The synthetic tetrapeptide Ac-SDKP (Seraspenide) is involved in angiogenesis and regulation of the immune response by blocking the proliferation of lymphocytes. Seraspenide inhibits cell cycle entry of normal hematopoietic stem cells. In mice, the tetrapeptide protects hemopoiesis against damage caused by cytarabine, cyclophosphamide and carboplatin.Ac-Ser-Asp-Lys-Pro-OH or Ac-SDKP-OH