Ptc124

The HNSCC cell lines SAS, DOK, and HO-1-u-1 were maintained at 37 °C in 5% CO₂ in DMEM (for SAS and DOK) with 5 µg/mL hydrocortisone or DMEM/F12 (for HO-1-u-1) (Invitrogen, Carlsbad, CA, USA), supplemented with 10% FBS (Invitrogen), 100 U/mL penicillin, and 100 μg/mL streptomycin (both from Invitrogen). HNSCC cells were treated for 48 h with mock (DMSO only), 50 μM PTC124 (MedChemExpress, Monmouth Junction, NJ, USA), 10 μM FLI-06 (MedChemExpress, Monmouth Junction, NJ, USA), or 10 μM TT-10 (AOBIOUS, Gloucester, MA, USA).

Stocks of aminoglycoside antibiotics (All purchased from Sigma-Aldrich, St. Louis, MO, USA) were dissolved in sterile H₂O at a 100 mg/mL concentration, and stored at 4 °C. PTC124 (3-[5-(2-Fluorophenyl)-1,2,4-oxadiazol-3-yl]benzoic acid, MedChemExpress, Cat. #HY-14832), escin (Sigma-Aldrich, Cat. #E1378), VX-661 (MedChemExpress, Monmouth Junction, NJ, USA Cat. #HY-15448), NMDI-14 (Ethyl 2-(((6,7-dimethyl-3-oxo-1,2,3,4-tetrahydro-2-quinoxalinyl)acetyl)amino)-4,5-dimethyl-3-thiophenecarboxylate, EMD Millipore, Burlington, MA, USA, Cat. #530838), and amlexanox (MedChemExpress Cat. #HY-B0713) were dissolved in dimethylsulphoxide (DMSO). SMG1i (2-chloro-N,N-diethyl-5-((4-(2-(4-(3-methylureido)phenyl)pyridin-4-yl)pyrimidin-2-yl)amino)benzenesulfonamide) was received from Dr. Robert Bridges from Rosalind Franklin University of Medicine and Science through the CFFT compound distribution program, and was dissolved in DMSO. Working solutions were all ≤0.1% DMSO, with the exception of NMDI-14, which was 1% DMSO. The increased DMSO did not prevent G418-facilitated FIS (Supplementary Figure S9). Stocks of forskolin (Sigma-Aldrich, Cat. #F6886) were dissolved in 100% EtOH and stored at −20 °C.