A new drug combination rescues a rare Cystic Fibrosis mutation in patient tissue

University of Toronto researchers in the laboratory of Dr. Christine Bear, together with collaborators at SickKids Hospital (Toronto, Canada) and Proteostasis Therapeutics (Cambridge, Massachusetts), used computer simulations, cell-based systems and patient tissue to interrogate the consequences of a rare Cystic Fibrosis (CF) disease-causing mutation in the CFTR gene: c.3700 A>G (also called ΔI1234_R1239) and subsequently develop a novel mechanism-based therapeutic strategy.

Fig. 1. Comparison of CFTR expression and localization in healthy versus CF-affected tissues.
Top panel: Immunofluorescence showing expression and localization of normal CFTR (green) on primary nasal tissue obtained from a healthy, non-CF family member. Tight junction protein ZO-1 (red) and cell nuclei (DAPI) are also labeled for comparison as landmarks; scale bar represents 10 μm. Bottom panel: Lower expression and inappropriate localization of the rare variant (ΔI1234_R1239-CFTR, green) from a family member with CF (i.e. Patient CF-1).

In brief, this study determined that the rare variant exhibited several protein defects that were comparable to the most common CF mutation, ΔF508; suggesting that drugs designed for ΔF508 (i.e. ORKAMBI®) may also be effective for ΔI1234_R1239. However, patient-derived tissue from individuals bearing this rare mutation showed that additional unique defects were present (i.e. low CFTR protein abundance) and that ORKAMBI® alone would not be sufficient. In collaboration with Proteostasis Therapeutics, the authors determined that an investigational small molecule, an “amplifier” (PTI-CH), aimed at enhancing CFTR protein abundance, improved the rescue effect of ORKAMBI®, first in a CRISPR/Cas9 edited bronchial epithelial cell line and then in nasal epithelial tissue from individuals homozygous for this rare mutation.

This study highlights the importance of drug testing using relevant, patient-specific tissues for informing therapeutic strategies for CF individuals with rare mutations.

Steven V. Molinski1,2, Saumel Ahmadi2,3, Wan Ip4, Hong Ouyang4, Adriana Villella5, John P. Miller5, Po-Shun Lee5, Kethika Kulleperuma1,2, Kai Du2, Michelle Di Paola1,2, Paul D.W. Eckford2, Onofrio Laselva2, Ling Jun Huan2, Leigh Wellhauser2, Ellen Li2, Peter N. Ray6, Régis Pomès1,2, Theo J. Moraes4,7, Tanja Gonska4,7, Felix Ratjen8, Christine E. Bear1,2,3
1Department of Biochemistry, University of Toronto, Toronto, Ontario M5S 1A8, Canada
2Programme in Molecular Structure & Function, Research Institute, Hospital for Sick Children, Toronto, Ontario, M5G 0A4, Canada
3Department of Physiology, University of Toronto, Toronto, Ontario M5S 1A8, Canada
4Programme in Physiology & Experimental Medicine, Research Institute, Hospital for Sick Children, Toronto, Ontario M5G 0A4, Canada
5Proteostasis Therapeutics, Cambridge, MA 02139, USA
6Division of Molecular Genetics, Hospital for Sick Children, Toronto, Ontario, M5G 0A4, Canada
7Department of Paediatrics, University of Toronto, Toronto, Ontario M5S 1A8, Canada
8Division of Respiratory Medicine, Hospital for Sick Children, Toronto, Ontario, M5G 0A4, Canada



Orkambi® and amplifier co-therapy improves function from a rare CFTR mutation in gene-edited cells and patient tissue.
Molinski SV, Ahmadi S, Ip W, Ouyang H, Villella A, Miller JP, Lee PS, Kulleperuma K, Du K, Di Paola M, Eckford PD, Laselva O, Huan LJ, Wellhauser L, Li E, Ray PN, Pomès R, Moraes TJ, Gonska T, Ratjen F, Bear CE
EMBO Mol Med. 2017 Sep


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