(589) Combination treatment with CC-90009 and ELX-02 restores functional CFTR in patient derived intestinal organoids bearing PTC variants.

Thursday, November 3, 2022

12:45 PM – 1:25 PM ET

Presenting Author(s)

Alexander J. Stuffer, n/a

Research Associate IV
Cystic Fibrosis Foundation Lab
Lexington, Massachusetts, United States

Co-Author(s)

Eric Wong, MS

Scientist
Cystic Fibrosis Foundation
Lexington, Massachusetts, United States
CC

Calvin Cotton

Research Fellow
Cystic Fibrosis Foundation, United States
MM

Martin Mense

SVP Drug Discovery
Cystic Fibrosis Foundation, United States
JM

John Mahoney

Scientist IV
CFF, United States

Background: Cystic Fibrosis (CF) is caused by loss of function mutations in the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) gene. Greater than 2000 CFTR variants have been identified, with many confirmed as causative of disease. Recent developments in CFTR modulators, particularly Trikafta®, provide ~90% of people with CF access to efficacious treatments. For the remaining ~10% of people with CF, mostly carrying splice, premature termination codon (PTC), or other rare CFTR variants, no FDA approved therapies exist to treat underlying genetic defects. Recently, Eloxx Pharmaceuticals entered clinical trials with the aminoglycoside PTC readthrough drug ELX-02, but results suggest that in CF the drug may not be sufficiently efficacious as a monotherapy. The following data, under an in vitro context, assesses the potential for ELX-02 as a monotherapy, and in combination with CC-90009 (CC-9), a GSPT1-selective cereblon E3 ligase inhibitor [1], with and without the components of Trikafta®, i.e., elexacaftor (elexa), tezacaftor (teza) and ivcaftor (iva).

Methods: Briefly, 48-hour compound effect on PTC-CFTR function was assessed by the forskolin induced swelling (FIS) assay, known to be highly sensitive and quantitative, with patient derived intestinal organoid cultures homozygous for three CFTR PTC variants: CFTR W1282X, CFTR G542X and CFTR R1162X.

Results: Swelling of CFTR W1282X, CFTR G542X and CFTR R1162X intestinal organoids induced by 5 uM forskolin can be highly significant. Response sizes vary by treatment combination and genotype. While ELX-02 in combination with CC-9 enhances CFTR function in all three variants, the effect on CFTR W1282X and CFTR R1162X was increased with the addition of elexa/teza/iva. Further analysis of the individual effects of elexa, teza, and iva revealed that only CFTR W1282X appeared sensitive to potentiation with iva, whereas the response of CFTR R1162X was already maximized by the addition of the correctors elexa/teza. Interestingly, ELX-02 monotreatment of CFTR G542X was sensitive to correctors elexa/teza, yet under in-house assay conditions the combination treatment of CFTR G542X with ELX-02 and CC-9 resulted in maximal CFTR functional rescue that was insensitive to elexa/teza/iva.

Conclusions: Small molecule application can induce readthrough of PTC mutations in CFTR, yet the addition of CFTR modulators significantly enhances CFTR function compared to readthrough-only therapeutic approaches. We have observed PTC-genotype-specific responses to treatment with CC-9 and ELX-02, with differing sensitivity to elexa, teza, and/or iva. While further work will elucidate genotype-specific differences further, these results support that CFTR readthrough products are dependent on the specific PTC mutation. Therapeutic development for PTC-CFTR variants remains critically important to the CF community and is imperative to continue combination studies with both novel and existing agents that can promote translational readthrough. At present, at least in CF, it seems only drug combinations for PTC readthrough will be able to provide the efficacy required to achieve clinical benefit.

Acknowledgements:

References: Surka C, Jin L, Mbong N, et al. CC-90009, a novel cereblon E3 ligase modulator, targets acute myeloid leukemia blasts and leukemia stem cells. Blood. 2021;137(5):661-677. doi:10.1182/blood.2020008676