BACKGROUND Patients with anemia and lower-risk myelodysplastic syndromes in whom erythropoiesis-stimulating agent therapy is not effective generally become dependent on red-cell transfusions. Luspatercept, a recombinant fusion protein that binds transforming growth factor β superfamily ligands to reduce SMAD2 and SMAD3 signaling, showed promising results in a phase 2 study. METHODS In a double-blind, placebo-controlled, phase 3 trial, we randomly assigned patients with very-low-risk, low-risk, or intermediate-risk myelodysplastic syndromes (defined according to the Revised International Prognostic Scoring System) with ring sideroblasts who had been receiving regular red-cell transfusions to receive either luspatercept (at a dose of 1.0 up to 1.75 mg per kilogram of body weight) or placebo, administered subcutaneously every 3 weeks. The primary end point was transfusion independence for 8 weeks or longer during weeks 1 through 24, and the key secondary end point was transfusion independence for 12 weeks or longer, assessed during both weeks 1 through 24 and weeks 1 through 48. RESULTS Of the 229 patients enrolled, 153 were randomly assigned to receive luspatercept and 76 to receive placebo; the baseline characteristics of the patients were balanced. Transfusion independence for 8 weeks or longer was observed in 38% of the patients in the luspatercept group, as compared with 13% of those in the placebo group (P<0.001). A higher percentage of patients in the luspatercept group than in the placebo group met the key secondary end point (28% vs. 8% for weeks 1 through 24, and 33% vs. 12% for weeks 1 through 48; P<0.001 for both comparisons). The most common luspaterceptassociated adverse events (of any grade) included fatigue, diarrhea, asthenia, nausea, and dizziness. The incidence of adverse events decreased over time. CONCLUSIONS Luspatercept reduced the severity of anemia in patients with lower-risk myelodysplastic syndromes with ring sideroblasts who had been receiving regular red-cell transfusions and who had disease that was refractory to or unlikely to respond to erythropoiesisstimulating agents or who had discontinued such agents owing to an adverse event. (Funded by Celgene and Acceleron Pharma; MEDALIST ClinicalTrials.gov number, NCT02631070; EudraCT number, 2015-003454-41.)

Dissipating excess calories as heat through therapeutic stimulation of brown adipose tissues (BAT) has been proposed as a potential treatment for obesity-linked disorders. Here, we describe the generation of a humanized effector-less bispecific antibody that activates fibroblast growth factor receptor (FGFR) 1/βKlotho complex, a common receptor for FGF21 and FGF19. Using this molecule, we show that antibody-mediated activation of FGFR1/βKlotho complex in mice induces sustained energy expenditure in BAT, browning of white adipose tissue, weight loss, and improvements in obesity-associated metabolic derangements including insulin resistance, hyperglycemia, dyslipidemia and hepatosteatosis. In mice and cynomolgus monkeys, FGFR1/βKlotho activation increased serum high-molecular-weight adiponectin, which appears to contribute over time by enhancing the amplitude of the metabolic benefits. At the same time, insulin sensitization by FGFR1/βKlotho activation occurs even before the onset of weight loss in a manner that is independent of adiponectin. Together, selective activation of FGFR1/βKlotho complex with a long acting therapeutic antibody represents an attractive approach for the treatment of type 2 diabetes and other obesity-linked disorders through enhanced energy expenditure, insulin sensitization and induction of high-molecular-weight adiponectin.

FGF21 is a stress-induced hormone with potent anti-obesity, insulin-sensitizing, and hepatoprotective properties. Although proteolytic cleavage of recombinant human FGF21 in preclinical species has been observed previously, the regulation of endogenously produced FGF21 is not well understood. Here we identify fibroblast activation protein (FAP) as the enzyme that cleaves and inactivates human FGF21. A selective chemical inhibitor, immunodepletion, or genetic deletion of Fap stabilized recombinant human FGF21 in serum. In addition, administration of a selective FAP inhibitor acutely increased circulating intact FGF21 levels in cynomolgus monkeys. On the basis of our findings, we propose selective FAP inhibition as a potential therapeutic approach to increase endogenous FGF21 activity for the treatment of obesity, type 2 diabetes, non-alcoholic steatohepatitis, and related metabolic disorders.

Fibroblast Activation Protein (FAP) is a membrane-bound serine protease whose expression is often elevated in activated fibroblasts associated with tissue remodeling in various common diseases such as cancer, arthritis and fibrosis. Like the closely related dipeptidyl peptidase DPPIV, the extracellular domain of FAP can be released into circulation as a functional enzyme, and limited studies suggest that the circulating level of FAP correlates with the degree of tissue fibrosis. Here we describe a novel homogeneous fluorescence intensity assay for circulating FAP activity based on a recently identified natural substrate, FGF21. This assay is unique in that it can effectively distinguish endopeptidase activity of FAP from that of other related enzymes such as prolyl endopeptidase (PREP) and was validated using Fap-deficient mice. Structural modeling was used to elucidate the mechanistic basis for the observed specificity in substrate recognition by FAP, but not by DPPIV or PREP. Finally, the assay was used to detect elevated FAP activity in human patients diagnosed with liver cirrhosis and to determine the effectiveness of a chemical inhibitor for FAP in mice. We propose that the assay presented here could thus be utilized for diagnosis of FAP-related pathologies and for the therapeutic development of FAP inhibitors.

Introduction: Patients (pts) with higher-risk myelodysplastic syndromes (MDS) are typically treated with azacitidine (Aza). Venetoclax (Ven) is a selective, potent, oral BCL-2 inhibitor that has demonstrated synergy with Aza in preclinical studies of myeloid malignancies. Higher-risk MDS is associated with mutations in genes involved in RNA splicing, epigenetic regulation, transcription, and cellular signaling. Assessing the dynamics of genetic variants during treatment of higher-risk MDS enables understanding of the molecular determinants of response. This phase 1b study (NCT02942290) evaluates Ven + Aza for treatment-naïve higher-risk MDS, and we report efficacy among mutationally defined subgroups as well as the depth of molecular response. Methods: Pts (≥18 years) with higher-risk MDS enrolled in the study had International Prognostic Scoring System intermediate-2 or high-risk MDS, bone marrow (BM) blasts &lt;20% at baseline, and ECOG ≤2 performance status. Aza 75 mg/m 2 was administered on Days (d) 1-7 of each 28-d cycle. The Ven RP2D was 400 mg x 14 d of each 28-d cycle. Primary objectives were to assess the Ven+Aza safety profile and to establish the RP2D. Key secondary objectives were to assess the overall response rate (ORR), defined as complete remission (CR), marrow CR and partial remission (PR), and overall survival. Analyses were carried out on all pts who received ≥1 dose of study drug and efficacy was evaluated per IWG 2006 response criteria. Molecular responses were quantified by mutation analysis of baseline and serial BM aspirate (BMA) or peripheral blood (PB) samples collected at protocol-specified time points. Mutations were identified in BMA using Archer VariantPlex Myeloid 75-gene panel [limit of detection (LOD) 5%; time points: pre-treatment (n=43), on-treatment (n=32), and treatment completion visit (TCV) (n=25)] or TruSight Myeloid 54-gene Sequencing Panel in PB [LOD 2%; time points: pre-treatment (n=21), on-treatment (n=19), and TCV (n=8)] to assess molecular dynamics during Ven + Aza treatment. Molecular responses were only compared within the same tissue type. Results: At the Dec 15, 2020 cutoff, 78 pts had received Ven+Aza, including 51 who received Ven at the RP2D of 400 mg x 14 d, with median follow up time of 23 mos (range 0.1-44.2). Median age was 70 years (range 26-87); 72% male; and 91% had excess BM blasts (&gt;5 to ≤10%, n=21; &gt;10 to ≤20%, n=49; &gt;20%, n=1). For the entire population, mORR was 80% (CR 40% and mCR 40%; no PR). 42% with mCR also had hematologic improvement [HI]. Screening mutational profiling was performed on 46/51 pts who received the RP2D of Ven + Aza. The most common mutations were TP53 (26%), ASXL1 (24%), U2AF1 (17%), and RUNX1 (15%), consistent with a higher-risk MDS population. Clinical responses (CR + mCR) were observed across the mutational spectrum, including in pts with poor prognostic mutations in TP53 (83%), ASXL1 (82%), and RUNX1 (71%). Sixty-four pts treated with Ven + Aza (all Ven dosing cohorts) had paired BMA or PB pre-treatment and on-treatment and/or end of study samples available for serial analysis at the Dec 15, 2020 data cutoff. Ven + Aza resulted in robust and rapid molecular responses across the mutational spectrum. Pts who achieved CR at the time of serial sample acquisition had more significant reduction of variant allele frequencies (VAFs) (n=18 pts, mean VAF pre-treatment = 38.3; mean VAF at CR = 11.8) compared to pts who achieved stable disease or HI (n=11 pts, mean VAF pre-treatment = 29.8; mean VAF at SD or HI = 24.0) or progressive disease (n=10 pts, mean VAF pre-treatment = 27.4; mean VAF at PD = 26.9). Reductions of VAFs below the LOD were observed across the mutational spectrum, including in genes that are considered poor prognostic in higher-risk MDS (e.g., TP53, ASXL1 and RUNX1), demonstrating the broad molecular activity of Ven + Aza (Figure). Finally, molecular responses were observed quickly, with VAF reductions below the LOD observed as early as end of Cycle 1, consistent with the mechanism of action of Ven directly activating the mitochondrial apoptotic pathway in cells. Conclusions: Pts with higher-risk MDS treated with Ven + Aza had rapid, durable responses and high remission rates. Pts across key mutational profiles achieved meaningful clinical and molecular responses, supporting an all-comers approach. Updated data will be presented, which will provide more follow up time and durability of responses among mutational subsets. Figure 1 Figure 1. Disclosures Garcia: Genentech: Research Funding; Takeda: Consultancy, Membership on an entity's Board of Directors or advisory committees; Astellas: Consultancy, Membership on an entity's Board of Directors or advisory committees; AbbVie: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; AstraZeneca: Research Funding; Prelude: Research Funding; Pfizer: Research Funding. Wei: Novartis, Celgene, AbbVie, Servier, AstraZeneca, and Amgen: Research Funding; Novartis, Janssen, Amgen, Roche, Pfizer, Abbvie, Servier, BMS, Macrogenics, Agios, Gilead: Membership on an entity's Board of Directors or advisory committees; Astellas: Honoraria. Jacoby: Abbvie: Research Funding; Jazz: Research Funding. Fong: Amgen, BMS: Speakers Bureau; AbbVie, Amgen, Novartis, Pfizer, Astellas: Honoraria; Amgen: Research Funding. Borate: Jazz Pharma: Research Funding; Blueprint Medicine: Membership on an entity's Board of Directors or advisory committees; Astellas: Membership on an entity's Board of Directors or advisory committees; Pfizer: Membership on an entity's Board of Directors or advisory committees, Research Funding; AbbVie: Membership on an entity's Board of Directors or advisory committees, Research Funding; Genentech: Membership on an entity's Board of Directors or advisory committees, Other: Advisory Board; Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding; Takeda: Membership on an entity's Board of Directors or advisory committees; Daiichi-Sankyo: Membership on an entity's Board of Directors or advisory committees; incyte: Membership on an entity's Board of Directors or advisory committees, Research Funding; Rampal: Membership on an entity's Board of Directors or advisory committees; Galecto, Inc.: Consultancy; Promedior: Consultancy. Cunningham: AbbVie, Amgen, Astex, Celgene, Janssen, Novartis, Principia Biopharma, Rigel: Research Funding. Odenike: Celgene, Incyte, AstraZeneca, Astex, NS Pharma, AbbVie, Gilead, Janssen, Oncotherapy, Agios, CTI/Baxalta, Aprea: Research Funding; AbbVie, Celgene, Impact Biomedicines, Novartis, Taiho Oncology, Takeda: Consultancy. Jurcic: AbbVie, BMS/Celgene, Novartis: Consultancy; AbbVie, Arog Pharmaceuticals, Astellas, BMS/Celgene, Forma Therapeutics, Genentech, Gilead Sciences, PTC Therapeutics, Syros Pharmaceuticals: Research Funding. Nowak: Pharmaxis: Current holder of individual stocks in a privately-held company, Research Funding; AbbVie: Other: Investigator on funded clinical trial; Affimed: Research Funding; Tolero Pharma, Pharmaxis, Apogenix: Research Funding; Celgene: Honoraria; Takeda: Honoraria. Platzbecker: Janssen: Honoraria; Celgene/BMS: Honoraria; Geron: Honoraria; AbbVie: Honoraria; Novartis: Honoraria; Takeda: Honoraria. Dunshee: Genentech/Roche: Current Employment, Current equity holder in publicly-traded company. Zhou: AbbVie: Current Employment, Current holder of stock options in a privately-held company. Hoffman: AbbVie: Current Employment, Current holder of stock options in a privately-held company. Sun: AbbVie: Current Employment. Popovic: AbbVie: Current Employment, Current equity holder in publicly-traded company. Ainsworth: AbbVie: Current Employment, Current holder of stock options in a privately-held company. Naqvi: Genentech/Roche: Current Employment, Current holder of stock options in a privately-held company. Kye: AbbVie: Current Employment, Other: May hold equity. Hogdal: AbbVie: Current Employment, Current holder of stock options in a privately-held company.