Activated c-SRC in ductal carcinoma in situ correlates with high tumour grade, high proliferation and HER2 positivity

Tyrosine phosphorylation-mediated YAP1-TFAP2A interactions coordinate transcription and trastuzumab resistance in HER2+ breast cancer

Trastuzumab resistance in HER2+ breast cancer (BC) is the major reason leading to poor prognosis of BC patients. Oncogenic gene overexpression or aberrant activation of tyrosine kinase SRC is identified to be the key modulator of trastuzumab response. However, the detailed regulatory mechanisms underlying SRC activation-associated trastuzumab resistance remain poorly understood. In the present study, we discover that SRC-mediated YAP1 tyrosine phosphorylation facilitates its interaction with transcription factor AP-2 alpha (activating enhancer binding protein 2 alpha, TFAP2A), which in turn promotes YAP1/TEAD-TFAP2A (YTT) complex-associated transcriptional outputs, thereby conferring trastuzumab resistance in HER2+ BC. Inhibition of SRC kinase activity or disruption of YTT complex sensitizes cells to trastuzumab treatment in vitro and in vivo. Additionally, we also identify YTT complex co-occupies the regulatory regions of a series of genes related to trastuzumab resistance and directly regulates their transcriptions, including EGFR, HER2, H19 and CTGF. Moreover, YTT-mediated transcriptional regulation is coordinated by SRC kinase activity. Taken together, our study reveals that SRC-mediated YTT complex formation and transcriptions are responsible for multiple mechanisms associated with trastuzumab resistance. Therefore, targeting HER2 signaling in combination with the inhibition of YTT-associated transcriptional outputs could serve as the treatment strategy to overcome trastuzumab resistance caused by SRC activation.

Short-Term Biomarker Modulation Study of Dasatinib for Estrogen Receptor-Negative Breast Cancer Chemoprevention

Objective

Risk-reducing therapy with selective estrogen receptor (ER) modulators and aromatase inhibitors reduce breast cancer risk. However, the effects are limited to ER-positive breast cancer. Therefore, new agents with improved toxicity profiles that reduce the risk in ER-negative breast cancers are urgently needed. The aim of this prospective, short-term, prevention study was to evaluate the effect of dasatinib, an inhibitor of the tyrosine kinase Src, on biomarkers in normal (but increased risk) breast tissue and serum of women at high risk for a second, contralateral primary breast cancer.

Materials and Methods

Women with a history of unilateral stage I, II, or III ER-negative breast cancer, having no active disease, and who completed all adjuvant therapies were eligible. Patients underwent baseline fine-needle aspiration (FNA) of the contralateral breast and serum collection for biomarker analysis and were randomized to receive either no treatment (control) or dasatinib at 40 or 80 mg/day for three months. After three months, serum collection and breast FNA were repeated. Planned biomarker analysis consisted of changes in cytology and Ki-67 on breast FNA, and changes in serum levels of insulin-like growth factor 1 (IGF-1), IGF-binding protein 1, and IGF-binding protein 3. The primary objective was to evaluate changes in Ki-67 and secondary objective included changes in cytology in breast tissue and IGF-related serum biomarkers. Toxicity was also evaluated.

Results

Twenty-three patients started their assigned treatments. Compliance during the study was high, with 86.9% (20/23) of patients completing their assigned doses. Dasatinib was well tolerated and no drug-related grade 3 and 4 adverse events were observed. Since only one patient met the adequacy criteria for the paired FNA sample, we could not evaluate Ki-67 level or cytological changes. No significant change in serum biomarkers was observed among the three groups.

Conclusion

Dasatinib was well tolerated but did not induce any significant changes in serum biomarkers. The study could not fulfill its primary objective due to an inadequate number of paired FNA samples. Further, larger studies are needed to evaluate the effectiveness of Src inhibitors in breast cancer prevention.

SRC kinase-mediated signaling pathways and targeted therapies in breast cancer

Breast cancer (BC) has been ranked the most common malignant tumor throughout the world and is also a leading cause of cancer-related deaths among women. SRC family kinases (SFKs) belong to the non-receptor tyrosine kinase (nRTK) family, which has eleven members sharing similar structure and function. Among them, SRC is the first identified proto-oncogene in mammalian cells. Oncogenic overexpression or activation of SRC has been revealed to play essential roles in multiple events of BC progression, including tumor initiation, growth, metastasis, drug resistance and stemness regulations. In this review, we will first give an overview of SRC kinase and SRC-relevant functions in various subtypes of BC and then systematically summarize SRC-mediated signaling transductions, with particular emphasis on SRC-mediated substrate phosphorylation in BC. Furthermore, we will discuss the progress of SRC-based targeted therapies in BC and the potential future direction.

Downregulation of Src-family tyrosine kinases by Srcasm and c-Cbl: A comparative analysis

AIM

Elevated Src-Family tyrosine kinase (SFK) activity drives carcinogenesis in vivo and elevated SFK activity is found ubiquitously in human cancers. Although human squamous cell carcinomas (SCCs) demonstrate increased SFK activity, in silico analysis of SCCs demonstrates that only 0.4% of lesions contain mutations that could potentially increase SFK activity; similarly, a low frequency of activating SFK mutations is found in other major cancers. These findings indicate that SFK activation in cancers likely is not due to activating mutations but alternative mechanisms. To evaluate potential alternative mechanisms, we evaluated the selectivity of c-Cbl and Srcasm in downregulating native and activated mutant forms of SFKs.

MATERIALS AND METHODS

We co-transfected native and activated forms of Src and Fyn with c-Cbl and Srcasm into HaCaT cells and monitored the ability of Srcasm and c-Cbl to downregulate native and activated forms of SFKs by Western blotting. The mechanism of downregulation was probed using mutant forms of Srcasm and c-Cbl and using proteosomal and lysosomal inhibition.

RESULTS

The data indicate that Srcasm downregulates native Fyn and Src more effectively than c-Cbl, whereas c-Cbl preferentially downregulates activated SFK mutants, including Fyn Y528F, more effectively than Srcasm. Srcasm downregulates SFKs through a lysosomal-dependent mechanism while c-Cbl utilizes a proteosomal-dependent mechanism.

CONCLUSION

Given the rarity of activating SFK mutations in human cancer, these data indicate that decreasing Srcasm level/function may represent a mechanism for increasing SFK activity in SCC and other human tumors.

State-selective frustration as a key driver of allosteric pluripotency

Allosteric pluripotency arises when an allosteric effector switches from agonist to antagonist depending on the experimental conditions. For example, the Rp-cAMPS ligand of Protein Kinase A (PKA) switches from agonist to antagonist as the MgATP concentration increases and/or the kinase substrate affinity or concentration decreases. Understanding allosteric pluripotency is essential to design effective allosteric therapeutics with minimal side effects. Allosteric pluripotency of PKA arises from divergent allosteric responses of two homologous tandem cAMP-binding domains, resulting in a free energy landscape for the Rp-cAMPS-bound PKA regulatory subunit R1a in which the ground state is kinase inhibition-incompetent and the kinase inhibition-competent state is excited. The magnitude of the free energy difference between the ground non-inhibitory and excited inhibitory states (ΔG_R,Gap) relative to the effective free energy of R1a binding to the catalytic subunit of PKA (ΔG_R:C) dictates whether the antagonism-to-agonism switch occurs. However, the key drivers of ΔG_R,Gap are not fully understood. Here, by analyzing an R1a mutant that selectively silences allosteric pluripotency, we show that a major determinant of ΔG_R,Gap unexpectedly arises from state-selective frustration in the ground inhibition-incompetent state of Rp-cAMPS-bound R1a. Such frustration is caused by steric clashes between the phosphate-binding cassette and the helices preceding the lid, which interact with the phosphate and base of Rp-cAMPS, respectively. These clashes are absent in the excited inhibitory state, thus reducing the ΔG_R,Gap to values comparable to ΔG_R:C, as needed for allosteric pluripotency to occur. The resulting model of allosteric pluripotency is anticipated to assist the design of effective allosteric modulators.

The Rp-cAMPS ligand of protein kinase A switches from agonist to antagonist depending on metabolite and proteomic contexts. We show that the state-selective frustration is a key driver of this allosteric pluripotency phenomenon.

Anti-growth and pro-apoptotic effects of dasatinib on human oral cancer cells through multi-targeted mechanisms

Dasatinib is an inhibitor of Src that has anti-tumour effects on many haematological and solid cancers. However, the anti-tumour effects of dasatinib on human oral cancers remain unclear. In this study, we investigated the effects of dasatinib on different types of human oral cancer cells: the non-tumorigenic YD-8 and YD-38 and the tumorigenic YD-10B and HSC-3 cells. Strikingly, dasatinib at 10 µM strongly suppressed the growth and induced apoptosis of YD-38 cells and inhibited the phosphorylation of Src, EGFR, STAT-3, STAT-5, PKB and ERK-1/2. In contrast, knockdown of Src blocked the phosphorylation of EGFR, STAT-5, PKB and ERK-1/2, but not STAT-3, in YD-38 cells. Dasatinib induced activation of the intrinsic caspase pathway, which was inhibited by z-VAD-fmk, a pan-caspase inhibitor. Dasatinib also decreased Mcl-1 expression and S6 phosphorylation while increased GRP78 expression and eIF-2α phosphorylation in YD-38 cells. In addition, to its direct effects on YD-38 cells, dasatinib also exhibited anti-angiogenic properties. Dasatinib-treated YD-38 or HUVEC showed reduced HIF-1α expression and stability. Dasatinib alone or conditioned media from dasatinib-treated YD-38 cells inhibited HUVEC tube formation on Matrigel without affecting HUVEC viability. Importantly, dasatinib's anti-growth, anti-angiogenic and pro-apoptotic effects were additionally seen in tumorigenic HSC-3 cells. Together, these results demonstrate that dasatinib has strong anti-growth, anti-angiogenic and pro-apoptotic effects on human oral cancer cells, which are mediated through the regulation of multiple targets, including Src, EGFR, STAT-3, STAT-5, PKB, ERK-1/2, S6, eIF-2α, GRP78, caspase-9/3, Mcl-1 and HIF-1α.

An ErbB2/c-Src axis links bioenergetics with PRC2 translation to drive epigenetic reprogramming and mammary tumorigenesis

Dysregulation of histone modifications promotes carcinogenesis by altering transcription. Breast cancers frequently overexpress the histone methyltransferase EZH2, the catalytic subunit of Polycomb Repressor Complex 2 (PRC2). However, the role of EZH2 in this setting is unclear due to the context-dependent functions of PRC2 and the heterogeneity of breast cancer. Moreover, the mechanisms underlying PRC2 overexpression in cancer are obscure. Here, using multiple models of breast cancer driven by the oncogene ErbB2, we show that the tyrosine kinase c-Src links energy sufficiency with PRC2 overexpression via control of mRNA translation. By stimulating mitochondrial ATP production, c-Src suppresses energy stress, permitting sustained activation of the mammalian/mechanistic target of rapamycin complex 1 (mTORC1), which increases the translation of mRNAs encoding the PRC2 subunits Ezh2 and Suz12. We show that Ezh2 overexpression and activity are pivotal in ErbB2-mediated mammary tumourigenesis. These results reveal the hitherto unknown c-Src/mTORC1/PRC2 axis, which is essential for ErbB2-driven carcinogenesis.

Polycomb Repressor Complex 2 (PRC2) is frequently up-regulated in cancers. Here, the authors show that the tyrosine kinase c-Src stimulates mitochondrial function to signal energy sufficiency to mTORC1, increasing translation of the PRC2 subunits EZH2 and SUZ12 to support ErbB2-dependent tumours.

Bayesian Inference Identifies Combination Therapeutic Targets in Breast Cancer

OBJECTIVE

Breast cancer is the second leading cause of cancer death among US women; hence, identifying potential drug targets is an ever increasing need. In this paper, we integrate existing biological information with graphical models to deduce the significant nodes in the breast cancer signaling pathway.

METHODS

We make use of biological information from the literature to develop a Bayesian network. Using the relevant gene expression data we estimate the parameters of this network. Then, using a message passing algorithm, we infer the network. The inferred network is used to quantitatively rank different interventions for achieving a desired phenotypic outcome. The particular phenotype considered here is the induction of apoptosis.

RESULTS

Theoretical analysis pinpoints to the role of Cryptotanshinone, a compound found in traditional Chinese herbs, as a potent modulator for bringing about cell death in the treatment of cancer.

CONCLUSION

Using a mathematical framework, we showed that the combination therapy of mTOR and STAT3 genes yields the best apoptosis in breast cancer.

SIGNIFICANCE

The computational results we arrived at are consistent with the experimental results that we obtained using Cryptotanshinone on MCF-7 breast cancer cell lines and also by the past results of others from the literature, thereby demonstrating the effectiveness of our model.

Intratumoral Heterogeneity in Ductal Carcinoma In Situ: Chaos and Consequence

Ductal carcinoma in situ (DCIS) is a non-invasive proliferative growth in the breast that serves as a non-obligate precursor to invasive ductal carcinoma. The widespread adoption of screening mammography has led to a steep increase in the detection of DCIS, which now comprises approximately 20% of new breast cancer diagnoses in the United States. Interestingly, the intratumoral heterogeneity (ITH) that has been observed in invasive breast cancers may have been established early in tumorigenesis, given the vast and varied ITH that has been detected in DCIS. This review will discuss the intratumoral heterogeneity of DCIS, focusing on the phenotypic and genomic heterogeneity of tumor cells, as well as the compositional heterogeneity of the tumor microenvironment. In addition, we will assess the spatial heterogeneity that is now being appreciated in these lesions, and summarize new approaches to evaluate heterogeneity of tumor and stromal cells in the context of their spatial organization. Importantly, we will discuss how a growing understanding of ITH has led to a more holistic appreciation of the complex biology of DCIS, specifically its evolution and natural history. Finally, we will consider ways in which our knowledge of DCIS ITH might be translated in the future to guide clinical care for DCIS patients.

O-GlcNAc-Dependent Regulation of Progesterone Receptor Function in Breast Cancer

Emerging clinical trial data implicate progestins in the development of breast cancer. While the role for the progesterone receptor (PR) in this process remains controversial, it is clear that PR, a steroid-activated nuclear receptor, alters the transcriptional landscape of breast cancer. PR interacts with many different types of proteins, including transcriptional co-activators and co-repressors, transcription factors, nuclear receptors, and proteins that post-translationally modify PR (i.e., kinases and phosphatases). Herein, we identify a novel interaction between PR and O-GlcNAc transferase (OGT), the enzyme that catalyzes the addition of a single N-acetylglucosamine sugar, referred to as O-GlcNAc, to acceptor serines and threonines in target proteins. This interaction between PR and OGT leads to the post-translational modification of PR by O-GlcNAc. Moreover, we show that O-GlcNAcylated PR is more transcriptionally active on PR-target genes, despite the observation that PR messenger RNA and protein levels are decreased when O-GlcNAc levels are high. O-GlcNAcylation in breast cancer is clinically relevant, as we show that O-GlcNAc levels are higher in breast cancer as compared to matched normal tissues, and PR-positive breast cancers have higher levels of OGT. These data predict that under conditions where O-GlcNAc levels are high (breast cancer), PR, through an interaction with the modifying enzyme OGT, will exhibit increased O-GlcNAcylation and potentiated transcriptional activity. Therapeutic strategies aimed at altering cellular O-GlcNAc levels may have profound effects on PR transcriptional activity in breast cancer.

Rhodomycin A, a novel Src-targeted compound, can suppress lung cancer cell progression via modulating Src-related pathways

Src activation is involved in cancer progression and the interplay with EGFR. Inhibition of Src activity also represses the signalling pathways regulated by EGFR. Therefore, Src has been considered a target molecule for drug development. This study aimed to identify the compounds that target Src to suppress lung cancer tumourigenesis and metastasis and investigate their underlying molecular mechanisms. Using a molecular docking approach and the National Cancer Institute (NCI) compound dataset, eight candidate compounds were selected, and we evaluated their efficacy. Among them, rhodomycin A was the most efficient at reducing the activity and expression of Src in a dose-dependent manner, which was also the case for Src-associated proteins, including EGFR, STAT3, and FAK. Furthermore, rhodomycin A significantly suppressed cancer cell proliferation, migration, invasion, and clonogenicity in vitro and tumour growth in vivo. In addition, rhodomycin A rendered gefitinib-resistant lung adenocarcinoma cells more sensitive to gefitinib treatment, implying a synergistic effect of the combination therapy. Our data also reveal that the inhibitory effect of rhodomycin A on lung cancer progression may act through suppressing the Src-related multiple signalling pathways, including PI3K, JNK, Paxillin, and p130cas. These findings will assist the development of anti-tumour drugs to treat lung cancer.

SRC drives growth of antiestrogen resistant breast cancer cell lines and is a marker for reduced benefit of tamoxifen treatment

The underlying mechanisms leading to antiestrogen resistance in estrogen-receptor α (ER)-positive breast cancer is still poorly understood. The aim of this study was therefore to identify biomarkers and novel treatments for antiestrogen resistant breast cancer. We performed a kinase inhibitor screen on antiestrogen responsive T47D breast cancer cells and T47D-derived tamoxifen and fulvestrant resistant cell lines. We found that dasatinib, a broad-spectrum kinase inhibitor, inhibited growth of the antiestrogen resistant cells compared to parental T47D cells. Furthermore western blot analysis showed increased expression and phosphorylation of Src in the resistant cells and that dasatinib inhibited phosphorylation of Src and also signaling via Akt and Erk in all cell lines. Immunoprecipitation revealed Src: ER complexes only in the parental T47D cells. In fulvestrant resistant cells, Src formed complexes with the Human Epidermal growth factor Receptor (HER)1 and HER2. Neither HER receptors nor ER were co-precipitated with Src in the tamoxifen resistant cell lines. Compared to treatment with dasatinib alone, combined treatment with dasatinib and fulvestrant had a stronger inhibitory effect on tamoxifen resistant cell growth, whereas dasatinib in combination with tamoxifen had no additive inhibitory effect on fulvestrant resistant growth. When performing immunohistochemical staining on 268 primary tumors from breast cancer patients who had received tamoxifen as first line endocrine treatment, we found that membrane expression of Src in the tumor cells was significant associated with reduced disease-free and overall survival. In conclusion, Src was identified as target for treatment of antiestrogen resistant T47D breast cancer cells. For tamoxifen resistant T47D cells, combined treatment with dasatinib and fulvestrant was superior to treatment with dasatinib alone. Src located at the membrane has potential as a new biomarker for reduced benefit of tamoxifen.

Identification of a Src kinase SH3 binding site in the C-terminal domain of the human ErbB2 receptor tyrosine kinase

Overexpression of the ErbB2 receptor tyrosine kinase is associated with most aggressive tumors in breast cancer patients and is thus one of the main investigated therapeutic targets. Human ErbB2 C-terminal domain is an unstructured anchor that recruits specific adaptors for signaling cascades resulting in cell growth, differentiation and migration. Herein, we report the presence of a SH3 binding motif in the proline rich unfolded ErbB2 C-terminal region. NMR analysis of this motif supports a PPII helix conformation and the binding to Fyn-SH3 domain. The interaction of a kinase of the Src family with ErbB2 C-terminal domain could contribute to synergistic intracellular signaling and enhanced oncogenesis.

Phase I study of dasatinib in combination with capecitabine, oxaliplatin and bevacizumab followed by an expanded cohort in previously untreated metastatic colorectal cancer

PURPOSE

Dasatinib inhibits src family kinases and has anti-angiogenic properties. We conducted a phase I study of dasatinib, capecitabine, oxaliplatin, and bevacizumab (CapeOx/bevacizumab), with an expansion cohort in metastatic colorectal cancer (CRC).

METHODS

Patients were enrolled in a dose escalation cohort to establish the maximum tolerated dose (MTD) and the recommended phase II dose (RP2D). Using a "3 + 3" design, twelve patients with advanced solid tumors received dasatinib (50 mg twice daily or 70 mg daily), capecitabine (850 mg/m(2) twice daily, days 1-14), oxaliplatin (130 mg/m(2) on day 1) and bevacizumab (7.5 mg/kg on day1), every 3 weeks. Ten patients with previously untreated metastatic CRC were then enrolled in an expansion cohort. Activated src (src(act)) expression was measured by immunohistochemistry, using an antibody that selectively recognizes the active conformation of src (clone 28).

RESULTS

Twenty-two patients were enrolled between June 2009 and May 2011. Two DLTs were observed in the 50 mg bid dasatinib cohort, and one DLT was observed in the 70 mg daily dasatinib cohort. The MTD and RP2D for dasatinib was 70 mg daily. The most common treatment-related adverse events were fatigue (20; 91 %) and diarrhea (18; 82 %). Biomarker analysis of src(act) expression demonstrated that the overall response rate (ORR) was 75 % (6/8) for patients with high src(act) expression (IHC ≥ 2), compared to 0 % (0/8) for patients with low srcact expression (IHC 0 or 1); (p = 0.007).

CONCLUSIONS

The RP2D of dasatinib is 70 mg daily in combination with CapeOx/bevacizumab. High levels of srcact expression may predict those patients most likely to benefit from dasatinib.

PKA signaling drives mammary tumorigenesis through Src

Protein kinase A (PKA) hyperactivation causes hereditary endocrine neoplasias; however, its role in sporadic epithelial cancers is unknown. Here, we show that heightened PKA activity in the mammary epithelium generates tumors. Mammary-restricted biallelic ablation of Prkar1a, which encodes for the critical type-I PKA regulatory subunit, induced spontaneous breast tumors characterized by enhanced type-II PKA activity. Downstream of this, Src phosphorylation occurs at residues serine-17 and tyrosine-416 and mammary cell transformation is driven through a mechanism involving Src signaling. The phenotypic consequences of these alterations consisted of increased cell proliferation and, accordingly, expansion of both luminal and basal epithelial cell populations. In human breast cancer, low PRKAR1A/high SRC expression defines basal-like and HER2 breast tumors associated with poor clinical outcome. Together, the results of this study define a novel molecular mechanism altered in breast carcinogenesis and highlight the potential strategy of inhibiting SRC signaling in treating this cancer subtype in humans.

Combined SFK/MEK inhibition prevents metastatic outgrowth of dormant tumor cells

Breast cancer (BC) can recur as metastatic disease many years after primary tumor removal, suggesting that disseminated tumor cells survive for extended periods in a dormant state that is refractory to conventional therapies. We have previously shown that altering the tumor microenvironment through fibrosis with collagen and fibronectin deposition can trigger tumor cells to switch from a dormant to a proliferative state. Here, we used an in vivo preclinical model and a 3D in vitro model of dormancy to evaluate the role of Src family kinase (SFK) in regulating this dormant-to-proliferative switch. We found that pharmacological inhibition of SFK signaling or Src knockdown results in the nuclear localization of cyclin-dependent kinase inhibitor p27 and prevents the proliferative outbreak of dormant BC cells and metastatic lesion formation; however, SFK inhibition did not kill dormant cells. Dormant cell proliferation also required ERK1/2 activation. Combination treatment of cells undergoing the dormant-to-proliferative switch with the Src inhibitor (AZD0530) and MEK1/2 inhibitor (AZD6244) induced apoptosis in a large fraction of the dormant cells and delayed metastatic outgrowth, neither of which was observed with either inhibitor alone. Thus, targeting Src prevents the proliferative response of dormant cells to external stimuli, but requires MEK1/2 inhibition to suppress their survival. These data indicate that treatments targeting Src in combination with MEK1/2 may prevent BC recurrence.

A Common Docking Domain in Progesterone Receptor-B links DUSP6 and CK2 signaling to proliferative transcriptional programs in breast cancer cells

Progesterone receptors (PR) are transcription factors relevant to breast cancer biology. Herein, we describe an N-terminal common docking (CD) domain in PR-B, a motif first described in mitogen-activated protein kinases. Binding studies revealed PR-B interacts with dual-specificity phosphatase 6 (DUSP6) via the CD domain. Mutation of the PR-B CD domain (mCD) attenuated cell cycle progression and expression of PR-B target genes (including STAT5A and Wnt1); mCD PR-B failed to undergo phosphorylation on Ser81, a ck2-dependent site required for expression of these genes. PR-B Ser81 phosphorylation was dependent on binding with DUSP6 and required for recruitment of a transcriptional complex consisting of PR-B, DUSP6 and ck2 to an enhancer region upstream of the Wnt1 promoter. STAT5 was present at this site in the absence or presence of progestin. Furthermore, phospho-Ser81 PR-B was recruited to the STAT5A gene upon progestin treatment, suggestive of a feed-forward mechanism. Inhibition of JAK/STAT-signaling blocked progestin-induced STAT5A and Wnt1 expression. Our studies show that DUSP6 serves as a scaffold for ck2-dependent PR-B Ser81 phosphorylation and subsequent PR-B-specific gene selection in coordination with STAT5. Coregulation of select target genes by PR-B and STAT5 is likely a global mechanism required for growth promoting programs relevant to mammary stem cell biology and cancer.

Dasatinib inhibits mammary tumour development in a genetically engineered mouse model

Src family kinase activity is elevated in a number of human cancers including breast cancer. This increased activity has been associated with aggressive disease and poor prognosis. Src inhibitors are currently in clinical development with a number of trials currently assessing their activity in breast cancer. However, the results to date have been disappointing and a further evaluation of the preclinical effects of Src inhibitors is required to help establish whether these agents will be useful in the treatment of breast cancer. In this study we investigate the effects of dasatinib, which is a potent inhibitor of Src family kinases, on the initiation and development of breast cancer in a genetically engineered model of the disease. The mouse model utilized is driven by expression of activated ErbB-2 under the transcriptional control of its endogenous promoter coupled with conditional loss of Pten under the control of Cre recombinase expressed by the BLG promoter. We show that daily oral administration of dasatinib delays tumour onset and increases overall survival but does not inhibit the proliferation of established tumours. The striking difference between the dasatinib-treated group of tumours and the vehicle controls was the prominent squamous metaplasia that was seen in six out of 11 dasatinib-treated tumours. This was accompanied by a dramatic up-regulation of both E-cadherin and β-catenin and down-regulation of ErbB-2 in the dasatinib-treated tumours. Dasatinib also inhibited both the migration and the invasion of tumour-derived cell lines in vitro. Together these data support the argument that benefits of Src inhibitors may predominate in early or even pre-invasive disease.

Phosphorylated c-Src is a novel predictor for recurrence in cervical squamous cell cancer patients

AIMS

The molecular mechanisms of the tumorigenesis and recurrence of cervical cancer are poorly understood. The objective of this study was to analyze the expression of phosphorylated c-Src (phospho-c-Src) and its clinical significance in human cervical cancer.

METHODS

The expression of phospho-c-Src was determined by immunohistochemistry in a total of 127 cervical specimens including 20 normal cervix tissues, 20 cases of carcinoma in situ of cervix (CIS), and 87 cases of cervical squamous cell carcinoma (CSCC).

RESULTS

The expression of phospho-Src in normal cervix, CIS, and CSCC increased gradually in ascending order (p=0.026). In addition, the expression of phospho-Src was correlated with overall (p=0.037) and recurrence (p=0.001) survival of cervical cancer. In multivariate Cox regression analysis, phospho-Src expression was an independent prognosis factor for recurrence-free survival (p=0.004).

CONCLUSION

Our present study suggests that Src signaling may play essential role in cervical cancer progression. Phospho-Src expression may be considered as a prognostic marker to predict recurrence in CSCC.

CD24 induces expression of the oncomir miR-21 via Src, and CD24 and Src are both post-transcriptionally downregulated by the tumor suppressor miR-34a

Cancer is a complex disease process that evolves as a consequence of multiple malfunctions in key regulatory molecular networks. Understanding these networks will be essential to combat cancer. In this study, we focussed on central players in such networks. In a series of colon and breast cancer cell lines, we found that CD24 activates Src, and induces the activation of c-Jun and expression of c-Jun and c-Fos. Thereby CD24 increases the promoter activity and expression of miR-21, which in turn suppresses expression of Pdcd4 and PTEN. Co-transfection of a CD24 expression construct and an siRNA that silences Src showed that CD24-dependent upregulation of miR-21 is mediated by Src. Additionally, we found that miR-34a post-transcriptionally downregulates CD24 and Src expression, leading to the deactivation of c-Jun, reduced expression of c-Jun and c-Fos, inhibition of miR-21, and upregulation of Pdcd4 and PTEN. Furthermore, miR-34a-mediated inhibition of Src expression reduced migration and invasion of colorectal cancer cells. Resected tumor tissues from 26 colorectal patients showed significantly lower expression of Pdcd4 and miR-34a, and higher expression of CD24, Src and miR-21 compared to the corresponding normal tissues. Moreover, CD24 positively correlated with the amount of Src protein in tumor tissues, and a trend towards an inverse correlation between miR-34a and Src protein levels was also observed. Our results reveal essential players in the complex networks that regulate the progression of solid tumors such as colorectal cancer. These findings therefore identify novel therapeutic approaches for combating tumor growth and progression.

TCPTP regulates SFK and STAT3 signaling and is lost in triple-negative breast cancers

Tyrosine phosphorylation-dependent signaling, as mediated by members of the epidermal growth factor receptor (EGFR) family (ErbB1 to -4) of protein tyrosine kinases (PTKs), Src family PTKs (SFKs), and cytokines such as interleukin-6 (IL-6) that signal via signal transducer and activator of transcription 3 (STAT3), is critical to the development and progression of many human breast cancers. EGFR, SFKs, and STAT3 can serve as substrates for the protein tyrosine phosphatase TCPTP (PTPN2). Here we report that TCPTP protein levels are decreased in a subset of breast cancer cell lines in vitro and that TCPTP protein is absent in a large proportion of "triple-negative" primary human breast cancers. Homozygous TCPTP deficiency in murine mammary fat pads in vivo is associated with elevated SFK and STAT3 signaling, whereas TCPTP deficiency in human breast cancer cell lines enhances SFK and STAT3 signaling. On the other hand, TCPTP reconstitution in human breast cancer cell lines severely impaired cell proliferation and suppressed anchorage-independent growth in vitro and xenograft growth in vivo. These studies establish TCPTP's potential to serve as a tumor suppressor in human breast cancer.

Targeted silencing of elongation factor 2 kinase suppresses growth and sensitizes tumors to doxorubicin in an orthotopic model of breast cancer

Eukaryotic elongation factor 2 kinase (eEF-2K), through its phosphorylation of elongation factor 2 (eEF2), provides a mechanism by which cells can control the rate of the elongation phase of protein synthesis. The activity of eEF-2K is increased in rapidly proliferating malignant cells, is inhibited during mitosis, and may contribute to the promotion of autophagy in response to anti-cancer therapies. The purpose of this study was to examine the therapeutic potential of targeting eEF-2K in breast cancer tumors. Through the systemic administration of liposomal eEF-2K siRNA (twice a week, i.v. 150 µg/kg), the expression of eEF-2K was down-regulated in vivo in an orthotopic xenograft mouse model of a highly aggressive triple negative MDA-MB-231 tumor. This targeting resulted in a substantial decrease in eEF2 phosphorylation in the tumors, and led to the inhibition of tumor growth, the induction of apoptosis and the sensitization of tumors to the chemotherapy agent doxorubicin. eEF-2K down-modulation in vitro resulted in a decrease in the expression of c-Myc and cyclin D1 with a concomitant increase in the expression of p27^Kip1. A decrease in the basal activity of c-Src (phospho-Tyr-416), focal adhesion kinase (phospho-Tyr-397), and Akt (phospho-Ser-473) was also detected following eEF-2K down-regulation in MDA-MB-231 cells, as determined by Western blotting. Where tested, similar results were seen in ER-positive MCF-7 cells. These effects were also accompanied by a decrease in the observed invasive phenotype of the MDA-MB-231 cells. These data support the notion that the disruption of eEF-2K expression in breast cancer cells results in the down-regulation of signaling pathways affecting growth, survival and resistance and has potential as a therapeutic approach for the treatment of breast cancer.

Expression and prognostic significance of Src family members in renal clear cell carcinoma

BACKGROUND

The aim of this study was to determine whether Src family kinases (SFK) are expressed in renal cell cancer and to assess their prognostic significance.

METHODS

mRNA expression levels were investigated for the 8 SFK members by quantitative real-time PCR in 19 clear cell cancer tissue samples. Immunohistochemical staining was utilised to assess expression of Src kinase, dephosphorylated Src kinase at Y(530) (SrcY(530)), phosphorylated Src at Y(419) (SrcY(419)) and the downstream focal adhesion kinase (FAK) marker at the Y(861) site (FAK Y(861)) in a cohort of 57 clear cell renal cancer specimens. Expression was assessed using the weighted histoscore method.

RESULTS

Src, Lyn, Hck, Fgr and Fyn were the most highly expressed in renal cancer. All members were more highly expressed in T2 disease, and furthermore expression levels between T2 and T3 disease showed a significant decrease for Lck, Lyn, Fyn, Blk and Yes (P=0.032). Assessment of membrane, cytoplasm and nuclear expression of Src kinase, SrcY(530) and SrcY(419) were not significantly associated with cancer-specific survival. High expression of cytoplasmic FAK Y(861) was associated with decreased cancer-specific survival (P=0.001). On multivariate analysis, cytoplasmic FAK Y(861) was independently associated with cancer-specific survival (hazard ratio 3.35, 95% CI 1.40-7.98, P=0.006).

CONCLUSION

We have reported that all SFK members are expressed in renal cell carcinoma. The SFK members had their highest levels of expression before the disease no longer being organ confined. We hypothesise that these SFK members are upregulated before the cancer spreading out-with the organ and given that Src itself is not associated with cancer-specific survival but the presence of FAK Y(861), a downstream marker for SFK member activity is associated with decreased cancer-specific survival, we hypothesise that another SFK member is associated with decreased cancer-specific survival in renal cell cancer.

Role of phosphorylation in progesterone receptor signaling and specificity

Progesterone receptors (PR), in concert with peptide growth factor-initiated signaling pathways, initiate massive expansion of the epithelial cell compartment associated with the process of alveologenesis in the developing mammary gland. PR-dependent signaling events also contribute to inappropriate proliferation observed in breast cancer. Notably, PR-B isoform-specific cross talk with growth factor-driven pathways is required for the proliferative actions of progesterone. Indeed, PRs act as heavily phosphorylated transcription factor "sensors" for mitogenic protein kinases that are often elevated and/or constitutively activated in invasive breast cancers. In addition, phospho-PR-target genes frequently include the components of mitogenic signaling pathways, revealing a mechanism for feed-forward signaling that confers increased responsiveness of, PR +mammary epithelial cells to these same mitogenic stimuli. Understanding the mechanisms and isoform selectivity of PR/kinase interactions may yield further insight into targeting altered signaling networks in breast and other hormonally responsive cancers (i.e. lung, uterine and ovarian) in the clinic. This review focuses on PR phosphorylation by mitogenic protein kinases and mechanisms of PR-target gene selection that lead to increased cell proliferation.

Role of Src in breast cancer cell migration and invasion in a breast cell/bone-derived cell microenvironment

The preferential metastasis of breast cancer cells to bone comprises a complex set of events including homing and preferential growth, which may require unique factors produced by bone or other cells in the immediate microenvironment. In this study, an in vitro co-culture system composed of bone mesenchymal stem cells and breast cancer cell lines is used to examine the role of Src kinase on breast cancer cell migration and invasion in the presence of bone-derived cells. This research shows that Src kinase activity in breast cancer cell lines with either high or low levels of endogenous Src activity is increased by bone-derived cell-conditioned medium but not HS68 fibroblast-conditioned medium. Breast cancer cells exhibit enhanced migration in co-culture with bone-derived cells but not HS68 fibroblasts or no co-cultured cells. Inhibition of Src kinase activity using the inhibitors PP2 or saracatinib or using siRNA abrogates the preferential migration of the breast cancer cell lines in response to bone-derived cells. Inhibition of Src activity with saracatinib does not have any significant effect on breast cancer cell invasion in the presence of bone-derived cells. Factors are identified that are produced preferentially by bone-derived cells over HS68 cells that may impact breast cancer cell behavior. This research implicates Src kinase as an important effector of bone-derived cell signals on breast cancer cell migration.

Src family kinases and paclitaxel sensitivity

Src-family Kinases (SFKs) participate in the regulation of proliferation, differentiation, apoptosis, autophagy, adhesion, migration, invasion and angiogenesis in normal and cancer cells. Abnormal expression of SFKs has been documented in cancers that arise in breast, colon, ovary, melanocyte, gastric mucosa, head and neck, pancreas, lung, and brain. Targeting SFKs in cancer cells has been shown to be a promising therapeutic strategy in solid tumors, particularly in ovarian, colon and breast cancers. Paclitaxel is one of most widely used chemotherapeutic agents for the management of ovarian, breast, lung and head/neck cancers. As a microtubule-stabilizing agent, paclitaxel possesses both mitosis-dependent and mitosis-independent activities against cancer cells. A variety of mechanisms such as deregulation of P-glycoprotein, alteration of tubulin isotypes, alteration of microtubule-regulatory proteins, deregulation of apoptotic signaling pathways, mutation of tubulins and overexpression of copper transporters have been implicated in the development of primary or secondary resistance to paclitaxel. By affecting cancer cell survival, proliferation, autophagy, microtubule stability, motility, and/or angiogenesis, SFKs interact with mechanisms that regulate paclitaxel sensitivity. Inhibition of SFKs can potentiate the anti-tumor activity of paclitaxel by enhancing apoptosis, autophagy and microtubule stability. Based on pre-clinical observations, administration of SFK inhibitors in combination with paclitaxel could improve treatment for ovarian, breast, lung and head/neck cancers. Identification and validation of predictive biomarkers could also permit personalization of the therapy.

Expression and pharmacological inhibition of thymidylate synthase and Src kinase in nonsmall cell lung cancer

The combination of cytotoxic chemotherapy with signaling pathway inhibitors represents a potential strategy to improve the treatment of nonsmall cell lung cancer (NSCLC). Thymidylate synthase (TS) is an enzyme essential for DNA synthesis, and its overexpression has been associated with the reduced sensitivity to antifolate agents. Src is a tyrosine kinase that modulates the cytotoxicity of cancer cells after drug treatment, and in vitro data indicate that its inhibition could revert the resistance to TS-inhibiting drugs. Our study investigated the significance of TS and Src expression in NSCLC tissues, and the effects of their pharmacological inhibition in cell lines. In tumor and normal tissues from 94 resected NSCLC patients, TS and Src transcript levels were found positively correlated (R(S) = 0.66), associated with patients smoking history and overall survival. At multivariate analysis, TS gene expression was an independent prognostic factor (relative risk (RR) = 1.78, from 1.16 to 2.72; p < 0.01). Immunohistochemical detection in tumor specimens confirmed that Src kinase activation, evaluated by phospho-specific antibody, was associated to a higher TS expression. In cell lines, dasatinib, a Src-inhibiting agent, synergistically enhanced pemetrexed-cytotoxicity of A549 cells, as evaluated by MTT and apoptosis assays. The biological explanation for this interaction was based on the upregulation of TS messenger RNA and protein levels induced by pemetrexed, which was significantly prevented by dasatinib cotreatment. The data of our study suggest that TS and Src may belong to a common pathway that bears prognostic significance in NSCLC, and that Src represents a potential target to improve the efficacy of TS-inhibiting agents.

Src kinase: a therapeutic opportunity in endocrine-responsive and resistant breast cancer

The intracellular kinase, Src, interacts with a diverse array of signaling elements, including the estrogen receptor to regulate breast cancer progression. Recent evidence has also implicated Src in mediating the response of breast cancer to endocrine agents and in the acquisition of antihormone resistance, a significant limiting factor to the clinical effectiveness of systemic endocrine therapy. A number of pharmacological inhibitors of Src kinase have been developed that are effective at suppressing breast cancer growth and invasion in vitro and inhibiting disease spread in vivo. Significantly, there appears to be added benefit when these agents are given in combination with anti-estrogens in endocrine-sensitive and -resistant models. These new findings suggest that Src inhibitors might have therapeutic value in breast cancer patients to improve endocrine response and circumvent resistance.

Biological Markers in DCIS and Risk of Breast Recurrence: A Systematic Review

Understanding of the biology and clinical behavior of ductal carcinoma in situ (DCIS) is currently inadequate. The aim of this comprehensive review was to identify important molecular biological markers associated with DCIS and candidate markers associated with increased risk of ipsilateral recurrence after diagnosis of DCIS. A comprehensive systematic review was performed to identify studies published in the past 10 years that investigated biological markers in DCIS. To be included in this review, studies that investigated the rate of biological expression of markers had to report on at least 30 patients; studies that analyzed the recurrence risk associated with biomarker expression had to report on at least 50 patients. There were 6,252 patients altogether in our review. Biological markers evaluated included steroid receptors, proliferation markers, cell cycle regulation and apoptotic markers, angiogenesis-related proteins, epidermal growth factor receptor family receptors, extracellular matrix-related proteins, and COX-2. Although the studies in this review provide valuable preliminary information regarding the expression and prognostic significance of biomarkers in DCIS, common limitations of published studies (case-series, cohort, and case-control studies) were that they were limited to small patient cohorts in which the extent of surgery and use of radiotherapy or endocrine therapy varied from patient to patient, and variable methods of determining biomarker expression. These constraints made it difficult to interpret the absolute effect of expression of various biomarkers on risk of local recurrence. No prospective validation studies were identified. As the study of biomarkers are in their relative infancy in DCIS compared with invasive breast cancer, key significant prognostic and predictive markers associated with invasive breast cancer have not been adequately studied in DCIS. There is a critical need for prospective analyses of novel and other known breast cancer molecular markers in large cohorts of patient with DCIS to differentiate indolent from aggressive DCIS and better tailor the need and extent of current therapies.

ck2-dependent phosphorylation of progesterone receptors (PR) on Ser81 regulates PR-B isoform-specific target gene expression in breast cancer cells

Progesterone receptors (PR) are critical mediators of mammary gland development and contribute to breast cancer progression. Progestin-induced rapid activation of cytoplasmic protein kinases leads to selective regulation of growth-promoting genes by phospho-PR species. Herein, we show that phosphorylation of PR Ser81 is ck2 dependent and progestin regulated in intact cells but also occurs in the absence of PR ligands when cells enter the G(1)/S phase of the cell cycle. T47D breast cancer cells stably expressing a PR-B mutant receptor that cannot be phosphorylated at Ser79/81 (S79/81A) formed fewer soft agar colonies. Regulation of selected genes by PR-B, but not PR-A, also required Ser79/81 phosphorylation for basal and/or progestin-regulated (BIRC3, HSD11β2, and HbEGF) expression. Additionally, wild-type (wt) PR-B, but not S79/81A mutant PR, was robustly recruited to a progesterone response element (PRE)-containing transcriptional enhancer region of BIRC3; abundant ck2 also associated with this region in cells expressing wt but not S79/81A PR. We conclude that phospho-Ser81 PR provides a platform for ck2 recruitment and regulation of selected PR-B target genes. Understanding how ligand-independent PRs function in the context of high levels of kinase activities characteristic of breast cancer is critical to understanding the basis of tumor-specific changes in gene expression and will speed the development of highly selective treatments.

Association between patient and tumor characteristics with clinical outcomes in women with ductal carcinoma in situ

We synthesized the evidence of the association between patient and tumor characteristics with clinical outcomes in women with ductal carcinoma in situ of the breast. We identified five randomized controlled clinical trials and 64 observational studies that were published in English from January 1970 to January 2009. Younger women with clinically presented ductal carcinoma in situ had higher risk of ipsilateral recurrent cancer. African Americans had higher mortality and greater rates of advanced recurrent cancer. Women with larger tumor size, comedo necrosis, worse pathological grading, positive surgical margins, and at a higher risk category, using a composite prognostic index, had worse outcomes. Inconsistent evidence suggested that positive HER2 receptor and negative estrogen receptor status were associated with worse outcomes. Synthesis of evidence was hampered by low statistical power to detect significant differences in predictor categories and inconsistent adjustment practices across the studies. Future research should address composite prediction indices among race groups for all outcomes.

Bone metastases: molecular mechanisms and novel therapeutic interventions

It has been long recognized that skeleton represents one of the most favored metastatic sites for common cancers like breast and prostate. During the last decade the molecular mechanisms that are responsible for the development of bone metastasis have been gradually illuminated. It appears that the bone microenvironment has a pivotal role in this process. Metastatic tumor cells interact with bone triggering a cascade of molecular events that produce osteolytic and/or osteoblastic phenomena. In this review, we summarize and discuss the most significant factors and signaling pathways implicated in bone colonization. Moreover, based on the recent literature and data, we foresee the need for designing novel agents that will efficiently disrupt these interactions among cancer cells and bone microenvironment, bringing hope for more effective treatments.

Decreased Srcasm expression in esophageal squamous cell carcinoma in a Chinese population

BACKGROUND

Src-family tyrosine kinases (SFKs) play critical roles in regulating cellular differentiation and proliferation. Src-activating and signaling molecule (Srcasm) is a novel molecule that down-regulates SFK activity and promotes cell differentiation. The aim of this study was to determine whether Srcasm expression was altered in esophageal squamous epithelial carcinoma compared with normal epithelium in a Chinese population.

MATERIALS AND METHODS

We examined Srcasm immunohistochemical staining in 30 cases in both normal esophageal epithelium and esophageal squamous cell carcinoma (SCC) from the same patient in formalin-fixed paraffin embedded tissue blocks.

RESULTS

Srcasm protein expression levels are decreased in esophageal SCC compared to the esophageal normal epithelium.

CONCLUSION

This pattern of Srcasm expression suggests that it may act as a negative regulator in esophageal SCC cell signaling.

Emerging therapeutic targets in breast cancer bone metastasis

In the past decade, our understanding of the molecular mechanisms that underlie breast cancer pathology and progression has dramatically improved. Using this knowledge, we have identified additional targets and developed novel therapeutic interventions in breast cancer. Together, these translational research efforts are helping to usher us into an age of personalized cancer therapy. Metastasis to bone is a common and devastating consequence of breast cancer. Bisphosphonates, which represent the current gold standard in bone metastasis therapies, are being improved with newer and more efficacious generations of these compounds being developed. Breast cancer growth in the bone requires activation of various signaling pathways in both cancer cells and stromal cells, including those that are stimulated by TGF-β and RANKL, and mediated through the Src tyrosine kinase. Bone cells and cancer cells alike express promising targets for therapeutic intervention, including Cathepsin K, CXCR4 and GPNMB. In this article we discuss the molecular mechanisms behind these pro-metastatic molecules and review the most recent findings in the clinical development of their associated targeted therapies.

Effects of Src kinase inhibition induced by dasatinib in non-small cell lung cancer cell lines treated with cisplatin

c-Src is a tyrosine kinase involved in tumor proliferation, migration, and angiogenesis and has been shown to modulate the cytotoxicity following cisplatin-induced DNA damages. c-Src is frequently activated in non-small cell lung cancer (NSCLC) tissues and cell lines, but no preclinical data regarding the effects of the novel potent Src inhibitor, dasatinib (BMS-354825), in the modulation of cisplatin resistance are currently available. The present study reports that treatment with dasatinib completely abrogated Src phosphorylation in the majority of the NSCLC cell lines tested (n = 7), with modest effects on cell proliferation and survival. In five cell lines, a higher cytotoxicity was observed delivering cisplatin in combination with dasatinib: the most evident effects were found in the squamous H520 cells due to the effective block of cisplatin-induced Src phosphorylation. Moreover, dasatinib treatment significantly blocked cisplatin-induced transcription of a panel of DNA repair and synthesis genes. In addition, a real-time PCR analysis done on tumor and matched normal lung specimens from 44 surgically resected NSCLC patients showed that Src transcripts are significantly upregulated in 23% of cases. In conclusion, Src-directed therapeutic strategies could interfere with cisplatin resistance, possibly allowing to reduce cisplatin doses, thus improving its efficacy. The data of this study support further clinical studies aimed to evaluate the efficacy of Src-inhibiting agents in combination with cisplatin in the treatment of NSCLC.

Is expression or activation of Src kinase associated with cancer-specific survival in ER-, PR- and HER2-negative breast cancer patients?

The aim of the current study was to assess the expression levels of c-Src and phosphorylated Src kinase in human breast cancers and to establish if these are linked to oestrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2 status or patient survival. Tissue microarray technology was used to analyze 314 breast cancer specimens. Immunohistochemistry was performed using antibodies to c-Src, Y419Src, and Y215Src, and expression was assessed using the weighted histoscore method. High cytoplasmic c-Src kinase and high membrane phosphorylated activated Y419Src kinase was associated with decreased disease-specific survival. In contrast, phosphorylated activated nuclear and cytoplasmic Y215Src kinase expression levels were significantly associated with improved disease-specific survival. When the cohort was subdivided according to ER/PR/HER2 status, the ER-negative subgroup (105 patients) was associated with improved disease-specific survival and was found to be independent by multivariate analysis with a hazard ratio of 0.4 (interquartile range 0.2-0.8). High cytoplasmic c-Src expression was associated with decreased survival; high expression of activated c-Src (Y215) was associated with improved survival. This was potentiated in the ER/HER2-negative subgroup. Hence, administration of Src kinase inhibitors aiming to decrease phosphorylation should be approached with caution, especially in ER-negative patients. It is therefore essential to appropriately identify with the correct biomarkers which patients are most likely to respond to Src inhibitors.

Increased levels of active c-Src distinguish invasive from in situ lobular lesions

Introduction

Mounting molecular evidence suggests that invasive lobular carcinoma (ILC) is developing from in situ lesions, atypical lobular hyperplasia (ALH), and lobular carcinoma in situ (LCIS). However, little is known about the mechanisms promoting the progression of lobular breast cancer (LBC) to invasive disease. Here, we investigated whether c-Src kinase, an established inducer of invasive states, contributes to the progression from ALH/LCIS to ILC.

Methods

Immunochemistry for c-Src and other cancer-related molecules was performed on archived tissue specimens from 57 LBC patients. Relative c-Src activity was estimated by comparing fluorescence intensity of ILC with that of adjacent ALH/LCIS and nonneoplastic epithelia after staining with an antibody against active c-Src. Expression of active c-Src was correlated with markers of invasion and malignancy and with relapse among LBC patients.

Results

Levels of activated c-Src were increased in ILC relative to ALH/LCIS (1.63-fold ± 0.24 SD) and nonneoplastic epithelia (1.47 ± 0.18 SD). Increased c-Src levels correlated with the activation of c-Src downstream targets (Fak, Stat-3) and the expression of mesenchymal markers. ILC cells with activated c-Src co-expressed metastatic markers (Opn, Cxcr4) and included cells positive for the cancer stem cell marker Aldh1. A tendency for high c-Src levels (P = 0.072) was observed among the seven LBC patients with relapsed disease.

Conclusions

Our data indicate elevated c-Src activity in ILC relative to noninvasive neoplastic tissue. The associated molecular changes suggest that c-Src promotes LBC invasiveness by inducing an epithelial-mesenchymal transition. Therefore, c-Src antagonists might counteract the acquisition of invasiveness during LBC progression. Inhibition of c-Src may also affect ILC cells thought to have a high metastatic potential and to be capable of initiating/maintaining tumor growth. Together with the possible association between high c-Src levels and disease recurrence, our findings encourage the evaluation of c-Src antagonists for the treatment of LBC.

Activation of Src by protein tyrosine phosphatase 1B Is required for ErbB2 transformation of human breast epithelial cells

Protein tyrosine phosphatase (PTP) 1B plays a major role in inhibiting signaling from the insulin and leptin receptors. Recently, PTP1B was found to have an unexpected positive role in ErbB2 signaling in a mouse model of breast cancer, but the mechanism underlying this effect has been unclear. Using human breast epithelial cells grown in a three-dimensional matrix, we found that PTP1B, but not the closely related enzyme T-cell PTP, is required for ErbB2 transformation in vitro. Activation of ErbB2, but not ErbB1, increases PTP1B expression, and increased expression of PTP1B activates Src and induces a Src-dependent transformed phenotype. These findings identify a molecular mechanism by which PTP1B links an important oncogenic receptor tyrosine kinase to signaling pathways that promote aberrant cell division and survival in human breast epithelial cells.

Progesterone and breast cancer

Progesterone is an ovarian steroid hormone that is essential for normal breast development during puberty and in preparation for lactation and breastfeeding. The actions of progesterone are primarily mediated by its high-affinity receptors, which include the classical progesterone receptor (PR)-A and -B isoforms, located in diverse tissues, including the brain, where progesterone controls reproductive behavior, and the breast and reproductive organs. Progestins are frequently prescribed for contraception or during postmenopausal hormone replacement therapy, in which progestins are combined with estrogen as a means to block estrogen-induced endometrial growth. The role of estrogen as a potent breast mitogen is undisputed, and inhibitors of the estrogen receptor and estrogen-producing enzymes (aromatases) are effective first-line cancer therapies. However, PR action in breast cancer is grossly understudied and remains controversial. Herein, we review existing evidence and discuss the challenges to defining a role for progesterone in breast cancer.

Relevance of breast cancer antiestrogen resistance genes in human breast cancer progression and tamoxifen resistance

PURPOSE

We have previously identified a set of breast cancer antiestrogen resistance (BCAR) genes causing estrogen independence and tamoxifen resistance in vitro using a functional genetic screen. Here, we explored whether these BCAR genes provide predictive value for tamoxifen resistance and prognostic information for tumor aggressiveness in breast cancer patients.

PATIENTS AND METHODS

mRNA levels of 10 BCAR genes (AKT1, AKT2, BCAR1, BCAR3, EGFR, ERBB2, GRB7, SRC, TLE3, and TRERF1) were measured in estrogen receptor-positive breast tumors using quantitative reverse-transcriptase polymerase chain reaction. Normalized mRNA levels were evaluated for association with progression-free survival (PFS) in 242 patients receiving tamoxifen as first-line monotherapy for recurrent disease, and with distant metastasis-free survival (MFS) in 413 lymph node-negative (LNN) primary breast cancer patients who did not receive systemic adjuvant therapy.

RESULTS

Concerning tamoxifen resistance, BCAR3, ERBB2, GRB7, and TLE3 mRNA levels were predictive for PFS, independent of traditional predictive factors. By combining GRB7 (or ERBB2) and TLE3 mRNA levels, patients could be classified in three subgroups with distinct PFS. For the evaluation of tumor aggressiveness, AKT2, EGFR, and TRERF1 mRNA levels were all significantly associated with MFS, independent of traditional prognostic factors. Using the combined AKT2 and EGFR mRNA status, four prognostic groups were identified with different MFS outcomes.

CONCLUSION

The majority of BCAR genes, which were revealed to confer tamoxifen resistance and estrogen independence in vitro by functional screening, have clinical relevance, and associate with tamoxifen resistance and/or tumor aggressiveness in breast cancer patients.

Phosphorylated c-Src in the nucleus is associated with improved patient outcome in ER-positive breast cancer

Elevated c-Src protein expression has been shown in breast cancer and in vitro evidence suggests a role in endocrine resistance. To investigate whether c-Src is involved in endocrine resistance, we examined the expression of both total and activated c-Src in human breast cancer specimens from a cohort of oestrogen receptor (ER)-positive tamoxifen-treated breast cancer patients. Tissue microarray technology was employed to analyse 262 tumour specimens taken before tamoxifen treatment. Immunohistochemistry using total c-Src and activated c-Src antibodies was performed. Kaplan–Meier survival curves were constructed and log-rank test were performed. High level of nuclear activated Src was significantly associated with improved overall survival (P=0.047) and lower recurrence rates on tamoxifen (P=0.02). Improved patient outcome was only seen with activated Src in the nucleus. Nuclear activated Src expression was significantly associated with node-negative disease and a lower NPI (P<0.05). On subgroup analysis, only ER-positive/progesterone receptor (PgR)-positive tumours were associated with improved survival (P=0.004). This shows that c-Src activity is increased in breast cancer and that activated Src within the nucleus of ER-positive tumours predicts an improved outcome. In ER/PgR-positive disease, activated Src kinase does not appear to be involved in de novo endocrine resistance. Further study is required in ER-negative breast cancer as this may represent a cohort in which it is associated with poor outcome.

Challenges to defining a role for progesterone in breast cancer

Progesterone is an ovarian steroid hormone that is essential for normal breast development during puberty and in preparation for lactation. The actions of progesterone are primarily mediated by its high affinity receptors, including the classical progesterone receptor (PR) -A and -B isoforms, located in diverse tissues such as the brain where progesterone controls reproductive behavior, and the breast and reproductive organs. Progestins are frequently prescribed as contraceptives or to alleviate menopausal symptoms, wherein progestin is combined with estrogen as a means to block estrogen-induced endometrial growth. Estrogen is undisputed as a potent breast mitogen, and inhibitors of the estrogen receptor (ER) and estrogen producing enzymes (aromatases) are effective first-line cancer therapies. However, PR action in breast cancer remains controversial. Herein, we review existing evidence from in vitro and in vivo models, and discuss the challenges to defining a role for progesterone in breast cancer.