Hemotoxicity by prolonged etoposide administration to mice can be prevented by simultaneous growth factor therapy.

In this study, we determined in vivo interactions between hemopoietic growth factors and etoposide (VP-16) to assess whether normal blood cell production could be maintained during chemotherapy if hemopoietic growth factors were simultaneously administered. Groups of mice were treated for 7 consecutive days with four different doses of VP-16 in combination with three different doses of erythropoietin (EPO) or granulocyte colony-stimulating factor (G-CSF). In total, 12 combinations of VP-16 plus EPO and 12 combinations of VP-16 plus G-CSF were thus evaluated. Intricate dose-response surfaces of the effects of the different treatments on colony-forming units-erythroid, reticulocytes, hematocrit, colony-forming units-granulocyte/macrophage, and absolute neutrophil count were obtained, which revealed that: (a) simultaneous EPO administration was able to maintain reticulocyte production and to protect mice from VP-16 induced anemia; (b) simultaneous G-CSF administration was able to maintain granulocyte production and to protect mice from VP-16 induced neutropenia; (c) VP-16 dose escalation was feasible when EPO or G-CSF were simultaneously administered; and (d) no increased myelotoxicity on erythroid or granuloid progenitors was observed when EPO or G-CSF was simultaneously administered with VP-16. These results suggest that in vivo either individual hemopoietic progenitors can become resistant against VP-16-induced cell death by appropriate simultaneous growth factor administration or that the loss of overall cell amplification, induced by VP-16, can be compensated by extra amplification of surviving progenitors. Furthermore, these data indicate that a strict separation in time of cytostatic drug and growth factor treatment is not necessarily the optimal schedule with respect to the reduction of hemotoxicity.