Abstract 3981: Targeted delivery of temozolomide to pediatric brain tumors using micelle-based theranostic nanocarriers
Authors: Miller Kayla , Dixit Suraj K. , Bredlau Amy-Lee , Broome Ann-Marie 
Published: May 2015

Diffuse intrinsic pontine glioma (DIPG) is the single most devastating pediatric brain tumor. Surgical excision of these tumors, due to the exquisite location of the pons, is dangerous and is not curative. No chemotherapy has been identified that can control these tumors. One theory for this failure is that the pons is a unique location into which delivery of medications at therapeutic concentrations is singularly challenging. Current standard of care utilizes temozolomide (TMZ), a pro-drug that releases a DNA alkylating agent that is used to kill glial cells. TMZ is very toxic when delivered systemically and therapeutic dosages are limited by severe side effects. These factors necessitate a selectively targeted carrier for TMZ to deliver the drug efficiently to malignant cells avoiding nonspecific interaction and reducing offsite toxicity. In order to design an efficient and effective drug carrier, we addressed several issues: a tailored surface on the carrier to attach biomolecules for targeted drug delivery; a biocompatible coating which can efficiently encapsulate the hydrophobic drug thereby reducing cytotoxicity; and stimuli-induced (pH) disruption of the carrier agent for slow and controlled drug release to the desired environment. Micelles are the preferred choice of carrier as they fulfill these requirements based on their composition. Micelles containing drug are synthesized using PEG-PE-Amine and N-palmitoyl homocysteine (pH sensitive lipid breaks in endosome pH 5.5). Specific targeting of the micelles to glioblastoma cells is achieved by coupling a short 12 a.a. PDGF (platelet derived growth factor) peptide to the amine moeity of the DSPE-PEG. In addition, these micelles have been labeled with a NIR fluorophore to track them for cellular uptake and can be used to image tumor internalization in vivo. These micelles have an advantage of small size (&lt;80 nm, to cross blood brain barrier) and reduced toxicity due to robust packaging of TMZ drug inside the core as determined by dynamic light scattering and UV-vis spectroscopy. We have decreased the leaching of the drug in the circulation and in the extracellular microenvironment, resulting in reduced cytotoxicity. Cellular uptake studies via fluorescence imaging, flow cytometry, and spectroscopy of glioblastoma cells treated with either targeted or untargeted micellar nanoparticles demonstrate significant uptake of the PDGFR-targeted micelles, a 6-fold increase in delivered drug over untargeted micelle-TMZ. We show that uptake is mediated by receptor-mediated endocytosis using competition assays and is nontoxic to the cell until released as demonstrated by cytotoxicity assays. We can track the delivery of the micelle-encapsulated TMZ to tumors using NIR in vivo fluorescence imaging. Little drug escapes into the surrounding offsite organs. Future experiments involve pharmacokinetic and tissue distribution studies in in vivo orthotopic brain tumor models.

Citation Format: Kayla Miller, Suraj K. Dixit, Amy-Lee Bredlau, Ann-Marie Broome. Targeted delivery of temozolomide to pediatric brain tumors using micelle-based theranostic nanocarriers. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3981. doi:10.1158/1538-7445.AM2014-3981