Phosphatidylinositol-3-kinase (PI3K) pathway deregulation is a common event in human cancer, either through inactivation of the tumor suppressor phosphatase and tensin homologue deleted from chromosome 10 or activating mutations of p110-A. These hotspot mutations result in oncogenic activity of the enzyme and contribute to therapeutic resistance to the anti-HER2 antibody trastuzumab. The PI3K pathway is, therefore, an attractive target for cancer therapy. We have studied NVP-

There is a strong rationale to therapeutically target the phosphatidylinositol 3-kinase/protein kinase B/mammalian target of rapamycin (PI3K/AKT/mTOR) pathway in breast cancer since it is highly deregulated in this disease and it also mediates resistance to anti-HER2 therapies. However, initial studies with rapalogs, allosteric inhibitors of mTORC1, have resulted in limited clinical efficacy probably due to the release of a negative regulatory feedback loop that triggers AKT and ERK signaling. Since activation of AKT occurs via PI3K, we decided to explore whether PI3K inhibitors prevent the activation of these compensatory pathways. Using HER2-overexpressing breast cancer cells as a model, we observed that PI3K inhibitors abolished AKT activation. However, PI3K inhibition resulted in a compensatory activation of the ERK signaling pathway. This enhanced ERK signaling occurred as a result of activation of HER family receptors as evidenced by induction of HER receptors dimerization and phosphorylation, increased expression of HER3 and binding of adaptor molecules to HER2 and HER3. The activation of ERK was prevented with either MEK inhibitors or anti-HER2 monoclonal antibodies and tyrosine kinase inhibitors. Combined administration of PI3K inhibitors with either HER2 or MEK inhibitors resulted in decreased proliferation, enhanced cell death and superior anti-tumor activity compared with single agent PI3K inhibitors. Our findings indicate that PI3K inhibition in HER2-overexpressing breast cancer activates a new compensatory pathway that results in ERK dependency. Combined anti-MEK or anti-HER2 therapy with PI3K inhibitors may be required in order to achieve optimal efficacy in HER2-overexpressing breast cancer. This approach warrants clinical evaluation.

The phosphatidylinositol 3-kinase (PI3K) signalling pathway is integral to diverse cellular functions, including cellular proliferation, differentiation and survival. The 'phosphate and tensin homologue deleted from chromosome 10' (PTEN) tumor suppressor gene plays a critical role as a negative regulator of this pathway. An array of genetic mutations and amplifications has been described affecting key components of this pathway, with implications not only for tumorigenesis but also for resistance to some classic cytotoxics and targeted agents. Emerging preclinical research has significantly advanced our understanding of the PI3K pathway and its complex machinations and interactions. This knowledge has enabled the evolution of rationally designed drugs targeting elements of this pathway. It is important that the development of suitable biomarkers continues in parallel to optimize use of these agents. A new generation of PI3K inhibitors is now entering early clinical trials, with much anticipation that they will add to the growing armamentarium of targeted cancer therapeutics.

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Purpose: This phase I, first-in-human study evaluated the safety, maximum-tolerated dose (MTD), pharmacokinetics, pharmacodynamics, and preliminary efficacy of SAR245409, an inhibitor of pan-Class I phosphoinositide 3-kinase (PI3K) and mTOR, administered orally once or twice daily in patients with advanced solid tumors.Experimental Design: Eighty-three patients received SAR245409. Doses ranged from 15 to 120 mg twice daily, and 70 to 100 mg once daily. A 3þ3 dose-escalation design was used to determine the MTD. Patients were evaluated for adverse events and response. Assessments included pharmacokinetic, pharmacodynamic impact of SAR245409 on PI3K pathway signaling in hair sheath cells, skin and tumor, and characterization of tumor molecular alterations.Results: The MTDs were 50 mg twice daily and 90 mg once daily. The most frequent treatment-related adverse events were nausea (36.1%), diarrhea (21.7%), vomiting (19.3%), and decreased appetite (16.9%). The most frequent treatment-related grade 3/4 adverse events were increases in alanine aminotransferase (6.0%) and aspartate aminotransferase (4.8%). SAR245409 had a relatively short plasma half-life (2.96-7.52 hours). At MTDs, once-and twice-daily regimens yielded similar mean steady-state plasma exposure. A reduction in PI3K and mTORC1/mTORC2 pathway signaling was observed in serial hair sheath cells, skin, and tumor samples. Best response was stable disease in 48% of evaluable patients; seven patients had minor tumor regression. Twelve patients with stable disease were treated for !16 weeks. No trend was observed correlating tumor molecular alteration with antitumor activity.Conclusion: SAR245409 had a manageable safety profile, demonstrated reduced PI3K and mTORC1/ mTORC2 pathway signaling and was associated with clinically relevant stable disease. Clin Cancer Res; 20(9); 2445-56. Ó2014 AACR.