Discovery of drug-resistant and drug-sensitizing mutations in the oncogenic PI3K isoform p110 alpha.

Graduate Group in Biophysics, University of California, San Francisco, San Francisco, CA 94158, USA.
Cancer cell (Impact Factor: 25.29). 09/2008; 14(2):180-92. DOI: 10.1016/j.ccr.2008.06.014
Source: PubMed

ABSTRACT p110 alpha (PIK3CA) is the most frequently mutated kinase in human cancer, and numerous drugs targeting this kinase are currently in preclinical development or early-stage clinical trials. Clinical resistance to protein kinase inhibitors frequently results from point mutations that block drug binding; similar mutations in p110 alpha are likely, but currently none have been reported. Using a S. cerevisiae screen against a structurally diverse panel of PI3K inhibitors, we have identified a potential hotspot for resistance mutations (I800), a drug-sensitizing mutation (L814C), and a surprising lack of resistance mutations at the "gatekeeper" residue. Our analysis further reveals that clinical resistance to these drugs may be attenuated by using multitargeted inhibitors that simultaneously inhibit additional PI3K pathway members.

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    ABSTRACT: Phosphoinositide-3 kinase (PI3K) signaling pathway alterations occur broadly in cancer and PI3K is a promising therapeutic target. Here, we investigated acquired resistance to GDC-0941, a PI3K inhibitor in clinical trials. Colorectal cancer (CRC) cells made to be resistant to GDC-0941 were discovered to secrete amphiregulin, which resulted in increased EGFR/MAPK signaling. Moreover, prolonged PI3K pathway inhibition in cultured cells over a period of months led to a secondary loss of PTEN in 40% of the CRC lines with acquired resistance to PI3K inhibition. In the absence of PI3K inhibitor, these PTEN-null PI3K inhibitor-resistant clones had elevated PI3K pathway signaling and decreased sensitivity to MAPK pathway inhibitors. Importantly, PTEN loss was not able to induce resistance to PI3K inhibitors in the absence of amphiregulin, indicating a multimodal mechanism of acquired resistance. The combination of PI3K and MAPK pathway inhibitors overcame acquired resistance in vitro and in vivo.
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    ABSTRACT: Acquired resistance to targeted kinase inhibitors is a well-documented clinical problem that is potentially fatal for patients to whom a suitable back-up is not available. However, protein kinase alleles that promote resistance to inhibitors can be exploited experimentally as gold-standards for "on"- and "off"-target validation strategies and constitute a powerful resource for assessing the ability of new or combined therapies to override resistance. Clinical resistance to kinase inhibitors is an evident in all tyrosine kinase-driven malignancies, where high rates of mutation drive tumor evolution toward the insidious drug-resistant (DR) state through a variety of mechanisms. Unfortunately, this problem is likely to intensify in the future as the number of target kinases, approved inhibitors, and clinical indications increase. To empower the analysis of resistance in kinases, we have validated a bioinformatic, structural, and cellular workflow for designing and evaluating resistance at key mutational hotspots among kinome members. In this chapter, we discuss how mutation of amino acids in the gatekeeper and hinge-loop regions (collectively termed the "resistance tetrad") and the DFG motif represent an effective approach for generating panels of DR kinase alleles for chemical genetics and biological target validation.
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    ABSTRACT: The phosphatidylinositol-3-kinase (PI3K) pathway is an important nexus for integration of extracellular and intracellular signals, and there are very frequent perturbations of this pathway in breast cancer, making it an attractive target for therapeutic manipulation. Hotspot mutations in PIK3CA or AKT1 are found in nearly 30% of breast cancers, especially estrogen receptor-positive and Her-2/neu-positive subgroups. This review will emphasize experimental models, clinical characterization and implications of PIK3CA/AKT1 mutations in breast cancer. In vitro studies have demonstrated that these mutations are kinase-activating and can confer cellular transforming properties in the correct context. Further, overexpression of PIK3CA H1047R in a variety of murine models results in mammary proliferation and carcinomas, and established carcinomas may become PIK3CA H1047R-independent. Data from human breast carcinomas regarding the clinicopathologic significance of PIK3CA/AKT1 mutations were contradictory at first, yet trends are beginning to emerge. PIK3CA mutation seems to impart a favorable prognosis in estrogen-receptor positive breast cancers, and mutations are seen early, in pre-invasive breast lesions. Although larger studies are needed, PIK3CA mutations may not confer selective advantage in the metastatic setting. Numerous pharmacologic compounds targeting the PI3K pathway are in development. The complexity of PI3K crosstalk with other signaling cascades, negative feedback regulation, and the myriad of other genotypic and phenotypic deviations in breast cancers argues for thorough molecular characterization of tumors in cancer trials. Citation: Troxell ML (2012) PIK3CA/AKT1 Mutations in Breast Carcinoma: a Comprehensive Review of Experimental and Clinical Studies. J Clinic Experiment Pathol S1:002. Copyright: © 2012 Troxell ML. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
    01/2012; 02(01). DOI:10.4172/2161-0681.S1-002


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