The identification of a cell culture inhibitor in a tumour extract

Identification of a melanocyte growth-inhibiting tripeptide and determination of its structure

The function and proliferation of melanocyte cell populations are influenced by a wide range of hormones and growth factors. Local cell renewal after sudden melanocyte loss appears to be regulated according to a negative feedback principle, however. In accordance with this assumption, we have examined growth-inhibitory activity in water extracts of cultured non-transformed melanocytes and melanoma cells (B16 cells). The extracts were fractionated by gel filtration on Sephadex G-25 and Fractogel MG 2000, by ion-exchange chromatography on DEAE-cellulose and Dowex 50 and by reverse-phase high-performance liquid chromatography on Bondesil and Partisil columns. Two peptides were isolated with the structures pyroGlu-Phe-GlyNH2 and pyroGlu-Cys-GlyNH2 as revealed by mass spectrometry, peptide sequencing and amino acid analysis. The two peptides were synthesized and tested for the ability to inhibit the growth of melanocyte cultures. Only pyroGlu-Phe-GlyNH2 was inhibitory. The dose-response curve was bell-shaped with maximum inhibition around 10(-15) M. The melanocyte tripeptide thus appears to be a new member of a group of N-substituted growth-regulating oligopeptides found in other tissues.

Isolation and structure of an epidermal mitosis inhibiting pentapeptide

A mitosis inhibiting peptide pyroGlu-Glu-Asp-Ser-GlyOH has been isolated from mouse skin extracts. Both the biological and a synthetic peptide with the same structure reversibly inhibit epidermal mitoses in a curvilinear fashion after intraperitoneal injection. The two compounds are chromatographically identical.

Differential toxicity of methylglyoxal-bis [guanylhydrazone]

The toxicity to cultured cells of the cancer chemotherapeutic agent methylglyoxal-bis[guanylhydrazone] (MGBG) varies considerably between different cell lines and is always more toxic in the absence of exogenous polyamine. We have looked at the relative MGBG toxicity of two different murine melanoma tumour cell lines (Harding-Passey and Cloudman) and normal murine fibroblasts, and found wide variation with no correlation in sensitivity to MGBG between tumour and normal cells. High sensitivity to MGBG may be associated with high transport across the cell membrane.

Inhibition of lymphocyte DNA-synthetic responses by spermine-derived polycations

The polyamines putrescine, spermidine, and spermine are oxidized by the enzyme diamine oxidase to form the corresponding aldehyde derivatives. These aldehydes have been shown to undergo a variety of spontaneous reactions, some of which result in polycationic addition compounds. We have chemically synthesized some spermine-derived polycations by reaction with the dialdehyde glutaraldehyde followed by reduction of te resulting Schiff base with sodium borohydride. Their migration on ion exchange and gel filtration columns was consistent with the formation of polycations with properties similar to those reported for the spontaneous reaction products. When added to cultures of alloantigen or mitogen stimulated lymphocytes, these polycations were potent inhibitors of the incorporation of tritiated thymidine and blast cell formation. This inhibition was reversible, non-cytotoxic, and only apparent if the polycation was added early in the culture period. The concentration of polycation necessary to achieve 50% inhibition of the lymphocyte response decreased as the cationic nature relative to spermine increased.

Inhibition of proliferation of cultured cells by polyamine and cysteine interaction

Both L-cysteine and spermidine oxidation inhibited the proliferation of cultured cells when these reagents were added in low concentrations. Higher concentrations (above 1 mM) of cysteine were not cytotoxic. Furthermore, high concentrations of L-cysteine partially protected against spermidine oxidation toxicity. D-cysteine on its own behaved exactly the same as an equimolar concentration of L-cysteine, but instead of protecting against the effects of spermidine oxidation, the inhibition was enhanced. A possible mechanism for the interaction is discussed.

Inhibition of lymphocyte proliferation by polyamines requires ruminant-plasma polyamine oxidase

Spermine and spermidine in vitro are potent inhibitors of proliferation of phytohaemagglutinin-stimulated rat thymic lymphocytes, lymphoma cells and human lymphoblastic leukaemia cells, but only in media supplemented by foetal calf serum. This inhibition is shown to be due to a bovine plasma polyamine oxidase, with a high specificity for these polyamines. Spontaneously dividing lymphocytes are not subject to this inhibition. This, plus direct evidence from synchronous cultures of EB2 cells demonstrates that the inhibition is expressed in the late G1 or G1/S interface of the cell cycle. Putrescine was not an inhibitor in the presence of foetal calf serum but became so in the presence of human pregnancy serum, possibly due to the action of diamine oxidase.

Methyl glyoxal bis guanylhydrazone abolition of the toxic action of spermidine on cells in culture

Spermidine inhibits many cells in culture because amine oxidase in the serum converts spermidine to toxic products. Methyl glyoxal bis guanylhydrazone (Methyl GAG) inhibits cells in culture because it is a specific inhibitor of S-adenosylmethionine decarboxylase, preventing the conversion of putrescine to spermidine. When both spermidine and methyl GAG were added together, no inhibition was observed. The effect could be explained by the finding that methyl GAG was a powerful non-competitive inhibitor of the enzymatic oxidation of spermidine to acrolein.