ZCL-082, a boron-containing compound, induces apoptosis of non-Hodgkin's lymphoma via targeting p90 ribosomal S6 kinase 1/NF-κB signaling pathway.

Introduction: Despite the rapid progress in the diagnosis and treatment, the prognosis of some types of non-Hodgkin's lymphoma (NHL), especially those with double-hit or double-expressor genotypes, remains poor. Novel targets and compounds are needed to improve the prognosis of NHL.

Methods: We investigated the effect of ZCL-082, a novel boron-containing compound with anti-proliferating activity against ovarian cancer cells, on NHL cells and human peripheral blood mononuclear cells by CCK-8 assay, Annexin V/PI double staining assay, RH123/PI double staining, Western blot, and immunohistochemistry. NF-κB pathway activity was analyzed using luciferase reporter gene assay and RT-PCR. The location of p65 was detected by immunofluorescence and nuclear/cytoplasmic fractionation assay. Immunoprecipitation and chromatin immunoprecipitation assays were used to detect the binding between p65 and p300. CETSA and molecular docking assay were carried out to test the interaction between ZCL-082 and p90 ribosomal S6 kinase 1 (RSK1). Kinase reaction was conducted to examine the inhibition of RSK1 kinase activity by ZCL-082.

Results: We found that ZCL-082 can induce the apoptosis of various NHL cell lines in vitro and in vivo. ZCL-082 significantly inhibits TNFα- or LPS-induced NF-κB activation without disturbing TNFα-induced IκBα degradation or the nuclear translocation and DNA-binding ability of p65. However, ZCL-082 markedly suppresses the phosphorylation of p65 on Ser536 and the interaction between p65 and p300. The overexpression of the phosphomimetic mutant of p65 at Ser536 partially abrogates ZCL-082-induced cell death. We further found that ZCL-082 directly binds to and inhibits the activity of RSK1. RSK1 can phosphorylate RelA/p65 on Ser536 and its overexpression is associated with the poor prognosis of lymphoma. The overexpression of RSK1 partially rescues ZCL-082-induced cell death. Molecular docking studies show that ZCL-082 fits well with the N-terminal kinase domain of RSK1. Furthermore, the combination of ZCL-082 and BCL-2 inhibitor ABT-199 has a synergistic apoptosis-inducing effect against double-hit lymphoma cell line OCI-Ly10.

Discussion: We found that ZCL-082 is a highly promising anti-lymphoma compound that targets RSK1 and interferes with the RSK1/NF-κB signaling pathway. The combination of ZCL-082 with BCL-2 inhibitor may represent a novel strategy to improve the outcome of double-hit or double-expressor lymphoma.