Dual Blockade of Misfolded Alpha-Sarcoglycan Degradation by Bortezomib and Givinostat Combination

Abstract

Limb-girdle muscular dystrophy type R3 (LGMD R3) is a rare genetic disorder characterized by a progressive proximal muscle weakness and caused by mutations in the SGCA gene encoding alpha-sarcoglycan (α-SG). Here, we report the results of a mechanistic screening ascertaining the molecular mechanisms involved in the degradation of the most prevalent misfolded R77C-α-SG protein. We performed a combinatorial study to identify drugs potentializing the effect of a low dose of the proteasome inhibitor bortezomib on the R77C-α-SG degradation inhibition. Analysis of the screening associated to artificial intelligence-based predictive ADMET characterization of the hits led to identification of the HDAC inhibitor givinostat as potential therapeutical candidate. Functional characterization revealed that givinostat effect was related to autophagic pathway inhibition, unveiling new theories concerning degradation pathways of misfolded SG proteins. Beyond the identification of a new therapeutic option for LGMD R3 patients, our results shed light on the potential repurposing of givinostat for the treatment of other genetic diseases sharing similar protein degradation defects such as LGMD R5 and cystic fibrosis.

Histone Deacetylases: Molecular Mechanisms and Therapeutic Implications for Muscular Dystrophies

“…To strengthen these data, the authors also investigated the effect of another pan-HDACi, Belinostat, which induced a similar rescue of α-SG protein. Moreover, a synergistic effect was found by combining givinostat and the FDA-approved proteasome inhibitor Bortezomib, which blocks the proteasome activity and prevents the degradation of misfolded proteins: inhibition of both autophagic and proteasome pathways completely restored α-SG expression in the plasma membrane in mutant fibroblasts [212]. This evidence suggests a new therapeutic avenue for the treatment of LGMD-2D/R3, but also for other genetic diseases sharing similar protein degradation defects, as other sarcoglycanopathies.…”

“…Exploiting drug screening associated with artificial intelligence-based predictive AD-MET characterization of hits, givinostat was identified as a potential therapeutic drug for the sarcoglycanopathy LGMD-2D/R3, by inhibiting the autophagic pathway, likely by blocking HDAC6 activity, thereby leading to a partial α-SG protein rescue [212]. To strengthen these data, the authors also investigated the effect of another pan-HDACi, Belinostat, which induced a similar rescue of α-SG protein.…”

Identification of bazedoxifene for the treatment of LGMD R2 by high throughput screening

“…Although no treatment is currently available for LGMD R2, research directed towards missense protein refolding, or targeting cellular quality control to inhibit premature degradation of proteins in the ER with small molecules, opens up a therapeutic avenue for LGMD R2. Evidence in support of this strategy for rescuing missense mutations that cause LGMD has recently been described by our group for LGMD R3, as revealed by the positive impact of thiostrepton(Hoch et al , 2019) and the combination of givinostat and bortezomib on α-sarcoglycan missense mutant protein reallocation to the plasma membrane (Hoch et al , 2022), by disrupting proteasomal and autophagic degradation systems. Among the large panel of missense DYSF mutations that cause LGMD R2, we focused on the well characterized DYSF L1341P mutant for our proof of concept.…”