Zhen-Yi Wang

Acute promyelocytic leukemia.

Perhaps the most important advance in this field is not the specific actions of all-trans-retinoic acid in acute promyelocytic leukemia, but rather the conclusive documentation of differentiation as a practical and consistently effective method of treating human cancer. As a drug, all-trans-retinoic acid has certain undesirable pharmacologic properties that might be overcome by the use of alternative retinoids, such as 9-cis-retinoic acid, that are equally active against acute promyelocytic leukemia cells in vitro. In addition to retinoids that selectively activate RARs or RXRs, other ligands of the steroid-thyroid receptor superfamily, such as vitamin D3, glucocorticoids, and sex steroids also have cytodifferentiating actions in model systems. Numerous other agents can effect differentiation of neoplastic cells in such systems, including sodium butyrate, hexamethylene bisacetamide and its analogues, colony-stimulating factors, and interferons. Each of these compounds apparently acts through different pathways, and their activity may be greatly amplified when they are used in combination. Just as the practical usefulness of all-trans-retinoic acid in combination with conventional treatments continues to evolve, the use of differentiation agents in combination represents a novel and promising approach for oncologic therapy in the next decade. Although acute promyelocytic leukemia remains an orphan disease, its importance as a model for human neoplasia should not be minimized. The specific molecular lesion of acute promyelocytic leukemia is not shared by other cancers, but the physiologic actions of retinoids, their documented cytodifferentiating activity against a variety of human cancer cells in vitro, and their usefulness in cancer chemoprevention are clearly not mediated by identifiable mutations of retinoid receptors. The insights into transformation and leukemogenesis gained in acute promyelocytic leukemia may be a harbinger of further clinical applications and offer a glimpse into the next generation of cancer therapy.

Acute promyelocytic leukemia: from highly fatal to highly curable

Acute promyelocytic leukemia (APL) is a distinct subtype of acute myeloid leukemia. Morphologically, it is identified as the M3 subtype of acute myeloid leukemia by the French-American-British classification and cytogenetically is characterized by a balanced reciprocal translocation between chromosomes 15 and 17, which results in the fusion between promyelocytic leukemia (PML) gene and retinoic acid receptor alpha (RARalpha). It seems that the disease is the most malignant form of acute leukemia with a severe bleeding tendency and a fatal course of only weeks. Chemotherapy (CT; daunorubicin, idarubicin and cytosine arabinoside) was the front-line treatment of APL with a complete remission (CR) rate of 75% to 80% in newly diagnosed patients. Despite all these progresses, the median duration of remission ranged from 11 to 25 months and only 35% to 45% of the patients could be cured by CT. Since the introduction of all-trans retinoic acid (ATRA) in the treatment and optimization of the ATRA-based regimens, the CR rate was raised up to 90% to 95% and 5-year disease free survival (DFS) to 74%. The use of arsenic trioxide (ATO) since early 1990s further improved the clinical outcome of refractory or relapsed as well as newly diagnosed APL. In this article, we review the history of introduction of ATRA and ATO into clinical use and the mechanistic studies in understanding this model of cancer targeted therapy.

Apoptosis and growth inhibition in malignant lymphocytes after treatment with arsenic trioxide at clinically achievable concentrations.

BACKGROUNDnArsenic trioxide (As2O3) can induce clinical remission in patients with acute promyelocytic leukemia via induction of differentiation and programmed cell death (apoptosis). We investigated the effects of As2O3 on a panel of malignant lymphocytes to determine whether growth-inhibitory and apoptotic effects of As2O3 can be observed in these cells at clinically achievable concentrations.nnnMETHODSnEight malignant lymphocytic cell lines and primary cultures of lymphocytic leukemia and lymphoma cells were treated with As2O3, with or without dithiothreitol (DTT) or buthionine sulfoximine (BSO) (an inhibitor of glutathione synthesis). Apoptosis was assessed by cell morphology, flow cytometry, annexin V protein level, and terminal deoxynucleotidyl transferase labeling of DNA fragments. Cellular proliferation was determined by 5-bromo-2-deoxyuridine incorporation into DNA and flow cytometry and by use of a mitotic arrest assay. Mitochondrial transmembrane potential (delta psi(m)) was measured by means of rhodamine 123 staining and flow cytometry. Protein expression was assessed by western blot analysis or immunofluorescence.nnnRESULTSnTherapeutic concentrations of As2O3 (1-2 microM) had dual effects on malignant lymphocytes: 1) inhibition of growth through adenosine triphosphate (ATP) depletion and prolongation of cell cycle time and 2) induction of apoptosis. As2O3-induced apoptosis was preceded by delta psi(m) collapse. DTT antagonized and BSO enhanced As2O3-induced ATP depletion, delta psi(m) collapse, and apoptosis. Caspase-3 activation, usually resulting from delta psi(m) collapse, was not always associated with As2O3-induced apoptosis. As2O3 induced PML (promyelocytic leukemia) protein degradation but did not modulate expression of cell cycle-related proteins, including c-myc, retinoblastoma protein, cyclin-dependent kinase 4, cyclin D1, and p53, or expression of differentiation-related antigens.nnnCONCLUSIONSnSubstantial growth inhibition and apoptosis without evidence of differentiation were induced in most malignant lymphocytic cells treated with 1-2 microM As2O3. As2O3 may prove useful in the treatment of malignant lymphoproliferative disorders.

Arsenic trioxide, a therapeutic agent for APL

Acute promyelocytic leukemia (APL) is an interesting model in cancer research, because it can respond to the differentiation/apoptosis induction therapy using all-trans retinoic acid (ATRA) and arsenic trioxide (As2O3). Over the past 5 years, it has been well demonstrated that As2O3 induces a high complete remission (CR) rate in both primary and relapsed APL patients (around 85∼90%). The side effects are mild to moderate in relapsed patients, while severe hepatic lesions have been found in some primary cases. After CR obtained in relapsed patients, chemotherapy in combination with As2O3 as post-remission therapy has given better survival than those treated with As2O3 alone. The effect of As2O3 has been shown to be related to the expression of APL-specific PML–RARα oncoprotein, and there is a synergistic effect between As2O3 and ATRA in an APL mouse model. Cell biology studies have revealed that As2O3 exerts dose-dependent dual effects on APL cells. Apoptosis is evident when cells are treated with 0.5∼2.0u2009μM of As2O3 while partial differentiation is observed using low concentrations (0.1∼0.5u2009μM) of the drug. The apoptosis-inducing effect is associated with the collapse of mitochondrial transmembrane potentials in a thiol-dependent manner, whereas the mechanisms underlying APL cell differentiation induced by low dose arsenic remain to be explored. Interestingly, As2O3 over a wide range of concentration (0.1∼2.0u2009μM) induces degradation of a key leukemogenic protein, PML–RARα, as well as the wild-type PML, thus setting up a good example of targeting therapy for human cancers.

Treatment of acute promyelocytic leukaemia with all-trans retinoic acid and arsenic trioxide: a paradigm of synergistic molecular targeting therapy

To turn a disease from highly fatal to highly curable is extremely difficult, especially when the disease is a type of cancer. However, we can gain some insight into how this can be done by looking back over the 50-year history of taming acute promyelocytic leukaemia (APL). APL is the M3 type of acute myeloid leukaemia characterized by an accumulation of abnormal promyelocytes in bone marrow, a severe bleeding tendency and the presence of the chromosomal translocation t(15;17) or variants. APL was considered the most fatal type of acute leukaemia five decades ago and the treatment of APL was a nightmare for physicians. Great efforts have been made by scientists worldwide to conquer this disease. The first use of chemotherapy (CT) was unsuccessful due to lack of supportive care and cytotoxic-agent-related exacerbated coagulopathy. The first breakthrough came from the use of anthracyclines which improved the complete remission (CR) rate, though the 5-year overall survival could only be attained in a small proportion of patients. A rational and intriguing hypothesis, to induce differentiation of APL cells rather than killing them, was raised in the 1970s. Laudably, the use of all-trans retinoic acid (ATRA) in treating APL resulted in terminal differentiation of APL cells and a 90–95% CR rate of patients, turning differentiation therapy in cancer treatment from hypothesis to practice. The combination of ATRA with CT further improved the 5-year overall survival. When arsenic trioxide (ATO) was used to treat relapsed APL not only the patients but also the ancient drug were revived. ATO exerts dose-dependent dual effects on APL cells: at low concentration, ATO induces partial differentiation, while at relatively high concentration, it triggers apoptosis. Of note, both ATRA and ATO trigger catabolism of the PML–RARα fusion protein which is the key player in APL leukaemogenesis generated from t(15;17), targeting the RARα (retinoic acid receptor α) or promyelocytic leukaemia (PML) moieties, respectively. Hence, in treating APL both ATRA and ATO represent paradigms for molecularly targeted therapy. At molecular level, ATRA and ATO synergistically modulate multiple downstream pathways/cascades. Strikingly, a clearance of PML–RARα transcript in an earlier and more thorough manner, and a higher quality remission and survival in newly diagnosed APL are achieved when ATRA is combined with ATO, as compared to either monotherapy, making APL a curable disease. Thus, the story of APL can serve as a model for the development of curative approaches for disease; it suggests that molecularly synergistic targeted therapies are powerful tools in cancer, and dissection of disease pathogenesis or anatomy of the cancer genome is critical in developing molecular target-based therapies.

Differentiation and apoptosis induction therapy in acute promyelocytic leukaemia

Induction of differentiation and/or apoptosis is a new and promising approach to cancer therapy, well illustrated by the treatment of acute promyelocytic leukaemia with all-trans-retinoic acid and arsenic compounds. Treatment with all-transretinoic acid results in complete remission in 92 - 95% of patients with this disease. Using the recently advocated combination of all-transretinoic acid and chemotherapy, adverse effects such as retinoic acid syndrome have decreased, and long-term survival has improved. Chemotherapy in combination with all-trans-retinoic acid seems to be the best postremission treatment protocol, with a 5-year relapse-free survival rate of 50 - 60%. Arsenic compounds have recently proved effective in newly diagnosed and relapsed acute promyelocytic leukaemia, with complete remission rates of 80 - 90% according to most reports. As2O3, the most studied arsenic compound, can be given by intravenous infusion at a dose of 0.08 - 0.16 mg/kg daily. A course of 28 - 44 days is required to induce remission. Although the drug is safe in patients who have relapsed, severe liver damage has been observed in some newly diagnosed patients. Combined use of chemotherapy and arsenic as postremission treatment results in longer survival than arsenic alone. Although their mechanisms of action are distinct, both all-trans-retinoic acid and arsenic can modulate PML-RARalpha, an oncoprotein that has a central role in leukaemogenesis, and both can relieve ranscriptional repression by modifying chromatin structure.

Retinoic Acid and Arsenic for Treating Acute Promyelocytic Leukemia

What were the critical steps in the development of ATRA and arsenic as treatments for APL? Researchers in Shanghai tell the story and look to the future

Back to the future of oridonin: again, compound from medicinal herb shows potent antileukemia efficacies in vitro and in vivo

Back to the future of oridonin: again, compound from medicinal herb shows potent antileukemia efficacies in vitro and in vivo

Treatment of Acute Promyelocytic Leukemia with Arsenic Trioxide: Clinical and Basic Studies

Arsenic trioxide (As2O3) has recently been identified as an effective drug in the treatment of newly diagnosed and relapsed acute promyelocytic leukemia (APL) without cross-resistance to all-trans retinoic acid and achieved complete remission rates of 80–90% according to most reports. With intravenous infusion at a dose of 0.08–0.16 mg/kg daily, a course of 28–42 days is required to induce remission. As2O3 in combination with chemotherapy as postremission therapy results in longer survival than arsenic alone. In vitro, As2O3 exerts dose-dependent dual effect; triggering apoptosis at relatively high concentration (0.5–2.0 μmol/1), which is associated with the disruption of mitochondrial transmembrane potentials, while inducing partial differentiation at low concentration (0.1–0.5 μmol/1), which might be related to retinoic acid signaling pathway. Importantly, at both concentrations, As2O3 can degrade PML (promyelocytic leukemia)-RARα (retinoic acid receptor), an oncoprotein that has a central role in leukemogenesis.

Mutations of Epigenetic Modifier Genes as a Poor Prognostic Factor in Acute Promyelocytic Leukemia Under Treatment With All-Trans Retinoic Acid and Arsenic Trioxide

Background Acute promyelocytic leukemia (APL) is a model for synergistic target cancer therapy using all-trans retinoic acid (ATRA) and arsenic trioxide (ATO), which yields a very high 5-year overall survival (OS) rate of 85 to 90%. Nevertheless, about 15% of APL patients still get early death or relapse. We performed this study to address the possible impact of additional gene mutations on the outcome of APL. Methods We included a consecutive series of 266 cases as training group, and then validated the results in a testing group of 269 patients to investigate the potential prognostic gene mutations, including FLT3-ITD or -TKD, N-RAS, C-KIT, NPM1, CEPBA, WT1, ASXL1, DNMT3A, MLL (fusions and PTD), IDH1, IDH2 and TET2. Results More high-risk patients (50.4%) carried additional mutations, as compared with intermediate- and low-risk ones. The mutations of epigenetic modifier genes were associated with poor prognosis in terms of disease-free survival in both training (HR = 6.761, 95% CI 2.179–20.984; P = 0.001) and validation (HR = 4.026, 95% CI 1.089–14.878; P = 0.037) groups. Sanz risk stratification was associated with CR induction and OS. Conclusion In an era of ATRA/ATO treatment, both molecular markers and clinical parameter based stratification systems should be used as prognostic factors for APL.