Targeting the Non-Homologous End-Joining Pathway Sensitizes MDM2-Amplified Liposarcoma to Doxorubicin by Enhancing p53-Mediated Senescence

Dedifferentiated liposarcoma (DDLPS) is a rare cancer defined by amplification of MDM2 and CDK4. Conventional chemotherapy (doxorubicin) and targeted inhibition of MDM2 and CDK4 show sporadic responses, but most tumors display primary resistance. Here, we used an unbiased approach to identify therapeutic strategies sensitizing to these DDLPS therapies. Three parallel genome-wide CRISPR-Cas9 knockout screens were conducted in DDLPS cells to sensitize to palbociclib (CDK4 inhibitor), nutlin-3a (MDM2 inhibitor) or doxorubicin. Top screen hits were validated and characterized in both in vitro and in vivo models, while clinical data were used to corroborate molecular findings. Inactivation of genes related to G1/S transition (CDK2, CKS1B, E2F3 and CCNE1) and non-homologous end-joining (NHEJ; TDP2, PRKDC and XRCC4), enhanced sensitivity to palbociclib and doxorubicin, respectively. Genetic perturbation of TDP2 or pharmacological inhibition of DNA-PKcs using peposertib synergized with prolonged administration of low-dose doxorubicin to induce cell cycle arrest and senescence, and subsequent senolytic treatment with Bcl2 inhibitor navitoclax triggered senescent cells to undergo apoptosis. Despite the amplification of MDM2, senescence was mediated by p53. Consistently, TCGA and DepMap data suggested p53 activity in DDLPS. These findings provide a rationale for targeting the NHEJ pathway to enhance the efficacy of low-dose doxorubicin in DDLPS, highlighting a potential therapeutic strategy exploiting p53-mediated cell cycle arrest and senescence. Furthermore, this study provides evidence of maintained baseline p53 activity in MDM2-amplified DDLPS.