Combined STAT3 Degradation and RAS Inhibition Enhances Antiproliferative Activity in Myeloproliferative Neoplasm Cells

Philadelphia chromosome negative myeloproliferative neoplasms (MPNs), including polycythemia vera, essential thrombocythemia, and primary myelofibrosis, are clonal hematopoietic stem cell disorders driven predominantly by mutations in JAK2, CALR, or MPL, resulting in constitutive JAK-STAT signaling. Although JAK2 directed therapies improve disease related symptoms and splenomegaly, treatment resistance and disease progression to acute leukemia remain major therapeutic challenges. Persistent activation of downstream and compensatory signaling pathways may contribute to treatment resistance. KT-333, a selective STAT3 degrader, has demonstrated a tolerable safety profile, target degradation, and pathway inhibition in Phase 1 clinical trial evaluation. We investigated whether concurrent targeting of STAT3 with KT-333 and RAS signaling with RMC-6236 (daraxonrasib) reduces cell viability and alters oncogenic signaling in in-vitro models of MPN.

MPN cell lines, HEL and SET2, were treated with KT333, Daraxonrasib and their combination at multiple concentrations for 24-72 hours. Cell viability was assessed using CellTiter-Glo. Treatment associated changes in signaling proteins and apoptosis pathway were evaluated in SET2 cells by western blotting.

Combined KT333 and Daraxonrasib treatment significantly reduced viability of HEL and SET2 cells compared with single-agent treatment after 72 hours (p<0.0001, Figure 1). In SET2 cells, the combination also markedly reduced phospho-Ser-STAT3 and MYC protein levels after 24 hours, suggesting suppression of the STAT3–MYC signaling axis as a potential mechanism underlying the enhanced antiproliferative activity.

These findings support concurrent STAT3 and RAS targeting as a potential strategy to suppress compensatory survival signaling in JAK2 mutant cell lines. This is a novel therapeutic strategy to target compensatory survival pathways associated with resistance to JAK2 directed therapy. Future studies will assess MAPK activation, temporal changes in STAT3–MYC and apoptosis pathways, Annexin V/PI defined apoptosis. Furthermore, validation in primary MPN samples and ruxolitinib resistant cell lines will help define mechanism, synergy, and translational potential.