(644) Identification of organoid responders to CFTR modulators in the HIT-CF Europe project – Underlying the need for new treatment strategies for people with ultra-rare mutations

Background: People with cystic fibrosis (pwCF) who carry ultra-rare CFTR mutations are often not included in drug development pipelines of pharmaceutical companies. Currently, based on their genotype, no efficient modulator combination is approved for 15-20% of pwCF, while they could potentially benefit. These numbers are even higher outside Europe. The Forskolin-Induced Swelling (FIS) assay in intestinal organoids has demonstrated to be highly predictive of a donor’s clinical response [1]. The Human Individualized Treatment for CF project (HIT-CF; www.hitcf.org) was designed to bring drugs to pwCF who carry ultra-rare mutations. In this project intestinal organoids of pwCF with ultra-rare mutations were screened with compounds that already passed phase I/II clinical trials (dirocaftor(DIR)/ posenacaftor (POS)/nesolicaftor(NES) and/or ELX-02). DIR and POS represent a novel potentiator and corrector, respectively. NES, a first-in-class CFTR amplifier, selectively increases the amount of immature CFTR protein. ELX-02 is a readthrough compound designed for pwCF carrying nonsense mutations.

Methods: A total of 489 patient-derived organoids (PDO) were collected from adult pwCF from 17 European countries, Israel and the United Kingdom. All PDO with a minimum of 1 nonsense mutation were screened with ELX-02 and those with a maximum of 1 nonsense mutation with DIR/POS. The FIS assay was conducted as previously published [1].

Results: Screening was technically successful in 471 PDO with ELX-02 (n=221) and/or DIR/POS (n=380), with 130 PDO included in both screens. In the ELX-02 screen, PDO were incubated with the drug for 48h prior to FIS and a PDO sample from a G542X/G542X donor was used as positive control. In the DIR/POS/NES screen, PDO were incubated for 24 h with DIR/POS, using a PDO from a F508del/F508del donor incubated for 24h with tezacaftor/ivacaftor as the positive control. NES was only screened in a sub selection. FIS responses in the PDOs were categorized into 3 classes: (1) Higher response than in the positive control, (2) no organoid swelling, (3) organoid swelling, but not classified as 1 or 2. This classification allows estimation of proportions of pwCF that carry ultra-rare mutations with potential benefit from current and upcoming CFTR modulating therapies. It is important to note that the minimum swelling associated with clinical response is not yet known. The largest group (55% of PDO) was classified as class 3, followed by class 1 (23%) and class 2 (22%). These results are preliminary, a more detailed analysis will be presented at the conference.

Conclusions: Based on the organoid responsiveness to ELX-02 and/or DIR/POS up to 78% of pwCF that carry ultra-rare mutations could potentially benefit from upcoming CFTR modulating therapies. Although we have accomplished a great step forward in personalized medicine for pwCF there is still a large unmet need for those who have CFTR class VII ("unrescuable") mutations or variants that cannot be restored by the tested CFTR modulating therapies.

Acknowledgements: This work was supported by the EU (H2020-SC1-2017-755021)

References: [1] Berkers G, van Mourik P, Vonk AM, Kruisselbrink E, Dekkers JF, de Winter-de Groot KM, et al. Rectal Organoids Enable Personalized Treatment of Cystic Fibrosis. Cell Rep. 2019;26(7):1701-1708.e3. https://doi.org/10.1016/j.celrep.2019.01.068