Mutations in ESR1 have been associated with resistance to aromatase inhibitor (AI) therapy in patients with ER+ metastatic breast cancer. Little is known of the impact of these mutations in patients receiving selective oestrogen receptor degrader (SERD) therapy. In this study, hotspot mutations in ESR1 and PIK3CA from ctDNA were assayed in clinical trial samples from ER+ metastatic breast cancer patients randomized either to the SERD fulvestrant or fulvestrant plus a pan-PI3K inhibitor. ESR1 mutations are present in 37% of baseline samples and are enriched in patients with luminal A and PIK3CA-mutated tumours. ESR1 mutations are often polyclonal and longitudinal analysis shows distinct clones exhibiting divergent behaviour over time. ESR1 mutation allele frequency does not show a consistent pattern of increases during fulvestrant treatment, and progression-free survival is not different in patients with ESR1 mutations compared with wild-type patients. ESR1 mutations are not associated with clinical resistance to fulvestrant in this study.

ER-targeted therapeutics provide valuable treatment options for patients with ER+ breast cancer, however, current relapse and mortality rates emphasize the need for improved therapeutic strategies. The recent discovery of prevalent ESR1 mutations in relapsed tumors underscores a sustained reliance of advanced tumors on ERα signaling, and provides a strong rationale for continued targeting of ERα. Here we describe GDC-0810, a novel, non-steroidal, orally bioavailable selective ER downregulator (SERD), which was identified by prospectively optimizing ERα degradation, antagonism and pharmacokinetic properties. GDC-0810 induces a distinct ERα conformation, relative to that induced by currently approved therapeutics, suggesting a unique mechanism of action. GDC-0810 has robust in vitro and in vivo activity against a variety of human breast cancer cell lines and patient derived xenografts, including a tamoxifen-resistant model and those that harbor ERα mutations. GDC-0810 is currently being evaluated in Phase II clinical studies in women with ER+ breast cancer.

Activation of the PI3K pathway occurs commonly in a wide variety of cancers. Experience with other successful targeted agents suggests that clinical resistance is likely to arise and may reduce the durability of clinical benefit. Here, we sought to understand mechanisms underlying resistance to PI3K inhibition in PTEN-deficient cancers. We generated cell lines resistant to the pan-PI3K inhibitor GDC-0941 from parental PTEN-null breast cancer cell lines and identified a novel PIK3CB D1067Y mutation in both cell lines that was recurrent in cancer patients. Stable expression of mutant PIK3CB variants conferred resistance to PI3K inhibition that could be overcome by downstream AKT or mTORC1/2 inhibitors. Furthermore, we show that the p110b D1067Y mutant was highly activated and induced PIP3 levels at the cell membrane, subsequently promoting the localization and activation of AKT and PDK1 at the membrane and driving PI3K signaling to a level that could withstand treatment with proximal inhibitors. Finally, we demonstrate that the PIK3CB D1067Y mutant behaved as an oncogene and transformed normal cells, an activity that was enhanced by PTEN depletion. Collectively, these novel preclinical and clinical findings implicate the acquisition of activating PIK3CB D1067 mutations as an important event underlying the resistance of cancer cells to selective PI3K inhibitors.

Despite the large concordance between P and matched M for the evaluated molecular alterations, potential actionable targets such as ESR1 mutations were found only in M. This supports the importance of characterizing the M disease. Other targets we identified, such as HIF1A and IDO1, warrant further investigation in this patient population.

For standard IV insulin infusions, a priming volume of 20 mL is sufficient to minimize the effect of insulin adsorption losses to IV lines. Priming volumes exceeding 20 mL are wasteful, increase costs, and generate unnecessary work for nurses and pharmacists.

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Alterations of the phosphoinositide-3 kinase (PI3K)/Akt signaling pathway occur broadly in cancer via multiple mechanisms including mutation of the PIK3CA gene or loss of the tumor suppressor PTEN. The dysregulation of this pathway has been implicated in tumor initiation, cell growth and survival, invasion and angiogenesis, thus, PI3K is a promising therapeutic target for cancer. There are several PI3K inhibitors in clinical trials and the current study was intended to investigate preclinical mechanisms of acquired resistance to GDC-0941, a class I selective PI3K inhibitor. GDC-0941 resistant pools and clones were generated in both EVSA-T and HCC-1954 breast cancer cell lines by treating cells with increasing concentrations of drug. We found that resistant clones from both lines demonstrated marked increase of downstream PI3K pathway signaling and upregulation of the MAPK pathway, through two different mechanisms. In HCC-1954, autocrine signaling to EGFR was observed in the resistant clones and resulted in increased dependency on the downstream factor c-Myc. EVSA-T clones with acquired resistance to GDC-0941 had elevated HER2 copy number and protein expression levels. A corresponding increase in phosphorylation of HER2 binding partner ErbB3 was also discovered in the EVSA-T resistance cells. In both cases sensitivity to PI3K inhibition was restored by blocking the activated upstream receptor tyrosine kinase, EGFR for HCC-1954 and HER2 for EVSA-T. Additionally both models were re-sensitized to GDC-0941 by blocking downstream signaling of the MAPK pathway. These preclinical data may provide rationale for combination therapy with PI3K inhibitors in the clinic. Citation Format: Kyle A. Edgar, Ling Hwu, Kimberly Walter, Mark Lackner, Lori S. Friedman, Jeffrey J. Wallin. Mechanisms of acquired resistance to the PI3K inhibitor GDC-0941 in breast cancer cell lines. [abstract]. In: Proceedings of the AACR Special Conference: Targeting the PI3K-mTOR Network in Cancer; Sep 14-17, 2014; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(7 Suppl):Abstract nr B37.

The immune system has multiple mechanisms by which it can eliminate cancer and yet, tumors are able to adapt resistance to host immune surveillance and continue to survive and grow. One critical resistance mechanism involves Programmed cell death 1 ligand 1 (PD-L1, CD274, B7-H1), the predominant ligand for PD-1, an inhibitory receptor expressed on T cells following activation. PD-L1 also binds to B7.1 (CD80), inhibiting its ability to provide an immune stimulatory signal. PD-L1 is expressed broadly on multiple peripheral blood mononuclear cell subtypes, placenta, and numerous cancers, including NSCLC. Tumor-specific T cells infiltrate tumors and recognize tumor cells, releasing Interferon-gamma (IFNγ), initiating signaling of the Janus kinase/Signal Transducer and Activator of Transcription (JAK/STAT) pathway in the tumor cells. IFNγ induces and/or greatly enhances the expression of PD-L1 in the tumor, among other cell types, allowing the tumor to become resistant to the host T cell response. Blockade of PD-L1 binding to PD-1 and B7.1 can reinvigorate the host immune response against the tumor and overcome tumor adaptive resistance. The regulation of PD-L1 expression is complex and likely involves multiple types of pre- and post-translational events. We show that basal PD-L1 expression levels can vary greatly in cancer cells, as can PD-L1 induction by IFNγ. Here we describe the different categories of PD-L1 basal expression and IFNγ–dependent regulation across multiple lung cell lines and human tumor samples. Reverse Phase Protein Array and RNA microarray data show that the JAK/STAT canonical pathways are still intact among all of these distinct categories, so alternative mechanisms of expression regulation must be active in these cell lines and tumor samples. We provide evidence that a combination of mechanisms regulate both the basal and stimulated expression levels of PD-L1 across these distinct categories. This data regarding PD-L1 expression regulation provides valuable information to better understand the PD-1/PD-L1 pathway as a therapeutic target. Citation Format: Edward (Ward) E. Kadel, Kimberly Walter, Rupal Desai, Juliet Carbon, Marigold Boe, David Shames, Marcin Kowanetz. Lung cancers regulate the immune suppressor PD-L1 by multiple mechanisms, altering its role in tumor survival. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4978. doi:10.1158/1538-7445.AM2013-4978