PI3K and Bcl-2 inhibition primes glioblastoma cells to apoptosis through downregulation of Mcl-1 and Phospho-BAD.

Abstract

UNLABELLED:

Glioblastoma multiforme (GBM) is a highly malignant human brain neoplasm with limited therapeutic options. GBMs display a deregulated apoptotic pathway with high levels of the antiapoptotic Bcl-2 family of proteins and overt activity of the phosphatidylinositol 3-kinase (PI3K) signaling pathway. Therefore, combined interference of the PI3K pathway and the Bcl-2 family of proteins is a reasonable therapeutic strategy. ABT-263 (Navitoclax), an orally available small-molecule Bcl-2 inhibitor, and GDC-0941, a PI3K inhibitor, were used to treat established glioblastoma and glioblastoma neurosphere cells, alone or in combination. Although GDC-0941 alone had a modest effect on cell viability, treatment with ABT-263 displayed a marked reduction of cell viability and induction of apoptotic cell death. Moreover, combinatorial therapy using ABT-263 and GDC-0941 showed an enhanced effect, with a further decrease in cellular viability. Furthermore, combination treatment abrogated the ability of stem cell-like glioma cells to form neurospheres. ABT-263 and GDC-0941, in combination, resulted in a consistent and significant increase of Annexin V positive cells and loss of mitochondrial membrane potential compared with either monotherapy. The combination treatment led to enhanced cleavage of both initiator and effector caspases. Mechanistically, GDC-0941 depleted pAKT (Serine 473) levels and suppressed Mcl-1 protein levels, lowering the threshold for the cytotoxic actions of ABT-263. GDC-0941 decreased Mcl-1 in a posttranslational manner and significantly decreased the half-life of Mcl-1 protein. Ectopic expression of human Mcl-1 mitigated apoptotic cell death induced by the drug combination. Furthermore, GDC-0941 modulated the phosphorylation status of BAD, thereby further enhancing ABT-263-mediated cell death.

IMPLICATIONS:

Combination therapy with ABT-263 and GDC-0941 has novel therapeutic potential by specifically targeting aberrantly active, deregulated pathways in GBM, overcoming endogenous resistance to apoptosis.

• Authors: Fresia Pareja, David Macleod, Chang Shu, John F Crary, Peter D Canoll, Alonzo H Ross, Markus D Siegelin
• Journal: Molecular cancer research : MCR (Mol Cancer Res) Vol. 12 Issue 7 Pg. 987-1001 (Jul 2014) ISSN: 1557-3125 [Electronic] United States
• PMID: 24757258 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't)
• Copyright: ©2014 American Association for Cancer Research.

Chemical References

• 2-(1H-indazol-4-yl)-6-(4-methanesulfonylpiperazin-1-ylmethyl)-4-morpholin-4-ylthieno(3,2-d)pyrimidine
• Aniline Compounds
• BAD protein, human
• Indazoles
• MCL1 protein, human
• Myeloid Cell Leukemia Sequence 1 Protein
• Phosphoinositide-3 Kinase Inhibitors
• Proto-Oncogene Proteins c-bcl-2
• Sulfonamides
• bcl-Associated Death Protein
• navitoclax

Topics

• Aniline Compounds (pharmacology)
• Apoptosis (physiology)
• Cell Line, Tumor
• Down-Regulation
• Glioblastoma (drug therapy, enzymology, metabolism)
• Humans
• Indazoles (pharmacology)
• Myeloid Cell Leukemia Sequence 1 Protein (genetics, metabolism)
• Phosphatidylinositol 3-Kinases (metabolism)
• Phosphoinositide-3 Kinase Inhibitors
• Phosphorylation
• Proto-Oncogene Proteins c-bcl-2 (antagonists & inhibitors, metabolism)
• Signal Transduction
• Sulfonamides (pharmacology)
• Transfection
• bcl-Associated Death Protein (genetics, metabolism)