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

Mol Cancer Res. 2014 Jul;12(7):987-1001. doi: 10.1158/1541-7786.MCR-13-0650. Epub 2014 Apr 22.


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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

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


  • 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