gms | German Medical Science

Objective: Tumor stem cells (TSCs) are hold responsible for tumor initiation and therapy resistance in a variety of cancers, including leukemia, carcinomas of breast and colon as well as several types of brain tumors. Differentiation of TSCs has been discussed as a possible approach to eradicate the tumor-driving cell population disrooting the actively proliferating tumor bulk. Since all-trans retinoic acid (ATRA) is known as a modulator of differentiation and proliferation, we sought to elucidate whether ATRA induces differentiation of glioblastoma-derived TSC, so-called brain tumor stem cells (BTSCs) and if tumor-relevant properties of these cells are affected by differentiation.

Methods: BTSC lines (n=3) with high CD133 content (68-93%) were treated with ATRA-containing medium. Change in proliferation and CD133 content was monitored by BrdU-incorporation assay and FACS-analysis, respectively. Impact of differentiation on the angiogenic capacity of BTSCs was measured by quantification of angiogenic cytokines and assessed in a HUVEC-based tube formation assay. Potential effects on BTSC invasiveness were studied in a 3D-collagen invasion model. Finally, we studied whether in vitro effects could be confirmed in vivo using a NOD/SCID-mouse xenograft model.

Results: We present evidence that BTSCs exposed to ATRA increase their proliferative activity and simultaneously lower the expression of stem cell-related antigen CD133 by up to 75% in favor of incremented linage markers GFAP, MBP and beta3-tubulin. Furthermore, we report on significantly reduced VEGF and bFGF secretion by 70-82% and 95-99% respectively, as well as significantly lowered tube-formation by up to 55% following differentiation. Additionally, we show that differentiation elicits strong anti-invasive effects reducing collagen invasion by up to 46% and that these effects are associated with a marked downregulation of invasion-related MMP2 protein (up to sevenfold). Finally, we report that xenografted tumors of differentiated BTSCs are significantly smaller (only 15% of BTSC tumor volume) and less invasive than undifferentiated BTSC tumor xenografts. Correspondingly, animals bearing differentiated cells show both significantly better PFS and OS than mice with BTSC xenografts (p<0,016).

Conclusions: Altogether, these results highlight the potential of differentiation treatment to target the tumor-driving compartment in glioblastoma and point out a potential therapeutic value in the eradication of TSCs.