Recombinant human tumor necrosis factor-alpha (TNF-alpha) has demonstrable antitumor activity in transplantable murine tumor models and patients with cancer but is highly toxic to both animals and human beings. The narrow therapeutic index of TNF-alpha has limited its anticancer utility. Toxicity associated with many standard anticancer drugs is highly dependent upon the circadian timing of their administration. The effect of time of day of TNF-alpha administration on lethal toxicity was examined in 238 BALB/c female mice in two studies. Each mouse received a single intravenous injection of human TNF-alpha at one of six equispaced times within the first contiguous 24-h cycle. The probability of dying across all times of day of TNF-alpha treatment was not equal (p < 0.01) and varied up to ninefold. Significant time of day dependence of TNF-alpha toxicity was present over a full order of magnitude of TNF-alpha dose. The frequency of TNF-alpha-induced lethality was greatest and the time to death was most brief when TNF-alpha was administered just before awakening. The survival probability was highest when TNF-alpha was administered in the second half of the daily activity span corresponding roughly to late afternoon and evening hours for human beings. The optimization of TNF-alpha administration timing is a strategy that warrants further investigation for improving the toxic/therapeutic ratio of this important cytokine. From a more fundamental perspective, these data may be essential for achieving a fuller understanding of TNF-alpha in vivo biology.

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