State of the art chemotherapeutic management of pediatric brain tumors

NRP1 inhibition modulates radiosensitivity of medulloblastoma by targeting cancer stem cells

BACKGROUND

Medulloblastoma (MB) is the most common pediatric malignant brain tumor. Despite current therapies, the morbidity and recurrent risk remains significant. Neuropilin-1 receptor (NRP1) has been implicated in the tumor progression of MB. Our recent study showed that NRP1 inhibition stimulated MB stem cells differentiation. Consequently, we hypothesized that targeting NRP1 in medulloblastoma could improve current treatments.

METHODS

NRP1 inhibition with a novel peptidomimetic agent, MR438, was evaluated with radiotherapy (RT) in MB models (DAOY, D283-Med and D341-Med) in vitro on cancer stem-like cells as well as in vivo on heterotopic and orthotopic xenografts.

RESULTS

We show that NRP1 inhibition by MR438 radiosensitizes MB stem-like cells in vitro. In heterotopic DAOY models, MR438 improves RT efficacy as measured by tumor growth and mouse survival. In addition, clonogenic assays after tumor dissociation showed a significant reduction in cancer stem cells with the combination treatment. In the same way, a benefit of the combined therapy was observed in the orthotopic model only for a low cumulative irradiation dose of 10 Gy but not for 20 Gy.

CONCLUSIONS

Finally, our results demonstrated that targeting NRP1 with MR438 could be a potential new strategy and could limit MB progression by decreasing the stem cell number while reducing the radiation dose.

Celecoxib suppresses the phosphorylation of STAT3 protein and can enhance the radiosensitivity of medulloblastoma-derived cancer stem-like cells

Medulloblastoma (MB) is a malignant primary brain tumor with poor prognosis. MB-derived CD133/Nestin double-positive cells (MB-DPs) exhibit cancer stem-like cell (CSC)-like properties that may contribute to chemoradioresistance, tumorigenesis and recurrence. In various tumors, signal transducer and activator of transcription 3 (STAT3) upregulation including MB which can regulate the expression of Nestin. Celecoxib, a selective COX-2 inhibitor, has been shown to potentially reduce STAT3 phosphorylation. The aim of the present study was to investigate the role of celecoxib in enhancing the effects of ionizing radiotherapy (IR) on MB-DP. MB-DPs and MB-derived CD133/Nestin double-negative cells (MB-DNs) were isolated from medulloblastoma cell line Daoy. Then, both of them were treated with celecoxib in different concentrations, and cell viability was assessed. The assays of cell survival, sphere formation, radiosensitivity, colony formation, apoptotic activity and mouse xenografting experiments in MB-DPs and MB-DNs treated with celecoxib alone, radiation alone, or celecoxib combined with radiation were further evaluated. We isolated MB-DPs from MB cell line Daoy, which exhibited typical CSC-like characteristics. Microarray analysis and Western blotting both indicated the upregulation of Janus kinase (JAK)-STAT cascade and STAT3 phosphorylation. Incubation with celecoxib dose-dependently suppressed the CSC-like properties and enhanced the IR effect on the induction of apoptosis, as detected by TUNEL assay and staining for Caspase 3 and Annexin V. Finally, celecoxib also enhanced the IR effect to suppress tumorigenesis and synergistically improve the recipient survival in orthotopic MB-derived CD133/Nestin double-positive cells (MB-DP cells) bearing mice.

Rational identification of a novel peptide for targeting nanocarriers to 9L glioma

Traditional therapies for high grade gliomas are limited in part by collateral damage to normal tissues. Selective delivery of therapies to tumors is, therefore, needed. Here, we report that liposomal nanocarriers coated with a novel oligopeptide enhance uptake by 9L gliosarcoma. A targeting nine amino acid peptide sequence (RSI) was identified by differential panning of random peptide phage display libraries on 9L cells and rat blood cells and plasma. Peptides were coupled to the surface of liposomal nanocarriers which were subsequently loaded with doxorubicin. The ability of RSI coated liposomes to facilitate drug uptake and cytotoxicity was compared with conventional liposomal nanocarriers and controls. In addition, plasma clearance profiles of the RSI peptide coupled liposomal nanocarriers were evaluated in adult immuno-competent rats. RSI peptide-coupled liposomal nanocarriers enhanced drug uptake by 9L cells by 500% compared with conventional liposomal nanocarriers, and significantly increased cytotoxicity. The plasma half-lives confirmed that the presence of the RSI peptide on the liposomal nanocarriers did not compromise circulation time in the blood in comparison with Stealth liposomal nanocarriers. These data suggest that phage-identified oligopeptides could lead to the development of new tumor selective nanocarriers.

Dose intensive melphalan and cyclophosphamide with autologous hematopoietic stem cells for recurrent medulloblastoma or germinoma

PURPOSE

To determine the response, toxicity, and survival for children with progressive or recurrent medulloblastoma and germinoma using a single myeloablative course of chemotherapy supported by autologous hematopoietic stem cells.

PATIENTS AND METHODS

Subjects were in second remission or had minimal residual disease at the time of study entry. The conditioning regimen consisted of cyclophosphamide 6,000 mg/m(2) plus melphalan 180 mg/m(2).

RESULTS

Twenty-nine evaluable pediatric patients were accrued. The most frequent major toxicities were myelosuppression, infections, and stomatitis, but no toxic deaths were recorded. Best responses were: CR = 6, CCR = 13, PR = 6, SD = 2, and PD = 2. There were 6 medulloblastoma and 3 germinoma survivors with a median follow-up of 7.5 years (range = 2.8-10). Two germinoma survivors received radiotherapy after autografting for presumptive progressive disease.

CONCLUSION

Myeloablative chemotherapy consisting of cyclophosphamide and melphalan was tolerable in the relapsed brain tumor setting with 19/29 cases achieving CR or CCR status and 9/29 becoming long-term survivors.

Pediatric CNS tumors: current treatment and future directions

Pediatric CNS tumors are the most common solid tumor of childhood and are the leading cause of cancer-related death in this age group. Improving prognosis is not the only challenge facing physicians managing these young patients as it is vital to consider the quality of survival. Current management strategies rely on surgery, radiotherapy and conventional cytotoxic chemotherapy, and although ongoing clinical trials continue to refine these treatments, newer approaches are required. This article will discuss current treatment standards for the most common pediatric CNS tumors: astrocytomas (low- and high-grade glioma), ependymoma and primitive neuroectodermal tumors (medulloblastoma), as well as future biological-based novel therapies.