Small doses of ARA-C in the treatment of acute myeloid leukaemia: differentiation of myeloid leukaemia cells?

Treatment of Acute Myeloid Leukemia in Older Adults

Acute Myeloid Leukemia (AML) is an aggressive myeloid malignancy predominantly affecting older adults. Despite the advancements in new therapies for AML, older and medically unfit patients continue to suffer from poor outcomes due to disease-related factors such as the mutational profile and patient-related factors such as comorbidities and performance status. In this review, we discuss a spectrum of therapeutic options for older patients with AML starting with a historical perspective and ending with therapies being investigated in clinical trials. We review the standard of care treatment options including combination venetoclax and hypomethylating agents, in addition to targeted therapies such as FLT3 and IDH inhibitors. Lastly, we shed light on challenges facing the care of older adults and their representation in clinical trials.

Cytarabine-induced differentiation of AML cells depends on Chk1 activation and shares the mechanism with inhibitors of DHODH and pyrimidine synthesis

Acute myeloid leukemia (AML) is characterized by arrested differentiation making differentiation therapy a promising treatment strategy. Recent success of inhibitors of mutated isocitrate dehydrogenase (IDH) invigorated interest in differentiation therapy of AML so that several new drugs have been proposed, including inhibitors of dihydroorotate dehydrogenase (DHODH), an enzyme in pyrimidine synthesis. Cytarabine, a backbone of standard AML therapy, is known to induce differentiation at low doses, but the mechanism is not completely elucidated. We have previously reported that 5-aminoimidazole-4-carboxamide ribonucleoside (AICAr) and brequinar, a DHODH inhibitor, induced differentiation of myeloid leukemia by activating the ataxia telangiectasia and Rad3-related (ATR)/checkpoint kinase 1 (Chk1) via pyrimidine depletion. In this study, using immunoblotting, flow cytometry analyses, pharmacologic inhibitors and genetic inactivation of Chk1 in myeloid leukemia cell lines, we show that low dose cytarabine induces differentiation by activating Chk1. In addition, cytarabine induces differentiation ex vivo in a subset of primary AML samples that are sensitive to AICAr and DHODH inhibitor. The results of our study suggest that leukemic cell differentiation stimulated by low doses of cytarabine depends on the activation of Chk1 and thus shares the same pathway as pyrimidine synthesis inhibitors.

Differentiation therapy revisited

The concept of differentiation therapy emerged from the fact that hormones or cytokines may promote differentiation ex vivo, thereby irreversibly changing the phenotype of cancer cells. Its hallmark success has been the treatment of acute promyelocytic leukaemia (APL), a condition that is now highly curable by the combination of retinoic acid (RA) and arsenic. Recently, drugs that trigger differentiation in a variety of primary tumour cells have been identified, suggesting that they are clinically useful. This Opinion article analyses the basis for the clinical successes of RA or arsenic in APL by assessing the respective roles of terminal maturation and loss of self-renewal. By reviewing other successful examples of drug-induced tumour cell differentiation, novel approaches to transform differentiating drugs into more efficient therapies are proposed.

Characteristics and outcomes of older patients with secondary acute myeloid leukemia according to treatment approach

BACKGROUND

The development of newer strategies to improve outcomes for older patients with secondary acute myeloid leukemia (s-AML) is a critical unmet need. Establishing baseline metrics for evaluating newer approaches is important.

METHODS

s-AML was defined as 1 or more of the following: a history of an antecedent hematologic disorder (AHD), a diagnosis of therapy-related acute myeloid leukemia (AML), and AML with karyotype abnormalities characteristic of myelodysplastic syndrome. Newly diagnosed s-AML patients aged 60 to 75 years were grouped into 5 treatment cohorts: 1) patients receiving high- or intermediate-dose cytarabine-based intensive chemotherapy (IC), 2) patients receiving a hypomethylating agent (HMA) or HMA combinations, 3) patients receiving low-dose cytarabine (LDAC) combinations, 4) patients receiving CPX-351, and 5) patients receiving investigational (INV) agents. Nine hundred thirty-one patients met the age and s-AML criteria.

RESULTS

Complete remission rates were statistically lower in the HMA group (36%) versus the IC (46%), CPX-351 (45%), and LDAC groups (43%). Patients receiving less intensive regimens (the HMA and LDAC groups combined) had superior overall survival (OS) in comparison with patients receiving IC-based regimens (median 6.9 vs 5.4 months; P = .048). Only 4.3% of the IC patients proceeded to transplantation, whereas 10.3% of the patients on lower intensity regimens did (P = .001). There was no difference in median survival between patients treated with CPX-351 and patients treated with conventional lower intensity approaches (P = .75). Age > 70 years, an adverse karyotype, and a prior AHD were associated with decreased OS in a multivariate analysis.

CONCLUSIONS

Lower intensity approaches are associated with lower early mortality rates and improved OS in comparison with intensive regimens. OS is poor with currently available therapies with a median OS of 6 months (5.4-7.6 months across regimens). Unsatisfactory outcomes with other INV agents underscore the need for more effective therapies. Cancer 2017;123:3050-60. © 2017 American Cancer Society.

Enhancement of arabinocytosine (AraC) toxicity to AML cells by a differentiation agent combination

Arabinocytosine (AraC, also known as cytarabine) is one of the mainstays of AML therapy, but like other DNA damaging therapeutic agents it is rarely curative by itself. There is an emerging realization that the therapeutic outcomes may be improved by combining AraC with other compounds. Here we report that the addition of a differentiating agent combination immediately following AraC damage to AML blasts, selectively increases the cell kill. The experiments were performed using cultured cells from established cell lines of AML (HL60 and U937). The cells were exposed to 100nM AraC, a concentration which produced approximately 25-50% cell kill, followed by a combination of 100nM 1alpha-hydroxyvitamin D2 (1-D2) and 10μM carnosic acid (CA), which together can serve as a powerful differentiating agent combination for AML cells, but are not toxic alone. AraC-induced cell death, measured by annexin V/propidium iodide, was significantly (p<0.01) increased by the 1-D2/CA combination in both cell lines, but not by 1-D2 or CA alone. The enhancement of cell death occurred by both apoptosis and necrosis, was associated with increased DNA damage and with higher levels of DNA damage response (DDR) activated marker Chk1, but the expression of p27, a cell cycle inhibitor protein, was not enhanced by 1-D2/CA. The principal finding is that a vitamin D analog 1-D2 combined with a plant-derived antioxidant CA can markedly augment the cytotoxic action of AraC, an anti-leukemia therapeutic agent.

The safety of treatment options for elderly people with acute myeloid leukemia

INTRODUCTION

Life expectancy in elderly patients with acute myeloid leukemia (AML) is a function of age, disability, and co-morbidity, combined with leukemia characteristics. There is currently no consensus regarding the optimal therapeutic strategy for older adults with AML. Although selected older adults with AML can benefit from intensive therapies, recent evidence supports the use of lower-intensity therapies in most patients and emphasizes the importance of tolerability and quality of life.

AREAS COVERED

Results of the current clinical trials and safety data are reviewed.

EXPERT OPINION

Treatment recommendations for elderly patients with AML need to be individualized. In order to avoid toxicities, hematologists should collaborate more with geriatricians to identify clues of vulnerability in elderly patients through the study of functional physical, physiological, cognitive, social, and psychological parameters.

Treatment with Low-Dose Cytarabine in Elderly Patients (Age 70 Years or Older) with Acute Myeloid Leukemia: A Single Institution Experience

Objectives

Low-dose cytarabine (LD-AraC) is still regarded as the standard of care in elderly patients with acute myeloid leukemia (AML) ‘unfit’ for intensive chemotherapy. In this study, we reported our experience with LD-AraC in patients ≥ 70 years old and compared the results to those of intensive chemotherapy, best supportive care (BSC), or hypomethylating agents in the same age population.

Methods

Between 2000 and 2014, 60 patients received LD-AraC at 20 mg once or twice daily by subcutaneous injection for 10 consecutive days every 4–6 weeks.

Results

Complete remission rate with LD-AraC was 7% versus 56% with intensive chemotherapy and 21% with hypomethylating agents. Median overall survival (OS) of patients treated with LD-AraC was 9.6 months with 3-year OS of 12%. Survival with LD-AraC was better than with BSC only (P = 0.001). Although not statistically significant, intensive chemotherapy and hypomethylating agents tended to be better than LD-AraC in terms of OS (median: 12.4 months and 16.1 months, respectively). There was no clear evidence that a beneficial effect of LD-AraC was restricted to any particular subtype of patients, except for cytogenetics. There was a trend for a better OS in LD-AraC treated patients in the setting of clinical trials as compared with those treated outside of a clinical trial.

Conclusions

Despite a trend in favor of intensive chemotherapy and hypomethylating agents over LD-AraC, no real significant advantage could be demonstrated, while LD-AraC showed a significant advantage comparatively to BSC. All this tends to confirm that LD-AraC can still represent a baseline against which new promising agents may be compared either alone or in combination.

Decitabine Compared with Low-Dose Cytarabine for the Treatment of Older Patients with Newly Diagnosed Acute Myeloid Leukemia: A Pilot Study of Safety, Efficacy, and Cost-Effectiveness

Introduction. The incidence of Acute Myeloid Leukemia (AML) increases progressively with age and its treatment is challenging. This prospective case control study was undertaken to compare the safety, efficacy, and cost-effectiveness of decitabine with those of cytarabine in older patients with newly diagnosed AML who are not fit for intensive chemotherapy. Materials and Methods. 30 eligible patients above 60 years old with newly diagnosed AML were assigned to receive decitabine or cytarabine. The primary end point was overall survival (OS). The secondary objective was to compare adverse events and cost-effectiveness of therapy in the two study groups. Results. In this study, 15 patients received decitabine and 15 patients received cytarabine. The median OS was 5.5 months for each of the treatment groups. The hazard ratio between the treatment groups was 0.811 with 95% CI of 0.390 to 1.687. Toxicity profile was similar in both groups. Cost per cycle of chemotherapy in INR was 24,200 for decitabine and 1,600 for low-dose cytarabine group. Median of simplified cost-effectiveness ratio was 0.00022 for decitabine group and 0.0034 for low-dose cytarabine group. Conclusions. For elderly patients with AML, decitabine and low-dose cytarabine should be chosen based on the patient's choice and affordability. Our study has shown that both of these agents have similar OS and toxicity. Low-dose cytarabine scores over decitabine in developing countries as it is more cost-effective.

Role of low dose cytarabine in elderly patients with acute myeloid leukemia: An experience

PURPOSE

To highlight the acceptable results seen after use of low dose cytarabine in elderly patients of acute myeloid leukemia (AML) with comorbidities.

MATERIALS AND METHODS

This was a prospective study carried on 30 newly diagnosed patients of AML over 60 years of age who were unfit for standard treatment regimens. We did not use azacytidine and decitabine in our patients because these therapeutic modalities being extremely costly and our patient affordability being poor. After taking patient consent and institutional ethical clearance these patients were treated with 20 mg/m(2) cytarabine subcutaneously in two divided doses 12 h apart for 4 days every week for 4 weeks which constituted a cycle before disease, re-assessment was done. A repeat cycle was administered where ever needed and after attainment of remission, we continued low dose cytarabine for 2 days/week as maintenance after complete or partial response was documented.

RESULTS

In our study, we found that around 20% of patients achieved complete remission and 30% partial remission. The remission rates were definitely influenced by counts at presentation, performance at presentation, comorbidities, underlying myelodysplastic syndrome and baseline cytogenetics.

CONCLUSION

Low dose cytarabine is effective treatment option for elderly patients with AML when standard treatment options are not warranted.

Novel drugs for older patients with acute myeloid leukemia

Acute myeloid leukemia (AML) is the second most common form of leukemia and the most frequent cause of leukemia-related deaths in the United States. The incidence of AML increases with advancing age and the prognosis for patients with AML worsens substantially with increasing age. Many older patients are ineligible for intensive treatment and require other therapeutic approaches to optimize clinical outcome. To address this treatment gap, novel agents with varying mechanisms of action targeting different cellular processes are currently in development. Hypomethylating agents (azacitidine, decitabine, SGI-110), histone deacetylase inhibitors (vorinostat, pracinostat, panobinostat), FMS-like tyrosine kinase receptor-3 inhibitors (quizartinib, sorafenib, midostaurin, crenolanib), cytotoxic agents (clofarabine, sapacitabine, vosaroxin), cell cycle inhibitors (barasertib, volasertib, rigosertib) and monoclonal antibodies (gentuzumab ozogamicin, lintuzumab-Ac225) represent some of these promising new treatments. This review provides an overview of novel agents that have either completed or are currently in ongoing phase III trials in patients with previously untreated AML for whom intensive treatment is not an option. Other potential drugs in earlier stages of development will also be addressed in this review.

Wee1 inhibition by MK-1775 leads to tumor inhibition and enhances efficacy of gemcitabine in human sarcomas

Sarcomas are rare and heterogeneous mesenchymal tumors affecting both pediatric and adult populations with more than 70 recognized histologies. Doxorubicin and ifosfamide have been the main course of therapy for treatment of sarcomas; however, the response rate to these therapies is about 10-20% in metastatic setting. Toxicity with the drug combination is high, response rates remain low, and improvement in overall survival, especially in the metastatic disease, remains negligible and new agents are needed. Wee1 is a critical component of the G2/M cell cycle checkpoint control and mediates cell cycle arrest by regulating the phosphorylation of CDC2. Inhibition of Wee1 by MK1775 has been reported to enhance the cytotoxic effect of DNA damaging agents in different types of carcinomas. In this study we investigated the therapeutic efficacy of MK1775 in various sarcoma cell lines, patient-derived tumor explants ex vivo and in vivo both alone and in combination with gemcitabine, which is frequently used in the treatment of sarcomas. Our data demonstrate that MK1775 treatment as a single agent at clinically relevant concentrations leads to unscheduled entry into mitosis and initiation of apoptotic cell death in all sarcomas tested. Additionally, MK1775 significantly enhances the cytotoxic effect of gemcitabine in sarcoma cells lines with different p53 mutational status. In patient-derived bone and soft tissue sarcoma samples we showed that MK1775 alone and in combination with gemcitabine causes significant apoptotic cell death. Magnetic resonance imaging (MRI) and histopathologic studies showed that MK1775 induces significant cell death and terminal differentiation in a patient-derived xenograft mouse model of osteosarcoma in vivo. Our results together with the high safety profile of MK1775 strongly suggest that this drug can be used as a potential therapeutic agent in the treatment of both adult as well as pediatric sarcoma patients.

Defective osteogenic differentiation in the development of osteosarcoma

Osteosarcoma (OS) is associated with poor prognosis due to its high incidence of metastasis and chemoresistance. It often arises in areas of rapid bone growth in long bones during the adolescent growth spurt. Although certain genetic conditions and alterations increase the risk of developing OS, the molecular pathogenesis is poorly understood. Recently, defects in differentiation have been linked to cancers, as they are associated with high cell proliferation. Treatments overcoming these defects enable terminal differentiation and subsequent tumor inhibition. OS development may be associated with defects in osteogenic differentiation. While early regulators of osteogenesis are unable to bypass these defects, late osteogenic regulators, including Runx2 and Osterix, are able to overcome some of the defects and inhibit tumor propagation through promoting osteogenic differentiation. Further understanding of the relationship between defects in osteogenic differentiation and tumor development holds tremendous potential in treating OS.

Therapeutic Implications of PPARgamma in Human Osteosarcoma

Osteosarcoma (OS) is the most common nonhematologic malignancy of bone in children and adults. Although dysregulation of tumor suppressor genes and oncogenes, such as Rb, p53, and the genes critical to cell cycle control, genetic stability, and apoptosis have been identified in OS, consensus genetic changes that lead to OS development are poorly understood. Disruption of the osteogenic differentiation pathway may be at least in part responsible for OS tumorigenesis. Current OS management involves chemotherapy and surgery. Peroxisome proliferator-activated receptor (PPAR) agonists and/or retinoids can inhibit OS proliferation and induce apoptosis and may inhibit OS growth by promoting osteoblastic terminal differentiation. Thus, safe and effective PPAR agonists and/or retinoid derivatives can be then used as adjuvant therapeutic drugs for OS therapy. Furthermore, these agents have the potential to be used as chemopreventive agents for the OS patients who undergo the resection of the primary bone tumors in order to prevent local recurrence and/or distal pulmonary metastasis.

Prolonged survival with improved tolerability in higher-risk myelodysplastic syndromes: azacitidine compared with low dose ara-C

In the phase III AZA-001 trial, low-dose cytarabine (LDara-C), the most widely used low-dose chemotherapy in patients with higher-risk myelodysplastic syndrome (MDS) who are ineligible for intensive treatment, was found to be associated with poorer survival compared with azacitidine. This analysis further compared the efficacy and the toxicity of these two drug regimens. Before randomization, investigators preselected patients to receive a conventional care regimen, one of which was LDara-C. Of 94 patients preselected to LDara-C, 45 were randomized to azacitidine and 49 to LDara-C. Azacitidine patients had significantly more and longer haematological responses and increased red blood cell transfusion independence. Azacitidine prolonged overall survival versus LDara-C in patients with poor cytogenetic risk, presence of -7/del(7q), and French-American-British subtypes refractory anaemia with excess blasts (RAEB) and RAEB in transformation. When analyzed per patient year of drug exposure, azacitidine treatment was associated with fewer grade 3-4 cytopenias and shorter hospitalisation time than LDara-C in these higher-risk MDS patients.

Low-dose cytosine arabinoside therapy in a patient with myelofibrosis during transformation to acute non-lymphocytic leukemia

A patient with myelofibrosis transforming into acute non-lymphocytic leukaemia (ANLL) was treated with low doses of cytosine arabinoside (ARA-C). Complete remission was obtained twice without serious toxicity. It is suggested that low-dose ARA-C may be an effective and rather non-toxic therapy in patients with myeloproliferative disorders transforming to ANLL.

A critical role for the co-repressor N-CoR in erythroid differentiation and heme synthesis

Co-repressor N-CoR (nuclear receptor co-repressor) has important roles in different biological processes, including proliferation, differentiation and development. Mutant mice lacking N-CoR are embryonically lethal and appear to die from anemia owing to defects in definitive erythropoiesis. However, the underlying molecular mechanisms of N-CoR-mediated erythroid differentiation are largely unknown. Using the human erythroleukemic K562 cell line, which can be chemically induced to differentiate into either erythroid or megakaryocytic lineages depending on the inducers used, we have investigated the role of N-CoR in erythroid differentiation. We show that knockdown of N-CoR either transiently (siRNA) or permanently (shRNA) impairs the cytosine arabinoside (Ara-C)- but not hemin-induced erythroid differentiation of K562 cells. RT-PCR analysis reveals that N-CoR is required for induction by Ara-C of 5-aminolevulinate synthase (ALA-S2), a key enzyme involved in heme biosynthesis. Furthermore, the amount of N-CoR proteins increases significantly during Ara-C-induced K562 differentiation, apparently through a post-transcriptional mechanism. Consistent with the data from N-CoR-null mice, N-CoR is not required for the differentiation of K562 cells into megakaryocytic lineages, induced by phorbol 12-myristate 13-acetate. Thus, our in vitro study confirms a role for N-CoR in erythroid differentiation and reveals for the first time that N-CoR is required for the induction of a key enzyme involved in heme synthesis.

The value of oral cytarabine ocfosfate and etoposide in the treatment of refractory and elderly AML patients

Twenty-one acute myeloid leukemia (AML) patients were enrolled and received oral induction therapy with cytarabine ocfosfate (SPAC) and etoposide (EP). The median age was 69 years (range: 33-86). There were 11 patients with de novo AML and 10 AML cases that had evolved from myelodysplastic syndromes. Seventeen patients had abnormal karyotypes including eight complex abnormalities, various complications, and 7 of 21 had a poor performance status (PS) with Eastern Cooperative Oncology Group (ECOG) scores of 3-4. All patients completed induction therapy without severe adverse events. Seven achieved complete remission (CR), and two achieved partial remission (PR). Uni- and multivariate analyses demonstrated a positive and significant correlation between the results of therapy (CR +/- PR) and overall survival. The plasma concentrations of cytosine arabinoside (ara-C) in some cases were higher than those previously reported, indicating the accumulation of ara-C with increasing numbers of days of SPAC administration. We conclude that this therapy is well tolerated and useful for refractory and elderly AML patients.

A comparison of low-dose cytarabine and hydroxyurea with or without all-trans retinoic acid for acute myeloid leukemia and high-risk myelodysplastic syndrome in patients not considered fit for intensive treatment

BACKGROUND

The survival of older patients with acute myeloid leukemia has not improved. Few clinical trials have been available for older patients who are not considered fit for an intensive chemotherapy approach.

METHODS

Between December 1998 and November 2003, as part of National Cancer Research Institute Acute Myeloid Leukemia 14 Trial, 217 patients, who were deemed unfit for intensive chemotherapy were randomized to receive low-dose cytarabine (Ara-C) (20 mg twice daily for 10 days) or hydroxyurea with or without all-trans retinoic acid (ATRA).

RESULTS

Low-dose ara-C produced a better remission rate (18% vs 1%; odds ratio [OR], 0.15; 95% confidence interval [95% CI], 0.06-0.37; P = .00006) and better overall survival (OR, 0.60; 95% CI, 0.44-0.81; P = .0009), which was accounted for by the achievement of complete remission (CR) (duration of CR: 80 weeks vs 10 weeks for patients with no CR). Patients who had adverse cytogenetics did not benefit. ATRA had no effect. Toxicity scores or supportive care requirements did not differ between the treatment arms.

CONCLUSIONS

Older, less fit patients have a poor outcome, and few trials have been conducted in this patient group. Low-dose ara-C treatment was superior to best supportive care and hydroxyurea because it had greater success in achieving CR, and it could represent standard care against which new treatments may be compared in this patient group.

cDNA microarray analysis of altered gene expression in Ara-C-treated leukemia cells

The acute lymphoblastic leukemia cell line CCRF-CEM is sensitive to Ara-C and undergoes apoptosis. In contrast, the chronic myelogenous leukemia (CML) cell line K562 is highly resistant to Ara-C, which causes the cells to differentiate into erythrocytes before undergoing apoptosis. We used cDNA microarrays to monitor the alterations in gene expression in these two cell lines under conditions leading to apoptosis or differentiation. Ara-C-treated CCRF-CEM cells were characterized by a cluster of down-regulated chaperone genes, whereas Ara-C-treated K562 cells were characterized by a cluster of up-regulated hemoglobin genes. In K562 cells, Ara-C treatment induced significant down-regulation of the asparagine synthetase gene, which is involved in resistance to L-asparaginase. Sequential treatment with Ara-C and L-asparaginase had a synergistic effect on the inhibition of K562 cell growth, and combination therapy with these two anticancer agents may prove effective in the treatment of CML, which cannot be cured by either drug alone.

Leukemia cutis in an elderly patient treated with low dose cytosine arabinoside and etoposide

A 78-year-old man presented with a generalized erythematous papular rash. Such skin lesions were not painful, tender or pruritic, and spread over the truncus. He was admitted to our hospital for examination of the skin lesions. Laboratory tests indicated microcytic hypochromatic anemia and thrombocytopenia, although gave a normal leukocyte count with normal differentiation. His bone marrow showed hypercellularity, with 43% peroxidase positive blasts that displayed positive immunophenotypes for CD4, CD13, CD33, CD41a, KP-1 (CD68), and HLA-DR. His skin specimen revealed infiltration in the dermis and subcutaneous fat tissue by leukemic cells that were positive for the leukocyte common antigen (LCA, CD45), CD15, CD33, CD68, and HLA-DR. He was diagnosed as having M4 subtype of acute myelogeneous leukemia (AML) with leukemia cutis. After three courses of low dose cytosine arabinoside (LDAC), combined with low dose etoposide, he achieved complete remission (CR). He remained well, with no evidence of relapse nine months later. LDAC should be considered as initial treatment for such cases of leukemia cutis with poor general condition.

All-trans retinoic acid and hematopoietic growth factors regulating the growth and differentiation of blast progenitors in acute promyelocytic leukemia

Although acute leukemia is generally thought to be characterized by maturation arrest, it has been shown that differentiation occurs in blast cells of acute myelogenous leukemia (AML) in vitro as well as in vivo, and that morphologically abnormal mature polymorphonuclear neutrophils (PMNs) often seen in patients with AML are possibly derived from spontaneously differentiating leukemic cells. Acute promyelocytic leukemia (APL) is an unique example in which these features of AML are evident in an almost complete form; administration of all-trans retinoic acid (ATRA) induces differentiation of neoplastic cells into mature neutrophils and successfully induce complete remission in most patients. However, PMNs appearing during ATRA treatment are morphologically abnormal, as indicated not only by the presence of Auer rods but also by neutrophil secondary-granule deficiency that is commonly seen in AML. Moreover, ATRA has heterogeneous effects on the growth of blast progenitors in APL in different patients, being inhibitory, stimulatory or ineffective, which might account in part for the leukemia relapse in patients treated with ATRA alone. Hematopoietic growth factors regulate the growth of blast progenitors in APL. Among them, granulocyte colony-stimulating factor (G-CSF) is unique in that it preferentially stimulates clonal growth, but not self-renewal, in many APL cases, and synergistically enhances the differentiation-inducing effect of ATRA when used in combination. Many other compounds also exert such synergistic effects with ATRA, for which a variety of mechanisms have been suggested. It is crucial to precisely elucidate the functions of these molecules governing the growth/differentiation balance of AML blast progenitors and the mechanisms underlying their deregulated differentiation program in order to achieve effective differentiation therapy for patients with AML, not restricted to APL.

Growth inhibition and differentiation induction in human monoblastic leukaemia cells by 1alpha-hydroxyvitamin D derivatives and their enhancement by combination with hydroxyurea

The active form of vitamin D, 1alpha,25-dihydroxyvitamin D3 (1,25(OH)2D3), is a potent inducer of differentiation in myeloid leukaemia cells, but its clinical use is limited because of its hypercalcaemic activity. We examined the ability of 1,25(OH)2D3 in combination with several anti-cancer drugs to inhibit the proliferation of, and induce differentiation in, human monoblastic leukaemia U937 cells. Hydroxyurea (HU), cytarabine and camptothecin showed effective synergism with 1,25(OH)2D3 with regard to growth inhibition, while daunorubicin and etoposide had only modest synergistic effects. HU and cytarabine effectively enhanced nitroblue tetrazolium-reducing activity induced by 1,25(OH)2D3. HU also enhanced the morphological maturation and expression of CD11b and CD14 in cells treated with 1,25(OH)2D3. Among the anti-cancer drugs examined, HU had the greatest synergistic effects with 1,25(OH)2D3 with regard to growth inhibition and differentiation induction in U937 cells. HU also enhanced the differentiation of other myeloid leukaemia HL-60, ML-1, THP-1, P39/TSU, P31/FUJ and NB4 cells induced by 1,25(OH)2D3 and that of U937 cells induced by 24-epi-1,25(OH)2D2 and 1,25(OH)2D7. Interestingly, 1alpha(OH)D derivatives (1alpha-hydroxyvitamin D3, D2, D4 and D7) effectively induced the differentiation of monoblastic leukaemia U937, P39/TSU and P31/FUJ cells. HU also enhanced the growth inhibition and differentiation of U937 cells induced by 1alpha(OH)D derivatives. As 1alpha(OH)D derivatives preferentially act on monocytic cells, they may be useful in the treatment of acute monocytic leukaemia, both alone and in combination with HU.

Differentiation, differentiation/gene therapy and cancer

"Differentiation, Differentiation/Gene Therapy and Cancer" is intended to suggest that an understanding of the cell and molecular biology of cell differentiation should advance the development of new cancer therapies. This article, therefore, reviews four general topics and their relationship to each other: (1) the multistep process of cell differentiation in nontransformed and transformed cells, (2) the use of drugs that induce differentiation in vitro as potential clinical differentiation therapy agents for cancer, (3) the evolving emphasis on gene therapy as a new cancer therapy modality, and (4) the concept of differentiation/gene therapy.

Childhood myelodysplastic syndromes: clinical features, cytogenetics and prognosis

Sixteen children with myelodysplastic syndrome as defined by the French-American-British co-operative group are presented. The mean age was 10.5 (2.5 to 16) years, with a male predominance. All patients belonged to the more aggressive subtypes of myelodysplastic syndromes. Seven patients presented with refractory anaemia with excess blasts, six had refractory anemia with excess blasts in transformation, and three had chronic myelomonocytic leukemia. Cytogenetic analysis done in 7 of the 16 patients, revealed karyotype abnormalities involving chromosomes 7, 8 and 17. One patient with Down's syndrome had karyotype of 47, XY, +21 (major clone) and 46, XY (minor clone). Five of these patients evolved to acute leukemia. The mean duration of survival was 5.5 months. Aggressive chemotherapy as a primary line of treatment induced remission in five out of six patients. Predominance of aggressive types of myelodysplastic syndromes in children and their good but short-lived response to aggressive chemotherapy suggests the need for early bone marrow transplantation following chemotherapy.

All-trans-retinoic acid treatment and retinoic acid receptor alpha gene rearrangement in acute promyelocytic leukemia: a model for differentiation therapy

All-trans-retinoic acid (ATRA), a vitamin A derivative, is a safe and effective drug in the obtention of complete remission in acute promyelocytic leukemia (APL). ATRA is able to activate the maturation of malignant cells from patients with APL either in vitro or in vivo. Complete remission was obtained without any feature of aplastic phase and the severe bleeding diathesis rapidly disappeared. The major adverse effect is the occurrence of hyperleukocytosis which is prevented by the addition of chemotherapy. A progressive acquired resistance appears during ATRA treatment and prolonged event free survival time is obtained after consolidation with cytotoxic drugs. In APL the retinoic acid receptor alpha gene is rearranged and fused with a novel gene called PML. The hybrid PML-RAR product could have a role in the leukemogenesis blocking the effect of the normal RAR on target genes. Retinoic acid exerts a differentiating effect either by the induction of a normal activity of the aberrant product in the presence of pharmacological concentration, or by an over-expression of the normal allele. The results obtained by cellular and molecular biology gave opportunities to confirm the diagnosis, to follow the assessment of the minimal residual disease and to understand the acquired resistance.

Low-dose cytosine arabinoside for treating hypocellular acute leukemia in the elderly

Ten previously untreated elderly patients with hypocellular acute leukemia received a low dose of cytosine arabinoside (Ara-C), 10 mg/m2 injected subcutaneously every 12 hours for 14-28 days. Six patients achieved a complete remission (CR) for periods ranging for 6-23 months (median 8.5 months) and the others had a partial remission (PR). Relapse has occurred in three patients to date. The median survival ranged from 10-24 months (median 14.5 months). Only two of the six patients, in whom bone marrow biopsy was performed at CR, had a normal cellularity. This change, however, did not appear to be a significant prognostic factor in those patients. In seven patients who achieved a CR or PR low-dose Ara-C was administrated as maintenance therapy at the same low dose for 10 days each month. Treatment was well tolerated in all patients despite for myelosuppression. There were no drug-related deaths. These observations suggest that low-dose Ara-C is effective in treating elderly patients with hypocellular acute leukemia.

Low-dose cytarabine for acute myeloid leukaemia and myelodysplastic syndromes: in vivo and in vitro cytotoxicity

14 patients with acute myeloid leukaemia (AML) and 7 with myelodysplastic syndrome (MDS) were treated with cytarabine in low dosage. In AML a complete remission rate of 43% was found and in all patients profound cytopenia was noticed without any sign of maturation induction. In MDS no effect of low-dose cytarabine could be detected. We also studied the effect of low-dose cytarabine in vitro in freshly isolated leukaemic cells of 10 patients with AML. Maturation induction was measured by a comprehensive panel of quantitative and qualitative markers of maturation. No differentiation inducing effect of low-dose cytarabine could be found. We conclude on the basis of our own results and after reviewing the literature that low-dose cytarabine exerts its effect by cytotoxicity instead of maturation induction.

Pharmacological studies of retinol palmitate and its clinical effect in patients with acute non-lymphocytic leukemia

The pharmacokinetics of retinol palmitate were studied, and a therapeutic trial was performed in patients with ANLL. In the pharmacokinetics study, retinol was the only metabolite that was detected in plasma, and the peak concentration was 332 micrograms/dl (about 1.2 x 10(-5) M) 2.1 h after administration of retinol palmitate. Five patients with ANLL (4 with ANLL-M3 and one with ANLL-M2) were treated with retinol palmitate. In all patients with ANLL-M3, bone marrow suspension culture studies revealed that retinol induced both morphological and functional differentiation of immature leukemic cells. During the course of the treatment with retinol palmitate, morphological differentiation of bone marrow immature leukemic cells was observed in all patients with ANLL-M3 within 3-4 days after initiation of the therapy. In three of the four patients who underwent conventional chemotherapy, the sequential treatment with retinol palmitate resulted in a complete remission: controlling residual bone marrow leukemic cells. None of the patients showed any signs of aggravation of DIC in the coagulation parameters. These findings suggest the possibility that retinol palmitate functions as salvage therapy by inducing maturation and slowing proliferation, there by clearing out the residual leukemic cells following conventional chemotherapy.

Differentiating agents in the treatment of leukemia and myelodysplastic syndromes

Differentiation therapies try to change the malignant cell in order to acquire a more mature or normal phenotype. Various ways were tested in leukemia: suppression the proliferative pressure by low dose Ara-C, enhancement of the differentiation by retinoic acid derivatives or by differentiation factors, and modulation of the cell metabolism interrupting an autocrine loop (a growth factor and its receptor). The treatment is given continuously at small doses, during a long period of time. In all these cases it seems necessary to tailor the differentiation therapy to each category of leukemia.

Reduction of leukemia cell growth in a patient with acute promyelocytic leukemia treated by retinol palmitate

A 67-year-old woman with acute promyelocytic leukemia (APL) showed a marked decrease in leukemic promyelocytes with concomitant maturation of leukemic cells during treatment with retinol palmitate. A culture study in vitro revealed that retinol, which is the main metabolite of retinol palmitate detected in plasma, induced morphological and functional maturation of leukemic promyelocytes. These findings may indicate that retinol palmitate induces cell differentiation and slows proliferation of leukemic cells in vivo, and that the reduction in cell growth is the key phenomenon in the clearing of leukemic cells, rather than the maturation phenomenon itself.

Differentiating agents in the treatment of leukemia

The aim of differentiation therapy is to induce a maturation of the leukemic clone. Various approaches have been used: suppression of proliferation by low dose Ara-C in acute myeloid leukemia (AML); enhancement of differentiation by retinoic acid derivatives in acute promyelocytic leukemia (APL) or by differentiation-inducing factors; modulation of cell metabolism by breaking an autocrine loop in hairy cell leukemia (HCL). In all cases the treatment is given continuously at small doses over a long period of time. The very significant clinical results which have been obtained mainly in APL with all-trans retinoic acid and in HCL with alpha-interferon are briefly discussed.

Induction of differentiation of HL-60 cells along the monocytic pathway by 5-methyltetrahydrofolate

Many compounds of different chemical structure can induce the HL-60 cell line to differentiate along the monocytic or granulocytic pathway, but the mechanism(s) of differentiation by these agents is not known. Experimental evidence suggests that DNA and/or membrane phospholipid transmethylation reactions may be of importance. Based on this background, we have studied the effects of various concentrations of (dl)-5-methyltetrahydrofolate (mTHF), a folate coenzyme involved in transmethylation reactions, on differentiation of HL-60 cells. Differentiation along the monocytic pathway was evidenced in kinetic, functional, cytochemical and immunophenotypical studies when cells were treated with high-dose (dl)-mTHF (1 x 10(-3)M). Some hypotheses on the mechanism(s) of (dl)-mTHF induced HL-60 cell differentiation are discussed with particular regard to a possible enhancement of lipid or DNA methylation via methionine formation by the (l) form or to inhibition of folate-dependent metabolism by the unnatural (d) form, hence of purine and thymine nucleotide synthesis.

In vitro evidence for dose-dependent cytotoxicity as the predominant effect of low dose Ara-C on human leukemic and normal marrow cells

To determine whether cytosine arabinoside (Ara-C) has a differentiating effect in vitro, marrow cells from nine patients with acute non-lymphocytic leukemia or myelodysplastic syndrome and eight non-leukemic controls were exposed to drug concentrations comparable to those achieved in vivo with low-dose Ara-C therapy. In soft agar cultures, the predominant effect of Ara-C at concentrations between 10(-8) M and 10(-6) M was cytotoxicity with a dose-dependent decrement in Colony Forming Unit of the granulocyte and monocyte lineage (CFUg/m) at 14 days. Growth in liquid cultures containing Giant Cell Tumor(GCT)-conditioned media without Ara-C resulted in a significant increment in the recovery of mature cells at day 10 from the non-leukemic cultures (P = 0.03), while only a minor increase was found in the leukemic cultures (P = 0.09). All liquid cultures exposed to greater than or equal to 10(-9) M Ara-C showed a marked reduction in the immature proliferating cell pool, with a concomitant increase in the percentage of mature non-dividing cells at 10 days. However, the absolute number of differentiated cells recovered remained constant or decreased in all non-leukemic and eight of nine leukemic cultures, compared with cultures without Ara-C. Enhanced recovery of differentiated cells was also never observed in any culture exposed to the relatively non-toxic 10(-9) M Ara-C. These in vitro findings support clinical observations suggesting that cytotoxicity rather than differentiation is the major mechanism involved in the therapeutic effect of low-dose Ara-C in acute leukemia and myelodysplasia.

Low-dose cytosine arabinoside in acute non-lymphoblastic leukemia

Eighteen previously untreated patients with acute non-lymphoblastic leukemia (ANLL) were treated with cytosine arabinoside (Ara-C) in low doses (10 mg/m2 every 12 hours) subcutaneously for 3 weeks. Complete remission (CR) was achieved in four patients (22.2%), and myelosuppression was observed in nearly all of them. Thrombocytopenia (20 X 10(3)/microliters) was pronounced in the third week of treatment and six patients (33.3%) needed platelet support. Contrary to earlier claims, our experience suggests that treatment with low-dose Ara-C is associated with significant cytopenias. Ara-C does not obviate the need for intensive supportive care and CR rates are no longer better. Low-dose Ara-C does not seem to be a choice in previously untreated ANLL patients who otherwise have a high probability of achieving a CR with standard multidrug chemotherapy protocols.

Clinical pharmacology of N4-palmitoyl-1-beta-D-arabinofuranosylcytosine in patients with hematologic malignancies

The pharmacokinetics of oral N4-palmitoyl-1-beta-D-arabinofuranosylcytosine (PLAC), a lipophilic and deaminase-resistant derivative of 1-beta-D-arabinofuranosylcytosine (ara-C), were determined in patients with hematologic malignancies. The concentration of ara-C and 1-beta-D-arabinofuranosyluracil (ara-U), metabolites of PLAC, were measured by radioimmunoassay and gas chromatography-mass spectrometry-mass fragmentography, respectively. The concentration of PLAC was determined by measuring ara-C, which was derived from PLAC by hydrolyzation. In six patients given an oral bolus of PLAC (300 mg/m2), the plasma-disappearance curve of PLAC corresponded to a one-compartment open model, including first-order absorption. The peak plasma level was 22.9 +/- 6.4 ng/ml, and the predicted time to reach the peak level was 2.5 +/- 1.0 h. The elimination half-life was 3.8 +/- 2.7 h. The plasma ara-C level increased slowly to 6.9 ng/ml during the 1st 2-3 h after administration and remained over 1.0 ng/ml for 12 h. Plasma ara-U was detectable for at least 24 h, with a peak concentration of 376 ng/ml at 6 h. Urinary PLAC excretion was below the limit of detection (5 ng/ml) in all cases. Prolonged urinary ara-C and ara-U excretion was detected, but the total recovery rate was low (6.7% in 24 h) and varied between patients. In spite of the lipophilic nature of the drug, the PLAC concentration in the cerebrospinal fluid, measured at 3 or 6 h, was below the limit of detection in all four patients with no meningeal involvement. This study showed low but persistent levels of PLAC in plasma and tissues, with a continuous release of small amounts of ara-C, which demonstrated antitumor activity in patients with hematologic malignancies.

Low dose cytosine arabinoside in refractory anemia with excess of blasts in transformation

Myelodysplastic syndromes (MDS) are heterogeneous diseases. Patients with blast counts of more than 20% of nucleated bone marrow cells have a high risk of short survival. We treated six patients with refractory anemia with excess of blast in transformation (RAEBiT) with low dose cytosine arabinoside (LD Ara-C). We had one partial remission (PR), surviving 16 weeks and two complete remissions (CR), surviving 22 and 55+ months. Myelosuppression was dominant in all patients, but was not as serious as with conventional remission-induction treatments for leukemias. Bone marrow aplasia occurred in all responding patients, but a differentiation effect is possible too. Maintenance therapy with LD Ara-C may be important for the two long-lasting CR.

Effectiveness of attenuated chemotherapy in myelodysplastic syndromes: a preliminary report

A small group of elderly male patients received attenuated doses of daunomycin, cytosine arabinoside (Ara-C), and 6-thioguanine for treatment of myelodysplastic syndrome (MDS). Three patients had refractory anemia with excess blasts (RAEB), and two had chronic myelomonocytic leukemia (CMMoL). All five patients had developed severe transfusion requirements for platelets and red blood cells before therapy was begun. One patient developed necrosis of the cecum and expired 19 days after therapy, but the other four all showed substantial benefit from treatment. Three of those patients received multiple courses of chemotherapy which led to improvement in peripheral blood counts in each case. Duration of responses as noted by improvement in peripheral blood counts compared to pretreatment levels ranged from 1.5 to 9 months. Despite considerable improvement in peripheral blood parameters, some of the abnormal morphologic features of MDS persisted after each course of chemotherapy. These results obtained with attenuated chemotherapy schedules in a small group of patients are sufficiently encouraging to warrant an expanded phase II trial, which is under way at the University of Rochester Cancer Center.

Effect of fagaronine on cell cycle progression of human erythroleukemia K562 cells

Fagaronine (Fine) is a novel antileukemic drug extracted from Fagara xanthoxyloides Lam. (Rutaceae). In an attempt to know more about its mechanism of action we describe here its inhibitory activity on cell division, 3H-thymidine incorporation and on cell cycle progression. Fine inhibits cell proliferation of K562 cells by 50% at a concentration of 3 x 10(-6) mol/l at day 4. It stimulates incorporation of labelled macromolecular thymidine on day 1, but decreases incorporation on days 2, 3 and 4. Fine induces a cell accumulation in G2 and late-S phases. This accumulation (i) increases with Fine concentration, but a complete blockade is not observed, (ii) reaches a plateau after approximately 48 h, (iii) is reversible, whereas we have previously shown that cell growth inhibition and differentiation were not reversible.