Doxorubicin potentiates TRAIL cytotoxicity and apoptosis and can overcome TRAIL-resistance in rhabdomyosarcoma cells

Doxorubicin (DOX) and ifosfamide (IFO) are the most active single agents in soft tissue sarcomas (STS). Tumour necrosis factor-α (TNF-α) is used for STS in the setting of isolated limb perfusions. Like TNF-α, TNF-related apoptosis-inducing ligand (TRAIL) induces apoptosis. In contrast to TNF-α preliminary studies suggest that TRAIL lacks systemic side effects. The effects of TRAIL alone and in combination with DOX or 4-hydroxy-IFO were evaluated in the TNF-α sensitive rhabdomyosarcoma cell line KYM-1, its 5-fold TNF-α sensitive subline KD4 and its >150-fold TNF-α resistant subline 37B8R. Membrane expression of TRAIL-receptors DR4 (death receptor 4), DR5 (pro-apoptotic), DcR1 (decoy receptor 1), DcR2 (anti-apoptotic) was assessed by flow cytometry. Cytotoxicity was determined by microculture tetrazolium assays. Apoptosis assays were performed with acridine orange. DOX (doxorubicin) and 4-OH-IFO decreased survival in all cell lines; a 2-fold resistance was observed for both drugs in 37B8R. All cell lines expressed DR4 and DR5, but hardly any DcR1 or DcR2. TRAIL was cytotoxic in KYM-1, even more in KD4 and induced massive apoptosis; 37B8R was >500-fold resistant to TRAIL and little apoptosis could be observed. TRAIL plus DOX showed synergistic cytotoxicity in KYM-1 and 37B8R. TRAIL plus 4-OH-IFO showed addition in all three cell lines. DOX plus TRAIL-induced more cytotoxicity and apoptosis in all cell lines compared to TRAIL alone. In 37B8R, DOX overcame resistance to TRAIL. In KYM-1, KD4 and 37B8R, sensitivity and resistance to TNF-α and TRAIL parallels. TRAIL-resistance was independent from expression of TRAIL-receptors. DOX with TRAIL could overcome TRAIL-resistance in 37B8R cells.