Targeting signaling rewiring and resistant subpopulations in Philadelphia Chromosome-like Acute Lymphoblastic Leukemia [Bulk ATAC-seq]

Philadelphia chromosome-like acute lymphoblastic leukemia (Ph-like ALL) is a common high-risk leukemia subtype defined by a kinase-activated gene expression pattern and chemoresistance, with low overall survival rates in both children and adults. Clinical responses of patients with Ph-like ALL to tyrosine kinase inhibitor (TKI)-based therapies are incomplete, suggesting partial oncogene addiction and highlighting the need to elucidate alternative biologic dependencies to cure patients. Herein, we report integrated bulk and single-cell multiomics studies of Ph-like ALL cells treated in vitro and in vivo with targeted agents to comprehensively define signaling adaptations and resistant subpopulations. Characterizing residual/resistant human ALL cells harvested from murine spleens revealed transcriptional regulatory network changes and kinase signaling adaptations. We identified key transcription factors including c-MYC and AP1 that mediate transcriptional rewiring associated with therapeutic escape, and demonstrate a specific MYC dependency in Ph-like ALL cells. We found a sub-population of leukemia blasts that have high senescence-associated stem cell-like features that is effectively eradicated only with combined STAT and BCL-2 inhibition. This is clinically significant since both conventional chemotherapy and ruxolitinib are ineffective against senescent stem-like blasts, which may mediate therapeutic tolerance and repopulate relapse. Our findings demonstrate that systems level discovery of key oncogenic dependencies and escape pathways can be exploited for co-targeting or sequential treatment to optimally eradicate blasts and cure this high-risk leukemia subtype. Overall design: Bulk ATAC-seq was performed on Ph-like ALL PDX models treated with control or ruxolitinib at 5 timepoints (0, 3, 7, 28, 56 days).