Dual role of hexadecylphosphocholine (miltefosine) in thermosensitive liposomes: Active ingredient and mediator of drug release

Hyperthermia-triggered drug delivery from temperature-sensitive liposomes using MRI-guided high intensity focused ultrasound

In the continuous search for cancer therapies with a higher therapeutic window, localized temperature-induced drug delivery may offer a minimal invasive treatment option. Here, a chemotherapeutic drug is encapsulated into a temperature-sensitive liposome (TSL) that is released at elevated temperatures, for example, when passing through a locally heated tumor. Consequently, high drug levels in the tumor tissue can be achieved, while reducing drug exposure to healthy tissue. Although the concept of temperature-triggered drug delivery was suggested more than thirty years ago, several chemical and technological challenges had to be addressed to advance this approach towards clinical translation. In particular, non-invasive focal heating of tissue in a controlled fashion remained a challenge. For the latter, high intensity focused ultrasound (HIFU) allows non-invasive heating to establish hyperthermia (40-45 °C) of tumor tissue over time. Magnetic resonance imaging (MRI) plays a pivotal role in this procedure thanks to its superb spatial resolution for soft tissue as well as the possibility to acquire 3D temperature information. Consequently, MRI systems emerged with an HIFU ultrasound transducer embedded in the patient bed (MR-HIFU), where the MRI is utilized for treatment planning, and to provide spatial and temperature feedback to the HIFU. For tumor treatment, the lesion is heated to 42 °C using HIFU. At this temperature, the drug-loaded TSLs release their payload in a quantitative fashion. The concept of temperature-triggered drug delivery has been extended to MR image-guided drug delivery by the co-encapsulation of a paramagnetic MRI contrast agent in the lumen of TSLs. This review will give an overview of recent developments in temperature-induced drug delivery using HIFU under MRI guidance.

Nanoscale Drug Delivery and Hyperthermia: The Materials Design and Preclinical and Clinical Testing of Low Temperature-Sensitive Liposomes Used in Combination with Mild Hyperthermia in the Treatment of Local Cancer

The overall objective of liposomal drug delivery is to selectively target drug delivery to diseased tissue, while minimizing drug delivery to critical normal tissues. The purpose of this review is to provide an overview of temperature-sensitive liposomes in general and the Low Temperature-Sensitive Liposome (LTSL) in particular. We give a brief description of the material design of LTSL and highlight the likely mechanism behind temperature-triggered drug release. A complete review of the progress and results of the latest preclinical and clinical studies that demonstrate enhanced drug delivery with the combined treatment of hyperthermia and liposomes is provided as well as a clinical perspective on cancers that would benefit from hyperthermia as an adjuvant treatment for temperature-triggered chemotherapeutics. This review discusses the ideas, goals, and processes behind temperature-sensitive liposome development in the laboratory to the current use in preclinical and clinical settings.

Triggering liposomal drug release with a lysosomotropic agent

Drug release from liposomes in the endosome-lysosomal organelles into cytoplasm is critical to cytotoxicity and anticancer effects. Chloroquine is a lysosomotropic agent that has been reported to enhance in vitro cytotoxicity of basic anticancer drugs. To investigate the mechanism of chloroquine triggering basic anticancer drugs release from liposomes and the potential to treat solid tumors in clinic, daunorubicin was loaded into folate-targeted liposomes by ammonium sulfate remote loading method. In vitro triggered release profiles showed that chloroquine can instantly expel about 11% daunorubicin out of liposomes. In vitro cytotoxicity of folate-targeted liposomal daunorubicin on L1210JF(FR+) was enhanced by chloroquine, which was further confirmed by confocal micrographs. Intraliposomal pH was increased by adding chloroquine into 8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt (HPTS) liposomes with ammonium sulfate gradient, but was not higher than 5.5. Ion exchange and pH rising are the most plausible mechanisms of chloroquine triggering daunorubicin release from liposomes. In vivo anticancer effects on a murine solid tumor model with L1210JF indicated that chloroquine induced daunorubicin release from liposomes as well. Overall, these results support the potential application of chloroquine to trigger the release of liposomal drugs and ultimately to improve the therapeutic efficacy.

"Smart" liposomal nanocontainers in biology and medicine

The perspectives of using liposomes for delivery of drugs to desired parts of the human body have been intensively investigated for more than 30 years. During this time many inventions have been suggested and different kinds of liposomal devices developed, and a number of them have reached the stages of preclinical or clinical trials. The latest techniques can be used to develop biocompatible nano-sized liposomal containers having some abilities of artificial intellect, such as the presence of sensory and responsive units. However, only a few have been clinically approved. Further improvements in this area depend on our knowledge of the interactions of drugs with the lipid bilayer of liposomes. Further studies on liposomal transport through the human body, their targeting of cells requiring therapeutic treatment, and finally, the development of techniques for controlled drug delivery to desired acceptors on cell surfaces or in cytoplasm are still required.