Targeting Key Signaling Pathways in Glioblastoma Stem Cells for the Development of Efficient Chemo- and Immunotherapy.

Glioblastoma multiforme (GBM) is the most aggressive and most common malignant brain tumor with poor patient survival despite therapeutic intervention. On the cellular level, GBM comprises a rare population of glioblastoma stem cells (GSCs), driving therapeutic resistance, invasion, and recurrence. GSCs have thus come into the focus of therapeutic strategies, although their targeting remains challenging. In the present study, we took advantage of three GSCs-populations recently established in our lab to investigate key signaling pathways and subsequent therapeutic strategies targeting GSCs. We observed that NF-κB, a crucial transcription factor in GBM progression, was expressed in all CD44+/CD133+/Nestin+-GSC-populations. Exposure to TNFα led to activation of NF-κB-RELA and/or NF-κB-c-REL, depending on the GBM type. GSCs further expressed the proto-oncogene MYC family, with MYChigh GSCs being predominantly located in the tumor spheres ("GROW"-state) while NF-κB-RELAhigh GSCs were migrating out of the sphere ("GO"-state). We efficiently targeted GSCs by the pharmacologic inhibition of NF-κB using PTDC/Bortezomib or inhibition of MYC by KJ-Pyr-9, which significantly reduced GSC-viability, even in comparison to the standard chemotherapeutic drug temozolomide. As an additional cell-therapeutic strategy, we showed that NK cells could kill GSCs. Our findings offer new perspectives for developing efficient patient-specific chemo- and immunotherapy against GBM.

Analysis of Several Pathways for Efficient Killing of Prostate Cancer Stem Cells: A Central Role of NF-κB RELA.

Prostate cancer is a common cause of death worldwide. Here, we isolated cancer stem cells (CSCs) from four adenocarcinomas of the prostate (Gleason scores from 3 + 3 up to 4 + 5). CSCs were characterized by the expression of the stem cell markers TWIST, the epithelial cell adhesion molecule (EPCAM), the transcription factors SNAI1 (SNAIL) and SNAI2 (SLUG) and cancer markers such as CD44 and prominin-1 (CD133). All investigated CSC populations contained a fraction highly positive for aldehyde dehydrogenase (ALDH) function and displayed robust expressions of programmed cell death 1 (PD-1) ligands. Furthermore, we investigated immunotherapeutic approaches but had no success even with the clinically used PD-1 inhibitor pembrolizumab. In addition, we studied another death-inducing pathway via interferon gamma signaling and detected high-level upregulations of human leukocyte antigen A (HLA-A) and beta 2-microglobulin (B2M) with only moderate killing efficacy. To examine further killing mechanisms in prostate cancer stem cells (PCSCs), we analyzed NF-κB signaling. Surprisingly, two patient-specific populations of PCSCs were found: one with canonical NF-κB signaling and another one with blunted NF-κB activation, which can be efficiently killed by tumor necrosis factor (TNF). Thus, culturing of PCSCs and analysis of respective NF-κB induction potency after surgery might be a powerful tool for optimizing patient-specific treatment options, such as the use of TNF-inducing chemotherapeutics and/or NF-κB inhibitors.