A combination of two chemical modulators of gene activity can stably reactivate the FMR1 gene, the gene that is “switched off” in those with fragile X syndrome, according to a study in human cells and mouse models of the disease.
These results add to prior evidence that supports FMR1 reactivation treatments as a possible way to treat fragile X.
The study, “FMR1 Reactivating Treatments in Fragile X iPSC-Derived Neural Progenitors In Vitro and In Vivo,” was published in the journal Cell Reports.
With the development of advanced technologies for genome editing, a few studies have shown that it is possible to rescue the genetic defects underlying fragile X by editing the DNA sequence of the FMR1 gene or by reducing the levels of gene inactivation marks known as DNA methylation.
DNA methylation is a chemical modification whereby the addition of small chemical groups (methyl) is able to turn “off” a gene, or prevent it from being expressed.
In patients with fragile X, portions of the FMR1 gene necessary for its activation are excessively methylated (hypermethylated), which renders the gene inactive and prevents it from giving instructions for production of the FMRP protein.
This can be reversed by using what are known as demethylation agents to block the process of DNA methylation.
Researchers developed a way to screen a group of gene-modulating agents and identify those with the best capacity to reactivate the FMR1 gene.
They focused on a compound called 3-deazaneplanocin A (DZNep), to show that combining this agent with the demethylating agent 5-aza-2-deoxycytidine (5-azadC or decitabine) significantly enhanced the reactivation of FMR1 and restarted the production of FMRP in induced pluripotent stem cells (iPSCs) derived from fragile X patients.
iPSCs are derived from either skin or blood cells and are reprogrammed back into a stem cell-like state, which allows for the development of an unlimited source of any type of human cell needed for therapeutic purposes.
To assess the efficacy of this treatment in a living organism, researchers developed two “humanized” mouse models, which were implanted with neurons derived from either fragile X-corrected iPSCs or fragile X iPSCs.
When these mice were treated with the demethylating agent 5-azadC together with DZNep, FMR1 activity was restored at the transplanted tissues, including the brain. Combination treatment resulted in higher levels of FMR1 mRNA (the template molecule that is then transformed into a protein) than treatment with 5-azadC alone.
After treatment withdrawal, no reversal of FMR1 activation was observed, suggesting that the effect was stable for a prolonged period.
These results “suggest a different paradigm for FMR1-reactivating treatment: the utilization of a combination of agents with different mechanisms to target FMR1 inactivation,” researchers said.
With an eye on a potential application for patients, researchers argue that combining therapies would required lower doses of the demethylating agent, minimizing unwanted side effects.
The study also sheds light on the process of gene reactivation and the consequences of this kind of treatment for other genes, aspects that should be considered when considering this strategy as a potential therapy.
In addition, the two humanized animal models “could serve as a platform for the analysis of FMR1-reactivating treatments” in preclinical validation studies before advancing to tests in patients.