Shweta Chakrabarti, MSc
Jr. scientist – Omics
Multifunctional silica-coated mixed polymeric micelles for integrin-targeted therapy of pediatric patient-derived Glioblastoma.
Published on: July 15, 2022
Original author: Chauhan et al. 2021 (doi: 10.1016/j.msec.2021.112261)
Glioblastoma (GBM) is the malignant brain tumor of the primary central nervous system (CNS) arising from the glial cells having an incidence ranging from 5 to 8 persons per 100,000 individuals. The median survival rate is around 12 to 18 months with the current therapies. Only around 10% of the patients survive for more than 5 years. Various limitations prevent the existing therapies from removing cancer cells completely. They are the blood-brain barrier (BBB) and the blood-brain tumor barrier found in the vasculature of GBM affecting the bioavailability of chemotherapeutic agents. The reasons behind chemotherapy being not so effective are unfavorable pharmacokinetics, toxicity, and side effects of the drug. During cancer development, disruption of BBB takes place and hence, the Blood-brain tumor barrier (BBTB), which is more permeable to molecules, comes into the picture. Therefore, the idea of focusing on overcoming these barriers for chemotherapeutic treatment could be of great efficiency. Core-shell polymeric micelles (PMs) are nanocarriers of drugs having high permeability and chemical flexibility, good biocompatibility, high encapsulation ability, and it’s easy to prepare. Being constructed of polymeric amphiphiles has provided them with the better physicochemical ability and better loading capacity. The most prevalent pathway which is used to transfer drug nanocarriers passing BBB and BBTB to the CNS is Receptor-mediated transcytosis (RMT). Different integrins such as integrin αvβ3 which has a role in cancer progression, GBM invasion, and growth are overexpressed in the BBB. There are short cyclic Arg-Gly-Asp-Phe-Val (cRGDfV) peptides that bind with these integrins and help in the regulation of tumor progression, angiogenesis, and metastasis. The affinity among the BBB, cRGDfV and the integrins has enabled its use as a ligand for integrin-targeted drug and gene delivery. However, have their limitations in physical stability and controlling the release of the encapsulated cargo. The drug which has been selected for this research was pitavastatin (PTV) which has a good encapsulation ability with PMs. The work aims at investigating the nanoencapsulation of PTV within cRGDfV-decorated mixed Pluronic® _F127 (F127) and Tetronic® _1307 (T1307) PMs that were further coated with silica gel for more physical stability and better control of kinetics release for brain targeting. Finally, the endothelial cells (hCMEC/D3), brain vascular pericytes (hBVPs), and astrocytes (hAs) cell lines from pediatric patient-derived GBM were used to assess the cell uptake, anti-proliferative, and apoptotic properties of PMs in vitro. Methodology The methodology of this research includes various analyses to evaluate the cRGDfV conjugated PMs as the drug delivery system. The first step in the methodology is synthesizing carboxylated Pluronic® _F127 (F127) and Tetronic® _1307 (T1307) and conjugating with cRGDfV and fluorescein isothiocyanate (FITC), respectively. Next, the PMs decorated with cRGDfV were coated with silica shells (SiO2/cRGDFV PMs). These PMs we analyzed to characterize their nanostructure and morphology using field emission gun-transmission electron microscopy. Optimization of response surface methodology (RSM) was performed for the optimization of the copolymer, PTV, and water volume concentration using encapsulation ratio (ER%) and drug loading efficiency (DL%) as responses. In the next step, the colloidal stability of PTV-loaded SiO2/cRGDFV mixed PMs was studied. Further, the drug PTV release in vitro was assessed using the dialysis membrane method. The cell uptake and the cell viability when exposed to SiO2 PMs and SiO2/cRGDfV PMs were assessed by performing an MTT assay using the BBB endothelial cell lines hCMEC/D3, hBVPs, and hAs cell lines. The antiproliferative and apoptotic activity and the cytotoxicity of the PTV, SiO2 PMs, SiO2/cRGDfV PMs, PTV-loaded SiO2 PMs, PTV-loaded SiO2/cRGDfV PMs were studied in the pediatric patient-derived HSJD-GBM-001 glioma cell line by carrying out the MTT assay. Further, mRNA was extracted and quantified to analyze the expression of genes associated with glioma cell apoptosis. Finally, all the assays were statistically analyzed using Prism version 5.0 (GraphPad Software, Inc.). Results & discussion During the synthesis of F127, conjugation of cRGDfV to the activation of F127 was completed with an efficiency of 84 ± 2%. Similarly, conjugation of T1307 with FITC results in the animation of T1307 resulting in T1307-NH2. It was observed that animated nanoparticles showed better cell uptake due to the electrostatic interaction between the negatively charged cell membrane and positively charged amino moieties. The combination of F127 and T1307 allowed the encapsulation of a hydrophobic cargo and better solubility in water due to the presence of the long T1307 PEO chains. The coating with silica shell provides physical stability and prevents the PMs from disassembling during the high level of dilution which may take place below critical micelle concentration (CMC). Encapsulated PTV is released in a controlled way before precipitating. RSM optimization enables better solubility of PTV in the mixed PMs and reduces the leakage of PTV. Controlled release kinetics of PTV due to silica shell was found to be beneficial due to the reduced release of the drug in the systemic circulation that helps in targeting the drug to the tumor. However, silica coating fails in controlling and reducing the drug release during the first 48 hours of the assay. The assays performed on the BBB cells showed no major toxicity by PMs and were highly compatible. BBB cells showed 80% cell viability with both of the mixed PMs. During the transportation of nanoparticulate matter across the BBB in the brain, nanoparticle uptake takes place in the initial stage where cRGDfV binds to the αvβ3 and αvβ5 integrins. Antiproliferative and apoptotic assays in the glioma cells showed high antiproliferative activity. It was strongly suggested that encapsulated PTV PMs surface-modified with RGD peptide showed increased permeability across the BBB and better bioavailability of the drug in the tumor of the brain. The apoptotic activity of the SiO2/cRGDfV mixed PMs was confirmed by observing the size of nuclei that were decreased and DNA fragmentation had taken place which is associated with apoptosis when compared to PTV-loaded SiO2 PMs. The higher affinity for SiO2/cRGDfV mixed PMs was observed more than peptide-free PTV-loaded SiO2 PMs due to the recognition of this ligand by the αvβ3 and αvβ5 integrins that are overexpressed in the cancer cells. This further results in internalization inside the glioma cells and high apoptosis. This study clearly showed the role of cRGDfV in targeting glioblastoma cells using PMs. PTV-loaded SiO2/cRGDfV PMs were found to be the most pro-apoptotic. The change in cell morphology and shape also confirmed apoptosis. To further understand the role of PTV in decreasing glioma cell proliferation, NF-kβ, IL-6, BIRC1, and BIRC5 were analyzed which are associated with the molecular changes that take place during glioma cell apoptosis. The reduction in the expression of the genes NF-kβ, IL-6, BIRC1, and BIRC5 was observed in the HSJD-GBM-001 cells when treated with PTV-loaded SiO2/cRGDfV mixed PMs. Impact of the research The research study by Chauhan et al., showed how nanocarrier for the drug PTV could be used to target the brain tumor in pediatric patient-derived glioblastoma. The significance of this research is as follows: 1. Using mixed PMs coated with silica shell and surface modified using a peptide could be used as an effective nanocarrier of the drug PTV for targeting brain tumors. 2. The peptide bound with the mixed PMs, which is a substrate of the integrins overexpressed in the glioma cells, results in increased nanoparticle uptake and anticancer activity. 3. PTV-loaded SiO2/cRGDfV PMs enable upregulation of the genes NF-kβ, IL-6, BIRC1, and BIRC5 which are involved in the apoptosis of the glioma cells.