Treatment of superior mesenteric artery mycotic aneurysm by synthetic vascular graft: A case report

Superior mesenteric artery (SMA) aneurysm is a rare disease, especially if it is mycotic (infective) in origin. It is difficult to detect the problem during its initial natural course and usually presents in late phase due to its complications such as rupture, dissection, haemorrhage, and mesenteric ischaemia. Initially, the patient present with non-specific symptoms like vague colicky abdominal pain, nausea, vomiting, discomfort, malaise, and low-grade fever but prompt workup and intervention can lead to definitive diagnosis and uneventful outcome. This report describes the case of a 60-year-old male patient who presented with non-specific abdominal symptoms and, on workup, was diagnosed with superior mesenteric artery mycotic aneurysm. It was successfully treated surgically by resection of aneurysm and reconstruction of superior mesenteric artery by inter-positional Polytetrafluoroethylene (PTFE) synthetic vascular graft.

Abstract PD9-12: Integrative molecular profiling of breast cancer brain metastasis and patient-derived xenograft organoids from resected breast cancer brain metastases to interrogate and prioritize therapeutic personalized strategies

Background: Breast cancer brain metastasis (BM) is an area of unmet need in metastatic breast cancer patients. Novel therapeutic interventions to help prevent and treat BM are warranted. We conducted integrative molecular profiling of BM and matched primary tumors (PT) using next-generation DNA and RNA sequencing to examine the molecular landscape. In addition, we established patient-derived xenograft/organoid (PDX/PDO) to examine drug sensitivity according to the molecular and clinical features of the BM.

Methods: Archived, formalin fixed paraffin-embedded BM was collected retrospectively. BM were also collected prospectively at the time of clinically indicated surgical resection through the central nervous system tissue banking and the Michigan Oncology Sequencing Center (MI-ONCOSEQ) protocols. Matched archived PT tissues were collected when available. Integrative next-generation sequencing was conducted using the MI-ONCOSEQ platform. The prospectively collected BM were further used to establish PDXs/ PDOs. Successfully established PDXs/PDOs were used for ex vivo drug testing via MiDrugScreen, a novel drug sensitivity testing platform, where testing was performed in a dose-response format with drug selection prioritized by clinical scenario and molecular alterations if known a priori.

Results: 12 matched BM-PT pairs were analyzed: 6 triple negative, 5 HER2 positive, and 1 ER positive HER2 negative. All except one (11/12) had TP53 mutations. When present, TP53 mutations in BM were also found in PT (except for 1 unknwon case in PT due to low coverage). ER+HER2- was the only one without TP53 mutation but had hyper-mutation (APOBEC signature). Driver mutations and unique copy number alterations (CDKN2A loss in 1/12, mutations in PIK3CA in 1/12 and ESR1 in 1/12, CCNE1 amplification in 1/12) were noted in BMs. In 75% of cases, mutational burden was higher in BM vs. PT. 2 PDX/PDO were available for drug testing. PDO-BC9 was noted to have RB1 (splice acceptor) and LOH. As predicted by this alteration, PDO-BC9 was insensitive to CDK4/6 inhibitors (palbociclib, abemaciclib) tested on MiDrugScreen panel. PDX-BC4 was established from PIK3CA and ESR1 mutated BM from an ER+HER2- patient who had previously progressed on endocrine therapy with a CDK4/6 inhibitor. As predicted, the PDX-BC4 was resistant to CDK4/6 inhibitor but interestingly sensitive to PIK3CA, ERK, and MEK inhibitors.

Conclusions: TP53 mutation was highly prevalent and may be a biomarker for increased risk of BM. Further study is warranted to see if specific TP53 mutations are associated with a risk of BM development and can be used in risk stratification for BM specific intervention. Unique molecular alterations in BM compared to matched PT may have a therapeutic implication as a target or resistance biomarker. Conducting drug testing in addition to molecular profiling has the strong potential of being informative in tailoring or prioritizing therapeutic agents in the era of precision medicine. Additional BM PDXs/PDOs from breast and other solid tumors are being examined using this novel therapeutic tailoring approach with the combination of MIONCOSEQ and MiDrugScreen.

Citation Format: Morikawa A, Robinson DR, Soellner M, Wu Y-M, Lonigro R, Gilani R, Cheng X, Lachacz E, Thomas D, McMurray K, Smerage J, Henry NL, Heth J, Chinnaiyan A, Hayes DF, Merajver S. Integrative molecular profiling of breast cancer brain metastasis and patient-derived xenograft organoids from resected breast cancer brain metastases to interrogate and prioritize therapeutic personalized strategies [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 PD9-12.

Creating Models to Identify New Therapeutic Options for Aggressive African Breast Cancers

Background: Population-based incidence rates of breast cancer (BC) that does not express the estrogen receptor (ER), progesterone receptor (PR) or overexpress the human epidermal growth factor 2 HER2/ neu (triple negative breast cancer, TNBC) are higher among Africans compared with white women. However the underlying biologic and genetic differences among different ethnicities are poorly understood and there are currently very few ethnically diverse BC models available for identifying new therapeutic options. Aim: Establish an international collaboration to: i, characterize African breast tumors ii, create models for studying these tumors and iii, identify biomarkers for early detection and treatment personalization. Methods: We have collected tumors from 154 white Americans WA, 76 African Americans, AA, 190 Ethiopians, Eth, and 286 Ghanaian (Gh) BC patients. We then established a unique resource of patient derived xenografts (PDX) from these tumors. The PDXs were then fully characterized using whole exome and RNA sequencing for the primary tumor, matched normal DNA, and corresponding low passage PDXs. Using immunohistochemistry, we evaluated the ER, PR, HER2/ neu, androgen receptor (AR), and ALDH1 (cancer stem cell marker) expression among these tumors. Based on biomarker expression the PDXs were then tested against a panel of IND drugs, either alone or in combinations, in an ex vivo organoid culture system to discover potential new therapeutic options. Results: Mean age at BC diagnosis was 43; 49; 60; and 57 years for the Eth; Gh; AA; and WA patients, respectively. The proportion of TNBC was significantly higher for the AA and Gh patients (41% and 54%, respectively) compared with the WA and Eth patients (23% and 15%, respectively); P < 0.001. Significant differences were observed for distribution of AR positivity, which was 71%; 55%; 42% and 50% for the WA; AA; Gh; and Eth cases, respectively ( P = 0.008). The Gh breast tumors exhibited the highest number of loss of function and missense mutations that are likely to impact therapy with a high frequency of P53, APC, and FGFR mutations. These mutations were maintained in the corresponding PDXs that were developed, and were thus used as biomarkers for drug screening. These tumors exhibited a gene expression signature based on the ethnicity of the patients with 2385 genes differentially expressed between Gh and AA, 1573 between AA and CA and 1317 between GH and CA. Results from our ongoing drug screening and biomarker identification will be available soon. Conclusions: Establishing the molecular and genetic platform of aggressive breast cancers occurring in women with African ancestry will help in identifying biomarkers for early cancer detection and targeted treatment stratification for optimum patient outcome. The availability of tumor models based on tumors from diverse African populations is the important missing pieces that have to be incorporated into current drug discovery efforts.

Synergistic inhibition of aggressive breast cancer cell migration and invasion by cytoplasmic delivery of anti-RhoC silencing RNA and presentation of EPPT1 peptide on "smart" particles

Overexpression of RhoC protein in breast cancer patients has been linked to increased cancer cell invasion, migration, and metastases. Suppressing RhoC expression in aggressive breast cancer cells using silencing RNA (siRNA) molecules is a viable strategy to inhibit the metastatic spread of breast cancer. In this report, we describe the synthesis of a series of asymmetric pH-sensitive, membrane-destabilizing polymers engineered to complex anti-RhoC siRNA molecules forming "smart" nanoparticles. Using β-CD as the particle core, polyethylene glycol (PEG) chains were conjugated to the primary face via non-cleavable bonds and amphiphilic polymers incorporating hydrophobic and cationic monomers were grafted to the secondary face via acid-labile linkages. We investigated the effect of PEG molecular weight (2 & 5 kDa) on transfection capacity and serum stability of the formed particles. We evaluated the efficacy of EPPT1 peptides presented on the free tips of the PEG brush to function as a targeting ligand against underglycosylated MUC1 (uMUC1) receptors overexpressed on the surface of metastatic breast cancer cells. Results show that "smart" nanoparticles successfully delivered anti-RhoC siRNA into the cytoplasm of aggressive SUM149 and MDA-MB-231 breast cancer cells, which resulted in a dose-dependent inhibition of cell migration and invasion. Further, EPPT1-targeted nanoparticles demonstrate a synergistic inhibition of cell migration and invasion imparted via RhoC knockdown and EPPT1-mediated signaling via the uMUC1 receptor.

Abstract P6-07-01: Withdrawn

This abstract was withdrawn by the authors.

Abstract 3371: Aldh expressing stem cells mediate tumor initiation and metastasis in triple negative breast cancers across different ethnicities

TNBC is the only subtype of breast cancer for which there are no approved targeted therapies. In the US, its incidence is highest in women with African ancestry (AA); in western sub-Saharan Africa, single-institution studies show that TNBC constitutes 40- 80% of all breast cancers. Given the Caucasian/AA survival disparity in breast cancer, there is an urgent need to find actionable targets in TNBC of all ethnicities, but especially in TNBC in AA, which are suspected to be more aggressive. Breast cancer stem cells, the small population of cells that have been shown to mediate breast tumor initiation, metastasis, and resistance to conventional therapy have also been reported to mediate the heterogeneity of TNBC and are especially abundant in TNBC in AA women. Here, we sought to better understand the biology of TNBC by finding genes and pathways that are differentially expressed in the stem cell population of patient derived xenografts (PDX) from TNBC from Ghanaian (G), AA and Caucasian (C) women and the effect of these differentially expressed genes on the stem cell phenotype in these primary tumors. We isolated the ALDH+ and the CD44+/CD24- stem cell populations from the bulk cells from 15 PDXs using flow cytometry. We performed RNA sequencing (Illumina HiSeq platform) on the isolated populations and bulk cells (45). Comprehensive bioinformatics analyses led to the identificationof highly significantly differentially expressed genes and pathways between the cell populations. By principal component analysis, the tumors were very heterogeneous. However, the ALDH+ cells separated out from the CD44+/CD24- and the bulk cells. We identified 14 genes that were simultaneously differentially expressed between the ALDH+ vs the CD44+/CD24- as well as ALDH+ VS bulk (p-value &lt;0.001, FDR &lt; 0.05). The 3 most significant genes were MMP2 and PCDH7, both known to be involved in breast cancer metastasis and CPXM1, a carboxylase. Inhibiting MMP2 expression in the PDX cells grown in suspension resulted in significant reduction in the ALDH+ cell population. Also, the ALDH+ and not the CD44+/CD24- cells formed spheres in serum free media. The WNT, MAPK and TGF-beta pathways known to mediate metastasis were all significantly up-regulated in the ALDH+ population with down regulation of biosynthetic pathways which were up-regulated in the CD44+/CD24- population. Further studies are ongoing on pathway modulation in ALDH1+ cells based on these findings. Our data demonstrate that the ALDH+ stem cell population is enriched for tumor initiating cells in aggressive TNBCs across different ethnicities. These cells may play a role in mediating the aggressive behavior of TNBC’s found in African women.

Citation Format: Evelyn M. Jiagge, Shukmei Wong, Rabia Gilani, Sean Mcdermott, Lisa Newman, Jessica Bensenhaver, Max Wicha, John Carpten, Sofia Merajver. Aldh expressing stem cells mediate tumor initiation and metastasis in triple negative breast cancers across different ethnicities [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 3371. doi:10.1158/1538-7445.AM2017-3371

Abstract 1311: Preclinical assessment of an HDAC inhibitor combined with a retinoid in AI resistant breast cancer

Treatment with aromatase inhibitors (AI's) is highly effective against breast cancer in ER positive postmenopausal women. However, some patients eventually become resistant to AIs. Tumor initiating cells (TIC's) represent a subpopulation of tumor cells, which show self-renewal capacity. We are focused towards discovering strategies to reduce the growth of breast cancer TICs, which may result in resistance. We have developed a xenograft model that mimics post-menopausal hormone responsive breast cancer. In this model, aromatase transfected human hormone sensitive MCF-7 cells (MCF-7Ca) are inoculated in ovariectomized athymic nude mice and allowed to grow in presence of Δ4A (aromatizable substrate of estrogen). Using this model, we have established that although AI letrozole provides a longer control over tumor growth, tumors eventually began to grow. In the current study, we investigated the effect of ATRA (All-trans Retinoic acid) (125μg/day, ip) and a histone deacetylase (HDAC) inhibitor entinostat (SNDX- 275) (50μg/day, po) with or without letrozole on letrozole resistant tumors in a xenograft model system. Ovariectomized athymic nude mice bearing xenografts of MCF-7Ca cells were treated with letrozole till they became resistant (15 weeks). At this time, the mice were grouped to receive ATRA, entinostat plus ATRA or the combination of ATRA plus entinostat plus letrozole till week 23. The mice treated with entinostat plus ATRA plus letrozole showed a significant decrease in tumor growth rate compared to mice treated with single agents or entinostat plus ATRA (p&lt;0.0001, p=0.02). On week 20, two mice from each treatment group were euthanized and tumors were harvested. The tumors were digested enzymatically with collagenase and hyaluronidase and freed of debris using centrifugation and filtration. Mammosphere forming ability of TICs in the tumor tissue was measured by seeding 10,000 viable cells from each treated tumors under non-adherent conditions to access the self-renewal capacity. The combination of ATRA plus ENT plus letrozole significantly (p&lt;0.01) reduced number of mammospheres formed compared to single agents alone. Quantitative PCR analysis of tumors cells showed a significant downregulation of the known TIC molecular markers, BCRP, ALDH, BMI-1 and Nanog compared to letrozole treated tumors. Similar results were also obtained when LTLT-Ca (long term letrozole treated MCF-7Ca) cells were treated with ATRA and entinostat in combination with letrozole and then seeded (5000 cells) in non-adherent conditions. Combination of ATRA plus entinostat plus letrozole significantly (p&lt;0.0001) reduced mammosphere-forming ability of the LTLT-Ca cells. Overall, these studies indicate that the combination of ATRA, entinostat and letrozole is effective in reducing tumor recurrence in letrozole resistant tumors.

Citation Format: Preeti Shah, Gauri J. Sabnis, Olga Goloubeva, Armina Kazi, Amanda Schech, Rabia Gilani, Yael Gau, Saranya Chumsri, Angela Brodie. Preclinical assessment of an HDAC inhibitor combined with a retinoid in AI resistant breast cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1311. doi:10.1158/1538-7445.AM2013-1311

Abstract 787: Involvement of HER2, HIF-1, and BCRP in cancer stem cell characteristics of letrozole-resistant breast cancer cells

Studies by us and others suggest that acquired resistance to aromatase inhibitors (AIs; i.e., letrozole) involves a switch from dependence on ER signaling to dependence on growth factor-mediated pathways, such as epidermal growth factor receptor (EGFR)/HER2. Recent work in our lab has also linked hypoxia inducible factor 1 (HIF-1) and breast cancer resistance protein (BCRP, a stem cell marker) to HER2 and AI resistance. Other studies have associated each of these factors with cancer stem cells (CSCs) and CSCs have been implicated in drug resistance. Therefore, this current study aimed to 1) compare the CSC characteristics of letrozole-resistant (LTLTCa) and parental letrozole-sensitive (MCF-7Ca) breast cancer cells; 2) determine the roles of HER2, BCRP, and HIF-1 on CSC characteristics; and 3) compare the effects of HER2 inhibition and of differentiating agent all-trans retinoic acid (ATRA) on CSC population of the LTLTCa cells. LTLTCa cells were found to have higher expression of CSC characteristics compared to parental MCF-7Ca cells: 9.17%±2.0% vs. 0.02% ±0.01% (p &lt;0.01) measured by side population, and 3.08% vs. 0.53% (p&lt;0.05) by aldehyde dehydrogenase (ALDH) activity. Consistent with previous results, inhibition of HER2, HIF-1, or BCRP resulted in decreased CSC characteristics in LTLTCa cells. Inhibition of HER2 by treatment with 1 μM lapatinib (Lap) decreased side population (from 7.91%±2.10 to 0.76%±0.20) and mammosphere formation (from &gt;200 mammospheres/10,000 cells to ∼50 mammospheres/10,000 cells). Flow cytometry also demonstrated that LTLTCa cells high in both ALDH activity and CD44 positivity, were also high in HER2. Inhibition of HIF-1 (by siRNA) or BCRP (by pharmacological inhibitors or siRNA) significantly decreased mammosphere formation from 406 mammospheres/80,000 cells to 93 and 81 mammospheres/80,000 cells, respectively (p&lt;0.01). Pharmacological inhibition of BCRP also decreased side population. Comparing the effects of Lap and ATRA on LTLTCa cells, both drugs decreased mammosphere formation after 48 h and cell viability after 7 days of treatment (p&lt;0.05 for each). Both drugs also increased ERα and decreased BCRP expression in LTLTCa cells. Lastly, Lap and ATRA each increased the expression ratio of epithelial markers versus mesenchymal markers, but they did this by affecting different proteins. Lap increased expression of epithelial marker E-cadherin, but had no effect on mesenchymal marker N-cadherin. ATRA decreased N-cadherin but had no effect on E-cadherin. Overall, the results from this study suggest that HER2-HIF-1-BCRP signaling in contributes to acquired breast cancer cell resistance to letrozole by 1) increasing the cancer stem cell population, and possibly by 2) promoting epithelial mesenchymal transition (EMT), an indicator of cancer cell invasive and metastatic potential.

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 787. doi:1538-7445.AM2012-787

Sensitivity to the aromatase inhibitor letrozole is prolonged after a "break" in treatment

Using a hormone-dependent xenograft model, we established that loss of response to letrozole was accompanied by upregulation of the Her-2/mitogen-activated protein kinase (MAPK) pathway and downregulation of estrogen receptor alpha (ERalpha) and aromatase activity. In our previous study, we showed that stopping letrozole treatment or adding trastuzumab could reverse acquired resistance. In this study, we compared the effects of intermittent letrozole treatment and switching treatment between letrozole and trastuzumab on tumor growth in an attempt to optimize discontinuous letrozole treatment. The mice were treated with letrozole until the tumors developed resistance and then were divided into three groups: (a) letrozole, (b) trastuzumab, and (c) "off" (Delta(4)A supplement only); tumors were collected every week to examine changes in tumor protein expression and activity. In off group tumors, Her-2/p-MAPK activation gradually decreased and ERalpha and aromatase protein (and activity) increased. Within the first week of trastuzumab treatment, Her-2 and MAPK were downregulated and ERalpha was upregulated. When letrozole-resistant MCF-7Ca tumors were taken off treatment for 4 weeks, the second course of letrozole treatment provided a much longer duration of response (P = 0.02). However, switching treatment to trastuzumab for 4 weeks did not provide any inhibition of tumor growth. Our studies revealed that the adaptation of cells to a low-estrogen environment by upregulation of Her-2/MAPK and downregulation of ERalpha/aromatase was reversed on letrozole withdrawal. The tumors once again became responsive to letrozole for a significant period. These results suggest that response to letrozole can be prolonged by a short "break" in the treatment.

Expression of ERα and Aromatase in MDA-MB-231 Tumors by HDAC Inhibitor Entinostat Leads to Growth Inhibition by Aromatase Inhibitor Letrozole

The treatment for hormone receptor-positive breast cancer has improved significantly since the development of aromatase inhibitors (AIs). Nevertheless, AIs are ineffective in estrogen receptor-negative (ER-) tumors, which comprise of approximately 25% of breast cancers and tend to be more aggressive. Studies have shown that repression of ER in these hormone receptor-negative tumors may be due to epigenetic modifications. The discovery of recruitment of histone deacetylase enzymes in gene silencing provides a rationale for inhibition of HDAC activity to release transcriptional repression as a potential therapeutic strategy. The objective of the present study was to express ERα and aromatase with HDACI treatment and thereby sensitize tumors to growth inhibition with aromatase inhibitors. In this study we used ER negative, hormone refractory MDA-MB-231 human breast cancer cells. Treatment with HDAC inhibitor entinostat led to upregulation of ERα, aromatase and its activity in a dose dependent manner in cells and xenografts. MDA-MB-231 xenografts were grown in ovariectomized female nude mice. Mice were inoculated with 2.5 X 106 cells per site subcutaneously. When the tumors reached 150 mm3, the mice were grouped into 4 groups (n=10), so that the mean tumor volume was not statistically different across groups (p=0.88). Tumor volumes were measured twice weekly. The mice in the letrozole group had a mean tumor growth rate (β = 0.023 ± 0.014) that was not statistically different (p=0.76) from that of the control group (β = 0.038 ± 0.007). Also, the growth rate of entinostat group (β = 0.034 ± 0.011) was not significantly lower than that of the control (p=0.33). However, the growth rate of entinostat plus letrozole group ((β = -0.003 ± 0.013) was significantly lower than that of the control (p=0.01), entinostat (p=0.03) and letrozole (p=0.049) groups. The combined treatment of entinostat plus letrozole was significantly more effective than either agent alone. In addition, the ability of this combination to inhibit migration in vitro was examined by wound healing assay. The combination of entinostat plus letrozole provides superior inhibition of migration (p&lt;0.001) compared to control, entinostat and letrozole alone. To test the efficacy of this combination in preventing the outgrowth of tumor foci in the lung, mice received an inoculation of 3 X 106 cells intravenously via the tail vein. They were treated three weeks later with entinostat alone, letrozole alone, or the combination. Mice were treated for six weeks, and then euthanized. Treatment with entinostat alone or letrozole was not significantly effective, but the combination resulted in a significantly reduced number of both visible and micrometastases (p=0.03) compared to no treatment (control) and the entinostat alone group. Thus, up-regulation of ERα and aromatase resulted in sensitization of tumors to significant inhibition of growth, cell migration and formation of micro-metastases by the aromatase inhibitor letrozole.Our results provide the basis for possible use of AIs in combination with HDAC inhibitors for the treatment of hormone refractory ERα negative breast cancer. This could open a new avenue for the management of ER- breast cancer.

Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 401.

Combination of HDACi entinostat (SNDX-275) with letrozole provides control over tumor growth in MDA-MB-231 xenograft model

Abstract #6128

It is well established that approximately 75% of human breast cancers are ER+ and therefore treated with endocrine therapy. In a past few decades endocrine therapy has made significant advancements. However, the application of these agents is limited to ER+ cancers since ER- patients are unresponsive to endocrine therapy primarily due to lack of ER expression in the tumor. The main purpose of this project is to determine whether ER- breast cancer tumors that display poor anti-proliferative response to aromatase inhibitor (AI) letrozole, can be sensitized by co-treatment with HDACi entinostat. Based on preliminary studies, we hypothesize that by inhibiting HDAC ER is re-expressed making the cells sensitive to the anti-proliferative effects of AIs. In our previous studies we have shown that HDACi entinostat can revert the ERα repression and upregulate ERα and aromatase in vitro and in vivo. In this study we are showing that this activation of aromatase and re-expression of ERα renders ER- breast cancer tumors (xenografts of MDA-MB-231 cells) responsive to letrozole.&#x2028; MDA-MB-231 xenografts were grown in ovariectomized female nude mice. Mice were inoculated with 2.5X 106 cells per site subcutaneously. When the tumors reached a measurable size ∼150 mm3, the mice were grouped into 6 groups (n=10), such that the mean tumor volumes across the groups was not statistically different (p=0.99). The mice were injected with Δ4A (100 μg/day), Δ4A plus letrozole (10 μg/day), entinostat (2.5 mg/kg/day), entinostat plus Δ4A, entinostat plus Δ4A plus letrozole or vehicle. The mice were injected 5 times a week. The tumors were measured every week with calipers and the tumor volumes were calculated using formula, 4/3 π r12r2. The mice in the entinostat plus Δ4A plus letrozole group had the least tumor growth rate (0.004+0.081), which was lower than entinostat plus Δ4A (0.115+0.079) and Δ4A plus letrozole (0.096+0.080). This data suggests a trend towards improved inhibition of tumor growth with combination of entinostat plus letrozole. The mice were sacrificed on week 9 due to large tumor volumes. The tumors and uteri were excised, cleaned, weighed and stored for additional analysis.&#x2028; In addition, ability of this combination to inhibit migration in vitro was examined by wound healing assay. The combination of entinostat plus letrozole provides superior inhibition of migration (p&lt;0.001) compared to control, entinostat and letrozole alone. This suggests that the combination of entinostat plus letrozole has potential of inhibiting metastatic spread along with tumor growth.&#x2028; These findings indicate that ERα in ER- breast cancer cells is silenced along with aromatase but can be restored with HDACi. Thus activation of silenced ER and intratumoral aromatase by HDACi could open a new avenue for management of ER- advanced breast cancer.

Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 6128.