The objective of this study was to analyse the FDA approvals and orphan drug designations for compounds to treat alpha-1-antitypsin deficiency (AATD) in order to gain a comprehensive overview of the status of current therapy developments for this rare hereditary disease.
Primary endpoint: orphan drug approvals by the FDA.
Since 1984, only one compound received FDA approval for the treatment of alpha-1-antitrypsin deficiency. Administration of purified human AAT is the only specific treatment; prospective randomized-controlled and open-label studies have shown a slowed decline in lung density with weekly infusions of 60mg AAT/kg21,22. Whether AAT augmentation therapy has a positive effect on the extrapulmonary manifestations of the disease is currently unproven; moreover, weekly i.v. therapy is time-consuming and the treatment costs are high. In addition to preventive measures such as abstinence from nicotine, alcohol and the prompt treatment of respiratory infections, various symptomatic therapies for emphysema e.g. bronchodilators, inhaled steroids, the administration of oxygen or non-invasive ventilation are available if needed23.
Of note, alpha-1-proteinase inhibitors of human origin are subjected to availability of plasma donors and, despite manufacturing precautions, the risks related to plasma donations, e.g., virus contamination or Creutzfeldt-Jakob disease. Interestingly, the development of a recombinant alpha-1-proteinase inhibitor, which would mitigate these risks, has never been successful until close of database. One example for successful transition from donor-based protein sources to recombinant production is Gaucher disease, a rare neurogenetic disorder due to the inherited deficiency of the enzyme glucocerebrosidase. Here, the missing enzyme was initially produced from collected placenta tissue (alglucerase, approved by the FDA in 1994) and subsequently switched swiftly towards recombinant production in Chinese hamster ovary cell cultures (imiglucerase, approved by the FDA in 1994)20,24.
Early identification of gene carriers and education about necessary preventive measures such as nicotine abstinence and vaccination are essential for all individuals with severe AAT deficiency (genotype PI ZZ, ZNull or NullNull and other rarer gene variants) to avoid premature loss of lung function25. AAT augmentation therapy, as the only available therapeutic option with a causal approach, is usually administered in the late stages of the disease and therefore does not contribute to the prevention of lung disease, but only serves to slow the progression of the disease. An important characteristic of the disease that can be insufficiently addressed by early detection and appropriate lifestyle changes such as alcohol abstinence and weight reduction is AATD liver disease. Approximately one third of adults with PI ZZ AAT deficiency develop clinically significant liver fibrosis during the course of the disease26,27. Despite more than three decades of intensive research activity, no drug has yet been approved for this manifestation of AATD.
Major limitations of alpha-1-proteinase inhibitor augmentation therapy are its inconvenient application and lack of effect on extrapulmonary manifestations, which defines the current unmet medical need. The attempt of alternative alpha-1-proteinase inhibitor applications as well as the efforts to develop inhaled therapies28 have not yet led to a marketing approval. The possibility of intravenous self-administration at home allows suitable patients some freedom despite fixed weekly treatment schedules, at least because of the time savings and flexibility of self-administration29.
With respect to liver manifestation, emerging RNAi-based therapeutics targeting hepatic Z-AAT production currently in development may, if proven to be safe and efficacious, benefit patients with AATD-associated liver disease in the future 30,31.
Secondary endpoint: orphan drug designations by the FDA.
Alpha-1-proteinase inhibitors of human origin were the first compounds intended to treat AATD that received an orphan drug designation in 1984 (Fig. 1).
Only one new compound (an anti-inflammatory) received an orphan drug designation during the marketing exclusivity period of the protein therapy alpha1-proteinase inhibitor (human) (Fig. 1), whereas thirteen orphan drug designation were granted after expiration of this marketing exclusivity in 1994. This could mean that exclusivity protected the pharmaceutical market whereas the absence of marketing exclusivity in a drug development environment with previously demonstrated success in orphan drug approval may stimulate innovation.
There are both commercial as well as economical aspects that play a role in drug development for rare diseases. From a patient’s perspective, the driver should be the unmet medical need. From a pharmaceutical company’s perspective, the main leitmotiv is returns on investment influenced by likelihood of success in the clinical development program and commercialization24. Therefore, as further explained in the introduction, in 1983, the US Orphan Drug Act passed, in order to provide incentives to pharmaceutical companies to invest into the development of drugs for rare diseases15. The output and impact can vary: medicines developed under the US orphan drug act in the very active field of rare cancers were in general very innovative, and had shifted from non-cytotoxic agents to targeted therapies19,32. Likewise, in lysosomal storage diseases, orphan drug development was very innovative with “a drug made for a disease”20,24. In lysosomal storage disorders, success factors for approval included disease prevalence, the choice of endpoints, regulatory precedence and technology platform20,24. In contrast to this, the development output in rare epilepsies and rare rheumatological diseases delivered little innovation, or focused mainly on compounds with other indications or similar molecular pathways33,34. Overall, the drug development activities in AATD were quantitively similar to the spectrum observed within the family of lysosomal storage diseases, but the technological approach of the FDA-approved therapy for AATD remains rather simple and is still based on human protein sources.
Limitations and directions for future research
As pointed out previously, this analysis has some limitations that have to be taken into account for the correct interpretation of the present findings19,20,24,32−34. Guided by strategic and patent related considerations manufacturers may choose not to reveal the intent to develop a drug in a publicly visible way at an early stage which may have influenced the timeline to approval in Fig. 1. This analysis focusses intentionally on the FDA perspective35 and did therefore not consider regulatory jurisdictions elsewhere. Because in general drug development for rare diseases is a global endeavour, we regard the findings of the present analysis generalizable within the context of the limitations described19. This report serves as a baseline for future progress.