Study suggests JEB treatment could be tailored to specific mutation
Targeted therapies provide clues in preclinical experiments
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A cell-based study found that a group of experimental drugs designed to restore missing protein production in junctional epidermolysis bullosa (JEB) showed different responses to specific mutations in the COL17A1 gene, a finding researchers said could be used to work toward tailored treatment approaches.
The researchers also identified a compound called N-oxalylglycine (NOG) that, when combined with certain existing drugs, boosted protein levels in some of the mutations tested.
“Our results support mutation-dependent [drug] selection for further preclinical scientific investigations and highlight personalized therapeutic approaches as a key strategy for [JEB],” the researchers wrote.
The study, “Differential Responses of COL17A1 Nonsense Mutations to Readthrough Drugs and NOG as a Novel Enhancer in Junctional Epidermolysis Bullosa,” was published in Molecular Therapy Nucleic Acids.
Mutations in the COL17A1 gene cause generalized intermediate JEB, a milder form of the disease. These mutations disrupt the production of part of type XVII collagen (C17), which gives connective tissues strength and structure, leading to skin fragility and chronic wounds.
Nonsense mutations
About 20% of COL17A1 mutations are so-called nonsense mutations, which create an early stop signal in the gene and lead to a shortened, nonfunctional C17 protein. Nonsense mutations can also trigger nonsense-mediated decay (NMD), a cellular process that breaks down the faulty genetic instructions before protein production.
One approach to treat nonsense mutations is translational readthrough-inducing drug (TRID) therapy. These drugs are designed to help the cell’s protein-making machinery read through the premature stop signal and generate a more complete, functional protein.
Researchers at the University of Freiburg in Germany evaluated a panel of several TRIDs across six different COL17A1 nonsense variants using patient-derived skin cells. They aimed to identify TRIDs that could be developed into mutation-dependent treatments.
C17 protein was undetectable in patient cells with the nonsense mutations p.Arg169, p.Trp464, p.Arg688, and p.Arg1226. Cells with p.Arg145 and p.Gly803 mutations retained about 24% and 2.4% of normal protein levels, respectively. Protein levels appeared to correlate with JEB severity.
Initial screening found variable responses to TRIDs across mutations. The TRID gentamicin produced a robust response in p.Trp464, while PTC124 induced readthrough activity in p.Arg145 cells. Most other compounds showed either a weak or no response to other mutations. These findings led the researchers to focus on gentamicin and PTC124.
To improve treatment efficacy, they combined different gentamicin concentrations with molecules that block NMD and/or antioxidants, called TRID-cocktails.
In p.Trp464 cells, adding the NMD inhibitor NOG boosted C17 protein levels by about 70% compared with a cocktail containing gentamicin, paromomycin, and CC-90009, another NMD blocker. This combination restored about 15% of C17 protein relative to normal skin cells, with no effect on cell viability or the cells’ ability to close a wound in a laboratory model.
In cells that only responded to gentamicin, like p.Gly803-stop, NOG increased C17 levels by approximately 60% in combination with gentamicin and CC-90009. No NOG-based enhancement was observed in p.Arg145 cells, nor did NOG boost PTC124-mediated readthrough in these cells.
A separate cocktail combining low-dose gentamicin with NMD inhibitors and antioxidants increased C17 levels by 38% in p.Gly803 cells, but did not affect p.Arg145 cells. Increasing gentamicin concentrations did not enhance C17 levels in cells with either mutation.
When analyzed independently of normal-cell comparisons, the gentamicin-based cocktail enhanced C17 restoration by 1.7 times compared with untreated p.Gly803 cells. However, absolute C17 levels in these cells remained much lower than levels in normal skin cells.
PTC124 alone increased C17 protein levels by about twofold in p.Arg145 cells compared with untreated control cells, without affecting cell viability or wound closure capacity. Restored C17 amount increased from 25.6% to 52% following PTC124 treatment in these cells, relative to normal skin cells. Combining PTC124 with the additional cocktail compounds did not further increase C17 levels beyond PTC124 alone.
“Our results revealed substantial variability in readthrough efficacy across different mutations and highlighted the molecular complexity underlying this phenomenon,” adding that these findings “support a personalized approach to readthrough therapy for JEB-C17,” the researchers wrote.
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