Goralatide (AcSDKP) selectively protects murine hematopoietic progenitors and stem cells against hyperthermic damage

Hyperthermic purging procedures may be improved by methods that selectively inhibit the proliferative activity of normal hematopoietic progenitors and stem cells, since active proliferation of these subsets is accompanied by increased heat sensitivity. For this reason, bone marrow cells from CBA/H mice were incubated with Goralatide (tetrapeptide Acetyl-N-Ser-Asp-Lys-Pro), a well-known inhibitor of normal hematopoietic progenitor cells to enter the S phase of the cell cycle. Subsequently, the cell suspensions were heat-treated at 43 degrees C for up to 90 minutes. After an exposure of 8 hours to 10(-9) M Goralatide, the number of CFU-GM cells in S phase decreased from 30 to 10%, resulting in an almost 10-fold increase in survival after 90 minutes at 43 degrees C. No effect on the primitive subsets could be detected because of their quiescent cell cycle state in normal bone marrow. To investigate the potential vulnerability of these subsets for Goralatide, bone marrow cells from 5-fluorouracil (5-FU)-pretreated mice were used. 5-FU induced increase in proliferative activity of the CFU-S-12 (day-12 colony-forming units-spleen), and the stem cell with marrow repopulating ability could be abolished by an incubation period with 10(-9) M Goralatide for 16 and 24 hours, respectively. Hence, this decrease in proliferative activity confers a decrease in hyperthermic sensitivity for the primitive hematopoietic subsets. The cytotoxic effect of the incubation on the absolute number of the hematopoietic progenitors and stem cells was <10%. Goralatide treatment (10(-8), 10(-9), and 10(-10) M) up to 24 hours had no effect on the growth kinetics and cell cycle distribution and consequently on the hyperthermic sensitivity of L1210 cells. Based on these results, it can be concluded that Goralatide will have a positive effect on the survival of hematopoietic progenitors and stem cells after hyperthermia and may lead to a gain in the therapeutic window of this purging modality.