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Calcitriol promotes differentiation of glioma stem-like cells and increases their susceptibility to temozolomide

ABSTRACT: Cancer cells with a stem-like phenotype are commonly described in glioblastoma, the most common primary adult brain cancer, that are thought to be highly tumorigenic. This phenotype comprimes high self renewal capacity and resistance against chemotherapy and radiation therapy, thereby promoting tumor progression and disease relapse. Here we show for the first time that calcitriol, the hormonally active form of the “sun hormone” vitamin D3, effectively suppresses stemness properties in glioblastoma stem-like cells (GSCs), supporting the hypothesis that cal-citriol sensitizes them to additional chemotherapy. Indeed, a physiologically relevant organotypic brain slice model was used to monitor tumor growth of GSCs and the effectiveness of combined treatment with temozolomide, the current standard-of-care, and calcitriol was proven. These findings indicate that further research on applying calcitriol, a well known and safe drug, as a potential adjuvant therapy for glioblastoma is both justified and necessary.

INSTRUMENT(S): Orbitrap Fusion Lumos

ORGANISM(S): Homo Sapiens (human)

TISSUE(S): Cell Culture

DISEASE(S): Brain Cancer

SUBMITTER: Süleyman Bozkurt

LAB HEAD: Christian Münch

PROVIDER: PXD026789 | Pride | 2021-07-19

REPOSITORIES: Pride

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Project description:Although malignant gliomas frequently show aberrant activation of the mammalian target of rapamycin (mTOR), mTOR inhibitors have performed poorly in clinical trials. Besides regulating cell growth and translation, mTOR controls the initiation of autophagy. By recycling cellular components, autophagy can mobilize energy resources, and has thus been attributed cancer-promoting effects. Here, we asked whether the activation of autophagy represents an escape mechanism to pharmacological mTOR inhibition, and explored co-treatment with mTOR and autophagy inhibitors as a therapeutic strategy. Mimicking conditions of the glioma microenvironment, glioma cells were exposed to nutrient starvation and hypoxia. Following treatment with mTOR inhibitor torin2 or rapamycin, and autophagy inhibitors bafilomycin A1 or MRT68921, we analyzed autophagic activity, cell growth, viability and oxygen consumption. Changes in global proteome were quantified by mass spectrometry. In the context of hypoxia and starvation, autophagy was strongly induced in glioma cells, and further increased by mTOR inhibition. While torin2 enhanced glioma cell survival, co-treatment with torin2 and bafilomycin A1 failed to promote cell death. Importantly, treatment with bafilomycin A1 alone also protected glioma cells from cell death. Mechanistically, both compounds significantly reduced glioma growth and oxygen consumption. Mass spectrometry analysis showed that bafilomycin A1 induced broad changes in the cellular proteome. More specifically, proteins downregulated by bafilomycin A1 were associated with the mitochondrial respiratory chain and ATP synthesis. Taken together, our results show that activation of autophagy does not account for the cytoprotective effects of mTOR inhibition in our in vitro model of the glioma microenvironment. Our proteomic findings suggest that the pharmacological inhibition of autophagy induces extensive changes in the cellular proteome that can support glioma cell survival under nutrient-deplete and hypoxic conditions. These findings provide a novel perspective on the complex role of autophagy in gliomas and may have implications for the design of future trials.

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Calcitriol promotes differentiation of glioma stem-like cells and increases their susceptibility to temozolomide

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