Combined effect of hydrocortisone and X irradiation on spontaneous lymphoma cells

The combination of hydrocortisone and other cytotoxic agents has been shown to exert a synergistic killing of corticosteroid sensitive spontaneous AKR lymphoma cells in vivo. The investigation was designed to study whether hydrocortisone acetate (HCA) could also enhance the killing of lymphoma cells by X irradiation (RAD). Four peripheral lymph nodes, both anterior axillary and inguinal, from the same AKR mouse with spontaneous lymphoma were used since they contained about the same number of lymphoma stem cells. There were 4 groups: untreated control, local RAD (200 rads) alone, HCA (6 mg/mouse) s.c. alone and RAD + HCA given 30 min apart. The number of lymphoma stem cells was determined by the splenomegaly assay (Ser. Haematol. 5:73). Untreated lymph node contained a median value of 1.8 x 10⁵ splenomegaly units (SU). The number of U was reduced to 1.8 x 10⁴ after RAD alone. After the treatment with RAD + HCA, the number of SU decreased to 4 x 10²SU which was significantly lower than that obtained by RAD alone. The combination was also tested on two normal cell populations, pluripotent hemopoietic stem cells and limited stem cells for granulocytes and/or macrophages. The administration of HCA in conjunction with RAD neither increased the killing nor delayed the recovery of these two cell populations.