Abstract 6001: Repurposing dihydroergotamine mesylate as a potential MCL-1 inhibitor and its antitumor effect in pancreatic cancer cells

Abstract Background: Myeloid cell leukemia 1 (MCL-1) is an anti-apoptotic member of the BCL-2 protein family which is involved in intrinsic (mitochondrial) pathway of apoptosis and is deregulated in several cancers. Current MCL-1 specific inhibitors have limitations in terms of efficiency, tolerability, and off-target effects and challenges associated with shallow binding groove of MCL-1. In this study, dihydroergotamine mesylate (DHE), an approved anti-migraine drug, was found as a potential ligand of the MCL-1 BH3-binding pocket and was further evaluated for its potential MCL-1 inhibition and effect on pancreatic cancer cells. Methods: PubChem Database was used for library preparation and virtual screening (OpenBabel and AutoDock Vina). The 55 crystal structures available for MCL-1 in Protein Data Bank (PDB) were clustered using principal component analysis with Bio3D R-package to select representative PDBs for further screening. Consensus voting and k-means clustering was used to shortlist compounds for Molecular dynamics (MD) simulations. MD simulations (100 nanoseconds) by GROMACS were employed to measure stability of ligands in MCL-1 binding pocket. DHE efficacy on cell proliferation was evaluated with MTS and clonogenic assays and on apoptosis using the FITC/Annexin V flow cytometry assay in MiaPaCa-2 and PANC-1 pancreatic cancer cell lines. Effect of DHE treatment on MCL-1 gene and protein expression was analyzed using qRT-PCR and western blotting, respectively. Results: Computational screening identified DHE (PubChem ID: 12308974) as a top hit exhibiting consistent interactions within the MCL-1 BH3-binding pocket. Notably, DHE displayed stable RMSD and formed four hydrogen bonds throughout MD simulations. In vitro results showed that DHE significantly reduced viability of MiaPaCa-2 and PANC-1 pancreatic cancer cells with IC50 values of 31 μM and 47 μM, respectively. DHE significantly (P0. 001) suppressed colony formation by pancreatic cancer cells in a dose-dependent (10μM, 20μM, and 40μM) manner. The percentage of Annexin V-positive and Propidium iodide-negative fraction in MiaPaCa-2 cells treated with DHE also increased in a dose-dependent manner. DHE did not have significant effect on MCL-1 mRNA expression. However, western blotting demonstrated MCL-1 protein levels were significantly reduced in both pancreatic cancer cell lines upon DHE treatment. Conclusion: Our findings showed DHE suppresses the pancreatic cancer cells viability and proliferation, and significantly increased early apoptotic cells. DHE treatment had no effect on MCL-1 at the transcription level but significantly reduced the protein, suggesting posttranslational modifications, and thus future mechanism of action studies is required. The present study reports that the anti-migraine drug DHE might be a novel therapeutic agent for pancreatic cancer and needs to be explored further. Citation Format: Pooja Mittal, Jae Ho Lo, Shivani Soni, Francesca Battaglin, Shradheya RR Gupta, Lesly Torres-Gonzalez, Yan Yang, Sandra Algaze, Priya Jayachandran, Karam Ashouri, Alexandra Wong, Wu Zhang, Jian Yu, Lin Zhang, Joshua Millstein, Indrakant Kumar Singh, Heinz Josef Lenz. Repurposing dihydroergotamine mesylate as a potential MCL-1 inhibitor and its antitumor effect in pancreatic cancer cells abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 6001.