Tasisulam sodium, previously known as LY573636, were initially recognized by Eli Lilly for their significant antiproliferative activities in solid tumor cell lines, but their mechanism of action was unknown. Subsequent studies have revealed that LY573636 induces apoptosis via a mitochondrial-mediated mechanism that appears unique among other anti-cancer compounds. This drug was in the phase III clinical trial for the treatment of Metastatic Melanoma and in phase II for the treatment Non-Small-Cell Lung Cancer, breast cancer, ovarian cancer, but these studies were discontinued. In vivo pharmacokinetic studies in rats and dogs indicate that tasisulam is metabolized primarily by the liver, and has low total plasma clearance with a relatively long half-life. In addition, there was preclinical evidence of a correlation between the maximum plasma concentration (Cmax) of tasisulam and toxicity.

Retaspimycin (IPI-504) was previously under development by manufacturer Infinity Pharmaceuticals in conjunction with MedImmune, a part of AstraZeneca. Retaspimycin is a small-molecule inhibitor of heat shock protein 90 (HSP90) with antiproliferative and antineoplastic activities. Retaspimycin binds to and inhibits the cytosolic chaperone functions of HSP90, which maintains the stability and functional shape of many oncogenic signaling proteins and may be overexpressed or overactive in tumor cells. Retaspimycin-mediated inhibition of HSP90 promotes the proteasomal degradation of oncogenic signaling proteins in susceptible tumor cell populations, which may result in the induction of apoptosis. Orphan drug designation was assigned to the compound by the FDA for the treatment of gastrointestinal stromal cancer (GIST). Infinity Pharmaceuticals has discontinued the development of retaspimycin (IPI-504) an inhibitor of the HSP-90) complex, for the treatment of cancer due to lack of efficacy in 1913.