Duchenne Musküler Distrofinin Tedavisinde Ekson Atlama Yaklaşımındaki Gelişmeler
Özet
Duchenne müsküler distrofi (DMD), distrofin genindeki mutasyonların açık okuma çerçevesini bozması ve bunun sonucunda işlevsel protein üretilememesi nedeniyle ortaya çıkan, ilerleyici kas yıkımıyla karakterize ölümcül bir genetik hastalıktır. Günümüzde hastalığın kesin bir tedavisi bulunmamakla birlikte, pre-mRNA üzerinde splicing sürecini modüle ederek okuma çerçevesini yeniden kurmayı amaçlayan ekson atlama yaklaşımları en umut verici primer tedavi yöntemi olarak öne çıkmaktadır. Bu doğrultuda FDA; Eteplirsen, Golodirsen ve Casimersen gibi fosforodiamidat morfolino oligomeri (PMO) tabanlı antisens oligonükleotitlerin (ASO) kullanımına şartlı onay vermiştir. Ancak, bu moleküllerin klinik denemelerde sağladığı distrofin restorasyon seviyeleri, anlamlı bir kas iyileşmesi için gereken en az %10'luk eşiğin oldukça altındadır ve kas dokusu genelinde yamalı bir dağılım sergilemektedir. Buna karşın, klinik öncesi hayvan modellerinde çok daha yüksek PMO dozları güvenle kullanılmış ve doza bağlı olarak başarılı, terapötik düzeyde ve daha homojen bir distrofin restorasyonu elde edilmiştir. İnsan klinik denemelerinde yüksek dozların tercih edilmesini kısıtlayan en temel engel ise PMO üretim süreçlerinin oldukça yüksek maliyetli olmasıdır. Bu maliyet baskısını azaltmak adına Eteplirsen ile aynı bölgeyi hedefleyen daha kısa alternatif PMO tasarımları geliştirilmiş; yapılan in vitro ve in vivo analizlerde, hücre ve dokulara doygunluk seviyesinde ulaştırıldıklarında bu kısa izoformların etkinliğinin uzun olanlarla özdeş olduğu kanıtlanmıştır. Bu durum, yeni klinik deneme tasarımlarında dokunun maksimum PMO kapasitesini ifade eden doygunluk seviyesinin belirlenmesinin önemini ve daha ekonomik tedavi alternatiflerinin varlığını açıkça ortaya koymaktadır.
Duchenne muscular dystrophy (DMD) is a fatal genetic disorder characterized by progressive muscle wasting and destruction caused by mutations that disrupt the open reading frame of the dystrophin gene. Currently, there is no curative treatment for DMD; however, exon skipping approaches, which aim to re-establish the open reading frame by modulating the pre-mRNA during splicing using antisense oligonucleotides, stand out as the most promising primary therapeutic method. Accordingly, the FDA has granted conditional approval for phosphorodiamidate morpholino oligomer (PMO) based antisense oligonucleotides (ASOs) such as Eteplirsen, Golodirsen, and Casimersen. Nevertheless, the dystrophin restoration levels achieved by these molecules in clinical trials remain well below the minimum 10% threshold required for meaningful functional recovery and display a patchy distribution across muscle tissues. Conversely, preclinical animal models safely utilized significantly higher PMO doses, resulting in successful, dose-dependent, therapeutic-level, and more homogeneous dystrophin restoration. The primary constraint limiting the adoption of higher doses in human clinical trials is the exceptionally high cost associated with PMO manufacturing processes. To alleviate this financial pressure, shorter alternative PMO designs targeting the exact same region as Eteplirsen were developed; in vitro and in vivo analyses demonstrated that when delivered to cells and tissues at saturation levels, the efficiency of these shorter isoforms is identical to the longer ones. These findings clearly underscore the necessity of determining the PMO saturation level, which represents the maximum PMO capacity of a muscle tissue, in designing new clinical trials and highlight the existence of more economically viable therapeutic alternatives.
Referanslar
Hoffman, E.P., R.H. Brown, Jr., and L.M. Kunkel, Dystrophin: the protein product of the Duchenne muscular dystrophy locus. Cell, 1987. 51(6): p. 919-28.
Emery, A.E., Population frequencies of inherited neuromuscular diseases--a world survey. Neuromuscul Disord, 1991. 1(1): p. 19-29.
Bello, L., et al., DMD genotypes and loss of ambulation in the CINRG Duchenne Natural History Study. Neurology, 2016. 87(4): p. 401-9.
Cirak, S., et al., Exon skipping and dystrophin restoration in patients with Duchenne muscular dystrophy after systemic phosphorodiamidate morpholino oligomer treatment: an open-label, phase 2, dose-escalation study. Lancet, 2011. 378(9791): p. 595-605.
Cirak, S., et al., Restoration of the dystrophin-associated glycoprotein complex after exon skipping therapy in Duchenne muscular dystrophy. Mol Ther, 2012. 20(2): p. 462-7.
Muntoni, F., S. Torelli, and A. Ferlini, Dystrophin and mutations: one gene, several proteins, multiple phenotypes. Lancet Neurol, 2003. 2(12): p. 731-40.
Bushby, K., et al., Diagnosis and management of Duchenne muscular dystrophy, part 1: diagnosis, and pharmacological and psychosocial management. Lancet Neurol, 2010. 9(1): p. 77-93.
Gao, Q.Q. and E.M. McNally, The Dystrophin Complex: Structure, Function, and Implications for Therapy. Compr Physiol, 2015. 5(3): p. 1223-39.
Bushby, K.M., et al., The clinical, genetic and dystrophin characteristics of Becker muscular dystrophy. II. Correlation of phenotype with genetic and protein abnormalities. J Neurol, 1993. 240(2): p. 105-12.
McDonald, C.M., et al., Long-term effects of glucocorticoids on function, quality of life, and survival in patients with Duchenne muscular dystrophy: a prospective cohort study. Lancet, 2018. 391(10119): p. 451-461.
Lim, K.R., R. Maruyama, and T. Yokota, Eteplirsen in the treatment of Duchenne muscular dystrophy. Drug Des Devel Ther, 2017. 11: p. 533-545.
Arechavala-Gomeza, V., et al., Comparative analysis of antisense oligonucleotide sequences for targeted skipping of exon 51 during dystrophin pre-mRNA splicing in human muscle. Hum Gene Ther, 2007. 18(9): p. 798-810.
Yokota, T., W. Duddy, and T. Partridge, Optimizing exon skipping therapies for DMD. Acta Myol, 2007. 26(3): p. 179-84.
van Deutekom, J.C., et al., Antisense-induced exon skipping restores dystrophin expression in DMD patient derived muscle cells. Hum Mol Genet, 2001. 10(15): p. 1547-54.
Mann, C.J., et al., Antisense-induced exon skipping and synthesis of dystrophin in the mdx mouse. Proc Natl Acad Sci U S A, 2001. 98(1): p. 42-7.
Yokota, T., et al., Efficacy of systemic morpholino exon-skipping in Duchenne dystrophy dogs. Ann Neurol, 2009. 65(6): p. 667-76.
van den Bergen, J.C., et al., Dystrophin levels and clinical severity in Becker muscular dystrophy patients. J Neurol Neurosurg Psychiatry, 2014. 85(7): p. 747-53.
Kinali, M., et al., Local restoration of dystrophin expression with the morpholino oligomer AVI-4658 in Duchenne muscular dystrophy: a single-blind, placebo-controlled, dose-escalation, proof-of-concept study. Lancet Neurol, 2009. 8(10): p. 918-28.
Mendell, J.R., et al., Eteplirsen for the treatment of Duchenne muscular dystrophy. Ann Neurol, 2013. 74(5): p. 637-47.
Charleston, J.S., et al., Eteplirsen treatment for Duchenne muscular dystrophy: Exon skipping and dystrophin production. Neurology, 2018. 90(24): p. e2146-e2154.
Sazani, P., D.L. Weller, and S.B. Shrewsbury, Safety pharmacology and genotoxicity evaluation of AVI-4658. Int J Toxicol, 2010. 29(2): p. 143-56.
Wu, B., et al., Dose-dependent restoration of dystrophin expression in cardiac muscle of dystrophic mice by systemically delivered morpholino. Gene Ther, 2010. 17(1): p. 132-40.
Wu, B., et al., One-year treatment of morpholino antisense oligomer improves skeletal and cardiac muscle functions in dystrophic mdx mice. Mol Ther, 2011. 19(3): p. 576-83.
Novak, J.S., et al., Myoblasts and macrophages are required for therapeutic morpholino antisense oligonucleotide delivery to dystrophic muscle. Nat Commun, 2017. 8(1): p. 941.
Akpulat, U., et al., Shorter Phosphorodiamidate Morpholino Splice-Switching Oligonucleotides May Increase Exon-Skipping Efficacy in DMD. Mol Ther Nucleic Acids, 2018. 13: p. 534-542.
