Docetaxel Nanostructured lipid carrier with enhanced blood brain barrier permeability for targeted glioblastoma therapy

Abstract

The major clinical challenge in the treatment of glioblastoma is the inability of chemotherapeutic agents to pass the blood-brain barrier (BBB). Docetaxel a hydrophobic anticancer drug used alone and in combination with other drugs to treat tumours is a P-glycoprotein substrate and suffers from the drawback of non-specific cytotoxicity and limited accumulation in the brain. To address these clinical challenges and enhance therapeutic potential for glioblastoma treatment and penetration of BBB, the project investigated nanostructured lipid carrier (NLC) for encapsulation of docetaxel and explored two polyunsaturated fatty acids (PUFAs) gamma-linolenic acid (GLA) and Alpha-linolenic acid (ALA), and a novel selective aptamer (SA43) as targeting ligands for specific glioblastoma targeting.
A novel, simple and sensitive HPLC method was developed and validated for quantification of docetaxel from BBB cell culture medium. The method exhibited high precision and accuracy with sample recovery ranging from 90.03- 100.02% and was used to determine the permeated drug in the 3D in-vitro BBB model. Validated HPLC methods with high precision and accuracy were also developed for quantification of docetaxel from the NLCs and release media. Docetaxel-NLC were formulated using biodegradable materials combining Dynasan 114 as solid lipid with three liquid lipids and surfactants employing hot homogenisation technique on probe sonicator. A 32 factorial design was used for optimisation of critical factors to get docetaxel-NLCs with particles size (136.8 nm), relatively low polydispersity index (PDI 0.231), high entrapment efficiency (99.1%) and high total drug content (80.6%) with zeta potential of -32.4 mV contributing to the stability of the docetaxel-NLC over a six months period. Docetaxel-NLCs was successfully lyophilised with an only a small increase in particle size (13nm) using 10% trehalose as a cryo-protectant. All three ligands (GLA, ALA and SA43) were successfully conjugated to Docetaxel-NLCs and covalent bonding was confirmed with a reduction of surface free amines, FTIR and Raman spectroscopy. DSC and XRD confirmed the presence of docetaxel in an amorphous state within the NLCs.
In-vitro cell lines studies revealed the high efficacy of PUFAs surface modified docetaxel-NLCs (GLA-docetaxel-NLC and ALA-docetaxel-NLC) where IC50 showed ~ 6.5 fold increase in docetaxel activity at 24h towards glioblastoma (U87MG) cells and ~ 10 fold higher cytotoxicity in patient-derived short-term culture obtained from Brain Tumour North West organisation (BTNW911) glioblastoma cells at 24 and 48 h. Aptamer surface modified docetaxel-NLC (SA43-docetaxel-NLC) showed high selectivity towards glioblastoma cell lines with high potency as compared to non-cancerous brain cells (SVG P12) with a preferable lower toxicity. Moreover, all developed formulations showed significantly higher cellular uptake by U87MG and BTNW911 cells as compared to SVG P12 cells. Active transport through endocytosis was determined as the internalisation mechanism for the all surface modified docetaxel-NLCs. Furthermore, bare and surface modified docetaxel-NLCs exhibited cell cycle arrest at G2/M phase with the highest percentage of distribution in G2/M phase obtained with SA43-docetaxel-NLCs. Docetaxel-NLC also showed high toxicity and penetration in 3D U87MG spheroids in comparison to native docetaxel through surface modification of docetaxel-NLCs did not enhance the uptake by 3D U87MG spheroids.
Docetaxel encapsulation within the NLCs exhibited enhanced permeability when studied in all human 3D in-vitro BBB model. Notably, functionalisation of docetaxel-NLC with GLA and ALA further enhanced the permeation across the BBB while SA43-docetaxel-NLC displayed similar permeability as docetaxel-NLC. Distinctive increase in the apparent permeability through the BBB and uptake by U87MG cells was observed for all the surface modified docetaxel-NLCs when studied in diseased in-vitro BBB model in the presence of a tumour monolayered cell line (U87MG).
The aforementioned research has demonstrated that docetaxel-NLCs is a viable potential product for use in the treatment of glioblastoma, exhibiting selective uptake and BBB permeability when conjugated with appropriate targeting ligands. This research could contribute widely to treating and targeting brain tumour.