Identification of novel aptamers for the diagnosis of oligodendroglioma

Abstract

Oligodendroglioma has a favourable prognosis compared to other gliomas as it is responsive to PCV treatment. Oligodendroglioma is initially diagnosed using histopathology and is then classified as oligodendroglioma (IDH mutant and 1p/19q co-deleted). Diagnosis currently requires the use of molecular testing that is costly and delays diagnosis as there are no reliable histological markers. The overall aim of this project was to identify aptamers that could specifically bind to oligodendroglioma tissue. In order to identify aptamers that could be used diagnostically, multiple patient samples were used to take into account the heterogeneous nature of tumours. To ensure that any identified aptamers were specific to oligodendroglioma, tissue from other grades of glioma and non-tumour tissue were used in the counter-selection. To optimise the method, selection was performed initially on cell lines, targeted towards U87MG (grade IV glioblastoma), using MCF-7 (breast cancer), 1321N1 (grade II astrocytoma), and SVGp12 (foetal astrocytes) in the counter-selection. It was found that pooling of the counter-selections is an efficient method for the selection of specific aptamers. Mouse tissue was utilised to confirm that pooling of counter-selection samples could be used to identify target specific aptamers. A tissue microarray (TMA) containing mouse tissue was constructed to demonstrate that selective aptamers can be identified using tissue in a TMA. Antigen retrieval was found to be an unnecessary step in identifying target specific aptamers. Human patient tissue obtained from Brain Tumour North West was used to construct TMAs for each tumour type (oligodendroglioma, grade II astrocytoma, grade III astrocytoma, glioblastoma, and non-tumour) containing cores of patient tissue. The TMAs were used in the selection process to identify aptamers specific to oligodendroglioma. A pool of aptamers was identified, some with high similarity, but their ability to bind to oligodendroglioma tissue is still to be determined.