DIFFERENTIAL-EFFECTS OF SMALL TUMOR-NECROSIS-FACTOR-ALPHA PEPTIDES ONTUMOR-CELL CYTOTOXICITY, NEUTROPHIL ACTIVATION AND ENDOTHELIAL-CELL PROCOAGULANT ACTIVITY

Tumour necrosis factor-alpha (TNF-alpha) is a pluripotent cytokine wit h its receptors distributed throughout many different cell types. Beca use of the diverse effects of the cytokine, it is difficult to clearly define its role in infection and immunity, and appreciate its clinica l therapeutic value. We have identified peptides derived from the prim ary amino acid sequence of human TNF-alpha that have neutrophil-stimul ating activity, as measured by enhanced chemiluminescence and superoxi de production, and peptides which are both directly cytotoxic for tumo ur cells (WEHI-164) in vitro and also prevent TNF binding to tumour ce lls. However, only one of these neutrophil-stimulating peptides was to xic for tumour cells in vitro. Our results indicate that the region of amino acids 54-94 of human TNF-alpha has previously undescribed human neutrophil-stimulatory activity, while peptides encompassing the regi ons 43-68 and 132-150, which are in close proximity, as indicated in t he recently determined three-dimensional structure of human TNF-alpha, have in vitro anti-tumour activity. These peptides also slowed tumour growth or induced tumour regression in WEHI-164 tumour-bearing mice. The peptide 73-94, which activated neutrophils but which was not cytot oxic for tumour cells in vitro, also caused in vivo tumour regression, presumably by activating neutrophils with the consequent release of f ree radicals at the tumour site. Peptide 63-83, which was able to acti vate neutrophils in vitro, did not possess tumour regression activity in vivo. The TNF peptides described in this report did not elicit proc oagulant activity in cultured bovine aortic endothelial cells and as s uch are devoid of at least one of the potentially lethal side-effects of elevated TNF levels in vivo.