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 (intrinsic) resistance. We used an unbiased approach to identify therapeutic strategies sensitizing to these current 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 leveraged to confirm molecular findings on a larger scale.

We found pathways related to G1/S transition (CDK2, CKS1B, E2F3 and CCNE1) and Non-Homologous End-Joining (NHEJ; TDP2, PRKDC and XRCC4) to sensitize 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 PRKDC using peposertib. Synergy was achieved by prolonged administration of low-dose doxorubicin in vitro and in vivo, driven by increased cell cycle arrest and senescence. Senescent cells were triggered to undergo into apoptosis by subsequent senolytic therapy. Surprisingly, despite the amplification of MDM2, senescence was dependent on p53. Leveraging TCGA and DepMap data, we confirm potential p53 activity in DDLPS.

These findings provide a rationale for targeting the NHEJ pathway to enhance the efficacy of doxorubicin in an MDM2-amplified cancer, highlighting a potential therapeutic strategy that exploits p53-dependent cell cycle arrest and senescence for improved treatment outcomes. Furthermore, we provide, to our knowledge, the first evidence of maintained p53 activity in untreated MDM2 amplified DDLPS.