Abstract

Myelosuppression is a major and frequently dose limiting side-effect of anticancer therapy and responsible for most treatment-related morbidity and mortality. In addition, repeated cycles of DNA damage and cell death of hematopoietic stem and progenitor cells, followed by compensatory proliferation and selection pressure, lead to genomic instability and pave the way for therapy-related myelodysplastic syndromes and secondary acute myeloid leukemia. Protection of hematopoietic stem and progenitor cells from chemo- and radiotherapy in patients with solid tumors would reduce both immediate complications and long-term sequelae. EGF and PGE2 were reported to prevent chemo- or radiotherapy-induced myelosuppression in mice. We tested both molecules for potentially protective effects on human CD34+ cells in vitro and established a xenograft mouse model to analyze stress resistance and regeneration of human hematopoiesis in vivo. EGF was neither able to protect human stem and progenitor cells in vitro nor to promote hematopoietic regeneration following sublethal irradiation in vivo. PGE2 significantly reduced in vitro apoptotic susceptibility of human CD34+ cells to taxol and etoposide. This could, however, be ascribed to reduced proliferation rather than to a change in apoptosis signaling and BCL-2 protein regulation. Accordingly, dmPGE2 did not accelerate regeneration of the human hematopoietic system in vivo. Also repeated treatment of sublethally irradiated xenograft mice with known antiapoptotic substances such as human FLT3L and TPO, which suppress transcription of the proapoptotic BCL-2 proteins BIM and BMF, did only marginally promote human hematopoietic regeneration in vivo.