ALBERT

Description: Background:MDM2, a negative regulator of the tumor suppressor p53, is overexpressed in a number of cancers including hematological malignancies. Disrupting the MDM2-p53 interaction represents an attractive approach to treat cancers expressing wild-type functional p53, and the inhibition of MDM2 and antitumor activity with the small molecule DS3032b has been demonstrated in preclinical studies and in patients with solid tumors. Here, we report the initial results of the Phase I trial aimed at characterizing the safety, tolerability, pharmacokinetic (PK), and pharmacodynamic (PD) profiles and preliminary efficacy of DS3032b in in patients with hematological malignancies. Methods:This study (NCT02319369) is a dose escalation study of DS-3032b as an oral single agent with a starting dose of 60 mg and escalating through 90 mg, 120 mg, 160 mg and 210 mg dose levels guided by a modified continuous reassessment method using a Bayesian logistic regression model following escalation with overdose control principle. The drug was administered orally once daily (QD) in 21 of 28 days per cycle (QD 21/28). The patient population included relapsed/refractory AML and high-risk MDS. Results:Thirty eight subjects with relapsed/refractory AML or high-risk MDS were enrolled in the study in 5 dose levels; 60 mg (7 pts), 90 mg (6 pts), 120 mg (12 pts), 160 mg (8 pts) and 210 mg (5 pts). Twenty four (63%) subjects were males. The median age was 68.5 (range 30-88) years, with approximately two-thirds over 65 years. Thirty-seven of 38 patients were p53 wild type, and one subject had known pathogenic insertion mutation with an allele frequency of about 20%. DS-3032b was tolerated up to 160 mg QD in the 21/28 days schedule that was determined to be the maximum tolerated dose. All subjects experienced at least one treatment emergent adverse event (TEAE) of any grade, and 93% subjects experienced a grade ≥3 TEAE at a data cut off on May 2, 2016. The most common (≥20%) TEAEs of any grade regardless of attribution were nausea (73%), diarrhea (57%) vomiting (33%), fatigue (37%), anemia (33%), thrombocytopenia (33%), neutropenia (20%) hypotension (30%), hypokalemia (23%) and hypomagnesemia (20%). A total of 5 subjects experienced dose limiting toxicities; two subjects in the 160 mg cohort due to grade 3 hypokalemia and grade 3 diarrhea, and three subjects in the 210 mg cohort due to grade 3 nausea and vomiting, grade 2 creatinine elevation/ renal insufficiency, and grade 3 anorexia and fatigue.. Preliminary PK results showed plasma exposure (Cmax and AUClast) increased with dose; and approximately 2-fold drug accumulation was observed on Day 15 following the daily oral dosing. Increase in the serum levels of macrophage inhibitory cytokine (MIC-1) as a p53 target gene was used as a circulating pharmacodynamic biomarker, where magnitude of MIC-1 serum level increase corresponded with DS3032 plasma exposure. Clinical activity of single agent DS-3032b was observed from the reduction in bone marrow blasts by the end of cycle 1 (4 weeks) in 15 of 38 patients. Complete remission was observed in 2 subjects with AML; 1 subject each at 120 mg and at 160 mg, with a remission duration of 〉4 and 〉10 months, respectively. One subject with MDS achieved marrow CR with platelet improvement, of 4 months duration, at the 120 mg dose level. Of note, each of these three subjects developed a TP53 mutation while on treatment, two at the time of disease progression and one subject who remains in an ongoing response. Further evaluation of DS-3032b in rational combinations such as with hypomethylating agents is being planned. Conclusions: Disruption of MDM2-p53 interaction by DS-3032b appears to be a promising approach to treat haematological malignancies. MDM2 expression/amplification in leukemic blasts is being investigated as a potential predictor of response. Rational combinations with agents targeting different mechanistic pathways may offer the most promise for further development. Disclosures DiNardo: Novartis: Other: advisory board, Research Funding; Abbvie: Research Funding; Daiichi Sankyo: Other: advisory board, Research Funding; Celgene: Research Funding; Agios: Other: advisory board, Research Funding. Zernovak:Daiichi Sankyo: Employment. Kumar:Daiichi Sankyo: Employment. Gajee:Daiichi Sankyo: Employment. Chen:Daiichi Sankyo: Employment. Rosen:Daiichi Sankyo: Employment. Song:Daiichi Sankyo: Employment. Kochan:Daiichi Sankyo: Employment. Limsakun:Daiichi Sankyo: Employment.

Description: Background: FMS-like tyrosine kinase 3 internal tandem duplication (FLT3-ITD) mutations occur in ≈ 25% of patients with AML and are associated with poor prognosis. Quizartinib is a once-daily, oral, highly potent and selective FLT3 inhibitor. In the phase 3 QuANTUM-R trial (NCT02039726; Cortes et al. Lancet Oncol 2019), quizartinib prolonged overall survival compared with salvage chemotherapy in patients with R/R FLT3-ITD AML. Murine double minute 2 (MDM2), an E3 ubiquitin ligase, negatively regulates the p53 tumor suppressor and has been shown to be upregulated in patients with AML; TP53 mutations in AML are infrequent except within complex karyotypes. Milademetan, a novel and specific MDM2 inhibitor, showed activity in an ongoing phase 1 trial in patients with AML or myelodysplastic syndromes (MDS) [DiNardo et al. ASH 2016, abstract 593]. Preclinical studies have shown that quizartinib plus milademetan may act synergistically to target FLT3-ITD and restore p53 activity in FLT3-ITD/TP53 wild-type AML [Andreeff et al. ASH 2018, abstract 2720]. Targeting MDM2 may restore p53 activity in cell signaling pathways altered by FLT3-ITD in patients with wild-type TP53 AML. Methods: This open-label, 2-part, phase 1 study (NCT03552029) evaluates quizartinib in combination with milademetan in patients with FLT3-ITD AML. Key inclusion criteria comprise a diagnosis of FLT3-ITD AML (de novo or secondary to MDS) and adequate renal, hepatic, and clotting functions. Key exclusion criteria include acute promyelocytic leukemia, prior treatment with a MDM2 inhibitor, QTcF interval 〉 450 ms, significant cardiovascular disease, and unresolved toxicities from prior therapies. Dose-escalation (part 1) comprises patients with R/R AML. In part 1, quizartinib will be administered once daily in 28-day cycles, at 3 proposed levels (30, 40, and 60 mg) with appropriate dose modifications based on QTcF monitoring and concomitant use of strong CYP3A inhibitors. Milademetan will be administered on days 1-14 of each 28-day cycle, at 3 proposed levels (90, 120, and 160 mg). Dose escalation will be guided by modified continual reassessment with overdose control. The primary objectives of part 1 are to evaluate the safety and tolerability, optimum dosing schedule, maximum tolerated dose (MTD), and recommended dosing for the expansion (RDE) cohort. Dose expansion (part 2) comprises a cohort of patients with R/R FLT3-ITD AML who have not received 〉 1 salvage therapy and not received 〉 1 prior FLT3 inhibitor, and a second cohort including ND patients with FLT3-ITD AML who are unfit for intensive chemotherapy. Patients in part 2 will be treated with quizartinib plus milademetan at the RDE doses identified in part 1. The objectives of part 2 are to confirm the safety and tolerability of quizartinib plus milademetan at RDE and identify the recommended phase 2 dose. Pharmacokinetics and preliminary assessment of efficacy are also being evaluated as secondary outcomes. Pharmacodynamic and biomarker assessments such as leukemic stem cell numbers, STAT5 downstream signaling, minimal residual disease measured by flow cytometry, and gene mutations will be evaluated as exploratory endpoints. Approximately 24 to 36 dose-limiting toxicity-evaluable patients are needed in part 1 to determine the MTDs and the RDE; approximately 40 patients per cohort will be treated at the RDE in part 2. This study is currently recruiting at multiple sites in the United States for part 1; recruitment for part 2 may be expanded to additional sites worldwide as necessary. Disclosures Daver: Jazz: Consultancy; Glycomimetics: Research Funding; Immunogen: Consultancy, Research Funding; Forty-Seven: Consultancy; Novartis: Consultancy, Research Funding; Servier: Research Funding; Karyopharm: Consultancy, Research Funding; Celgene: Consultancy; Abbvie: Consultancy, Research Funding; Agios: Consultancy; Daiichi Sankyo: Consultancy, Research Funding; Otsuka: Consultancy; BMS: Consultancy, Research Funding; Pfizer: Consultancy, Research Funding; Hanmi Pharm Co., Ltd.: Research Funding; Genentech: Consultancy, Research Funding; Astellas: Consultancy; Incyte: Consultancy, Research Funding; Sunesis: Consultancy, Research Funding; NOHLA: Research Funding. Graydon:Daiichi Sankyo, Inc.: Employment. Dawra:Daiichi Sankyo, Inc.: Employment; Pfizer Inc: Employment. Xie:Daiichi Sankyo, Inc.: Employment. Kumar:Daiichi Sankyo, Inc.: Employment, Equity Ownership. Andreeff:Daiichi Sankyo, Inc.: Consultancy, Patents & Royalties: Patents licensed, royalty bearing, Research Funding; Jazz Pharmaceuticals: Consultancy; Celgene: Consultancy; Amgen: Consultancy; AstaZeneca: Consultancy; 6 Dimensions Capital: Consultancy; Reata: Equity Ownership; Aptose: Equity Ownership; Eutropics: Equity Ownership; Senti Bio: Equity Ownership, Membership on an entity's Board of Directors or advisory committees; Oncoceutics: Equity Ownership; Oncolyze: Equity Ownership; Breast Cancer Research Foundation: Research Funding; CPRIT: Research Funding; NIH/NCI: Research Funding; Center for Drug Research & Development: Membership on an entity's Board of Directors or advisory committees; Cancer UK: Membership on an entity's Board of Directors or advisory committees; NCI-CTEP: Membership on an entity's Board of Directors or advisory committees; German Research Council: Membership on an entity's Board of Directors or advisory committees; Leukemia Lymphoma Society: Membership on an entity's Board of Directors or advisory committees; NCI-RDCRN (Rare Disease Cliln Network): Membership on an entity's Board of Directors or advisory committees; CLL Foundation: Membership on an entity's Board of Directors or advisory committees; BiolineRx: Membership on an entity's Board of Directors or advisory committees.

Description: Background: MDM2, a negative regulator of the tumor suppressor p53, is overexpressed in several cancers including hematological malignancies. Disrupting the MDM2-p53 interaction represents an attractive approach to treat cancers expressing wild-type functional p53. Anticancer activity of small molecule MDM2 inhibitor milademetan (DS-3032b) has been demonstrated in preclinical studies and in a phase 1 trial in patients with acute myeloid leukemia (AML) or myelodysplastic syndrome. Quizartinib is a highly selective and potent FLT3 inhibitor that has demonstrated single-agent activity and improvement in overall survival in a phase 3 clinical study in relapsed/refractory AML with FLT3-internal tandem duplication (FLT3-ITD) mutations. We present here the preclinical studies exploring the rationale and molecular basis for the combination of quizartinib and milademetan for the treatment of FLT3-ITD mutant/TP53 wild-type AML. Methods: We investigated the effect of quizartinib and milademetan combination on cell viability and apoptosis in established AML cell lines, including MV-4-11, MOLM-13 and MOLM-14, which harbor FLT3-ITD mutations and wild type TP53. Cells were treated with quizartinib and milademetan at specified concentrations; cell viability and caspase activation were determined by chemiluminescent assays, and annexin V positive fractions were determined by flow cytometry. We further investigated the effect of the combination of quizartinib and the murine specific MDM2 inhibitor DS-5272 in murine leukemia cell lines Ba/F3-FLT3-ITD, Ba/F3-FLT3-ITD+F691L and Ba/F3-FLT3-ITD+D835Y, which harbor FLT3-ITD, ITD plus F691L and ITD plus D835Y mutations, respectively. F691L or D835Y mutations are associated with resistance to FLT3-targeted AML therapy. In vivo efficacy of combination treatment was investigated in subcutaneous and intravenous xenograft models generated in male NOD/SCID mice inoculated with MOLM-13 and MV-4-11 human AML cells. Results: Combination treatment with milademetan (or DS-5272) and quizartinib demonstrated synergistic anti-leukemic activity compared to the respective single-agent treatments in FLT3 mutated and TP53 wild type cells. Combination indices (CIs) were 0.25 ± 0.06, 0.61 ± 0.03, 0.62 ± 0.06, 0.29 ± 0.004 and 0.50 ± 0.03, respectively, in MV-4-11, MOLM-13, MOLM-14, Ba/F3-FLT3-ITD+F691L and D835Y cell lines, all of which harbor FLT3-ITD or ITD plus TKD point mutations. The combination regimen triggered synergistic pro-apoptotic effect in a p53-dependent manner as shown by annexin-V staining and caspase 3/7 assays. Mechanistically, the combination treatment resulted in significant suppression of phospho-FLT3, phospho-ERK and phospho-AKT and anti-apoptotic Bcl2 family proteins (eg, Mcl-1), as well as up-regulation of p53, p21 and pro-apoptotic protein PUMA, compared to single agent treatments. Of note, the combination regimen also exerted a synergistic pro-apoptotic effect on venetoclax (BCL-2 inhibitor)-resistant MOLM-13 cells (CI: 0.39 ± 0.04) through profound suppression of Mcl-1. In an in vivo study using the MOLM-13 subcutaneous mouse xenograft model, quizartinib at 0.5 and 1 mg/kg and milademetan at 25 and 50 mg/kg demonstrated a significant tumor growth inhibition compared with vehicle treatment or respective single-agent treatments. In MV-4-11 intravenous mouse xenograft model, the combination of quizartinib plus milademetan showed a significantly prolonged survival, with no animal death in the combination group during the study period, compared to respective single agent treatments and untreated control (Figure). Conclusion: Synergistic anti-leukemic activity was observed for quizartinib plus milademetan combination treatment in preclinical AML models. A phase I clinical trial of quizartinib/milademetan combination therapy in patients with FLT3-ITD mutant AML is underway. Figure. Effects of quizartinib, milademetan and their combination on survival of mice intravenously inoculated with human MV-4-11 AML cells Disclosures Andreeff: Oncoceutics: Equity Ownership, Membership on an entity's Board of Directors or advisory committees; Jazz Pharma: Consultancy; Aptose: Equity Ownership, Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy; Eutropics: Equity Ownership, Membership on an entity's Board of Directors or advisory committees; Amgen: Consultancy, Research Funding; United Therapeutics: Patents & Royalties: GD2 inhibition in breast cancer ; Oncolyze: Equity Ownership; Astra Zeneca: Research Funding; Reata: Equity Ownership; Daiichi-Sankyo: Consultancy, Patents & Royalties: MDM2 inhibitor activity patent, Research Funding; SentiBio: Equity Ownership. Kumar:Daiichi Sankyo: Employment, Equity Ownership. Zernovak:Daiichi Sankyo: Employment, Equity Ownership. Daver:Pfizer: Research Funding; ImmunoGen: Consultancy; Otsuka: Consultancy; Karyopharm: Research Funding; Alexion: Consultancy; ARIAD: Research Funding; Daiichi-Sankyo: Research Funding; BMS: Research Funding; Karyopharm: Consultancy; Novartis: Consultancy; Novartis: Research Funding; Incyte: Research Funding; Kiromic: Research Funding; Sunesis: Research Funding; Incyte: Consultancy; Pfizer: Consultancy; Sunesis: Consultancy. Isoyama:Daiichi SANKYO CO., LTD.: Employment. Iwanaga:Daiichi Sankyo Co., Ltd.: Employment. Togashi:Daiichi SANKYO CO., LTD.: Employment. Seki:Daiichi Sankyo Co., Ltd.: Employment.

Description: Background: The tumor suppressor p53, encoded by the TP53 gene, is negatively regulated by murine double minute 2 (MDM2), an E3 ubiquitin ligase. Deregulation of MDM2 results in the degradation of p53, leading to cessation of the protein's multiple tumor-suppressive functions, including the induction of apoptosis and reactivation of aberrantly silenced genes. Although TP53 is not frequently mutated in AML, p53 pathway dysfunction is prevalent, with MDM2 overexpression being frequently observed. Disrupting MDM2's negative regulatory effect to reactivate functional p53 is a promising strategy for the treatment of AML. Milademetan (DS-3032b) is a small-molecule MDM2 inhibitor that disrupts the p53-MDM2 interaction and has demonstrated single-agent activity in preclinical and clinical studies of AML. Survival rates are poor for patients with relapsed/refractory (R/R) AML or high-risk MDS which underpins the rationale for combination treatments to build on the efficacy of available agents. AZA, a hypomethylating agent, is part of the standard of care for AML and MDS. Reactivation of p53-inducible genes with milademetan combined with hypomethylation and direct cytotoxicity with AZA has shown activity in preclinical models of AML. Study Design and Methods: This open-label, 2-part, multicenter, phase 1 dose-escalation and -expansion study (NCT02319369) evaluates milademetan in combination with AZA in patients with R/R AML or high-risk MDS. Key inclusion criteria comprise a diagnosis of R/R AML or high-risk MDS; Eastern Cooperative Oncology Group performance status (ECOG PS) of 0-2; and adequate renal, hepatic, and clotting functions. Additional inclusion criteria for newly diagnosed patients is ineligibility for intensive induction chemotherapy due to advanced age (≥ 75 years), congestive heart failure, or ECOG PS of 3 that is not related to leukemia. Key exclusion criteria include acute promyelocytic leukemia, central nervous system leukemia, unresolved toxicity from previous anticancer therapy, mean QTcF interval 〉450 ms for males or 〉470 ms for females, or prior treatment with an MDM2 inhibitor. During part 1 (dose escalation), patients with R/R AML or high-risk MDS receive single-agent milademetan (part 1; completed) or milademetan in combination with AZA at different dose schedules (part 1A; ongoing). Milademetan is administered as a single agent on days 1-21 of each 28-day cycle (21/28 schedule) at a starting dose of 60 mg and escalating to 90, 120, 160, and 210 mg. Less frequent dosing schedules will also be evaluated, starting with the maximum tolerated dose (MTD) determined from the 21/28 schedule. In part 1A, AZA will be administered at 75 mg/m2 subcutaneously or intravenously on days 1-7 of each 28-day cycle, with milademetan treatment on days 5-14 or 8-14. The primary objectives of part 1 are to assess safety and tolerability, determine the MTD of single-agent milademetan and in combination with AZA, and identify the recommended dose for expansion (RDE) for milademetan plus AZA. During part 2 (dose expansion), 3 cohorts of patients with either (1) R/R AML, (2) newly diagnosed AML, or (3) high-risk MDS will receive milademetan in combination with AZA at the RDE. The primary objectives of part 2 are to confirm safety and tolerability, evaluate response to combination treatment, and identify a recommended phase 2 dose. Pharmacokinetics and pharmacodynamics of milademetan as a single agent and in combination with AZA will be evaluated in both parts. Approximately 80 patients are planned to be enrolled in part 1, and up to 40 patients are planned to be enrolled for each cohort in part 2. This study is currently recruiting in the United States. Disclosures DiNardo: agios: Consultancy, Honoraria; medimmune: Honoraria; celgene: Consultancy, Honoraria; syros: Honoraria; jazz: Honoraria; notable labs: Membership on an entity's Board of Directors or advisory committees; daiichi sankyo: Honoraria; abbvie: Consultancy, Honoraria. Olin:Spectrum: Research Funding; Revolution Medicine: Consultancy; Mirati Therapeutics: Research Funding; Genentech: Consultancy, Research Funding; Astellas: Research Funding; Ignyta: Research Funding; Jazz Pharmaceuticals: Consultancy; Novartis: Research Funding; Astrazeneca: Research Funding; Daiichi Sankyo: Research Funding; Clovis: Research Funding. Ishizawa:Daiichi Sankyo: Patents & Royalties: Joint submission with Daiichi Sankyo for a PTC patent titled "Predictive Gene Signature in Acute Myeloid Leukemia for Therapy with the MDM2 Inhibitor DS-3032b," United States, 62/245667, 10/23/2015, Filed. Sumi:Daiichi Sankyo, Inc.: Employment. Xie:Daiichi Sankyo, Inc.: Employment. Kato:Daiichi Sankyo, Inc.: Employment; Celgene: Employment, Equity Ownership. Kumar:Daiichi Sankyo, Inc.: Employment, Equity Ownership. Andreeff:NIH/NCI: Research Funding; Center for Drug Research & Development: Membership on an entity's Board of Directors or advisory committees; Oncoceutics: Equity Ownership; Senti Bio: Equity Ownership, Membership on an entity's Board of Directors or advisory committees; Oncolyze: Equity Ownership; Breast Cancer Research Foundation: Research Funding; CPRIT: Research Funding; BiolineRx: Membership on an entity's Board of Directors or advisory committees; CLL Foundation: Membership on an entity's Board of Directors or advisory committees; NCI-RDCRN (Rare Disease Cliln Network): Membership on an entity's Board of Directors or advisory committees; Leukemia Lymphoma Society: Membership on an entity's Board of Directors or advisory committees; German Research Council: Membership on an entity's Board of Directors or advisory committees; NCI-CTEP: Membership on an entity's Board of Directors or advisory committees; Cancer UK: Membership on an entity's Board of Directors or advisory committees; Eutropics: Equity Ownership; Aptose: Equity Ownership; Reata: Equity Ownership; 6 Dimensions Capital: Consultancy; Daiichi Sankyo, Inc.: Consultancy, Patents & Royalties: Patents licensed, royalty bearing, Research Funding; Jazz Pharmaceuticals: Consultancy; Celgene: Consultancy; Amgen: Consultancy; AstaZeneca: Consultancy.

Description: Background: Human resources are essential to the sustainability and scalability of health interventions. A barrier to global cancer efforts has been the scarcity of trained pediatric hematology/oncology (PHO) professionals in low- and middle-income countries (LMIC). Studies highlight this inequity and the need to develop a global PHO workforce through allocation of financial resources, strengthening of healthcare infrastructure, and development of innovative training programs. Ethiopia is the second most populous country in Africa. Because of recent reduction in infant mortality and improved treatment of Malaria and HIV in Ethiopia, non-communicable diseases contribute an increasing proportion of childhood mortality. The annual incidence of pediatric cancer in Ethiopia is estimated to be 6000-8000 cases. Prior to 2013, no dedicated PHO programs existed in Ethiopia, and there was no formal process for training local physicians in PHO. The following intervention aimed to increase local capacity for treating childhood cancer through the creation of a formal two-year PHO fellowship. Strategy: The PHO fellowship program was created by The Aslan Project, a US non-profit led by a group of experts in PHO, pediatric oncology nursing, and pathology with experience practicing in LMIC, in collaboration with Addis Ababa University (AAU). The goal was to provide a robust educational experience for fellows within the existing resource-constrained clinical environment. Tikur Anbessa Specialized Hospital (TASH) was the initial clinical site (in 2013) for the training program with a second at Jimma University Medical Center (JUMC) in 2016. An Aslan clinical director was present throughout the first year at each location. Visiting faculty from the US and Canada provided clinical supervision, on-site didactics, and professional mentorship. The second year of training included a six-month rotation at a high-functioning cancer institution in India. Fellows were expected to complete a scholarly activity, pass a certification exam, and serve as pediatric hematologist-oncologists in Ethiopia for a minimum of two years following training. Outcomes: Since 2013, four physicians completed PHO fellowship based in Ethiopia, with extensive support of local healthcare leadership and visiting faculty. One additional fellow left training prior to completion and one fellow currently is in training. Twenty-three faculty members from 18 Universities made 51 trips to Ethiopia for onsite training of fellows from 2013-2019. Each fellow completed a rotation in India in his/her second year (Tata Memorial Hospital, Mumbai, or TMC Kolkata). Fellowship projects included a comprehensive pediatric cancer unit assessment, safe chemotherapy practices, and the role of diagnostic pathology. The four subspecialty-trained physicians have remained local, two at TASH, one at JUMC, and one returned to Gertrude's Children's Hospital in Nairobi, Kenya. JUMC now supports a 22 bed PHO unit running at 90% capacity with over 300 new diagnoses since August 2016. TASH supports a 26 bed inpatient unit and 16 additional inpatient beds at a nearby oncology center, treating over 600 new patients annually. The fellowship structure has succeeded in training subspecialty physicians to establish PHO care in Ethiopia. Discussion: Developing specialized care in LMIC requires a multifaceted approach, including nursing training, social support, health system buy-in, diagnostic expertise and facility, pharmacy services, and subspecialty physicians. Focusing on physician training for PHO in Ethiopia, we designed a training structure and curriculum to 1) teach resource appropriate medical care, 2) provide sustained clinical mentorship, 3) develop health system leadership skills, and 4) retain physicians to support local pediatric oncology units. Onsite training by visiting faculty was augmented by sending fellows to a mature, middle-income country program and the support of full-time clinical faculty/mentorship for a large portion of the program. Challenges included fellow recruitment, pathologic accuracy, chemotherapy access, nutritional support, and treatment retention. Formal subspecialty PHO training can be implemented in LMIC without established subspecialty physicians, but requires ongoing commitment of administrators, visiting faculty, local universities, and a multidisciplinary team of health professionals. Disclosures Alexander: AbbVie: Other: travel funding.

Description: MDM2 inhibition by small molecules as a means of restoring p53 function has shown clinical activity against acute myeloid leukemia (AML) (Andreeff, Clin Cancer Res 2015). However, we and others have found increased variant allele frequencies (VAFs) of TP53 mutations in AML cells after treatment with MDM2 inhibitors, either as monotherapy or in combination with other agents (Daver ASH 2019), which suggests that MDM2 inhibition selects preexisting clones or generates de novo clones with TP53 mutations. We performed a long-term culture of AML cells (MOLM-13, an AML cell line with wild-type p53 and FLT3-ITD) treated with increasing concentrations of an MDM2 inhibitor idasanutlin (up to 320 nM, less than 10% concentration of Cmax) (Selleck). We obtained MDM2 inhibitor-resistant (R) AML cells after 96 days of the drug exposure and found that the resistant cells harbor hotspot TP53 p.R248W (R248W) mutation. We next isolated single cell clones from MOLM-13 R cells by limiting dilution, and obtained twelve subclones (subclones #1-12 in order of development). All clones carried the same R248W mutation. To determine clonal patterns of these cells, we performed single cell DNA sequencing (scDNAseq) of MOLM-13 parental, R and subclone #1 and #2 (SC1 and SC2) cells using the MissionBio Tapestry system covering 125 amplicons of 19 genes frequently mutated in AML. scDNAseq identified FLT3-ITD mutations in all cells analyzed, as expected. In the parental cells we identified only 0.02% cells (1/ 5,240) with the identical R248W mutation found in MOLM-13 R cells. MOLM-13 R cells had only 0.6% of wild-type TP53 cells, 51% carrying R248W only, and 43% R248W/R213* mutation (R248W/R213*). SC1 and SC2 cells had 1% and 99% of R248W and R248W/R213* clones, respectively (Fig.1). Seven other mutations were detected by scDNAseq. Results suggest that MDM2 inhibition can accelerate the selection of TP53-mutant AML cells in vitro. Of note, the parental cells had remained mostly p53 wild-type, where the subclone with mutant R248W did not have a growth advantage over other cells. Next we analyzed patient samples enrolled in the phase 1 clinical trial (NCT02319369) for the MDM2 inhibitor milademetan (DS-3032b; Daiichi-Sankyo) in relapsed/refractory AML or high-risk MDS patients. Fifty seven patients were treated with single agent milademetan in the study. All but one patient had wild-type TP53 as determined by NGS at baseline. One patient (1.8%) had a TP53 p.R213* mutation at baseline with VAF of 91%. Four patients (7%) developed different TP53 mutations (R248Q, R248W, P250fs, V122fs and V274L), with increasing VAFs that were not detected at baseline to 19% average, ranging from 11% to 28% post treatment, One patient (anonymized ID 1001-1005) developed both, R248Q and R248W mutations, detected at cycle 2 day1 (C2D1, day 29). The pre-existing R213* mutation detected in one patient persisted with increased VAF after treatment (91% to 100%). To detect p53 mutations with higher sensitivity than NGS, we performed droplet digital PCR (ddPCR) for R248W/Q and R273H in samples from two patients. ddPCR detected 0.46% and 0.62% of R248Q and R248W mutations, respectively, at baseline, which were not detected by NGS, with increased VAFs of 18.2 and 27.6% at C2D1, respectively. ddPCR detected additional R273H mutations with VAFs of 0.08% and 0.18% at baseline, and 2.2% and 2.6% in these patients at C2D1, respectively. Conclusion: Data suggest that MDM2 inhibition selects rare AML subpopulations with TP53 mutations and careful monitoring of patients treated with MDM2 inhibitors with sensitive methods to detect TP53 mutant clones is warranted. This finding also points to the need to develop strategies to prevent/suppress these clones early on. Disclosures Kumar: Daiichi-Sankyo Inc.: Current Employment. Patel:Daiichi-Sankyo Inc.: Current Employment. Dos Santos:Daiichi Sankyo, Inc.: Current Employment. DiNardo:Daiichi Sankyo: Consultancy, Honoraria, Research Funding; Novartis: Consultancy; ImmuneOnc: Honoraria; Calithera: Research Funding; Celgene: Consultancy, Honoraria, Research Funding; Notable Labs: Membership on an entity's Board of Directors or advisory committees; AbbVie: Consultancy, Honoraria, Research Funding; MedImmune: Honoraria; Jazz: Honoraria; Agios: Consultancy, Honoraria, Research Funding; Takeda: Honoraria; Syros: Honoraria. Andreeff:Daiichi-Sankyo; Jazz Pharmaceuticals; Celgene; Amgen; AstraZeneca; 6 Dimensions Capital: Consultancy; Daiichi-Sankyo; Breast Cancer Research Foundation; CPRIT; NIH/NCI; Amgen; AstraZeneca: Research Funding; Centre for Drug Research & Development; Cancer UK; NCI-CTEP; German Research Council; Leukemia Lymphoma Foundation (LLS); NCI-RDCRN (Rare Disease Clin Network); CLL Founcdation; BioLineRx; SentiBio; Aptose Biosciences, Inc: Membership on an entity's Board of Directors or advisory committees; Amgen: Research Funding.