Anti-tumor activities of luteolin and silibinin in glioblastoma cells: overexpression of miR-7-1-3p augmented luteolin and silibinin to inhibit autophagy and induce apoptosis in glioblastoma in vivo

Abstract

Glioblastoma is the deadliest brain tumor in humans. High systemic toxicity of conventional chemotherapies prompted the search for natural compounds for controlling glioblastoma. The natural flavonoids luteolin (LUT) and silibinin (SIL) have anti-tumor activities. LUT inhibits autophagy, cell proliferation, metastasis, and angiogenesis and induces apoptosis; while SIL activates caspase-8 cascades to induce apoptosis. However, synergistic anti-tumor effects of LUT and SIL in glioblastoma remain unknown. Overexpression of tumor suppressor microRNA (miR) could enhance the anti-tumor effects of LUT and SIL. Here, we showed that 20 µM LUT and 50 µM SIL worked synergistically for inhibiting growth of two different human glioblastoma U87MG (wild-type p53) and T98G (mutant p53) cell lines and natural combination therapy was more effective than conventional chemotherapy (10 µM BCNU or 100 µM TMZ). Combination of LUT and SIL caused inhibition of growth of glioblastoma cells due to induction of significant amounts of apoptosis and complete inhibition of invasion and migration. Further, combination of LUT and SIL inhibited rapamycin (RAPA)-induced autophagy, a survival mechanism, with suppression of PKCα and promotion of apoptosis through down regulation of iNOS and significant increase in expression of the tumor suppressor miR-7-1-3p in glioblastoma cells. Our in vivo studies confirmed that overexpression of miR-7-1-3p augmented anti-tumor activities of LUT and SIL in RAPA pre-treated both U87MG and T98G tumors. In conclusion, our results clearly demonstrated that overexpression of miR-7-1-3p augmented the anti-tumor activities of LUT and SIL to inhibit autophagy and induce apoptosis for controlling growth of different human glioblastomas in vivo.

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Abbreviations

LUT:

Luteolin

SIL:

Silibinin

miR:

microRNA

BCNU:

Bis-chloroethylnitrosourea

TMZ:

Temozolomide

NF-κB:

Nuclear transcription factor-kappa B

RAPA:

Rapamycin

PKCα:

Protein kinase C alpha

XIAP:

X-linked inhibitor of apoptosis protein

iNOS:

Inducible nitric oxide synthase

PCNA:

Proliferating cell nuclear antigen

VEGF:

Vascular endothelial growth factor

COX-2:

Cyclooxygenase-2

DMSO:

Dimethyl sulfoxide

FBS:

Fetal bovine serum

MTT:

3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide

IgG:

Immunoglobulin G

ECL:

Enhanced chemiluminescence

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Acknowledgments

This work was supported in part by the awards from the Research Development Fund (University of South Carolina School of Medicine, Columbia, SC, USA), the United Soybean Board (USB, Chesterfield, MO, USA), and the Spinal Cord Injury Research Fund (SCIRF-2015-I-01, Columbia, SC, USA).

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Correspondence to Swapan K. Ray.

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Chakrabarti, M., Ray, S.K. Anti-tumor activities of luteolin and silibinin in glioblastoma cells: overexpression of miR-7-1-3p augmented luteolin and silibinin to inhibit autophagy and induce apoptosis in glioblastoma in vivo. Apoptosis 21, 312–328 (2016). https://doi.org/10.1007/s10495-015-1198-x

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Keywords

  • Apoptosis
  • Autophagy
  • Glioblastoma
  • Luteolin
  • Silibinin
  • miR-7-1-3p