ZNF397 Loss Triggers TET2-driven Epigenetic Rewiring, Lineage Plasticity, and AR-targeted Therapy Resistance in AR-dependent Cancers

Cancer cells exhibit phenotypical plasticity and epigenetic reprogramming, which allows them to evade lineage-dependent targeted treatments by adopting lineage plasticity. The underlying mechanisms by which cancer cells exploit the epigenetic regulatory machinery to acquire lineage plasticity and therapy resistance remain poorly understood. We identified Zinc Finger Protein 397 (ZNF397) as a bona fide co-activator of the androgen receptor (AR), essential for the transcriptional program governing AR-driven luminal lineage. ZNF397 deficiency facilitates the transition of cancer cell from an AR-driven luminal lineage to a Ten-Eleven Translocation 2 (TET2)-driven lineage plastic state, ultimately promoting resistance to therapies inhibiting AR signaling. Intriguingly, our findings indicate that TET2 inhibitor can eliminate the AR targeted therapies resistance in ZNF397-deficient tumors. These insights uncover a novel mechanism through which prostate and breast cancers acquire lineage plasticity via epigenetic rewiring and offer promising implications for clinical interventions designed to overcome therapy resistance dictated by lineage plasticity.

Statement of Significance

This study reveals a novel epigenetic mechanism regulating tumor lineage plasticity and therapy response, enhances understanding of drug resistance and unveils a new therapeutic strategy for prostate cancer and other malignancies. Our findings also illuminate TET2's oncogenic role and mechanistically connect TET2-driven epigenetic rewiring to lineage plasticity and therapy resistance.

Dendritic cell therapy augments antitumor immunity triggered by CDK4/6 inhibition and immune checkpoint blockade by unleashing systemic CD4 T-cell responses

BACKGROUND

Cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) combined with endocrine therapy are a mainstay treatment for hormone receptor-positive breast cancer. While their principal mechanism is inhibition of cancer cell proliferation, preclinical and clinical evidence suggests that CDK4/6i can also promote antitumor T-cell responses. However, this pro-immunogenic property is yet to be successfully harnessed in the clinic, as combining CDK4/6i with immune checkpoint blockade (ICB) has not shown a definitive benefit in patients.

METHOD

We performed an in-depth analysis of the changes in the tumor immune microenvironment and systemic immune modulation associated with CDK4/6i treatment in muring breast cancer models and in patients with breast cancer using high dimensional flow cytometry and RNA sequencing. Gain and loss of function in vivo experiments employing cell transfer and depletion antibody were performed to uncover immune cell populations critical for CDK4/6i-mediated stimulation of antitumor immunity.

RESULTS

We found that loss of dendritic cells (DCs) within the tumor microenvironment resulting from CDK4/6 inhibition in bone marrow progenitors is a major factor limiting antitumor immunity after CDK4/6i and ICB. Consequently, restoration of DC compartment by adoptively transferring ex vivo differentiated DCs to mice treated with CDK4/6i and ICB therapy enabled robust tumor inhibition. Mechanistically, the addition of DCs promoted the induction of tumor-localized and systemic CD4 T-cell responses in mice receiving CDK4/6i-ICB-DC combination therapy, as characterized by enrichment of programmed cell death protein-1-negative T helper (Th)1 and Th2 cells with an activated phenotype. CD4 T-cell depletion abrogated the antitumor benefit of CDK4/6i-ICB-DC combination, with outgrowing tumors displaying an increased proportion of terminally exhausted CD8 T cells.

CONCLUSIONS

Our findings suggest that CDK4/6i-mediated DC suppression limits CD4 T-cell responses essential for the sustained activity of CD8 T cells and tumor inhibition. Furthermore, they imply that restoring DC-CD4 T-cell crosstalk via DC transfer enables effective breast cancer immunity in response to CDK4/6i and ICB treatment.

Abstract P5-02-14: Identification of mechanisms of acquired resistance to ribociclib plus endocrine therapy using baseline and end-of-treatment circulating tumor DNA samples in the MONALEESA-2, -3, and -7 trials

Background: Genetic alterations that contribute to resistance to therapy may be acquired during treatment (tx) for hormone receptor−positive/human epidermal growth factor receptor−negative (HR+/HER2−) advanced breast cancer (ABC). A previous pooled analysis of circulating tumor DNA (ctDNA) in MONALEESA (ML)-2, -3, and -7 identified potential predictive biomarkers for response and resistance to ribociclib (RIB) at baseline (BL). Here, we describe an analysis of paired BL and end of treatment (EOT) samples from ML-2, -3, and -7 to identify acquired mechanisms that may impact resistance to RIB + endocrine therapy (ET) vs placebo (PBO) + ET. Methods: ML-2 (NCT01958021), ML-3 (NCT02422615), and ML-7 (NCT02278120) evaluated efficacy and safety of RIB + ET vs PBO + ET in pre- and postmenopausal patients (pts) with HR+/HER2− ABC treated in first-line (1L) and second-line (2L) settings. Plasma samples were collected at cycle 1 day 1 (C1D1; prior to first therapy exposure) and at EOT (± 28 days of recorded progression). ctDNA was sequenced using a targeted next-generation sequencing panel of ≈550 genes. Genes with an alteration frequency of >5% at EOT, regardless of their frequency at BL, were included. Tumor mutational burden (TMB) was assessed by tx arm; a TMB cutoff of 10 mutations/MB was used to categorize pts as TMB high vs low. To assess differences in the presence of alterations, a McNemar test was performed on paired samples and adjusted (adj) for multiple testing using the false discovery rate (FDR). A Bayesian mixed effects model was used to account for ctDNA fraction and trial and to test for tx-specific resistance by including a tx × visit interaction term. Results: A total of 905 paired samples from ML-2, -3, and -7 were included in this analysis, 441 and 464 samples from pts treated with RIB + ET and PBO + ET, respectively. Overall, 17 genes had an alteration frequency of >5% at EOT. The ctDNA fraction was higher at EOT vs C1D1 in both the RIB (P=.037) and PBO (P=.033) arms. The frequency of alterations in RB1 (10.4% vs 2.0%), ATM (11.3% vs 8.4%), FAT1 (4.8% vs 3.0%), and FAT3 (5.0% vs 2.5%) was higher at EOT vs C1D1 in the RIB arm (FDR-adj P<.10). Alterations in ESR1 were also higher at EOT vs C1D1 in both the RIB (26.3% vs 9.1%) and PBO arms (28.9% vs 5.4%) (FDR-adj P<.0001). Conversely, alterations in GATA3 were higher at EOT in the PBO arm (FDR-adj P=.11). These results were consistent after adjusting for ctDNA fraction. The most common ESR1 mutations were D538G, Y537S/N/C/D, E380Q, and L536H/P/R. Tx × visit interaction effects were observed for RB1 in the RIB arm and GATA3 in the PBO arm, suggesting tx-specific resistance. A tx × visit interaction for ESR1 was also observed, suggesting a larger relative increase in ESR1 mutations with PBO vs RIB. The percentage of pts with high TMB (>10) at EOT increased from 1.1% to 5.7% in the RIB arm and from 1.7% to 3% in the PBO arm. After accounting for ctDNA fraction and trial, a larger numerical increase in TMB was observed for RIB (odds ratio [OR], 9.0; 95% CI, 2.9-32.7) vs PBO (OR, 2.1; 95% CI, 0.7-6.5); however, the model did not support a differential tx effect. Conclusions: This comprehensive analysis of pooled samples from ML-2, -3, and -7 identified acquired gene alterations in pts with HR+/HER2− ABC treated with 1L or 2L RIB + ET or PBO + ET. The frequency of several genes known to contribute to resistance (ESR1, RB1, ATM, FAT1, and FAT3) was higher at EOT vs C1D1 in pts treated with RIB + ET, while ESR1 and GATA3 alterations were higher at EOT vs C1D1 in pts treated with PBO + ET. This paired dataset of BL and EOT samples from pts with HR+/HER2− ABC treated with a CDK4/6 inhibitor and ET is the largest to date and could be used to validate and confirm acquired resistance mechanisms with low alteration frequency.

Citation Format: Fabrice Andre, Nadia Solovieff, Faye Su, Aditya Bardia, Patrick Neven, Yoon-Sim Yap, Debu Tripathy, Yen-Shen Lu, Dennis Slamon, Stephen K. Chia, Mukta Joshi, Arunava Chakravartty, Agnes Lteif, Tetiana Taran, Carlos Arteaga. Identification of mechanisms of acquired resistance to ribociclib plus endocrine therapy using baseline and end-of-treatment circulating tumor DNA samples in the MONALEESA-2, -3, and -7 trials [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P5-02-14.

Abstract P2-20-01: Patient-derived triple-negative breast cancer organoids as a platform for glucocorticoid receptor- mediated mechanisms of immunotherapy response and resistance

Background: In early-stage triple-negative breast cancer (TNBC), high glucocorticoid receptor (GR) expression correlates with worse relapse-free survival across TNBC subtypes, induces oncogenic gene expression and tumor cell survival, and potentiates anti-inflammatory or an anti-immunogenic phenotype. Immune checkpoint therapy has increased pathologic complete response rates in the neoadjuvant setting, however response to immunotherapy remains modest overall and the explanatory mechanisms for this phenomenon are incompletely understood. We sought a three-dimensional model of the TNBC immune microenvironment using patient-derived organoids (PDOs) that capture tumor heterogeneity, partially recapitulates tumor microenvironment, and can be established for longer-term in vitro/in-vivo translational study after exposure to immunotherapy. We hypothesize that during chemoimmunotherapy treatment of early-stage triple-negative breast cancer, high glucocorticoid receptor activity mediates an immunosuppressive phenotype and glucocorticoid receptor modulation can restore anti-tumor immunity. Methods and Results: We are successfully growing 5 PDOs out of 8 surgically resectedion samples tumors from patients with early-stage triple-negative breast cancer treated with chemotherapy vs. chemoimmunotherapy as per KEYNOTE-522. Interrogation of complementary TNBC cell line data revealed that GR activation downregulates the expression of immune checkpoint genes (PD-L1, B7-H3, B7-H4), while GR knockdown or treatment with a selective GR modulator restores expression of these immune checkpoint genes. TNBC-intrinsic GR activation increases the proportion of regulatory T cells vs. CD8+ T cells. In a coculture system of TNBC spheroids and T cells, GR activation in TNBC results in decreased activated CD8+ CD137+ T cells and use of the selective GR modulator increases the proportion of activated CD8+ CD137+ T cells. Conclusions and Future Directions: In early-stage triple-negative breast cancer, GR activation downregulates expression of immune checkpoint genes and reduction of GR activity restores expression. In a coculture system that recapitulates T cell repertoire found in triple-negative breast cancer, tumor-intrinsic GR activation results in increased regulatory T cell population and reduction of GR activity increases activated CD8+ CD137+ T cells. Ongoing analyses of TNBC organoid-immune coculture systems modeling high GR states will be used to (i) define cooperativity amongst immune checkpoint proteins in costimulation vs. coinhibition of anti-tumor responses and (ii) define novel pairs of receptor-ligands amongst TNBC:CD8+ vs. TNBC:Treg vs. CD8+:Treg as discovery of potential new therapeutic targets.

Citation Format: Christine Shiang, Candace Frerich, Ishrat Durdana, Cheryl Lewis, Lynda B. Bennett, Carlos Arteaga, Suzanne D. Conzen. Patient-derived triple-negative breast cancer organoids as a platform for glucocorticoid receptor- mediated mechanisms of immunotherapy response and resistance [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P2-20-01.

Abstract P5-02-02: Genomic Landscape of ER+/HER2- metastatic breast cancer as a function of prior treatment with a CDK4/6 inhibitor

Background CDK4/6 inhibitors (CDK4/6i), like palbociclib, ribociclib, and abemaciclib, along with antiestrogens, have revolutionized treatment for ER+/HER2- metastatic breast cancer (MBC). Although most patients initially respond, almost all eventually progress, and ER+ HER2- MBC remains incurable. There is an urgent need to understand the molecular processes that drive resistance in order to improve survival. The landscape of acquired somatic alterations causal to CDK4/6i resistance remains unknown. Here we report differences in mutational landscapes between ER+ HER2- MBC patients treated with and without CDK4/6i. Methods Deidentified data from 780 and 1073 ER+ HER2- MBC patients (solid tumor or ctDNA liquid biopsy sequencing respectively) with at least 6 months between diagnosis of Stage 4 disease and biopsy were analyzed. Patients were divided into either treated or untreated with CDK4/6i prior to biopsy. Sequencing was performed using the Tempus xT tumor assay (DNA sequencing of 595-648 genes at 500x coverage) and Tempus xF liquid biopsy (ctDNA sequencing of 105-523 genes). Gene alterations (consisting of pathogenic/likely pathogenic short variants and copy number alterations) were compared between groups by Chi-squared/Fisher’s Exact tests and p-values adjusted for false-discovery. Results We first analyzed sequencing data of both solid tumor and liquid ctDNA from ER+/HER2- MBC patients. ESR1 mutations were significantly more frequent in those that received CDK4/6i than those that did not (Solid tumor 33% vs 16%, p < 0.001, q = 0.001; Liquid biopsy 32% vs 16%, p < 0.001 and q < 0.001). We also saw more frequent mutations/amplifications in the following genes in the CDK4/6i treated cohort vs. those that were not. These results trended towards significance in our solid tumor, but not in our liquid biopsy cohort: CCND1 (18% vs 11% p = 0.028 q =0 .3); FGF3 (17% vs 9.5% p = 0.010 q = 0.2); FGF4 (17% vs 11% p = 0.035 q = 0.3), GATA3 (17% vs 8.9% p = 0.008 q = 0.2), PTEN (12% vs 6.1% p = 0.030 q = 0.3) and FGF19 (8.2% vs 1.7% p = 0.002 q = 0.12). Interestingly, 96-98% of CCND1, FGF3, FGF4 and FGF19 alterations were copy number amplifications. Conversely, we saw a trend towards significance for more mutations in TP53 (37% vs 27% p=0.008 and q=0.2) in those that had not received a CDK4/6i than those that did. Conclusions Here we present the landscape of somatic alterations in ER+/HER2- MBC patients with and without prior CDK4/6i therapy from our large real world de-identified data set. Patients with prior CDK4/6i therapy harbored significantly more ESR1 somatic alterations, demonstrated in both solid tissue and liquid biopsies. In solid tissue biopsies, patients with prior CDK4/6i therapy harbored more CCND1, FGF3, FGF4, and GATA3 alterations and less TP53 alterations. These trends were not significant after adjustment for multiple testing. CCND1, FGF3, FGF4 and FGF19 alterations were copy number amplifications, which may be consistent with 11q13 amplification. Further studies will provide insights into how these trends translate towards our understanding of CDK4/6i related resistance mechanisms.

Citation Format: M Rosario Chica-Parrado, Chang-Ching Lin, Timothy Mahoney, Elizabeth Mauer, Ariella Hanker, Carlos Arteaga. Genomic Landscape of ER+/HER2- metastatic breast cancer as a function of prior treatment with a CDK4/6 inhibitor. [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P5-02-02.

Abstract PD17-08: Pooled gene expression analysis and association with treatment response in patients with HR+/HER2− advanced breast cancer in the MONALEESA-2, -3, and -7 trials

Background: The Phase III MONALEESA (ML)-2, -3, and -7 trials showed significant improvement in progression-free survival (PFS) and overall survival (OS) with ribociclib (RIB) + endocrine therapy (ET) over placebo (PBO) + ET in patients (pts) with HR+/HER2− advanced breast cancer (ABC); improvement in OS with cyclin-dependent kinase 4 and 6 inhibitors (CDK4/6i) has been observed in some, but not all clinical trials. Gene expression analyses for each separate ML study were reported previously. Given the differences in CDK4 vs CDK6 inhibition between RIB and other CDK4/6i, we evaluated the association between cell cycle (CC)–related genes and outcomes based on pooled analysis of gene expression using tumor samples from the ML-2, -3, and -7 trials.

Methods: Gene expression data were generated from pre-treatment archival tumor samples (primary, 73%; metastatic, 27%) with a customized NanoString nCounter panel (781 genes) including genes involved in CC, other signaling pathways, and breast cancer biology. Samples were pooled from 1139 pre- and postmenopausal pts with HR+/HER2− ABC across the 3 ML studies, which included pts on first- and second-line therapy. Data were categorized into training (80%) and test (20%) datasets. The training dataset was used to analyze each gene (modeled continuously) individually for an association with PFS, and genes with a gene × treatment (tx) interaction P value <.10 were evaluated in the test dataset. Genes or gene signatures were classified by tertiles based on expression level (low/medium/high). For each tertile, median (m) PFS was calculated by the Kaplan-Meier method, and hazard ratios (HRs) of tx benefit (RIB vs PBO) were estimated. A Cox proportional hazards model adjusting for clinical covariates was used. A machine learning approach (elastic net survival model with stability selection), which used available gene expression data and select clinical factors and their interactions with tx arms, was applied to predict PFS.

Results: This report focused on CC-related genes and signatures. Gene expression levels of CDKN2B and the expression ratio of CCND1/CDKN2A showed a predictive relationship with benefit from RIB in both training and test sets (Table). PFS benefit with RIB was consistent regardless of the CDK4/CDK6 expression ratio or level of expression of CCNE1, CDK2, RB1, combined CC-related genes, E2F gene signatures, RB gene signature, combined DNA-replication genes, or combined proliferation-related genes. A machine learning approach identified a clinico-genomic signature that was prognostic for PFS benefit with RIB. Selected variables included gene expression levels of FXBO5, PGR, RBBP8, and STC2 and several clinical features (tx arm, de novo disease, prior ET, and visceral disease). Pts with a low signature score had a longer mPFS vs pts with a high signature score, in the RIB (HR, 0.37; 95% CI, 0.22-0.62) and PBO (HR, 0.30; 95% CI, 0.15-0.59) arms.

Conclusion: In the largest pooled analysis of the association of gene expression profile data with CDK4/6i tx response in pts with HR+/HER2− ABC, the PFS benefit with RIB + ET over ET alone was consistent irrespective of expression levels of most CC genes. Variation in magnitude of RIB benefit was observed, depending on CDKN2B expression levels, CCND1/CDKN2A expression ratio, and machine learning–derived signature scores. The clinico-genomic CDK4/6i signature requires validation in additional datasets.

Table 1: Progression-Free Survival by Gene Expression Subgroup

Citation Format: Aditya Bardia, Faye Su, Nadia Solovieff, Fabrice Andre, Carlos Arteaga, Patrick Neven, Yoon-Sim Yap, Yen-Shen Lu, Stephen K. Chia, Dennis Slamon, Seock-Ah Im, Arunava Chakravartty, Agnes Lteif, Tetiana Taran, Debu Tripathy. Pooled gene expression analysis and association with treatment response in patients with HR+/HER2− advanced breast cancer in the MONALEESA-2, -3, and -7 trials [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr PD17-08.

Abstract OT2-17-01: Phase 1 trial of anthracycline chemotherapy in combination with CD40 agonist and Flt3 ligand in metastatic triple-negative breast cancer

Background: Only a subset of patients with metastatic triple-negative breast cancers (TNBC) demonstrate response to FDA approved PD-1 immune checkpoint blockade (ICB), and few have durable responses. Data suggests that breast cancers have defects in antigen presentation and that antigen presenting cells especially the DC1 subtype of dendritic cells (DCs) are required for response to ICB. CD40 agonists activate antigen presenting cells including DCs and B cells and also repolarize macrophages to an anti-tumor phenotype. Flt3 ligand is a growth factor that increases differentiation and expansion of DCs. We recently demonstrated in pre-clinical TNBC models that the combination of liposomal-doxorubicin chemotherapy, a CD40 agonist, and a Flt3 ligand improves outcomes compared to alternate combinations. Methods: This is a single arm phase I pilot study of liposomal-doxorubicin, CDX-1140 (CD40 agonist), and CDX-301 (Flt3 ligand) combination therapy in patients with metastatic or unresectable locally advanced metastatic TNBC. Patients will be randomized to 3 lead-in arms (triplet therapy, doublet immunotherapy only, or liposomal-doxorubicin only) for 1 cycle prior to receiving triplet therapy with fresh tissue biopsies before and after the lead-in treatment. CDX-301 will be discontinued after 2 cycles; liposomal-doxorubicin and CDX-1140 will be continued until disease progression or clinically limiting toxicities. Primary endpoint is determination of a recommended phase 2 dose based on treatment-related adverse events including dose-limiting toxicities. Secondary endpoints include anti-tumor immune response after triplet therapy, after immunotherapy alone, and after liposomal-doxorubicin alone; median progression-free survival, overall response rate, duration of response, and clinical benefit rate. Key eligibility criteria are unresectable stage III or stage IV TNBC (ER ≤10%, PR ≤10%, HER2/neu negative), 1st to 3rd line metastatic treatment setting (1st line patients need to be PD-L1 negative by 22C3 assay), measurable disease by RECIST 1.1 criteria, consent for pre-treatment and on-treatment biopsies of amenable soft tissue tumor lesions, no prior treatment with an anti-CD40 antibody or a Flt3 ligand, no anthracycline treatment in the metastatic setting, no prior progression while on anthracycline-based therapy or within 6 months of completing neoadjuvant chemotherapy, and no history of non-infectious pneumonitis or current pneumonitis. This trial will enroll up to 45 patients across multiple sites (NCT05029999).

Citation Format: Sangeetha Reddy, Meredith Carter, Isaac Chan, Nisha Unni, Namrata Peswani, Dawn Klemow, Samira Syed, Shahbano Shakeel, Farjana Fattah, Chul Ahn, Yisheng Fang, Heather McArthur, Nicole Sinclair, Michael Yellin, Denise Yardley, Nan Chen, Joyce O’Shaughnessy, Rita Nanda, Suzanne D. Conzen, Carlos Arteaga. Phase 1 trial of anthracycline chemotherapy in combination with CD40 agonist and Flt3 ligand in metastatic triple-negative breast cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr OT2-17-01.

Embolic stroke of undetermined source: beyond atrial fibrillation

INTRODUCTION

Embolic stroke of undetermined source (ESUS) accounts for 25% of all cerebral infarcts; only 30% are associated with paroxysmal atrial fibrillation (AF). Various biochemical, electrocardiographic, and echocardiographic findings may suggest left atrial damage and increased risk of embolism in the absence of clinically documented AF or atrial flutter. In this review, we analyse the available evidence on atrial cardiopathy or atrial disease, its involvement in ESUS, and its identification through electrocardiographic, echocardiographic, and serum markers and its possible therapeutic implications.

DEVELOPMENT

A systematic search was conducted on MEDLINE (PubMed) using the following MeSH terms: MeSH [ESUS]+[atrial cardiopathy]+[atrial fibrillation]+[interatrial block]+[treatment]. We selected what we considered to be the most useful original prospective or retrospective studies and systematic reviews. We then read the full texts of the articles and checked the references cited in each article. We analyse epidemiological and demographic variables of patients with ESUS, as well as recent evidence related to presentation and prognosis and factors associated with recurrence and mortality. We review the contribution of atrial cardiopathy diagnosis prior to the detection of AF and the clinical, electrocardiographic, and echocardiographic variables and the biochemical markers associated with its development and its potential contribution to cerebral embolism.

CONCLUSIONS

The systematic search of biochemical and electrocardiographic, and echocardiographic alterations can be useful to identify ESUS patients at higher risk of recurrence.

Embolic stroke of undetermined source: Beyond atrial fibrillation

INTRODUCTION

Embolic stroke of undetermined source (ESUS) accounts for 25% of all cerebral infarcts; only 30% are associated with paroxysmal atrial fibrillation (AF). Various biochemical, electrocardiographic, and echocardiographic findings may suggest left atrial damage and increased risk of embolism in the absence of clinically documented AF or atrial flutter. In this review, we analyse the available evidence on atrial cardiopathy or atrial disease, its involvement in ESUS, and its identification through electrocardiographic, echocardiographic, and serum markers and its possible therapeutic implications.

DEVELOPMENT

A systematic search was conducted on MEDLINE (PubMed) using the following MeSH terms: MeSH [ESUS]+[atrial cardiopathy]+[atrial fibrillation]+[interatrial block]+[treatment]. We selected what we considered to be the most useful original prospective or retrospective studies and systematic reviews. We then read the full texts of the articles and checked the references cited in each article. We analyse epidemiological and demographic variables of patients with ESUS, as well as recent evidence related to presentation and prognosis and factors associated with recurrence and mortality. We review the contribution of atrial cardiopathy diagnosis prior to the detection of AF and the clinical, electrocardiographic, and echocardiographic variables and the biochemical markers associated with its development and its potential contribution to cerebral embolism.

CONCLUSIONS

The systematic search of biochemical and electrocardiographic, and echocardiographic alterations can be useful to identify ESUS patients at higher risk of recurrence.

Abstract PD3-07: Combined inhibition of CDK4/6 and AKT is effective in Rb-intact triple-negative breast cancer of the luminal androgen receptor (LAR) subtype

Background: Triple-negative breast cancer (TNBC) is a heterogeneous disease group with variable clinico-pathologic features. Based on gene expression profiles, TNBCs are grouped into 6 major subtypes. The Luminal androgen receptor (LAR) subtype is enriched for potentially targetable biomarkers, including high androgen receptor (AR) expression, high rates of PIK3CA mutations, and intact Rb. The purpose of this study was to investigate the most effective combinations of CDK4/6, AR, and PI3K-AKT inhibitors in pre-clinical models of LAR TNBC for future clinical trial design. Methods: MDA-MB-453 and MFM-223 (both Rb-intact/PTEN-intact/PIK3CA-mutant) and CAL-148 (Rb-null/PTEN-null/PIK3CA-mutant) LAR TNBC cell lines were treated with the CDK4/6 inhibitor palbociclib, the PI3Kα inhibitor alpelisib, the AKT inhibitor capivasertib, and the AR antagonist enzalutamide, each alone or in different combinations. Drug sensitivity was determined by coulter counter cell counts in 2D, colony formation, and the CellTiterGlo cell viability assay. The combination index (CI) which defines synergism (CI < 1), additive effect (CI = 1) and antagonism (CI > 1), calculated by the CompuSyn method, was used to evaluate the synergistic effects of drug combinations. Expression of cell cycle and PI3K-AKT downstream signaling molecules was measured by western blot analysis. An androgen response element (ARE) luciferase-based reporter assay was used to evaluate AR transcriptional activity. Results: Rb-intact LAR TNBC cell lines were sensitive to single-agent palbociclib, alpelisib or capivasertib (IC50, ~500 nM). Enzalutamide had minimal growth inhibitory activity (IC50, 15-25 μM). Palbociclib combined with either alpelisib or capivasertib synergistically inhibited proliferation of LAR TNBC cells (CI values, 0.07-0.86). Treatment of Rb-intact LAR TNBC cells with palbociclib monotherapy suppressed Rb phosphorylation and resulted in adaptive phosphorylation/activation of S473 AKT and AKT substrates GSKβ and PRAS40 at 24h. These responses were not observed in Rb-null CAL-148 cells. Palbociclib-induced phosphorylation of AKT substrates as well as induction P-S6 and P-4EBP1 were better suppressed by capivasertib than by alpelisib over a dose range. Addition of the PI3Kβ/δ inhibitor AZD8186 to alpelisib markedly enhanced the inhibition of P-AKT, P-PRAS40 and P-Sin, suggesting inhibition of PI3Kα is inadequate to block the adaptive response to palbociclib in these cells. Mean CI values showed that the combination of palbociclib/capivasertib was more synergistic against LAR TNBC cells compared to palbociclib/alpelisib (mean CI, 0.29 vs. 0.78). ARE reporter activity did not change upon inhibition of PI3K or AKT with alpelisib or capivasertib, respectively. Conclusions: Our results suggest that addition of an AKT inhibitor to palbociclib suppresses the rebound activation of AKT following treatment with the CDK4/6i and is effective in LAR TNBC with wild type Rb. In vivo studies are underway to investigate the antitumor activity of the combination of palbociclib and capivasertib in LAR TNBC xenografts.

Citation Format: Gun Min Kim, Kyung-min Lee, Dhivya Sudhan, Albert Lin, Arnaldo Marin, Sumanta Chatterjee, Dan Ye, Vishal Kandagatla, Saurabh Mendiratta, Ariella Hanker, Carlos Arteaga. Combined inhibition of CDK4/6 and AKT is effective in Rb-intact triple-negative breast cancer of the luminal androgen receptor (LAR) subtype [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr PD3-07.

Abstract GS2-01: Overall survival subgroup analysis by metastatic site from the phase 3 MONALEESA-2 study of first-line ribociclib + letrozole in postmenopausal patients with advanced HR+/HER2− breast cancer

Background: MONALEESA-2 (ML-2) recently reported a statistically significant overall survival (OS) benefit with first-line ribociclib (RIB) + letrozole (LET) over placebo (PBO) + LET in postmenopausal patients with HR+/HER2- advanced breast cancer (ABC) (median, 63.9 vs 51.4 months; hazard ratio, 0.76; 95% CI, 0.63-0.93; P = .004). Understanding OS outcomes in clinically relevant subgroups of patients is important for improving personalized care and prognosis. Here, we report the results of a prespecified exploratory OS analysis in select patient subgroups by baseline location and number of metastatic sites.. Methods: Postmenopausal patients with HR+/HER2− ABC were randomized 1:1 to receive first-line RIB or PBO with LET. Prespecified exploratory OS analyses were performed for subgroups of special interest by baseline location (bone only [yes or no], liver involvement [yes or no], liver or lung involvement [yes or no]) and number of metastatic sites (< 3 or ≥ 3). The data are hypothesis generating since this analysis was exploratory and not powered for statistical significance.. Results: A total of 668 patients were included in the analysis. A consistent improvement in OS was observed with RIB + LET vs PBO + LET in all subgroups regardless of baseline metastatic site (Table). RIB + LET demonstrated an OS benefit over PBO + LET in clinically relevant subgroups by baseline location and number of metastatic sites, including subgroups of patients with liver metastases, liver or lung metastases, and ≥ 3 metastatic sites, who generally have a worse prognosis.. Conclusion: Consistent with the intent-to-treat population of ML-2, the results of this prespecified exploratory analysis demonstrated an OS benefit with RIB + LET independent of the site and number of metastatic lesions.

TableTreatment Arm (n)HR (95% CI)Bone-only metastasisYesRIB + LET (69)0.78 (0.50-1.21)PBO + LET (79)NoRIB + LET (265)0.77(0.61-0.96)PBO + LET (255)Liver involvementYesRIB + LET (59)0.81 (0.54-1.24)PBO + LET (72)NoRIB + LET (275)0.77 (0.62-0.97)PBO + LET (262)Liver or lung involvementYesRIB + LET (182)0.81(0.62-1.05)PBO + LET (190)NoRIB + LET (152)0.71 (0.53-0.96)PBO + LET (144)No. of metastatic sites< 3RIB + LET (220)0.78(0.61-1.00)PBO + LET (222)≥ 3RIB + LET (114)0.71(0.51-0.98)PBO + LET (112)

Citation Format: Joyce O'Shaughnessy, Salomon M Stemmer, Howard A Burris, Yoon-Sim Yap, Gabe Sonke, Lowell Hart, Mario Campone, Katarina Petrakova, Eric P Winer, Wolfgang Janni, Pierfranco Conte, David A Cameron, Fabrice André, Carlos Arteaga, Juan Pablo Zarate, Arunava Chakravartty, Tetiana Taran, Fabienne Le Gac, Paolo Serra, Gabriel N Hortobagyi. Overall survival subgroup analysis by metastatic site from the phase 3 MONALEESA-2 study of first-line ribociclib + letrozole in postmenopausal patients with advanced HR+/HER2− breast cancer [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr GS2-01.

Metabolic modulation by CDK4/6 inhibitor promotes chemokine-mediated recruitment of T cells into mammary tumors

Inhibitors of cyclin-dependent kinases 4 and 6 (CDK4/6i) delay progression of metastatic breast cancer. However, complete responses are uncommon and tumors eventually relapse. Here, we show that CDK4/6i can enhance efficacy of T cell-based therapies, such as adoptive T cell transfer or T cell-activating antibodies anti-OX40/anti-4-1BB, in murine breast cancer models. This effect is driven by the induction of chemokines CCL5, CXCL9, and CXCL10 in CDK4/6i-treated tumor cells facilitating recruitment of activated CD8+ T cells, but not Tregs, into the tumor. Mechanistically, chemokine induction is associated with metabolic stress that CDK4/6i treatment induces in breast cancer cells. Despite the cell cycle arrest, CDK4/6i-treated cells retain high metabolic activity driven by deregulated PI3K/mTOR pathway. This causes cell hypertrophy and increases mitochondrial content/activity associated with oxidative stress and inflammatory stress response. Our findings uncover a link between tumor metabolic vulnerabilities and anti-tumor immunity and support further development of CDK4/6i and immunotherapy combinations.

30 Informant-Reported Decline Associates with Silent Acute Stroke Lesions and Worse Small Vessel Disease in Mild Stroke Patients

Introduction

Small vessel disease (SVD) commonly causes stroke and dementia. Early clinical predictors of disease progression are lacking. We aimed to determine whether informant reports of chronic cognitive/functional decline, prerequisites for dementia diagnosis, are associated with (a)baseline SVD burden, measured by Fazekas scores and (b)SVD change, measured by incident subcortical Diffusion-weighted Imaging (DWI) lesions.

Method

We prospectively recruited patients with mild ischaemic stroke, performed diagnostic MRI, and invited participants to repeat MRI 3- to 6-monthly. Informants completed the Informant Questionnaire for Cognitive Decline in the Elderly (IQCODE) prior to baseline visit, a 16-item questionnaire which assesses patients’ cognitive and functional decline in the preceding ten years. Scores range from 1–5: a score above 3.3 has high sensitivity/specificity for dementia post-stroke. We conducted linear regression with IQCODE as the dependent variable, adjusting for age, sex, baseline MoCA, disability (modified Rankin Scale).

Results

We recruited 106 participants (mean age 67 years;range 40–86;33% female). Ninety-three informant questionnaires were returned. IQCODE associated with baseline Fazekas score; Fazekas 6 (β = 0.28, p = 0.04) vs. Fazekas 3 (β = 0.03, p = 0.67), R2 = 0.11, adjusted for age, sex, baseline MoCA, disability.

Incident DWI lesions were common (15/106; 14/15 subcortical; no active embolic sources; median 67 days post-stroke). Four were asymptomatic, two reported stroke-like symptoms and nine had neuropsychiatric/non-focal symptoms. IQCODE was higher in those with a new lesion vs. without (β = 0.21, p = 0.02), R2 = 0.09, while age (β = −0.004, p = 0.19), MoCA (β = −0.006, p = 0.56) and disability (β = 0.06, p = 0.2) were not.

Conclusions

Higher SVD burden and incident, mostly “silent” stroke lesions associate more strongly with informant concerns of cognitive/functional decline than age or objective cognitive tests. These findings are novel in an ischaemic stroke population and the first to assess IQCODE/SVD progression. Future work should determine whether combining informant reports with imaging features of small vessel disease improves early detection of dementia.

Abstract CT061: Binimetinib in patients with tumors with NRAS mutations: NCI-MATCH ECOG-ACRIN Cancer Research Group subprotocol EAY131-Z1A

Background: NRAS-mutations are established oncologic drivers in many malignancies with no effective targeted therapy options. Preclinical and clinical data have suggested that downstream inhibition with a MEK inhibitor, such as binimetinib, might be efficacious for NRAS-mutated cancers. Methods: Patients who enrolled in the multicenter NCI-MATCH trial master protocol underwent tumor biopsy and molecular profiling by targeted next generation sequencing with a custom Oncomine AmpliSeq™ panel. Patients with refractory solid tumors harboring codon 12, 13, or 61 NRAS-mutations were enrolled in subprotocol Z1A, a single arm study of binimetinib 45 mg twice daily. Patients with melanoma were excluded. The primary endpoint was objective response rate (ORR). Secondary endpoints included progression-free survival (PFS) and overall survival (OS). A post-hoc analysis examined association of NRAS-mutation allele with outcome and histology. Results: 47 eligible patients with refractory solid tumors harboring codon 12, 13, or 61 NRAS-mutations were treated on this trial. The most common cancer types enrolled on this subprotocol were colorectal adenocarcinoma (24/47, 51%), cholangiocarcinoma (7/47, 15%), low-grade papillary serous carcinoma of the ovary (3/47, 6%), and endometrioid endometrial adenocarcinoma patients (3/47, 6%). Observed toxicity was moderate, similar to previous reports, and 27.7% (13 of 47) of eligible patients discontinued binimetinib because of adverse events. The ORR was 2.1% (1 of 47 patients), and the median PFS was 3.5 months. The sole confirmed partial response (PR) was observed in a codon 61 NRAS-mutated indolent malignant ameloblastoma. One patient with a colorectal cancer harboring a NRAS codon 61 mutation had an unconfirmed PR, and two others with NRAS codon 61 mutated colorectal cancer had stable disease for at least 12 months. In a post-hoc analysis, patients with cancers bearing a codon 61 NRAS-mutation (n=22) had a significantly longer OS (p=0.04) and PFS (p=0.006) than those with tumors harboring codon 12 or 13 NRAS-mutations (n=25). Similarly, colorectal cancer patients with NRAS codon 61 mutations treated with binimetinib (n=8) had a significantly longer OS (p=0.03) and PFS (p=0.007) than those with NRAS codon 12 or 13 mutated (n=16) tumors. Conclusions: Single-agent binimetinib did not demonstrate promising efficacy in NRAS-mutated solid tumors. Further studies are needed to clarify whether the increased OS and PFS observed in codon 61 NRAS-mutated cancers reflects a more favorable prognosis for this subtype.

Citation Format: James M. Cleary, Victoria Wang, Rebecca Heist, Scott Kopetz, Edith P. Mitchell, James Zwiebel, Helen X. Chen, Shuli Li, Robert Gray, Lisa McShane, Larry Rubinstein, David Patton, Funda Meric-Bernstam, Melissa Dillmon, Mickey Williams, Stanley Hamilton, Barbara Conley, Peter O'Dwyer, Lyndsay Harris, Carlos Arteaga, Alice Chen, Keith Flaherty. Binimetinib in patients with tumors with NRAS mutations: NCI-MATCH ECOG-ACRIN Cancer Research Group subprotocol EAY131-Z1A [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr CT061.

TROPiCS-02: A Phase III study investigating sacituzumab govitecan in the treatment of HR+/HER2- metastatic breast cancer

Patients with HR+/HER2- metastatic breast cancer (MBC) whose cancers have progressed despite conventional therapies represent an unmet clinical need. Trop-2, a transmembrane calcium signal transducer, is highly expressed in MBC and plays a role in tumor growth and progression. Sacituzumab govitecan (SG) is a novel antibody-drug conjugate comprising an Trop-2 antibody coupled to SN-38, the active metabolite of irinotecan, via a unique hydrolyzable linker. SG has demonstrated promising activity in a Phase I/II IMMU-132-01 basket study in heavily pretreated solid tumors, including HR+/HER2- MBC. We describe the registrational Phase III TROPiCS-02 study (NCT03901339), evaluating SG versus treatment of physician's choice in HR+/HER2- MBC. Trial registration number: NCT03901339.

Abstract GS6-06: A neoadjuvant trial with letrozole identifies PRR11 in the 17q23 amplicon as a mechanism of resistance to endocrine therapy in ER-positive breast cancer

Although the 17q23 amplicon has been associated with luminal B breast cancer (BC) and high risk of recurrence, a specific gene or genes in this region that would be causal to endocrine resistance have not yet been uncovered. We performed whole transcriptome analysis on RNA extracted from 58 estrogen receptor (ER)+ BCs treated with neoadjuvant letrozole for median 7.2 months. PRR11 (Proline rich 11), located in 17q23, was upregulated in non-responding tumors as defined by relapse after a median follow up of 5 years and/or a preoperative endocrine prognostic index (PEPI) ≥4. Differential gene expression analysis between tumors expressing low vs high PRR11 mRNA showed that BC signatures associated with proliferation, IGF-1 and PI3K signaling were enriched in tumors with high PRR11 expression.

Rate of PRR11 amplification is 15.2% in the Metastatic Breast Cancer project, but 9.5% and 9.4% in METABRIC and The Cancer Genome Atlas (TCGA), respectively. Gene Set Enrichment Analysis revealed an enrichment of hallmark gene sets associated with proliferation in PRR11-amplified ER+ BCs in METABRIC and TCGA. Integrated analysis of gene expression with on-treatment Ki67 levels from three independent studies with operable ER+ BCs treated with neoadjuvant aromatase inhibitor (ACOSOG-Z1031, NCT00651976, Llombart-Cussac et al.) showed that PRR11 was the only gene in 17q23 with a significant correlation with a high Ki67 levels across all studies.

PRR11 knockdown inhibited E2-independent growth of HCC1428 LTED (long-term estrogen deprived) and MCF7 LTED cells in culture and MCF7 xenografts. PRR11 siRNA also inhibited growth of fulvestrant-resistant and tamoxifen-resistant MCF7 cells. Conversely, PRR11 transduction induced MDA-MB-134VI cell growth under estrogen-depleted conditions. Using a PCR array with 84-cell cycle genes, we identified SKP2, CDKN1A, CCNB2, CCNA2, CKS2 and CCNB1 as genes downregulated by PRR11 knockdown. Except for SKP2 and CDKN1A, expression of all those genes was elevated in PRR11-amplifiedER+ BCs in TCGA and METABRIC.

Suggesting a link to activation of PI3K signaling, we found the proline-rich motif of PRR11 associates with the SH3 domain of the p85 regulatory subunit of PI3K. We hypothesized that this association suppresses p85 homodimer formation, thus facilitating binding of PI3Kα (p110α)-p85 dimers to IRS1, retention of p110α at the plasma membrane and, hence, activation of PI3K/AKT. To test this, we co-transfected HEK293T cells with HA-p85 and FLAG-p85. Forced expression of PRR11 reduced HA-p85 and FLAG-p85 homodimers as shown by HA and FLAG pulldowns followed by FLAG and HA immunoblots, respectively. PRR11 overexpression enhanced insulin-stimulated association of IRS1 to p110α and activation of AKT. PRR11 knockdown reduced insulin/IGF-1/2-stimulated p-AKT. In METABRIC and TCGA, PRR11 amplification and PIK3CA mutations are exclusive of each other, suggesting these alterations would be functionally linked with the same pathway.

Connectivity map analysis with the list of genes significantly overexpressed in ER+/PRR11-amplified BCs predicted PI3K inhibitors as perturbations that suppress such gene list. In the MGH/Sanger dataset, PRR11-amplified BC cell lines displayed significantly higher sensitivity to the pan-PI3K inhibitor pictilisib compared to cell lines without PRR11 amplification. Finally, inhibition of PI3Kα by siRNA or alpelisib abrogated E2-independent growth and insulin-stimulated growth of PRR11-transduced MDA-MB-134VI and MCF10A cells, respectively, suggesting p110α is required for the growth promoting effects of PRR11.

These data suggest that 1) PRR11 is a mediator of resistance to antiestrogens via amplification of PI3K/AKT signaling, and 2) PI3Kα is a potential therapeutic target in ER+ BCs harboring PRR11 amplification.

Citation Format: Kyung-min Lee, Angel Guerrero-Zotano, Ariella Hanker, Alberto Servetto, Dhivya Sudhan, Luigi Formisano, Valerie Jansen, Paula González-Ericsson, Melinda Sanders, Thomas Stricker, Lewis Cantley, Carlos Arteaga. A neoadjuvant trial with letrozole identifies PRR11 in the 17q23 amplicon as a mechanism of resistance to endocrine therapy in ER-positive breast cancer [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr GS6-06.

Abstract OT1-07-05: TROPiCS-02: phase 3 study of Sacituzumab Govitecan (IMMU-132) in relapsed/refractory hormonal receptor-positive (HR+) human epidermal growth factor receptor 2 negative (HER2-) metastatic breast cancer (MBC)

Background: Patients (pts) with HR+/HER2- MBC for whom first- and second-line treatments have failed need additional treatment approaches. Trophoblast cell surface antigen 2 (Trop-2) is highly expressed in breast cancer and linked to poor prognosis. Sacituzumab govitecan (SG) is a novel antibody-drug conjugate comprising an anti-Trop-2 monoclonal antibody conjugated to SN-38 (active metabolite of irinotecan) in a high drug-to-antibody ratio of 7.6. It has a unique hydrolysable linker that allows release of SN-38 intracellularly and in the tumor microenvironment. In the HR+/HER2- MBC cohort in the IMMU 132-01 phase 1/2 basket study, SG showed a 31% objective response rate (ORR), median progression-free survival (PFS) of 6.8 mo, and a predictable and manageable safety profile with low discontinuation rates due to adverse events (Kalinsky 2018 SABCS).

Trial Design: Trop-2 Investigation in Cancer with Sacituzumab (TROPiCS-02; NCT03901339) is a randomized, open-label, phase 3 study in pts with HR+/HER2- MBC and ≥1 measurable target lesion according to Response Evaluation Criteria in Solid Tumors version 1.1 after failure of ≥2, but ≤4 prior chemotherapy regimens. Pts are randomized 1:1 to receive SG (10 mg/kg intravenously, days 1 and 8 every 21 days) or treatment of physician’s choice (TPC, determined pre-randomization: eribulin, capecitabine, gemcitabine, vinorelbine). Pts continue treatment until progression requiring discontinuation or unacceptable toxicity. Eligible pts are females or males ≥18 y old with documented evidence of HR+/HER2- MBC, Eastern Cooperative Oncology Group score of 0 or 1, and adequate safety laboratories. Pts must have received prior taxanes in any setting, ≥1 prior anticancer hormonal treatment, and ≥1 cyclin dependent kinase 4/6 inhibitor in the metastatic setting, with documented progression after most recent therapy. Pts also must be eligible to receive one of the TPC agents. The primary endpoints are PFS (local assessment) and ORR; additional endpoints include overall survival (OS), duration of response (DOR), and safety. The hazard ratio of the primary endpoint of PFS and its associated 95% confidence interval (CI) will be estimated using a Cox proportional-hazards model; the 2-sided 95% CIs of ORR will be calculated by the Clopper-Pearson exact method. Exploratory endpoints include Trop-2 expression and efficacy in relation to Trop-2 expression and blood and tumor biomarkers. Biomarker samples are taken at baseline, pre-dose at cycle 2, and at disease progression/end of treatment. Approximately 400 pts will be randomized across multiple countries.

Citation Format: Hope S Rugo, Aditya Bardia, Sara M. Tolaney, Carlos Arteaga, Javier Cortes, Joohyuk Sohn, Frederik Marmé, Quan Hong, Scott Hofsess, Martin Olivo, André Fabrice, Peter Schmid. TROPiCS-02: phase 3 study of Sacituzumab Govitecan (IMMU-132) in relapsed/refractory hormonal receptor-positive (HR+) human epidermal growth factor receptor 2 negative (HER2-) metastatic breast cancer (MBC) [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr OT1-07-05.

Estrogen receptor coregulator binding modulator (ERX-11) enhances the activity of CDK4/6 inhibitors against estrogen receptor-positive breast cancers

BACKGROUND

CDK4/6 inhibitors in combination with endocrine therapy (AE/AI/SERDs) are approved for the treatment of ER+ advanced breast cancer (BCa). However, not all patients benefit from CDK4/6 inhibitors therapy. We previously reported a novel therapeutic agent, ERX-11, that binds to the estrogen receptor (ER) and modulates ER-coregulator interactions. Here, we tested if the combination of ERX-11 with agents approved for ER+ BCa would be more potent.

METHODS

We tested the effect of combination therapy using BCa cell line models, including those that have acquired resistance to tamoxifen, letrozole, or CDK4/6 inhibitors or have been engineered to express mutant forms of the ER. In vitro activity was tested using Cell Titer-Glo, MTT, and apoptosis assays. Mechanistic studies were conducted using western blot, reporter gene assays, RT-qPCR, and mass spectrometry approaches. Xenograft, patient-derived explants (PDEs), and xenograft-derived explants (XDE) were used for preclinical evaluation and toxicity.

RESULTS

ERX-11 inhibited the proliferation of therapy-resistant BCa cells in a dose-dependent manner, including ribociclib resistance. The combination of ERX-11 and CDK4/6 inhibitor was synergistic in decreasing the proliferation of both endocrine therapy-sensitive and endocrine therapy-resistant BCa cells, in vitro, in xenograft models in vivo, xenograft-derived explants ex vivo, and in primary patient-derived explants ex vivo. Importantly, the combination caused xenograft tumor regression in vivo. Unbiased global mass spectrometry studies demonstrated profound decreases in proliferation markers with combination therapy and indicated global proteomic changes in E2F1, ER, and ER coregulators. Mechanistically, the combination of ERX-11 and CDK4/6 inhibitor decreased the interaction between ER and its coregulators, as evidenced by immunoprecipitation followed by mass spectrometry studies. Biochemical studies confirmed that the combination therapy significantly altered the expression of proteins involved in E2F1 and ER signaling, and this is primarily driven by a transcriptional shift, as noted in gene expression studies.

CONCLUSIONS

Our results suggest that ERX-11 inhibited the proliferation of BCa cells resistant to both endocrine therapy and CDK4/6 inhibitors in a dose-dependent manner and that the combination of ERX-11 with a CDK4/6 inhibitor may represent a viable therapeutic approach.

Abstract 929: Paired tumor and cfDNA in patients with HER2-mutant solid tumors treated with neratinib reveals convergence of multiple on-target resistance mechanisms: Results from the SUMMIT "Basket" Trial

Background: Somatic mutations in ERBB2 occur across various tumor types at relatively low frequencies and can lead to constitutive kinase signaling and oncogenic transformation. SUMMIT is an ongoing basket trial of neratinib, an irreversible pan-HER tyrosine kinase inhibitor, in pts with ERBB2 mutant cancers (NCT01953926).

Methods: Pts with advanced solid tumors and locally documented ERBB2 mutations received neratinib 240 mg daily (N=8) +/- fulvestrant at the labeled dose for pts with ER+ breast cancer (N=6) as part of the global Phase II SUMMIT basket study. Pre- and post-treatment tumor and cfDNA were subjected to NGS using MSK-IMPACT for tissue (410 genes) and MSK-ACCESS for plasma (129 genes) to identify SNVs, indels, and copy number alterations.

Results: In total, 14 pts had successful sequencing of both paired tissue and cfDNA sample (10 breast, 2 gallbaldder, 1 bladder, and 1 unknown primary). All pts achieved clinical benefit on neratinib including 2 CRs, 7 PRs, and 5 SDs. In 1 gallbladder pt, paired tissue sequencing identified loss of the pretreatment clonal ERBB2 mutation but retention of a truncal TP53 mutation, suggesting emergence of a distantly related ERBB2 wildtype clone. In the remaining 13 patients, the pretreatment ERBB2 mutation was retained in tissue at progression. 64% (9/14) pts had at ≥1 acquired alteration in tissue including 3 pts who acquired secondary alterations in ERBB2, both clonal and subclonal ERBB2 mutations as well new focal amplifications. Consistent with this finding, plasma cfDNA sequencing revealed 57% (8/14) of pts acquired ≥1 secondary ERBB2 mutation with the majority occurring at known activating hotspots. Analysis of mutant allele frequencies of these emergent ERBB2 alterations, in comparison to other variants, suggested the majority were subclonal with evidence of multiple independent subclones arising in the same patient. Two pts developed known ERBB2 gatekeeper mutations (T798I and L785F).

Conclusion: In pts with ERBB2-mutant solid tumors with clinical benefit on neratinib, a potential on-target resistance mechanism was identified in 71% (10/14, including 7 with acquired gain-of-function ERBB2 mutations, 2 with ERBB2 both gain-of-function and gatekeeper mutations, and 1 with outgrowth of an ERBB2 wildtype clone). Collectively, these data provide additional evidence that ERBB2 mutations lead to oncogene addiction in solid tumors. We also demonstrate that tumor and cfDNA sequencing provides complementary information that can be integrated to more fully elucidate potential resistance mechanisms.

Citation Format: Helen H. Won, S. Duygu Selcuklu, Sarina A. Piha-Paul, Cristina Saura, Jordi Rodon, Ingrid A. Mayer, Sherene Loi, Geoffrey I. Shapiro, Janice Lu, Adam Brufsky, Catherine Zimel, Myra Melcer, Maurizio Scaltriti, Lisa D. Eli, Richard E. Cutler Jr., Alshad S. Lalani, Richard P. Bryce, Carlos Arteaga, Funda Meric-Bernstam, Michael F. Berger, David B. Solit, Alison Schram, David M. Hyman. Paired tumor and cfDNA in patients with HER2-mutant solid tumors treated with neratinib reveals convergence of multiple on-target resistance mechanisms: Results from the SUMMIT "Basket" Trial [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 929.

Abstract P1-15-01: Withdrawn

This abstract was withdrawn by the authors.

Citation Format: Metzger Filho O, Janiszewska M, Guo H, Yardley D, Mayer I, Spring L, Arteaga C, Wrabel E, DeMeo M, Freedman R, Tolaney S, Waks A, Bardia A, Parsons H, Partridge A, Mayer E, King T, Polyak K, Viale G, Winer E, Krop I. Withdrawn [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P1-15-01.

Abstract P5-04-23: Enhancing the activity of a novel estrogen receptor coregulator binding modulator (ERX-11) against ER-positive therapy resistant breast cancer

Background:We had previously reported a novel small molecule, ERX-11, that directly interacts with ER and blocks the interaction between a subset of coregulators with both native and mutant forms of ER. ERX-11 effectively blocks ER oncogenic signaling and has potent anti-proliferative activity against therapy-sensitive and therapy-resistant human breast cancer cells. To enhance the clinical translation of ERX-11, we sought to pursue both lead optimization and evaluate combinations of ERX-11 with other approved agents in breast cancer.

Methods: We designed, synthesized and tested 500 derivatives of ERX-11 in multiple models of ER+ breast cancer. We also tested combinations of ERX-11 with multiple agents, including other ER targeting agents, chemotherapies and CDK4/6 inhibitors. We tested the effect of combination therapy using breast cancer cells with acquired resistance (Tamoxifen, Letrozole, Ribociclib resistant) and engineered models that express ER mutations. In vitro activity was tested using Cell titer glo, MTT, and apoptosis assays. Mechanistic studies were conducted using Western blot, reporter gene assays and RNA-seq analysis. Xenograft, patient derived xenograft (PDX), patient derived explant (PDE) and xenograft derived explant (XDE) models were used for preclinical evaluation and toxicity.

Result: Evaluation of 500 analogs of ERX-11 identified a number of leads with differential activity against ER+ and ER- breast cancer cells, identified several analogs including ERX-144, 208, 296, 315 with nanomolar potency against ER+ and therapy-resistant ER+ breast cancers. Validation of the mechanism of action of these analogs is ongoing. The combination of ERX-11 and palbociclib significantly blocked ER-mediated and ER-coregulators mediated oncogenic signaling and showed potent anti-proliferative activity against both endocrine therapy-sensitive and resistant breast cancer cells. In addition, ERX-11 inhibited ribociclib-resistant ER+ cell proliferation in a dose dependent manner. Mechanistic studies using IP-Mass spectrometry demonstrated that ERX-11 and palbociclib blocks the interaction between larger subset of coregulators with ER in therapy resistant breast cancer models. ERX-11 and palbociclib both exhibited potent anti-proliferative activity against therapy-sensitive and therapy-resistant ER+ve breast cancer cells, in xenograft models and in PDEs. Importantly, combination therapy of ERX-11 and palbociclib synergistically reduced the growth of tamoxifen and letrozole resistant xenograft tumors compared to either drug alone. Mass spec based DIA analyses and RNA-seq studies revealed that combinational treatment uniquely activated p53, unfolded response mediated apoptotic pathways, altered DNA damage response and suppressed E2F and Myc target genes. Biochemical studies confirmed combination therapy significantly altered E2F1, ER and DNA damage response pathways.

Conclusion: We have successfully pursued two avenues to improving ERX-11 for clinical translation. We have developed ERX-11 analogs with higher potency against ER+ breast cancer. We have shown that combinational treatment with ERX-11 and palbociclib may overcome endocrine therapy resistance and CDK4/6 inhibitor (ribociclib) resistance.

Citation Format: Viswanadhapalli S, Ma S, Lee T-K, Sareddy GR, Liu X, Ekoue D, Alluri A, Luo Y, Kassees K, Arteaga C, Alluri P, Weintraub SE, Tekmal RR, Ahn J-M, Raj GV, Vadlamudi RK. Enhancing the activity of a novel estrogen receptor coregulator binding modulator (ERX-11) against ER-positive therapy resistant breast cancer [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P5-04-23.

Abstract PD7-10: Neoadjuvant trial with letrozole identifies PRR11 in 17q21-23 amplicon as a resistance mechanism to endocrine therapy in ER-positive breast cancer

Approximately 20% of patients with early ER+ breast cancer (BC) treated with adjuvant antiestrogen therapy relapse with metastatic disease. Previously, we identified 3 amplicons (11q11.3, 8p11.23, and 17q21-23) associated with endocrine-resistance (Giltnane et al. Sci Transl Med 2017). The 17q21-23 amplicon has been associated with highly proliferative luminal B tumors and cancers with high genomic instability. A causal role of this region in endocrine resistance is unclear. We performed whole transcriptome analysis on RNA extracted from 58 ER+ breast cancers of patients treated with letrozole for 5.4-9.2 months (median 7.2 months). PRR11 (Proline rich 11), located in 17q21-23, was significantly upregulated in non-responding tumors as defined by cancer relapse after a median follow up of 5 years and/or a preoperative endocrine prognostic index (PEPI) ≥4. Differential gene expression analysis between tumors expressing low vs high PRR11 mRNA showed that BC signatures associated with proliferation, cell cycle, IGF-1 and PI3K signaling were enriched in tumors with high PRR11 expression. In the Metastatic Breast Cancer Project and TCGA, PRR11 amplification was higher in metastatic vs. primary BCs (16.5% and 8.5%, respectively; Fisher's p=0.0088). Gene Set Enrichment Analysis of mRNA expression in METABRIC and TCGA revealed significant enrichment of hallmark gene sets associated with proliferation in PRR11 amplified ER+ BCs. Genome-scale RNAi screening in Project Achilles showed that among all genes in the 17q21-23 amplicon, PRR11 knockdown results in the 4th strongest anti-proliferative effect in MCF7 cells. PRR11 knockdown with siRNA inhibited proliferation, cell cycle progression, and RB phosphorylation in HCC1428 LTED (long-term estrogen deprived), MCF7 LTED, and fulvestrant-resistant MCF7 cells. Using a PCR array with 84-cell cycle genes, we identified SKP2, CDKN1A, CCNB2, CCNA2, CKS2 and CCNB1 as genes downregulated by PRR11 knockdown. Except for CDKN1A, expression of all those genes was elevated ER+ BCs with PRR11 gain or amplification in TCGA. PRR11 associates with the p85 regulatory subunit of PI3K via its SH3 domain. We speculated this association would suppress p85 homodimers, thus permitting binding of PI3Kα (p110α)-p85 dimers to IRS1 and, hence, activating PI3K/AKT. To test this, we co-transfected HEK293T cells with HA-p85 and FLAG-p85. Transfection of PRR11 into these HEK293T cells reduced HA-p85 and FLAG-p85 homodimers as shown by HA and FLAG pulldowns followed by FLAG and HA immunoblots, respectively. Finally, PRR11 knockdown resulted in a reduction of p110a and S473 P-AKT levels and inhibition of IGF-1/2 stimulated P-AKT. Not inconsistent with these data, PRR11 amplification and PIK3CA mutations in METABRIC and TCGA are exclusive of each other, suggesting these alterations are functionally linked with the same signaling pathway. These data support a role of PRR11 in PI3K/AKT activation that may be causal to resistance to estrogen deprivation. We propose PRR11, located in the 17q21-23 amplicon, is a potential mediator of resistance to antiestrogen therapy by amplifying PI3K/AKT signaling, suggesting PI3K may be a therapeutic target in ER+ BCs harboring PRR11 amplification.

Citation Format: Lee K-M, Guerrero-Zotano A, Formisano L, Jansen V, Gonzalez Ericsson P, Arteaga C. Neoadjuvant trial with letrozole identifies PRR11 in 17q21-23 amplicon as a resistance mechanism to endocrine therapy in ER-positive breast cancer [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr PD7-10.

Abstract PD3-06: Neratinib + fulvestrant for HER2-mutant, HR-positive, metastatic breast cancer: Updated results from the phase 2 SUMMIT trial

Background: HER2 mutations define a rare subset of metastatic breast cancer (MBC) with a unique mechanism of oncogenic addiction to HER2 signaling. Neratinib, an irreversible pan-HER tyrosine kinase inhibitor, has demonstrated single-agent clinical activity in HER2-mutant MBC. In HER2-mutant, HR+ MBC, neratinib + fulvestrant (N+F) appears synergistic vs single-agent neratinib, possibly due to more complete inhibition of bi-directional signaling between HER2 and estrogen receptors. Here we describe interim efficacy results of the expanded HER2-mutant, HR+ MBC cohort treated with N+F from SUMMIT (NCT01953926).

Methods: HR+ MBC patients (pts) with HER2 mutations documented by local testing received oral neratinib 240mg qd and intramuscular fulvestrant (labeled dose). Intensive loperamide prophylaxis was mandatory during cycle 1. Efficacy endpoints include objective response rate at week 8 (ORR8); confirmed objective response rate (ORR); clinical benefit rate (CBR); duration of response (DOR); progression-free survival (PFS); response was assessed by RECIST 1.1 and/or PET Response Criteria. Genomic profiling from fresh/archival tumor tissues and/or plasma cfDNA was performed retrospectively by next-generation sequencing (MSK-IMPACT).

Results: As of 18 May 2018, 46 HER2-mutant HR+ MBC pts have been treated with N+F. Most pts were pretreated, with 91% having received prior anti-cancer medication for MBC (range 0–10). ORR was 33% and median DOR in the 15 pts with a confirmed response was 9.2 months (95% CI 3.9–18.5). Twenty-four pts had prior fulvestrant exposure, and 19 had received prior CDK4/6i-based therapy. Clinical activity was observed with ORRs of 17% and 26% in prior fulvestrant-treated and prior CDK4/6i-treated pts, respectively. ORRs by HER2 mutation were: V777L 63% (5/8 pts); S310F/Y 67% (4/6 pts); G778_P780dup 50% (3/6 pts). Diarrhea was the most common adverse event (grade 3, 24%; grade 4, 0%). Median cumulative duration of grade 3 diarrhea was 3 days. There were no treatment discontinuations due to diarrhea.

 Neratinib + fulvestrantOutcomeaAll patients (N=46)Prior fulvestrant (N=24)Prior CDK4/6i-based therapy (N=19)ORR8 – n (%)19 (41.3)8 (33.3)7 (36.8)95% CI27.0–56.815.6–55.316.3–61.6ORR – n (%)15 (32.6)4 (16.7)5 (26.3)95% CI19.5–48.04.7–37.49.1–51.2DOR for each responder, months 5.6b; 9.2; 9.6b; 18.55.6b; 5.7b; 9.3; 9.6b; 12.9bCBR – n (%)27 (58.7)11 (45.8)9 (47.4)95% CI43.2–73.025.6–67.224.4–71.1Median (95% CI) time to event,c monthsPFS3.9 (3.6–5.7)3.7 (3.5–12.8)3.9 (1.9–NA)DOR9.2 (3.9–18.5)NANAaFor pts with both RECIST- and PET-evaluable lesions, the best of either RECIST or PET response was used to determine response; the earliest progression by RECIST or PET was used for progression; bPt has not progressed; cKaplan-Meier analysis; NA, not applicable

Conclusions: N+F demonstrates encouraging clinical activity with durable responses in heavily pretreated pts with HER2-mutant, HR+ MBC. Of note, responses were observed in pts who had received prior fulvestrant or CDK4/6 inhibitors. No new safety signals were identified; the rate of diarrhea was similar to single-agent neratinib and not dose limiting. Updated data after additional follow-up and genomic data will be presented.

Citation Format: Smyth LM, Piha-Paul SA, Saura C, Loi S, Lu J, Shapiro GI, Juric D, Mayer IA, Arteaga C, de la Fuente M, Brufksy AM, Mau-Sørensen M, Arnedos M, Moreno V, Sohn J-H, Schwartzberg L, Gonzàlez-Farré X, Cervantes A, Mann G, Shahin S, Cutler, Jr. RE, Eli LD, Xu F, Bagulho T, Lalani AS, Bryce R, Solit DB, Hyman DM, Meric-Bernstam F, Baselga J. Neratinib + fulvestrant for HER2-mutant, HR-positive, metastatic breast cancer: Updated results from the phase 2 SUMMIT trial [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr PD3-06.

Correction to: Unexpected Benefit from Alpelisib and Fulvestrant in a Woman with Highly Pre-treated ER-Positive, HER2-Negative PIK3CA Mutant Metastatic Breast Cancer

Dr. Arteaga serves on an Advisory Board for Novartis and was a consultant for AstraZeneca from 2015 to 2016. All other authors declare that they have no competing interests.

Unexpected Benefit from Alpelisib and Fulvestrant in a Woman with Highly Pre-treated ER-Positive, HER2-Negative PIK3CA Mutant Metastatic Breast Cancer

We present the case of a postmenopausal patient with a secondary metastatic ER-positive, HER2-negative breast cancer who was successfully treated with fulvestrant and alpelisib following six lines of therapy. The tumour showed two uncommon PIK3CA mutations, and with the combination of alpelisib and fulvestrant the patient went from ECOG grade 3, before the start of this therapy, to ECOG grade 1 during treatment until progressive disease after 6 months. This unexpected benefit emphasizes the importance of performing a Next Generation Sequencing (NGS)-based assay to screen for several cancer genes in the metastatic setting, even after more than four lines of therapy and a high ECOG grade. Moreover, the use of alpelisib may be beneficial for uncommon PIK3CA mutations.

Abstract 3890: Mitochondrial MCL1 maintains triple negative breast cancer stem cells and contributes to chemotherapy resistance

Cytotoxic chemotherapy is the standard of care for patients with triple negative breast cancer (TNBC). Most patients with advanced TNBC progress after chemotherapy and die from metastatic disease. MCL1 is an anti-apoptotic Bcl-2 family member known to sequester and inactivate pro-apoptotic Bcl-2 family proteins and, thus, contribute to chemotherapy resistance. We previously reported that ~45% of residual TNBCs that remain in the breast after neoadjuvant chemotherapy harbor MCL1 amplification, suggesting a causal role for MCL1 in drug resistance. A recent report (Goodwin et al. 2015) suggested that siRNA-mediated ablation of MCL1 does not induce apoptosis in claudin-low TNBC cells with a cancer stem cell (CSC) gene expression signature. CSCs comprise a rare population of cells with tumor-initiating properties and refractoriness to chemotherapy. In this study, we showed that MCL1 expression is elevated in claudin-low TNBC SUM159PT and MDA436 CSCs as measured by ALDH+ by flow cytometry and ability to form mammospheres. RNA interference of MCL1 in SUM159PT cells reduced CSCs and attenuated tumor formation in vivo. Mitochondrial oxidative phosphorylation (mtOXPHOS) plays a crucial role in maintenance of CSCs. MCL1 has been shown to localize in the mitochondrial matrix and contribute to mitochondrial respiration. Thus, we hypothesized that MCL1 contributes to enrichment of TNBC CSCs and chemotherapy resistance via mitochondrial regulation. Stable transfection and overexpression of MCL1 in MDA468 cells increased oxygen consumption ratio, mitochondrial membrane potential, and production of reactive oxygen species (ROS), all features of activated mtOXPHOS. Conversely, RNAi-mediated ablation of MCL1 in SUM159PT and MDA436 cells repressed these markers of activated mtOXPHOS. A mutant of MCL1 lacking its mitochondrial target sequences (MTS) was unable to localize in mitochondria and, when transfected into MDA468 cells, reduced the CD44high/CD24low fraction and mammosphere formation. We next tested VU0659158, a BH3 mimetic in development at Vanderbilt that disrupts MCL1 interactions with BH3 domain-containing proteins, such as BID, BIM, NOXA and PUMA. Treatment of SUM159PT cells with VU0659158 increased caspase activity but did not attenuate mammosphere formation. Analysis of mRNA expression in TCGA revealed that genes induced by mtOXPHOS involved in the hypoxia pathway are significantly up-regulated in MCL1 amplified breast cancers. Finally, pharmacological inhibition of HIF-1α, a key regulator of hypoxia, with digoxin decreased CSCs and attenuated tumor formation in vivo. These data suggest that 1) MCL1 confers resistance to chemotherapy by expanding CSCs via mtOXPHOS independent of its BH3 domain-mediated, anti-apoptotic function, and 2) targeting mitochondrial respiration and the hypoxia pathway may delay or reverse chemotherapy resistance in MCL1 amplified TNBC.

Citation Format: Kyung-min Lee, Jennifer Giltnane, Justin Balko, Luis Schwarz, Angel Guerrero, Katie Hutchinson, Mellissa Hicks, Violeta Sanchez, Melinda Sanders, Taekyu Lee, Edward Olejniczak, Stephen Fesik, Carlos Arteaga. Mitochondrial MCL1 maintains triple negative breast cancer stem cells and contributes to chemotherapy resistance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3890. doi:10.1158/1538-7445.AM2017-3890

Abstract CT232: SU2C Phase Ib study of the PI3K-alpha inhibitor BYL719 (alpelisib) with letrozole in ER+/HER2-metastatic breast cancer

Background: Mutations in PIK3CA, the gene encoding the p110α subunit of PI3K, have been associated with antiestrogen resistance in ER+ BC. In general, antiestrogen-resistant cancers retain ER and responsiveness to estradiol. This suggests that treatment of ER+ BC with PI3K inhibitors should also include antiestrogens.

Methods: We conducted a phase Ib 3+3 dose escalation trial of letrozole (2.5 mg/day) with the PI3Kα inhibitor BYL719 in post-menopausal patients (pts) with ER+/HER2- metastatic breast cancer (MBC) refractory to previous endocrine therapy. BYL719 doses ranged from 300-400 mg/daily. Treatment continued until unacceptable toxicity or disease progression. Disease was assessed every 2 months. PIK3CA mutation status was determined by SNaPshot or targeted next generation sequencing (NGS) in all patients’ tumors.

Results: Twenty-six pts were accrued; all patients were refractory to endocrine therapies in the metastatic setting, 18 had prior aromatase inhibitor (AI) therapy in their first or second-line MBC treatment. Median age was 53 years (31-72); 76% of pts had bone and 61% had visceral metastases; 50% of pts had a somatic PIK3CA hotspot mutation. Toxicities are summarized in Table 1. Rash was the dose limiting toxicity* at 350 mg/day. Of the 5 pts with a partial response, 3 (60%) had a PI3KCA mutation, 6/9 pts (67%) that were on treatment for ≥6 months; 3/6 pts (50%) that were on treatment for ≥12 months and 4/6 pts (67%) that are still on study (range 11 - 19 months) had a PI3KCA mutation.

Discussion: The combination of letrozole/ BYL719 is safe and tolerable in pts with AI-refractory ER+/HER2-negative MBC. The MTD and recommended dose for phase II trials of BYL719 in combination with letrozole was 300 mg/day. Rash and hyperglycemia were observed at this dose, suggesting drug-induced inhibition of PI3K. Pts with PIK3CA-mutant tumors appeared to derive better clinical benefit, although activity of the combination was also seen in patients with PIK3CA-wild type cancers. Additional NGS of >300 cancer genes and their correlation with clinical response will be updated at the meeting. Clinical trial information: NCT01791478.

Adverse Events (% by Grade)Toxicity300 mg (N = 20)300 mg (N = 20)350 mg (N = 6)350 mg (N = 6)% by Grade% by Grade% Total% by Grade% by Grade% Total2323Hyperglycemia181256202070Diarrhea12128110050Fatigue2504330080Rash180431020*40Nausea0062101060Vomiting00250030Anorexia602510040Dysgeusia00180050

Citation Format: Ingrid A. Mayer, Vandana Abramson, Justin Balko, Melinda Sanders, Dejan Juric, David Solit, Yisheng Li, Lewis Cantley, Eric Winer, Carlos Arteaga. SU2C Phase Ib study of the PI3K-alpha inhibitor BYL719 (alpelisib) with letrozole in ER+/HER2-metastatic breast cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr CT232. doi:10.1158/1538-7445.AM2015-CT232

Abstract 1945: TORC inhibitors increase the cancer stem cell (CSC) population and Notch signaling in triple negative breast cancer

Tumor-initiating cells (TICs) or cancer stem cells (CSCs) are resistant to chemotherapy and have been associated with metastatic recurrences and poor patient outcome particularly among patients with triple negative breast cancer (TNBC). Genomic and proteomic data have indicated more than 30% of TNBC patients have PI3K/mTOR pathway lesions making this pathway a promising therapeutic target. Recent publications have demonstrated mechanisms of resistance (JAK2/STAT5 and MYC amplification) to PI3K pathway inhibitors. We hypothesized that resistance to TORC inhibition is due to the survival of a CSC population and that targeting pathways that sustain these cells can provide a significant therapeutic benefit. Treatment of TNBC cell lines with the PI3K/mTOR inhibitor NVP-BEZ235 or the TORC1/2 inhibitor MLN128 resulted in a significant reduction of proliferation in vitro. However, we observed that both BEZ235 and MLN128 enriched for a CSC population as assessed by FACS analysis of cancer stem-like markers and mammosphere formation. This observation was specific to TNBC cell lines since BEZ235 and MLN128 significantly abrogated the CSC population in ER+ (MCF7) and HER2+ (HCC1954) breast cancer cell lines. To determine the mechanisms involved in this CSC enrichment we used a Stem Cell specific PCR Array. We observed an increase in Notch1, FGF1 and ABCG2 mRNA levels in TNBC cells treated with BEZ235 and MLN128. Treatment with these inhibitors also increased the expression of the active Notch intracellular domain, the Notch ligand Jagged1, and the Notch1 target genes Hes1 and Hey1 by qRT-PCR and transcriptional reporter activity. In addition to Hes1 and Hey1, c-myc, another Notch target gene, expression was augmented in 2 of the 3 TNBC cell lines tested. Treament with the γ-secretase inhibitor, DAPT and transfection with Notch1 siRNA oligonucleotides abrogated BEZ235 and INK128-mediated enrichment of CSC populations as measured by FACS analysis and mammosphere formation assays. To determine whether inhibition of either TORC1 or TORC2 enriched for the CSC population, we used RNAi against Rictor (TORC2), Raptor (TORC2) or both. We observed that only the combined knockdown of Rictor and raptor increased the CSC population in TNBC cell lines.

These observations suggest that treatment of TNBC harboring PI3K pathway aberrations with TORC1/2 inhibitors results in an initial reduction of tumor burden but do not eradicate the drug-resistant, slow cycling CSC population driven by Notch signaling. Thus, combination of a Notch inhibitor with TORC1/2 inhibitors and chemotherapy may be an effective therapeutic strategy to decrease primary tumor growth and prevent recurrences in patients with TNBC.

Citation Format: Neil E. Bhola, Valerie Jansen, Carlos Arteaga. TORC inhibitors increase the cancer stem cell (CSC) population and Notch signaling in triple negative breast cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1945. doi:10.1158/1538-7445.AM2014-1945

Mite species identification in the production of allergenic extracts for clinical use and in environmental samples by ribosomal DNA amplification

The identification of allergy-causing mites is conventionally based on morphological characters. However, molecular taxonomy using ribosomal DNA (rDNA) may be particularly useful in the analysis of mite cultures and purified mite fractions in the production of allergenic extracts. Full-length internal transcribed spacers (ITS1 and ITS2) were obtained from Dermatophagoides farinae, Dermatophagoides pteronyssinus, Dermatophagoides microceras and Euroglyphus maynei (Astigmata: Pyroglyphidae), Glycyphagus domesticus and Lepidoglyphus destructor (Astigmata: Glycyphagidae), Tyrophagus fanetzhangorum, Tyrophagus putrescentiae, Tyrophagus longior, Tyrophagus neiswanderi, Acarus farris and Acarus siro (Astigmata: Acaridae), and Blomia tropicalis (Astigmata: Echymopodidae), using mite-specific primers. Polymerase chain reaction (PCR) products were digested with HpaII and RsaI restriction enzymes in order to produce species-specific PCR restricted fragment length polymorphism (RFLP) profiles. A semi-nested re-amplification step was introduced before the RFLP in order to apply the method to environmental samples. Results demonstrate that rDNA sequences can be used for the unambiguous identification of mite species. The PCR-RFLP system allows the identification of species in purified mite fractions when the availability of intact adult mite bodies for morphological identification is limited. This reliable and straightforward PCR-RFLP system and the rDNA sequences obtained can be of use in the identification of allergy-causing mite species.

Abstract PD5-1: The type II TGFb receptor neutralizing antibody, TR1, abrogates the tumor-initiating cell (TIC) population in triple negative breast cancer (TNBC) via inhibition of SMAD and non-SMAD pathways

Tumor-initiating cells (TICs) or cancer stem cells (CSCs) are resistant to chemotherapy and have been associated with metastatic recurrences and poor patient outcome. We have shown that the TGFb pathway plays a crucial role in the expansion of TICs and that inhibition of the type I TGFβ receptor (ALK5) decreases chemotherapy-resistant TICs. Further, a TGFβ-responsive gene signature is enriched in TNBCs upon treatment with chemotherapy and is predictive of poor prognosis (Bhola et al. JCI 2013). Herein we investigated the molecular and antitumor effects of TR1, a TGFβRII neutralizing antibody currently in phase I clinical trials, against TNBC. TR1 recognizes the TGFβ ligand binding epitope in the extracellular domain of TGFβRII; it blocks ligand binding in the nM range. Small molecule TGFβRI kinase inhibitors are another approach to inhibit TGFβ/SMAD signaling. However, they cross-react with other type I receptors (ALK1, 4, 7), some of which are important for normal physiology. Furthermore, TGFβRII can induce EMT in breast cancer cells independent of dimerization with TGFβRI. Therefore, we hypothesized that, by neutralizing TGFβRII, TR1 can abrogate the breast TIC population via inhibition of SMAD and non-SMAD signaling.

Using the pCAGA12-luciferase reporter to assess SMAD-dependent transcriptional activity, TR1 decreased luciferase activity in TNBC cell lines (SUM159 and BT549) and steady-state levels of P-SMAD2, suggesting it inhibited autocrine TGFβ signaling. TR1 decreased the TIC fraction as identified by FACS analysis of cell line-specific TIC markers (ALDH for SUM159; CD44hi/PROCR+ for BT549; PROCR+/ESA+ for MDA231 cells). Although TR1 displayed no effects on TNBC growth in vitro, it decreased tumor growth in vivo. We used a phospho-kinase array (45 kinases) to elucidate the non-SMAD pathways altered by TR1. TR1 decreased phosphorylated EGFR (Tyr1068) and STAT3 (Tyr705) in TNBC cell lines. By flow cytometry, the cell-surface expression of EGFR was also lowered upon treatment with TR1. TR1 also reduced P-ERK1/2 and P-Akt (Ser473) levels, and lowered NFκB transcriptional activity as measured by luciferase reporter assay. Using a cytokine array (120 cytokines) and qRT-PCR we observed that TR1 decreased the expression and release of cytokines involved in TIC enrichment such as IL-6 and IL-8. Inhibition of EGFR (with gefitinib) and MEK1/2 (with selumetinib) decreased the TIC population while augmenting pCAGA luciferase activity. The combination of SMAD2 siRNA with each EGFR or MEK inhibitors significantly decreased the TIC population. We speculate based on these data that inhibition of both SMAD and non-SMAD signaling is necessary for complete abrogation of TICs. This may explain the efficacy of TR1 as a single agent.

These findings suggest that targeting TGFβRII with TR1 exerts its anti-tumor effects via inhibition of both SMAD and non-SMAD (EGFR, ERK) pathways that are important to TIC survival. The results also encourage combination therapies of chemotherapy with TR1 to reduce tumor recurrences in patients with TNBC.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr PD5-1.

Targeted cancer therapies

With unprecedented understanding of molecular events underlying human cancer in this genomic era, a large number of drugs specifically targeting hypothesized oncogenic drivers to which tumors are potentially addicted to have been developed and continue to be developed. These targeted cancer therapies are being actively tested in clinical trials with mixed successes. This editorial provides an overview on successful targeted cancer drugs on the market and those drugs that are in late clinical development stages. Importantly, the article lays out main challenges in developing molecular targeted therapies and potential path forward to overcome these challenges, as well as opportunities for China in this new era of targeted agents. The editorial serves as an introduction to the Targeted Cancer Therapies series that will review in depth of major pathways and drugs targeting these pathways to be published in the coming issues of the Chinese Journal of Cancer.

Abstract 3475: Inhibition of the TGFβ pathway inhibits chemotherapy-induced enrichment of breast cancer stem cells in triple-negative breast cancer

Triple-negative breast cancer (TNBC) is the most virulent form of breast cancer and is associated with a worse prognosis compared to hormone receptor- and HER2-positive tumors. The standard treatment of TNBC is cytotoxic chemotherapy. TNBC patients tend to display an initial response to chemotherapy; however, they exhibit higher recurrence rates and overall poor long term survival. Reasons for this high metastatic recurrence rate and mortality are believed to be the existence of a chemo-resistant tumor-initiating population called cancer stem cells (CSCs). CSCs are defined as cells with the ability to self-renew, differentiate into non-tumorigenic cells, and initiate tumors in vivo. CSCs isolated from breast cancer tissue display increased transforming growth factor (TGF) ≤ and TGFβ type 2 receptor (TGFβR2) mRNA expression compared to the non-CSC population. Furthermore, breast CSCs exhibit characteristics of the TGFβ-driven epithelial to mesenchymal transition (EMT). Therefore, we hypothesize that inhibiting the TGFβ pathway can abrogate the breast CSC population and sensitize TNBC to chemotherapy, thus reducing metastatic recurrences and tumor progression. From a cohort of pre and post-chemotherapy treated TNBC patient samples we observed increased TGFβ signaling receptors and ligands, CD44 and ALDH1 levels in post-chemotherapy treated patients. We examined the effect of TGFβ1, the TGFβ receptor 1/2 kinase inhibitor LY2157299, the TGFβR2 receptor neutralizing antibody TR1, and paclitaxel on the CSC population in TNBC cell lines by 1) FACS analysis of CSC markers (ALDH, CD44, and PROCR); and 2) mammosphere formation assays. Paclitaxel treatment resulted in an enrichment of CSCs as measured by FACS and mammosphere formation (p≤0.005) both in vitro and in SUM159 xenografts. Further, treatment with paclitaxel upregulated TGFβR2 and TGFβ1 mRNAs and phosphorylated SMAD2 levels from post-therapy SUM159 xenografts. LY2157299 and TR1 abrogated TGFβ-mediated CSC enrichment and mammosphere formation (p≤0.01). Specific targeting of TGFβR2 and SMAD4 by RNAi decreased the CD44hi/CD24lo population in both cell lines. SMAD4 downmodulation also decreased mammosphere formation and interleukin-8 (IL-8) expression in three TNBC cell lines. Finally, a combination of either LY2157299 or SMAD4 siRNA with paclitaxel decreased CSC marker expression, IL-8, and mammosphere formation compared to each treatment alone (p≤0.006) from bulk and sorted CSC populations. These findings suggest that TGFβ signaling plays a maintenance role in breast CSCs viability. Second, blockade of the TGFβ pathway with genetic or pharmacological inhibitors can ameliorate or prevent the enrichment of drug-resistant CSCs by chemotherapy. These studies provide a rationale for studies of chemotherapy ± TGFβ inhibitors in patients with TNBC using CSC markers as surrogates of clinical response.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3475. doi:1538-7445.AM2012-3475

A note on the connectedness locus of the families of polynomials P(c)(z)=z(n) - cz(n-j)

Let j be a positive integer. For each integer n > j we consider the connectedness locus M(n) of the family of polynomials P(c)(z)=z(n) - cz(n-j), where c is a complex parameter. We prove that lim n→∞ M(n) = D in the Hausdorff topology, where D is the unitary closed disk {c;|c|≤1}.

PD08-04: Inhibition of the TGFb/TGFbR2 Pathway Prevents Enrichment of Drug-Resistant Breast Cancer Stem Cells by Anti-Cancer Chemotherapy

Triple-negative breast cancer (TNBC) is the most virulent form of breast cancer and is associated with a worse prognosis compared to hormone receptor- and HER2−positive tumors. The standard treatment of TNBC is cytotoxic chemotherapy. TNBC patients tend to display a good initial response to chemotherapy; however, they exhibit higher recurrence rates and overall poor long term survival. Reasons for this high metastatic recurrence rate and mortality are believed to be the existence of a chemo-resistant tumor-initiating population called cancer stem cells (CSCs). CSCs are defined as cells with the ability to self-renew, differentiate into non-tumorigenic cells, and initiate tumors in vivo. CSCs isolated from breast cancer tissue display increased transforming growth factor (TGF) β and TGFβ type II receptor (TGFβR2) mRNA expression compared to the non-CSC population. Furthermore, breast CSCs exhibit characteristics of an epithelial to mesenchymal transition (EMT), a process driven by the TGFβ signaling and associated with metastatic progression. Therefore, we hypothesize that inhibiting the TGFβ/TGFβR2 pathway can abrogate the breast CSC population and sensitize TNBC to chemotherapy, thus reducing metastatic recurrences and tumor progression.

To address this hypothesis, we used the TNBC cell lines SUM159 and BT549. We examined the effect of TGFβ1, the TGFβ receptor I/II kinase inhibitor LY2157299, the TGFbRII receptor and TGFb1 neutralizing antibodies TR1, and LY2424087 and paclitaxel on the CSC population of these cell lines by 1) flow cytometric analysis of stem cell markers (ALDH, CD44, and PROCR); and 2) mammosphere formation assays. In both cell lines, LY2157299, LY2424087, and TR1 abrogated TGFβ-mediated CSC enrichment and mammosphere formation (p≤0.01). Treatment with paclitaxel resulted in an enrichment of CSCs as measured by FACS and mammosphere formation (p≤0.005) both in vitro and in SUM159 xenografts established in athymic mice. Further, treatment with paclitaxel upregulated TGFβR2 and TGFβ1 mRNAs and phosphorylated SMAD2 levels in CSCs sorted from post-therapy SUM159 xenografts. RNAi-mediated knockdown of TGFβR2 in BT549 cells decreased mammosphere formation but did not affect the proportion of CSCs analyzed by FACS (p≤0.005 and p=0.03, respectively). TGFβR2 and SMAD4 siRNA decreased the CD44hi/CD24lo population in both cell lines. SMAD4 siRNA also decreased CSCs, mammosphere formation, and viability in SUM159, BT549, and MDA-231 basal-like and HCC1954 (HER2+) cells. SMAD4 knockdown resulted in a significant decrease in the CSC-associated genes interleukin-8 (IL-8) and Nanog. Finally, a combination of either LY2157299 or SMAD4 siRNA with paclitaxel decreased both stem cell marker expression, IL-8 and mammosphere formation compared to each treatment alone (p≤0.006). These findings suggest that autocrine TGFb signaling plays a maintenance role in breast CSCs viability. Second, blockade of the TGFb/TGFbR2 pathway with genetic or pharmacological inhibitors can ameliorate or prevent the enrichment of drug-resistant CSCs by anti-cancer chemotherapy. These studies provide a rationale for studies of chemotherapy ± TGFb inhibitors in patients with TNBC using stem cell markers as surrogates of clinical response.

Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr PD08-04.

P1-07-19: Analysis of HER2−Status in Breast Cancer by Mass Spectrometry in Archival, Formalin-Fixed Tissues

HER2 (ERBB2) is overexpressed in about 25% of breast cancers and predicts clinical benefit from trastuzumab, as well as response to anthracycline-based chemotherapy. Fluorescence in situ hybridization (FISH) to detect HER2 gene copy number and immunohistochemistry (IHC) to detect HER2 protein levels are approved by the FDA to identify HER2−positive (H2) tumors. However, the 2007 ASCO/CAP report concluded that approximately 20% of HER2 testing may be inaccurate. Further, the available data did not clearly demonstrate clear superiority of either IHC or FISH as a predictor of benefit from anti-HER2 therapy. Discordance between these methods is as high as 5%. Thus, novel complementary quantitative methods for interrogating HER2 expression in tumors are needed.

Targeted protein analysis by multiple reaction monitoring mass spectrometry (MRM-MS) offers a powerful approach to configure assays for specific proteins without using antibodies. Our studies using this platform have demonstrated applicability to formalin-fixed, paraffin-embedded (FFPE) specimens. In the current studies, we used this approach to measure signals from two tryptic peptides specific to HER2, one each from the extracellular and intracellular domains, selected from among 28 candidates based on their signal intensity and sharpness of their chromatographic profiles. Preliminary studies with a HER2−overexpressing BT474 xenograft in mice demonstrated quantitation and detected previously reported HER2 ectodomain shedding. Subsequent analysis of FFPE tissue from five H2 and five triple-negative (TN) tumors yielded measurement of at least 1 femptomole of receptor for H2 tumors and less than 0.2 femptomole of receptor for TN tumors per microgram of digest analyzed. If we assume 200 picograms of protein per cell, the results suggest 110,00 to 468,000 receptors per cell in the H2 tumors and only 2,000 to 14,000 receptors per cell in the TN tumors. Despite significant biological variability in receptor levels measured among the specimens of each type, a clear separation of the H2 and TN tumors was achieved based on the peptide quantitation. This preliminary study demonstrates the potential of MRM-MS in FFPE tissue to provide an alternate approach to IHC-based protein analysis. MRM-MS offers the potential for more, accurate and robust HER2 quantification in clinical breast cancer tissues. The next phase of this work will encompass a larger sample set, including tumors with equivocal and negative FISH and/or IHC test results. Correlation with response to anti-Her2 therapy will be performed in samples with available follow-up data.

Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P1-07-19.

Abstract 231: Upregulation of HER3 (ErbB3) levels and function counteracts the antitumor effect of HER2 and PI3K inhibitors

We examined HER3 by immunohistochemistry in formalin-fixed tumor blocks of patients with HER2-overexpressing breast cancer treated with the HER2 tyrosine kinase inhibitor (TKI) lapatinib. HER3 levels increased 135% after 2 weeks of lapatinib therapy compared to pre-therapy levels (n=8; p=0.03). Treatment of mice bearing BT474 xenografts with lapatinib also increased levels of both HER3 mRNA and protein. Treatment with lapatinib of HER2-overexpressing BT474, SKBR3, and SUM225 cells also induced upregulation of HER3 RNA and protein. There was recovery of HER3 phosphorylation that correlated with recovery of P-Akt when P-HER2 was still inhibited. Inhibition of PI3K or Akt with small molecule inhibitors or with Akt1, Akt2, and Akt3 siRNA resulted in upregulation of HER3 mRNA/protein. Expression of myristoylated Akt reduced basal and lapatinib-induced HER3 mRNA and protein, suggesting that PI3K/Akt signaling downstream of HER2 represses HER3 expression.

We identified three putative FoxO3a sites in the ERRB3 promoter. The transcription factor FoxO3a is negatively regulated by AKT-induced phosphorylation. FoxO3a knockdown with siRNA reduced basal and lapatinib-induced increase in HER3 mRNA. We next conducted chromatin immunoprecipitation (ChIP) with FoxO antibodies. There was an increase in the HER3 PCR product using all three sets of primers specific to the FoxO binding sites upon treatment of BT474 cells with lapatinib, supporting direct FoxO protein binding to the HER3 promoter.

We hypothesized that sustained inhibition of HER3 and its output to PI3K/Akt is required for the optimal antitumor effect of HER2 inhibitors. Indeed, transfection with HER3 siRNA sensitized HER2+ cancer cells 3-fold to lapatinib-induced apoptosis. Similarly, the HER3 monoclonal antibody AMG-888 sensitized cells to lapatinib both in vitro and in vivo. Combined treatment with lapatinib and AMG-888 of mice bearing BT474 xenografts inhibited [18F]-FDG-PET uptake, P-HER3, and P-Akt and increased nuclear FoxO3a, all pharmacodynamic biomarkers of PI3K/Akt activity, more effectively than each inhibitor alone. The recovery of P-HER3 following lapatinib-induced inhibition of HER2 was not blocked by MET, FGFR2, EGFR, Src, and IGF-IR inhibitors, nor by pertuzumab. However, trastuzumab prevented recovery of P-HER3, suggesting that a ligand-independent HER2-HER3 interaction was involved in partial maintenance of P-HER3. Finally, treatment of mice bearing BT474 xenografts with lapatinib and trastuzumab eliminated 16/16 tumors within ≪3 weeks. Therefore, in HER2+ cancers, inhibition of HER2 with TKIs will inhibit PI3K/Akt and relieve suppression of HER3 expression. In turn, FoxO-induced upregulation of HER3 counteracts the full response to HER2 TKIs. These data suggest that current inhibitors of HER2 and PI3K/Akt will not block the PI3K pathway in sustained fashion unless combined with HER3 antagonists.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 231. doi:10.1158/1538-7445.AM2011-231

Loss of phosphatase and tensin homolog or phosphoinositol-3 kinase activation and response to trastuzumab or lapatinib in human epidermal growth factor receptor 2-overexpressing locally advanced breast cancers

PURPOSE

Phosphatase and tensin homolog (PTEN) loss or activating mutations of phosphoinositol-3 (PI3) kinase (PIK3CA) may be associated with trastuzumab resistance. Trastuzumab, the humanized human epidermal growth factor receptor 2 (HER2) monoclonal antibody, and lapatinib, an epidermal growth factor receptor/HER2 tyrosine kinase inhibitor, are both established treatments for HER2-overexpressing breast cancers. Understanding of the cellular response to HER2-targeted therapies is needed to tailor treatments and to identify patients less likely to benefit.

METHODS

We evaluated the effect of trastuzumab or lapatinib in three HER2-overexpressing cell lines. We confirmed the in vitro observations in two neoadjuvant clinical trials in patients with HER2 overexpression; 35 patients received trastuzumab as a single agent for the first 3 weeks, then docetaxel every 3 weeks for 12 weeks (trastuzumab regimen), whereas 49 patients received lapatinib as a single agent for 6 weeks, followed by trastuzumab/docetaxel for 12 weeks before primary surgery (lapatinib regimen). Apoptosis, Ki67, p-MAPK, p-AKT, and PTEN were assessed by immunohistochemistry. Genomic DNA was sequenced for PIK3CA mutations.

RESULTS

Under low PTEN conditions, in vitro data indicate that lapatinib alone and in combination with trastuzumab was effective in decreasing p-MAPK and p-AKT levels, whereas trastuzumab was ineffective. In the clinical trials, we confirmed that low PTEN or activating mutation in PIK3CA conferred resistance to the trastuzumab regimen (P = .015), whereas low PTEN tumors were associated with a high pathologic complete response rate (P = .007).

CONCLUSION

Activation of PI3 kinase pathway is associated with trastuzumab resistance, whereas low PTEN predicted for response to lapatinib. These observations support clinical trials with the combination of both agents.

Elevation of receptor tyrosine kinase EphA2 mediates resistance to trastuzumab therapy

One arising challenge in the treatment of breast cancer is the development of therapeutic resistance to trastuzumab, an antibody targeting the human epidermal growth factor receptor-2 (HER2), which is frequently amplified in breast cancers. In this study, we provide evidence that elevated level of the receptor tyrosine kinase Eph receptor A2 (EphA2) is an important contributor to trastuzumab resistance. In a screen of a large cohort of human breast cancers, we found that EphA2 overexpression correlated with a decrease in disease-free and overall survival of HER2-overexpressing patients. Trastuzumab-resistant cell lines overexpressed EphA2, whereas inhibiting EphA2 restored sensitivity to trastuzumab treatment in vivo. Notably, trastuzumab treatment could promote EphA2 phosphorylation by activating Src kinase, leading in turn to an amplification of phosphoinositide 3-kinase/Akt and mitogen-activated protein kinase signaling in resistant cells. Our findings offer mechanistic insights into the basis for trastuzumab resistance and rationalize strategies to target EphA2 as a tactic to reverse trastuzumab resistance.