Venetoclax rewires Notch signaling to drive resistance in North American adult T-cell leukemia/lymphoma

Purpose: North American Adult T-cell leukemia/lymphoma (NA-ATLL) is an aggressive HTLV-1-associated T-cell malignancy with median survival of less than 2 years. NA-ATLL cases are distinct from those in endemic regions like Japan and exhibit a correlation with poor prognosis and therapeutic resistance. Interferon-alpha/Zidovudine, when combined with other chemotherapy regimens, has shown efficacy in acute and chronic malignancies. We previously showed that Venetoclax induces mitochondrial apoptosis in NA-ATLL; however, resistance inevitably emerges despite initial sensitivity. As limited epidemiologic data delay ATLL research, our center accomplishes one of the nation's first cohorts, with ~150 cases annually, predominantly among Caribbean-descent patients. In this study, the use of Venetoclax-treated patient-derived NA-ATLL cells led to prominent Notch pathway activation, highlighting a key adaptive resistance mechanism. Methods: Preclinically, patient-derived NA-ATLL cell lines (Pt-4a, 5a, 6a, 15a) along with Japanese patient-derived ATLL cell lines [ATL43Tb(−)] (J-ATLL) were treated with Venetoclax. RNA-seq identified adaptive survival pathways. Clinically, several patients with aggressive subtypes of NA-ATLL (Shimoyama types: lymphomatous and acute) were treated with Venetoclax-based treatment at our Institution. Results: Preclinical: Both NA-ATLL and J-ATLL cells responded heterogeneously to Venetoclax. In responsive lines, Venetoclax-treated cells enhanced apoptotic priming with caspase-3/PARP-1 activation, and reduced HTLV-1 HBZ and Tax expression whereas non-responders showed minimal effect, while ferroptosis was excluded. BH3 profiling confirmed NA-ATLL has unique apoptotic priming compared to J-ATLL. RNA-seq revealed robust induction of NOTCH1/2, DLL1/4, JAG1/2, and canonical targets HES1. Noteworthy, Venetoclax also upregulated the Fring e glycosylation genes (LFNG, MFNG, RFNG), which augment Notch receptor responsiveness, indicating a glycan-optimized Notch activation program that supports survival under BCL-2 inhibition. Clinical: NA-ATLL patients received Venetoclax-based combinations across multiple therapy lines. Mutation profiling (TP53, NOTCH1) by NGS was correlated with outcomes. Notably, the Venetoclax-based regimes (PEG-IFN + Biktarvy + VEN) produced durable complete responses, with patients remaining alive beyond 95 and 234 days at data cutoff. Conclusion: Venetoclax shows a significant effect in NA-ATLL both at preclinical and clinical settings, but emerging adaptive Notch signaling activation represents a crucial resistance mechanism. Our study supports evaluating Notch-directed agents (gamma-secretase inhibitors/Nirogacestat) in combination with Venetoclax to overcome therapeutic resistance and improve outcomes in NA-ATLL.