A major gap in interleukin-17 inhibitor (IL-17i) therapy for axial spondyloarthritis (axSpA) was evidence of efficacy in nonradiographic axSpA. At ACR 2019, we saw two different IL-17i studies showing efficacy in nr-axSpA patients. Now we know that both secukinumab and ixekizumab are effective in the full spectrum of axSpA patients (ankylosing spondylitis [AS] and nr-axSpA).
The majority of clinicians would consider both AS and nr-axSpA to be driven by common processes and so drugs that are effective on one should have the same effect in the other as well. Hence the results are not a big surprise. In certain places, an approved indication for use may be important especially for reimbursement purposes. These results are likely to have maximal impact there.
The COAST-X study on ixekizumab was designed in a way similar to that of thewith certolizumab pegol. There was an extended 52-week placebo arm to study the natural history of nr-axSpA patients who are not actively treated with biologics. This design was necessary to respond to the Food and Drug Administration’s concern that, in the absence of this prolonged observation on placebo, we cannot be sure that nr-axSpA patients are not spontaneously remitting (not due to biologics).
However, the results here did surprise me. Unlike in the C-axSpAnd trial where only 13% of actively treated patients (on certolizumab pegol) switched to open-label treatment, in the COAST-X study 40% of patients on both doses of ixekizumab opted for open-label treatment. The number of patients moving out of the placebo arm was around 60% (similar in both studies). There are no straightforward factors evidently explaining this discrepancy. Between 15% and 25% of patients who switched had achieved the primary endpoint of ASAS40. Does this reflect that ASAS40 is not acceptable to patients? As the results show responses plateaued after week 16, it could be that the patients who switched might have done so well into the 52-week observation period.
Patients in the COAST-X study had slightly longer disease duration and marginally lower HLA-B27 prevalence (both factors may indicate lower chance of treatment response).
The primary endpoint of ASAS40 was met at weeks 16 and 52 with significantly higher rates seen with ixekizumab than with placebo. Again the response seems to plateau around 16 weeks with minimal gain up to week 52.
The results from the secukinumab PREVENT study are very similar to those of the COAST-X study showing the superiority of secukinumab over placebo in treating nr-axSpA patients. Interestingly, if we do not use the loading dose for secukinumab, there does not seem to be any difference from standard treatment with loading. This may have economic and administrative implications on the decision to use loading doses of secukinumab. We should carefully consider theresults before making decisions on the utility of loading doses. In the MEASURE 4 study on AS patients, although there was no difference between load and no load arms of secukinumab (around 60% ASAS20 response in both arms), there was no significant gain above placebo with both doses. (The primary endpoint was not met.) This is likely due to the high placebo response (47% ASAS20 response). Similarly, we see a high placebo response in the COAST-X study as well, with an ASAS40 response rate of about 40% in active secukinumab arms vs. 30% in the placebo arm.
The number of patients dropping out over the 52-week follow-up period was not discussed in the PREVENT trial presentation.
There is not much here to favor one IL-17i over the other.
Dr. Haroon is codirector of the Spondylitis Program at University Health Network and associate professor of medicine and rheumatology at the University of Toronto. He is chair of the scientific committee of the Spondyloarthritis Research and Treatment Network. He disclosed serving as a consultant for Amgen, AbbVie, Janssen, Lilly, Novartis, and UCB.