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Potentiation of Growth Inhibitory Responses of the mTOR Inhibitor Everolimus by Dual mTORC1/2 Inhibitors in Cultured Breast Cancer Cell Lines.

Leung EY, Askarian-Amiri M, Finlay GJ, Rewcastle GW, Baguley BC - PLoS ONE (2015)

Bottom Line: We then carried out combination studies with four everolimus resistant triple-negative breast cancer cell lines, and found an unexpectedly high degree of synergy between everolimus and the other inhibitors tested.The level of potentiation of everolimus inhibitory activity (measured by IC50 values) was found to be cell line-specific for all the kinase inhibitors tested.The results suggest that judicious combination of mTOR inhibitors with different modes of action could have beneficial effects in the treatment of breast cancer.

View Article: PubMed Central - PubMed

Affiliation: Auckland Cancer Society Research Centre, University of Auckland, Grafton, Auckland, New Zealand; Department of Molecular Medicine and Pathology, University of Auckland, Grafton, Auckland, New Zealand.

ABSTRACT
The mammalian target of rapamycin (mTOR), a vital component of signaling pathways involving PI3K/AKT, is an attractive therapeutic target in breast cancer. Everolimus, an allosteric mTOR inhibitor that inhibits the mTOR functional complex mTORC1, is approved for treatment of estrogen receptor positive (ER+) breast cancer. Other mTOR inhibitors show interesting differences in target specificities: BEZ235 and GSK2126458 are ATP competitive mTOR inhibitors targeting both PI3K and mTORC1/2; AZD8055, AZD2014 and KU-0063794 are ATP competitive mTOR inhibitors targeting both mTORC1 and mTORC2; and GDC-0941 is a pan-PI3K inhibitor. We have addressed the question of whether mTOR inhibitors may be more effective in combination than singly in inhibiting the proliferation of breast cancer cells. We selected a panel of 30 human breast cancer cell lines that included ER and PR positive, HER2 over-expressing, and "triple negative" variants, and determined whether signaling pathway utilization was related to drug-induced inhibition of proliferation. A significant correlation (p = 0.005) was found between everolimus IC50 values and p70S6K phosphorylation, but not with AKT or ERK phosphorylation, consistent with the mTOR pathway being a principal target. We then carried out combination studies with four everolimus resistant triple-negative breast cancer cell lines, and found an unexpectedly high degree of synergy between everolimus and the other inhibitors tested. The level of potentiation of everolimus inhibitory activity (measured by IC50 values) was found to be cell line-specific for all the kinase inhibitors tested. The results suggest that judicious combination of mTOR inhibitors with different modes of action could have beneficial effects in the treatment of breast cancer.

No MeSH data available.


Related in: MedlinePlus

Relationship between drug sensitivity and pathway utilization in MCF-7 parental and sub-lines.IC50 values for everolimus are represented on the y-axis and individual cell lines on the x-axis. Orange shading in the matrix indicates estrogen receptor positive (ER), and triple-negative (TN) cell lines. Relative levels of phosphorylation of p70S6K, AKT and ERK of breast cancer cell lines are shown as bar graphs. Bands are normalized to tubulin or actin control and bars represent changes in fold compared with MCF-7 and expressed as the mean of two experiments.
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pone.0131400.g003: Relationship between drug sensitivity and pathway utilization in MCF-7 parental and sub-lines.IC50 values for everolimus are represented on the y-axis and individual cell lines on the x-axis. Orange shading in the matrix indicates estrogen receptor positive (ER), and triple-negative (TN) cell lines. Relative levels of phosphorylation of p70S6K, AKT and ERK of breast cancer cell lines are shown as bar graphs. Bands are normalized to tubulin or actin control and bars represent changes in fold compared with MCF-7 and expressed as the mean of two experiments.

Mentions: The lack of correlation among cell lines with widely varying properties raised the question of whether there was a relationship between the level of p70S6K phosphorylation and proliferation inhibition by everolimus in a series of lines that had a common genetic background. Hence, we utilized a series of well characterized receptor positive (ER+) MCF-7 tamoxifen-resistant sub-lines [16,19,20,23,27], as well as a series of triple negative MCF-7 fulvestrant-resistant sub-lines [23] (Fig 3). The MCF-7 parental line and nine of its sub-lines were sensitive to everolimus with IC50 values of less than 20 nM, while two sub-lines TamC3 and TamR3 (both with IC50 > 100 nM) showed relative resistance. However, no significant correlation was observed between the degree of p70S6K phosphorylation, AKT phosphorylation, ERK phosphorylation and everolimus sensitivity (Fig 3).


Potentiation of Growth Inhibitory Responses of the mTOR Inhibitor Everolimus by Dual mTORC1/2 Inhibitors in Cultured Breast Cancer Cell Lines.

Leung EY, Askarian-Amiri M, Finlay GJ, Rewcastle GW, Baguley BC - PLoS ONE (2015)

Relationship between drug sensitivity and pathway utilization in MCF-7 parental and sub-lines.IC50 values for everolimus are represented on the y-axis and individual cell lines on the x-axis. Orange shading in the matrix indicates estrogen receptor positive (ER), and triple-negative (TN) cell lines. Relative levels of phosphorylation of p70S6K, AKT and ERK of breast cancer cell lines are shown as bar graphs. Bands are normalized to tubulin or actin control and bars represent changes in fold compared with MCF-7 and expressed as the mean of two experiments.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4492962&req=5

pone.0131400.g003: Relationship between drug sensitivity and pathway utilization in MCF-7 parental and sub-lines.IC50 values for everolimus are represented on the y-axis and individual cell lines on the x-axis. Orange shading in the matrix indicates estrogen receptor positive (ER), and triple-negative (TN) cell lines. Relative levels of phosphorylation of p70S6K, AKT and ERK of breast cancer cell lines are shown as bar graphs. Bands are normalized to tubulin or actin control and bars represent changes in fold compared with MCF-7 and expressed as the mean of two experiments.
Mentions: The lack of correlation among cell lines with widely varying properties raised the question of whether there was a relationship between the level of p70S6K phosphorylation and proliferation inhibition by everolimus in a series of lines that had a common genetic background. Hence, we utilized a series of well characterized receptor positive (ER+) MCF-7 tamoxifen-resistant sub-lines [16,19,20,23,27], as well as a series of triple negative MCF-7 fulvestrant-resistant sub-lines [23] (Fig 3). The MCF-7 parental line and nine of its sub-lines were sensitive to everolimus with IC50 values of less than 20 nM, while two sub-lines TamC3 and TamR3 (both with IC50 > 100 nM) showed relative resistance. However, no significant correlation was observed between the degree of p70S6K phosphorylation, AKT phosphorylation, ERK phosphorylation and everolimus sensitivity (Fig 3).

Bottom Line: We then carried out combination studies with four everolimus resistant triple-negative breast cancer cell lines, and found an unexpectedly high degree of synergy between everolimus and the other inhibitors tested.The level of potentiation of everolimus inhibitory activity (measured by IC50 values) was found to be cell line-specific for all the kinase inhibitors tested.The results suggest that judicious combination of mTOR inhibitors with different modes of action could have beneficial effects in the treatment of breast cancer.

View Article: PubMed Central - PubMed

Affiliation: Auckland Cancer Society Research Centre, University of Auckland, Grafton, Auckland, New Zealand; Department of Molecular Medicine and Pathology, University of Auckland, Grafton, Auckland, New Zealand.

ABSTRACT
The mammalian target of rapamycin (mTOR), a vital component of signaling pathways involving PI3K/AKT, is an attractive therapeutic target in breast cancer. Everolimus, an allosteric mTOR inhibitor that inhibits the mTOR functional complex mTORC1, is approved for treatment of estrogen receptor positive (ER+) breast cancer. Other mTOR inhibitors show interesting differences in target specificities: BEZ235 and GSK2126458 are ATP competitive mTOR inhibitors targeting both PI3K and mTORC1/2; AZD8055, AZD2014 and KU-0063794 are ATP competitive mTOR inhibitors targeting both mTORC1 and mTORC2; and GDC-0941 is a pan-PI3K inhibitor. We have addressed the question of whether mTOR inhibitors may be more effective in combination than singly in inhibiting the proliferation of breast cancer cells. We selected a panel of 30 human breast cancer cell lines that included ER and PR positive, HER2 over-expressing, and "triple negative" variants, and determined whether signaling pathway utilization was related to drug-induced inhibition of proliferation. A significant correlation (p = 0.005) was found between everolimus IC50 values and p70S6K phosphorylation, but not with AKT or ERK phosphorylation, consistent with the mTOR pathway being a principal target. We then carried out combination studies with four everolimus resistant triple-negative breast cancer cell lines, and found an unexpectedly high degree of synergy between everolimus and the other inhibitors tested. The level of potentiation of everolimus inhibitory activity (measured by IC50 values) was found to be cell line-specific for all the kinase inhibitors tested. The results suggest that judicious combination of mTOR inhibitors with different modes of action could have beneficial effects in the treatment of breast cancer.

No MeSH data available.


Related in: MedlinePlus