Viscum album neutralizes tumor-induced immunosuppression in a human in vitro cell model.

Tumor cells have the capacity to secrete immunosuppressive substances in order to diminish dendritic cell (DC) activity and thereby escape from immune responses. The impact of mistletoe (Viscum album) extracts (VAE), which are frequently used as an additive anti-cancer therapy to stimulate the immune response, is still unknown. Using a human cellular system, the impact of two different VAE (VAEA + VAEI) on the maturation of human dendritic cells and on T cell function has been investigated using flow cytometry, automated fluorescence microscopy and cytokine bead array assays. Furthermore, we examined whether VAEI was able to counteract tumor-induced immunosuppression within this cellular system using a renal cancer cell model. The role of mistletoe lectin (ML) was analyzed using ML-specific antibodies and ML-depleted VAEI. VAEI and VAEA augmented the maturation of dendritic cells. VAEI abrogated tumor-induced immunosuppression of dendritic cells and both processes were partially mediated by ML since ML-depleted VAEI and ML-specific antibodies almost neutralized the rehabilitative effects of VAEI on DC maturation. Using these settings, co-culture experiments with purified CD4+ T cells had no influence on T cell proliferation and activation but did have an impact on IFN-γ secretion. The study provides a potential mode-of-action of VAE as an additive cancer therapy based on immunomodulatory effects. However, the impact on the in vivo situation has to be evaluated in further studies.

Potent in vitro and in vivo activity of sorafenib in multiple myeloma: induction of cell death, CD138-downregulation and inhibition of migration through actin depolymerization.

Despite considerable advances, multiple myeloma (MM) remains incurable and the development of novel therapies targeting the interplay between plasma cells (PCs) and their bone marrow (BM) microenvironment remains essential. We investigated the effect of various agents in vitro on the proliferation, phenotype, morphology, actin polymerization and migration of MM cells and, in vivo, the tumour growth of L363-bearing non-obese diabetic severe combined immunodeficient mice with a deficient interleukin-2 receptor gamma chain (NSG). In vitro, we observed a dose-dependent cytotoxicity with bortezomib and sorafenib. Using RPMI8226 cells co-expressing histone 2B-mCherry and cytochrome c-GFP, bortezomib- and sorafenib-induced apoptosis was confirmed, and both agents combined showed synergism. Sorafenib induced CD138-downregulation and abolished CXCL12-induced actin polymerization. L363 cells expressed CCR4 and CCR5 and migrated to their common ligand CCL5. Chemotaxis to BM stroma cells was notable and significantly reduced by sorafenib. Downregulation of phospho-ERK appeared relevant for the inhibition of actin polymerization and chemotaxis. Sorafenib alone, and combined with bortezomib, showed substantial antitumour activity in L363-bearing NSG. Correspondingly, sorafenib induced clinical responses in MM-/AL-amyloidosis patients. We conclude that, in addition to the cytotoxic and anti-angiogenic effects of sorafenib, blocking of MM cell migration and homing represent promising mechanisms to interrupt the interplay between PCs and their supportive microenvironment.