Use Of Non-Ablative Dose Of Radiation To Enhance Delivery Of Unmodified Morpholino Oligonucleotides In A Brain Tumor Model To Silence MGMT And Enhance The Efficacy Of Chemo-Radiation (4281)

Objective: Non-ablative Ionizing radiation ( XRT) is well known to alter neuro-vascular unit (NVU) permeability. We evaluate the use of XRT to enhance delivery of intravenously administered Morpholino Oligonucleotides designed to silence O6-methylguanine DNA methyltransferase (MGMT) in a MGMT expressing human derived brain tumor xenograft model. Background: MGMT, a key DNA repair enzyme is associated with resistance to temozolomide (TMZ). We have previously reported the use of a non-ablative dose of ionizing radiation (XRT) to prime human cancer cells to enhance the uptake of unmodified anti-MGMT morpholino oligonucleotides (AMONs) to achieve statistically significant reduction in the in-vitro proliferation index and cell viability with a single dose of AMONs and TMZ. Our prior work has demonstrated that this is by enlarge mediated by up regulation of physiologic endocytosis after XRT. Design/Methods: Intracranial tumor (MGMT expressing human derived H460 non-small cell lung cancer, n=12) bearing athymic nude rats received a single dose of cranial radiation (2Gy) with oral TMZ for 4 consecutive days starting on the day of XRT. In addition, six animals were randomly selected to receive AMON (10.5mg/kg) 24 hrs after XRT, the remaining served as controls. All animals were euthanized and brains harvested 7 days after XRT and tumor volumes measured by immunoblotting. This experiments was repeated in human derived D283 medulloblastoma xenografts (n=12) Results: A 60% (p=0.034) reduction in MGMT expression was noted in brain tumors treated with XRT and iv AMONs. Although not significant, a 40% reduction in tumors volumes were noted in the animals treated with a single dose of AMONs and chemo-radiation. Conclusions: We demonstrate the first use of XRT to guide and enhance delivery of AMONS to brain tumors. In this proof of concept study, silencing MGMT enhances the toxicity of XRT and TMZ. This approach warrants further evaluation and may improve outcomes in patients with tumors with un-methylated MGMT. Disclosure: Dr. Ambady has nothing to disclose. Dr. Wu has nothing to disclose. Dr. Walker has nothing to disclose. Dr. Kersch has nothing to disclose. Dr. Morris has nothing to disclose. Dr. Bills has nothing to disclose. Dr. Holland has nothing to disclose. Dr. Pagel has nothing to disclose. Dr. Muldoon has nothing to disclose. Dr. Neuwelt has nothing to disclose.