Advances in the treatment of acute myeloid leukemia: From chromosomal aberrations to biologically targeted therapy

The landscape of novel strategies for acute myeloid leukemia treatment: Therapeutic trends, challenges, and future directions

Acute myeloid leukemia (AML) is a highly heterogeneous subtype of hematological malignancies with a wide spectrum of cytogenetic and molecular abnormalities, which makes it difficult to manage and cure. Along with the deeper understanding of the molecular mechanisms underlying AML pathogenesis, a large cohort of novel targeted therapeutic approaches has emerged, which considerably expands the medical options and changes the therapeutic landscape of AML. Despite that, resistant and refractory cases caused by genomic mutations or bypass signalling activation remain a great challenge. Therefore, discovery of novel treatment targets, optimization of combination strategies, and development of efficient therapeutics are urgently required. This review provides a detailed and comprehensive discussion on the advantages and limitations of targeted therapies as a single agent or in combination with others. Furthermore, the innovative therapeutic approaches including hyperthermia, monoclonal antibody-based therapy, and CAR-T cell therapy are also introduced, which may provide safe and viable options for the treatment of patients with AML.

SERS-Based Assessment of MRD in Acute Promyelocytic Leukemia?

Acute promyelocytic leukemia (APL) is characterized by a unique chromosome translocation t(15;17)(q24;q21), which leads to the PML/RARA gene fusion formation. However, it is acknowledged that this rearrangement alone is not able to induce the whole leukemic phenotype. In addition, epigenetic processes, such as DNA methylation, may play a crucial role in leukemia pathogenesis. DNA methylation, catalyzed by DNA methyltransferases (DNMTs), involves the covalent transfer of a methyl group (-CH3) to the fifth carbon of the cytosine ring in the CpG dinucleotide and results in the formation of 5-methylcytosine (5-mC). The aberrant gene promoter methylation can be an alternative mechanism of tumor suppressor gene inactivation. Understanding cancer epigenetics and its pivotal role in oncogenesis, can offer us not only attractive targets for epigenetic treatment but can also provide powerful tools in monitoring the disease and estimating the prognosis. Several genes of interest, such as RARA, RARB, p15, p16, have been studied in APL and their methylation status was correlated with potential diagnostic and prognostic significance. In the present manuscript we comprehensively examine the current knowledge regarding DNA methylation in APL pathogenesis. We also discuss the perspectives of using the DNA methylation patterns as reliable biomarkers for measurable residual disease (MRD) monitoring and as a predictor of relapse. This work also highlights the possibility of detecting aberrant methylation profiles of circulating tumor DNA (ctDNA) through liquid biopsies, using the conventional methods, such as methylation-specific polymerase chain reaction (MS-PCR), sequencing methods, but also revolutionary methods, such as surface-enhanced Raman spectroscopy (SERS).

Preparation and in vitro characterization of retinoic acid-loaded poly(ε-caprolactone)-poly(ethylene glycol)-poly(ε-caprolactone) micelles

In order to achieve the controlled release of all-trans-retinoic acid (ATRA), poly(ε-caprolactone)-poly(ethylene glycol)-poly(ε-caprolactone) (PCL-PEG-PCL) copolymer with average molecular weight of 5.34 kDa was synthesized. The nanosized micelles were prepared from copolymer by nano-precipitation method. Critical association concentration (CAC) of micelles was measured by fluorimetry and results indicated low CAC value of micelles (1.9 × 10^-3 g/L). ATRA was encapsulated in the core of micelles using different ratios of drug to copolymer. In the case of 10% drug to polymer ratio, more than 80% of the drug was released within 3 days, whereas for ratio of 2% more than 90% of the drug was released within 3 h. The cytotoxic study performed by MTT assay showed that H1299 survival percent decreased significantly (P ≤ 0.05) after exposure to drug-loaded micelles, while no proliferation inhibition effect was observed by either free ATRA or blank PCL-PEG-PCL micelles.

A robust and rapid xenograft model to assess efficacy of chemotherapeutic agents for human acute myeloid leukemia

Relevant preclinical mouse models are crucial to screen new therapeutic agents for acute myeloid leukemia (AML). Current in vivo models based on the use of patient samples are not easy to establish and manipulate in the laboratory. Our objective was to develop robust xenograft models of human AML using well-characterized cell lines as a more accessible and faster alternative to those incorporating the use of patient-derived AML cells. Five widely used AML cell lines representing various AML subtypes were transplanted and expanded into highly immunodeficient non-obese diabetic/LtSz-severe combined immunodeficiency IL2Rγ_c^null mice (for example, cell line-derived xenografts). We show here that bone marrow sublethal conditioning with busulfan or irradiation has equal efficiency for the xenotransplantation of AML cell lines. Although higher number of injected AML cells did not change tumor engraftment in bone marrow and spleen, it significantly reduced the overall survival in mice for all tested AML cell lines. On the basis of AML cell characteristics, these models also exhibited a broad range of overall mouse survival, engraftment, tissue infiltration and aggressiveness. Thus, we have established a robust, rapid and straightforward in vivo model based on engraftment behavior of AML cell lines, all vital prerequisites for testing new therapeutic agents in preclinical studies.

The role of human equilibrative nucleoside transporter 1 on the cellular transport of the DNA methyltransferase inhibitors 5-azacytidine and CP-4200 in human leukemia cells

The nucleoside analog 5-azacytidine is an archetypical drug for epigenetic cancer therapy, and its clinical effectiveness has been demonstrated in the treatment of myelodysplastic syndromes (MDS) and acute myelogenous leukemia (AML). However, therapy resistance in patients with MDS/AML remains a challenging issue. Membrane proteins that are involved in drug uptake are potential mediators of drug resistance. The responsible proteins for the transport of 5-azacytidine into MDS/AML cells are unknown. We have now systematically analyzed the expression and activity of various nucleoside transporters. We identified the human equilibrative nucleoside transporter 1 (hENT1) as the most abundant nucleoside transporter in leukemia cell lines and in AML patient samples. Transport assays using [¹⁴C]5-azacytidine demonstrated Na⁺-independent uptake of the drug into the cells, which was inhibited by S-(4-nitrobenzyl)-6-thioinosine (NBTI), a hENT1 inhibitor. The cellular toxicity of 5-azacytidine and its DNA demethylating activity were strongly reduced after hENT1 inhibition. In contrast, the cellular activity of the 5-azacytidine derivative 5-azacytidine-5'-elaidate (CP-4200), a nucleoside transporter-independent drug, persisted after hENT1 inhibition. A strong dependence of 5-azacytidine-induced DNA demethylation on hENT1 activity was also confirmed by array-based DNA methylation profiling, which uncovered hundreds of loci that became demethylated only when hENT1-mediated transport was active. Our data establish hENT1 as a key transporter for the cellular uptake of 5-azacytidine in leukemia cells and raise the possibility that hENT1 expression might be a useful biomarker to predict the efficiency of 5-azacytidine treatments. Furthermore, our data suggest that CP-4200 may represent a valuable compound for the modulation of transporter-related 5-azacytidine resistances.

Parameters detected by geriatric and quality of life assessment in 195 older patients with myelodysplastic syndromes and acute myeloid leukemia are highly predictive for outcome

Myelodysplastic syndromes and acute myeloid leukemia exemplify the complexity of treatment allocation in older patients as options range from best supportive care, non-intensive treatment (e.g. hypomethylating agents) to intensive chemotherapy/hematopoietic cell transplantation. Novel metrics for non-disease variables are urgently needed to help define the best treatment for each older patient. We investigated the feasibility and prognostic value of geriatric/quality of life assessments aside from established disease-specific variables in 195 patients aged 60 years or over with myelodysplastic syndromes/acute myeloid leukemia. These patients were grouped according to treatment intensity and assessed. Assessment consisted of eight instruments evaluating activities of daily living, depression, mental functioning, mobility, comorbidities, Karnofsky Index and quality of life. Patients with a median age of 71 years (range 60-87 years) with myelodysplastic syndromes (n=63) or acute myeloid leukemia (n=132) were treated either with best supportive care (n=47), hypomethylating agents (n=73) or intensive chemotherapy/hematopoietic cell transplantation (n=75). After selection of variables, pathological activities of daily living and quality of life/fatigue remained highly predictive for overall survival in the entire patient group beyond disease-related risk factors adverse cytogenetics and blast count of 20% or over. In 107 patients treated non-intensively activities of daily living of less than 100 (hazard ratio, HR 2.94), Karnofsky Index below 80 (HR 2.34) and quality of life/'fatigue' of 50 or over (HR 1.77) were significant prognosticators. Summation of adverse features revealed a high risk of death (HR 9.36). In-depth evaluation of older patients prior to individual treatment allocation is feasible and provides additional information to standard assessment. Patients aged 60 years or over with newly diagnosed myelodysplastic syndromes/acute myeloid leukemia and impairments in activities of daily living, Karnofsky Index below 80%, quality of life/'fatigue' of 50 or over, are likely to have poor outcomes.

A novel thiazolidine compound induces caspase-9 dependent apoptosis in cancer cells

The forward chemogenomics strategy allowed us to identify a potent cytotoxic thiazolidine compound as an apoptosis-inducing agent. Chemical structures were designed around a thiazolidine ring, a structure already noted for its anticancer properties. Initially, we evaluated these novel compounds on liver, breast, colon and endometrial cancer cell lines. The compound 3 (ALC67) showed the strongest cytotoxic activity (IC(50) ∼5 μM). Cell cycle analysis with ALC67 on liver cells revealed SubG1/G1 arrest bearing apoptosis. Furthermore we demonstrated that cytotoxicity of this compound was due to the activation of caspase-9 involved apoptotic pathway, which is death receptor independent.

DNMT3B gene amplification predicts resistance to DNA demethylating drugs

Disruption of the DNA methylation landscape is one of the most common features of human tumors. However, genetic alterations of DNA methyltransferases (DNMTs) have not been described in carcinogenesis. Herein, we show that pancreatic and breast cancer cells undergo gene amplification of the DNA methyltransferase 3B (DNMT3B). The presence of extra copies of the DNMT3B gene is linked to higher levels of the corresponding mRNA and protein. Most importantly, the elevated gene dosage of DNMT3B is associated with increased resistance to the growth-inhibitory effect mediated by DNA demethylating agents. In particular, cancer cells harboring DNMT3B gene amplification are less sensitive to the decrease in cell viability caused by 5-azacytidine (Vidaza), 5-aza-2-deoxycytidine (Decitabine), and SGI-1027. Overall, the data confirm DNMT3B as a bona fide oncogene in human cancer and support the incorporation of the DNMT3B copy number assay into current clinical trials assessing the efficacy of DNA demethylating drugs in solid tumors.

Differentiation therapy of acute myeloid leukemia

Acute Myeloid Leukemia (AML) is a predominant acute leukemia among adults, characterized by accumulation of malignantly transformed immature myeloid precursors. A very attractive way to treat myeloid leukemia, which is now called 'differentiation therapy', was proposed as in vitro studies have shown that a variety of agents stimulate differentiation of the cell lines isolated from leukemic patients. One of the differentiation-inducing agents, all-trans retinoic acid (ATRA), which can induce granulocytic differentiation in myeloid leukemic cell lines, has been introduced into clinics to treat patients with acute promyelocytic leukemia (APL) in which a PML-RARA fusion protein is generated by a t(15;17)(q22;q12) chromosomal translocation. Because differentiation therapy using ATRA has significantly improved prognosis for patients with APL, many efforts have been made to find alternative differentiating agents. Since 1,25-dihydroxyvitamin D3 (1,25D) is capable of inducing in vitro monocyte/macrophage differentiation of myeloid leukemic cells, clinical trials have been performed to estimate its potential to treat patients with AML or myelodysplastic syndrome (MDS). Unfortunately therapeutic concentrations of 1,25D can induce potentially fatal systemic hypercalcemia, thus limiting clinical utility of that compound. Attempts to overcome this problem have focused on the synthesis of 1,25D analogs (VDAs) which retain differentiation inducing potential, but lack its hypercalcemic effects. This review aims to discuss current problems and potential solutions in differentiation therapy of AML.

The cyclin-dependent kinase inhibitor SNS-032 has single agent activity in AML cells and is highly synergistic with cytarabine

SNS-032 (BMS-387032) is a selective cyclin-dependent kinase (CDK) inhibitor. In this study, we evaluated its effects on primary acute myeloid leukemia (AML) samples (n=87). In vitro exposure to SNS-032 for 48 h resulted in a mean LD(50) of 139±203 nM; Cytarabine (Ara-C) was more than 35 times less potent in the same cohort. SNS-032-induced a dose-dependent increase in annexin V staining and caspase-3 activation. At the molecular level, SNS-032 induced a marked dephosphorylation of serine 2 and 5 of RNA polymerase (RNA Pol) II and inhibited the expression of CDK2 and CDK9 and dephosphorylated CDK7. Furthermore, the combination of SNS-032 and Ara-C showed remarkable synergy that was associated with reduced mRNA levels of the antiapoptotic genes XIAP, BCL2 and MCL1. In conclusion, SNS-032 is effective as a single agent and in combination with Ara-C in primary AML blasts. Treatment with Ara-C alone significantly induced the transcription of the antiapoptotic genes BCL2 and XIAP. In contrast, the combination of SNS-032 and Ara-C suppressed the transcription of BCL2, XIAP and MCL1. Therefore, the combination of SNS-032 and Ara-C may increase the sensitivity of AML cells to the cytotoxic effects of Ara-C by inhibiting the transcription of antiapoptotic genes.

Prognostic Impact of Specific Chromosomal Aberrations in a Large Group of Pediatric Patients With Acute Myeloid Leukemia Treated Uniformly According to Trial AML-BFM 98

Purpose

Because cytogenetic data are essential for risk stratification of childhood acute myeloid leukemia (AML), the impact of chromosomal aberrations is crucial.

Patients and Methods

Data of a large group of patients younger than 18 years treated according to study AML–Berlin-Frankfurt-Münster (BFM) 98 (n = 454), including their cytogenetics, were analyzed.

Results

The favorable outcome in the subgroups of patients with t(8;21), inv(16), and t(15;17), with an overall survival of 91% (SE, 4%), 92% (SE, 6%), and 87% (SE, 5%), respectively, was confirmed. Within this group, the 5-year probability of event-free survival (pEFS) of all 17 children with t(8;21) and additional aberrations apart from del(9q) or −X/−Y was 100%. As expected, the cytogenetic finding of a complex karyotype (n = 35; pEFS, 33%; SE, 8%) or a monosomy 7 (n = 12; pEFS, 17%; SE, 11%) was associated with a poor outcome. Compared with remaining patients with cytogenetic data (pEFS, 48%; SE, 2%), prognosis in patients with an MLL rearrangement (n = 91) was inferior (pEFS, 34%; SE, 5%; P = .0005). Particularly, children with t(9;11) and additional aberrations (n = 13; pEFS, 31%; SE, 14%) and MLL rearrangements other than t(9;11) and t(11;19) (n = 41; pEFS, 24%; SE, 7%) had an unfavorable outcome. Nine patients with aberrations in 12p showed an adverse prognosis (pEFS, 11%; SE, 10%). The outcome of patients with aberrations of chromosome 5 (n = 13) was better than expected (pEFS, 50%; SE, 13%).

Conclusion

Because the prognostic value of rare recurrent chromosomal aberrations still has to be elucidated, these data will contribute to future risk stratification for the treatment of pediatric AML.

AML1 is overexpressed in patients with myeloproliferative neoplasms and mediates JAK2V617F-independent overexpression of NF-E2

The transcription factor NF-E2 is overexpressed in the majority of patients with polycythemia vera (PV). Concomitantly, 95% of these patients carry the JAK2(V617F) mutation. Although NF-E2 levels correlate with JAK2(V671F) allele burden in some PV cohorts, the molecular mechanism causing aberrant NF-E2 expression has not been described. Here we show that NF-E2 expression is also increased in patients with essential thrombocythemia and primary myelofibrosis independent of the presence of the JAK2(V617F) mutation. Characterization of the NF-E2 promoter revealed multiple functional binding sites for AML1/RUNX-1. Chromatin immunoprecipitation demonstrated AML1 binding to the NF-E2 promoter in vivo. Moreover, AML1 binding to the NF-E2 promoter was significantly increased in granulocytes from PV patients compared with healthy controls. AML1 mRNA expression was elevated in patients with PV, essential thrombocythemia, and primary myelofibrosis both in the presence and absence of JAK2(V617F). In addition, AML1 and NF-E2 expression were highly correlated. RNAi-mediated suppression of either AML1 or of its binding partner CBF-beta significantly decreased NF-E2 expression. Moreover, expression of the leukemic fusion protein AML/ETO drastically decreased NF-E2 protein levels. Our data identify NF-E2 as a novel AML1 target gene and delineate a role for aberrant AML1 expression in mediating elevated NF-E2 expression in MPN patients.

Mutations of polycomb-associated gene ASXL1 in myelodysplastic syndromes and chronic myelomonocytic leukaemia

The myelodysplastic syndromes (MDSs) are a heterogeneous group of clonal haematological diseases characterized by ineffective haematopoiesis and predisposition to acute myeloid leukaemia (AML). The pathophysiology of MDSs remains unclear. A definition of the molecular biology of MDSs may lead to a better classification, new prognosis indicators and new treatments. We studied a series of 40 MDS/AML samples by high-density array-comparative genome hybridization (aCGH). The genome of MDSs displayed a few alterations that can point to candidate genes, which potentially regulate histone modifications and WNT pathways (e.g. ASXL1, ASXL2, UTX, CXXC4, CXXC5, TET2, TET3). To validate some of these candidates we studied the sequence of ASXL1. We found mutations in the ASXL1 gene in four out of 35 MDS patients (11%). To extend these results we searched for mutations of ASXL1 in a series of chronic myelomonocytic leukaemias, a disease classified as MDS/Myeloproliferative disorder, and found mutations in 17 out of 39 patients (43%). These results show that ASXL1 might play the role of a tumour suppressor in myeloid malignancies.