Bhuvaneswari Ramaswamy

MicroRNA-221/222 Confers Tamoxifen Resistance in Breast Cancer by Targeting p27Kip1

We explored the role of microRNAs (miRNAs) in acquiring resistance to tamoxifen, a drug successfully used to treat women with estrogen receptor-positive breast cancer. miRNA microarray analysis of MCF-7 cell lines that are either sensitive (parental) or resistant (4-hydroxytamoxifen-resistant (OHTR)) to tamoxifen showed significant (>1.8-fold) up-regulation of eight miRNAs and marked down-regulation (>50%) of seven miRNAs in OHTR cells compared with parental MCF-7 cells. Increased expression of three of the most promising up-regulated (miR-221, miR-222, and miR-181) and down-regulated (miR-21, miR-342, and miR-489) miRNAs was validated by real-time reverse transcription-PCR. The expression of miR-221 and miR-222 was also significantly (2-fold) elevated in HER2/neu-positive primary human breast cancer tissues that are known to be resistant to endocrine therapy compared with HER2/neu-negative tissue samples. Ectopic expression of miR-221/222 rendered the parental MCF-7 cells resistant to tamoxifen. The protein level of the cell cycle inhibitor p27Kip1, a known target of miR-221/222, was reduced by 50% in OHTR cells and by 28–50% in miR-221/222-overexpressing MCF-7 cells. Furthermore, overexpression of p27Kip1 in the resistant OHTR cells caused enhanced cell death when exposed to tamoxifen. This is the first study demonstrating a relationship between miR-221/222 expression and HER2/neu overexpression in primary breast tumors that are generally resistant to tamoxifen therapy. This finding also provides the rationale for the application of altered expression of specific miRNAs as a predictive tamoxifen-resistant breast cancer marker.

Phase II Trial of Bevacizumab in Combination with Weekly Docetaxel in Metastatic Breast Cancer Patients

Purpose: To evaluate the safety and efficacy of bevacizumab and weekly docetaxel as first- or second-line therapy in patients with metastatic breast cancer (MBC). Patients and Methods: Twenty-seven MBC patients received i.v. bevacizumab at 10 mg/kg on days 1 and 15 in combination with i.v. docetaxel 35 mg/m2 on days 1, 8, and 15 of a 28-day cycle. Primary end points were to assess toxicity, overall response rate, and progression-free survival. A secondary end point was to assess the relationship between plasma endothelial and cell adhesion markers and clinical outcomes. Results: One-hundred fifty-eight treatment cycles were administered with a median of six cycles (range 1-15 cycles) per patient. The most common grade 4 toxicities per patient were as follows: 2 (7%)—pulmonary embolus, 1 (4%)—febrile neutropenia, and 1 (4%)—infection; grade 3 toxicities were 4 (15%)—neutropenia, 4 (15%)—fatigue, 2 (7%)—neuropathy, 2 (7%)—athralgias, 2 (7%)—stomatitis, 1 (7%)—pleural effusion, and 1 (4%)—hypertension. The overall response rate was 52% [95% confidence interval (95% CI), 32-71%], median response duration was 6.0 months (95% CI, 4.6-6.5 months), and the median progression-free survival was 7.5 months (95% CI, 6.2-8.3 months). In hypothesis-generating univariate and limited multivariate analyses, E-selectin was statistically significantly associated with response to the combination. Conclusion: Bevazicumab in combination with weekly docetaxel is active with acceptable toxicities in MBC. Additional studies evaluating E-selectin as a marker of response to bevacizumab-containing chemotherapy are warranted.

Hedgehog Signaling Is a Novel Therapeutic Target in Tamoxifen-Resistant Breast Cancer Aberrantly Activated by PI3K/AKT Pathway

Endocrine resistance is a major challenge in the management of estrogen receptor (ER)-positive breast cancers. Although multiple mechanisms leading to endocrine resistance have been proposed, the poor outcome of patients developing resistance to endocrine therapy warrants additional studies. Here we show that noncanonical Hedgehog (Hh) signaling is an alternative growth promoting mechanism that is activated in tamoxifen-resistant tumors. Importantly, phosphoinositide 3-kinase inhibitor/protein kinase B (PI3K/AKT) pathway plays a key role in regulating Hh signaling by protecting key components of this pathway from proteasomal degradation. The levels of Hh-signaling molecules SMO and GLI1 and the targets were significantly elevated in tamoxifen-resistant MCF-7 cells and T47D cells. Serial passage of the resistant cells in mice resulted in aggressive tumors that metastasized to distant organs with concurrent increases in Hh marker expression and epithelial mesenchymal transition. RNAi-mediated depletion of SMO or GLI1 in the resistant cells resulted in reduced proliferation, clonogenic survival and delayed G(1)-S transition. Notably, treatment of resistant cells with PI3K inhibitors decreased SMO and GLI1 protein levels and activity that was rescued upon blocking GSK3β and proteasomal degradation. Furthermore, treatment of tamoxifen-resistant xenografts with anti-Hh compound GDC-0449 blocked tumor growth in mice. Importantly, high GLI1 expression correlated inversely with disease-free and overall survival in a cohort of 315 patients with breast cancer. In summary, our results describe a signaling event linking PI3K/AKT pathway with Hh signaling that promotes tamoxifen resistance. Targeting Hh pathway alone or in combination with PI3K/AKT pathway could therefore be a novel therapeutic option in treating endocrine-resistant breast cancer.

Anti-microRNA-222 (Anti-miR-222) and -181B Suppress Growth of Tamoxifen-resistant Xenografts in Mouse by Targeting TIMP3 Protein and Modulating Mitogenic Signal

Background: MicroRNAs-221/222 and 181b are up-regulated in tamoxifen-resistant breast cancer. Results: Anti-miRs-222/181b regressed tamoxifen-resistant xenografts. Down-regulation of TIMP3, a common target of these miRs, facilitated growth factor signaling by regulating metalloproteases. Conclusion: Survival of tamoxifen-resistant breast cancer is dependent on miR-mediated suppression of TIMP3. Significance: Anti-miRs-222/221 and -181b can be used to render tamoxifen-resistant tumors responsive to the drug. We have shown earlier that miR-221 and -222 are up-regulated in tamoxifen-resistant MCF-7 (OHTR) cells and Her2-positive human breast tumors when compared with Her2 negative tumors. In this study, we report markedly enhanced expression of miR-181b in OHTR cells and endocrine-resistant tumors. Further, anti-miR-222 or -181b in combination with tamoxifen suppressed growth of tamoxifen-resistant xenografts in mice. Luciferase reporter assay and expression analysis showed that TIMP3, a tissue metalloproteinase inhibitor, is a common target of miR-221/222 and -181b. In situ hybridization and immunohistochemical analysis demonstrated reciprocal relationships between TIMP3 and miR-221/222/181b expression in primary human breast carcinomas. Ectopic expression of TIMP3 inhibited growth of the OHTR cells, and its depletion in MCF-7 cells reduced sensitivity to tamoxifen in vitro and in vivo. EGF-induced MAPK and AKT phosphorylation were significantly higher in OHTR cells and miR-221/222-overexpressing MCF-7 cells than in control cells, which suggests modulation of mitogenic signaling by TIMP3 and the miRs. On the contrary, phosphoMAPK and phosphoAKT levels were diminished in TIMP3-overexpressing OHTR cells and increased in TIMP3-depleted MCF-7 cells. Low levels of estrogen or tamoxifen elicited similar differences in phosphoMAPK levels in these cells. Reduced levels of TIMP3 facilitated growth of tamoxifen-resistant cells by alleviating its inhibitory effect on ADAM10 and ADAM17, which are critical for OHTR cell growth. In conclusion, miR-221/222 and -181b facilitate growth factor signaling in tamoxifen-resistant breast cancer by down-regulating TIMP3, and corresponding anti-miRs can be used to render these tumors responsive to tamoxifen.

Heterogeneous atypical cell populations are present in blood of metastatic breast cancer patients

IntroductionCirculating tumor cells (CTCs) are commonly isolated from the blood by targeting the epithelial cell adhesion molecule (EpCAM) through positive selection. However, EpCAM can be downregulated during metastatic progression, or it can be initially not present. We designed the present prospective trial to characterize CTCs as well as other circulating cell populations in blood samples from women with metastatic breast cancer without EpCAM-dependent enrichment and/or isolation technology.MethodsA total of 32 patients with metastatic breast cancer were enrolled, and blood samples were processed using a previously described negative depletion immunomagnetic methodology. Samples from healthy volunteers were run as controls (n = 5). Multistep sequential labeling was performed to label and fix cell-surface markers followed by permeabilization for cytokeratins (CK) 8, 18 and 19. Multiparametric flow cytometry (FCM) analysis was conducted using a BD LSR II flow cytometer or a BD FACSAria II or FACSAria III cell sorter. Immunocytochemical staining on postenrichment specimens for DAPI, EpCAM, CD45, CK, epidermal growth factor receptor and vimentin was performed. Expression of these markers was visualized using confocal microscopy (CM).ResultsCD45-negative/CK-positive (CD45− CK+) populations with EpCAM + and EpCAM − expression were identified with both FCM and CM from the negatively enriched patient samples. In addition, EpCAM + and EpCAM − populations that were CK + and coexpressing the pan-hematopoietic marker CD45 were also noted. There were more CK + EpCAM − events/ml than CK + EpCAM + events/ml in both the CD45− and CD45+ fractions (both statistically significant at P ≤ 0.0005). The number of CK + CD45− and CK + CD45+ events per milliliter in blood samples (regardless of EpCAM status) was higher in patient samples than in normal control samples (P ≤ 0.0005 and P ≤ 0.026, respectively). Further, a significant fraction of the CK + CD45+ events also expressed CD68, a marker associated with tumor-associated macrophages. Higher levels of CD45-CK + EpCAM − were associated with worse overall survival (P = 0.0292).ConclusionsMetastatic breast cancer patients have atypical cells that are CK + EpCAM − circulating in their blood. Because a substantial number of these patients do not have EpCAM + CTCs, additional studies are needed to evaluate the role of EpCAM − circulating cells as a prognostic and predictive marker.

Epigenetic silencing mediated through activated PI3K/AKT signaling in breast cancer.

Trimethylation of histone 3 lysine 27 (H3K27me3) is a critical epigenetic mark for the maintenance of gene silencing. Additional accumulation of DNA methylation in target loci is thought to cooperatively support this epigenetic silencing during tumorigenesis. However, molecular mechanisms underlying the complex interplay between the two marks remain to be explored. Here we show that activation of PI3K/AKT signaling can be a trigger of this epigenetic processing at many downstream target genes. We also find that DNA methylation can be acquired at the same loci in cancer cells, thereby reinforcing permanent repression in those losing the H3K27me3 mark. Because of a link between PI3K/AKT signaling and epigenetic alterations, we conducted epigenetic therapies in conjunction with the signaling-targeted treatment. These combined treatments synergistically relieve gene silencing and suppress cancer cell growth in vitro and in xenografts. The new finding has important implications for improving targeted cancer therapies in the future.

Higher tamoxifen use as chemoprophylaxis in patients with ductal carcinoma in situ (DCIS) in the last decade.

191 Background: The incidence of DCIS over the last two decades has increased, with over 62,000 new cases diagnosed annually in the United States. Tailored management of DCIS is still a work in progress and currently treatment options are varied. We sought to identify changes in patterns of care in individual and physician choices for surgery and chemoprophylaxis over the last two decades at our institution. METHODS We performed a retrospective chart review and identified 773 eligible patients using the James Cancer Registry and the NCCN database at The Ohio State University between 1990 and 2010. We compared the proportion of patients undergoing mastectomy vs breast conserving surgery (BCT), use of radiation and hormone therapy, and recurrence rates between the years 1990-2000 and 2001-2010 using Chi-square test. RESULTS There was no significant difference in race (p=0.21) or age (p=0.09) among patients diagnosed with DCIS between 1990-2000 (Group A, N=462) and 2001-2010 (Group B, N=311). There was no significant difference in mastectomy rates between the two groups (31% vs. 27%, p= 0.26). Patients less than 50 years old were more likely to undergo mastectomy in both groups (p=0.02). Use of radiation therapy following BCT was similar between the two groups (52% vs. 53%, p=0.76). Interestingly more patients received hormone therapy during 2001-2010 than 1990-2000 (48% vs. 26%, p < 0.0001). Patients undergoing mastectomy were less likely to receive radiation (2% vs. 74%, p<0.0001) and hormone therapy (25% vs. 39%, p<0.0001). There was no significant correlation between race and type of surgery. We are in the process of comparing recurrence rates between the two groups which will be reported. CONCLUSIONS Previously published studies have reported higher rates of mastectomy among patients with early stage breast cancer in the recent years. Data from our institution over the last two decades did not corroborate this finding, although interestingly we have found increasing use of tamoxifen therapy for DCIS in the second decade. Understanding current practices is helpful in designing future studies for management of DCIS using novel prognostic assays such as Oncotype Dx assay.

Estrogen-Mediated Suppression of the Gene Encoding Protein Tyrosine Phosphatase PTPRO in Human Breast Cancer: Mechanism and Role in Tamoxifen Sensitivity

We have previously demonstrated the tumor suppressor characteristics of protein tyrosine phosphatase receptor-type O (PTPRO) in leukemia and lung cancer, including its suppression by promoter methylation. Here, we show tumor-specific methylation of the PTPRO CpG island in primary human breast cancer. PTPRO expression was significantly reduced in established breast cancer cell lines MCF-7 and MDA-MB-231 due to promoter methylation compared with its expression in normal human mammary epithelial cells (48R and 184). Further, the silenced gene could be demethylated and reactivated in MCF-7 and MDA-MB-231 cells upon treatment with 5-Azacytidine, a DNA hypomethylating agent. Because PTPRO promoter harbors estrogen-responsive elements and 17beta-estradiol (E2) plays a role in breast carcinogenesis, we examined the effect of E2 and its antagonist tamoxifen on PTPRO expression in human mammary epithelial cells and PTPRO-expressing breast cancer cell line Hs578t. Treatment with E2 significantly curtailed PTPRO expression in 48R and Hs578t cells, which was facilitated by ectopic expression of estrogen receptor (ER)beta but not ERalpha. On the contrary, treatment with tamoxifen increased PTPRO expression. Further, knockdown of ERbeta by small interfering RNA abolished these effects of E2 and tamoxifen. Chromatin immunoprecipitation assay showed association of c-Fos and c-Jun with PTPRO promoter in untreated cells, which was augmented by tamoxifen-mediated recruitment of ERbeta to the promoter. Estradiol treatment resulted in dissociation of c-Fos and c-Jun from the promoter. Ectopic expression of PTPRO in the nonexpressing MCF-7 cells sensitized them to growth-suppressive effects of tamoxifen. These data suggest that estrogen-mediated suppression of PTPRO is probably one of the early events in estrogen-induced tumorigenesis and that expression of PTPRO could facilitate endocrine therapy of breast cancer.

Mechanisms and therapeutic advances in the management of endocrine-resistant breast cancer.

The estrogen receptor (ER) pathway plays a critical role in breast cancer development and progression. Endocrine therapy targeting estrogen action is the most important systemic therapy for ER positive breast cancer. However its efficacy is limited by intrinsic and acquired resistance. Mechanisms responsible for endocrine resistance include deregulation of the ER pathway itself, including loss of ER expression, post-translational modification of ER, deregulation of ER co-activators; increased receptor tyrosine kinase signaling leading to activation of various intracellular pathways involved in signal transduction, proliferation and cell survival, including growth factor receptor tyrosine kinases human epidermal growth factor receptor-2, epidermal growth factor receptor, PI3K/AKT/mammalian target of rapamycin (mTOR), Mitogen activated kinase (MAPK)/ERK, fibroblast growth factor receptor, insulin-like growth factor-1 receptor; alterations in cell cycle and apoptotic machinery; Epigenetic modification including dysregulation of DNA methylation, histone modification, and nucleosome remodeling; and altered expression of specific microRNAs. Functional genomics has helped us identify a catalog of genetic and epigenetic alterations that may be exploited as potential therapeutic targets and biomarkers of response. New treatment combinations targeting ER and such oncogenic signaling pathways which block the crosstalk between these pathways have been proven effective in preclinical models. Results of recent clinical studies suggest that subsets of patients benefit from the combination of inhibitor targeting certain oncogenic signaling pathway with endocrine therapy. Especially, inhibition of the mTOR signaling pathway, a key component implicated in mediating multiple signaling cascades, offers a promising approach to restore sensitivity to endocrine therapy in breast cancer. We systematically reviewed important publications cited in PubMed, recent abstracts from ASCO annual meetings and San Antonio Breast Cancer Symposium, and relevant trials registered at ClinicalTrials.gov. We present the molecular mechanisms contributing to endocrine resistance, in particular focusing on the biological rationale for the clinical development of novel targeted agents in endocrine resistant breast cancer. We summarize clinical trials utilizing novel strategies to overcome therapeutic resistance, highlighting the need to better identify the appropriate patients whose diseases are most likely to benefit from these specific strategies.

Phase II trial of exemestane in combination with fulvestrant in postmenopausal women with hormone responsive advanced breast cancer: no evidence of a pharmacokinetic interaction between exemestane and fulvestrant.

Abstract #6131 Background: Treatment options for postmenopausal women (PW) with hormone responsive breast cancer (HRBC) involve blocking estrogen receptor (ER) with anti-estrogens or inhibiting estrogen synthesis with aromatase inhibitors (AI). A mouse xenograft model showed that combination of the pure estrogen antagonist fulvestrant (FUL) and an AI was more effective in suppressing tumor growth than either treatment alone. We hypothesized this combination would have an enhanced anti-tumor activity in PW with HRBC. To test this hypothesis a phase II trial of FUL and the steroidal AI exemestane (EXE) was designed.
 Materials & Methods: Eligible PW may have received prior adjuvant chemotherapy (CT), treatment with tamoxifen, anastrazole or letrozole in the adjuvant or advanced disease setting. EXE at a dose of 25 mg daily was started on Day 1. On day 8, FUL was added and administered as an IM injection of 250 mg every 28 days. Response was assessed every 2 cycles by physical examination and imaging studies. The steady-state pharmacokinetics of EXE when administered alone (Day 7) and in combination with FUL (Day 120) was assessed in a subset of PW. Plasma samples were obtained before and 1, 2, 4, 6, 8, and 24 hours after dosing on each occasion. Plasma concentrations of EXE and 17-hydroxyEXE were analyzed using a validated liquid chromatographic method with mass spectrometric detection. Serum concentrations of insulin growth factor I (IGF-I) were determined prior to dosing, on Day 7 and Day 120. The primary clinical endpoint is the proportion of patients free of progressive disease at 6 months. A Fleming single-stage design (with P0 =0.5, P1= 0.7, α=0.10 and β=0.10) requires a sample size of 40 women. If 24 of the 40 PW are progression-free at 6-months, this treatment will be worthy of future study.
 Results: Nineteen women were enrolled. The median age was 64 years (range 48-83 years); 42% had prior adjuvant CT, 53% had prior hormonal therapy; and 47% had visceral metastases. Nine (47%) had a PFS ≥ 6 months (range 6 to 20 months) with 8 still on treatment; 8 (42%) progressed prior to 6 mo; and 2 (11%) have been on treatment for Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 6131.