ACTIVITY OF ACETYL-N-SER-ASP-LYS-PRO (ACSDKP) ON HEMATOPOIETIC PROGENITOR CELLS IN SHORT-TERM AND LONG-TERM MURINE BONE-MARROW CULTURES

The tetrapeptide AcSDKP is a potent inhibitor of hematopoietic stem ce ll proliferation. Its activity was systematically examined in murine l ong-term bone marrow cultures (LTBMC) and short-term liquid cultures i n the presence or absence of exogenous cytokines. The effects of AcSDK P on the production of granulocyte-macrophage colony-forming cells (CF U-GM) and high proliferative potential colony-forming cells (HPP-CFC) in LTBMCs were examined. AcSDKP was added daily to LTBMCs at various c oncentrations (10(-3)-10(-16) M) for up to 5 weeks. AcSDKP inhibited t he entry of progenitor cells into S phase as measured by H-3-thymidine suicide assay and the absolute number of progenitor cells with peak a ctivity at 10(-12) M with less activity seen at higher or lower concen trations. The number of nonadherent CFU-GM per LTBMC was unchanged fro m control values at 1 week of treatment with AcSDKP but was significan tly depressed at weeks 3 and 5. In contrast, HPP-CFC progenitor cells were decreased throughout the treatment period, and the numbers of CFU -GM and HPP-CFC in S phase were significantly decreased throughout the culture period. Maximum S-phase inhibitory activity was observed at 1 0(-12) M AcSDKP. AcSDKP had no effect on the number of adherent CFU-GM or HPP-CFC, cellularity per culture, or percent of adherent progenito r cells in S phase. Murine,short-term bone marrow cultures were also t reated with AcSDKP in the presence or absence of cytokines (interleuki n-3 [IL-3], stem cell factor [SCF], or granulocyte colony-stimulating factor [G-CSF]) for various;time periods. Dose-response studies showed maximum effects at 10(-12) M AcSDKP when no cytokines were added and 10(-14) M AcSDKP when exogenous cytokines were added. These studies in dicate that the concentration of the tetrapeptide is critical in obtai ning an effect on hematopoietic progenitor cells, and furthermore, we report that the presence of cytokines or stromal cells also affects th e response of progenitor cells to AcSDKP.