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Abstract Maintenance of telomeres in the absence of telomerase is known as Alternative Lengthening of Telomeres (ALT), which is prevalent in 10-15% of all cancers. Tessellate BIO targets ALT mechanisms to drive cell death by synthetic lethality. To identify patients who will benefit from our therapy, we are developing companion diagnostics (CDx). In this study, established hallmarks of ALT are investigated as CDx target in tissue-derived samples. In fresh and FFPE tumor tissue, presence and abundance of different ALT hallmarks were measured, including RPA phosphorylation, C-circles and telomeric single stranded DNA. While not all markers pass the stringent requirements of a CDx, C-circles prove to be a reliable biomarker. To measure C-circles, a robust and scalable PCR-based protocol was developed, facilitating easy implementation in the clinic. Utilizing this protocol, C-circles were successfully measured across different tissue types. Further, the protocol allowed for C-circle quantification in cell lines, showcasing its utility across matrices of varying complexity. Successful development of the C-circle CDx enables patients selection based on ALT mechanisms herewith improving the response rate of targeted therapies in patients and accelerating new discoveries in the ALT space. Citation Format: Ganesh Kadamur, Dalia Tarantino, Freddie Grogono, Patrick Von Morgen, Salvina Tammaccaro, Diana Zatreanu, Donata Federici Canova, Jana Wolf, Corne van den Kieboom, Katie Chapman, Joris Schuurmans, Jurgen Moll. Companion Diagnostics (CDx) to identify hallmarks of Alternative Lengthening of Telomeres (ALT) abstract. In: Proceedings of the AACR Special Conference in Cancer Research: Expanding and Translating Cancer Synthetic Vulnerabilities; 2024 Jun 10-13; Montreal, Quebec, Canada. Philadelphia (PA): AACR; Mol Cancer Ther 2024;23(6 Suppl):Abstract nr A016.
Kadamur et al. (Mon,) studied this question.