Beyond the EPR effect: targeting of nanoparticles to pediatric brain tumors

Abstract

Event Abstract Back to Event Beyond the EPR effect: targeting of nanoparticles to pediatric brain tumors Elizabeth Doolittle1, 2, 3, Peter Bielecki1, 2, 3, Amy Goldberg1 and Efstathios Karathanasis1, 2, 3 1 Case Western Reserve University, Biomedical Engineering, United States 2 Case Western Reserve University, Radiology, United States 3 Case Western Reserve University, Case Comprehensive Cancer Center, United States Introduction: In cancer applications, nanoparticles should selectively deposit to tumor areas due to the enhanced permeability and retention (EPR) effect. However, recent reports generated controversy over the benefits of EPR. Further, in the case of brain tumors, while the blood-brain barrier is compromised, tumor-associated blood vessels are not as leaky as in other tumor types. We previously showed vascular targeting nanoparticles lead to successful imaging of breast tumor micrometastatic sites (Figure 1) [1],[2] suggesting an approach appropriate for tumor types in which EPR alone is ineffective. Here, we investigated nanoparticles in murine models of adult and pediatric glioblastoma multiforme for targeted particle delivery for imaging and therapy. Materials and Methods: Experiments used invasive glioma orthotopic murine models: an established murine glioma (CNS-1) and a patient derived pediatric brain tumor (SJ-GBM2). Biomarkers used for targeting were validated using tumor section immunohistochemistry. Various nanoparticles (liposomes, gold or iron oxide) with surface PEG-amines were conjugated with selected biomarker ligands and imaging probes for particle detection. Brains were inoculated with GFP-positive CNS-1 or SJ-GBM2 cells. Particles were intravenously injected and animals were sacrificed 8-14 days after tumor inoculation. Organs were analyzed using 2D and 3D fluorescence imaging. Histological analyses validated intratumoral deposition of particles. Results and Discussion: Targeting ligands were based on high affinity peptides against known receptors overexpressed by the brain tumor’s vascular bed (integrins, VEGFR2). Dynamic light scattering and TEM characterized particle size. Surface ligands added at varying surface densities (1000-2500 ligands per particle) were confirmed by direct protein assay. Animal studies showed patterns of nanoparticle deposition dependent on targeting strategy (vascular vs deep tissue). Vascular targeting was more effective than deep tissue targeting in most occasions, since deep tissue targeting requires prerequisite EPR. In particular, histological analyses showed that while EPR-driven deposition resulted in accumulation in cancerous sites, vascular targeting yielded higher, more consistent capture of the majority of tumor sites. Further, size of the nanoparticles and resulting multivalent avidity makes nanoparticles ideal to vascular targeting. In a recent study, vascular targeting of a gold nanoparticle radiotracer led to 5.2-fold higher deposition in lung metastases than the equivalent small molecule analogue. Figure 1 is an example of the result of vascular targeting. The left image gamma scintigraphy shows radiolabeled nanoparticle accumulation corresponding to GFP positive tumor cells shown in the right image[1]. Conclusion: When one considers the targeted tumor microenvironment’s biophysical and biochemical uniqueness, rationale design of nanoparticles and targeting strategy can result in enhancements. This work was supported by grants from the National Cancer Institute (U01CA198892, R01CA177716) and the Prayers from Maria Children's Glioma Cancer Foundation (E.K.).; E.D. and P.B were supported by the NIH Interdisciplinary Biomedical Imaging Training Program (5T32EB007509).