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Strategically Timing Inhibition of Phosphatidylinositol 3-Kinase to Maximize Therapeutic Index in Estrogen Receptor Alpha-Positive, PIK3CA-Mutant Breast Cancer.


ABSTRACT: Phosphatidylinositol 3-kinase (PI3K) inhibitors are being developed for the treatment of estrogen receptor ? (ER)-positive breast cancer in combination with antiestrogens. Understanding the temporal response and pharmacodynamic effects of PI3K inhibition in ER(+) breast cancer will provide a rationale for treatment scheduling to maximize therapeutic index.Antiestrogen-sensitive and antiestrogen-resistant ER(+) human breast cancer cell lines and mice bearing PIK3CA-mutant xenografts were treated with the antiestrogen fulvestrant, the PI3K inhibitor GDC-0941 (pictilisib; varied doses/schedules that provided similar amounts of drug each week), or combinations. Cell viability, signaling pathway inhibition, proliferation, apoptosis, tumor volume, and GDC-0941 concentrations in plasma and tumors were temporally measured.Treatment with the combination of fulvestrant and GDC-0941, regardless of dose/schedule, was significantly more effective than that with single-agent treatments in fulvestrant-resistant tumors. Short-term, complete PI3K inhibition blocked cell growth in vitro more effectively than chronic, incomplete inhibition. Longer-term PI3K inhibition hypersensitized cells to growth factor signaling upon drug withdrawal. Different schedules of GDC-0941 elicited similar tumor responses. While weekly high-dose GDC-0941 with fulvestrant continuously suppressed PI3K signaling for 72 hours, inducing a bolus of apoptosis and inhibiting proliferation, PI3K reactivation upon GDC-0941 washout induced a proliferative burst. Fulvestrant with daily low-dose GDC-0941 metronomically suppressed PI3K for 6 to 9 hours/day, repeatedly inducing small amounts of apoptosis and temporarily inhibiting proliferation, followed by proliferative rebound compared with fulvestrant alone.Continuous and metronomic PI3K inhibition elicits robust anticancer effects in ER(+), PIK3CA-mutant breast cancer. Clinical exploration of alternate treatment schedules of PI3K inhibitors with antiestrogens is warranted. Clin Cancer Res; 22(9); 2250-60. ©2016 AACRSee related commentary by Toska and Baselga, p. 2099.

SUBMITTER: Yang W 

PROVIDER: S-EPMC4854767 | biostudies-literature | 2016 May

REPOSITORIES: biostudies-literature

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Strategically Timing Inhibition of Phosphatidylinositol 3-Kinase to Maximize Therapeutic Index in Estrogen Receptor Alpha-Positive, PIK3CA-Mutant Breast Cancer.

Yang Wei W   Hosford Sarah R SR   Dillon Lloye M LM   Shee Kevin K   Liu Stephanie C SC   Bean Jennifer R JR   Salphati Laurent L   Pang Jodie J   Zhang Xiaolin X   Nannini Michelle A MA   Demidenko Eugene E   Bates Darcy D   Lewis Lionel D LD   Marotti Jonathan D JD   Eastman Alan R AR   Miller Todd W TW  

Clinical cancer research : an official journal of the American Association for Cancer Research 20160105 9


<h4>Purpose</h4>Phosphatidylinositol 3-kinase (PI3K) inhibitors are being developed for the treatment of estrogen receptor α (ER)-positive breast cancer in combination with antiestrogens. Understanding the temporal response and pharmacodynamic effects of PI3K inhibition in ER(+) breast cancer will provide a rationale for treatment scheduling to maximize therapeutic index.<h4>Experimental design</h4>Antiestrogen-sensitive and antiestrogen-resistant ER(+) human breast cancer cell lines and mice be  ...[more]

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