HSP90 empowers evolution of resistance to hormonal therapy in human breast cancer models

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 111; no. 51; pp. 18297 - 18302
• Main Authors: Whitesell, Luke, Santagata, Sandro, Mendillo, Marc L., Lin, Nancy U., Proia, David A., Lindquist, Susan
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 23-12-2014; National Acad Sciences
• Subjects: Antineoplastic Agents, Hormonal - therapeutic use; Biological Sciences; Breast cancer; Breast Neoplasms - drug therapy; Breast Neoplasms - genetics; Breast Neoplasms - pathology; Cancer; Cell Cycle; Cell lines; Cultured cells; Drug Resistance, Neoplasm; Estrogens; Evolution; Female; Genes; Heat shock proteins; Heterografts; Heterologous transplantation; HSP90 Heat-Shock Proteins - physiology; Humans; Proteins; Rodents; Tumors; Yeast; antiestrogen; tumor progression; drug resistance; estrogen receptor; tamoxifen
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1421323111

The efficacy of hormonal therapies for advanced estrogen receptorpositive breast cancers is limited by the nearly inevitable development of acquired resistance. Efforts to block the emergence of resistance have met with limited success, largely because the mechanisms underlying it are so varied and complex. Here, we investigate a new strategy aimed at the very processes by which cancers evolve resistance. From yeast to vertebrates, heat shock protein 90 (HSP90) plays a unique role among molecular chaperones by promoting the evolution of heritable new traits. It does so by regulating the folding of a diverse portfolio of metastable client proteins, many of which mediate adaptive responses that allow organisms to adapt and thrive in the face of diverse challenges, including those posed by drugs. Guided by our previous work in pathogenic fungi, in which very modest HSP90 inhibition impairs resistance to mechanistically diverse antifungals, we examined the effect of similarly modest HSP90 inhibition on the emergence of resistance to antiestrogens in breast cancer models. Even though this degree of inhibition fell below the threshold for proteotoxic activation of the heat-shock response and had no overt anticancer activity on its own, it dramatically impaired the emergence of resistance to hormone antagonists both in cell culture and in mice. Our findings strongly support the clinical testing of combined hormone antagonist-low-level HSP90 inhibitor regimens in the treatment of metastatic estrogen receptor-positive breast cancer. At a broader level, they also provide promising proof of principle for a genera I izable strategy to combat the pervasive problem of rapidly emerging resistance to molecularly targeted therapeutics.