An organic heterotetracyclic compound that is 5-oxo-5H-[1,3]benzothiazolo[3,2-a][1,8]naphthyridine-6-carboxylic acid substituted by a 4-methyl-1,4-diazepan-1-yl group at position 2 and in which the carboxy group at position 6 is substituted by a [(5-methylpyrazin-2-yl)methyl]nitrilo group. An inhibitor of ribosomal RNA (rRNA) synthesis which specifically inhibits RNA polymerase I-driven transcription of rRNA in several cancer cell lines. It is currently in phase I/II clinical trials for advanced hematologic malignancies and triple-negative breast cancer with BRCA1/2 mutation.