Sreedhar Venkannagari

Targeting levels or oligomerization of nucleophosmin 1 induces differentiation and loss of survival of human AML cells with mutant NPM1

Nucleophosmin 1 (NPM1) is an oligomeric, nucleolar phosphoprotein that functions as a molecular chaperone for both proteins and nucleic acids. NPM1 is mutated in approximately one-third of patients with AML. The mutant NPM1c+ contains a 4-base insert that results in extra C-terminal residues encoding a nuclear export signal, which causes NPM1c+ to be localized in the cytoplasm. Here, we determined the effects of targeting NPM1 in cultured and primary AML cells. Treatment with siRNA to NPM1 induced p53 and p21, decreased the percentage of cells in S-phase of the cell cycle, as well as induced differentiation of the AML OCI-AML3 cells that express both NPMc+ and unmutated NPM1. Notably, knockdown of NPM1 by shRNA abolished lethal AML phenotype induced by OCI-AML3 cells in NOD/SCID mice. Knockdown of NPM1 also sensitized OCI-AML3 to all-trans retinoic acid (ATRA) and cytarabine. Inhibition of NPM1 oligomerization by NSC348884 induced apoptosis and sensitized OCI-AML3 and primary AML cells expressing NPM1c+ to ATRA. This effect was significantly less in AML cells coexpressing FLT3-ITD, or in AML or normal CD34+ progenitor cells expressing wild-type NPM1. Thus, attenuating levels or oligomerization of NPM1 selectively induces apoptosis and sensitizes NPM1c+ expressing AML cells to treatment with ATRA and cytarabine.

Combination of Pan-Histone Deacetylase Inhibitor and Autophagy Inhibitor Exerts Superior Efficacy against Triple-Negative Human Breast Cancer Cells

Histone deacetylase (HDAC) inhibitors (HDI) induce endoplasmic reticulum (ER) stress and apoptosis, while promoting autophagy, which promotes cancer cell survival when apoptosis is compromised. Here, we determined the in vitro and in vivo activity of the combination of the pan-HDI panobinostat and the autophagy inhibitor chloroquine against human estrogen/progesterone receptor and HER2 (triple)-negative breast cancer (TNBC) cells. Treatment of MB-231 and SUM159PT cells with panobinostat disrupted the hsp90/histone deacetylase 6/HSF1/p97 complex, resulting in the upregulation of hsp. This was accompanied by the induction of enhanced autophagic flux as evidenced by increased expression of LC3B-II and the degradation of the autophagic substrate p62. Treatment with panobinostat also induced the accumulation and colocalization of p62 with LC3B-II in cytosolic foci as evidenced by immunofluorescent confocal microscopy. Inhibition of panobinostat-induced autophagic flux by chloroquine markedly induced the accumulation of polyubiquitylated proteins and p62, caused synergistic cell death of MB-231 and SUM159PT cells, and inhibited mammosphere formation in MB-231 cells, compared with treatment with each agent alone. Finally, in mouse mammary fat pad xenografts of MB-231 cells, a tumor size–dependent induction of heat shock response, ER stress and autophagy were observed. Cotreatment with panobinostat and chloroquine resulted in reduced tumor burden and increased the survival of MB-231 breast cancer xenografts. Collectively, our findings show that cotreatment with an autophagy inhibitor and pan-HDI, for example, chloroquine and panobinostat results in accumulation of toxic polyubiquitylated proteins, exerts superior inhibitory effects on TNBC cell growth, and increases the survival of TNBC xenografts. Mol Cancer Ther; 11(4); 973–83. ©2012 AACR.

Heat shock protein 90 inhibitor is synergistic with JAK2 inhibitor and overcomes resistance to JAK2-TKI in human myeloproliferative neoplasm cells

Purpose: We determined the activity of hsp90 inhibitor, and/or Janus-activated kinase 2 (JAK2) tyrosine kinase inhibitor (TKI), against JAK2-V617F–expressing cultured mouse (Ba/F3-JAK2-V617F) and human (HEL92.1.7 and UKE-1) or primary human CD34+ myeloproliferative neoplasm (MPN) cells. Experimental Design: Following exposure to the hsp90 inhibitor AUY922 and/or JAK2-TKI TG101209, the levels of JAK2-V617F, its downstream signaling proteins, as well as apoptosis were determined. Results: Treatment with AUY922 induced proteasomal degradation and depletion of JAK2-V617F as well as attenuated the signaling proteins downstream of JAK2-V617F, that is, phospho (p)-STAT5, p-AKT, and p-ERK1/2. AUY922 treatment also induced apoptosis of HEL92.1.7, UKE-1, and Ba/F3-hJAK2-V617F cells. Combined treatment with AUY922 and TG101209 caused greater depletion of the signaling proteins than either agent alone and synergistically induced apoptosis of HEL92.1.7 and UKE-1 cells. Cotreatment with AUY922 and TG101209 also induced significantly more apoptosis of human CD34+ MPN than normal hematopoietic progenitor cells. As compared with the sensitive controls, JAK2-TKI–resistant HEL/TGR and UKE-1/TGR cells exhibited significantly higher IC50 values for JAK2-TKI (P < 0.001), which was associated with higher expression of p-JAK2, p-STAT5, p-AKT, and Bcl-xL, but reduced levels of BIM. Unlike the sensitive controls, HEL/TGR and UKE/TGR cells were collaterally sensitive to the hsp90 inhibitors AUY922 and 17-AAG, accompanied by marked reduction in p-JAK2, p-STAT5, p-AKT, and Bcl-xL, with concomitant induction of BIM. Conclusions: Findings presented here show that cotreatment with hsp90 inhibitor and JAK2-TKI exerts synergistic activity against cultured and primary MPN cells. In addition, treatment with hsp90 inhibitor may overcome resistance to JAK2-TKI in human MPN cells. Clin Cancer Res; 17(23); 7347–58. ©2011 AACR.

Hsp90 inhibitor-mediated disruption of chaperone association of ATR with Hsp90 sensitizes cancer cells to DNA damage

Following DNA damage that results in stalled replication fork, activation of ATR-CHK1 signaling induces the DNA damage response (DDR) in transformed cells. In the present studies on human cervical and breast cancer cells, we determined the effects of hsp90 inhibition on the levels and accumulation of DNA damage/repair–associated proteins following exposure to γ-ionizing radiation (IR; 4 Gy). We show that hsp90 inhibition with 17-allylamino-demehoxygeldanamycin or the novel, nongeldanamycin analogue AUY922 (resorcinylic isoxazole amide; Novartis Pharma) dose-dependently reduced the levels of ATR and CHK1 without affecting ATM levels. AUY922-mediated depletion of ATR and CHK1 was associated with an increase in their polyubiquitylation and decreased binding to hsp90. Cotreatment with bortezomib partially restored AUY922-mediated depletion of ATR and CHK1 levels. Additionally, treatment with AUY922 reduced the accumulation of ATR, p53BP1, and CHK1 but not γ-H2AX to the sites of DNA damage. Following exposure to IR, AUY922 treatment abrogated IR-induced phospho (p)-ATR and p-CHK1 levels, but significantly enhanced γ-H2AX levels. AUY922 treatment also increased IR-induced accumulation of the cells in G2–M phase of the cell cycle, inhibited the repair of IR-induced DNA damage, and augmented IR-mediated loss of clonogenic survival. Short hairpin RNA–mediated depletion of ATR also inhibited IR-induced p-ATR and p-CHK1, but increased γ-H2AX levels, sensitizing cancer cells to IR-induced apoptosis and loss of clonogenic survival. These findings indicate that ATR is a bona fide hsp90 client protein and post-IR administration of AUY922, by inhibiting ATR-CHK1–mediated DDR, sensitizes cancer cells to IR. Mol Cancer Ther; 10(7); 1194–206. ©2011 AACR.

Co-treatment with vorinostat synergistically enhances activity of Aurora kinase inhibitor against human breast cancer cells

Aurora kinases (AKs) regulate multiple components of mitotic cell division in eukaryotic cells. Aurora A is frequently amplified or overexpressed in breast cancer cells leading to aberrant chromosome segregation, genomic instability, and activation of oncogenic pathways. In the present studies, we determined the effects of treatment with the pan-AK inhibitor MK-0457 and/or the pan-histone deacetylase inhibitor vorinostat against human breast cancer cells that were either ER-, PR-, and HER2- (MDA-MB-468 and MDA-MB-231) or exhibited Aurora A amplification (BT-474 and MDA-MB-231 cells). Treatment with MK-0457 depleted p-AKs levels and their activity, as well as induced G2/M accumulation, DNA endoreduplication, multipolar mitotic spindles, and apoptosis of the breast cancer cells. Similar apoptotic effects were observed with treatment with the Aurora A-specific inhibitor, MLN8237. Treatment with vorinostat induced hsp90 acetylation and inhibited its chaperone association with AKs, leading to depletion of AKs and Survivin. Exposure of the siRNA to AK A also induced apoptosis, which was augmented by co-treatment with MK-0457 and vorinostat. Co-treatment with vorinostat enhanced MK-0457-mediated inhibition of the activities of Aurora A and Aurora B, leading to synergistic in vitro activity against human breast cancer cells. Co-treatment with MK-0457 and vorinostat also caused greater tumor growth inhibition and superior survival of mice bearing MDA-MB-231 xenografts. These pre-clinical findings indicate that combined treatment with a pan-AK inhibitor or an Aurora A-specific inhibitor and vorinostat represents a novel therapeutic strategy for the treatment of Aurora A-amplified and/or triple negative breast cancers.

Abstract 4698: Inhibition of histone deacetylase (HDAC) 3 induces hyperacetylation and inhibition of nuclear heat shock protein (hsp) 90 leading to depletion of ATR and CHK1 with sensitization to DNA damage in breast and cervical cancer cells

Proceedings: AACR 103rd Annual Meeting 2012‐‐ Mar 31‐Apr 4, 2012; Chicago, IL We have recently reported that in addition to checkpoint kinase 1 (CHK1), ataxia-telangiectasia mutated and Rad3- related (ATR) is chaperoned by hsp90. Treatment of breast and cervical cancer cells with hsp90 inhibitor induces proteasomal degradation and depletion of ATR and CHK1. This results in impairment of the DNA damage response (DDR) and causes sensitization to α-irradiation and replication stress due to hydroxyurea (Mol Cancer Ther 10:1194, 3011). In the present studies, we determined that treatment with pan-histone deacetylase (HDAC) inhibitor panobinostat (20 to 50 nM) or vorinostat (0.5 to 2 μM) induced polyubiquitylation and depletion of ATR and CHK1. Co-treatment with bortezomib, a proteasome inhibitor, restored PS-mediated depletion of ATR and CHK1. Notably, treatment with panobinostat induced hyperacetylation of both nuclear and cytoplasmic hsp90. This inhibited the chaperone association of nuclear hsp90 with ATR and CHK1, thereby promoting their degradation. PS treatment induced γ-H2AX levels, which were inhibited by co-treatment with N-acetylcysteine, suggesting that PS-induced ROS is involved in DNA damage. Moreover, PS treatment further increased α-irradiation induced DNA damage and its repair, characterized by the increase in α-irradiation-induced comet tail moment and the lack of DNA repair-mediated attenuation of the comet tail moment. To determine which class I HDAC is involved in deacetylation of nuclear hsp90, we individually knocked down (KD) HDAC 1, 2 and 3, by utilizing specific shRNA, and determined the effect on nuclear hsp90 hyperacetylation and the levels of ATR and CHK1. Our findings show that HDAC3 binds to hsp90 and KD of HDAC3, but not of HDAC1 or 2, caused hyperacetylation of nuclear hsp90 and depletion of ATR and CHK1. This was also observed in HDAC3 null mouse embryonic fibroblasts (MEFs). Ectopic overexpression of HDAC3 inhibited nuclear hsp90 acetylation in transformed cells. These findings demonstrate that HDAC3 is the nuclear hsp90 lysine deacetylase. They also demonstrate that genetic KD of HDAC3, or its inhibition by pan-HDAC inhibitors, induces hyperacetylation of hsp90, mediates loss of hsp90 chaperone association and depletion of ATR and CHK1, abrogates α-irradiation-induced DDR, and results in sensitization of transformed cells to DNA damage due to α-irradiation or replication stress. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4698. doi:1538-7445.AM2012-4698

Abstract 1043: Combined targeting of chromatin modifying enzymes LSD1, histone deacetylases (HDACs) and EZH2 has superior efficacy against human acute myeloid leukemia cells.

Proceedings: AACR 103rd Annual Meeting 2012‐‐ Mar 31‐Apr 4, 2012; Chicago, IL LSD1 or KDM1A is a FAD-dependent demethylase, with homology to amine oxidases. LSD1 demethylates di- and mono-methylated lysine (K)4 on histone H3, reducing the permissive H3K4Me3 chromatin mark. LSD1 inhibition attenuates growth of pluripotent cancer cells with OCT4 and SOX2 expression. LSD1 complexes with HDAC1/2 and Co-REST, and high LSD1 expression confers poor prognosis in cancers. Previous studies have shown that HDAC inhibitors downregulate LSD1 thru Sp1 inhibition. Inhibition of LSD1 leads to increase in H3K4Me3-a permissive mark for gene expression. HCI2509 is an FAD-binding pocket, non-MAOA and MAOB LSD1 inhibitor. In the present studies, we determined the chromatin-modifying and cytotoxic effects of HCI2509 alone and in combination with the pan-histone deacetylase inhibitor, panobinostat (PS) in cultured (HL-60 and OCI-AML3) and primary human acute myeloid leukemia (AML) cells. Treatment with HCI2509 (100 to 500 nM), dose-dependently increased the levels of H3K4Me2 & Me3, p16 and p27, which was associated with inhibition of cell proliferation as measured by a decrease in Ki-67 expression. Chromatin immunoprecipitation followed by PCR demonstrated that treatment with HCI2509 increased the H3K4Me3 mark on the promoters of KLF4, HMOX1, and CDH1 in AML cells. Treatment with HCI2509 also induced C/EBPα expression and features of morphologic differentiation of cultured and primary AML cells. Treatment with HCI2509 (25 mg/kg B.I.W. via IP injection) significantly improved the survival of NOD/SCID mice bearing OCI-AML3- AML xenografts. We have previously reported that treatment with PS (Novartis Pharma) depleted PRC2 complex proteins EZH2, and SUZ12 but also modestly depleted LSD1 expression in AML cells. Co-treatment with PS enhanced the chromatin modifying effects of HCI2509 on K4 of Histone H3 in AML cells. Co-treatment with HCI2509 and PS synergistically induced apoptosis of the cultured AML cells (combination indices, CI <1.0). This was associated with greater induction of p16, and p27. Co-treatment with HCI2509 and PS also induced significantly greater loss of viability of primary AML cells but not of normal CD34+ cells. We have previously reported that treatment with the S-adenosylhomocysteine hydrolase and EZH2 inhibitor, DZNep, dose-dependently depleted EZH2, and SUZ12 levels in cultured and primary AML cells. Combined treatment with HCI2509 enhanced the apoptosis of AML cells induced by DZNep. Taken together, these findings indicate that combined targeted depletion of the level and activity of LSD1 and HDACs by PS and HCI2509, along with PS-mediated depletion of PRC2 proteins, exerts superior and selective cytotoxic activity against AML cells. These findings also support the in vivo testing of combined epigenetic therapies in the treatment of AML. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1043. doi:1538-7445.AM2012-1043

Abstract 2078: Treatment with auranofin induces oxidative and lethal endoplasmic reticulum (ER) stress exerting single agent activity against mantle cell lymphoma cells

Proceedings: AACR 103rd Annual Meeting 2012‐‐ Mar 31‐Apr 4, 2012; Chicago, IL Auranofin (AF) (Ridaura®) is an oral, FDA-approved, lipophilic, gold-containing compound used for the treatment of rheumatoid arthritis. In the present studies, we determined for the first time the lethal activity of AF (100 to 1000 nM) and its underlying mechanism(s) in cultured and primary Mantle Cell Lymphoma (MCL) cells. We demonstrate that treatment with AF in JeKo-1 and Z138C cells induced 2 to 3.5 fold increase in reactive oxygen species (ROS) levels (assessed by flow cytometry), decrease in thioredoxin reductase (TRR) activity (mean reduction of 35-40%) without alteration in the expression of TRR. These findings were associated with induction of nuclear factor erythroid 2-related factor 2 (NRF2) activity marked by substantial increase in heme oxygenase-1 (HMOX1) expression. Microarray analysis revealed that AF treatment significantly upregulated ER stress and oxidative stress inducible genes including that of the ER-stress induced pro-apoptotic transcription factor CHOP (CAAT/enhancer binding protein homologous protein), ATF3 (Activated Transcription Factor 3) and Glutamate-cysteine ligase (GCL), modifier subunit (GCLM), the rate-limiting enzyme in the glutathione (GSH) biosynthesis. Exposure to AF induced significantly more apoptosis in primary MCL cells, as compared to CD19+ normal B cells, CD34+ human cord blood and bone marrow progenitor cells (< 15% apoptosis) (p < 0.01). Based on the observations that AF treatment induced oxidative and ER stress, we determined whether exposure to AF increased the intracellular levels of misfolded and polyubiquitylated proteins, which would disrupt the cytosolic complex consisting of the heat shock protein (hsp) 90, heat shock factor (hsf) 1, histone deacetylase 6 (HDAC6) and p97/VCP, resulting in hyperacetylation and inhibition of the chaperone function of hsp90. Indeed, treatment with AF disrupted the association between hsp90 and HDAC6, HSF1 and p97, resulting in hyperacetylation of hsp90 and depletion of the levels of hsp90 client proteins including HDAC6, AKT and Cyclin D1 in MCL cells. Co-treatment of MCL cells with AF and the proteasome inhibitor carfilzomib (CZ) resulted in synergistic apoptosis in cultured MCL cells and significantly more apoptosis in primary MCL cells, than treatment with each agent alone. Based on the induction of GCLM and anti-oxidant response genes following AF treatment, we tested the anti-MCL activity of the combination of AF and the GCL inhibitor Buthionine sulphoximine (BSO), against MCL cells. Co-treatment with BSO and AF resulted in significantly more apoptosis of MCL cells than treatment with each agent alone. Collectively, our data creates a strong rationale for determining the in vivo activity of AF in patients with MCL as a single agent and in combination with other ER and oxidative stress-inducing agents, especially GCL inhibitors. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2078. doi:1538-7445.AM2012-2078

Abstract 2076: HSF1 inhibition accentuates the lethal activity of proteasome inhibitor in human pancreatic cancer cells

Proceedings: AACR 102nd Annual Meeting 2011‐‐ Apr 2‐6, 2011; Orlando, FL Presence of aneuploidy increases the intracellular levels of misfolded proteins and proteotoxic stress phenotype in cancer cells, which is exploited and further accentuated by the therapeutic use of a proteasome inhibitor, e.g., the novel, orally bioavailable carfilzomib (CF). This results in the disruption of the cytosolic complex of the histone deacetylase 6 (HDAC6), the ATPase and segregase p97 and the heat shock factor 1 (HSF1)-a transcription factor involved in the transactivation of heat shock proteins (hsps). In the present studies, we demonstrate that treatment of the pancreatic cancer Hs766T and Panc1 cells with CF increased the levels of misfolded polyubiquitylated proteins, which disrupts the repressive HSF1/hsp90/HDAC6/Vp97 complex. This induces the phosphorylation, nuclear localization and activation of HSF1, which transactivated hsps (e.g., hsp70, hsp40 and hsp27) as an adaptive response to CF-induced proteotoxic stress. Treatment with CF also induced endoplasmic reticulum (ER) stress, represented by upregulation of GRP78 and the pro-apoptotic transcription factor CHOP, which induced the BH3 only pro-apoptotic protein Bim. Treatment with CF also dose-dependently decreased the viability of Hs766T and Panc1 cells. To further elucidate the role of HSF1 in the adaptive, protective response to CF-induced proteotoxic stress, we stably knocked down HSF1 in Hs766T cells. As compared to the control cells, following heat shock, Hs766T cells with knockdown (KD) of HSF1 displayed reduced expression of hsps. In the HSF1-KD versus the control Hs766T cells, treatment with CF resulted in a dose-dependent induction of polyubiquitylated proteins, GRP78, CHOP, and Bim, as well as induced significantly more apoptosis. HSF1-KD versus the control Hs766T cells exhibited markedly lower levels of HDAC6 and, consequently, displayed reduced CF-induced perinuclear protective aggresome formation, as determined by confocal microscopy. Additionally, as compared to the control cells, Hs766T cells with HSF1-KD demonstrated higher levels of p-AMPK and CF (5 to 20 nM) or the pan-HDAC inhibitor panobinostat (PS, 50 nM)-induced autophagy, as demonstrated by the accumulation of LC3-II (by immunoblot analysis) and LC3 puncta by immunofluorescent staining. Importantly, co-treatment with the autophagy inhibitor hydroxy-chloroquine (HCQ) induced more CF-induced cell death of HSF1-KD versus the control Hs766T cells. Using an acid-sensitive mCherry-GFP-LC3 reporter, we determined that the induction of LC3-II in the Hs766T HSF1-KD cells is the result of enhanced autophagic flux and not due to inefficient fusion of autophagosomes with lysosomes. Collectively, these findings indicate that inhibition of the transcriptional activity of HSF1 sensitizes pancreatic cancer cells to CF or PS-induced cells death, which is augmented by co-treatment with an autophagy inhibitor. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2076. doi:10.1158/1538-7445.AM2011-2076

Abstract 3539: Targeting levels and oligomerization of mutant nucleophosmin induces differentiation and loss of survival of human AML cells with mutant NPM1

NPM1 is an oligomeric, nucleolar phosphoprotein that functions as a molecular chaperone for both proteins and nucleic acids. NPM1 plays multiple roles in cell growth and proliferation by participating in diverse biological processes, including ribosome biogenesis and transport, centrosome duplication, DNA repair, transcriptional regulation and histone chaperoning. NPM1 has an N-terminal conserved, hydrophobic, oligomerization domain (residues, 1-110), which is common to all isoforms of NPM1 and critical for its chaperone activity. Recently, NSC348884 was identified as a small molecule inhibitor that disrupts NPM1 dimer/oligomer formation, inducing apoptosis of cancer cells. NPM1 is mutated in approximately one-third of patients with AML. The mutant NPM1c+ contains a 4-base insert that results in extra C-terminal residues encoding a nuclear export signal (NES), which causes NPM1c+ to be aberrantly localized in the cytoplasm. Here, we determined the effects of targeting NPM1 in cultured and primary AML cells. Treatment with siRNA to NPM1, which depleted both NPM1c+ and un-mutated NPM1, significantly induced p21, decreased the % of cells in S-phase of the cell cycle, as well as induced differentiation of the AML OCI-AML3 cells that express both NPMc+ and un-mutated NPM1. This was associated with up-regulation of C/EBPα but attenuation of the levels of HOXA9 and MEIS1. Notably, treatment with NPM1 siRNA sensitized OCI-AML3 more than HL-60 cells (expressing only wild-type NPM1) to all-trans retinoic acid (ATRA) and cytarabine. Moreover, inhibition of NPM1 oligomerization by NSC348884-induced apoptosis and sensitized OCI-AML3 and primary AML cells expressing NPM1c+, but not AML or normal CD34+ progenitor cells expressing wild-type NPM1, to ATRA and cytarbine. NSC348884 was also able to sensitize primary AML cells that expressed NPM1c+ as well as FLT3-ITD to ATRA and cytarbine. Addtionally, co-treatment with NSC384884 sensitized these primary AML cells to the lethal effects of the FLT3 kinase inhibitor PKC412 (Novartis Pharma). These results show that attenuating levels or oligomerization of NPM1 selectively induces apoptosis and sensitizes AML cells expressing NPM1c+ alone or with FLT3-ITD to treatment with ATRA, cytarabine and FLT3 kinase inhibitor. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3539. doi:10.1158/1538-7445.AM2011-3539