P054: The Kinase CK2 is deregulated and targetable in classical Hodgkin Lymphoma

Introduction: CK2 is a pleiotropic kinase consisting of 2 catalytic (a) and 2 regulatory (b) subunits, usually overexpressed, that sustains cancer signaling cascades through the activation of NF-kB, PI3K and STAT pathways. Considering that NF-kB, STAT and PI3K pathways are key players in Hodgkin lymphoma (HL), it is likely that CK2 might play a role in the pathogenesis of this disease. Methods: Experiments were performed and replicated at least for five times employing 4 HL cell lines (L-428, L-540, KM-H2 and HDLM-1) cultured in RPMI. CK2a, CK2b, RelA-Serine (S)529, RelA, PARP, AKT-S473, AKT, STAT3-S727, STAT3, tubulin, ubiquitin expression levels were evaluated by western blot analysis (WB). Silmitasertib and bortezomib were used as CK2a and proteasome inhibitors. Apoptosis was assessed by Annexin V/Propidium iodide assay and PARP cleavage by WB. Immunohistochemistry (IHC) for CK2a and CK2b was performed on formalin fixed paraffin embedded sections of lymph-nodes from patients with HL, indolent and aggressive NHL. Chou-Talalay methods was used to calculate the combination index (C.I.) of two drugs. Results: By WB and IF we found that all the 4 HL cell lines expressed higher levels of CK2a, but not CK2b, as compared to normal B lymphocytes (p<0.001). By IHC on 35 patients’ lymph-nodes, we confirmed that CK2a but not CK2b was highly expressed in Reed-Sternberg cells. In addition, patients with lower levels of CK2b display a better progression-free survival (p<0.05). The unbalance between a and b subunits was not observed in low or high-grade NHL (p<0.001). Furthermore, we observed that mRNA levels of both CSNK2A and CSNK2B were similar to normal B lymphocytes, and that proteasome inhibition with bortezomib caused the upregulation of CK2b. AKT, RelA and STAT3 were constitutively phosphorylated in HL at their activatory S-residue (S473, S529, and S727 respectively). Treatment of HL cell lines with silmitasertib caused down-regulation of these phospho-serine proteins, time and dose-dependent apoptosis (p<0.0001). In addition, we found that silmitasertib did not modulate surface CD30 and had a synergistic anti-apoptotic effect in combination with monomethyl auristatin E (C.I.<1) Conclusions: We demonstrated that CK2a is overexpressed, active, induced key pro-survival signals in HL, and its inhibition trigger apoptosis. CK2b is likely downregulated due to proteasome degradation. These preliminary data suggest that CK2 might be a new therapeutic target in HL.