Exploring the Potentials and Limitations of Solid Tumor Treatment by Thermosensitive Liposomes and Hyperthermia

Traditional chemotherapy for solid tumors is often associated with undesired side effects in treated patients. Furthermore, infused drugs are rapidly cleared from the circulation which largely hinders accumulation in the target tissue. An emerging therapeutic strategy consists in the encapsulation of chemotherapeutic drugs inside liposomes in order to prevent side effects and rapid clearance. Throughout the last decades of research, there has been an increasing interest in liposomes that are able to locally release their contents at the site of solid tumors. This has led to the initiation of clinical trials for the evaluation of thermosensitive liposomes (TSLs), which are drug-loaded nanoparticles that rapidly release the drug within mildly heated tissue (40-43 °C). However, these liposomes are relatively unstable in circulation during the tumor heating period, which may lead to sub-optimal drug delivery to the tumor. This thesis first describes the improved design of TSLs for enhanced cancer therapy, as well as a comprehensive characterization of such formulations in a pre-clinical setting. Subsequently, a comparative study was conducted to assess the influence of varying delivery strategies, which focused either on intravascular drug release of TSLs or their prior accumulation in the tumor tissue, in generating a therapeutic response. Furthermore, the relationship between variation in tumor biology, drug delivery kinetics, and therapeutic response was investigated. Lastly, a feasibility study on magnetic nanoparticle entrapment into liposomes was performed for potential applications in image-guided drug delivery. The present findings contribute to the improvement of existing therapies using TSLs, provide an improved understanding of the mechanism of their delivery, and of cancer types that are more likely to respond to TSL-based therapy

Investigation of particle accumulation, chemosensitivity and thermosensitivity for effective solid tumor therapy using thermosensitive liposomes and hyperthermia

Doxorubicin (Dox) loaded thermosensitive liposomes (TSLs) have shown promising results for hyperthermia-induced local drug delivery to solid tumors. Typically, the tumor is heated to hyperthermic temperatures (41-42 °C), which induced intravascular drug release from TSLs within the tumor tissue leading to high local drug concentrations (1-step delivery protocol). Next to providing a trigger for drug release, hyperthermia (HT) has been shown to be cytotoxic to tumor tissue, to enhance chemosensitivity and to increase particle extravasation from the vasculature into the tumor interstitial space. The latter can be exploited for a 2-step delivery protocol, where HT is applied prior to i.v. TSL injection to enhance tumor uptake, and after 4 hours waiting time for a second time to induce drug release. In this study, we compare the 1- and 2-step delivery protocols and investigate which factors are of importance for a therapeutic response. In murine B16 melanoma and BFS-1 sarcoma cell lines, HT induced an enhanced Dox uptake in 2D and 3D models, resulting in enhanced chemosensitivity. In vivo, therapeutic efficacy studies were performed for both tumor models, showing a therapeutic response for only the 1-step delivery protocol. SPECT/CT imaging allowed quantification of the liposomal accumulation in both tumor models at physiological temperatures and after a HT treatment. A simple two compartment model was used to derive respective rates for liposomal uptake, washout and retention, showing that the B16 model has a twofold higher liposomal uptake compared to the BFS-1 tumor. HT increases uptake and retention of liposomes in both tumors models by the same factor of 1.66 maintaining the absolute differences between the two models. Histology showed that HT induced apoptosis, blood vessel integrity and interstitial structures are important factors for TSL accumulation in the investigated tumor types. However, modeling data indicated that the intraliposomal Dox fraction did not reach therapeutic relevant concentrations in the tumor tissue in a 2-step delivery protocol due to the leaking of the drug from its liposomal carrier providing an explanation for the observed lack of efficacy