Lisofylline, a dimethylxanthine derivative, has been shown to block the induction of hematopoietic growth inhibitors produced in response to cytotoxic anticancer therapy. In the current study, mice bearing established EMT-6 mammary carcinoma were treated with high dose cyclophosphamide, melphalan, BCNU, 5-fluorouracil or with total body radiation alone or with peripheral blood cells. The effect of lisofylline and/or G-CSF on leukocyte recovery was examined. Lisofylline was as effective as G-CSF in accelerating the recovery of white blood cells and granulocytes after treatment with high dose chemotherapy or total body radiation. Lisofylline alone or along with G-CSF was effective in protecting animals from the weight loss caused by high dose melphalan but not from weight loss caused by other cytotoxic therapies. Administration of lisofylline did not alter the killing of bone marrow CFU-GM by single doses of cyclophosphamide, melphalan or BCNU. However, administration of lisofylline increased the killing of EMT-6 tumor cells taken from the same animals. Administration of lisofylline had no effect on EMT-6 tumor growth. However, treatment with lisofylline along with high dose cyclophosphamide: melphalan, BCNU or 5-fluorouracil significantly increased the tumor growth delay produced by these agents. Overall, in the high dose therapy/EMT-6 mammary carcinoma model, lisofylline selectively enhanced hematopoietic recovery and increased tumor response to cytotoxic therapy.

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