Doubling down on the PI3K-AKT-mTOR pathway enhances the antitumor efficacy of PARP inhibitor in triple negative breast cancer model beyond BRCA-ness

Neoplasia. 2014 Jan;16(1):43-72. doi: 10.1593/neo.131694.

Abstract

Phosphoinositide 3-kinase (PI3K) pathway, in addition to its pro-proliferative and antiapoptotic effects on tumor cells, contributes to DNA damage repair (DDR). We hypothesized that GDC-0980, a dual PI3K-mammalian target of rapamycin (mTOR) inhibitor, would induce an efficient antitumor effect in BRCA-competent triple negative breast cancer (TNBC) model when combined with ABT888 and carboplatin. Mechanism-based in vitro studies demonstrated that GDC-0980 treatment alone or in combination led to DNA damage (increased pγH2AX(S139); Western blot, immunofluorescence), gain in poly ADP-ribose (PAR), and a subsequent sensitization of BRCA-competent TNBC cells to ABT888 plus carboplatin with a time-dependent 1) decrease in proliferation signals (pAKTT308/S473, pP70S6KT421/S424, pS6RPS235/236), PAR/poly(ADP-ribose) polymerase (PARP) ratios, PAR/pγH2AX ratios, live/dead cell ratios, cell cycle progression, and three-dimensional clonogenic growths and 2) increase in apoptosis markers (cleaved caspases 3 and 9, a pro-apoptotic BH3-only of Bcl-2 family (BIM), cleaved PARP, annexin V). The combination was effective in vitro in BRCA-wild-type PIK3CA-H1047R-mutated BT20 and PTEN-null HCC70 cells. The combination blocked the growth of established xenograft tumors by 80% to 90% with a concomitant decrease in tumor Ki67, CD31, phosphorylated vascular endothelial growth factor receptor, pS6RPS235/236, and p4EBP1T37/46 as well as an increase in cleaved caspase 3 immunohistochemistry (IHC) levels. Interestingly, a combination with GDC-0941, a pan-PI3K inhibitor, failed to block the tumor growth in MDA-MB231. Results demonstrate that the dual inhibition of PI3K and mTOR regulates DDR. In a BRCA-competent model, GDC-0980 enhanced the antitumor activity of ABT888 plus carboplatin by inhibiting both tumor cell proliferation and tumor-induced angiogenesis along with an increase in the tumor cell apoptosis. This is the first mechanism-based study to demonstrate the integral role of the PI3K-AKT-mTOR pathway in DDR-mediated antitumor action of PARP inhibitor in TNBC.

Publication types

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

MeSH terms

  • Adaptor Proteins, Signal Transducing / metabolism
  • Animals
  • Antineoplastic Agents / pharmacology*
  • Apoptosis / drug effects
  • Benzimidazoles / pharmacology
  • Carboplatin / pharmacology
  • Caspase 3 / metabolism
  • Cell Cycle / drug effects
  • Cell Cycle Proteins
  • Cell Line, Tumor
  • Cell Proliferation
  • Drug Screening Assays, Antitumor
  • Female
  • Gene Expression Regulation, Neoplastic*
  • Genes, BRCA1
  • Genes, BRCA2
  • Humans
  • Ki-67 Antigen / metabolism
  • Mice
  • Mice, Nude
  • Neoplasm Transplantation
  • Phosphatidylinositol 3-Kinases / metabolism*
  • Phosphoproteins / metabolism
  • Platelet Endothelial Cell Adhesion Molecule-1 / metabolism
  • Poly(ADP-ribose) Polymerase Inhibitors*
  • Proto-Oncogene Proteins c-akt / metabolism*
  • Ribosomal Protein S6 Kinases, 70-kDa / metabolism
  • TOR Serine-Threonine Kinases / metabolism*
  • Triple Negative Breast Neoplasms / metabolism*
  • Vascular Endothelial Growth Factor A / metabolism

Substances

  • Adaptor Proteins, Signal Transducing
  • Antineoplastic Agents
  • Benzimidazoles
  • Cell Cycle Proteins
  • EIF4EBP1 protein, human
  • Ki-67 Antigen
  • Phosphoproteins
  • Platelet Endothelial Cell Adhesion Molecule-1
  • Poly(ADP-ribose) Polymerase Inhibitors
  • Vascular Endothelial Growth Factor A
  • veliparib
  • Carboplatin
  • MTOR protein, human
  • AKT1 protein, human
  • Proto-Oncogene Proteins c-akt
  • Ribosomal Protein S6 Kinases, 70-kDa
  • TOR Serine-Threonine Kinases
  • Caspase 3