Dolastatin 10 is an unusual peptide of marine origin which binds to tubulin, inhibits microtubule assembly, resulting in the formation of tubulin aggregates and inhibition of mitosis. Dolastatin 10 has been used in trials phase II studying the treatment of Sarcoma, Leukemia, Lymphoma, Liver Cancer, among others. In case of hormone-refractory prostate cancer, it lacks significant clinical activity as a single agent and also dolastatin-10 is inactive against hepatobiliary and pancreatic carcinomas.

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.