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A Agrawal, E Gutteridge, J M W Gee, R I Nicholson, and J F R Robertson

Studies of cell models and profiling of clinical breast cancer material to reveal the mechanisms of resistance to anti-oestrogen therapy, and to tamoxifen in particular, have reported that this phenomenon can be associated with increased expression and signalling through erbB Type 1 growth factor receptors, notably the epidermal growth factor receptor (EGFR) and HER2. Further molecular studies have revealed an intricate interlinking between such growth factor receptor pathways and oestrogen receptor (ER) signalling. Inhibition of receptor tyrosine kinase activity involved in the EGFR signalling cascade forms the basis for the use of EGFR specific tyrosine kinase inhibitors exemplified by gefitinib (ZD1839, Iressa) and erlotinib (OSI-774, Tarceva). Such agents have proved promising in pre-clinical studies and are currently in clinical trials in breast cancer, where gefitinib has been studied more extensively to date. Here, we present an overview of the current development of gefitinib in clinical breast cancer. This includes results from our clinical breast cancer trial 1839IL/0057 that demonstrate the efficacy of gefitinib within ER-positive, tamoxifen-resistant patients with locally advanced/metastatic disease, where parallel decreases in EGFR signal transduction and the Ki67 (MIB1) proliferation marker can be detected as predicted from model system studies. We also consider trials examining combination treatment with gefitinib and anti-hormonal strategies that will begin to address the clinically important question of whether gefitinib can delay/prevent onset of anti-hormone resistance.

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R I Nicholson, A B Francis, R A McClelland, D L Manning, and J M W Gee

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R I Nicholson, J M W Gee, A Harris, and E Anderson

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R I Nicholson, C Staka, F Boyns, I R Hutcheson, and J M W Gee

There is an increasing body of evidence demonstrating that elevated growth signaling in breast cancer cells can promote forms of endocrine resistance in either an estrogen receptor-dependent or -independent manner. The current article reviews what is known about such growth factor signaling networks and resistance to estrogen withdrawal and considers the many novel therapeutic opportunities that stem from this knowledge.

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R I Nicholson, I R Hutcheson, S E Hiscox, J M Knowlden, M Giles, D Barrow, and J M W Gee

De novo insensitivity and acquired resistance to the selective oestrogen receptor modulator tamoxifen and the pure anti-oestrogen fulvestrant (faslodex) severely limit their effectiveness in breast cancer patients. This is a major clinical problem, since each year upward of 1 million women are dispensed anti-oestrogenic drugs. In order to investigate the phenomenon of anti-oestrogen resistance and to rapidly screen drugs that target the resistance mechanism(s), we have previously established several in vitro breast cancer models that have acquired resistance to anti-hormones. Such cells commonly develop an ability to proliferate after approximately 3 months of exposure to 4-hydroxytamoxifen or fulvestrant, despite an initial endocrine-responsive (i.e. growth-suppressive) phase. The current paper explores the role that growth factor signalling plays in the transition of oestrogen receptor-positive endocrine-responsive breast cancer cells to anti-oestrogen resistance or insensitivity and how we might, in the future, most effectively use anti-growth factor therapies to treat or delay endocrine-resistant states.

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R I Nicholson, J M W Gee, M E Harper, IO Ellis, P Willsher, and J F R Robertson

Abstract

A common phenotypic consequence of the genetic changes that occur in breast cancer is a loss of steroid hormone growth sensitivity, a feature manifested clinically by primary or acquired resistance to antihormones. Although it appears that the absence of steroid receptor machinery determines the failure of oestrogen receptor (ER) negative tumours to respond to endocrine therapies, the erbB signalling pathway seems far from redundant in these tumours and in vivo evidence suggests that elevated epidermal growth factor receptor (EGFR) and c-erbB-2 proteins are fundamental elements in ER negative disease growth control. In contrast, neither diminished ER nor elevated EGFR expression appears to be essential in determining any primary endocrine insensitivity demonstrated by ER positive tumours, although elevated expression of additional erbB pathway components (e.g. transforming growth factor-α, Fos, Myc and c-erbB-2 protein) may be important. However, none of these factors appears to direct endocrine unresponsive, ER positive cell proliferation. Furthermore, it is unlikely that selective outgrowth of endocrine unresponsive, EGFR membrane positive/ER negative cells constitutes a major event in ER positive tumours during their progression towards endocrine resistance.

Endocrine-Related Cancer (1997) 4 297-305

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H E Jones, J M W Gee, K M Taylor, D Barrow, H D Williams, M Rubini, and R I Nicholson

Aberrant signalling through the epidermal growth factor receptor (EGFR) is associated with increased cancer cell proliferation, reduced apoptosis, invasion and angiogenesis. Over-expression of the EGFR is seen in a variety of tumours and is a rational target for antitumour strategies. Among the classes of agent targeting the EGFR are small-molecule inhibitors, which include gefitinib (IRESSA™), which acts by preventing EGFR phosphorylation and downstream signal transduction. De novo and acquired resistance, however, have been reported to gefitinib and here we describe evidence which indicates that the type II receptor tyrosine kinases (RTKs) insulin-like growth factor-I receptor (IGF-IR) and/or insulin receptor (InsR) play important roles in the mediation of responses to gefitinib in the de novo- and acquired-resistance phenotypes in several cancer types. Moreover, combination strategies that additionally target the IGF-IR/InsR can enhance the antitumour effects of gefitinib.

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R I Nicholson, J M W Gee, A B Francis, D L Manning, A E Wakeling, and B S Katzenellenbogen

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J M W Gee, V E Shaw, S E Hiscox, R A McClelland, N K Rushmere, and R I Nicholson

Breast cancer inhibition by antihormones is rarely complete, and our studies using responsive models reveal the remarkable flexibility of breast cancer cells in recruiting alternative signalling to limit maximal anti-tumour effects of oestrogen receptor α (ER) blockade. The recruited mechanism involves antihormone-induced expression of oestrogen-repressed signalling genes. For example, epidermal growth factor receptor gene (EGFR) is induced by antioestrogens and maintains residual kinase and ER phosphorylation, cell survival genes, and thereby allows incomplete antihormone response and emergence of resistance. Microarrays are revealing the breadth of antihormone-induced genes that may attenuate growth inhibition, including NFκB, Bag1, 14-3-3ζ and tyrosine kinases, such as HER2 and Lyn. Three concepts are emerging: first, some genes are induced exclusively by antioestrogens, while others extend to oestrogen deprivation; secondly, some are transiently induced, while others persist into resistance; finally, some confer additional adverse features when tumour cells are in an appropriate context. Among the latter is CD59 whose antioestrogen induction may permit evasion of immune surveillance in vivo. Also, induction of pro-invasive genes (including NFκB, RhoE and δ-catenin) may underlie our findings that antioestrogens can markedly stimulate migratory behaviour when tumour intercellular contacts are compromised. Based on our promising studies selectively inhibiting EGFR (gefitinib), NFκB (parthenolide) or CD59 (neutralising antibody) together with antioestrogens, we propose that co-targeting strategies could markedly improve anti-tumour activity (notably enhancing cell kill) during the antihormone-responsive phase. Furthermore, subverting those induced signalling genes that are retained into resistance (e.g. EGFR, NFκB, HER2) may prove valuable in this state. Alongside future deciphering and targeting of genes underlying antioestrogen-promoted invasiveness, embracing of intelligent combination strategies could significantly extend patient survival.

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H E Jones, L Goddard, J M W Gee, S Hiscox, M Rubini, D Barrow, J M Knowlden, S Williams, A E Wakeling, and R I Nicholson

De novo and acquired resistance to the anti-tumour drug gefitinib (ZD1839; Iressa), a specific epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor (TKI) has been reported. We have determined whether signalling through the IGF-I receptor (IGF-1R) pathway plays a role in the gefitinib-acquired resistance phenotype. Continuous exposure of EGFR-positive MCF-7-derived tamoxifen resistant breast cancer cells (TAM-R) to 1 μM gefitinib resulted in a sustained growth inhibition (90%) for 4 months before the surviving cells resumed proliferation. A stable gefitinib-resistant subline (TAM/TKI-R) was established after a further 2 months and this showed no detectable basal phosphorylated EGFR activity. Compared with the parental TAM-R cells, the TAM/ TKI-R cells demonstrated (a) elevated levels of activated IGF-1R, AKT and protein kinase C (PKC)δ, (b) an increased sensitivity to growth inhibition by the IGF-1R TKI AG1024 and (c) an increased migratory capacity that was reduced by AG1024 treatment. Similarly, the EGFR-positive androgen-independent human prostate cancer cell line DU145 was also continuously challenged with 1 μM gefitinib and, although substantial growth inhibition (60%) was seen initially, a gefitinib-resistant variant (DU145/TKI-R) developed after 3 months. Like their breast cancer counterparts, the DU145/TKI-R cells showed increases in the levels of components of the IGF-1R signalling pathway and an elevated sensitivity to growth inhibition by AG1024 compared with the parent DU145 cell line. Additionally, DU145/TKI-R cell migration was also decreased by this inhibitor. We have therefore concluded that in breast and prostate cancer cells acquired resistance to gefitinib is associated with increased signalling via the IGF-1R pathway, which also plays a role in the invasive capacity of the gefitinib-resistant phenotype.