Polar Lipid Fraction E from Sulfolobus acidocaldarius and Dipalmitoylphosphatidylcholine Can Form Stable yet Thermo-Sensitive Tetraether/Diester Hybrid Archaeosomes with Controlled Release Capability

Abstract

Archaeosomes have drawn increasing attention in recent years as novel nano-carriers for therapeutics. The main obstacle of using archaeosomes for therapeutics delivery has been the lack of an efficient method to trigger the release of entrapped content from the otherwise extremely stable structure. Our present study tackles this long-standing problem. We made hybrid archaeosomes composed of tetraether lipids, called the polar lipid fraction E (PLFE) isolated from the thermoacidophilic archaeon Sulfolobus acidocaldarius, and the synthetic diester lipid dipalmitoylphosphatidylcholine (DPPC). Differential polarized phase-modulation and steady-state fluorometry, confocal fluorescence microscopy, zeta potential (ZP) measurements, and biochemical assays were employed to characterize the physical properties and drug behaviors in PLFE/DPPC hybrid archaeosomes in the presence and absence of live cells. We found that PLFE lipids have an ordering effect on fluid DPPC liposomal membranes, which can slow down the release of entrapped drugs, while PLFE provides high negative charges on the outer surface of liposomes, which can increase vesicle stability against coalescence among liposomes or with cells. Furthermore, we found that the zeta potential in hybrid archaeosomes with 30 mol% PLFE and 70 mol% DPPC (designated as PLFE/DPPC(3:7) archaeosomes) undergoes an abrupt increase from −48 mV at 37 °C to −16 mV at 44 °C (termed the ZP transition), which we hypothesize results from DPPC domain melting and PLFE lipid ‘flip-flop’. The anticancer drug doxorubicin (DXO) can be readily incorporated into PLFE/DPPC(3:7) archaeosomes. The rate constant of DXO release from PLFE/DPPC(3:7) archaeosomes into Tris buffer exhibited a sharp increase (~2.5 times), when the temperature was raised from 37 to 42 °C, which is believed to result from the liposomal structural changes associated with the ZP transition. This thermo-induced sharp increase in drug release was not affected by serum proteins as a similar temperature dependence of drug release kinetics was observed in human blood serum. A 15-min pre-incubation of PLFE/DPPC(3:7) archaeosomal DXO with MCF-7 breast cancer cells at 42 °C caused a significant increase in the amount of DXO entering into the nuclei and a considerable increase in the cell’s cytotoxicity under the 37 °C growth temperature. Taken together, our data suggests that PLFE/DPPC(3:7) archaeosomes are stable yet potentially useful thermo-sensitive liposomes wherein the temperature range (from 37 to 42–44 °C) clinically used for mild hyperthermia treatment of tumors can be used to trigger drug release for medical interventions.

Bipolar Imidazolium-Based Lipid Analogues for Artificial Archaeosomes

“…Interestingly, pure BImN32 remains in a fluid-like state even at kilobar pressures. Of note, also the polar lipid fraction E (PLFE) isolated from the thermoacidophilic archaeon Sulfoloabus acidocaldarius has been shown to have an ordering effect on fluid DPPC, which can slow down the release of entrapped drugs. − In addition, compressibilities and volume fluctuations in PLFE liposomes are much less temperature-sensitive than those in DPPC bilayer liposomes, echoing that PLFE liposomes are rigid and tightly packed. − Incorporation of BImN32 into heterogeneous anionic phospholipid membranes led to marked changes in lateral domain structure and topology already at concentrations beyond 5 mol % BImN32. Changes in the lateral organization accompanied by lipid sorting of the membrane components resulted in significant changes in the bending rigidity and curvature.…”

“…Archaea encompass different membrane lipid structures compared to their bacterial and eukaryotic phospholipid counterparts (an example is given in Figure ). − Archaeal membranes are essentially composed of saturated isoprenoic lipid chains of varying lengths and ether linkage to glycerol carbons, containing diether or tetraether lipids. − Because ether bonds are less prone to chemical reactions compared to the ester bond in phospholipids, archaeal membranes can be considered chemically more robust. Of special interest are the unusual bipolar lipids, also denoted bolaamphiphiles, which are found in thermoacidophilic, methanogenic, and some psychrophilic species. − Here, two polar groups of the membrane surfaces are connected by isoprenoid ethers through the membrane, while maintaining a liquid-like state, which is prerequisite for the proper function of the living cell.…”

“…In extreme thermal environments with temperatures near the boiling point of water, a lipid cell membrane based on isoprenoid ethers is one conceivable strategy to ensure functionality. Generally, archaeal membranes are more stable and have lower permeability to ions, small molecules and water, and reveal a higher packing density. − In deep sea smoker areas, archaea have also to resist to high hydrostatic pressures up to the 1000 bar range . Several archaea have their best growth conditions at high salinity, low pH, high temperature, and/or high pressure. , …”

Vesicular and Planar Membranes of Archaea Lipids: Unusual Physical Properties and Biomedical Applications

“…Physical properties of PLFE tetraether archaeosomes have been studied extensively (reviewed in [ 3 , 35 ]) and have been utilized to make archaeosomal therapeutics [ 16 , 26 , 36 , 37 , 38 , 39 ]. In terms of therapeutics delivery, archaeosomes are favored over conventional liposomes mainly because archaeosomes, particularly those containing tetraether lipids, are of much higher stability in many different aspects.…”

Metal‐Organic Frameworks Deliver a Conjugate of Functional Oligonucleotides and Photosensitizer to Induce Apoptosis for Enhancing Chemotherapy

“…Currently, many strategies are used for cancer treatment, such as chemotherapy, [3] radiation therapy, [4] photodynamic therapy (PDT) [5] and photothermal therapy (PTT) [6] . Among these strategies, chemotherapy is the most widely used treatment method which mainly exert action to prevent the cancer cells proliferation, invasion and metastasis, and finally kill them main by inducing apoptosis [7] . Small molecule anti‐cancer drugs are the most commonly used chemotherapeutics, which exhibit promising anti‐cancer effects [8] .…”