Outcomes in patients with high-risk and treatment-resistant myelofibrosis (MF) post-JAK inhibitor therapy remain poor, with no approved drug therapies beyond the JAK inhibitor class. In certain clinical situations, such as severe thrombocytopenia, administration of most JAK inhibitors are contraindicated. Thus, there is an unmet medical need for the development of novel agents for patients with MF. SMAC mimetics [or inhibitor of apoptosis (IAP) antagonists] induce apoptosis in cancer cells. Because these agents are hypothesized to have increased activity in a tumor necrosis factor-A cytokine-rich microenvironment, as is the case with MF, we conducted a single-center, investigator-initiated phase 2 clinical trial, with a monovalent SMAC mimetic LCL161 (oral, starting dose, 1500 mg per week) in patients with intermediate to high-risk MF. In an older group, 66% with $2 prior therapies and a median baseline platelet count of 52 3 103/mL and 28% with ASXL1 mutations, we observed a 30% objective response by Revised International Working Group-Myeloproliferative Neoplasms Research and Treatment (IWG-MRT) 2013 criteria. Notably, 6 responding patients achieved clinical improvement of anemia: 4, hemoglobin response; 2, transfusion independence. Median OS was 34 months (range, 2.2-60.11). Reductions of cIAPs were observed in all responders. The most common toxicity was nausea/vomiting (N/V) in 64% (mostly grade 1/2); fatigue in 46%; and dizziness/vertigo in 30%. There were 4 grade 3/4 adverse events (2, syncope; 1, N/V; 1, skin eruption/pruritis). There were 2 deaths during the study period, both unrelated to the study drug. SMAC mimetics may represent an option for older patients with thrombocytopenia or for those in whom prior JAK inhibitors has failed. This trial was registered at www.clinicaltrials.gov as #NCT02098161.
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