Citations

Abstract Background: Overall survival (OS) remains the definitive primary efficacy endpoint to evaluate previously untreated acute myeloid leukemia (AML) therapies, but it requires prolonged follow-up. An earlier endpoint assessed post-treatment would expedite clinical trial conduct and accelerate patient access to effective new therapies. Our objective was to formally evaluate event-free survival (EFS) as a surrogate endpoint for OS in untreated AML. Methods: Individual patient data were analyzed from 2,475 patients (pts) from 4 multicenter, randomized controlled phase III trials of active treatment in previously untreated AML using anthracycline and cytarabine induction chemotherapy as the concurrent control (CALGB 10201, n=506, enrollment period 2003-2006, age 60-88 years (y); CALGB 10603, n=717, enrollment period 2008-2015, age 18-60 y, FLT3-mutated pts only; SWOG 0106, n=595, enrollment period 2004-2009, age 18-60 y; ECOG-ACRIN 1900, n=657, enrollment period 2002-2008, age 17-60 y). Individual patient-level surrogacy examines the association between the individual patients' EFS and OS time after adjusting for treatment effect, and was assessed using the copula bivariate survival model (Kendall's tau). Trial-level surrogacy measures how precisely the treatment effect on OS can be predicted on the basis of observed treatment effect on EFS, and was evaluated using both linear regression (R2WLS) weighted by trial size and Copula bivariate (R2Copula) models. Pre-specified criteria for surrogacy required either R2WLS or R2Copula ≥0.80, neither below 0.7, with either lower bound 95% Confidence Interval (CI) >0.60. Sensitivity analyses were conducted using different EFS definitions (Table 1). Results: With a median follow-up of 50.2 months for the 896 patients still alive, the median OS and EFS across all four trials were 20.9 months (95% CI: 19.0-22.7) and 5.6 months (95% CI: 4.5-6.4), respectively. Trial-level surrogacy for EFS was strong (R2WLS=0.79; R2Copula=0.89), indicating a high correlation of treatment effect between EFS and OS. At the individual patient-level, however, EFS showed weak association with OS (tau= 0.52), compared to the strength of trial-level surrogacy. The discrepancy between patient-level EFS and OS was greatest among patients who did not achieve a CR, followed by those who achieved a CR but relapsed (Figure 1). Sensitivity analysis on alternative EFS definitions showed that the trial-level surrogacy was similar, but individual patient-level surrogacy varied across different EFS definitions (Table 1). This is consistent with what we previously reported (ASH 2016): EFS estimates differed considerably based on the definition of induction failure (IF) in a single arm setting, but this had minimal impact on the estimation of the treatment effect using EFS in randomized trials. In addition, when considering only relapse and death as events (definition 4), both individual patient- and trial-level correlations were high. Conclusions: Correlation between EFS and OS was impacted by patients not achieving CR during induction. Despite the lack of patient-level correlation, a strong correlation between hazard ratios for treatment effects was observed between EFS and OS on the trial level. Hence, it remains debatable whether EFS represents a clinical benefit in itself for patient with untreated AML considering the strong correlation in treatment effects. Further validation is needed due to the small number of trials included and the heterogeneity across trials. Acknowledgment: We gratefully acknowledge the important contributions of the late Dr. Stephen H. Petersdorf, SWOG S0106 Study Chair. Support: U10CA180821, U10CA180882, U10CA180794, U10CA180820, U10CA180888; Clinicaltrials.gov Identifiers: NCT00085124 (10201), NCT00651261 (10603), NCT01253070 (11001), NCT00085709 (SWOG S0106), and NCT00049517 (ECOG-ACRIN E1900) Disclosures Uy: Curis: Consultancy; GlycoMimetics: Consultancy. Larson:Pfizer: Consultancy, Research Funding; BristolMyers Squibb: Consultancy, Research Funding; Novartis: Consultancy, Research Funding; Ariad/Takeda: Consultancy, Research Funding.

Abstract Abstract 845 Background: Waldenstrom's macroglobulinemia (WM) is a relatively uncommon plasma cell disorder and most of previous literature is limited to small patient series. We have noted ethnic disparities in multiple myeloma, another plasma cell disorder. We undertook a large Surveillance Epidemiology and End Results (SEER) based analysis to describe outcome disparities in different subgroups of WM patients, with a focus on various ethnicities, so that therapeutic resources can be targeted more effectively. Methods: The SEER 17 Registry data (1973–2008) was utilized for patients with confirmed diagnosis of WM. To avoid bias of under representation of different ethnicities, analysis was restricted to patients with a diagnosis date of 1992 or later. Cases that received a diagnosis at death certificate or autopsy, no follow-up records, as well as lacking documentation on age at diagnosis, sex, or race/ethnicity were excluded. Cox proportional hazards models, adjusted for gender, age, race, year of diagnosis, marital status and stratified by SEER registries were used to evaluate associatio n between patient characteristics and survival. All statistical tests were two-sided and utilized the SAS software (v9.2) with a significance level of 0.05. Results: The final analysis included 2,840 WM patients (1,759 males; 62%, 1,081 females; 38%). The studied age-group cohorts included: 18–64 yrs (845; 30%), 65–74 yrs (795; 28%) and >75 yrs (1,200; 42%). Patients were stratified by race/ethnicity: White (2,471; 87%), African-American (AA) (102; 4%), Hispanic (133; 5%), Asian (129; 5%), and Native American (5; 0.1%). Patients were also stratified based on year of diagnosis (before or after 2002) to study the impact of certain novel agents (proteasome inhibitors, IMiDs) on WM treatment. There was a significant difference in the age at diagnosis of WM patients across different ethnicities, with AA the youngest (median 61.5 years) and Whites the oldest (median 73 years) subgroup (p<0.001). (Figure 1) Cause-specific mortality could not be evaluated due to variable documentation of reported causes of death for WM patients in the database. Survival analysis revealed that for all patients, females had better median overall survival (OS) than males (7.3 years vs. 6.2 years, HR 0.834; 95% CI 0.740, 0.939; p=0.003). Among the different age cohorts, patients with age ≥75 years had a significantly worse median OS (4.1 years) than those 65–74 year-old (7.3 years) or 18–64 year-old (10+ years) (p<0.001). Patients diagnosed after 2002 had a significantly better median OS (7.3 years) as compared to patients diagnosed previously (6.1 years) (p=0.002). Hispanics had the worst median OS (5 years) and Whites had the best median OS (6.8 years) across various ethnicities. In a multivariate model using gender, age, marital status, year of diagnosis and race, a significant interaction was noted between race, age and survival, with Hispanics having a significantly worse OS than Whites (HR 1.86; 95% CI 1.269, 2.726; p=0.003) (Figure 2). Conclusions: Studies of outcome disparities are important for evaluating disease characteristics and management needs of specific patient populations as well as optimal triaging of healthcare resources. We have performed the largest population-based analysis for WM including various ethnicities in the novel therapeutic agent era. We observed that AA patients had a significantly younger age at WM diagnosis. Older patients had worse OS across all ethnic subgroups and patients diagnosed after 2002 had a better OS suggesting an impact of novel therapeutic agents (e.g., proteasome inhibitors, IMiDs). Hispanic WM patients had the worst OS among all ethnicities. This survival difference was more significant and pronounced in patients >75 years. This suggests that the impact of race on survival is influenced by patient's age. These results will help in better understanding of various influences on disease biology and clinical behavior. Disclosures: No relevant conflicts of interest to declare.

Abstract Abstract 602 The molecular target(s) which co-operate with proteasome inhibition in inducing drug sensitivity or resistance in Multiple Myeloma (MM) remain unknown. We therefore conducted a genome scale small interfering RNA (siRNA) lethality study in KMS11 MM cells in the presence or absence of bortezomib without regard to pre-conceived mechanistic notions. Primary screening was performed in a single-siRNA-per-well format with the human druggable genome siRNA set V4 comprising 13,984 siRNA targeting 6,992 genes and comprising two RNAi per gene. siRNA were transfected at low concentration (13nM) to minimize off-target effects using conditions that resulted in transfection of >95% cells and <5% background cytotoxicity. Bortezomib was added (at the IC10, 25, 70 and 90) 24 hours post transfection. After 96 hours (72 hours after bortezomib), viability was measured by ATP-dependent luminescence. In primary screening 320 candidate bortezomib sensitizing genes were identified and rescreened with four siRNA oligos each gene. 57 of the top sensitizer hits were selected for which at least two distinct siRNA decreased the EC50 by 2 standard deviations from cells treated with control siRNAs. By cross referencing gene expression profile (GEP) data of KMS11, we furthered pared the list to 37 plausibly expressed targets (0.5% of those genes originally screened) as bortezomib sensitizers. After silencing, 50% of these 37 genes also sensitized the lung cancer cell line A549 to bortezomib. After further parsing of genes which also modulated the sensitivity of MM to Melphalan (non specific chemosensitizers), 34 genes remained: The strongest sensitizers to bortezomib were the proteasome subunits PSMA5, PSMB2, PSMB3, PSMB7 but included less obvious targets such as BAZ1B, CDK5, CDC42SE2, MDM4, NME7, TFE3, TNFAIP3, TNK1, TOP1, VAMP2 and YY1 were also identified. Of these, the most potent synergetic effects were observed with siRNAs against the proteasome subunits and against cyclin dependent kinase 5 (CDK5), which caused the greatest shift in EC50. CDK5 is of particular interest as a therapeutic target as it is expressed at high levels in MM and neural tissues but has low expression in other organs. Using viral shRNA expression, silencing CDK5 consistently increased the sensitivity of genetically variable MM cell lines (n=5) to all of the proteasome inhibitors tested: bortezomib, carfilzomib and PR047, and the effect could be at least partially rescued by overexpression of an RNAi resistant CDK5. To explore therapeutic relevance the small molecule CDK5 inhibitor, Roscovitin, was shown to be synergistic or additive with bortezomib in both MM cell lines and primary patient samples. Gene expression profiling was then performed to seek an explanation for the CDK5 sensitization effect and regulation of a proteasome subunit PSMB5 by CDK5 was identified as a probable route to sensitization. In summary inhibition of the existing proteasome either directly by suppression of proteasome subunits, or indirectly by suppression of modulators such as CDK5 appears to confer the greatest sensitization effect suggesting that combinations of bortezomib with other unique proteasome inhibitor drugs or combinations with inhibitors of CDK5 is a logical avenue for clinical exploration. Disclosures: No relevant conflicts of interest to declare.

Abstract Abstract 601 A paucity of validated kinase targets in human multiple myeloma (MM) has delayed clinical deployment of kinase inhibitors in treatment strategies. We therefore conducted a kinome-wide small interfering RNA (siRNA) lethality study in MM tumor lines bearing common t(4;14), t(14;16) and t(11;14) translocations to identify critically vulnerable kinases in MM tumor cells without regard to preconceived mechanistic notions. Primary screening was performed in duplicate using an 1800-oligo siRNA library in a single-siRNA-per-well format. siRNA were transfected at low concentration (13nM) to minimize off-target effects using conditions that resulted in transfection of >95% cells and <5% background cytotoxicity. After 96 hours, viability was measured by ATP-dependent luminescence. Fifteen kinases were consistently vulnerable in MM cells, including AKT1, AK3L1, AURKA, AURKB, CDC2L1, CDK5R2, FES, FLT4, GAK, GRK6, HK1, PKN1, PLK1, SMG1, and TNK2. While several kinases (PLK1, HK1) were equally vulnerable in epithelial cells, others and particularly the G-protein coupled receptor kinase, GRK6, appeared selectively vulnerable in MM. GRK6 inhibition is selectively lethal to KMS11, OPM1, H929, KMS18 and OCI-MY5 myeloma cells and has minimal effect on 293, MCF7, SF767, A375 or A549 epithelial cells. Persistent expression of FLAG-GRK6 via cDNA rescued KMS11 cells from the lethal effect of a 3'UTR-targeted GRK6 siRNA, but not from control siRNA, validating identification of GRK6 as an essential myeloma survival kinase. Furthermore, concordant results were obtained using four different exon-based GRK6 siRNA, all of which induced GRK6 silencing and similar inhibition of KMS11 proliferation and viability. Significantly, GRK6 is ubiquitously expressed in lymphoid tissues and myeloma, but by comparison appears absent or only weakly expressed in most primary human somatic tissues. From co-immunoprecipitation experiments we demonstrate that GRK6 is highly expressed in myeloma cells via direct association with the HSP90 chaperone. Inhibition of HSP90 with geldanamycin blocks GRK6 protein expression. Importantly, direct GRK6 silencing causes rapid and selective suppression of STAT3 phosphorylation that is associated with sustained reductions in total MCL1 protein levels and MCL1 phosphorylation (within 24 hours), providing a potent mechanism for the cytotoxicity of GRK6 inhibition in MM tumor cells. GF109203X is an inhibitor of both protein kinase C and of GRK6 that causes near total inhibition of these kinases in vitro at distinct concentrations of 0.1μM and 1-10μM respectively. Notably, GF109203X was substantially cytotoxic to 10/14 myeloma tumor lines at concentrations most consistent with GRK6 inhibition (5-20μM), and was selectively more cytotoxic to myeloma tumor cells than to non-myeloma cell lines (P=0.01), highlighting the potential of GRK6 as a pharmaceutical target for selective therapeutic intervention in myeloma. As mice that lack GRK6 are healthy, inhibition of GRK6 represents a uniquely targeted novel therapeutic strategy in human multiple myeloma. Disclosures: Perkins: MMRC: Employment. Reeder:Celgene: Research Funding; Millennium: Research Funding. Fonseca:Otsuka: Consultancy; BMS: Consultancy; Amgen: Consultancy; Medtronic: Consultancy; Genzyme: Consultancy.

Abstract Background: CP-751,871, a fully human IgG2 subtype monoclonal antibody, is a potent and specific inhibitor of the insulin- like growth factor type I receptor (IGF-IR). The IGF-IR regulates the growth, survival, adhesion and invasiveness of multiple myeloma cells. High IGF-IR expression is observed in poor-prognostic subtypes of multiple myeloma and its inhibition has been long proposed as a potential therapeutic approach for treatment of this disease. Methods: A phase 1 dose escalation study was conducted to define the safety and tolerability, and to characterize the pharmacokinetic and pharmacodynamic (granulocyte surface IGF-IR expression and serum IGF-I levels) properties of CP-751,871 in patients with multiple myeloma. Patient’s eligibility included previously treated multiple myeloma in relapse or refractory phase including those less than complete remission to autologous stem cell transplant or tandem transplant. Results: Following informed consent and screening, 47 patients were enrolled into 11 dose-escalation cohorts of CP-751,871 at doses from 0.025 to 20 mg/Kg. Median patient age was 60 years. Median number of previous regimens was 4 (range 1–8). CP-751,871 was given as an IV infusion on Day 1 of 4-week cycles. Patients with a suboptimal response to CP-751,871 alone were eligible to receive CP-751,871 in combination with either oral dexamethasone and/or rapamycin at the discretion of the investigator. Twenty-seven patients received CP-751, 871 in combination with dexamethasone, while four patients received rapamycin in combination with either CP-751,871 or CP-751,871 and dexamethasone. Median number of treatment cycles was 3 (range 1–16). Ten patients were dosed at the highest cohort of 20 mg/Kg. No CP-751,871 related dose limiting toxicities were identified. Grade 3 toxicities were all observed at the 20 mg/Kg cohort (1 hyperglycemia, 1 anemia, 1 AST increase, 1 accidental fall, 1 muscle weakness). Plasma CP-751,871 exposure increased with dose, and the pharmacokinetic characteristics were consistent with target-mediated disposition. Granulocyte IGF-IR expression was maximally down-regulated for the entire duration of the dosing period at doses ≥1.5 mg/kg, indicating a saturation of circulating targets. CP-751,871 also led to a dose-dependent increase in circulating IGF-I concentrations. Tumor response was assessed according to Blade criteria. Two remissions and 4 partial remissions were reported in patients treated with different doses of CP-751,871 in combination with dexamethasone. Interestingly, the 2 patients with remission were previously found to be refractory to dexamethasone treatment. Conclusions: These data indicate that CP-751,871 is well tolerated either as a single agent or in combination with dexamethasone. Furthermore, CP-751,981 in combination with dexamethasone, may constitute a novel and effective therapeutic approach for patients with multiple myeloma.

Abstract Abstract 229 Introduction: Optimal rational combination targets with Cytarabine (AraC) have not been identified. After the development of a high-throughput, small-interfering RNA (siRNA) platform for suspension cells, we performed the first RNAi sensitizer screen of the human kinome with AraC in myeloid cell lines. Herein we present the final data of this first siRNA-sensitizer screen in leukemias in combination with AraC. Our results include full validation of the selected targets as well as ex vivo data assessing the first in class clinically tested WEE1 inhibitor MK1775 with AraC providing a pre-clinical rationale for using the combination of AraC with WEE1 inhibitors in leukemias. RNAi Screens and siRNA Validation: In siRNA sensitizer screens, we silenced 572 kinases of the human kinome in combination with AraC. Few kinases strongly sensitized to AraC and the targets CHEK1 and the WEE1 related kinase PKMYT1 emerged as the most potent genes whose silencing sensitized leukemia cells to AraC. In secondary siRNA validation experiments, silencing of WEE1 kinase was found to be more potent than silencing of CHEK1, PKMYT1 or other kinases (i.e. ATR, BRCA, AURKB) in combination with AraC treatment. Importantly, the sensitizing activity observed with WEE1 inhibition was universal across all AML cell lines examined, whereas it was not for CHEK1 inhibition. siRNA assays were robust, exhibiting little (<10%) non-specific toxicity and siRNA silencing was specific for individual genes (i.e. WEE1 or CHEK1) as demonstrated by selective reduction of mRNA and protein level for the respective genes; confirming the validity of the siRNA assay. Pharmacological WEE1 Inhibitor Experiments In vitro and Ex vivo: In vitro treatment of eight AML, ALL and CML cell lines with commercial and the first clinically developed WEE1 kinase inhibitor MK1775, demonstrated strong sensitization to AraC up to 97-fold in individual cell lines. Ex vivo, MK1775 substantially reduced viability in 13 of 14 AML, MDS and CML patient samples compared to AraC alone. The optimal dose to achieve maximum sensitization was observed for AraC between ∼10–120 nM and for MK1775 between 200–400 nM. Synergy at these optimal concentrations was confirmed in all ex vivo samples tested for which sufficient data for analysis with CalcuSyn Software was available (n=7): with Combination Indices (CI) ranging from 0.21–0.45. At higher AraC and MK1775 concentrations antagonism was observed both ex vivo and in vitro. Thus, we have also established optimal suggested concentration dose ranges for the currently ongoing design of a clinical trial. Clinically relevant, WEE1 is expressed in primary AML, ALL and advanced CML specimens with a trend towards higher expression in relapsed samples. However, there was no direct correlation with WEE1 mRNA expression or TP53 status. Our initial in vitro experiments further suggest that inhibition of WEE1 with MK1775 in combination with AraC at optimal concentrations was associated with higher degree of caspase 3 cleavage, DNA damage induction as measured by gamma-H2AX, and greatest inhibition of proliferation. Thereby establishing a context of optimal drug concentration ranges with molecular correlates and anti-leukemic activity directly informing design of the clinical trial and correlative biomarkers. In conclusion, data from this first siRNA sensitizer screen of the kinome in leukemias identifies inhibition of WEE1 kinase as the most potent sensitizing target to AraC. Inhibiting WEE1 with pharmacological inhibitors in combination with AraC is a rational treatment strategy for myeloid and lymphoid leukemias that warrants clinical investigation. Furthermore, our RNAi loss-of-function genomics approach has high potential to rapidly identify and validate crucial genes whose inhibition modulate the response to cytotoxic agents. Establishment of the siRNA sensitizer platform allows accelerating the development of new rational combinations for leukemia therapy. Disclosures: Off Label Use: AraC in combination with the experimental Wee1 inhibitor MK1775. Mesa:NS Pharma: Research Funding; Astra Zeneca: Research Funding; SBio: Research Funding; Lilly: Research Funding; Incyte: Research Funding; Celgene: Research Funding. Demuth:Merck and CO: Employment.

Abstract Background: Potent inhibitors of BCR-ABL1have improved remission results and altered post-remission therapy for Philadelphia chromosome-positive (Ph+) acute lymphoblastic leukemia (ALL). Dasatinib plus dexamethasone followed by hematopoietic cell transplantation (HCT) promises high response rates, reduced toxicity, and durable remissions. Methods: We conducted a Phase II trial at 17 U.S. centers with the primary objective being to estimate the 3-year overall survival and disease-free survival of patients with Ph+ ALL treated with dasatinib and dexamethasone for remission induction and intensification, central nervous system (CNS) prophylaxis, consolidation with reduced-intensity conditioning (RIC) allogeneic HCT, autologous HCT, or etoposide and cytarabine, and dasatinib-based maintenance. Eligible patients had untreated Ph+ ALL, were ≥18 years old, and had normal cardiac function. Induction (Course I) used dasatinib 140 mg oral daily and dexamethasone 10 mg/m2/day oral or intravenous (IV) days 1-7. For patients with ≤20% blasts in the Course I, Day 15 bone marrow biopsy, intensification (course II) continued daily dasatinib with another 7 days of dexamethasone. Those with >20% lymphoblasts also received vincristine (VCR) and daunorubicin (DNR). Patients (n=3) not in CR/CRi after Course II received a second induction (Course III) with dasatinib, cyclophosphamide, VCR, DNR, and dexamethasone. After Course II or III, CNS prophylaxis (Course IV) consisted of IV VCR and IV, oral, and intrathecal methotrexate (MTX). Dasatinib was restarted at serum [MTX] <0.05 microM. Course V consisted of HCT or chemotherapy. Patients aged 18-70 years with an HLA-matched donor underwent RIC allogeneic HCT; otherwise they underwent autologous HCT. Allogeneic HCT conditioning used fludarabine 30 mg/m2/day IV day -7 through -3, alemtuzumab 20 mg/day IV day -7 through -3, and melphalan 140 mg/m2 once on day -2. GVHD prophylaxis with tacrolimus began day -2. Patients undergoing autologous HCT received etoposide 10 mg/kg/day (age >65 years, 5 mg/kg/day) continuous IV for 4 days and cytarabine 2 g/m2 (age >65 years, 1 g/m2) IV every 12 hours for 8 doses (EA) then G-CSF for mobilization. Autologous HCT conditioning used melphalan 100 mg/m2/day on days -2 and -1. Patients >70 years or unable to undergo HCT received EA alone. Dasatinib maintenance (Course VI) began on day 30 of Course V and continued for 12 months and until 2 consecutively negative bone marrow BCR-ABL1RT-PCR assays 3 months apart or until relapse. Dasatinib levels were measured on day 15 of induction. Results: Sixty-six patients enrolled from 12/15/2010 to 11/14/2014; 65 received dasatinib and are evaluable. Median age was 60 years (22-87); 49% were male. Median presenting WBC count was 23.1 x 103/ul (0.3-453.6). No deaths occurred during induction or intensification. CR or CRi occurred 31 patients (48%) by Day 15 of induction and in 62 patients overall (95%; CR 86%). Median dasatinib levels in serum and CSF on Day 15 of induction were 30.3 ng/mL (<3-308) and 0.29 ng/mL (<0.2-1.37), respectively suggesting approximately 1% of plasma dasatinib penetrates into the CSF, less than the unbound fraction (6%). Fifty-four patients started Course IV, 38 Course V, and 37 Course VI. Fourteen patients continue on protocol therapy. Of 38 patients receiving Course V, 22 had allogeneic HCT, 6 had autologous HCT, and 10 had EA chemotherapy. Median age of allogeneic HCT recipients was 61 years (31-69). Robust autologous stem cell mobilization was observed [median CD34+ cell count, 90 x 106/kg (31-166, n=6)]. Dasatinib maintenance was feasible after allogeneic HCT, autologous HCT, and chemotherapy alone with no missed doses in 59%, 83%, and 63% of cycles, respectively. Ten patients have relapsed with one isolated CNS relapse. No relapses have occurred after allogeneic HCT with 3 relapses after autologous HCT and one after Course V EA alone. Median follow up for survivors is 22.8 months (longest, 51 months). There have been 23 deaths: 5 treatment-related (4 after allogeneic HCT, 1 after course V EA), 16 disease-related and 2 unrelated. Conclusions: Dasatinib with dexamethasone yields CR rates comparable to those reported with tyrosine kinase inhibitors combined with conventional chemotherapy. Post-remission therapy with reduced-intensity allogeneic HCT, autologous HCT, or chemotherapy followed by dasatinib maintenance is feasible. Survival follow up is maturing. Disclosures Stock: Sigma-Tau: Honoraria, Research Funding; Royalties for a chapter in Up to Date: Patents & Royalties; ADC Therapeutics: Honoraria; Amgen: Honoraria; Gilead Sciences: Honoraria. Beumer:Bristol-Myers Squibb: Research Funding. Stone:Abbvie: Consultancy, Membership on an entity's Board of Directors or advisory committees; Pfizer: Consultancy; Juno Therapeutics: Consultancy; Karyopharm: Consultancy; Sunesis Pharmaceuticals: Consultancy; Agios: Consultancy; Amgen: Consultancy; Celator: Consultancy; Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy; Jansen: Consultancy; Merck: Consultancy; ONO: Consultancy; Roche: Consultancy; Seattle Genetics: Consultancy; Xenetic Biosciences: Consultancy. Larson:Bristol-Myers Squibb: Consultancy; Astellas: Consultancy, Research Funding.

Abstract The lysine deacetylase inhibitor suberoylanilide acid (SAHA) exhibits promising but limited activity in the treatment of acute myeloid leukemia (AML). To identify potential targets for rational combination therapies that increase the efficacy of SAHA in AML, we performed a functional RNA-interference (RNAi) drug modifier screen to identify genes that, when inhibited, potentiate or antagonize the in vitro anti-leukemic activity of SAHA. A total of 901 kinase, phosphatase and closely associated signaling genes were silenced in TF-1, HEL and THP-1 cells, with four different siRNA sequences per gene, both alone and in combination with SAHA treatment. Screen hit lists for each cell line were over-laid on an integrated functional relationship network. A community detection algorithm was then applied to this sub-network and siRNA sensitive modules were identified. Each module represents a highly connected set of genes in the integrated network. To identify pathways represented by each module, enrichment was evaluated using the National Cancer Institute (NCI) Protein Interaction Database (PID) pathways. Both cell line-specific and universal sensitizing targets, grouped into a small number of pathways, emerged from these screens. Seven pharmacologic inhibitors interfering with these pathways have been assessed in a panel of four or five AML cell lines, including SET-2, TF-1, HEL, THP-1, and OCI-AML3. Of the seven tested inhibitors targeting SAHA sensitizing networks, one combination exhibiting universal SAHA sensitization in all AML cell lines tested was further assessed in drug dose response assays using ex vivo cultures of bone marrow mononuclear cell populations derived from patients with various myeloid malignancies. The combination demonstrated “one-sided” SAHA EC50 fold-enhancement, as well as strong synergy by “two-sided” CalcuSyn combination index determination in all ex vivo specimens examined to date (N=6), including polycythemia vera (PV), chronic myelomonocytic leukemia (CMML), myelodysplastic syndrome/myeloproliferative neoplasm (MDS/MPN) overlap syndrome, MDS transformed to AML, and de novo AML samples. Thus, this first reported large-scale SAHA RNAi modifier screen in AML has identified a specific pathway/target whose inhibition broadly synergizes with HDAC inhibition in myeloid malignancies. A novel compound putatively targeting this respective pathway/target is currently in early clinical development and has shown limited single-agent activity. With the full dataset presented, we will propose a novel rational combination to enhance the activity of HDAC inhibition in AML and other myeloid malignancies that could be translated into design of a clinical trial. Disclosures: No relevant conflicts of interest to declare.

Abstract Abstract 2801 Poster Board II-777 To provide a rationale basis for targeted drug development for multiple myeloma patients, we have conducted high-throughput genome-scale RNA interference (RNAi) synthetic lethality studies in human myeloma cell lines (HMCL) to generate a comprehensive map of critical genes and molecular vulnerabilities in human myeloma tumor cells. KMS11 human myeloma cells were screened with a 13,982-oligo library targeting the ‘druggable' genome (6,991 genes) using optimized conditions that resulted in >95% transfection efficiency. Each gene was screened with 2 or more distinct oligos, in duplicate, using a single-siRNA-per-well format, testing >34,000 wells. Replicate high throughput experiments yielded highly reproducible results (R2=0.82). Viability was measured at 96h by ATP-dependent luminescence. Universally lethal siRNA and non-targeted siRNA were employed as controls. The specificity (FDR) of lethal RNAi was evaluated by custom-developed statistical methods based on RNAi result concordancy. From screening, 5.8% of druggable genome siRNA caused statistically relevant reductions in HMCL viability (greater than three standard deviations from control samples treated with non-silencing siRNA, compared with an anticipated rate due to chance of only 0.135%). Of these, two hundred and nineteen genes, targeted by the most lethal siRNA, were forwarded to validation studies. Validation high-throughput RNAi studies, using 4 oligos per gene, were conducted in order to verify target gene vulnerability. Ultimately, seventy two genes were validated as highly critical for myeloma cell survival (each with multiple concordant siRNA hits plus high reproducibility of R2 =0.94). Among top-ranked lethal molecular vulnerabilities in KMS11 myeloma cells we recurrently identified the proteasome (8 PSM subunits were independently identified as highly vulnerable); and BCL2 family member MCL1; both known therapeutic targets, validating a functional genomics approach to target discovery. In addition, a number of novel, equally lethal, molecular vulnerabilities were identified in KMS11 including WEE1, kinetochore complex component KNTC2, the aurora kinases, polo-like kinase 1, a previously uncharacterized DNA methyl transferase, ribonucleotide reductase, ribosomal protein L38, leptin receptor overlapping transcript LEPROT and SLC25A23 (a carrier responsible for mitochondrial adenine nucleotide flux). Various ubiquitous cellular proteins involved in RNA or protein processing (e.g. SF3a, SNW1, SNRPA1, EIF3s8, amongst others) were also identified as non redundant and critical for cellular viability. Thirty nine top-ranked molecular vulnerabilities in KMS11 were evaluated for comparative vulnerability in a second myeloma cell line, JJN3, and in A549 and 293 epithelial cells. A majority were vulnerable in JJN3. While 25 genes proved equally lethal on silencing in A549 and 293 epithelial cells, several, notably including MCL1 and three proteasome subunits, appear differentially susceptible in myeloma cells versus epithelial cells. From this genome scale study, MCL1 ranks third as a target capable of inducing cell death in myeloma cells, highlighting the potent vulnerability of myeloma cell viability to alterations in this anti-apoptosis regulator. Moreover, from active comparative studies of molecular vulnerability in myeloma versus epithelial cell lines, MCL1 as an RNAi target demonstrates perhaps the greatest cytotoxic selectivity between myeloma and epithelial cell lines of all targets examined. Gene expression studies indicate that MCL1 is highly expressed in myeloma tumor cells but is absent or only weakly expressed in human primary somatic tissues. Overall, therefore, from an unsupervised genome-scale screening approach, our data support MCL1 as an optimal Achilles heel molecular target in multiple myeloma, potentially offering greater specificity and deeper cytotoxic effect than proteasome inhibition. Disclosures: No relevant conflicts of interest to declare.

Abstract Background: Event free survival (EFS) is often used as an endpoint in AML clinical trials. EFS-based endpoints are controversial due to the lack of a consistent definition for the timing of complete remission (CR), and consideration of hematopoietic cell transplantation (HCT). Here, we examined the impact of the timing of achievement of CR and censoring for HCT in the estimation of the EFS, and assessed its robustness as an endpoint in AML. Methods: All prospective trials since 2003 using anthracycline and cytarabine chemotherapy for newly diagnosed patients (pts) with AML conducted through the Alliance for Clinical Trials in Oncology, and whose primary endpoint data has been reported, were included (5 trials total). Trial 1 - randomized phase III study in older AML pts (n=504, median age 69, 61% male); trial 2 - single-arm phase II study in older FLT3-mutated AML pts (n=54, median age 67, 56% male); trial 3 - randomized phase III study in younger AML pts (n=546, median age 48, 55% male); trial 4 - randomized phase III study in younger FLT3-mutated AML pts (n=717, median age 48, 45% male); and trial 5 - single arm phase II study in core-binding factor AML pts with no restriction on age (n=61, median age 51, 51% male). Induction failure was defined as one of: no CR by 60 days (Definition 1), no CR by the end of all protocol induction courses (Definition 2), or no CR by the end of all protocol treatment (Definition 3). CR was defined as <5% blasts in a cellular marrow with recovery of >1000 neutrophils/ul (>1500 neutrophils/ul for trial 1), >100,000 platelets/ul, and no red cell transfusion requirement. EFS was defined as the time from randomization / registration to the first evidence of induction failure using each of the 3 methods above, relapse, or death from any cause. Patients last known to be alive without relapse were censored at the date of last contact. Including the 3 induction failure definitions and consideration of censoring or no censoring for HCT, the Kaplan Meier estimates of EFS were computed for the six different definitions of EFS. Results: The number of deaths was respectively 464, 38, 307, 357, and 13 across the 5 trials, with a median follow-up of 99.7, 28.2, 60.1, 58.2, and 33.5 months on the alive patients, respectively. Not considering HCT, in trial 1, the median EFS ranged from 2.0 to 4.3 months (115% difference); in trial 2, the median EFS ranged from 6.9 to 8.3 months (20% difference); in trial 3, the median EFS ranged from 9.8 to11.2 months (14% difference); and in trial 4, the median EFS ranged from 5.5 to 9.7 months (76% difference). The median EFS was not achieved in trial 5; however the 1-year EFS estimates ranged from 78 to 83% (6% difference). Consistently across all trials, as expected, the EFS estimate using the 60-day induction failure yielded the shortest estimates, whereas the end-of-treatment induction failure yielded the longest estimates. Results were similar both with and without censoring at the time of HCT as the event of interest occurred prior to transplantation in most cases. Conclusions: Although relapse and death are firm endpoints, the determination of failure to achieve CR is not consistent across studies. While there is minimal impact of censoring at HCT on EFS estimates, the median EFS estimates differed considerably based on the timing of CR used to define induction failure, with the magnitude of difference being large enough in most cases (observed range: 14% to >100%) to lead to incorrect conclusions about efficacy in a single arm trial if the trial definition was not consistent with the definition used for the historical control. The timing of CR should be carefully examined in the historical control data used to guide the design of the next trial. Table. Table. Disclosures Uy: Glycomimetics: Consultancy; Boehringer Ingelheim: Consultancy. Stone:Celator: Consultancy; Abbvie: Consultancy, Membership on an entity's Board of Directors or advisory committees; Agios: Consultancy; Amgen: Consultancy; Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees; Karyopharm: Consultancy; Novartis: Consultancy; Jansen: Consultancy; Pfizer: Consultancy; ONO: Consultancy; Juno Therapeutics: Consultancy; Merck: Consultancy; Roche: Consultancy; Seattle Genetics: Consultancy; Sunesis Pharmaceuticals: Consultancy; Xenetic Biosciences: Consultancy.