Scientists crack the code to tamoxifen resistance

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Scientists crack the code to tamoxifen resistance

WEDNESDAY 12 NOVEMBER 2008

Cancer Research UK Press Release
CANCER RESEARCH UK scientists have discovered the molecular basis for tamoxifen response in breast cancer cells - and the reason why some women can develop resistance to the treatment, according to a study published in Nature* today (Wednesday).
Tamoxifen is given to most women for five years after they are first diagnosed with breast cancer to help prevent the disease from coming back but some women develop resistance to the treatment after time, meaning their cancer is more likely to return.
Researchers at the Cancer Research UK Cambridge Research Institute have discovered for the first time the mechanism by which the breast cancer therapy tamoxifen operates. It switches off a breast cancer gene ErbB2 via a protein called Pax2. Pax2 acts as a 'switch' to keep ErbB2 switched off. Tamoxifen resistance occurs when ErbB2 remains switched on.
Previously it was known that tamoxifen worked by blocking oestrogen from causing unchecked cell growth in breast cancer by switching certain genes on but the mechanism by which this occurred was unknown.
Lead author, Dr Jason Carroll said: "We knew that women developed resistance to tamoxifen but previously our understanding of why this occurred could be compared with trying to fix a broken car without knowing how the engine worked. Now we understand how all the engine parts operate and we can try to think about ways to make repairs.
"We have discovered that for tamoxifen to work it has to block the gene ErbB2 and it does this by using a control switch that is hidden in the background of the genome, within the ErbB2 gene itself. In order for tamoxifen to be effective, this switch must be held in the off position by Pax2. Now we understand how women can develop tamoxifen resistance."
The production of oestrogen can cause breast cancer cells to grow and divide but tamoxifen prevents oestrogen from causing breast cancer cells to grow, helping to lower the risk of the disease returning. Most women have breast cancers that are stimulated to grow by oestrogen but not all.**
Breast cancer is the most common cancer in women in the UK. More than 45,500 women are diagnosed with the disease each year – 125 women a day, and the disease causes almost 12,500 deaths each year. Eight in 10 cases of breast cancer are diagnosed in women over the age of 50.
Professor Sir David Lane, Cancer Research UK's chief scientist said: "Cancer Research UK's early clinical trials of tamoxifen helped transform the way that women were treated for early breast cancer saving ten's of thousands of lives, and this work is yet another step forward.
"More women are surviving breast cancer than ever before thanks to improvements in diagnosis and treatment as well as important fundamental science discoveries like this."
He added: "Tamoxifen has been a huge success story helping to prevent breast cancer recurring for many women.
"Understanding why it occasionally stops working is really important because it allows us to identify new targets for drug development and who will need such treatments."
ENDS
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Notes to Editors:
Listen to Dr Carroll talking about his work:
Antoni Hurtado et al. *ERBB2 regulation by Estrogen Receptor-Pax2 determines tamoxifen response. (2008) Nature. Wednesday 12 November.
The scientists used microarray technology (genomic technology) to define a genomic map of where oestrogen receptor interacts with the genome. The oestrogen receptor was found to interact with unexpected areas in the genome, which were then identified as the 'switches' for gene regulation. This provided insight into how oestrogen receptor worked. Using this information, the scientists could find the switch for the important cancer related gene, ErbB2.
Microarray technology involves scanning millions of DNA sequences to detect the association with a target sequence of DNA (in this case the regions of the genome that make contact points with the oestrogen receptor).
Breast cancer

Survival rates for breast cancer have been improving for more than twenty years and more women are being successfully treated than ever before. Nowadays more than 80 per of women diagnosed with the disease will be alive five years after diagnosis – compared with only 50 percent of women 30 years ago. This is thanks to better detection, development of new drugs and improved treatment of the disease.
Treatment

The main treatment options for breast cancer include: surgery, radiotherapy, chemotherapy or hormone treatment, but usually involve a combination of all. Visit our patient information website www.cancerhelp.org.uk for more information on breast cancer. Or contact our care information nurses on 020 7061 8355, or freephone on 0808 800 4040. Lines are open from 9am to 5pm, Monday to Friday.
Tamoxifen

**There are 45,000 new breast cancer cases in the UK each year of which about 35,000 women have oestrogen receptor (ER) positive breast cancer cells. Around 28,000 women receive tamoxifen as a first line therapy.
Tamoxifen formerly known by its brand name Nolvadex is a hormone treatment for breast cancer developed thirty years ago.
Many breast cancers are stimulated to grow by the female sex hormone oestrogen. These breast cancers are called 'hormone sensitive' or 'hormone receptor positive' and can be treated with drugs that block the effects of these hormones.
Tamoxifen is usually prescribed for women who have oestrogen receptor (ER) positive breast cancer cells. The oestrogen receptor is the part of the breast cancer cell that oestrogen locks on to, to stimulate the cell to multiply. Tamoxifen is able to lock on to the oestrogen receptor and stop the oestrogen from causing cells to grow.
In the 1990s, Cancer Research UK scientists found that giving the drug, tamoxifen, to all breast cancer patients who need it, whatever their age, could save an extra 20,000 lives each year worldwide. This overturned accepted wisdom that the drug had no benefit for younger women.
In 1969, the synthetic oestrogen-blocker tamoxifen was first used to treat breast cancer at the Christie Hospital in Manchester. Tamoxifen is now widely used in breast cancer treatment, and Cancer Research UK has been at the forefront of research into the drug's effectiveness.
In 2002, a Cancer Research UK study, IBIS I, showed that tamoxifen could also be used to prevent breast cancer in high-risk post-menopausal women. However, tamoxifen is not without side effects, so Cancer Research UK is now looking at another anti-oestrogen drug, arimidex, in a study called IBIS II. Arimidex seems to be as effective as tamoxifen, but causes fewer side effects.

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Tamoxifen induces oxidative stress and apoptosis in oestrogen receptor-negative human cancer cell lines‏

http://www.nature.com/bjc/journal/v7...f/6690042a.pdf

Summary Recent data have demonstrated that the anti-oestrogen tamoxifen (TAM) is able to facilitate apoptosis in cancer cells not expressing oestrogen receptor (ER). In an attempt to identify the biochemical pathway for this phenomenon, we investigated the role of TAM as an oxidative stress agent. In two ER-negative human cancer cell lines, namely T-leukaemic Jurkat and ovarian A2780 cancer cells, we
have demonstrated that TAM is able to generate oxidative stress, thereby causing thiol depletion and activation of the transcriptional factor NF-kB. As described for other oxidative agents, TAM was able to induce either cell proliferation or apoptosis depending on the dose. When used at the lowest dose tested (0.1 mM), a slight proliferative effect of TAM was noticed in terms of cell counts and DNA synthesis rate,
whereas at higher doses (10 mM) a consistent occurrence of apoptosis was detected. Importantly, the induction of apoptosis by TAM is not linked to down-regulation or functional inactivation by phosphorylation of the antiapoptotic bcl-2 protein.

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http://www.sciencedaily.com/releases/2009/06/ 090623215852.htm

New Take On Growth Factor Signaling In Tamoxifen Resistance

ScienceDaily (June 22, 2009) — Differences in growth factor (GF) signaling may cause the poor prognosis in some breast cancer cases. A new study, published in the open access journal BMC Medical Genomics, suggests that some estrogen receptor-positive breast cancers respond poorly to tamoxifen because of increased GF signaling.
Sherene Loi, from the Peter MacCallum Cancer Centre, Melbourne, worked with a team of Australian and Belgian researchers to investigate the differences between those estrogen receptor positive (ER+) cancers that respond well to tamoxifen (luminal-A) and those that do not (luminal-B). She said, “This is the first study specifically investigating the biology of the luminal-B, ER+ breast cancer subtype. We propose that activation of GF signaling contributes to this highly proliferative, relatively tamoxifen-insensitive, phenotype and that this exists independently of HER2 overexpression. Targeting this pathway and its upstream mediators could prove to be a useful therapeutic strategy”.
The researchers used a new computational method of analysis of gene expression data called gene set enrichment analysis (GSEA) to determine that there is increased growth factor activation from the gene expression profiles of nearly 100 luminal-B breast cancers samples. They then validated this finding by showing that treatment with the growth factor heregulin, which induced growth factor signaling an in-vitro model, could overcome tamoxifen-induced cell cycle arrest.
This research represents a departure from the informative, but sometimes not terribly useful, process of identifying genes associated with given conditions. Dr Loi said, “Although gene expression data has demonstrated its ability to identify subsets of disease and predict outcomes or drug responses, identifying new therapeutic approaches based on whole genome microarray profiling has, to date, been a significant challenge. By using GSEA, we’ve been able to use gene expression data to identify that activation of GF signaling pathways as a possible therapeutic target for further exploration in the clinical setting for these particular breast cancer patients”.

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Journal reference:

• Sherene Loi, Christos Sotiriou, Benjamin Haibe-Kains, Francoise Lallemand, Nelly M

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1: Br J Cancer. 1997;75(6):884-91.Links

Synergistic antiproliferative activity of tamoxifen and docetaxel on three oestrogen receptor-negative cancer cell lines is mediated by the induction of apoptosis.

Ferlini C, Scambia G, Distefano M, Filippini P, Isola G, Riva A, Bombardelli E, Fattorossi A, Benedetti Panici P, Mancuso S.
Department of Obstetrics and Gynecology, Catholic University of Sacred Heart, Rome, Italy.

The taxanes are a promising family of anti-tumour drugs that block cell cycle replication by interfering with the microtubule network. The clinical use of these drugs involves some problems related to their low solubility and occurrence of resistance, which is mainly dependent on the multidrug-resistant (MDR) phenotype. To investigate the possible interaction between docetaxel and tamoxifen (TAM), three oestrogen receptor-negative cancer cell lines, MDR- MDA-MB 231, MDR + CEM-VBLr and MCF-7 ADRr, were used. In all three cell lines, the combination of docetaxel and TAM was more effective in terms of growth inhibition than single drug exposure. Isobolic analysis confirmed the presence of synergism in all cell lines when docetaxel was used at 0.2 microM and TAM at a dose equal to or higher than 1 microM. Flow cytometric DNA analysis performed on the three cell lines showed that TAM was able to increase the G2/M blocking activity of docetaxel. This blocking activity was followed by an increased flow cytometric DNA fragmentation suggestive of the presence of apoptosis, which was confirmed by DNA gel fragmentation and morphological analysis. While an antagonistic effect on P-glycoprotein (P-gp) activity may contribute to the synergistic effect of tamoxifen and docetaxel on CEM-VBLr and MCF-7 ADRr, other mechanisms must be involved, as the synergistic effect is also apparent with a P-gp-negative cell line.
PMID: 9062411 [PubMed - indexed for MEDLINE

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1: Anticancer Drugs. 2009 Sep;20(8):723-35. Links

The antipsychotic drug chlorpromazine enhances the cytotoxic effect of tamoxifen in tamoxifen-sensitive and tamoxifen-resistant human breast cancer cells.

Yde CW, Clausen MP, Bennetzen MV, Lykkesfeldt AE, Mouritsen OG, Guerra B.
Department of Biochemistry and Molecular Biology, Institute of Cancer Biology, Danish Cancer Society, Copenhagen, Denmark.
Tamoxifen resistance is a major clinical problem in the treatment of estrogen receptor alpha-positive breast tumors. It is, at present, unclear what exactly causes tamoxifen resistance. For decades, chlorpromazine has been used for treating psychotic diseases, such as schizophrenia. However, the compound is now also recognized as a multitargeting drug with diverse potential applications, for example, it has antiproliferative properties and it can reverse resistance toward antibiotics in bacteria. Furthermore, chlorpromazine can reverse multidrug resistance caused by overexpression of P-glycoprotein in cancer cells. In this study, we have investigated the effect of chlorpromazine on tamoxifen response of human breast cancer cells. We found that chlorpromazine worked synergistically together with tamoxifen with respect to reduction of cell growth and metabolic activity, both in the antiestrogen-sensitive breast cancer cell line, MCF-7, and in a tamoxifen-resistant cell line, established from the MCF-7 cells. Tamoxifen-sensitive and tamoxifen-resistant cells were killed equally well by combined treatment with chlorpromazine and tamoxifen. This synergistic effect could be prevented by addition of estrogen, suggesting that chlorpromazine enhances the effect of tamoxifen through an estrogen receptor-mediated mechanism. To investigate this putative mechanism, we applied biophysical techniques to simple model membranes in the form of unilamellar liposomes of well-defined composition and found that chlorpromazine interacts strongly with lipid bilayers of different composition leading to increased permeability. This implies that chlorpromazine can change influx properties of membranes hence suggesting that chlorpromazine may be a promising chemosensitizing compound for enhancing the cytotoxic effect of tamoxifen.
PMID: 19584708 [PubMed - in process]

chlorpromazine:
http://www.nlm.nih.gov/medlineplus/d...s/a682040.html