It’s tough to keep up with the proliferation of monoclonal antibodies. Seems every day I’m confronted by a patient who’s using a new drug with a name ending in “mab.” That drug blocks a cellular receptor I haven’t heard of that’s involved in a cascade of interactions I haven’t thought about since medical school. The resulting disruption reduces disease burden, typically at great expense to the medical system, the patient, or both. We’ve truly entered the era of precision medicine. It’s not enough to understand disease; you also must know its heterogeneous expression so that you can prescribe the ‘mab that targets the biology responsible for variants in behavior. All diseases are, in fact, syndromes. This isn’t a bad thing, but it’s a challenge.
A series of ‘mabs have been approved for treating type 2 high (TH2) or eosinophilic asthma. We refer to this group of ‘mabs generically as biologics. The group includes omalizumab, mepolizumab, dupilumab, benralizumab, reslizumab, and tezepelumab. While mechanism of action varies slightly across drugs, the biologics all target a specific arm of the immune system. Efficacy is linearly related to serum eosinophil count and there’s little clinically or pharmacologically to distinguish one from another. Of course, no head-to-head comparisons of efficacy are available and there’s no financial incentive for them to be performed.
Latest research
A new randomized controlled trial (RCT) of dupilumab for chronic obstructive pulmonary disease (COPD) adds to the aforementioned biologic knowledge base. Turns out it works as long as the patients are carefully selected. Researchers enrolled GOLD D (or E depending on which iteration of the GOLD Statement you use) patients on triple inhaler therapy (inhaled corticosteroids [ICS]/long-acting beta-agonist [LABA]/long-acting muscarinic antagonist [LAMA]) with two moderate exacerbations or one exacerbation requiring hospitalization in the past year. Blood eosinophil counts were > 300 cells/mcL and chronic bronchitis was present clinically. The primary and multiple secondary outcomes were improved with dupilumab.
This is welcome news. I’ve treated countless patients with severe COPD who have repeated exacerbations despite my efforts to prevent them. These patients are on ICS/LABA/LAMA and azithromycin or roflumilast, and occasionally both. While every COPD guideline known to man forbids using chronic oral corticosteroids (OCS), I’ve prescribed them repeatedly because the benefits to keeping a recalcitrant, exacerbating patient out of the hospital seem to outweigh OCS risks. It would be nice to have a better option. Although we were taught that they were immutably distinct in medical school, every first-year pulmonary fellow knows that asthma and COPD share more similarities than differences, so it makes sense that proven asthma therapies would work for some patients with COPD.
However, the dupilumab study must be placed in context. Past studies haven’t been as positive. In 2017, two separate RCTs found that mepolizumab reduced the annual rate of moderate to severe exacerbations (primary outcome) in one trial but not the other. Interpretation gets more complicated when broken down by intention to treat (ITT) vs. modified ITT and when secondary outcomes are considered. Sparing you those details, this trial does not instill confidence, leading the Food and Drug Administration to refuse approval for mepolizumab for COPD. A second RCT of benralizumab for COPD was published in 2019. Much less cognitive load was required to interpret this one; it was negative. FDA approval was not requested.
Looking through the trial designs for the three RCTs of biologics for COPD, I couldn’t find major differences that could explain the discordant results. Sample size and enrollment criteria were similar. As stated, I don’t believe that the biologic data in asthma allow for predicting efficacy in one eosinophilic patient vs. another and I assume the same would be true for COPD. All three trials found that eosinophils were eliminated, so responses were biologically equivalent.