Reference Detail

Ref Type

Journal Article

PMID

(26733612)

Authors

Yang W, Hosford SR, Dillon LM, Shee K, Liu SC, Bean JR, Salphati L, Pang J, Zhang X, Nannini MA, Demidenko E, Bates D, Lewis LD, Marotti JD, Eastman AR, Miller TW

Title

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

Journal	Vol	Issue	Date	Pages	Journal Short Title
Clinical cancer research : an official journal of the American Association for Cancer Research	22	9	2016 May 01	2250-60	Clin Cancer Res

URL

Abstract Text

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.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.

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Molecular Profile	Treatment Approach

Gene Name	Source	Synonyms	Protein Domains	Gene Description	Gene Role

Therapy Name	Drugs	Efficacy Evidence	Clinical Trials

Drug Name	Trade Name	Synonyms	Drug Classes	Drug Description

Gene	Variant	Impact	Protein Effect	Variant Description	Associated with drug Resistance

Molecular Profile	Indication/Tumor Type	Response Type	Therapy Name	Approval Status	Evidence Type	Efficacy Evidence	References
PTEN inact mut	estrogen-receptor positive breast cancer	sensitive	Pictilisib	Preclinical - Cell culture	Actionable	In a preclinical study, a PTEN deficient estrogen-receptor (ER) positive breast cancer cell line demonstrated increased sensitivity to treatment in culture when Pictilisib (GDC-0941) was given at a higher dose for a shorter duration, resulting in inhibition of cell growth (PMID: 26733612).	26733612
PTEN inact mut	estrogen-receptor positive breast cancer	sensitive	Fulvestrant + Pictilisib	Preclinical - Cell culture	Actionable	In a preclinical study, the combination of Faslodex (fulvestrant) and PIctilisib (GDC-0941) resulted in decreased cell viability and increased apoptotic activity in PTEN deficient estrogen-receptor (ER) positive breast cancer cells in culture (PMID: 26733612).	26733612