Impact of Clinical Practice Gaps on the Implementation of Personalized Medicine in Advanced Non–Small-Cell Lung Cancer

Personalized medicine presents new opportunities for patients with cancer. However, many patients do not receive the most effective personalized treatments because of challenges associated with integrating predictive biomarker testing into clinical care. Patients are lost at various steps along the precision oncology pathway because of operational inefficiencies, limited understanding of biomarker strategies, inappropriate testing result usage, and access barriers. We examine the impact of various clinical practice gaps associated with diagnostic testing-informed personalized medicine strategies on the treatment of advanced non–small-cell lung cancer (aNSCLC).

179 Improving Operative Notes in Upper GI Surgery: An Innovative QI Project Utilising Existing Electronic Hospital Systems

Introduction

Operative notes play a valuable role in ensuring that surgical patients receive consistent and adequate care. There are many inherent difficulties affecting their quality. We performed a QI project to improve surgical operative notes at our centre.

Method

A questionnaire assessing subjective quality of operative notes was sent to all foundation doctors delivering post-operative care. Compliance to each inclusion recommendation in the RCS guidelines was analysed. A standardised template for operative notes was incorporated into the hospital’s electronic records system, compliance was then reassessed.

Results

Questionnaire responses (16) were better for typed vs hand-written notes in all domains: ease of accessing notes, following intra-operative steps, following post-operative plans and frequency of asking for additional information regarding plans. After implementation of the template, mean compliance across 19 RCS parameters improved from 69% (55 operations) to 89% (46 operations). Number of parameters with 100% compliance improved from 2/19 to 8/19. Compliance increased in 14/19 parameters, there was no change in 2/19 (already 100%) and a reduction was seen in 3/19.

Conclusions

Results from our analysis and questionnaire showed that typed notes were favourable when compared to hand-written. The introduction of a standardised electronic template, without investment in new software, improved compliance to RCS guidelines.

Induction of cell cycle arrest and inflammatory genes by combined treatment with epigenetic, differentiating, and chemotherapeutic agents in triple-negative breast cancer

Background

A combination of entinostat, all-trans retinoic acid, and doxorubicin (EAD) induces cell death and differentiation and causes significant regression of xenografts of triple-negative breast cancer (TNBC).

Methods

We investigated the mechanisms underlying the antitumor effects of each component of the EAD combination therapy by high-throughput gene expression profiling of drug-treated cells.

Results

Microarray analysis showed that entinostat and doxorubicin (ED) altered expression of genes related to growth arrest, inflammation, and differentiation. ED downregulated MYC, E2F, and G2M cell cycle genes. Accordingly, entinostat sensitized the cells to doxorubicin-induced growth arrest at G2. ED induced interferon genes, which correlated with breast tumors containing a higher proportion of tumor-infiltrating lymphocytes. ED also increased the expression of immune checkpoint agonists and cancer testis antigens. Analysis of TNBC xenografts showed that EAD enhanced the inflammation score in nude mice. Among the genes differentially regulated between the EAD and ED groups, an all-trans retinoic acid (ATRA)-regulated gene, DHRS3, was induced in EAD-treated xenografts. DHRS3 was expressed at lower levels in human TNBC metastases compared to normal breast or primary tumors. High expression of ED-induced growth arrest and inflammatory genes was associated with better prognosis in TNBC patients.

Conclusions

Entinostat potentiated doxorubicin-mediated cell death and the combination induced inflammatory signatures. The ED-induced immunomodulation may improve immunotherapy. Addition of ATRA to ED may potentiate inflammation and contribute to TNBC regression.

Electronic supplementary material

The online version of this article (10.1186/s13058-018-1068-x) contains supplementary material, which is available to authorized users.

HOXC10 Expression Supports the Development of Chemotherapy Resistance by Fine Tuning DNA Repair in Breast Cancer Cells

Development of drug resistance is a major factor limiting the continued success of cancer chemotherapy. To overcome drug resistance, understanding the underlying mechanism(s) is essential. We found that HOXC10 is overexpressed in primary carcinomas of the breast, and even more significantly in distant metastasis arising after failed chemotherapy. High HOXC10 expression correlates with shorter recurrence-free and overall survival in patients with estrogen receptor-negative breast cancer undergoing chemotherapy. We found that HOXC10 promotes survival in cells treated with doxorubicin, paclitaxel, or carboplatin by suppressing apoptosis and upregulating NF-κB Overexpressed HOXC10 increases S-phase-specific DNA damage repair by homologous recombination (HR) and checkpoint recovery in cells at three important phases. For double-strand break repair, HOXC10 recruits HR proteins at sites of DNA damage. It enhances resection and lastly, it resolves stalled replication forks, leading to initiation of DNA replication following DNA damage. We show that HOXC10 facilitates, but is not directly involved in DNA damage repair mediated by HR. HOXC10 achieves integration of these functions by binding to, and activating cyclin-dependent kinase, CDK7, which regulates transcription by phosphorylating the carboxy-terminal domain of RNA polymerase II. Consistent with these findings, inhibitors of CDK7 reverse HOXC10-mediated drug resistance in cultured cells. Blocking HOXC10 function, therefore, presents a promising new strategy to overcome chemotherapy resistance in breast cancer. Cancer Res; 76(15); 4443-56. ©2016 AACR.

Combined Treatment with Epigenetic, Differentiating, and Chemotherapeutic Agents Cooperatively Targets Tumor-Initiating Cells in Triple-Negative Breast Cancer

Efforts to induce the differentiation of cancer stem cells through treatment with all-trans retinoic acid (ATRA) have yielded limited success, partially due to the epigenetic silencing of the retinoic acid receptor (RAR)-β The histone deacetylase inhibitor entinostat is emerging as a promising antitumor agent when added to the standard-of-care treatment for breast cancer. However, the combination of epigenetic, cellular differentiation, and chemotherapeutic approaches against triple-negative breast cancer (TNBC) has not been investigated. In this study, we found that combined treatment of TNBC xenografts with entinostat, ATRA, and doxorubicin (EAD) resulted in significant tumor regression and restoration of epigenetically silenced RAR-β expression. Entinostat and doxorubicin treatment inhibited topoisomerase II-β (TopoII-β) and relieved TopoII-β-mediated transcriptional silencing of RAR-β Notably, EAD was the most effective combination in inducing differentiation of breast tumor-initiating cells in vivo Furthermore, gene expression analysis revealed that the epithelium-specific ETS transcription factor-1 (ESE-1 or ELF3), known to regulate proliferation and differentiation, enhanced cell differentiation in response to EAD triple therapy. Finally, we demonstrate that patient-derived metastatic cells also responded to treatment with EAD. Collectively, our findings strongly suggest that entinostat potentiates doxorubicin-mediated cytotoxicity and retinoid-driven differentiation to achieve significant tumor regression in TNBC. Cancer Res; 76(7); 2013-24. ©2016 AACR.

Abstract 4231: Combination of epigenetic, differentiation and DNA damaging agents induce tumor cell death and stem cell depletion in breast cancer

The histone deacetylase inhibitor, entinostat, is a new-generation epigenetic drug, which has recently demonstrated notable clinical efficacy when used in combination with standard therapy. Retinoids induce differentiation in various types of stem cells. However, its delivery to patients is challenging because of its rapid metabolism. Also, epigenetic changes in the retinoic acid receptors often render cancer cells retinoid-resistant. We have shown that a combination of entinostat, all-trans retinoic acid (ATRA) and doxorubicin causes significant regression of xenografts of triple negative breast cancer (TNBC) cells and investigated the mechanism underlying the effectiveness of this combination therapy. Combinations of entinostat, retinoic acid and doxorubicin were optimal in causing tumor regression in triple negative breast cancer xenografts. Gene expression analysis of treated TNBC cells identified genes most effectively reprogrammed by entinostat and doxorubicin (ED) combination therapy. These genes are involved in cell cycle arrest, inflammation and differentiation, which are related to better survival outcome in patients. Entinostat sensitizes the cells to doxorubicin-induced growth arrest, resulting in increased apoptosis and necrosis. Adding ATRA to ED regulated interferon genes and members of the cancer/testis antigens (CTA) and tripartite motif (TRIM) family of proteins and induces inflammation in nude mice. Entinostat/ATRA/dox therapy was most effective to target breast cancer stem cells (BCSC) in limiting dilution assays of growth in mammary fat pads. The epithelium-specific ETS transcription factor-1 (ESE-1 or ELF3), known to regulate cellular proliferation and differentiation mediates the epigenetic differentiation effect. Patient-derived distant metastases responded to entinostat/ATRA/dox therapy in culture. Thus, the combination therapy may have significant effects in decreasing both local and metastatic growth in breast cancer, especially in decreasing recurrence by targeting breast cancer stem cells.

Citation Format: Vanessa F. Merino, Nguyen Nguyen, Helen Sadik, Soonweng Cho, Leslie Cope, Xian C. Zhou, Zhe Zhang, Qian Chen, Duojia Pan, David L. Huso, Syed Ali, Christina Adams, Balázs Győrffy, Saraswati Sukumar. Combination of epigenetic, differentiation and DNA damaging agents induce tumor cell death and stem cell depletion in 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 4231. doi:10.1158/1538-7445.AM2015-4231

Targeting Glutamine Metabolism in Breast Cancer with Aminooxyacetate

PURPOSE

Glutamine addiction in c-MYC-overexpressing breast cancer is targeted by the aminotransferase inhibitor, aminooxyacetate (AOA). However, the mechanism of ensuing cell death remains unresolved.

EXPERIMENTAL DESIGN

A correlation between glutamine dependence for growth and c-MYC expression was studied in breast cancer cell lines. The cytotoxic effects of AOA, its correlation with high c-MYC expression, and effects on enzymes in the glutaminolytic pathway were investigated. AOA-induced cell death was assessed by measuring changes in metabolite levels by magnetic resonance spectroscopy (MRS), the effects of amino acid depletion on nucleotide synthesis by cell-cycle and bromodeoxyuridine (BrdUrd) uptake analysis, and activation of the endoplasmic reticulum (ER) stress-mediated pathway. Antitumor effects of AOA with or without common chemotherapies were determined in breast cancer xenografts in immunodeficient mice and in a transgenic MMTV-rTtA-TetO-myc mouse mammary tumor model.

RESULTS

We established a direct correlation between c-MYC overexpression, suppression of glutaminolysis, and AOA sensitivity in most breast cancer cells. MRS, cell-cycle analysis, and BrdUrd uptake measurements indicated depletion of aspartic acid and alanine leading to cell-cycle arrest at S-phase by AOA. Activation of components of the ER stress-mediated pathway, initiated through GRP78, led to apoptotic cell death. AOA inhibited growth of SUM159, SUM149, and MCF-7 xenografts and c-myc-overexpressing transgenic mouse mammary tumors. In MDA-MB-231, AOA was effective only in combination with chemotherapy.

CONCLUSIONS

AOA mediates its cytotoxic effects largely through the stress response pathway. The preclinical data of AOA's effectiveness provide a strong rationale for further clinical development, particularly for c-MYC-overexpressing breast cancers.

Abstract P3-01-01: Targeting glutamine metabolism in breast cancer for therapy

Metabolic reprogramming of cancer cells is observed in different types of tumors including breast. Oncogenic signals aid changes in metabolism that provide selective advantage to the cancer cells to meet their energy requirements to accomplish rapid proliferation. The increased dependence on the glycolytic pathway for energy called the “Warburg effect” was reported by Otto Warburg several decades ago. Our recent understanding of cancer metabolism has thrown light on alternative energy sources, especially glutamine and other branched chain amino acids. The role of glutamine in breast cancer cell growth has not yet been studied extensively.

In this study we found that a number of breast cancer cell lines, especially those negative for ER, PR, HER2, display a high dependence on glutamine for their survival and growth. Interestingly, most of these glutamine-dependent cell lines express high levels of c-myc protein. Consistent with their growth dependency on glutamine, transaminases responsible for entry of glutamine into the tricarboxylic acid cycle are transcriptionally up regulated under low glutamine conditions. Consequently, growth of these cancer cell lines was found to be specifically inhibited by the transaminase inhibitor, amino oxyacetate (AOA). Moreover, the AOA mediated cytotoxic effect was partially c-myc dependent. Through 1H-NMR studies of AOA-treated cells we show that in addition to glutamine, AOA treatment decreases the aspartate and alanine content in the cells. In line with these findings, exogenous supplementation with aspartate partially rescued the cells from the growth inhibitory effects of AOA. Flow cytometry analysis showed that AOA causes cell cycle arrest in the S phase. AOA also had significant inhibitory effect on in vivo growth of rapidly growing SUM 149 and SUM159 xenografts in immunodeficient mice. When combined with chemotherapeutic agents, doxorubicin and carboplatin, AOA inhibited growth of MDA-MB-231 xenograft tumors more effectively than AOA alone. Lastly we present evidence that the cytotoxic effect of AOA is mediated through activation of the ER stress pathway, combined with depletion of key amino acids and likely, a reduction in the nucleoside pool in the cells. Our preclinical studies, both in vitro and in vivo, combined with development of intermediate markers of response, provide a strong rationale for testing AOA for therapy in Phase 0 clinical trials.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P3-01-01.

HOXB13 mediates tamoxifen resistance and invasiveness in human breast cancer by suppressing ERα and inducing IL-6 expression

Most breast cancers expressing the estrogen receptor α (ERα) are treated successfully with the receptor antagonist tamoxifen (TAM), but many of these tumors recur. Elevated expression of the homeodomain transcription factor HOXB13 correlates with TAM-resistance in ERα-positive (ER+) breast cancer, but little is known regarding the underlying mechanism. Our comprehensive evaluation of HOX gene expression using tiling microarrays, with validation, showed that distant metastases from TAM-resistant patients also displayed high HOXB13 expression, suggesting a role for HOXB13 in tumor dissemination and survival. Here we show that HOXB13 confers TAM resistance by directly downregulating ERα transcription and protein expression. HOXB13 elevation promoted cell proliferation in vitro and growth of tumor xenografts in vivo. Mechanistic investigations showed that HOXB13 transcriptionally upregulated interleukin (IL)-6, activating the mTOR pathway via STAT3 phosphorylation to promote cell proliferation and fibroblast recruitment. Accordingly, mTOR inhibition suppressed fibroblast recruitment and proliferation of HOXB13-expressing ER+ breast cancer cells and tumor xenografts, alone or in combination with TAM. Taken together, our results establish a function for HOXB13 in TAM resistance through direct suppression of ERα and they identify the IL-6 pathways as mediator of disease progression and recurrence.

Abstract 3726: Combinations of HDAC inhibitor, chemotherapeutic agent and retinoic acid induce growth arrest, differentiation and tumor regression in preclinical models of breast cancer

The histone deacetylase inhibitor (HDACi), entinostat, is being actively explored as a new-generation epigenetic drug which can lead to the change in the expression status of genes/pathways, but has low efficacy in cancer monotherapy. All-trans retinoic acid (ATRA) induces the differentiation of various types of stem cells. Data from cell culture and xenograft models from our lab showed that a combination of entinostat (MS-275), doxorubicin and ATRA effectively decreased tumor size in three breast cancer cell line xenograft models. Here, we sought to further investigate the mechanism of action of the triple drug combination in cancer cells; in particular, its effect on the breast cancer stem cell population. We performed a comprehensive genome wide analysis of gene expression of MDA-MB-231 breast cancer cells treated with ATRA, MS-275 and doxorubicin as monotherapies and as combination therapies. We saw that the drug-response gene profile of ATRA is very similar to DMSO (vehicle)-treated cells. Accordingly, the addition of ATRA (A) to MS-275 (MA), Dox (AD) and MS-275/Dox (MAD) displayed minimal changes in the gene expression profile of each of the other treatments. Addition of Dox to MS-275 (MD), on the other hand, potentiated the “reprograming” effect of MS-275 and affected the expression of many antitumor genes known to be related to cell cycle and growth arrest. It also altered expression of genes involved in development and inflammation. The most differentially expressed genes, validated by qPCR, were novel genes from the cancer/testis antigens and tripartite motif (TRIM) family of proteins. Interestingly, in MDA-MB-231and SUM149 cells, even the addition of low doses of doxorubicin (12.5 nM) to MS-275 increased 2 and 2.6 fold the G2 cell cycle arrest in comparison to Dox and MS-275, respectively. Despite the gene expression pattern similarity between MS-275/Dox (MD) and MS-275/Dox/ATRA (MAD) groups, we saw that MAD was more effective in inducing cell death and apoptosis in vitro and in vivo. The epithelium specific ETS transcription factor-1 (ESE-1) was differentially regulated between MAD and MD and is, in fact, part of the MS-275/ATRA (MA) signature. Using limiting dilution transplantation assays in mammary fat pads of immunodeficient mice we observed that MAD treatment in vivo most effectively targeted breast cancer stem cells (BCSC) compared to any other combination of drugs. The cancer stem cell frequency of the cells isolated from MAD treated mice was 1 in 236,570. The second most effective treatment for BCSC was MA (1 in 150,721), followed by ATRA> MS-275>MD>Dox>DMSO>AD. In conclusion, the reprogramming events initiated by HDACi and retinoid sensitize the cells to low doses of doxorubicin. The combination therapy may have a significant effect in decreasing breast tumor growth and recurrence.

Citation Format: Vanessa F. Merino, Nguyen Nguyen, Helen Sadik, Sean Cho, Xian Chong Zhou, Qian Chen, Duojia Pan, Saraswati Sukumar. Combinations of HDAC inhibitor, chemotherapeutic agent and retinoic acid induce growth arrest, differentiation and tumor regression in preclinical models of 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 3726. doi:10.1158/1538-7445.AM2013-3726

Abstract P4-08-08: HOXC10, a homeobox protein overexpressed in breast cancer, modulates the response to chemotherapy treatment

Background: Breast cancer is the second leading cause of cancer deaths in women worldwide. Although chemotherapy is effective, resistance to drugs develops over time and can account for treatment failure in over 90% of metastatic breast cancer patients. HOX genes are homeobox-containing transcription factors well-known for their role in morphogenesis. and during carcinogenesis and metastasis. The goal of this study is to understand the role of HOXC10 in breast cancer and mainly in response to chemotherapy.

Methods: Using a tiling array of all four HOX clusters in a panel of primary and metastatic breast cancer tissues, we identified HOXC10 as being among the highly overexpressed genes in breast cancer. Then using a panel of cell lines that either stably overexpress exogenous HOXC10 or cell lines with stably downregulated endogenous HOXC10 (mediated by shRNA), we investigated the role of HOXC10 in proliferation, response to chemotherapy treatment and repair of DNA damage.

Results: HOXC10 is overexpressed in 67% of primary breast tumors (n = 31), in 82% of the metastatic tissues (n = 49) and in most breast cancer cell lines (n = 48). In vitro and in vivo investigation confirmed that HOXC10 plays an oncogenic role in breast cancer. Further, knockdown of HOXC10 in a panel of breast cancer cell lines slowed their proliferation and arrested them at the G1 phase, by inactivating the RB/E2F pathway, decreasing the number of new origins and eventually reducing the polyploidy population.

Cell survival assays after different chemotherapeutic drug treatment showed that overexpression of the exogenous HOXC10 in MCF10A led to less susceptibility to most drugs. This was partially due to a protection from apoptosis by upregulating and activating the anti-apoptotic machinery such as the NF-kb pathway. Further investigation revealed the involvement of HOXC10 in DNA repair (and not initial response), especially after DNA crosslink damage. Interestingly, the binding of HOXC10 to CDK7 in a region outside its homeodomain activates CDK7 activity towards RNA polymerase II mainly in response to DNA damage. Since HOX genes are difficult to target therapeutically, one potential approach to overcome chemoresistance in HOXC10 overexpressing cells is by including CDK7 inhibitors (already in clinical trials).

All these results were confirmed in the SUM159 model which stably expresses a HOXC10-shRNA.

Finally, HOXC10 was found to be significantly overexpressed in MCF7 isogenic cell lines gradually selected to be resistant to some chemotherapeutic drugs. By knocking down HOXC10 in these sublines, resistance to the drug was reduced. Further, SUM159 and MDAMD231 xenografts that were treated with chemotherapy over weeks and that show partial to no response tend to have a higher expression of HOXC10.

Conclusion: This study shows that HOXC10, a homeobox protein previously shown to be regulated during the cell cycle and to have a positive effect on proliferation, is overexpressed in the majority of breast cancers. This upregulation may have clinical implications since cells with higher expression of HOXC10 tend to have more genomic instability and activation of anti-apoptotic and DNA repair pathways, which eventually modulate the response to some chemotherapy drugs.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P4-08-08.

Abstract P2-09-01: Reactivation of epigenetically silenced retinoic acid receptor-beta for therapy of breast cancer- from molecular mechanism to potential clinical applications

Background: Triple negative breast cancer (TNBC) is a subgroup of breast cancer that is characterized by a lack of expression of targets for validated targeted therapies. Although responses to chemotherapy are observed, resistance develops rapidly. Genomic and molecular profiling of TNBC has identified multiple contributors to their uncontrolled growth including epigenetic dysregulation of genes important for normal cell growth and differentiation. Recent studies have shown that histone deacetylase (HDAC) inhibitors reverse the epigenetic profile of tumors, resulting in the re-expression of silenced genes encoding proteins such as ERα, EGFR, and RARβ. Entinostat is an oral, class 1 isoform selective HDACi recently shown in a phase 2 study to be active in ER+ breast cancer. Clinical trials with entinostat in HER2+ and TNBC are also in progress. We hypothesized that combining epigenetic therapy using entinostat, with differentiation therapy using a retinoic acid receptor agonist- All Trans Retinoic Acid (ATRA) will provide an effective strategy for impeding the growth of TNBC and potentially sensitize tumors to commonly used chemotherapies (doxorubicin, carboplatin, paclitaxel).

Methods: Combination studies of entinostat combined with ATRA with and without non-toxic doses (half clinical) of chemotherapy were carried out in vitro and in xenograft models of TNBC. Expression of RARb and downstream effectors were measured in cell lines and tumors from xenograft studies.

Results: Nontoxic (half clinical) doses of doxorubicin when combined with entinostat and ATRA in vitro and in vivo exerted the best response when compared with combinations using paclitaxel and carboplatin. Re-expression of the silenced RARβ and downstream effectors was observed in the cell lines treated in vitro and in tumor xenografts of MDA-MB-231 and SUM159 cells in vivo. To gain insight into mechanism of action for the entinostat – doxorubicin combinations we examined the expression of enzyme targets of doxorubicin and determined that entinostat treatment reduced the expression of topoisomerase (Topo) II enzymes. Besides its conventional role in cell replication and division, Topo II has an important function in regulating transcription, especially in the nuclear receptor pathways such as ER and RAR. Our results demonstrated that Topo IIβ has a dual role in regulating the expression of RARβ. Inhibition of Topo IIβ in a time- and dose dependent manner up-regulated the expression of RARβ and its downstream genes. However, completely eliminating Topo IIβ decreased expression of RARβ.

Conclusions: Our detailed study provides a new approach to treating TNBC using combinations of nontoxic doses of chemotherapeutic drugs with epigenetic therapy, and a deeper understanding of the molecular pathways involved in this response. These results suggest that combination of entinostat and a retinoic acid receptor agonist with low dose doxorubicin will provide an effective strategy for treatment of TNBC.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P2-09-01.

Myeloid progenitor cells in the premetastatic lung promote metastases by inducing mesenchymal to epithelial transition

Tumors systemically initiate metastatic niches in distant target metastatic organs. These niches, composed of bone marrow-derived hematopoietic cells, provide permissive conditions for future metastases. However, the mechanisms by which these cells mediate outgrowth of metastatic tumor cells are not completely known. Using mouse models of spontaneous breast cancer, we show enhanced recruitment of bone marrow-derived CD11b(+)Gr1(+) myeloid progenitor cells in the premetastatic lungs. Gene expression profiling revealed that the myeloid cells from metastatic lungs express versican, an extracellular matrix proteoglycan. Notably, versican in metastatic lungs was mainly contributed by the CD11b(+)Ly6C(high) monocytic fraction of the myeloid cells and not the tumor cells or other stromal cells. Versican knockdown in the bone marrow significantly impaired lung metastases in vivo, without impacting their recruitment to the lungs or altering the immune microenvironment. Versican stimulated mesenchymal to epithelial transition of metastatic tumor cells by attenuating phospho-Smad2 levels, which resulted in elevated cell proliferation and accelerated metastases. Analysis of clinical specimens showed elevated versican expression within the metastatic lung of patients with breast cancer. Together, our findings suggest that selectively targeting tumor-elicited myeloid cells or versican represents a potential therapeutic strategy for combating metastatic disease.

Abstract P4-01-03: The Homeobox Protein H0XC10 Is Overexpressed in Breast Cancer and Confers Resistance to Chemotherapy

Background: Breast cancer is the second leading cause of cancer deaths in women worldwide. Although chemotherapy is effective, resistance to drugs develops over time and can account for treatment failure in over 90% of metastatic breast cancer patients. HOX genes are homeobox-containing transcription factors well-known for their role in morphogenesis. However, accumulating evidence has emphasized their importance during carcinogenesis and metastasis. The goal of this study is to understand the role of HOXC10 in breast cancer and the consequence of its overexpression in conferring chemotherapy resistance.

Methods: We conducted a tiling array of all four HOX clusters to identify dysregulated HOX genes in a panel of primary and metastatic breast cancer tissues, and validated the overexpression of HOXC10 in metastatic breast cancer. Next we established cell lines that stably overexpress HOXC10 and others where endogenously overexpressed HOXC10 was silenced by shRNAs, and determined phenotypic and biochemical changes resulting from these manipulations.

Results: HOXC10 is overexpressed in 67% of primary breast tumors (n=31), in 82% of the metastatic tissues (n=49) and in most breast cancer cell lines. When compared to cancers at other sites, overexpression tends to be significantly higher in breast cancer, and correlates with increasing grade and tumor size. Cell survival assays (MTT and colony formation) after drug treatment show that overexpression of exogenous HOXC10 in MCF10A conferred drug resistance. Further molecular examination revealed that overexpression of HOXC10 led to a dysregulation in the Rb-E2F pathway, and therefore the G1/S checkpoint was affected. In addition, the tendency for the formation of 8N cells and the concomitant protection from apoptosis suggested that HOXC10 overexpression might lead to genomic endoreduplication and instability. This fact along with the strikingenhanced recovery of the cells from pactitaxel treatment (as compared to the recovery from any other chemotherapeutic drug) and the protection from mitotic catastrophe implied a role of HOXC10 in the mitotic checkpoint. This was confirmed by a dysregulation of the expression of the genes involved in this checkpoint. All these experiments were further validated by stably expressing a shRNA to HOXC10 in SUM159 breast cancer cells with high endogenous HOXC10 levels. Conclusion: Our studies show for the first time that HOXC10, a homeobox protein previously shown to be regulated during the cell cycle and to have a positive effect on proliferation, is overexpressed in the majority of breast cancers. This upregulation may have some clinical implications since cells with higher expression of HOXC10 tend to have more invasive properties, more genomic instability, and are more resistant to some chemotherapy drugs.

Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P4-01-03.

Epigenetic inactivation of the potential tumor suppressor gene FOXF1 in breast cancer

The expression of several members of the FOX gene family is known to be altered in a variety of cancers. We show that in breast cancer, FOXF1 gene is a target of epigenetic inactivation and that its gene product exhibits tumor-suppressive properties. Loss or downregulation of FOXF1 expression is associated with FOXF1 promoter hypermethylation in breast cancer cell lines and in invasive ductal carcinomas. Methylation of FOXF1 in invasive ductal carcinoma (37.6% of 117 cases) correlated with high tumor grade. Pharmacologic unmasking of epigenetic silencing in breast cancer cells restored FOXF1 expression. Re-expression of FOXF1 in breast cancer cells with epigenetically silenced FOXF1 genes led to G(1) arrest concurrent with or without apoptosis to suppress both in vitro cell growth and in vivo tumor formation. FOXF1-induced G(1) arrest resulted from a blockage at G(1)-S transition of the cell cycle through inhibition of the CDK2-RB-E2F cascade. Small interfering RNA-mediated depletion of FOXF1 in breast cancer cells led to increased DNA re-replication, suggesting that FOXF1 is required for maintaining the stringency of DNA replication and genomic stability. Furthermore, expression profiling of cell cycle regulatory genes showed that abrogation of FOXF1 function resulted in increased expression of E2F-induced genes involved in promoting the progression of S and G(2) phases. Therefore, our studies have identified FOXF1 as a potential tumor suppressor gene that is epigenetically silenced in breast cancer, which plays an essential role in regulating cell cycle progression to maintain genomic stability.