Development of a Chemoablative, Thermoresponsive Hydrogel as a Drug Delivery Platform for Lung Cancer Applications
Systemic chemotherapy has long been the mainstay of cancer chemotherapy treatment for all cancer types. The lack of specificity, and subsequent destructive off-target side-effects, has prompted alternative delivery methods to be considered, in particular for solid tumour cancers. Direct injection of chemotherapeutics into solid tumours can increase local concentrations and reduce off-site toxicity, but such an approach is challenged by rapid clearance of the drug, resulting in inaccurate and unpredictable dosing. Attention has, therefore, turned to the development of drug delivery platforms, which can facilitate improved retention and sustained release of chemotherapeutics after direct intratumoural injection. Thermoresponsive hydrogels are amenable to intratumoural administration as they are liquids at room temperature and undergo gelation at a characteristic temperature. Drug-loading of thermoresponsive hydrogels creates an in situ-forming drug delivery platform. Lung cancer is the leading cause of cancer-related death worldwide, with current systemic treatment strategies failing to address this large, unmet clinical need. Locoregional administration of thermoresponsive hydrogels to lung cancer can be achieved using interventional oncology techniques, which employs image guidance to perform minimally invasive procedures. The overall aim of this thesis was to develop and characterise a chemoablative, thermoresponsive hydrogel as a drug delivery platform for intratumoural administration in a lung cancer application.
Formulation optimisation of the blank thermoresponsive hydrogel was undertaken to adjust the sol-gel transition temperature to within clinically relevant parameters. A dual drug-loaded thermoresponsive hydrogel was successfully formulated with “gold-standard” chemotherapeutics, cisplatin and paclitaxel. In vitro disintegration and release profiles of the lead blank and drug-loaded formulations were determined over 28 and 10 days respectively, with the drug-loaded thermoresponsive hydrogel demonstrating sustained release of both chemotherapeutics.
An in vitro cytotoxicity assessment of the lead blank and drug-loaded thermoresponsive hydrogels was undertaken in a non-small cell lung cancer cell line, A549, which demonstrated a dose-dependent cytotoxicity of both formulations at all doses evaluated. A non-cancerous fibroblast cell line, Balb/c 3T3 clone A31, was used to assess in vitro cytotoxicity of the blank thermoresponsive hydrogel in 3 non-target tissue, which revealed that it was biocompatible at lower doses. A 3D in vitro model of lung cancer was established to create a biomimetic model for IT injection of ChemoGel. The cytotoxic capacity of the lead blank and drug-loaded thermoresponsive hydrogels was subsequently confirmed in the 3D model over 14 days.
In order to facilitate clinical intra-procedural imaging of administration, a radiopaque variation of the lead thermoresponsive hydrogel was formulated with the addition of an iodinated contrast agent, Visipaque®. Rheological behaviour, radiopacity and injectability of the lead radiopaque formulation was assessed. Distribution of the injected thermoresponsive hydrogel in an ex vivo tissue model was assessed. In vitro cytotoxicity of the radiopaque formulations was confirmed using the 3D in vitro lung cancer model previously developed in this thesis. Sterilisation of the lead formulations was evaluated using pharmacopoeial methods, and ethylene oxide gas sterilisation was identified as the most suitable method. Thermoresponsivity, disintegration and release profiles were evaluated post-sterilisation, and it was confirmed that ethylene oxide sterilisation did not negatively impact the behaviour of the lead thermoresponsive hydrogels.
Lead radiopaque thermoresponsive hydrogels were assessed in a murine lung cancer xenograft model, using A549-luciferase cells. Retention of intratumourally administered blank and drug-loaded thermoresponsive hydrogels at the site of injection was confirmed using in vivo and ex vivo fluorescent imaging over 14 days. Efficacy of treatment was monitored using physical tumour volume measurements and bioluminescent imaging. Tumour volume increase was determined to be statistically significantly reduced following blank and drug-loaded thermoresponsive hydrogel treatment, compared to saline treatment for at least 14 days. 100% survival of treated mice was observed at Day 14. No statistically significant difference observed between selected welfare indicators following intratumoural administration of the blank or drug-loaded thermoresponsive hydrogel compared to saline.
Presented in this thesis is the development and optimisation of a chemoablative thermoresponsive hydrogel, which can be dual drug-loaded with chemotherapeutics intended for the treatment of lung cancer.