Enhanced cytotoxic interaction between 5-fluorouracil and 4-hydroperoxycyclophosphamide against L1210 murine leukemic cells: Applicability to ex vivopurging

Eradication of contaminated tumor cells in bone marrow is a matter of utmos t concern in the setting of autologous bone marrow transplantation. 4-Hydro peroxycyclophosphamide (4-HC) is often used for ex vivo chemical purging of contaminated tumor cells in bone marrow. The marrow from patients pretreat ed with 5-fluorouracil (5-FU) is enriched with multifactor-responsive high proliferative potential colony-forming cells. To develop an efficient ex vi vo chemical purging system, we evaluated interaction between 4-HC and 5-FU. We investigated the antitumor effect of cyclophosphamide, a mother compoun d of 4-HC, and 5-FU against L1210 ascites tumor in B6D2F1 mice. The median lifespan of the mice treated with 4-HC or 5-FU alone was 8 and 12 days, res pectively. The combination of both drugs significantly extended the median lifespan to 18.5 days. The median effect plot analysis indicated a synergis tic cytotoxic interaction between 5-FU and 4-HC in 3-(4,5-dimethylthiazol-2 -yl)-2,5-diphenyl. terazolium bromide (MTT) assay. Clonogenic assay also sh owed that combination of 4-HC and 5-FU significantly reduced L1210 leukemic colonies to 20% of untreated control. Bone marrow cells from the mice trea ted with 5-FU at 150 mg/kg body weight was resistant to 4-HC at concentrati ons as high as 0.2 mu g/ml, which was mor-e than 70% inhibitory concentrati on for colony formation in L1210 leukemic cells. Findings suggest that sequ ential treatment with in vivo 5-FU followed by ex vivo 4-HC could selective ly enhance antitumor effects of 4-HC in tumor cells remaining in bone marro w.