Abstract A138: Profiling of harmine and select analogs as differential inhibitors of DYRK1A and monoamine oxidase A: Exploring the potential for anti-cancer efficacy and minimizing off-target activity

DYRK1A (dual-specificity tyrosine phosphorylation-regulated kinase 1a) phosphorylates a number of substrates on serine/threonine residues, including tau, amyloid precursor protein, DREAM, and GLI1. DYRK1A is expressed in both the adult and fetal brain, plays a key role in neurodevelopment and is critical for cell proliferation and differentiation in the brain. DYRK1A has been extensively studied as a drug target for Down syndrome (DS) and neurodegenerative diseases such as Alzheimer’s and Parkinson’s. DYRK1A has also been proposed as a therapeutic target for cancer, e.g., DYRK1A is highly expressed in glioma, an aggressive brain tumor that is resistant to chemo- and radio-therapy, and in a subset of glioblastoma (GBM) cell lines. Downregulation of DYRK1A in GBM cell lines decreases viability and reduces tumor growth in vivo. The β-carboline alkaloid harmine is one of the most potent and selective DYRK1A inhibitors and has been utilized as a specific tool compound to probe DYRK1A function in vitro and in vivo. We previously demonstrated that DYRK1A phosphorylates GLI1 at Ser-408 within a putative nuclear localization sequence and that this phosphorylation event is blocked by harmine. Harmine exhibits anti-cancer activity in vitro on a number of cancer cell lines, including glioma, breast, gastric and AML. However, harmine’s potential therapeutic use has been hampered by its potent “off-target” activity for monoamine oxidase A (MAO-A), impacting multiple nervous system targets. Harmine causes tremors in mice, thus limiting its in vivo dosing potential. In this current study, we have optimized and validated a TR-FRET based DYRK1A assay for high-throughput screening in 384-well format. A small-scale inhibitor screen of the FDA-approved Prestwick drug collection identified harmine and four of its analogs as DYRK1A inhibitors. Hits were confirmed by dose response and in an orthogonal DYRK1A assay. Selectivity profiling of harmine and a broader collection of analogs allowed us to map some divergent SAR (structure-activity relationships) for the DYRK1A and MAO-A activities. The panel of harmine analogs had varying activities in GBM cell lines when tested for anti-proliferative effects using a high content imaging assay. One of the analogs with reduced MAO-A activity relative to DYRK1A was tested in vivo in a glioma tumor model and demonstrated better characteristics/safety profile compared to harmine. Citation Format: Hassan Shehata, Michael Tarpley, Helen O Oladapo, Dillon Strepay, Jose R Roques, Rob U Onyenwoke, David B Darr, Kevin P Williams. Profiling of harmine and select analogs as differential inhibitors of DYRK1A and monoamine oxidase A: Exploring the potential for anti-cancer efficacy and minimizing off-target activity [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr A138. doi:10.1158/1535-7163.TARG-19-A138