A synthetic hemoregulatory peptide (HP5B) inhibits human myelopoietic colony formation (CFU-GM) but not leukocyte phagocytosis in vitro

Oligopeptide fragments of the enkephalin molecule interfere with hematopoietic cell colony formation

Dipeptide Tyr-Gly and tripeptide Tyr-Gly-Gly representing the NH(2)-end of the Met-enkephalin molecule inhibited the GM-colony formation in clonal cultures of mouse bone marrow cells. Intermediate or C00H-terminal dipeptides Gly-Gly and Phe-Met respectively were inneffective. The suppressive effects were not abolished by opioid receptor blocking agent naloxone and only partly so by depletion of the accessory (adherent) cells. The results are congruent with idea that neuropeptides and products of their enzymatic degradation participate in the regulation of hematopoiesis.

SK&F107647: a synthetic hematoregulatory peptide in patients with solid tumor malignancies: a phase I trial

SK&F107647 is a synthetic hematoregulatory peptide (HP) increases both the number and function of progenitor cells, enabling improved survival after lethal myelosuppression, lethal fungal infection, and lethal herpes simplex virus infection in murine models. This Phase I single-blind placebo-controlled dose-rising crossover trial examined the efficacy of SK&F107647 in patients who had incurable solid tumor malignancies. Sixteen patients were treated. Six adverse events in 3 patients were considered to be possibly related to SK& F107647; all were mild to moderate in nature (mild nervousness and agitation at 0.01 ng/kg, moderate fever and mild nausea at 0.1 ng/kg, elevated hepatic enzymes at 0.1 ng/kg, and mild vomiting at 1.0 ng/kg). Plasma half-life was 2.44 hours (+/-1.07 standard deviation). The observed area volume of distribution was 16.7 L (+/-7.7 standard deviation) and clearance was 5.04 L/hour (+/-1.83 standard deviation). When administered as a single 2-hour intravenous infusion at doses ranging from 0.01 to 100 ng/kg, SK&F107647 is safe and well tolerated.

Inhibition of enriched stem cells in vivo and in vitro by the hemoregulatory peptide SK&F108636

Replacement of the labile sulfhydryl group (-SH) of the hemoregulatory peptide monomer pyroGluGluAspCysLys (HP5b) with an isosteric methylene group yields a chemically stable compound, SK&F108636. In this study, we describe the effects of SK&F108636 on highly enriched Lin-Sca1+ hematopoietic stem cells. SK&F108636 significantly reduced the fraction of cycling progenitor cells, granulocyte macrophage colony-forming cells (GM-CFC), in vitro and in vivo. There was no effect on GM-CFC or Mix-CFC colony formation. SK&F108636 significantly inhibited proliferation of high proliferative potential (HPP)-CFC in semisolid agar cultures stimulated by stem cell factor + interleukin 3 (IL-3) + IL-1, but had no effect in cultures stimulated with M-CSF + IL-3 + IL-1. SK&F108636 was shown to act directly on the stem cells since SK&F108636 inhibited proliferation of Lin-Sca1+ cells in single cell assays. Administration of SK&F108636 to lethally irradiated mice transplanted with 2000 Lin-Sca1+ cells significantly inhibited proliferation/differentiation of cells developing into colony forming units-spleen (CFU-S) (preCFU-S) and the reconstitution of HPP-CFC and GM-CFC. There was no effect of SK&F108636 on CFU-S colony formation or mature cell regeneration in bone marrow, spleen and blood. Hence, the hemoregulatory peptide monomer SK&F108636 is a potent primitive stem cell inhibitor in vivo and in vitro. Inhibition of stem cell proliferation by small specific inhibitors may protect hematopoiesis from myelotoxic side effects during chemotherapy treatment.

Feedback inhibitors in normal and tumor tissues

Negative feedback represents the principal mechanism for regulating growth in biological systems. Over the past 20 years, our understanding of the role played by inhibitory factors governing this process has advanced considerably. This is particularly well illustrated in the field of experimental hematology with the recognition of hemopoietic progenitor cell proliferation inhibitors, an expanding group of unrelated peptides that act to limit proliferation in hemopoietic precursor cells. The characterization and subsequent production of these molecules by chemical synthesis or recombinant DNA technology has enabled investigators to explore their role in normal hemopoiesis and define a potential role in clinical medicine. A number of inhibitory factors, including macrophage inflammatory protein-1 alpha (MIP-1 alpha) and the tetrapeptide AcSDKP appear to share a relative specificity to hemopoietic progenitor cell subsets. Others, such as interferon and tumor necrosis factor, have a more complex action and their hemopoietic effects are likely to be indirect and nonspecific. In addition to the role of inhibitors in normal steady state, it has become increasingly evident that loss of sensitivity to the normal feedback inhibitory signals may be of central importance in carcinogenesis and tumor promotion. This presumably represents a developmental strategy that allows the neoplastic cell to maintain a growth advantage over its normal cell counterpart. The underlying mechanisms that terminate in inhibitor-resistance are yet to be elucidated, but in some instances they may be associated with aberrant tumor suppressor gene function.

Inhibitors of haemopoiesis and their potential clinical relevance

Current cytotoxic treatment regimens are most frequently dose-limited by the problem of myelotoxicity, and this could theoretically be prevented or reduced by the use of stem-cell inhibitors, since protection of this compartment during treatment could result in a more favourable outcome in terms of bone-marrow regeneration. Several negative stem-cell regulators have been identified, including macrophage inflammatory protein-1 alpha, transforming growth factor-beta, tumour necrosis factor-alpha, tetrapeptide and pentapeptide. All of these molecules have been shown to inhibit the proliferation of normal haemopoietic progenitors in bone marrow, and stem-cell protection from cytotoxic agents both in vitro and in vivo has been demonstrated. The potential use of inhibitors for the purging of tumour cells from stem-cell grafts is suggested by the observation that there is a differential response between normal and leukaemic progenitors to some inhibitors.

Hemoregulatory peptide (HP5b) dimer effects on normal and malignant cells in culture

The dimer of the hemoregulatory peptide HP5b has been investigated for biological effects on various cell types in culture including mouse granulocyte-macrophage colony forming units (CFU-GM) from agar and murine long-term bone marrow culture (LTBMC). While CFU-GM were significantly stimulated in both systems, mitogen activation of mouse T, B and natural killer (NK) cells was not affected. Peptide treated mouse 3T3 fibroblasts reached a higher saturation density than controls; otherwise no effect was seen. A series of malignant cell lines was also tested. On a human glioblastoma cell line (GaMg) and rat glioma cell line (BT5C) a slight but significant stimulatory effect was found, while human mammary carcinoma cells (MCF7) were not affected. On SC1 mouse lymphoma cells a slight stimulation of cell growth was seen during the first part of exponential growth. Since HP5b acts as a stimulator for stromal cell secretion of other growth factors, supernatants from a human bone marrow stromal cell line stimulated with HP5b were tested on various cell lines. The effects of the supernatants on cell growth of the tested cell lines were not affected by HP5b treatment. Taken together with available in vivo data, the results indicate that the hemoregulatory peptide is a selective stimulator of myelopoiesis.

Haemoprotection against cytostatic drugs by stem cell inhibition

Cytostatic drug-induced haematopoietic damage is a major problem in tumour chemotherapy, due to the intensive proliferation of many bone marrow constituents and to the drug-induced recruitment of immature pluripotent haematopoietic cells (spleen colony-forming units, CFU-S). Marie-Hélène Moser and Walter Paukovits discuss how it should be possible to minimize such proliferation-associated damage by inhibiting CFU-S during the most dangerous treatment phases, with factors such as transforming growth factor beta, tumour necrosis factor alpha, macrophage inflammatory protein 1 alpha, and the CFU-S-inhibitory peptides N-acetyl-Ser-Asp-Lys-Pro and pyroGlu-Glu-Asp-Cys-Lys (pEEDCK). Clinically relevant data are available for pEEDCK, showing that application of this peptide leads to a delayed, shorter, and less severe neutropenia, combination of pEEDCK with a stimulator avoids neutropenia, and stem cell preservation with pEEDCK improves long-term reconstitution of the haematopoietic system. Stem cell inhibition by synthetic peptides like pEEDCK may provide a useful strategy for bone marrow protection.

Selectivity of hemoregulatory peptide (HP5b) action in culture

A synthetic analog of a hemoregulatory peptide associated with mature human granulocytes (HP5b) has been investigated for inhibitory effects on various cell types in culture as compared to inhibitory action on mouse and human myelopoietic colonies (CFU-gm), which occurs from 1 X 10(-13) to 1 X 10(-6) M in vitro. This includes colony formation by lymphoid T and B cells in capillary cultures, as well as mitogen activation of T, B and NK cells. At higher concentrations, i.e., above 1 X 10(-7) M, an inhibitory effect was found on colony formation. Neither the production of interleukin (IL) 3 by mitogen-activated T cells, nor the proliferation of the IL-3-dependent L/B cell line were affected by the peptide up to 1 X 10(-5) M. A slight inhibitory effect was found above 1 X 10(-9) M on mouse 3T3 fibroblasts. A series of malignant cell lines was also tested. No effect was seen between 1 X 10(-11) and 1 X 10(-7) M on human mammary carcinoma cells in culture. On Ehrlich ascites mouse mammary carcinoma cells a 30% inhibition was seen at 10(-6) M. On a human glioblastoma cell line (GaMg) no effect was seen, and on a rat glioma cell line (BT5C) an inhibitory effect was seen at 1 X 10(-7) M and above. No significant inhibition of cell growth was seen on SC1 mouse lymphoma cells from 1 X 10(-9) to 1 X 10(-5) M during 7 days of culture. The investigated normal and malignant cell types in culture were thus not inhibited in very low concentrations which act on CFU-gm. However, a variable inhibitory effect was found at higher concentrations where the inhibition of myelopoiesis was maximal and at concentrations where the inhibition is released. The hemoregulatory peptide thus seems to be a concentration-dependent selective inhibitor of myelopoiesis. The finding that various malignant cells do not respond at lower concentrations supports the possibility of using the peptide as a protector of normal cells during cancer chemotherapy.

The use of haemoregulatory peptides (pEEDCK monomer and dimer) for reduction of cytostatic drug induced haemopoietic damage

We have previously shown that the stem cell inhibitory peptide pGlu-Glu-Asp-Cys-Lys (pEEDCK monomer) leads to a good tolerance of otherwise lethal multiple ara-C doses and an increased survival of ara-C + peptide treated mice. This effect was due to the prevention of drug-induced CFU-S proliferation, thus keeping stem cells in a quiescent state insensitive to ara-C. Here we show that the pEEDCK monomer also inhibits stem cell proliferation after clinically relevant (non-lethal) ara-C doses. This leads to a sustained (100%) stem cell number in the femoral bone marrow, which was greatly reduced without protective peptide treatment (27%). We have measured the kinetics of influx of CFU-S into the empty S-phase (after two consecutive ara-C injections). This influx reached peak levels of 60-70%; pEEDCK treatment reduced it to 25-30%. Due to its cysteine content the pEEDCK monomer is easily oxidized and forms a symmetric disulfide-bonded dimer (pEEDCK)2. This dimer is a potent stimulator of haemopoiesis. Various modes of protective peptide treatment (monomer and dimer) were investigated in conjunction with a standardized protocol of 2 x 300 mg/kg ara-C given 12 h apart. (a) ara-monomer-ara: The administration of pEEDCK-monomer 2 h before the second ara-C injection retarded the onset of neutropenia, shortened its duration and improved recovery after depression. The degree of short-term neutropenia was not changed. (b) ara-ara-HN2-dimer: Post chemotherapy infusion of the stimulatory (pEEDCK)2 dimer led to considerable increases of progenitor levels (6.8 CFU-GM/1000 bone marrow cells vs. 1.2 CFU-GM/1000 in normal mice) 2 days after cytostatic treatment when CFU-GM were not detectable in unprotected mice. This increase was followed by greatly elevated granulocyte counts (8000 PMN/mm3 vs. 750 PMN/mm3 in normal mice). In the dimer-treated mice, up to 75% of the peripheral leukocytes were mature PMN (normal, 10%). (c) ara-monomer-ara-dimer: ara-C and monomer treatment as above (a) followed by dimer infusion led to complete protection of haemopoiesis. Mice treated with the protective pEEDCK monomer plus stimulatory dimer did not develop the leukocyte depression seen in unprotected animals. Our results show that the haemoregulatory peptide monomer and dimer can be used to improve the haematological status of mice treated with clinically relevant doses of cytostatic drugs (anti-metabolite and alkylating, alone and in combination). The pEEDCK monomer and dimer are equally active also on human haemopoietic cells.(ABSTRACT TRUNCATED AT 400 WORDS)

The sequence of the hemoregulatory peptide is present in Gi alpha proteins

The hemoregulatory peptide PyroGlu-Glu-Asp-Cys-Lys (HP5b), which inhibits myelopoietic colony formation in vitro, is shown to be a sequence motif which is also part of the effector domain of Gi alpha proteins. Out of 8 synthetic peptides with sequence variations of HP5b, those with the closest similarity to the Gi alpha sequence are biologically active. The inhibitory effect appears to be dependent on the blocked N-terminus. It is postulated that these peptides may interfere with signal transduction mediated by Gi alpha proteins.