CCL5 mediates target-kinase independent resistance to FLT3 inhibitors in FLT3-ITD-positive AML.

FLT3-ITD tyrosine kinase inhibitors (TKI) show limited clinical activity in acute myeloid leukemia (AML) due to emerging resistance. TKI resistance is mediated by secondary FLT3-ITD mutations only in a minority of cases. We hypothesize that the cytokine CCL5 protects AML cells from TKI-mediated cell death and contributes to treatment resistance. We generated PKC412- and sorafenib-resistant MOLM-13 cell lines as an in vitro model to study TKI resistance in AML. Increased CCL5 levels were detected in supernatants from PKC412-resistant cell lines compared to TKI-sensitive cells. Moreover, CCL5 treatment of TKI-sensitive cells induced resistance to PKC412. In resistant cell lines with high CCL5 release, we observed a significant downregulation of the CCL5-receptor CCR5 and CXCR4. In these cell lines, TKI resistance could be partly overcome by addition of the CXCR4-receptor antagonist plerixafor. Microarray and intracellular flow cytometry analyses revealed increased p-Akt or p-Stat5 levels in PKC412-resistant cell lines releasing high amounts of CCL5. Treatment with the CXCR4 antagonist plerixafor, αCCL5, or CCR5-targeting siRNA led to a decrease of p-Akt-positive cells. Transient transfection of sensitive MOLM-13 cells with a CCL5-encoding vector mediated resistance against PKC412 and led to an increase in p-Akt-positive and p-Stat5-positive cells. Isolated AML blasts from patients treated with PKC412 revealed that CCL5 transcript levels increase significantly at relapse. Taken together, our findings indicate that CCL5 mediates resistance to FLT3-TKIs in FLT3-ITD-mutated AML and could possibly serve as a biomarker to predict drug resistance.

Antitumor activities of PSMA×CD3 diabodies by redirected T-cell lysis of prostate cancer cells.

AIM: Although prostate cancer is one of the most commonly diagnosed malignancies in men, there is no effective curative therapy for the advanced disease. Therefore, the aim of the present study was to generate prostate-specific membrane antigen (PSMA)×CD3 diabodies as a novel treatment option for this tumor. METHODS: A PSMA×CD3 diabody and a covalently linked single-chain diabody were constructed from the anti-PSMA single-chain Fv fragment D7 and an anti-CD3 single-chain Fv fragment. The fusion proteins were periplasmatically expressed in Escherichia coli. The binding properties were tested on PSMA-expressing C4-2 prostate cancer cells and CD3(+) Jurkat cells by flow cytometry. For in vitro functional analysis, a cell viability assay was used. T-cell activation was determined by flow cytometry. In vivo activity of the diabody was tested in SCID mice reconstituted with human peripheral blood lymphocytes bearing C4-2 tumor xenografts. RESULTS: Bacterial expression levels were significantly higher for the diabody (1-1.5 mg/l culture) compared with the single-chain diabody (0.2-0.4 mg/l culture). Specific binding on CD3-expressing Jurkat cells and PSMA-expressing C4-2 cells was shown with both diabody formats. In vitro, both diabodies proved to be potent agents for retargeting human CD4(+) and CD8(+) lymphocytes to lyse C4-2 prostate cancer cells. The formation of conjugates between T cells and target cells with clustering of the diabody at sites of interaction could be shown. SCID mice reconstituted with human peripheral blood lymphocytes bearing C4-2 tumor xenografts with the diabody showed an efficient inhibition of tumor growth. CONCLUSION: Both diabody formats showed a highly efficient and specific T cell-mediated killing of prostate cancer cells and are encouraging for further development in preclinical and clinical studies.

Trisomy 12 and elevated GLI1 and PTCH1 transcript levels are biomarkers for Hedgehog-inhibitor responsiveness in CLL.

Hedgehog (HH) signaling is activated in various lymphoid malignancies, but conflicting results exist about its role in chronic lymphocytic leukemia (CLL). Here, we demonstrate that the expression of essential HH pathway components like GLI1, PTCH1, and the HH ligands is highly diverse in CLL. A subset of 36.7% of 60 tested CLL samples responded to all 3 SMOOTHENED (SMO) inhibitors, whereas 40% were completely resistant. Responsiveness correlated with elevated GLI1 and PTCH1 transcript levels and the presence of trisomy 12, whereas no other karyotype correlated with responsiveness. All trisomy 12 CLLs displayed constitutive HH pathway activation driven by autocrine DESERT HH (DHH) ligand secretion, which could be blocked by the HH-blocking Ab 5E1. Cocultures with DHH-expressing BM stromal cells reduced sensitivity of CLLs to SMO-inhibitor treatment by activation of noncanonical ERK phosphorylation directly downstream of the PTCH1 receptor without involvement of SMO and could be overcome by the HH-blocking Ab 5E1 or a combination of SMO and ERK inhibitors. Our results demonstrate that the HH-signaling pathway is an interesting therapeutic target for a subset of patients with CLL, characterized by high GLI1 and PTCH1 transcript levels, and all patients with trisomy 12 and indicate HH-blocking Abs to be favorable over SMO inhibitors in overcoming stroma-mediated protective effects.

The ITK-SYK fusion oncogene induces a T-cell lymphoproliferative disease in mice mimicking human disease.

Peripheral T-cell lymphomas (PTCL) constitute a major treatment problem with high mortality rates due to the minimal effectiveness of conventional chemotherapy. Recent findings identified ITK-SYK as the first recurrent translocation in 17% of unspecified PTCLs and showed the overexpression of SYK in more than 90% of PTCLs. Here, we show that the expression of ITK-SYK in the bone marrow of BALB/c mice causes a T-cell lymphoproliferative disease in all transplanted mice within 8 weeks after transplantation. The disease was characterized by the infiltration of spleen, lymph nodes, bone marrow, and skin with CD3+CD4+CD8- and CD3+CD4-CD8- ITK-SYK-positive T-cells accompanied by a systemic inflammatory reaction with upregulation of interleukin 5 and INF-gamma. ITK-SYK-positive T-cells showed enhanced apoptosis resistance and INF-gamma production in vitro. The disease was serially transplantable, inducing clonal T-cell expansion in secondary recipients. The action of ITK-SYK in vivo was dependent on SYK kinase activity and disease development could be inhibited by the treatment of mice with SYK inhibitors. Interestingly, the translocation of ITK-SYK from the membrane to the cytoplasm, using a point mutation in the pleckstrin homology domain (ITK-SYK R29C), did not abolish, but rather, enhanced disease development in transplanted mice. CBL binding was strongly enhanced in membrane-associated ITK-SYK E42K and was causative for delayed disease development. Our results show that ITK-SYK causes a T-cell lymphoproliferative disease in mice, supporting its role in T-cell lymphoma development in humans. Therefore, pharmacologic inhibition of SYK in patients with U-PTCLs carrying the ITK-SYK fusion protein might be an effective treatment strategy.

Allogeneic HLA-matched donor dendritic cells loaded with patient leukemic blasts preferentially induce CD4-positive leukemia-reactive donor lymphocytes.

BACKGROUND: The therapeutic value of donor lymphocyte infusions in patients who relapse with acute myeloid leukemia (AML) after allogeneic hematopoietic stem cell transplantation (HSCT) is limited by a low efficacy and the risk of graft-versus-host disease. We aimed at generating leukemia-reactive donor T cells for patients with AML. METHODS: Peripheral blood mononuclear cells of the donor were stimulated with mature donor dendritic cells, pulsed with irradiated patient leukemic blasts (LB), or directly with cytokine-treated LB. After 3 weekly stimulations, donor cells were tested for anti-leukemic reactivity in an IFNgamma Elispot. RESULTS: In 5 of 6 donors, cells with reactivity against patient LB with low or absent reactivity against non-leukemic cells could be generated. T cell subset analyses in 2 donors indicated that specific anti-leukemic reactivity was mainly mediated by CD4+ T cells, which were also the predominant cell fraction in 4 of 6 donors. One leukemia-reactive donor T cell line was expanded with a recently developed system. One week of expansion resulted in a 10-fold increase in reactivity with sustained specificity of the resulting T cell line. CONCLUSIONS: Our results show the feasibility of the in vitro generation of leukemia-reactive donor lymphocytes, rendering this method a promising tool for post-HSCT immunotherapy.