Abstract P5-04-06: Analysis of STEAP1 expression as a therapeutic target in breast cancer

Objective: The six transmembrane epithelial antigen of the prostate (STEAP1) is predominantly overexpressed in human prostate cancer. STEAP1 was first identified as a prostate-specific cell-surface antigen and found to be up-regulated in various cancers including lung, bladder, colon, and ovarian with little expression in normal tissue. An anti-STEAP1 monoclonal antibody linked to an antimitotic agent is currently in Phase I clinical trials for prostate cancer patients. Microarray data from our lab suggested that STEAP1 is also highly expressed in human breast cancers and bone marrow disseminated tumor cells. In this study we evaluate expression STEAP1 in primary tumors, and bone marrow (BM) from breast cancer patients.

Experimental procedures: RNA was isolated from primary tumor, non-malignant breast tissue and bone marrow (BM) from stage II and III breast cancer patients, healthy volunteers, breast cancer cell lines and BM from patient derived xenographs (PDX). Disseminated tumor cells (DTCs) from patient BM were enriched by microfiltration and analyzed by RNA-in situ hybridization (ISH). STEAP1 RNA expression was analyzed by Nanostring nCounter and qRT-PCR using human specific probes. STEAP1 immunohistochemical (IHC) staining of human tissue was performed using standard protocols. Knockdown of steap1 expression was accomplished using a lentiviral system.

Results: STEAP1 mRNA was up-regulated in 77% of tumors (28/36) compared to the corresponding normal tissue. STEAP1 protein was expressed in 100% of tumors (8/8) and was absent in non-malignant breast tissue (7/7) by IHC staining. STEAP1 mRNA was not expressed normal BM, but was detected in 8% (6/74) of BM from patients with early stage breast cancer. STEAP1 expression in the BM was associated with triple negative disease (3/6) and recurrent disease development (4/6, p=.028). STEAP1 expression was observed in individual DTCs isolated from patients BM, while no expression was observed in normal BM. In a PDX model of breast cancer, STEAP1 expression in BM was only observed in mouse who developed metastatic disease associated (7/10, p=.004). Knockdown of STEAP1 in the breast cancer cell line MDA-MB231 cells inhibited cell growth by 80-90%.

Conclusion: STEAP1 is expressed in human breast tumors and disseminated tumor cells found in the bone marrow of breast cancer patients. Expression of STEAP1 in the BM is significantly associated with the development of metastatic disease in patients as well as in a mouse model of breast cancer. Our data indicate that STEAP1 could serve as a therapeutic target for the treatment of minimal residual disease in breast cancer.

Citation Format: Aft R, Mudalagiriyappa C, Pillai S, Watson M. Analysis of STEAP1 expression as a therapeutic target in breast cancer. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P5-04-06.

CXCR4 Protein Epitope Mimetic Antagonist POL5551 Disrupts Metastasis and Enhances Chemotherapy Effect in Triple-Negative Breast Cancer

The SDF-1 receptor CXCR4 has been associated with early metastasis and poorer prognosis in breast cancers, especially the most aggressive triple-negative subtype. In line with previous reports, we found that tumoral CXCR4 expression in patients with locally advanced breast cancer was associated with increased metastases and rapid tumor progression. Moreover, high CXCR4 expression identified a group of bone marrow-disseminated tumor cells (DTC)-negative patients at high risk for metastasis and death. The protein epitope mimetic (PEM) POL5551, a novel CXCR4 antagonist, inhibited binding of SDF-1 to CXCR4, had no direct effects on tumor cell viability, but reduced migration of breast cancer cells in vitro. In two orthotopic models of triple-negative breast cancer, POL5551 had little inhibitory effect on primary tumor growth, but significantly reduced distant metastasis. When combined with eribulin, a chemotherapeutic microtubule inhibitor, POL5551 additively reduced metastasis and prolonged survival in mice after resection of the primary tumor compared with single-agent eribulin. Hypothesizing that POL5551 may mobilize tumor cells from their microenvironment and sensitize them to chemotherapy, we used a "chemotherapy framing" dosing strategy. When administered shortly before and after eribulin treatment, three doses of POL5551 with eribulin reduced bone and liver tumor burden more effectively than chemotherapy alone. These data suggest that sequenced administration of CXCR4 antagonists with cytotoxic chemotherapy synergize to reduce distant metastases.

Abstract 5258: Expression analysis of STEAP1 in breast cancer patients as therapeutic target

Objective: The six transmembrane epithelial antigen of the prostate (STEAP1) is predominantly overexpressed in human prostate cancer. STEAP1 was first identified as a prostate-specific cell-surface antigen and found to be up-regulated in multiple cancer cell lines and in various cancers, including lung, bladder, colon and ovarian cancers. However no significant expression in normal tissue has been reported suggesting its potential use as a target for anti-STEAP1 immunotherapy. An anti-STEAP1 monoclonal antibody linked to an antimitotic agent is in Phase I clinical trials for prostate cancer patients. Microarray data from our lab suggested that STEAP1 is also highly expressed in human breast cancers. In this study we evaluate expression STEAP1 in primary tumors and the bone marrow from breast cancer patients as a therapeutic target for minimal residual disease.

Experimental procedures: RNA was isolated from primary tumor and non-malignant breast tissue. RNA was also isolated from bone marrow of state II and III breast cancer patients, healthy volunteers and breast cancer cell lines. STEAP1 expression was analyzed by nanostring nCounter and real time qRT-PCR using human specific probes. STEAP1 immunohistochemical (IHC) staining of human tissue was performed using standard IHC Protocol.

Results: STEAP1 mRNA was up-regulated in 77% of tumors (28/36) compared to the corresponding normal tissue. STEAP1 protein was expressed in 100% of tumors (8/8) and was absent in non-malignant breast tissue (7/7) by IHC staining. STEAP1 mRNA was not expressed normal BM, but was detected in 8% (6/74) of BM from patients with early stage breast cancer. Of patients with STEAP1 positive BM, 50% (3/6) had triple negative disease and 66% (4/6) developed recurrent disease (p = .028).

Conclusion: STEAP1 is expressed in human breast tumors and the BM of breast cancer patients. Expression of STEAP1 in the BM is significantly associated with the development of metastatic disease. Our data indicate that STEAP1 could serve as a therapeutic target for the treatment of minimal residual disease in breast cancer.

Citation Format: Chidananda Mudalagiriyappa, Sreeraj Pillai, Mark Watson, Rebecca Aft. Expression analysis of STEAP1 in breast cancer patients as therapeutic target. [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 5258. doi:10.1158/1538-7445.AM2015-5258

Abstract OT1-1-02: A phase II randomized trial evaluating the effect of trastuzumab on disease free survival in early stage HER2-negative breast cancer patients with ERBB2-expressing bone marrow disseminated tumor cells

Background: Adjuvant trastuzumab administered concurrently with chemotherapy improves survival in women with Her2-positive breast cancers (BC). A subset of patients with Her2-negative tumors benefit from trastuzumab treatment. We and others have reported discordance in Her2 expression between primary tumors, circulating tumor cells, disseminated tumor cells (DTCs), and metastases. Our data indicate that patients with Her2-negative tumors and Her2-positive DTCs have a greater hazard of recurrence than patients with Her2-negative tumors and Her2-negative DTCs or Her2-positive DTCs treated with trastuzumab. We hypothesize that the subgroup of patients with Her2-negative primary tumors and Her2-positive DTCs will benefit from trastuzumab therapy.

Trial Design: We are conducting a randomized phase II trial in early stage Her2-negative BC patients with Her2-positive DTCs in their bone marrow (BM) at the time of diagnosis who are candidates for chemotherapy. Chemotherapy is doxorubicin/cyclophosphamide q2 weeks for 4 cycles followed by weekly paclitaxel for 12 weeks. Patients randomized to the trastuzumab arm will receive IV trastuzumab concomitant with taxane treatment and then q3 weeks for a total of 52 weeks.

Specific Aims: The primary endpoints are two year recurrence and death rates. Additional endpoints include: elimination of Her2-positive DTCs at completion of therapy, PAM50 analysis of the primary tumor, and association of DTC specific gene expression with outcome.

Eligibility: Patients with newly diagnosed Her2-negative, stage I-III invasive BC who are eligible for chemotherapy and have Her2-positive BM DTCs, as defined by a molecular based assay performed in a CLIA-licensed facility are eligible.

Statistical Methods: Based on our preliminary data, we estimate that 25% of stage II/III Her2-negative breast cancer patients will harbor Her2-positive DTCs in their BM. 200 patients will have their BM screened for Her2-positive DTCs to enroll 50 patients into the trial. Based on the literature and preliminary data, the expected 2-year recurrence rate is 75% in the placebo arm and 40% in the trastuzumab arm. A sample of 46 patients, 23 per arm, will provide power = 0.8 to detect this difference at a 0.05 significance level. The expected proportion of patients who eliminate Her2-positive DTCs from BM is < 10% in the placebo arm and 80% in the trastuzumab arm. The proposed sample will provide power > 0.9 to distinguish Her2-positive DTC elimination rates of 10% vs. 80% and at least 80% power to distinguish a difference of 50% in the elimination rates (e.g. 29% vs. 70%). One interim analysis will be conducted after the first 15 patients have completed 2 years of follow-up and 2 year recurrence rates have been determined. Conditional study power will be used to evaluate the estimates on which study power has been calculated, and the sample size will be adjusted, if necessary. Analysis of the primary endpoints will be at a significance level of 0.0052 for the interim analysis and 0.048 for the final analysis in order to preserve an overall significance level of 0.05.

Accrual: Accrual is anticipated to open August 2013. Target = 25 per arm. NCT01779050.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr OT1-1-02.

Identification of patients at high risk of recurrent disease development by detection of HER2-positive disseminated tumor cells in bone marrow of patients with HER2-negative tumors

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Background: A subpopulation of patients with HER2-negative tumors benefit from HER2 therapy. HER2 expression can be discordant between primary tumors and metastases. We have examined the bone marrow (BM) of early stage breast cancer patients for HER2-expression by disseminated tumor cells (DTCs) and the association with disease recurrence. Methods: BM was collected from clinical stage II-III breast cancer prior to treatment between 2007-2011. Gene expression of ERBB2 was determined by multiplex PCR (Fluidigm Biomark [FB]). Positive expression was defined as at least 1.4 fold above a pool of normal BM. Expression was confirmed by single gene PCR and Nanostring nCounter (NC) assays. Cox proportional model was used to estimate hazard ratios (HR). Results: BM from 74 patients was analyzed. Median follow-up was 3.4 years (range 8 months-84 months). 24% of the patients developed metastatic disease. For ERBB2 detection, there was excellent correlation between NC and the FB assays (kappa=0.87, 95% CI [0.62, 1.00]). Nine patients expressed ERBB2 in their BM. Five of the 9 patients had Her2-positive tumors and were treated with trastuzumab. One of 5 (20%) of these patients relapsed whereas 75% (3 of 4) of the patients with HER2-negative tumors but ERBB2-positive DTCs relapsed. Patients with HER2-negative tumors/ERBB2-positive BM were found to have a greater hazard of recurrence than patients with HER2-negative tumors/ERBB2-negative BM or ERBB2-positive DTCs treated with trastuzumab (p=.0069; Table). Those patients with ERBB2-positive BM who did not receive trastuzumab had a decreased disease free survival (p=.016). Conclusions: We have found discordant expression of HER2/ERBB2 in tumors and BM of stage II-III breast cancer patients. The presence of ERBB2 expressing DTCs in patients with HER2-negative tumors identifies a subset of patients at increased risk of recurrence who may benefit from targeted HER2-therapy. [Table: see text] .

Abstract P2-04-02: Identification of genes associated with breast cancer micrometastatic disease in bone marrow using a human-in-mouse xenograft system

Disseminated tumor cells (DTCs) found in the bone marrow (BM) of breast cancer patients portend a poor prognosis and are thought to be the intermediaries in the metastatic process. Study of these cells has been limited due to their scarcity. To develop a clinically relevant model to characterize hese cells, we have employed a human in mouse (HIM) xenograft model for propagating, isolating, and molecularly characterizing DTCs. Human breast adenocarcinomas were prospectively collected from 5 patients and implanted into humanized NOD/SCID mouse mammary fat pads. BM was collected from the long bones at varying passages of the tumors and analyzed for human-specific gene expression by qRT-PCR and gene expression microarray. Human-specific gene expression of SNAI1, GSC, FOXC2, KRT19, and STAM2, presumably originating from disseminated tumor cells, was detectable in the BM of all mice that had developed metastatic disease to other solid organs, but was not detectable in xenotransplanted mice that did not develop metastatic disease. Comparative gene expression microarray analysis of the HIM primary tumor, the corresponding BM from mice with metastatic disease, and BM from control mice identified additional patterns of gene expression enriched in BM-associated DTCs which included several genes associated with epithelial-mesenchymal transition, aggressive clinical phenotype, and metastatic disease development in primary human tumors. We have found that BM DTCs can be detected using the HIM xenograft model and have identified unique patterns of gene expression associated with BM DTCs, which may provide further insight into the biology and therapeutic vulnerability of metastatic tumor cell populations in breast cancer patients.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P2-04-02.

P4-06-03: Multiplex Gene Expression of Disseminated Tumor Cells in the Bone Marrow of Breast Cancer Patients Identifies Novel Therapeutic Targets

Background: Disseminated tumor cells (DTCs) are detected in the bone marrow (BM) of up to 40% of breast cancer patients at the time of diagnosis and are an independent prognostic factor for recurrent disease. Present techniques for detection of DTC are often laborious, and insensitive due to the molecular heterogeneity of the DTCs. We have previously optimized and validated a novel, multiplexed gene expression technology platform, Nanostring nCounter™ (NC) which counts single molecules of RNA, for the multi-marker detection of DTCs in BM at a sensitivity of 1 cancer cell per 1 million nucleated BM cells. We now validate a 36 gene panel for the detection and molecular characterization of DTCs in BM.

Methods: Hybridization probes for 36 genes whose expression are associated with breast cancer, metastasis, and/or the cancer stem cell phenotype, and which exhibit no or low expression levels in normal bone marrow by qRT-PCR were developed for the NC assay. Total RNA was isolated from whole BM collected from the right and left iliac crest from breast cancer patients and healthy volunteers. 5 ug of RNA was analyzed, in duplicate with the NC assay. BM was scored positive for expression of an individual gene if expression in duplicate samples was 2 standard deviations above mean expression in a set of 11 independent normal BM samples.

Results: Bilateral BM samples were analyzed prior to any therapy from 20 patients: 8 developed metastatic disease within 2–48 months (mean of 23 months) after diagnosis, and 12 had no evidence of metastatic disease with 3–5 years follow-up. Overall, expression of at least one gene in the 36-gene multi-marker panel was detected in 17 patients (85%). There was excellent correlation between individual gene expression in both the right and left iliac crest samples from the same patient. Six of the 8 patients (75%) who developed metastatic disease had detectable expression of 1–3 genes. Two genes were commonly associated with metastatic disease development. 50% (3 of 6) of the patients who had detectable expression of EBB2 in their BM developed metastatic disease, although this did not correlate with expression in the corresponding primary tumor from the same patient. 80% (4 of5) of the patients who expressed the hedgehog pathway gene, Ptch1, in their BM developed metastatic disease. Conclusions: Our data demonstrate the feasibility of using a 36-plex NC assay to detect gene expression associated with BM DTCs in breast cancer patients. We found expression of 2 targetable genes associated with the development of metastatic disease, ERBB2 and Ptch1. ERBB2 expression in BM did not correlate with expression in the primary tumor. The molecular diversity of gene expression observed underscores the need for a multiplexed gene expression panel. Ongoing studies are evaluating the clinical utility of this assay to detect DTCs relative to existing techniques, for predicting relapse-free survival, molecular classification, and selecting appropriate targeted therapeutics based on BM DTC profiles in breast cancer patients.

Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P4-06-03.

Abstract 1589: Development of a mouse model for bone marrow disseminated tumor cells with human tumor xenografts

Objective: Disseminated tumor cells (DTCs) found in the bone marrow (BM) of breast cancer patients portends a poor prognosis. BM DTCs are thought to be intermediaries in the metastatic process. Study of these cells has been limited due to their scarcity. To overcome this limitation, we have developed an animal model for DTCs employing the Human and Mouse Linked Evaluation of Tumor (HAMLET) system.

Experimental procedures: After informed consent, human breast adenocarcinomas were prospectively collected from 5 patients with estrogen receptor negative/Her2 negative tumors and implanted into a humanized NOD/SCID mouse mammary fat pad as previous described. BM was collected from the femur and tibia from mice at varying passages of the tumors and analyzed for human-specific GADPH (hGAPDH) expression by qRT-PCR. The presence of other human gene transcripts, previously detected in the BM of breast cancer patients and believed to be associated with the presence of DTCs, was also determined by qRT-PCR. Human gene expression array analysis (Affymetrix Human gene 1.0ST) was performed on the primary xenograft tumor, a spleen metastatic nodule and BM from all WHIM17 mice.

Results: BM was screened from 16 tumor bearing mice for the presence of DTCs. 10 animals, with tumors derived from 2 patients, developed metastatic disease and 9 had detectable levels of hGAPDH. The CT ratio human to mouse GAPDH varied from 1.06 to 2.23. In particular, high levels of hGAPDH were found in one HAMLET mouse line, WHIM 17, in which all animals developed metastases (CT ratio human to mouse GAPDH=1.06 to 1.31). One mouse with detectable hGAPDH died of other causes and could not be assed for metastatic disease development. There was no detectable hGAPDH in five mice, derived from 3 patient tumors, which did not develop metastatic tumors and in control mice with humanized mammary fat pads. Human-specific transcripts for SNAIL1, GSC, FOXC2 and KRT19 were detectable in the BM of the WHIM 17 mice whereas control, non-tumor bearing humanized mice demonstrated no expression of any of these markers. Microarray analysis confirmed the presence of human cells in mouse BM, allowing the identification of genes specifically associated with BM DTC cell populations.

Conclusion: We have utilized a mouse xenograft model for the study of DTCs using primary human breast adenocarcinomas transplanted into NOD/SCID mice. The presence of human cells in mice BM appears to correlate with metastatic tumor development. The gene expression patterns of these cells indicate that they maintain molecular profiles similar to DTCs isolated directly from the BM of breast cancer patients. We believe that this model will allow for a better understanding of the metastatic process in breast cancer patients and provide an in vivo model for monitoring and assessing the efficacy of new therapeutic agents in eradicating micrometastatic disease and ultimately, improving survival in breast cancer patients.

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 1589. doi:10.1158/1538-7445.AM2011-1589

Abstract 2234: Detection of minimal residual disease in the bone marrow of breast cancer patients using multiplex gene expression measurements with the Nanostring nCounter Assay

Background: Disseminated tumor cells (DTCs) are detected in up to 40% of breast cancer patients at the time of diagnosis and are an independent prognostic factor for recurrent disease. Presently DTCs are identified by immunohistochemical staining for cytokeratins and/or by molecular detection of single gene expression associated with DTCs. These diagnostic approaches are often subjective, laborious, and insensitive due to the molecular heterogeneity of the DTCs. In this study, we have determined whether a novel, multiplexed gene expression technology platform, Nanostring nCounterTM (NC), could be used for the multi-marker detection of DTCs.

Methods: Total RNA was isolated from bone marrow (BM) of breast cancer patients, breast cancer cell lines, and healthy volunteers. RNA was analyzed directly with the NC assay or converted to cDNA and analyzed by qRT-PCR for DTC associated gene-expression.

Results: Expression of 9 genes associated with breast cancer and DTC (TWIST1, PITX2, TACSTD1, SCGB2A2, EGFR, SNAI2, S100A3, KRT17 and KRT19) were examined by the NC assay and qRT-PCR. Using cell lines representing 3 main molecular breast tumor subtypes diluted into normal human BM at varying concentrations, we found that expression of KRT19, SNAI2, and EGFR could be simultaneously detected at a sensitivity of 1 cancer cell per 100,000 BM cells, using 0.5ug of input RNA. Expression measurements were quantitative, reproducible, and varied over a 20-fold linear dynamic range, depending on the cell line and its inherent expression of each transcript. Sensitivity was improved approximately 20-fold by Ficoll gradient enrichment of DTCs (a standard methodology for ICC-based detection) and increasing the amount of input RNA to 5 ug. This increased the sensitivity from 1 DTC per 1 million BM cells. The NC assay applied to BM collected prior to treatment from 5 patients with stage II/III breast cancer who had known DTCs detected by conventional ICC. 8 normal BM were used to establish baseline and threshold cutoff values. At least one of the nine genes in the multi-marker panel was detected in four of the five breast cancer patient BM samples. Interestingly, KRT19 itself was detected in only one specimen. The BM from two patients (ER-/Her2-) expressed genes known to be associated with this tumor type (TACSTD1, SNAI2, KRT17).

Conclusion: Our data demonstrate the potentiality of the NC platform to detect multigene expression in rare cell populations like DTCs, with sensitivity equal to that of qRT-PCR. Using this approach, 1 DTC per 1 million BM cells can be detected, which is equal to the reported sensitivity of IHC detection (gold standard). Based on this data, we believe that the NC assay, with a more elaborated probe panel, will be a sensitive, specific, and diagnostically useful for the detection and molecular classification of DTCs in bone marrow from breast cancer patients.

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 2234. doi:10.1158/1538-7445.AM2011-2234