ALBERT

Description: Synthesis of histamine in hematopoietic progenitor cells may be one of the earliest events in mast cell-development from pluripotent hematopoietic progenitor cells. In the present study, we asked whether the key enzyme involved in histamine generation, histidine decarboxylase (HDC), can be employed as an immunohistochemical marker for the detection of (neoplastic) mast cells (MC) in patients with cutaneous (CM) or systemic mastocytosis (SM). To address this question, we examined bone marrow biopsy specimens in a cohort of 101 patients (CM, n=10; indolent SM, n=46; SM with associated clonal non-MC lineage disease, n=31; aggressive SM, n=10; MC leukemia, n=3; MC sarcoma, n=1) using an antibody against HDC. Independent of the maturation stage of MC or subtype of disease, the anti-HDC antibody produced clear diagnostic staining results in all patients with bone marrow involvement examined including those with MC leukemia and MC sarcoma, in which MC are particularly immature and often escape analysis when examined by conventional stains. In these patients (MC leukemia, n=2; MC sarcoma, n=1), expression of HDC was reconfirmed at the mRNA level by RT-PCR analysis performed with RNA of highly enriched sorted CD117+ MC. In patients with CM or normal/reactive bone marrow (n=30), no HDC-positive infiltrates were detected. In these patients, only a few hematopoietic cells, presumably basophils, were found to react with the anti-HDC antibody. In summary, HDC is expressed in neoplastic bone marrow MC in patients with SM independent of the maturation stage of cells or the variant of disease. HDC should therefore be considered as a new MC marker in the screen panel of antigens employed to diagnose high grade MC malignancies.

Description: Resistance toward imatinib and other BCR/ABL tyrosine kinase inhibitors remains an increasing clinical problem in the treatment of advanced stages of chronic myeloid leukemia (CML). We recently have identified the heat shock protein 32 (Hsp32)/heme oxygenase-1 (HO-1) as a BCR/ABL-dependent survival molecule in CML cells. We here show that silencing Hsp32/HO-1 in CML cells by an siRNA approach results in induction of apoptosis. Moreover, targeting Hsp32/HO-1 by either pegylated zinc protoporphyrine (PEG-ZnPP) or styrene maleic acid-micelle–encapsulated ZnPP (SMA-ZnPP) resulted in growth inhibition of BCR/ABL-transformed cells. The effects of PEG-ZnPP and SMA-ZnPP were demonstrable in Ba/F3 cells carrying various imatinib-resistant mutants of BCR/ABL, including the T315I mutant, which exhibits resistance against all clinically available BCR/ABL tyrosine kinase inhibitors. Growth-inhibitory effects of PEG-ZnPP and SMA-ZnPP also were observed in the CML-derived human cell lines K562 and KU812 as well as in primary leukemic cells obtained from patients with freshly diagnosed CML or imatinib-resistant CML. Finally, Hsp32/HO-1–targeting compounds were found to synergize with either imatinib or nilotinib in producing growth inhibition in imatinib-resistant K562 cells and in Ba/F3 cells harboring the T315I mutant of BCR/ABL. In summary, these data show that HO-1 is a promising novel target in imatinib-resistant CML.

Description: Systemic mastocytosis (SM) is a myeloid neoplasm characterized by abnormal growth and accumulation of mast cells (MC) in various internal organs. In most patients, the D816V-mutated variant of c-KIT, which mediates resistance against several tyrosine kinase (TK) inhibitors like imatinib, is found. In advanced SM, the response of neoplastic MC to conventional drugs is poor and the prognosis is grave. Therefore current research is attempting to identify novel targets in neoplastic MC. Polo-like kinase 1 (Plk-1) is a serine/threonine kinase that plays an essential role in mitosis and has recently been introduced as a new target in myeloid leukemias. In the present study, we analyzed expression and function of Plk-1 in neoplastic human MC, and asked whether Plk-1 can serve as a target of therapy in SM. As determined by immunohistochemistry, primary neoplastic MC were found to display activated/phosphorylated Plk-1 in all patients examined (n=5). The human MC leukemia cell line HMC-1 was also found to exhibit activated Plk-1. In addition, we found that primary neoplastic MC as well as HMC-1 cells express Plk-1 mRNA in RT-PCR experiments. As assessed by 3H-thymidine-uptake experiments, the Plk-1-targeting drug BI 2536 (Boehringer Ingelheim GmbH, Germany) was found to inhibit the proliferation of HMC-1 cells in a dose-dependent manner (IC50 5–15 nM). The effect of BI 2536 was seen in both subclones of HMC-1, i.e. in HMC-1.1 cells displaying KIT G560V (but not KIT D816V), and HMC-1.2 cells exhibiting both KIT G560V and KIT D816V, with comparable IC50 values. Moreover, BI 2536 was found to inhibit the proliferation of primary neoplastic cells, with IC50 values ranging between 5 and 50 nM. The growth-inhibitory effects of BI 2536 on HMC-1 cells were found to be associated with mitotic arrest and G2-M cell cycle arrest as well as consecutive apoptosis. In normal bone marrow or peripheral blood mononuclear cells, neither mitotic cell arrest nor apoptosis were observed after treatment with BI 2536. In a consecutive phase of the study, we asked whether combined targeting of KIT D816V and Plk-1 would lead to synergistic drug-interactions. For this purpose, HMC-1 cells and primary neoplastic MC were coincubated with BI 2536 and midostaurin (PKC412), a multitargeted kinase inhibitor that blocks KIT D816V TK activity. In these experiments, BI 2536 was found to synergize with midostaurin in counteracting the proliferation of HMC-1 cells and primary neoplastic MC. In conclusion, our data show that activated Plk-1 is detectable in MC neoplasms and plays a role in cell cycle progression and viability of neoplastic MC. Targeting of Plk-1 with BI 2536 leads to growth inhibition and apoptosis in neoplastic MC. Furthermore, BI 2536 synergizes with midostaurin in counteracting growth of neoplastic MC. Targeting of Plk-1 may be an attractive new pharmacologic concept in advanced SM.

Description: The mammalian target of rapamycin (mTOR), a key-regulator of cell cycle progression, has recently been implicated in growth of neoplastic cells and tumor- and leukemia-associated angiogenesis. In addition, mTOR has been described as a regulator of expression of vascular endothelial growth factor (VEGF), a cytokine involved in tumor-related angiogenesis, in various neoplasms. We asked whether mTOR can be employed as a new therapeutic target in acute myeloid leukemia (AML) using the mTOR-targeting drug rapamycin and its derivatives RAD001 (everolimus) and CCI-779. As assessed by 3H-thymidine incorporation, rapamycin was found to counteract growth of AML cells in vitro in 9/11 patients examined as well as in the AML-derived cell lines U937, HL60, and KG1a. The effects of rapamycin on growth of AML cells were dose-dependent (primary AML cells: IC50: 10 pM - 1 nM; inhibition of 3H-thymidine uptake at 1 nM of rapamycin: 43±15 % of control; p

Description: The pathologic hallmark of systemic mastocytosis (SM) is differentiation and cluster formation of mast cells (MC) in hematopoietic tissues. The somatic c-kit mutation D816V is detectable in a majority of all SM patients independent of the proliferation-status of MC or subtype (indolent or aggressive) of disease. To investigate the role of c-kit D816V in the pathogenesis of SM, we established a Ba/F3 cell line with doxycycline-inducible expression of c-kit D816V. We found that c-kit D816V provides a strong signal for mast cell differentiation and cluster formation in Ba/F3 hematopoietic progenitor cells without enhancing their growth thereby resembling the clinical presentation of indolent SM (ISM). As assessed by gene chip analysis, induction of c-kit D816V resulted in expression of various differentiation antigens including mouse mast cell protease 5, mi transcription factor, histidine decarboxylase (HDC), secretory granule proteoglycan, IL-4 receptor, ICAM-1, and CD63 consistent with an early phase of mastopoiesis. By contrast, c-kit D816V did neither induce expression of granulo-monocytic antigens such as myeloperoxidase, IL-3 receptor, or GM-CSF receptor, nor expression of ‘late stage’ mast cell antigens such as FcεRI. The c-kit D816V-induced synthesis of histamine in Ba/F3 cells was confirmed by RIA. To examine the role of c-kit D816V in the pathogenesis of mastocytosis, we extended our analysis to bone marrow biopsy sections obtained from patients with ISM. In these experiments, the D816V-mutated form of c-kit was detected more frequently in micro-dissected tryptase-positive MC obtained from dense compact infiltrates (44.2%) than in diffusely spread MC in these patients (22.6%) (p

Description: The BCR-ABL tyrosine kinase inhibitor STI571 (Imatinib) has successfully been introduced in the treatment of patients with CML. However, despite encouraging initial data and high expectations long term results are not available yet, and recent data suggest that resistance against STI571 can occur. Therefore, current studies focus on novel potential drug targets in CML cells. Recently, several anti-apoptotic members of the Bcl-2-family including Mcl-1 have been implicated in the regulation of survival of BCR/ABL+ cell lines and therefore proposed as potential targets. We have examined expression of Mcl-1 in primary CML cells and various BCR/ABL-transformed cell lines. Independent of the phase of disease, isolated primary CML cells expressed Mcl-1 mRNA and the Mcl-1 protein in a constitutive manner. The BCR/ABL-inhibitor STI571 decreased the expression of Mcl-1 in these cells. Correspondingly, BCR/ABL enhanced Mcl-1 promoter activity, Mcl-1 mRNA, and Mcl-1 protein in Ba/F3 cells. BCR/ABL-dependent expression of Mcl-1 in Ba/F3 cells was counteracted by the MEK-inhibitor PD98059, but not by the PI3-kinase inhibitor LY294002. Identical results were obtained for constitutive expression of Mcl-1 in primary CML cells and the CML-derived cell lines K562 and KU812. To investigate the role of Mcl-1 as a survival-related target gene in CML cells, Mcl-1 siRNA or an Mcl-1 antisense oligonucleotide (ASO) were applied. Both the ASO and the siRNA-induced downregulation of Mcl-1 were found to be associated with a substantial decrease in viability of K562 cells. Moreover, the Mcl-1 ASO was found to cooperate with STI571 in producing growth-inhibition in both STI571-sensitive and STI571-resistant K562 cells. Together, our data identify Mcl-1 as a survival factor and novel target in CML. Whether this concept is of clinical significance remains to be determined in forthcoming clinical trials.

Description: Systemic mastocytosis (SM) is a hematologic neoplasm characterized by abnormal expansion and accumulation of neoplastic mast cells (MC) in various organs, including the bone marrow, skin, liver, spleen and gastrointestinal tract. In a majority of all patients, the transforming KIT mutation D816V is detectable. The clinical picture and prognosis in SM vary, depending on the variant of SM and the presence of an associated hematologic non-MC-lineage disease (AHNMD). The WHO classification discriminates between indolent SM (ISM), SM-AHNMD, aggressive SM (ASM) and MC leukemia (MCL). Recent data suggest that neoplastic MC in ASM and MCL express substantial amounts of cytoplasmic Ki-1 (CD30), a lymphoid antigen otherwise expressed in neoplastic cells in anaplastic large cell lymphoma and Hodgkin lymphoma, where CD30 serves as a therapy target. In the present study, we examined the expression of CD30 in various human MC-lines (HMC-1, MCPV) and primary neoplastic MC in patients with ISM (n=20) and advanced SM (ASM/MCL; n=10) and asked whether CD30 may serve as potential therapeutic target in SM. We found that CD30 is expressed abundantly in the cytoplasm of neoplastic MC in ASM and MCL in almost all patients, whereas in a majority of patients with ISM, MC expressed only low amounts or did not express cytoplasmic CD30. As assessed by flow cytometry, neoplastic MC in SM were also found to express cell surface CD30. In contrast to cytoplasmic expression, no clear correlation was found between the type of SM and CD30 surface expression on MC. Notably, MC expressed surface CD30 in 8/9 ISM patients and in 2/6 ASM/MCL patients. The immature human RAS-transformed MCL line MCPV (KIT D816V negative) also expressed cell surface CD30, whereas the MCL line HMC-1.1 (lacking KIT D816V) expressed only low levels, and the HMC-1.2 subclone (KIT D816V+) was found to stain CD30 negative. To examine whether CD30 may serve as a therapy target in SM, we applied brentuximab vedotin (provided by Millennium: The Takeda Oncology Company, Cambridge, MA, USA), which is an antibody-drug conjugate consisting of a chimeric anti-CD30 antibody and the microtuble inhibitor monomethyl auristatin E (MMAE). Brentuximab vedotin has recently been described to induce dose-dependent growth arrest in human CD30+ lymphoblastic cell lines. In the present study, brentuximab vedotin was found to inhibit the proliferation of MCPV and HMC-1 cells in a dose-dependent manner, with lower IC50 values found in CD30+ MCPV and HMC-1.1 cells (5 µg/ml) than in CD30− HMC-1.2 cells (10 µg/ml). As assessed by AnnexinV/PI staining and staining for active-caspase-3, brentuximab vedotin also induced dose-dependent apoptosis in CD30+ MCPV and HMC-1.1 cells, but did not induce substantial apoptosis in CD30− HMC-1.2 cells. Brentuximab vedotin was also found to induce growth inhibition and apoptosis in the CD30+ canine-mastocytoma cell line C2. We next examined the effects of brentuximab vedotin on in vitro survival (apoptosis) of primary neoplastic MC in patients with CD30− SM (n=3) and in patients with CD30+ SM (n=3). In these experiments, brentuximab vedotin was found to induce dose-dependent apoptosis at pharmacologically relevant concentrations in neoplastic MC in patients with CD30+ SM, whereas no effects were seen in patients with CD30− SM (Figure). Finally, we examined the effects of a drug combination consisting of brentuximab vedotin and the KIT D816V targeting drug PKC412 (midostaurin). We found that both drugs synergize with each other in inhibiting the in vitro proliferation of CD30+ MCPV cells. In conclusion, our data provide evidence that the target-antigen CD30 is expressed on the surface of neoplastic MC in patients with indolent and advanced SM. In addition, our data show that the CD30-targeting antibody brentuximab vedotin induces growth arrest and apoptosis in neoplastic MC and synergizes with midostaurin in inhibiting the growth of CD30+ neoplastic MC. Whether these effects also occur in vivo in patients with advanced mastocytosis remains to be determined in clinical trials. Neoplastic MC from patients with CD30− SM (n=3, grey bars) and CD30+ SM (n=3, black bars) were incubated in control medium (Co) or in various concentrations of brentuximab vedotin (37°C). After 96 hours, the percentage of AnnexinV+ viable DAPI-negative MC was determined by flow cytometry. Results represent the mean±S.D. of 3 independent experiments. Asterisk: p

Description: Chronic myeloid leukemia (CML) is a myeloproliferative disease characterized by the BCR/ABL oncogene and an increased survival of leukemic cells. The BCR-ABL tyrosine kinase inhibitor imatinib has successfully been introduced as a treatment of CML. However, resistance after an intitial response is common in patients with advanced disease, and it is not yet clear if responses in early disease phases will be durable. Therefore, current studies focus on novel potential drug-targets in CML cells. We have recently identified heme oxygenase-1 (HO-1) as a novel BCR/ABL-dependent survival-molecule in primary CML cells. In this study, we analyzed signal transduction pathways underlying BCR/ABL-induced expression of HO-1 and evaluated the role of HO-1 as a potential new target of drug therapy. We found that the PI3-kinase inhibitor LY294002 and MEK inhibitor PD98059 downregulate expression of HO-1 in CML cells. In addition, constitutively active Ras- and Akt -mutants were found to promote expression of HO-1 in Ba/F3 cells, further supporting the involvement of the PI3-kinase/Akt as well as the MAPK pathway in regulating HO-1 expression. To establish a role for HO-1 in survival of CML cells, expression of HO-1 was silenced by siRNAs which resulted in apoptosis of K562 cells. Next, HO-1 was targeted in CML cells by pegylated zinc protoporphyrin (PEG-ZnPP), a competitive inhibitor of HO-1. Exposure to PEG-ZnPP resulted in growth inhibition and induction of apoptosis in primary CML cells as well as in the CML-derived cell lines K562 and KU812 with IC50 values ranging between 1–10 μM. The growth-inhibitory effects of PEG-ZnPP were not only observed in CML cells responsive to imatinib, but also in imatinib-resistant K562 cells and Ba/F3 cells expressing various imatinib-resistant mutants of BCR/ABL (T315I, E255K, M351T, Y253F, Q252H, H396P). Moreover, imatinib and PEG-ZnPP were found to exert synergistic growth inhibitory effects on imatinib-resistant leukemic cells. Together, these data suggest that HO-1 represents a novel drug target in cells expressing BCR/ABL, including those with resistance to imatinib.

Description: Abstract 213 Systemic mastocytosis (SM) is a neoplastic disease of mast cells (MC) and their bone marrow-derived progenitors. The clinical picture in SM is variable ranging from an indolent course to highly aggressive variants with short survival time. The pathologic hallmark in SM is the multifocal dense infiltrate of MC in the bone marrow. Other typical features of SM include alterations of the bone marrow microenvironment such as increased angiogenesis and fibrosis. In a majority of patients, MC display the KIT mutation D816V which affects the activation loop at the entrance to the enzymatic pocket of the KIT kinase. As a consequence, KIT D816V exhibits constitutive tyrosine kinase activity and promotes cytokine-independent differentiation of MC. However, so far, little is known about KIT D816V-dependent expression of pathogenetically relevant molecules in neoplastic MC. Oncostatin M (OSM) is a pleiotropic cytokine of the interleukin-6 family which is produced mainly by activated T cells and monocytes. OSM has been shown to inhibit cell growth in cell lines derived from solid tumors but to stimulate proliferation of fibroblasts and endothelial cells. Recently, it has been reported that OSM produced by activated MC promotes growth of human dermal fibroblasts. Moreover, it has been suggested that OSM stimulates growth of murine bone marrow-derived mast cells in a mast cell/fibroblast coculture. However, expression of OSM in neoplastic MC or a potential pathogenetic role of OSM in SM have not been examined so far. The aim of the present study was to analyze expression of OSM in neoplastic human MC and to determine the role of KIT D816V in OSM expression. As assessed by immunohistochemistry performed on bone marrow sections of patients with SM, typical spindle-shaped neoplastic MC were found to express OSM. Serial section-staining confirmed that tryptase-positive MC co-express OSM. Expression of OSM was found in neoplastic MC in all patients investigated (n=15) and in all variants of SM (indolent SM as well as aggressive variants) with comparable staining intensities. Preincubation of anti-OSM antibody with a specific blocking peptide resulted in a negative stain. In Ba/F3 cells, doxycycline-inducible expression of KIT D816V led to a substantial upregulation of OSM mRNA and OSM protein, whereas expression of wild type KIT did not affect expression of OSM. In addition, the KIT D816V-positive HMC-1.2 mast cell line was found to express OSM at high levels, whereas the KIT D816V-negative HMC-1.1 subclone expressed only baseline levels of OSM. Correspondingly, the KIT D816V-targeting drug midostaurine (PKC412) decreased the expression of OSM in HMC-1.2 cells as well as in KIT D816V-expressing Ba/F3 cells in a dose-dependent manner. To investigate signaling pathways involved in KIT D816V-dependent expression of OSM, we applied pharmacologic inhibitors and dominant negative-acting signaling molecules. We found that KIT D816V-dependent expression of OSM is inhibited by the mitogen-activated protein-kinase/extracellular signal-regulated kinase (MEK) inhibitor, PD98059, but not by the phosphoinositide 3-kinase inhibitor, LY294002. Expression of dominant negative mutants of signal transducer and activator of transcription 5 (STAT5) did not affect expression of OSM in KIT D816V-expressing cells. In summary, our data identify OSM as a novel cytokine expressed in neoplastic MC in patients with SM and show that KIT D816V directly promotes expression of OSM through activation of the mitogen-activated protein-kinase pathway. OSM may be an important KIT D816V-dependent effector promoting angiogenesis and fibrogenesis/sclerosis in patients with SM. Disclosures: No relevant conflicts of interest to declare.