Aims: The Canakinumab Antiinflammatory Thrombosis Outcomes Study (CANTOS) established that targeting inflammation with interleukin-1β (IL-1β) inhibition can significantly reduce cardiovascular (CV) event rates in the absence of any beneficial effects on cholesterol. Yet, CANTOS participants treated with both high-intensity statins and canakinumab remain at considerable risk for recurrent CV events. Both interleukin-18 (IL-18, which like IL-1β requires the NLRP3 inflammasome for activation) and interleukin-6 (IL-6, a pro-inflammatory cytokine downstream of IL-1) may contribute to the recurrent events that occur even on canakinumab therapy, and thus represent novel targets for treating atherothrombosis.
Methods and results: Plasma samples from 4848 stable post-myocardial infarction patients who were assigned to active IL-1β inhibition or placebo within CANTOS underwent measurement of IL-18 and IL-6 both before and after initiation of canakinumab using validated ELISA. All participants were followed over a median 3.7-year period (maximum 5 years) for recurrent major adverse cardiovascular events (MACE) and for all-cause mortality. Compared to placebo, canakinumab significantly reduced IL-6 levels in a dose-dependent manner yielding placebo-subtracted median percent reductions in IL-6 at 3 months of 24.8%, 36.3%, and 43.2% for the 50, 150, and 300 mg doses, respectively (all P-values <0.001). By contrast, no dose of canakinumab significantly altered IL-18 levels measured at 3 months (all effects <1%, all P-values > 0.05). Yet, despite these differential plasma effects, either baseline and on-treatment levels of IL-18 or IL-6 associated with rates of future CV events. For example, for MACE, each tertile increase in IL-18 measured 3 months after canakinumab initiation associated with a 15% increase in risk [95% confidence interval (CI) 3-29%, P = 0.016], while each tertile increase in IL-6 measured 3 months after canakinumab initiation associated with a 42% increase in risk (95% CI 26-59%, P < 0.0001). Similar effects were observed for MACE-plus, CV death, all-cause mortality, and the for the combination endpoint of all vascular events inclusive of revascularization procedures and hospitalization for congestive heart failure. In baseline as well as on-treatment analyses, risks were highest among those with the highest levels of both IL-18 and IL-6.
Conclusion: There remains substantial residual inflammatory risk related to both IL-18 and IL-6 after IL-1β inhibition with canakinumab These data support further pharmacologic development of therapies for atherothrombosis that target IL-18 or IL-6 signalling, or that can simultaneously inhibit both IL-1β and IL-18 (such as NLRP3 inflammasome inhibitors).
Clinical trial registration: ClinicalTrials.gov NCT01327846.
Keywords: Cardiovascular disease; Clinical trial; Inflammation; Interleukin-18; Interleukin-6.
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