Combined inhibition of BCL-2 and MCL-1 overcomes BAX deficiency-mediated resistance of TP53-mutant acute myeloid leukemia to individual BH3 mimetics

TP53-mutant acute myeloid leukemia (AML) respond poorly to currently available treatments, including venetoclax-based drug combinations and pose a major therapeutic challenge. Analyses of RNA sequencing and reverse phase protein array datasets revealed significantly lower BAX RNA and protein levels in TP53-mutant compared to TP53-wild-type (WT) AML, a finding confirmed in isogenic CRISPR-generated TP53-knockout and -mutant AML. The response to either BCL-2 (venetoclax) or MCL-1 (AMG176) inhibition was BAX-dependent and much reduced in TP53-mutant compared to TP53-WT cells, while the combination of two BH3 mimetics effectively activated BAX, circumventing survival mechanisms in cells treated with either BH3 mimetic, and synergistically induced cell death in TP53-mutant AML and stem/progenitor cells. The BH3 mimetic-driven stress response and cell death patterns after dual inhibition were largely independent of TP53 status and affected by apoptosis induction. Co-targeting, but not individual targeting of BCL-2 and MCL-1 in mice xenografted with TP53-WT and TP53-R248W Molm13 cells suppressed both TP53-WT and TP53-mutant cell growth and significantly prolonged survival. Our results demonstrate that co-targeting BCL-2 and MCL-1 overcomes BAX deficiency-mediated resistance to individual BH3 mimetics in TP53-mutant cells, thus shifting cell fate from survival to death in TP53-deficient and -mutant AML. This concept warrants clinical evaluation.

Concomitant targeting of FLT3 and BTK overcomes FLT3 inhibitor resistance in acute myeloid leukemia through inhibition of autophagy

Strategies to overcome resistance to FMS-like tyrosine kinase 3 (FLT3)-targeted therapy in acute myeloid leukemia (AML) are urgently needed. We identify autophagy as one of the resistance mechanisms, induced by hypoxia and the bone marrow (BM) microenvironment via Bruton's tyrosine kinase (BTK) activation. Suppressing autophagy/BTK sensitized FLT3-mutated AML to FLT3 inhibitor-induced apoptosis. Further, co-targeting FLT3/BTK/Aurora kinases (AURKs) with a novel multi-kinase inhibitor CG-806 (luxeptinib) induced profound apoptosis induction in FLT3-mutated AML by co-suppressing FLT3/BTK, antagonizing autophagy, and causing leukemia cell death in FLT3 wild-type AML by AURK-mediated G2/M arrest and polyploidy, in addition to FLT3 inhibition. Thus, CG-806 exerted profound anti-leukemia activity against AMLs regardless of FLT3 mutation status. CG-806 further significantly reduced AML burden and extended survival in an in vivo PDX leukemia murine model of FLT3 inhibitorresistant FLT3-ITD/TKD double mutant primary AML. Taken together, CG-806 exerts a unique mechanistic action and pre-clinical activity, suggesting further development in FLT3 wild-type and mutant AML.

Abstract 5337: Tolinapant (ASTX660) enhances the anti-leukemic activity of Venetoclax and Dexamethasone in T cell acute lymphoblastic leukemia (T-ALL)

Background: Inhibitors of apoptosis proteins (IAPs) are overexpressed in ALL leading to resistance to apoptosis and chemo-resistance. Tolinapant, a non-peptidomimetic antagonist of the cellular and X-linked inhibitors of apoptosis (cIAP1/2 and XIAP) being evaluated in Phase 1/2 clinical trial [NCT02503423] showed single-agent activity in T-cell lymphoma. Objectives: Herein, we analyzed the preclinical activity of tolinapant in combination with ABT199 and Dexamethasone (DEX) in T-ALL (in vitro and ex-vivo patient derived xenografts (PDX).

Results: Using a panel of 8 T-ALL cell lines we analyzed the single agent activity of tolinapant. Loucy and SUP-T11 were most sensitive (IC50 = 190-309 nM). CCRF-CEM and ALL-SIL showed moderate sensitivity (IC50 = 10-18 µM) while Jurkat, MOLT16, MOLT4 and PF382 were resistant. Western blotting (WB) showed decreased levels of cIAP1and cIAP2 with no change in XIAP in response to tolinapant as a single agent. We next investigated the efficacy of tolinapant with Bcl2 inhibitor ABT199. The combination of ABT199 and ASTX660 was synergistic in Loucy cell line with combination index (CI) of 0.14. Cell death was increased to 64±3% in combination v/s 27±0.9% in ABT199. WB showed decreased cIAP2 and increased levels of cleaved caspase 7 and cleaved caspase 9 in combination compared to single agents, suggesting increased apoptosis. Treatment of PDX-derived cells with tolinapant and ABT199 was more effective than monotherapy in inducing apoptosis in CD45+ bulk (46±0.7% to 63±6%, p<0.0001) and leukemia initiating cells (LICs, CD45+ CD7+ CD19- CD34+) (39±3% to 54±8%, p=0.003). Next, we checked the effect of combination of DEX with tolinapant in T-ALL cell lines. CCRF-CEM cell line is from a relapsed patient and is resistant to DEX. The combination was synergistic with CI of 0.26 and cell death of 50±4% compared to 20±3% by DEX. A triple combination of DEX, ABT199 and tolinapant increased apoptotic response to 82.9±1%, compared to DEX+ABT199 dual combination where apoptosis was induced to 52.4±2%. Strong synergy in terms of both cytoreduction as well as apoptosis induction was observed in SUP-T11 cells. Tolinapant sensitized SUP-T11 cells to DEX with ED50 value of 542 nM in combination compared to ~2 µM with DEX treatment. Simultaneous analysis of cell proliferation, stress response and DNA damage using single-cell proteomics analysis showed downregulation of proliferation (Ki-67), stress response (ATF4, LC3B) and increased levels of cleaved PARP, cleaved caspase 3 suggesting increased apoptosis in combination of tolinapant with DEX. Treatment of PDX-derived cells with tolinapant enhanced the cytotoxic effect of DEX in CD45+ bulk (58±2% to 71±0.1%, p<0.0001) and LICs (62±2% to 78±0.9%, p<0.0001).

Conclusion: Tolinapant synergizes with the anti-leukemic activity of ABT199 and DEX, establishing a therapeutic rationale for IAP antagonist in T-ALL.

Citation Format: Priyanka Sharma, Sujan Piya, Huaxian Ma, Natalia Baran, Muharrem Muftuoglu, Mahesh Basyal, Vivian Ruvolo, George Ward, Tomoko Smyth, Martin J. Sims, Michael Andreeff, Gautam Borthakur. Tolinapant (ASTX660) enhances the anti-leukemic activity of Venetoclax and Dexamethasone in T cell acute lymphoblastic leukemia (T-ALL) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5337.

Inhibition of mitochondrial complex I reverses NOTCH1-driven metabolic reprogramming in T-cell acute lymphoblastic leukemia

T-cell acute lymphoblastic leukemia (T-ALL) is commonly driven by activating mutations in NOTCH1 that facilitate glutamine oxidation. Here we identify oxidative phosphorylation (OxPhos) as a critical pathway for leukemia cell survival and demonstrate a direct relationship between NOTCH1, elevated OxPhos gene expression, and acquired chemoresistance in pre-leukemic and leukemic models. Disrupting OxPhos with IACS-010759, an inhibitor of mitochondrial complex I, causes potent growth inhibition through induction of metabolic shut-down and redox imbalance in NOTCH1-mutated and less so in NOTCH1-wt T-ALL cells. Mechanistically, inhibition of OxPhos induces a metabolic reprogramming into glutaminolysis. We show that pharmacological blockade of OxPhos combined with inducible knock-down of glutaminase, the key glutamine enzyme, confers synthetic lethality in mice harboring NOTCH1-mutated T-ALL. We leverage on this synthetic lethal interaction to demonstrate that IACS-010759 in combination with chemotherapy containing L-asparaginase, an enzyme that uncovers the glutamine dependency of leukemic cells, causes reduced glutaminolysis and profound tumor reduction in pre-clinical models of human T-ALL. In summary, this metabolic dependency of T-ALL on OxPhos provides a rational therapeutic target.

Maximal activation of apoptosis signaling by co-targeting anti-apoptotic proteins in BH3 mimetic-resistant AML and AML stem cells

MCL-1 is known to play a major role in resistance to BCL-2 inhibition, but the contribution of other BCL-2 family proteins has not been fully explored. We here demonstrate ineffectiveness of MCL-1 inhibitor AMG176 in venetoclax-resistant, and conversely, of venetoclax in AMG176-resistant AML. Like cells with acquired resistance to venetoclax, cells with acquired resistance to AMG176 express increased MCL-1. Both cells with acquired resistance to venetoclax and to AMG176 express increased levels of BCL-2 and BCL-2A1, decreased BAX, and/or altered levels of other BCL-2 proteins. Co-targeting BCL-2 and MCL-1 was highly synergistic in AML cell lines with intrinsic or acquired resistance to BH3 mimetics or engineered to genetically-overexpress BCL-2 or BCL-2A1 or downregulate BAX. The combination effectively eliminated primary AML blasts and stem/progenitor cells resistant to or relapsed after venetoclax-based therapy irrespective of mutations and cytogenetic abnormalities. Venetoclax and AMG176 combination markedly suppressed anti-apoptotic BCL-2 proteins and AML stem/progenitor cells and dramatically extended mouse survival (median 336 vs control 126 d, P<0.0001) in a PDX model developed from a venetoclax/hypomethylating agent therapy-resistant AML patient. However, decreased BAX levels in the bone marrow residual leukemia cells after 4-wk combination treatment may represent a resistance mechanism that contributed to their survival. Enhanced anti-leukemia activity was also observed in a PDX model of monocytic AML, known to be resistant to venetoclax therapy. Our results support co-dependence on multiple anti-apoptotic BCL-2 proteins and suppression of BAX as mechanisms of AML resistance to individual BH3 mimetics. Co-targeting of MCL-1 and BCL-2 eliminates otherwise apoptosis-resistant cells.

Targeting the NOTCH1-MYC-CD44 axis in leukemia-initiating cells in T-ALL

The NOTCH1-MYC-CD44 axis integrates cell-intrinsic and extrinsic signaling to ensure the persistence of leukemia-initiating cells (LICs) in T-cell acute lymphoblastic leukemia (T-ALL) but a common pathway to target this circuit is poorly defined. Bromodomain-containing protein 4 (BRD4) is implicated to have a role in the transcriptional regulation of oncogenes MYC and targets downstream of NOTCH1, and here we demonstrate its role in transcriptional regulation of CD44. Hence, targeting BRD4 will dismantle the NOTCH1-MYC-CD44 axis. As a proof of concept, degrading BRD4 with proteolysis targeting chimera (PROTAC) ARV-825, prolonged the survival of mice in Notch1 mutated patient-derived xenograft (PDX) and genetic models (ΔPTEN) of T-ALL. Single-cell proteomics analysis from the PDX model, demonstrated quantitative reduction of LICs (CD34+ CD7+ CD19−) and downregulation of the NOTCH1-MYC-CD44 axis, along with cell cycle, apoptosis and PI3K/Akt pathways. Moreover, secondary transplantation from PDX and ΔPTEN models of T-ALL, confirmed delayed leukemia development and extended survival of mice engrafted with T-ALL from ARV-825 treated mice, providing functional confirmation of depletion of LICs. Hence, BRD4 degradation is a promising LIC-targeting therapy for T-ALL.

Inhibition of BCL2A1 by STAT5 inactivation overcomes resistance to targeted therapies of FLT3-ITD/D835 mutant AML

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BCL2A1 is upregulated and exerts a pro-survival function in FLT3-ITD/D835 AML cells.

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Upregulation of BCL2A1 attenuates sensitivity to quizartinib in FLT3-ITD/D835 cells.

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Gilteritinib decreases BCL2A1 through inactivation of STAT5 in FLT3-ITD/D835 cells.

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Gilteritinib/Venetoclax has a synergistic anti-tumor activity in FLT3-ITD/D835 cells.

Tyrosine kinase inhibitors (TKIs) are established drugs in the therapy of FLT3-ITD mutated acute myeloid leukemia (AML). However, acquired mutations, such as D835 in the tyrosine kinase domain (FLT3-ITD/D835), can induce resistance to TKIs. A cap analysis gene expression (CAGE) technology revealed that the gene expression of BCL2A1 transcription start sites was increased in primary AML cells bearing FLT3-ITD/D835 compared to FLT3-ITD. Overexpression of BCL2A1 attenuated the sensitivity to quizartinib, a type II TKI, and venetoclax, a selective BCL2 inhibitor, in AML cell lines. However, a type I TKI, gilteritinib, inhibited the expression of BCL2A1 through inactivation of STAT5 and alleviated TKI resistance of FLT3-ITD/D835. The combination of gilteritinib and venetoclax showed synergistic effects in the FLT3-ITD/D835 positive AML cells. The promoter region of BCL2A1 contains a BRD4 binding site. Thus, the blockade of BRD4 with a BET inhibitor (CPI-0610) downregulated BCL2A1 in FLT3-mutated AML cells and extended profound suppression of FLT3-ITD/D835 mutant cells. Therefore, we propose that BCL2A1 has the potential to be a novel therapeutic target in treating FLT3-ITD/D835 mutated AML.

Quizartinib with decitabine and venetoclax (triplet) is highly active in patients with FLT3-ITD mutated acute myeloid leukemia (AML)

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Background: The outcomes in patients (pts) with newly diagnosed FLT3 mutated AML who are ineligible for intensive induction chemotherapy are poor. Added to a low intensity chemotherapy backbone, FLT3 inhibitors, such as midostaurin, sorafenib, and quizartinib, result in median OS of 8-17 months in the frontline (Gallogly ASH 2017, Ohanian AJH 2018, Swaminathan ASH 2017), and 4-8 months in relapsed/refractory (R/R) settings (Yilmaz JHO 2020, Ravandi Blood 2013). Quizartinib, a potent second generation FLT3 inhibitor demonstrated synergy with venetoclax (VEN) (a BCL-2 inhibitor) in AML cell lines and PDX models (Mali Haematologica 2020). We designed this study to evaluate the safety and efficacy of quizartinib, venetoclax, and decitabine combination in pts with R/R or newly diagnosed FLT3 mutated AML. Methods: Frontline cohort included pts who are ineligible for intensive induction chemotherapy, and R/R cohort included pts who received 5 or less prior treatments. All patients had a performance status of ECOG ≤2, adequate organ functions, and QTcF <450 msec prior to therapy. All pts underwent day 14 bone marrow, and venetoclax (400 mg/day) was put on hold in patients with bone marrow blasts ≤ 5% (or marrow aplasia). Those with day14 bone marrow blast >5% continued venetoclax for 21 days during cycle 1. All pts induced with 10 days of decitabine (20 mg/m2). In subsequent cycles, decitabine administered for 5 days. Quizartinib (30 or 40 mg/day) was administered daily continuously. Results: 21 pts were enrolled and 17 pts evaluable at the time of this report (4 are still within cycle 1). Of 13 pts with R/R AML (median 3 [range 1-5] prior therapies, 85% with ≥1 prior FLT3 inhibitor), 9 (69%) achieved CRc (2 CR, 7 CRi) with 4/9 and 5/9 responders FLT3-PCR and multicolor flow cytometry (MFC) negative, respectively. Thirty and 60-day mortality rates were 0% and 8%. Of 4 patients with newly diagnosed AML (median age 72), all achieved CRc (2 CR, 2 CRi) with 4/4 and 2/3 responders FLT3-PCR and MFC negative, respectively. 60-day mortality was 0% in the frontline cohort. No pts developed a dose limiting toxicity (DLT) with 30 mg/day quizartinib, however with the 40mg/day quizartinib 2 pts developed hematologic DLT (grade ≥3 neutropenia with a <5% cellular bone marrow lasting ≥42 days). Hence, quizartinib 30 mg/day dose was determined as recommended phase 2 dose for the triplet. Grade 3/5 non-hematologic toxicities in >2 pts included lung infections (N=9) and neutropenic fever (N=6). No QTcF prolongations >450 msec were noted. With a median follow-up of 7.2 months, the median OS was not reached in frontline cohort and was 7.1 months in R/R cohort. 2/4 and 5/9 responders underwent ASCT in frontline and R/R cohorts, respectively. All frontline pts were alive at the last follow-up; 3 were in CR and 1 relapsed disease. Of 9 responders in R/R cohort, 4 were alive (3 CR, 1 relapse) and 5 died (4 relapse, 1 CR). Conclusions: Decitabine + venetoclax + quizartinib is highly active in R/R FLT3-ITD mutated AML pts, with CRc rates of 69% and the median OS of 7.1 months. Accrual to the triplet continues and updated clinical and correlative data will be presented. Clinical trial information: NCT03661307.

Targeting MCL-1 dysregulates cell metabolism and leukemia-stroma interactions and resensitizes acute myeloid leukemia to BCL-2 inhibition

MCL-1 and BCL-2 are both frequently overexpressed in acute myeloid leukemia (AML) and critical for the survival of AML cells and AML stem cells. MCL-1 is a key factor in venetoclax resistance. Using genetic and pharmacological approaches, we discovered that MCL-1 regulates leukemia cell bioenergetics and carbohydrate metabolisms, including the TCA cycle, glycolysis and pentose phosphate pathway and modulates cell adhesion proteins and leukemia-stromal interactions. Inhibition of MCL-1 sensitizes to BCL-2 inhibition in AML cells and AML stem/progenitor cells, including those with intrinsic and acquired resistance to venetoclax through cooperative release of pro-apoptotic BIM, BAX, and BAK from binding to anti-apoptotic BCL- 2 proteins and inhibition of cell metabolism and key stromal microenvironmental mechanisms. The combined inhibition of MCL-1 by MCL-1 inhibitor AZD5991 or CDK9 inhibitor AZD4573 and BCL-2 by venetoclax greatly extended survival of mice bearing patient-derived xenografts established from an AML patient who acquired resistance to venetoclax/decitabine. These results demonstrate that co-targeting MCL-1 and BCL-2 improves the efficacy of and overcomes pre-existing and acquired resistance to BCL-2 inhibition. Activation of metabolomic pathways and leukemia-stroma interactions are newly discovered functions of MCL-1 in AML, which are independent from canonical regulation of apoptosis by MCL-1. Our data provide new mechanisms of synergy and a rationale for co-targeting MCL-1 and BCL-2 clinically in patients with AML and potentially other cancers.

Bone marrow stromal cells induce an ALDH+ stem cell-like phenotype and enhance therapy resistance in AML through a TGF-β-p38-ALDH2 pathway

The bone marrow microenvironment (BME) in acute myeloid leukemia (AML) consists of various cell types that support the growth of AML cells and protect them from chemotherapy. Mesenchymal stromal cells (MSCs) in the BME have been shown to contribute immensely to leukemogenesis and chemotherapy resistance in AML cells. However, the mechanism of stroma-induced chemotherapy resistance is not known. Here, we hypothesized that stromal cells promote a stem-like phenotype in AML cells, thereby inducing tumorigenecity and therapy resistance. To test our hypothesis, we co-cultured AML cell lines and patient samples with BM-derived MSCs and determined aldehyde dehydrogenase (ALDH) activity and performed gene expression profiling by RNA sequencing. We found that the percentage of ALDH+ cells increased dramatically when AML cells were co-cultured with MSCs. However, among the 19 ALDH isoforms, ALDH2 and ALDH1L2 were the only two that were significantly upregulated in AML cells co-cultured with stromal cells compared to cells cultured alone. Mechanistic studies revealed that the transforming growth factor-β1 (TGF-β1)-regulated gene signature is activated in AML cells co-cultured with MSCs. Knockdown of TGF-β1 in BM-MSCs inhibited stroma-induced ALDH activity and ALDH2 expression in AML cells, whereas treatment with recombinant TGF-β1 induced the ALDH+ phenotype in AML cells. We also found that TGF-β1-induced ALDH2 expression in AML cells is mediated by the non-canonical pathway through the activation of p38. Interestingly, inhibition of ALDH2 with diadzin and CVT-10216 significantly inhibited MSC-induced ALDH activity in AML cells and sensitized them to chemotherapy, even in the presence of MSCs. Collectively, BM stroma induces ALDH2 activity in AML cells through the non-canonical TGF-β pathway. Inhibition of ALDH2 sensitizes AML cells to chemotherapy.

Combinatorial Inhibition of Focal Adhesion Kinase and BCL-2 Enhances Antileukemia Activity of Venetoclax in Acute Myeloid Leukemia

Focal adhesion kinase (FAK) promotes cancer cell growth and metastasis. We previously reported that FAK inhibition by the selective inhibitor VS-4718 exerted antileukemia activities in acute myeloid leukemia (AML). The mechanisms involved, and whether VS-4718 potentiates efficacy of other therapeutic agents, have not been investigated. Resistance to apoptosis inducted by the BCL-2 inhibitor ABT-199 (venetoclax) in AML is mediated by preexisting and ABT-199-induced overexpression of MCL-1 and BCL-XL. We observed that VS-4718 or silencing FAK with siRNA decreased MCL-1 and BCL-XL levels. Importantly, VS-4718 antagonized ABT-199-induced MCL-1 and BCL-XL. VS-4718 markedly synergized with ABT-199 to induce apoptosis in AML cells, including primary AML CD34+ cells and AML cells overexpressing MCL-1 or BCL-XL. In a patient-derived xenograft (PDX) model derived from a patient sample with NPM1/FLT3-ITD/TET2/DNMT3A/WT1 mutations and complex karyotype, VS-4718 statistically significantly reduced leukemia tissue infiltration and extended survival (72 vs. control 36 days, P = 0.0002), and only its combination with ABT-199 effectively decreased systemic leukemia tissue infiltration and circulating blasts, and prolonged survival (65.5 vs. control 36 days, P = 0.0119). Furthermore, the combination decreased NFκB signaling and induced the expression of IFN genes in vivo The combination also markedly extended survival of a second PDX model developed from an aggressive, TP53-mutated complex karyotype AML sample. The data suggest that the combined inhibition of FAK and BCL-2 enhances antileukemia activity in AML at least in part by suppressing MCL-1 and BCL-XL and that this combination may be effective in AML with TP53 and other mutations, and thus benefit patients with high-risk AML.

Abstract 342: S63845, a novel BH3 mimetic Mcl-1 inhibitor synergizes with midostaurin to induce potent apoptosis in acute myeloid leukemia cells carrying FLT3-ITD mutations

Myeloid cell leukemia 1 (Mcl-1) is one of the key anti-apoptotic Bcl-2 family proteins that binds and neutralizes pro-apoptotic BIM, BAX and BAK at the mitochondrial outer membrane, preventing cytochrome c release and caspase activation. Selective upregulation of Mcl-1 functionally contributes to resistance of acute myeloid leukemias (AML) with FMS-like tyrosine kinase-3-internal tandem duplications (FLT3-ITD) to chemotherapy (Kasper S. et al. 2012, Blood Cancer J. 2:e60, doi:10.1038/bcj.2012.5). Here we show that a novel Mcl-1 inhibitor S63845 (Kotschy A. et al. 2016, Nature 538, 477-482), has synergistic proapoptotic activity in combination with FLT3-ITD kinase inhibitor midostaurin in pre-clinical models of AML. Our studies demonstrate that S63845 has potent single agent activity in AML cell lines and primary AML samples harboring FLT3-ITD with IC50 values in low nanomolar range. Co-targeting of Mcl-1 and FLT3-ITD with S63845 and midostaurin, respectively, significantly increased apoptosis in FLT3-ITD cells with caspase-3 activation and PARP cleavage occurring rapidly within 6 hours of treatment. Consistent with markedly reduced cell growth and viability, analysis of drug combinations efficacy using Bliss independence model revealed strong synergistic interactions between S63845 and midostaurin in FLT3-ITD cell lines and primary AML samples. Midostaurin caused de-phosphorylation of FLT3-ITD and its downstream targets such as STAT5, AKT and MAPK. This was accompanied by significant downregulation of MAPK-mediated phosphorylation of Mcl-1 at Thr163 required for Mcl-1 stability. Consequently, midostaurin reduced Mcl-1 protein levels, with no major changes in antiapoptotic Bcl-2 or Bcl-XL. Importantly, midostaurin increased expression of pro-apoptotic Bim, which could in turn bind and negate residual Mcl-1 pro-survival activity. Elevated Bim was sustained upon S63845 co-treatment, suggesting that Bim plays functional role in midostaurin/S63845-mediated lethality. Dynamic BH3 profiling showed that midostaurin primed FLT3-ITD cells to Mcl-1 and Bcl-2 inhibitors and facilitated general apoptosis priming in response to Bim peptide. Importantly, given that Mcl-1 is a major contributing factor to resistance of AML to Bcl-2 selective BH3-mimetic venetoclax, S63845/midostaurin treatment induced cell death in venetoclax-resistant FLT3-ITD mutants. In summary, S63845/midostaurin is highly synergistic in FLT3-ITD mutated AML cells including those resistant to venetoclax. In vivo experiments of tolerability and efficacy are ongoing and will be reported.

Citation Format: Anna Skwarska, Qi Zhang, Shelley M. Herbrich, Natalia Baran, Ensar Halilovic, Peter Ruvolo, Vivian Ruvolo, Erick Morris, Andrew Wei, Donia Moujalled, Michael Andreff, Marina Konopleva. S63845, a novel BH3 mimetic Mcl-1 inhibitor synergizes with midostaurin to induce potent apoptosis in acute myeloid leukemia cells carrying FLT3-ITD mutations [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 342.

Imipridone ONC212 activates orphan G protein-coupled receptor GPR132 and integrated stress response in acute myeloid leukemia

Imipridones constitute a novel class of antitumor agents. Here, we report that a second-generation imipridone, ONC212, possesses highly increased antitumor activity compared to the first-generation compound ONC201. In vitro studies using human acute myeloid leukemia (AML) cell lines, primary AML, and normal bone marrow (BM) samples demonstrate that ONC212 exerts prominent apoptogenic effects in AML, but not in normal BM cells, suggesting potential clinical utility. Imipridones putatively engage G protein-coupled receptors (GPCRs) and/or trigger an integrated stress response in hematopoietic tumor cells. Comprehensive GPCR screening identified ONC212 as activator of an orphan GPCR GPR132 and Gαq signaling, which functions as a tumor suppressor. Heterozygous knock-out of GPR132 decreased the antileukemic effects of ONC212. ONC212 induced apoptogenic effects through the induction of an integrated stress response, and reduced MCL-1 expression, a known resistance factor for BCL-2 inhibition by ABT-199. Oral administration of ONC212 inhibited AML growth in vivo and improved overall survival in xenografted mice. Moreover, ONC212 abrogated the engraftment capacity of patient-derived AML cells in an NSG PDX model, suggesting potential eradication of AML initiating cells, and was highly synergistic in combination with ABT-199. Collectively, our results suggest ONC212 as a novel therapeutic agent for AML.

BETP degradation simultaneously targets acute myelogenous leukemia stem cells and the microenvironment

Anti-leukemic effect of BET/BRD4 (BETP) protein inhibition has been largely attributed to transcriptional downregulation of cellular anabolic/anti-apoptotic processes but its effect on bone marrow microenvironment, a sanctuary favoring persistence of leukemia stem/progenitor cells, is unexplored. Sustained degradation of BETP with small-molecule BET proteolysis-targeting chimera (PROTAC), ARV-825, resulted in marked downregulation of surface CXCR4 and CD44, key proteins in leukemia-microenvironment interaction, in AML cells. Abrogation of surface CXCR4 expression impaired SDF-1α directed migration and was mediated through transcriptional down-regulation of PIM1 kinase that in turn phosphorylates CXCR4 and facilitates its surface localization. Down-regulation of CD44/CD44v8-10 impaired cystine uptake, lowered intracellular reduced glutathione and increased oxidative stress. More importantly, BETP degradation markedly decreased CD34+CD38-CD90-CD45RA+ leukemic stem cell population and alone or in combination with Cytarabine, prolonged survival in mouse model of human leukemia including AML-PDX. Gene expression profiling and single cell proteomics confirmed down regulation of the gene signatures associated with 'stemness' in AML and Wnt/β-catenin, Myc pathways. Hence, BETP degradation by ARV-825 simultaneously targets cell intrinsic signaling, stromal interactions and metabolism in AML.

An ARC-Regulated IL1β/Cox-2/PGE2/β-Catenin/ARC Circuit Controls Leukemia-Microenvironment Interactions and Confers Drug Resistance in AML

The apoptosis repressor with caspase recruitment domain (ARC) protein is a strong independent adverse prognostic marker in acute myeloid leukemia (AML). We previously reported that ARC regulates leukemia-microenvironment interactions through the NFκB/IL1β signaling network. Malignant cells have been reported to release IL1β, which induces PGE2 synthesis in mesenchymal stromal cells (MSC), in turn activating β-catenin signaling and inducing the cancer stem cell phenotype. Although Cox-2 and its enzymatic product PGE2 play major roles in inflammation and cancer, the regulation and role of PGE2 in AML are largely unknown. Here, we report that AML-MSC cocultures greatly increase Cox-2 expression in MSC and PGE2 production in an ARC/IL1β-dependent manner. PGE2 induced the expression of β-catenin, which regulated ARC and augmented chemoresistance in AML cells; inhibition of β-catenin decreased ARC and sensitized AML cells to chemotherapy. NOD/SCIDIL2RγNull-3/GM/SF mice transplanted with ARC-knockdown AML cells had significantly lower leukemia burden, lower serum levels of IL1β/PGE2, and lower tissue human ARC and β-catenin levels, prolonged survival, and increased sensitivity to chemotherapy than controls. Collectively, we present a new mechanism of action of antiapoptotic ARC by which ARC regulates PGE2 production in the tumor microenvironment and microenvironment-mediated chemoresistance in AML.Significance: The antiapoptotic protein ARC promotes AML aggressiveness by enabling detrimental cross-talk with bone marrow mesenchymal stromal cells.

Inhibition of FAO in AML co-cultured with BM adipocytes: mechanisms of survival and chemosensitization to cytarabine

Adipocytes are the prevalent stromal cell type in adult bone marrow (BM), and leukemia cells continuously adapt to deficiency of nutrients acquiring chemoresistant profiles in the BM microenvironment. We have previously shown that fatty acid metabolism is a key energy pathway for survival of acute myeloid leukemia (AML) cells in the adipocyte-abundant BM microenvironment. The novel fatty acid β-oxidation (FAO) inhibitor avocatin B, an odd-numbered carbon lipid derived from the avocado fruit, induced apoptosis and growth inhibition in mono-cultured AML cells. In AML cells co-cultured with BM adipocytes, FAO inhibition with avocatin B caused adaptive stimulation of free fatty acid (FFA) uptake through upregulation of FABP4 mRNA, enhanced glucose uptake and switch to glycolysis. These changes reflect the compensatory response to a shortage of FFA supply to the mitochondria, and facilitate the protection of AML cells from avocatin B-induced apoptosis in the presence of BM adipocytes. However, the combination treatment of avocatin B and conventional anti-AML therapeutic agent cytarabine (AraC) increased reactive oxygen species and demonstrated highly synergistic effects on AML cells under BM adipocyte co-culture condition. These findings highlight the potential for combination regimens of AraC and FAO inhibitors that target bone marrow-resident chemoresistant AML cells.

Combinatorial targeting of XPO1 and FLT3 exerts synergistic anti-leukemia effects through induction of differentiation and apoptosis in FLT3-mutated acute myeloid leukemias: from concept to clinical trial

Targeted therapies against FLT3-mutated acute myeloid leukemias have shown limited clinical efficacy primarily because of the acquisition of secondary mutations in FLT3 and persistent activation of downstream pro-survival pathways such as MEK/ERK, PI3K/AKT, and STAT5. Activation of these additional kinases may also result in phosphorylation of tumor suppressor proteins promoting their nuclear export. Thus, co-targeting nuclear export proteins (e.g., XPO1) and FLT3 concomitantly may be therapeutically effective. Here we report on the combinatorial inhibition of XPO1 using selinexor and FLT3 using sorafenib. Selinexor exerted marked cell killing of human and murine FLT3-mutant acute myeloid leukemia cells, including those harboring internal tandem duplication and/or tyrosine kinase domain point mutations. Interestingly, selinexor treatment of murine FLT3-mutant acute myeloid leukemia cells activated FLT3 and its downstream MAPK or AKT signaling pathways. When combined with sorafenib, selinexor triggered marked synergistic pro-apoptotic effects. This was preceded by elevated nuclear levels of ERK, AKT, NFκB, and FOXO3a. Five days of in vitro combination treatment using low doses (i.e., 5 to 10 nM) of each agent promoted early myeloid differentiation of MOLM13 and MOLM14 cells without noticeable cell killing. The combinatorial therapy demonstrated profound in vivo anti-leukemia efficacy in a human FLT3-mutated xenograft model. In an ongoing phase IB clinical trial the selinexor/sorafenib combination induced complete/partial remissions in six of 14 patients with refractory acute myeloid leukemia, who had received a median of three prior therapies (ClinicalTrials.gov: NCT02530476). These results provide pre-clinical and clinical evidence for an effective combinatorial treatment strategy targeting XPO1 and FLT3 in FLT3- mutated acute myeloid leukemias.

Abstract 4957: The novel imipridone ONC212 highly synergizes with the BCL-2 inhibitor ABT-199 in AML and activates orphan receptor GPR132

Imipridones are first-in-class anti-tumor compounds including ONC201, which has shown promising clinical activity. ONC212 was designed as a second-generation imipridone. We first confirmed the ONC212 effects in a collection of 1,088 human cancer cell lines available from the Genomic of Drug Sensitivity in Cancer Project; leukemia was identified as the most sensitive tumor type. In fact, ONC212 exerted prominent apoptogenic effects in acute myeloid leukemia (AML) cell lines and primary AML, but not normal bone marrow (BM) cells. We investigated the effects of ONC212 in vivo in an aggressive systemic AML xenograft model using OCI-AML3 cells. ONC212 markedly inhibited AML expansion and prolonged median survival (controls: 43 d, ONC212: 49 d; p = 0.0003). For in vivo functional assessment of ONC212's anti-tumor effects against leukemia stem and progenitor cells (LSPCs), we treated patient-derived xenograft (PDX) cells with ONC212 (250 nM, 36 hr) ex vivo, and then injected into recipient NSG mice. After one month, the human leukemic CD45+ cells in the peripheral blood, spleen, and BM were significantly decreased in the ONC212 treated group. The median survival was remarkably prolonged (controls: 36 d, ONC212: 82 d; p &lt; 0.0001). These results indicate that ONC212 has anti-LSPC effects to reduce the engraftment potential. We previously demonstrated that the prototype it compound ONC201 induces apoptosis via an atypical integrated stress response (ISR; Ishizawa et al., Sci Signal, 2016). As expected, ONC212 induced the transcription factor ATF4, a key effector of ISR. Because BCL-2 is generally considered to be protective against ISR-mediated apoptosis, we hypothesized that the BCL-2 inhibitor ABT-199 could further sensitize AML cells to ONC212. Indeed, the in vitro combination of ONC212 plus ABT-199 synergistically induced apoptosis in AML cells. Furthermore, the combination showed highly significant synergistic anti-leukemia effects in vivo. The combinatorial treatment prolonged overall median survival (controls: 20 d, each agent: 21 d, the combination 30 d; p &lt; 0.0001). Since the G-protein-coupled receptor (GPCR) dopamine receptor D2 is the putative target of ONC201, we hypothesized that ONC212 also targets GPCRs. The PathHunter β-arrestin screening discovered that ONC212 specifically activated the orphan GPCR GPR132. Consistently, the GPR132 mRNA expression was correlated with ONC212 sensitivity. On the other hand, GPR132 overexpression induced cell death in AML cells, which is consistent with previous reports implicating GPR132 as a tumor suppressor. Furthermore, ONC212 increased GPR132 mRNA expression. These results suggest that GPR132 could be a potential therapeutic target in AML. Taken together, ONC212 has potential as a novel agent for AML therapy. This study provides the first reported opportunity to therapeutically target GPR132 in oncology.

Citation Format: Takenobu Nii, Jo Ishizawa, Varun V. Prabhu, Vivian Ruvolo, Neel Madhukar, Ran Zhao, Hong Mu, Lauren Heese, Kensuke Kojima, Mathew Garnett, Ultan McDermott, Cyril Benes, Neil Charter, Sean Deacon, Olivier Elemento, Joshua Allen, Wolfgang Oster, Martin Stogniew, Michael Andreeff. The novel imipridone ONC212 highly synergizes with the BCL-2 inhibitor ABT-199 in AML and activates orphan receptor GPR132 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4957.

Oxidized analogs of Di(1H-indol-3-yl)methyl-4-substituted benzenes are NR4A1-dependent UPR inducers with potent and safe anti-cancer activity

Di(1H-indol-3-yl)(4-trifluoromethylphenyl)methane (DIM-Ph-4-CF3) is an analog of orphan nuclear receptor 4A1 (NR4A1) ligand cytosporone B. We have synthesized several oxidation products of DIM-Ph-4-CF3, focusing on analogs with electron-withdrawing or donating groups at their phenyl ring 4-positions, and examined their anti-cancer activity and mechanism-of-action. Mesylates (DIM-Ph-4-X+ OMs-s) having CF3, CO2Me and Cl groups were more effective inhibitors of cancer cell viability than their precursors. 19F NMR spectroscopy and differential scanning calorimetry strongly indicated interactions of DIM-Ph-4-CF3+ OMs- with the NR4A1 ligand binding domain, and compound-induced apoptosis of prostate cancer cells was dependent on NR4A1. DIM-Ph-4-CF3+ OMs- showed robust inhibition of LNCaP prostate cancer xenografts with no apparent toxicity. In vitro and in vivo, DIM-Ph-4-CF3+ OMs- activated proapoptotic unfolded protein response (UPR) signaling in prostate cancer cells. Independently of DIM-Ph-4-CF3+ OMs-, the bulk of NR4A1 localized to the cytoplasm in various cancer cell lines, suggesting a cytoplasmic mechanism-of-action of DIM-Ph-4-CF3+ OMs- in UPR induction and cell death. In summary, the data suggest that oxidized analogs of DIM-Ph-4-CF3 possess potent and safe anti-cancer activity which is mediated through UPR signaling downstream of NR4A1 binding.

Anti-apoptotic ARC protein confers chemoresistance by controlling leukemia-microenvironment interactions through a NFκB/IL1β signaling network

To better understand how the apoptosis repressor with caspase recruitment domain (ARC) protein confers drug resistance in acute myeloid leukemia (AML), we investigated the role of ARC in regulating leukemia-mesenchymal stromal cell (MSC) interactions. In addition to the previously reported effect on AML apoptosis, we have demonstrated that ARC enhances migration and adhesion of leukemia cells to MSCs both in vitro and in a novel human extramedullary bone/bone marrow mouse model. Mechanistic studies revealed that ARC induces IL1β expression in AML cells and increases CCL2, CCL4, and CXCL12 expression in MSCs, both through ARC-mediated activation of NFκB. Expression of these chemokines in MSCs increased by AML cells in an ARC/IL1β-dependent manner; likewise, IL1β expression was elevated when leukemia cells were co-cultured with MSCs. Further, cells from AML patients expressed the receptors for and migrated toward CCL2, CCL4, and CXCL12. Inhibition of IL1β suppressed AML cell migration and sensitized the cells co-cultured with MSCs to chemotherapy. Our results suggest the existence of a complex ARC-regulated circuit that maintains intimate connection of AML with the tumor microenvironment through NFκB/IL1β-regulated chemokine receptor/ligand axes and reciprocal crosstalk resulting in cytoprotection. The data implicate ARC as a promising drug target to potentially sensitize AML cells to chemotherapy.

Synthetic Lethality of Combined Bcl-2 Inhibition and p53 Activation in AML: Mechanisms and Superior Antileukemic Efficacy

Evasion of apoptosis is a hallmark of cancer. Bcl-2 and p53 represent two important nodes in apoptosis signaling pathways. We find that concomitant p53 activation and Bcl-2 inhibition overcome apoptosis resistance and markedly prolong survival in three mouse models of resistant acute myeloid leukemia (AML). Mechanistically, p53 activation negatively regulates the Ras/Raf/MEK/ERK pathway and activates GSK3 to modulate Mcl-1 phosphorylation and promote its degradation, thus overcoming AML resistance to Bcl-2 inhibition. Moreover, Bcl-2 inhibition reciprocally overcomes apoptosis resistance to p53 activation by switching cellular response from G₁ arrest to apoptosis. The efficacy, together with the mechanistic findings, reveals the potential of simultaneously targeting these two apoptosis regulators and provides a rational basis for clinical testing of this therapeutic approach.

Tumor Trp53 status and genotype affect the bone marrow microenvironment in acute myeloid leukemia

The genetic heterogeneity of acute myeloid leukemia (AML) and the variable responses of individual patients to therapy suggest that different AML genotypes may influence the bone marrow (BM) microenvironment in different ways. We performed gene expression profiling of bone marrow mesenchymal stromal cells (BM-MSC) isolated from normal C57BL/6 mice or mice inoculated with syngeneic murine leukemia cells carrying different human AML genotypes, developed in mice with Trp53 wild-type or nullgenetic backgrounds. We identified a set of genes whose expression in BM-MSC was modulated by all four AML genotypes tested. In addition, there were sets of differentially-expressed genes in AML-exposed BM-MSC that were unique to the particular AML genotype or Trp53 status. Our findings support the hypothesis that leukemia cells alter the transcriptome of surrounding BM stromal cells, in both common and genotype-specific ways. These changes are likely to be advantageous to AML cells, affecting disease progression and response to chemotherapy, and suggest opportunities for stroma-targeting therapy, including those based on AML genotype.

AML-induced osteogenic differentiation in mesenchymal stromal cells supports leukemia growth

Genotypic and phenotypic alterations in the bone marrow (BM) microenvironment, in particular in osteoprogenitor cells, have been shown to support leukemogenesis. However, it is unclear how leukemia cells alter the BM microenvironment to create a hospitable niche. Here, we report that acute myeloid leukemia (AML) cells, but not normal CD34+ or CD33+ cells, induce osteogenic differentiation in mesenchymal stromal cells (MSCs). In addition, AML cells inhibited adipogenic differentiation of MSCs. Mechanistic studies identified that AML-derived BMPs activate Smad1/5 signaling to induce osteogenic differentiation in MSCs. Gene expression array analysis revealed that AML cells induce connective tissue growth factor (CTGF) expression in BM-MSCs irrespective of AML type. Overexpression of CTGF in a transgenic mouse model greatly enhanced leukemia engraftment in vivo. Together, our data suggest that AML cells induce a preosteoblast-rich niche in the BM that in turn enhances AML expansion.

Bone Marrow Adipocytes Facilitate Fatty Acid Oxidation Activating AMPK and a Transcriptional Network Supporting Survival of Acute Monocytic Leukemia Cells

Leukemia cells in the bone marrow must meet the biochemical demands of increased cell proliferation and also survive by continually adapting to fluctuations in nutrient and oxygen availability. Thus, targeting metabolic abnormalities in leukemia cells located in the bone marrow is a novel therapeutic approach. In this study, we investigated the metabolic role of bone marrow adipocytes in supporting the growth of leukemic blasts. Prevention of nutrient starvation-induced apoptosis of leukemic cells by bone marrow adipocytes, as well as the metabolic and molecular mechanisms involved in this process, was investigated using various analytic techniques. In acute monocytic leukemia (AMoL) cells, the prevention of spontaneous apoptosis by bone marrow adipocytes was associated with an increase in fatty acid β-oxidation (FAO) along with the upregulation of PPARγ, FABP4, CD36, and BCL2 genes. In AMoL cells, bone marrow adipocyte coculture increased adiponectin receptor gene expression and its downstream target stress response kinase AMPK, p38 MAPK with autophagy activation, and upregulated antiapoptotic chaperone HSPs. Inhibition of FAO disrupted metabolic homeostasis, increased reactive oxygen species production, and induced the integrated stress response mediator ATF4 and apoptosis in AMoL cells cocultured with bone marrow adipocytes. Our results suggest that bone marrow adipocytes support AMoL cell survival by regulating their metabolic energy balance and that the disruption of FAO in bone marrow adipocytes may be an alternative, novel therapeutic strategy for AMoL therapy. Cancer Res; 77(6); 1453-64. ©2017 AACR.

Abstract CT069: Correlative biomarkers of clinical activity of the BCL-2 inhibitor, venetoclax (ABT-199/ GDC-0199), in acute myeloid leukemia patients

A phase 2 trial evaluated the efficacy and safety of venetoclax monotherapy in 32 patients (pts) with relapsed/refractory acute myeloid leukemia (AML) or those unfit for intensive therapy. Venetoclax demonstrated activity and a tolerable safety profile in these pts. We evaluated potential clinical biomarkers that correlated with venetoclax sensitivity and/or intrinsic/acquired resistance.

Given the selectivity of venetoclax to inhibit BCL-2, protein expression of BCL-2 family members BCL-2 and BCL-XL was determined by flow cytometry in tumor cells from peripheral blood collected at baseline (22 pts) and post venetoclax therapy (21 pts). Six pts had a sensitive protein index (?35% of blast expressing BCL-2 protein and &lt;40% blasts expressing BCL-XL) prior to therapy and the remaining 16 pts had a resistant protein index (7 pts had &lt;35% of blasts expressing BCL-2, 9 pts had ?40% blasts expressing BCL-XL). The median time on venetoclax therapy was 30 days for pts with a resistant index vs 104 days for pts with a sensitive index (P = 0.0381, Wilcoxon). AML blasts analyzed at relapse demonstrated a resistant BCL-2/BCL-XL protein index in 20 of 21 pts analyzed: 9 pts had &lt;35% blasts with BCL-2 expression and 11 pts had ?40% blasts with BCL-XL protein expression. All 6 pts with a sensitive protein index prior to therapy expressed a resistant protein index at relapse.

Occurrence of genetic mutations known to be associated with myeloid malignancies was investigated by next generation sequencing on blood and bone marrow specimens collected at baseline (32 pts) and relapse (20 pts). Biological activity defined as any measurable reduction in bone marrow blast counts after initiation of venetoclax therapy was observed in 17 pts. Eleven of 17 (65%) pts with biological activity had blasts containing mutations in the splicing factor genes SRSF2/ZRSR2, among them 6 pts also had blasts with mutations in IDH1/IDH2. Of the remaining 6 pts with biological activity, 1 pt had an IDH2 mutation and the remaining 5 pts were wild-type for SRSF2/ZRSR2/IDH1/IDH2. Six of 15 pts without biological response to venetoclax had blasts with either FLT3-ITD or PTPN11 mutation prior to therapy. Five of the 17 pts with initial biological response to venetoclax acquired a new FLT3-ITD or PTPN11 mutation at loss of response. Previous studies have shown that both these genetic alterations affect the expression of BCL-2 family members, suggesting that FLT3-ITD or PTPN11 mutations may be responsible for primary and acquired resistance to venetoclax in AML pts by deregulating anti-apoptotic proteins.

These findings suggest that BCL-2 protein expression patterns and/or presence of genetic mutations including splicing factors, IDH, PTPN11, and FLT3 may predict venetoclax monotherapy activity in pts with relapsed AML.

[R.P. and N.D. contributed equally to this work.]

Citation Format: Relja Popovic, Naval Daver, Vivian Ruvolo, Ken Chen, Zixing Wang, Xin Huang, Mack Mabry, Jalaja Potluri, Evelyn McKeegan, Marina Konopleva, Brenda J. Chyla. Correlative biomarkers of clinical activity of the BCL-2 inhibitor, venetoclax (ABT-199/ GDC-0199), in acute myeloid leukemia patients. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr CT069.

ATF4 induction through an atypical integrated stress response to ONC201 triggers p53-independent apoptosis in hematological malignancies

The clinical challenge posed by p53 abnormalities in hematological malignancies requires therapeutic strategies other than standard genotoxic chemotherapies. ONC201 is a first-in-class small molecule that activates p53-independent apoptosis, has a benign safety profile, and is in early clinical trials. We found that ONC201 caused p53-independent apoptosis and cell cycle arrest in cell lines and in mantle cell lymphoma (MCL) and acute myeloid leukemia (AML) samples from patients; these included samples from patients with genetic abnormalities associated with poor prognosis or cells that had developed resistance to the nongenotoxic agents ibrutinib and bortezomib. Moreover, ONC201 caused apoptosis in stem and progenitor AML cells and abrogated the engraftment of leukemic stem cells in mice while sparing normal bone marrow cells. ONC201 caused changes in gene expression similar to those caused by the unfolded protein response (UPR) and integrated stress responses (ISRs), which increase the translation of the transcription factor ATF4 through an increase in the phosphorylation of the translation initiation factor eIF2α. However, unlike the UPR and ISR, the increase in ATF4 abundance in ONC201-treated hematopoietic cells promoted apoptosis and did not depend on increased phosphorylation of eIF2α. ONC201 also inhibited mammalian target of rapamycin complex 1 (mTORC1) signaling, likely through ATF4-mediated induction of the mTORC1 inhibitor DDIT4. Overexpression of BCL-2 protected against ONC201-induced apoptosis, and the combination of ONC201 and the BCL-2 antagonist ABT-199 synergistically increased apoptosis. Thus, our results suggest that by inducing an atypical ISR and p53-independent apoptosis, ONC201 has clinical potential in hematological malignancies.

Results of the Phase I Trial of RG7112, a Small-Molecule MDM2 Antagonist in Leukemia

PURPOSE

RG7112 is a small-molecule MDM2 antagonist. MDM2 is a negative regulator of the tumor suppressor p53 and frequently overexpressed in leukemias. Thus, a phase I study of RG7112 in patients with hematologic malignancies was conducted.

EXPERIMENTAL DESIGN

Primary study objectives included determination of the dose and safety profile of RG7112. Secondary objectives included evaluation of pharmacokinetics; pharmacodynamics, such as TP53-mutation status and MDM2 expression; and preliminary clinical activity. Patients were divided into two cohorts: Stratum A [relapsed/refractory acute myeloid leukemia (AML; except acute promyelocytic leukemia), acute lymphoblastic leukemia, and chronic myelogenous leukemia] and Stratum B (relapsed/refractory chronic lymphocytic leukemia/small cell lymphocytic leukemia; CLL/sCLL). Some Stratum A patients were treated at the MTD to assess clinical activity.

RESULTS

RG7112 was administered to 116 patients (96 patients in Stratum A and 20 patients in Stratum B). All patients experienced at least 1 adverse event, and 3 dose-limiting toxicities were reported. Pharmacokinetic analysis indicated that twice-daily dosing enhanced daily exposure. Antileukemia activity was observed in the 30 patients with AML assessed at the MTD, including 5 patients who met International Working Group (IWG) criteria for response. Exploratory analysis revealed TP53 mutations in 14% of Stratum A patients and in 40% of Stratum B patients. Two patients with TP53 mutations exhibited clinical activity. p53 target genes were induced only in TP53 wild-type leukemic cells. Baseline expression levels of MDM2 correlated positively with clinical response.

CONCLUSIONS

RG7112 demonstrated clinical activity against relapsed/refractory AML and CLL/sCLL. MDM2 inhibition resulted in p53 stabilization and transcriptional activation of p53-target genes. We provide proof-of-concept that MDM2 inhibition restores p53 function and generates clinical responses in hematologic malignancies.

MDM2 Inhibitor, Nutlin 3a, Induces p53 Dependent Autophagy in Acute Leukemia by AMP Kinase Activation

MDM2 (mouse double minute 2) inhibitors that activate p53 and induce apoptosis in a non-genotoxic manner are in clinical development for treatment of leukemias. P53 can modulate other programmed cell death pathways including autophagy both transcriptionally and non-transcriptionally. We investigated autophagy induction in acute leukemia by Nutlin 3a, a first-in-class MDM2 inhibitor. Nutlin 3a induced autophagy in a p53 dependent manner and transcriptional activation of AMP kinase (AMPK) is critical, as this effect is abrogated in AMPK -/- mouse embryonic fibroblasts. Nutlin 3a induced autophagy appears to be pro-apoptotic as pharmacological (bafilomycin) or genetic inhibition (BECLIN1 knockdown) of autophagy impairs apoptosis induced by Nutlin 3a.

Mitochondrial Profiling of Acute Myeloid Leukemia in the Assessment of Response to Apoptosis Modulating Drugs

BH3 profiling measures the propensity of transformed cells to undergo intrinsic apoptosis and is determined by exposing cells to BH3-mimicking peptides. We hypothesized that basal levels of prosurvival BCL-2 family proteins may modulate the predictive power of BH3 profiling and termed it mitochondrial profiling. We investigated the correlation between cell sensitivity to apoptogenic agents and mitochondrial profiling, using a panel of acute myeloid leukemias induced to undergo apoptosis by exposure to cytarabine, the BH3 mimetic ABT-199, the MDM2 inhibitor Nutlin-3a, or the CRM1 inhibitor KPT-330. We found that the apoptogenic efficacies of ABT-199 and cytarabine correlated well with BH3 profiling reflecting BCL2, but not BCL-XL or MCL-1 dependence. Baseline BCL-2 protein expression analysis increased the ability of BH3 profiling to predict resistance mediated by MCL-1. By utilizing engineered cells with overexpression or knockdown of BCL-2 family proteins, Ara-C was found to be independent, while ABT-199 was dependent on BCL-XL. BCL-2 and BCL-XL overexpression mediated resistance to KPT-330 which was not reflected in the BH3 profiling assay, or in baseline BCL-2 protein levels. In conclusion, mitochondrial profiling, the combination of BH3 profiling and prosurvival BCL-2 family protein analysis, represents an improved approach to predict efficacy of diverse agents in AML and may have utility in the design of more effective drug combinations.

Apoptosis repressor with caspase recruitment domain is regulated by MAPK/PI3K and confers drug resistance and survival advantage to AML

The apoptosis repressor with caspase recruitment domain (ARC) protein is known to suppress both intrinsic and extrinsic apoptosis. We previously reported that ARC expression is a strong, independent adverse prognostic factor in acute myeloid leukemia (AML). Here, we investigated the regulation and role of ARC in AML. ARC expression is upregulated in AML cells co-cultured with bone marrow-derived mesenchymal stromal cells (MSCs) and suppressed by inhibition of MAPK and PI3K signaling. AML patient samples with RAS mutations (N = 64) expressed significantly higher levels of ARC than samples without RAS mutations (N = 371) (P = 0.016). ARC overexpression protected and ARC knockdown sensitized AML cells to cytarabine and to agents that selectively induce intrinsic (ABT-737) or extrinsic (TNF-related apoptosis inducing ligand) apoptosis. NOD-SCID mice harboring ARC-overexpressing KG-1 cells had significantly shorter survival than mice injected with control cells (median 84 vs 111 days) and significantly fewer leukemia cells were present when NOD/SCID IL2Rγ null mice were injected with ARC knockdown as compared to control Molm13 cells (P = 0.005 and 0.03 at 2 and 3 weeks, respectively). Together, these findings demonstrate that MSCs regulate ARC in AML through activation of MAPK and PI3K signaling pathways. ARC confers drug resistance and survival advantage to AML in vitro and in vivo, suggesting ARC as a novel target in AML therapy.

Apoptosis repressor with caspase recruitment domain modulates second mitochondrial-derived activator of caspases mimetic-induced cell death through BIRC2/MAP3K14 signalling in acute myeloid leukaemia

Overexpression of the apoptosis repressor with caspase recruitment domain (ARC, also termed NOL3) protein predicts adverse outcome in patients with acute myeloid leukaemia (AML) and confers drug resistance to AML cells. The second mitochondrial-derived activator of caspases (SMAC, also termed DIABLO) mimetic, birinapant, promotes extrinsic apoptosis in AML cells. SMAC mimetics induce cleavage of cellular inhibitor of apoptosis (cIAP) proteins, leading to stabilization of the nuclear factor-κB (NF-κB)-inducing kinase (MAP3K14, also termed NIK) and activation of non-canonical NF-κB signalling. To enhance the therapeutic potential of SMAC mimetics in AML, we investigated the regulation and role of ARC in birinapant-induced apoptosis. We showed that birinapant increases ARC in AML and bone marrow-derived mesenchymal stromal cells (MSCs). Downregulation of MAP3K14 by siRNA decreased ARC levels and suppressed birinapant-induced ARC increase. Reverse-phase protein array analysis of 511 samples from newly diagnosed AML patients showed that BIRC2 (also termed cIAP1) and ARC were inversely correlated. Knockdown of ARC sensitized, while overexpression attenuated, birinapant-induced apoptosis. Furthermore, ARC knockdown in MSCs sensitized co-cultured AML cells to birinapant-induced apoptosis. Our data demonstrate that ARC is regulated via BIRC2/MAP3K14 signalling and its overexpression in AML or MSCs can function as a resistant factor to birinapant-induced leukaemia cell death, suggesting that strategies to inhibit ARC will improve the therapeutic potential of SMAC mimetics.

Induction of p53-mediated transcription and apoptosis by exportin-1 (XPO1) inhibition in mantle cell lymphoma

The nuclear transporter exportin-1 (XPO1) is highly expressed in mantle cell lymphoma (MCL) cells, and is believed to be associated with the pathogenesis of this disease. XPO1-selective inhibitors of nuclear export (SINE) compounds have been shown to induce apoptosis in MCL cells. Given that p53 is a cargo protein of XPO1, we sought to determine the significance of p53 activation through XPO1 inhibition in SINE-induced apoptosis of MCL cells. We investigated the prognostic impact of XPO1 expression in MCL cells using Oncomine analysis. The significance of p53 mutational/functional status on sensitivity to XPO1 inhibition in cell models and primary MCL samples, and the functional role of p53-mediated apoptosis signaling, were also examined. Increased XPO1 expression was associated with poor prognosis in MCL patients. The XPO1 inhibitor KPT-185 induced apoptosis in MCL cells through p53-dependent and -independent mechanisms, and p53 status was a critical determinant of its apoptosis induction. The KPT-185-induced, p53-mediated apoptosis in the MCL cells occurred in a transcription-dependent manner. Exportin-1 appears to influence patient survival in MCL, and the SINE XPO1 antagonist KPT-185 effectively activates p53-mediated transcription and apoptosis, which would provide a novel strategy for the therapy of MCL.

Selective BCL-2 inhibition by ABT-199 causes on-target cell death in acute myeloid leukemia

B-cell leukemia/lymphoma 2 (BCL-2) prevents commitment to programmed cell death at the mitochondrion. It remains a challenge to identify those tumors that are best treated by inhibition of BCL-2. Here, we demonstrate that acute myeloid leukemia (AML) cell lines, primary patient samples, and murine primary xenografts are very sensitive to treatment with the selective BCL-2 antagonist ABT-199. In primary patient cells, the median IC50 was approximately 10 nmol/L, and cell death occurred within 2 hours. Our ex vivo sensitivity results compare favorably with those observed for chronic lymphocytic leukemia, a disease for which ABT-199 has demonstrated consistent activity in clinical trials. Moreover, mitochondrial studies using BH3 profiling demonstrate activity at the mitochondrion that correlates well with cytotoxicity, supporting an on-target mitochondrial mechanism of action. Our protein and BH3 profiling studies provide promising tools that can be tested as predictive biomarkers in any clinical trial of ABT-199 in AML.

Prognostic impact and targeting of CRM1 in acute myeloid leukemia

Chromosomal region maintenance 1 (CRM1) is a nuclear export receptor recognizing proteins bearing a leucine-rich nuclear export signal. CRM1 is involved in nuclear export of tumor suppressors such as p53. We investigated the prognostic significance of CRM1 in acute myeloid leukemia (AML) and effects of a novel small-molecule selective inhibitor of CRM1. CRM1 protein expression was determined in 511 newly diagnosed AML patients and was correlated with mouse double minute 2 (MDM2) and p53 levels. High CRM1 expression was associated with short survival of patients and remained an adverse prognostic factor in multivariate analysis. CRM1 inhibitor KPT-185 induced mainly full-length p53 and apoptosis in a p53-dependent manner, whereas inhibition of proliferation was p53 independent. Patient samples with p53 mutations showed low sensitivity to KPT-185. Nuclear retention of p53 induced by CRM1 inhibition synergized with increased levels of p53 induced by MDM2 inhibition in apoptosis induction. KPT-185 and Nutlin-3a, alone and in combination, induced synergistic apoptosis in patient-derived CD34(+)/CD38(-) AML, but not in normal progenitor cells. Data suggest that CRM1 exerts an antiapoptotic function and is highly prognostic in AML. We propose a novel combinatorial approach for the therapy of AML, aimed at maximal activation of p53-mediated apoptosis by concomitant MDM2 and CRM1 inhibition.

Abstract 1666: Targeting autophagy-related E1 ligase Atg7 increases chemosensitivity in acute myelogenous leukemia cells and overcomes stroma mediated resistance

In the context of chemotherapy (CT), autophagy is a resistance mechanism. Atg7 is an key autophagy-related E1 ligase that can switch transcription downstream of p53 between cell cycle arrest and apoptosis induction (Lee, IH et al. Science 2012;336: 225). p53 mutations are infrequent in newly diagnosed normal karyotype acute myelogenous leukemias (NK-AML) and thus we used a genetic model to evaluate the potential of targeting Atg7 in AML therapy in the context of wild type p53. As autophagy is critical for the mutual metabolic dependence between tumor and stroma (Martinez-Outschroom et al. Cell Cycle 2010;9:4297), we evaluated, in a co-culture model, whether ATG7 knockdown in AML can overcome ‘stroma-mediated’ chemoresistance. We also correlated expression of Atg7 protein in primary AML blasts to clinical outcome in 511 newly diagnosed patients (pts).

Methods: In a syngeneic background we studied the effect of stable Atg7 knockdown (shRNA mediated) in p53 wild type (WT) AML cells on apoptosis (Annexin binding by flowcytometry) after CT and nutrient deprivation. Role of ATG7 in stroma mediated chemoresistance was tested by co-culturing AML cells (WT and Atg7 KD) with normal bone marrow stromal cells and measuring apoptosis after treatment with CT. Finally we correlated expression of Atg7 protein in the AML blasts of 511 newly diagnosed pts with AML by reverse phase protein array (RPPA) with clinical outcomes.

Results: Stable knockdown (KD) of Atg7 in OCI-AML3 cells increased apoptosis upon exposure to two CT agents most commonly used in AML therapy: cytarabine (1 μmol for 48 hrs) (33.6% apoptosis in WT vs 66.2% in Atg7 KD, p=.04) and idarubicin (50 nG/ml for 48 hrs) (33% apoptosis in WT vs 54% in Atg7 KD, p=.001) as well as serum deprivation (8.5% apoptosis in WT vs 28% in Atg7 KD, p=.00005). Treatment with cytarabine was associated with increased induction of pro-apoptotic protein PUMA and decreased induction of cell cycle arrest mediator p21 in Atg7 KD OCI-AML3 cells, as compared to WT. In co-culture model, co-culture with normal marrow stromal cells failed to protect Atg7 KD cells from apoptosis after treatment with cytarabine (5 μmol for 48 hrs) while the WT cells were protected (27% apoptosis in WT vs 57% in Atg7 KD, p=0.0007).

Finally, reverse-phase protein array demonstrated that abnormal expression of Atg7 in primary AML blasts (higher or lower compared to normal CD34+ cells) among 511 newly diagnosed pts was associated with shorter overall survival (p=.007) and this effect was most prominent among pts with both good-risk (p=.02) and poor-risk cytogenetics AML (p=.0005).

Conclusion: Our results highlight the role of autophagy as chemo-resistance mechanism in AML, identify Atg7 as a potential therapeutic target to enhance CT induced apoptosis and overcome stroma-mediated resistance to CT.

Citation Format: Gautam Borthakur, Seshagiri Duvvuri, Yongsheng Lan, Vivian Ruvolo, Peter Ruvolo, Yihua Qiu, Marina Konopleva, Steven Kornblau, Michael Andreeff. Targeting autophagy-related E1 ligase Atg7 increases chemosensitivity in acute myelogenous leukemia cells and overcomes stroma mediated resistance. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1666. doi:10.1158/1538-7445.AM2013-1666

Abstract 605: Apogossypolone derivative -BI97D6 effectively targets MCL1 overexpressing Acute Myeloid Leukemia cells

Aberrant expression of anti-apoptotic proteins such as BCL2, MCL1, and BCL-XL is observed in many tumors including Acute Myeloid Leukemia (AML). An obvious strategy for AML therapy would be to target the anti-apoptotic BCL2 family members. While compounds such as ABT-737 have shown promise for treatment of some malignancies, the compound binds poorly to MCL1 and thus cells that overexpress MCL1 usually display high resistance to the drug. Furthermore, ABT-737 activates ERK signaling resulting in MCL1 overexpression in surviving cells (Konopleva, et al, Leukemia 2011). The apogossypolone derivative -BI97D6 binds MCL1 and BCL2, BCL-XL, BFL1 with high affinities (Wei, et al, J Med Chem 2010). We recently reported that -BI97D6 (a) efficiently kills AML cell lines even in the presence of protective mesenchymal stroma cells, (b) interferes with the association between MCL1/BIM and BCL2/BAX, (c) stimulates BAX conformational change, (d) requires BAX or BAK for cell killing, and (e) does not induce ER stress. These data suggests that -BI97D6, unlike other gossypol or apogossypol compounds, acts mainly as a BH3 mimetic.

In the current study, we first examined the role of MCL1 in -BI97D6-mediated killing. OCI-AML3 cells are extremely resistant to ABT-737 due to its high expression of MCL1. MCL1 expression was suppressed by lenti-viral shRNA in OCI-AML3 cells and knockdown of MCL1 protein by 80% was achieved as determined by quantitative western blot. Compared to cells with non-specific control shRNA, cells with MCL1 shRNA were greatly sensitized to ABT-737, and significantly sensitized to AraC, while -BI97D6, which binds MCL1 with high affinity, is almost equipotent in knockdown and control cells. Since results with AML cell lines have been promising, we examined the efficacy of -BI97D6 on primary AML samples. Flow cytometry analysis revealed that -BI97D6 potently induced apoptosis in AML blast cells at low nM concentration (EC50&lt;50nM). -BI97D6 also effectively killed putative CD34+CD38- leukemia stem cells (LSC). Importantly, primary AML with FLT3-ITD and FLT3-D835 mutations showed similar sensitivity as those without FLT3 mutations (EC50&lt;50nM). As FLT3 mutations are associated with poor prognosis in AML, these findings suggests that -BI97D6 can target AML LSC and could benefit even high risk patients. In summary, compound -BI97D6 may be a promising drug candidate for MCL1-targeted AML therapy.

Citation Format: Rongqing Pan, Vivian Ruvolo, Maurizio Pellecchia, Jun Wei, Marina Konopleva, John C. Reed, Peter Ruvolo, Michael Andreeff. Apogossypolone derivative -BI97D6 effectively targets MCL1 overexpressing Acute Myeloid Leukemia cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 605. doi:10.1158/1538-7445.AM2013-605

Abstract 3871: Insulin-like growth factor 1 receptor (IGF1R) inhibitor BMS754807 is active against FLT3-ITD mutated acute myelogenous leukemia and activity is p53 dependent

The Internal tandem mutation (ITD) in the FLT3 gene is associated with shorter remission duration, overall survival and relapse free survival in patients with normal karyotype acute myelogenous leukemia (AML). FLT3-ITD inhibitors are in clinical development but single agent clinical activity is of limited duration with activation of parallel signaling pathways potentially contributing to most relapses thus highlighting the need for new agents. Because common signaling pathways are activated downstream of FLT3 and IGF1R, we investigated the preclinical activity of IGF1R antagonist BMS754807 against AML cells with FLT3-ITD mutations. Results: BMS 754807 induced apoptosis (Annexin V binding by flow cytometry) in MOLM13 cells (AML cell line with FLT3-ITD mutation and wild type p53) at 48 hrs at submicromolar concentrations, while OCI AML3 cells (p53 and FLT3 wild type) were resistant. Similarly, murine BAF3 cells expressing human FLT3-ITD underwent prompt apoptosis with BMS 754807 while the same cells with human wt-FLT3 were resistant to BMS 754807(IC50s 2.5 μmol vs &gt;10 μmol). Western blot analysis confirmed reduction in FLT3, Akt, ERK, S6 ribosomal protein and GSK3 beta phosphorylation and increase in p53 levels in MOLM13 cells. Interestingly, apoptosis induction was not associated with caspase activation. Moreover, apoptosis induction by BMS 754807 appeared to be p53 dependent as MOLM13 cells with stable expression of short hairpin RNA (sh-RNA) targeting p53 (p53-shRNA) were resistant, while MOLM13 cells expressing scramble sh-RNA underwent apoptosis comparable to parental MOLM13 cells. Surface expression of IGF1R was comparable among parental and p53-shRNA MOLM13 cells. Apoptosis induction by BMS 754807 in p53-WT and FLT3-ITD cells was associated with phosphorylation of p53 at serine 15. Conclusion: BMS 754807 has selective activity against AML cells with FLT3-ITD mutation and this activity is p53 dependent and associated with phosphorylation of p53 at serine 15. Results suggest that IGF1R inhibition has therapeutic potential as novel targeted therapy for AML with FLT3-ITD mutation.

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 3871. doi:1538-7445.AM2012-3871

Decreased sensitivity of 17p-deleted chronic lymphocytic leukemia cells to a small molecule BCL-2 antagonist ABT-737

BACKGROUND

Despite the high complete response rates achieved with fludarabine-based regimens, relapse is inevitable in chronic lymphocytic leukemia (CLL). Relapsed patients often acquire deletions of the short arm of chromosome 17 (del[17p]), which are closely associated with tumor protein 53 (TP53) mutations. Wild-type p53 up-regulates and activates B-cell CLL/lymphoma 2 (BCL-2)-associated X protein (BAX), and it down-regulates and inactivates BCL-2. The small-molecule BCL-2 inhibitor ABT-737 induces apoptosis in a BAX-dependent and BCL-2 homologous antagonist-killer (BAK)-dependent manner. The role of p53 in sensitivity of CLL cells to BCL-2 inhibition has not been extensively investigated.

METHODS

The authors investigated the association of del(17p) with ABT-737 sensitivity in CLL cells from 50 patients. Stable p53 and BAX knockdown cells were used for mechanistic studies.

RESULTS

CLL cells with del(17p) were less sensitive to ABT-737-induced BAX activation and apoptosis than CLL cells without del(17p) (39% ± 7.3% vs 63.7% ± 2.9% [specific annexin V induction]; P < .01). A positive correlation between the degrees of apoptosis induced by ABT-737 and by the p53-activating binding protein homolog murine double minute (MDM2) antagonist nutlin-3a (correlation coefficient [r] = 0.75; P < .0001) was observed. CLL cells with del(17p) expressed lower levels of BAX than those without del(17p) (0.67 ± 0.12 vs 1.27 ± 0.10 in relative protein expression levels; P < .01). Knockdown of p53 or BAX in leukemia cells resulted in decreased apoptosis induced by ABT-737.

CONCLUSIONS

The current data indicated that p53 dysfunction may lead to decreased apoptosis induction by ABT-737.

Activation of p53 signaling by MI-63 induces apoptosis in acute myeloid leukemia cells

Non-mutational inactivation of p53 is frequent in acute myeloid leukemia (AML) via overexpression of MDM2. We report that treatment with MI-63, a novel inhibitor of MDM2, activates p53 signaling to induce apoptosis in AML cell lines and primary samples. Cell lines naturally devoid of p53 or expressing shRNA targeting p53 are refractory to apoptosis induction by MI-63, indicating that the effects of MI-63 require p53 expression. MI-63 induced G1 phase arrest and increased p21 expression. MI-63 induced pronounced apoptosis in all primary AML samples tested, and most important, was effective in inducing cell death of leukemia 'stem' cells. In addition, MI-63 showed synergy with both doxorubicin and AraC. Interestingly, treatment with MI-63 also led to a reduction in levels of MDM4 protein, a repressor of p53 mediated transcription, in AML cells. Our results warrant investigation of MI-63 or its analogs as anti-leukemic agents, alone or in combination with traditional chemotherapeutic agents.

Role of peroxisome proliferator-activated receptor-gamma and its coactivator DRIP205 in cellular responses to CDDO (RTA-401) in acute myelogenous leukemia

Peroxisome proliferator-activated receptor-gamma (PPARgamma) is a member of the nuclear receptor (NR) family of transcription factors with important regulatory roles in cellular growth, differentiation, and apoptosis. Using proteomic analysis, we showed expression of PPARgamma protein in a series of 260 newly diagnosed primary acute myelogenous leukemia (AML) samples. Forced expression of PPARgamma enhanced the sensitivity of myeloid leukemic cells to apoptosis induced by PPARgamma agonists 2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid (CDDO) and 15-deoxy-(12,14)-15DPGJ(2), through preferential cleavage of caspase-8. No effects on cell cycle distribution or differentiation were noted, despite prominent induction of p21 in PPARgamma-transfected cells. In turn, antagonizing PPARgamma function by small interfering RNA or pharmacologic PPARgamma inhibitor significantly diminished apoptosis induction by CDDO. Overexpression of coactivator protein DRIP205 resulted in enhanced differentiation induction by CDDO in AML cells through PPARgamma activation. Studies with DRIP205 deletion constructs showed that the NR boxes of DRIP205 are not required for this coactivation. In a phase I clinical trial of CDDO (RTA-401) in leukemia, CDDO induced an increase in PPARgamma mRNA expression in six of nine patient samples; of those, induction of differentiation was documented in four patients and that of p21 in three patients, all expressing DRIP205 protein. In summary, these findings suggest that cellular levels of PPARgamma regulate induction of apoptosis via caspase-8 activation, whereas the coactivator DRIP205 is a determinant of induction of differentiation, in response to PPARgamma agonists in leukemic cells.

[Oncoplastic surgery for the treatment of breast cancer]

Surgery is still the gold standard in breast cancer. Also if the elective treatment, thanks to the adjuvant therapy, ha became more conservative than once was, breast surgery remains, in the mind of the woman affected by breast cancer, a demolitive surgery. The collaboration bet-ween the breast surgeon and the plastic surgeon has to be closer than it is, in order to obtain the total asportation of the tumor and an esthetic result that limits the psychological trauma to the woman. Oncoplastic surgery is the answer to these human and medical necessities, giving the correct approaches about breast volume, tumor volume, radicality of the treatment and esthetic outcome. This review will focus on different oncoplastic approaches, to help improving both the esthetic outcome of breast cancer resection and the likelihood of surgeons obtaining wide surgical margins in preparation for breast-conserving radiotherapy.

The dual PI3 kinase/mTOR inhibitor PI-103 prevents p53 induction by Mdm2 inhibition but enhances p53-mediated mitochondrial apoptosis in p53 wild-type AML

Activation of the phosphatidylinositol-3 kinase/Akt/mammalian target of the rapamycin (PI3K/Akt/mTOR) pathway and inactivation of wild-type p53 by murine double minute 2 homologue (Mdm2) overexpression are frequent molecular events in acute myeloid leukemia (AML). We investigated the interaction of PI3K/Akt/mTOR and p53 pathways after their simultaneous blockade using the dual PI3K/mTOR inhibitor PI-103 and the Mdm2 inhibitor Nutlin-3. We found that PI-103, which itself has modest apoptogenic activity, acts synergistically with Nutlin-3 to induce apoptosis in a wild-type p53-dependent fashion. PI-103 synergized with Nutlin-3 to induce Bax conformational change and caspase-3 activation, despite its inhibitory effect on p53 induction. The PI-103/Nutlin-3 combination caused profound dephosphorylation of 4E-BP1 and decreased expression of many proteins including Mdm2, p21, Noxa, Bcl-2 and survivin, which can affect mitochondrial stability. We suggest that PI-103 actively enhances downstream p53 signaling and that a combination strategy aimed at inhibiting PI3K/Akt/mTOR signaling and activating p53 signaling is potentially effective in AML, where TP53 mutations are rare and downstream p53 signaling is intact.

HOX expression patterns identify a common signature for favorable AML

Deregulated HOX expression, by chromosomal translocations and myeloid-lymphoid leukemia (MLL) rearrangements, is causal in some types of leukemia. Using real-time reverse transcription-PCR, we examined the expression of 43 clustered HOX, polycomb, MLL and FLT3 genes in 119 newly diagnosed adult acute myeloid leukemias (AMLs) selected from all major cytogenetic groups. Downregulated HOX expression was a consistent feature of favorable AMLs and, among these cases, inv(16) cases had a distinct expression profile. Using a 17-gene predictor in 44 additional samples, we observed a 94.7% specificity for classifying favorable vs intermediate/unfavorable cytogenetic groups. Among other AMLs, HOX overexpression was associated with nucleophosmin (NPM) mutations and we also identified a phenotypically similar subset with wt-NPM. In many unfavorable and other intermediate cytogenetic AMLs, HOX levels resembled those in normal CD34+ cells, except that the homogeneity characteristic of normal samples was not present. We also observed that HOXA9 levels were significantly inversely correlated with survival and that BMI-1 was overexpressed in cases with 11q23 rearrangements, suggesting that p19(ARF) suppression may be involved in MLL-associated leukemia. These results underscore the close relationship between HOX expression patterns and certain forms of AML and emphasize the need to determine whether these differences play a role in the disease process.

The novel triterpenoid C-28 methyl ester of 2-cyano-3, 12-dioxoolen-1, 9-dien-28-oic acid inhibits metastatic murine breast tumor growth through inactivation of STAT3 signaling

We and others have reported that C-28 methyl ester of 2-cyano-3, 12-dioxoolen-1, 9-dien-28-oic acid (CDDO-Me) effectively inhibits the growth of multiple cancer cell types. Our previous studies indicated that prolonged CDDO-Me treatment inactivated extracellular signal-regulated kinase signaling in acute myelogenous leukemia cells. Whether treatment with CDDO-Me has an earlier effect on other proteins that are important for either signal transduction or oncogenesis is unknown. Constitutively activated signal transducer and activator of transcription 3 (STAT3) is frequently found in human breast cancer samples. Constitutively activated STAT3 was shown to up-regulate c-Myc in several types of cancer and has a feedback effect on Src and Akt. To examine the effects of CDDO-Me on STAT3 signaling in breast cancer, we used the murine 4T1 breast tumor model, which is largely resistant to chemotherapy. In vitro, after treatment of 4T1 cells with 500 nmol/L CDDO-Me for 2 h, we found (a) inactivation of STAT3, (b) inactivation of Src and Akt, (c) 4-fold reduction of c-Myc mRNA levels, (d) accumulation of cells in G(2)-M cell cycle phase, (e) abrogation of invasive growth of 4T1 cells, and (f) lack of apoptosis induction. In in vivo studies, CDDO-Me completely eliminated 4T1 breast cancer growth and lung metastases induced by 4T1 cells in mice when treatment started 1 day after tumor implantation and significantly inhibited tumor growth when started after 5 days. In vivo studies also indicated that splenic mature dendritic cells were restored after CDDO-Me treatment. In summary, these data suggest that CDDO-Me may have therapeutic potential in breast cancer therapy, in part, through inactivation of STAT3.

Abrogation of nuclear receptors Nr4a3 and Nr4a1 leads to development of acute myeloid leukemia

Nur77 (NR4A1) and Nor-1 (NR4A3) are highly homologous orphan nuclear receptors that regulate the transcription of overlapping target genes. The transcriptional activity of both proteins is regulated in a ligand-independent manner by cell- and stimulus-specific gene induction and protein phosphorylation. Nor-1 and Nur77 have been implicated in a variety of cellular processes, including the transduction of hormonal, inflammatory, mitogenic, apoptotic and differentiative signals. Cellular responses to these proteins suggest that they may function as homeostatic regulators of proliferation, apoptosis and differentiation, and thus may regulate cellular susceptibility to tumorigenesis. Their physiological functions, however, remain poorly understood. Here we describe a previously unsuspected function of Nor-1 and Nur77-as critical tumor suppressors of myeloid leukemogenesis. The abrogation of these proteins in mice led to rapidly lethal acute myeloid leukemia (AML), involving abnormal expansion of hematopoietic stem cells (HSCs) and myeloid progenitors, decreased expression of the AP-1 transcription factors JunB and c-Jun and defective extrinsic apoptotic (Fas-L and TRAIL) signaling. We found that downregulation of NR4A3 ( NOR-1 ) and NR4A1 ( NUR77 ) was a common feature in leukemic blasts from human AML patients, irrespective of karyotype. Thus Nor-1 and Nur77 may provide potential targets for therapeutic intervention in AML.

Mitogen-activated protein kinase kinase inhibition enhances nuclear proapoptotic function of p53 in acute myelogenous leukemia cells

Activation of the Raf/MEK/ERK pathway and inactivation of wild-type p53 by Mdm2 overexpression are frequent molecular events in acute myelogenous leukemia (AML). We investigated the interaction of Raf/MEK/ERK and p53 pathways after their simultaneous blockades using a selective small-molecule antagonist of Mdm2, Nutlin-3a, and a pharmacologic MEK-specific inhibitor, PD98059. We found that PD98059, which itself has minimal apoptogenic activity, acts synergistically with Nutlin-3a to induce apoptosis in wild-type p53 AML cell lines OCI-AML-3 and MOLM-13. Interestingly, PD98059 enhanced nuclear proapototic function of p53 in these cells. In accordance with the activation of transcription-dependent apoptosis, PD98059 treatment promoted the translocation of p53 from the cytoplasm to the nucleus in OCI-AML-3 cells, in which p53 primarily initiates transcription-independent apoptosis when cells are treated with Nutlin-3a alone. The critical role of p53 localization in cells with increased p53 levels was supported by enhanced apoptosis induction in cells cotreated with Nutlin-3a and the nuclear export inhibitor leptomycin B. PD98059 prevented p53-mediated induction of p21 at the transcriptional level. The repressed expression of antiapototic p21 also seemed to contribute to synergism between PD98059 and Nutlin-3a because (a) the synergistic apoptogenic effect was preserved in G(1) cells, (b) p53-mediated induction of p21 was preferentially seen in G(1) cells, (c) PD98059 strongly antagonized p21 induction by Nutlin-3a, and (d) cells with high p21 levels were resistant to apoptosis. This is the first report showing that the Raf/MEK/ERK pathway regulates the subcellular localization of p53 and the relative contribution of transcription-dependent and transcription-independent pathways in p53-mediated apoptosis.