BCL-2 inhibition in North American adult T-cell leukemia/lymphoma: Preclinical insights and early clinical outcomes

Abstract

Abstract Background: North AmericanAdult T-cell leukemia/lymphoma (NA ATLL) is an aggressive malignancy of mature CD4⁺ T cells associated with the human T-cell leukemia virus type 1 (HTLV-1). NA ATLL has a higher frequency of TP53 mutations, BCL2 overexpression, and worse overall survival ranging from six months to 2 years. NA ATLL cases are distinct from those in endemic regions like Japan and exhibit a correlation with poor prognosis and therapeutic resistance. Major challenge of ATLL research is the limited epidemiological and clinical data available. Based on our epidemiologic study, we treats more ATLL patients than most U.S. centers and first to report ~150 case annually in immigrants of Caribbean descent. BCL-2 inhibition with Venetoclax has demonstrated activity in numerous lymphoid malignancies. Hence, we evaluated the preclinical efficacy of BCL-2 inhibitors in NA ATLL cells and explored clinical outcomes in chemotherapy-refractory ATLL patients. Methods Preclinical: A panel of well-characterized North American patient-derived ATLL cell lines [Pt-4a, Pt-5a, Pt-6a, Pt-15a] along with Japanese patient-derived ATLL cell lines [ATL43T (−)] (J-ATLL) were used to evaluate the efficacy of different BCL-2 inhibitors, including Venetoclax, Sonrotoclax, and Lisaftoclax. Mitochondrial membrane potential (MOMP) and key HTLV-1 viral proteins (HBZ, Tax) were evaluated to understand the mechanism of action and potential viral involvement. BH3 profiling and Bulk RNA sequencing were performed to confirm the apoptotic dependency and key signaling pathways involved in both NA-ATLL and J-ATLL models. Clinical Immunohistochemical staining of paraffin-embedded lymph node biopsy tissue from NA ATLL patient demonstrated strong BCL-2 expression, supporting the dependency of the ATLL cells on BCL-2 for survival. Nine 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 showed sensitivity to BCL-2 inhibitors (Venetoclax, Sonrotoclax, and Lisaftoclax) with IC50 values ranging from 0.5 to 10µM. Venetoclax induced apoptotic cell death, as evidenced by PARP cleavage and Caspase-3 cleavage, and significantly reduced the expression of HTLV-1 HBZ and HTLV-1 Tax proteins. Moreover, Venetoclax triggers mitochondrial outer membrane permeabilization (MOMP), leading to the release of pro-apoptotic factors and activation of the intrinsic apoptotic pathway. Additionally, BH3 profiling confirmed dependency on BCL-2, MCL-1, and BCL-XL for cell survival, suggesting a heterogeneous apoptotic landscape. Bulk RNA-seq analysis revealed Venetoclax promote mitochondrial reprogramming and transcriptional regulation in NA-ATLL compared to the J-ATLL model. Notably, NA ATLL has distinct subpopulations (1,215 DEGs), which have unique differentially expressed genes compared to the J-ATLL (300 DEGs), and only ~3% (40/1,555) of DEGs are shared across both populations, underscoring a population-specific transcriptional response. Clinical NA ATLL Patients received combinations including Venetoclax across different lines of therapy. Several mutation profiles such as TP53 and NOTCH1, were assessed using next-generation sequencing (NGS). Overall survival (OS) and progression-free survival (PFS) outcomes were correlated with molecular features. Overall response rate was 77% with complete responses observed in 22% of patients. Partial responses in 55% and progressive disease in 23% of cases. Remarkably, complete responses were observed in patients receiving Venetoclax-based triplets (PEG-IFN, Biktarvy, VEN), with survival >95 and >234 days (both alive at data cutoff). Conclusion Both North American and Japanese ATLL cell lines have shown preclinical sensitivity to BCL-2 inhibition using Venetoclax and other emerging inhibitors. Distinct molecular dependencies identified through BH3 profiling and transcriptional analyses. Venetoclax induces mitochondrial apoptosis and downregulates key HTLV-1 viral oncogenes, targeting both survival pathways and viral factors. Clinically, Venetoclax-based regimens show substantial responses in relapsed/refractory NA ATLL patients, particularly when combined with PEG-IFN and antiretrovirals (e.g., Biktarvy). Our combined preclinical findings and early clinical experience support the incorporation of Venetoclax and other BCL-2 inhibitors into therapeutic regimens of chemotherapy-refractory ATLL cases.