Tanespimycin (17-allylamino-17-demethoxygeldanamycin, 17-AAG) is a synthetic analogue of geldanamycin, an antibiotic first purified in 1970 from Streptomyces hygroscopicus. Tanespimycin is an Hsp90 inhibitor that has demonstrated the potential to disrupt the activity of multiple oncogenes and cell signaling pathways implicated in tumor growth, including HER2, a key pathway in breast cancer. Tanespimycin was being under development by Kosan Biosciences. It was in phase 3 clinical development with bortezomib for the treatment of multiple myeloma (MM). However, in 2010 the company halted development of tanespimycin, during late-stage clinical trials as a potential treatment for multiple myeloma. While no definitive explanation was given, it has been suggested that Bristol-Myers Squibb halted development over concerns of the financial feasibility of tanespimycin development given the 2014 expiry of the patent on this compound, and the relative expense of manufacture.

Soblidotin is a derivative of dolastatin 10, which was isolated from the Indian Ocean sea hare, Dolabella auricularia, in 1987. Soblidotin inhibits tubulin polymerization, resulting in cell cycle arrest and induction of apoptosis. It has a broad spectrum of antitumor activity against various murine tumors – P388 leukemia, Colon26 and LLC carcinomas, B16 melanoma and M5076 sarcoma – as well as human tumor xenografts, MX-1, LX-1 and SBC-3 carcinomas. Soblidotin is currently undergoing clinical evaluation and, in phase II clinical trials for solid tumours.