Fenretinide-dependent upregulation of death receptors through ASK1 and p38α enhances death receptor ligand-induced cell death in Ewing's sarcoma family of tumours.

BACKGROUND: Sustained p38MAPK phosphorylation upregulates p75 neurotrophin (p75NTR) and induces apoptosis in Ewing’s sarcoma

family of tumours (ESFT). As fenretinide induces ESFT death through sustained p38MAPK phosphorylation, we hypothesised that this

may be effected through upregulation of death receptors (DRs) and that treatment of fenretinide plus DR ligands may enhance

apoptosis.

METHODS: DR expression was determined by flow cytometry. Trypan blue exclusion assays, caspase-8 flow cytometry and

immunoblotting for Bid were used to measure cell death.

RESULTS: Fenretinide upregulated cell surface expression of tumour necrosis factor-related apoptosis-inducing ligand (TRAIL)

receptors, FAS and p75NTR, in an ASK1- and p38a-dependent manner. Cotreatment with fenretinide and DR ligands resulted in

synergistic death compared with either agent alone; caspase-8 and Bid were cleaved in a time-dependent manner. Fenretinide did not

increase DR expression in non-malignant cells. Furthermore, fenretinide, TRAIL or a combination of both agents was non-cytotoxic

to non-malignant cells. Etoposide and actinomycin D increased expression of all DRs examined, whereas vincristine increased FAS

alone. Only actinomycin D and TRAIL, and etoposide with TRAIL or FasL, enhanced death compared with either agent alone.

CONCLUSION: The synergistic death observed with fenretinide and DR ligands suggests that this combination may be an attractive

strategy for the treatment of ESFT.