Reduced 4E-BP1 activity leads to acquired capivasertib resistance via increased cap-dependent protein synthesis.

BackgroundThe PI3K/AKT/mTOR (PAM) pathway is frequently dysregulated in human cancers and is a major target of therapeutic intervention, exemplified by the newly approved AKT inhibitor capivasertib. However, clinical responses are often limited by the emergence of acquired drug resistance. MethodsTo uncover potential mechanisms underlying acquired resistance to capivasertib, we developed a drug-resistant ovarian cancer model (A2780 254R) through chronic exposure to the capivasertib precursor CCT129254. ResultsThe 254R cells exhibit broad cross-resistance to AKT inhibitors, including capivasertib, along with mTORC1 and PI3K inhibitors, in the absence of AKT mutations or elevated kinase activity. A defining feature of resistance is the reduced expression and phosphorylation of 4E-BP1, a key negative regulator of cap-dependent protein synthesis (CDPS). mcGTP pull-down assays revealed impaired 4E-BP1-eIF4E binding and persistent eIF4F complex formation, which was consistent with enhanced CDPS. An [~]9-fold increase in CDPS activity was observed in 254R cells, without corresponding increases in global protein synthesis or the expression of canonical eIF4E targets. Strikingly, ectopic expression of wild-type or constitutively active 4E-BP1 restored capivasertib sensitivity, re-established the 4E-BP1-eIF4E interaction, and significantly reduced resistance to capivasertib. These findings identify impaired 4E-BP1 function and elevated CDPS as central mediators of acquired resistance to capivasertib. ConclusionOverall, this work underscores the therapeutic vulnerability of the translational machinery to AKT inhibitor resistance. Targeting the eIF4F complex may offer a promising strategy to overcome acquired resistance, and the expression or phosphorylation of 4E-BP1 and eIF4E may serve as predictive biomarkers to guide use of capivasertib in the clinic.