Medulloblastoma (MB), the most common malignant paediatric brain tumor, is currently treated using a combination of surgery, craniospinal radiotherapy and chemotherapy. Owing to MB stem cells (MBSCs), a subset of MB patients remains untreatable despite standard therapy. CD133 is used to identify MBSCs although its functional role in tumorigenesis has yet to be determined. In this work, we showed enrichment of CD133 in Group 3 MB is associated with increased rate of metastasis and poor clinical outcome. The signal transducers and activators of transcription-3 (STAT3) pathway are selectively activated in CD133+ MBSCs and promote tumorigenesis through regulation of c-MYC, a key genetic driver of Group 3 MB. We screened compound libraries for STAT3 inhibitors and treatment with the selected STAT3 inhibitors resulted in tumor size reduction in vivo. We propose that inhibition of STAT3 signaling in MBSCs may represent a potential therapeutic strategy to treat patients with recurrent MB.

Current therapies to limit the neural tissue destruction following the spinal cord injury are not effective. Our recent studies indicate that the injury to the white matter of the spinal cord results in a severe inflammatory response where macrophages phagocytize damaged myelin and the fluid-filled cavity of injury extends in size with concurrent and irreversible destruction of the surrounding neural tissue over several months. We previously established that a high dose of 4mg/rat of dexamethasone administered for 1 week via subdural infusion remarkably lowers the numbers of infiltrating macrophages leaving large amounts of un-phagocytized myelin debris and therefore inhibits the severity of inflammation and related tissue destruction. But this dose was potently toxic to the rats. In the present study the lower doses of dexamethasone, 0.125-2.0mg, were administered via the subdural infusion for 2 weeks after an epidural balloon crush of the mid-thoracic spinal cord. The spinal cord cross-sections were analyzed histologically. Levels of dexamethasone used in the current study had no systemic toxic effect and limited phagocytosis of myelin debris by macrophages in the lesion cavity. The subdural infusion with 0.125-2.0mg dexamethasone over 2 week period did not eliminate the inflammatory process indicating the need for a longer period of infusion to do so. However, this treatment has probably lead to inhibition of the tissue destruction by the severe, prolonged inflammatory process.

No abstract

An alternative and potentially cost-effective approach to somatic gene therapy is to engineer a universal cell line secreting the desired product suitable for implantation into different patients without immune rejection. Encapsulating these cells in immunoprotective alginate microcapsules showed that this approach was effective in treating murine models of human diseases. We now report that this approach is also effective in delivering recombinant gene products to large animals. Canine MDCK cells encapsulated in alginate microcapsules were able to deliver recombinant human growth hormone to nonautologous dogs in vivo. However, the same microcapsules capable of prolonged delivery in mice soon disappeared after implantation in dogs. In contrast, when these microcapsules were modified by using a higher concentration of alginate cross-linked with barium instead of calcium, and by fabricating the alginate as a gelled bead without solubilizing the core, more prolonged and higher levels of recombinant product were obtained. Laminating the surface of the beads with poly-L-lysine and alginate provided an even more mechanically stable device that lasted for >2 months instead of <14 days in vivo and delivered >20 ng of human growth hormone/ml of plasma within the first week. The apparent disappearance of the growth hormone from the circulation after day 14 was due to rapid clearance by anti-human growth hormone antibodies and not due to loss of cell viability. However, all microcapsules provoked an inflammatory reaction, causing mild omentitis, and eventually disappeared from the intraperitoneal cavity. In conclusion, systemic delivery of recombinant gene products with nonautologous cells protected in alginate microcapsules has been shown to be feasible in canine recipients. While improved level and duration of delivery have been achieved by increasing the mechanical stability of the microcapsules, further improvements in biocompatibility and stability will be required for human application.

Our understanding of myelination has been greatly enhanced via the study of spontaneous mutants that harbor a defect in a gene encoding one of the major myelin proteins (myelin mutants). In this study, we describe a unique genetic defect in a new myelin mutant called the Long Evans shaker (les) rat that causes severe dysmyelination of the CNS. Myelin deficits result from disruption of the myelin basic protein (Mbp) gene caused by the insertion of an endogenous retrotransposon [early transposons (ETn) element] into a noncoding region (intron 3) of the gene. The ETn element alters the normal splicing dynamics of MBP mRNA, leading to a dramatic reduction in the levels of full-length isoforms (<5% of normal) and the appearance of improperly spliced, chimeric transcripts. Although these aberrant transcripts contain proximal coding regions of the MBP gene (exons 1-3), they are unable to encode functional proteins required to maintain the structural integrity of the myelin sheath. These chimeric transcripts seem capable, however, of producing the necessary signal to initiate and coordinate myelin gene expression because normal numbers of mature oligodendrocytes synthesizing abundant levels of other myelin proteins are present in the mutant CNS. The les rat is thus an excellent model to study alternative functions of MBP beyond its well characterized role in myelin compaction.