IAP dependency of T-cell prolymphocytic leukemia identified by high-throughput drug screening.

T-cell prolymphocytic leukemia (T-PLL) is an aggressive lymphoid malignancy with limited treatment options. To discover new treatment targets for T-PLL, we performed high-throughput drug sensitivity screening on 30 primary patient samples ex-vivo. After screening over 2'800 unique compounds, we found T-PLL to be more resistant to most drug classes, including chemotherapeutics, compared to other blood cancers. Furthermore, we discovered previously not reported vulnerabilities of T-PLL. T-PLL cells exhibited a particular sensitivity to drugs targeting autophagy (thapsigargin, bafilomycin A1), nuclear export (selinexor), and inhibitor of apoptosis proteins (IAPs) (birinapant), sensitivities that were also shared by other T-cell malignancies. Through bulk and single-cell RNA-Sequencing we found these compounds to activate the toll-like-receptor (TLR) (bafilomycin A1), p53 (selinexor), and TNF-ɑ/NFκB signaling pathways (birinapant) in T-PLL cells. Focussing on birinapant for its potential in drug repurposing, we uncovered that IAP inhibitor-induced cell death was primarily necroptotic and dependent on TNF-ɑ. Through spectral flow cytometry we confirmed the absence of cleaved caspase-3 in IAP inhibitor treated T-PLL cells and show that IAP inhibition reduces the proliferation of T-PLL cells stimulated ex-vivo, while showing only a limited effect on non-malignant T-cells. In summary, our study maps the drug sensitivity of T-PLL across a broad range of targets and identifies new therapeutic approaches for T-PLL by targeting IAPs, XPO1 and autophagy, highlighting potential candidates for drug repurposing and novel treatment strategies.