Differentiation therapy for acute promyelocytic leukemia

Retinoic acid receptors: from molecular mechanisms to cancer therapy

Retinoic acid (RA), the major bioactive metabolite of retinol or vitamin A, induces a spectrum of pleiotropic effects in cell growth and differentiation that are relevant for embryonic development and adult physiology. The RA activity is mediated primarily by members of the retinoic acid receptor (RAR) subfamily, namely RARα, RARβ and RARγ, which belong to the nuclear receptor (NR) superfamily of transcription factors. RARs form heterodimers with members of the retinoid X receptor (RXR) subfamily and act as ligand-regulated transcription factors through binding specific RA response elements (RAREs) located in target genes promoters. RARs also have non-genomic effects and activate kinase signaling pathways, which fine-tune the transcription of the RA target genes. The disruption of RA signaling pathways is thought to underlie the etiology of a number of hematological and non-hematological malignancies, including leukemias, skin cancer, head/neck cancer, lung cancer, breast cancer, ovarian cancer, prostate cancer, renal cell carcinoma, pancreatic cancer, liver cancer, glioblastoma and neuroblastoma. Of note, RA and its derivatives (retinoids) are employed as potential chemotherapeutic or chemopreventive agents because of their differentiation, anti-proliferative, pro-apoptotic, and anti-oxidant effects. In humans, retinoids reverse premalignant epithelial lesions, induce the differentiation of myeloid normal and leukemic cells, and prevent lung, liver, and breast cancer. Here, we provide an overview of the biochemical and molecular mechanisms that regulate the RA and retinoid signaling pathways. Moreover, mechanisms through which deregulation of RA signaling pathways ultimately impact on cancer are examined. Finally, the therapeutic effects of retinoids are reported.

Where can biology of childhood ALL be attacked by new compounds?

Although the majority of children with acute lymphoblastic leukemia (ALL) can be cured with combination chemotherapy, the challenge remains to salvage patients with resistant disease and to reduce treatment related toxicity. To meet this challenge, it will be essential to incorporate new agents targeting the biological Achilles Heels of this cancer more rapidly into currently available treatment regimen. Here we review the principles of current ALL therapy, recent advances in understanding ALL biology and discuss a selection of promising areas for drug development that may take advantage of the underlying leukemia biology. We focus particularly on strategies to interfere with common effector mechanisms that can be trigged by different individual oncogenic lesions and on new agents from drug development programs in adult oncology, as such agents will come with better chances for sustainable commercial development.

Oncogenic and cell survival properties of the retinoic acid metabolizing enzyme, CYP26A1

Vitamin A deficiency (VAD) is associated with increased susceptibility to carcinogenesis in animal models and elevated risk for a number of human cancers. Here, we found that CYP26A1, the gene encoding a cytochrome P450 enzyme specifically involved in metabolic inactivation of retinoic acid (RA), the most active vitamin A derivative, is highly expressed in 42% (27/65) of primary breast cancers. We also showed that enhanced expression of CYP26A1 suppresses cellular responses to anoikis and consequently promotes anchorage-independent growth. This transformed phenotype was sufficient to markedly increase tumorigenic and metastatic potential. Suppression of CYP26A1 significantly reversed the CYP26A1-mediated oncogenic characteristics, suggesting a direct link between intracellular RA status and tumorigenicity. Our observations provide strong evidence for oncogenic and cell survival properties of CYP26A1 in carcinogenesis, and suggest mechanisms whereby VAD might promote cancer development.

A study on the antitumoral and differentiation effects of peganum harmala derivatives in combination with ATRA on leukaemic cells

Plant derived agents may exert a new approach to the treatment of leukaemia. The present study was an evaluation of proliferation, cytotoxicity and differentiation of harmine and harmaline on HL60 cells, alone or in combination with ATRA and G-CSF. Counting of cells, viability, MTT assay, morphology, NBT reduction and flow cytometry analysis were performed using CD11b and CD 14 monoclonal antibodies. The data showed that harmine and harmaline reduced proliferation in dose and time dependent manner. Optimal antiproliferative concentration of these agents was chosen. However, both agents in higher doses were cytotoxic. Combination of ATRA, G-CSF and each agent alone, particularly harmaline in optimal dose, resulted in partially additive decrease in cell proliferation. Cells treated with both harmaline and ATRA demonstrated some morphological changes and NBT positivity, but the extent of changes observed following treatment with harmaline was less than ATRA. Flow cytometric analysis showed that ATRA induced a neutrophilic differentiation, while harmaline led to a predominantly monocytic differentiation. Combination of harmine and harmaline with ATRA and G-CSF did not change the extent of differentiation, and the cells differentiated into the neutrophilic lineage. This shows that the direction of differentiation is dominantly determined by ATRA. These preliminary data implies a new approach in treatment of leukemia.

Heterochromatic gene repression of the retinoic acid pathway in acute myeloid leukemia

Alteration of lineage-specific transcriptional programs for hematopoiesis causes differentiation block and promotes leukemia development. Here, we show that AML1/ETO, the most common translocation fusion product in acute myeloid leukemia (AML), counteracts the activity of retinoic acid (RA), a transcriptional regulator of myelopoiesis. AML1/ETO participates in a protein complex with the RA receptor alpha (RARalpha) at RA regulatory regions on RARbeta2, which is a key RA target gene mediating RA activity/resistance in cells. At these sites, AML1/ETO recruits histone deacetylase, DNA methyltransferase, and DNA-methyl-CpG binding activities that promote a repressed chromatin conformation. The link among AML1/ETO, heterochromatic RARbeta2 repression, RA resistance, and myeloid differentiation block is indicated by the ability of either siRNA-AML1/ETO or the DNA methylation inhibitor 5-azacytidine to revert these epigenetic alterations and to restore RA differentiation response in AML1/ETO blasts. Finally, RARbeta2 is commonly silenced by hypermethylation in primary AML blasts but not in normal hematopoietic precursors, thus suggesting a role for the epigenetic repression of the RA signaling pathway in myeloid leukemogenesis.

Lineage dependency and lineage-survival oncogenes in human cancer

Although cell-lineage and differentiation models dominate tumour classification and treatment, the recognition that cancer is also a genomic disease has prompted a reconfiguration of cancer taxonomies according to molecular criteria. Recent evidence indicates that a synthesis of lineage-based and genetic paradigms might offer new insights into crucial and therapeutically pliable tumour dependencies. For example, MITF (microphthalmia-associated transcription factor), which is a master regulator of the melanocyte lineage, might become a melanoma oncogene when deregulated in certain genetic contexts. MITF and other lineage-survival genes therefore implicate lineage dependency (or lineage addiction) as a newly recognized mechanism that is affected by tumour genetic alterations.

Dynamic and reversibility of heterochromatic gene silencing in human disease

In eukaryotic organisms cellular fate and tissue specific gene expression are regulated by the activity of proteins known as transcription factors that by interacting with specific DNA sequences direct the activation or repression of target genes. The post genomic era has shown that transcription factors are not the unique key regulators of gene expression. Epigenetic mechanisms such as DNA methylation, post-translational modifications of histone proteins, remodeling of nucleosomes and expression of small regulatory RNAs also contribute to regulation of gene expression, determination of cell and tissue specificity and assurance of inheritance of gene expression levels. The relevant contribution of epigenetic mechanisms to a proper cellular function is highlighted by the effects of their deregulation that cooperate with genetic alterations to the development of various diseases and to the establishment and progression of tumors.

Acute Promyelocytic Leukemia After Iodine-131 Therapy for Graves' Disease

Graves' disease is an autoimmune process in which the thyroid gland is stimulated by autoantibodies, leading to hyperthyroidism. Graves' disease is the most common cause of hyperthyroid function, primarily affecting women in their 40s and 50s. Treatment may involve oral radioiodine, which is taken up by the follicular cells of the thyroid, where it emits ionizing radiation to promote destruction of those cells. Radioiodine therapy is typically safe, effective, and inexpensive. We describe the case of a 51-year-old woman who developed acute promyelocytic leukemia within 27 months of completing a cumulative dose of radioiodine 22.1 mCi (817.7 MBq) for treatment of Graves' disease. Assessment of causality using the Naranjo probability scale showed that a possible relationship existed between this patient's acute promyelocytic leukemia and the use of radioiodine. Strict hematologic follow-up of patients treated with radioiodine may be warranted, along with a high index of suspicion in those with coagulopathy.

Treatments of AIDS-related Kaposi's sarcoma

Although Kaposi's sarcoma (KS) has decreased in countries where the highly active antiretroviral therapy (HAART) regimen is available, however it remains, after non-Hodgkin's lymphomas, the most common malignancy in HIV+ patients. Advances in the treatment of AIDS-KS have been achieved, even though a gold standard therapy has not been yet defined. With the availability of HAART, a dramatic KS clinical response has been documented, making HAART essential in all patients. In case of aggressive and/or life threatening KS, more complex therapeutic schedules have to be taken into account, including chemotherapy and/or immunotherapy. Liposomal anthracyclines and paclitaxel have been approved by FDA as first line and second line mono-therapy, respectively. Interferon-alpha (INF-alpha) is the only immunomodulant agent to have shown a therapeutic effect. Among the new drugs, many antiangiogenetic agents have produced encouraging responses. Finally, the identification of the HHV-8 as a causative agent and new metalloproteinase inhibitors may offer promising targets for the KS treatment.

Expression of the retinoic acid-metabolizing enzyme CYP26A1 limits programmed cell death

Vitamin A deficiency has been associated with increased incidence of certain types of cancer; however, the mechanisms by which vitamin A depletion promotes tumorigenesis are poorly understood. In addition all-trans-retinoic acid (RA), the most active form of vitamin A metabolites, has been shown to limit carcinogenesis in animal models and to trigger programmed cell death (apoptosis) in certain types of tumor cells. On the other hand, we show here that various cell lines overexpressing CYP26A1, a cytochrome P450 enzyme specifically involved in the catabolic inactivation of RA, exhibit increased resistance to various apoptogenic factors, including death receptor ligands such as tumor necrosis factor-related apoptosis-inducing ligand. This resistance could be reversed by pretreatment with ketoconazole, a broad-spectrum inhibitor of cytochrome P450 enzymes. In addition, synthetic retinoids Am80 (4[(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-naphthalenyl)carbamoyl]benzoic acid) and Am580 [4(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-naphtamido)benzoic acid], which are resistant to CYP26A1 metabolism, can restore the sensitivity of these cells to apoptogens. Thus, these findings support the idea that CYP26 expression levels may play a role in determining cellular commitment to apoptosis, and increased RA metabolism may be at least partially responsible for these observed effects.

An overview of targeted treatments in cancer

BACKGROUND

The concept behind cancer treatment has evolved over the past decade from systemic, nonspecific, high-dose chemotherapy to targeted therapy and the introduction of cancer vaccines. Advanced technology and a better understanding of the cellular mechanisms that control cancer biology have helped in the development of such targeted treatment.

OBJECTIVE

The aim of this article was to review some of the new and commonly used targeted treatments in cancer, emphasizing their mechanisms of action, safety profiles, and clinical applications.

METHODS

The terms cancer, chemotherapy, monoclonal antibodies, targeted treatment, tyrosine kinase, epidermal growth factors, epidermal growth factor receptor, and cancer vaccines were used to search MEDLINE for English-language studies in humans, published between 1966 and March 2003. Identified publications addressing the objectives of this article were selected for review.

RESULTS

All-trans-retinoic acid, imatinib, gemtuzumab ozogamicin, rituximab, alemtuzumab, trastuzumab, cetuximab, and gefitinib are recently developed cancer therapies that target specific types of cells and receptors. They have been used in a variety of hematologic and solid tumors, and their tolerability makes them attractive for use even in elderly and extensively pretreated patients. Vaccines using dendritic cells, tumor cells, and fusions of tumor cells and antigen-presenting cells have also shown some promise in research, but further study is needed to obtain better, sustained results.

CONCLUSIONS

Targeted treatment and cancer vaccines are novel approaches in the treatment of cancer. Both fields are expanding rapidly, with new technology and ongoing medical research. The clinical implications of such agents, administered either solely or in combination with established chemotherapeutic agents, may ultimately lead to better regimens and improved clinical responses.

Chemoprevention of superficial bladder cancer

Patients who have bladder cancer with superficial disease are at high risk for recurrence but low risk for progression to muscle invasive disease and are regularly monitored with cystoscopy to detect recurrent tumors. This clinical setting (high recurrence rate, excellent surveillance, and low risk of progression in stage) provides an ideal setting for secondary chemoprevention. Vitamins, difluoromethylornithine, and cyclooxygenase inhibitors have demonstrated activity in preclinical models of bladder cancer. Limited clinical data suggests that vitamins and their analogs may be useful for decreasing the rate of tumor recurrence in patients with superficial bladder cancer. Ongoing clinical trials are exploring the roles of fenretinide, difluoromethylornithine, and celecoxib in the treatment of patients with a history of superficial bladder cancer.

Therapy-related acute promyelocytic leukemia

PURPOSE

To analyze patient cases of therapy-related acute promyelocytic leukemia (tAPL), occurring after chemotherapy (CT), radiotherapy (RT) or both for a prior disorder, diagnosed during the last 20 years in three European countries.

PATIENTS AND METHODS

The primary disorder and its treatment, interval from primary disorder to tAPL, characteristics of tAPL, and its outcome were analyzed in 106 patients.

RESULTS

Eighty of the 106 cases of tAPL were diagnosed during the last 10 years, indicating an increasing incidence of tAPL. Primary disorders were predominantly breast carcinoma (60 patients), non-Hodgkin's lymphoma (15 patients), and other solid tumors (25 patients). Thirty patients had received CT alone, 27 patients had received RT alone, and 49 patients had received both. CT included at least one alkylating agent in 68 patients and at least one topoisomerase II inhibitor in 61 patients, including anthracyclines (30 patients), mitoxantrone (28 patients), and epipodophyllotoxins (19 patients). Median interval from primary disorder to tAPL diagnosis was 25 months (range, 4 to 276 months). Characteristics of tAPL were generally similar to those of de novo APL. With treatment using anthracycline-cytarabine-based CT or all-trans-retinoic acid combined with CT, actuarial survival was 59% at 8 years.

CONCLUSION

tAPL is not exceptional, and develops usually less than 3 years after a primary neoplasm (especially breast carcinoma) treated in particular with topoisomerase II-targeted drugs (anthracyclines or mitoxantrone and less often etoposide). Characteristics and outcome of tAPL seem similar to those of de novo APL.

Recent advances in the treatment of AIDS-related Kaposi's sarcoma

Kaposi's sarcoma (KS) is the most common malignancy associated with HIV infection and is considered an AIDS defining condition by the US Centers of Disease Control Guidelines. Several advances in the treatment of AIDS-related KS have been achieved over the past few years, even though a gold standard therapy for KS has not yet been defined and treatment must be tailored to individual needs. Since the availability of highly active antiretroviral therapy (HAART), a dramatic clinical response has been documented in patients with KS, making HAART an essential approach in the management of KS in most, if not all, patients with AIDS-related KS. However, in case of aggressive, visceral, and/or life-threatening KS, more complex therapeutic schedules have to be taken into account, including chemotherapy, radiotherapy, and/or immunotherapy. In general, systemic treatment for KS is limited to widespread, symptomatic disease, whereas local interventions are indicated for minimal, cosmetically troublesome lesions. Among new cytotoxic agents, liposomal anthracyclines and paclitaxel are highly effective molecules for KS and have been approved by the US Food and Drug Administration (FDA) as first-line and second-line monotherapy, respectively, for advanced KS. Furthermore, a greater understanding of the pathogenesis of KS has lead to the development of an array of new experimental agents. Many antiangiogenic agents such as AGM 1470 (TNP 470), thalidomide, and glufanide disodium (IM 862) have produced encouraging responses in patients with KS and large clinical trials are in progress. Retinoic acids may also block neoangiogenesis as well as proliferation of KS cells in vitro, and they have been used either systemically or topically with a high response rate. Thus, a topical compound 0.1% alitretinoin gel was approved in 1999 by the FDA for the treatment of skin lesions associated with KS. Human chorionic gonadotropin, a hormonal agent, has shown a strong inhibitory activity in KS cells, but its role in the regression of KS lesions is not clear. Finally, the identification of a novel gamma-herpesvirus, human herpesvirus-8, as a causative agent for KS, together with novel antiangiogenic compounds, such as metalloproteinase inhibitors, may offer promising targets for the therapy of KS.

ARHGAP10, a novel human gene coding for a potentially cytoskeletal Rho-GTPase activating protein

Rho-GTPase activating proteins (Rho-GAPs) are negative regulators of Rho-GTPase signaling pathways related to actin cytoskeleton dynamics, cell proliferation, and differentiation. We have identified a novel human gene, termed ARHGAP10, that codes for a 1957-aminoacid Rho-GAP, containing a PDZ, a PH, and a Rho-GAP domain. The cDNA is 7118 bp long and has an open reading frame of 5874 bp. A computational analysis located this gene on chromosome 10 band 10p12.32 suggesting that it is composed of 25 exons. Northern analysis revealed that it is widely expressed, with high levels in brain and muscle. Real-time quantitative PCR analysis confirmed an increase in ARHGAP10 expression during differentiation of HL-60 cells with all-trans-retinoic acid and hematopoietic stem cells with erythropoietin, suggesting that this gene could play a role in normal hematopoiesis. The fact that this gene is highly expressed in muscle and brain, which are highly differentiated tissues, further supports the hypothesis that ARHGAP10 is important for cell differentiation.

Modelling haematopoietic malignancies in the mouse and therapeutical implications

Modelling human disease in the mouse has become an essential activity in biomedical research in order to unravel molecular mechanisms underlying pathological conditions as well as to determine in vivo the consequences of aberrant gene function. The mouse is by far the most accessible mammalian system physiologically similar to humans. Furthermore, the development of novel techniques for manipulating the murine genome, which allow the in vivo modification of virtually any genomic region in a time and/or tissue specific manner, renders the mouse an ideal model system to study human pathological conditions. Modelling human diseases in mice has reached an even greater relevance in the field of haematological malignancies, due to the already advanced characterization of the molecular basis of many haematological disorders. In this review, we describe the most important technological developments that made it possible to reproduce in the mouse the genetic lesions that characterize human haematological malignancies, thus often generating faithful mouse models of the human condition. We provide specific examples of the advantages and limitations of the various genetic approaches utilized to model leukaemia and lymphoma in the mouse. Finally, we discuss the power of mouse modelling in developing and testing novel therapeutic modalities in pre-clinical studies.

Up-regulation of acid sphingomyelinase during retinoic acid-induced myeloid differentiation of NB4, a human acute promyelocytic leukemia cell line

All-trans-retinoic acid (ATRA) induces myeloid differentiation of a human promyelocytic leukemia cell line, NB4, but does not affect its subclone NB4/RA harboring a point-mutated ligand-binding domain (AF2) in retinoic acid receptor alpha (RARalpha) gene. We found that ATRA induced the 4-fold elevation of acid sphingomyelinase (ASMase) activity 24 h after treatment in NB4 cells, but not in NB4/RA cells. ATRA did not affect neutral sphingomyelinase activity in either NB4 or NB4/RA. Upon treatment with ATRA, ceramide, the product of an ASMase reaction, accumulated in NB4 cells. Northern blot analysis showed a marked elevation of the ASMase mRNA 8 h after ATRA treatment, reaching a plateau at 24 h. Regulation of ASMase gene expression was studied by a promoter analysis using luciferase reporter assay. The 5'-upstream flanking region of human ASMase gene (-519/+300) conjugated with the luciferase gene was introduced into COS-7 cells. Luciferase activity in transformed cells markedly increased in response to ATRA stimulation when the wild type RARalpha or the PML/RARalpha hybrid protein was co-expressed. Deletion experiments revealed that a short sequence at the 5'-end (-519/-485) was indispensable for the ATRA response. Within this short region, two retinoic acid-responsive element-like motifs (TGCCCG and TCTCCT) and one AP2-like motif (CCCTTCCC) were identified. Deletion and base-substitution experiments showed that all three motifs are required for the full expression induced by ATRA. Electrophoresis mobility shift assays with the nuclear extract of ATRA-treated NB4 cells showed that proteins were bound specifically to the probe being mediated by all three motifs in the promoter sequence.

The search for optimal treatment in relapsed and refractory acute myeloid leukemia

Despite the significant progress in the treatment of AML during the last 5-10 years, 20-40% of patients still do not achieve remission with standard induction therapy. In addition, 50-70% of patients in CR are likely to relapse. A major limitation of successful AML therapy is intrinsic or acquired drug resistance. Several pharmacological inhibitors of mechanisms inducing chemoresistance in leukemic cells have been investigated. New cytotoxic drugs, agents with novel mechanisms of action, and new treatment strategies are currently being investigated. The management of refractory or relapsed AML patients is reviewed in this study.

Nuclear receptors in cell life and death

The balance between cell proliferation and programmed cell death (apoptosis) determines body patterns during animal development and controls compartment sizes, tissue architecture and remodeling. The removal of primordial structures by apoptosis allows the organism to develop sex specifically and to adapt for novel functions at later stages; apoptosis also limits the size of evolving structures. It is a ubiquitous function that is essential for all cells. Although inappropriate regulation or execution of apoptosis leads to disease, such as cancer, there is now evidence for its great therapeutic potential. This would be particularly true if apoptosis could be targeted at defined cell compartments, rather than acting ubiquitously like chemotherapy. Here, we discuss the potential of nuclear receptor ligands, many of which act through their cognate receptors in defined body compartments as modulators of cell life and death, with special emphasis on the molecular pathways by which these receptors affect cell-cycle progression, survival and apoptosis.

Retinoic acid-induced apoptosis in leukemia cells is mediated by paracrine action of tumor-selective death ligand TRAIL

The therapeutic and preventive activities of retinoids in cancer are due to their ability to modulate the growth, differentiation, and survival or apoptosis of cancer cells. Here we show that in NB4 acute promyelocytic leukemia cells, retinoids selective for retinoic-acid receptor-alpha induced an autoregulatory circuitry of survival programs followed by expression of the membrane-bound tumor-selective death ligand, TRAIL (tumor necrosis factor-related apoptosis-inducing ligand, also called Apo-2L). In a paracrine mode of action, TRAIL killed NB4 as well as heterologous and retinoic-acid-resistant cells. In the leukemic blasts of freshly diagnosed acute promyelocytic leukemia patients, retinoic-acid-induced expression of TRAIL most likely caused blast apoptosis. Thus, induction of TRAIL-mediated death signaling appears to contribute to the therapeutic value of retinoids.

Analysis of the molecular genetics of acute promyelocytic leukemia in mouse models

Acute promyelocytic leukemia (APL) is characterized by reciprocal chromosomal translocations that always Involve the retinoic acid receptor-alpha (RARalpha) gene on chromosome 17. RARalpha variably fuses to the PML, PLZF, NPM, NuMA, and STAT 5b genes (X genes), leading to the generation of X-RARalpha and RARalpha-X fusion genes. The aberrant X-RARalpha proteins retain the dimerization domains of their parental proteins and therefore can act as dominant negative oncogenic products on both RARalpha/RXR and X pathways. Studies in transgenic mice harboring X-RARalpha and RARalpha-X fusion genes and In mice lacking X genes have helped unravel the molecular mechanisms underlying APL leukemogenesis, which lead to the development of novel therapeutic strategies. Moreover, transgenic mouse models of APL were useful to test in vivo the efficacy of these novel therapeutic approaches as well as of drug combinations such as retinoic acid and As2O3 that were previously known to be effective as single agents in human APL.

Diffuse alveolar hemorrhage in acute promyelocytic leukemia patients treated with ATRA--a manifestation of the basic disease or the treatment

All-trans-retinoic acid (ATRA) is considered the recommended induction treatment for acute promyelocytic leukemia. In the pre-ATRA era pulmonary bleeding was a common cause of death in these patients, mostly due to disseminated intravascular coagulation which was further exacerbated by the administration of chemotherapy. Although ATRA syndrome, the most serious adverse effect of ATRA treatment, involves the lungs, pulmonary hemorrhage has only rarely been reported as a manifestation of ATRA syndrome. Here we describe 2 patients who developed diffuse alveolar hemorrhage during treatment with ATRA. The possible mechanisms of pulmonary bleeding in these cases are discussed.

The incidence of acute promyelocytic leukemia appears constant over most of a human lifespan, implying only one rate limiting mutation

It is believed that most malignancies become more common with increasing age due to the requirement for several mutations to accumulate and subsequently interact. The age specific incidence of acute promyelocytic leukemia (APL) was investigated using population-based data from 77 million subject years of observation, yielding 149 consecutive cases. The incidence appears approximately constant with respect to age, an observation not previously reported with any other malignancy. These findings are most easily explained by there being only one rate limiting genetic event required to initiate the disease, although other, non-rate limiting mutations may also be necessary for disease development. It is also argued that this mutation is probably restricted to cells committed to differentiation, which may explain why APL is curable by chemotherapy.

In vivo analysis of the molecular pathogenesis of acute promyelocytic leukemia in the mouse and its therapeutic implications

Acute promyelocytic leukemia (APL) is characterized by the expansion of malignant myeloid cells blocked at the promyelocytic stage of hemopoietic development, and is associated with reciprocal chromosomal translocations always involving the retinoic acid receptor alpha (RARalpha) gene on chromosome 17. As a consequence of the translocation RARalpha variably fuses to the PML, PLZF, NPM and NUMA genes (X genes), leading to the generation of RARalpha-X and X-RARalpha fusion genes. The aberrant chimeric proteins encoded by these genes may exert a crucial role in leukemogenesis. Retinoic acid (RA), a metabolite of vitamin A, can overcome the block of maturation at the promyelocytic stage and induce the malignant cells to terminally mature into granulocytes resulting in complete albeit transient disease remission. APL has become, for this reason, the paradigm for 'cancer differentiation therapy'. Furthermore, APL associated with translocation between the RARalpha and the PLZF genes (PLZF-RARalpha) shows a distinctly worse prognosis with poor response to chemotherapy and little or no response to treatment with RA, thus defining a new APL syndrome. Here we will focus our attention on the recent progresses made in defining the molecular mechanisms underlying the pathogenesis of this paradigmatic disease in vivo in the mouse. We will review the critical contribution of mouse modeling in unraveling the transcriptional basis for the differential response to RA in APL. We will also discuss how this new understanding has allowed to propose, develop and test in these murine leukemia models as well as in human APL patients novel therapeutic strategies.

A phase I/II study of intensive dose escalation of cytarabine in combination with idarubicin and etoposide in induction and consolidation treatment of adult acute myeloid leukemia. Australian Leukaemia Study Group (ALSG)

To determine the safety and efficacy of the combination of idarubicin, cytarabine and etoposide ("ICE") for induction and consolidation treatment of acute myeloid leukemia (AML), and of dose-intensification of cytarabine in this setting, 54 previously untreated patients in three cohorts were studied by sequential dose escalation of cytarabine, in combination with standard doses of idarubicin and etoposide. Cytarabine was given to Cohort 1 at the conventional dosage of 100 mg/m2 per day by continuous infusion for 7 days in induction and 5 days in consolidation; to Cohort 2 at high-dose (HiDAC) (3 g/m2 intravenously twice daily on days 1, 3, 5 and 7) during induction with conventional dosage during consolidation; to Cohort 3 HiDAC was given for both induction and consolidation. In addition, Cohort 3 patients received lenograstim (Granocyte; rHuG-CSF) after both induction and consolidation courses. We found that there was no significant difference between the three cohorts in hematological toxicity in induction, but that HiDAC was associated with a greater incidence of gastro-intestinal toxicities. There was no difference in induction mortality between the three cohorts, which was 11% overall. Consolidation with HiDAC led to a significant increase in hematological toxicity. Overall, the complete remission (CR) rate was 80% with no significant difference between the three regimens. The estimated disease free survival at 3 years was 28%, 67% and 54% respectively for Cohorts 1, 2 and 3 with an estimated overall survival of 38%, 63% and 47%. We conclude that cytarabine dosage can be escalated safely in combination with idarubicin and etoposide in both induction and consolidation. The combination is effective for induction treatment of AML and its side-effects appear similar to those of standard regimens. Whether its use offers long-term benefits compared with standard regimens is the subject of ongoing controlled randomized studies.

Treatment of early AIDS-related Kaposi's sarcoma with oral all-trans-retinoic acid: results of a sequential non-randomized phase II trial. Kaposi's Sarcoma ANRS Study Group. Agence Nationale de Recherches sur le SIDA

OBJECTIVE

To assess the efficacy and safety of all-trans-retinoic acid (ATRA), a retinoid with antitumour activity that inhibits in vitro the growth of Kaposi's sarcoma cells, in patients with low-risk AIDS-associated Kaposi's sarcoma.

DESIGN

Non-randomized phase II study, using a group sequential procedure to determine whether the response rate to ATRA was above 10%.

SETTING

Nine referral French centres.

PATIENTS

Twenty HIV-seropositive men with CD4 cells > or = 200 x 10(6)/l, low-risk Kaposi's sarcoma [T0I0S0 according to the classification of AIDS Clinical Trials Group (ACTG)] not previously treated with systemic anti-Kaposi's sarcoma agents, and with at least four measurable lesions were included.

INTERVENTIONS

ATRA was given orally 45 mg/m2 daily for 12 weeks.

MAIN OUTCOME MEASURE

Tumour response evaluated according to ACTG criteria.

RESULTS

Nineteen patients were evaluated for response: partial response, stabilization and progression were found in eight (42%), seven (37%), and four (21%) patients, respectively. Gradual flattening and lightening of lesions was observed in responders after at least 2 months of ATRA. All patients with partial response at week 12 pursued ATRA for another 15+/-7 weeks. Further improvement was observed in six patients. Median duration of response was 332 days. Cheilitis, transient headaches and skin dryness were the main toxicities noted. No significant changes in HIV viral burden or serum interleukin-6 pathways were observed.

CONCLUSIONS

ATRA is well tolerated and effective enough in Kaposi's sarcoma patients to warrant further evaluation.