Effective targeting of chronic myeloid leukemia initiating activity with the combination of arsenic trioxide and interferon alpha

Imatinib is the standard of care in chronic meloid leukemia (CML) therapy. However, imatinib is not curative since most patients who discontinue therapy relapse indicating that leukemia initiating cells (LIC) are resistant. Interferon alpha (IFN) induces hematologic and cytogenetic remissions and interestingly, improved outcome was reported with the combination of interferon and imatinib. Arsenic trioxide was suggested to decrease CML LIC. We investigated the effects of arsenic and IFN on human CML cell lines or primary cells and the bone marrow retroviral transduction/transplantation murine CML model. In vitro, the combination of arsenic and IFN inhibited proliferation and activated apoptosis. Importantly, arsenic and IFN synergistically reduced the clonogenic activity of primary bone marrow cells derived from CML patients. Finally, in vivo, combined interferon and arsenic treatment, but not single agents, prolonged the survival of primary CML mice. Importantly, the combination severely impaired engraftment into untreated secondary recipients, with some recipients never developing the disease, demonstrating a dramatic decrease in CML LIC activity. Arsenic/IFN effect on CML LIC activity was significantly superior to that of imatinib. These results support further exploration of this combination, alone or with imatinib aiming at achieving CML eradication rather than long-term disease control.

Loss of the Y chromosome in Philadelphia-positive cells predicts a poor response of chronic myeloid leukemia patients to imatinib mesylate therapy

In chronic myeloid leukemia (CML), cytogenetic abnormalities found in addition to the t(9;22) translocation may impact the response to therapy. Loss of the Y chromosome is generally overlooked in this context, owing to its relatively frequent occurrence in healthy elderly patients. In this multicenter retrospective study, the outcome after imatinib treatment of 30 CML patients with karyotype showing Y chromosome loss (Y-) was compared to 30 Y+ control males diagnosed and treated at the same time in the same institutions. Y- patients had significantly delayed cytogenetic and molecular responses, lower event-free survival and shorter overall survival than Y+ patients. The negative impact of this abnormality was particularly marked when it occurred in a sub-clone (clonal evolution) rather than in all mitoses. These data indicate that loss of the Y chromosome should be taken into account in the prognostic evaluation of chronic myelogenous leukemia patients.

Adherence is the critical factor for achieving molecular responses in patients with chronic myeloid leukemia who achieve complete cytogenetic responses on imatinib

PURPOSE

There is a considerable variability in the level of molecular responses achieved with imatinib therapy in patients with chronic myeloid leukemia (CML). These differences could result from variable therapy adherence.

METHODS

Eighty-seven patients with chronic-phase CML treated with imatinib 400 mg/d for a median of 59.7 months (range, 25 to 104 months) who had achieved complete cytogenetic response had adherence monitored during a 3-month period by using a microelectronic monitoring device. Adherence was correlated with levels of molecular response. Other factors that could influence outcome were also analyzed.

RESULTS

Median adherence rate was 98% (range, 24% to 104%). Twenty-three patients (26.4%) had adherence <or= 90%; in 12 of these patients (14%), adherence was <or= 80%. There was a strong correlation between adherence rate (<or= 90% or > 90%) and the 6-year probability of a 3-log reduction (also known as major molecular response [MMR]) in BCR-ABL1 transcripts (28.4% v 94.5%; P < .001) and also complete molecular response (CMR; 0% v 43.8%; P = .002). Multivariate analysis identified adherence (relative risk [RR], 11.7; P = .001) and expression of the molecular human organic cation transporter-1 (RR, 1.79; P = .038) as the only independent predictors for MMR. Adherence was the only independent predictor for CMR. No molecular responses were observed when adherence was <or= 80% (P < .001). Patients whose imatinib doses were increased had poor adherence (86.4%). In this latter population, adherence was the only independent predictor for inability to achieve an MMR (RR, 17.66; P = .006).

CONCLUSION

In patients with CML treated with imatinib for some years, poor adherence may be the predominant reason for inability to obtain adequate molecular responses.

The effect of imatinib (Glivec) on scleroderma and normal dermal fibroblasts: a preclinical study

BACKGROUND

Scleroderma skin overexpresses the platelet-derived growth factor receptor beta-subunit (PDGFR-beta) in dermal vessels and PDGFR-beta messenger RNA in cultured fibroblasts. Moreover, increased levels of PDGF and stimulatory autoantibodies to PDGFR have been identified in the serum of scleroderma patients.

OBJECTIVE

Imatinib being an inhibitor of tyrosine kinase receptors such as PDGFR, its effect on scleroderma fibroblasts was evaluated in vitro as a preclinical therapeutic step.

METHODS

The effect of imatinib on fibroblasts grown from normal or involved/uninvolved scleroderma skin was studied by Western blot and the methyltetrazolium test. The pattern of distribution of PDGFR-beta in scleroderma versus normal skin was studied by immunohistochemistry.

RESULTS

In vitro, imatinib inhibited the proliferation of normal dermal and scleroderma fibroblasts at least partly via the inhibition of the phosphorylation of PDGFR. PDGFR-beta was expressed in the epidermis and adnexae in 5 lesional scleroderma biopsies and not in controls.

CONCLUSION

This study suggests that imatinib can serve as therapy to limit dermal fibroblast proliferation in scleroderma.

Trough imatinib plasma levels are associated with both cytogenetic and molecular responses to standard-dose imatinib in chronic myeloid leukemia

Using high-performance liquid chromatography-tandem mass spectrometry, we assessed trough imatinib plasma levels in 68 patients with chronic myeloid leukemia (CML) who responded or not to standard-dose imatinib, after at least 12 months' treatment. Mean trough imatinib plasma levels were significantly higher in the group with complete cytogenetic response (56 patients) than in the group without (12 patients; P = .03) and higher in the group with major molecular response (MMR) than in the group without (34 patients [1452 +/- 649 ng/mL] versus 34 patients [869 +/- 427 ng/mL]; P < .001). Regarding trough imatinib plasma levels and their discrimination potential for MMR, the area under receiver operating characteristic curve was 0.775, with best sensitivity (77%) and specificity (71%) at a plasma threshold of 1002 ng/mL. Therefore, monitoring of imatinib plasma levels could be very useful for the management of patients with CML or should at least be checked in the case of treatment failure or suboptimal response.

Lack of response to imatinib mesylate in a patient with accelerated phase myeloproliferative disorder with rearrangement of the platelet-derived growth factor receptor beta-gene

Imatinib mesylate has been reported to produce positive results in atypical chronic myeloproliferative disorders (CMD) with chromosomal translocations that disrupt the platelet-derived growth factor receptor beta gene (PDGFRB). We used imatinib to treat a 49-year old man with atypical CMD in accelerated phase and the H4 (D10S170)-PDGFRB fusion gene. After 3 months of treatment, we observed grade 4 hematologic toxicity and a lack of response.

Efficacy of dual-specific Bcr-Abl and Src-family kinase inhibitors in cells sensitive and resistant to imatinib mesylate

Monotherapy of chronic myeloid leukemia (CML) with imatinib mesylate has been cast into shadow by the evolution of clinical resistance during therapy. Resistance to imatinib can arise by multiple mechanisms including amplification or mutation of Bcr-Abl, and continuity of imatinib therapy is probably a poor option for either of these patient groups. Recently, however, a structurally distinct new class of drugs, the pyrido[2,3-d]pyrimidines, has been described, and these compounds are predicted to make different molecular contacts in the Abl kinase domain. These drugs potently target both the Bcr-Abl and Src-family kinase activities, both of which are thought to be relevant to survival of the leukemic cell. We asked whether these drugs could selectively induce cell death in murine cell line models of CML cells sensitive and resistant to imatinib by different mechanisms. We show that whereas the pyrido[2,3-d] pyrimidines are indeed highly potent in suppressing proliferation of Bcr-Abl-overexpressing imatinib-resistant cells, they are almost completely ineffective against cells expressing the T315I mutant. This implies that despite structural differences from imatinib, these drugs are unlikely to be useful in patients expressing this mutant Bcr-Abl protein, but may be effective in cases where selection of cells overexpressing the oncoprotein leads to refractoriness to imatinib.

Results of a prospective phase 2 study combining imatinib mesylate and cytarabine for the treatment of Philadelphia-positive patients with chronic myelogenous leukemia in chronic phase

In chronic myelogenous leukemia (CML) imatinib mesylate has been shown to selectively inhibit the tyrosine kinase domain of the oncogenic bcr-abl fusion protein. Using this agent alone high rates of cytogenetic responses were recorded. However, several mechanisms of resistance have been described. In vitro studies examining the effects of imatinib mesylate plus cytarabine have shown synergistic antiproliferative effects of this combination. Thus, the CML French Group decided to perform a phase 2 trial testing a combination of imatinib mesylate and low-dose cytarabine in 30 previously untreated patients in chronic phase. Treatment was administered on 28-day cycles. Patients were treated continuously with imatinib mesylate orally at a dose of 400 mg daily. Cytarabine was given on days 15 to 28 of each cycle at an initial dose of 20 mg/m2/d via subcutaneous injection. Adverse events were frequently observed with grade 3 or 4 hematologic toxicities and nonhematologic toxicities in 53% (n = 16) and 23% (n = 7) of patients, respectively. The cumulative incidence of complete cytogenetic response (CCR) at 12 months was 83% and at 6 months 100% of the patients achieved complete hematologic response (CHR). We concluded that the combination was safe and promising given the rates of response.

Prognosis and prognostic factors for patients with chronic myeloid leukemia: nontransplant therapy

Reliable knowledge about an individual's prognosis is needed to select the appropriate treatment for patients with chronic myeloid leukemia (CML). The New CML score using age, spleen size, blast cell count, eosinophil count, basophil count, and platelet count shows good discrimination for survival (96, 65, or 42 months, P </=.0001) and has been thoroughly validated. Careful analyses indicate that the New CML score is considerably more precise in identifying high-risk patients than the Sokal score. Achievement of complete hematologic response (CHR) up to 9 months shows a distinct impact on survival, which, however, depends on the baseline prognosis. Ten-year survival probabilities for low- and intermediate-risk patients with a CHR were 0.51 (95% confidence interval [CI], 0.42 to 0.60) and 0.23 (95% CI, 0.15 to 0.31) and without a CHR were 0.26 (95% CI, 0.16 to 0.37) and 0.12 (95% CI, 0.04 to 0.20). In high-risk patients CHR had no impact on prognosis. Therapeutic options were widened by the approval of imatinib for the treatment of CML. However, it will still take 2 or more years to know whether the high rates of CHR and cytogenetic complete remission (CCR) achieved with imatinib translate into a clinically relevant survival advantage for all patients.

Drug responses of imatinib mesylate-resistant cells: synergism of imatinib with other chemotherapeutic drugs

Imatinib mesylate (STI571, Glivec, Gleevec) is a powerful inhibitor of the tyrosine kinase activity of Bcr-Abl, the oncoprotein responsible for chronic myeloid leukemia (CML). The drug shows great efficacy in chronic phase, but is less effective in maintaining hematologic remissions in blast crisis patients. Our group has previously described several cell lines made resistant to imatinib. We now examine the question of cross-resistance to other chemotherapeutic drugs used in CML. Four paired imatinib-sensitive/resistant CML cell lines were assessed by caspase-3 and MTS assays for their proliferative response to cytosine arabinoside (Ara-C), daunorubicin (DNR), homoharringtonine (HHT) and hydroxyurea (HU), either alone or in combination with imatinib. Primary blasts from advanced-stage CML patients refractory to imatinib therapy were studied by semi-solid media clonogenic assays. We found that these drugs are generally capable of major inhibition of proliferation of the CML cell lines, although differential responses to DNR and HHT were noted between some sensitive and resistant cell line pairs, implying that resistance to imatinib may confer a growth advantage under such conditions. The four drugs were also effective in preventing the formation of progenitor cell colonies from CML patients both before treatment with imatinib, and after relapse on the drug. Isobolographic analysis implied that these drugs will generally combine well with imatinib, and in some cases will be synergistic. We conclude that Ara-C, DNR or HHT, either alone or in combination with imatinib, are likely to be the best therapeutic alternatives in the management of patients who become resistant to imatinib monotherapy.

Overcoming STI571 resistance with the farnesyl transferase inhibitor SCH66336

The development of chronic myeloid leukemia (CML) is dependent on the deregulated tyrosine kinase of the oncoprotein BCR-ABL. STI571 (imatinib mesylate), an abl tyrosine kinase inhibitor, has proven remarkably effective for the treatment of CML. However, resistance to STI571 because of enhanced expression or mutation of the BCR-ABL gene has been detected in patients. In the current study we show that the farnesyl transferase inhibitor (FTI) SCH66336 (lonafarnib) inhibits the proliferation of STI571-resistant BCR-ABL-positive cell lines and hematopoietic colony formation from peripheral blood samples of STI571-resistant patients with CML. Moreover, SCH66336 enhances STI571-induced apoptosis in STI571-sensitive cells and, in patients with STI571 resistance from gene amplification, cooperates with STI571 to induce apoptosis. Our data provide a rationale for combination clinical trials of STI571 and SCH66336 in CML patients and suggest that combination therapy may be effective in patients with STI571 resistance.

Resistance to daunorubicin-induced apoptosis is not completely reversed in CML blast cells by STI571

The leukemogenic property of BCR-ABL in chronic myeloid leukemia (CML) is critically dependent on its protein tyrosine kinase activity. STI571 inhibits the BCR-ABL kinase activity, the growth and the viability of BCR-ABL expressing cells. In this study, we report the apoptotic effect of STI571 in combination with daunorubicin (DNR) on peripheral blood mononuclear cells from 11 CML patients and four BCR-ABL-positive cell lines: AR230, LAMA84, K562 and KCL22. Primary blast cells were identified by flow cytometry on the basis of their low CD45 expression. Nucleus fragmentation, exposure of phosphatidylserines and decrease in mitochondrial membrane potential were measured using acridine orange, FITC-annexin V and DiOC6(3), respectively, to evaluate apoptosis. On cell lines, the effect of DNR was negligible, whereas STI571 induced 10 to 35% of apoptosis in 18 h. STI571 sensitized AR230, LAMA84 and K562 cells to DNR when apoptosis was measured at the mitochondrial and membrane but not the nuclear levels. On CML blast cells, phosphatidyl serine exposure was significantly induced by both DNR and STI571 and was higher when these drugs were used in combination (P < 0.0003). However, the effects of this drug combination were only additive and no sensitization of blast cells to DNR by STI571 was observed. Interestingly, sensitization was evidenced in CML but not normal lymphocytes. These results suggest that other mechanisms additional to Bcr-Abl tyrosine kinase activity could be responsible for DNR resistance, and further investigations are needed to understand its origin.

Imatinib induces durable hematologic and cytogenetic responses in patients with accelerated phase chronic myeloid leukemia: results of a phase 2 study

Chronic myelogenous leukemia (CML) is caused by expression of the BCR-ABL tyrosine kinase oncogene, the product of the t(9;22) Philadelphia translocation. Patients with CML in accelerated phase have rapidly progressive disease and are characteristically unresponsive to existing therapies. Imatinib (formerly STI571) is a rationally developed, orally administered inhibitor of the Bcr-Abl kinase. A total of 235 CML patients were enrolled in this study, of whom 181 had a confirmed diagnosis of accelerated phase. Patients were treated with imatinib at 400 or 600 mg/d and were evaluated for hematologic and cytogenetic response, time to progression, survival, and toxicity. Imatinib induced hematologic response in 82% of patients and sustained hematologic responses lasting at least 4 weeks in 69% (complete in 34%). The rate of major cytogenetic response was 24% (complete in 17%). Estimated 12-month progression-free and overall survival rates were 59% and 74%, respectively. Nonhematologic toxicity was usually mild or moderate, and hematologic toxicity was manageable. In comparison to 400 mg, imatinib doses of 600 mg/d led to more cytogenetic responses (28% compared to 16%), longer duration of response (79% compared to 57% at 12 months), time to disease progression (67% compared to 44% at 12 months), and overall survival (78% compared to 65% at 12 months), with no clinically relevant increase in toxicity. Orally administered imatinib is an effective and well-tolerated treatment for patients with CML in accelerated phase. A daily dose of 600 mg is more effective than 400 mg, with similar toxicity.

Follow-up of complete cytogenetic remission in patients with chronic myeloid leukemia after cessation of interferon alfa

PURPOSE

A small proportion of patients with chronic myeloid leukemia (CML) achieve a complete cytogenetic response (CCR), defined as the disappearance of Philadelphia (Ph) chromosome-positive metaphases, after treatment with interferon alfa (IFN). In this population of patients, the question of whether treatment should then be withdrawn is not yet resolved.

PATIENTS AND METHODS

In the present study, we followed 15 patients who stopped IFN after achieving CCR. In nine patients IFN was stopped in view of adverse reactions (n = 8) or patient's choice (n = 1). For the remaining six patients, the treatment was stopped because no BCR/ABL rearrangement could be detected by reverse transcriptase polymerase chain reaction (RT-PCR) in four successive analyses using peripheral-blood samples.

RESULTS

Loss of CCR and survival were not statistically different (P =.48; P =.7) for the 15 patients who stopped IFN compared with 41 other CCR patients who continued IFN therapy in our institution. The median follow-up after discontinuation of IFN treatment was 36 months (range, 6 to 108 months). Seven patients (47%) (females, or CCR > 24 months and RT-PCR negative before IFN cessation; P <.0001) did not relapse. Eight other patients (53%) relapsed (lost CCR) within 3 to 33 months of treatment discontinuation. One of them relapsed in major cytogenetic remission (MCR) and was still in MCR 87 months after stopping therapy without any treatment.

CONCLUSION

It is possible to stop IFN treatment at least in some patients with CML who achieve a prolonged period of CCR. This study also illustrates the hypothesis that persistence of low numbers of Ph-positive cells does not necessarily imply hematologic relapse.

Restoration of sensitivity to STI571 in STI571-resistant chronic myeloid leukemia cells

STI571 induces sustained hematologic remission in patients with chronic myeloid leukemia (CML) in chronic phase. However, in advanced phases, especially blast crisis, the leukemia usually becomes resistant within months. It has been investigated whether resistance to STI571 is stable and immutable or whether it can be reversed in selected CML cell lines. Withdrawal of STI571 for varying lengths of time from cultures of 3 resistant lines (K562-r, KCL22-r, and Baf/BCR-ABL-r1) did not restore sensitivity to the inhibitor. In contrast, LAMA84-resistant cells experienced a sharp reduction in survival and proliferation during the first week of STI571 withdrawal but recovered thereafter. Moreover, when left off the inhibitor for 2 months or longer, this cell line reacquired sensitivity to STI571. It is hypothesized, therefore, that patients who have become resistant to the drug may respond again if STI571 therapy is temporarily interrupted.

Chronic myeloid leukemia and interferon-alpha: a study of complete cytogenetic responders

Achieving a complete cytogenetic response (CCgR) is a major target in the treatment of chronic myeloid leukemia (CML) with interferon-alpha (IFN-alpha), but CCgRs are rare. The mean CCgR rate is 13%, in a range of 5% to 33%. A collaborative study of 9 European Union countries has led to the collection of data on 317 patients who were first seen between 1983 and 1997 and achieved CCgRs with IFN-alpha alone or in combination with hydroxyurea. The median time to first CCgR was 19 months (95% CI, 17-21; range, 3-84 months). At last contact, 212 patients were still alive and in continuous CCgR; 105 patients had lost CCgR, but 53% of them were still alive and in chronic phase. IFN-alpha treatment was discontinued permanently in 23 cases for response loss, in 36 cases for chronic toxicity (15 are still in unmaintained continuous CCgR), and in 8 cases because it was believed that treatment was no longer necessary (7 of these 8 patients are still in unmaintained continuous CCgR). The 10-year survival rate from first CCgR is 72% (95% CI, 62%-82%) and is related to the risk profile. High-risk patients lost CCgR more frequently and more rapidly and none survived more than 10 years. Low-risk patients survived much longer (10-year survival probability 89% for Sokal low risk and 81% for Euro low risk). These data point out that a substantial long-term survival in CCgRs is restricted mainly to low-risk and possibly intermediate-risk patients and occurs significantly less often in high-risk patients.

Direct relation between BCR-ABL tyrosine kinase activity and cyclin D2 expression in lymphoblasts

Leukemia cells bearing the Philadelphia (Ph) chromosome express a Bcr-Abl fusion protein with deregulated protein tyrosine kinase (PTK) activity, which plays a central role in the malignant transformation. Many different signal transduction pathways are activated by Bcr-Abl, but little is known about their downstream targets in specific cell lineages. We show here that Ph-positive cell lines as well as primary cells derived from chronic myeloid leukemia (CML) in lymphoid blast crisis or from acute lymphoblastic leukemia (ALL) consistently express high levels of cyclin D2, whereas expression of this protein is low or absent in comparable Ph-negative lines and Ph-positive myeloid lines. Inhibition of Bcr-Abl with STI571 resulted in down-regulation of cyclin D2 and reduction of the number of cells in S phase, although complete G1 arrest was not induced. The expression of cyclin D2 in Ph-positive lymphoblasts was mediated via the phosphatidyl-inositol-3 kinase pathway. Analogous results were seen in murine BaF/3 cells transfected with a BCR-ABL expression vector. In contrast to the human cell lines, murine Baf/BCR-ABL cells exposed to STI571 inhibitor were all arrested in G1. This arrest could be abrogated by exogenous expression of cyclin D2 from a transfected cDNA construct. We conclude that a direct connection exists between Bcr-Abl PTK activity and cell cycle progression in which cyclin D2 plays a critical role. However, cell cycle progression in human Ph-positive lymphoid cells is not entirely dependent on Bcr-Abl PTK, and additional genetic lesions must be present.

[Chronic myeloid leukemia and tyrosine kinase inhibitors]

INTRODUCTION

Chronic myeloid leukemia is a myeloproliferative disorder clinically characterised by a triphasic course: after a chronic phase over a median time of 4 years, patients developed an accelerated phase, then a blastic phase, resulting in the patient's death with 3 to 6 months.

PURPOSE

During the last past years, progress have been made in the understanding of the molecular mechanism responsible of leukemic growth. This has also provided support for a therapeutic improvement with the appearance of treatment such as tyrosine kinase inhibitors which specifically target the oncoprotein inside the leukemic cells.

CONCLUSION

These treatments, such as STI571 or Glivec, are at present in clinical trials, and could be the medicines for the future. Thus, chronic myeloid leukemia is also a model for the development of the new therapeutic drugs.

[Leukemogenesis and new therapy development: the example of chronic myelogenous leukemia]

During the past ten years, the improvements of our understanding of cellular signal transduction pathways provide new targets for drug therapies. Chronic myeloid leukemia (CML), a malignant hematopoietic stem cell disorder, is characterised by an acquired genetic abnormality: the Philadelphia chromosome (Ph) and its molecular counterpart, the oncogene BCR-ABL. The latter, which is translated in an active BCR-ABL protein, exhibited a deregulated tyrosine kinase activity inducing malignant transformation. Produced from the 2-phenylaminopyrimidine class, a novel synthetic inhibitor, identified as CGP57148 (STI571), inhibits tyrosine kinase activity of c-ABL, BCR-ABL, PDGF-R and c-kit at micromolar concentrations. It suppresses the proliferation of the majority of BCR-ABL positive cell lines. The phases I-II clinical trials in CML have demonstrated promising results, especially in the chronic phase of the disease. STI571 is an original therapeutic approach which may be used as a model for the development of other drugs in cancer.

Expression of interferon-α (IFN-α) receptor 2c at diagnosis is associated with cytogenetic response in IFN-α–treated chronic myeloid leukemia

For the management of chronic myeloid leukemia (CML), prediction or early determination of the response to interferon-alpha (IFN-α) treatment is important for identifying nonresponder patients to whom alternative therapy may be proposed. In this study, the levels of expression of both BCR-ABL and subunit 2c of IFN-α receptor (IFN-αR2c) genes were analyzed at diagnosis in 74 patients with chronic phase CML treated with an IFN-α monotherapy. By using blood samples, real-time quantitative polymerase chain reaction was performed to quantify BCR-ABL, IFN-αR2c, and G6PDH mRNA as external control. The results were compared with hematologic and cytogenetic responses to IFN-α. A wide variation in the BCR-ABL/G6PDH ratio was observed at diagnosis (median, 6.68%; range, 0.18%-41.31%), but no significant association with response to IFN-α was observed. In contrast, the variation of IFN-αR2c/G6PDH ratio at diagnosis was significantly associated with the achievement of major cytogenetic response (MCR; 34% or lower Ph+metaphases). Median values of IFN-αR2c/G6PDH ratio for patients achieving MCR and for those who did not achieve it were 110.75% (range, 9.47%-612.30%) and 64.42% (range, 5.96%-425.40%), respectively (P = .037). In addition, this novel molecular factor, combined with the achievement of complete hematologic response at 3 months, makes it possible to predict MCR achievement with high probability by Kaplan-Meier analysis (91% ± 17% at 24 months; P = .0001).

A new morphologic classification system for acute promyelocytic leukemia distinguishes cases with underlying PLZF/RARA gene rearrangements

Acute promyelocytic leukemia (APL) is typified by the t(15;17) translocation, which leads to the formation of the PML/RARA fusion gene and predicts a beneficial response to retinoids. However, approximately 10% of all APL cases lack the classic t(15;17). This group includes (1) cases with cryptic PML/RARA gene rearrangements and t(5;17) that leads to the NPM/RARA fusion gene, which are retinoid-responsive, and (2) cases with t(11;17)(q23;q21) that are associated with the PLZF/RARA fusion gene, which are retinoid-resistant. A key issue is how to rapidly distinguish subtypes of APL that demand distinct treatment approaches. To address this issue, a European workshop was held in Monza, Italy, during June 1997, and a morphologic, immunophenotypic, cytogenetic, and molecular review was undertaken in 60 cases of APL lacking t(15;17). This process led to the development of a novel morphologic classification system that takes into account the major nuclear and cytoplasmic features of APL. There were no major differences observed in morphology or immunophenotype between cases with the classic t(15;17) and those with the cryptic PML/RARA gene rearrangements. Auer rods were absent in the t(5;17) case expressing NPM/RARA. Interestingly, this classification system distinguished 9 cases with t(11;17)(q23;q21) and, in addition, successfully identified 2 cases lacking t(11;17), which were subsequently shown to have underlying PLZF/RARA fusions. The PLZF/RARA cases were characterized by a predominance of blasts with regular nuclei, an increased number of Pelger-like cells, and by expression of CD56 in 4 of 6 cases tested. Use of this classification system, combined with an analysis for CD56 expression, should allow early recognition of APL cases requiring tailored molecular investigations. (Blood. 2000;96:1287-1296)

Selection and characterization of BCR-ABL positive cell lines with differential sensitivity to the tyrosine kinase inhibitor STI571: diverse mechanisms of resistance

Targeting the tyrosine kinase activity of Bcr-Abl with STI571 is an attractive therapeutic strategy in chronic myelogenous leukemia (CML). A few CML cell lines and primary progenitors are, however, resistant to this compound. We investigated the mechanism of this resistance in clones of the murine BaF/3 cells transfected with BCR-ABL and in 4 human cell lines from which sensitive (s) and resistant (r) clones were generated by various methods. Although the resistant cells were able to survive in the presence of STI571, their proliferation was approximately 30% lower than that of their sensitive counterparts in the absence of the compound. The concentration of STI571 needed for a 50% reduction in viable cells after a 3-day exposure was on average 10 times higher in the resistant (2-3 micromol/L) than in the sensitive (0.2-0.25 micromol/L) clones. The mechanism of resistance to STI571 varied among the cell lines. Thus, in Baf/BCR-ABL-r, LAMA84-r, and AR230-r, there was up-regulation of the Bcr-Abl protein associated with amplification of the BCR-ABL gene. In K562-r, there was no Bcr-Abl overexpression, but the IC(50) for the inhibition of Bcr-Abl autophosphorylation was increased in the resistant clones. Sequencing of the Abl kinase domain revealed no mutations. The multidrug resistance P-glycoprotein (Pgp) was overexpressed in LAMA84-r, indicating that at least 2 mechanisms of resistance operate in this cell line. KCL22-r showed neither Bcr-Abl up-regulation nor a higher threshold for tyrosine kinase inhibition by STI571. We conclude that BCR-ABL-positive cells can evade the inhibitory effect of STI571 by different mechanisms, such as Bcr-Abl overexpression, reduced intake mediated by Pgp, and, possibly, acquisition of compensatory mutations in genes other than BCR-ABL.

Retroviral coexpression of IFN-alpha and IFN-gamma genes and inhibitory effects in chronic myeloid leukemia cells

Interferon (IFN) is an effective treatment for chronic myeloid leukemia (CML) in chronic phases, and a number of in vitro antileukemic effects of IFN on CML cells have been reported. The transfer of cytokine genes into tumor cells is reportedly a valuable approach to improve the antitumor activity of cytokines in various models. We first investigated the possibility of transducing CML cells with the retroviral vectors LIalpha2SN and LIgammaSN, encoding the IFN-alpha2 and IFN-gamma genes, respectively, and with the bicistronic vector LIalpha2IrIgammaSN coexpressing the IFN-alpha2 and IFN-gamma genes. We then analyzed the effects of IFN-alpha2 and IFN-gamma produced alone or simultaneously on the proliferation of CML cells. We optimized the transduction efficiency by using the CML-derived K562 cell line. We then introduced IFN genes into CML CD34+ cells. Secretion of IFN-alpha and IFN-gamma was demonstrated in K562 and CML CD34+ cells transduced with the different vectors. The MHC class I antigens were overexpressed in both K562 and CML CD34+ transduced cells. Inhibition of the proliferation of LIalpha2IrIgammaSN-transduced CML cells was greater than with the LIalpha2SN and the LIgammaSN-transduced CML cells. We demonstrate an additive effect of IFN-alpha and IFN-gamma on the inhibition of K562 and CML CD34+ cell proliferation.

Differential effect of interferon alpha on chronic myelogenous leukaemia and normal haematopoietic progenitors in a stromal cell co-culture context: role of the flt3 ligand

Interferon alpha (IFN-alpha) is used to treat chronic myelogenous leukaemia (CML) patients. However, its target(s) remain(s) unknown. One possibility is that there is a differing sensitivity of the leukaemic from the normal colony-forming cell (CFC) compartments to IFN-alpha. Co-cultures of progenitors with stromal cells provide a valuable tool to dissect direct and indirect activities of IFN-alpha. In this study, we have used endothelial cells (EC) as a source of stromal cells. In co-cultures of normal progenitors with EC, IFN-alpha increased the generation of clonogenic cells, mainly via an increased production of flt3 ligand (FL) by EC. In contrast, in co-cultures of CML progenitors with EC, IFN-alpha inhibited the generation of clonogenic cells, mainly by direct inhibition on the progenitors, the up-regulation of FL production by stromal cells being unable to compensate for the direct inhibitory effects of IFN-alpha. These data provide evidence for a differential effect of IFN-alpha on the growth of CML and normal CFC cells in a stromal context and suggest that an alteration in the response of CML progenitor cells to FL is important in the explanation of this differential effect.