ALBERT

Description: Abstract 1026 Poster Board I-48 Background: FLT3 mutations (ITD or D835 point mutation) are frequently observed in patients (pts) with AML and they confer an adverse prognosis, particularly among pts with diploid karyotype. This has made FLT3 an important target for drug development in AML. Several FLT3 inhibitors are currently being developed (eg, sorafenib, PKC-412, AC-220, CEP-701, IMC EB10, sunitinib). Results from early trials with many of these agents suggest they have clinical activity in the treatment of MDS and AML, although most responses are represented by a marked decrease in blast counts, with few complete remissions(CR). Whether these responses ultimately improve long-term outcome of pts, and whether they may be particularly beneficial for pts with FLT3 mutations compared to those with FLT3 wild-type (WT) is being investigated. Aims: To ascertain outcomes of patients given treatment with FLT3 inhibitors, alone or in combination with other therapies, and to compare outcomes in those patients with FLT3 mutations (ITD or D835) versus those with FLT3-WT. Methods: We reviewed the records of patients with MDS and AML who were enrolled on clinical trials with FLT3 inhibitors at our institution. We compared patient outcomes in those who received a FLT3 inhibitor in both FLT3 positive and FLT3 negative patients. Pts were classified as receiving FLT3 inhibitors 1) as part of their initial therapy, 2) as first salvage, or 3) as second salvage or beyond. Results: A total of 128 pts were included: 51 (40%) with FLT3-WT, 56 (44%) with FLT3-ITD, 11 (9%) with D835, and 10 (8%) had both FLT3-ITD and D835. The overall median age was 62 yrs (range, 17-88); by FLT3 status, median age was 70 yrs (35-88) for FLT3-WT pts and 58 yrs (17-81) for FLT3 mutated. Sixty-four pts (50%) were female. Twenty-three (18%) pts received FLT3 inhibitors as part of their induction therapy (18 FLT3-WT, 5 FLT3 mutated; median age 74 yrs); 22 (17%) as first salvage (4 FLT3-WT, 18 mutated; median age 67 yrs); and 83 (65%) as second or later salvage (29 FLT3-WT, 54 mutated; median age 59 yrs). Nine pts overall, all of whom were FLT3 mutated, achieved either CR (n=6) or CRp (n=3) with FLT3 inhibitors. Eight of the nine CR/CRp have been lost with a median CR duration of 8 months (mo) (3-12+). After a median follow-up of 3.5 mo, 115 (90%) pts have died, including 47 (92%) FLT3-WT, and 68 (88%) FLT3 mutated. The median survival is 3.8 mo for the total population. Survival by mutation status and timing of FLT3 inhibitor therapy is presented in table 1. Conclusions: Despite the inferior outcome expected for pts with FLT3 mutations, and the low rate of CR/CRp with FLT3 inhibitors, these results suggest that therapy with FLT3 inhibitors has the potential to improve the outcome of pts with FLT3 mutations. Additional studies incorporating these agents in AML therapy are warranted. Disclosures: Off Label Use: Sorafenib has not been FDA approved for use in MDS and AML. Kantarjian:Novartis: Research Funding. Cortes:Ambit: Research Funding; Novartis: Research Funding; ImClone: Research Funding.

Description: Clofarabine (CLO) is a second-generation nucleoside analog with activity in acute leukemias. Whereas it has received FDA approval in children with relapsed acute lymphoblastic leukemia, the focus of clinical research in adults has shifted to AML. To improve single agent activity, various CLO combinations are being studied. Here we present the results of two dose-finding phase I studies, exploring combinations of CLO with idarubicin (IDA) [CI] and CLO+IDA+Ara−C [CIA] in patients (pts) with relapsed or refractory AML and high-risk MDS. Eligibility for CI required previous Ara-C and primary refractory disease, or relapsed AML with first remission duration (CRD1) 〈 12 mos. Eligibility for CIA required either no previous Ara-C or Ara-c with CRD1 ≥ 12 mos. Maximum tolerated dose (MTD) was determined by “3+3” method. Forty-four pts (CI 23; CIA 21) have been accrued and are evaluable. The median age of pts on CI was 56 yrs (range 24–71), 9 were primary refractory and 14 in first relapse (median CRD1 2 mos. [0–9]). Fifteen pts had abnormal cytogenetics (including 6 with -5, -7, or 11q23). Sixteen pts had intermediate- or high-dose Ara-C-based prior therapy, 2 relapsed from allogeneic transplant (SCT). The median age of pts on CIA was 56 yrs (23–78), 8 were primary refractory and 13 in first relapse (median CRD1 9 mos [0–61]). Twelve pts had an abnormal karyotype (-5, -7, or 11q23 in 6 pts). Twelve pts received intermediate dose Ara-C-based prior therapy and 2 failed unrelated donor SCT. The starting dose level of the CI group was CLO 22.5 mg/m2 iv daily x 5d and IDA 12 mg/m2 iv daily x 3d. Three DLTs occurred (diarrhea, rash, ↑ bilirubin) requiring dose de-escalation to CLO 15 mg/m2/d x 5d and IDA 8 mg/m2/d x 3d. Gradual re-escalation led to CLO 30 mg/m2/d x 5d and IDA 10 mg/m2/d x 3d where 2/5 pts experienced DLTs (↑ SGPT, ↑ bilirubin, headache). MTD was defined by the next lower dose level: CLO 22.5 mg/m2/d x 5d and IDA 10 mg/m2/d x 3d. Three (13%) CR occurred. The CIA group started at CLO 22.5 mg/m2/d x 5d, IDA 8 mg/m2/d x 3d, and Ara-C 1g/m2/d x 5d. Two pts developed DLTs (diarrhea, ↑ bilirubin, renal failure) requiring de-escalation to CLO 15 mg/m2/d x 5d, IDA 6 mg/m2/d x 3d, and Ara-C 0.75 g/m2/d x 5d. Re-escalation to CLO 30mg/m2/d x 5d, IDA 6mg/m2/d x 3d, and Ara-C 0.75 g/m2/d x 5d revealed DLTs in 2/6 pts (diarrhea, mucositis, ↑ bilirubin). MTD was thus defined at next lower dose level of CLO 22.5 mg/m2/d x 5d, IDA 6 mg/m2/d x 3d, and Ara-C 0.75 g/m2/d x 5d. Ten (48%) responses (9 CR, 1 CRp) occurred. The higher response rate of CIA may be due to the difference in pt characteristics between the two trials. A phase II study is now in progress adaptively randomizing patients with AML relapse to CI versus CIA versus CLO (40 mg/m2/d x 5d) plus Ara-C (1 g/m2/d x 5d) (as established in an earlier study) to assess activity of the combinations.

Description: Introduction: Approximately 77% of younger pts and 49% of older pts with newly diagnosed AML achieve CR after induction chemotherapy (chemo). The majority of pts who achieve CR eventually relapse, with only approximately 30% of pts maintaining CR for 3 yrs or longer. Long-term outcomes in pts maintaining 1st CR for at least 3 yrs (AML survivors) remain largely unknown. The purpose of this study was to investigate long-term outcomes in this subset of pts. Methods: We performed a chart review of pts with AML treated at our institution from 2000-2015 who achieved CR for at least 3 yrs after their initial chemo ± allogeneic stem cell transplant (ASCT) to analyze their long-term outcomes. Results: 2779 pts with AML were treated between 2000 and 2015 at our institution with 1686 (61%) pts achieving CR. Among them, 455 (27%; 16% of all treated) maintained 1st CR for at least 3 years and constitute the focus of this analysis. Among them 309 received chemo alone and 146 chemo followed by ASCT. The median time from the initiation of induction chemo to the first CR was 29 days [10-207] for the entire cohort, and it was similar for pts treated with chemo only versus those who later received ASCT. Baseline characteristics for AML survivors were as follows: hypertension (HTN) in 27% of pts; dyslipidemia (DLD) in 16%; pulmonary disease in 10%; cardiac disease in 9%; diabetes mellitus (DM) in 9%; depression in 5%, renal disease in 5%; gastroesophageal reflux disease (GERD) in 5%; hypothyroidism in 5%; anxiety in 4%; osteopenia/osteoporosis in 1%. Late relapses (i.e., after 3 years in CR) occurred in 11% of pts - 14% treated with chemo alone and 6% treated with ASCT. Such relapses occurred after a median CR duration of 6 yrs (3-12) and 7 yrs (4-12) respectively. A change in karyotype compared to the original karyotype was seen in 51% of relapsed chemo pts and 56% of relapsed ASCT pts. The most common new cytogenetic abnormalities were 7q del (22%), Trisomy 8 (11%), and 5q del (7%). The two most common mutational status changes seen in relapsed pts were FLT3-ITD appearing in 5% of chemo pts while disappearing in 11% of ASCT pts and FLT3-D835 appearing in 5% of chemo pts while disappearing in 2% of chemo pts. Patients treated with ASCT did not display a change in FLT3-D835. At relapse, TP53 mutation was seen in 7% of pts; however, TP53 status at the time of diagnosis was unknown. A 2nd complete remission (CR2) was achieved in 54% of late relapse pts: 51% of chemo only pts and 67% of ASCT pts. The median CR2 duration was 18 months (mo) [3-127] and 15 [7-23] respectively. The median survival after relapse was 10 mo in chemo only pts and 14 mo in ASCT pts. Of chemo pts who relapsed, 30% underwent an ASCT and 4 ASCT pts received a 2nd ASCT. New comorbidities that were present at or after the 3 yr mark included: HTN in 15%; osteopenia/osteoporosis in 15%; renal disease in 14%; pulmonary disease in 11%; hematologic complications in 11%; DLD in 9%; GERD in 8%; cardiac ailments in 7%; depression and anxiety in 7% and 6% respectively; DM in 6%; hypothyroidism in 4%. Osteopenia/osteoporosis was seen in 39% of ASCT pts and 3% of chemo pts. Renal disease was seen in 23% of ASCT pts and 10% of chemo pts. Pulmonary disease was seen in 16% of ASCT pts and 9% of chemo pts. Second malignancies occurred in 17% of pts with the most common being skin cancer (7%), prostate cancer (2%), breast cancer (1%), and lymphoma (1%). Skin cancer occurred in 12% of ASCT pts and 5% of chemo pts. The median survival for the entire cohort starting from 3 yrs in CR is 10.7 yrs (0.1-14.3) with chemo pts having a median survival of 10.7 yrs (0.1-14.3) and 12.7 yrs (0.1-12.7) for ASCT pts (Fig 1). The most common causes of death (COD) for relapse ASCT pts was relapsed AML (33%), complications secondary to 2nd ASCT (22%), and infection (11%); the most common COD for relapse chemo pts was relapsed AML (47%), complications secondary to ASCT (14%), and second malignancy (2%). The most common COD for CR1 ASCT pts was ASCT-related complications (2%), malignancy (

Description: BCR-ABL1-like B-progenitor acute lymphoblastic leukemia (B-ALL) accounts for 10-15% of childhood B-ALL and is characterized by alteration of IKZFI, a gene expression profile similar to BCR-ABL1 ALL and poor outcome. Using next-generation sequencing, we have shown that BCR-ABL1-like ALL patients harbor genetic alterations activating kinase pathways that are sensitive to tyrosine kinase inhibitors (TKIs), and have shown that refractory BCR-ABL1-like ALL is responsive to TKIs in vivo (Weston et al., J. Clin. Oncol 2013). Furthermore, the outcome of ALL in adolescent and young adult (AYA) patients is inferior to children, yet the genetic basis underlying treatment failure is poorly understood. To define the frequency and genomic landscape of BCR-ABL1-like ALL in children, adolescents, and young adults we have extended our studies to include 665 high-risk childhood (

Description: Abstract 3625 Background: SL-401 is a novel biologic targeted therapy, comprised of human IL-3 coupled to a truncated diphtheria toxin payload that inhibits protein synthesis, directed at the interleukin-3 receptor (IL-3R). IL-3R is overexpressed on leukemia blasts and cancer stem cells (CSCs) relative to normal hematopoietic cells. Since SL-401 uniquely targets both the leukemia blasts (tumor bulk) and CSCs, it would be expected to induce tumor regression (anti-tumor bulk effect), as well as inhibit tumor repopulation (anti-CSC effect), thereby improving survival. SL-401 has been evaluated in a Phase 1/2 clinical trial in patients with advanced hematologic cancers. In this study, SL-401 has demonstrated objective clinical responses, including durable complete responses (CRs) and protracted overall survival (OS) in patients with heavily pretreated AML. The current report is a final analysis of the patients with AML or MDS. Study Design: Seventy-eight patients with advanced hematologic cancers, including relapsed or refractory AML (n = 59), de novo AML unfit for chemotherapy (n = 11), high-risk MDS (n = 7), and other (n = 1), were enrolled in a multicenter study. Among the patients with relapsed or refractory AML, the numbers of patients receiving SL-401 as 2nd, 3rd, or 〉3rd line therapy were 24, 16, and 19, respectively. The median (range) age for AML patients was 65 (7, 84) years. Patients received SL-401 as a 15-minute intravenous infusion in one of two dosing regimens for a single cycle to determine the maximum tolerated dose (MTD) and assess antitumor activity. In Regimen A, 45 patients received doses ranging from 4 to 12.5 μg/kg every other day for up to 6 doses. In Regimen B, 33 patients received doses ranging from 7.1 to 22.1 μg/kg daily for up to 5 doses. Results: A single cycle of SL-401 demonstrated single agent activity in patients with relapsed or refractory AML, including 2 durable CRs of 8 and 〉25 months duration and 5 partial responses (PRs). OS was also notable among patients who received one cycle of SL-401 as ≥3rd line therapy for AML; the median OS was 3.6 (2.3, 6.1) months. Moreover, at therapeutically relevant doses, defined as the MTD or one or two dose levels below the MTD (9.4, 12.5, or 16.6 μg/kg/day), the median OS among AML patients who received SL-401 as ≥3rdline therapy (n = 16) was 5.6 (2.5, 10.8) months. These OS values compared favorably to historical results of 1.5 months for patients treated with standard chemotherapy. SL-401 was well tolerated. The MTD was not achieved with Regimen A, whereas the MTD for Regimen B was 16.6 μg/kg/day, with manifestations of capillary leak syndrome, including hypoalbuminemia and edema, as the dose-limiting toxicity (DLT) at the 22.1 μg/kg/day dose level. Transient (i.e., lasting ≤2 weeks) transaminase elevations were among the most common ≥Grade 3 AEs. Notably, there was no evidence of treatment-related bone marrow suppression. Conclusion: SL-401 demonstrated single agent anti-tumor activity and was well tolerated in patients with advanced AML. Improved survival was observed among patients who received a single cycle of SL-401 as ≥3rd line treatment, a disease setting in which there is no standard therapy. SL-401 may be an attractive treatment option for these patients given their tendency to be myelosuppressed and therefore are often poor candidates for myelosupressive therapies that have limited benefit on clinical response and survival in this setting. Based on these positive findings, SL-401 will be advanced into a randomized Phase 2b trial to treat patients with AML in the 3rd line setting. Patients will be randomized to treatment with either multiple cycles of SL-401 or physician's choice, which will consist of available standard therapeutic agents. In addition, the efficacy and safety of SL-401-based combination therapy will also be studied in earlier lines of AML given the lack of overlapping toxicities with existing hematologic cancer therapies. Disclosures: Konopleva: Stemline Therapeutics: Research Funding. Cirrito:Stemline Therapeutics: Employment, Equity Ownership, Patents & Royalties. Hoberman:Stemline Therapeutics: Employment, Equity Ownership. Szarek:Stemline Therapeutics: Consultancy, Equity Ownership. Rowinsky:Stemline Therapeutics: Employment, Equity Ownership. Bergstein:Stemline Therapeutics: Employment, Equity Ownership, Patents & Royalties. Frankel:Stemline Therapeutics: Research Funding.

Description: Background: Patients (pt) with acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS) who are elderly, or have secondary AML (sAML), or relapsed/refractory (R/R) disease have poor outcomes. Venetoclax (VEN), an oral BCL2 inhibitor, has shown activity in R/R AML as single-agent and in combination with hypomethylating agents (HMA) in newly diagnosed unfit AML. We designed a phase II trial to evaluate the safety and efficacy of VEN with 10-days (D) of decitabine (DEC) in AML and high risk MDS. Methods: Eligible AML pts included those who had failed prior therapy, or were newly diagnosed (ND) elderly pts (〉60 years), or had sAML. ECOG score ≤3, WBC count ≤10 x109/L, and adequate organ function were required. VEN was given on day 1-28 in cycle (cy) 1 and D1-21 in cy 2 onwards; and was interrupted on C1D21 if the 21D bone marrow showed clearance of blasts, until count recovery. VEN was dosed 200 mg PO daily (50% dose reduction) in pts needing CYP3A4 inhibitors. DEC was given 20 mg/m2 IVdaily on D1-10 until CR/CRi, followed by 5-day cycles. Hydroxyurea or ara-C could be used for cytoreduction prior to starting therapy. Prophylactic antimicrobials were used until neutrophil recovery. Tyrosine kinase inhibitors could be used in applicable patients. Primary objective was to determine overall response rate (ORR) including complete remission (CR), CR with incomplete blood count recovery (CRi), partial remission (PR), and morphologic leukemia-free state in pts with AML. Secondary objectives were to determine safety of the combination; duration of response (DOR), disease-free survival (DFS) and overall survival (OS). Results: 48 pts were enrolled between January and May 2018 (Table 1). 24 pts (50%) had ND AML, 7 pts (15%) had sAML, and 16 pts (33%) had R/R AML. Prior therapies are listed in Table 1. The overall CR/CRi rate was 71% (34/48). CR/CRi rate for ND, sAML and R/R AML were 92%, 71% and 44%, respectively (Table 2). Negative minimal residual disease (MRD-) by flow cytometry at the time of response was achieved in 16/33 responding pts (49%). CR/CRi with MRD- was achieved in 11/21 pts with ND AML (52%), 2/5 pts with sAML (40%), and 3/6 pts w R/R AML (50%). CR/CRi rate in TP53 mutated pts was 67% (8/12, Table 2). Additional therapies included ponatinib in 1 pt with AML and t(9;22) who achieved a CRi; and sorafenib in 5 pts (4 FLT3-ITD, 1 FLT3 S749L variant) of which 2 ITD pts achieved CRi and 3 pts did not respond. Median time to first response was 43D (range 20-110) with a median of 1 cy to best response (range 1-3). At a median follow-up of 2.3 months (mo; range 1.4-5.7), pts had received a median of 2 cy (range 2-5) and 32 pts continue on study. Reasons for discontinuation are shown in Table 3. Median OS has not been reached (NR) for ND and sAML pts (NR, range 1.8 mo-NR) and R/R AML (NR, range 0.4 mo-NR, Fig 1a). Median DFS (Fig 1b) and DOR for ND and sAML pts are also NR (range 0.9 mo-NR). Median DFS and DOR for R/R AML pts were 3.3 mo (range 0.5-NR). 10 pts received GCSF. 59 treatment-emergent adverse events (TEAE) occurred in 31 pts, out of which 48 were grade (gr) 3/4. The most frequent gr 3/4 TEAE were infections, with gr 3/4 neutropenia (53%), febrile neutropenia (14%), and tumor lysis syndrome (TLS, n=2, 4%). 1 pt with WBC count 12 x109/L developed TLS on C1D2 which resolved with rasburicase and holding VEN; another pt with WBC count 28 x109/L developed TLS on C1D2 needing hemodialysis for 12 days, prompting study amendment to the current baseline WBC≤10 x109/L. Time to blood count recovery are shown in Table 4. There were total 6 deaths, all in pts with R/R AML (n=5) and treated sAML (n=1), including 3 deaths in hospice, 2 early deaths in relapsed AML pts due to infection; and 1 early death in a relapsed MDS pt due to pneumonia and acute kidney injury unrelated to therapy. There were no deaths in the ND AML pts. 30D and 60D mortality rates were 8% and 10%, respectively. Preliminary BH3 profiling data in R/R cohort showed BCL-2 priming (by assessing cytochrome C release to recombinant BAD peptide and ABT-199) in 7/8 pts irrespective of their response; however, pts who failed to achieve CR/CRi demonstrated co-dependence on other anti-apoptotic proteins MCL-1, BCL-XL and A1 (Fig 2). Additional BH3 profiling and CyTOF analyses are ongoing. Conclusion: The DEC10-VEN regimen had an acceptable safety profile and excellent response rates with CR/CRi of 92% in ND AML, 71% in sAML, and 44% in R/R AML with MRD- in 52% of ND AML, 40% of sAML and 50% of R/R AML. Trial is continuing to accrue (NCT03404193). Disclosures Maiti: Celgene Corporation: Other: Research funding to the institution. DiNardo:AbbVie: Consultancy, Other: Advisory role; Agios: Consultancy, Other: Advisory role; Bayer: Other: Advisory role; Celgene: Other: Advisory role; Medimmune: Other: Advisory role; Karyopharm: Other: Advisory role. Cortes:Novartis: Consultancy, Research Funding; Arog: Research Funding; Daiichi Sankyo: Consultancy, Research Funding; Astellas Pharma: Consultancy, Research Funding; Pfizer: Consultancy, Research Funding. Pemmaraju:plexxikon: Research Funding; novartis: Research Funding; Affymetrix: Research Funding; samus: Research Funding; cellectis: Research Funding; celgene: Consultancy, Honoraria; SagerStrong Foundation: Research Funding; abbvie: Research Funding; daiichi sankyo: Research Funding; stemline: Consultancy, Honoraria, Research Funding. Kadia:Celgene: Research Funding; Amgen: Consultancy, Research Funding; Jazz: Consultancy, Research Funding; Takeda: Consultancy; BMS: Research Funding; BMS: Research Funding; Pfizer: Consultancy, Research Funding; Amgen: Consultancy, Research Funding; Novartis: Consultancy; Celgene: Research Funding; Abbvie: Consultancy; Jazz: Consultancy, Research Funding; Abbvie: Consultancy; Novartis: Consultancy; Takeda: Consultancy; Pfizer: Consultancy, Research Funding. Ravandi:Amgen: Honoraria, Research Funding, Speakers Bureau; Abbvie: Research Funding; Bristol-Myers Squibb: Research Funding; Jazz: Honoraria; Sunesis: Honoraria; Abbvie: Research Funding; Xencor: Research Funding; Sunesis: Honoraria; Seattle Genetics: Research Funding; Seattle Genetics: Research Funding; Macrogenix: Honoraria, Research Funding; Orsenix: Honoraria; Astellas Pharmaceuticals: Consultancy, Honoraria; Xencor: Research Funding; Astellas Pharmaceuticals: Consultancy, Honoraria; Jazz: Honoraria; Bristol-Myers Squibb: Research Funding; Amgen: Honoraria, Research Funding, Speakers Bureau; Macrogenix: Honoraria, Research Funding; Orsenix: Honoraria. Short:Takeda Oncology: Consultancy. Daver:BMS: Research Funding; ImmunoGen: Consultancy; Incyte: Consultancy; Otsuka: Consultancy; Daiichi-Sankyo: Research Funding; Incyte: Research Funding; Novartis: Consultancy; Sunesis: Research Funding; Karyopharm: Research Funding; Pfizer: Research Funding; Alexion: Consultancy; Karyopharm: Consultancy; Pfizer: Consultancy; Sunesis: Consultancy; Kiromic: Research Funding; ARIAD: Research Funding; Novartis: Research Funding. Sasaki:Otsuka Pharmaceutical: Honoraria. Thompson:Gilead Sciences: Honoraria, Membership on an entity's Board of Directors or advisory committees; Adaptive Biotechnologies: Research Funding; AbbVie: Honoraria, Research Funding; Pharmacyclics: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Genentech: Honoraria, Membership on an entity's Board of Directors or advisory committees. Jain:Servier: Honoraria, Membership on an entity's Board of Directors or advisory committees; Servier: Research Funding; Adaptive Biotechnologies: Honoraria, Membership on an entity's Board of Directors or advisory committees; Abbvie: Research Funding; Pfizer: 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; Pfizer: Research Funding; ADC Therapeutics: Research Funding; Adaptive Biotechnologies: Honoraria, Membership on an entity's Board of Directors or advisory committees; Pharmacyclics: Research Funding; ADC Therapeutics: 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; Verastem: Honoraria, Membership on an entity's Board of Directors or advisory committees; Cellectis: Research Funding; Pharmacyclics: Research Funding; Novimmune: Honoraria, Membership on an entity's Board of Directors or advisory committees; Seattle Genetics: Research Funding; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Abbvie: Research Funding; Infinity: Research Funding; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees; Pharmacyclics: Honoraria, Membership on an entity's Board of Directors or advisory committees; Novimmune: Honoraria, Membership on an entity's Board of Directors or advisory committees; Adaptive Biotechnologioes: Research Funding; Genentech: Research Funding; Verastem: Research Funding; Servier: Honoraria, Membership on an entity's Board of Directors or advisory committees; BMS: Research Funding; ADC Therapeutics: Honoraria, Membership on an entity's Board of Directors or advisory committees; Astra Zeneca: Research Funding; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Research Funding; Verastem: Honoraria, Membership on an entity's Board of Directors or advisory committees; Incyte: Research Funding; Astra Zeneca: Honoraria, Membership on an entity's Board of Directors or advisory committees; Seattle Genetics: Research Funding; Abbvie: Honoraria, Membership on an entity's Board of Directors or advisory committees; ADC Therapeutics: Research Funding; Pharmacyclics: Honoraria, Membership on an entity's Board of Directors or advisory committees; Adaptive Biotechnologioes: Research Funding; Pfizer: Research Funding; Cellectis: Research Funding; Verastem: Research Funding; BMS: Research Funding; Servier: Research Funding; Infinity: Research Funding; Astra Zeneca: Research Funding; Celgene: Research Funding; Genentech: Research Funding; Incyte: Research Funding; Abbvie: Honoraria, Membership on an entity's Board of Directors or advisory committees; Astra Zeneca: Honoraria, Membership on an entity's Board of Directors or advisory committees. Jabbour:Pfizer: Consultancy, Research Funding; Novartis: Research Funding; Bristol-Myers Squibb: Consultancy, Research Funding; Takeda: Consultancy, Research Funding; Abbvie: Research Funding. Andreeff:AstraZeneca: Research Funding. Konopleva:Stemline Therapeutics: Research Funding.

Description: Abstract 1490 Background: The tumor suppressor p53 is frequently mutated in human cancer, including acute myeloid leukemia (AML). In AML, p53 mutations have been associated with poor risk cytogenetics (i.e. complex karyotype, −5/−7). However, the function of p53 can also be compromised by protein stabilization and/or expression. The implications of p53 protein expression have not been studied in AML. Methodology: We assessed p53 expression by high-throughput reverse phase protein array (RPPA) technology in 511 pts (719 samples). Eleven CD34+ bone marrow (BM) and 10 normal peripheral blood (PB) lymphocyte samples were used as controls. Samples were printed as 5 serial 1: 2 dilutions in duplicate using an Aushon 2470 Arrayer. Mutational status was determined by Sanger sequencing of exons 5 through 9 of the p53 gene. Results: Paired PB- and BM-derived AML samples expressed similar p53 levels (p=0.25). A trend towards higher p53 expression at relapsed was observed among 47 paired diagnosis/relapse samples (p=0.07). Cases of AML-M3 and –M6 exhibited higher expression of p53 than other FAB subtypes. p53 expression directly correlated with age (p=0.01) and CD34 (p=0.001) and inversely correlated with WBC (p=0.007), BM (p=0.0001) and PB (p=0.0001) blasts, platelets (p=0.007), HLA-DR (p=0.01), CD19 (p=0.02), and survival (p=0.01). High p53 (p53high) expression level was more associated with unfavorable cytogenetics than with favorable or intermediate cytogenetics (p=0.00001). When all cytogenetic abnormalities were considered, pts with −5 had the highest levels of p53 (p=0.00001). Pts with RAS mutations, but not those with FLT3-ITD, NPM1, or IDH1/2, had lower levels of p53 protein. When pts were divided according to the level of p53 protein expression p53high was associated with lower complete remission (CR) rates (51% vs 56%; p=??) and higher relapsed rates (82% vs 62%; p=??). The median overall survival (OS) of pts with p53high and p53low were 29.8 vs. 51 wks (p=0.009). Most cases with p53high had unfavorable cytogenetics and the effect on OS was predominantly seen in that subpopulation with p53high and p53low pts living a medina of 23.4 vs. 36 wks (p=0.07), respectively. In order to determine whether the poor outcomes associated with p53high were due to the presence of a higher rate of p53 mutations among pts with p53high, we determined the p53 mutational status of 55 pts. p53high was highly correlated with the presence of p53 mutations as the latter were detected in 17/40 pts with p53high but in only 1/16 pts with p53low. Importantly, the presence of p53high, both in the presence (29 wks) or in the absence (24 wks) of p53 mutations, was associated with significantly worse overall survival compared with pts with p53low (56 wks; p=0.05, Figure 1). Multivariate analysis indicated that p53 is a significant independent risk factor for survival in AML. The final model included: age (p=0.000001), favorable cytogenetics (0.01), unfavorable cytogenetics (p=0.00001), WBC (p=0.0005), albumin (p=0.0003), FLT3-ITD (P=0.04), and P53 (P=0.02). p53high was positively correlated with p53pSER15 (p=0.00001), Rbp807p811 (p=0.0002), c-MET (p=0.01), FoxO3a (p=0.004), KIT (p=0.001), p38p180p182 (p0.02), BAD (p=0.0001), cleaved PARP (p=0.002), cleaved PARP (p=0.01), TCF4 (p=0.02), fibronectin (p=0.02), and hsp70 (p=0.003), and negatively with AKTp473 (p=0.01), ERK (p=0.002), mTOR (p=0.005), PI3Kp85 (p=0.002), PKCδ (p=0.00002), GAB2 (p=0.00005), beclin (p=0.007), JMJD6 (p=0.001), Gata3 (p=0.02), p21 (p=0.01), and Mdm2 (p=0.001). Conclusions: Our results suggest that high levels of p53 protein constitute a powerful marker of short survival in AML. This effect is independent of p53 mutational status. The poor outcome of pts with high level of expression of p53 in the absence of p53 mutations suggests that the p53 pathway may be functionally perturbed in a much higher proportion of pts with AML than previously recognized. These data support the use of p53 protein expression levels in prognostication and in the development of targeted therapeutics. Disclosures: No relevant conflicts of interest to declare.

Description: Key Points High miR-10 family expression levels in AML patients are associated with achieving complete remission to induction chemotherapy. Functional experiments did not show any impact of miR-10a-5p in AML blast growth or survival at baseline conditions or after chemotherapy.

Description: Aberrations in the DNA damage responses contributes to the uncontrolled proliferation and therapy resistance in many cancers. Acute myeloid leukemia (AML) presents enhanced DNA damage as compared to MDS characterized by induced levels γ-2HAX and phosphorylated ATM that correlated with AML blast percentages (Boehrer et al. Oncogene 2009). The low incidence of p53 mutations (7% in adult AML, The Cancer Genome Atlas Research Network, N Engl J Med 2013) in AML indicates downstream suppression of DNA damage control system proteins, as was proposed previously by overexpression of MDM2 and BCL-2 (Wojcik et al. Neoplasma 2005). However, the role of p53 and downstream effectors regulating the DNA damage pathway in CD34+ AML blasts is still relatively unclear. Surprisingly, using RPPA analysis, we found a common significant increase in p53 phosphorylation at serine 15 in pediatric AML as compared to CD34+ NBM (AML n=31 and NBM n=10, Mann-Whitney U, P = 0.003). Therefore, we challenged to target p53 using a shRNA approach. In the sh-p53 model, primary pediatric AML samples transduced with sh-p53 showed a significant increase in AML proliferation over time as compared to scrambled control (paired-samples t-test, P = 0.005). The overall AML cell viability was significantly improved in sh-p53 AML cultures (paired-samples t-test P = 0.001). DNA cell cycle analysis revealed that sh-p53 AML cultures contained significant increased percentages of cells in S and G2/M phases of the cell cycle as compared to their scrambled controls (paired samples t-test, P = 0.015). The CD34+ leukemic population was maintained in p53 knockdown cultures and thereby outcompeted scrambled control cultures. Knockdown of p53 in primary pediatric AML samples resulted in a higher proliferation rate, repressed differentiation and prolonged survival of AML blasts, especially in MLL-rearranged AML. Interestingly, we previously showed that MLL-rearranged AML samples express significantly higher BCL-2 peptide phosphorylation as compared to NBM (Kampen et al. Leukemia 2014). Growth factors are extrinsic cues that can regulate BCL-2 expression (Pidgeon et al. Br J Cancer 2001). Growth factors like VEGF, have been shown to be involved in leukemia pathogenesis in the bone marrow where leukemic stem cells are preserved in tightly controlled niches (Kampen et al. Cell Mol Life Sci 2013). Accordingly, we found that FGF and VEGFC stimulation of CD34+ AML blasts both significantly accelerated BCL-2 mRNA expression by 28-fold and 2-fold, indicating that indeed the niche is important for inhibiting pro-apoptotic p53-dependent signals further downstream the pathway, which protects AML CD34+ blasts (Student’s t-test, both P 〈 0.001), where p53 and p21 mRNA expression remained unchanged. The availability of VEGFR-2 and FGFR1 previously highlighted their therapeutic targeting potential in AML (Kampen et al. Leukemia 2006, Kentsis et al, Nature Med 2012). This study presents the effect of p53 suppression on AML blast proliferation, survival and maintenance in pediatric AML and indicates the importance of exploring extrinsic factors that contribute to DNA damage control system suppression in vivo for therapeutic interventions. Disclosures No relevant conflicts of interest to declare.

Description: Background and hypothesis: CD25 (IL2RA, interleukin 2 receptor α chain) is a transmembrane protein with a 13aa cytoplasmic tail. CD25 cooperates with β- and γ-chains in binding IL-2, but does not contribute to cytokine signaling. During normal B cell development, CD25 is specifically upregulated on the surface of IL7-dependent pre-B cells and is also expressed on the surface of a subset of human pre-B ALL cases. CD25-expressing ALL is typically associated with poor clinical outcome. For these reasons, we studied the functional significance of CD25 expression on human pre-B ALL cells. Results: Flow cytometry and immunohistochemistry staining on a large panel of patient samples (n=416; MDACC, ECOG) revealed specific cell surface expression of CD25 in Ph+ ALL and Ph-like ALL, which are both high-risk subtypes of ALL. In agreement with selective expression on high-risk subsets, high expression levels of CD25 at the time of diagnosis were predictive of poor overall clinical outcome in these studies (P=0.005). BCR-ABL1 in Ph+ ALL and related tyrosine kinases in Ph-like ALL strongly activate STAT5, which then induces transcriptional activation of the IL2RA locus. Since Stat5 is also active during normal pre-B cell differentiation, we first analyzed B cell development in Il2ra-/- mouse bone marrow. Il2ra-/- B cell development was blocked at the pre-B cell stage, consistent with specific upregulation of CD25 on pre-B cells. In human Ph+ ALL cells, we found IL2RB and IL2RG were not co-expressed with CD25, suggesting a function of CD25 in Ph+ALL that is distinct from IL2 signaling. To test the biological significance of tyrosine kinase/STAT5-induced activation of CD25, we developed an Il2ra-/- mouse model for BCR-ABL1 pre-B ALL. Interestingly, the cytoplasmic tail of CD25 includes phosphorylation sites (S268 and T271) that are known substrates for serine/threonine phosphorylation by PKCα, which was reported to regulate protein phosphatase 2A (PP2A). To investigate interacting proteins with the cytoplasmic tail of CD25, we performed immune precipitation (IP) against the flag-tagged CD25-tail in primary Ph+ ALL cells which were transduced with either a CD25-tail-flag or an EV-flag vector. 2D mass spectrometry and Western blot on the IP products confirmed strong interactions with PKCα and PP2A. Weestern blot analysis confirmed additional interactions with inhibitory phosphatases including PTEN, PTPN6 (SHP1) and Inpp5d (SHIP1) in human Ph+ALL cells. In addition, both 2D MS and Westernblot showed recruitment of the Stat5-feedback inhibitors CISH, SOCS2 and SOCS3 at the CD25 cytoplasmic tail. Studying functional parameters of Il2ra-/-BCR-ABL1 ALL cells, we found impaired proliferation and colony formation capacity and drastically increased increased phosphorylation levels of pABLY412, pSTAT5Y694, pERKT202/Y204, pAKTS473, pP38T180/Y182 and p53. Reconstitution of CD25 expression restored normal phosphorylation levels of these molecules, as well as proliferation and colony formation.In a serial transplant setting, we observed that leukemia initiation in transplant recipients from Il2ra-/- BCR-ABL1 ALL cells required 10- to 100-times higher cell numbers, suggesting that CD25 contributes to leukemia initiation. In addition, CD25 expression is associated with a higher level of drug-resistance: In patient-derived pre-B ALL cells with mixed CD25Low and CD25High populations, the standard chemotherapy agent vincristine selectively induced apoptosis of in CD25Low but not CD25High ALL cells. An anti-CD25 immunotoxin drugs efficiently eradiated CD25High leukemia cells and thereby overcame drug-resistance against vincristine. Conclusions: Our studies identified CD25 as a surface receptor that mediates membrane recruitment of PP2A and CISH, SOCS2, negative feedback regulators of STAT5. CD25 is transcriptionally activated by STAT5 and therefore specifically expressed on high-risk ALL subtypes with oncogenic activation of the Stat5 pathway (Ph+ ALL and Ph-like ALL). We propose that CD25-mediated negative feedback control stabilizes oncogenic tyrosine kinase signaling and mediates drug-resistance in Ph+ ALL and Ph-like ALL cells. Targeted inhibition using CD25-directed immunotoxins may be useful in new approaches to overcome drug-resistance in Ph+ ALL and Ph-like ALL. Disclosures No relevant conflicts of interest to declare.