sirolimus and entinostat

The use of molecularly targeted drugs as single agents has shown limited utility in many tumor types, largely due to the complex and redundant nature of oncogenic signaling networks. Targeting of the PI3K/AKT/mTOR pathway through inhibition of mTOR in combination with aromatase inhibitors has seen success in particular sub-types of breast cancer and there is a need to identify additional synergistic combinations to maximize the clinical potential of mTOR inhibitors. We have used loss-of-function RNAi screens of the mTOR inhibitor rapamycin to identify sensitizers of mTOR inhibition. RNAi screens conducted in combination with rapamycin in multiple breast cancer cell lines identified six genes, AURKB, PLK1, PIK3R1, MAPK12, PRKD2, and PTK6 that when silenced, each enhanced the sensitivity of multiple breast cancer lines to rapamycin. Using selective pharmacological agents we confirmed that inhibition of AURKB or PLK1 synergizes with rapamycin. Compound-associated gene expression data suggested histone deacetylation (HDAC) inhibition as a strategy for reducing the expression of several of the rapamycin-sensitizing genes, and we tested and validated this using the HDAC inhibitor entinostat in vitro and in vivo. Our findings indicate new approaches for enhancing the efficacy of rapamycin including the use of combining its application with HDAC inhibition.

Topics: Animals; Antineoplastic Combined Chemotherapy Protocols; Aurora Kinase B; Benzamides; Breast Neoplasms; Cell Cycle Proteins; Cell Line, Tumor; Class Ia Phosphatidylinositol 3-Kinase; Drug Screening Assays, Antitumor; Drug Synergism; Female; Humans; MCF-7 Cells; Mice; Mice, SCID; Mitogen-Activated Protein Kinase 12; Neoplasm Proteins; Phosphoinositide-3 Kinase Inhibitors; Polo-Like Kinase 1; Protein Kinase D2; Protein Kinase Inhibitors; Protein Kinases; Protein Serine-Threonine Kinases; Protein-Tyrosine Kinases; Proto-Oncogene Proteins; Pyridines; Random Allocation; RNA Interference; Sirolimus; Xenograft Model Antitumor Assays

This study found that MS-275, a novel synthetic benzamide histone deacetylase inhibitor (HDACI), blocked Akt/mammalian target of rapamycin (mTOR) signaling in acute myelogenous leukemia (AML) HL60 and acute promyelocytic leukemia (APL) NB4 cells, as assessed by decreased levels of the phosphorylated (p)-Akt, p-p70 ribosomal S6 kinase (p70S6K) and p-S6K by western blot analysis. Interestingly, further inactivation of mTOR by rapamycin analog RAD001 (everolimus) significantly enhanced MS-275-mediated growth inhibition and apoptosis of these cells in parallel with enhanced upregulation of p27(kip1) and downregulation of c-Myc. In addition, RAD001 potentiated the ability of MS-275 to induce differentiation of HL60 and NB4 cells, as measured by the expression of CD11b cell surface antigens, as well as reduction of nitroblue tetrazolium. Importantly, RAD001 potentiated the ability of MS-275 to induce the expression of the myeloid differentiation-related transcription factor, CCAAT enhancer-binding protein-epsilon, in these cells in association with enhanced acetylation of histone H3 on its promoter. Furthermore, RAD001 (5 mg/kg) significantly enhanced the effects of MS-275 (10 mg/kg) to inhibit proliferation of HL60 tumor xenografts in nude mice without adverse effects. Taken together, concomitant administration of an HDACI and an mTOR inhibitor may be a promising treatment strategy for the individuals with a subset of human leukemia.

Topics: Acetylation; Animals; Apoptosis; Benzamides; CCAAT-Enhancer-Binding Proteins; Cell Differentiation; Cell Division; Drug Synergism; Everolimus; Female; Histone Deacetylase 1; Histone Deacetylase Inhibitors; Histone Deacetylases; Histones; HL-60 Cells; Humans; Immunosuppressive Agents; Leukemia, Myeloid, Acute; Leukemia, Promyelocytic, Acute; Mechanistic Target of Rapamycin Complex 1; Mice; Mice, Inbred BALB C; Mice, Nude; Multiprotein Complexes; Promoter Regions, Genetic; Proteins; Proto-Oncogene Proteins c-akt; Pyridines; Signal Transduction; Sirolimus; TOR Serine-Threonine Kinases; Transcription Factors; Xenograft Model Antitumor Assays