What is Glioblastoma Multiforme?
Glioblastoma Multiforme (GBM) is the most common tumor in the central nervous system (CNS) and accounts for 65% of all CNS malignancies. GBM is one of the most deadly forms of cancer, with a median survival rate of just 12.6 months after diagnosis. Attributing to this severe prognosis is the tumor’s location in the brain or spinal cord, severely limiting the success of traditional chemotherapies, radiation therapies, and surgical removal.
What are Silk Nanoparticles?
Nanoparticles, however, can mitigate many of the obstacles that currently available therapies cannot overcome. Their advantages include biocompatibility, reduced toxicity, excellent stability, enhanced permeability and retention effect, and precise targeting. The unique targeting ability of these nanoparticles can be enhanced with antibodies that bind to proteins on the surface of the selected cancer cells and deliver the drug of interest. While nanoparticles can be composed of various materials, silk was selected as the appropriate material due to its biocompatibility, availability, and ease of size optimization and loading. Nanoparticles around 100 nm in the bloodstream are known to be too big to enter healthy tissue but can enter tumors due to their leaky vasculature. Once they have entered the tumor and bound to the cell receptors, they can be endocytosed to deliver the drug. Larger nanoparticles have been found to have longer rates of internalization; therefore, it may be advantageous to a nanoparticle large enough to only target cancerous tissue, yet small enough to be engulfed at an appropriate rate.
What are antibodies and what is dual conjugation?
Epidermal growth factor receptors (EGFR) are transmembrane receptor tyrosine kinases (RTK) and are overexpressed in 50% of glioblastomas. Epidermal growth factor variant three (EGFRviii) is a mutated wildtype EGFR expressed on the surface of GBM cells and commonly associated with GBM. This mutation can lead to continued expression of tyrosine kinases, and activate uncontrolled cell proliferation, growth, etc. EGFRviii is expressed in 25-33% of all GBM tumors in patients, and it is not expressed in normal brain tissue. Some studies go so far as to claim that EGFRviii has never been detected in healthy tissue. Its low expression in normal tissue makes it a suitable target for GBM therapies. Gliomas with EGFRviii have increased Ras activity, Akt/PI3k signaling, and expression of VEGF and IL-8. EGFRviii CAR T cells are in Phase I studies and have shown low off-target toxicity.
Interleukin-13 receptor alpha2 (IL-13Rɑ2) was discovered as a glioma marker in 1995 by the Debinski laboratory, since then it has become one of the most studied tumor-specific antigens in glioblastoma research. IL-13Rɑ2 is a high-affinity membrane receptor of IL-13 and is expressed in many tumors. It has been found to be overexpressed in up to 75% of glioma patients. Expression of IL-13Rɑ2 is high in the testis and placenta but has low expression in other organs. A phase III trial targeting IL-13Rɑ2 reported high levels of neurotoxicity due to off-target interactions with IL-13Rɑ1, a related receptor that is expressed in healthy brain tissue. While this trial revealed the dangers of working with IL-13Rɑ2, it suggests a promise of an antibody more specific to IL-Rɑ2 to be found and used. Currently, CAR T-cell therapy targeting IL-13Rɑ2 is now in Phase I clinical trials. Dual combinations of IL-13Rɑ2 and EphA2 have been shown to be expressed in 90% of GBM patients indicating promising data for better targeting specificity. EGFRviii and IL-13Rɑ2 targeted therapy have both been associated with recurrent antigen loss variants after initial treatment.
The combination of two receptor targets would allow for a greater number of GBM cell targets among its heterogeneous population, while also maintaining selectivity and reducing off-target interactions. Silk nanoparticles offer a unique opportunity to customize the drug, target, and dose of interest. Silk will be made using a previously established protocol from Kaplan et al. The target size distribution will be 100-120 nm, based on literature that linked the clinical efficacy of tumor vasculature penetration to this size range. To achieve this size, a silk solution will be produced using 6% concentration, boiled for 30 min, and spun at 500 rpm for nanoparticle formulation. The nanoparticles will be fabricated by solvent emulsion techniques shown in the methods section, chosen because it allows for precise control over nanoparticle size formation at this range. The size will be measured by dynamic light scattering (DLS), and a distribution of 100-120 nm will be acceptable for further processing. In this project, dual-antibody conjugated nanoparticles will allow for more direct targeting of GBM cells; compared to traditional therapies, a successful formulation will result in more efficacious treatment for better patient outcomes.
References
Kanderi T, Gupta V. Glioblastoma Multiforme. [Updated 2022 Sep 12]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK558954/
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