Beyond JAK2 Inhibitors: A Systematic Review of Management Strategies for Myelofibrosis

Introduction Drugs that target activating mutations of Janus Kinase 2 (JAK2) have been the backbone of myelofibrosis (MF) management. With recent advancements in our understanding of the underlying molecular mechanisms involved in myelofibrosis (MF) pathogenesis, numerous novel agents have been developed in the last decade. We have systematically reviewed the mechanisms of actions, efficacy and safety of these drugs. Methods A comprehensive literature research was performed using PubMed, Cochrane, EMBASE, Web of Science and Clinicaltrials.gov. We included all trials that were under development in phase I/II/III trials. Our search identified 1642 full-length manuscripts or abstracts with published results in the last decade were screened for relevant studies. Of these, 212 articles were finalized for our final analyses. Results Hedgehog inhibitors (saridegib, glasdegib and sonidegib) targets signaling membrane protein, smoothened. The combination of sonidegib + ruxulotinib (RUX) elicited the best response. Spleen volume reduction (SVR) ≥35% and spleen length reduction (SLR) ≥50% was reported in 15 (55.6%) and 25 (92.6%) patients. Histone deacetylase inhibitors (panobinostat, pracinostat, vorinostat, givinostat) target JAK2-H3Y41-HP1 pathway involved in hematopoiesis and leukemogenesis. The combination of pracinostat + RUX demonstrated the best response in a phase II trial (n=22), with clinical improvement (IWG-MRT) in splenomegaly, symptoms and both were reported in four (18%), two (9%), and ten (45%) patients that were durable for a median of 7.5 months. Immunomodulators: Lenalidomide has shown anemia responses in 32% of patients in combination with prednisone, in a phase II trial (n=40). Improvement in bone marrow fibrosis (10/11 patients with G4 reduced to G2 or better) was also seen. Pomalidomide with or without prednisone has shown anemia responses varying from 17-24% across different trials. However, a recent phase III trial (n=32) comparing pomalidomide vs. placebo, found no difference in transfusion independence rates (16% vs. 16%, p=1.00). Azacytidine (AZA) and decitabine (DCB) are hypomethylating agents. An objective response rate (ORR) of 69% (n=39) with AZA+RUX was noted. DCB+RUX demonstrated an ORR of 57% with a median overall survival of 10.4 months, in a phase I trial (n=21). Imetelstat is a telomerase inhibitor that has shown an ORR of 21% among 33 MF patients. Responses were characterized by BMF improvement (n=4) and transfusion independenc