Making sense of nonsense in the context of Cystic Fibrosis

Cystic Fibrosis (CF) is a genetic, severe, respiratory disease that can be caused by different mutations in the CFTR gene. Whilst for some mutations highly efficient treatments are available, roughly 10% of all people with CF suffer from a large unmet clinical need. One type of mutation that has proven to be challenging in the context of therapy development in particular, is a so-called nonsense mutation. The main studied treatment regimen for treating nonsense mutations is based on compounds that induce translational readthrough. Such readthrough compounds act through various mode-of-actions to promote the incorporation of non-cognate amino acids (AAs), which consequently results in translation beyond the nonsense mutation site. However, preclinical studies often show contradictory results on readthrough compound efficacy when comparing different nonsense mutations, genetic diseases, model systems and read-outs. Additionally, whilst preclinical studies showed promising results in many cases, clinical studies, in a CF-overarching context, on readthrough compounds are so far disappointing.

In the studies described in this thesis, we therefore set out to study novel strategies for treating nonsense mutations. For example, we show that by combining different drugs with different modes of action (MoAs), nonsense mutations cán be rescued. Furthermore, we characterized the efficiency of drugs that are already used in a clinical setting to see whether they may have repurposing potential for CF. Developing new drugs is exceptionally time-consuming and expensive, especially in the context of rare diseases. In this regard, drug repurposing is an attractive solution that holds economical and time-wise benefits. Indeed, we found that several drug families hold repurposing potential for CF.

Importantly, throughout the studies described in this thesis, we exploited CF patient-derived intestinal organoids (PDIOs): primary cells that recapitulate the genetic background of the person from whom the cells were isolated. We used PDIOs harboring different mutations in the forskolin-induced swelling assay, which allows characterization of CFTR function and as such allows for assessing treatment efficiency in a personalized context. In one of our studies, we indeed treated an individual with CF successfully based on results obtained in our preclinical experiments.

Whilst many challenges need to be tackled, we envisage that the work presented in this thesis aids in advancing precision medicine for CF and that concepts we explore here can be transferred to other diseases. We hope and expect that additional ongoing and future studies, that build on the work presented here, will further pave the way towards therapy development and availability for all people with CF.