Cystinosis is an autosomal recessive lysosomal storage disorder caused by mutations in the CTNS-gene (Chr17p13). CTNS codes for the lysosomal protein cystinosin, a cystine-proton symporter taking cystine out of the lysosome. The current standard therapy for cystinosis, cysteamine, only delays the progression of renal and extra-renal disease manifestations. Therefore, the search for new therapies in cystinosis is ongoing [1].
Messenger RNA (mRNA)-based therapies have revolutionised the field of molecular medicine and have been applied in several genetic disorders. Importantly, in vitro transcribed (IVT) mRNA is optimised for therapeutic application by means of chemical and sequence modifications that reduce the immunogenicity of the RNA and enhance stability. In order to reach the kidneys in vivo, several strategies can be employed [2]. Notably, size and charge of the delivery vehicles determine if the construct is filtered, while specific targeting molecules can increase cell-specific targeting potential. Finally, different injection strategies can be employed to reach specific kidney tissues (for example, renal vein or ureter injection to reach the kidney). The combination of these approaches has also been applied to direct RNA-based therapeutics to the kidneys [4].
Our approach is to apply a CTNS-mRNA LNP therapy to alleviate the cystinosis phenotype by reintroducing the functional cystinosin. In cystinosis cell models, we already successfully applied a lipofectamine mediated mRNA transfection to obtain lysosomal cystinosin expression. Functional assays will be employed to assess the in vitro phenotype restoration post-transfection (metabolomics, endocytosis function, etc.). In the rat model, we will mainly focus on the renal phenotype, but a general assessment of the animal health will also be performed. We will also be able to explore different injection strategies and targeting molecules, and assess the biodistribution of the cystinosin in the extra-renal cystinosis phenotype (muscle, eye, liver, …).
