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


CONCLUSIONS
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' Affiliations: Department of Pathology & Cell Biology, Columbia University Medical Center, New York, New York; and.
Fresia
F
Pareja
Authors' Affiliations: Department of Pathology & Cell Biology, Columbia University Medical Center, New York, New York; and.
David
D
Macleod
Authors' Affiliations: Department of Pathology & Cell Biology, Columbia University Medical Center, New York, New York; and.
Chang
C
Shu
Authors' Affiliations: Department of Pathology & Cell Biology, Columbia University Medical Center, New York, New York; and.
John F
JF
Crary
Authors' Affiliations: Department of Pathology & Cell Biology, Columbia University Medical Center, New York, New York; and.
Peter D
PD
Canoll
Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, Massachusetts.
Alonzo H
AH
Ross
Authors' Affiliations: Department of Pathology & Cell Biology, Columbia University Medical Center, New York, New York; and ms4169@columbia.edu ms4169@cumc.columbia.edu msiegelin@gmail.com.
Markus D
MD
Siegelin
D000814:Aniline Compounds / Q000494:pharmacology; D017209:Apoptosis / Q000502:physiology; D045744:Cell Line, Tumor; D015536:Down-Regulation; D005909:Glioblastoma / Q000188:drug therapy* / Q000201:enzymology / Q000378:metabolism*; D006801:Humans; D007191:Indazoles / Q000494:pharmacology; D064549:Myeloid Cell Leukemia Sequence 1 Protein / Q000235:genetics / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000037:antagonists & inhibitors* / Q000378:metabolism; D015398:Signal Transduction; D013449:Sulfonamides / Q000494:pharmacology; D014162:Transfection; D051025:bcl-Associated Death Protein / Q000235:genetics / Q000378:metabolism*
D000814:Aniline Compounds; D007191:Indazoles; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D019253:Proto-Oncogene Proteins c-bcl-2; D013449:Sulfonamides; D051025:bcl-Associated Death Protein; C532162:2-(1H-indazol-4-yl)-6-(4-methanesulfonylpiperazin-1-ylmethyl)-4-morpholin-4-ylthieno(3,2-d)pyrimidine; C494819:BAD protein, human; C579095:MCL1 protein, human; C528561:navitoclax