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are negative for mTNFR-1, but upregulate their expression upon in vitro cultivation. Consistent with our data, TNFR- 1 expression was reported on malignant cells in diffuse large B-cell lymphoma (DLBCL), which correlated with significantly shorter OS and progression-free survival rates compared to patients with TNFR-1 negative lymphoma cells.32 TNFR-1 induction upon malignant transformation has also been described in colorectal adenoma and prostate cancer, underlining its role in carcinogenesis.33,34
is currently restricted to global TNF-α neutralization, using etanercept in combination with rituximab.19 However, less attention has been paid to the receptors that mediate the pathogenic effect of TNF-α. In particular, selective TNFR-1 inhibition showed promising results in the treatment of inflammatory diseases in mice.41-43 Wogonin, a naturally occurring monoflavonoid, was shown to attenuate TNF-α-conferred NFκB activity and thereby sensitize malignant T cells to apoptosis. Moreover, wogonin was reported to exert cytostatic and cytotoxic activities against several cancer cell lines in vitro and in vivo, accompanied by no or only mild side effects and low toxicity for non-malignant cells.44-46 The mecha- nism of action of wogonin is based on CDK9 inhibition and interference with reactive oxygen species (ROS) homeostasis.22,45 Wogonin was shown to shift the redox status of malignant T cells to a more reduced state by
BCR and TNFR signaling as well as canonical NFκB activity characterize the LN microenvironment in CLL.5,35 TNFR-1 is a pleiotropic receptor which induces either cel- lular activation via NFκB or apoptosis via activation of cas- pases. NFκB activation appears to be the default pathway resulting in expression of anti-apoptotic proteins, whereas specific inhibition of NFκB prior to TNF-α stimulation triggers cell death.36 Our data, procured from tissue microarray staining of human BM and LN sections, sug- gests that TNFR-1 signaling contributes to NFκB activity in CLL cells. Thereby TNFR-1 expression was enriched within B-cell rich proliferation centers in CLL samples and germinal centers in reactive LN, the sites of NFκB activi- ty.37 Along the same line, malignant B cells in the blood of Em-TCL1 mice were negative for TNFR-1, but upregulated the receptor upon recirculation to the spleen, stressing the hypothesis that TNFR-1 might be involved in CLL cell activation and survival maintenance.
22 increasing H O levels and decreasing ·O levels. This
Inflammatory pathways are central for CLL cell survival.3 In agreement with this fact, elevated TNF-α lev- els were identified in CLL patients and correlated with poor prognosis.13-15 Nonetheless, data on the role of TNF- α in CLL pathogenesis are controversial. It has been sug- gested that it acts as an autocrine and paracrine growth factor which induces CLL cell proliferation in vitro.17,18,38 However, Foa et al. showed that in the majority of CLL cases, proliferation was reduced upon TNF-α treatment.39 In our study, TNF-α had no effect on CLL cell proliferation (data not shown), but rather induced canonical NFκB activi- ty in CLL cells in vitro. Similar results were reported by Coscia et al., who demonstrated that NFκB is activated in CLL cells with unmutated IGHV genes upon TNF-α expo- sure.40
Clinical intervention with TNF/TNFR signaling in CLL
Pre-clinical testing of wogonin after adoptive transfer of CLL in mice revealed that early treatment start resulted in a reduced tumor load in all tissues affected by disease, which might be due to the inhibition of tumor cell survival or proliferation. Accordingly, studies with several cancer cell lines showed that wogonin attenuates cyclin expres- sion.44,49,50 When we treated animals with full-blown leukemia, starting 21 days after tumor engraftment, wogo- nin reduced the CLL cell content in the spleen and signifi- cantly increased tumor load in PB. This effect was accom- panied by the loss of mTNFR-1 expression in CLL cells and elevated sTNFR-1 serum levels, suggesting that the shedding of mTNFR-1 from the surface of CLL cells might be causally involved in the observed accumulation of cells in the blood. Targeting CLL cells with drugs that are cur- rently used in clinical treatment for CLL is much more effective in the blood. Therefore, combination therapy approaches with wogonin and, for example, therapeutic antibodies like rituximab might result in improved treat- ment responses.
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resulted in an inhibition of the redox-sensitive protein
NFκB.47,48 In the study herein, wogonin reduced TNF-α- mediated NFκB activity and induced apoptosis in CLL cells. Future studies need to investigate whether this effect is based on interference with ROS levels.
haematologica | 2018; 103(4)