Development of Blood Plasma cfDNA Assay to Detect the Alternative Lengthening of Telomeres (ALT) Phenotype in Pediatric High-Grade Glioma Patients

Telomeres are the protective repeats of DNA sequences and proteins at the ends of chromosomes. (1) Cancer cells rely on the extension and maintenance of telomere length to avoid cell death. (1) About 85-90% of cancers use telomerase to maintain telomere length while 10-15% of cancers utilize the alternative lengthening of telomeres (ALT) mechanism. (2-3) ALT cancers are known to have worse outcomes and increased resistance to therapies. (3) Pediatric high-grade gliomas (HGG) are aggressive brain tumors in children About 40% of pediatric HGG are  ALT-positive. (4-5) A known biomarker of ALT in tumor tissue is the telomeric DNA C-circle assay. (8) C-circles have been found in tumors and serum of ALT patients. (9-10) We have modified the C-circle assay to work with cell-free DNA (cfDNA) from plasma and we have observed a strongly positive C-circle assay when testing cfDNA from plasma of  3 pediatric HGG patients with known ATRX inactivating mutations (indicating the tumors were ALT-positive). (12) Collecting plasma, a component of blood, from pediatric patients is less invasive than a tumor biopsy. (7) Plasma samples provided by CBTN will be used to validate the detection of C-Circles in cfDNA from plasma as a biomarker for ALT-positive pediatric high-grade gliomas. As therapies against ALT pediatric high-grade glioma are being developed, the novel blood-based C-Circle assay may better guide treatment options for patients and could potentially provide an assay to monitor therapy response and tumor recurrence.