QR-444

QR-444 is an investigational antisense oligonucleotide (ASO) developed by ProQR Therapeutics for the treatment of cystic fibrosis (CF) caused by the W1282X nonsense mutation in the *CFTR* gene. The W1282X mutation introduces a premature termination codon that leads to the production of a truncated, non-functional protein and triggers nonsense-mediated decay (NMD), a cellular surveillance mechanism that degrades the mutant mRNA transcripts. QR-444 is designed to bind specifically to the *CFTR* mRNA and selectively inhibit the NMD process, thereby stabilizing the transcript and increasing the levels of the truncated CFTR protein. This approach aims to provide a sufficient protein substrate that can be further enhanced by CFTR modulators, such as potentiators, to restore chloride channel function. Development of QR-444 was discontinued in the preclinical stage as ProQR shifted its strategic focus toward its Axiomer RNA editing platform.