Cell-state-dependent responses to PLK1 inhibition reveal a non-canonical microtubule-endolysosomal vulnerability in quiescent leukemia stem cells

Relapse in acute myeloid leukemia (AML) is frequently driven by therapy-resistant quiescent leukemia stem cells (LSCs). We show that inhibition of the mitotic master regulator Polo-like kinase 1 (PLK1), a kinase extensively pursued for antiproliferative therapy, unexpectedly eradicates quiescent LSCs through a mechanism distinct from its canonical mitotic function. In proliferating AML cells, PLK1 inhibition (PLK1i) induced G2/M arrest and mitotic catastrophe. In contrast, quiescence-enriched LSCs underwent apoptosis independent of mitotic arrest, revealing a cell-state-dependent mode of drug action. Mechanistically, PLK1i perturbed vesicle trafficking and endolysosomal homeostasis in LSC by disrupting a previously unrecognized PLK1-MAP1A interaction, leading to apoptotic cell death. Combinatorial pharmacologic perturbation studies established microtubule regulation as a critical determinant of quiescent LSC survival, while ex vivo and in vivo assays demonstrated depletion of functionally-defined LSC following PLK1i. These findings identify non-canonical effects of PLK1i in LSC and uncover a targetable vulnerability linked to microtubule and endolysosomal homeostasis.