Selectivity of hemoregulatory peptide (HP5b) action in culture

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Abstract
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 × 10-13 to 1 × 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 × 10-7 M, an inhibitory effect was found on colony formation. Neither the production of interleukin (IL) 3 by mitogenactivated T cells, nor the proliferation of the IL-3-dependent L/B cell line were affected by the peptide up to 1 × 10-5 M. A slight inhibitory effect was found above 1 × 10-9 M on mouse 3T3 fibroblasts. A series of malignant cell lines was also tested. No effect was seen between 1 × 10-11 and 1 × 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 (BTSC) an inhibitory effect was seen at 1 × 10-7 M and above. No significant inhibition of cell growth was seen on SC1 mouse lymphoma cells from 1 × 10-9 to 1 × 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.