Towards a pathogenesis-oriented therapy of acute myeloid leukemia

Effective elimination of acute myeloid leukemic cells by recombinant bispecific antibody derivatives directed against CD33 and CD16

Single-chain Fv triplebodies (sctb), consisting of a single polypeptide chain with 3 single-chain antibody variable fragments connected in tandem, were generated as antileukemic agents. A CD19-specific sctb of this format has previously been shown to be superior to a bispecific single-chain Fv antibody fragment (bsscFv) for the elimination of leukemic B-lineage cells, but corresponding targeted agents for the treatment of acute myeloid leukemia are still lacking. For this purpose, both a bsscFv and a sctb specific for CD33 and the trigger molecule CD16 (FcgammaRIII) were produced. The sctb displayed 3.5-fold greater avidity for CD33 than the bsscFv 33xds16, whereas both had close to equal affinity for CD16. In antibody-dependent cellular cytotoxicity (ADCC) reactions with human mononuclear cells as effectors, both the bsscFv 33xds16 and the sctb induced lysis of tumor cells with half maximum effective concentrations (EC50) in the low picomolar range. It is interesting to note that the sctb promoted equal lysis of human leukemia-derived cell lines at 10 to 200-fold lower concentrations than the bsscFv. Both molecules mediated ADCC of primary patient cells. In conclusion, both the bsscFv 33xds16 and the sctb 33xds16x33 eliminated acute myeloid leukemia cells in ADCC reactions, but the novel sctb format showed significantly greater specific activity.

A recombinant trispecific single-chain Fv derivative directed against CD123 and CD33 mediates effective elimination of acute myeloid leukaemia cells by dual targeting

Two trivalent constructs consisting of single-chain Fv antibody fragments (scFvs) specific for the interleukin-3 receptor alpha chain (CD123), CD33 and the Fcgamma-receptor III (CD16) were designed and characterized for the elimination of acute myeloid leukaemia (AML) cells. The dual targeting single-chain Fv triplebody (sctb) [123 x ds16 x 33] and the mono targeting sctb [123 x ds16 x 123] both specifically bound their respective target antigens and were stable in human serum at 37 degrees C for at least 5 d. Both constructs induced potent antibody-dependent cellular cytotoxicity (ADCC) of two different AML-derived CD33- and CD123 double-positive cell lines in the low picomolar range using isolated mononuclear cells (MNCs) as effector cells. In these experiments the dual targeting molecule produced significantly stronger lysis than the mono targeting agent. In addition, the sctbs showed a high potency in mediating ADCC of primary leukaemia cells isolated from peripheral blood or bone marrow of seven AML patients. Hence, these novel molecules displayed potent anti-leukaemic effects against AML cells in vitro and represent attractive candidates for further preclinical development.

Cytogenetic findings and clinical outcomes of adult acute myeloid leukaemia patients

The role of cytogenetic findings in determining the diagnosis, therapy and prognosis of acute myeloid leukaemia (AML) has become more valuable by the day. In this study, the results of conventional and molecular cytogenetic analyses and clinical outcomes of 66 AML patients of different subgroups aged between 16 and 82 were evaluated. Chromosomal abnormalities were detected in 17 (25.7%) patients cytogenetically at the time of diagnosis, whereas molecular cytogenetic abnormalities were detected in 21 (31.8%) patients by fluorescence in situ hybridisation (FISH). Thirty-eight (57.6%) patients had a normal karyotype. In 8 patients, we did not obtain suitable chromosomes for karyotype analysis and in 3 patients conventional cytogenetics were not requested by the physician. During clinical follow-up, 21 patients (31.8%) achieved complete remission (CR), 2 had partial remission (PR) (3.0%) and 4 patients had progressive disease (6.06%). Twenty-eight (42.4%) patients died during treatment and no follow-up data were available in 7 cases. Among patients with chromosome abnormalities detected by either one of the two cytogenetic methods (n=28), 12 had achieved CR, 9 of whom were already categorised in the good prognostic group with t(15;17), inv16 or t(8;21). As for the normal karyotype, each patient displayed a different clinical course, which is probably due to the molecular changes in leukaemia-related genes. Here we report our findings, which correlate with previous reports and conclude that cytogenetics is a crucial marker in leukaemia diagnosis and conventional and molecular cytogenetics should be performed as well as molecular genetic diagnostic methods.

Targeting receptor tyrosine kinase signaling in acute myeloid leukemia

Acute myeloid leukemia (AML) is a quickly progressing, heterogeneous clonal disorder of hematopoietic progenitor cells. Significant progress in understanding the pathogenesis of AML has been achieved in the past few years. Two major types of genetic events are thought to give rise to leukemic transformation: alterations in the activity of transcription factors controlling hematopoietic differentiation and activation of components of receptor tyrosine kinase (RTK) signaling pathways. This has led to the development of promising new therapeutic strategies for the disease. In this article, we will discuss recent developments in the field of molecularly targeted therapies for AML, which involve RTKs such as FMS-like tyrosine kinase 3 (Flt3), c-Kit and signal transduction via the phosphoinositide 3-kinase (PI3K) and mitogen-activated protein kinase (MAPK) pathways. Initial results imply that targeting RTKs is a very promising approach for AML and that other receptors, such as the insulin-like growth factor receptor (IGF-IR), could also represent new targets in the future.

Acute myeloid leukemia is propagated by a leukemic stem cell with lymphoid characteristics in a mouse model of CALM/AF10-positive leukemia

A challenge for the development of therapies selectively targeting leukemic stem cells in acute myeloid leukemia (AML) is their similarity to normal hematopoietic stem cells (HSCs). Here we demonstrate that the leukemia-propagating cell in murine CALM/AF10-positive AML differs from normal HSCs by B220 surface expression and immunoglobulin heavy chain rearrangement. Furthermore, depletion of B220+ cells in leukemic transplants impaired development of leukemia in recipients. As in the murine model, human CALM/AF10-positive AML was characterized by CD45RA (B220)-positive, IG DH-JH rearranged leukemic cells. These data demonstrate in a murine leukemia model that AML can be propagated by a transformed progenitor with lymphoid characteristics, which can be targeted by antibodies that do not crossreact with normal HSCs.

[Secondary malignancies after successful primary treatment of malignant Hodgkin's lymphoma]

Malignant Hodgkin's lymphoma (HL) has become a curable disease through the increasing intensity of the treatment strategies applied. These regimens are aggressive, including radiotherapy and chemotherapy leading to the possibility of secondary malignancies. The German Hodgkin Lymphoma Study Group considered three cohorts including 5,411 patients with all stages of HL. In 127 patients a secondary solid tumor was diagnosed (cumulative risk 2%, median follow-up 72 months), with bronchial carcinomas (23.6%) and colorectal adenocarcinomas (20.5%) being the most frequent neoplasms. Secondary acute myeloid leukemia was found in 36 patients, another ten developed myeloid dysplasia (cumulative risk 1%, median follow-up 55 months). A total of 52 patients revealed a non-Hodgkin's lymphoma (NHL; cumulative risk 0.9%, median follow-up 46 months). The overall incidence of secondary malignancies was 3.9% in patients who had been treated successfully for their HL with radio- and/or chemotherapy.A secondary NHL can be particularly difficult to be distinguished from the preceding HL. Therefore, in case of a suspected relapse, a complete histopathological work-up must be performed.