Abstract 705: A cell-based screening assay to identify agents interfering protein-protein interaction of MAPKAPK2 and OCT4
Authors: Yang Inhyoung , Wei Sung-Jen , Mohiuddin Ismail , Martinez Gloria M. , Kang Min H. 
Published: September 2020

Abstract
c-MYC overexpression plays an important role in tumorigenesis as well as in the progression of tumors. Historically, direct targeting strategies have been challenging due to c-MYC being a transcription factor. Our observation demonstrated that MAPKAPK2 as one of the two major protein kinases involved in binding and phosphorylating OCT4 at serine 111 residue to induce c-MYC activation in progressive disease neuroblastoma. In targeting this novel pathway of c-MYC activation, we considered two options: direct inhibition of MAPKAPK2 or inhibition of MAPKAPK2-OCT4 protein-protein interaction. Given the limitations of direct targeting kinases, namely resistance and off-target effect, we pursued the inhibition of the protein-protein interaction. The purpose of this study is to introduce a novel cell-based assay for compound screening and validation steps to identify compounds that inhibit OCT4-MAPKAPK2 interaction. First, OCT4 (NTD and POUs: the domains critical for c-MYC activation) and MAPKAPK2 were exogenously expressed by a single vector with CMV promoter using a lentiviral vector system in NCI-H82, a small cell lung cancer cell line. Upon the optimization of the assay, we screened approximately 100,000 compounds to identify “hits” by statistically analyzing the reduction in luminescence. Seventy-six compounds were found to inhibit the interaction of MAPKAPK2-OCT4. Subsequently, we have used a two-step hit validation for the 76 compounds: 1) the decrease in pOCT4S111 expression along with the reduction in c-MYC expression by immunoblotting: 2) and the inhibition of binding between MAPKAPK2 and OCT4 by co-immunoprecipitation. The validation step further narrowed down the hits to three compounds that reduced the phosphorylation of OCT4 at S111 and inhibited the MAPKAPK2-OCT4 interaction. To verify the compounds interfering the MAPKAPK2-OCT4 interaction, we used in vitro assay using recombinant human MAPKAPK2 kinase and OCT4 and all three compounds inhibited phosphorylation of OCT4S111. These all compounds also tested minimally affected ATP-dependent MAPKAPK2 kinase relative to the known MAPKAPK2 inhibitor (PF3644022). In conclusion, our screening assay and validation experiments was successfully implemented in identifying hits and the validation step confirmed three novel compounds that demonstrated: 1) impairment of MAPKAPK2-mediated phosphorylation of OCT4; and 2) inhibition of the MAPKAPK2-OCT4 kinase-substrate interaction. These compounds may be further optimized to minimize systemic toxicities and improve the anti-cancer activity for the treatment of neuroblastoma or small cell lung cancer with high c-MYC expression.
Citation Format: Inhyoung Yang, Sung-Jen Wei, Ismail Mohiuddin, Gloria M. Martinez, Min H. Kang. A cell-based screening assay to identify agents interfering protein-protein interaction of MAPKAPK2 and OCT4 [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 705.