Reverse transcription polymerase chain reaction for the rearranged retinoic acid receptor alpha clarifies diagnosis and detects minimal residual disease in acute promyelocytic leukemia

A novel retinoic acid receptor-γ agonist antagonizes immune checkpoint resistance in lung cancers by altering the tumor immune microenvironment

All-trans-retinoic acid (ATRA), the retinoic acid receptors (RARs) agonist, regulates cell growth, differentiation, immunity, and survival. We report that ATRA-treatment repressed cancer growth in syngeneic immunocompetent, but not immunodeficient mice. The tumor microenvironment was implicated: CD8+ T cell depletion antagonized ATRA's anti-tumorigenic effects in syngeneic mice. ATRA-treatment with checkpoint blockade did not cooperatively inhibit murine lung cancer growth. To augment ATRA's anti-tumorigenicity without promoting its pro-tumorigenic potential, an RARγ agonist (IRX4647) was used since it regulates T cell biology. Treating with IRX4647 in combination with an immune checkpoint (anti-PD-L1) inhibitor resulted in a statistically significant suppression of syngeneic 344SQ lung cancers in mice-a model known for its resistance to checkpoints and characterized by low basal T cell and PD-L1 expression. This combined treatment notably elevated CD4+ T-cell presence within the tumor microenvironment and increased IL-5 and IL-13 tumor levels, while simultaneously decreasing CD38 in the tumor stroma. IL-5 and/or IL-13 treatments increased CD4+ more than CD8+ T-cells in mice. IRX4647-treatment did not appreciably affect in vitro lung cancer growth, despite RARγ expression. Pharmacokinetic analysis found IRX4647 plasma half-life was 6 h in mice. Yet, RARα antagonist (IRX6696)-treatment with anti-PD-L1 did not repress syngeneic lung cancer growth. Together, these findings provide a rationale for a clinical trial investigating an RARγ agonist to augment check point blockade response in cancers.

Intravenous As2O3 as a promising treatment for psoriasis - an experimental study in psoriasis-like mouse model

OBJECTIVE

To evaluate the efficacy and mechanistic bases of the intravenous injection of arsenic trioxide at clinical-relevant doses for treating an imiquimod-induced psoriasis-like mouse model.

METHODS

After inducing psoriasis-like skin lesions on the back of mice with imiquimod, mice in each group were injected with a clinical dose of arsenic trioxide through the tail vein. The changes in the gene expression, protein expression and distribution of relevant inflammatory factors were evaluated in the inflicted skin area, for mechanisms underlying the efficacy of intravenous As₂O₃ intervention. HaCaT cells were used to establish an in vitro psoriasis model and pcDNA3.1-NF-κB overexpression plasmid was transfected into cells to overexpress P65, which further confirmed the role of the NF-κB signaling pathway in the effectiveness of As₂O₃.

RESULTS

Clinical dose of As₂O₃ can significantly improve abnormal symptoms and pathological changes in psoriasis-like skin lesions induced by IMQ in mice. While IMQ induced abnormal expression and distribution of inflammatory factors in the RIG-I pathway and the microRNA-31 (miR-31) pathway in psoriatic skin tissues, intravenous As₂O₃ can effectively regulate and restore the normality. The leading role of NF-κB signaling was evidenced in vivo and validated in vitro using the NF-κB-overexpressed HaCaT cell model.

CONCLUSION

Clinical dosage of As₂O₃ may achieve effective treatment of IMQ-induced psoriatic skin lesions by modulating the NF-κB signaling pathway which regulates both the RIG-I and the miR-31 lines of action. Our data provided strong evidence supporting the claim that systemic As₂O₃ administration of clinical doses can be a promising treatment for psoriasis patients.

How retinoic acid and arsenic transformed acute promyelocytic leukemia therapy

Acute promyelocytic leukemia (APL) is associated with severe coagulopathy leading to rapid morbidity and mortality if left untreated. The definitive diagnosis of APL is made by identifying a balanced reciprocal translocation between chromosomes 15 and 17. This t(15;17) results in a fusion transcript of promyelocytic leukemia (PML) and retinoic acid receptor alpha (RARA) genes and the expression of a functional PML/RARA protein. Detection of a fused PML/RARA genomic DNA sequence using fluorescence in situ hybridization (FISH) or by detection of the PML/RARA fusion transcript via reverse transcriptase polymerase chain reaction (RT-PCR) has revolutionized the diagnosis and monitoring of APL. Once confirmed, APL is cured in over 90% of cases, making it the most curable subtype of acute leukemia today. Patients with low-risk APL are successfully treated using a chemotherapy-free combination of all-trans retinoic acid and arsenic trioxide (ATO). In this review, we explore the work that has gone into the modern-day diagnosis and highly successful treatment of this once devastating leukemia.

History of Acute Promyelocytic Leukemia

In this article, we discuss the history of acute promyelocytic leukemia (APL) from the pre-therapeutic era, which began after its recognition by Hillestad in 1947 as a nosological entity, to the present day. It is a paradigmatic history that has transformed the “most malignant leukemia form” into the most curable one. The identification of a balanced reciprocal translocation between chromosomes 15 and 17, resulting in fusion between the promyelocytic leukemia gene and the retinoic acid receptor alpha, has been crucial in understanding the mechanisms of leukemogenesis, and responsible for the peculiar response to targeted therapy with all-trans retinoic acid (ATRA) and arsenic trioxide (ATO). We review the milestones that marked successive therapeutic advances, beginning with the introduction of the first successful chemotherapy in the early 1970s, followed by a subsequent incorporation of ATRA and ATO in the late 1980s and early 1990s which have revolutionized the treatment of this disease. Over the past two decades, treatment optimization has relied on the combination of ATRA, ATO, and chemotherapy according to risk-adapted approaches, which together with improvements in supportive therapy have paved the way for cure for most patients with APL.

Acute Promyelocytic Leukemia: A Constellation of Molecular Events around a Single PML-RARA Fusion Gene

Although acute promyelocytic leukemia (APL) is one of the most characterized forms of acute myeloid leukemia (AML), the molecular mechanisms involved in the development and progression of this disease are still a matter of study. APL is defined by the PML-RARA rearrangement as a consequence of the translocation t(15;17)(q24;q21). However, this abnormality alone is not able to trigger the whole leukemic phenotype and secondary cooperating events might contribute to APL pathogenesis. Additional somatic mutations are known to occur recurrently in several genes, such as FLT3, WT1, NRAS and KRAS, whereas mutations in other common AML genes are rarely detected, resulting in a different molecular profile compared to other AML subtypes. How this mutational spectrum, including point mutations in the PML-RARA fusion gene, could contribute to the 10%–15% of relapsed or resistant APL patients is still unknown. Moreover, due to the uncertain impact of additional mutations on prognosis, the identification of the APL-specific genetic lesion is still the only method recommended in the routine evaluation/screening at diagnosis and for minimal residual disease (MRD) assessment. However, the gene expression profile of genes, such as ID1, BAALC, ERG, and KMT2E, once combined with the molecular events, might improve future prognostic models, allowing us to predict clinical outcomes and to categorize APL patients in different risk subsets, as recently reported. In this review, we will focus on the molecular characterization of APL patients at diagnosis, relapse and resistance, in both children and adults. We will also describe different standardized molecular approaches to study MRD, including those recently developed. Finally, we will discuss how novel molecular findings can improve the management of this disease.

Acute Promyelocytic Leukemia: A History over 60 Years-From the Most Malignant to the most Curable Form of Acute Leukemia

Acute promyelocytic leukemia (APL) is a distinct subtype of acute myeloid leukemia (AML) that is cytogenetically characterized by a balanced reciprocal translocation between chromosomes 15 and 17, which results in the fusion of the promyelocytic leukemia (PML) and retinoic acid receptor alpha (RARα) genes. Because patients with APL present a tendency for severe bleeding, often resulting in an early fatal course, APL was historically considered to be one of the most fatal forms of acute leukemia. However, therapeutic advances, including anthracycline- and cytarabine-based chemotherapy, have significantly improved the outcomes of APL patients. Due to the further introduction of all-trans retinoic acid (ATRA) and-more recently-the development of arsenic trioxide (ATO)-containing regimens, APL is currently the most curable form of AML in adults. Treatment with these new agents has introduced the concept of cure through targeted therapy. With the advent of revolutionary ATRA-ATO combination therapies, chemotherapy can now be safely omitted from the treatment of low-risk APL patients. In this article, we review the six-decade history of APL, from its initial characterization to the era of chemotherapy-free ATRA-ATO, a model of cancer-targeted therapy.

Advances in Molecular Testing Techniques in Cytologic Specimens

There has been a paradigm shift in the practice of cytopathology with the advent of highly sensitive molecular tests using small amounts of tissue that can provide diagnostic, prognostic, and predictive information for clinical management. The cytopathologist plays a key role in providing a timely and accurate diagnosis as well as ensuring appropriate processing and handling of the specimen and judicious triaging of the tissue for molecular testing that guide therapeutic decisions. As the era of "precision medicine" continues to evolve and expand, cytopathology remains a dynamic field with advances in the practice of molecular cytopathology providing new paradigms in clinical care.

Molecular remission as a therapeutic objective in acute promyelocytic leukemia

Acute promyelocytic leukemia (APL) is a subtype of acute leukemia characterized by a unique t(15;17) translocation generating the PML/RARA fusion gene and hybrid oncoprotein. Besides its critical role in leukemogenesis, this genetic aberration serves as a disease-specific biomarker for rapid diagnosis and monitoring of minimal residual disease (MRD). Moreover, PML/RARA is specifically targeted by All-trans retinoic acid (ATRA) and arsenic trioxide (ATO), two agents that synergistically act to induce degradation of the oncoprotein. Large clinical studies including two randomized trials conducted in newly diagnosed APL patients have shown that the ATRA-ATO combination is superior to conventional ATRA and chemotherapy both in terms of efficacy and safety. Preliminary studies using oral formulations of arsenic and ATRA suggest that oral arsenic is as effective and manageable as intravenous ATO. Following early retrospective studies indicating the prognostic relevance of PML/RARA monitoring, several prospective studies were conducted in large cohorts of APL patients enrolled in clinical trials with the aim of better assessing the prognostic value of longitudinal PCR testing. The results consistently showed that molecular remission (defined as negativization of the PCR test for PML/RARA) correlates with a significantly decreased risk of relapse, whereas persistence of PCR positivity for PML/RARA after consolidation or conversion from negative to positive during follow-up is strongly associated with hematologic relapse. Based on these data, various groups started using pre-emptive salvage therapy for patients who persisted PCR-positive after frontline consolidation or converted from negative to positive PCR during follow-up. Finally, several expert panels have recommended that molecular remission should be considered a therapeutic objective in APL, and molecular response has been adopted as a study endpoint in modern clinical trials.

Influence of initiation time and white blood cell count on the efficacy of cytotoxic agents in acute promyelocytic leukemia during induction treatment

The present study retrospectively analyzed 96 newly diagnosed acute promyelocytic leukemia (APL) patients with low-intermediate mortality risk to identify the optimum timing to initiate cytotoxic chemotherapy following all-trans retinoic acid (ATRA) administration. Based on white blood cell (WBC) at chemotherapy initiation, the patients were divided into three groups: low WBC (WBC count ≤4×10⁹/l), intermediate WBC (WBC count >4×10⁹/l and <15×10⁹/l) and high WBC group (WBC count ≥15×10⁹/l). According to the period from ATRA commencement to chemotherapy, 96 patients were further divided into two groups: ≤3 days group (chemotherapy within 3 days of ATRA) and >3 days group (chemotherapy >3 days after ATRA). Clinical effects were compared by univariate analysis and multivariate analyses. The incidence rate of differentiation syndrome (DS; also termed retinoic acid syndrome) was 0.0, 11.1 and 40.0% in the low, intermediate and high WBC groups, respectively (P<0.001); complete remission (CR) rate was 90.5, 100.0 and 73.3%, respectively (P<0.001); and the rate of early mortality (defined as fatality during induction treatment) was 4.8, 0.0 and 26.7%, respectively (P<0.001). No differences were identified in clinicolaboratory parameters between the ≤3 days and >3 days groups, except in time to achieve CR (P=0.004) and rate of bleeding related to chemotherapy (P=0.009), both being higher in the >3 days group. Multivariate analyses indicated WBC count at chemotherapy was the only independent risk factor for the occurrence of DS [P=0.002; odds ratio (OR) =1.058, 95% confidence interval (CI) =1.021-1.095] and early mortality (P=0.036; OR =1.036, 95% CI =1.002-1.070). For newly diagnosed APL patients with low-intermediate risk, chemotherapy initiation should be recommended until WBC count rises to between 4×10⁹/l and 15×10⁹/l during induction treatment.

Initial Diagnostic Workup of Acute Leukemia: Guideline From the College of American Pathologists and the American Society of Hematology

CONTEXT

- A complete diagnosis of acute leukemia requires knowledge of clinical information combined with morphologic evaluation, immunophenotyping and karyotype analysis, and often, molecular genetic testing. Although many aspects of the workup for acute leukemia are well accepted, few guidelines have addressed the different aspects of the diagnostic evaluation of samples from patients suspected to have acute leukemia.

OBJECTIVE

- To develop a guideline for treating physicians and pathologists involved in the diagnostic and prognostic evaluation of new acute leukemia samples, including acute lymphoblastic leukemia, acute myeloid leukemia, and acute leukemias of ambiguous lineage.

DESIGN

- The College of American Pathologists and the American Society of Hematology convened a panel of experts in hematology and hematopathology to develop recommendations. A systematic evidence review was conducted to address 6 key questions. Recommendations were derived from strength of evidence, feedback received during the public comment period, and expert panel consensus.

RESULTS

- Twenty-seven guideline statements were established, which ranged from recommendations on what clinical and laboratory information should be available as part of the diagnostic and prognostic evaluation of acute leukemia samples to what types of testing should be performed routinely, with recommendations on where such testing should be performed and how the results should be reported.

CONCLUSIONS

- The guideline provides a framework for the multiple steps, including laboratory testing, in the evaluation of acute leukemia samples. Some aspects of the guideline, especially molecular genetic testing in acute leukemia, are rapidly changing with new supportive literature, which will require on-going updates for the guideline to remain relevant.

Development of Reverse Transcription Loop-Mediated Isothermal Amplification for Simple and Rapid Detection of Promyelocytic Leukemia-Retinoic Acid Receptor α mRNA

BACKGROUND

Acute promyelocytic leukemia (APL) is a disease characterized by expression of Promyelocytic Leukemia-Retinoic Acid Receptor α (PML-RARα) chimeric mRNA. Although APL is curable, early death due to hemorrhage is a major problem. Here, we report the development of a simple and rapid diagnostic method for APL based on reverse transcription loop-mediated isothermal amplification (RT-LAMP).

METHODS

An RT-LAMP primer set was designed to detect three types of PML-RARα mRNA in a single reaction. Serial dilutions of plasmid DNA containing bcr1, bcr2, or bcr3 PML-RARα sequences and RNA extracted from bone marrow aspirates of 6 patients with APL were used to compare the results of RT-LAMP and nested PCR assays.

RESULTS

Plasmid DNA was amplified by RT-LAMP, for which the reaction time was > 4 h shorter and the lower detection limit was higher than for nested RT-PCR. Six of 7 samples tested positive by both methods.

CONCLUSION

We developed an RT-LAMP assay for simple and rapid PML-RARα mRNA detection that may be clinically useful for point-of-care testing and APL diagnosis.

PHA-Induced Peripheral Blood Cytogenetics and Molecular Analysis: a Valid Diagnostic and Follow-up Modality for Acute Promyelocytic Leukemia Patients Treated with ATRA and/or Arsenic Tri-oxide

BACKGROUND

Acute promyelocytic leukemia (APML) is characterized by the reciprocal translocation t(15;17) (q22;q12) resulting in the PML-RARα fusion gene. A dual diagnostic and follow up approach was applied including cytogenetic demonstration of the t(15;17) translocation and detection of PML-RARα chimeric transcripts by molecular means.

PURPOSE

Conventional cytogenetics involving bone marrow is beset with high probability of poor metaphase index and was substituted with phytohemagglutinin (PHA)-induced peripheral blood culture based cytogenetic analysis as a diagnostic and follow up modality in APML patients of Kashmir (North India). Both qualitative (RT-PCR) and quantitative (Q-PCR) tests were simultaneously carried out to authenticate the modified cytogenetics.

MATERIALS AND METHODS

Patient samples were subjected to the said techniques to establish their baseline as well as follow-up status.

RESULTS

Initial cytogenetics revealed 30 patients (81%) positive for t(15;17) whereas 7 (19%) had either cryptic translocation or were negative for t(15;17). Two cases had chromosome 16q deletion and no hallmark translocation t(15;17). Q-PCR status for PML-RARα was found to be positive for all patients. All the APML patients were reassessed at the end of consolidation phase and during maintenance phase of chemotherapy where 6 patients had molecular relapse, wherein 4 also demonstrated cytogenetic relapse.

CONCLUSIONS

It was found that PHA-induced peripheral blood cytogenetics along with molecular analysis could prove a reliable modality in the diagnosis and assessment of follow up response of APML patients.

Retinal toxicities of cancer therapy drugs: biologics, small molecule inhibitors, and chemotherapies

PURPOSE

To review reported retinal side effects from current cancer therapy drugs.

METHODS

Retinal toxicities from ophthalmologic or oncologic case reports, case series, and clinical trials were identified by a systematic literature search using Lexicomp and PubMed.

RESULTS

Four biologics, 8 small molecule inhibitors, and 17 traditional chemotherapy agents had reported retinal side effects. For biologics, interferon alpha 2b was associated with retinopathy, denileukin diftitiox with pigmentary retinopathy, ipilimumab with a Vogt-Koyanagi-Harada-like syndrome, and trastuzumab with retinal ischemia. For small molecule inhibitors, v-raf murine sarcoma viral oncogene homolog B (BRAF) inhibitors were associated with uveitis, mitogen-activated protein kinase/extracellular signal-regulated kinase inhibitors with pigment epithelium detachments, and tyrosine kinase inhibitors with macular edema. Steroid antagonists were associated with crystalline retinopathy and macular edema. Nitrosoureas, platinum analogs, and cytosine arabinoside were associated with retinal vascular occlusions. Antimicrotubular agents were associated with cystoid macular edema but without fluorescein leakage. Retinoic acid derivatives were associated with impaired night vision, and mitotane was associated with a pigmentary retinopathy and papilledema.

CONCLUSION

Certain agents used in the treatment of systemic cancer are associated with ocular complications. Awareness of these complications will allow early detections and maybe reversal of some of the ocular problems.

Promyelocytic leukemia nuclear bodies support a late step in DNA double-strand break repair by homologous recombination

The PML protein and PML nuclear bodies (PML-NB) are implicated in multiple cellular functions relevant to tumor suppression, including DNA damage response. In most cases of acute promyelocytic leukemia, the PML and retinoic acid receptor alpha (RARA) genes are translocated, resulting in expression of oncogenic PML-RARα fusion proteins. PML-NB fail to form normally, and promyelocytes remain in an undifferentiated, abnormally proliferative state. We examined the involvement of PML protein and PML-NB in homologous recombinational repair (HRR) of chromosomal DNA double-strand breaks. Transient overexpression of wild-type PML protein isoforms produced hugely enlarged or aggregated PML-NB and reduced HRR by ~2-fold, suggesting that HRR depends to some extent upon normal PML-NB structure. Knockdown of PML by RNA interference sharply attenuated formation of PML-NB and reduced HRR by up to 20-fold. However, PML-knockdown cells showed apparently normal induction of H2AX phosphorylation and RAD51 foci after DNA damage by ionizing radiation. These findings indicate that early steps in HRR, including recognition of DNA double-strand breaks, initial processing of ends, and assembly of single-stranded DNA/RAD51 nucleoprotein filaments, do not depend upon PML-NB. The HRR deficit in PML-depleted cells thus reflects inhibition of later steps in the repair pathway. Expression of PML-RARα fusion proteins disrupted PML-NB structure and reduced HRR by up to 10-fold, raising the possibility that defective HRR and resulting genomic instability may figure in the pathogenesis, progression and relapse of acute promyelocytic leukemia.

How to manage acute promyelocytic leukemia

Acute promyelocytic leukemia (APL) is a unique subtype of acute myeloid leukemia (AML). The prognosis of APL is changing, from the worst among AML as it used to be, to currently the best. The application of all-trans-retinoic acid (ATRA) to the induction therapy of APL decreases the mortality of newly diagnosed patients, thereby significantly improving the response rate. Therefore, ATRA combined with anthracycline-based chemotherapy has been widely accepted and used as a classic treatment. It has been demonstrated that high doses of cytarabine have a good effect on the prevention of relapse for high-risk patients. However, as the indications of arsenic trioxide (ATO) for APL are being extended from the original relapse treatment to the first-line treatment of de novo APL, we find that the regimen of ATRA, combined with ATO, seems to be a new treatment option because of their targeting mechanisms, milder toxicities and improvements of long-term outcomes; this combination may become a potentially curable treatment modality for APL. We discuss the therapeutic strategies for APL, particularly the novel approaches to newly diagnosed patients and the handling of side effects of treatment and relapse treatment, so as to ensure each newly diagnosed patient of APL the most timely and best treatment.

Advances in therapies for acute promyelocytic leukemia

Acute promyelocytic leukemia (APL), a distinct subtype of acute myelogenous leukemia (AML), results from the arrest of the maturation of hematopoietic progenitors at the promyelocyte stage. It has been shown that APL is associated with a reciprocal chromosomal translocation, involving chromosomes 15 and 17, which fuses the gene encoding the retinoic acid receptor α (RARα) and the promyelocytic leukemia (PML) gene. The resultant PML-RARα fusion protein plays a critical role in the pathogenesis of APL. Although there are many subtypes of AML, all are typically managed using a standard chemotherapy regimen of an anthracycline plus cytarabine arabinoside (CA). Despite high rates of complete remission following standard chemotherapy, most patients relapse and long-term disease-free survival is only 30-40%. The introduction of drugs such as all-trans retinoic acid (ATRA) that promote progenitor differentiation by directly inhibiting the PML-RARα fusion protein has changed the treatment paradigm for APL and markedly improved patient survival. The purposes of the present review are to provide the latest results and future directions of clinical research into APL and to illustrate how new therapies, such as ATRA plus anthracycline-based induction and consolidation therapy, risk-adapted therapy, salvage therapy containing arsenic trioxide-based regimens, and hematopoietic stem cell transplantation, have improved the treatment outcomes for APL patients.

How I treat acute promyelocytic leukemia

Acute promyelocytic leukemia is the first malignant disease highly curable with targeted therapy directed at a unique molecular abnormality. The characteristic bleeding diathesis is the most notorious manifestation of the disease, which historically has accounted for a high mortality rate during induction. Acute promyelocytic leukemia is one of the few hematologic diseases that must be recognized under the microscope by the practicing hematologist because early institution of all-trans retinoic acid (ATRA) at the first suspicion of the disease before confirmation of the diagnosis and aggressive blood product support are critical to reduce early mortality. ATRA plus anthracycline-based chemotherapy for induction and consolidation followed by maintenance ATRA with low-dose chemotherapy is currently the standard of care. However, the combination of ATRA and arsenic trioxide, with minimal chemotherapy to control leukocytosis, is very effective therapy for newly diagnosed patients. This combination may replace conventional approaches for most, if not all, patients in the very near future. Acute promyelocytic leukemia should be considered in any patient with newly diagnosed acute myeloid leukemia because the treatment is urgent and different from all other subtypes.

UBE1L represses PML/RAR{alpha} by targeting the PML domain for ISG15ylation

Acute promyelocytic leukemia (APL) is characterized by expression of promyelocytic leukemia (PML)/retinoic acid (RA) receptor alpha (RARalpha) protein and all-trans-RA-mediated clinical remissions. RA treatment can confer PML/RARalpha degradation, overcoming dominant-negative effects of this oncogenic protein. The present study uncovered independent retinoid degradation mechanisms, targeting different domains of PML/RARalpha. RA treatment is known to repress PML/RARalpha and augment ubiquitin-activating enzyme-E1-like (UBE1L) protein expression in NB4-S1 APL cells. We previously reported RA-induced UBE1L and the IFN-stimulated gene, 15-kDa protein ISG15ylation in APL cells. Whether the ubiquitin-like protein ISG15 directly conjugates with PML/RARalpha was not explored previously and is examined in this study. Transient transfection experiments with different PML/RARalpha domains revealed that RA treatment preferentially down-regulated the RARalpha domain, whereas UBE1L targeted the PML domain for repression. As expected, ubiquitin-specific protease 18 (UBP43/USP18), the ISG15 deconjugase, opposed UBE1L but not RA-dependent PML/RARalpha degradation. In contrast, the proteasomal inhibitor, N-acetyl-leucinyl-leucinyl-norleucinal, inhibited both UBE1L- and RA-mediated PML/RARalpha degradation. Notably, UBE1L induced ISG15ylation of the PML domain of PML/RARalpha, causing its repression. These findings confirmed that RA triggers PML/RARalpha degradation through different domains and distinct mechanisms. Taken together, these findings advance prior work by establishing two pathways converge on the same oncogenic protein to cause its degradation and thereby promote antineoplastic effects. The molecular pharmacologic implications of these findings are discussed.

Diagnosis and treatment of acute promyelocytic leukemia

Acute promyelocytic leukemia (APL), characterized by a translocation between the promyelocytic leukemia gene (PML) on chromosome 15 and the retinoic acid receptor-alpha (RARalpha) gene on chromosome 17, has become a model for targeted treatment of cancer. Advances in our understanding of the fundamental biology of this disease have led to the development of tools for diagnosis, monitoring of minimal residual disease, and detection of early relapse. Differentiation therapy with all-trans retinoic acid in combination with chemotherapy has significantly improved survival in patients with APL. Moreover, arsenic trioxide, which induces differentiation and apoptosis of APL cells, has become standard treatment for relapsed disease, and its role in the treatment of newly diagnosed APL is under active investigation. The lessons learned from APL have broad applications to other forms of leukemia and to cancer in general, whereby molecularly targeted therapy is directed to specifically defined subgroups.

A randomized study with or without intensified maintenance chemotherapy in patients with acute promyelocytic leukemia who have become negative for PML-RARα transcript after consolidation therapy: The Japan Adult Leukemia Study Group (JALSG) APL97 study

To examine the efficacy of intensified maintenance chemotherapy, we conducted a prospective multicenter trial in adult patients with newly diagnosed acute promyelocytic leukemia treated with all-trans retinoic acid and chemotherapy. Of the 302 registered, 283 patients were assessable and 267 (94%) achieved complete remission. Predicted 6-year overall survival in all assessable patients and disease-free survival in patients who achieved complete remission were 83.9% and 68.5%, respectively. A total of 175 patients negative for PML-RARα at the end of consolidation were randomly assigned to receive either intensified maintenance chemotherapy (n = 89) or observation (n = 86). Predicted 6-year disease-free survival was 79.8% for the observation group and 63.1% for the chemotherapy group, showing no statistically significant difference between the 2 groups (P = .20). Predicted 6-year survival of patients assigned to the observation was 98.8%, which was significantly higher than 86.2% in those allocated to the intensified maintenance (P = .014). These results indicate that the intensified maintenance chemotherapy did not improve disease-free survival, but rather conferred a significantly poorer chance of survival in acute promyelocytic leukemia patients who have become negative for the PML-RARα fusion transcript after 3 courses of intensive consolidation therapy.

Blood donor derived dendritic cells and cytotoxic T cells for specific fusion-gene adoptive immunotherapy

BACKGROUND AND OBJECTIVES

Therapeutic immunological reagents tailored to individual patients have been shown to be a viable treatment strategy for some forms of leukaemia. This work investigates the possibility of using blood donations as a source of leukaemia-specific immune therapeutics.

MATERIALS AND METHODS

The acute promyelocytic cell line NB4 carrying the PML-RAR alpha fusion was used as a target for cytotoxic T lymphocytes (CTL) stimulated to recognize the fusion. Stimulation of CTL was by production of dendritic cells pulsed with plasmid vectors containing polymerase chain reaction (PCR)-generated sequences of PML-RAR alpha derived from NB4 cells. PCR primer design included a Kozak consensus sequence to allow correct translation of the nucleic acid into protein. Identification of specific cytotoxicity was by both Granzyme B ELISPOT and by (51)Cr-release assays.

RESULTS

Specific CTL activity targeting NB4 cells can be generated from donor-derived peripheral blood mononuclear cells. However, individual donors appear to respond differently to the length of stimulatory sequence encoded in the vector. Use of an internal methionine in the PML gene, which also satisfies the Kozak rules, allows translation in vitro and, thus, might provide a suitable start site for stimulation using acute promyelocytic leukaemia-specific sequence.

CONCLUSION

The work presented here suggests that blood donor derived dendritic cells can be used to stimulate leukaemia-specific CTL from the same donation ex vivo. This would enable the generation of patient-specific therapeutics from major histocompatibility (MHC)-matched allogeneic donors. However, different MHC-matched donors might vary in their response depending on the length of the antigenic sequence.

Monoclonal antibody therapy of APL

Acute promyelocytic leukemia (APL) is a rare subtype of acute myeloid leukemia (AML) for which a number of targeted therapies have been developed. The "targets" have included both genotypic and phenotypic features of the disease. The application of monoclonal antibodies (MAbs) to this disease to date have been limited to a relatively small number of studies where this therapy has been used to supplement effective approaches to the disease. The preliminary results have been promising, and further development of this modality as an effective adjunct to existing treatment regimens will most certainly occur in the near future.

Front line clinical trials and minimal residual disease monitoring in acute promyelocytic leukemia

In spite of the very high cure rate (70%-80%) achieved in APL with combinatorial all-trans retinoic acid (ATRA) and anthracycline-based chemotherapy regimens, a number of issues are still open for investigation in front-line therapy of this disease. These include, among others, improvements in early death rate, the role of arsenic trioxide (ATO) and maintenance treatment, and, finally, optimization of molecular monitoring to better identify patients at increased risk of relapse. The current consensus on the most appropriate induction therapy consists of the concomitant administration of ATRA and anthracycline-based chemotherapy. Although the antileukemic benefit provided by the addition of ATRA to consolidation therapy has not been demonstrated in randomized studies, historical comparisons of consecutive studies carried out by Spanish and Italian cooperative groups suggest that the combination of ATRA and chemotherapy for consolidation may also contribute to improving therapeutic results. While a variety of distinct treatments are being investigated for front-line therapy, most experts agree that a risk-adapted therapy represents the optimal approach, through the use of more intensive therapy in patients with initial hyperleukocytosis. Longitudinal RT-PCR of PML/RARalpha allows sensitive assessment of response to treatment and minimal residual disease (MRD) monitoring in APL. Achievement of negative PCR status or molecular remission at the end of consolidation is now universally accepted and recommended as a therapeutic objective in this disease. On the other hand, persistence of, or conversion to, PCR positive in the marrow during follow-up is associated with impending relapse. Preliminary studies on therapy of molecular relapse indicate a survival advantage as compared to administering salvage treatment at time of hematologic relapse. The more accurate and reproducible real-time PCR method to detect at quantitative levels the PML/RARalpha hybrid will likely provide better inter-laboratory standardization and trial results comparison in the near future.

A complex, four-way variant t(15;17) in acute promyelocytic leukemia

Complex variant 15;17 translocations are increasingly recognized in acute promyelocytic leukemia (APL). We report the case of a 47-year-old woman with APL harboring a novel four-way translocation. She presented with persistent bleeding after a tooth extraction. Blood cell counts at admission were hemoglobin at 9.0 g/dL, platelets at 15 x 10(9)/L, and white blood cells at 0.460 x 10(9)/L with abnormal promyelocytes. Most nucleated cells of bone marrow aspirates were abnormal promyelocytes with Auer rods. Chromosome analysis of unstimulated bone marrow cell cultures revealed a variant t(15;17) in the form of t(10;17;15;22)(q22;q21;q22;q11.2). Fluorescence in situ hybridization with a PML/RARA dual-color DNA probe showed the fusion signals on der(15) and the residual PML signals on der(22). RT-PCR showed long-form PML/RARA fusion transcripts. A complete remission was attained with a course of conventional chemotherapy including ATRA. A literature review revealed that our case is one of the very rare four-way translocations and the first report of the involvement of chromosomes 10 and 22 in a variant t(15;17).

Acute promyelocytic leukemia and constitutional trisomy 21

The incidence of acute myelogenous leukemia (AML) in patients with constitutional trisomy 21 is estimated to be 1 in 300; it is usually seen before age four. Clinical and epidemiological data confirm the improved life expectancy of patients with Down syndrome and their increased susceptibility to the development of leukemia, among other cancers. The most frequent subtype of AML associated with Down syndrome is acute megakaryoblastic leukemia (FAB: M7). The description of acute promyelocytic leukemia (APL) in adult patients with Down syndrome is exceedingly rare. Herein, we describe the unusual presentation, treatment, results, and clinical course of an adult patient with APL and constitutional trisomy 21 and provide a brief review of the literature.

Retinoid- and sodium-butyrate-induced decrease in heat shock protein 70 membrane-positive tumor cells is associated with reduced sensitivity to natural killer cell lysis, growth delay, and altered growth morphology

Human tumors frequently present heat shock protein 70 (Hsp70) on their cell membranes, whereas corresponding normal tissues fail to do so. Therefore, an Hsp70 membrane-positive phenotype provided a tumor-specific marker. Moreover, membrane-bound Hsp70 provides a target structure for the cytolytic attack mediated by natural killer (NK) cells. Vitamin A derivatives 13-cis retinoic acid (13-RA) and all-trans retinoic acid (ATRA) and sodium-butyrate (SBU) are known for their redifferentiating capacity. Therefore, we asked the question whether loss in tumorigenicity might be associated with a reduced Hsp70 membrane expression. For our studies we used epithelial colon (CX+/CX-) and thyroid (ML-1) cancer cells, with initially different Hsp70 cell surface expression pattern. After treatment up to 7 weeks with freshly prepared 13-RA, ATRA, and SBU at nonlethal concentrations of 10 microM, 1 microM, and 0.5 mM, respectively, growth morphology, Hsp70 levels, and sensitivity toward Hsp70-specific NK cells were compared with that of untreated tumor cells. Significant growth delay was determined in CX+ tumor cells after 6 weeks treatment with 13-RA. Concomitantly, growth morphology changed from spheroid cell clusters to monolayers. Despite a weak increase in cytosolic Hsp70, the percentage of Hsp70 membrane-positive cells dropped significantly after repeated treatments with 13-RA and ATRA in CX+ and ML-1 but not in CX- tumor cells. Similar results were observed with SBU. Functionally, the decrease in Hsp70 membrane-positive CX+ and ML-1 cells correlated with a reduced sensitivity to lysis mediated by NK cells. In summary, redifferentiating agents predominantly affected Hsp70 membrane-positive tumors. The decrease in Hsp70 membrane positivity correlated with a lower sensitivity to NK lysis, growth delay, and altered growth morphology.

Combination of all-trans retinoic acid and lithium chloride surmounts a retinoid differentiation block induced by expression of Scl and Rbtn2 transcription factors in myeloid leukemia cells

We have previously shown that forced expression of the transcription factor Scl in WEHI-3B D(+) cells prevents ATRA-induced cell differentiation. We now find that the overexpression of Rbtn2 also interferes with induction of differentiation by ATRA. Addition of LiCl to ATRA treatment restored the capacity of both Scl- and Rbtn2-expressing cells to respond to the retinoid in a synergistic manner. Similar results were obtained with Scl-transfected HL60 cells where its expression diminished responsiveness to ATRA. These findings suggest that if Scl and/or Rbtn2 are involved in the non-responsiveness of AML patients to ATRA-induced differentiation, addition of LiCl may reverse insensitivity.

Rapid diagnosis and characterization of acute promyelocytic leukaemia in routine laboratory practice

The rapid diagnosis of the t(15;17)(q22;q21) promyelocytic leukaemia is important in the early introduction of targeted therapy with all-trans retinoic acid plus chemotherapy. It has been noted that these are usually myeloperoxidase (MPO)-positive and HLA-DR-negative with homogenous expression of CD33 and heterogeneous expression of CD13. We evaluated the use of immunophenotyping, morphology and cytogenetics in our own practice. Cascade testing, using cytoplasmic MPO expression in a high percentage of blast cells in bone marrow as the primary screen and PML (promyelocytic leukaemia protein) expression as the secondary confirmatory test, allowed rapid identification of the cases with t(15;17). This approach allows early instigation of appropriate therapy.

Involvement of UBE1L in ISG15 conjugation during retinoid-induced differentiation of acute promyelocytic leukemia

Acute promyelocytic leukemia (APL) cases expressing the t(15,17) product, promyelocytic leukemia (PML)/retinoic acid receptor alpha (RARalpha), have clinical remissions through leukemic cell differentiation after all-trans-retinoic acid (RA) treatment. This differentiation therapy propelled interest in uncovering molecular mechanisms for RA-dependent APL differentiation. We previously identified the ubiquitin-activating enzyme-E1-like protein (UBE1L) as an RA-regulated target gene in APL that triggers PML/RARalpha degradation and apoptosis. This study reports that conjugation of the ubiquitin-like species, interferon-stimulated gene, 15-kDa protein (ISG15), also occurs during RA-induced APL differentiation. Knock-down of UBE1L expression inhibited this conjugation. RA treatment of APL and other RA-responsive leukemic cells induced expression of UBE1L and ISG15 as well as intracellular ISG15 conjugates. Notably, ISG15 conjugation did not occur in RA-resistant NB4-R1 APL cells. Induction of UBE1L and ISG15 along with ISG15 conjugation in RA-sensitive NB4-S1 APL cells were detected following treatment with specific retinoids and type I interferon (IFN). UBE1L and ISG15 mRNAs were co-expressed in normal human tissues that were examined. In contrast, UBE1L mRNA expression was markedly repressed in several cancer cell lines. A physical association was found between UBE1L and ISG15 in vivo. This required the conserved diglycine motif in the carboxyl terminus of ISG15. Targeting UBE1L expression with small inhibitory RNA or small hairpin RNA inhibited IFN and RA-induced ISG15 conjugation. Formation of ISG15 conjugates through induction of an activating enzyme represents a novel pharmacologic mechanism for regulation of this ubiquitin-related species. Taken together, the observed rela tionship between expression of UBE1L and ISG15, their physical association and coordinate regulation, and induced ISG15 conjugation during leukemic cell differentiation implicate an important role for these proteins in retinoid response.

Retinoid target genes in acute promyelocytic leukemia

All-trans-retinoic acid (RA)-based differentiation therapy induces clinical remissions in acute promyelocytic leukemia (APL). This has propelled interest in elucidating the molecular mechanisms responsible for these remissions. The t(15;17) rearrangement results in the expression of the PML/RARalpha fusion transcript that is paradoxically linked to the etiology and clinical retinoid response in APL. PML/RARalpha expression blocks terminal myeloid differentiation in APL. Treatment with pharmacological RA dosages overcomes the dominant-negative effects of PML/RARalpha to activate transcription of retinoid target genes. This regulation is linked directly to RA effects in APL, including PML/RARalpha degradation and induction of differentiation. Identifying retinoid target genes is an important step in developing a mechanistic understanding of RA effects in APL. RA target genes have been uncovered through the use of molecular genetic approaches as well as unique cellular and transgenic APL models. Recent developments in the proteomic and functional genomic fields are providing useful tools for elucidating mechanisms of RA response or resistance in APL. These target genes represent potential therapeutic targets in APL and other retinoid-responsive diseases. Previous spotlights in Leukemia have highlighted the importance of cytokine effects and signal transduction crosstalk in retinoid response in APL and in normal hematopoiesis. This review builds on prior work by addressing the role of retinoid target genes in mediating retinoid response or resistance in APL.

The importance of molecular monitoring in acute promyelocytic leukaemia

Acute promyelocytic leukaemia (APL) is characterized by a unique genetic marker in virtually 100% of cases, i.e. the PML/RARalpha fusion gene which is readily amplified by the reverse transcriptase-polymerase chain reaction (RT-PCR) method. Several international groups reported the prognostic significance of minimal residual disease (MRD) assessment in APL, indicating that sequential PCR analysis should be used as a guide to therapy. In fact, such evaluation offers the possibility of identifying, after front-line treatment, either patients requiring additional therapy or patients at low risk who are presumably cured and who may be spared unnecessary toxicity. In this view, the terms molecular remission and molecular relapse are now widely employed to define a more advanced therapeutic objective and a condition necessitating anticipated salvage, respectively. The introduction of quantitative PCR through automated technologies is likely to further improve standardization of the method and comparison of results obtained in the context of large clinical trials.

Monitoring PML-RARalpha in acute promyelocytic leukemia

Acute promyelocytic leukemia (APL) is characterized by a translocation between the promyelocytic leukemia gene (PML) on chromosome 15 and the retinoic acid receptor-alpha (RARalpha) gene on chromosome 17. Reverse-transcription polymerase chain reaction (RT-PCR) amplification of PML-RARalpha messenger RNA can establish the diagnosis of APL, predict response to all-trans retinoic acid and arsenic trioxide, detect minimal residual disease, and predict relapse. Quantitative "real-time" RT-PCR techniques may improve residual disease assessment by facilitating more rapid and standardized results. APL provides a useful model in which therapy is targeted to an underlying genetic aberration and treatment is adapted based on monitoring of residual disease.

Screening and quantification of multiple chromosome translocations in human leukemia

BACKGROUND

Characterization of fusion gene transcripts in leukemia that result from chromosome translocations provides valuable information regarding appropriate treatment and prognosis. However, screening for multiple fusion gene transcripts is difficult with conventional PCR and state-of-the-art real-time PCR and high-density microarrays.

METHODS

We developed a multiplex reverse transcription-PCR (RT-PCR) assay for screening and quantification of fusion gene transcripts in human leukemia cells. Chimeric primers were used that contained gene-specific and universal sequences. PCR amplification of fusion and control gene transcripts was achieved with use of an excess of universal primers to allow the ratio of abundance of fusion gene to endogenous or exogenous controls to be maintained throughout PCR. Multiplex RT-PCR products analyzed by an ABI 310 Genetic Analyzer were consistent with those of duplex RT-PCR (single analytical sample plus control). In addition, multiplex RT-PCR results were analyzed by an assay using an oligonucleotide microarray that contained probes for the splice-junction sequences of various fusion transcripts.

RESULTS

The multiplex RT-PCR assay enabled screening of >10 different fusion gene transcripts in a single reaction. RT-PCR followed by analysis with the ABI Prism 310 Genetic Analyzer consistently detected 1 fusion-transcript-carrying leukemia cell in 100-10 000 cells. The assay covered a 1000-fold range. Preliminary results indicate that multiplex RT-PCR products can also be analyzed by hybridization-based microarray assay.

CONCLUSIONS

The multiplex RT-PCR analyzed by either ABI Prism 310 Genetic Analyzer or microarray provides a sensitive and specific assay for screening of multiple fusion transcripts in leukemia, with the latter an assay that is adaptable to a high-throughput system for clinical screening.

Acute promyelocytic leukemia: a model for the role of molecular diagnosis and residual disease monitoring in directing treatment approach in acute myeloid leukemia

Acute promyelocytic leukemia (APL) is characterized by a number of features that underpin the need for rapid and accurate diagnosis and demand a highly specific treatment approach. These include the potentially devastating coagulopathy, sensitivity to anthracycline-based chemotherapy regimens, as well as unique responses to all-trans retinoic acid and arsenic trioxide that have revolutionized therapy over the last decade. The chromosomal translocation t(15;17) which generates the PML-RARalpha fusion gene has long been considered the diagnostic hallmark of APL; however, this abnormality is not detected in approximately 10% cases with successful karyotype analysis. In the majority of these cases, the PML-RARalpha fusion gene is still formed, resulting from insertion events or more complex rearrangements. These cases share the beneficial response to retinoids and favorable prognosis of those with documented t(15;17), underscoring the clinical relevance of molecular analyses in diagnostic refinement. In other cases of t(15;17) negative APL, various chromosomal rearrangements involving 17q21 have been documented leading to fusion of RARalpha to alternative partners, namely PLZF, NPM, NuMA and STAT5b. The nature of the fusion partner has a significant bearing upon disease characteristics, including sensitivity to retinoids and arsenic trioxide. APL has provided an exciting treatment model for other forms of AML whereby therapeutic approach is directed towards cytogenetically and molecularly defined subgroups and further modified according to response as determined by minimal residual disease (MRD) monitoring. Recent studies suggest that rigorous MRD monitoring, coupled with pre-emptive therapy at the point of molecular relapse improves survival in the relatively small subgroup of PML-RARalpha positive patients with 'poor risk' disease. Advent of 'real-time' quantitative RT-PCR technology seems set to yield further improvements in the predictive value of MRD assessment, achieve more rapid sample throughput and facilitate inter- and intra-laboratory standardization, thereby enabling more reliable comparison of data between international trial groups.

Management of acute promyelocytic leukemia

Acute promyelocytic leukemia (APL) has become the most potentially curable subtype of acute myeloid leukemia (AML) in adults. With current treatment strategies that incorporate all-trans retinoic acid (ATRA), long-term disease-free survival and potential cure rates of 70% to 80% can be expected. Such progress reflects what can be accomplished with insights into the molecular pathogenesis of leukemia, identification of a molecular target, and rapid accrual to a series of clinical trials. The leukemic promyelocytes from patients with APL are uniquely susceptible to a variety of novel agents in addition to ATRA, including arsenic trioxide, and in preliminary studies, gemtuzumab ozogamicin, the immunoconjugate comprised of an anti-CD33 monoclonal antibody linked to the potent cytotoxic agent calicheamicin. Incorporation of such agents into the treatment of patients with high-risk disease may be an important future direction to pursue.

Variant-type PML-RAR(alpha) fusion transcript in acute promyelocytic leukemia: use of a cryptic coding sequence from intron 2 of the RAR(alpha) gene and identification of a new clinical subtype resistant to retinoic acid therapy

The physiologic actions of retinoic acids (RAs) are mediated through RA receptors (RARs) and retinoid X receptors (RXRs). The RAR(alpha) gene has drawn particular attention because it is the common target in all chromosomal translocations in acute promyelocytic leukemia (APL), a unique model in cancer research that responds to the effect of RA. In the great majority of patients with APL, RAR(alpha) is fused to the PML gene as a result of the t(15;17) translocation. Three distinct types of PML-RAR(alpha) transcripts, long (L), short (S), and variant (V), were identified. The V-type is characterized by truncation of exon 6 of PML and in some cases by the insertion of a variable "spacer" sequence between the truncated PML and RAR(alpha) mRNA fusion partners, although the precise mechanisms underlying formation of the V-type transcript remain unclear. To get further insights into the molecular basis of the t(15;17), we sequenced the entire genomic DNA region of RAR(alpha). Of note, all previously reported "spacer" sequences in V-type transcripts were found in intron 2 of the RAR(alpha) gene and most of these sequences were flanked by gt splice donor sites. In most cases, these "cryptic" coding sequences maintained the ORF of the chimeric transcript. Interestingly, two cases with a relatively long spacer sequence showed APL cellular and clinical resistance to RA treatment. In these cases, the aberrant V-type PML-RAR(alpha) protein displayed increased affinity to the nuclear corepressor protein SMRT, providing further evidence that RA exerts the therapeutic effect on APL through modulation of the RAR-corepressor interaction. Finally, among patients with the L- or S-type PML-RAR(alpha) fusion transcript, some consensus motifs were identified at the hotspots of the chromosome 17q breakpoints within intron 2 of RAR(alpha), strengthening the importance of this intron in the molecular pathogenesis of APL.

Molecular monitoring of hematologic malignancies: current and future issues

Genetic markers associated with hematologic malignancies such as acute promyelocytic leukemia (APL) can be detected with high sensitivity and specificity using the reverse-transcription polymerase chain reaction (RT-PCR). This procedure can be applied to monitor minimal residual disease. In patients with APL, RT-PCR is now being used to detect molecular relapse, and a strong association has been found between outcome and the treatment of molecular as opposed to hematologic relapse. In APL, results from PCR assays are also being used to guide therapy. Prognostic groups can be defined using molecular and clinical characteristics of the disease as well as patient characteristics. In the future, PCR monitoring strategies may be adapted to the risk of relapse of individual patients. Patients at high risk of relapse may be monitored much more rigorously than patients at low risk of relapse. Although RT-PCR is in routine use as a clinical tool, the lack of standardization of techniques in different laboratories has resulted in some difficulties in interpretation of results. There is a real need for an international consensus on standardization of PCR techniques.

The significance of minimal residual disease in patients with t(15;17)

Acute promyelocytic leukaemia (APL) is characterized by the t(15;17)(q22;q21) leading to the formation of PML-RARalpha and RARalpha-PML fusion genes which provide suitable targets for the assessment of minimal residual disease (MRD). Studies have focused upon detection of PML-RARalpha because, although assays for RARalpha-PML transcripts are more sensitive, they are not applicable to 25% of cases. Among patients receiving standard therapy (ATRA and anthracycline-based chemotherapy), qualitative assays using a nested reverse transcriptase-polymerase chain reaction (RT-PCR), which typically achieve sensitivities of 1 in 10(4), have been found to provide independent prognostic information suitable for directing an approach to treatment. Detection of PML-RARalpha at the end of consolidation, or subsequent recurrence of PCR positivity, heralds relapse, which may, however, be averted by additional therapy leading to improvements in survival for this "high-risk" subgroup of patients. MRD analysis has also proved of value in predicting response to autologous transplant procedures undertaken in second complete remission and in directing the need for additional therapy in the post-transplantation setting. Overall, these studies undertaken within the context of a relatively homogeneous disease entity confirm that MRD monitoring provides independent prognostic information, serving as a valuable model for improving treatment strategy in other molecularly defined subsets of acute myeloid leukaemia (AML). Nevertheless, conventional nested RT-PCR assays fail to detect residual disease in a significant proportion of patients who ultimately relapse, which may be a reflection of RNA quality and/or assay sensitivity. Therefore, it is hoped that "real-time" quantitative RT-PCR technology (RQ-PCR) which permits quantification of fusion gene transcripts in relation to endogenous control genes will be even more predictive of outcome and achieve greater standardization of MRD detection in the context of large-scale clinical trials.

Advances in the understanding and management of acute promyelocytic leukemia

Considerable progress has been made over the past decade in the understanding and management of acute promyelocytic leukemia (APL). At the laboratory level, molecular mechanisms underlying the arrest of differentiation that typically features in this malignancy, have been clarified and currently provide important models for addressing future investigation aimed at releasing the maturation block in other malignancies. In the clinic, advances in the management of APL have converted this rapidly fatal disease into the most frequently curable leukemia in adults. Use of retinoids in combinatorial protocols with anthracycline-based chemotherapy for front line treatment currently results in long-term survival and potential cure in at least 60% of newly diagnosed patients. Even after relapse, the disease is still curable in a high percentage of cases by various approaches including combinations of chemotherapy, retinoids, arsenic trioxide, stem cell transplantation and antibody-targeted chemotherapy. Genetic testing for identification of the disease-specific gene rearrangement and monitoring of residual disease have proved critical in establishing correct diagnosis and better evaluate the response to therapy at the molecular level. Current 'hot' issues for clinical investigation include: (i) better understanding and management of the severe coagulopathy present at diagnosis in most patients; (ii) the definition of risk categories to improve identification of patients at highest risk of relapse and (iii) the translation of successful differentiation therapy to other leukemia subsets.

Acute promyelocytic leukemia: evolving therapeutic strategies

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

Cyclin proteolysis as a retinoid cancer prevention mechanism

The retinoids, natural and synthetic derivatives of vitamin A, are active in cancer therapy and prevention. Their biological effects are mediated through ligand-dependent interactions with retinoid receptors that associate with specific co-regulators. A better understanding of retinoid chemopreventive mechanisms is needed. Our prior work revealed that all-trans-retinoic acid (RA) prevented tobacco-specific carcinogenic transformation of cultured human bronchial epithelial cells. RA signaled G1 arrest that permitted repair of genomic DNA damage caused by these carcinogens. RA triggered G1 arrest at least partly through proteasome-dependent degradation of cyclin D1. Proteasomal inhibitors blocked RA-mediated cyclin D1 degradation. To confirm that a specific proteolysis pathway was induced by RA-treatment, a degradation assay was established using in vitro translated cyclin D1 and cellular extracts from RA-treated or untreated human bronchial epithelial cells. Incubation of RA-treated but not the control cellular extracts with in vitro translated cyclin D1 led to cyclin degradation. This degradation depended on the PEST domain of cyclin D1, implicating ubiquitination in this retinoid degradation. Retinoid receptor selective agonists demonstrated that retinoic acid receptor (RAR)beta and retinoid X receptor (RXR) but not RARalpha- or RARgamma-dependent pathways signaled this cyclin degradation. Findings were extended to the NT2/D1 human embryonal carcinoma differentiation model where a similar pathway was activated by RA-treatment. To determine whether G1 cyclins were involved directly in bronchial preneoplasia, immunohistochemical expression profiles for cyclins D1 and E were examined. Aberrant expression of these cyclins was frequent in bronchial preneoplasia. Taken together, these findings indicate that ubiquitin-dependent proteolysis of G1 cyclins is a retinoid chemoprevention mechanism. Whether the retinoids represent the optimal agents to activate this pathway is the subject of ongoing work. These findings provide a rationale for combining the retinoids in chemoprevention trials with other agents that do not activate this proteolysis pathway. What is now known about the retinoids as cancer prevention agents will be reviewed. Emphasis is placed on retinoid effects on cell cycle progression at G1.

Prognostic significance of minimal residual disease detection and PML/RAR-alpha isoform type: long-term follow-up in acute promyelocytic leukemia

The t(15;17) translocation in acute promyelocytic leukemia (APL) yields a PML/RAR-alpha fusion messenger RNA species that can be detected by reverse transcription-polymerase chain reaction (RT-PCR) amplification. Breakpoints within intron 3 of PML produce a short PML/RAR-alpha isoform, whereas breakpoints within intron 6 result in a longer form. Using RT-PCR, serial evaluations were performed on the bone marrow of 82 patients with APL (median follow-up, > 63 months) who received retinoic acid (RA) induction followed by postremission treatment with chemotherapy, RA, and biologic agents. Sixty-four patients attained a clinical complete remission and had at least 2 RT-PCR assays performed after completing therapy. Forty of 47 patients (85%) with newly diagnosed APL who were induced using RA had residual disease detectable by RT-PCR before additional therapy. After 3 cycles of consolidation therapy, residual disease was found in only 4 of 40 evaluable patients (10%). Among newly diagnosed patients who had 2 or more negative RT-PCR assays, only 3 of 41 (7%) had a relapse, whereas all 4 patients (100%) who had 2 or more positive results had a relapse. Among 63 newly diagnosed patients, those who expressed the short isoform appeared to have shorter disease-free and overall survival durations than patients who expressed the long isoform. These data indicate that 2 or more negative RT-PCR assays on bone marrow, performed at least 1 month apart after completing therapy, are strongly associated with long-term remissions. Conversely, a confirmed positive test is highly predictive of relapse.

Pulsed ATRA as single therapy restores long-term remission in PML-RARalpha-positive acute promyelocytic leukemia patients: real time quantification of minimal residual disease. A pilot study

All-trans retinoic acid (ATRA), alone or combined with chemotherapy (CHT) is widely used to induce complete remission (CR) in newly diagnosed acute promyelocytic leukemia (APL). If used alone, ATRA results in a substantial proportion of CRs. To maintain remission further, ATRA is commonly used with cycles of CHT, frequently followed by autologous (auto) or allogeneic (allo) stem cell transplantation (SCT), as early reports have shown that the continuous administration of ATRA as single therapy almost invariably leads to relapse in a short period of time (months). Pharmacokinetic studies have shown that induced resistance to ATRA is frequently suppressed by the intermittent use of the drug. In this study we applied an intermittent therapeutic protocol with ATRA in five APL patients who were either molecularly refractory after combined ATRA/CHT treatment, or relapsed, or at diagnosis, but not eligible for the combination treatment because of previous toxicity. They were treated with ATRA (45 mg/m2/day) for 21 days. The treatment was then prolonged continuously for 1 week every 2 weeks. Molecular analysis was performed by qualitative and quantitative reverse transcription-polymerase chain reaction (RT-PCR). All patients obtained molecular remission, as assessed by qualitative RT-PCR, in a median of 3 months (range 1-15). Quantitative RT-PCR confirmed these data, showing a progressive reduction (1 or 2 logs) to a 'negligible quantity' of PML-RARalpha fusion transcript (ratio PML-RARalpha/ABL x 10(4) ABL < 10(-1)) in all but one patient treated with pulsed ATRA therapy. These data were confirmed with qualitative and quantitative RT-PCR. After a median follow-up of 17 months from the start of ATRA therapy, 4/5 patients (80%) are in continuous complete molecular remission. To our knowledge, this is the first clinical observation that intermittent ATRA therapy (without chemotherapy) is effective not only in inducing but also in maintaining long-term molecular remission in APL patients. This approach could therefore be effective, if confirmed in larger series, in relapsed/refractory patients unsuitable for high-dose therapy and SCT; it may be proposed as induction therapy for selected older APL patients if considered not to be eligible for combined ATRA/CHT due to inadequate performance status or concurrent disease.