Altered toxicity of 5-fluorouracil following treatment with Corynebacterium parvum

Recent studies have demonstrated that systemic Corynebacterium parvum increases serum granulocyte-macrophage colony-stimulating factor and stimulates the proliferation of granulocyte-macrophage progenitor cells. It was hypothesized that more rapid cycling of granulocyte-macrophage progenitor cells would render the cells more sensitive to a cell cycle-specific chemotherapeutic agent. The colony-forming ability of bone marrow granulocyte-macrophage progenitor cells was assayed in vitro with soft agar cultures. C. parvum given before 5-fluorouracil in C57BL/6 mice increased the granulocyte-macrophage progenitor cell toxicity, the lymphopenic effect, and the lethality of 5-fluorouracil. When C. parvum was given after 5-fluorouracil, there was more rapid rebound of granulocyte counts to normal or supranormal levels.