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

ABSTRACT: The efficacy of hormonal therapies for advanced estrogen receptor-positive 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 generalizable strategy to combat the pervasive problem of rapidly emerging resistance to molecularly targeted therapeutics.

SUBMITTER: Whitesell L

PROVIDER: S-EPMC4280614 | biostudies-literature | 2014 Dec

REPOSITORIES: biostudies-literature

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

Whitesell Luke L Santagata Sandro S Mendillo Marc L ML Lin Nancy U NU Proia David A DA Lindquist Susan S

Proceedings of the National Academy of Sciences of the United States of America 20141208 51

The efficacy of hormonal therapies for advanced estrogen receptor-positive 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 molecul ...[more]

PMID: 25489079

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Project description:Endocrine therapy agents (the selective estrogen receptor (ER) modulators such as tamoxifen or the selective ER down-regulators such as ICI 182,780) are key treatment regimens for hormone receptor-positive breast cancers. While these drugs are very effective in controlling ER-positive breast cancer, many tumors that initially respond well to treatment often acquire drug resistance, which is a major clinical problem. In clinical practice, hormonal therapy agents are commonly used in combination or sequence with radiation therapy. Tamoxifen treatment and radiotherapy improve both local tumor control and patient survival. However, tamoxifen treatment may render cancer cells less responsive to radiation therapy. Only a handful of data exist on the effects of radiation on cells resistant to hormonal therapy agents. These scarce data show that cells that were resistant to tamoxifen were also resistant to radiation. Yet, the existence and mechanisms of cross-resistance to endocrine therapy and radiation therapy need to be established. Here, we for the first time examined and compared radiation responses of MCF-7 breast adenocarcinoma cells (MCF-7/S0.5) and two antiestrogen resistant cell lines derived from MCF-7/S0.5: the tamoxifen resistant MCF-7/TAMR-1 and ICI 182,780 resistant MCF-7/182R-6 cell lines. Specifically, we analyzed the radiation-induced changes in the expression of genes involved in DNA damage, apoptosis, and cell cycle regulation. We found that the tamoxifen-resistant cell line in contrast to the parental and ICI 182,780-resistant cell lines displayed a significantly less radiation-induced decrease in the expression of genes involved in DNA repair. Furthermore, we show that MCF-7/TAMR-1 and MCF-7/182R-6 cells were less susceptible to radiation-induced apoptosis as compared to the parental line. These data indicate that tamoxifen-resistant breast cancer cells have a reduced sensitivity to radiation treatment. The current study may therefore serve as a roadmap to the future analysis of the mechanisms of cross-resistance between hormonal therapy and radiation.

Project description:OBJECTIVE:High-deductible health plans (HDHPs) have become the predominant commercial health insurance arrangement in the US. HDHPs require substantial out-of-pocket (OOP) costs for most services but often exempt medications from high cost sharing. We examined effects of HDHPs on OOP costs and utilization of adjuvant hormonal therapy (AHT), which are fundamental care for patients with breast cancer. METHODS:This controlled quasi-experimental study used claims data (2003-2012) from a large national health insurer. We included 986 women with incident early-stage breast cancer, age 25-64 years, insured by employers that mandated a transition from low-deductible (??$500/year) to high-deductible (??$1000/year) coverage, and 3479 propensity score-matched controls whose employers offered only low-deductible plans. We examined AHT utilization and OOP costs per person-year before and after the HDHP switch. RESULTS:At baseline, the OOP costs for AHT were $40.41 and $36.55 per person-year among the HDHP and control groups. After the HDHP switch, the OOP costs for AHT were $91.76 and $72.98 per person-year among the HDHP and control groups, respectively. AHT OOP costs increased among HDHP members relative to controls but the change was not significant (relative change 13.72% [95% CI -?9.25, 36.70%]). AHT use among HDHP members did not change compared to controls (relative change of 2.73% [95% CI -?14.01, 19.48%]); the change in aromatase inhibitor use was -?11.94% (95% CI -?32.76, 8.88%) and the change in tamoxifen use was 20.65% (95% CI -?8.01, 49.32%). CONCLUSION:We did not detect significant changes in AHT use after the HDHP switch. Findings might be related to modest increases in overall AHT OOP costs, the availability of low-cost generic tamoxifen, and patient awareness that AHT can prolong life and health. Minimizing OOP cost increases for essential medications might represent a feasible approach for maintaining medication adherence among HDHP members with incident breast cancer.

Dataset Information

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

Publications

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

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