Unwinding Histone Deacetylase Inhibitors: Givinostat in Duchenne Muscular Dystrophy

Kevin Chang, PharmD

Duchenne muscular dystrophy (DMD) is a debilitating and progressive X-linked genetic disorder characterized by the absence of the dystrophin protein, which plays a crucial role in maintaining the structural integrity of muscle fibers. Without dystrophin, muscles are prone to damage during contraction, eventually leading to muscle fiber degeneration, inflammation, and fibrosis. Current treatments for DMD primarily involve corticosteroids, which help to slow disease progression and preserve muscle strength.¹ However, their long-term use is associated with significant side effects. As a result, there is a pressing need for alternative therapies that can effectively manage DMD. Histone deacetylase (HDAC) inhibitors have emerged as promising candidates in this regard, with givinostat (Duvyzat; ITF Therapeutics)², in particular, showing potential in preclinical and clinical studies.

The mechanism of action of HDAC inhibitors involves altering the acetylation status of histones and other proteins, thereby affecting gene expression. HDACs are enzymes that remove acetyl groups from histone proteins, leading to chromatin condensation and transcriptional repression. Inhibition of HDACs results in increased histone acetylation, promoting a more open chromatin structure and enhanced gene transcription. (see FIGURE). In the skeletal muscles of dystrophin-deficient mdx mice, HDAC activity was elevated making HDAC a prime target for pharmacologic intervention.^3,4

HDAC2 has been identified as a key regulator of follistatin transcription, and its inhibition leads to the suppression of myostatin activity, enhancing myogenic differentiation and muscle growth.^5,6 Consalvi and colleagues highlighted the importance of HDAC-mediated control of follistatin transcription in maintaining proper muscle size and structure, especially after contraction-induced stress.⁵ HDAC inhibitors have been shown to enhance muscle regeneration by promoting the formation of larger myofibers and activating the transcription of follistatin, a myostatin antagonist.^3,5 Direct myostatin inhibition or follistatin delivery yielded similar benefits in mdx mice, a model for DMD, highlighting the importance of HDAC2 in controlling muscle size and structure.⁵ Moreover, miR-1-mediated suppression of HDAC4 promotes follistatin production and subsequent myocyte fusion, demonstrating another pathway through which HDAC inhibition can enhance muscle regeneration.⁵

Additionally, HDAC inhibitors help prevent fibro-adipogenic degeneration by reducing fibrosis and fatty infiltration in muscle tissues, which are hallmark features of DMD progression.⁷ HDAC inhibitors modulate the expression of cytokines and inflammatory mediators, reducing chronic inflammation in muscle tissues.^4,8 This creates a more favorable environment for muscle repair and decreases muscle damage. HDAC inhibitors also downregulate pro-fibrotic gene expression and inhibit fibroblast proliferation, helping to prevent the accumulation of fibrotic tissue in muscles.^6,7

Preclinical studies have provided compelling evidence for the use of HDAC inhibitors in treating DMD. In a study by Consalvi et al, givinostat was shown to increase the cross-sectional area of myofibers and decrease inflammatory infiltrates and fibrotic scars in mdx mice.^7,8 These findings underscore the potential of HDAC inhibitors to ameliorate muscle pathology by promoting muscle fiber growth and reducing fibrosis. This study also found that MS275, a selective Class I HDAC inhibitor, exhibited comparable effects to givinostat, a pan-HDAC inhibitor, opening the possibility for selective HDAC inhibition.⁸ Another study by Spreafico and colleagues demonstrated the overexpression of HDAC8 in human DMD primary myoblasts and zebrafish DMD models.⁴ Inhibition of HDAC8 using the selective inhibitor PCI-34051 rescued the DMD phenotype, similar to the effects observed with givinostat.⁴ The study reported increased myoblast differentiation, reduced lesion extent, restored skeletal muscle histomorphology, and decreased inflammation in zebrafish embryos treated with HDAC8 inhibitor.⁴ The findings suggest that selective inhibition of HDACs may represent another promising strategy for addressing the underlying pathophysiology of DMD.^4,8

The transition from preclinical success to clinical application has been marked by promising trials of givinostat in DMD patients. A pivotal Phase 2 trial demonstrated the safety and tolerability of givinostat in boys with DMD.⁹ The Phase 2 trial was an open-label, two-part, study with primary endpoints focusing on histological changes before and after ≥12 months of treatment, alongside secondary endpoints assessing safety, tolerability, and functional outcomes.⁹ The study involved 20 boys from ages 7 up to 11 years old, all of whom were stable on corticosteroids for at least 6 months.⁹ Although the study was not designed to test efficacy and no functional improvement was observed, the study confirmed that givinostat counteracts DMD progression after 1 year of treatment, as evidenced by increased myofiber cross-sectional area, muscle fiber area fraction, and reduced fibrosis, necrosis, and fat deposition in muscle biopsies from the brachial biceps.⁹ This study provided the foundation for subsequent clinical investigations and paved the way for a comprehensive Phase 3 trial.

The Epigenetic Rescue of Dystrophin Dysfunction (EPIDYS) study was a multicenter, randomized, double-blind, placebo-controlled phase 3 trial with a total of 179 participants enrolled.¹⁰ The primary endpoint was the change between baseline and 72 weeks in a four-stair climb assessment.10 Secondary endpoints included changes from baseline in the North Star Ambulatory Assessment (NSAA) total score, NSAA cumulative loss-of-function, time-to-rise, 6-minute walk test, knee extension, elbow flexion, and velocity of lower limb flexion and function (VLFF).¹⁰ In the givinostat group, mean four-stair climb change from baseline was 1.25s vs 3.03s with placebo.10 For the secondary endpoints, the givinostat group had a lower decrease in NSAA score (-2.66 vs -4.58), loss-of-function (3.42 vs 5.56), time-to-rise (9.33 vs 12.61), 6-min walk test (-38.4 vs -48.4s).¹⁰ The trial demonstrated that givinostat improved muscle histology and stabilized functional outcomes, providing strong support for its therapeutic indication in DMD.¹⁰

HDAC: histone deacetylase, Ac: acetyl groups (Click to enlarge)

In conclusion, HDAC inhibitors, particularly givinostat, represent a promising class of therapeutic agents for DMD. By targeting specific molecular pathways involved in muscle regeneration and fibro-adipogenic degeneration, these compounds have demonstrated potential in both preclinical and clinical settings. The ability of HDAC inhibitors to modulate gene expression, promote muscle growth, and reduce fibrosis highlights their potential to address key pathological features of DMD. Ongoing research and future clinical trials will further elucidate the optimal use of HDAC inhibitors and their long-term effects.

In mdx mice, HDAC inhibitors allow for acetylation of the histones leading to an open chromatin structure allowing for gene expression. HDAC inhibitors allow for gene transcription that promotes myoblast differentiation and increased myofiber cross sectional area.⁶ In animal studies, HDAC inhibitors were found to decrease inflammation and fibrosis.⁶

For correspondence:
Kevin Chang, PharmD
kevinchang1@gmail.com

REFERENCES
1. Shieh PB. Emerging Strategies in the Treatment of Duchenne Muscular Dystrophy. Neurotherapeutics. 2018;15(4):840-848. doi:10.1007/s13311-018-00687-z
2. Lamb YN. Givinostat: First Approval. Drugs. Published online July 5, 2024. doi:10.1007/s40265-024-02052-1
3. Colussi C, Mozzetta C, Gurtner A, et al. HDAC2 blockade by nitric oxide and histone deacetylase inhibitors reveals a common target in Duchenne muscular dystrophy treatment. Proc Natl Acad Sci U S A. 2008;105(49):19183-19187. doi:10.1073/pnas.0805514105
4. Spreafico M, Cafora M, Bragato C, et al. Targeting HDAC8 to ameliorate skeletal muscle differentiation in Duchenne muscular dystrophy. Pharmacol Res. 2021;170:105750. doi:10.1016/j.phrs.2021.105750
5. Consalvi S, Saccone V, Giordani L, Minetti G, Mozzetta C, Puri PL. Histone deacetylase inhibitors in the treatment of muscular dystrophies: epigenetic drugs for genetic diseases. Mol Med Camb Mass. 2011;17(5-6):457-465. doi:10.2119/molmed.2011.00049
6. Sandonà M, Cavioli G, Renzini A, et al. Histone Deacetylases: Molecular Mechanisms and Therapeutic Implications for Muscular Dystrophies. Int J Mol Sci. 2023;24(5). doi:10.3390/ijms24054306
7. Minetti GC, Colussi C, Adami R, et al. Functional and morphological recovery of dystrophic muscles in mice treated with deacetylase inhibitors. Nat Med. 2006;12(10):1147-1150. doi:10.1038/nm1479
8. Consalvi S, Mozzetta C, Bettica P, et al. Preclinical Studies in the mdx Mouse Model of Duchenne Muscular Dystrophy with the Histone Deacetylase Inhibitor Givinostat. Mol Med. 2013;19(1):79-87. doi:10.2119/molmed.2013.00011
9. Bettica P, Petrini S, D’Oria V, et al. Histological effects of givinostat in boys with Duchenne muscular dystrophy. Neuromuscul Disord. 2016;26(10):643-649. doi:10.1016/j.nmd.2016.07.002
10. Mercuri E, Vilchez JJ, Boespflug-Tanguy O, et al. Safety and efficacy of givinostat in boys with Duchenne muscular dystrophy (EPIDYS): a multicentre, randomised, double-blind, placebo-controlled, phase 3 trial. Lancet Neurol. 2024;23(4):393-403. doi:10.1016/S1474-4422(24)00036-X