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

Abstract

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.

Keywords: Low Temperature-Sensitive Liposomes; cancer; drug delivery; hyperthermia.

Fig. (1)

Schematic of temperature-triggered drug releasing liposome (with kind permission from Celsion Corporation).

Fig. (2)

Flow diagram depicting the multifactorial therapeutic benefits of hyperthermia. Hyperthermia enhances drug delivery and efficacy by increasing vascular perfusion and permeability and by enabling drug release from thermosensitive liposomes. Hyperthermia itself can be cytotoxic, but enhanced cytotoxicity is the result of the increased drug delivery and the synergistic interaction hyperthermia has with many anticancer drugs.

Fig. (3)

Schematic showing how thermal ablation alone would miss the microscopic deposits of tumor cells around the tumor periphery, but how, with ThermoDox^® in the blood stream, drug release is triggered in the 39–50°C thermal zone (with kind permission from Celsion Corporation).

Fig. (4)

Schematic showing (left to right) the solid all trans lipid bilayer that forms the faceted structure of the 100 nm Low Temperature-Sensitive Liposome [94]; grain structure is also evident in solid lipid monolayers on larger gas particles [93], prompting the term “Nanosoccerball”.

Fig. (5)

Dithionite permeability of two membranes of liposomes composed of either (a) DPPC(96%):DSPE-PEG²⁰⁰⁰(4%) or (b) DPPC(86%):MSPC(10%):DSPC-PEG²⁰⁰⁰(4%) at 30, 37, 40, 42, and 43°C. The absorbance of NBD slowly decreases in DPPC(96%):DSPE-PEG ²⁰⁰⁰(4%) liposomes (a) but quickly decreases in DPPC(86%):MSPC(10%):DSPE-PEG²⁰⁰⁰(4%) (b) due to increased bilayer permeability for liposomes composed of DPPC(86%):MSPC(10%):DSPE-PEG²⁰⁰⁰(4%). Reproduced with permission from Mills [95].

Fig. (6)

Doxorubicin release vs. molar fraction of lysolipid in the bilayer (from 0 mol% to 15 mol%) at 41.3°C [74]. (Bilayers also contained the usual 3.8 mol% DSPE-PEG²⁰⁰⁰).

Fig. (7)

Comparison between the Differential Scanning Calorimetry (DSC) thermal profile and the doxorubicin (DOX) release rate for LTSL-doxorubicin [74].

Fig. (8)

Dithionite ion permeability rates for DPPC, POPC and lysolipid-containing (MPPC and MSPC) membranes. All liposomes also contained 4 mol% DSPE-PEG²⁰⁰⁰. At the phase transition temperature, permeability rates are ~10-fold higher for the lysolipid-containing LTSL when compared to the pure DPPC bilayer [74].

Fig. (9)

Schematics of postulated defect structures that result in membrane permeability for: A) DPPC Bilayer in Phase Transition Region; B) DPPC:MSPC Bilayer in Phase Transition Region--No Pore; C) DPPC:MSPC Bilayer in Phase Transition Region with Enhanced Permeability Through MSPC Pore; D) DPPC:MSPC:DSPE-PEG²⁰⁰⁰ Bilayer in Phase Transition Region with Enhanced Permeability Through MSPC Pore Stabilized by DSPE-PEG²⁰⁰⁰.

Fig. (10)

Dithionite ion, ~ 0.5 nm in size, compared to doxorubicin, ~ 2.5 nm across; chemical structures and dimensions drawn to scale.

Fig. (11)

Temperature effects on tumor vasculature. Mild hyperthermia increases blood flow (ideal for drug transport) whereas hyperthermia temperatures above 43°C result in hemorrhage, which may reduce or cease blood flow, hampering drug delivery.

Fig. (12)

A comparison of tumor doxorubicin concentrations 1 hour after LTSL-doxorubicin treatment with or without hyperthermia (HT). Hyperthermia enhances drug delivery and tumor accumulation. Adapted with permission from Informa Healthcare: [International Journal of Hyperthermia] [75], copyright (2010).

Fig. (13)

A tumor growth delay study comparing the efficacy of LTSL-doxorubicin (Dox-LTSL) with or without hyperthermia (HT) in five different cancer cell lines, 4T07 (murine mammary carcinoma), HCT116 (human colon carcinoma), FaDu (human squamous cell carcinoma), PC-3 (human prostate adenocarcinoma), and SKOV-3 (human ovarian carcinoma). Kaplan-Meier plots for each tumor type are provided where the percent survival is defined as the percentage of animals with a tumor volume less than five times the original tumor volume. Adapted with permission from Informa Healthcare: [International Journal of Hyperthermia] [75], copyright (2010).

Fig. (14)

Comparative paradigms for liposomal drug delivery. Shown are (a) Non-temperature sensitive liposomes (blue/yellow circles) preferentially extravasate from pores in tumor vessel walls; this is the standard EPR effect in normothermic systems, (b) hyperthermia increases tumor vessel pore size and thus increases non-temperature-sensitive liposome extravasation, and (c) hyperthermia can trigger drug (yellow) release from LTSL in the tumor vessel at mild hyperthermic temperatures. (c) depicts intravascular drug release and deeper penetration in to tumor tissue, representing a new paradigm of thermosensitive drug release.

Fig. (15)

Human plasma clearance of 50 mg/m² ThermoDox^® (Mean +/−SE). Reprinted with permission [216].