread use of banding techniques, enabled the precise definition of the chromosome breakpoints. In this review the common cytogenetic abnormalities seen in AML with reference to associations with the French-American-British (FAB) classification, their possible prognostic significance and their associated molecular biology are summarized.