CRISPR-based interrogation of alternative lengthening of telomeres: mapping dependencies, stress-buffering pathways,...

Alternative lengthening of telomeres (ALT) is a telomerase-independent telomere maintenance mechanism that supports the growth of approximately 5-10% of human tumors and represents an attractive but insufficiently explored therapeutic target. CRISPR-based functional genomics has emerged as a powerful approach to systematically interrogate ALT biology and identify genetic dependencies associated with the ALT state. In this Review, we discuss the CRISPR-based strategies applied to ALT, including hypothesis-driven targeted loss-of-function screens, phenotype-driven optical screens, in silico mining of large-scale dependency datasets, and genome-wide screens in ALT-adjacent states. Across these approaches, recurrent dependencies converge on pathways mediating replication stress buffering, DNA repair, and telomere maintenance, including FANCM, SMARCAL1, and SUB1. Collectively, these findings support a model in which ALT-positive cells rely not on a unique ALT-specific factor, but rather on stress-buffering mechanisms that prevent chronic telomeric dysfunction from triggering replication catastrophe and cell death, highlighting these pathways as promising candidates for further therapeutic investigation.