Bovine seminal ribonuclease exerts selective cytotoxicity toward neuroblastoma cells both sensitive and resistant to chemotherapeutic drugs

Background. Bovine seminal ribonuclease (BS-RNase) exerts selective cytotox icity toward different types of tumor cells. In the present study, we teste d the effects of BS-RNase on cultured neuroblastoma (NB) cells resistant to chemotherapeutic agents. The selectivity of the antitumoral activity of BS -RNase was evaluated using cultures of CD34(+) hematopoietic stem cells. Ma terials and Methods Human NE cell lines including IMR-32, UKF-NB-2 and UKF- NB-3 were selected for resistance against vincristine, doxorubicin or cispl atin by exposure to increasing concentrations of the respective drug. The c ytotoxicity of the drugs to NE cells was evaluated using a clonogenic assay in a methylcellulose medium. Peripheral blood progenitor cells were obtain ed from adult healthy donors by positive selection using specific anti-CD34 (+) antibodies. The toxicity of BS-RNase to CD34(+) cells was assessed in t he direct clonogenic assay using methylcellulose medium of in ex vivo expan sion culture supplemented with hematopoietic growth factors. Results. In th e clonogenic assay it was shown that BS-RNase completely inhibits growth of both parental NE cells and their sublines resistant to chemotherapeutic dr ugs at concentrations (up to 50 mu g/ml) which have no significant influenc e on the growth of colony-forming units, granulocyte macrophage and erythro id burst-forming units. Moreover, BS-RNase had no effect on the ex vivo exp ansion of total hematopoietic cells or of colony-forming cells from CD34(+) progenitors. Conclusions. BS-RNase is a highly efficient agent against NE cells resistant to chemotherapeutic drugs. The lack of toxicity to hematopo ietic progenitor cells suggests that BS-RNase is also likely to have tolera ble hematopoietic toxicity.