Targeting the Non-Homologous End-Joining Pathway Sensitizes MDM2-Amplified Liposarcoma to Doxorubicin-Induced Senescence, p53-Mediated Senescence.

Introduction 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. We used an unbiased approach to identify therapeutic strategies sensitizing to these DDLPS therapies. Methods 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. Results We uncovered pathways related to G1/S transition (CDK2, CKS1B, E2F3 and CCNE1) and Non-Homologous End-Joining (NHEJ; TDP2, PRKDC and XRCC4), inactivation of which sensitized to palbociclib and Doxorubicin, respectively. Following validation of both pathways, we focused on mechanistic characterization of Doxorubicin sensitization by genetic perturbation of TDP2 or pharmacological inhibition of DNA-PKcs using peposertib. Synergistic cell cycle arrest and senescence were induced by prolonged administration of low-dose doxorubicin. Senescent cells were triggered to undergo apoptosis by subsequent senolytic treatment with Bcl2 inhibitor navitoclax. Despite the amplification of MDM2, senescence proved dependent on p53. Consistent with this, TCGA and DepMap data suggest p53 activity in DDLPS. Conclusion 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-dependent cell cycle arrest and senescence. Furthermore, we provide, to our knowledge, the first evidence of maintained baseline p53 activity in MDM2-amplified DDLPS.