Multiple patient-derived glioblastoma models reveal synthetic lethality through concurrent PI3K and CDK4/6 inhibition by blocking trans-active cooperation

BACKGROUND: Dysregulation of the phosphoinositide 3-kinase (PI3K) signaling pathway has been recognized as a pivotal oncogenic driver in Glioblastoma multiforme (GBM) progression. Although PI3K inhibitors have demonstrated initial therapeutic efficacy, the development of resistance through compensatory upregulation of alternative signaling pathways substantially limits their clinical benefits. However, the molecular mechanisms underlying this resistance to PI3K monotherapy in GBM remain incompletely understood. METHODS: Multiple patient-derived glioblastoma models including organoids (GBOs), primary dissociated cells (PDCs) and xenografts (PDCX) were established as clinically relevant platforms to evaluate the feasibility of tailored therapy. Comprehensive molecular profiling and functional analyses were conducted across these patient-derived models. RNA sequencing, mass spectrometry, DNA spreading assays, HR/NHEJ reporter assays and mIF were performed to elucidate the molecular underpinnings of PI3K and cyclin-dependent kinase 4/6 (CDK4/6) co-activation in driving tumor evolution, and to reveal the synthetic lethality efficacy of the concurrent strategy. RESULTS: Our findings demonstrate that PI3K monoinhibition induces aberrant CDK4/6 activation, and co-activation of PI3K-CDK4/6 signaling positively correlates with monotherapy resistance, which is driven by tumor evolution. The concurrent strategies with PI3K and CDK4/6 inhibition synergistically achieve therapeutic efficacy in suppressing the growth of GBOs, PDCs and PDCX. Mechanistically, insufficient DNA damage response under PI3Ki mono-therapy upregulated CDK4/6, driving aberrant cell cycle progression. The small-molecule inhibitors paxalisib and ribociclib potently suppress tumor proliferation, which induced persistent replication stress and genomic instability. CONCLUSIONS: Employing multiple patient-derived models, our study uncovers clinically relevant PI3Ki resistance mechanisms and advocates a rationale for synthetic lethality through combined PI3K-CDK4/6 inhibition, offering substantial therapeutic potential for GBM patients.