Molecularly-Targeted Theranostic Probes for EGFRmt+ Brain Tumors

Lay Summary

PET imaging agent may effectively deliver treatment to malignant cancers in the brain

Researchers will undertake studies in cancer patients and animal models to determine whether a PET imaging agent effectively carries and delivers a drug treatment for fighting metastatic cancers in the brain.

The two most common metastatic cancers in the brain are glioma, a primary brain tumor, and non-small cell lung carcinoma, which metastasizes to the brain. Both cancers are deadly. The drug Iressa is approved by the Food and Drug Administration for treating non-small cell lung cancer by inhibiting “epidermal growth factor” from attaching to a receptor located on cancer cells’ surface and speeding their rapid spread. The receptor is present on about half of all glioma cells and about a quarter of the lung cancer cells. Iressa and other drugs have not worked well for brain cancers, though, largely because drugs have difficulty crossing the blood brain barrier and specifically targeting cancer cells. But, this situation may change due to a miniscule “nanoparticle” that is being tested as a PET imaging tracer. The nanoparticle recognizes the epidermal growth factor receptor, is tiny enough to cross the blood brain barrier, and it can carry a drug with it to the receptor target. The investigators have fluorescently labeled the nanoparticle so that its actions can be visualized using PET and cellular imaging techniques.  They hypothesize that attaching Iressa to PET imaging nanoparticles will improve drug delivery and the response of malignant brain cancer cells beyond that of current therapies.

They first will inject the intravenous nanoparticle into six patients with malignant brain tumor and use PET imaging to assess whether the nanoparticle sensitively detects, localizes, and accumulates within the malignant brain tumors. They will surgically remove tumor tissue and use optical imaging to confirm the PET results. Then they will customize synthesis of the nanoparticle to enable Iressa to be attached either to the surface or a pore in the nanoparticle. Thereafter they will take tumor tissue from the patients, transplant it into mice, and use optical imaging and tissue examination in the laboratory to assess the drug’s activities and determine the dose of Iressa that produces optimal activity.

Significance: These studies will provide the basis for undertaking a larger clinical study of the potential effectiveness of using a PET agent to both deliver and visualize the action of drug therapies in treating deadly brain cancers.

Abstract

PET imaging agent may effectively deliver treatment to malignant cancers in the brain

One of the current challenges in treating patients with EGFR mutant (EGFRmt+) malignant brain tumors is the limited CNS penetration of EGFR tyrosine kinase inhibitors (TKI), such as gefitinib and erlotinib, at standard daily dosing. One-third of patients with EGFRmt+ NSCLC develop CNS metastases after initially responding to EGFR TKIs. This has been attributed to lower TKI concentrations in the brain or CSF, which are inadequate for killing EGFRmt+ tumor cells. Improved drug delivery vehicles are thus acutely needed for clinical treatment of such tumors. One ideal platform for this purpose may be an ultrasmall (<10nm), integrin-targeting silica nanoparticle, 124I-cRGDY-PEG-C dot, which has been translated to the clinic as a dual-modality (PET-optical) imaging platform. Its favorable kinetic and enhanced tumor retention properties have suggested that systemic delivery of these particles to the CNS will be adequate to achieve therapeutic concentrations and improve treatment response.



We first aim to monitor targeted delivery and penetration of 124I-cRGDY-bound-C dots in pre-surgical patients harboring either brain metastases from non-small cell lung cancer (NSCLC) or glioblastoma multiforme (GBM), two tumor types for which improved delivery of EGFR inhibitors to the CNS is likely to be clinically significant. Following intravenous injection of 124I-cRGDY-bound C dots, serial PET-CT imaging will be used to detect, localize, and assess accumulations of the particle tracer within brain tumors over a 24 hour period. Imaging will also permit particle uptake and clearance to be monitored within the remaining major organs/tissues of the body. To correlate imaging with molecular abnormalities and tissue particle distributions, we will analyze tissue from tumor biopsies targeting regions of tracer uptake within and about the tumor. The experimental protocol will involve: (1) preoperative MRI per routine and PET-CT imaging p.i. 124I-cRGDY-PEG-C dots will be performed and co-registered for identification of potential biopsy target/s; (2) surgical resection with targeted tissue acquisition will take place per routine, with integrated frameless stereotactic tracking used to annotate sites of biopsies, and updated by intraoperative MRI (iMRI,1.5T Siemens magnet). Tissue samples from several regions will be collected within and around the tumor. Tumor tissue regions showing particle tracer uptake and other tissue showing little or no uptake will be analyzed for integrin expression. Assays will include immunohistochemistry with commercially available antibodies.



We next aim to synthesize and characterize new silica nanocarriers, as both diagnostic and therapeutic agents for the controlled delivery of the EGFR TKI, gefitinib, to EGFRmt+ brain tumor models. Two types of gefitinib-modified platforms, less than 10 nm in diameter, will be evaluated by optical imaging, one in which gefitinib is attached to the particle surface (C dots) and the other in which it is attached to the pore of a mesoporous C dot (mC dot) by peptide linkers. Drug release profiles will be assessed in serum-supplemented media. We will investigate viability, cellular internalization, and inhibitory profiles in EGFRmt+ tumor cell lines incubated with gefitinib-modified cRGDY-bound C dots and mC dots over a range of times and particle concentrations, relative to the native drug. These findings will be used to select lead candidates for in vivo studies. EGFR phosphorylation status will be assayed by western blot.



Finally, we will determine the utility of lead targeted therapeutic candidate/s over the native drug for improving penetration and response in EGFRmt+ NSCLC xenograft and GBM models using serial PET-optical imaging methods. We hypothesize that these platforms will increase effective drug concentrations at tumor sites on the basis of previously observed preferential tumor retention and estimated therapeutic dosing requirements. To this end, we will employ a dose escalation procedure in which increasing numbers of non-radiolabeled, drug-bound particles will be administered to achieve maximum treatment response and limit radiation exposure. 18F-FDG PET will be used for monitoring response, and imaging findings will be confirmed histologically. The successful coupling of these dual-modality drug delivery vehicles with molecular imaging technologies may ultimately guide therapeutic decision-making and inform the design of future translational brain tumor studies.