Background: Sabatolimab (MBG453) is a high-affinity, humanized, IgG4 (S228P) antibody targeting TIM-3, an inhibitory receptor that regulates adaptive and innate immune responses. TIM-3 is expressed on immune cells as well as leukemic stem cells (LSCs) and blasts, but not normal hematopoietic stem cells, making it a promising target in AML/MDS. Sabatolimab is a potential first-in-class immunotherapeutic agent that can target TIM-3 on immune and myeloid cells. Blockade of TIM-3 by sabatolimab may restore immune function while also directly targeting LSCs and blasts. Study Design and Methods : This is a phase Ib, open-label, multicenter, dose-escalation study of sabatolimab + HMA (decitabine [Dec] or azacitidine [Aza]) in patients (pts) with AML or HR-MDS (NCT03066648). Pts were adults with newly diagnosed (ND) or relapsed/refractory (R/R; ≥1 prior therapy) AML or IPSS-R high- or very high-risk MDS; pts with chronic myelomonocytic leukemia (CMML) were also eligible. Pts were HMA naive and ineligible for intensive chemotherapy. Escalating dose cohorts of IV sabatolimab examined were: 240 or 400 mg Q2W (D8, D22) or 800 mg Q4W (D8) combined with Dec (20 mg/m2; IV D1-5) or Aza (75 mg/m2; IV/SC D1-7) per 28-day cycle. Primary objectives included safety/tolerability; secondary objectives included preliminary efficacy and pharmacokinetics. Results: As of the data cutoff (25 Jun 2020), 48 pts with ND AML, 39 pts with HR-MDS, and 12 pts with CMML received sabatolimab + HMA. Data from 29 pts with R/R AML were previously reported. For a broader understanding of the effect of sabatolimab + HMA, results are reported here for the Dec and Aza arms both combined and separately (Table). Median (range) duration of sabatolimab exposure was 4.5 (0.3-28.3) mo for ND AML and 4.1 (0.7-33.6) mo for HR-MDS, with 17 and 11 pts ongoing, respectively. With sabatolimab + HMA, the most common (>10% in either disease cohort) gr ≥3 treatment-emergent adverse events (TEAEs) in pts with ND AML and HR-MDS, respectively, were thrombocytopenia (45.8%, 51.2%), neutropenia (50%, 46.1%), febrile neutropenia (29.2%, 41%), anemia (27.1%, 28.2%), and pneumonia (10.4%, 5.1%). Discontinuation due to AE was infrequent among pts with ND AML (6.3% [3/48]; 1 each of fatigue, febrile neutropenia, and possible HLH); none occurred among pts with HR-MDS. One dose-limiting toxicity occurred with sabatolimab 240 mg Q2W + Dec (gr 3 ALT elevation); the maximum tolerated dose was not reached with either combination. To comprehensively assess possible immune-mediated AEs (imAEs), events were evaluated across all disease cohorts. Seven gr 3 treatment-related possible imAEs were reported in 5 pts: arthritis, rash, possible HLH, and increased ALT in 1 pt each, and hypothyroidism, infusion-related reaction, and increased ALT in 1 pt. No gr 4 treatment-related possible imAEs occurred; however, there was a case of enterocolitis in a pt with HR-MDS who died of septic shock with neutropenic colitis. No other treatment-related deaths were reported. Among 34 evaluable pts with ND AML, overall response rate (ORR) was 41.2%: 8 CR, 3 CRi, 3 PR. Median (range) time to response (TTR) was 2.1 (1.8-13.1) mo and estimated 6-mo duration of response (DOR) rate was 85.1% (95% CI: 68-100%). Estimated 12-mo progression-free survival (PFS) rate was 44% (95% CI: 28-69.3%). Among 35 evaluable pts with HR-MDS, ORR was 62.9%: 8 CR, 8 mCR (5 with hematologic improvement [HI]), 6 SD with HI. Median (range) TTR was 2.0 (1.7-9.6) mo and estimated 6-mo DOR rate for CR/mCR/PR was 90% (95% CI: 73.2-100%). Encouraging response rates were achieved in both pts with high-risk MDS (ORR 50% [11/22]) and very high-risk MDS (ORR 84.6% [11/13]). Of pts with HR-MDS, 8 (5 high-risk, 3 very high-risk) proceeded to transplant. Estimated 12-mo PFS rate was 58.1% (95% CI: 39.9-84.6%). Among 12 pts with CMML, the safety profile of sabatolimab + HMA was generally consistent with that for AML/HR-MDS (most common gr ≥3 TEAEs: thrombocytopenia, n=7; neutropenia, n=7; anemia, n=6). ORR among 11 evaluable pts was 63.6%: 2 CR, 3 mCR, 1 PR, 1 SD with HI. Conclusions: Sabatolimab + HMA is well tolerated in pts with AML and HR-MDS and continues to show promising antileukemic activity and emerging durability. These results support TIM-3 as a potential therapeutic target and provide a basis for further development of sabatolimab + HMA in pts with AML or higher-risk MDS. Co-senior authors Uma Borate and Andrew H. Wei contributed equally to the work. Table Disclosures Brunner: Acceleron Pharma Inc.: Consultancy; Biogen: Consultancy; Celgene/BMS: Consultancy, Research Funding; Forty Seven, Inc: Consultancy; Jazz Pharma: Consultancy; Novartis: Consultancy, Research Funding; Takeda: Consultancy, Research Funding; Xcenda: Consultancy; GSK: Research Funding; Janssen: Research Funding; Astra Zeneca: Research Funding. Porkka:Novartis: Consultancy, Honoraria, Research Funding; BMS/Celgene: Honoraria, Research Funding. Knapper:Novartis: Consultancy, Honoraria, Research Funding. Garcia-Manero:Novartis: Research Funding; Genentech: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Onconova: Research Funding; Bristol-Myers Squibb: Consultancy, Research Funding; Amphivena Therapeutics: Research Funding; Jazz Pharmaceuticals: Consultancy; Merck: Research Funding; Acceleron Pharmaceuticals: Consultancy, Honoraria; AbbVie: Honoraria, Research Funding; Helsinn Therapeutics: Consultancy, Honoraria, Research Funding; H3 Biomedicine: Research Funding; Celgene: Consultancy, Honoraria, Research Funding; Astex Pharmaceuticals: Consultancy, Honoraria, Research Funding. Wermke:MacroGenics: Honoraria. Janssen:Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; BMS: Other: Founder of the HematologyApp which is supported by Janssen, BMS, Incyte, MSD, Pfizer, Daiichi-Sankyo, Roche and Takeda, Research Funding; Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Founder of the HematologyApp which is supported by Janssen, BMS, Incyte, MSD, Pfizer, Daiichi-Sankyo, Roche and Takeda; Incyte: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Founder of the HematologyApp which is supported by Janssen, BMS, Incyte, MSD, Pfizer, Daiichi-Sankyo, Roche and Takeda; Abbvie: Membership on an entity's Board of Directors or advisory committees; Janssen: Other: Founder of the HematologyApp which is supported by Janssen, BMS, Incyte, MSD, Pfizer, Daiichi-Sankyo, Roche and Takeda; Takeda: Other: Founder of the HematologyApp which is supported by Janssen, BMS, Incyte, MSD, Pfizer, Daiichi-Sankyo, Roche and Takeda; Daiichi-Sankyo: Other: Founder of the HematologyApp which is supported by Janssen, BMS, Incyte, MSD, Pfizer, Daiichi-Sankyo, Roche and Takeda; Roche: Other: Founder of the HematologyApp which is supported by Janssen, BMS, Incyte, MSD, Pfizer, Daiichi-Sankyo, Roche and Takeda; MSD: Other: Founder of the HematologyApp which is supported by Janssen, BMS, Incyte, MSD, Pfizer, Daiichi-Sankyo, Roche and Takeda. Traer:Daiichi Sankyo: Membership on an entity's Board of Directors or advisory committees; Agios: Membership on an entity's Board of Directors or advisory committees; Genentech: Membership on an entity's Board of Directors or advisory committees; Astellas: Membership on an entity's Board of Directors or advisory committees; Incyte: Research Funding; Notable Labs: Consultancy, Current equity holder in private company; Abbvie: Consultancy, Membership on an entity's Board of Directors or advisory committees. Narayan:Sanofi-Genzyme: Other: Current Spouse employment ; Takeda: Other: Prior Spouse employment within 24 months; Genentech: Other: Prior Spouse employment within 24 months and prior spouse equity divested within past 24 months. Kontro:Celgene: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Astellas: Consultancy, Membership on an entity's Board of Directors or advisory committees; Jazz Pharma: Membership on an entity's Board of Directors or advisory committees; Abbvie: Research Funding. Ottmann:Novartis: Honoraria; Amgen: Honoraria, Research Funding; Celgene: Honoraria, Research Funding; Fusion Pharma: Honoraria; Incyte: Honoraria, Research Funding. Naidu:Novartis Pharmaceuticals: Current Employment. Kurtulus:Novartis: Current Employment. Makofske:Novartis: Current Employment. Liao:Novartis: Current Employment. Sabatos-Peyton:Novartis: Current Employment, Patents & Royalties: Yes, patent related to MBG453 and also prior TIM-3 patents from grad student/ postdoc work at Harvard/BWH; CoStim Pharmaceuticals: Patents & Royalties: Held shares as employee, now paid via Novartis. Rinne:Qiagen: Consultancy; Novartis: Current Employment. Borate:Pfizer: Membership on an entity's Board of Directors or advisory committees, Research Funding; AbbVie: Other: Investigator in AbbVie-funded clinical trials; Jazz Pharmaceuticals: Research Funding; Takeda: Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding; Daiichi Sankyo: Membership on an entity's Board of Directors or advisory committees; Genentech: Membership on an entity's Board of Directors or advisory committees. Wei:BMS: Consultancy, Honoraria, Research Funding, Speakers Bureau; Pfizer: Honoraria; Amgen: Honoraria, Research Funding; Janssen: Honoraria; Walter and Eliza Hall Institute of Medical Research: Patents & Royalties; Astellas: Honoraria, Membership on an entity's Board of Directors or advisory committees; Genetech: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; AbbVie: Honoraria, Research Funding, Speakers Bureau; Servier: Consultancy, Honoraria, Research Funding; Novartis: Honoraria, Research Funding, Speakers Bureau; AstraZeneca: Honoraria, Research Funding.

p300 and CBP are highly related histone acetyltransferase (HAT) enzymes that regulate gene expression, and their dysregulation has been linked to cancer and other diseases. p300/CBP is composed of a number of domains including a HAT domain which is inhibited by the small molecule A-485 and an acetyl-lysine binding bromodomain which was recently found to be selectively antagonized by the small molecule I-CBP112. Here we show that the combination of I-CBP112 and A-485 can synergize to inhibit prostate cancer cell proliferation. We find that the combination confers a dramatic reduction in p300 chromatin occupancy compared to the individual effects of blocking either domain alone. Accompanying this loss of p300 on chromatin, combination treatment leads to the reduction of specific mRNAs including androgen-dependent and pro-oncogenic prostate genes such as KLK3 (PSA) and c-Myc. Consistent with p300 chromatin binding directly affecting gene expression, mRNAs that are significantly reduced by combination treatment also exhibit a strong reduction in p300 chromatin occupancy at their gene promoters. The relatively few mRNAs that are up-regulated upon combination treatment show no correlation with p300 occupancy. These studies provide support for the pharmacologic advantage of concurrent targeting of two domains within one key epigenetic modification enzyme.

Understanding the genetic control of human embryonic stem cell function is foundational for developmental biology and regenerative medicine. Here we describe an integrated genome-scale loss- and gain-of-function screening approach to identify genetic networks governing embryonic stem cell proliferation and differentiation into the three germ layers. We identified a deep link between pluripotency maintenance and survival by showing that genetic alterations that cause pluripotency dissolution simultaneously increase apoptosis resistance. We discovered that the chromatin-modifying complex SAGA and in particular its subunit TADA2B are central regulators of pluripotency, survival, growth, and lineage specification. Joint analysis of all screens revealed that genetic alterations that broadly inhibit differentiation across multiple germ layers drive proliferation and survival under pluripotency-maintaining conditions and coincide with known cancer drivers. Our results show the power of integrated multilayer genetic screening for the robust mapping of complex genetic networks.

Infant B-cell acute lymphoblastic leukemias (B-ALLs) that harbor MLL-AF4 rearrangements are associated with a poor prognosis. One important obstacle to progress for this patient population is the lack of immunocompetent models that faithfully recapitulate the short latency and aggressiveness of this disease. Recent whole-genome sequencing of MLL-AF4 B-ALL samples revealed a high frequency of activating RAS mutations; however, single-agent targeting of downstream effectors of the RAS pathway in these mutated MLL-r B-ALLs has demonstrated limited and nondurable antileukemic effects. Here, we demonstrate that the expression of activating mutant N-RasG12D cooperates with Mll-Af4 to generate a highly aggressive serially transplantable B-ALL in mice. We used our novel mouse model to test the sensitivity of Mll-Af4/N-RasG12D leukemia to small molecule inhibitors and found potent and synergistic preclinical efficacy of dual targeting of the Mek and Atr pathways in mouse- and patient-derived xenografts with both mutations in vivo, suggesting this combination as an attractive therapeutic opportunity that might be used to treat patients with these mutations. Our studies indicate that this mouse model of Mll-Af4/N-Ras B-ALL is a powerful tool to explore the molecular and genetic pathogenesis of this disease subtype, as well as a preclinical discovery platform for novel therapeutic strategies.