imetelstat and Brain-Neoplasms

A fundamental limitation in the treatment of brain tumors is that < 1% of most therapeutic agents administered systemically are able to cross the blood-brain barrier (BBB). The development of new strategies that circumvent the BBB should increase the likelihood of tumor response to selected therapeutic agents. Intranasal delivery (IND) is a practical, noninvasive method of bypassing the BBB to deliver therapeutic agents to the brain. This technique has demonstrated promising results in the treatment of neurological disorders. Telomerase is a reverse transcriptase that is expressed in the vast majority of malignant gliomas, although not in the healthy brain. Telomerase inhibition can therefore be used as a therapeutic strategy for selectively targeting malignant gliomas. The first successful IND of a telomerase inhibitor as a therapy for brain tumors was GRN-163, an oligonucleotide N3'-->5' thiophosphoramidate telomerase inhibitor, which was successfully administered into intracerebral tumors in rats with no apparent toxicity. GRN-163 exhibited favorable tumor uptake and inhibited tumor growth, leading to prolonged lifespan in treated animals. The IND of telomerase inhibitors represents a new therapeutic approach that appears to selectively kill tumor cells, without inducing toxic effects in the surrounding healthy brain tissue.

Topics: Administration, Intranasal; Animals; Blood-Brain Barrier; Brain Neoplasms; Enzyme Inhibitors; Humans; Indoles; Neoplasms; Neural Pathways; Niacinamide; Oligonucleotides; Telomerase

A truncation mutant of the epidermal growth factor receptor, EGFRvIII, is commonly expressed in glioma, an incurable brain cancer. EGFRvIII is tumorigenic, in part, through its transactivation of other receptor tyrosine kinases (RTKs). Preventing the effects of this transactivation could form part of an effective therapy for glioma; however, the mechanism by which the transactivation occurs is unknown. Focusing on the RTK MET, we show that MET transactivation in U87MG human glioma cells in vitro is proportional to EGFRvIII activity and involves MET heterodimerization associated with a focal adhesion kinase (FAK) scaffold. The transactivation of certain other RTKs was, however, independent of FAK. Simultaneously targeting EGFRvIII (with panitumumab) and the transactivated RTKs themselves (with motesanib) in an intracranial mouse model of glioma resulted in significantly greater survival than with either agent alone, indicating that cotargeting these RTKs has potent antitumor efficacy and providing a strategy for treating EGFRvIII-expressing gliomas, which are usually refractory to treatment.

Topics: Analgesics; Animals; Antibodies, Monoclonal; Apoptosis; Brain Neoplasms; Cell Line, Tumor; ErbB Receptors; Female; Focal Adhesion Kinase 1; Glioma; Indoles; Mice, Inbred BALB C; Niacinamide; Oligonucleotides; Panitumumab; Protein Kinase Inhibitors; Proto-Oncogene Proteins c-met; Receptor Protein-Tyrosine Kinases; Signal Transduction; Transcriptional Activation; Xenograft Model Antitumor Assays

Glioblastoma (GBM) is the most frequent and aggressive type of adult brain tumor. Most GBMs express telomerase; a high level of intra-tumoral telomerase activity (TA) is predictive of poor prognosis. Thus, telomerase inhibitors are promising options to treat GBM. These inhibitors increase the response to radiotherapy (RT), in vitro as well as in vivo. Since typical treatments for GBM include RT, our objective was to evaluate the efficiency of Imetelstat (TA inhibitor) combined with RT.. We used a murine orthotopic model of human GBM (N = 8 to11 mice per group) and μMRI imaging to evaluate the efficacy of Imetelstat (delivered by intra-peritoneal injection) alone and combined with RT. Using a clinically established protocol, we demonstrated that Imetelstat significantly: (i) inhibited the TA in the very center of the tumor, (ii) reduced tumor volume as a proportion of TA inhibition, and (iii) increased the response to RT, in terms of tumor volume regression and survival increase.. Imetelstat is currently evaluated in refractory brain tumors in young patients (without RT). Our results support its clinical evaluation combined with RT to treat GBM.

Topics: Animals; Antineoplastic Agents; Brain Neoplasms; Disease Models, Animal; Glioblastoma; Humans; Indoles; Mice; Niacinamide; Oligonucleotides; Radiation Tolerance; Telomerase; Xenograft Model Antitumor Assays

Pediatric ependymomas are highly recurrent tumors resistant to conventional chemotherapy. Telomerase, a ribonucleoprotein critical in permitting limitless replication, has been found to be critically important for the maintenance of tumor-initiating cells (TICs). These TICs are chemoresistant, repopulate the tumor from which they are identified, and are drivers of recurrence in numerous cancers. In this study, telomerase enzymatic activity was directly measured and inhibited to assess the therapeutic potential of targeting telomerase. Telomerase repeat amplification protocol (TRAP) (n = 36) and C-circle assay/telomere FISH/ATRX staining (n = 76) were performed on primary ependymomas to determine the prevalence and prognostic potential of telomerase activity or alternative lengthening of telomeres (ALT) as telomere maintenance mechanisms, respectively. Imetelstat, a phase 2 telomerase inhibitor, was used to elucidate the effect of telomerase inhibition on proliferation and tumorigenicity in established cell lines (BXD-1425EPN, R254), a primary TIC line (E520) and xenograft models of pediatric ependymoma. Over 60 % of pediatric ependymomas were found to rely on telomerase activity to maintain telomeres, while no ependymomas showed evidence of ALT. Children with telomerase-active tumors had reduced 5-year progression-free survival (29 ± 11 vs 64 ± 18 %; p = 0.03) and overall survival (58 ± 12 vs 83 ± 15 %; p = 0.05) rates compared to those with tumors lacking telomerase activity. Imetelstat inhibited proliferation and self-renewal by shortening telomeres and inducing senescence in vitro. In vivo, Imetelstat significantly reduced subcutaneous xenograft growth by 40 % (p = 0.03) and completely abolished the tumorigenicity of pediatric ependymoma TICs in an orthotopic xenograft model. Telomerase inhibition represents a promising therapeutic approach for telomerase-active pediatric ependymomas found to characterize high-risk ependymomas.

Topics: Animals; Brain Neoplasms; Carcinogenesis; Cell Line, Tumor; Cell Proliferation; Child, Preschool; Cohort Studies; Disease-Free Survival; Enzyme Inhibitors; Ependymoma; Female; Humans; Indoles; Mice; Neoplasm Recurrence, Local; Neoplasm Transplantation; Neoplastic Stem Cells; Niacinamide; Oligonucleotides; Telomerase; Telomere