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Best Group Publishes ATP-Responsive Liposomes in JACS

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The research group of Michael Best in Tennessee Chemistry, led by graduate student Jinchao Lou, recently published an article describing the development of ATP-responsive liposomes in the Journal of the American Chemical Society. The nanocarriers reported in this work show strong prospects for enhancing clinical drug delivery applications.

Liposomes are highly effective nanocarriers for therapeutics due to their ability to encapsulate drugs with wide-ranging properties and enhance their circulation and delivery to cells. However, their potential could be improved by achieving control over the release of cargo to maximize drug potency and diseased-cell selectivity. While liposome-triggered release represents a vibrant field of research due to this significance, the toolbox for controlling liposome release remains limited and prior strategies face many challenges that obstruct clinical application.

The Best Group has explored a new paradigm for triggered release in which cargo escape is triggered only when liposomes encounter specific small molecule metabolites that are overly abundant in disease states. This is achieved using synthetic stimuli-responsive lipid switches designed to undergo programmed conformational changes upon the binding of small molecule targets, events that compromise membrane packing and thereby drive release.

In this work, Lou and co-workers developed liposomes that selectively respond to ATP over eleven other structurally similar phosphorylated small molecules. ATP is a critical target for metabolite-mediated drug delivery since this molecule is a universal energy source that is known to be heavily upregulated in-and-around cancer cells. This opens up the potential for selective drug delivery and release driven by overly abundant ATP associated with diseased cells.

This project also entailed a collaboration with the group of Dr. Francisco Barrera in the Tennessee Biochemistry & Cellular and Molecular Biology (BCMB) Department. Through cellular delivery and fluorescence imaging experiments, graduate student Jennifer Schuster showed that modulation of cellular ATP levels using drugs led to direct control of cellular delivery of ATP-responsive liposomes. These results demonstrate the key advancement that liposome delivery can be modulated by the cellular abundance of ATP.

A provisional patent has been filed for this ATP-responsive liposome technology. Additionally, the Best Group is currently working on advancing this platform for clinical delivery applications and developing liposomes that respond to other disease-associated small molecule metabolites.  

Best Group Published in Chemistry and Physics of Lipids

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The Best Group’s article titled “Metabolic labeling of glycerophospholipids via clickable analogs derivatized at the lipid headgroup” was published in Chemistry and Physics of Lipids.

Metabolic labeling, in which substrate analogs containing diminutive tags can infiltrate biosynthetic pathways and generate labeled products in cells, has led to dramatic advancements in the means by which complex biomolecules can be detected and biological processes can be elucidated.

Within this realm, metabolic labeling of lipid products, particularly in a manner that is headgroup-specific, brings about a number of technical challenges including the complexity of lipid metabolic pathways as well as the simplicity of biosynthetic precursors to headgroup functionality. As such, only a handful of strategies for metabolic labeling of lipids have thus far been reported. However, these approaches provide enticing examples of how strategic modifications to substrate structures, particularly by introducing clickable moieties, can enable the hijacking of lipid biosynthesis.

Furthermore, early work in this field has led to an explosion in diverse applications by which these techniques have been exploited to answer key biological questions or detect and track various lipid-containing biological entities. In this article, the group reviews these efforts and emphasize recent advancements in the development and application of lipid metabolic labeling strategies.

Best Group’s Recent Work

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Recent work in the Best Group has culminated in the development of stimuli-responsive liposomes for drug delivery designed to release therapeutic cargo when they come into contact with diseased cells, specifically based on overexpressed enzymes and reactive oxygen species. “These smart liposomes show strong prospects for advancing drug delivery by targeting therapeutics directly to the site of the disease,” Jinchao Lou, graduate student in the Best Group, said.

Liposomes are effective nanocarriers for drug delivery due to their ability to encapsulate and deliver a wide variety of therapeutic cargo to cells. Nevertheless, liposome delivery would be improved by enhancing the ability to control the release of contents within diseased cells. Toward this end, stimuli-responsive liposomes, in which the drug carrier decomposes when it comes in contact with conditions associated with disease, are of great interest for enhancing drug potency while minimizing side effects.

While various stimuli have been explored for triggering liposome release, both enzymes and reactive oxygen species (ROS) provide excellent targets due to their key roles in biology and overabundance in diseased cells. In two separate papers, the Best Group presented a general approach to enzyme‐responsive liposomes exploiting targets that are commonly aberrant in disease, including esterases, phosphatases, and β‐galactosidases (Chem. Eur. J. 2020, 26, 8597-8607), as well as an ROS-responsive liposomal delivery platform (Bioconjugate Chem. 2020, 31, 2220-2230).

In both of the cases, responsive lipids designed to target each stimulus were designed and synthesized bearing a responsive headgroup attached via a self‐immolating linker to a non‐bilayer lipid scaffold. In this way, stimulus addition triggers chemical lipid decomposition in a manner that disrupts membrane integrity and releases contents. Release properties were fully characterized by fluorescence-based dye leakage assays, dynamic light scattering and electron microscopy, among other techniques.

Due to their recent works in this field, the Best group was also invited to write a review describing advances in the design of stimuli-responsive liposome strategies for drug delivery with an eye towards emerging trends in the field (Chem. Phys. Lipids. In Press. DOI 10.1016/j.chemphyslip.2020.104966). Smart liposomes show strong prospects for advancing drug delivery by targeting drugs directly to the site of the disease.