DOXORUBICIN PLUS TUMOR-NECROSIS-FACTOR-ALPHA COMBINATION TREATMENTS IN EL4-LYMPHOMA-BEARING C57BL 6 MICE/

The therapeutic efficacy of a total of 42 single-agent or combination protocols involving doxorubicin (Adriamycin, ADM) and tumor necrosis f actor alpha (TNF alpha) were evaluated in the syngeneic murine lymphom a model, C57BL/6-EL4. Combination treatments were the most effective a nd the therapeutic effects were schedule-dependent; e.g. it was genera lly advantageous for ADM to precede TNF alpha administration. Two prot ocols selected for further study were 4 mg/kg ADM i.v. on days 1 and 8 plus TNF alpha i.v., at either 16000 U (7 mu g)/injection, on days 1 and 8 or 4000 U (1.7 mu g)/injection, on days 11-15. Survival of mice bearing one of four EL4 sublines having different in vitro drug sensit ivities was assessed. These sublines were E10 (ADM-sensitive/TNF alpha -resistant), E16 (sensitive/sensitive), ER2 (ADM-resistant/TNF alpha-s ensitive) and ER13 (resistant/resistant). Between 80% and 100% long-te rm survivors (i.e. tumor free on day 60) were obtained with the two tr eatments in mice bearing ADM-sensitive sublines, even though one of th ese sublines, E10, was resistant to TNF alpha in vitro. Induction of l ong-term survival appeared, therefore, to correlate with in vitro defi ned sensitivity/resistance to ADM, but not to TNF alpha. Treatment-ind uced modulations of tumoricidal immune effector functions were also ex amined. Taken together, the results indicated that induction of longte rm survival involved complex interactions of: (1) ADM-induced tumor mo difications, including, but not limited to, tumor debulking, (2) combi nation-treatment-induced modifications of splenic cytolytic T cell and macrophage activities, and (3) the restoration of thymus cellularity. Finally, when long-term survivors resulting from treatment of E10- or E16-bearing mice were implanted with ER2 on day 120, the majority sur vived, indicating that long-term immune memory, capable of recognizing drug resistant variants, had been established.