Brain cancer is a life threatening disease characterized by low survival rates. The development of selectively targeted nanoparticles conjugated with drugs is critical for improving the treatment and monitoring of this aggressive type of cancer. Photodynamic therapy (PDT) is a localized treatment modality that is promising for brain tumor treatment. Although improvements in survival were reported, the widespread use of PDT in brain tumor therapy has been partially hampered by non-targeted phototoxicity towards healthy tissue. Improving the selectivity of tumor targeting and sustained delivery of PDT drugs will dramatically enhance the success of brain cancer therapy. Pc 4 is a highly promising PDT drug, approved for clinical trials, characterized by virtual non-toxicity in the dark, high phototoxicity, and well defined chemical structure and purity. This drug operates in the near infrared (NIR) spectral range, which penetrates brain tissue most efficiently for both diagnostic optical imaging and phototherapy. The objective of the proposed research is to develop Pc 4 loaded gold nanoparticle (Au NP-Pc 4) conjugates with a thiolated PEG coating for targeted imaging-guided therapy of glioma brain cancers. We will adapt a novel cross-disciplinary approach to synthesize PEG-coated gold nanoparticles conjugated to Pc 4 and tethered peptide ligands for targeting epidermal growth factor (EGF) and transferrin (Tf) cell surface receptors, which are overexpressed in brain cancer cells. By applying genetic cell engineering, we will develop model cell lines and animal systems with human EGF and Tf receptors, expressed separately or jointly as viable cancer biomarkers on rat 9L glioma cells. We will perform state of the art in vitro and in vivo fluorescence imaging to characterize the delivery and targeting of the conjugates, as well as determining their therapeutic (PDT) efficacy. The central hypothesis is that using a dual-targeting ligand concept will dramatically improve PDT nanoparticle selectivity to brain cancers. To test this hypothesis, we will develop and test both in vitro and in vivo nanoparticle PDT efficacy to fulfill the following aims:
Specific Aim 1 : Development and characterization of PEGylated Au NP-Pc 4 conjugates containing EGFR and TfR binding peptide ligands. Targeted NPs loaded with the PDT drug Pc 4 will be synthesized, fully characterized (in terms of structure, ligand density, and drug loading), and optimized for selective targeting and drug release. To support the optimization process, we will perform Au NP: receptor interaction studies of each NP conjugate design, including not only equilibrium data, but also kinetic parameters of the interactions using surface plasmon resonance (SPR) Biacore technology.
Specific Aim 2 : Targeted nanoparticle conjugate delivery and PDT efficacy testing in vitro in Tf and EGF receptor-bearing 9L glioma cell lines. The ability to target overexpressed human receptors will be studied using engineered 9L glioma cell lines overexpressing human EGFR and TFR, separately and in combination. We will examine the uptake and localization of targeted NPs using various experimental techniques, including silver enhancement immunohistochemistry, real time confocal laser scanning microscopy, and transmission electron microscopy. The cells will then be subjected to PDT, and cellular viability will be assessed using the MTT assay. Since intracellular localization of the PDT drug is a precursor to downstream cellular events, such as apoptosis, we will also assess the mechanism of Pc 4-mediated programmed cell death using a mitochondrial membrane potential assay, TUNEL and DNA fragmentation assays, and cell permeability assays, including trypan blue staining and Annexin V/ propidium iodide flow cytometry.
Specific Aim 3 : In vivo translation of PDT therapy and post-therapy monitoring in glioma tumor bearing mice. We will investigate the NP targeting and the PDT efficacy of the NP conjugates in vivo in receptor overexpressing 9L tumor bearing mice using 3-dimensional fluorescence molecular tomography (FMT). We will determine circulation, biodistribution, and clearance of the targeted Au NPs and the drug Pc 4 using ICP/AAS elemental analysis and silver enhancement immunohistochemistry, and fluorescence imaging to evaluate relative concentrations of Pc 4 and the Au NPs. We will also examine the pathology of the tumors after PDT using dynamic fluorescent imaging over a seven day period. The ultimate goal of this project is a drastic improvement of combined brain cancer treatment and monitoring using a highly targeted, virtually non-toxic PDT sensitizer that can be locally activated and interrogated in real time with high spatio-temporal resolution.
Malignant gliomas are the most common primary brain tumors and among the most lethal cancers in man. Cell surface receptor-targeted gold nanoparticles when conjugated with Pc 4, a photodynamic therapy drug, can be molecular imaging agents used to improve the specificity of detection of these brain cancers. Our multidisciplinary research plan involves chemical synthesis and characterization of targeted nanoparticles, in vitro cell culture studies, and in vivo studies of mouse models of human glioma carcinomas. By improving the selectivity of tumor targeting, we can potentially sustain local delivery of PDT drugs, thus dramatically enhancing the success of brain cancer therapy.
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