LDC195943 (IMT1) is a specific and noncompetitive inhibitor of human mitochondrial RNA polymerase (POLRMT). IMT1 causes a conformational change of POLRMT, which blocks substrate binding and transcription in a dose-dependent way in vitro. IMT1 reduces deoxynucleoside triphosphate levels and citric acid cycle intermediates, resulting in a marked depletion of cellular amino acid levels. IMT1 has the potential for mitochondrial transcription disorders related diseases.