Novel Thio-lipids Developed Capable of Reaching Eyes and Lungs in Animals

Scientists who work with lipid nanoparticles (LNPs) say they have developed a new type of material capable of reaching the lungs and the eyes. They call their study “Thiophene-based lipids for mRNA delivery to pulmonary and retinal tissues,” which appears in PNAS, an important step toward genetic therapy for hereditary conditions like cystic fibrosis and inherited vision loss.

Unlike other types of LNPs that tend to accumulate in the liver, the ones in this study, based on the compound thiophene, are able to navigate their way to the tissues of the lungs and retina, where they deliver their therapeutic payload, according to the researchers, who refer to these new lipids as Thio-lipids.

The collaboration, between Oregon State University (OSU) College of Pharmacy and Oregon Health & Science University, demonstrated, by using animal models, the possibility of using Thio-lipids in LNPs to deliver messenger RNA, the technology underpinning COVID-19 vaccines, to combat genetic blindness and pulmonary disease.

“The Thio-lipids can be readily synthesized via the Gewald reaction, allowing for modular lipid design with functional constituents at various positions of the thiophene ring. Through the rational design of ionizable lipid structure, we prepared 47 Thio-lipids and identified some structural criteria required in Thio-lipids for efficient mRNA (messenger RNA) encapsulation and delivery in vitro and in vivo. Notably, none of the tested lipids have a pH-response profile-like traditional ionizable lipids, potentially due to the electron delocalization in the thiophene core.

“Placement of the tails and localization of the ionizable headgroup in the thiophene core can endow the nanoparticles with the capability to reach various tissues. Using high-throughput formulation and barcoding techniques, we optimized the formulations to select two top lipids—20b and 29d—and investigated their biodistribution in mice. Lipid 20b enabled LNPs to transfect the liver and spleen, and 29d LNP transfected the lung and spleen.

“Unexpectedly, LNP with lipid 20b was especially potent in mRNA delivery to the retina with no acute toxicity, leading to the successful delivery to the photoreceptors and retinal pigment epithelium in non-human primates.”

Encapsulate genetic medicines

“These nanoparticles filled with fatty lipids can encapsulate genetic medicines like mRNA and CRISPR-Cas9 gene editors, which can be used to treat and even cure rare genetic diseases,” said Yulia Eygeris, PhD, a senior research associate at OSU. “Chemical structures of the lipids determine how potent are the lipid nanoparticles and which organ they can reach from the bloodstream.”

With the coronavirus vaccines, the mRNA carried by the lipid nanoparticles instructs cells to make a harmless piece of the virus’ spike protein, which triggers an immune response from the body.

As a therapy for vision impairment resulting from inherited retinal degeneration, the mRNA would instruct cells in the retina, which are impaired because of a genetic mutation, to manufacture the proteins needed for sight. Inherited retinal degeneration, commonly abbreviated to IRD, encompasses a group of disorders of varying severity and prevalence that affect one out of every few thousand people worldwide.

An example of a genetic pulmonary condition is cystic fibrosis, a progressive disorder that results in persistent lung infection and affects 30,000 people in the U.S., with about 1,000 new cases identified every year. One faulty gene—the cystic fibrosis transmembrane conductance regulator, or CFTR—causes the disease, which is characterized by lung dehydration and mucus buildup that blocks the airway.

The thiophene-based LNP study, which involved mice and non-human primates, stems from a $3.2 million grant from the National Eye Institute. The grant’s purpose is addressing limitations associated with the current primary means of delivery for gene editing: adeno-associated virus, or AAV.

“AAV has limited packaging capacity compared to lipid nanoparticles and it can prompt an immune system response,” said Gaurav Sahay, PhD, a professor of pharmaceutical sciences, at OSU. “It also doesn’t do fantastically well in continuing to express the enzymes the editing tool uses as molecular scissors to make cuts in the DNA to be edited.”

Sahay calls the Thio-lipid findings “highly encouraging” but says more studies are needed, including research on the lipids’ long-term impact on retinal health.

“But we think our results serve as a proof of concept and we will continue to explore Thio-lipids in potential treatments of pulmonary and retinal genetic diseases,” he added.