Chlorsulfaquinoxaline is a halogenated derivative of sulfaquixonaline, an immunosuppressive and antifungal agent used in the control of coccidiosis in poultry, rabbit, sheep, and cattle. In vitro, Chlorsulfaquinoxaline acts as a topoisomerases IIα and IIβ poison, thus inhibiting DNA replication. Chlorsulfaquinoxaline shows good activity against human tumor cells in the human tumor colony-forming assay and subsequently has shown activity against murine and human solid tumors. No major objective antitumor responses was observed during Chlorsulfaquinoxaline Phase II clinical evaluation in non-small-cell lung cancer and metastatic colorectal cancer. Chlorsulfaquinoxaline was well tolerated with hypoglycemia being the most clinically significant toxicity.