Selective degradation of oncogenic signaling nodes by momelotinib-based protacs exerts potent anti-leukemic response in B-ALL, AML, and MF while sparing normal cells Free

Despite notable advancements in developing targeted tyrosine kinase inhibitors (TKIs) therapy for hematologic malignancies such as chronic myeloid leukemia (CML), myeloproliferative neoplasms (MPNs), B-cell acute lymphoblastic leukemia (B-ALL), and acute myeloid leukemia (AML), durable clinical efficacy is limited except for CML. TKI therapy in JAK2/CALR/MPL-mutated MPNs remains largely cytostatic while its efficacy in acute leukemias (B-ALL and AML) is transient. Treatment refractoriness and the emergence of resistance limits the prospect for effective treatment outcome. Growth factor (GF) signaling engaging alternative survival pathways and the acquisition of drug-evading mutations within the targeted kinases are the key mechanisms driving treatment failure and resistance. While kinase inhibitors effectively block the enzymatic activity of oncogenic kinases, their scaffolding functions remain unaffected and are implicated in driving resistance, particularly under growth factor signaling. Hematologic malignancies such as MPN, B-ALL, and AML, which are fueled by inflammatory cytokines, exhibit persistent activation of MAPK-AP1, JAK-STAT, and IKK-NFκB pathways. We reasoned that simultaneous degradation of these kinases through proteolysis targeting chimera (PROTACs), while targeting their oncogenic driver functions may overcome resistance mediated by GF signaling and provide better therapeutic efficacy. Our recent chemical screening identified momelotinib as a polypharmacological agent, which beside inhibiting JAK2 and FLT3, also targets PI3K, IKK1/2, and ERK. We engineered a series of momelotinib-based PROTACs using IAP ligands as warheads, optimizing linker chemistry to enhance target degradation. One lead molecule, termed Mom-PR, effectively degraded JAK2, FLT3, IKK1/2, IRAK1, PI3K, and ERK1, achieving ED90 values between 20–400 nM. Notably, Mom-PR induced selective cytotoxicity in cells expressing JAK2-V617F, BCR-ABL, or FLT3-ITD, with IC50 values ranging from 90–200 nM, whereas parental BaF3 cells exhibited an IC50 >4000 nM. Importantly, Mom-PR exhibited a robust anti-leukemic response against human leukemic cells derived from myelofibrosis (MF), B-ALL, and AML, and effectively blocked the GF mediated resistance. Collectively, these findings demonstrate that depleting key signaling nodes induces a selective anti-leukemic response while sparing normal hematopoietic cells with a favorable therapeutic index. While these results are promising, in vivo studies are currently underway to evaluate the therapeutic efficacy of this novel PROTAC in leukemic models. These findings provide a proof of concept to deplete the oncogenic kinases and key signaling nodes to target intrinsic resistance for enhanced therapeutic outcome.