Specific Monoclonal Antibody Against Bcr/Abl Out-of-Frame Alternative Proteins as Diagnostic Tool in Chronic Myelogenous Leukemia Patients

More recently, alternative splicing of specific genes are investigated for their therapeutic potential. In particular, we reported the existence of BCR-ABL alternative splicing isoforms, in about 80% of Philadelphia-positive patients, which lead to the expression of aberrant proteins. These fusion proteins are characterized by an orphan initial and correct Bcr portion attached to a 112 amino acid sequence, arising from the impairment in the reading frame (reading of ABL exon 4 and 5). We demonstrated that these Abl-out-of-frame (OOF) isoforms could have an immunological role with therapeutic implications. The aim of this study was to characterize a new monoclonal antibody (MAb) specific for Abl-OOF protein portion, for diagnostic use, to detect this biomarker in Philadelphia chromosome-positive chronic myelogenous leukemia (CML) patients and to generate novel approaches in the immunotherapy. 5F11G11 MAb recognizes the OOF protein portion of the native full-length Bcr/Abl-OOF protein expressed in cells transiently transfected, as demonstrated by immunoprecipitation and immunofluorescence. In addition, we demonstrate the MAb's ability to recognize the alternative hybrid Bcr/Abl fusion protein expressed in leukemic cells from CML patients, to support the possible use of 5F11G11 MAb as a diagnostic tool to select patients with Philadelphia chromosome-positive CML that could be eligible for an immunotherapeutic approach with this new antigen.

Characterization of a Monoclonal Antibody Specific for the Growth Hormone Secretagogue Receptor

Ghrelin is an orexigenic peptide hormone that primarily regulates growth hormone secretion, food intake, and energy homeostasis. It has been shown to also play a role in numerous higher brain functions, such as the regulation of inflammation and cell proliferation. Ghrelin is the endogenous ligand of the growth hormone secretagogue receptor (GHSR), a G-protein-coupled receptor highly expressed in brain and detectable in some peripheral tissues. The wide distribution of ghrelin receptor and the number of tissues and cell types known to respond to ghrelin suggest that a number of systems may be affected by treatment with this hormone or its analogues. In this study, we characterized a new GHSR specific monoclonal antibody recognizing specifically the ghrelin receptor. This could be a useful tool for immunoassays aimed at obtaining insights into the physiological and pathological significance of the GHSR/ghrelin system.

New alternative splicing BCR/ABL-OOF shows an oncogenic role by lack of inhibition of BCR GTPase activity and an increased of persistence of Rac activation in chronic myeloid leukemia

In Chronic Myeloid Leukemia 80% of patients present alternative splice variants involving BCR exons 1, 13 or 14 and ABL exon 4, with a consequent impairment in the reading frame of the ABL gene. Therefore BCR/ABL fusion proteins (BCR/ABL-OOF) are characterized by an in-frame BCR portion followed by an amino acids sequence arising from the out of frame (OOF) reading of the ABL gene. The product of this new transcript contains the characteristic BCR domains while lacking the COOH-terminal Rho GTPase GAP domain. The present work aims to characterize the protein functionality in terms of cytoskeleton (re-)modelling, adhesion and activation of canonical oncogenic signalling pathways. Here, we show that BCR/ABL-OOF has a peculiar endosomal localization which affects EGF receptor activation and turnover. Moreover, we demonstrate that BCR/ABL-OOF expression leads to aberrant cellular adhesion due to the activation of Rac GTPase, increase in cellular proliferation, migration and survival. When overexpressed in a BCR/ABL positive cell line, BCR/ABL-OOF induces hyperactivation of Rac signaling axis offering a therapeutic window for Rac-targeted therapy. Our data support a critical role of BCR/ABL-OOF in leukemogenesis and identify a subset of patients that may benefit from Rac-targeted therapies.

Proapoptotic activity of a monomeric smac mimetic on human fibroblast-like synoviocytes from patients with rheumatoid arthritis

Inhibitors of apoptosis proteins (IAPs) block cell death in response to diverse stimuli. The mitochondrial protein, second mitochondria-derived activator of caspase (Smac), negatively regulates IAP inhibition of caspase activity. We investigated the proapoptotic activity of a synthetic Smac (Smac 066) on fibroblast-like synoviocytes (FLS) derived from patients with active rheumatoid arthritis (RA). We found that Smac 066 induced significant apoptosis in all RA-FLS samples. Furthermore, IAPs, which are upregulated in RA-FLS, were downregulated by Smac 066. This suggested that IAPs upregulation was responsible for RA-FLS sensitivity to Smac 066. Next, we analysed caspase activation and found that Smac 066 was associated with caspase 8 and caspase 3 activities. We then investigated the mechanism underlying Smac 066 downregulation of IAPs in RA-FLS with an apoptotic pathway array. Interestingly, Smac 066 significantly upregulated IGFBP-5, a protein involved in differentiation, apoptosis, and osteoblastic activation. Smac 066 may represent a new therapeutic approach to RA treatment.

Characterization of a monoclonal antibody specific for novel Bcr/Abl out-of-frame fusion proteins

The new tumor-specific antigens Bcr/Abl-OOF, identified in Philadelphia chromosome (Ph)-positive leukemia cells, are derived from an alternative splicing event involving BCR exons 1, 13, or 14 and ABL exons 4 and 5. The COOH-terminus of these transcription products contain an amino acid portion derived from an out-of-frame (OOF) reading of the ABL gene; these variants are expressed in Ph-positive chronic myelogenous leukemia (CML) and acute lymphocytic leukemia patients. Previously, we confirmed the presence of out-of-frame peptide-specific T cells in the peripheral blood of CML patients with the ability to lyse primary autologous CML cells. We also demonstrated that the out-of-frame Abl portion was immunogenic in HLA-A2.1 transgenic mice. Here we describe the production and characterization of monoclonal antibody 1D8G8, a new tool for localization and functional studies of the tumor antigen Bcr/Abl-OOF. This antibody recognizes the out-of-frame protein portion of the native full-length Bcr/Abl-OOF protein expressed in cells transiently transfected, as demonstrated by immunoprecipitation and immunofluorescence, and binds to a specific epitope of this antigen presented in association with HLA-A2.1 molecules at the surface of these cells, as demonstrated by flow cytometry. Thus this MAb could be useful to better understand how this new protein presents in Ph-positive cells beside the canonical Bcr/Abl fusion proteins.

Out of frame peptides from BCR/ABL alternative splicing are immunogenic in HLA A2.1 transgenic mice

New, potentially tumor-specific antigens have been described in Bcr/Abl positive leukemias. Besides the main BCR/ABL hybrid fusion transcripts, a small number of transcripts derived from alternative splicing between BCR exons 1, 13, and 14 with ABL exons 4 and 5 have been identified. These variants are expressed in chronic myelogenous leukemia and acute lymphocytic leukemia patients. The transcriptional products were characterized at their C-terminus by a large amino acid portion derived from out of frame (OOF) reading of the ABL gene. This OOF peptide is expressed only in leukemic cells and has no homology with known human proteins. In order to study an in vivo model, three 39-amino acid peptides, each corresponding to a third of the whole human OOF peptide sequence, were tested for their capacity to elicit specific immune responses in HLA A2.1 transgenic mice. Peptides A and B, but not C, induced the production of specific antisera, while A and C induced the generation of specific cytotoxic T lymphocytes.

Inhibitory effect of pasireotide and octreotide on lymphocyte activation

Somatostatin (SST) regulates the function of the central and peripheral nervous system, the endocrine and exocrine organs, as well as the vascular and immune system. These actions are mediated by five specific membrane somatostatin receptors. This study compares the effects on human lymphocytes of two long-acting somatostatin analogues that have different receptor affinity: octreotide and pasireotide. Both analogues have an antiproliferative effect on human lymphocyte proliferation, but they act at different concentration and, while octreotide enhances IL10 and inhibits gamma IFN pasireotide inhibits IL2 and gamma IFN. In both sets of experiment the different behaviour of the two analogues could be due to their different affinity to the SSTR subtypes. Finally this study suggest that the growth inhibitory action of somatostatin analogues is an apoptotic phenomenon and it can be mediated by SSTR2a, in the case of octreotide, and by SSTR3 when pasireotide is used or it can be mediated by the heterodimerization of the two receptor.

Effects of chimeric somatostatin–dopamine molecules on human peripheral blood lymphocytes activation

BIM 23A761, selective for somatostatin receptors subtypes 2, 5 and the dopamine receptor subtype 2, and BIM 23A757 with affinity for SSTR2 and DAR2 were studied on human PBL proliferation and activation. BIM 23A761 was significantly more potent than specific SSTR and DAR2 agonists in suppressing lymphocyte proliferation induced by mitogen or alloantigen, while BIM 23A757 was more potent than specific SSTR2 and DAR2 agonists in suppressing antigen induced proliferation only. Both molecules displayed enhanced potency in suppressing IFNgamma and IL-6 secretion compared with the SSTR and DAR2 analogs, while only BIM 23A761 was able to inhibit IL-2 secretion and its effect is more potent than the control analogs. Furthermore BIM 23A761 inhibit cell progression into the S phase and then into the G2/M, while BIM 23A757 inhibited bromodeoxyuridine incorporation only during the S phase. Both chimeric molecules resulted significantly more effective than the respective controls.