grn163 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

The blood-brain barrier is a substantial obstacle for delivering anticancer agents to brain tumors, and new strategies for bypassing it are greatly needed for brain-tumor therapy. Intranasal delivery provides a practical, noninvasive method for delivering therapeutic agents to the brain and could provide an alternative to intravenous injection and convection-enhanced delivery. We treated rats bearing intracerebral human tumor xenografts intranasally with GRN163, an oligonucleotide N3'-->P5'thio-phosphoramidate telomerase inhibitor. 3'-Fuorescein isothiocyanate (FITC)-labeled GRN163 was administered intranasally every 2 min as 6 microl drops into alternating sides of the nasal cavity over 22 min. FITC-labeled GRN163 was present in tumor cells at all time points studied, and accumulation of GRN163 peaked at 4 h after delivery. Moreover, GRN163 delivered intranasally, daily for 12 days, significantly prolonged the median survival from 35 days in the control group to 75.5 days in the GRN163-treated group. Thus, intranasal delivery of GRN163 readily bypassed the blood-brain barrier, exhibited favorable tumor uptake, and inhibited tumor growth, leading to a prolonged lifespan for treated rats compared to controls. This delivery approach appears to kill tumor cells selectively, and no toxic effects were noted in normal brain tissue. These data support further development of intranasal delivery of tumor-specific therapeutic agents for brain tumor patients.

Topics: Administration, Intranasal; Animals; Brain Neoplasms; Cell Line, Tumor; Dose-Response Relationship, Drug; Enzyme Inhibitors; Glioma; Humans; Male; Oligonucleotides; Rats; Rats, Nude; Telomerase; Xenograft Model Antitumor Assays

Telomerase is a ribonucleoprotein complex that elongates telomeric DNA and appears to play an important role in cellular immortalization of cancers. Because telomerase is expressed in the vast majority of malignant gliomas but not in normal brain tissues, it is a logical target for gliomaspecific therapy. The telomerase inhibitor GRN163, a 13-mer oligonucleotide N3'-->P5' thio-phosphoramidate (Geron Corporation, Menlo Park, Calif.), is complementary to the template region of the human telomerase RNA subunit hTR. When athymic mice bearing U-251 MG human brain tumor xenografts in their flanks were treated intratumorally with GRN163, a significant growth delay in tumor size was observed (P < 0.01 in all groups) as compared to the tumor size in mice receiving a mismatched oligonucleotide or the carrier alone. We also investigated biodistribution of the drug in vivo in an intracerebral rat brain-tumor model. Fluorescein-labeled GRN163 was loaded into an osmotic minipump and infused directly into U-251 MG brain tumors over 7 days. Examination of the brains revealed that GRN163 was present in tumor cells at all time points studied. When GRN163 was infused into intracerebral U-251 MG tumors shortly after their implantation, it prevented their establishment and growth. Lastly, when rats with larger intracerebral tumors were treated with the inhibitor, GRN163 increased animal survival times. Our results demonstrate that the antitelomerase agent GRN163 inhibits growth of glioblastoma in vivo, exhibits favorable intracerebral tumor uptake properties, and prevents the growth of intracerebral tumors. These findings support further development of this compound as a potential anticancer agent.

Topics: Animals; Antineoplastic Agents; Brain Neoplasms; Enzyme Inhibitors; Female; Glioblastoma; Humans; Male; Mice; Mice, Inbred BALB C; Mice, Nude; Oligonucleotides; Rats; Rats, Nude; Telomerase; Xenograft Model Antitumor Assays