denileukin diftitox denileukin diftitox denileukin diftitox (trade name ontak) was an antineoplastic agent, an engineered protein combining interleukin-2 and diphtheria toxin. denileukin diftitox could bind to interleukin-2 receptors and introduce the diphtheria toxin into cells that express those receptors, killing the cells. in some leukemias and lymphomas, malignant cells express these receptors, so denileukin diftitox can target these. denileukin diftitoxclinical datatrade namesontakahfs/drugs.commonographmedlineplusa611024routes ofadministrationintravenousatc codel01xx29 (who) legal statuslegal status us: ℞-only pharmacokinetic dataelimination half-life70-80 minidentifiers iupac name diphtheria toxin-interleukin-2 fusion protein cas number173146-27-5 yiuphar/bps7044drugbankdb00004 ychemspidernoneunii25e79b5ctmchemblchembl1201550 nchemical and physical dataformulac2560h4042n678o799s17molar mass57647.46 g·mol−1 ny (what is this?) (verify) in 1999, ontak was approved by the u.s. food and drug administration (fda) for treatment of cutaneous t-cell lymphoma (ctcl). there is some evidence tying it to vision loss, and in 2006 the fda added a black box warning to the drug's label. in 2014, marketing of ontak was discontinued in the us.