Calcitriol Promotes Differentiation of Glioma Stem-Like Cells and Increases their Susceptibility to Temozolomide

Abstract

: Glioblastoma (GBM) is the most common and most aggressive primary brain tumor with a very high rate of recurrence and a median survival of 15 months after diagnosis. Abundant evi-dence suggests that a certain sub-population of cancer cells harbors a stem-like phenotype and is likely responsible for disease recurrence, treatment resistance and potentially even for the infil-trative growth of GBM. GBM incidence has been negatively correlated with the serum levels of 25-hydroxy-vitamin D3, while the low pH within tumors has been shown to promote the ex-pression of the vitamin D3-degrading enzyme 24-hydroxylase, encoded by the CYP24A1 gene. Therefore, we hypothesized that calcitriol can specifically target stem-like glioblastoma cells and induce their differentiation. Here, we show using in vitro limiting dilution assays, quantita-tive real-time PCR and ex vivo adult organotypic brain slice transplantation cultures that thera-peutic doses of calcitriol, the hormonally active form of vitamin D3, reduces stemness to varying extent in a panel of investigated GSC lines and effectively hinders tumor growth of responding GSCs ex vivo. We further show that calcitriol synergizes with Temozolomide ex vivo to com-pletely eliminate some GSC tumors. These findings indicate that calcitriol carries potential as an adjuvant therapy for a subgroup of GBM patients and should be analyzed in more detail in fol-low-up studies.

Pathway-based Approach Reveals Differential Sensitivity to E2F1 Inhibition in Glioblastoma

“…Calcitriol is an active form of vitamin D that can be used to regulate the cell cycle and induce apoptosis. It has also been associated with promoting differentiation of glioma stem-like cells and increasing susceptibility to temozolomide (46). While preliminary, these studies support our approach to identifying targetable pathways and the repurpose of FDA-approved drugs.…”

Combining organotypic tissue culture with multi-color fluorescence light-sheet microscopy (OTCxLSFM) – a novel tool to study glioma invasion/migration

“…Some reports show applicability towards analysis on angiogenesis and tumor microenvironment however, these studies mainly rely on further sectioning the slices thereby further increasing the workload. More recent studies, including our own, developed an OTC platform based on adult murine brain slices grown under serum-free conditions (Marques-Torrejon et al 2018;Meyer et al 2018;Remy et al 2018;Linder et al 2019;Gerstmeier et al 2021), thereby ensuring that tumors grow in a more relevant environment, because GBM is a tumor of adult patients. One major drawback of current approaches is the lack of properly investigating the three-dimensional tissue invasion of GBM cells within these slices.…”

“…A rarely used, but powerful method consists of placing fluorescently labeled tumor cells onto murine brain slices and monitor tumor development for several days to weeks. We have successfully applied these so-called organotypic tissue slice cultures (OTCs) in previous studies and could show that this method has potential for further development (Remy et al 2018;Linder et al 2019;Gerstmeier et al 2021;Linder et al 2022). So far, we have analyzed tumor growth using an epifluorescence microscope and measured the tumor area on top of the brain slices.…”