Brenda Auffinger

Blood‐Brain Barrier Permeable Gold Nanoparticles: An Efficient Delivery Platform for Enhanced Malignant Glioma Therapy and Imaging

The blood-brain barrier (BBB) remains a formidable obstacle in medicine, preventing efficient penetration of chemotherapeutic and diagnostic agents to malignant gliomas. Here, a transactivator of transcription (TAT) peptide-modified gold nanoparticle platform (TAT-Au NP) with a 5 nm core size is demonstrated to be capable of crossing the BBB efficiently and delivering cargoes such as the anticancer drug doxorubicin (Dox) and Gd(3+) contrast agents to brain tumor tissues. Treatment of mice bearing intracranial glioma xenografts with pH-sensitive Dox-conjugated TAT-Au NPs via a single intravenous administration leads to significant survival benefit when compared to the free Dox. Furthermore, it is demonstrated that TAT-Au NPs are capable of delivering Gd(3+) chelates for enhanced brain tumor imaging with a prolonged retention time of Gd(3+) when compared to the free Gd(3+) chelates. Collectively, these results show promising applications of the TAT-Au NPs for enhanced malignant brain tumor therapy and non-invasive imaging.

IDO Expression in Brain Tumors Increases the Recruitment of Regulatory T Cells and Negatively Impacts Survival

Purpose: Glioblastoma multiforme (GBM) is an aggressive adult brain tumor with a poor prognosis. One hallmark of GBM is the accumulation of immunosuppressive and tumor-promoting CD4+FoxP3+GITR+ regulatory T cells (Tregs). Here, we investigated the role of indoleamine 2,3 dioxygenase (IDO) in brain tumors and the impact on Treg recruitment. Experimental Design: To determine the clinical relevance of IDO expression in brain tumors, we first correlated patient survival to the level of IDO expression from resected glioma specimens. We also used novel orthotopic and transgenic models of glioma to study how IDO affects Tregs. The impact of tumor-derived and peripheral IDO expression on Treg recruitment, GITR expression, and long-term survival was determined. Results: Downregulated IDO expression in glioma predicted a significantly better prognosis in patients. Coincidently, both IDO-competent and deficient mice showed a survival advantage bearing IDO-deficient brain tumors, when compared with IDO-competent brain tumors. Moreover, IDO deficiency was associated with a significant decrease in brain-resident Tregs, both in orthotopic and transgenic mouse glioma models. IDO deficiency was also associated with lower GITR expression levels on Tregs. Interestingly, the long-term survival advantage conferred by IDO deficiency was lost in T-cell–deficient mice. Conclusions: These clinical and preclinical data confirm that IDO expression increases the recruitment of immunosuppressive Tregs that lead to tumor outgrowth. In contrast, IDO deficiency decreases Treg recruitment and enhances T-cell–mediated tumor rejection. Thus, the data suggest a critical role for IDO-mediated immunosuppression in glioma and support the continued investigation of IDO–Treg interactions in the context of brain tumors. Clin Cancer Res; 18(22); 6110–21. ©2012 AACR.

Cell-Penetrating Peptide-Modified Gold Nanoparticles for the Delivery of Doxorubicin to Brain Metastatic Breast Cancer

As therapies continue to increase the lifespan of patients with breast cancer, the incidence of brain metastases has steadily increased, affecting a significant number of patients with metastatic disease. However, a major barrier toward treating these lesions is the inability of therapeutics to penetrate into the central nervous system and accumulate within intracranial tumor sites. In this study, we designed a cell-penetrating gold nanoparticle platform to increase drug delivery to brain metastatic breast cancer cells. TAT peptide-modified gold nanoparticles carrying doxorubicin led to improved cytotoxicity toward two brain metastatic breast cancer cell lines with a decrease in the IC50 of at least 80% compared to free drug. Intravenous administration of these particles led to extensive accumulation of particles throughout diffuse intracranial metastatic microsatellites with cleaved caspase-3 activity corresponding to tumor foci. Furthermore, intratumoral administration of these particles improved survival in an intracranial MDA-MB-231-Br xenograft mouse model. Our results demonstrate the promising application of gold nanoparticles for improving drug delivery in the context of brain metastatic breast cancer.

Multifunctional nanoparticles for brain tumor imaging and therapy

Brain tumors are a diverse group of neoplasms that often carry a poor prognosis for patients. Despite tremendous efforts to develop diagnostic tools and therapeutic avenues, the treatment of brain tumors remains a formidable challenge in the field of neuro-oncology. Physiological barriers including the blood-brain barrier result in insufficient accumulation of therapeutic agents at the site of a tumor, preventing adequate destruction of malignant cells. Furthermore, there is a need for improvements in brain tumor imaging to allow for better characterization and delineation of tumors, visualization of malignant tissue during surgery, and tracking of response to chemotherapy and radiotherapy. Multifunctional nanoparticles offer the potential to improve upon many of these issues and may lead to breakthroughs in brain tumor management. In this review, we discuss the diagnostic and therapeutic applications of nanoparticles for brain tumors with an emphasis on innovative approaches in tumor targeting, tumor imaging, and therapeutic agent delivery. Clinically feasible nanoparticle administration strategies for brain tumor patients are also examined. Furthermore, we address the barriers towards clinical implementation of multifunctional nanoparticles in the context of brain tumor management.

Conversion of differentiated cancer cells into cancer stem-like cells in a glioblastoma model after primary chemotherapy.

Glioblastoma multiforme patients have a poor prognosis due to therapeutic resistance and tumor relapse. It has been suggested that gliomas are driven by a rare subset of tumor cells known as glioma stem cells (GSCs). This hypothesis states that only a few GSCs are able to divide, differentiate, and initiate a new tumor. It has also been shown that this subpopulation is more resistant to conventional therapies than its differentiated counterpart. In order to understand glioma recurrence post therapy, we investigated the behavior of GSCs after primary chemotherapy. We first show that exposure of patient-derived as well as established glioma cell lines to therapeutic doses of temozolomide (TMZ), the most commonly used antiglioma chemotherapy, consistently increases the GSC pool over time both in vitro and in vivo. Secondly, lineage-tracing analysis of the expanded GSC pool suggests that such amplification is a result of a phenotypic shift in the non-GSC population to a GSC-like state in the presence of TMZ. The newly converted GSC population expresses markers associated with pluripotency and stemness, such as CD133, SOX2, Oct4, and Nestin. Furthermore, we show that intracranial implantation of the newly converted GSCs in nude mice results in a more efficient grafting and invasive phenotype. Taken together, these findings provide the first evidence that glioma cells exposed to chemotherapeutic agents are able to interconvert between non-GSCs and GSCs, thereby replenishing the original tumor population, leading to a more infiltrative phenotype and enhanced chemoresistance. This may represent a potential mechanism for therapeutic relapse.

Fibrin-binding, peptide amphiphile micelles for targeting glioblastoma.

Glioblastoma-targeted drug delivery systems facilitate efficient delivery of chemotherapeutic agents to malignant gliomas, while minimizing systemic toxicity and side effects. Taking advantage of the fibrin deposition that is characteristic of tumors, we constructed spherical, Cy7-labeled, targeting micelles to glioblastoma through the addition of the fibrin-binding pentapeptide, cysteine–arginine–glutamic acid–lysine–alanine, or CREKA. Conjugation of the CREKA peptide to Cy7-micelles increased the average particle size and zeta potential. Upon intravenous administration to GL261 glioma bearing mice, Cy7-micelles passively accumulated at the brain tumor site via the enhanced permeability and retention (EPR) effect, and Cy7-CREKA-micelles displayed enhanced tumor homing via active targeting as early as 1 h after administration, as confirmed via in vivo and ex vivo imaging and immunohistochemistry. Biodistribution of micelles showed an accumulation within the liver and kidneys, leading to micelle elimination via renal clearance and the reticuloendothelial system (RES). Histological evaluation showed no signs of cytotoxicity or tissue damage, confirming the safety and utility of this nanoparticle system for delivery to glioblastoma. Our findings offer strong evidence for the glioblastoma-targeting potential of CREKA-micelles and provide the foundation for CREKA-mediated, targeted therapy of glioma.

The role of glioma stem cells in chemotherapy resistance and glioblastoma multiforme recurrence

Glioma stem cells (GSCs) constitute a slow-dividing, small population within a heterogeneous glioblastoma. They are able to self-renew, recapitulate a whole tumor, and differentiate into other specific glioblastoma multiforme (GBM) subpopulations. Therefore, they have been held responsible for malignant relapse after primary standard therapy and the poor prognosis of recurrent GBM. The failure of current therapies to eliminate specific GSC subpopulations has been considered a major factor contributing to the inevitable recurrence in GBM patients after treatment. Here, we discuss the molecular mechanisms of chemoresistance of GSCs and the reasons why complete eradication of GSCs is so difficult to achieve. We will also describe the targeted therapies currently available for GSCs and possible mechanisms to overcome such chemoresistance and avoid therapeutic relapse.

A Preclinical Evaluation of Neural Stem Cell–Based Cell Carrier for Targeted Antiglioma Oncolytic Virotherapy

BACKGROUND Oncolytic adenoviral virotherapy (OV) is a highly promising approach for the treatment of glioblastoma multiforme (GBM). In practice, however, the approach is limited by poor viral distribution and spread throughout the tumor mass. METHODS To enhance viral delivery, replication, and spread, we used a US Food and Drug Administration-approved neural stem cell line (NSC), HB1.F3.CD, which is currently employed in human clinical trials. HB1.F3.CD cells were loaded with an oncolytic adenovirus, CRAd-Survivin-pk7, and mice bearing various human-derived GBMs were assessed with regard to NSC migration, viral replication, and therapeutic efficacy. Survival curves were evaluated with Kaplan-Meier methods. All statistical tests were two-sided. RESULTS Antiglioma activity of OV-loaded HB1.F3.CD cells was effective against clinically relevant human-derived glioma models as well as a glioma stem cell-enriched xenograft model. Median survival was prolonged by 34% to 50% compared with mice treated with OV alone (GBM43FL model median survival = 19.5 days, OV alone vs NSC + OV, hazard ratio of survival = 2.26, 95% confidence interval [CI] = 1.21 to 12.23, P = .02; GBM12 model median survival = 43.5 days, OV alone vs NSC + OV, hazard ratio of survival = 2.53, 95% CI = 1.21 to 10.38, P = .02). OV-loaded HB1.F3.CD cells were shown to effectively migrate to the contralateral hemisphere and hand off the therapeutic payload of OV to targeted glioma cells. In vivo distribution and migratory kinetics of the OV-loaded HB1.F3.CD cells were successfully monitored in real time by magnetic resonance imaging. OV-loaded NSCs retained their differentiation fate and were nontumorigenic in vivo. CONCLUSIONS HB1.F3.CD NSCs loaded with CRAd-Survivin-pk7 overcome major limitations of OV in vivo and warrant translation in a phase I human clinical trial for patients with GBM.

Nanoparticle‐Programmed Self‐Destructive Neural Stem Cells for Glioblastoma Targeting and Therapy

A 3-step glioblastoma-tropic delivery and therapy method using nanoparticle programmed self-destructive neural stem cells (NSCs) is demonstrated in vivo: 1) FDA-approved NSCs for clinical trials are loaded with pH-sensitive MSN-Dox; 2) the nanoparticle conjugates provide a delayed drug-releasing mechanism and allow for NSC migration towards a distant tumor site; 3) NSCs eventually undergo cell death and release impregnated MSN-Dox, which subsequently induces toxicity towards surrounding glioma cells.

Understanding glioma stem cells: rationale, clinical relevance and therapeutic strategies.

Glioblastoma multiforme is one of the most aggressive brain tumors in adults. Despite the use of the best available multimodal therapeutic approaches, the prognosis remains dismal. The identification of glioma stem cells (GSCs) has offered new hope to affected patients, since it could explain, in part, the highly heterogeneous nature of this tumor and its chemo- and radio-resistance. Although still in its infancy, GSC research has unveiled many of its complexities and the theory itself remains controversial. GSC phenotype can significantly vary between patients and a single tumor may present several distinct GSCs. New therapeutic solutions that effectively target this population are of utmost importance, since they may be able to decrease neoplastic recurrence and improve patient survival. Here, we discuss the mechanisms by which GSCs lead to glioma relapse, the main controversies in this field and the most recent treatments that could successfully target this population.