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

Umme Ayesa,Parkson Lee-Gau Chong

doi:10.3390/ijms21218388

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.

Highlights

Conventional chemotherapeutic drugs such as doxorubicin (DXO) are highly effective
While monolayer liposomes made of polar lipid fraction E (PLFE) alone or bilayer liposomes made of DPPC alone have been studied extensively [41,47], PLFE/DPPC hybrid archaeosomes have not yet been characterized to a great extent
We have evaluated how mild hyperthermia might affect the interactions of PLFE/DPPC(3:7) archaeosomal DXO with live cells

Summary

Introduction

Conventional chemotherapeutic drugs such as doxorubicin (DXO) are highly effective. They have short half-lives and cause severe side effects like cardio and gastrointestinal toxicity [1,2]. Various types of liposomal doxorubicin, such as Doxil, Caelyx, and Myocet, have been demonstrated to reduce systemic toxicity, prolong circulation time, and increase accumulation at tumor sites [8,9,10]. They have major drawbacks including low stability and slow drug release at physiological conditions [11,12]. Liposomes that accumulate at tumor site often fail to penetrate deep into tumor tissue, rendering the drug therapeutic efficacy low [13,14]

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Results

Conclusion