Hemophilia A
Hemophilia is a bleeding disorder caused by a deficiency in one of the blood clotting factors. Hemophilia A accounts for about 80 percent of all hemophilia cases and results from a deficiency in clotting factor VIII (FVIII). The factor VIII protein is produced in part by the hepatocytes in the liver. Hemophilia A is a hereditary disorder that affects approximately 1 in 10,000 males. There are approximately 17,000 affected individuals, mostly males, in the Unites States alone.
RNA Therapy for Hemophilia A
The first approach VIRxSYS tested with its SMaRT™ RNA technology in hemophilic FVIII knockout mice was to repair the defective gene transcript, artificially created by the insertion of a foreign sequence (neo) into the gene (figure below). With the presence of the inserted sequence, knockout mice are unable to produce a functional factor VIII protein and cannot survive a bleeding episode. Using different modes of delivery, we have repaired the FVIII by trans-splicing RNA transcripts with a PTM providing the necessary sequences to bypass the disruptive neo insert. As a result functional factor VIII proteins were produced and SMaRTTM treated animals were able to clot and survive after a tail vein cut. Altogether, activity and phenotypic data showed that we have achieved significant and therapeutic levels of factor VIII repair in this animal model [1].
Following the successful demonstration in RNA repair of the defective Factor VIII gene in mice, VIRxSYS next successfully demonstrated for Factor VIII the same innovative SMaRTTM RNA strategy previously demonstrated in the Company’s HDL program, i.e. re-program the abundant pre-mRNA transcript from the albumin gene to encode for production of Factor VIII. This was successful and the results have been published [2].
Advantages of SMaRT™ for Hemophilia A
Transgene regulation:
One major concern with standard gene therapy approaches is the potential to generate an immune response against newly produced proteins following the transduction of immune cells from the intra-venous injection of the therapy. With VIRxSYS' SMaRTTM technology, this issue is avoided because the generation of missing factor VIII proteins is performed by trans-splicing and will occur only in cells which normally express factor VIII, the hepatocytes in the liver. This avoids the potential for expressing the factor VIII protein in an improper cell.
Complete Factor FVIII protein:
With the VIRxSYS SMaRTTM approach for factor VIII therapy, trans-splicing generates a complete factor VIII protein that contains a portion of the B-domain, an important component in the release of factor VIII from hepatocytes.
References:
[1] Chao et al. Phenotype Correction of Hemophilia A Mice by Spliceosome-Mediated RNA Trans-Splicing. Nature Medicine 9: 1015-19, 2003 (http://www.nature.com/nm/journal/v9/n8/full/nm900.html)
[2] Wang et al. Trans-splicing into highly abundant albumin transcripts for production of therapeutic proteins in vivo. Molecular Therapy 17:343-351, 2009 (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2835072/pdf/mt2008260a.pdf)