Researchers have developed a multi-functional, small molecule that can tag mutant mitochondrial gene sequences for removal.
The mitochondria are best known as the powerhouse of the cell, but they are also considered special because they possess their own DNA, which replicates independently to that of nuclear DNA. Because of this, the mitochondrial DNA is prone to its own share of errors, mismatches, and mutations that can cause debilitating metabolic disorders and other fatal diseases. To date, there has yet to be an effective treatment for mitochondrial diseases, but scientists at Kyoto University’s Institute for Integrated Cell-Material Science in Japan have recently come up with a novel approach to eliminate mutant DNA sequences inside cellular mitochondria using a special chemical compound.
In some mitochondrial diseases, research has shown that mutated DNA and normal DNA can co-exist. According to Takuya Hidaka, the first author of the study, “This state is called heteroplasmy.” He further explained, “Mitochondrial function can be maintained by normal mitochondrial DNA when the heteroplasmy level is low. But it is impaired when mutated DNA exceeds a critical threshold. To cure mitochondrial diseases, we need to be able to remove mutant mitochondrial DNA from cells.”
Unfortunately, current treatment methods for mitochondrial diseases are problematic, as said by bioengineer Ganesh Namasivayam Pandian, who led the study. This is because some treatment methods, like ones that involve injecting genetic material into cells, could lead to unwanted alterations. Other therapeutic agents like antioxidant drugs have also been ineffective because they do not directly address the root of the mutation. In light of these challenges, Pandian, together with chemical biologist Hiroshi Sugiyama, Takuya Hidaka, and colleagues were determined to come up with a solution.
In their recent study, the team proposed a chemical-based approach to treat mitochondrial diseases. They designed a compound made of a mitochondria-penetrating peptide that is bound to a polymer called pyrrole-imidazole polyamide. The polyamide can be modified to target and bind to a specific DNA sequence in the mitochondria. They then attached the compound to an existing anti-cancer drug known as chlorambucil, which serves to target the DNA for elimination.
To determine the efficacy of their novel compound, the researchers performed analyses using lab cultures of human cells. Their findings revealed that the technique successfully reduced the amount of mutant mitochondrial DNA. By adapting the chemical make-up of pyrrole-imidazole polyamide, the therapeutic compounds can be also made highly versatile; it can be programmed to bind to different DNA sequences and so target a wide range of mitochondrial genetic diseases.
While further investigations using disease models are still needed to determine whether the technique is effective inside living organisms and can be used in clinical settings, the study’s findings have brought hope for a new treatment option. Pandian believes that their “proof-of-concept study can be extended to mitochondrial mutations that cause diseases like Leber’s hereditary optic neuropathy, an inherited form of vision loss that currently has no proven treatment.”
Source: Hidaka et al. (2021). Targeted elimination of mutated mitochondrial DNA by a multi-functional conjugate capable of sequence-specific adenine alkylation. Cell Chemical Biology.