A high-throughput screen indicates gemcitabine and JAK inhibitors may be useful for treating pediatric AML

Improvement in survival has been achieved for children and adolescents with AML but is largely attributed to enhanced supportive care as opposed to the development of better treatment regimens. High risk subtypes continue to have poor outcomes with event free survival rates <40% despite the use of high intensity chemotherapy in combination with hematopoietic stem cell transplant. Here we combine high-throughput screening, intracellular accumulation assays, and in vivo efficacy studies to identify therapeutic strategies for pediatric AML. We report therapeutics not currently used to treat AML, gemcitabine and cabazitaxel, have broad anti-leukemic activity across subtypes and are more effective relative to the AML standard of care, cytarabine, both in vitro and in vivo. JAK inhibitors are selective for acute megakaryoblastic leukemia and significantly prolong survival in multiple preclinical models. Our approach provides advances in the development of treatment strategies for pediatric AML.

Therapeutic Targeting of KDM1A/LSD1 in Ewing Sarcoma with SP-2509 Engages the Endoplasmic Reticulum Stress Response

Multi-agent chemotherapeutic regimes remain the cornerstone treatment for Ewing sarcoma, the second most common bone malignancy diagnosed in pediatric and young adolescent populations. We have reached a therapeutic ceiling with conventional cytotoxic agents, highlighting the need to adopt novel approaches that specifically target the drivers of Ewing sarcoma oncogenesis. As KDM1A/lysine-specific demethylase 1 (LSD1) is highly expressed in Ewing sarcoma cell lines and tumors, with elevated expression levels associated with worse overall survival (P = 0.033), this study has examined biomarkers of sensitivity and mechanisms of cytotoxicity to targeted KDM1A inhibition using SP-2509 (reversible KDM1A inhibitor). We report, that innate resistance to SP-2509 was not observed in our Ewing sarcoma cell line cohort (n = 17; IC₅₀ range, 81 -1,593 nmol/L), in contrast resistance to the next-generation KDM1A irreversible inhibitor GSK-LSD1 was observed across multiple cell lines (IC₅₀ > 300 μmol/L). Although TP53/STAG2/CDKN2A status and basal KDM1A mRNA and protein levels did not correlate with SP-2509 response, induction of KDM1B following SP-2509 treatment was strongly associated with SP-2509 hypersensitivity. We show that the transcriptional profile driven by SP-2509 strongly mirrors KDM1A genetic depletion. Mechanistically, RNA-seq analysis revealed that SP-2509 imparts robust apoptosis through engagement of the endoplasmic reticulum stress pathway. In addition, ETS1/HIST1H2BM were specifically induced/repressed, respectively following SP-2509 treatment only in our hypersensitive cell lines. Together, our findings provide key insights into the mechanisms of SP-2509 cytotoxicity as well as biomarkers that can be used to predict KDM1A inhibitor sensitivity in Ewing sarcoma. Mol Cancer Ther; 17(9); 1902-16. ©2018 AACR.

Hypoxia-induced upregulation of BMX kinase mediates therapeutic resistance in acute myeloid leukemia

Oncogenic addiction to the Fms-like tyrosine kinase 3 (FLT3) is a hallmark of acute myeloid leukemia (AML) that harbors the FLT3-internal tandem duplication (FLT3-ITD) mutation. While FLT3 inhibitors like sorafenib show initial therapeutic efficacy, resistance rapidly develops through mechanisms that are incompletely understood. Here, we used RNA-Seq-based analysis of patient leukemic cells and found that upregulation of the Tec family kinase BMX occurs during sorafenib resistance. This upregulation was recapitulated in an in vivo murine FLT3-ITD-positive (FLT3-ITD+) model of sorafenib resistance. Mechanistically, the antiangiogenic effects of sorafenib led to increased bone marrow hypoxia, which contributed to HIF-dependent BMX upregulation. In in vitro experiments, hypoxia-dependent BMX upregulation was observed in both AML and non-AML cell lines. Functional studies in human FLT3-ITD+ cell lines showed that BMX is part of a compensatory signaling mechanism that promotes AML cell survival during FLT3 inhibition. Taken together, our results demonstrate that hypoxia-dependent upregulation of BMX contributes to therapeutic resistance through a compensatory prosurvival signaling mechanism. These results also reveal the role of off-target drug effects on tumor microenvironment and development of acquired drug resistance. We propose that the bone marrow niche can be altered by anticancer therapeutics, resulting in drug resistance through cell-nonautonomous microenvironment-dependent effects.

OCTN1 Is a High-Affinity Carrier of Nucleoside Analogues

Resistance to xenobiotic nucleosides used to treat acute myeloid leukemia (AML) and other cancers remains a major obstacle to clinical management. One process suggested to participate in resistance is reduced uptake into tumor cells via nucleoside transporters, although precise mechanisms are not understood. Through transcriptomic profiling, we determined that low expression of the ergothioneine transporter OCTN1 (SLC22A4; ETT) strongly predicts poor event-free survival and overall survival in multiple cohorts of AML patients receiving treatment with the cytidine nucleoside analogue cytarabine. Cell biological studies confirmed OCTN1-mediated transport of cytarabine and various structurally related cytidine analogues, such as 2'deoxycytidine and gemcitabine, occurs through a saturable process that is highly sensitive to inhibition by the classic nucleoside transporter inhibitors dipyridamole and nitrobenzylmercaptopurine ribonucleoside. Our findings have immediate clinical implications given the potential of the identified transport system to help refine strategies that could improve patient survival across multiple cancer types where nucleoside analogues are used in cancer treatment. Cancer Res; 77(8); 2102-11. ©2017 AACR.

Abstract 4786: Integrated high-throughput screen to identify treatment leads for pediatric AML

While dramatic improvements in survival have been achieved for children and adolescents with acute myeloid leukemia (AML), some subtypes are associated with event free survival of &lt;40%. Given that significant improvements in long-term outcome are not expected with conventional therapy alone, new therapeutic strategies are urgently needed. Therefore, we conducted a high-throughput screen (HTS) to identify novel therapeutics for the treatment of pediatric AML. We selected a panel of 8 AML cell lines representing subtypes with the poorest prognosis. An initial primary screen was performed at a single concentration (10μM) with &gt;8000 compounds. Compounds with &gt;50% activity (N = 285) in the primary screen and known clinical candidates were prioritized for a secondary HTS performed in a dose-response manner (10 point curve, 0-10μM). Screening was performed using a 348-well plate format and a Biomek automation workstation for drug delivery. At 72 h cell viability was determined using Cell Titer Glo and automated Envision plate reader. Multiple drug classes had broad activity including: anti-malarials, cytotoxics (antimicrotubules, purine/pyrimidine antimetabolites, floxuridine, trimetrexate, topoI/II inhibitors), epigenetic modifiers (BET, DNMT and HDAC inhibitors), and agents targeting Bcl-2, Chk1, Parp, Hsp90, NF-êB, NAMPT, p53, proteasome, and Wee1. We validated 13 compounds from select drug classes (artesunate, cytarabine, gemcitabine, cabazitaxel, depsipeptide, panobinostat, vorinostat, ABT-199, RG117, bortezomib, carfilizomab, BMN673, MK-1775) using primary blast samples representing 3 high-risk groups (FLT3-ITD-positive, MLL-rearranged, FAB M7). Given the broad activity of gemcitabine and cabazitaxel across AML subtypes and the ability for repurposing in childhood AML, we further evaluated these agents alone and in combination in vitro. After 72h exposure, cabazitaxel was a potent inhibitor of viability in AML cell lines (IC50, 3-11nM) and primary blast samples (IC50, 3.4nM to &gt;10μM); gemcitabine had similar activity (IC50, 3-62nM and 102nM to &gt;10μM, respectively). The combination was evaluated using continuous and sequential administration schedules for up to 72h of treatment in several cell lines; simultaneous treatments were synergistic (CI, 0.2-0.45) and sequential treatments were additive to synergistic (CI, 0.82-0.95). Tolerable combination regimens were identified in NSG mice (5mg/kg cabazitaxel + 50mg/kg gemcitabine q3d x 4 weeks or q4d x 3 weeks) and efficacy studies in AML xenografts and primagrafts are ongoing. Further studies will aim to determine the underlying mechanisms of AML sensitivity to gemcitabine, cabazitaxel, and the combination. Our comprehensive approach to identify treatment leads provide advances in understanding the biology of a heterogeneous disease and development of novel treatment strategies with potential clinical benefit for pediatric AML.

Citation Format: Christina D. Drenberg, Anang Shelat, Shelley J. Orwick, Hiroto Inaba, Raul C. Ribeiro, Jeffrey E. Rubnitz, Tanja A. Gruber, R K. Guy, Sharyn D. Baker. Integrated high-throughput screen to identify treatment leads for pediatric AML. [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 4786.

Evaluation of artemisinins for the treatment of acute myeloid leukemia

PURPOSE

Investigate antileukemic activity of artemisinins, artesunate (ART), and dihydroartemisinin (DHA), in combination with cytarabine, a key component of acute myeloid leukemia (AML) chemotherapy using in vitro and in vivo models.

METHODS

Using ten human AML cell lines, we conducted a high-throughput screen to identify antimalarial agents with antileukemic activity. We evaluated effects of ART and DHA on cell viability, cytotoxicity, apoptosis, lysosomal integrity, and combination effects with cytarabine in cell lines and primary patient blasts. In vivo pharmacokinetic studies and efficacy of single-agent ART or combination with cytarabine were evaluated in three xenograft models.

RESULTS

ART and DHA had the most potent activity in a panel of AML cell lines, with selectivity toward samples harboring MLL rearrangements and FLT3-ITD mutations. Combination of ART or DHA was synergistic with cytarabine. Single-dose ART (120 mg/kg) produced human equivalent exposures, but multiple dose daily administration required for in vivo efficacy was not tolerated. Combination treatment produced initial regression, but did not prolong survival in vivo.

CONCLUSIONS

The pharmacology of artemisinins is problematic and should be considered in designing AML treatment strategies with currently available agents. Artemisinins with improved pharmacokinetic properties may offer therapeutic benefit in combination with conventional therapeutic strategies in AML.

Inherited variation in OATP1B1 is associated with treatment outcome in acute myeloid leukemia

Using broad interrogation of clinically relevant drug absorption, distribution, metabolism, and excretion (ADME) genes on the DMET platform, we identified a genetic variant in SLCO1B1 (rs2291075; c.597C>T), encoding the transporter OATP1B1, associated with event-free (P = 0.006, hazard ratio = 1.74) and overall survival (P = 0.012, hazard ratio = 1.85) in children with de novo acute myeloid leukemia (AML). Lack of SLCO1B1 expression in leukemic blasts suggested the association might be due to an inherited rather than a somatic effect. rs2291075 was in strong linkage with known functional variants rs2306283 (c.388A>G) and rs4149056 (c.521T>C). Functional studies in vitro determined that four AML-directed chemotherapeutics (cytarabine, daunorubicin, etoposide, and mitoxantrone) are substrates for OATP1B1 and the mouse ortholog Oatp1b2. In vivo pharmacokinetic studies using Oatp1b2-deficient mice further confirmed our results. Collectively, these findings demonstrate an important role for OATP1B1 in the systemic pharmacokinetics of multiple drugs used in the treatment of AML and suggest that inherited variability in host transporter function influences the effectiveness of therapy.

ABCC4 Is a Determinant of Cytarabine-Induced Cytotoxicity and Myelosuppression

Resistance to cytarabine remains a major challenge in the treatment of acute myeloid leukemia (AML). Based on previous studies implicating ABCC4/MRP4 in the transport of nucleosides, we hypothesized that cytarabine is sensitive to ABCC4‐mediated efflux, thereby decreasing its cytotoxic response against AML blasts. The uptake of cytarabine and its monophosphate metabolite was found to be facilitated in ABCC4‐expressing vesicles and intracellular retention was significantly impaired by overexpression of human ABCC4 or mouse Abcc4 (P < 0.05). ABCC4 was expressed highly in AML primary blasts and cell lines, and cytotoxicity of cytarabine in cells was increased in the presence of the ABCC4 inhibitors MK571 or sorafenib, as well as after ABCC4 siRNA. In Abcc4‐null mice, cytarabine‐induced hematological toxicity was enhanced and ex vivo colony‐forming assays showed that Abcc4‐deficiency sensitized myeloid progenitors to cytarabine. Collectively, these studies demonstrate that ABCC4 plays a protective role against cytarabine‐mediated insults in leukemic and host myeloid cells.

Abstract 5464: Host variation in OATP1B1 is associated with treatment outcome in pediatric AML

Improvements in survival have been achieved for children and adolescents with acute myeloid leukemia (AML), with the 5-year survival rate increasing between 1975 and 2010 from &lt;20% to 70%. However in the past decade, outcome has not improved. Therapeutic approach in AML consists of intensive combination chemotherapy and hematopoietic stem cell transplantation. Although several prognostic factors have been identified, current predictive analysis remains inadequate. We performed a pharmacogenetic-association study on leukemic and/or germline DNA of 164 pediatric patients with AML receiving cytarabine (Ara-C), daunorubicin (Dauno), etoposide (VP16) and mitoxantrone (MTZ) using the DMET platform involving 1,936 variants in 225 genes related to drug metabolism and transport. After adjusting for age, risk group and treatment arm, among the top-ranking variants associated with event-free survival (P = 0.0060) and overall survival (P = 0.012) was a silent single-nucleotide polymorphism (SNP) in SLCO1B1 (c.597C&gt;T), a gene encoding the hepatocellular uptake transporter OATP1B1. This SNP was not correlated with gene expression in leukemic blasts (P = 0.58), suggesting the association might be due to a host rather than a leukemia effect. Since this SNP is in strong linkage disequilibrium (P&lt;0.0001) with two non-synonymous coding variants in SLCO1B1 that encode known functional variants OATP1B1*1B (Asn130Asp) and OATP1B1*5 (Val174Ala), we hypothesized that one or more of the AML drugs may be a substrate of OATP1B1. In vitro transport studies using mammalian cells stably transfected with OATP1B1*1A (wild-type) revealed that the intracellular uptake of Ara-C, Dauno, VP16 and MTZ was enhanced compared with control cells in a time- and concentration-dependent manner. Moreover, the efficiency of drug transport was impaired in cells expressing either OATP1B1*1B or OATP1B1*5, or both (OATP1B1*15) compared with OATP1B1*1A. To test whether Ara-C, Dauno, VP16 and/or MTZ are transported by OATP1B-type carriers in vivo, we determined the pharmacokinetic profile of these agents (1-100 mg/kg; i.v. or i.p.) in mice deficient in the ortholog transporter Oatp1b2 [Oatp1b2(-/-) mice]. We found the concentrations of Dauno, VP16 and MTZ in livers of Oatp1b2(-/-) mice were reduced (1.4-2.8 fold) compared to wild-type mice, and this phenomenon was accompanied by significant increases in plasma area under the curve. Despite being a transported substrate of OATP1B1*1A and Oatp1b2 in vitro (4.7-fold vs control), plasma concentrations of Ara-C were not affected by Oatp1b2 deficiency, which may reflect a differential contribution of the liver in drug elimination between different species. Collectively, these findings indicate an important role for OATP1B1 in the systemic pharmacokinetics of multiple drugs used in the treatment of pediatric AML and suggest that inherited variability in host transporter function may indirectly regulate the effectiveness of therapy.

Citation Format: Christina D. Drenberg, Stanley Pounds, Lei Shi, Shelley Orwick, Lie Li, Shuiying Hu, Alice Gibson, Raul Ribeiro, Jeffrey Rubnitz, Alex Sparreboom, Sharyn D. Baker. Host variation in OATP1B1 is associated with treatment outcome in pediatric AML. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5464. doi:10.1158/1538-7445.AM2015-5464

Abstract C170: GDC-0941 inhibits cytarabine-induced PI3K/AKT signaling and promotes synergistic activity in acute myeloid leukemia

Introduction: We previously identified genes associated with cytarabine (AraC) response in acute myeloid leukemia (AML) and demonstrated increased expression of PIK3C3 to be significantly associated with a detrimental pattern of association (p=0.016) and multiple phenotypes (increased DNA synthesis, increased blast AraC IC50, poor clinical response, and worse event free survival) (Lamba et al., 2011). Here we evaluate the anti-leukemic activity of a selective PI3K inhibitor, GDC-0941, alone and in combination with AraC.

Methods and Materials: A panel of 6 AML cell lines were assessed for potential activity of GDC-0941 alone (0.0625-4µM) and in combination with AraC (72h continuous, 4h pulse sequential or simultaneous exposure). We assessed cell viability by MTT assay and implemented the median effect approach to determine if combination drug effects, assessed as the combination index (CI) value, were synergistic, additive, or antagonistic. Induction of apoptosis and alterations in cell cycle were detected by caspase activation and propidium iodide staining, respectively. Western blot analyses were performed to determine drug effects on expression of PI3K isoforms, pAkt, pS6, and pErk signaling. Ex vivo cytotoxicity assays were performed on leukemic blasts isolated from murine primary c-Myc recipients to determine sensitivity to GDC-0941, AraC, and the combination. To evaluate in vivo efficacy, survival studies were performed using a c-Myc induced murine model of AML. Sublethally irradiated (550cGy) syngeneic tertiary recipients were randomized to receive vehicle, GDC-0941 (50mg/kg daily x 5 days, po), AraC (100mg/kg daily x 5 days, ip) or combination (week 1: AraC100mg/kg daily x 5 days; week 2: GDC-0941 50mg/kg daily x 5,) (N=8/treatment arm). Pharmacodynamic assessment of pAkt levels in leukemic blasts among the different treatment arms were also evaluated.

Results: GDC-0941 treatment reduced cell viability in a dose-dependent manner and IC50s ranged from 0.36-4µM in AML cell lines. Caspase activity was induced by GDC-0941 alone and enhanced with the combination. For combination treatment, CI values were synergistic in all but 1 cell line (range, 0.20-0.97). Western blot analyses of the U937 cell line revealed that AraC induced both PI3Kα and pAkt signaling which could be abrogated by cotreatment with GDC-0941. Ex vivo combination drug treatments of c-Myc leukemic blasts demonstrated synergistic CI values. Combination treatment significantly prolonged survival in the c-Myc AML model compared to either drug alone or controls (control, median survival=21; GDC-0941, median survival=22; AraC, median survival=26; combination, median survival=28 days; p=0.01 and p=0.03 for AraC vs control and combination vs AraC, respectively)

Conclusions: Our results show that AraC mediated induction of PI3Kα and pAkt in AML cells can be augmented by selective targeting of the PI3K/Akt pathway with GDC-0941. From these lines of preclinical evidence, combination of AraC with PI3K inhibitors is a promising strategy to enhance AraC efficacy in AML.

Citation Information: Mol Cancer Ther 2013;12(11 Suppl):C170.

Citation Format: Christina D. Drenberg, Brian Fermanski, Steven Zatechka, Yiping Fan, Shelley Orwick, Laura Janke, Sharyn D. Baker. GDC-0941 inhibits cytarabine-induced PI3K/AKT signaling and promotes synergistic activity in acute myeloid leukemia. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr C170.

Abstract 3208: Semaphorin 3F suppresses telomerase activity

Objectives: Telomerase is a ribonucleoprotein that is active in more than 90% of human tumors, including ovarian cancers. We have previously demonstrated that vascular endothelial growth factor (VEGF) stimulates telomerase activity in ovarian cancer cell lines through cellular VEGF receptors and the ERK1/2 pathway targeting Sp1 sites within the hTERT promoter. Since semaphorin 3F (S3F), a proposed tumor suppressor, has been shown to antagonize VEGF, the purpose of this study was to determine whether S3F inhibits telomerase

Methods: Telomerase-positive ovarian cancer cell lines (OV2008, C-13, SW626) and telomerase-negative non-tumorigenic, SV-40 large-T antigen-transfected human ovarian surface epithelium (HOSE) cell lines were evaluated for endogenous RNA and protein expression of S3F, VEGF, and their shared receptors. Cultured cells were either treated with recombinant S3F protein or transiently transfected with cDNA to over-express S3F. Conversely, these cells were transiently transfected with siRNA targeting S3F ± specific receptor inhibitors. RT-PCR and western blot confirmed S3F over-expression, knock-down of S3F, or inhibition of receptors. Telomerase activity was measured by telomerase PCR-ELISA, while RT-PCR and western immunoblotting were utilized to detect S3F as well as to explore the signaling pathway involved in S3F-mediated telomerase regulation.

Results: Telomerase activity was suppressed in ovarian cancer cell lines following treatment with S3F recombinant protein or S3F over-expression by transient transfection. Furthermore, siRNAs targeting S3F and NP-2 or treatment with the VEGF receptor inhibitor, CBO-P11, abrogated S3F mediated telomerase inhibition. Over-expression of S3F resulted in up-regulation of phosphorylation of Erk1/2.

Conclusions: These data suggest that telomerase is a novel molecular target of S3F. Since, angiogenic and angiostatic factors play an important role in ovarian cancer tumorigenesis, S3F-mediated inhibition of telomerase represents a potential novel target for therapeutic intervention.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3208.