Tamoxifen-resistant Human Breast Cancer Cell Research Articles

Pterostilbene-isothiocyanate reduces miR-21 level by impeding Dicer-mediated processing of pre-miR-21 in 5-fluorouracil and tamoxifen-resistant human breast cancer cell lines.

Converging evidences identifies that microRNA-21 (miR-21) is responsible for drug resistance in breast cancer. This study aims to evaluate the miR-21-modulatory potential of a hybrid compound, pterostilbene-isothiocyanate (PTER-ITC), in tamoxifen-resistant MCF-7 (TR/MCF-7) and 5-fluorouracil-resistant MDA-MB 231 (5-FUR/MDA-MB 231) breast cancer cell lines, established by repeated exposure to gradually increasing the concentrations of tamoxifen and 5-fluorouracil, respectively. The outcome of this study shows that PTER-ITC effectively reduced the TR/MCF-7 (IC50: 37.21µM) and 5-FUR/MDA-MB 231 (IC50: 47.00µM) cell survival by inducing apoptosis, inhibiting cell migration, colony and spheroid formations in TR/MCF-7 cells, and invasiveness of 5-FUR/MDA-MB 231 cells. Most importantly, PTER-ITC significantly reduced the miR-21 expressions in these resistant cell lines. Moreover, the downstream tumor suppressor target gene of miR-21 such as PTEN, PDCD4, TIMP3, TPM1, and Fas L were upregulated after PTER-ITC treatment, as observed from transcriptional (RT-qPCR) and translational (immunoblotting) data. In silico and miR-immunoprecipitation (miR-IP) results showed reduced Dicer binding to pre-miR-21, after PTER-ITC treatment, indicating inhibition of miR-21 biogenesis. Collectively, the significance of this study is indicated by preliminary evidence for miR-21-modulatory effects of PTER-ITC that highlights the potential of this hybrid compound as an miR-21-targeting therapeutic agent.

Abstract P5-13-06: Overexpression of somatic mutation in NSDHL promotes breast cancer cell migration and tumor growth

Abstract Background: We had identified somatic mutations of the NAD(P) Dependent Steroid Dehydrogenase-Like (NSDHL) gene from breast tumors of patients with distant metastasis using whole-exome sequencing. This study aimed to investigate the function of NSDHL mutants in breast cancer. Methods: ER-positive and tamoxifen-resistant human breast cancer cell line (ZR75-1) and mouse macrophage cell line (RAW264,7) were used. GFP-tagged NSDHL mutants were generated by subcloning the mutant NDHL into a lentiviral vector yielding an in-frame fusion of 3′ to GFP. ZR75-1 cells expressing the GFP-tagged NSDHL mutants were selected by puromycin with subsequent FACS analysis. The following experiments were performed: western blot, immunofluorescence staining, qRT-PCR, CellTiter-Glo assay, cell cycle assay, transwell migration assay, wound healing assay, tumor spheroid formation assay, and total cellular cholesterol measurement. An orthotopic breast tumor mouse model by injection of ZR75.1 cells into mammary gland fat pad was used in vivo. Results: Four novel NSDHL somatic mutations were discovered in the breast tumor tissues of patients. While total cholesterol levels in NSDHL mutant-transduced cells did not significantly increase, they were notably higher in wild-type NSDHL-transduced cells than in parent ZR75-1 cells. When compared to the parent and wild-type NSDHL-transduced cells, there was a minor increase in growth rate and a large increase in migratory capacities in NSDHL mutant-transduced cells (P< 0.05). The size of tumor spheroids is significantly larger in NSDHL mutant-transduced cells than in wild-type NSDHL-transduced cells. Both EGFR expression and epithelial to mesenchymal transition (EMT) markers were higher in NSDHL mutant-transduced cells than in parent and wild-type NSDHL-transduced cells. The NSDHL mutant-transduced cells’ conditioned media promoted the migratory ability and M2 polarization of RAW264.7 cells. In an orthotopic xenograft mouse model, NSDHL mutant-transduced cells were shown to promote tumor growth better than parent and wild-type NSDHL-transduced cells, suggesting that somatic mutation of the NSDHL contributes to the malignant progression of breast cancer cells. Conclusion: The present data indicate that breast cancer cells harboring somatic mutants of the NSDHL gene seem to display more aggressive behavior by gaining biological worse phenotype both in vitro and in vivo. More investigation is required into the mechanisms behind the function and accumulation of mutant NSDHL proteins to speed the development of therapies for patients with breast cancer harboring mutant NSDHL. Citation Format: Moonjou Baek, Hoe Suk Kim, So-Hyun Yoon, Seungyeon Ryu, Sangeun Lee, Kyoungsook Park, Han-Byoel Lee, Wonshik Han. Overexpression of somatic mutation in NSDHL promotes breast cancer cell migration and tumor growth [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P5-13-06.

Tamoxifen-resistant breast cancer cells exhibit reactivity with Wisteria floribunda agglutinin.

Glycosylation is one of the most important post-translational modifications of cell surface proteins involved in the proliferation, metastasis and treatment resistance of cancer cells. However, little is known about the role of glycosylation as the mechanism of breast cancer cell resistance to endocrine therapy. Herein, we aimed to identify the glycan profiles of tamoxifen-resistant human breast cancer cells, and their potential as predictive biomarkers for endocrine therapy. We established tamoxifen-resistant cells from estrogen receptor-positive human breast cancer cell lines, and their membrane-associated proteins were subjected to lectin microarray analysis. To confirm differential lectin binding to cellular glycoproteins, we performed lectin blotting analyses after electrophoretic separation of the glycoproteins. Mass spectrometry of the tryptic peptides of the lectin-bound glycoproteins was further conducted to identify glycoproteins binding to the above lectins. Finally, expression of the glycans that were recognized by a lectin was investigated using clinical samples from patients who received tamoxifen treatment after curative surgery. Lectin microarray analysis revealed that the membrane fractions of tamoxifen-resistant breast cancer cells showed increased binding to Wisteria floribunda agglutinin (WFA) compared to tamoxifen-sensitive cells. Glycoproteins seemed to be responsible for the differential WFA binding and the results of mass spectrometry revealed several membrane glycoproteins, such as CD166 and integrin beta-1, as candidates contributing to increased WFA binding. In clinical samples, strong WFA staining was more frequently observed in patients who had developed distant metastasis during tamoxifen treatment compared with non-relapsed patients. Therefore, glycans recognized by WFA are potentially useful as predictive markers to identify the tamoxifen-resistant and relapse-prone subset of estrogen receptor-positive breast cancer patients.

Targeting Pin1 by All-Trans Retinoic Acid (ATRA) Overcomes Tamoxifen Resistance in Breast Cancer via Multifactorial Mechanisms

Breast cancer is the most prevalent tumor in women worldwide and about 70% patients are estrogen receptor positive. In these cancer patients, resistance to the anticancer estrogen receptor antagonist tamoxifen emerges to be a major clinical obstacle. Peptidyl-prolyl isomerase Pin1 is prominently overexpressed in breast cancer and involves in tamoxifen-resistance. Here, we explore the mechanism and effect of targeting Pin1 using its chemical inhibitor all-trans retinoic acid (ATRA) in the treatment of tamoxifen-resistant breast cancer. We found that Pin1 was up-regulated in tamoxifen-resistant human breast cancer cell lines and tumor tissues from relapsed patients. Pin1 overexpression increased the phosphorylation of ERα on S118 and stabilized ERα protein. ATRA treatment, resembling the effect of Pin1 knockdown, promoted ERα degradation in tamoxifen-resistant cells. Moreover, ATRA or Pin1 knockdown decreased the activation of ERK1/2 and AKT pathways. ATRA also reduced the nuclear expression and transcriptional activity of ERα. Importantly, ATRA inhibited cell viability and proliferation of tamoxifen-resistant human breast cancer cells in vitro. Slow-releasing ATRA tablets reduced the growth of tamoxifen-resistant human breast cancer xenografts in vivo. In conclusion, ATRA-induced Pin1 ablation inhibits tamoxifen-resistant breast cancer growth by suppressing multifactorial mechanisms of tamoxifen resistance simultaneously, which demonstrates an attractive strategy for treating aggressive and endocrine-resistant tumors.

Differential microRNA profiles between fulvestrant-resistant and tamoxifen-resistant human breast cancer cells

Increasing evidence has shown that the dysregulation of microRNAs (miRNAs) is associated with drug resistance. Fulvestrant and tamoxifen represent the major endocrine drugs for the treatment of breast cancer patients, and yet little is known about the biological mechanisms of acquiring resistance to fulvestrant and tamoxifen, let alone the differences between cell lines resistant to these two drugs. Exploration of the differential miRNA profiles between these two cell lines is a useful way to further clarify these resistance mechanisms. The fulvestrant-resistant cell line (MCF7-F) and the tamoxifen-resistant cell line (MCF7-T) were established from the drug-sensitive parental MCF7 cell line using a 21-day high-dose antiestrogen induction method. Differentially expressed miRNA profiles of MCF7-F and MCF7-T were detected using microarray; then, multiple bioinformatic analyses were carried out, including protein-protein interaction network, Gene Ontology, and Kyoto Encyclopedia of Genes and Genomes pathway analysis. Compared with the parental MCF7 cell line, more miRNAs were found to be participating in the process of acquiring fulvestrant resistance than tamoxifen resistance. miR-4532, miR-486-5p, miR-138, miR-1228, and miR-3178 could be new targets for combating both fulvestrant resistance and tamoxifen resistance. miR-3188, miR-21, miR-149, and others may be associated with fulvestrant resistance, whereas miR-342 and miR-1226 may be associated with tamoxifen resistance in breast cancer cells. We found differential miRNA profiles between fulvestrant-resistant and tamoxifen-resistant breast cancer cells, but the definite mechanism involved in gaining resistance still needs further study.

Differential microRNA expression profiles in tamoxifen-resistant human breast cancer cell lines induced by two methods.

Tamoxifen (TAM) resistance has become a severe problem for endocrine therapy of breast cancer. The present study investigated the association between microRNA (miRNA) expression and TAM resistance in breast cancer. The TAM-resistant breast cancer MCF-7C and MCF-7T cell lines were established using the human breast cancer cell line MCF-7 as the parental cell line and 4-hydroxytamoxifen (OHT) as the screening drug in vitro. The MCF-7C cell line was established by dose stepwise induction beginning with a low concentration of OHT; the MCF-7T cell line was established by temporal stepwise induction beginning with a high concentration of OHT. Differential miRNA expression profiles between TAM-sensitive (MCF-7) and TAM-resistant (MCF-7C and MCF-7T) breast cancer cell lines were detected and analyzed using RNA sequencing technology. The results of western blot analysis indicated that the level of ERα protein expression in drug-resistant cells was significantly increased. A total of 1,646 miRNAs were detected in all samples, including 1,376 known miRNAs and 270 predicted miRNAs. There were 118 miRNAs expressed at significantly different levels between MCF-7C and MCF-7 cells (P<0.05); among them, 67 miRNAs were upregulated (P<0.05) and 51 miRNA were downregulated (P<0.05). There were 42 miRNAs expressed at significantly different levels between MCF-7T and MCF-7 (P<0.05); among them, 23 miRNAs were upregulated (P<0.05) and 19 miRNAs were downregulated (P<0.05). There were 126 miRNAs with significant differences between MCF-7C and MCF-7T (P<0.05); among them, 76 miRNAs were upregulated (P<0.05) and 50 miRNAs were downregulated. On the basis of the results of the present study, we hypothesize that miR-21, miR-146a, miR-148a, miR-34a and miR-27a may serve important roles in mediating TAM resistance in breast cancer, and have potential as therapeutic targets for TAM-resistant breast cancer.

Establishment of an acquired tamoxifen-resistant human breast cancer cell line and its mechanism of 18F-FDG uptake reduction

Objective To establish the acquired tamoxifen (TAM)-resistant human breast cancer cell line T47D-TamR, compare the 18F-FDG uptake rate between T47D-TamR and its parental cell line T47D, and study the mechanism. Methods Long-term step-wise drug stimulation was used for cell line T47D-TamR establishment and then the cell proliferation and resistance index (RI) were determined by MTT assay. The 18F-FDG uptake rates of T47D-TamR and T47D cells were measured in the setting of different cell counts, reaction time, 18F-FDG dosages and glucose concentrations. The LDH activity, cellular ATP level and lactic acid concentration in cell supernatant of T47D-TamR and T47D cells were detected. Western blot was used to examine the expression of ERα, Glut-1, phosphorylated AMPK (p-AMPK) and phosphorylated mTOR (p-mTOR). Two-sample t test and two-way analysis of variance were used to analyze the data. Results T47D-TamR cell line was successfully established and its drug RI was 1.97±0.08, with a significantly decreased cell proliferation efficacy (F=230.10, P<0.05). Significant differences of 18F-FDG uptake rates were found between T47D-TamR cell and T47D cell when changing the cell count, reaction time, and 18F-FDG dosage (F values: 419.00-1 116.00, all P<0.05). The LDH activities of T47D cell and T47D-TamR cell were (0.42±0.04) and (0.32±0.02) U/mg protein, cellular ATP levels were (19.99±0.32) and (14.01±0.70) nmol/mg protein, lactic acid concentrations in cell supernatant were (2.95±0.05) and (2.02±0.07) mmol/L, respectively. The differences of above parameters between the two groups were significant (t values: 4.39-18.80, all P<0.05). The relative expressions of ERα, p-AMPK, p-mTOR, Glut-1 were 0.26±0.03, 0.36±0.06, 0.75±0.11, 0.35±0.07 in T47D cell, and 0.17±0.02, 0.61±0.09, 0.52±0.08, 0.21±0.04 in T47D-TamR cell, and there were significant differences (t values: 12.20-16.45, all P<0.05) between the two groups. Conclusions Compared with parental cells, T47D-TamR cells have lower 18F-FDG uptake rate, LDH activity, cellular ATP level and lactic acid concentration, increased p-AMPK expression and decreased ERα, p-mTOR, Glut-1 expression, indicating the decreased glycolysis ability in TAM-resistant breast cancer cells. Key words: Breast neoplasms; Tumor cells, cultured; Tamoxifen; Fluorine radioisotopes; Deoxyglucose

Molecular Analysis of Acquired Tamoxifen Resistance in Breast Cancer Cell Line

Background: Tamoxifen is an FDA approved drug for the prevention and the treatment of breast cancer, but its therapeutic benefit is limited by the development of drug resistance. Many Studies suggest that a basic biological difference exists between tumors with acquired tamoxifen resistance and those with intrinsic resistance to the drug. However the reasons why human mammary tumors become resistant to tamoxifen therapy are mainly unknown. Changes in gene expression may occur as cells acquire resistance to tamoxifen. A better understanding of gene expression alterations associated with tamoxifen resistance will facilitate circumventing this problem.Methods: We undertook a comparative gene expression analysis of tamoxifen-sensitive (MCF7 and T47D) and acquired tamoxifen-resistant human breast cancer cell lines (T47D tamoxifen resistant) in vitro models using Real-time PCR, to analyze differential gene expression. These genes were functionally linked to 4 major groups named as ER signaling/cell cycling, EGFR signaling, cancer stem cell (CSCs) and apoptosis.Results: Our results have been widely demonstrated that the altered expression of some genes involved in apoptosis, EGFR signaling, CSCs and Cell cycle-independent expression of estrogen receptor such as ESR1, TP53, CDKN1B, Casp3, CD44, CD24, BAX, Bcl2, Her2, and PTEN in T47D tamoxifen resistant cell line can be resulted in drug resistance in long-term treatment.Conclusions: Our findings correspond with the results of many earlier studies indicated tamoxifen resistance can be a result from combination of molecular mechanisms including Her2 activation, cell cycle progression out of ESR1 control, increased ratio of CSCs and inhibition of mitochondrial apoptosis.

Inhibition of Aerobic Glycolysis Represses Akt/mTOR/HIF-1α Axis and Restores Tamoxifen Sensitivity in Antiestrogen-Resistant Breast Cancer Cells.

Tamoxifen resistance is often observed in the majority of estrogen receptor–positive breast cancers and it remains as a serious clinical problem in breast cancer management. Increased aerobic glycolysis has been proposed as one of the mechanisms for acquired resistance to chemotherapeutic agents in breast cancer cells such as adriamycin. Herein, we report that the glycolysis rates in LCC2 and LCC9—tamoxifen-resistant human breast cancer cell lines derived from MCF7— are higher than those in MCF7S, which is the parent MCF7 subline. Inhibition of key glycolytic enzyme such as hexokinase-2 resulted in cell growth retardation at higher degree in LCC2 and LCC9 than that in MCF7S. This implies that increased aerobic glycolysis even under O2-rich conditions, a phenomenon known as the Warburg effect, is closely associated with tamoxifen resistance. We found that HIF-1α is activated via an Akt/mTOR signaling pathway in LCC2 and LCC9 cells without hypoxic condition. Importantly, specific inhibition of hexokinase-2 suppressed the activity of Akt/mTOR/HIF-1α axis in LCC2 and LCC9 cells. In addition, the phosphorylated AMPK which is a negative regulator of mTOR was decreased in LCC2 and LCC9 cells compared to MCF7S. Interestingly, either the inhibition of mTOR activity or increase in AMPK activity induced a reduction in lactate accumulation and cell survival in the LCC2 and LCC9 cells. Taken together, our data provide evidence that development of tamoxifen resistance may be driven by HIF-1α hyperactivation via modulation of Akt/mTOR and/or AMPK signaling pathways. Therefore, we suggest that the HIF-1α hyperactivation is a critical marker of increased aerobic glycolysis in accordance with tamoxifen resistance and thus restoration of aerobic glycolysis may be novel therapeutic target for treatment of tamoxifen-resistant breast cancer.

Abstract B103: Expression of n-3 fatty acid desaturase suppresses tamoxifen-resistant breast cancer in vitro and in fat-1 transgenic mice

Abstract Tamoxifen-resistance remains a significant clinical problem in breast cancer treatment. Currently, hormonal therapies can achieve 50-60% breast cancer remission rate in ERα+ patients, who will mostly develop resistance. We have hypothesized that fat-1 gene therapy, which introduce an n-3 fatty acid desaturase to convert n-6 to n-3 polyunsaturated fatty acids (PUFA), as an adjuvant treatment will enhance hormonal therapy of breast cancer. We have previously reported that C57BL/6 fat-1 transgenic mice suppress breast cancer growth and the inflammation/chemically induced lung metastasis of E0771 murine mammary tumors. This corroborates the experimental reports about the tumor suppression effect of n-3 PUFA, a main component of fish or fish oil. In this report, we will present experimental evidence that fat-1 gene expression suppresses tamoxifen-resistant human breast cancer in vitro; in addition, expression of n-3 fatty acid desaturase encoded by fat-1 gene in transgenic mice significantly suppresses murine tamoxifen-resistant E0771TamR mammary tumor growth in vivo. Methods: The tamoxifen-resistant human breast cancer cells MCF-7TamR and MDA-MB-231 (ER-), as well as the tamoxifen-sensitive human breast cancer T47D cells, were transfected with pST180 plasmid carrying fat-1 gene and the control empty pST128 plasmid. These cells were characterized in proliferation and caspase-3 apoptosis assays. The non-tumorigenic MCF-10A cells were also transfected with fat-1 gene to investigate the n-3 fatty acid desaturase effect on non-malignant human epithelial mammary cells. Two experimental groups of the fat-1 transgenic female C57BL/6 mice and wild type C57BL/6 control mice, were injected with tamoxifen-resistant E0771TamR tumor cells, or the parental E0771 cells, into breast fat pad of the 4th nipple and flank subcutaneously. Tumor sizes were measured daily until tumors reach 2 cm, when mice were sacrificed and tumor tissues and internal organs were harvested for fatty acid analysis and histology staining. Results: In cell culture studies, introduction of fat-1 gene significantly reduced the proliferation rate of the tamoxifen-resistant MCF-7TamR cells (37.3%), MDA-MB-231 cells (27.5%), and T47D cells (67.7%). The MCF-10A cells transfected with fat-1 gene did not show any change of cell proliferation rate compared to the control cells. The caspase-3 activities in MCF-7TamR cells, MDA-MB-231 cells, and T47D cells were respectively increased by 1.3-, 2.1- and 5.6-fold when expressing fat-1 gene, as compared to the control cells. In vivo, n-3 fatty acid desaturase expressed in fat-1 mice significantly suppressed growth of tamoxifen-resistant murine E0771TamR mammary tumors grown in flank and breast fat pad, as compared to the control mice. The fat-1 growth inhibition effect is more dramatic for E0771TamR tumors than the parental E0771 tumors in fat-1 mice. Fatty acid analysis has shown a significant decrease of long chain n-6/n-3 PUFA ratio in breast tumor tissues (33.5%), flank tumor tissues (33.9%), kidney (32.7%), muscle (43.8%), and adipose tissues (69.1%) in fat-1 mice compared to wild type mice. Conclusions: Introducing an n-3 fatty acid desaturase in tumor cells and transgenic animals has reduced long chain n-6/n-3 PUFA ratio and imposed an anti-tumor effect against tamoxifen-resistant breast cancer growth. Tamoxifen-sensitive breast cancer were also inhibited in Fat-1 gene therapy. Citation Format: Raghunatha Reddy, Ian Bayles, Qiuhong He. Expression of n-3 fatty acid desaturase suppresses tamoxifen-resistant breast cancer in vitro and in fat-1 transgenic mice. [abstract]. In: Proceedings of the Eleventh Annual AACR International Conference on Frontiers in Cancer Prevention Research; 2012 Oct 16-19; Anaheim, CA. Philadelphia (PA): AACR; Cancer Prev Res 2012;5(11 Suppl):Abstract nr B103.

Abstract 2279: The response of breast cancer cell lines to HET0016 alone or in combination with other chemotherapeutics

Abstract One of the vexing problems in controlling breast cancer is the emergence of acquired endocrine-resistance in estrogen receptor positive breast cancers that initially respond to endocrine therapy. Published reports suggest there is a close overlap between the signal transduction pathways affected by 20-hydroxyeicosatetraenoic acid (20-HETE) and those which may confer endocrine-resistance. Preliminary data indicate that 20-HETE-targeted drugs have direct cytotoxic and indirect anti-angiogenic effects on multiple carcinomas, and they therefore might be extended to unsolved problems in breast cancer control. Yet almost nothing is known about the specific role(s) of 20-HETE in either healthy breast tissue or in breast cancer. We observed that treatment of certain tamoxifen-resistant human breast cancer cell lines with HET0016, a compound which inhibits the biosynthesis of 20-HETE, restores sensitivity to tamoxifen in cell culture. We are elucidating the signal transduction pathways involved in this phenomenon. We also observed that certain human breast cancer cell lines with intrinsic tamoxifen resistance (such as the “triple-negative” MDA-MB-468 cell line) express cytochrome P450 isoforms essential for the synthesis of 20-HETE, and we are evaluating whether we can exploit a synergistic effect of HET0016 with anti-cancer drugs currently used to treat aggressive “triple-negative” breast cancers which have an intrinsic resistance to endocrine therapy. We hypothesize that a 20-HETE-targeted agent such as HET0016 will provide an additional anti-cancer benefit due to its anti-angiogenic activities, and we are further exploring the characteristics of breast cancers that may be susceptible to combination therapy involving HET0016 and related compounds. 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 2279. doi:10.1158/1538-7445.AM2011-2279

The anti-proliferative effects of tyrosine kinase inhibitors towards tamoxifen-sensitive and tamoxifen-resistant human breast cancer cell lines in relation to the expression of epidermal growth factor receptors (EGF-R) and the inhibition of EGF-R tyrosine kinase

We have investigated the anti-proliferative effect of the tyrosine kinase inhibitors genistein, lavendustin A and 2,5-dihydromethylcinnimate (2,5-MeC) (a stable erbstatin analogue) against the epidermoid A431 cell line, the ZR-75-1 human breast cancer cell line and tamoxifen-resistant (ZR-75-9a1) and oestrogen-independent (ZR-PR-LT) variants. Increased EGF-R expression by ZR-75-9a1 was associated with decreased sensitivity to genistein and 2,5-MeC whilst decreased EGF-R expression (ZR-PR-LT) cells was associated with increased sensitivity to lavendustin A and 2,5-MeC. Anti-proliferative IC 50 concentrations of 2,5-MeC, but not genistein or lavendustin A, inhibited EGFR-R associated tyrosine kinase activity of ZR-75-1 cells and variants by 20–50%.

Altered expression of the IGF-1 receptor in a tamoxifen-resistant human breast cancer cell line.

The relationship between oestrogen (E2) and insulin-like growth factor-one (IGF-1) was examined in both tamoxifen-sensitive (MCF 7/5–21) and tamoxifen-resistant (MCF 7/5–23) subclones of the MCF 7 cell line. Both subclones were grown in defined, serum-free (SF) medium over a period of 7 days with the addition of E2 or IGF-1 or a combination of both agents. Growth of both MCF 7/5–21 and 7/5–23 cells was stimulated (245% and 350%, respectively) by E2. However, only the growth of MCF 7/5–23 cells was stimulated (266%) by IGF-1. A combination of E2 and IGF-1 significantly enhanced MCF 7/5–21 and 7/5–23 cell growth (581% and 695%, respectively). E2-induced IGF-1 receptor (IGF-1R) levels (as measured by 125 I-IGF-1 binding and Northern analyses) in only MCF 7/5–23 cells. This effect was partially inhibited by tamoxifen. In medium containing serum, the growth of only the MCF 7/5–23 cells was significantly inhibited by the IGF-1R monoclonal antibody, αIR-3. The detection of E2-induced expression of IGF-2 using RT-PCR was demonstrated in the MCF 7/5–23 cells. These experiments indicate that E2 may sensitize tamoxifen-resistant MCF 7/5–23 cells to the growth stimulatory actions of IGF-2 via up-regulation of the IGF-1R and describes a cell-survival mechanism that may manifest itself as tamoxifen resistance. © 1999 Cancer Research Campaign