Formulation and evaluation of ATP-containing liposomes including lactosylated ASGPr ligand

Adenosine and lipids: A forced marriage or a love match?

Adenosine is a fascinating compound, crucial in many biochemical processes: this ubiquitous nucleoside serves as an essential building block of RNA, is also a component of ATP and regulates numerous pathophysiological mechanisms via binding to four extracellular receptors. Due to its hydrophilic nature, it belongs to a different world than lipids, and has no affinity for them. Since the 1970's, however, new discoveries have emerged and prompted the scientific community to associate adenosine with the lipid family, especially via liposomal preparations and bioconjugation. This seems to be an arranged marriage, but could it turn into a true love match? This review considered all types of unions established between adenosine and lipids. Even though exciting supramolecular structures were observed with adenosine-lipid conjugates, as well as with liposomal preparations which resulted in promising pre-clinical results, the translation of these technologies to the clinic is still limited.

A nanoparticle-incorporated STING activator enhances antitumor immunity in PD-L1-insensitive models of triple-negative breast cancer

Triple-negative breast cancer (TNBC) has few therapeutic options, and alternative approaches are urgently needed. Stimulator of IFN genes (STING) is becoming an exciting target for therapeutic adjuvants. However, STING resides inside the cell, and the intracellular delivery of CDNs, such as cGAMP, is required for the optimal activation of STING. We show that liposomal nanoparticle-delivered cGAMP (cGAMP-NP) activates STING more effectively than soluble cGAMP. These particles induce innate and adaptive host immune responses to preexisting tumors in both orthotopic and genetically engineered models of basal-like TNBC. cGAMP-NPs also reduce melanoma tumor load, with limited responsivity to anti-PD-L1. Within the tumor microenvironment, cGAMP-NPs direct both mouse and human macrophages (M), reprograming from protumorigenic M2-like phenotype toward M1-like phenotype; enhance MHC and costimulatory molecule expression; reduce M2 biomarkers; increase IFN-γ-producing T cells; augment tumor apoptosis; and increase CD4+ and CD8+ T cell infiltration. Activated T cells are required for tumor suppression, as their depletion reduces antitumor activity. Importantly, cGAMP-NPs prevent the formation of secondary tumors, and a single dose is sufficient to inhibit TNBC. These data suggest that a minimal system comprised of cGAMP-NP alone is sufficient to modulate the tumor microenvironment to effectively control PD-L1-insensitive TNBC.

Enhanced cell survival of pH-sensitive bioenergetic nucleotide nanoparticles in energy/oxygen-depleted cells and their intranasal delivery for reduced brain infarction

Nucleotides (NTs) (e.g., adenosine triphosphate) are very important molecules in the body. They generate bioenergy through phosphate group release, are involved in various biological processes, and are used to treat various diseases that involve energy depletion. However, their highly anionic characteristics might limit delivery of exogenous NTs into the cell, which is required to realize their functions as bioenergy sources. In this study, ionic complexation between Ca(2+) and NT phosphates was used to form Ca(2+)/NT nanocomplexes (NCs), and branched polyethyleneimine (bPEI1.8kDa) was coated on the surface of Ca(2+)/NT NCs via a simple electrostatic coating. The resultant Ca(2+)/NT/bPEI1.8kDa NCs were approximately 10-25nm in size and had positive zeta-potentials, and their NT loading efficiency and content were approximately 60-75% and 10-20 wt%, respectively. Faster NT release from Ca(2+)/NT/bPEI1.8kDa NCs was induced by lower pH and by NTs with fewer phosphates. Reductions in cell viability in response to low temperature, serum deprivation, or hypoxia were recovered by NT delivery in Ca(2+)/NT/bPEI1.8kDa NCs. In a middle cerebral artery occlusion (MCAO)-induced post-ischemic rat model, the BBB (blood brain barrier)-detoured intranasal administration of Ca(2+)/ATP/bPEI1.8kDa NCs induced a better reduction in infarct volume and neurological deficits than did free ATP. In conclusion, intracellular NT delivery using Ca(2+)/NT/bPEI1.8kDa NCs might potentially enhance cell survival and reduce infarction in energy-/oxygen-depleted environments.

STATEMENT OF SIGNIFICANCE

This study describes bioenergetic nucleotide delivery systems and their preparation, physicochemical characterization, and biological characterization both in vitro and in vivo. Nucleotides, such as adenosine triphosphate (ATP) and guanosine triphosphate (GTP), are very important signaling and energy molecules in the body. However, research on these nucleotides using nanosized carriers has been very limited. Liposomal ATP delivery has been reported in heart and renal ischemia studies. Notably, although this delivery system has potential in energy-depleted environments (e.g., low temperature, serum deprivation, and hypoxia) and in brain ischemia, studies are lacking regarding these systems. Thus, we designed polycation-shielded Ca(2+)/nucleotide nanocomplexes using simple mixing, which produced 10- to 25-nm-sized particles. The nanocomplexes released nucleotides in response to acidic pH, and they enhanced cell survival rates under conditions of low temperature, serum deprivation, or hypoxia. Importantly, the nanocomplexes reduced cerebral infarct volumes in a post-ischemic rat model. Thus, our study demonstrates that a novel nucleotide nanocomplex could have potential for preventing or treating diseases that involve energy depletion, such as cardiac, cerebral, and retinal ischemia, and liver failure.

Nucleotides as nontoxic endogenous endosomolytic agents in drug delivery

Nontoxic endogenous nucleotides such as adenosine triphosphate and guanosine triphosphate have secondary phosphate groups, causing proton-buffering capacity and/or hemolytic activity in endolysosomal pH ranges. Nucleotides co-delivered in single polymeric pDNA nanocarrier induce highly enhanced transfection efficiency with negligible cytotoxicity due to their endosomolytic functions.

Maintenance of ischemic β cell viability through delivery of lipids and ATP by targeted liposomes

Islet transplantation is a promising treatment for type 1 diabetes, but despite the successes, existing challenges prevent widespread application. Ischemia, occurring during pancreas preservation and isolation, as well as after islet transplantation, decreases islet viability and function. We hypothesized that the liposomal delivery of adenosine triphosphate (ATP) could prevent the loss of cell viability during an ischemic insult. In this work we use a model β cell line, INS-1 to probe the liposome/cell interactions and examined the ability of liposomes functionalized with the fibronectin-mimetic peptide PR_b to facilitate the delivery of ATP to ischemic β cells. We demonstrate that PR_b increases the binding and internalization of liposomes to the β cells. Unexpectedly, when comparing the ability of PR_b liposomes with and without ATP to protect INS-1 cells from ischemia we found that both formulations increased cell survival. By probing the functional activity of ischemic cells treated with PR_b functionalized liposomes with and without ATP we find that both lipids and ATP play a role in maintaining cell metabolic activity after an ischemic insult and preventing cell necrosis. This approach may be beneficial for preventing ischemia related damage to islet cells, especially in the organ preservation stage.

Altered HepG2 cell models using etomoxir versus tert-butylhydroperoxide

Energetic failure which occurs in both ischemia/reperfusion and acute drug-induced hepatotoxicity is frequently associated with oxidative stress. This study displays the setting of a new cell culture model for hepatic energetic failure, i.e., HepG2 models modified by etomoxir [ETO] addition [0.1 mM to 1 mM] and compares the cell impact versus tert-butylhydroperoxide [TBOOH; 0.2 mM], an oxidative stress inducer. As it was observed with Minimum Essential Medium (MEM) without any interfering agent, decreasing temperature drastically lowered adenosine triphosphate (ATP) levels, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) viability test, and protein content, compared to 37 °C (p=0.02, p<0.001 and p<0.001, respectively), but to a larger extent in the presence of ETO or TBOOH. The alteration was generally highly dependent on the ETO concentration, time, and temperature. At 37 °C 24 h after (T24h), regarding ETO concentration, R² correlation ratio was 0.65 (p<0.001), 0.70 (p<0.001), and 0.89 (p<0.001) for ATP levels, protein content, and viability, respectively. The lowest ETO concentration producing a significant effect was 0.25 mM. Concerning time dependency (i.e., T24h versus after 5 h (T5h)), at 37 °C with ETO, ATP level continued to significantly decrease between T5h and T24h. In a similar way, at 37 °C, the MTT viability test decrease was accelerated only between T5h and T24h for ETO concentrations higher than 0.5 mM (p=0.016 and p=0.0001 for 0.75 and 1 mM, respectively). On the contrary, with TBOOH, comparing T24h versus T5h, cellular indicators were improved but generally remained lower than MEM without any interfering agent at T24h, suggesting that TBOOH action was time limited probably in relation with its oxidation in cell medium. This study confirms the interest of altered ETO cell model to screen agents (or formulation) prone to prevent or treat energetic depletion in relation with oxidative stress.

Freeze-drying of ATP entrapped in cationic, low lipid liposomes

Concerning the instability of ATP liposomes formulated to easily diffuse through the liver (size approximately 100 nm), this work targets the key parameters that influence the freeze-drying of a preparation that combines cholesterol, DOTAP and phosphatidylcholine (either natural soybean or egg (SPC or EPC) or hydrogenated (HSPC)). After freeze-drying blank liposomes, size increased significantly when initial lipid concentration was lowered from 20 to 5mM (p=0.0018). With low lipid concentration preparation (5mM), SPC limited size increase (SI) more efficiently compared to EPC or HSPC. With SPC and EPC, sucrose showed better size results compared to trehalose (Lyoprotectant/Lipid ratio (w/w) avoiding any SI: approximately 5 and approximately 10 (for SPC), approximately 10 and approximately 15 (for EPC), for sucrose and trehalose, respectively), but the opposite was evidenced with HSPC liposomes where a Trehalose/Lipid ratio of 25 barely prevented SI. In addition, slow versus quick cooling rate led to limiting SI for HSPC liposomes (p=0.0035). With sucrose or trehalose at both Lyoprotectant/Lipid ratios ensuring size stabilisation (10:1 and 15:1, respectively), ATP leakage ranged between 38.8+/-7.9% and 58.2+/-1.4%. In conclusion, this study emphasizes that using strict size maintenance as the primary objective does not result in drug complete retention inside the liposome core.