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A mechanism for synergy with combined mTOR and PI3 kinase inhibitors.

Yang S, Xiao X, Meng X, Leslie KK - PLoS ONE (2011)

Bottom Line: Proliferation assays revealed that BEZ235 (dual PI3K/mTOR inhibitor) or ZSTK474 (pan PI3K inhibitor) combined with temsirolimus synergistically inhibited cell growth compared to cells treated with any of the agents alone.Co-treatment resulted in G0/G1 cell cycle arrest and up-regulation of p27.While molecular profiling revealed that, in most cases, sensitivity to temsirolimus alone was most marked in cells with high basal phospho-Akt resulting from PTEN inactivation, combining a PI3K inhibitor with temsirolimus prevented compensatory Akt phosphorylation and synergistically enhanced cell death regardless of PTEN status.

View Article: PubMed Central - PubMed

Affiliation: Department of Obstetrics & Gynecology, The University of Iowa, Iowa City, Iowa, United States of America.

ABSTRACT
Dysregulation of the mammalian target of rapamycin (mTOR) signaling has been found in many human cancers, particularly those with loss of the tumor suppressor PTEN. However, mTORC1 inhibitors such as temsirolimus have only modest activity when used alone and may induce acquired resistance by activating upstream mTORC2 and Akt. Other tumors that do not depend upon PI3K/Akt/mTOR signaling for survival are primarily resistant. This study tested the hypothesis that the limited clinical efficacy of temsirolimus is due to a compensatory increase in survival signaling pathways downstream of Akt as well as an incomplete block of 4E-BP1-controlled proliferative processes downstream of mTOR. We explored the addition of a PI3K inhibitor to temsirolimus and identified the mechanism of combinatorial synergy. Proliferation assays revealed that BEZ235 (dual PI3K/mTOR inhibitor) or ZSTK474 (pan PI3K inhibitor) combined with temsirolimus synergistically inhibited cell growth compared to cells treated with any of the agents alone. Co-treatment resulted in G0/G1 cell cycle arrest and up-regulation of p27. Cell death occurred through massive autophagy and subsequent apoptosis. While molecular profiling revealed that, in most cases, sensitivity to temsirolimus alone was most marked in cells with high basal phospho-Akt resulting from PTEN inactivation, combining a PI3K inhibitor with temsirolimus prevented compensatory Akt phosphorylation and synergistically enhanced cell death regardless of PTEN status. Another molecular correlate of synergy was the finding that temsirolimus treatment alone blocks downstream S6 kinase signaling, but not 4E-BP1. Adding BEZ235 completely abrogated 4E-BP1 phosphorylation. We conclude that the addition of a PI3K inhibitor overcomes cellular resistance to mTORC1 inhibitors regardless of PTEN status, and thus substantially expands the molecular phenotype of tumors likely to respond.

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Related in: MedlinePlus

Combination treatment of BEZ235 or ZSTK474 with temsirolimus synergistically inhibits cell proliferation.A, B, Cell viability was determined in the indicated endometrial cancer cell lines after treatment with increasing concentrations of (A) BEZ235 or (B) ZSTK474 alone or in the presence of 1 nM temsirolimus for 72 hrs.
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pone-0026343-g004: Combination treatment of BEZ235 or ZSTK474 with temsirolimus synergistically inhibits cell proliferation.A, B, Cell viability was determined in the indicated endometrial cancer cell lines after treatment with increasing concentrations of (A) BEZ235 or (B) ZSTK474 alone or in the presence of 1 nM temsirolimus for 72 hrs.

Mentions: After demonstrating BEZ235 and ZSTK474's effectiveness in down-regulating temsirolimus-induced Akt hyper-phosphorylation, we examined the anti-proliferative properties of combined treatment of temsirolimus with BEZ235 or ZSTK474. A broad range of doses — either BEZ235 or ZSTK474 alone or in combination with temsirolimus— were tested in order to determine the optimal concentration for eliciting growth inhibitory effects. First, the panel of endometrial cancer cells were treated with single drug (BEZ235 or ZSTK474 at 1–1000 nM) and compared to vehicle (DMSO) control. BEZ235 alone reduced cell proliferation by 50% at doses as low as 1–50 nM (Fig. 4A). ZSTK474 alone was cytostatic in all the eight tested endometrial cancer cell lines; it inhibited cell growth at about 100–1000 nM (Fig. 4B).


A mechanism for synergy with combined mTOR and PI3 kinase inhibitors.

Yang S, Xiao X, Meng X, Leslie KK - PLoS ONE (2011)

Combination treatment of BEZ235 or ZSTK474 with temsirolimus synergistically inhibits cell proliferation.A, B, Cell viability was determined in the indicated endometrial cancer cell lines after treatment with increasing concentrations of (A) BEZ235 or (B) ZSTK474 alone or in the presence of 1 nM temsirolimus for 72 hrs.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3198385&req=5

pone-0026343-g004: Combination treatment of BEZ235 or ZSTK474 with temsirolimus synergistically inhibits cell proliferation.A, B, Cell viability was determined in the indicated endometrial cancer cell lines after treatment with increasing concentrations of (A) BEZ235 or (B) ZSTK474 alone or in the presence of 1 nM temsirolimus for 72 hrs.
Mentions: After demonstrating BEZ235 and ZSTK474's effectiveness in down-regulating temsirolimus-induced Akt hyper-phosphorylation, we examined the anti-proliferative properties of combined treatment of temsirolimus with BEZ235 or ZSTK474. A broad range of doses — either BEZ235 or ZSTK474 alone or in combination with temsirolimus— were tested in order to determine the optimal concentration for eliciting growth inhibitory effects. First, the panel of endometrial cancer cells were treated with single drug (BEZ235 or ZSTK474 at 1–1000 nM) and compared to vehicle (DMSO) control. BEZ235 alone reduced cell proliferation by 50% at doses as low as 1–50 nM (Fig. 4A). ZSTK474 alone was cytostatic in all the eight tested endometrial cancer cell lines; it inhibited cell growth at about 100–1000 nM (Fig. 4B).

Bottom Line: Proliferation assays revealed that BEZ235 (dual PI3K/mTOR inhibitor) or ZSTK474 (pan PI3K inhibitor) combined with temsirolimus synergistically inhibited cell growth compared to cells treated with any of the agents alone.Co-treatment resulted in G0/G1 cell cycle arrest and up-regulation of p27.While molecular profiling revealed that, in most cases, sensitivity to temsirolimus alone was most marked in cells with high basal phospho-Akt resulting from PTEN inactivation, combining a PI3K inhibitor with temsirolimus prevented compensatory Akt phosphorylation and synergistically enhanced cell death regardless of PTEN status.

View Article: PubMed Central - PubMed

Affiliation: Department of Obstetrics & Gynecology, The University of Iowa, Iowa City, Iowa, United States of America.

ABSTRACT
Dysregulation of the mammalian target of rapamycin (mTOR) signaling has been found in many human cancers, particularly those with loss of the tumor suppressor PTEN. However, mTORC1 inhibitors such as temsirolimus have only modest activity when used alone and may induce acquired resistance by activating upstream mTORC2 and Akt. Other tumors that do not depend upon PI3K/Akt/mTOR signaling for survival are primarily resistant. This study tested the hypothesis that the limited clinical efficacy of temsirolimus is due to a compensatory increase in survival signaling pathways downstream of Akt as well as an incomplete block of 4E-BP1-controlled proliferative processes downstream of mTOR. We explored the addition of a PI3K inhibitor to temsirolimus and identified the mechanism of combinatorial synergy. Proliferation assays revealed that BEZ235 (dual PI3K/mTOR inhibitor) or ZSTK474 (pan PI3K inhibitor) combined with temsirolimus synergistically inhibited cell growth compared to cells treated with any of the agents alone. Co-treatment resulted in G0/G1 cell cycle arrest and up-regulation of p27. Cell death occurred through massive autophagy and subsequent apoptosis. While molecular profiling revealed that, in most cases, sensitivity to temsirolimus alone was most marked in cells with high basal phospho-Akt resulting from PTEN inactivation, combining a PI3K inhibitor with temsirolimus prevented compensatory Akt phosphorylation and synergistically enhanced cell death regardless of PTEN status. Another molecular correlate of synergy was the finding that temsirolimus treatment alone blocks downstream S6 kinase signaling, but not 4E-BP1. Adding BEZ235 completely abrogated 4E-BP1 phosphorylation. We conclude that the addition of a PI3K inhibitor overcomes cellular resistance to mTORC1 inhibitors regardless of PTEN status, and thus substantially expands the molecular phenotype of tumors likely to respond.

Show MeSH
Related in: MedlinePlus