Purpose MDM2 and CDK4 are frequently co-amplified in well-differentiated/dedifferentiated liposarcoma (WDLPS/DDLPS). We aimed to determine whether combined MDM2/CDK4 targeting is associated with higher antitumour activity than a single agent in preclinical models of DDLPS.Experimental designDDLPS cells were exposed to RG7388 (MDM2 antagonist) and palbociclib (CDK4 inhibitor), and apoptosis and signalling/survival pathway perturbations were monitored by flow cytometry and Western blotting. Xenograft mouse models were used to assess tumour growth and survival. Treatment efficacy was assessed by Western blotting, histopathology and tumour volume.ResultsRG7388 and palbociclib together exerted a greater antitumour effect than either drug alone, with significant differences in cell viability after a 72-h treatment with RG7388 and/or palbociclib. The combination treatment significantly increased apoptosis compared to the single agents. We then analysed the in vivo antitumour activity of RG7388 and palbociclib in a xenograft model of DDLPS. The combination regimen reduced the tumour growth rate compared with a single agent alone and significantly increased the median progression-free survival.ConclusionsOur results provide a strong rationale for evaluating the therapeutic potential of CDK4 inhibitors as potentiators of MDM2 antagonists in DDLPS and justify clinical trials in this setting.

BackgroundThe aim of this study was to explore the efficacy and define mechanisms of action of PRIMA-1MET as a TP53 targeted therapy in soft-tissue sarcoma (STS) cells.MethodsWe investigated effects of PRIMA-1MET on apoptosis, cell cycle, and induction of oxidative stress and autophagy in a panel of 6 STS cell lines with different TP53 status.ResultsCell viability reduction by PRIMA-1MET was significantly observed in 5 out of 6 STS cell lines. We found that PRIMA-1MET was capable to induce cell death not only in STS cells harboring mutated TP53 but also in TP53-null STS cells demonstrating that PRIMA-1MET can induce cell death independently of TP53 in STS cells. We identified an important role of reactive oxygen species (ROS), involved in PRIMA-1MET toxicity in STS cells leading to a caspase-independent cell death. ROS toxicity was associated with autophagy induction or JNK pathway activation which represented potential mechanisms of cell death induced by PRIMA-1MET in STS.ConclusionsPRIMA-1MET anti-tumor activity in STS partly results from off-target effects involving ROS toxicity and do not deserve further development as a TP53-targeted therapy in this setting.