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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.
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 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
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