We recently demonstrated that sc administered interleukin-6 (IL-6) strongly stimulates the human hypothalamic-pituitary-adrenal (HPA) axis, with mild toxicity and no hypotensive effects. In this study, we evaluated the response of the human HPA axis to escalating iv doses of recombinant IL-6 in six patients with cancer and good performance status who received daily, every 8 h, three equal doses of 0.3-30 micrograms/kg IL-6. The plasma levels of IL-6 assayed by a specific enzyme-linked immunosorbent assay during the 4 h following the first IL-6 injection were elevated for 2-4 h, proportionally to the amount of injected IL-6. Administration of the cytokine was followed by marked elevations of plasma ACTH (53.0-98.6 pmol/L) and cortisol (824.9-1729.9 nmol/L) independently of the IL-6 dose administered, suggesting that the doses employed were at the top of the dose-response curve for these hormones. Interestingly, plasma arginine vasopressin (AVP) levels were also elevated during the 2 h after IL-6 injection in all patients who received a dose of 3 micrograms/kg or more, suggesting that IL-6 activated the magnocellular AVP-secreting neurons and that it might be involved in the syndrome of inappropriate AVP secretion. Cortisol elevations with peaks similar to those observed after the first injection of IL-6 were also detected in plasma sampled every 2 h after the second and third injections, suggesting that there was no rapid tachyphylaxis in response to IL-6 administration. Plasma IL-1 beta and tumor necrosis factor-alpha concentrations, assayed by specific enzyme-linked immunosorbent assays during the 4 h after the first IL-6 injection, were either within the normal range or undetectable, confirming in vitro observations that IL-6 does not stimulate IL-1 beta or tumor necrosis factor-alpha secretion and suggesting that it exerts its effect on the HPA axis and AVP secretion independently of them. We conclude that IL-6 is a potent stimulator of the human HPA axis and a secretagogue of magnocellular AVP secretion, which might be employed as a challenge test of the axis and the magnocellular AVP neuron.
A safely tolerated dose of daily subcutaneous IL-6 is 10 micrograms/kg, with hepatotoxicity and cardiac arrhythmia being the dose-limiting toxicities at 30 micrograms/kg. Phase II trials of IL-6 administered subcutaneously daily for at least 7 days for two cycles with an intervening week of rest are recommended for phase II trials. However, patients with extensive replacement of liver by tumor and abnormal liver functions should receive IL-6 therapy with caution.
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