TLR-4/Wnt modulation as new therapeutic strategy in the treatment of glioblastomas

Abstract

PurposeGlioblastomas are highly aggressive brain tumors. Various pathways are involved in gliomagenesis, among which the Wingless (Wnt) signaling. Dickkopf protein-related protein 3 (Dkk-3) interacts with proteins of Wnt pathwayas inhibitor. The Wnt signaling contributes to activity of the claudins, that are critical components of tight junctions, whose expression was altered selectively in cerebral microvessels of glioblastoma. The aim of this study was to determine the role of Wnt pathways in the regulation of tumor growth, apoptosis process by targeting Dkk-3, tight junctions alteration involving claudin-5, suggesting possible therapeutic interactions involving Wnt/Toll-like receptors (TLRs) pathways.ResultsWe showed a significant decreasing of Dkk-3 and claudin-5 in human glioblastoma cell lines, as well as in U-87 MG xenograft tumors and in glioblastoma human patient’s tissues, with an involvement of the apoptosis process. Also, an interesting TLR-4/Wnt modulation highlighted that the absence of TLR-4 determined resistance to the tumor onset.ConclusionsWe concluded that combined modulation of Wnt/Dkk-3/claudin-5 and TLR-4 pathways, simultaneously targeting apoptosis and survival signaling defects, might shift the balance from tumor growth stasis to cytotoxic therapeutic responses, flowing in greater therapeutic benefits.MethodsIn the present study we investigated the expression of Dkk-3, claudin-5, apoptosis markers and TLR-4 receptor protein levels in in vitro studies on U-138MG, A-172, LN-18 and LN-229 human glioblastoma cell lines, and in vivo study using TLR-4 KO mice and in glioblastoma human patient’s tissues.

TLR-4 Signaling vs. Immune Checkpoints, miRNAs Molecules, Cancer Stem Cells, and Wingless-Signaling Interplay in Glioblastoma Multiforme—Future Perspectives

“…Overexpression of TLR-4 results in an increase of PD-1L in GBM patients and is associated with unfavorable outcome [61]. Additionally, the increase inTLR-4 expression results in Wnt/claudine signaling forwarding to the progression of GBM and limits the effective apoptosis [62]. Progression of glioblastoma is also controlled and modulated by multiple miRNAs molecules.…”

“…Moreover, DKK-3 seems to be an effective inhibitor of tumor-cell growth molecules. Casili et al performed a study revealing DKK-3 to have a regulating influence on the Wnt pathway, resulting in increased caspase-3-dependent apoptosis [62].…”

“…Interestingly, caspase-9, a less apoptotic molecule, is downexpressed after Dickkopf WNT Signaling Pathway Inhibitor 3 (DKK-3) upregulation, usually increasing after TLR-4 stimulation. Highly invasive cancer-cell lines express caspase-9 more intensively [62,[149][150][151].…”

“…Additionally, the lack of TLR-4 maintains claudin-5 and DKK-3 proapoptotic properties, resulting in the limitation of tumor expansion. To sum up, the downexpression of TLR-4 promotes Wnt/DKK-3/claudin-5 signaling, which limits GBM invasiveness [62,152,153].…”

Toll-Like Receptors as Therapeutic Targets in Central Nervous System Tumors

“…Furthermore, TLR4 gene deficiency induced apoptosis process (caspase-3-dependent), resulting in a decrease in tumor growth. This suggests that TLR4 is a biomarker of interest for tumor metastasis and prognosis [52].…”