The hydrochloride salt of a small molecule inhibitor of human metal-regulatory transcription factor 1 (MTF-1) with potential antitumor activity. MTF-1 inhibitor APTO-253 inhibits MTF-1 activity and thereby induces the expression of MTF-1 dependent tumor suppressor factor Kruppel like factor 4 (KLF4). This subsequently leads to the downregulation of cyclin D1, blocking cell cycle progression and proliferation. This agent also causes decreased expression of genes involved in tumor hypoxia and angiogenesis.