Targeting Musashi-2 to counteract senescence and resistance in chronic myeloid leukemia: enhancing the efficacy of imatinib therapy

Chronic myeloid leukemia (CML) is a myeloproliferative malignancy marked through the excessive proliferative growth of functional myeloid cells. Approximately 95% of CML patients harbor the BCR-ABL fusion gene (Philadelphia chromosome), key driver of leukemogenesis. Despite therapeutic advancements with tyrosine kinase inhibitors (TKIs) such as imatinib, challenges including drug resistance, tumor cell senescence, and minimal residual disease (MRD) persist, primarily due to leukemic stem cells (LSCs) and senescent cells that evade TKI-mediated eradication. Musashi-2 (MSI2), an RNA-binding protein, is elevated in aggressive CML and is associated with poor disease prognosis. While its role in LSCs is emerging, its contribution to resistance and senescence remains unclear. This study investigated the role of MSI2 in proliferation and senescence by using pharmacological and biochemical approaches in imatinib sensitive (K562 S) and resistant (K562 R) models. Proliferation was assessed by MTT and colony formation assays. Apoptosis and expression analysis were performed using DNA fragmentation assay and Real time polymerase chain reaction (RT-PCR) respectively. MSI2 was significantly overexpressed in both models (p = 0.0004 and p < 0.001). Pharmacological targeting of MSI2 reduced cell viability and colony formation in both sensitive (p < 0.001) and resistant (p < 0.001) cells. Combined therapy with imatinib and MSI2 inhibition had an additive effect on K562 S (p = 0.002) and a synergistic effect in K562 R (p = 0.0017). Mechanistically, MSI2 inhibition moderately induced apoptosis and significantly upregulated p53 (p = 0.004), indicating activation of apoptotic pathways. Notably, the levels of senescence-associated cell cycle regulators, p16, p21, and p27, were significantly decreased (p = 0.0025, 0.0052, and 0.0015, respectively), suggesting that growth suppression was not due to classical cell cycle arrest. MSI2 inhibition also disrupted Wnt/β-catenin signaling by downregulating Eya3 (p = 0.0008), c-Myc (p = 0.0128), and HIF-1α (p = 0.0050) expression. Imatinib monotherapy increased p16, p21, and p27 expression, indicating therapy-induced senescence (TIS). Subsequent MSI2 inhibition reduced the levels of these markers and IL-6, highlighting its role in regulating TIS at the transcriptional level. In conclusion, MSI2 inhibition, in combination with TKI therapy, has shown to overcome drug resistance and mitigate senescence in preclinical CML models, and suggesting a potential strategy to target CML LSCs.