Targeted Delivery of Temozolomide by iRGD-Functionalized Exosomes Derived from HEK-293 Cells

Technical Summary: Targeted Delivery of Temozolomide by iRGD-Functionalized Exosomes Derived from HEK-293 Cells

Problem Statement
Glioblastoma (GBM) remains one of the most aggressive and lethal malignancies, with a five-year survival rate below 10% and a median survival of less than two years. While the standard of care involves surgical resection followed by radiotherapy and chemotherapy with the alkylating agent Temozolomide (TMZ), efficacy is limited by severe systemic side effects (e.g., anemia, peripheral neuropathy) and the drug's inability to selectively target tumor cells. There is an urgent need for therapeutic strategies that enhance drug specificity to GBM cells while minimizing off-target toxicity. Exosomes, natural nanoscale extracellular vesicles, offer a potential solution as biocompatible drug carriers that can be engineered to target specific tissues.

Methodology
The study employed a multi-step approach to engineer, characterize, and evaluate a targeted exosome-based delivery system:

1. Exosome Engineering: Human embryonic kidney 293 (HEK-293) cells were transfected with a plasmid encoding a fusion protein: EGFP–LAMP-2B–iRGD. This construct links the tumor-penetrating peptide iRGD (CRGDKGPD) to the N-terminal domain of the lysosomal-associated membrane protein 2B (LAMP-2B), which anchors the peptide to the exosome surface. EGFP serves as a fluorescent reporter.
2. Isolation and Characterization: Exosomes were harvested from the conditioned media of transfected cells 48 hours post-transfection using an ExoCib™ isolation kit. The engineered exosomes were characterized for:
   • Fluorescence: To confirm the presence of the EGFP-tagged fusion protein.
   • Physicochemical Properties: Size and zeta potential were measured via Dynamic Light Scattering (DLS); morphology was assessed using Field Emission Scanning Electron Microscopy (FE-SEM) and Transmission Electron Microscopy (TEM).
   • Biomarkers: Western blotting was performed to verify the presence of canonical exosomal markers (CD9, CD63) and the EGFP–LAMP-2B–iRGD fusion protein.
3. Drug Loading: Temozolomide (TMZ) was loaded into the engineered exosomes using a sonication method. Entrapment efficiency was determined by separating free drug from exosome-bound drug via centrifugal filtration and quantifying the filtrate using High-Performance Liquid Chromatography (HPLC).
4. In Vitro Evaluation: The cytotoxicity of the formulations was tested against U87 human glioblastoma cells using an MTT assay. Four treatment groups were compared:
   • Free TMZ.
   • Empty engineered exosomes (iRGD-exosomes without drug).
   • TMZ-loaded non-engineered exosomes (untargeted).
   • TMZ-loaded engineered exosomes (iRGD-targeted).
   • IC50 values were calculated to determine the concentration required to reduce cell viability by 50%.

Key Results

• Production and Characterization: Transfection of HEK-293 cells successfully resulted in the expression of the EGFP–LAMP-2B–iRGD fusion protein, confirmed by green fluorescence. Isolated exosomes displayed an average diameter of approximately 68.8 nm (DLS) and 80–120 nm (microscopy), with a zeta potential of –15.6 mV. Western blotting confirmed the presence of CD9, CD63, and the specific fusion protein, validating the successful engineering of the vesicles.
• Drug Loading: The sonication method achieved an exceptionally high entrapment efficiency of approximately 99% for TMZ, indicating that the drug was successfully encapsulated within the exosomal lumen.
• Cytotoxicity:
  • Empty Exosomes: Engineered exosomes without drug showed no inherent cytotoxicity, confirming their biocompatibility.
  • Free TMZ: Exhibited a dose-dependent reduction in U87 cell viability with an IC50 of ~24 µg/mL.
  • Targeted Delivery: TMZ-loaded iRGD-functionalized exosomes demonstrated significantly enhanced efficacy, achieving an IC50 of ~16 µg/mL. This represents a ~33% reduction in the IC50 compared to free TMZ.
  • Non-Targeted Control: TMZ-loaded non-engineered exosomes showed limited efficacy, with cell viability remaining higher than in the targeted group at equivalent doses, underscoring the necessity of the iRGD ligand for effective delivery.

Significance and Claims
The authors claim that this study provides proof-of-concept that engineering exosomes with the iRGD peptide significantly improves the targeted delivery and therapeutic efficacy of Temozolomide against glioblastoma cells in vitro. The study demonstrates that:

1. HEK-293 cells can be effectively used to produce exosomes displaying the iRGD targeting ligand on their surface via LAMP-2B fusion.
2. The sonication method is a highly efficient technique for loading small-molecule chemotherapeutics like TMZ into exosomes without compromising vesicle integrity.
3. The iRGD functionalization enhances cellular uptake and cytotoxicity, likely through integrin-mediated endocytosis, resulting in a lower IC50 compared to both free drug and non-targeted exosomal delivery.

The paper concludes that while these findings are promising for improving drug specificity and reducing systemic side effects, the approach requires further investigation in vivo to evaluate stability, blood-brain barrier penetration, and therapeutic outcomes in animal models before clinical translation. The work establishes a foundation for using engineered exosomes as a nanocarrier platform for GBM therapy.