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

United States multicenter study of arsenic trioxide in relapsed acute promyelocytic leukemia

PURPOSE

To determine the safety and efficacy of arsenic trioxide (ATO) in patients with relapsed acute promyelocytic leukemia (APL).

PATIENTS AND METHODS

Forty patients experiencing first (n = 21) or > or = second (n = 19) relapse were treated with daily infusions of ATO to a maximum of 60 doses or until all leukemic cells in bone marrow were eliminated. Patients who achieved a complete remission (CR) were offered one consolidation course of ATO that began 3 to 4 weeks later. Patients who remained in CR were eligible to receive further cycles of ATO therapy on a maintenance study.

RESULTS

Thirty-four patients (85%) achieved a CR. Thirty-one patients (91%) with CRs had posttreatment cytogenetic tests negative for t(15;17). Eighty-six percent of the patients who were assessable by reverse transcriptase polymerase chain reaction converted from positive to negative for the promyelocytic leukemia/retinoic acid receptor-alpha transcript by the completion of their consolidation therapy. Thirty-two patients received consolidation therapy, and 18 received additional ATO as maintenance. Eleven patients underwent allogeneic (n = 8) or autologous (n = 3) transplant after ATO treatment. The 18-month overall and relapse-free survival (RFS) estimates were 66% and 56%, respectively. Twenty patients (50%) had leukocytosis (> 10,000 WBC/microL) during induction therapy. Ten patients developed signs or symptoms suggestive of the APL syndrome and were effectively treated with dexamethasone. Electrocardiographic QT prolongation was common (63%). One patient had an absolute QT interval of > 500 msec and had an asymptomatic 7-beat run of torsades de pointe. Two patients died during induction, neither from drug-related causes.

CONCLUSION

This study establishes ATO as a highly effective therapy for patients with relapsed APL.

Checking the scoreboard: the impact of cancer genetics on clinical practice

Improvements in cancer care have historically been predicated on significant scientific and technological advances, such as antisepsis in surgery, and the discovery of the therapeutic benefits of radiation and chemotherapeutic drugs. The past 30 years have seen an exponential increase in our knowledge of the biology and genetics of cancer, built on a massive and sustained research effort worldwide. Yet over the same period, significant changes in cancer outcomes have occurred largely as a result of public health measures and through incremental advances in existing technologies. The present paper examines the extent to which the new knowledge of cancer genetics has impacted on current patient care. It considers some of the issues that may have served to lessen this impact, as well as some of the reasons for this apparent imbalance between action and outcome.

Prolonged molecular and clinical remission after treatment of a patient with follicular lymphoma with rituximab

Rituximab is a chimeric anti-CD20 monoclonal antibody that has approval for single agent therapy in the treatment of relapsed/refractory low grade or follicular non-Hodgkin's Lymphoma. In published phase II trials, molecular remissions of PCR detectable t(14;18) disease in the peripheral blood have been reported in up to 62% of patients by three months. We report a case of a patient who achieved prolonged clinical and molecular remission following a single four week course of Rituximab that has exceeded any previous remission achieved with chemo-radiotherapy. The implications of molecular remission as a surrogate of clinical remission and molecular relapse as a harbinger of clinical relapse are reviewed and discussed.

Flow cytometric analysis of aberrant antigen expression of blasts using CD45 blast gating for minimal residual disease in acute leukemia and high-risk myelodysplastic syndrome

To evaluate the availability of quantification of blasts with aberrant antigen expression (AAE) using CD45 gating for minimal residual disease (MRD), 15 patients with acute leukemia (AL) and myelodysplastic syndrome (MDS) were studied. In patients with complete remission (CR), the frequency of blasts with AAE (%AAE) by CD45/side scatter (SSC) gating was significantly higher than that by the traditional forward scatter (FSC)/SSC combination (median, 4.1 vs. 0.3%, P<0.0001). We also demonstrated two representative cases, in which leukemia relapse could be predicted before 3 weeks and the early treatment for MRD could be performed for MRD after allogeneic bone marrow transplantation (BMT). These results indicate that this procedure is very useful for the evaluation of the quality of CR.

Quantitative monitoring of the PRAME gene for the detection of minimal residual disease in leukaemia

PRAME (Preferentially expressed antigen of melanoma) has been previously identified as a melanoma antigen recognized by cytotoxic T cells (CTLs) and found to be expressed in a variety of cancer cells including leukaemic cells. We have screened 98 Japanese patients with leukaemia and lymphoma for expression of the PRAME gene using semiquantitative reverse transcription polymerase chain reaction (RT-PCR). Forty-one patients (42%) showed high levels of PRAME expression. Eight of these patients were then monitored using real-time PCR for a period of 10-37 months. Significant reductions in the PRAME expression were observed in all patients after chemotherapy. An increased expression was detected in the two patients who relapsed, one of which was before cytological diagnosis. These changes were correlated with those of other known genetic markers, such as the bcr-abl gene. Therefore, quantitative monitoring of the PRAME gene using real-time PCR method may be useful for detecting minimal residual disease and to predict subsequent relapse, especially in patients without known genetic markers. In addition, a PRAME-positive leukaemia cell line and fresh leukaemic cells were found to be susceptible to lysis by PRAME-specific CTLs established from a patient with melanoma, suggesting that the PRAME peptide can also be a target leukaemia antigen for T cells.

The retinoids and cancer prevention mechanisms

Carcinogenesis is a multistep process that converts normal cells into malignant cells. Once transformed, malignant cells acquire the ability to invade and metastasize, leading to clinically evident disease. During this continuum from normal to metastatic cells, carcinogenic steps can be arrested or reversed through pharmacological treatments, known as cancer chemoprevention. Chemoprevention strategies represent therapeutic interventions at early stages of carcinogenesis, before the onset of invasive cancer. Effective chemoprevention should reduce or avoid the clinical consequences of overt malignancies by treating early neoplastic lesions before development of clinically apparent signs or symptoms. Preclinical, clinical, and epidemiological data provide considerable support for cancer chemoprevention as an attractive therapeutic strategy. This clinical approach was validated in the recent tamoxifen randomized trial, demonstrating that a selective estrogen receptor modulator reduces the risk of breast cancer in women at high risk for this malignancy. Derivatives of vitamin A, the retinoids, have reported activity in treating specific premalignant lesions and reducing incidence of second primary tumors in patients with prior head and neck, lung or liver cancers. Whether the retinoids will prevent primary cancers at these sites is not yet known. Notably, a carotenoid (beta-carotene) was shown as inactive in primary prevention of lung cancers in high-risk individuals. This underscores the need for relevant in vitro models to identify pathways signaling chemopreventive effects. These models should assess the activity of candidate chemoprevention agents before the conduct of large and costly prevention trials. An improved understanding of cancer prevention mechanisms should aid in the discovery of new therapeutic targets and chemoprevention agents. Ideally, these agents should have tolerable clinical toxicities suitable for chronic administration to individuals at high risk for developing primary or second cancers. This article reviews what is now known from clinical and preclinical studies about the retinoids as cancer prevention agents.

Treatment of newly diagnosed and relapsed acute promyelocytic leukemia with intravenous liposomal all-trans retinoic acid

A novel intravenous liposomal formulation of all-trans retinoic acid (ATRA) was evaluated in 69 patients with acute promyelocytic leukemia (APL): 32 new diagnoses, 35 relapses, and 2 oral ATRA failures. Liposomal ATRA (90 mg/m(2)) was administered every other day until complete remission (CR) or a maximum of 56 days. Treatment following CR was liposomal ATRA with or without chemotherapy. In an intent-to-treat (ITT) analysis of all patients, CR rates were 62%, 70%, and 20% in newly diagnosed, group 1 first relapses (ATRA naive or off oral ATRA more than or equal to 1 year), or group 2 relapses (second or subsequent relapse or first relapses off oral ATRA less than 1 year), respectively. In 56 evaluable patients (receiving 4 or more doses), CR rates for the same groups were 87% (20 of 23), 78% (14 of 18), and 23% (3 of 13). Remission failure in newly diagnosed patients was not from resistant disease. Several patients in CR became polymerase chain reaction (PCR) negative for promyelocytic leukemia/retinoic acid receptor-alpha (PML/RARalpha) after liposomal ATRA alone. Toxicity was generally mild, most commonly headaches (67. 5%). Eighteen patients (26%) had ATRA syndrome develop during induction. One-year survival of ITT patients was 62%, 56%, and 20% for newly diagnosed, group 1, and group 2, respectively. The medium duration of CR has not yet been reached and was 18 and 5.5 months in the same groups. These results demonstrate that liposomal ATRA is effective in inducing CR in newly diagnosed or group 1 APL patients. It provides a reliable dosage of ATRA for patients with APL unable to swallow or absorb medications and can induce molecular remissions without chemotherapy.

Maintenance of retinoic acid receptor alpha pools by granulocyte colony-stimulating factor and lithium chloride in all-trans retinoic acid–treated WEHI-3B leukemia cells: relevance to the synergistic induction of terminal differentiation

Previous studies have demonstrated that combinations of all-trans retinoic acid (ATRA) with either granulocyte-colony stimulating factor (G-CSF) or lithium chloride (LiCl) produced synergistic terminal differentiation of WEHI-3B myelomonocytic leukemia (D+) cells. It was found that steady-state retinoic acid receptor alpha (RARα) protein levels were markedly reduced in these cells after exposure to ATRA. Because the presence of receptors for a hormone ligand is required for its action, differentiation therapy with ATRA may be self-limiting. The combination of G-CSF with ATRA significantly attenuated the loss of RARα protein, and synergistic terminal differentiation occurred. LiCl was more effective than G-CSF in preserving RARα pools and synergized with ATRA more strongly than G-CSF. These findings suggested that the prevention of RARα protein loss by G-CSF or LiCl in ATRA-treated cells functioned to extend the differentiation response to the retinoid and was responsible, at least in part, for the observed synergism. D+ cells transfected with an expression plasmid containing RARα cDNA had a 6- to 8-fold increase in steady-state RARα mRNA compared with vector-transfected cells and showed a 2- to 3-fold increase in RARα protein. ATRA caused a reduction, but not a complete loss, of RARα protein in these transfectants, which were considerably more responsive than parental D+ cells to ATRA as a single agent, supporting the concept that the protection of RARα pools results in a heightened differentiation response to ATRA.

Maintenance of retinoic acid receptor alpha pools by granulocyte colony-stimulating factor and lithium chloride in all-trans retinoic acid–treated WEHI-3B leukemia cells: relevance to the synergistic induction of terminal differentiation

Previous studies have demonstrated that combinations of all-trans retinoic acid (ATRA) with either granulocyte-colony stimulating factor (G-CSF) or lithium chloride (LiCl) produced synergistic terminal differentiation of WEHI-3B myelomonocytic leukemia (D+) cells. It was found that steady-state retinoic acid receptor alpha (RARα) protein levels were markedly reduced in these cells after exposure to ATRA. Because the presence of receptors for a hormone ligand is required for its action, differentiation therapy with ATRA may be self-limiting. The combination of G-CSF with ATRA significantly attenuated the loss of RARα protein, and synergistic terminal differentiation occurred. LiCl was more effective than G-CSF in preserving RARα pools and synergized with ATRA more strongly than G-CSF. These findings suggested that the prevention of RARα protein loss by G-CSF or LiCl in ATRA-treated cells functioned to extend the differentiation response to the retinoid and was responsible, at least in part, for the observed synergism. D+ cells transfected with an expression plasmid containing RARα cDNA had a 6- to 8-fold increase in steady-state RARα mRNA compared with vector-transfected cells and showed a 2- to 3-fold increase in RARα protein. ATRA caused a reduction, but not a complete loss, of RARα protein in these transfectants, which were considerably more responsive than parental D+ cells to ATRA as a single agent, supporting the concept that the protection of RARα pools results in a heightened differentiation response to ATRA.

Pathologic, cytogenetic and molecular assessment of acute promyelocytic leukemia patients treated with arsenic trioxide (As2O3)

Arsenic trioxide (As2O3) shows great promise as an effective therapy for patients with all-trans retinoic acid (ATRA)-resistant acute promyelocytic leukemia (APL). Little data is available addressing the pathology of As2O3 treated APL and whether the antileukemic mechanism of As2O3 is primarily cytolysis or through stimulation of cell differentiation. In this report, we made a morphologic, cytogenetic, and molecular evaluation of five ATRA-refractory APL patients who were treated with As2O3. Four of the five patients had morphologic responses after one or two cycles of As2O3 treatment. Of the four responders based on bone marrow morphology, two achieved molecular remission (negative RT-PCR for PML- RAR alpha fusion transcripts) by the end of the second and third cycles of As2O3 therapy. Two patients exhibited marked leukocytosis during the first cycle of As2O3, and at that time point the APL cells were largely replaced by the cells showing partial differentiation towards myelocytes with co-expression of CD11b and CD33. Nevertheless, these "myelocyte-like" cells that showed the t(15;17) translocation eventually disappeared with continuous As2O3 therapy. As2O3 treatment appears to be effective therapy for the patients with relapsed APL after the failure of conventional chemotherapy and ATRA therapy. The pathologic findings in these five cases suggest that at low doses As2O3 primarily induces differentiation of the APL cells, generating abnormal myelocytes resembling APL cells treated with ATRA, whereas at higher doses AS2O3 induces marrow necrosis.

Retinoids in chemoprevention and differentiation therapy

Retinoids are essential for the maintenance of epithelial differentiation. As such, they play a fundamental role in chemoprevention of epithelial carcinogenesis and in differentiation therapy. Physiological retinoic acid is obtained through two oxidation steps from dietary retinol, i.e. retinol-->retinal-->retinoic acid. The latter retinal-->retinoic acid step is irreversible and eventually marks disposal of this essential nutrient, through cytochrome P450-dependent oxidative steps. Mutant mice deficient in aryl hydrocarbon receptor (AHR) accumulate retinyl palmitate, retinol and retinoic acid. This suggests a direct connection between the AHR and retinoid homeostasis. Retinoids control gene expression through the nuclear retinoic acid receptors (RARs) alpha, beta and gamma and 9-cis-retinoic acid receptors alpha, beta and gamma, which bind with high affinity the natural ligands all-trans-retinoic acid and 9-cis-retinoic acid, respectively. Retinoids are effective chemopreventive agents against skin, head and neck, breast, liver and other forms of cancer. Differentiation therapy of acute promyelocytic leukemia (APL) is based on the ability of retinoic acid to induce differentiation of leukemic promyelocytes. Patients with relapsed, retinoid-resistant APL are now being treated with arsenic oxide, which results in apoptosis of the leukemic cells. Interestingly, induction of differentiation in promyelocytes and consequent remission of APL following retinoid therapy depends on expression of a chimeric PML-RAR alpha fusion protein resulting from a t(15;17) chromosomal translocation. This protein functions as a dominant negative against the function of both PML and RARs and its overexpression is able to recreate the phenotypes of the disease in transgenic mice. The development of new, more effective and less toxic retinoids, alone or in combination with other drugs, may provide additional avenues for cancer chemoprevention and differentiation therapy.

Double induction strategy including high dose cytarabine in combination with all-trans retinoic acid: effects in patients with newly diagnosed acute promyelocytic leukemia. German AML Cooperative Group

A prospective multicenter study was performed to investigate the clinical and molecular results of intensified double induction therapy including high-dose cytarabine (ara-C) in combination with ATRA in newly diagnosed acute promyelocytic leukemia (APL), followed by consolidation and 3 years maintenance therapy. Fifty-one patients, diagnosed and monitored from December 1994 to June 1999, were evaluated. The median age was 43 (16-60) years. The morphologic diagnosis was M3 in 40 (78%) and M3v in 11 (22%) patients. In 15 (30%) patients the initial white blood cell counts were > or =5 x 10(9)/l. The cytogenetic or molecular proof of the translocation t(15;17) was a mandatory prerequisite for eligibility. The diagnosis was confirmed by karyotyping in 46 and by RT-PCR of the PML/RARalpha transcript in 45 cases. The rate of complete hematological remission was 92% and the early death rate 8%. Monitoring of minimal residual disease by RT-PCR of PML/RARalpha (sensitivity 10(-4)) showed negativity in 29 of 32 (91%) evaluable cases after induction, in 23 of 25 (92%) after consolidation, and in 27 of 30 (90%) during maintenance, after a median time of 2, 4 and of 18 months after diagnosis, respectively. After a median follow-up of 27 months, the estimated actuarial 2 years overall and event-free survival were both 88% (79, 97), and the 2 years relapse-free survival 96% (90, 100). The high antileukemic efficacy of this treatment strategy is demonstrated by a rapid and extensive reduction of the malignant clone and by a low relapse rate. The results suggest that the intensity of the induction chemotherapy combined with ATRA is one of the factors which may have a critical influence on the outcome of APL. A randomized trial should assess the value of an induction therapy including ATRA and high-dose ara-C in comparison to standard-dose ara-C.

Leukocytosis and the retinoic acid syndrome in patients with acute promyelocytic leukemia treated with arsenic trioxide

PURPOSE

Arsenic trioxide, like all-trans-retinoic acid (RA), induces differentiation of acute promyelocytic leukemia (APL) cells in vivo. Treatment of APL patients with all-trans RA is commonly associated with leukocytosis, and approximately 50% of patients develop the RA syndrome. We reviewed our clinical experience with arsenic trioxide to determine the incidence of these two phenomena.

PATIENTS AND METHODS

Twenty-six patients with relapsed or refractory APL were treated with arsenic trioxide for remission induction at daily doses that ranged from 0.06 to 0.17 mg/kg.

RESULTS

Twenty-three patients (88%) achieved complete remission. Leukocytosis was observed in 15 patients (58%). The median baseline leukocyte count for patients with leukocytosis was 3,900 cells/microL (range, 1,200 to 72,300 cells/microL), which was higher than that for patients who did not develop leukocytosis (2,100 cells/microL; range, 500 to 5,400 cells/microL; P =.01). No other cytotoxic therapy was administered, and the leukocytosis resolved in all cases. The RA syndrome was observed in eight patients (31%). Patients who developed leukocytosis were significantly more likely to develop the RA syndrome (P <.001), and no patient without a peak leukocyte count greater than 10,000 cells/microL developed the syndrome. Among the patients with leukocytosis, there was no observed relation between the leukocyte peak and the probability of developing the syndrome (P =.37).

CONCLUSION

Induction therapy of APL with all-trans RA and arsenic trioxide is associated with leukocytosis and the RA syndrome. These clinical effects seem to be intrinsically related to the biologic responsiveness and the differentiation process induced by these new agents.

Treatment of relapsing acute promyelocytic leukemia by all-trans retinoic acid therapy followed by timed sequential chemotherapy and stem cell transplantation. APL Study Group. Acute promyelocytic leukemia

The purpose of this study was to assess the safety and efficacy of stem cell transplantation (SCT) mainly autologous SCT as consolidation therapy in APL patients who relapsed and achieved a second complete remission (CR2). Fifty adult patients with a first relapsed APL, of whom 39 had been previously treated with ATRA, entered a multicenter trial of oral ATRA until complete remission (CR) achievement followed by timed sequential chemotherapy (EMA combining etoposide 200 mg/m2/day for 3 days, mitoxantrone 12 mg/m2/day for 3 days, and cytarabine 500 mg/m2/day for two sequences of 3 days). EMA was started either after CR achievement, or on day 1 of ATRA because of initial white blood cell (WBC) counts >5 x 10(9)/l, or rapidly added to ATRA in order to prevent ATRA syndrome because WBC count increased under ATRA. Forty-five patients (90%, 95% CI 78%-97%) were in CR after induction therapy. Five patients died from infection during aplasia following EMA chemotherapy. Eleven patients who achieved CR had a familial HLA-identical donor and were allografted. The median disease-free survival (DFS) of allografted patients was 8.2 months. The 34 other CR patients were scheduled for autologous peripheral blood (PB) SCT (intent-to-treat group). Actually, autologous transplantation was only carried out in 22 patients (65%) (17 PBSCT and five autologous bone marrow transplantation (BMT)). Reasons for not autografting were early relapse (three patients), severe toxicity of EMA chemotherapy (six patients), and refusal or failure of stem cell harvest (three patients). The 3-year DFS rate of patients actually autografted was 77%. Among the 17 autografted patients still in CR2, nine patients have already reached a longer CR2 than first CR (CR1). Results of detection of PML/RARalpha by RT-PCR after autologous transplantation show negative findings in eight of the nine patients tested. We conclude that (1) ATRA combined to EMA chemotherapy is effective in the treatment of relapsed APL; (2) allogeneic BMT may be too toxic after salvage treatment including EMA intensive chemotherapy; (3) clinical outcome of autografted patients and preliminary molecular results regarding detection of PML/RARalpha after autologous PBSCT are encouraging.

Quantitation of minimal residual disease in acute promyelocytic leukemia patients with t(15;17) translocation using real-time RT-PCR

We took advantage of a recently developed system allowing performance of real-time quantitation of polymerase chain reaction to develop a quantitative method of measurement of PML-RARalpha transcripts which are hallmarks of acute promyelocytic leukemia (APL) with t(15;17) translocation. Indeed, although quantitation of minimal residual disease has proved to be useful in predicting clinical outcome in other leukemias such as chronic myeloid leukemia or acute lymphoblastic leukemia, no quantitative data have been provided in the case of APL. We present here a method for quantitation of the most frequent subtypes of t(15;17) transcripts (namely bcr1 and bcr3). One specific forward primer is used for each subtype in order to keep amplicon length under 200 bp. The expression of PML-RARalpha transcripts is normalized using the housekeeping porphobilinogen deaminase (PBGD) gene. This technique allows detection of 10 copies of PML-RARalpha or PBGD plasmids, and quantitation was efficient up to 100 copies. One t(15;17)-positive NB4 cell could be detected among 106 HL60 cells, although quantitation was efficient up to one cell among 105. Repeatability and reproducibility of the method were satisfying as intra- and inter-assay variation coefficients were not higher than 15%. The efficiency of the method was finally tested in patient samples, showing a decrease of the PML-RARalpha copy number during therapy, and an increase at the time of relapse.

All trans-retinoic acid decreases early mortality in patients with promyelocytic leukemia and can be given entirely on an outpatient basis

The results of the treatment of 43 patients with acute promyelocytic leukemia (PML) are reported: 27 were treated initially with all-trans-retinoic acid (ATRA), whereas 16 were treated with conventional chemotherapy. All patients received myelosuppressive chemotherapy after the initial treatment. Respectively, the complete remission rate was 92% and 37% (P < 0.01), the 5-day mortality rate was 0% and 44% (P < 0.001), and the 28-day mortality rate was 4% and 44% (P < 0.001). The median disease-free survival was 12 and 1 months (P < 0.01), whereas the 12-month disease-free survival was 50% and 13% (P < 0.01) and the 36-month disease-free survival was 41% and 9% (P < 0.01). Thirteen of the patients treated with ATRA were given the treatment fully as outpatients. ATRA given as initial therapy decreased significantly early mortality in promyelocytic leukemia patients; because some promyelocytic leukemia patients given ATRA as initial therapy can be treated as outpatients, the costs of this treatment modality may be diminished.

Therapy of Molecular Relapse in Acute Promyelocytic Leukemia

Fourteen patients with PML/RAR-positive acute promyelocytic leukemia (APL) were given salvage therapy at the time of first molecular relapse. All patients had achieved first molecular remission after the AIDA protocol (all-trans retinoic acid [ATRA] + idarubicin) and were being prospectively monitored by reverse transcriptase-polymerase chain reaction (RT-PCR). Molecular relapse was defined as reappearance of RT-PCR–positivity for the PML/RAR fusion (sensitivity 10−4) in 2 successive marrow samples collected during postconsolidation monitoring. The median duration of first molecular remission was 7.5 months (range, 2 to 25). Salvage therapy consisted of oral ATRA for 30 days followed by 4 daily courses of chemotherapy (CHT) with cytarabine 1 g/m2/d and mitoxantrone 6 mg/m2/d. Second molecular remission was obtained in 12 of 14 patients (86%). Seven of these 12 attained molecular remission after ATRA alone. Of the 2 patients who persisted PCR+ after CHT, 1 died in remission and 1 progressed to hematologic relapse. Of 12 patients PCR−, 8 received consolidation with autologous bone marrow transplantation (ABMT), and 4 received ATRA-containing maintenance. Ten patients in this group are in sustained second molecular remission at a median time of 9.5+ months (range, 4 to 22+) and 2 underwent hematologic relapse 6 and 13 months, respectively, after transient second molecular remission. The 2-year Kaplan and Meier survival estimate from time of relapse was 92% (95% confidence interval [CI]: 61% to 98%) in this series, and 44% (95% CI: 35% to 52%) in a previous series of 37 patients who received the same treatment at the time of hematologic recurrence (P &lt; .05, by log-rank test). This study suggests that early administration of salvage therapy is advantageous in APL and represents the first experience on therapy of molecular relapse in acute leukemia.

Translocation (15;17)(q22;q21) as a secondary chromosomal abnormality in a case of acute monoblastic leukemia with tetrasomy 8

We describe a case of acute monoblastic leukemia (AML M5a), originally presenting as granulocytic sarcoma of the testis, showing unusual cytogenetic abnormalities. Tetrasomy 8 (primary) and t(15;17)(q22;q21) (secondary) were detected in bone marrow cells 6 months post-diagnosis, both by routine karyotype analysis and by fluorescence in situ hybridization (FISH) studies on metaphases and interphase nuclei. Retrospectively, the same abnormalities were identified in the primary testicular lesion using interphase FISH. However, reverse transcriptase polymerase chain reaction (RT-PCR) did not reveal the presence of a classic PML/RAR alpha fusion transcript. To the best of our knowledge, this is the first case to be reported in the literature of AML showing tetrasomy 8 in combination with secondary t(15;17).

Adenosine analogs as possible differentiation-inducing agents against acute myeloid leukemia

Several adenosine analogs induce the functional and morphological differentiation of myelomonocytic leukemia cells. They can be classified into two types; i.e., those that do/do not require phosphorylation to induce the differentiation of leukemia cells. Neplanocin A, a potent S-adenosylhomocysteine hydrolase inhibitor, induces the differentiation of some leukemia cells without phosphorylation. On the other hand, deoxycoformycin (dCF), a potent adenosine deaminase inhibitor, also induces the myelomonocytic differentiation of leukemia cells when it is treated with deoxyadenosine (dAdo). This differentiation is inhibited by 5'-amino-deoxyadenosine, an inhibitor of (deoxy)adenosine kinase, suggesting that kinase-dependent phosphorylation is involved in the differentiation-inducing effect of dCF plus dAdo. Retinoids induce the differentiation of NB4 cells, a cell line derived from human promyelocytic leukemia. When used in combination with all-trans retinoic acid (ATRA), both NPA and dCF plus dAdo greatly enhance the granulocytic differentiation of NB4 cells. This enhancing effect is greatest when the cells are pretreated with NPA and then with ATRA. On the other hand, pre-exposure of NB4 cells to ATRA greatly potentiates the differentiation induced by dCF plus dAdo, while pretreatment with dCF plus dAdo before exposure to ATRA is less effective. The ATRA-induced differentiation of NB4 cells is effectively augmented by clinically applicable concentrations of these analogs. A clinical strategy that combines intermittent treatment with these analogs and a low dose of ATRA may increase the clinical response and decrease the adverse effects of ATRA.

Dithiothreitol enhances arsenic trioxide-induced apoptosis in NB4 cells

Recently, arsenic trioxide (As2O3) was reported to induce clinical remission in patients with acute promyelocytic leukemia. Modulation of protein phosphorylation by binding to the vicinal thiols has been suggested as a possible mechanism. We found that phenylarsine oxide, a strong vicinal thiol-binding agent, neither induced nuclear fragmentation or DNA laddering nor increased caspase activity in NB4 cells; however, As2O3 and a weak thiol-binding agent, dimethylarsinic acid, did increase activity. Dithiothreitol (DTT) effectively suppressed the phenylarsine oxide-inhibited cellular reductive capacity, but unexpectedly, enhanced As2O3-induced apoptosis in NB4 cells. As2O3-induced and As2O3-plus-DTT-induced apoptosis in NB4 cells was modulated by oxidant modifiers, but not by nitric oxide synthase inhibitors. These results demonstrate that DTT, a dithiol agent and known antidote for trivalent inorganic arsenic, enhances the toxicity of As2O3, thereby opening a new research direction for the mechanisms of arsenic toxicity and perhaps also helping in the development of new therapeutic strategies for treating leukemias.

Presenting White Blood Cell Count and Kinetics of Molecular Remission Predict Prognosis in Acute Promyelocytic Leukemia Treated With All-Trans Retinoic Acid: Result of the Randomized MRC Trial

All-trans retinoic acid (ATRA) is an essential component of the treatment of acute promyelocytic leukemia (APL), but the optimal timing and duration remain to be determined. Molecular characterization of this disease can refine the diagnosis and could be potentially useful in monitoring response to treatment. Patients defined morphologically to have APL were randomized to receive a 5-day course of ATRA before commencing chemotherapy or to receive daily ATRA commencing with chemotherapy and continuing until complete remission (CR). The chemotherapy was that used in current MRC Leukaemia Trials. Outcome comparisons were by intention to treat with additional analysis for relevant risk factors. Patients were characterized by molecular techniques for the fusion products of the t(15;17) and monitored by reverse transcriptase-polymerase chain reaction (RT-PCR) during and after treatment. Two hundred thirty-nine patients were randomized. Treatment with extended ATRA resulted in a superior remission rate (87% v 70%, P < .001), due to fewer early and induction deaths (12% v 23%, P = .02), and less resistant disease (2% v 7%, P = .03), which was associated with a significantly more rapid recovery of neutrophils and platelets. Extended ATRA reduced relapse risk (20%v 36% at 4 years, P = .04) and resulted in superior survival (71% v 52% at 4 years, P = .005). Presenting white blood cell count (WBC) was a key determinant of outcome. The 70% of patients who presented with a WBC less than 10 × 109/L had a better CR (85% v62%, P = .0001) and reduced relapse risk (22% v42%, P = .002) and superior survival (69%v 43%, P < .0001). Within the low count group, extended ATRA resulted in a better CR (94% v 76%, P= .001), reduced relapse risk (13% v 35%, P = .04), and improved survival (80% v 57%, P = .0009). There was no evidence of benefit in patients presenting with a higher WBC (>10 × 109/L). Molecular monitoring after the third chemotherapy course had a correlation with risk of relapse. The relapse risk was 57% if the RT-PCR was positive versus 27% if the RT-PCR was negative (P = .006). APL patients who present with a low WBC derive substantial benefit from combining ATRA with induction chemotherapy until remission is achieved, whereas patients with a higher WBC did not benefit. Molecular characterization of disease can improve diagnostic precision and a positive RT-PCR after consolidation identifies patients at a higher risk of relapse.

Presenting White Blood Cell Count and Kinetics of Molecular Remission Predict Prognosis in Acute Promyelocytic Leukemia Treated With All-Trans Retinoic Acid: Result of the Randomized MRC Trial

All-trans retinoic acid (ATRA) is an essential component of the treatment of acute promyelocytic leukemia (APL), but the optimal timing and duration remain to be determined. Molecular characterization of this disease can refine the diagnosis and could be potentially useful in monitoring response to treatment. Patients defined morphologically to have APL were randomized to receive a 5-day course of ATRA before commencing chemotherapy or to receive daily ATRA commencing with chemotherapy and continuing until complete remission (CR). The chemotherapy was that used in current MRC Leukaemia Trials. Outcome comparisons were by intention to treat with additional analysis for relevant risk factors. Patients were characterized by molecular techniques for the fusion products of the t(15;17) and monitored by reverse transcriptase-polymerase chain reaction (RT-PCR) during and after treatment. Two hundred thirty-nine patients were randomized. Treatment with extended ATRA resulted in a superior remission rate (87% v 70%, P &lt; .001), due to fewer early and induction deaths (12% v 23%, P = .02), and less resistant disease (2% v 7%, P = .03), which was associated with a significantly more rapid recovery of neutrophils and platelets. Extended ATRA reduced relapse risk (20%v 36% at 4 years, P = .04) and resulted in superior survival (71% v 52% at 4 years, P = .005). Presenting white blood cell count (WBC) was a key determinant of outcome. The 70% of patients who presented with a WBC less than 10 × 109/L had a better CR (85% v62%, P = .0001) and reduced relapse risk (22% v42%, P = .002) and superior survival (69%v 43%, P &lt; .0001). Within the low count group, extended ATRA resulted in a better CR (94% v 76%, P= .001), reduced relapse risk (13% v 35%, P = .04), and improved survival (80% v 57%, P = .0009). There was no evidence of benefit in patients presenting with a higher WBC (&gt;10 × 109/L). Molecular monitoring after the third chemotherapy course had a correlation with risk of relapse. The relapse risk was 57% if the RT-PCR was positive versus 27% if the RT-PCR was negative (P = .006). APL patients who present with a low WBC derive substantial benefit from combining ATRA with induction chemotherapy until remission is achieved, whereas patients with a higher WBC did not benefit. Molecular characterization of disease can improve diagnostic precision and a positive RT-PCR after consolidation identifies patients at a higher risk of relapse.

Extramedullary disease in acute promyelocytic leukemia

All-trans retinoic acid (ATRA) is currently recommended as standard treatment for acute promyelocytic leukemia (APL). However there has been increasing concern that ATRA is associated with unusual sites of relapse. Although there is insufficient evidence so far to substantiate this, we review the potential mechanisms by which ATRA may increase the incidence of extramedullary and, in particular, central nervous system (CNS) relapse.

Diagnostic approaches to acute promyelocytic leukaemia

Delivering the most effective clinical therapy in acute promyelocytic leukaemia (APL) is dependent on accurately making the diagnosis. The morphological diagnosis can be improved by detecting the presence of a specific chromosome translocation, the t(15;17)(q22;q21). This can be achieved using cytogenetics, RT-PCR, FISH and anti-PML monoclonal antibody. The optimal approach will be rapid, accurate and readily integrated into the routine haematology laboratory. Immunofluorescent detection of microparticulate PML protein fulfils these criteria, however, karyotyping will also detect the variant translocations and remains the 'gold-standard'.

Adult acute myeloid leukaemia: update on treatment

Adult acute myeloid leukaemia (AML) is uncommon, with an age-standardised incidence of approximately 3 per 100,000. Patients present (median age, > 60 years) with evidence of bone marrow failure, anaemia, leukopenia or thrombocytopenia and their sequelae, or AML is detected incidentally by a full blood count. Treatment for AML aims to eliminate leukaemia from bone marrow with intensive chemotherapy: age (over or under 60 years) and performance status determines whether standard or high-dose chemotherapy can be used, but fewer than half the patients with AML are under 60 years. Supportive therapy during initial induction chemotherapy is needed to control neutropenic sepsis and thrombocytopenic bleeding, and to ameliorate the side effects of chemotherapy. Standard induction chemotherapy produces complete remission in 56%-74% of patients; 20% are long term survivors; 10%-15% of patients die in the induction period. Allogeneic haemopoietic stem cell transplantation is recommended in patients under 50 years with an HLA- compatible sibling, with the best outcomes achieved in patients transplanted in first complete remission. It can also provide long term survival in patients who fail to achieve remission after induction therapy. The outcome of AML has improved, particularly for younger patients, but treatment outcomes for older patients and those with secondary leukaemia are still unsatisfactory. The mean overall survival of patients in randomised studies treated with standard therapy is still only 9-15 months.

Complete remission after treatment of acute promyelocytic leukemia with arsenic trioxide

BACKGROUND

Two reports from China have suggested that arsenic trioxide can induce complete remissions in patients with acute promyelocytic leukemia (APL). We evaluated this drug in patients with APL in an attempt to elucidate its mechanism of action.

METHODS

Twelve patients with APL who had relapsed after extensive prior therapy were treated with arsenic trioxide at doses ranging from 0.06 to 0.2 mg per kilogram of body weight per day until visible leukemic cells were eliminated from the bone marrow. Bone marrow mononuclear cells were serially monitored by flow cytometry for immunophenotype, fluorescence in situ hybridization, reverse-transcription-polymerase-chain-reaction (RT-PCR) assay for PML-RAR-alpha fusion transcripts, and Western blot analysis for expression of the apoptosis-associated proteins caspases 1, 2, and 3.

RESULTS

Of the 12 patients studied, 11 achieved complete remission after treatment that lasted from 12 to 39 days (range of cumulative doses, 160 to 495 mg). Adverse effects were relatively mild and included rash, lightheadedness, fatigue, and musculoskeletal pain. Cells that expressed both CD11b and CD33 (antigens characteristic of mature and immature cells, respectively), and which were found by fluorescence in situ hybridization to carry the t(15;17) translocation, increased progressively in number during treatment and persisted in the early phase of complete remission. Eight of 11 patients who initially tested positive for the PML-RAR-alpha fusion transcript by the RT-PCR assay later tested negative; 3 other patients, who persistently tested positive, relapsed early. Arsenic trioxide induced the expression of the proenzymes of caspase 2 and caspase 3 and activation of both caspase 1 and caspase 3.

CONCLUSIONS

Low doses of arsenic trioxide can induce complete remissions in patients with APL who have relapsed. The clinical response is associated with incomplete cytodifferentiation and the induction of apoptosis with caspase activation in leukemic cells.

Detection of karyotypic aberrations in acute myeloblastic leukaemia: a prospective comparison between PCR/FISH and standard cytogenetics in 140 patients with de novo AML

In 140 patients with de novo acute myeloid leukaemia (AML) standard cytogenetics were compared with RT-PCR for the detection of t(8;21), t(15;17) and inv(16) and fluorescence in situ hybridization (FISH) for numerical aberrations of chromosomes 7, 8, X and Y. RT-PCR detected 18 cases with t(8;21), 12 with t(15;17) and seven with inv(16). In two cases with t(8;21), two with t(15;17) and four with inv(16) these aberrations had not been detected by standard cytogenetics. There were no false negative PCR results. In 12 patients with these chromosomal changes, standard cytogenetics revealed additional chromosomal aberrations. In 16 patients sole numerical aberrations of the chromosomes 7, 8, X or Y were found by FISH. In these patients the sensitivity of FISH and standard cytogenetics was comparable. In 87 patients no aberrations could be found by PCR and FISH whereas in 24 of these patients standard cytogenetics revealed an abnormal karyotype. These data recommend the combination of standard cytogenetics and molecular techniques to improve the sensitivity for the detection of genetic lesions in AML. Once chromosomal markers have been identified by combined analysis these markers could be used to monitor residual disease during/after chemotherapy, by RT-PCR and/or FISH.

Targeting of PML/RAR Is Lethal to Retinoic Acid–Resistant Promyelocytic Leukemia Cells

Acute promyelocytic leukemia (APL) cells, containing the t(15;17) rearrangement, express the fusion protein, PML/RAR. Clinically, patients respond to all-trans retinoic acid (ATRA) through complete remissions associated with myeloid maturation of leukemic cells. This clinical ATRA response of APL is linked to PML/RAR expression. Unfortunately, these remissions are transient and relapsed APL is often ATRA-resistant. The role PML/RAR plays in the growth and maturation of these APL cells with acquired ATRA resistance has not been fully explored. This study uses an ATRA-resistant NB4 cell line (NB4-R1) to investigate the contribution of PML/RAR expression to ATRA resistance. Targeting of PML/RAR in NB4-R1 cells was undertaken using two approaches: homologous recombination and hammerhead ribozyme-mediated cleavage. Reducing PML/RAR protein in NB4-R1 cells rendered these cells more sensitive to ATRA. These cells were growth-inhibited in ATRA, apoptosis was induced, and there was no apparent signaling of differentiation. Sequence analysis identified a mutation in the ligand binding domain (LBD) of the RAR portion of PML/RAR. Results show that these retinoid-resistant NB4 cells require persistent PML/RAR expression for leukemic cell growth. Taken together, these findings can account for why these cells do not respond to ATRA and how reduction of PML/RAR abrogates the antiapoptotic effect it confers to these leukemic cells.

© 1998 by The American Society of Hematology.

Targeting of PML/RAR Is Lethal to Retinoic Acid–Resistant Promyelocytic Leukemia Cells

Acute promyelocytic leukemia (APL) cells, containing the t(15;17) rearrangement, express the fusion protein, PML/RAR. Clinically, patients respond to all-trans retinoic acid (ATRA) through complete remissions associated with myeloid maturation of leukemic cells. This clinical ATRA response of APL is linked to PML/RAR expression. Unfortunately, these remissions are transient and relapsed APL is often ATRA-resistant. The role PML/RAR plays in the growth and maturation of these APL cells with acquired ATRA resistance has not been fully explored. This study uses an ATRA-resistant NB4 cell line (NB4-R1) to investigate the contribution of PML/RAR expression to ATRA resistance. Targeting of PML/RAR in NB4-R1 cells was undertaken using two approaches: homologous recombination and hammerhead ribozyme-mediated cleavage. Reducing PML/RAR protein in NB4-R1 cells rendered these cells more sensitive to ATRA. These cells were growth-inhibited in ATRA, apoptosis was induced, and there was no apparent signaling of differentiation. Sequence analysis identified a mutation in the ligand binding domain (LBD) of the RAR portion of PML/RAR. Results show that these retinoid-resistant NB4 cells require persistent PML/RAR expression for leukemic cell growth. Taken together, these findings can account for why these cells do not respond to ATRA and how reduction of PML/RAR abrogates the antiapoptotic effect it confers to these leukemic cells.

© 1998 by The American Society of Hematology.

Early Detection of Relapse by Prospective Reverse Transcriptase-Polymerase Chain Reaction Analysis of the PML/RARα Fusion Gene in Patients With Acute Promyelocytic Leukemia Enrolled in the GIMEMA-AIEOP Multicenter “AIDA” Trial

Although the majority of patients with acute promyelocytic leukemia (APL) are potentially cured by treatments combining all-trans retinoic acid (ATRA) and chemotherapy (CHT), a sizable proportion (around 30%) will relapse during follow-up. Retrospective molecular monitoring studies using reverse transcriptase-polymerase chain reaction (RT-PCR) for the specific PML/RARα fusion gene, have shown that a positive test usually precedes the occurrence of hematologic relapse. Prospective RT-PCR analyses were performed since 1993 at diagnosis and at preestablished time intervals during follow-up in bone marrow (BM) samples of 163 patients with PML/RARα+ APL enrolled in the multicenter Gruppo Italiano Malattie Ematologiche Maligne dell' Adulto (GIMEMA) trial AIDA (All-trans retinoic acid plus Idarubicin). Treatment consisted of ATRA and idarubicin for induction followed by three polychemotherapy courses as consolidation. The sensitivity level of the RT-PCR assay for PML/RARα, as assessed by serial dilution experiments, was 10−4. All patients were in hematologic remission and tested PCR− at the end of consolidation. Of 21 who converted to PCR-positive thereafter, 20 underwent hematologic relapse at a median time of 3 months (range, 1 to 14) from the first PCR+ result. Seventeen of these 21 (81%) PCR+ conversions were recorded within the first 6 months postconsolidation. Of 142 who tested persistently PCR− in ≥2 tests after consolidation, 8 had hematologic relapse and 134 remained in complete remission (CR) after a median follow-up of 18 months (range, 6 to 38) postconsolidation. Using a time-dependent Cox model, the relative risk of hematologic relapse of patients who converted to PCR+ was 31.8 (confidence limits 95%, 12.9 to 78.3). Our results indicate that conversion to PCR positivity for PML/RARα during remission is highly predictive of subsequent hematologic relapse and highlight the prognostic value of stringent molecular monitoring during the early postconsolidation phase in APL. As a result of the present study, salvage treatment in patients enrolled in the GIMEMA trial AIDA is now anticipated at the time of molecular relapse, defined as the conversion to PCR positivity in two successive BM samplings during follow-up.

© 1998 by The American Society of Hematology.

Early Detection of Relapse by Prospective Reverse Transcriptase-Polymerase Chain Reaction Analysis of the PML/RARα Fusion Gene in Patients With Acute Promyelocytic Leukemia Enrolled in the GIMEMA-AIEOP Multicenter “AIDA” Trial

Although the majority of patients with acute promyelocytic leukemia (APL) are potentially cured by treatments combining all-trans retinoic acid (ATRA) and chemotherapy (CHT), a sizable proportion (around 30%) will relapse during follow-up. Retrospective molecular monitoring studies using reverse transcriptase-polymerase chain reaction (RT-PCR) for the specific PML/RARα fusion gene, have shown that a positive test usually precedes the occurrence of hematologic relapse. Prospective RT-PCR analyses were performed since 1993 at diagnosis and at preestablished time intervals during follow-up in bone marrow (BM) samples of 163 patients with PML/RARα+ APL enrolled in the multicenter Gruppo Italiano Malattie Ematologiche Maligne dell' Adulto (GIMEMA) trial AIDA (All-trans retinoic acid plus Idarubicin). Treatment consisted of ATRA and idarubicin for induction followed by three polychemotherapy courses as consolidation. The sensitivity level of the RT-PCR assay for PML/RARα, as assessed by serial dilution experiments, was 10−4. All patients were in hematologic remission and tested PCR− at the end of consolidation. Of 21 who converted to PCR-positive thereafter, 20 underwent hematologic relapse at a median time of 3 months (range, 1 to 14) from the first PCR+ result. Seventeen of these 21 (81%) PCR+ conversions were recorded within the first 6 months postconsolidation. Of 142 who tested persistently PCR− in ≥2 tests after consolidation, 8 had hematologic relapse and 134 remained in complete remission (CR) after a median follow-up of 18 months (range, 6 to 38) postconsolidation. Using a time-dependent Cox model, the relative risk of hematologic relapse of patients who converted to PCR+ was 31.8 (confidence limits 95%, 12.9 to 78.3). Our results indicate that conversion to PCR positivity for PML/RARα during remission is highly predictive of subsequent hematologic relapse and highlight the prognostic value of stringent molecular monitoring during the early postconsolidation phase in APL. As a result of the present study, salvage treatment in patients enrolled in the GIMEMA trial AIDA is now anticipated at the time of molecular relapse, defined as the conversion to PCR positivity in two successive BM samplings during follow-up.

© 1998 by The American Society of Hematology.

Wilms tumor gene (WT1) as a new marker for the detection of minimal residual disease in leukemia

WT1 (Wilms tumor gene) expression is a new tumor marker of leukemic blast cells of AML, ALL, and CML. Minimal residual disease (MRD) of leukemia can be detected at frequencies as low as 1 in 10(3) to 10(4) normal bone marrow (BM) cells and 1 in 10(5) normal peripheral blood (PB) cells by means of the quantitation of expression levels of the WT1 gene using reverse transcriptase-polymerase chain reaction (RT-PCR). This is regardless of the types of leukemia or the presence or absence of tumor-specific DNA markers. Thus, the WT1 assay makes it possible to rapidly assess the effectiveness of treatment and to evaluate the degree of eradication of leukemic cells in individual leukemia patients. Moreover, molecular relapse using PCR can be diagnosed by the monitoring of WT1 expression levels in BM or PB 1-24 months (means, 7 months for BM and 8 months for PB) before the clinical relapse became apparent. In case of rapid or gradual increase in WT1 expression levels to or over 10(-2) after return to normal BM levels during CR; or retention of the WTI expression at levels near or over 10(-2) in BM without return to normal BM levels even in CR (WT1 expression level in K562 cells was defined as 1.0), it seems that clinical relapse is impending. Since WT1 antisense oligomers inhibit the growth of leukemic cells, it is apparent that the WT1 gene plays an important role in leukemogenesis.

A study to determine whether trisomy 8, deleted 9q and trisomy 22 are markers of cryptic rearrangements of PML/RARalpha, AML1/ETO and CBFB/MYH11 respectively in acute myeloid leukaemia. MRC Adult Leukaemia Working Party. Medical Research Council

Acute myeloid leukaemia (AML) patients with either a t(15;17), t(8;21) or inv(16) at diagnosis have 'good-risk' disease with a favourable response to therapy and improved survival. Detection of cryptic fusion genes created by these translocations has been reported where there is no cytogenetic evidence of the corresponding abnormality. It is likely that these cases share the same favourable prognosis. Secondary cytogenetic changes commonly associated with these rearrangements are +8 with t(15;17), del(9q) with t(8;21) and +22 with inv(16). These secondary abnormalities are also observed alone, raising the possibility that they may be markers of underlying cryptic rearrangements. In order to determine the frequency of these rearrangements in AML cases with +8, del(9q) or +22 we have performed an analysis of 63 such patients in whom there was no evidence of a t(15;17), t(8;21) or inv(16) by cytogenetics. No disease-related fusion transcripts were identified, indicating that the secondary changes are rarely markers for cryptic rearrangements.

All-trans-retinoic acid in acute promyelocytic leukemia

BACKGROUND

All-trans-retinoic acid induces complete remission in acute promyelocytic leukemia. However, it is not clear whether induction therapy with all-trans-retinoic acid is superior to chemotherapy alone or whether maintenance treatment with all-trans-retinoic acid improves outcome.

METHODS

Three hundred forty-six patients with previously untreated acute promyelocytic leukemia were randomly assigned to receive all-trans-retinoic acid or daunorubicin plus cytarabine as induction treatment. Patients who had a complete remission received consolidation therapy consisting of one cycle of treatment identical to the induction chemotherapy, then high-dose cytarabine plus daunorubicin. Patients still in complete remission after two cycles of consolidation therapy were then randomly assigned to maintenance treatment with all-trans-retinoic acid or to observation.

RESULTS

Of the 174 patients treated with chemotherapy, 120 (69 percent) had a complete remission, as did 124 of the 172 (72 percent) given all-trans-retinoic acid (P=0.56). When both induction and maintenance treatments were taken into account, the estimated rates of disease-free survival at one, two, and three years were 77, 61, and 55 percent, respectively, for patients assigned to chemotherapy then all-trans-retinoic acid; 86, 75, and 75 percent for all-trans-retinoic acid then all-trans-retinoic acid; 75, 60, and 60 percent for all-trans-retinoic acid then observation; and 29, 18, and 18 percent for chemotherapy then observation. By intention-to-treat analysis, the rates of overall survival at one, two, and three years after entry into the study were 75, 57, and 50 percent, respectively, among patients assigned to chemotherapy, and 82, 72, and 67 percent among those assigned to all-trans-retinoic acid (P= 0.003).

CONCLUSIONS

All-trans-retinoic acid as induction or maintenance treatment improves disease-free and overall survival as compared with chemotherapy alone and should be included in the treatment of acute promyelocytic leukemia.

Characterization of the Retinoid Binding Properties of the Major Fusion Products Present in Acute Promyelocytic Leukemia Cells

The bcr1- and bcr3- promyelocytic leukemia/retinoic acid receptor α (PML/RARα) are the two major fusion proteins expressed in acute promyelocytic leukemia (APL) patients. These proteins, which are present in different lengths of PML (amino acids 1-552 and 1-394, respectively), contain most of the functional domains of PML and RARα, bind all-trans-retinoic acid (t-RA), and act as t-RA–dependent transcription factors. T-RA is an effective inducer of clinical remission only in patients carrying the t(15; 17) and expressing the PML/RARα products. However, in APL patients achieving complete remission with t-RA therapy the bcr3-PML/RARα product has been found associated with a poorer prognosis than bcr1-PML/RARα. In the present study we have investigated the structural and functional properties of the bcr3-PML/RARα in comparison to the previously characterized bcr1-PML/RARα. In particular, we have measured the binding properties of the two endogenous ligands t-RA and 9-cis-RA to both of these isoforms. T-RA binding analysis of nuclear and cytosolic extracts prepared from bcr3-PML/RARα APL patients and from bcr3-PML/RARα COS-1 transfected cells indicates that this protein is present only as high-molecular-weight nuclear complexes. Using saturation binding assays and Scatchard analyses we found that t-RA binds with slightly less affinity to the bcr3-PML/RARα receptor than to bcr1-PML/RARα or RARα (Kd = 0.4 nmol/L, 0.13 nmol/L or 0.09 nmol/L, respectively). Moreover, two different high-affinity 9-cis-RA binding sites (Kd = 0.45 and 0.075 nmol/L) were detectable in the bcr3-PML/RARα product but not in the bcr1-PML/RARα product (Kd = 0.77 nmol/L). By competition binding experiments we showed that 9-cis-RA binds with higher specificity to the bcr3-PML/RARα isoform than to the bcr1-PML/RARα or RARα. Consistent with these data, the binding of 9-cis-RA to the bcr3-PML/RARα product resulted in increased transcriptional activation of the RA-responsive element (RARE) TRE, but not of the βRARE, in transiently transfected COS-1 cells. These results provide evidence indicating that preferential retinoid binding to the different PML/RARα products can be measured.

Autologous Bone Marrow Transplantation for Acute Promyelocytic Leukemia in Second Remission: Prognostic Relevance of Pretransplant Minimal Residual Disease Assessment by Reverse-Transcription Polymerase Chain Reaction of the PML/RARα Fusion Gene

Reverse-transcription polymerase chain reaction (RT-PCR) of the PML/RARα fusion gene may predict relapse in acute promyelocytic leukemia (APL) patients in hematologic complete remission (CR). We have prospectively studied by RT-PCR 15 PML/RARα+ APL patients undergoing autologous bone marrow transplantation (ABMT) in second CR. The median time of first CR duration was 12 months (range, 6 to 40). All patients were reinduced with all-trans retinoic acid (ATRA), followed in 12 of 15 cases by mitoxantrone and Ara-C as consolidation. Fourteen patients received the BAVC (BCNU, Ara-C, m-AMSA, and VP-16) schedule as conditioning regimen. Unpurged marrows were collected immediately before conditioning treatment, analyzed by RT-PCR, and reinfused at median of 2 months (range, 2 to 7) from the achievement of second CR. Seven patients were PCR+ and eight PCR− for PML/RARα in their pretransplant marrows. All seven patients of the former group remained PCR+ during the follow-up and relapsed at a median time of 5 months (range, 2 to 9) from ABMT and 9 months (range, 4 to 14) from second CR. Of the eight PCR− patients, all remained PCR− during the follow-up controls. One patient relapsed at 10 months from ABMT, one died of a secondary (PML/RARα−) leukemia, and six are in hematologic and molecular remission at a median time of 28 months (range, 15 to 60) after ABMT and 32 months (range, 17 to 62) from second CR. Our results indicate that, in APL patients in second CR, ABMT with PML/RARα− marrow cells is likely to result in prolonged clinical and molecular remissions. Conversely, patients who test PCR+ after reinduction necessitate the use of alternative aggressive approaches, including unrelated allogeneic transplant.

Autologous Bone Marrow Transplantation for Acute Promyelocytic Leukemia in Second Remission: Prognostic Relevance of Pretransplant Minimal Residual Disease Assessment by Reverse-Transcription Polymerase Chain Reaction of the PML/RARα Fusion Gene

Reverse-transcription polymerase chain reaction (RT-PCR) of the PML/RARα fusion gene may predict relapse in acute promyelocytic leukemia (APL) patients in hematologic complete remission (CR). We have prospectively studied by RT-PCR 15 PML/RARα+ APL patients undergoing autologous bone marrow transplantation (ABMT) in second CR. The median time of first CR duration was 12 months (range, 6 to 40). All patients were reinduced with all-trans retinoic acid (ATRA), followed in 12 of 15 cases by mitoxantrone and Ara-C as consolidation. Fourteen patients received the BAVC (BCNU, Ara-C, m-AMSA, and VP-16) schedule as conditioning regimen. Unpurged marrows were collected immediately before conditioning treatment, analyzed by RT-PCR, and reinfused at median of 2 months (range, 2 to 7) from the achievement of second CR. Seven patients were PCR+ and eight PCR− for PML/RARα in their pretransplant marrows. All seven patients of the former group remained PCR+ during the follow-up and relapsed at a median time of 5 months (range, 2 to 9) from ABMT and 9 months (range, 4 to 14) from second CR. Of the eight PCR− patients, all remained PCR− during the follow-up controls. One patient relapsed at 10 months from ABMT, one died of a secondary (PML/RARα−) leukemia, and six are in hematologic and molecular remission at a median time of 28 months (range, 15 to 60) after ABMT and 32 months (range, 17 to 62) from second CR. Our results indicate that, in APL patients in second CR, ABMT with PML/RARα− marrow cells is likely to result in prolonged clinical and molecular remissions. Conversely, patients who test PCR+ after reinduction necessitate the use of alternative aggressive approaches, including unrelated allogeneic transplant.

Common defects of different retinoic acid resistant promyelocytic leukemia cells are persistent telomerase activity and nuclear body disorganization

The acute promyelocytic leukemia (APL) t(15;17) rearrangement fuses the promyelocytic leukemia (PML) gene to the retinoic acid receptor-alpha (RAR alpha). There is expression of the chimeric transcript, PML/RAR alpha, in these APL cells. These clinical APL cases respond to the differentiation agent all-trans retinoic acid (ATRA) with complete but not durable remissions because ATRA resistance develops. The NB4 APL cell line expresses PML/RAR alpha and responds to the growth inhibitory and differentiation-inducing signals of ATRA. To identify mechanisms responsible for ATRA resistance in APL, ATRA-resistant NB4 cell lines were derived from parental NB4 cells using different strategies. These lines were resistant to the growth inhibition and differentiation effects of ATRA. ATRA-resistant cells were isolated as a de novo resistant line from parental NB4 cells (NB4-R1), following chemical mutagenization and selection in ATRA (NB4-R2), or after chronic selection in ATRA (NB4-R3). Common defects linked to this ATRA resistance were found. When cultured in ATRA, these resistant cells still express PML, RAR alpha, and PML/RAR alpha proteins. Sequence abnormalities were not detected in the RAR alpha DNA binding domains cloned from a representative RA-resistant NB4 line. In ATRA-sensitive but not ATRA-resistant NB4 cells, ATRA down-regulated retinoid X receptor-alpha (RXR alpha) expression, a known marker of ATRA response in parental NB4 cells. Notably, engineered overexpression of RXR alpha in ATRA-sensitive NB4 cells did not block ATRA-mediated growth suppression. ATRA treatment of these resistant NB4 lines did not signal a decline in telomerase activity or reorganization of PML-associated nuclear bodies, but both events occurred in ATRA-sensitive NB4 cells. These ATRA-resistant NB4 lines are not fully differentiation-defective, since monocytic maturation was induced following treatment with phorbol 12-myristate 13-acetate (PMA) and 1,25 dihydroxy vitamin D3 (vitamin D3). Notably, induced monocytic differentiation of these distinct ATRA-resistant APL lines markedly repressed telomerase activity. Thus, this study suggests that persistent telomerase activity and nuclear body disorganization are linked to ATRA resistance in APL.