We have previously shown that the synthetic
peptide pGlu-
Glu-Asp-Cys-Lys (
pEEDCK monomer) inhibits the
cytostatic drug-induced proliferation of hematopoietic stem cells CFU-S. Keeping CFU-S quiescent by
pEEDCK treatment renders them insensitive to cycle-specific
cytostatic drugs and leads to reduced toxicity. Here we show that
pEEDCK application during repeated (twice) administration of clinically relevant (nonlethal) 1-beta-D-arabinofuranosylcytosine (
Ara-C) doses reduced the percentage of CFU-S in S-phase from 60%-70% to 25%-30% and led to a sustained stem cell number in the bone marrow (BM), whereas unprotected mice had lost about 75% of their CFU-S population. Owing to its
cysteine content, the
pEEDCK monomer is easily oxidized. The resulting dimer (
pEEDCK)2 is a potent stimulator of hematopoiesis. As we show, it can be used for postchemotherapy acceleration of hematologic recovery, similar to the use of recombinant hematopoietic
growth factors. A single injection of 30 micrograms/kg
pEEDCK monomer to mice 2 hours before the second
Ara-C injection retarded onset of
neutropenia (by 2 to 3 days) and improved recovery after depression. The quantitative degree of
neutropenia was not changed. Postchemotherapy (
Ara-C administered twice, followed by N-mustard) infusion of the stimulatory (
pEEDCK)2 dimer (1.4 micrograms/kg/d) produced a 4.6-fold increase of progenitor levels (6.7 CFU-GM/1,000 BM cells v 1.45 CFU-GM/1,000 in normal mice) 2 days after the end of the
cytostatic treatment when CFU-GM were not detectable in unprotected mice. This increase was followed after several days by strongly elevated granulocyte counts, which remained high for approximately 1 week. Up to 75% of the peripheral leukocytes were mature polymorphonuclear leukocytes (PMN) during this phase.
Ara-C (twice) and monomer treatment as above followed by dimer infusion resulted in the complete protection of hematopoiesis. Mice treated with the protective
pEEDCK monomer plus stimulatory dimer did not develop the leukocyte depression noted in unprotected animals. The inhibitory monomer appears to keep the stem cell population numerically and qualitatively intact, thus providing optimum target cell conditions for the subsequent stimulator (dimer) treatment. Our results show that the hemoregulatory
peptide monomer and dimer can be used for improving the hematologic status of mice treated with clinically relevant doses of
cytostatic drugs (
antimetabolite and alkylating, alone and in combination). Combining both
peptides can prevent occurrence of
neutropenia completely. Both
peptides can be obtained easily by chemical synthesis and are also active on human cells. They are thus highly promising candidates for application as multilevel hemoprotectors in
cancer chemotherapy.