Synergism and schedule dependent cytotoxicity of cyclophosphamide and CCNU in experimental cancer chemotherapy

Abstract A synergistic degree of cell killing was obtained with cyclophosphamide and CCNU in the L 1210 leukaemia, the Lewis lung carcinoma and the mouse C 22 LR osteosarcoma. Drug synergism was also demonstrated in both resting and rapidly proliferating haemopoietic stem cells. By scheduling the 2 drugs we attempted to obtain selective cell kill of tumour cells over vital normal cells. The optimum antitumour schedule was found to be that when the drugs were given simultaneously. This tumour based schedule however, proved to be the most toxic for bone marrow stem cells as well. Therefore, the clinical relevance of this synergistic drug combination is expected to be limited.