Pegylated liposome-encapsulated doxorubicin and cisplatin in the treatment of head and neck xenograft tumours

Purpose: To evaluate the in vitro and in vivo activity of unencapsulated doxorubicin (DOX) and cisplatin (CDDP) and their pegylated liposome encapsulated counterparts (PLED and PLEC) in a subcutaneous model of human squamous cell cancer of the head and neck. Methods: In vitro cytotoxicity was determined by means of the sulphorhodamine B assay and in vivo activity was assessed in terms of tumour growth delay following single intravenous doses of the various agents. Treatment-related toxicity was evaluated by means of serial weight measurement. Results: The IC50 values for DOX (12.1-fold) and CDDP (21.5-fold) were lower than for their liposome-encapsulated counterparts. When the two unencapsulated agents were compared, the IC50 value for DOX was 16-fold lower than that for CDDP. In the in vivo studies. liposomes containing DTPA (PLEDTPA) exerted no effect on KB xenograft tumours when compared to untreated controls (P > 0.1). PLED was significantly more effective than DOX at doses of 2 mg/kg, 4 mg/kg and 8 mg/kg (P < 0.001 for all comparisons). At the 8 mg/kg dose, 7/13 animals treated with PLED were free of disease at 60 days, compared to 0/12 treated with DOX. PLEC displayed superior activity in comparison to CDDP at the 4 mg/kg dose level (P < 0.001), although at doses of 2 mg/kg and 10 mg/kg this comparison only reached borderline statistical significance(0.1 > P > 0.05). The highest dose level of 20 mg/kg was fatal to all animals in the CDDP group but well-tolerated by the animals in the PLEC group. On the basis of serial weight measurements, both PLED and PLEC were shown to be tolerated better than DOX and CDDP. Conclusion: Both PLED and PLEC were shown to exert significant activity against head and neck xenograft tumours, with PLED showing particular efficacy.