Emerging EGFR antagonists for breast cancer.

Review

Emerging EGFR antagonists for breast cancer

Expert Opin. Emerging Drugs Downloaded from informahealthcare.com by University Library Utrecht on 06/02/14 For personal use only.

Ana Lluch†, Pilar Eroles & Jose-Alejandro Perez-Fidalgo †

Hospital Clinico Universitario, INCLIVA Biomedical Research Institute, Department of Oncology and Hematology, Valencia, Spain

1.

Background

2.

Medical need

3.

Existing treatments

4.

Current research goals

5.

Scientific rationale

6.

Competitive environment

7.

Potential development issues

8.

Conclusion

9.

Expert opinion

Introduction: The EGFR has been associated with the pathogenesis and progression of breast cancer. Treatment based on an EGFR target is emerging as a promising option, especially in combination with conventional therapies. Unfortunately, there are no validated predictor biomarkers, and combinatorial treatments are meeting new resistance. Areas covered: The purpose of this review is to summarize the existing treatments and the current research based on targeting the EGFR pathway. Expert opinion: The existing EGFR treatments in breast cancer have shown limited benefit. The combination of the monoclonal antibody cetuximab and platinum salts achieves a 15 -- 20% response rate. The effectiveness of tyrosine kinase inhibitors is not completely clear, showing modest or no benefits. Gefitinib treatment has offered some promising results in estrogen receptor + breast cancer. However, it has not been identified as a predictive factor for the appropriate selection of patients. Radioimmunotherapy with anti-EGFR radiolabeled antibodies is a promising strategy in BRCA-mutated breast cancer, but it still requires clinical confirmation. Nevertheless, the crosstalk between pathways frequently leads to treatment resistance. Current research is focused on increasing knowledge about the mechanisms of response and the discovery of predictive markers. Targeting several pathways simultaneously and a correct selection of patients seem essential. Keywords: angiogenesis, breast cancer, cetuximab, EGFR, erlotinib, gefitinib, tyrosine kinase inhibitor Expert Opin. Emerging Drugs (2014) 19(2):165-181

1.

Background

The EGFR or HER1 and its ligands have been shown to contribute to the pathogenesis and progression of breast cancer [1-3]. The EGFR-dependent pathway appears to be a driver mechanism for malignant carcinogenesis, particularly in some breast cancer subtypes. Approximately 50% of all cases of triple-negative breast cancer (TNBC) and inflammatory breast cancer overexpress EGFR [4]. Moreover, the growth of TNBC cell lines overexpressing this receptor is inhibited by anti-EGFR therapies [5,6]. Hence, the development of anti-EGFR therapy is focused mainly on TNBC. Nowadays, EGFR-targeted therapies are available, but unfortunately, none of these have identified a validated predictive biomarker [7-9]. 2.

Medical need

Treatments are becoming more and more heterogeneous depending on the breast cancer subtype. Luminal breast cancer is often susceptible to endocrine therapy, and therefore, this is a preferred strategy in this subset. However, most luminal breast cancers will develop hormone resistance over time. Strategies to overcome this resistance have gained interest in recent years. EGFR overexpression has been 10.1517/14728214.2014.903919 © 2014 Informa UK, Ltd. ISSN 1472-8214, e-ISSN 1744-7623 All rights reserved: reproduction in whole or in part not permitted

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Table 1. Most relevant studies focused on anti-EGFR therapy in breast cancer. Compound

Target

Cetuximab

EGFR

O’Shaughnessy et al. (2007) [48] Carey et al. (2012) [50] Baselga et al. (2013) [51]

Panitumumab Erlotinib

EGFR EGFR

Gefitinib

EGFR

Lapatinib*

Neratinib*

Afatinib*

Vandetanib

Study

Stage

N

Regimen

Phase II Phase II Phase II

72 102 173

+Irinotecan/carboplatin +Carboplatin +Cisplatin

Nabholtz et al. (2011) [55] Twelves et al. (2008) [66] Dickler et al. (2008) [18] Dickler et al. (2009) [58] Montagna et al. (2012) [65] Baselga et al. (2005) [77] Von Minckwitz et al. (2005) [73] Polychronis et al. (2005) [75] Ciardiello et al. (2006) [109] Smith et al. (2007) [110] Arteaga et al. (2008) [74] Cristofanilli et al. (2010) [111] Osborne et al. (2011) [76] Bernsdorf et al. (2011) [112] Carlson et al. (2012) [113]

Phase Phase Phase Phase Phase Phase Phase Phase Phase Phase Phase Phase Phase Phase Phase

II I/II II II II II II II II II I/II II II II II

58 24 38 69 24 31 58 56 41 206 41 93 290 180 141

EGFR HER2

Di Leo et al. (2008) [80] Pestrin et al. (2012) [83]

Phase III Phase II

406 96

+FEC 100 - docetaxel +capecitabine/docetaxel +Bevaciz Monotherapy +CC+bevaciz Monotherapy Monotherapy +Anastrozole +Docetaxel +Anastrozole +Trastuzumab +Anastrozole +Tamoxifen +EC 4 cycles +Anastrozole or fulvestrant +Paclitaxel Monotherapy

EGFR HER2 HER4 EGFR HER2 HER3 HER4 EGFR VEGFR

Bose et al. (2013) [90]

Preclinical

-

Monotherapy

Schuler et al. (2012) [94]

Phase II

50

Monotherapy

Miller et al. (2005) [97] Boer et al. (2012) [98]

Phase II Phase II

64

Monotherapy +Docetaxel

Evidence in breast cancer Advanced TNBC (subgroup) Advanced TNBC Advanced TNBC Neoadj TNBC Advanced BC Advanced BC Advanced BC Advanced TNBC Advanced BC Advanced BC Neoadj ER+, EGFR+ Advanced BC Neoadj HR+ Advanced HER2+ Advanced HR+ Advanced HR+ Neoadj ERAdvanced HR+ Cohort: HER2Advanced HER2- but CTC HER2+ HER2- tumor samples

Advanced BC: cohort TNBC/cohort HR+

Advanced BC

*In order to show the real impact of pure EGFR blockage induced by lapatinib, neratinib or afatinib, avoiding the confounding of the anti-HER2 effect, only those studies including cohorts of HER2- tumors have been considered. The sample size and characteristics shown are related only to those cohorts including HER2patients. BC: Breast cancer; Bevaciz: Bevacizumab; CC: Metronomic chemotherapy containing capecitabine and cyclophosphamide; CT: Chemotherapy; CTC: Circulant tumor cells; EC: Epirubicin and cyclophosphamide; ER: Estrogen receptors; FEC: fluouracil, epirubicin and cyclophosphamide; HR: Hormone receptors; N: Sample size; Neoadj: Neoadjuvant; TNBC: Triple-negative breast cancer.

linked to a poorer prognosis and less benefit for patients treated with tamoxifen [10,11]. It has been suggested that EGFR may be involved in the process of de novo resistance to endocrine therapy [12]. In this context, EGFR is an attractive target to overcome resistance to endocrine therapy. The HER2 breast cancer subtype is characterized by overexpression of the HER2 receptor. The blockade of the HER2-dependent signaling pathway has been demonstrated to be very beneficial in this subtype of breast cancer. HER2, like EGFR, is a member of the ErbB receptor family. The formation of heterodimers between HER2 and other members of the ErbB family leads to the initiation of the HER2-dependant cascade. Thus, a double blockade of HER2 and other receptors of the ErbB family could help in increasing the benefit achieved by anti-HER2 therapies. EGFR targeting therapy could be of interest in this breast cancer subtype. 166

Finally, TNBC is a subtype characterized by the absence of expression of estrogen receptors (ERs) and progesterone receptors (PRs) and of HER2. Treating TNBC is a challenging issue for two reasons: first, it lacks a recognized target for molecular-oriented therapy, and second, it is a subset of breast cancer with a relatively poor prognosis, especially in those with advanced-stage disease [13]. Many TNBCs overexpress EGFR, which is an adverse prognostic factor [14]; therefore, the development of EGFR-based targeted strategies is a matter of high concern. 3.

Existing treatments (Table 1)

Nowadays, the only anti-EGFR compound approved for the treatment of breast cancer is lapatinib. However, lapatinib activity obeys the anti-HER2 effect and not the anti-EGFR effect, and so its use is restricted to HER2+ breast cancer.

Expert Opin. Emerging Drugs (2014) 19(2)



4.

Current research goals

The role of EGFR and its ligands in breast cancer prognosis is not totally defined. However, recent findings are changing this idea and new molecules are being developed using this receptor as a target. Breast cancer treatments based on the EGFR target are emerging as promising options, especially in combination with existing therapies. This is the case of the combination of gefitinib and hormone therapy [15,16] or the combination of erlotinib with trastuzumab [17] or bevacizumab [18]. Current research is aimed at improving the most effective way to make these combinations, something which often requires a careful selection of eligible patients for treatment. The second line of research that is underway, regarding treatments that target the EGFR pathway, aims at mitigating or avoiding, as much as possible, the resistance to treatment. In this regard, it is of great interest to delve into the mechanisms involved in angiogenesis, alterations in the internalization and the degradation processes and mechanism of nuclear localization of the receptor. Overexpression of other receptors or growth factors of the HER family may also influence the response to the targeted therapy, as well as many other downstream signaling pathways such as phosphoinositide 3-kinase (PI3K)/AKT or those involved in the epithelial-to-mesenchymal transition. 5.

Angiogenesis pathway implications The activation of the angiogenic pathway seems responsible for some of the resistance to anti-EGFR treatments, and the experimental evidence [23] provides the rationale for targeting this pathway. Inflammatory breast cancer is one of the most aggressive forms of breast cancer, with frequent positive lymph nodes and distant metastases. It is characterized by MAPK hyperactivation, presumably mediated by the overexpression of EGFR and/or ErbB2 [24]. MAPK signaling induces the activation of NF-kB leading to RhoC overexpression and a highly angiogenic phenotype [24]. In vitro experiments show that cell lines resistant to EGFR antibodies expressed more VEGF and VEGFR1 mRNA and responded to antiangiogenic treatment. For example, the dual VEGFR--EGFR TKI vandetanib (ZD6474) is capable of overcoming this resistance. ZD6474 reduces the activation (phosphorylation) of VEGFR1 and VEGFR2, and the siRNA for each of these receptors restores the sensitivity to EGFR inhibitors and the migratory potential. However, until now, the efficacy of this combinatorial treatment has not been proven. In metastatic colorectal cancer, dual VEGF and EGFR targeting was not promising, as it showed a poor clinical response [25]. Mammalian target of rapamycin (mTOR) is a downstream signal regulated by the PI3K/AKT pathway whose activation promotes the translation of VEGF mRNA into VEGF protein, mediated by the p70S6 kinase [26]. The mTOR inhibitor everolimus (Ev) has been combined in clinical trials with standard treatments to evaluate the clinical benefits. Two major Phase III trials, BOLERO 1 and BOLERO 3, are underway. These studies combined trastuzumab and Ev with paclitaxel or with vinorelbine in metastatic breast cancer. The selective COX-2 inhibitor celecoxib has been proven to exert an antiangiogenic activity in pancreatic cancer. In breast cancer cells, celecoxib is capable of increasing the sensitivity of the cells by the hypermethylation of the MDR1 gene promoter that inhibits the expulsion of cytotoxics from the cells [27]. The combination of cetuximab and trastuzumab is well tolerated, but it is not active in trastuzumab-refractory patients [28]. 5.1

Scientific rationale

Activation of the receptor EGFR after ligand binding leads to cell proliferation and metastases via the PI3K/AKT, RAS/ RAF/MEK/ERK and PKCg/PKC pathways. EGFR is important in the normal regulation of tissues; however, on amplification, protein overexpression or mutation can be a determinant in the development of a new tumor. To date, three small tyrosine kinase inhibitors (TKIs) and two monoclonal antibodies have been approved by the FDA for use in cancer treatment. The appearance of resistance led to the investigation of the mechanisms responsible and a way to inactivate them. High expression of EGFR has been detected in breast cancer, mainly in the basal subtype with poor prognosis generally associated with high grade, visceral liver and brain metastases [19,20]. Even EGFR mutations are rare, the gene showing amplification in the metaplastic subtype [21], and its overexpression is more frequent in breast cancer 1 (BRCA1) cases than in sporadic breast cancer (67 vs 18%). Experimental data support the idea that this receptor provides a growth advantage at the early stages of carcinogenesis [22]. To date, clinical trials do not show a favorable response in unselected patients [21]. The EGFR inhibitor erlotinib increases the time-to-development of a breast tumor in transgenic mice, but the effect is exclusive to the ER-subtype (Figure 1) [22].

EGFR internalization and degradation Despite the above, impaired EGFR internalization and degradation may lead to altered EGFR levels and to resistance. Experiments in cetuximab-resistant colorectal cancer cell lines show the development of acquired resistance by decreasing EGFR protein levels through the promotion of EGFR association with Cbl, ubiquitination and degradation. The authors believe that activation of the Src-mediated pathway is a mechanism to bypass the EGFR-dependent cell signaling. Indeed, the inhibition of Src kinase activity reversed the resistance to cetuximab-induced apoptosis [29]. Other authors show high levels of EGFR in a cetuximabresistant non-small-cell lung carcinoma cell line secondary to 5.2


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Potential mechanisms of resistance to anti-EGFR treatments TGF-α

HB-EGF

EGFR overexpression Angiogenesis

VEGF

EGF

HER family growth factors overexpression

HER family overexpression

E-Cadherin

HER4

HER2

EGFR

P

P

GRB2

PI3K

P

P

HSP90

AKT


HER3

FRs

VEG

nin

ate

C β-

P

α-Catenin

PTEN

Ras

Downstream activation pathways

mTOR

Endosome

Raf 4EBP1

EGFR impaired internalization/degradation

S6K1/2

Actin cytoskeleton Epithelial to mesenchymal transition

Mek Ub Ub Erk1/2

Lysosome

Nucleus

TF NFκB

INOS Cox2 STAT3

B-Myc

Cyclin D

E2F1

PCNA

Proliferation Survival Invasion Metastasis

EGFR nuclear

Figure 1. Potential mechanisms of resistance to anti-EGFR treatments are shown.

altered trafficking/degradation of the receptor. The Src-family kinases (SFKs) are highly activated in cetuximab-resistant cells and these cells were resensitized to cetuximab when treated with the Src inhibitor dasatinib. These data indicate that SFKs and EGFR cooperate in acquired resistance to cetuximab [30]. HER family Upregulation of different HER family members, such as HER2, HER3 or the MET receptor, may lead to ligandindependent receptor dimerization, and consequently, the activation of downstream pathways [31]. This anomalous activation has been suggested as a mechanism for overcoming cetuximab treatment. The hepatocyte growth factor (HGF) had been a mediator of motility, invasion and proliferation in breast cancer. Expression of HGF and/or MET is associated with poor prognosis, because of its mitogen capacity. There is a crosstalk between these receptor tyrosine kinases. EGFR ligands activate c-MET, and HGF transactivates EGFR. All of this supports the use of anti-EGFR therapy that would consequently reduce the proliferation and invasion of cancer cells. 5.3

168

The simultaneous blockade of these receptors has been proposed as a possibility to prevent or reverse resistance. Nuclear EGFR The nuclear EGFR location identified in many breast cancers is a possible prognostic factor. Cells resistant to cetuximab show increased nuclear EGFR and a high expression of EGFR-regulated genes such as cyclin D1, B-myb and PCNA. Additionally, the expression of SFKs has been increased in cases of cetuximab resistance, and some data suggest its requirement for EGFR nuclear translocation. In that sense, treatment with SFK inhibitors (e.g., dasatinib) is a reasonable choice to overcome resistance. 5.4

Epithelial-to-mesenchymal transition Another mechanism proposed to avoid anti-EGFR treatment is the epithelial-to-mesenchymal transition. The loss of adherent junctions and the gain of cytoskeletal filaments increase the motility and invasiveness of the cells. These changes are combined with an increased activation of the integrin-linked kinases STAT3 and the downstream protein AKT. Xenograft model experiments confirm that the inactivation of 5.5



STAT3 restores the sensitivity to EGFR inhibitors [32]. Further, low levels of the adherent protein E-cadherin have been related to decreased EGFR expression levels in cellular models [33] and consequent resistance to EGFR inhibitors. Constitutive PI3K/AKT activation Given the importance of PI3K/ATK pathway in survival and proliferation, the constitutive activation of this pathway has been related to resistance to anti-EGFR therapy. Cetuximabresistant cells show increased activation of AKT and SFKs and decreased phosphatase and tensin homolog (PTEN) levels. The combination of AKT inhibitors and cetuximab, or Src inhibitors and cetuximab, shows an antiproliferative synergistic effect, in both cases [34], by decreasing AKT downstream signaling. Similarly, the Src blockade sensitizes KRASmutant colon cancer cells to cetuximab treatment [35].


5.6

Increased expression of HER family growth factors

5.7

An increase in the HER family growth factors has been identified as another potential mechanism of resistance to anti-EGFR therapy. Increased amounts of heparin-binding EGF are present in head and neck squamous carcinoma, cetuximab-resistant cells, and its decline can sensitize the cells to the drug [36]. Moreover, the overexpression of the EGFR ligand TGF-a has been suggested as a cause of the EGFR pathway deregulation through the development of an autocrine loop [37]. Downstream components of the EGFR/ HER2 pathway, such as Erk1/2 and AKT, can phosphorylate ER at the activation domain, leading to a ligand-independent activation of ER [38,39]. This ER signaling activation could additionally induce EGFR ligands, including TGF-a [40-42]. These data suggest the importance of the crosstalk between ER and EGFR receptors and notes that the ER pathway status should be considered in EGFR-based treatments. Among the newly proposed mechanisms to prevent EGFR function is the use of heat shock protein 90 (Hsp90) chaperone inhibitors. In preclinical models, few of them demonstrated potent antitumor and antiangiogenic activity [43,44]; however, recent clinical trials in metastatic breast cancer are very promising [45]. 6.

Competitive environment (Table 2)

6.1

Monoclonal antibodies Cetuximab

6.1.1

Cetuximab is a chimeric IgG1 monoclonal antibody that targets the ligand-binding domain of the EGFR and is widely used in colorectal or head and neck cancer. As an IgG1 antibody, cetuximab may exert its antitumor efficacy through both EGFR antagonism and antibody-dependent cell-mediated cytotoxicity [46]. Preclinical studies have shown that cetuximab presents a synergistic effect when combined with cisplatin in gefitinibresistant TNBC cell lines [47].

The preliminary results of the USOR-04-070 study, a randomized Phase II trial comparing the combination of irinotecan and carboplatin with or without cetuximab in firstand second-line metastatic breast cancer patients, resulted in improved response rates (RRs) among a subset of TNBC patients (n = 72, overall RR 30 vs 49%). However, no improvement in progression-free survival (PFS) or overall survival (OS) was found for this subgroup. Moreover, the combination resulted in an important increase of the grade 3/4 diarrhea compared with chemotherapy alone (11 vs 25%). This results were confirm in a later analysis. However a biomarker evaluation have identified PTEN as a predictive factor to cetuximab therapy in TNBC patients with improved PFS (HR = 0.40; p = 0.04) [48,49]. More recently, two randomized Phase II trials have assessed the role of cetuximab in metastatic TNBC in combination with platinum salts. In 2012, Carey et al. published the results of the TBCRC-001 trial [50], in which 102 TNBC patients were randomized to receive cetuximab monotherapy with the addition of carboplatin after disease progression versus the combination of both drugs from the beginning of the trial. The primary end point was the RR. RRs were 6% for cetuximab in monotherapy and 16% for the addition of carboplatin after progression. In the combination of cetuximab plus carboplatin arm, from the beginning the RRs were 17%. Of note, up to 31% of the patients responded or had prolonged disease stabilization. The regimen combining cetuximab and carboplatin was well tolerated. Nevertheless, time-toprogression (TTP) and OS were short at 2.1 and 10.4 months, respectively. This study included a genomic analysis of archived tumor tissue. Of the 73 patients with available tissue, 74% had the basal-like molecular subtype. A total of 16 patients had tumor biopsies before therapy and 1 week after, and genomic patterns of the EGFR pathway showed activation in 13 and inhibition by therapy in 5 of the patients. These results demonstrated that despite strong preclinical evidence, inhibition of the EGFR pathway is a discouraging strategy with a RR of < 20%. These data suggest that alternative activated pathways are present in the majority of TNBC. More recently, Baselga et al. [51] conducted a trial, the BALI-1 study, including 115 patients with TNBC who were randomized in a 2:1 design to receive no > 6 cycles of cisplatin and cetuximab versus cisplatin alone. Patients receiving cisplatin alone were allowed to switch to cetuximab plus cisplatin after progression. The RR was 20% with cisplatin plus cetuximab versus 10% with cisplatin alone (odds ratio: 2:13; 95% CI: 0.81 -- 5.59; p = 0.11). However, cisplatin plus cetuximab resulted in a longer PFS compared with cisplatin alone (median 3.7 vs 1.5 months; hazard ratio (HR): 0.67; 95% CI: 0.47 -- 0.97; p = 0.032). Median OS was not significantly longer in the combination arm (median 12.9 vs 9.4 months; HR: 0.82; 95% CI: 0.56 -- 1.20; p = 0.31). The combination was well tolerated, with acne-like rash, neutropenia and fatigue being the most frequent adverse events. Although this is a negative study, as the primary end point (RR) was not met,


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Table 2. Competitive environment.


Compound

Company

Structure

Explored

Studies in advanced TNBC

Phase II

Targets EGFR

Studies in neoadjuvant TNBC Studies in advanced BC and TNBC Studies in early and advanced BC (including HER2+, HR+ and HRtumors) HER2+ Activity by EGFR inhibition remains unclear HER2- tumor samples

Phase II

Targets EGFR

Phase II

Targets EGFR

Phase II

Targets EGFR

Phase III

Targets EGFR and HER2

Preclinical

Targets EGFR, HER2 and HER4 Targets EGFR, HER2, HER3 and HER4 Targets EGFR and VEGFR

Cetuximab

Merck

Panitumumab

Amgem Inc.

Erlotinib

Genetech-Roche

Monoclonal antibody Monoclonal antibody TKI

Gefitinib

AstraZeneca

TKI

Lapatinib

GSK

TKI

Neratinib

Puma Biotech

TKI

Afatinib

Boehringer-Ingelheim

TKI

Vandetanib

AstraZeneca

TKI

Studies in advanced BC in TNBC and HR+ Advanced BC

Stage of development

Phase II Phase II

Mechanism of action

BC: Breast cancer; HR: Hormone receptors; TKI: Tyrosine kinase inhibitor; TNBC: Triple-negative breast cancer.

the addition of cetuximab doubled the RR and showed ncouraging results in PFS versus cisplatin alone. It should be underlined that in the TBCRC-001 trial, only 3 -- 6% of the patients (depending on the arm considered) had never received chemotherapy before entering the trial; however, in BALI-1, 17% of the patients in both arms had not been treated with chemotherapy in either a neoadjuvant or a metastatic setting. In summary, the combination of cetuximab and platinum salts is feasible and achieves a RR of approximately 15 -- 20%. Nevertheless, the outstanding increase in the median PFS in the BALI-1 trial, which was more than double in the arm with cetuximab, is promising data. Two trials whose results are pending publication assessed the combination of ixabepilone with or without cetuximab in TNBC. The NCT00633464 trial in metastatic or locally advanced TNBC included 79 patients, but the results have not yet been communicated [52]. The NCT01097642 trial in the neoadjuvant setting is recruiting patients and its completion date is projected as 2014 [53]. Panitumumab Panitumumab, a fully human monoclonal antibody, blocks the extracellular domain of EGFR. Due to its human origin, it has not been associated with the formation of any antibodies against it [54]. Panitumumab has been studied in colorectal and head and neck cancers. In 2011, the preliminary results of a Phase II study combining panitumumab and FEC100 followed by docetaxel as neoadjuvant therapy for TNBC was communicated at American Society of Clinical Oncology. A total of 58 patients with stage II -- IIIA were included. The primary end point was pathologic complete response (pCR) which was assessed using 6.1.2

170

two different methods (Sataloff and Chevallier). The rates of pCR achieved were 65% (Sataloff) and 56% (Chevallier). After neoadjuvant treatment, conservative surgery was possible in 87% of the patients. Skin toxicity was the main side effect with 69% having grade II and 19% grade III skin rashes. Neutropenia grade IV appeared in 27% of the patients [55]. In 2012 and 2013, two studies of biomarkers associated with this trial were communicated. The first one showed that high Ki-67 was predictive of response. However, high EGFR, low cytokeratin 5 -- 6 and low p53, although associated with a better response, were not statistically significant. Of note, skin rash was not predictive of a better response [56]. In the more recent study, tumor levels of IGFR-1 appeared to play a role as a predictive factor for panitumumab therapy in this context [57]. Tyrosine kinase inhibitors EGFR inhibitors 6.2.1.1 Erlotinib 6.2

6.2.1

Erlotinib is an oral EGFR TKI used in the treatment of non-small-cell lung cancer and pancreatic cancer. In monotherapy, erlotinib has shown a very limited activity in previously treated, locally advanced or metastatic breast cancer. In a study published in 2009, 69 patients were recruited into two different cohorts (cohort one included patients progressing after previous treatment with anthracyclines, taxanes and capecitabine, and cohort two included patients with advanced diseased treated in second or latter lines) [58]. Erlotinib was given orally at 150 mg/day. Only one patient in each cohort (3%) had a partial response. Common adverse events were diarrhea, rash, dry skin, asthenia, nausea and anorexia. Data from preclinical studies suggested that the EGFR signaling pathway may play a role in the regulation of angiogenesis [59-62]. Anti-EGFR therapy decreases the production of




antiangiogenic factors, including VEGF, basic fibroblast growth factor and IL-8 [62]. In xenograft models, anti-EGFR and anti-VEGF therapy has increased activity compared with either agent alone [63,64]. In this context, a Phase II study was performed in order to assess the efficacy of erlotinib 150 mg orally in combination with intravenous bevacizumab (an anti-VEGF antibody) 15 mg/kg every 21 days. Again, erlotinib showed limited activity even in this schedule. Only 1 patient out of 38 achieved a partial response for > 52 months. Only 15 patients had stable disease at 9 weeks and only 4 of these patients remained in stable disease beyond 26 weeks. The level of EGFR was tested in tumor tissue, but it was not predictive of response to therapy [18]. More recently, another trial tried to elucidate the potential role of double blockade of EGFR/VEGF. A Phase II study assessed the combination of metronomic chemotherapy with capecitabine (500 mg thrice daily) and cyclophosphamide (50 mg/day) with bevacizumab (15 mg/kg every 3 weeks) and erlotinib (100 mg/day) in TNBC patients. Of the 24 patients assessable for response, 1 complete response (4%) and 14 partial responses (58%) were obtained. Moreover, 21% had stable disease > 9 weeks. The overall clinical benefit defined as the proportion of partial plus complete responses plus stable disease > 24 weeks was 75%. Toxicity was mild, and most common grade III adverse events were hypertension (two patients), thrombosis (one patient) and diarrhea (one patient). The authors concluded that this is an active regimen; however, it is uncertain if these results are due to the addition of erlotinib or if the responses observed could be exclusively justified by the combination of bevacizumab and metronomic chemotherapy in a selected TNBC population [65]. In 2008, a dose-escalation study in patients with metastatic breast cancer confirmed that erlotinib 100 mg/day continuously combined with capecitabine 825 mg/m2/12 h from days 1 to 14 and docetaxel 75 mg/m2 every 21 days was well tolerated. A dose of 100 mg/day was considered the maximal tolerated dose for erlotinib in combination with capecitabine [66]. Of note, the overall RR was 67%, comprising 2 complete and 12 partial responders in 21 assessable patients. The most common treatment-related adverse events were gastrointestinal disorders and skin toxicities. In fact, skin toxicity is a frequently seen side effect of anti-EGFR agents with an incidence of 47 -- 100% [67]. It has been speculated that cutaneous toxicity from anti-EGFR therapy may be a result of an inflammatory response secondary to EGFR inhibition. A prospective study performed in metastatic breast cancer patients treated with erlotinib analyzed different markers in skin biopsies and correlated them to the development of skin rash. The AKT phosphorylation at baseline was significantly associated with not developing a rash, suggesting a potential relationship of the PI3K--AKT pathway and skin rash [68]. Gefitinib Gefitinib is a reversible and specific TKI of the EGFR that has been assessed in several clinical trials. Preclinical studies with 6.2.1.2

gefitinib in TNBC and HER2+ cell lines have shown that gefitinib was an active compound for inhibiting the EGFR pathway and that this activity enhanced response to chemotherapy [14]. Response to gefitinib was associated with reduced phosphorylation of both MAPK and AKT and induction of G1 arrest. In vitro studies showed that gefitinib reduced EGFR phosphorylation and downstream MAPK signaling [69] in tamoxifen-resistant cells. Later data confirmed evidence of productive crosstalk between the ER and EGFR pathways that were crucial to cell growth [70,71]. In Phase I trials, oral administration of gefitinib 500 mg was well tolerated [72], and the Phase II trial in breast cancer showed better tolerability at a lower dose [73]. In Phase I trials, the oral form was well tolerated, with 700 mg/day being the dose-limiting toxicity [72]. Later Phase II trials in breast cancer showed better tolerability at a lower dose (250 mg) [74]. Taking into account its oral bioavailability and the preclinical evidence of crosstalk between the EGFR and ER pathways, gefitinib became an attractive option in combination with endocrine therapy. In this context, several clinical trials have been conducted in hormone receptor-positive breast cancer. Some data suggested that gefitinib may have a role in this context. A Phase II preoperative study of gefitinib versus gefitinib plus anastrozole in EGFR+ and ER+ postmenopausal patients conducted by Polychronis in 2005 showed a reduction in Ki-67 levels in both branches, with a higher reduction in the combination arm [75]. A second randomized Phase II clinical trial that compared tamoxifen with tamoxifen plus gefitinib in ER+ metastasis breast cancer patients showed a nonsignificant advantage for the combination group in terms of PFS [76]. These data suggest that gefitinib may have some potential to delay the development of acquired endocrine resistance but not in the de novo resistance. Nevertheless, most clinical studies conducted in multiple breast cancer subtypes have shown modest or very limited activity of gefitinib in monotherapy or combined with either anti-HER2 or chemotherapy (Table 3). Another important concern is toxicity. Despite initial monotherapy trials that showed gefitinib to be well tolerated at doses < 700 mg [72,73,77], when gefitinib was combined with trastuzumab [74] or chemotherapy, toxicity (mainly diarrhea) was very limited. In 2012, the NCT00319618 study, a randomized Phase II placebo-controlled trial comparing weekly docetaxel with weekly docetaxel plus gefitinib in metastatic breast cancer, showed unexpectedly high toxicity [78]. The most frequent severe adverse events were dehydration and diarrhea. Adverse events were found in both arms, but toxicity was increased by the addition of gefitinib. After including 18 of the planned 66 patients, the study was prematurely closed due to toxicity. Moreover, although the expression of EGFR has been tested as a possible biomarker, no predictive factor has been identified to date, thus preventing selection of appropriate patients. In this context, gefitinib in breast cancer can only


171

172

Single arm Phase II trial Previously treated advanced breast cancer

Design


Anastrozole 16 weeks: + gefitinib 250 mg 16 weeks + placebo 2 weeks! gefitinib 250 mg 14 weeks + placebo 16 weeks

Randomized Phase II trial (2:5:5) Neoadjuvant setting HR+, stage I to IIIB operable breast cancer

Smith et al. (2007) [110]

85

90

31

14 27

29

27

58

31

N

Ki-67 changes at 2 and 16 weeks of anastrozole alone vs gefitinib + anastrozole Between baseline and 16 weeks!-77.4 and -83.6% Between baseline and 2 weeks!-80.1 and -71.3% Between 2 weeks and 16 weeks!-19.3 and -43%

ORR: 54% (22/41)

Ki-67 index changes between pre- and post-treatment values Reduction: 98% Reduction: 92.4%

RR: 1.7% (98.3% nonresponders due to disease progression or not evaluable)

RR: 0% CR; 0% pCR; 38.7% SD

Primary end point

Geometric mean ratio (-1.37; 95% CI: 0.79 -- 2.39; p = 0.26) Geometric mean ratio (-0.7; 95% CI: 0.39 -- 1.25; p = 0.22) Geometric mean ratio (-1.42; 95% CI: 0.86 -- 2.35; p = 0.16)

NA

Difference between groups 5.6% (95% CI: 5.1 -- 6.0; p = 0.0054)

NA

NA

Comparison

ORR (secondary end point) nonsignificant trend against gefitinib which is significant in the PR+ subgroup (48% for gefitinib + anastrozole vs 72% in anastrozole alone, p = 0.03)

Reduction in phosphorylation of ER at Ser 118 was similar in both groups Both dosages of docetaxel showed similar activity Grade 3/4 neutropenia: 49% ER+ more likely to respond Nonsignificant

Significant for addition of anastrozole

Good tolerance (only 5.2% discontinued therapy due to toxicity)

EGFR inhibition shown in all cases after gefitinib treatment Decrease in p26 and Ki-67 seen in skin but not in tumor tissues Inefficacy in heavily pretreated breast cancer

Observations

*Initial dose was 500 mg, but due to diarrhea the dose was reduced to 250 mg CBR: Clinical benefit rate; CR: Complete response; CT: Chemotherapy; ER: Estrogen receptor; ev: Evaluable; HR: Hazard ratio; NA: Not available; ORR: Overall response rate; pCR: pathologic complete response; PFS: Progression-free survival; PR: Progesterone receptor; RR: Response rate; SD: Stable disease; TTP: Time-to-progression.

Gefitinib 250 mg +docetaxel 75 mg/m2 +docetaxel 100 mg/m2

Single arm Phase II trial (2:5:5) First-line advanced breast cancer

Neoadjuvant setting ER+, EGFR+ operable breast cancer

Gefitinib 250 mg + anastrozole Gefitinib 250 mg + placebo

Gefitinib 500 mg

Gefitinib 500 mg

Arms

Ciardiello et al. (2006) [109]

Polychronis et al. (2005) [75]

Heavily pretreated (taxanes and anthracycline) advanced breast cancer Randomized Phase II trial

Von Minckwitz et al. Single arm Phase II trial (2005) [73]

Baselga et al. (2005) [77]

Study

Table 3. Relevant trials of gefitinib.


A. Lluch et al.


94 (71 ev) 86 (73 ev)

EC 4 cycles ! gefitinib 250 mg 12 weeks EC 4 cycles ! placebo 12 weeks

Gefitinib 250 mg*-anastrozole Gefitinib 250 mg*-fulvestrant

CBR: 31.4%

36

CBR: 44% CBR: 41%

72 69

pCR:12% (9/73)

pCR:17% (12/71)

CBR: 29.2%

48

PFS: 8.8 months

PFS: 10.9 months

Gefitinib 250 mg-tamoxifen Placebo-tamoxifen

101

105

Not given

Difference 4.57% (95% CI: -7.19 -- 6.33; p = 0.44)

HR: 0.72 (95% CI: 0.26 -- 1.95; p = 0.52)

HR: 0.55 (95% CI: 0.35 -- 0.94; p value not given) All (n = 206): HR: 0.84 (95% CI: 0.59 -- 1.18; p = 0.31) Naı¨ve (n = 158): HR: 0.78 (95% CI: 0.52 -- 1.15) After adjuvant tamoxifen (n = 48): HR: 1.47 (95% CI: 0.63 -- 3.45)

NA

Comparison

Nonsignificant A significantly higher pCR in post-hoc analysis was seen in TNBC More patients discontinued gefitinib due to toxicity Similar activity Grade 3 -- 4 toxicity: 36 and 35% in anastrozole and fulvestrant arms, respectively

Nonsignificant

Closed prematurely due to slow recruitment Nonsignificant Biomarker analysis! greater benefit of gefitinib if ER(-) or low levels of ER protein

Gefitinib 250 mg is the only tolerable dosage with trastuzumab Interim analysis of efficacy suggested that the combination was unlikely to result in clinical benefit compared with trastuzumab alone Significant

Observations

*Initial dose was 500 mg, but due to diarrhea the dose was reduced to 250 mg CBR: Clinical benefit rate; CR: Complete response; CT: Chemotherapy; ER: Estrogen receptor; ev: Evaluable; HR: Hazard ratio; NA: Not available; ORR: Overall response rate; pCR: pathologic complete response; PFS: Progression-free survival; PR: Progesterone receptor; RR: Response rate; SD: Stable disease; TTP: Time-to-progression.

Carlson et al. (2012) [113]

Bernsdorf et al. (2011) [112]

Randomized Phase II trial HR+ advanced breast cancer

Randomized Phase II trial HR+ advanced breast cancer After first line with aromatase inhibitors Randomized Phase II trial Neoadjuvant setting ER (-), ‡ 2 cm, operable breast cancer

Gefitinib 250 mg-tamoxifen Placebo-tamoxifen

Osborne et al. (2011) [76] Stratum 2

Osborne et al. (2011) [76] Stratum 1

PFS: 8.4 months

50

43

Gefitinib 250 mg-anastrozole Placebo-anastrozole

Randomized Phase II trial HR+ advanced breast cancer Randomized Phase II trial HR+ advanced breast cancer Endocrine therapy-naı¨ve or after adjuvant tamoxifen

Cristofanilli et al. (2010) [111]

Phase I: all patients treated with gefitinib 500 mg had diarrhea grade 3. Phase II (only with 250 mg): median TTP 3 and 5.3 months in patients without and with previous CT, respectively PFS: 14.7 months

Primary end point

Phase I: 3 + 3

Phase II: 35

Arteaga et al. (2008) [74]

Gefitinib 500 mg + trastuzumab 2 mg/kg weekly

N

HER2+ advanced breast cancer

Arms Gefitinib 250 mg + trastuzumab 2 mg/kg weekly

Design

Single arm Phase I/II trial

Study

Table 3. Relevant trials of gefitinib (continued).



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A. Lluch et al.

be recommended in clinical trials. The most relevant trials of gefitinib are shown in Table 3.

6.2.2

EGFR and HER2 inhibitors Lapatinib


6.2.2.1

Lapatinib is a reversible and selective inhibitor of the intracellular domains of the tyrosine kinases HER1 (EGFR) and HER2. It competes with ATP for the ATP-binding pocket, leading to downstream blocking of the PI3K/AKT/mTOR pathway [79]. Potentially, the clinical benefit induced by lapatinib could be a result of its EGFR inhibitory effect in HER2-- breast cancer patients. In EGF30001, a Phase III randomized placebo-controlled trial, lapatinib 1500 mg/day was given orally in combination with paclitaxel 175 mg/m2 every 21 days and was compared with placebo plus paclitaxel in two cohorts of patients, HER2+ and HER2- [80]. In the cohort of HER2+ patients, the addition of lapatinib resulted in significantly better outcomes in terms of TTP, event-free survival, clinical benefit and RR. However, in the cohort of HER2- or HER2 unknown, lapatinib was ineffective. These results suggested that the role of EGFR inhibition induced by lapatinib was modest in comparison with the effect on the HER2 pathway. A retrospective analysis of data from the EGF3001 trial showed that lapatinib activity in HER2- breast cancer patients varied depending on the PR expression. No benefit or strong expression of PR was found in the TNBC subtype, but lapatinib was efficacious in patients with weak PR expression. On the contrary, lapatinib was deleterious in PR- breast cancer patients. This retrospective subgroup analysis suggested that the hormone receptor could be a surrogate for HER2or EGFR-dependent therapy. Nevertheless, these results must be taken with caution because of the small sample size and the retrospective nature of the analysis [81]. The lack of lapatinib activity in HER2- breast cancer was confirmed in a meta-analysis of three Phase III trials. The trials included randomized studies looking at a combination of lapatinib with chemotherapy or with endocrine therapy in the investigational arm. The HR for PFS and OS in HER2+ breast cancer was 0.69 and 0.76, respectively, and significantly favored the addition of lapatinib. However, in HER2- patients, the HR for PFS and OS were 0.98 (95% CI: 0.80 -- 1.19) and 0.89 (95% CI: 0.65 -- 1.21), respectively [82]. Moreover, in a Phase II trial evaluating lapatinib in monotherapy in patients with HER2- tumors, but with HER2+ circulating tumor cells, of the 96 patients included in the study, only 1 patient achieved a response confirming the absence of effect of lapatinib in this subtype [83]. Finally, a more recent preclinical study suggested that instead of controlling the growth, lapatinib increased the migration and invasion when administered to a triple-negative cell line of breast cancer, by upregulating EGFR and COX-2 [84]. 174

The mTOR inhibitors have shown modest activity in monotherapy in breast cancer. This issue is thought to be partly due to an increase in the phosphorylated AKT levels following an exposure to rapalogues. The AKT activation can be abrogated by the inhibition of upstream regulators in the PI3K/AKT pathway. Given the fact that many TNBCs express EGFR [85] and that EGFR is an upstream regulator of the PI3K/AKT pathway, it has been considered that mTOR inhibitors may play a role as a sensitizer to upstream inhibitors of the EGFR family. Based on this rationale, the combination effects of the mTOR inhibitor rapamycin with lapatinib have been examined in TNBC in vitro and in vivo. The combination of EGFR inhibition using lapatinib and mTOR inhibition with rapamycin resulted in significantly greater cytotoxicity than the single agents alone, and these effects were synergistic in vitro. The combination of rapamycin and lapatinib significantly decreased growth of TNBC in vivo compared with either agent alone. EGFR inhibition abrogated the expression of rapamycin-induced activated AKT in cancer cells in vitro. These results suggest that mTOR inhibitors could sensitize a subset of TNBC to EGFR inhibitors [86]. Neratinib Neratinib is a potent, orally administered, irreversible pan-HER inhibitor that inhibits EGFR, HER2 and HER4. Some data suggest that neratinib can potentially overcome the acquired resistance of EGFR T790M mutations, which are considered responsible for resistance to anti-EGFR in lung cancer. Its development was focused on tumors that express a high level of ErbB2. A Phase I trial was performed in EGFR or HER2+ tumors and the maximum tolerated dose for neratinib was 320 mg/day. Dose-limiting toxicity was diarrhea grade III. Of the 39 evaluable patients, 25 were breast cancer patients and 14 were non-small-cell lung cancer patients. RR in the breast cancer cohort was 32% [87]. Neratinib has been developed mainly in the treatment of HER2+ breast cancer patients. Some Phase II trials have shown promising activity in monotherapy [88] or in combination with chemotherapy [89] in this setting. There are scarce data about the role of neratinib in HER2breast cancer. Thus, the real impact of EGFR blockade induced by neratinib remains uncertain. A recent preclinical study performed by the University of Washington identified 13 HER2 somatic mutations in breast cancers lacking amplification of the HER2 gene. Seven of these mutations were activating mutations. Among these, the HER2 in-frame deletion 755 -- 759, which is homologous to the EGFR exon 19 in-frame deletions, had a neomorphic phenotype with increased phosphorylation of EGFR or HER3. Mutation L755S produced lapatinib resistance; however, all of these mutations were sensitive to the irreversible kinase inhibitor, neratinib. These findings showed that the HER2 somatic mutation may be a valuable predictive biomarker for treatment with neratinib in HER2- patients [90]. 6.2.2.2



Afatinib Afatinib is a novel, potent, orally bioavailable, pan-HER blocker, which irreversibly inhibits all ErbB family members, including EGFR, HER2, HER3 and HER4. As in other pan-HER inhibitors, afatinib has been assessed in HER2+ breast cancer. A Phase II trial administered afatinib monotherapy in patients with HER2+ breast cancer whose disease progressed after trastuzumab treatment. Afatinib showed promising activity in this setting in a heavily pretreated population [91]. As a pan-HER inhibitor, afatinib may play a role by blocking both EGFR and HER2 pathways. In fact, in vitro, afatinib has demonstrated antiproliferative activity in HER2+ and TNBC cell lines [92,93]. The activity of afatinib in HER2- cell lines had been confirmed in vivo in xenografts [92]. In 2012, a European Phase II study assessed the efficacy of afatinib against HER2- breast cancer [94]. The rationale for assessing afatinib in this setting was based on the high EGFR expression in TNBC and the assumption that uncontrolled ErB signaling is related to an increased oncogenic potential in TNBC subtypes. Moreover, the transcriptional repressor activity of the ER on ErbB family members suggested that in ER+ patients, abating the natural activation of ER signaling by its ligand estradiol may bring about the use of alternative proliferation pathways, including the ErbB signaling network. A total of 50 patients were included in the trial in two different cohorts, cohort A with TNBC patients (n = 29) and cohort B with ER or PR+ and HER2- breast cancer patients (n = 21). Afatinib was given orally at 50 mg/day and no objective responses were seen in either cohort. The most frequent afatinib-associated adverse events were gastrointestinal and skin disorders, which were manageable. Afatinib was ineffective in this setting.


6.2.2.3

6.2.3

EGFR and VEGFR inhibitors Vandetanib

6.2.3.1

Vandetanib is a novel, orally available inhibitor of different intracellular signaling pathways involved in tumor growth, progression and angiogenesis, including the VEGFR-2 and EGFR pathways. Phase I trials have shown that vandetanib is well tolerated as a single £ 300 mg/day dose [95]. Vandetanib has shown activity in combination with chemotherapy in non-small-cell lung cancer [96]. In metastatic breast cancer, vandetanib in monotherapy has been studied in 46 pretreated patients in one of two cohorts (100 or 300 mg/day) on 28-day cycles. Vandetanib was generally well tolerated. The most common toxicity was diarrhea which was dose-related (grade II diarrhea occurred in 4.5 and 37.5% of patients at 100 and 300 mg dose, respectively). However, the drug showed limited activity, with no objective responses, and only 1 out of 46 patients experienced stable disease longer than 24 weeks [97]. A randomized, double-blind, placebo-controlled Phase II trial evaluated the activity and safety of vandetanib 100 mg orally and docetaxel 100 mg/m2 intravenously as a second-line

treatment for metastatic breast cancer. The primary end point was the number of progression events. A total of 64 patients were randomized (n = 35 vandetanib and n = 29 placebo) and the combination of vandetanib plus docetaxel was well tolerated. No benefit was shown with the addition of vandetanib. In fact, a slightly greater number of patients experienced a progression event by the data cut-off in the vandetanib trial (69 vs 62%; HR: 1.19, two-sided 80% CI: 0.79 -- 1.81; p = 0.59) [98]. However, this study has some methodological problems and the main concern is the primary end point. In fact, considering the number of events of progression at a defined cut-off point for all patients may be an important confounding factor as a longer observation period prior to the cut-off may have influenced the final outcome. Skin toxicity is frequent in patients treated with vandetanib. In a meta-analysis of nine trials, including one in patients with metastatic breast cancer, the incidence of skin rash was 46.1% (95% CI: 40.6 -- 51.8%) and the incidence of highgrade skin rash was 3.5% (95% CI: 2.5 -- 4.7%). These results suggest that awareness and treatment of this unexpected event may be critical to ensure adherence to vandetanib therapy [99]. Anti-EGFR radioimmunotherapy Radioimmunotherapy or the administration of targeted radiotherapy with radiolabeled antibodies is an old strategy that has produced several discouraging results in solid tumors [100]. Such unsuccessful results can be partly explained by the impossibility of the radiolabeled antibodies to penetrate and deliver sufficient doses (typically < 30 Gy) to elicit responses. However, in non-Hodgkin’s lymphoma, lower doses are able to induce responses [101]. A possible reason for this effect on nonHodgkin’s lymphoma is the increased radiosensitivity (in a range of 1.3 -- 1.8 Gy) that can be attributed to impaired DNA repair from the inactivation of ataxia telangiectasia mutated (ATM), p53 and other DNA-repairing complexes [102]. DNA repair system impairment is present in not only hematologic malignancies but also some solid tumors. Hereditary breast cancer associated with BRCA germline mutations present alterations in the DNA repair mechanisms, and most breast cancer with BRCA mutations are TNBC, which importantly show EGFR overexpression. In this sense, an in vivo study in a mouse model of TNBC showed that tumor breast cancer cells could be targeted by the antibody 213Bicetuximab [101]. A second preclinical study analyzed the role of the combination of the radiolabeled antibody 177Lu-antiEGFR monoclonal antibody, chemotherapy and poly (ADPribose) polymerase 1 (PARP) inhibition in xenograph models in mice. TNBC orthotopic and metastatic lesions in the mice were eradicated with this triple combination, and the response was associated with apoptosis and eradication of putative breast cancer stem cells [103]. In conclusion, radioimmunotherapy with anti-EGFR radiolabeled antibodies is a promising strategy in BRCAmutated breast cancer, but the preclinical observations still need to be confirmed in the clinic. 6.3


175

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7.

Potential development issues

Although the antibody cetuximab directed against EGFR has been successful in many cases, there is still great interest in the identification of biomarkers that predict response to this treatment. Another crucial point in treatment is to reverse the resistance. Cetuximab-resistant cells show activation of the PI3K/AKT/ mTOR pathways and deregulation of the non-receptor c-Src cytoplasmic TK. Src and PI3K, together with ER-a , form a complex involved in non-genomic, estrogen-induced cell proliferation [104]. Usually resistance is accompanied by an increase in Src kinase activity. The Src inhibition exerts effects mainly by preventing dormant cells from becoming metastatic cells. Use of the Src/Abl kinase inhibitor AZD0530 synergizes with the EGFR inhibitor gefitinib in suppressing the invasive phenotype, at least in vivo [105]. Given the importance of the PI3K/AKT pathway as a key regulator of cell proliferation, another promising approach is the combination with dual inhibitors of PI3K and mTOR, such as the compound BEZ2235. Further, it has been described that the combination of cetuximab and AKT inhibitors or Src inhibitors shows an antiproliferative synergistic effect in non-small-cell lung cancer [34]. Lapatinib treatment against EGFR and HER2 decreases the phosphorylation of the Src family and AKT. Accordingly, both pathways seem as relevant potential targets in cases of resistance. One of the major drawbacks in the development of successful EGFR therapies is the redundant pathways and the multiple crosstalks that lead to resistance. Consequently, it is necessary to attack multiple targets to achieve the maximal therapeutic effect and minimize resistance. The combination of therapies against the Src family or against the PI3K/ AKT/mTOR pathway with anti-EGFR drugs is the main strategy, and it is where research is focused. However, we should not forget to explore other possible combinations with the thought that they could be used as HER2, IGFR1, VEGFR TKIs and PARP inhibitors or Hsp90 and integrin antagonists. 8.

Conclusion

A great challenge still lies ahead in order to improve the synthesis of compounds, identify new targets and improve strategies that target the EGFR pathway. Among the obstacles faced by EGFR drugs in order to be effective are the redundancy of pathways and the crosstalk mechanisms, leading to resistance in many cases. Targeting several pathways simultaneously seems the strategy to elect, and future research is headed in this direction. 9.

Expert opinion

Based on the existing evidence, EGFR is still far from being a valuable target in breast cancer. Probably the reason for some 176

of these discouraging results is the absence of an appropriate selection of patients. In fact, it appears that EGFR-targeted therapy in breast cancer could repeat the story of lung cancer. Anti-EGFR TKI s failed to demonstrate benefits in survival in the early clinical trials of unselected populations. Only the identification of a subset of patients defined by EGFR-specific mutations has shown that EGFR has a role in the management of lung cancer. This could be the future of the antiEGFR in breast cancer, and future investigations should focus on the identification of a subset of patients that could benefit more from anti-EGFR therapy. Hypothetically, the basal-like breast cancer subtype has some characteristics that lead us to consider that EGFR inhibition could be an attractive alternative in this subtype. First, the important overexpression of EGFR in this subset which is expressed in up to 60% of patients suggests that EGFR could be a driver pathway in this subtype. Second, there is an unmet medical need in basal-like breast cancer. This subtype has a worse prognosis and there is a lack of an approved targeted therapy that is specifically targeted against these tumors. In this context, there is an increasing interest to develop new targeted compounds. However, it appears that basal-like subtype is not a sufficient predictive factor for response to anti-EGFR therapy. Thus, a valuable predictive biomarker of activity is a strong need in this context. This biomarker could explain, for instance, the promising results on PFS with cetuximab in the BALI-1 trial. KRAS mutations seem not to be a valuable biomarker for anti-EGFR activity as these mutations are extremely infrequent in breast cancer. Considering the relevant role recently identified for NRAS and BRAF mutations in colorectal cancer, it is easy to establish a potential parallel with breast cancer. However, all these mutations are extremely rare in breast cancer [106]. Similar conclusions are drawn by analyzing the role of EGFR mutations. EGFR genomic aberrations are a valuable biomarker for anti-EGFR therapy in lung cancer, but the presence of this factor in breast cancer is very infrequent ranging from 0 to approximately 11.4% in TNBC cells [8,106,107]. Another topic of potential interest is the presence of a high EGFR gene copy number. A recent study in a population of Asiatic patients with TNBC showed that a high EGFR gene copy number was as frequent as 33% mainly due to high polisomy [108]. All these studies suggest a potential for many different factors that could eventually be predictive of anti-EGFR therapy, but there is an increasing need to incorporate a prospective evaluation of these genomic alterations in the upcoming studies. Another focus that is gaining special interest is the PI3K/ AKT/mTOR pathway. Up to 17% of TNBC show PI3K mutations, with the pH1047R mutation being the most frequently identified in this subset. Nevertheless, other alterations related to this pathway, such as PTEN loss, could play a relevant role in selecting the most appropriate population to treat. In this context, the future trials, not only in anti-EGFR therapy, must use massive sequencing strategies in order to




explore a huge number of relevant mutations that may eventually be predictive. Only with the help of this technology will the upcoming investigations find a trace to follow in the search for predictive biomarkers. Apart from the identification of a biomarker, which is a key issue in the future development of anti-EGFR targeted therapy, the strategy of blocking different pathways or the same pathway at different points is a topic with special interest. The double blockage strategy follows the same rationale; there is a second pathway or messenger that allows the tumor cell to escape from the effect of the anti-EGFR agent. Two situations could explain this resistance: a crosstalk that allows the cell to survive despite the inhibition of the EGFR pathway by using an alternative pathway or a mutation or specific alteration in a distal point of the EGFR pathway that turns the cell resistance to any upstream inhibition of this pathway. In both cases, dual blockade is the best alternative to overcome this resistance. In this context, future trial design should establish a dual inhibition targeting EGFR and a second molecule presumably related to the PI3K/AKT/mTOR or RAS/RAF/ MEK pathways. Moreover, the combination of anti-EGFR and MEK inhibitors is other alternative to consider. Finally, considering the relationship of TNBC and the homologous recombination deficiency, it appears reasonable Bibliography Papers of special note have been highlighted as either of interest () or of considerable interest () to readers. 1.

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Affiliation

Ana Lluch†1,2 MD PhD, Pilar Eroles2 PhD & Jose-Alejandro Perez-Fidalgo1,2 MD PhD † Author for correspondence 1 Hospital Clinico Universitario, INCLIVA Biomedical Research Institute, Department of Oncology and Hematology, Valencia, Spain Tel: +0034 963987659; E-mail: [email protected] 2 INCLIVA Biomedical Research Institute, Valencia, Spain

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Emerging treatment for advanced lung cancer with EGFR mutation.

epidermal growth factor receptor (EGFR) complexes in breast cancer--culprits for resistance to EGFR inhibitors?

Current and Emerging Treatment Regimens for HER2-Positive Breast Cancer.

Emerging strategies for treating brain metastases from breast cancer.

Nanoparticulate carriers: an emerging tool for breast cancer therapy.

Emerging nanotherapeutic strategies in breast cancer.

Emerging modalities in breast cancer imaging.

Exosome: emerging biomarker in breast cancer.

Emerging immunotherapy strategies in breast cancer.

Emerging Roles of MicroRNAs in EGFR-Targeted Therapies for Lung Cancer.

HER2 Bidirectional Crosstalk in Breast Cancer.

EGFR and HER2 signaling in breast cancer brain metastasis.

NR4A1 Antagonists Inhibit β1-Integrin-Dependent Breast Cancer Cell Migration.

The paradoxical functions of EGFR during breast cancer progression.

Anti-EGFR monoclonal antibodies and EGFR tyrosine kinase inhibitors as combination therapy for triple-negative breast cancer.

Hallmarks of triple negative breast cancer emerging at last?

Emerging Estrogenic Pollutants in the Aquatic Environment and Breast Cancer.

Leptin and adiponectin: emerging therapeutic targets in breast cancer.

Neurofibromatosis type 1 and male breast cancer: emerging risk factor?

Current Approaches and Emerging Directions in HER2-resistant Breast Cancer.

Emerging targeted combinations in the management of breast cancer.

Psychosocial factors in adjuvant hormone therapy for breast cancer: an emerging context for adherence research.

Correction for Hedrick et al., "NR4A1 Antagonists Inhibit β1-Integrin-Dependent Breast Cancer Cell Migration".

EGFR Is Regulated by TFAP2C in Luminal Breast Cancer and Is a Target for Vandetanib.