Fig. 1: HDAC inhibitor treatment before tumor onset significantly restricts NPM::ALK tumor development in the ALCL mouse model.

A Bar plots depicting the percentages of HDAC1 (left) or HDAC2 (right) staining intensities (weak, strong) on tissue microarrays (TMAs) containing specified numbers of ALK+ ALCL, ALK− ALCL, PTCL, and AITL patient samples, evaluated by immunohistochemistry (IHC). The right panel displays representative microscopic images of IHC stainings from the TMAs, as described above (scale bar representing 50 μm). Red cytoplasmic/membrane staining represents CD30/CD3 expression, while brown nuclear staining represents HDAC1/HDAC2 expression. Tissues were stained with the corresponding antibodies and counterstained with hematoxylin (blue). B UMAP plots of scRNA-seq data from CD45⁺ cells from a primary lymph node of an ALK+ ALCL patient. The left plot shows cells in a dimensional reduction embedding, color-coded according to the different annotated cell types, the middle and right plots show levels of normalized gene expression for HDAC1 and HDAC2. C Violin plots depicting normalized expression of HDAC1 (upper) and HDAC2 (lower) in color-coded cell types according to (B). D Dose-response curves of human ALK+ ALCL cell lines, derived from three individual PDX models [30], to Entinostat. Cells were treated for 48 h with a drug concentration range of 0.01 to 100 µM in technical replicates (n technical = 3). Each experiment was repeated 3 times (n = 3). Dose-response curves were generated with GraphPad Prism 10. Graphs show the mean with standard deviation (SD) for n = 3 replicates. E HDAC activity levels in thymi of WT mice after 2 weeks of treatment with Entinostat (n = 1 biological replicate for vehicle treatment and 50 μg/g/day treatment, n = 2 biological replicates for 5 μg/g/day, 10 μg/g/day and 20 μg/g/day treatment, n = 2 technical replicates for each biological replicate). Activity levels are measured as counts per minute beta (CPMB). GraphPad Prism version 8.4.3 was utilized for analysis. F Thymic weight of WT mice in biological replicates treated for 2 weeks with vehicle (n = 5), 5 μg/g/day Entinostat (n = 5), 10 μg/g/day Entinostat (n = 6), 20 μg/g/day Entinostat (n = 4) and 50 μg/g/day Entinostat (n = 2). The mean with standard deviation (SD) was plotted using GraphPad Prism version 8.4.3. Statistical significance is indicated by ** for p < 0.01 and **** for p < 0.0001. G Thymic weight of WT mice in biological replicates treated for 2 weeks with vehicle (n = 5) or 10 μg/g/day Entinostat (n = 5) and then recovered for an additional 2 weeks. Mean with standard deviation (SD) was plotted using GraphPad Prism version 8.4.3. “ns” indicates not significant. H Kaplan–Meier survival analysis of NPM::ALK mice (n = 6, blue line) and NPM::ALK mice treated with 10 μg/g/day Entinostat (n = 5, green line) in biological replicates. The median survival of different genotypes was compared using the Log-rank (Mantel–Cox) test with GraphPad Prism version 8.4.3. Statistical significance is denoted by ** for p = 0.0042. I Representative microscopic images of Ki67 and CC3 expression based on IHC staining of thymic sections from untreated WT mice, WT mice treated with 10 μg/g/day Entinostat, or NPM::ALK mice treated with 10 μg/g/day Entinostat mice. Thymi were excised immediately after the 2-week treatment period. Sections were counterstained with hematoxylin (blue). The scale bar represents 50 μm.