PP2A activation as a new therapeutic strategy in neuroblastoma: Making sense out of senescence.

Abstract

10055 Background: Neuroblastoma (NBL) is the most common extracranial solid tumor in children, accounting for 15% of all pediatric cancer deaths. The five-year survival rate for children with high-risk disease is less than 50%, with the primary reasons for mortality being refractory and relapsed disease. One hypothesis for the poor response to therapy and propensity for recurrent disease in high-risk patients is treatment-induced senescence (TIS). Protein phosphatase 2A (PP2A) is a known tumor suppressor that is downregulated in NBL. PP2A activation has been shown to reverse cellular senescence in non-cancerous pathologies, therefore we hypothesized that reactivation of PP2A using novel small molecule activators would function as a novel senotherapeutic in NBL. Methods: We employed MYCNamplified, SK-N-BE(2), and non-amplified, SK-N-AS, established human NBL cell lines. Topotecan, a common NBL chemotherapeutic, known to induce senescence, and ATUX-1215, a small molecule PP2A activator, were utilized. NBL cells were treated with topotecan and ATUX-1215 alone, as well as in combination. Colorimetric assays detected cell viability and proliferation. Immunoblotting identified proteins of interest including γ-H2AX and CCL2. TIS was detected by S-β galactosidase (Sβgal) assay. Results: We found increased expression of the senescence marker, histone γ-H2AX, and increased Sβgal-positive tumor cells supporting the ability of topotecan to generate TIS in NBL. Following treatment with PP2A activator in combination with topotecan, markers of TIS are decreased in both MYCN amplified and non-amplified NBL cells. Further, and importantly, PP2A activation reversed the effects of topotecan TIS and acted in a synergistic fashion to decrease NBL cell viability. Conclusions: Activation of PP2A with a novel small molecule ameliorates topotecan-induced TIS in NBL cells irrespective of MYCN status. These results are promising, providing a potential novel therapeutic adjunct to children who are most in need of innovative interventions.