Abstract: Activated Notch signaling is highly prevalent in T-cell acute lymphoblastic leukemia (T-ALL) but pan-Notch inhibitors showed excessive toxicity in clinical trials. To find alternative ways to target Notch signals, we investigated Cell division cycle 73 (Cdc73), which is a Notch cofactor and key component of the RNA polymerase-associated transcriptional machinery, an emerging target in T-ALL. While we confirmed previous work that CDC73 interacts with NOTCH1, we also found that the interaction in T-ALL was context-dependent and facilitated by the transcription factor ETS1. Using mouse models, we showed that Cdc73 is important for Notch-induced T-cell development and T-ALL maintenance. Mechanistically, chromatin and nascent gene expression profiling showed that Cdc73 intersects with Ets1 and Notch at chromatin within enhancers to activate expression of known T-ALL oncogenes through its enhancer functions. Cdc73 also intersects with these factors within promoters to activate transcription of genes that are important for DNA repair and oxidative phosphorylation through its gene body functions. Consistently, Cdc73 deletion induced DNA damage and apoptosis and impaired mitochondrial function. The CDC73-induced DNA repair expression program co-opted by NOTCH1 is more highly expressed in T-ALL than in any other cancer. These data suggest that Cdc73 might induce a gene expression program that was eventually intersected and hijacked by oncogenic Notch to augment proliferation and mitigate genotoxic and metabolic stresses of elevated Notch signaling. Our report supports studying factors like CDC73 that intersect with Notch in order to derive basic science understanding on how to combat Notch-dependent cancers without directly targeting the Notch complex.

Abstract: Introduction: Myelodysplastic syndromes (MDS) are characterized by bone marrow dysplasia and ineffective hematopoiesis. Zhou et al. showed that transforming growth factor-beta (TGF-β) signaling was constitutively activated in MDS CD34+ cells and that this over-activation and subsequent myelosuppression was based on reduced expression of SMAD7, the natural inhibitor of TGF-β, in MDS CD34+ cells (Zhou L et al. Cancer Res 2011;71:955-963). Galunisertib specifically inhibited the kinase activity of the TGF-β receptor type I (TGF-βRI) also known as ALK5 and its downstream signaling pathway theoretically replaced the SMAD7 function. Galunisertib reversed hematopoietic suppression in human MDS bone marrow assays, and in a murine model of TGF-β derived bone marrow failure. Based on these preclinical studies that demonstrate hematological improvement (HI) in MDS models following galunisertib treatment, a single-arm phase 2 part of a phase 2/3 proof-of-concept study in very low-, low-, and intermediate-risk patients with MDS was conducted. Methods: The primary objective of this study was to estimate the HI rate based on International Working Group (IWG) 2006 criteria in patients with very low-, low-, and intermediate-risk MDS by Revised International Prognostic Scoring System (IPSS-R), treated with galunisertib. Eligible patients were treated with galunisertib 300 mg/day (150 mg BID) orally for 14 days, followed by 14 days off, constituting a cycle of 28 days. Eligibility criteria permitted any prior therapy, all of which were required to be discontinued at least 28 days prior to initiation of galunisertib. Supportive therapies including ongoing transfusions were allowed. Eligibility criteria included confirmed diagnosis of MDS, anemia with hemoglobin ≤10.0 g/dL, and an Eastern Cooperative Oncology Group performance status (ECOG PS) ≤2. Safety was assessed and summarized using the Common Terminology Criteria for Adverse Events (CTCAE v4.0). Descriptive statistics were used to report baseline characteristics and response rates. Results: In this phase 2 study, 41 patients received galunisertib orally (N=39, 150 mg BID and N=2, 80 mg BID for PK comparison). Patients were 62% males. The median age was 71 years (range: 52-84), the majority of patients were classified as refractory cytopenia with multilineage dysplasia (66.7%) or refractory anemia with ringed sideroblasts (20.5%) based on WHO MDS classification. ECOG PS was 0/1 in 53.8%/46.2% of patients. Sixty-two percent of the patients received ≥6 cycles of treatment. Among the 39 patients receiving 150 mg BID, a total of 15 (38%) patients discontinued from the study within 6 cycles; one due to AE and 9 due to patient/physician decision. The most common possibly related any grade treatment-emergent adverse events (TEAEs) included fatigue (20.5%), diarrhea (15.4%), pyrexia (10.3%), vomiting (10.3%), anemia (7.7%), nausea (7.7%), urinary tract infection (7.7%), neutrophil count decreased (5.1%), and platelet count decreased (5.1%); 12 (30.8%) patients had grade 3/4 TEAEs, 4 (10.3%) were drug-related. One of the 39 patients was protocol ineligible and was removed from the efficacy analysis. Among the 38 evaluable patients in the ITT population, 14 of whom required fewer than 4 units of transfusion per 8 weeks, 10/38 (26%) patients achieved HI, defined as at least a continuous 8-week response with at least a 4-unit reduction in transfusion requirement from baseline or hemoglobin increase by at least 1.5 g/dL per 8-week period. Of these 10 patients, 4 became transfusion-independent, and 5 had transfusion reduction. In a subgroup of 24/38 patients who had a transfusion requirement of at least 4 units every 8 weeks at baseline, 9 (38%) of these patients achieved a transfusion reduction of at least 4 units. No apparent correlation between cytogenetics or MDS subtype including ringed sideroblasts and response was identified; however, only 14 patients had abnormal cytogenetics. No platelet or neutrophil responses were observed. Conclusion: Galunisertib is well tolerated in this MDS population where this ALK5 inhibitor was investigated for the first time. Patients most commonly discontinued from study treatment due to patient/physician decision and not for toxicity. The clinical endpoint of HI was observed in 26% of the ITT population, and no specific response sub-group was identified. Disclosures Valcarcel: GSK: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; NOVARTIS: Honoraria, Membership on an entity's Board of Directors or advisory committees; AMGEN: 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. Platzbecker:Boehringer: Research Funding; Celgene: Honoraria, Research Funding; Novartis: Honoraria, Research Funding. Santini:celgene, Janssen, Novartis, Onconova: Honoraria, Research Funding. Díez-Campelo:Celgene: Research Funding, Speakers Bureau; Novartis: Research Funding, Speakers Bureau; Janssen: Research Funding. Schlenk:Boehringer-Ingelheim: Honoraria; Pfizer: Honoraria, Research Funding; Arog: Honoraria, Research Funding; Janssen: Membership on an entity's Board of Directors or advisory committees; Teva: Honoraria, Research Funding; Novartis: Honoraria, Research Funding; Daiichi Sankyo: Membership on an entity's Board of Directors or advisory committees. Gaidano:MorphoSys; Roche; Novartis; GlaxoSmithKline; Amgen; Janssen; Karyopharm: Honoraria, Other: Advisory boards; Celgene: Research Funding. Perez de Oteyza:Eli Lilly and Company: Research Funding. Cleverly:Eli Lilly and Company: Employment, Equity Ownership. Chiang:Eli Lilly and Copany: Employment. Lahn:Eli Lilly and Company: Other: Former employee. Desiaih:Eli Lilly and Company: Employment. Guba:Eli Lilly and Company: Employment, Equity Ownership. List:Celgene Corporation: Honoraria, Research Funding. Komrokji:Pharmacylics: Speakers Bureau; Novartis: Research Funding, Speakers Bureau; Incyte: Consultancy; Celgene: Consultancy, Research Funding.