SP 6

Clinical application of TMM analysis scheme

The aim of SP6 is to apply a standardized telomere maintenance mechanism (TMM) analysis to patient clinical samples, based on the most informative methods derived from the results of subprojects SP3-SP5. The precise methodology (sequencing, automated imaging, qRT-PCR, etc.) will depend on the number and type of parameters that need to be assessed in order to provide the most relevant information. The development of the TMM analysis scheme will be a highly interactive and iterative process with SP3-SP5, involving continuous input of SP6 into experimental assessment and validation through several development cycles. These data, and complementary information produced in the context of other ongoing sequencing studies, will be used to generate a more rational targeted strategy for clinical applications. We will focus on the correlation of the TMM classification with prognostic impact or prediction of therapy response. Since genetically distinct subgroups are associated with very specific TMM patterns, we anticipate that TMM patterns will be an excellent surrogate marker for biological subgroups and thus clinical parameters such as response to therapy.

Alternative lengthening of telomeres (ALT) is associated with ATRX loss in pediatric glioblastoma. a) cell nuclei with small, localised telomere signals (green), indicating no ALT activity. b) Several large, bright signals can be seen in this cell, which indicates that ALT (telomere recombination) is present. c) Immunohistochemistry for ATRX shows that the protein is completely lost due to mutation in some tumors (inset shows a tumor without ATRX mutation with retained protein expression). d) There is a strong association between the loss of ATRX protein due to mutation and the presence of ALT in pediatric glioblastoma.

It may be assumed that DNA-damaging therapies like radiation or treatment with alkylating agents might promote the selection of ALT (Alternative Lengthening of Telomeres)-positive cells through increased recombination of telomeres, highlighting potential interactions between TMM and treatment response. The TMM of different tumor samples will be classified for a subsequent correlation with clinical data, in order to make better predictions about prognosis and for the choice of therapy based on tumor-biological markers.

An overview of telomere maintenance mechanisms. Mechanisms by which cells can activate telomere maintenance include i) mutation of the TERT promoter and ii) gene amplification (both of which lead to elevated expression of TERT) or iii) alternative lengthening of telomeres (ALT), in which recombination at chromosome ends introduces complex structures of canonical (TTAGGG) and non-canonical telomere repeats.

Keywords: Pediatric; cancer; brain; glioblastoma; medulloblastoma; histone; telomere