Prospective monitoring of minimal residual disease in acute myeloid leukemia with inversion(16) by CBFbeta/MYH11 RT-PCR: implications for a monitoring schedule and for treatment decisions

Current and emerging molecular and epigenetic disease entities in acute myeloid leukemia and a critical assessment of their therapeutic modalities

Acute myeloid leukemia (AML) is the most frequently diagnosed acute leukemia, and its incidence increases with age. Although the etiology of AML remains unknown, exposure to genotoxic agents or some prior hematologic disorders could lead to the development of this condition. The pathogenesis of AML involves the development of malignant transformation of hematopoietic stem cells that undergo successive genomic alterations, ultimately giving rise to a full-blown disease. From the disease biology perspective, AML is considered to be extremely complex with significant genetic, epigenetic, and phenotypic variations. Molecular and cytogenetic alterations in AML include mutations in those subsets of genes that are involved in normal cell proliferation, maturation and survival, thus posing significant challenge to targeting these pathways without attendant toxicity. In addition, multiple malignant cells co-exist in the majority of AML patients. Individual subclones are characterized by unique genetic and epigenetic abnormalities, which contribute to the differences in their response to treatment. As a result, despite a dramatic progress in our understanding of the pathobiology of AML, not much has changed in therapeutic approaches to treat AML in the past four decades. Dose and regimen modifications with improved supportive care have contributed to improved outcomes by reducing toxicity-related side effects. Several drug candidates are currently being developed, including targeted small-molecule inhibitors, cytotoxic chemotherapies, monoclonal antibodies and epigenetic drugs. This review summarizes the current state of affairs in the pathobiological and therapeutic aspects of AML.

Bone marrow evaluation for diagnosis and monitoring of acute myeloid leukemia

The diagnosis of acute myeloid leukemia (AML) can be made based on peripheral blood or bone marrow blasts. In this review, we will discuss the role of bone marrow evaluation and peripheral blood monitoring in the diagnosis, management, and follow up of AML patients. For patients with circulating blasts, it is reasonable to perform the necessary studies needed for diagnosis and risk stratification, including multiparametric flow cytometry, cytogenetics, and molecular analysis, on a peripheral blood specimen. The day 14 marrow is used to document hypocellularity in response to induction chemotherapy, but it is unclear if that assessment is necessary as it often does not affect immediate management. Currently, response assessments performed at count recovery for evaluation of remission and measurable residual disease rely on bone marrow sampling. For monitoring of relapse, peripheral blood evaluation may be adequate, but the sensitivity of bone marrow testing is in some cases superior. While bone marrow evaluation can certainly be avoided in particular situations, this cumbersome and uncomfortable procedure currently remains the de facto standard for response assessment.

Understanding the Clinical Implications of Minimal Residual Disease in Childhood Leukemia

Improved laboratory techniques now allow a more sensitive detection of leukemia cells at designated intervals throughout therapy. Using flow cytometry and polymerase chain reaction, it is possible to detect 1 leukemic cell among 10 4 normal cells (1 leukemia cell in 10,000 normal cells), representing a 100-fold greater sensitivity than morphological examination in acute lymphoblastic leukemia (ALL). Recently, it has been shown that the molecular presence of persistent acute lymphoblastic leukemia at the end of remission therapy is a poor indicator of clinical outcome. Now similar studies are being performed in acute myeloid leukemia (AML). While the sensitivity using flow cytometry is less in AML than in ALL (able to detect 1 leukemic cell among 1000 normal cells in AML), persistent or minimal residual AML provides the clinician guidance with future treatment recommendations. Minimal residual disease (MRD) is now considered an important indicator response of disease response to treatment. As such, MRD once considered a research variable is now influencing treatment decisions. Therefore, it is imperative that the nurse have an understanding of the newer techniques to study residual leukemia and their clinical implications for patients and their families.

Multistep targeted nano drug delivery system aiming at leukemic stem cells and minimal residual disease

Refractory leukemia remains the most common therapeutic problem in clinical treatment of leukemia. The key therapy of refractory leukemia is to kill, thoroughly, the minimal residual disease and leukemia stem cells in the highly vascularized red marrow areas. In this study, two new conjugates, alendronate-polyethylene glycol (100) monostearate and folate-polyethylene glycol (100) monostearate, were synthesized to develop a multistep targeting nanostructured lipid carriers by enhancing drug transport to the high bone turnover areas adjacent to the red marrow and targeting the minimal residual disease and leukemia stem cells. This dual targeting system demonstrated a great binding affinity to hydroxyapatite, a model component of bone minerals, and higher cell uptake (in the form of carriers but not drug) and cytotoxicity in the K562 cell line, a leukemia cell line with overexpressed folate receptors, were observed in vitro compared to unmodified carriers, especially when the cells were pretreated and the receptors were up-regulated by all-trans retinoic acid. The comodel test of K562 cells and HA showed that this dual targeting system could desorb from bone surface and be taken up by leukemia cells. For the in vivo study, this dual targeting system exhibited a significant increase in plasma half-life and could specifically accumulate in the bone tissue of rats or mice after intravenous injection. Ex vivo imaging of mice femurs and confocal laser scanning microscope imaging of mice femur slices further confirmed that this dual targeting system could favorably deposit to the osteoblast-enriched areas of high bone turnover in regions of trabecular bone surrounded by red marrow. In vivo antitumor activity in K562/BALB/c-nu leukemia mice showed that the treatment of this dual targeting system significantly reduced the white blood cell (WBC) number in peripheral blood and bone marrow to the normal level. In conclusion, this dual targeting system could precisely target to the regions where the minimal residual disease and leukemia stem cells are located and then be specifically uptaken in large amounts, which is a valuable target for refractory leukemia therapy.

Core binding factor (CBF) acute myeloid leukemia: is molecular monitoring by RT-PCR useful clinically?

Clonal chromosomal abnormalities are the most important prognostic indicators in acute myeloid leukemia (AML). Two of the most prevalent cytogenetic subtypes of adult primary AML, t(8;21)(q22;q22) and inv(16)(p13q22)/t(16;16)(p13;q22), are characterized by disruption of the AML1(CBFA2, RUNX1) and CBFbeta genes, respectively, which encode subunits of core binding factor (CBF), a regulator of normal hematopoiesis. At the molecular level, t(8;21) and inv(16)/t(16;16) result in the creation of novel fusion genes, AML1/ETO and CBFbeta/MYH11, respectively, which encode fusion transcripts readily detectable by the reverse transcription-polymerase chain reaction (RT-PCR). Although the detection of t(8;21) or inv(16)/t(16;16) in adult patients with primary AML represents a favorable independent prognostic indicator for achievement of cure following intensive chemotherapy or stem cell transplantation, a substantial number of these patients (i.e. 40-50%) relapse and eventually die of their disease. Therefore, timely identification and therapeutic stratification of those patients deemed at high risk for disease relapse could ultimately result in a further improvement of clinical outcome within these cytogenetic subgroups of AML. As relapse is likely to occur as the result of failure of treatment to completely eradicate leukemic blasts, the detection of the AML1/ETO and CBFbeta/MYH11 fusion transcripts using sensitive RT-PCR assays has been utilized as a surrogate marker for resistant disease and, in turn, to predict disease recurrence during remission. The purpose of this paper is to review the applicability of this strategy to the clinical management of t(8;21) and inv(16)/t(16;16) primary AML, here collectively referred to as CBF AML.

Detection of minimal residual disease in hematologic malignancies by real-time quantitative PCR: principles, approaches, and laboratory aspects

Detection of minimal residual disease (MRD) has prognostic value in many hematologic malignancies, including acute lymphoblastic leukemia, acute myeloid leukemia, chronic myeloid leukemia, non-Hodgkin's lymphoma, and multiple myeloma. Quantitative MRD data can be obtained with real-time quantitative PCR (RQ-PCR) analysis of immunoglobulin and T-cell receptor gene rearrangements, breakpoint fusion regions of chromosome aberrations, fusion-gene transcripts, aberrant genes, or aberrantly expressed genes, their application being dependent on the type of disease. RQ-PCR analysis can be performed with SYBR Green I, hydrolysis (TaqMan) probes, or hybridization (LightCycler) probes, as detection system in several RQ-PCR instruments. Dependent on the type of MRD-PCR target, different types of oligonucleotides can be used for specific detection, such as an allele-specific oligonucleotide (ASO) probe, an ASO forward primer, an ASO reverse primer, or germline probe and primers. To assess the quantity and quality of the RNA/DNA, one or more control genes must be included. Finally, the interpretation of RQ-PCR MRD data needs standardized criteria and reporting of MRD data needs international uniformity. Several European networks have now been established and common guidelines for data analysis and for reporting of MRD data are being developed. These networks also include standardization of technology as well as regular quality control rounds, both being essential for the introduction of RQ-PCR-based MRD detection in multicenter clinical treatment protocols.

Monitoring minimal residual disease in AML: the right time for real time

Detection of minimal residual disease (MRD) by polymerase chain reaction (PCR) has become an essential tool for molecular monitoring of acute myeloid leukemia (AML). Currently, specific translocation markers are available for 40-50% of AMLs. Expression markers may widen this spectrum to 70-90%. Quantitative PCR (Q-PCR, real-time PCR) is now as sensitive as conventional two-step PCR and could improve as well as facilitate clinical decision-making. Q-PCR has been applied to a variety of molecular markers, delineating threshold levels early after induction therapy, for postinduction monitoring, as well as for the detection of relapse. For most markers, lack of decline of transcript levels by less than 2 logs after chemotherapy has been established as a poor prognostic sign. Moreover, increases in transcript levels are almost invariably associated with relapse. However, the predictive value of PCR negativity after chemotherapy is not as clear. The major tasks for the future will be standardization of Q-PCR techniques, exact definition of threshold levels, and monitoring schedules in bone marrow (BM) and peripheral blood (PB), as well as investigation of novel markers found by microarray analysis.