ALBERT

Description: Background: R/R DLBCL remains an area of unmet medical need and treatments with novel mechanisms of action are urgently needed. Germinal center DLBCLs depend on the histone methyltransferase EZH2 to perpetuate a less-differentiated state and EZH2 activating mutations may be oncogenic drivers in a subset of patients (pts). Inhibition of EZH2 reprograms abnormal cell growth, leading to cell death or differentiation, and subsequent tumor regression. Tazemetostat, a potent, selective, oral EZH2 inhibitor has shown antitumor activity in a phase 1 study that included DLBCL pts with mutated (mt) or wild type (wt) EZH2 tumors, which provides rationale for further investigation of its single agent activity. This open-label, multicenter phase 2 study is evaluating tazemetostat in pts with either mt or wt EZH2 R/R DLBCL or follicular lymphoma (Grade 1-3b); results of an interim analysis of DLBCL pts treated with tazemetostat, as monotherapy or in combination with prednisolone are presented. Methods: Key inclusion criteria include: age ≥18 years, ≥2 prior treatment regimens, and measurable disease. Tazmetostat 800 mg is administered orally, twice daily (BID); prednisolone (40 mg/m2) on days 1 to 5 and days 15 to 19 in a 28-day cycle for 16 weeks. Response was assessed every 8 weeks using IWG-NHL assessment criteria (Cheson 2007). Tumor tissue was analyzed for EZH2 hot spot activating mutations (Y646X, A682G, A692V) using a cobas® EZH2 Mutation Test (Roche Molecular Systems; investigational use only). Hans algorithm was used to determine cell of origin. The primary endpoint is overall response rate (ORR). Secondary endpoints include progression-free survival (PFS), duration of response (DOR) and safety/tolerability. Results: As of May 1, 2018, interim phase 2 safety and activity data were summarized from 226 DLBCL pts (intent to treat analysis). Demographic and clinical activity information are provided in the table, including ORRs of 17% in both mt and wt arms and 9% in the prednisolone arm. Notably, DOR was substantially greater in the mt arm. Safety analysis showed that treatment-emergent adverse events (TEAE) leading to study drug discontinuation or withdrawal from study occurred in 12% of pts. Grade ≥3 treatment-related AEs were reported in 27% of pts. The most common (≥10%) TEAEs (all grades) were: thrombocytopenia (20%), nausea (17%), anemia (15%), neutropenia (15%), vomiting (15%), cough (14%), diarrhea (12%), fatigue (12%), pyrexia (12%), abdominal pain (11%) and asthenia (10%). Conclusion: Tazemetostat was generally well tolerated at a dose of 800 mg BID, as monotherapy or in combination with prednisolone. In this difficult to treat, heavily pretreated, refractory patient population, clinical activity was observed in approximately 20% of monotherapy pts, regardless of mutational status, many of whom had received multiple prior lines of therapy. Tazemetostat in combination with prednisolone did not result in improved activity compared with tazemetostat monotherapy. Disclosures Ribrag: Servier, Pharmamar, Nanostring, Gilead, Infinity, BMS, MSD, Epizyme: Consultancy; Roche: Other: Travel, expenses, accommodation; ESAI: Honoraria, Research Funding. Morschhauser:Epizyme: Consultancy; Roche/Genentech: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Gilead: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees; Servier: Membership on an entity's Board of Directors or advisory committees. McKay:Epizyme: Consultancy, Honoraria. Salles:Roche, Jannsen, Gilead, Celgene, Novartis, Amgen, BMS, Merck, Servier: Honoraria. Tilly:Roche: Membership on an entity's Board of Directors or advisory committees; BMS: Honoraria; Astra-Zeneca: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Karyopharm: Membership on an entity's Board of Directors or advisory committees. Cartron:Sanofi: Honoraria; Roche: Consultancy, Honoraria; Gilead Sciences: Honoraria; Janssen: Honoraria; Celgene: Consultancy, Honoraria. Gribben:Unum: Equity Ownership; Novartis: Honoraria; TG Therapeutics: Honoraria; Abbvie: Honoraria; Medical Research Council: Research Funding; Janssen: Honoraria, Research Funding; Roche: Honoraria; NIH: Research Funding; Wellcome Trust: Research Funding; Cancer Research UK: Research Funding; Pharmacyclics: Honoraria; Kite: Honoraria; Acerta Pharma: Honoraria, Research Funding; Celgene: Consultancy, Honoraria, Research Funding. Dickinson:GSK: Consultancy. Opat:Roche, Celgene, Mundipharma, Janssen: Honoraria; Roche, Celgene, Mundipharma, Janssen: Consultancy. Adib:Epizyme: Employment, Equity Ownership. Blakemore:Epizyme: Employment, Equity Ownership. Larus:Epizyme: Employment, Equity Ownership. Johnson:Zenyaku Kogyo: Other: Travel, accommodations, expenses; Eisai: Research Funding; Incyte: Consultancy; Genmab: Consultancy; Kite: Consultancy; Boeringher Ingelheim: Consultancy; Epizyme: Consultancy, Honoraria, Research Funding; Janssen: Consultancy, Research Funding; Celgene: Honoraria; Novartis: Honoraria; Takeda: Honoraria, Travel, accommodations, expenses; Bristol-Myers Squibb: Honoraria.

Description: Introduction: B-cell malignancies may depend on the histone methyltransferase EZH2 to perpetuate a less differentiated state, with activating mutations of EZH2 being potential oncogenic drivers. Tazemetostat, a potent, selective EZH2 inhibitor, is in phase 2 clinical development in relapsed or refractory (R/R) non-Hodgkin lymphoma (NHL). Objective responses were observed in patients (pts) with EZH2 mutant or wild type tumors in the phase 1 part of the phase 1/2 study. The ongoing phase 2 study is enrolling pts with mutant or wild type EZH2 having R/R diffuse large B-cell lymphoma (DLBCL) or follicular lymphoma (FL) to determine efficacy and safety. The primary endpoint is overall response rate. Here we report results of an updated molecular analysis of archived tumor and circulating tumor DNA (ctDNA) collected from pts plasma and associations with preliminary response data, including the discovery of novel candidate molecular predictors of tazemetostat response. Methods: Archived tumor and/or plasma-derived ctDNA samples were obtained during screening from R/R DLBCL and FL pts enrolled to the phase 2 trial of tazemetostat in NHL (NCT01897571). Next generation sequencing was performed retrospectively on archived tumor DNA (target coverage of 1,500X) and ctDNA (20,000X for somatic mutations and 5,000X for structural alterations). DNA was isolated from archived tumor and was tested across a panel of approximately 200 genes, including 62 genes commonly altered in NHL to identify somatic mutations, amplifications, and translocations. The ctDNA sequencing was restricted to the 62 gene NHL panel. Best objective overall response data (Cheson 2007) as of May 1, 2018 were used to generate two groups: responders (R = CR + PR), and non-responders (NR = progressive disease, stable disease, or unknown clinical response). Fisher's exact test (two tailed) was performed to identify DNA variants associated with either the R or NR groups for FL+DLBCL combined and for each NHL sub-type independently (Table 1). All gene associations met an unadjusted P-value threshold of ≤ 0.1. Results: In the combined analysis for all NHL pts, EZH2, BRCA2, ETV6, IKZF3 and TNFRSF14 mutations were associated with clinical response. Eleven genes, including BCL6, BCL2, TP53, PIM1, HIST1H1B and HIST1H1E, mutations were associated with a lack of response to tazemetostat. Association of detection of mutations in EZH2, BCL6 and HIST1H1E and response were detected in both ctDNA and archived tumor analysis, with all other genes achieving P ≤ 0.1 in either the ctDNA or the archived tumor analysis. Analysis of the NHL subcategories revealed in FL that mutations in EZH2 and STAT6 were associated with clinical response while mutations in BCL2, TNFAIP3, FOXO1 and MYD88 were identified as negative predictors. EZH2 was the only gene identified in both the ctDNA and archived tumor analyses in FL. In DLBCL, while EZH2 was not detected as a predictor of response to tazemetostat at P ≤ 0.1, the number of pts with mutant rather than wild type EZH2 was higher in responders than non-responders in both analyses. Positive predictors of tazemetostat response were detected in DLBCL: MYD88, MEF2B, ETV6, MLH1, RECQL4, and RNF43. Negative predictors of response were also identified in DLBCL: BCL2, PDL1, PDL2 and SOCS1. When the genes identified as associated with tazemetostat response in DLBCL were compared between the archived tumor and ctDNA analyses, no genes in common were identified. Conclusions: These analyses confirm genes previously described as potential predictors of tazemetostat response in analyses using smaller patient numbers and less mature clinical response data such as STAT6, EZH2, MYD88, TP53,BCL2, BCL6, PIM1 and HIST1H1E. In addition, identification of PDL1/PDL2 and RECQL4/MLH1/BRCA2 as novel predictors points to potential relevance of immune checkpoint and DNA damage repair pathways as additional pathways that may be of relevance to tazemetostat response in NHL. Subanalyses performed independently on each NHL subtype revealed disease specific biomarkers of response that may point to differences in the factors that can influence response to tazemetostat in DLBCL and FL. Disclosures McDonald: Epizyme: Employment, Equity Ownership. Thomas:Epizyme: Employment, Equity Ownership. Daigle:Epizyme: Employment, Equity Ownership. Morschhauser:Epizyme: Consultancy; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Roche/Genentech: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Gilead: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees; Servier: Membership on an entity's Board of Directors or advisory committees. Salles:Morphosys: Honoraria; Servier: Honoraria; Janssen: Honoraria, Other: Advisory Board; Takeda: Honoraria; Pfizer: Honoraria; Servier: Honoraria, Other: Advisory Board; Merck: Honoraria; BMS: Honoraria, Other: Advisory Board; Gilead: Honoraria, Other: Advisory Board; Amgen: Honoraria; Epizyme: Honoraria; Acerta: Honoraria; Abbvie: Honoraria; Celgene: Honoraria, Other: Advisory Board, Research Funding; F. Hoffmann-La Roche Ltd: Consultancy, Honoraria, Research Funding; Novartis: Consultancy, Honoraria. Ribrag:Servier, Pharmamar, Nanostring, Gilead, Infinity, BMS, MSD, Epizyme: Consultancy; ESAI: Honoraria, Research Funding; Roche: Other: Travel, expenses, accommodation. McKay:Epizyme: Consultancy, Honoraria. Tilly:Astra-Zeneca: Membership on an entity's Board of Directors or advisory committees; Karyopharm: Membership on an entity's Board of Directors or advisory committees; Roche: Membership on an entity's Board of Directors or advisory committees; BMS: Honoraria; Celgene: Membership on an entity's Board of Directors or advisory committees. Johnson:Kite: Consultancy; Genmab: Consultancy; Incyte: Consultancy; Zenyaku Kogyo: Other: Travel, accommodations, expenses; Bristol-Myers Squibb: Honoraria; Eisai: Research Funding; Takeda: Honoraria, Travel, accommodations, expenses; Boeringher Ingelheim: Consultancy; Epizyme: Consultancy, Honoraria, Research Funding; Janssen: Consultancy, Research Funding; Celgene: Honoraria; Novartis: Honoraria. Dickinson:GSK: Consultancy. Opat:Roche, Celgene, Mundipharma, Janssen: Honoraria; Roche, Celgene, Mundipharma, Janssen: Consultancy. Jurczak:Gilead: Consultancy; Morphosys: Research Funding; Roche: Research Funding; Servier: Research Funding; TG Therapeutics: Research Funding; Merck: Research Funding; Pharmacyclics: Research Funding; European Medicines Agency: Consultancy; AstraZeneca/Acerta: Consultancy, Research Funding; Sandoz-Nowartis: Consultancy; Afimed: Research Funding; BeiGene: Research Funding; Celgene: Research Funding; Epizyme: Research Funding; Gilead: Research Funding; Janssen: Research Funding; Nordic Nanovector: Research Funding; Janssen: Consultancy. Cartron:Gilead Sciences: Honoraria; Celgene: Consultancy, Honoraria; Janssen: Honoraria; Sanofi: Honoraria; Roche: Consultancy, Honoraria. Zinzani:Merck: Honoraria, Membership on an entity's Board of Directors or advisory committees; Roche: Honoraria, Membership on an entity's Board of Directors or advisory committees; PFIZER: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Speakers Bureau; Bayer: Membership on an entity's Board of Directors or advisory committees; Celltrion: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Bayer: Membership on an entity's Board of Directors or advisory committees; MSD: Honoraria, Speakers Bureau; Astra Zeneca: Speakers Bureau; Merck: Honoraria, Membership on an entity's Board of Directors or advisory committees; Gilead: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Verastem: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; SERVIER: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; TG Pharmaceuticals: Honoraria, Membership on an entity's Board of Directors or advisory committees; TG Pharmaceuticals: Honoraria, Membership on an entity's Board of Directors or advisory committees; PFIZER: Honoraria, Membership on an entity's Board of Directors or advisory committees; Takeda: Membership on an entity's Board of Directors or advisory committees. Assouline:Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Pfizer: Honoraria, Research Funding, Speakers Bureau; BMS: Honoraria, Research Funding, Speakers Bureau; Novartis: Research Funding; Roche: Honoraria, Research Funding, Speakers Bureau. Radford:BMS: Consultancy, Speakers Bureau; Seattle Genetics: Consultancy, Speakers Bureau; Novartis: Consultancy, Speakers Bureau; Pfizer: Research Funding; Celgene: Research Funding; Takeda: Consultancy, Research Funding, Speakers Bureau; GlaxoSmithKline: Equity Ownership; AstraZeneca: Equity Ownership; ADC Therapeutics: Consultancy, Research Funding. Gribben:Novartis: Honoraria; Medical Research Council: Research Funding; Acerta Pharma: Honoraria, Research Funding; Roche: Honoraria; Abbvie: Honoraria; Cancer Research UK: Research Funding; Kite: Honoraria; NIH: Research Funding; Celgene: Consultancy, Honoraria, Research Funding; Janssen: Honoraria, Research Funding; TG Therapeutics: Honoraria; Pharmacyclics: Honoraria; Unum: Equity Ownership; Wellcome Trust: Research Funding. Haioun:Celgene: Consultancy, Honoraria; Amgen: Consultancy, Honoraria; Takeda: Consultancy, Honoraria; Sciences: Consultancy, Honoraria; Gilead Sciences: Consultancy, Honoraria; Janssen: Consultancy, Honoraria; Roche: Consultancy, Honoraria. Le Gouill:Roche: Consultancy, Honoraria; Janssen-Cilag: Consultancy, Honoraria. Clawson:Epizyme: Employment, Equity Ownership. Larus:Epizyme: Employment, Equity Ownership. Blakemore:Epizyme: Employment, Equity Ownership.

Description: Key Points A high frequency of RAS/RAF mutations and recurrent mutations in PDGFRA and JAK3 were found in relapsed multiple myeloma patients. Patients with NRAS, but not KRAS, mutation exhibited significantly reduced sensitivity to bortezomib but not high-dose dexamethasone.

Description: Introduction: Aberrant fusion proteins involving the MLL histone methyltransferase (HMT) result in recruitment of another HMT, DOT1L, to a multi-protein complex. This leads to abnormal methylation of Histone H3 lysine 79 (H3K79) at MLL target genes and enhanced expression of leukemogenic genes such as HOXA9 and MEIS1 ( Krivstov, 2007). Pinometostat is a small molecule inhibitor of DOT1L with sub-nanomolar affinity and 〉37,000 fold selectivity against non-MLL HMTs. Pinometostat treatment of MLL-rearranged cells and xenografts reduced histone H3K79 methylation, decreased MLL target gene expression, and induced selective leukemia cell kill (Daigle, 2013). We report the safety, activity, pharmacokinetics (PK) and pharmacodynamics (PD) in the phase 1 trial of pinometostat in adult patients (pts) with relapsed/refractory (R/R) leukemia. Methods: This open label dose escalation/expansion study of pinometostat enrolled pts 〉18 years (yrs) with R/R leukemia (NCT01684150). In the dose-escalation phase, pts with AML, ALL, mixed lineage leukemia (MLL), myelodysplastic syndrome, myeloproliferative neoplasm or chronic myeloid leukemia were eligible. Eligibility in the two expansion cohorts: 90 mg/m2 (n = 17) and 54 mg/m2 (n = 6), was restricted to pts with MLL-r or MLL-partial tandem duplication (MLL-PTD). Pinometostat was given via continuous intravenous infusion (CIV) for 21 of 28 day cycles in the dose escalation phase and CIV for 28 of 28 day cycles in the expansion phases, until disease progression or unacceptable toxicity. All pts underwent serial collection of PK and peripheral blood mononuclear cells (PBMC) for PD. Leukemic blasts were isolated from PBMCs using flow cytometry and quantified for dimethylation of H3K79 (H3K79-me2) by ChIP-Seq. Results: As of 28-June-2015, 49 pts have enrolled in the dose escalation and expansion phases. Pts receiving 21/28 day infusions: 12 (n=1), 24 (n=5), 36 (n=4), 54 (n=6) and 80 mg/m2/day (n=3). Pts receiving 28/28 day infusions: 54 (n=6) and 90 mg/m2/day (n=24). Table 1. Patient Characteristics n (%) Median age, yrs (range) 51 (19 - 81) Sex (M / F) 27/22 Diagnosis MLL-r* 29 (59) AML MLL-PTD** 5 (9) MLL-wt 7 (14) ALL MLL-r* 5 (10) MLL-wt 1 (2) MLL MLL-r 1 (2) CMML MLL-r 1 (2) # of prior therapeutic regimens 1 - 2 29 (59) 3 - 4 18 (36) 〉4 2 (4) Prior allogeneic hematopoietic cell transplant 20 (41) * centrally confirmed by karyotype/FISH ** centrally confirmed by NGS (next generation sequencing) Adverse events (AEs) reported in 〉15% of pts regardless of attribution were: nausea, constipation, vomiting, abdominal pain, diarrhea, hypocalcemia, hypokalemia, hypomagnesemia, fatigue, fever, peripheral edema, mucositis, febrile neutropenia, leukocytosis, anemia, cough, dyspnea, and pneumonia. Grade ≥3 non-hematologic related toxicities include: hypophosphatemia (n=1), decreased ejection fraction (n=3), or elevated transaminases (n=1). Nine patients had leukocytosis (absolute monocyte and neutrophil 50% above baseline and above upper limit of normal) or differentiation. The median days of pinometostat treatment was 35 days (range 3-189 days). To date, objective responses observed are morphologic CR (1 pt), cytogenetic CR (MLL negative by FISH) (1 pt), PR (1 pt) and resolution of leukemia cutis (3 pts). Dose proportional PK was observed with rapid attainment of steady-state plasma concentrations (Css) on Day 1 of treatment. Plasma Css correlated with inhibition of global H3K79-me2 in PBMCs. H3K79-me2 ChIP-Seq demonstrated pinometostat induced reductions in methylation at MLL -r target genes HOXA9 and MEIS1 (median inhibition = 61%: range = 13-91%) in all 9 pts analyzed to date from the 90 mg/m2 expansion cohort. Inhibition of H3K79-me2 in leukemic blasts is consistent with DOT1L suppression. PK-PD relationships in both expansion cohorts using both free and total plasma Css are being explored. Conclusions: Pinometostat administered as a CIV to adults with R/R leukemia has an acceptable safety profile. Clinical activity as demonstrated by both marrow responses and resolution of leukemia cutis were observed. In addition, analysis of H3K79-me2 by ChIP-Seq demonstrated PD reductions in the methylation of MLL-r target genes following pinometostat exposure, as expected from DOT1L inhibition. Relationships between PK exposure, reductions in pinometostat induced H3K79-me2 levels and clinical response are being interrogated. Disclosures Stein: Seattle Genetics: Consultancy; Agios Pharmaceuticals: Consultancy. Rizzieri:Teva: Other: ad board, Speakers Bureau; Celgene: Other: ad board, Speakers Bureau. Berdeja:Novartis: Research Funding; Takeda: Research Funding; BMS: Research Funding; Curis: Research Funding; MEI: Research Funding; Abbvie: Research Funding; Onyx: Research Funding; Array: Research Funding; Janssen: Research Funding; Celgene: Research Funding; Acetylon: Research Funding. Altman:Novartis: Other: Advisory board; Spectrum: Other: Advisory board; Ariad: Other: Advisory board; Seattle Genetics: Other: Advisory board; BMS: Other: Advisory board; Astellas: Other: Participation in an advisory board December 2013. Thomson:Epizyme, Inc: Employment. Blakemore:Epizyme: Employment. Daigle:Epizyme, Inc: Employment. Fine:Epizyme: Employment. Waters:Epizyme, Inc: Employment. Armstrong:Epizyme, Inc: Consultancy. Ho:Epizyme, Inc: Employment.

Description: Introduction: MLL-rearranged (MLL-r) acute leukemia in children is characterized by young age at presentation and a poor overall prognosis despite multi-agent chemotherapy. Aberrant fusion proteins involving the MLL histone methyltransferase (HMT) recruit another HMT, DOT1L, to a multi-protein complex leading to aberrant methylation of histone H3 lysine 79 (H3K79) at MLL target genes. This results in enhanced expression of critical genes for hematopoietic differentiation, including HOXA9 and MEIS1, and has been established as a key mechanism for leukemogenesis in MLL-r leukemias (Krivstov, 2007). Pinometostat is a small molecule inhibitor of DOT1L with sub-nanomolar affinity and 〉37,000 fold selectivity against non-MLL HMTs. Treatment of MLL-rearranged cells and xenograft models with pinometostat led to reduced histone 3 lysine 79 methylation (H3K79me2), decreased MLL target gene expression and selective leukemia cell kill (Daigle, 2013). Here we report the final results of the pinometostat phase 1 trial in children with relapsed/refractory (R/R) MLL-r acute leukemia. Methods: An open label dose escalation study of pinometostat was performed in patients (pts) aged 3 months to 18 years (yr) with R/R MLL-r leukemia (NCT02141828). Pinometostat was administered via continuous intravenous infusion (CIV) until disease progression or unacceptable toxicity. Pts were assigned to one of two aged-based dose escalation schemas developed from simulations of pediatric exposures using a previously reported physiologically-based PK (PBPK) model (Waters, 2014). All patients underwent serial collection of PK and peripheral blood mononuclear cells (PBMC). Leukemic blasts were isolated from PBMCs using flow cytometry and quantified for H3K79me2 levels by ChIP-Seq. Results: 18 pts were enrolled on study with 9 pts dosed at 70 mg/m2/day and 7 pts at 90 mg/m2/day in the older age cohort (1 to 18 yr) plus 2 pts dosed at 45 mg/m2/day in the younger age cohort (20% of pts were: febrile neutropenia; anemia; leukopenia; thrombocytopenia; hypokalemia; respiratory failure; lymphopenia; neutropenia. Drug-related TEAEs reported in 〉15% of pts were: anemia; thrombocytopenia; leukopenia; rash; lymphopenia; hypocalcemia; hypophosphatemia; neutropenia; ALT elevation; nausea; vomiting. Dose-limiting toxicities (DLT) were: apnea (70 mg/m2); elevated transaminases (2 at 90 mg/m2) in the 〉1 year of age cohort, thus defining 70 mg/m2 as the recommended phase 2 dose (RP2D) in older pts. A RP2D was not determined in pts 〈 1 year of age. Median duration of treatment was 23 days (range 7- 53 days). Pinometostat induced transient decreases in peripheral or marrow leukemic blasts in 7/18 pts, however, these reductions did not meet formal thresholds for objective response. Adjusted mean plasma pinometostat concentrations during the infusion in children 〉1 yr at 70 and 90 mg/m2/d doses (1151 ng/mL) was comparable to mean steady-state concentrations observed in adult patients at the 80 mg/m2/d and 90 mg/m2/d doses (1320 ng/mL and 1410 ng/mL, respectively) and was within the range of 1000-1600 ng/mL at 90 mg/m2/d in ≥ 1 yr predicted by earlier PBPK modeling results. CSF concentrations of pinometostat were below the lower limit of quantification of 1 ng/mL (n = 8) or very low (〈 12 ng/mL) (n = 4), suggesting negligible CSF exposure. H3K79me2 ChIP-Seq on leukemic blasts demonstrated that pinometostat induced reductions in methylation at MLL-r target genes (e.g. HOXA9 and MEIS1) of ≥ 80 % at all post dose time points (15 and 28 days) and doses (70 & 90 mg/m2) tested consistent with DOT1L inhibition. Conclusions: In pediatric pts with R/R MLL-r pinometostat has an acceptable safety profile with a RP2D defined as 70 mg/m2 CIV in children 〉 1 yr. Pinometostat dose/exposure relationships were comparable between adults and children 〉 1 yr. Pharmacodynamic evidence of DOT1L inhibition was observed in leukemic blasts. Transient reductions in peripheral or bone marrow blasts were detected in ~40 % of pts, however no objective responses were observed. Based on the biological activity observed and evidence of combination benefit of pinometostat with standard of care and novel agents in preclinical MLL-r models (Daigle 2015 and Klaus 2015) further clinical investigation of pinometostat combinations is warranted. Figure Figure. Disclosures O'Brien: Seattle Genetics: Research Funding; Celgene: Other: travel expenses for required site investigator meeting, October 2015;; steering committee member for pediatric AML trial, Research Funding; Epizyme: Research Funding; Amgen: Other: participated in one pediatric advisory board for blinatumomab in May 2015, paid consultant fee and travel expenses, Research Funding. Blakemore:Epizyme: Employment. Daigle:Epizyme: Employment. Suttle:Epizyme: Employment. Armstrong:Epizyme, Inc: Consultancy; Vitae Pharmaceuticals: Consultancy; Imago Biosciences: Consultancy; Janssen Pharmaceutical: Consultancy. Ho:Epizyme: Employment, Equity Ownership.

Description: Abstract 1377 Background: MM is a plasma cell malignancy that remains generally incurable; however, there is significant inter-patient variation in the clinical course of MM and in survival, which is thought to relate, at least in part, to the biological heterogeneity of patients' tumors. At the molecular level, MM is sub-classified by chromosomal translocations, genetic mutations, and risk classifiers that integrate gene expression. Some of these genetic abnormalities have established associations with disease outcome in MM; for example, hyperdiploid patients have a better disease prognosis compared with non-hyperdiploid patients, and patients with a deletion of the p53 locus on chromosome 17 exhibit very poor clinical outcomes compared with patients who do not have this deletion. A better understanding of the molecular diversity of MM will likely inform therapeutic decision making and also identify additional intracellular targets for future drug development. A recent whole genome sequencing study of 38 MM patients described several somatic mutations that had not previously been described in MM or other cancers (Chapman et al, Nature 2011), as well as mutations in known cancer genes that had either not previously been reported in MM (BRAF), or that were observed at a higher frequency in MM than previously reported (KRAS, NRAS). The present study was conducted to confirm the prevalence of mutations in a panel of established cancer genes in tumor samples from patients with relapsed or refractory MM. Methods: Bone marrow aspirates were collected from 133 patients who participated in phase 2 (SUMMIT, CREST) and 3 (APEX) clinical studies of bortezomib for relapsed or refractory MM. Tumor DNA was amplified and screened for mutations in a panel of cancer genes using the MassARRAY®/Sequenom mass spectrometry-based methodology. This custom panel evaluates 514 known mutations in 43 distinct oncogenes and tumor suppressor genes. Mutations were identified with standard software and subsequently verified via manual inspection. Results: The most common mutations observed in MM tumor samples were in KRAS (n=32 [24.1%], 95% CI: 17.0–31.3) and NRAS (n=26 [19.5%], 95% CI: 12.8–26.3); for both genes, mutations in codon 61 were more common (47% and 85% for KRAS and NRAS, respectively) than mutations in codon 13, as previously described for MM (Chng et al, Leukemia 2008). Mutations in BRAF were detected in three patient samples (2.3%, 95% CI: 0–4.8). For all three genes, the mutation rate in this patient population was similar to that reported by Chapman et al (26.3%, 23.7%, and 4% for KRAS, NRAS, and BRAF, respectively). The frequency of mutations in KRAS and NRAS was similar in patients who had received one or more than one prior line of therapy, suggesting that these mutations arise early in the pathogenesis of MM and are not driven by treatment-exerted selection pressures. KRAS, NRAS, and BRAF mutations were mutually exclusive, consistent with their described biological roles in modulating a common signaling pathway. These data suggest that the RAS/RAF pathway is activated by mutation in 45.9% (95% CI: 37.0–54.3) of patients with relapsed or refractory MM. Mutations in a number of other genes, including PIK3CA, TP53, MET, PDGFRA, and JAK3 were detected in at least two patient tumor samples; several of these genes have not previously been reported to be mutated in MM. Conclusions: These data confirm the high prevalence of activating mutations in genes of the RAS/RAF pathway in patients with relapsed or refractory MM, and begin to shed light on additional mutations that may co-operate with or act independently of this key cellular signaling axis. Data on the co-occurrence of these mutations in patients with MM, and their association with clinical outcomes, will be presented. Disclosures: Mulligan: Millennium Pharmaceuticals, Inc.: Employment. Lichter:Millennium Pharmaceuticals, Inc: Employment. Di Bacco:Millennium Pharmaceuticals, Inc: Employment. Blakemore:Millennium Pharmaceuticals, Inc: Employment; Takeda Pharmaceuticals: Equity Ownership. Berger:Millennium Pharmaceuticals, Inc: Employment. Koenig:Millennium Pharmaceuticals, Inc: Employment. Bernard:Millennium Pharmaceuticals, Inc: Employment. Trepicchio:Millennium Pharmaceuticals, Inc: Employment. Li:Millennium Pharmaceuticals, Inc: Employment. Lonial:Bristol-Myers Squibb: Consultancy; Novartis: Consultancy; Celgene: Consultancy; Millennium Pharmaceuticals, Inc.: Consultancy; Onyx: Consultancy; Merck: Consultancy. Richardson:Millennium Pharmaceuticals, Inc.: Consultancy; Johnson & Johnson: Consultancy; Celgene: Consultancy. Anderson:Merck: Consultancy; Onyx: Consultancy; Novartis: Consultancy; Celgene: Consultancy; Millennium Pharmaceuticals, Inc.: Consultancy; Bristol-Myers Squibb: Consultancy; Actelion: Equity Ownership, Membership on an entity's Board of Directors or advisory committees. Sonneveld:Janssen: Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; Millennium Pharmaceuticals, Inc.: Membership on an entity's Board of Directors or advisory committees, Research Funding; Onyx: Membership on an entity's Board of Directors or advisory committees, Research Funding. San Miguel:Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Millennium Pharmaceuticals, Inc: Honoraria, Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees. Esseltine:Millennium Pharmaceuticals, Inc.: Employment; Johnson & Johnson: Equity Ownership. Schu:Millennium Pharmaceuticals, Inc.: Employment.

Description: Introduction: MLL-rearranged (MLL-r) acute leukemia in children is characterized by young age at presentation and a poor overall prognosis despite multi-agent chemotherapy. Aberrant fusion proteins involving the MLL histone methyltransferase (HMT) recruit another HMT, DOT1L, to a multi-protein complex leading to aberrant methylation of histone H3 lysine 79 (H3K79) at MLL target genes. This results in enhanced expression of critical genes for hematopoietic differentiation, including HOXA9 and MEIS1, and has been established as a key mechanism for leukemogenesis in MLL-r leukemias (Krivstov, 2007). Pinometostat is a small molecule inhibitor of DOT1L with sub-nanomolar affinity and 〉37,000 fold selectivity against non-MLL HMTs. Treatment of MLL-rearranged cells and xenograft models with pinometostat led to reduced histone 3, lysine 79 (H3K79) methylation, decreased MLL target gene expression and selective leukemia cell kill (Daigle, 2013). We report the preliminary safety, pharmacokinetics (PK), pharmacodynamics (PD) and target inhibition in leukemia cells of pinometostat in a phase 1 trial in children with relapsed/refractory (R/R) MLL-r acute leukemia. Methods: An open label dose escalation study of pinometostat was performed in patients (pts) aged 3 months to 18 years (yr) with R/R MLL-r leukemia (NCT02141828). Pinometostat was administered via continuous intravenous infusion until disease progression or unacceptable toxicity. Pts were assigned to one of two aged-based dose escalation schemas developed from simulations of pediatric exposures using a previously reported physiologically-based PK (PBPK) model (Waters, 2014). All patients underwent serial collection of PK and peripheral blood mononuclear cells (PBMC) for PD. Leukemic blasts were isolated from PBMCs using flow cytometry and quantified for di-methylation of H3K79 (H3K79-me2) by ChIP-Seq. Results: As of 28-June-2015, 11 pts have enrolled in the dose escalation of the study consisting of 10 pts (6 pts at 70 mg/m2/day, 4 pts at 90 mg/m2/day) in the older age cohort (1 to 18 yr) and 1 pt (45 mg/m2/day) in the younger age cohort (10 1 (9) Prior allogeneic hematopoietic cell transplant 6 (54) Adverse events (AEs) reported in 〉3 pts regardless of attribution were: anemia, febrile neutropenia, abdominal pain, diarrhea, nausea, vomiting, pain, grade 1 prolonged QTcF, lymphopenia, thrombocytopenia, leukopenia, hypocalcemia, hypokalemia, hypophosphatemia, pleural effusion, respiratory failure, dry skin, rash and hypertension. Grade ≥3 related non-hematologic toxicities include: apnea (n=1 and the only protocol defined dose limiting toxicity), organizing pneumonia (n=1), anorexia (n=1), and febrile neutropenia (n=1). The median duration of treatment was 26 days (range 7- 53 days). Updated response data will be provided. Steady-state plasma concentrations (Css) of pinometostat in children 〉1 yr at 70 and 90 mg/m2 doses were comparable to that observed in adult patients at equivalent doses and were in the range of 800 - 1600 ng/mL, corroborating earlier PBPK modeling results (projected Css range of 1000-1600 ng/mL at 90 mg/m2/d in ≥1 yr). Steady-state CSF concentrations of pinometostat were low ( 1 yr. Analysis of H3K79-me2 ChIP-Seq data demonstrated PD reductions in methylation of MLL-r target genes expected from DOT1L inhibition. Enrollment and dose escalation continue. Disclosures O'Brien: Seattle Genetics, Inc.: Research Funding. Pauly:Seattle Genetics, Inc.: Research Funding. Whitlock:Amgen: Honoraria. Thomson:Epizyme, Inc: Employment. Blakemore:Epizyme: Employment. Daigle:Epizyme, Inc: Employment. Pimentel:Epizyme, Inc: Employment. Waters:Epizyme, Inc: Employment. Armstrong:Epizyme, Inc: Consultancy. Ho:Epizyme, Inc: Employment.

Description: Background NEDD8-activating enzyme (NAE) regulates the NEDD8 conjugation pathway, and is required for activity of the cullin-RING E3 ligases (CRLs). CRLs control proteasomal degradation of several substrates involved in cell-cycle regulation, signal transduction, DNA replication and stress response including proteins important for survival of AML cells. MLN4924, a first-in-class NAE inhibitor, has shown antitumor activity in preclinical AML models. This study evaluated safety and tolerability of MLN4924 given on multiple dosing schedules. A maximum tolerated dose (MTD) of 59 mg/m2 given on days 1, 3 and 5 of a 21-day cycle (schedule A) was previously reported (Erba et al, EHA 2011); complete responses were observed in 4/27 patients for this schedule (most common AE: diarrhea [44%], most common Gr ≥3 AE: febrile neutropenia [33%]). Here we report on two additional schedules. Methods Adults with AML or MDS and good performance status received MLN4924 as a 60-min IV infusion on one of two schedules for up to 1 year or until disease progression. Schedule B patients received escalating doses of MLN4924 on days 1, 4, 8 and 11 every 21 days. Schedule E patients received a fixed dose of MLN4924 on days 1, 3 and 5 every 21 days. Adverse events (AEs) and responses were graded according to published guidelines. Serial blood samples were obtained during cycle 1 for pharmacokinetic (PK) and pharmacodynamic analyses. Results On schedule B: 26 patients were enrolled (77% male), median age was 70.5 yrs, 23 had AML and 3 had MDS (2 had advanced disease with marrow blasts exceeding 10%). Patients received MLN4924 at 83 (n=19), 110 (n=4), and 147 mg/m2 (n=3). On Schedule E: 16 patients (69% male) received 50 mg/m2 MLN4924, median age was 70.5 yrs, 14 AML and 2 MDS (1 with advanced disease). Three patients on schedule B had dose-limiting toxicities (DLTs): 1 patient at 110 mg/m2; orthostatic hypotension (Gr 3); 2 patients at 147 mg/m2; cardiac failure (Gr 4; n=1), fatal lactic acidosis, hypotension, gastrointestinal necrosis, acute renal failure and myocardial ischemia (each Gr 4; n=1). On schedule E, 2 patients had DLTs: morbilliform rash (Gr 3; n=1); and increased aspartate/alanine aminotransferases (Gr 2/3; n=1). Most common all-grade and Gr ≥3 AEs are shown in the table. The MTD for Schedule B was determined as 83 mg/m2. On schedules B/E, 3/2 patients received ≥4 cycles, 0/4 remain on treatment; discontinuations were due to progressive disease (11/10), AEs (8/0), and other reasons (7/2) respectively. In 17 patients treated at 83 mg/m2 on schedule B and 16 patients on schedule E, individual PK profiles showed a biphasic disposition phase following completion of the first infusion. MLN4924 plasma concentrations were detectable 24–48 hours (schedule B) and 24 hours (schedule E) post dosing. Schedule B geometric mean (%CV) Cmax was 1255 ng/mL (25.1%), AUC24hr was 3936 ng•h/mL (22.6%); schedule E values were Cmax of 669 ng/mL (24.4%) and AUC24hr of 2614 ng•h/mL (21.4%). Observed increases in mean Cmax and AUC24hr were dose-proportional between 50 and 83 mg/m2 after single dosing. Pharmacodynamic data demonstrated evidence of target and pathway inhibition for all patients on both schedules. On schedule B, of 20 response-evaluable patients (18 AML, 2 MDS), 2 (11%) AML patients had partial responses (PR), 13 (72%) had stable disease. On schedule E, of 12 response-evaluable patients (11 AML, 1 MDS), 1 (8%) AML patient had a PR, 7 (59%) maintained stable disease and the MDS patient (8%) had a response. Conclusions Both schedules appeared to be generally well tolerated and NAE inhibition with MLN4924 resulted in clinical activity in highly refractory/multiply relapsed patients. Based on safety and observed clinical activity across schedules, the recommended phase 2 dose for single agent MLN4924 in AML/MDS is 50 mg/m2 given on days 1, 3 and 5 of a 21-day cycle. A study of MLN4924 with azacitidine in treatment-naïve AML patients older than 60 years is ongoing (NCT01814826). Disclosures: Off Label Use: Investigational agent MLN4924 for the treatment of patients with AML and high-grade or low-grade MDS. Hua:Millennium: The Takeda Oncology Company: Employment. Blakemore:Millennium: The Takeda Oncology Company: Employment. Faessel:Millennium: The Takeda Oncology Company: Employment. Dezube:Millennium: The Takeda Oncology Company: Employment. Medeiros:Millennium: The Takeda Oncology Company: Research Funding.