Phase I/II study of sorafenib with anastrozole in patients with hormone receptor positive aromatase inhibitor resistant metastatic breast cancer. Breast Cancer Res Treat. 2011;125:137-143. [PMID: 20976541 DOI: 10.1007/s10549-010-1226-z]

Diverse roles of tumor-stromal PDGFB-to-PDGFRβ signaling in breast cancer growth and metastasis

Over the last couple of decades, it has become increasingly apparent that the tumor microenvironment (TME) mediates every step of cancer progression and solid tumors are only able to metastasize with a permissive TME. This intricate interaction of cancer cells with their surrounding TME, or stroma, is becoming more understood with an ever greater knowledge of tumor-stromal signaling pairs such as platelet-derived growth factors (PDGF) and their cognate receptors. We and others have focused our research efforts on understanding how tumor-derived PDGFB activates platelet-derived growth factor receptor beta (PDGFRβ) signaling specifically in the breast cancer TME. In this chapter, we broadly discuss PDGF and PDGFR expression patterns and signaling in normal physiology and breast cancer. We then detail the expansive roles played by the PDGFB-to-PDGFRβ signaling pathway in modulating breast tumor growth and metastasis with a focus on specific cellular populations within the TME, which are responsive to tumor-derived PDGFB. Given the increasingly appreciated importance of PDGFB-to-PDGFRβ signaling in breast cancer progression, specifically in promoting metastasis, we end by discussing how therapeutic targeting of PDGFB-to-PDGFRβ signaling holds great promise for improving current breast cancer treatment strategies.

Vascular Endothelial Growth Factor Receptors [VEGFR] as Target in Breast Cancer Treatment: Current Status in Preclinical and Clinical Studies and Future Directions

Breast cancer [BC] is one of the most common cancers among women, one of the leading causes of a considerable number of cancer-related death globally. Among all procedures leading to the formation of breast tumors, angiogenesis has an important role in cancer progression and outcomes. Therefore, various anti-angiogenic strategies have developed so far to enhance treatment's efficacy in different types of BC. Vascular endothelial growth factors [VEGFs] and their receptors are regarded as the most well-known regulators of neovascularization. VEGF binding to vascular endothelial growth factor receptors [VEGFRs] provides cell proliferation and vascular tissue formation by the subsequent tyrosine kinase pathway. VEGF/VEGFR axis displays an attractive target for anti-angiogenesis and anti-cancer drug design. This review aims to describe the existing literature regarding VEGFR inhibitors, focusing on BC treatment reported in the last two decades.

The genomic architecture of metastasis in breast cancer: focus on mechanistic aspects, signalling pathways and therapeutic strategies

Breast cancer is a multifactorial, heterogeneous disease and the second most frequent cancer amongst women worldwide. Metastasis is one of the most leading causes of death in these patients. Early-stage or locally advanced breast cancer is limited to the breast or nearby lymph nodes. When breast cancer spreads to farther tissues/organs from its original site, it is referred to as metastatic or stage IV breast cancer. Normal breast development is regulated by specific genes and signalling pathways controlling cell proliferation, cell death, cell differentiation and cell motility. Dysregulation of genes involved in various signalling pathways not only leads to the formation of primary tumour but also to the metastasis as well. The metastatic cascade is represented by a multi-step process including invasion of the local tumour cell followed by its entry into the vasculature, exit of malignant cells from the circulation and ultimately their colonization at the distant sites. These stages are referred to as formation of primary tumour, angiogenesis, invasion, intravasation and extravasation, respectively. The major sites of metastasis of breast cancer are the lymph nodes, bone, brain and lung. Only about 28% five-year survival rate has been reported for stage IV breast cancer. Metastasis is a serious concern for breast cancer and therefore, various therapeutic strategies such as tyrosine kinase inhibitors have been developed to target specific dysregulated genes and various signalling pathways involved in different steps of metastasis. In addition, other therapies like hyperbaric oxygen therapy, RNA interference and CRISPR/Cas9 are also being explored as novel strategies to cure the stage IV/metastatic breast cancer. Therefore, the current review has been compiled with an aim to evaluate the genetic basis of stage IV breast cancer with a focus on the molecular mechanisms. In addition, the therapeutic strategies targeting these dysregulated genes involved in various signalling pathways have also been discussed. Genome editing technologies that can target specific genes in the affected areas by making knock-in and knock-out alternations and thereby bring significant treatment outcomes in breast cancer have also been summarized.

Angiogenesis in Breast Cancer Progression, Diagnosis, and Treatment

Angiogenesis is a significant event in a wide range of healthy and diseased conditions. This process frequently involves vasodilation and an increase in vascular permeability. Numerous players referred to as angiogenic factors, work in tandem to facilitate the outgrowth of endothelial cells (EC) and the consequent vascularity. Conversely, angiogenic factors could also feature in pathological conditions. Angiogenesis is a critical factor in the development of tumors and metastases in numerous cancers. An increased level of angiogenesis is associated with decreased survival in breast cancer patients. Therefore, a good understanding of the angiogenic mechanism holds a promise of providing effective treatments for breast cancer progression, thereby enhancing patients' survival. Disrupting the initiation and progression of this process by targeting angiogenic factors such as vascular endothelial growth factor (Vegf)-one of the most potent member of the VEGF family- or by targeting transcription factors, such as Hypoxia-Inducible Factors (HIFs) that act as angiogenic regulators, have been considered potential treatment options for several types of cancers. The objective of this review is to highlight the mechanism of angiogenesis in diseases, specifically its role in the progression of malignancy in breast cancer, as well as to highlight the undergoing research in the development of angiogenesis-targeting therapies.

Investigation of the Prognostic Significance of Vasculogenic Mimicry and Its Inhibition by Sorafenib in Canine Mammary Gland Tumors

Canine mammary gland tumor (CMT) is one of the most important tumors in intact female dogs, and due its similarity to human breast cancer (BC), it is considered a model in comparative oncology. A subset of mammary gland tumors can show aggressive behavior, and a recurrent histological finding is the presence of vasculogenic mimicry (VM). VM is a process in which highly aggressive cancer cells fuse, forming fluid-conducting channels without endothelial cells. Although, VM has been described in canine inflammatory carcinoma, no previous studies have investigated the prognostic and predictive significance of VM in CMT. Thus, this research aimed to investigate the prognostic significance of VM in vivo and the capacity of sorafenib to inhibit VM in vitro. VM was identified in situ in formalin-fixed paraffin-embedded CMT samples (n = 248) using CD31/PAS double staining. VM was identified in 33% of tumors (82/248). The presence of VM was more strongly related to tumor grade than to histological subtype. Patients with positive VM experienced shorter survival times than dogs without VM (P < 0.0001). Due to the importance of the VEGF-A/VEGFR-2 autocrine feed-forward loop in epithelial tumors, we investigated the association between VEGF-A and VEGFR-2 expression by neoplastic tumor cells and the associations of VEGF-A or VEGFR-2 expression with VM. Among the VM-positive samples, all (n = 82) showed high scores (3 or 4) for VEGF-A and VEGFR-2, indicating that VM was a common finding in tumors overexpressing VEGF-A and VEGFR-2. Thus, we cultured two CMT primary cell lines with VM abilities (CM9 and CM60) in vitro and evaluated the anti-tumoral effect of sorafenib. The CM9 cell line showed a half maximal inhibitory concentration (IC50) of 2.61 μM, and the CM60 cell line showed an IC50 of 1.34 μM. We performed a VM assay in vitro and treated each cell line with an IC50 dose of sorafenib, which was able to inhibit VM in vitro. Overall, our results indicated that VM was a prognostic factor for dogs bearing CMT and that sorafenib had an inhibitory effect on VM in CMT cancer cells in vitro.

Expression of RET is associated with Oestrogen receptor expression but lacks prognostic significance in breast cancer

BACKGROUND

The Rearranged during Transfection (RET) protein is overexpressed in a subset of Estrogen Receptor (ER) positive breast cancer, with both signalling pathways functionally interacting. This cross-talk plays a pivotal role in the resistance of breast cancer cells to anti-endocrine therapies, and RET expression is assumed to correlate with poor prognosis based on findings in small patient cohorts. The aim of our study was to investigate the impact of RET expression on patient outcome in human breast cancer.

METHODS

We performed an immunohistochemical analysis of RET protein expression on a tissue microarray encompassing 990 breast cancer patients and correlated its expression with clinicopathological parameters and survival data.

RESULTS

Expression of RET was detected in 409 out of 990 cases (41.3%). RET and ER expression significantly correlated (p < 0.0001). The Luminal B HER2-positive subtype showed the highest expression rate (48.9%). In univariate and multivariate survival analyses, RET expression had no impact on overall survival.

CONCLUSION

We confirmed the co-expression of RET and ER, but we did not find RET expression to be an independent prognostic factor in human breast cancer. Clinical trials with newly developed RET inhibitors are needed to evaluate if RET inhibition has a beneficial impact on patient survival in ER positive breast cancer.

Sorafenib for the treatment of breast cancer

INTRODUCTION

Breast cancer treatment includes many options depending on the tumor clinicopathological profile, which groups breast cancer into various subtypes. Bevacizumab is currently the only drug capable of targeting angiogenesis in breast cancer. Sorafenib has also been studied in combination with other agents. Areas covered: Pharmacological aspects of sorafenib, including results from preclinical studies on breast cancer cells; findings about clinical efficacy and safety in both single-arm and randomized clinical trials; ongoing trials. Expert opinion: Since sorafenib as a single agent has shown limited efficacy in breast cancer, its combination with other drugs is under investigation. Dose reduction is the main challenge when sorafenib is combined with chemotherapy or endocrine therapy. Although randomized phase-II trials on sorafenib plus chemotherapy versus chemotherapy alone have shown potential benefits in progression-free survival, preliminary results from a phase-III study in combination with capecitabine are negative. The definitive results of this trial and results from other ongoing phase-II trials will determine further developments of sorafenib in breast cancer. Although these additional data could help determine the most appropriate dose, drug combination and patient settings, a confirmation of the preliminary negative results reported in the phase-III trial are likely to discourage further use of sorafenib in breast cancer, given its non-negligible toxicity, lack of predicting markers, and the number of more promising drugs for breast cancer.

Inefficiencies and Patient Burdens in the Development of the Targeted Cancer Drug Sorafenib: A Systematic Review

Failure in cancer drug development exacts heavy burdens on patients and research systems. To investigate inefficiencies and burdens in targeted drug development in cancer, we conducted a systematic review of all prelicensure trials for the anticancer drug, sorafenib (Bayer/Onyx Pharmaceuticals). We searched Embase and MEDLINE databases on October 14, 2014, for prelicensure clinical trials testing sorafenib against cancers. We measured risk by serious adverse event rates, benefit by objective response rates and survival, and trial success by prespecified primary endpoint attainment with acceptable toxicity. The first two clinically useful applications of sorafenib were discovered in the first 2 efficacy trials, after five drug-related deaths (4.6% of 108 total) and 93 total patient-years of involvement (2.4% of 3,928 total). Thereafter, sorafenib was tested in 26 indications and 67 drug combinations, leading to one additional licensure. Drug developers tested 5 indications in over 5 trials each, comprising 56 drug-related deaths (51.8% of 108 total) and 1,155 patient-years (29.4% of 3,928 total) of burden in unsuccessful attempts to discover utility against these malignancies. Overall, 32 Phase II trials (26% of Phase II activity) were duplicative, lacked appropriate follow-up, or were uninformative because of accrual failure, constituting 1,773 patients (15.6% of 11,355 total) participating in prelicensure sorafenib trials. The clinical utility of sorafenib was established early in development, with low burden on patients and resources. However, these early successes were followed by rapid and exhaustive testing against various malignancies and combination regimens, leading to excess patient burden. Our evaluation of sorafenib development suggests many opportunities for reducing costs and unnecessary patient burden in cancer drug development.

Sorafenib in breast cancer treatment: A systematic review and overview of clinical trials

AIM: To evaluate the current role of sorafenib, an oral multikinase inhibitor in the treatment of breast cancer.

METHODS: An extensive search of the literature until March 2016 was carried out in Medline and clinicaltrials.gov, by using the search terms “sorafenib” and “breast cancer”. Papers found were checked for further relevant publications. Overall, 21 relevant studies were found, 18 in advanced breast cancer (16 in stage IV and two in stages III-IV) and three in early breast cancer.

RESULTS: Among studies in advanced breast cancer, there were two trials with sorafenib as monotherapy, four trials of sorafenib in combination with taxanes, two in combination with capecitabine, one with gemcitabine and/or capecitabine, one with vinorelbine, one with bevacizumab, one with pemetrexed and one with ixabepilone, three trials of sorafenib in combination with endocrine therapy and two trials in women with brain metastases undergoing whole brain radiotherapy. In addition, there was one trial of sorafenib added to standard chemotherapy in the adjuvant setting, and two trials in the neoadjuvant setting. In general, sorafenib was well tolerated in breast cancer patients, though its dosage had to be adjusted in some trials, and discontinuation rates were high, particularly for the combination of sorafenib with anastrozole. Sorafenib monotherapy and combinations with taxanes, bevacizumab and ixabepilone showed inadequate efficacy, while efficacy results from combinations with gemcitabine and/or capecitabine and possibly tamoxifen were more promising.

CONCLUSION: At present, sorafenib should not be used for the treatment of breast cancer outside of clinical trials and more clinical data are needed in order to support its standard use in breast cancer therapy.

Novel antiangiogenic drugs for the management of breast cancer: new approaches for an old issue?

Since angiogenesis plays an important role in cancer growth, infiltration and metastasis, many agents targeting this pathway have been developed over the last decade. Antiangiogenic drugs interfere with this process and may inhibit neoplastic growth or induce tumor dormancy by blocking the expanding network of newly formed capillaries. Despite the initial promise, targeting angiogenesis in breast cancer has not reached major breakthroughs. Nevertheless, the immunologic role of VEGF deserves to be further explored. We aim to describe the biological mechanisms which underlie the role of angiogenesis in breast cancer carcinogenesis, to depict its contribution to the metastatic process and to review the most important clinical trials testing angiogenic inhibitors in breast cancer, including monoclonal antibodies and novel small molecules.

Combination of letrozole, metronomic cyclophosphamide and sorafenib is well-tolerated and shows activity in patients with primary breast cancer

PURPOSE

To assess whether the combination of letrozole, metronomic cyclophosphamide and sorafenib (LCS) is well tolerated and shows activity in primary breast cancer (BC).

METHODS

Thirteen oestrogen receptor-positive, postmenopausal, T2-4, N0-1 BC patients received the LCS combination for 6 months. In these patients we examined the pharmacokinetics of sorafenib and cyclophosphamide, toxicity of the regimen, the clinical response to therapy and changes in the levels of biologically relevant biomarkers.

RESULTS

Adequate plasma concentrations of sorafenib were achieved in patients when it was dosed in combination with L+C. The mean plasma concentrations of C were consistently lower following administration of LCS, compared with administration of L+C only. The most common drug-related grade 3/4 adverse events were skin rash (69.3%), hand-foot skin reaction (69.3%) and diarrhoea (46.1%). According to RECIST Criteria, a clinical complete response was observed in 6 of 13 patients. A significant reduction in tumour size, evaluated with MRI, was also observed between baseline and 14 days of treatment in all 13 patients (P=0.005). A significant reduction in SUV uptake, measured by (18)FDG-PET/CT, was observed in all patients between baseline and 30 days of treatment (P=0.015) and between baseline and definitive surgery (P=0.0002). Using modified CT Criteria, a response was demonstrated in 8 out of 10 evaluable patients at 30 days and in 11 out of 13 evaluable patients at the definitive surgery. A significant reduction in Ki67 expression was observed in all patients at day 14 compared with baseline (P<0.00001) and in 9 out of 13 patients at the definitive surgery compared with baseline (P<0.03). There was also a significant suppression of CD31 and VEGF-A expression in response to treatment (P=0.01 and P=0.007, respectively).

CONCLUSIONS

The LCS combination is feasible and tolerable. The tumour response and target biomarker modulation indicate that the combination is clinically and biologically active.

Impact of adding the multikinase inhibitor sorafenib to endocrine therapy in metastatic estrogen receptor-positive breast cancer

BACKGROUND

Targeting growth factor and survival pathways may delay endocrine-resistance in estrogen receptor-positive breast cancer.

MATERIALS & METHODS

A pilot Phase II study adding sorafenib to endocrine therapy in 11 patients with metastatic estrogen receptor-positive breast cancer was conducted. Primary end point was response by RECIST after 3 months of sorafenib. Secondary end points included safety, time to progression and biomarker modulation. The study closed early owing to slow accrual.

RESULTS

Eight out of 11 patients had progressive disease on study entry and three had stable disease. Of the ten evaluable patients, seven experienced stable disease (70%) and three experienced progressive diseas (30%), with a median time to progression of 6.1 months (8.4 months in the seven patients on tamoxifen). The serum samples demonstrated a significant reduction in VEGF receptor 2 and PDGF receptor-α. Microarray analysis identified 32 suppressed genes, no induced genes and 29 enriched Kyoto Encyclopedia of Genes and Genomes pathways.

CONCLUSION

The strategy of adding a targeted agent to endocrine therapy upon resistance may be worthwhile testing in larger studies.

Sorafenib-based therapy in HER2-negative advanced breast cancer: Results from a retrospective pooled analysis of randomized controlled trials

A standard systemic therapy for patients with human epidermal growth factor receptor 2 (HER2)-negative advanced breast cancer (ABC) is yet to be identified. Sorafenib has been developed for the treatment of solid tumors, including breast cancer, as an oral multikinase inhibitor with antiangiogenic and antiproliferative activity. The aim of the present study was to assess the efficacy and safety of sorafenib in patients with HER2-negative ABC by performing a meta-analysis. A literature search was applied to databases, including PubMed, EMBASE, the Cochrane Library Databases, American Society of Clinical Oncology and the European Society for Medical Oncology, with the search terms ‘advanced breast cancer’ and ‘sorafenib’ and relevant studies were selected for analysis. The data extracted from the selected studies included progression-free survival (PFS), time to progression (TTP), overall survival (OS) and overall response rate (ORR). Major adverse events (AEs) were also analyzed. A total of four randomized controlled trials containing 844 cases were identified. Combined results revealed that when compared with chemotherapy (or with anti-hormone receptor therapy) alone, sorafenib-based therapy significantly increased the PFS [hazard ratio (HR), 0.78; 95% confidence interval (CI), 0.54–1.02] and TTP (HR, 0.74; 95% CI, 0.50–0.97), but not the OS (HR, 0.95; 95% CI, 0.75–1.15) and ORR (relative risk, 1.19; 95% CI, 1.01–1.39). In addition, the incidence of grade 3/4 AEs, including hand-foot skin syndrome, anemia, fatigue, rash and stomatitis, were significantly increased in patients that received sorafenib-based therapy. Therefore, the results from the current meta-analysis indicated that sorafenib-based therapy improved the PFS and TTP in patients with HER2-negative ABC, but not the OS and ORR. In addition, combination treatment was associated with increased toxicities and frequently required dose reductions.

Sorafenib: targeting multiple tyrosine kinases in cancer

Sorafenib (BAY 43-9006, Nexavar®) is an oral multiple tyrosine kinase inhibitor. Main targets are receptor tyrosine kinase pathways frequently deregulated in cancer such as the Raf-Ras pathway, vascular endothelial growth factor (VEGF) pathway, and FMS-like tyrosine kinase 3 (FLT3). Sorafenib was approved by the FDA in fast track for advanced renal cell cancer and hepatocellular cancer and shows good clinical activity in thyroid cancer. Multiple clinical trials are undertaken to further investigate the role of sorafenib alone or in combination for the treatment of various tumor entities.

Effects of sorafenib on energy metabolism in breast cancer cells: role of AMPK-mTORC1 signaling

In this study, we investigated the effects and the underlying molecular mechanisms of the multi-kinase inhibitor sorafenib in a panel of breast cancer cell lines. Sorafenib inhibited cell proliferation and induced apoptosis through the mitochondrial pathway. These effects were neither correlated with modulation of MAPK and AKT pathways nor dependent on the ERα status. Sorafenib promoted an early perturbation of mitochondrial function, inducing a deep depolarization of mitochondrial membrane, associated with drop of intracellular ATP levels and increase of ROS generation. As a response to this stress condition, the energy sensor AMPK was rapidly activated in all the cell lines analyzed. In MCF-7 and SKBR3 cells, AMPK enhanced glucose uptake by up-regulating the expression of GLUT-1 glucose transporter, as also demonstrated by AMPKα1 RNA interference, and stimulated aerobic glycolysis thus increasing lactate production. Moreover, the GLUT-1 inhibitor fasentin blocked sorafenib-induced glucose uptake and potentiated its cytotoxic activity in SKBR3 cells. Persistent activation of AMPK by sorafenib finally led to the impairment of glucose metabolism both in MCF-7 and SKBR3 cells as well as in the highly glycolytic MDA-MB-231 cells, resulting in cell death. This previously unrecognized long-term effect of sorafenib was mediated by AMPK-dependent inhibition of the mTORC1 pathway. Suppression of mTORC1 activity was sufficient for sorafenib to hinder glucose utilization in breast cancer cells, as demonstrated by the observation that the mTORC1 inhibitor rapamycin induced a comparable down-regulation of GLUT-1 expression and glucose uptake. The key role of AMPK-dependent inhibition of mTORC1 in sorafenib mechanisms of action was confirmed by AMPKα1 silencing, which restored mTORC1 activity conferring a significant protection from cell death. This study provides insights into the molecular mechanisms driving sorafenib anti-tumoral activity in breast cancer, and supports the need for going on with clinical trials aimed at proving the efficacy of sorafenib for breast cancer treatment.

Anti-proliferative actions of N'-desmethylsorafenib in human breast cancer cells

The multi-kinase inhibitor sorafenib is used for the treatment of renal and hepatic carcinomas and is undergoing evaluation for treatment of breast cancer in combination with other agents. Cytochrome P450 (CYP) 3A4 converts sorafenib to multiple metabolites that have been detected in patient plasma. However, recent clinical findings suggest that combination therapy may elicit inhibitory pharmacokinetic interactions involving sorafenib that increase toxicity. While sorafenib N-oxide is an active metabolite, information on the anti-tumor actions of other metabolites is unavailable. The present study evaluated the actions of sorafenib and its five major metabolites in human breast cancer cell lines. All agents, with the exception of N'-hydroxymethylsorafenib N-oxide, decreased ATP formation in four breast cancer cell lines (MDA-MB-231, MDA-MB-468, MCF-7 and T-47D). Prolonged treatment of MDA-MB-231 cells with N'-desmethylsorafenib, N'-desmethylsorafenib N-oxide and sorafenib (10 μM, 72 h) produced small increases in caspase-3 activity to 128-139% of control. Sorafenib and its metabolites, again with the exception of N'-hydroxymethylsorafenib N-oxide, impaired MEK/ERK signaling in MDA-MB-231 cells and modulated the expression of cyclin D1 and myeloid cell leukemia sequence-1, which regulate cell viability. When coadministered with doxorubicin (0.5 or 1 μM), sorafenib and N'-desmethylsorafenib (25 μM) produced greater effects on ATP production than either treatment alone. Thus, it emerges that, by targeting the MEK/ERK pathway, multiple sorafenib metabolites may contribute to the actions of sorafenib in breast cancer. Because N'-desmethylsorafenib is not extensively metabolized and does not inhibit major hepatic CYPs, this metabolite may have a lower propensity to precipitate pharmacokinetic drug interactions than sorafenib.

Targeted therapies of metastatic breast cancer: relationships with cancer stem cells

In the last years, many targeted agents have been developed for metastatic breast cancer (MBC) treatment and are being tested in clinical trials. In spite of this, apart from epidermal growth factor receptor 2 (HER2) positive subset, no significant increase in the median overall survival (OS) has been reported. Similarly to conventional chemo- and radiotherapy, the cancer stem cell theory has been evoked to explain the frustrating results often obtained with this emerging category of drugs. This review examines the results in MBC of the approved targeted therapies or those currently under evaluation in experimental studies or in clinical trials, in the light of their relationships with breast CSCs and of the efforts to circumvent the development of resistance. In the next, there is the principal need to investigate if the effects on CSCs may be used to overcome cancer resistance and it will be opportune to consider whether molecular targeted therapies should be used alone or combined with conventional therapy, or with a different target drug specific for CSCs.

Current status and future perspectives in the endocrine treatment of postmenopausal, hormone receptor-positive metastatic breast cancer

INTRODUCTION

Endocrine therapy is a fundamental component of the therapeutic repertoire for treatment of metastatic, hormone receptor-positive breast cancer. Inevitably, however, tumors develop resistance to these compounds, and overcoming this phenomenon is a key motivator of research in this field.

AREAS COVERED

This review summarizes the current status of endocrine therapy for the treatment of metastatic disease, with a main focus on postmenopausal patients. Furthermore, strategies that could potentially sustain endocrine resistance and future perspectives in this direction are also to be described. Relevant references were identified by PubMed searches and from the abstract books of the annual meetings of The European Society of Clinical Oncology (ESMO), The American Society of Clinical Oncology (ASCO) and from the San Antonio Breast Cancer Symposia.

EXPERT OPINION

Combinations of endocrine therapy with HER2 targeting agents, as well as with compounds that can interfere with PI3K/Akt/mTOR signaling, are two promising strategies for delaying or overcoming endocrine resistance, mediated by these relevant biological pathways. Due to increased costs and the burden of toxicity associated with these combination therapies, compared to endocrine therapy alone, it is imperative to concentrate efforts on establishing biomarkers that can predict efficacy.

Validation of the Cancer BioChip System as a 3D siRNA screening tool for breast cancer targets

Genomic studies have revealed that breast cancer consists of a complex biological process with patient-specific genetic variations, revealing the need for individualized cancer diagnostic testing and selection of patient-specific optimal therapies. One of the bottlenecks in translation of genomic breakthroughs to the clinic is the lack of functional genomic assays that have high clinical translatability. Anchorage-independent three-dimensional (3D) growth assays are considered to be the gold-standard for chemosensitivity testing, and leads identified with these assays have high probability of clinical success. The Cancer BioChip System (CBCS) allows for the simultaneous, quantitative, and real time evaluation of multitudes of anchorage-independent breast cancer cell growth inhibitors. We employed a Test Cancer BioChip that contains silencing RNAs (siRNAs) targeting cancer-related genes to identify 3D-specific effectors of breast cancer cell growth. We compared the effect of these siRNAs on colony growth of the hormone receptor positive (MCF7) and Human Epidermal Growth Factor Receptor 2/c- Erythroblastic Leukemia Viral Oncogene Homolog 2 (HER2/c-erb-b2) positive (SK-BR-3) cells on the Test Cancer BioChip. Our results confirmed cell-specific inhibition of MCF7 and SK-BR-3 colony formation by estrogen receptor α (ESR1) and (ERBB2) siRNA, respectively. Both cell lines were also suppressed by Phosphoinositide-3-kinase Catalytic, alpha Polypeptide (PIK3CA) siRNA. Interestingly, we have observed responses to siRNA that are unique to this 3D setting. For example, ß-actin (ACTB) siRNA suppressed colony growth in both cell types while Cathepsin L2 (CTSL2) siRNA caused opposite effects. These results further validate the importance of the CBCS as a tool for the identification of clinically relevant breast cancer targets.

Targeting angiogenesis in metastatic breast cancer

Angiogenesis has become an important target in the treatment of several solid tumors, including breast cancer. As monotherapy, antiangiogenic agents have demonstrated limited activity in metastatic breast cancer (MBC); therefore, they have generally been developed for use in combination with chemotherapies. Thus far, the experience with antiangiogenic agents for MBC has been mixed. The results from one study assessing addition of the monoclonal antibody bevacizumab to paclitaxel led to approval of bevacizumab for MBC. However, the modest improvement of progression-free survival rates in subsequent MBC studies has led to reappraisal of bevacizumab. Phase III studies have not produced evidence supporting use of the multikinase inhibitor sunitinib alone or in combination with MBC chemotherapy. Experience with sorafenib in a phase IIb program indicates potential when used in select combinations, particularly with capecitabine; however, phase III confirmatory data are needed. Although antiangiogenic therapies combined with chemotherapy have increased progression-free survival rates for patients with MBC, increases in overall survival times have not been observed. Some studies have tried to combine antiangiogenic agents such as bevacizumab and sunitinib or sorafenib, but that approach has been limited because of toxicity concerns. Sequential use of antiangiogenic agents with differing mechanisms of action may be an effective approach. Despite setbacks, angiogenesis will likely remain an important target of treatment for selected patients with MBC.

Pharmacological strategies to overcome HER2 cross-talk and Trastuzumab resistance

Approximately 20-30% of breast cancers show increased expression of the HER2 receptor tyrosine kinase. Trastuzumab (Herceptin) is a clinically approved anti-HER2 monoclonal antibody. Many patients with HER2-overexpressing metastatic breast cancer respond to trastuzumab; however, a subset display primary drug resistance. In addition, many patients who initially respond to trastuzumab ultimately develop disease progression. Multiple molecular mechanisms contributing to trastuzumab resistance have been proposed in the literature. These mechanisms include cross-signaling from related HER/erbB receptors and compensatory signaling from receptors outside of the HER/erbB family, including receptors for insulin-like growth factor-I, vascular endothelial growth factor, and transforming growth factor beta. The major downstream signaling pathway activated by HER2 cross-talk is PI3K/mTOR, and a potential integrator of receptor cross-talk is Src-focal adhesion kinase (FAK) signaling. PI3K, Src, and FAK have independently been implicated in trastuzumab resistance. In this review, we will discuss pharmacological inhibition of HER2 cross-talk as a strategy to treat trastuzumab-refractory HER2-overexpresssing breast cancer.

Sorafenib in locally advanced or metastatic breast cancer

INTRODUCTION

Sorafenib is an oral multikinase inhibitor with anti-angiogenic and anti-proliferative activity that is indicated for use in hepatocellular and renal cell carcinomas. Sorafenib is being developed in a number of solid tumors, including breast cancer (BC).

AREAS COVERED

A series of four randomized, double-blind, placebo-controlled Phase IIb screening Trials were developed to Investigate the Efficacy of Sorafenib (TIES) when added to select chemotherapies for patients with HER2-negative advanced BC with a primary endpoint of progression-free survival (PFS). Results have been varied. SOLTI-0701 reported significant PFS benefit for sorafenib plus capecitabine as first- or second-line treatment, and AC01B07 reported a modest but significant PFS benefit when sorafenib was combined with gemcitabine or capecitabine for patients whose disease had progressed during or after bevacizumab. Sorafenib plus first-line paclitaxel did not significantly improve PFS (NU07B1 study), nor did its addition to first-line docetaxel and/or letrozole (FM-B07-01 study). A Phase III trial of sorafenib plus capecitabine has been initiated.

EXPERT OPINION

Phase IIb data indicate a potential role for sorafenib in combination with select chemotherapies for HER2-negative advanced BC, but Phase III confirmatory trials are necessary. The variability in results across studies with sorafenib may be related to the chemotherapy combination and/or patient population.

Novel targets for VEGF-independent anti-angiogenic drugs

INTRODUCTION

In the last decades, the active research in the field of tumor angiogenesis led to the development of a class of agents providing an effective inhibition of neovessels formation through the blockade of VEGF-related pathways. More recently, the identification of several non-VEGF factors such as PDGF, FGF, HGF, angiopoietins, ALK1/endoglin, endothelis and ephrins involved in tumor angiogenesis have emphasized the need to develop agents targeting multiple pro-angiogenic pathways.

AREAS COVERED

This review aimed at summarizing the role of non-VEGF molecular pathways in targeting tumor angiogenesis. Preclinical and clinical data for investigational agents against non-VEGF targets have been reviewed emphasizing the role of combined inhibition strategies.

EXPERT OPINION

Besides the successful development of drugs providing a specific VEGF blockade, novel agents targeting alternative angiogenesis-related pathways are being tested. Although it seems that the potential clinical usefulness of these novel compounds have been not yet fully investigated, sunitinib, sorafenib, pazopanib and other multikinase inhibitors have certainly displayed encouraging results. A more in-depth clarification of anti-angiogenic agents is still needed, in order to design the best clinical setting and schedule for target-based agents and possibly anticipate potential tools to overcome the emerging issue of anti-angiogenic drug resistance.

Emerging drugs in metastatic breast cancer: an update

INTRODUCTION

The incidence of breast cancer at an advanced stage has decreased in the modern world due to screening programs and usage of novel chemotherapy agents at an adjuvant setting. Recurrence is the major problem seen in > 50% of breast cancer patients diagnosed at an early stage. Developing new drugs for metastatic breast cancer is a huge and challenging research area.

AREAS COVERED

Emerging drugs showed positive results in clinical studies and agents in routine clinical usage are updated. Current treatment strategies as a combination of biologic agents and overcoming drug resistance are discussed. Literature search is made from PubMed, ASCO and San Antonio Breast Cancer Symposium Meeting abstracts.

EXPERT OPINION

A number of drugs caused survival benefit for advanced breast cancer. Hundreds of new studies with tens of agents are conducted for treatment of metastatic breast cancer. Tumor resistance and treatment related toxicities are unavoidable which are two main search areas for improving metastatic breast cancer management. Understanding the pathways of genesis and progression yielded many targets for treatment. However, cure in metastatic breast cancer is still a far aim and new agents and treatment strategies are needed.

Clinical presentation and management of hand-foot skin reaction associated with sorafenib in combination with cytotoxic chemotherapy: experience in breast cancer

Current combination therapies for advanced breast cancer provide a modest survival benefit but with greater toxicity than with monotherapies. New combinations are needed that improve the efficacy of current treatments and have acceptable tolerability profiles. Recent clinical trials have assessed the efficacy and safety of the multikinase inhibitor sorafenib in combination with common treatments for advanced breast cancer. Sorafenib has both antiangiogenic and antiproliferative activities and is indicated for patients with unresectable hepatocellular and advanced renal cell carcinoma. Generally, sorafenib is associated with manageable, non-life-threatening adverse events. One of the more common adverse events seen with sorafenib is hand-foot skin reaction, a dermatologic toxicity usually localized to the pressure points of the palms and soles. Although hand-foot skin reaction is reversible and not life threatening, it can have a significant impact on a patient's quality of life and may necessitate dose modification. Moreover, sorafenib is being evaluated in combination with breast cancer treatments that are associated with a similar dermatologic toxicity (e.g., capecitabine-induced hand-foot syndrome). This review looks at the use of sorafenib in combination with selected chemotherapies in patients with advanced breast cancer and considers the incidence, prevention, and management of hand-foot skin reaction.

RET in breast cancer: functional and therapeutic implications

Recent studies demonstrate that the receptor tyrosine kinase RET is overexpressed in a subset of ER-positive breast cancers and that crosstalk between RET and ER is important in responses to endocrine therapy. The development of small molecular inhibitors that target RET allows the opportunity to consider combination therapies as a strategy to improve response to treatment and to prevent and combat endocrine resistance. This review discusses: (i) the current knowledge about RET, its co-receptors and ligands in breast cancer; (ii) the breast cancer clinical trials involving agents that target RET; and (iii) the challenges that remain in terms of specificity of available inhibitors and in understanding the complex molecular mechanisms that underlie the resistance to endocrine therapy.