Src and CXCR4 are involved in the invasiveness of breast cancer cells with acquired resistance to lapatinib

Detailed curriculum vitae of HER2-targeted therapy

With the booming development of precision medicine, molecular targeted therapy has been widely used in clinical oncology treatment due to a smaller number of side effects and its superior accuracy compared to that of traditional strategies. Among them, human epidermal growth factor receptor 2 (HER2)-targeted therapy has attracted considerable attention and has been used in the clinical treatment of breast and gastric cancer. Despite excellent clinical effects, HER2-targeted therapy remains in its infancy due to its resulting inherent and acquired resistance. Here, a comprehensive overview of HER2 in numerous cancers is presented, including its biological role, involved signaling pathways, and the status of HER2-targeted therapy.

Experimental and computational assessment of the synergistic pharmacodynamic drug-drug interactions of a triple combination therapy in refractory HER2-positive breast cancer cells

The development of innate and/or acquired resistance to human epidermal growth factor receptor type-2 (HER2)-targeted therapy in HER2-positive breast cancer (HER2 + BC) is a major clinical challenge that needs to be addressed. One of the main mechanisms of resistance includes aberrant activation of the HER2 and phosphatidylinositol 3-kinase/AKT8 virus oncogene cellular homolog/mammalian target of rapamycin (PI3K/Akt/mTOR) pathways. In the present work, we propose to use a triple combination therapy to combat this resistance phenomenon. Our strategy involves evaluation of two targeted small molecule agents, everolimus and dasatinib, with complementary inhibitory circuitries in the PI3K/Akt/mTOR pathway, along with a standard cytotoxic agent, paclitaxel. Everolimus inhibits mTOR, while dasatinib inhibits Src, which is a protein upstream of Akt. An over-activation of these two proteins has been implicated in approximately 50% of HER2 + BC cases. Hence, we hypothesize that their simultaneous inhibition may lead to enhanced cell-growth inhibition. Moreover, the potent apoptotic effects of paclitaxel may help augment the overall cytotoxicity of the proposed triple combination in HER2 + BC cells. To this end, we investigated experimentally and assessed computationally the in vitro pharmacodynamic drug-drug interactions of the various dual and triple combinations to assess their subsequent combinatorial effects (synergistic/additive/antagonistic) in a HER2-therapy resistant BC cell line, JIMT-1. Our proposed triple combination therapy demonstrated synergism in JIMT-1 cells, thus corroborating our hypothesis. This effort may form the basis for further investigation of the triple combination therapy in vivo at a mechanistic level in HER2-therapy resistant BC cells.

The Role of the CXCL12/CXCR4/CXCR7 Chemokine Axis in Cancer

Chemokines are a family of small, secreted cytokines which regulate a variety of cell functions. The C-X-C motif chemokine ligand 12 (CXCL12) binds to C-X-C chemokine receptor type 4 (CXCR4) and C-X-C chemokine receptor type 7 (CXCR7). The interaction of CXCL12 and its receptors subsequently induces downstream signaling pathways with broad effects on chemotaxis, cell proliferation, migration, and gene expression. Accumulating evidence suggests that the CXCL12/CXCR4/CXCR7 axis plays a pivotal role in tumor development, survival, angiogenesis, metastasis, and tumor microenvironment. In addition, this chemokine axis promotes chemoresistance in cancer therapy via complex crosstalk with other pathways. Multiple small molecules targeting CXCR4/CXCR7 have been developed and used for preclinical and clinical cancer treatment. In this review, we describe the roles of the CXCL12/CXCR4/CXCR7 axis in cancer progression and summarize strategies to develop novel targeted cancer therapies.

Therapeutic resistance in breast cancer cells can result from deregulated EGFR signaling

The epidermal growth factor receptor (EGFR) interacts with various downstream molecules including phospholipase C (PLC)/protein kinase C (PKC), Ras/Raf/MEK/ERK, PI3K/PTEN/Akt/GSK-3, Jak/STAT and others. Often these pathways are deregulated in human malignancies such as breast cancer. Various therapeutic approaches to inhibit the activity of EGFR family members including small molecule inhibitors and monoclonal antibodies (MoAb) have been developed. A common problem with cancer treatments is the development of drug-resistance. We examined the effects of a conditionally-activated EGFR (v-Erb-B:ER) on the resistance of breast cancer cells to commonly used chemotherapeutic drugs such as doxorubicin, daunorubicin, paclitaxel, cisplatin and 5-flurouracil as well as ionizing radiation (IR). v-Erb-B is similar to the EGFR-variant EGFRvIII, which is expressed in various cancers including breast, brain, prostate. Both v-Erb-B and EGFRvIII encode the EGFR kinase domain but lack key components present in the extracellular domain of EGFR which normally regulate its activity and ligand-dependence. The v-Erb-B oncogene was ligated to the hormone binding domain of the estrogen receptor (ER) which results in regulation of the activity of the v-Erb-ER construct by addition of either estrogen (E2) or 4-hydroxytamoxifen (4HT) to the culture media. Introduction of the v-Erb-B:ER construct into the MCF-7 breast cancer cell line increased the resistance to the cells to various chemotherapeutic drugs, hormonal-based therapeutics and IR. These results point to the important effects that aberrant expression of EGFR kinase domain can have on therapeutic resistance.

Role of Chemokines in the Biology of Cholangiocarcinoma

Cholangiocarcinoma (CCA), a heterogeneous tumor with poor prognosis, can arise at any level in the biliary tree. It may derive from epithelial cells in the biliary tracts and peribiliary glands and possibly from progenitor cells or even hepatocytes. Several risk factors are responsible for CCA onset, however an inflammatory milieu nearby the biliary tree represents the most common condition favoring CCA development. Chemokines play a key role in driving the immunological response upon liver injury and may sustain tumor initiation and development. Chemokine receptor-dependent pathways influence the interplay among various cellular components, resulting in remodeling of the hepatic microenvironment towards a pro-inflammatory, pro-fibrogenic, pro-angiogenic and pre-neoplastic setting. Moreover, once tumor develops, chemokine signaling may influence its progression. Here we review the role of chemokines in the regulation of CCA development and progression, and the modulation of angiogenesis, metastasis and immune control. The potential role of chemokines and their receptors as possible biomarkers and/or therapeutic targets for hepatobiliary cancer is also discussed.

Synergistic effect of STAT3‑targeted small interfering RNA and AZD0530 against glioblastoma in vitro and in vivo

The aim of this study was to explore the synergistic effect of signal transducer and activator of transcription 3 (STAT3)-targeted small interfering (si)RNA and AZD0530 against glioblastoma in vitro and in vivo. Glioblastoma cell lines U87 and U251 were divided into four groups and treated with control, LV-STAT3 siRNA, AZD0530, and combined LV-STAT3 siRNA with AZD0530, respectively. The proliferation and apoptotic capacity of glioblastoma cells was assessed by Cell Counting Kit-8 and double staining flow cytometry assays, respectively. Additionally, the potential effect of LV-STAT3 siRNA and AZD0530 on glioblastoma was evaluated in vivo. Images were captured of the tumor formation in mice every week. Following three weeks of treatment, NMR scan and immunohistochemistry were performed. The treatment of combined LV-STAT3 siRNA and AZD0530 was more effective in inhibiting proliferation and inducing apoptosisof glioblastoma cells in comparison with the treatment of either LV-STAT3 siRNA or AZD0530 alone. Although LV-STAT3 siRNA or AZD0530 treatment alone suppressed tumor growth in mice, the combined treatment had a more significant effect than the treatment of LV-STAT3 siRNA or AZD0530 alone. According to the results of both in vitro and in vivo assays, a combined therapy of LV-STAT3 siRNA with AZD0530 could enhance therapeutic effects on glioblastoma, supporting the idea that the combination of LV-STAT3 siRNA and AZD0530 could serve as a novel and effective strategy to combat glioblastoma.

Combining Multiscale Experimental and Computational Systems Pharmacological Approaches to Overcome Resistance to HER2-targeted Therapy in Breast Cancer

The emergence of human epidermal growth factor receptor type-2 (HER2) therapy resistance in HER2-positive (HER2+) breast cancer (BC) poses a major clinical challenge. The primary mechanisms of resistance include aberrant activation of the HER2 and phosphatidylinositol 3-kinase/mammalian target of rapamycin/AKT8 virus oncogene cellular homolog (PI3K/Akt/mTOR) pathways. The existence of feedback loops in this pathway may engender resistance to targeted therapies such as everolimus, an mTOR inhibitor, resulting in a more aggressive form of refractory HER2+ BC. Here, we hypothesize that a triple and sequential combination therapy of paclitaxel, a potent cytotoxic agent, before concomitant administration of dasatinib, a SRC proto-oncogene nonreceptor tyrosine kinase (Src) family kinase inhibitor, with everolimus, restores sensitivity to treatment in refractory HER2+ BC. This was assessed by a combination of experimental and computational approaches. Quantitative systems pharmacological (QSP), pharmacokinetics (PK), and pharmacodynamics (PD) studies were conducted in static and three-dimensional and dynamic (3DD) cell culture systems using a HER2+ cell line resistant to HER2 therapy, JIMT-1. The dynamic responses in cellular viability and key signaling proteins in the HER2 and PI3K/Akt/mTOR pathways were measured upon treatments with single drugs, combinations, and appropriate controls. A QSP-PK/PD model was developed and used to optimize the sequence and interdose interval of the three agents in the combination. The proposed sequential combination therapy demonstrated strong cytotoxic effects in JIMT-1 cells, and our models predicted the usefulness of this combination over prolonged durations in the 3DD setting. Our combined experimental and QSP-PK/PD modeling approach may serve as a useful screening tool in predicting clinical efficacy of combination therapies in oncology. Nonetheless, further in vivo human xenograft tumor studies are warranted.

Nitric oxide functions in stromal cell-derived factor-1-induced cytoskeleton changes and the migration of Jurkat cells

Stromal cell-derived factor-1 (SDF-1) regulates multiple cell signal pathways in a variety of cellular functions, including cell migration, proliferation, survival and angiogenesis. SDF-1-induced chemotaxis is an important step of lymphocyte migration. However, the molecular mechanisms that modulate SDF-1-mediated lymphocyte migration are not well identified. Nitric oxide (NO) has been found to function as a signaling molecule in a number of signaling pathways, including migration. In the present study, the potential role of NO in SDF-1-induced migration and the association between NO and the cytoskeletal changes of Jurkat cells was investigated. The present study demonstrated that Jurkat cells induced the production of NO by SDF-1 stimulation, using Griess reaction method and western blot analysis, and that NO was involved in SDF-1-induced rearrangement and polymerization of the cytoskeleton, using NOS inhibitor L-NMMA. Furthermore, NO was required for the migration of Jurkat cells. The research suggested that NO signaling pathways exerted a critical role in SDF-1-induced cytoskeleton changes and the migration of Jurkat cells. This work provides insight into the migration mechanism of acute lymphoblastic leukemia and provides an effective theoretical basis for therapy strategies for acute lymphoblastic leukemia.

CD59 is a potential biomarker of esophageal squamous cell carcinoma radioresistance by affecting DNA repair

Radiation therapy is an important treatment modality for esophageal cancer. However, acquisition of radioresistance ultimately results in esophageal cancer relapse. CD59, a membrane-bound complement regulatory protein, can transduce signals via a Src kinase in the lipid raft, thus playing a complement-independent role. However, the effect of CD59 on the esophageal cancer response to ionizing radiation remains unclear. In this study, we found that the expression level of CD59 was positively correlated with the radioresistance of esophageal cancer cell lines and clinical specimens. High CD59 expression indicated poor overall survival (OS) and disease-free survival (DFS) in esophageal squamous cell carcinoma (ESCC) patients who received radiotherapy. Genetic alteration of CD59 expression modulated the radiosensitivity of esophageal cancer cells to ionizing radiation. CD59 deficiency exacerbated DNA damage, hindered cell proliferation, and induced G2/M cell cycle arrest and cellular senescence, leading to an impaired DNA damage repair ability. In addition, CD59 deficiency almost completely reduced the phosphorylation of Src at Y416 despite ionizing radiation. A Src inhibitor saracatinib sensitized esophageal cancer cells to irradiation. Therefore, CD59 may be a potential biomarker for predicting the radioresistance of ESCC to radiotherapy.

Utility of a Novel Three-Dimensional and Dynamic (3DD) Cell Culture System for PK/PD Studies: Evaluation of a Triple Combination Therapy at Overcoming Anti-HER2 Treatment Resistance in Breast Cancer

Background: Emergence of Human epidermal growth factor receptor 2 (HER2) therapy resistance in HER2-positive (HER2+) breast cancer (BC) poses a major clinical challenge. Mechanisms of resistance include the over-activation of the PI3K/mTOR and Src pathways. This work aims to investigate a novel combination therapy that employs paclitaxel (PAC), a mitotic inhibitor, with everolimus (EVE), an mTOR inhibitor, and dasatinib (DAS), an Src kinase inhibitor, as a modality to overcome resistance.

Methods: Static (two dimensional, 2D) and three-dimensional dynamic (3DD) cell culture studies were conducted using JIMT-1 cells, a HER2+ BC cell line refractory to HER2 therapies. Cell viability and caspase-3 expression were examined after JIMT-1 cell exposure to agents as monotherapy or in combination using a 2D setting. A pharmacokinetic/pharmacodynamic (PK/PD) combination study with PAC+DAS+EVE was conducted over 3 weeks in a 3DD setting. PAC was administered into the system via a 3 h infusion followed by the addition of a continuous infusion of EVE+DAS 24 h post-PAC dosing. Cell counts and caspase-3 expression were quantified every 2 days. A semi-mechanistic PK/PD model was developed using the 2D data and scaled up to capture the 3DD data. The final model integrated active caspase-3 as a biomarker to bridge between drug exposures and cancer cell dynamics. Model fittings were performed using Monolix software.

Results: The triple combination significantly induced caspase-3 activity in the 2D cell culture setting. In the 3DD cell culture setting, sequential dosing of PAC then EVE+DAS showed a 5-fold increase in caspase-3 activity and 8.5-fold decrease in the total cell number compared to the control. The semi-mechanistic PK/PD models fit the data well, capturing the time-course profiles of drug concentrations, caspase-3 expression, and cell counts in the 2D and 3DD settings.

Conclusion: A novel, sequential triple combination therapeutic regimen was successfully evaluated in both 2D and 3DD in vitro cell culture systems. The efficacy of this combination at inhibiting the cellular proliferation and re-growth of HER2/mTOR resistant cell line, JIMT-1, is demonstrated. A biomarker-linked PK/PD model successfully captured all time-course data. The latter can be used as a modeling platform for a direct translation from 3DD in vitro settings to the clinic.

Cytokine-mediated therapeutic resistance in breast cancer

Therapeutic resistance leading to tumor relapse is a major challenge in breast cancer (BCa) treatment. Numerous factors involved in multiple mechanisms promote the development of tumor chemo/radio-resistance. Cytokines/chemokines are important inflammatory factors and highly related to tumorigenesis, metastasis and tumors responses to treatment. A large number of studies have demonstrated that the network of cytokines activates multiple cell signaling pathways to promote tumor cell survival, proliferation, invasion, and migration. Particularly in BCa, cytokines-enhanced the epithelial-mesenchymal transition (EMT) process plays a pivotal role in the progression of metastatic phenotypes and resistance to the traditional chemo/radio-therapy. Virtually, therapeutic resistance is not entirely determined by tumor cell intrinsic characteristics but also dependent upon synchronized effects by numerous of local microenvironmental factors. Emerging evidence highlighted that exosomes secreted from various types of cells promote intercellular communication by transferring bioactive molecules including miRNAs and cytokines, suggesting that exosomes are essential for sustentation of tumor progression and therapeutic resistance within the tumor microenvironment. In this review, we discuss the mechanisms by which cytokines promote therapeutic resistance of BCa and suggest a potential approach for improving BCa therapeutics by inhibition of exosome function.

The erbB3- and IGF-1 receptor-initiated signaling pathways exhibit distinct effects on lapatinib sensitivity against trastuzumab-resistant breast cancer cells

Both erbB3 and IGF-1 receptor (IGF-1R) have been shown to play an important role in trastuzumab resistance. However, it remains unclear whether erbB3- and IGF-1R-initiated signaling pathways possess distinct effects on the sensitivity of lapatinib, a dual tyrosine kinase inhibitor against both EGFR and erbB2, in trastuzumab-resistant breast cancer. Here, we show that the trastuzumab-resistant SKBR3-pool2 and BT474-HR20 breast cancer sublines, as compared the parental SKBR3 and BT474 cells, respectively, exhibit refractoriness to lapatinib. Knockdown of erbB3 inhibited Akt in SKBR3-pool2 and BT474-HR20 cells, significantly increased lapatinib efficacy, and dramatically re-sensitized the cells to lapatinib-induced apoptosis. In contrast, specific knockdown of IGF-1R did not alter the cells' responsiveness to lapatinib. While the levels of phosphorylated Src (P-Src) were reduced upon IGF-1R downregulation, the P-Akt levels remained unchanged. Furthermore, a specific inhibitor of Akt, but not Src, significantly enhanced lapatinib-mediated anti-proliferative/anti-survival effects on SKBR3-pool2 and BT474-HR20 cells. These data indicate that erbB3 signaling is critical for both trastuzumab and lapatinib resistances mainly through the PI-3K/Akt pathway, whereas IGF-1R-initiated Src activation results in trastuzumab resistance without affecting lapatinib sensitivity. Our findings may facilitate the development of precision therapeutic regimens for erbB2-positive breast cancer patients who become resistant to erbB2-targeted therapy.

Immunohistochemical prediction of lapatinib efficacy in advanced HER2-positive breast cancer patients

Molecular mechanisms of lapatinib resistance in breast cancer are not well understood. The aim of this study was to correlate expression of selected proteins involved in ErbB family signaling pathways with clinical efficacy of lapatinib. Study group included 270 HER2-positive advanced breast cancer patients treated with lapatinib and capecitabine. Immunohistochemical expression of phosphorylated adenosine monophosphate-activated protein (p-AMPK), mitogen-activated protein kinase (p-MAPK), phospho (p)-p70S6K, cyclin E, phosphatase and tensin homolog were analyzed in primary breast cancer samples. The best discriminative value for progression-free survival (PFS) was established for each biomarker and subjected to multivariate analysis. At least one biomarker was determined in 199 patients. Expression of p-p70S6K was independently associated with longer (HR 0.45; 95% CI: 0.25–0.81; p = 0.009), and cyclin E with shorter PFS (HR 1.83; 95% CI: 1.06–3.14; p = 0.029). Expression of p-MAPK (HR 1.61; 95% CI 1.13–2.29; p = 0.009) and cyclin E (HR 2.99; 95% CI: 1.29–6.94; p = 0.011) was correlated with shorter, and expression of estrogen receptor (HR 0.65; 95% CI 0.43–0.98; p = 0.041) with longer overall survival. Expression of p-AMPK negatively impacted response to treatment (HR 3.31; 95% CI 1.48–7.44; p = 0.004) and disease control (HR 3.07; 95% CI 1.25–7.58; p = 0.015). In conclusion: the efficacy of lapatinib seems to be associated with the activity of downstream signaling pathways – AMPK/mTOR and Ras/Raf/MAPK. Further research is warranted to assess the clinical utility of these data and to determine a potential role of combining lapatinib with MAPK pathway inhibitors.

Lapatinib resistance in HER2+ cancers: latest findings and new concepts on molecular mechanisms

In the era of new and mostly effective molecular targeted therapies, human epidermal growth factor receptor 2 positive (HER2+) cancers are still intractable diseases. Lapatinib, a dual epidermal growth factor receptor (EGFR) and HER2 tyrosine kinase inhibitor, has greatly improved breast cancer prognosis in recent years after the initial introduction of trastuzumab (Herceptin). However, clinical evidence indicates the existence of both primary unresponsiveness and secondary lapatinib resistance, which leads to the failure of this agent in HER2+ cancer patients. It remains a major clinical challenge to target the oncogenic pathways with drugs having low resistance. Multiple pathways are involved in the occurrence of lapatinib resistance, including the pathways of receptor tyrosine kinase, non-receptor tyrosine kinase, autophagy, apoptosis, microRNA, cancer stem cell, tumor metabolism, cell cycle, and heat shock protein. Moreover, understanding the relationship among these mechanisms may contribute to future tumor combination therapies. Therefore, it is of urgent necessity to elucidate the precise mechanisms of lapatinib resistance and improve the therapeutic use of this agent in clinic. The present review, in the hope of providing further scientific support for molecular targeted therapies in HER2+ cancers, discusses about the latest findings and new concepts on molecular mechanisms underlying lapatinib resistance.

The voltage gated Ca(2+)-channel Cav3.2 and therapeutic responses in breast cancer

Background

Understanding the cause of therapeutic resistance and identifying new biomarkers in breast cancer to predict therapeutic responses will help optimise patient care. Calcium (Ca²⁺)-signalling is important in a variety of processes associated with tumour progression, including breast cancer cell migration and proliferation. Ca²⁺-signalling is also linked to the acquisition of multidrug resistance. This study aimed to assess the expression level of proteins involved in Ca²⁺-signalling in an in vitro model of trastuzumab-resistance and to assess the ability of identified targets to reverse resistance and/or act as potential biomarkers for prognosis or therapy outcome.

Methods

Expression levels of a panel of Ca²⁺-pumps, channels and channel regulators were assessed using RT-qPCR in resistant and sensitive age-matched SKBR3 breast cancer cells, established through continuous culture in the absence or presence of trastuzumab. The role of Ca_v3.2 in the acquisition of trastuzumab-resistance was assessed through pharmacological inhibition and induced overexpression. Levels of Ca_v3.2 were assessed in a panel of non-malignant and malignant breast cell lines using RT-qPCR and in patient samples representing different molecular subtypes (PAM50 cohort). Patient survival was also assessed in samples stratified by Ca_v3.2 expression (METABRIC and KM-Plotter cohort).

Results

Increased mRNA of Ca_v3.2 was a feature of both acquired and intrinsic trastuzumab-resistant SKBR3 cells. However, pharmacological inhibition of Ca_v3.2 did not restore trastuzumab-sensitivity nor did Ca_v3.2 overexpression induce the expression of markers associated with resistance, suggesting that Ca_v3.2 is not a driver of trastuzumab-resistance. Ca_v3.2 levels were significantly higher in luminal A, luminal B and HER2-enriched subtypes compared to the basal subtype. High levels of Ca_v3.2 were associated with poor outcome in patients with oestrogen receptor positive (ER+) breast cancers, whereas Ca_v3.2 levels were correlated positively with patient survival after chemotherapy in patients with HER2-positive breast cancers.

Conclusion

Our study identified elevated levels of Ca_v3.2 in trastuzumab-resistant SKBR3 cell lines. Although not a regulator of trastuzumab-resistance in HER2-positive breast cancer cells, Ca_v3.2 may be a potential differential biomarker for survival and treatment response in specific breast cancer subtypes. These studies add to the complex and diverse role of Ca²⁺-signalling in breast cancer progression and treatment.

Electronic supplementary material

The online version of this article (doi:10.1186/s12935-016-0299-0) contains supplementary material, which is available to authorized users.

Resistance to Targeted Therapies in Breast Cancer

Seventy five percent of all breast cancer (BC) patients express estrogen receptor (ER) but a quarter to half of patients with ER positive BC relapse on ET (endocrine therapy), tamoxifen, aromatase inhibitors (AIs), surgical castration, amongst other treatment strategies. ER positive BC at relapse loses ER expression in 20 % of cases and reduces quantitative ER expression most of the time. ER is not the only survival pathway driving ER positive BC and escape pathways intrinsic or acquired are activated during ET. This overview gives an account of ligand-independent ER activation, namely by receptor networks cross talk, and by the various genomic factors and mechanisms leading to ET response failure. Also the mechanisms of Her1 and Her2 inhibition resistance are dealt within this overview, along with the therapeutic indications and limitations of tyrosine kinase inhibitors, PARP inhibitors, PI3K/AKT/mTOR inhibitors, RAS/RAF/MEK/ERK/MAPK inhibitors, and antiangiogenic drugs. In spite of the many advances in controlling the division of BC cells and the progression of BC tumors these still remain the main cause of death among women in age range of 20-50 years requiring even more efforts in new therapeutic approaches besides the drugs within the scope of the overview.

Hypoxia/HIF1α induces lapatinib resistance in ERBB2-positive breast cancer cells via regulation of DUSP2

ERBB2/HER2 belongs to the EGFR-family of receptor tyrosine kinases and its overexpression can promote tumor progression. Breast cancer patients with ERBB2 amplifications are currently treated with lapatinib, a small-molecule kinase inhibitor that specifically blocks EGFR/ERBB2 signaling. Here, we show that hypoxia, via HIF-1, induces resistance to lapatinib-mediated effects in ERBB2-expressing mammary epithelial and ERBB2-positive breast cancer cells. Lapatinib-mediated growth inhibition and apoptosis in three-dimensional (3D) cultures are decreased under hypoxic conditions. Hypoxia can maintain activation of signaling pathways downstream from ERBB2 including AKT and ERK in the presence of lapatinib. HIF-1 is both required and sufficient to induce lapatinib resistance as overexpression of stable HIF-1 in ERBB2-expressing cells blocks lapatinib-mediated effects and maintains ERBB2-downstream signaling under normoxic conditions. Under hypoxia, activation of ERK signaling is required for lapatinib resistance as treatment with MEK inhibitor trametinib reverses hypoxia-mediated lapatinib resistance. HIF-1 can bypass the lapatinib-treated inhibition of the ERK pathway via inhibition of the dual-specificity phosphatase 2 (DUSP2). Indeed, overexpression of DUSP2 in ErbB2-positve breast cancer cells reverses hypoxia-mediated lapatinib resistance. Thus, our results provide rationale for therapeutic evaluation of the treatment of hypoxic ERBB2 expressing breast tumors with a combination of lapatinib and MEK inhibitors.

Niclosamide inhibits epithelial-mesenchymal transition and tumor growth in lapatinib-resistant human epidermal growth factor receptor 2-positive breast cancer

Acquired resistance to lapatinib, a human epidermal growth factor receptor 2 kinase inhibitor, remains a clinical problem for women with human epidermal growth factor receptor 2-positive advanced breast cancer, as metastasis is commonly observed in these patients. Niclosamide, an anti-helminthic agent, has recently been shown to exhibit cytotoxicity to tumor cells with stem-like characteristics. This study was designed to identify the mechanisms underlying lapatinib resistance and to determine whether niclosamide inhibits lapatinib resistance by reversing epithelial-mesenchymal transition. Here, two human epidermal growth factor receptor 2-positive breast cancer cell lines, SKBR3 and BT474, were exposed to increasing concentrations of lapatinib to establish lapatinib-resistant cultures. Lapatinib-resistant SKBR3 and BT474 cells exhibited up-regulation of the phenotypic epithelial-mesenchymal transition markers Snail, vimentin and α-smooth muscle actin, accompanied by activation of nuclear factor-кB and Src and a concomitant increase in stem cell marker expression (CD44(high)/CD24(low)), compared to naive lapatinib-sensitive SKBR3 and BT474 cells, respectively. Interestingly, niclosamide reversed epithelial-mesenchymal transition, induced apoptosis and inhibited cell growth by perturbing aberrant signaling pathway activation in lapatinib-resistant human epidermal growth factor receptor 2-positive cells. The ability of niclosamide to alleviate stem-like phenotype development and invasion was confirmed. Collectively, our results demonstrate that lapatinib resistance correlates with epithelial-mesenchymal transition and that niclosamide inhibits lapatinib-resistant cell viability and epithelial-mesenchymal transition. These findings suggest a role of niclosamide or derivatives optimized for more favorable bioavailability not only in reversing lapatinib resistance but also in reducing metastatic potential during the treatment of human epidermal growth factor receptor 2-positive breast cancer.

Protective autophagy promotes the resistance of HER2-positive breast cancer cells to lapatinib

Lapatinib, a tyrosine kinase inhibitor of HER2/EGFR, can inhibit the proliferation of HER2-positive breast cancer cells. Additionally, the combination of lapatinib and chemotherapy can markedly prolong patient survival time. However, the clinical therapeutic effect of lapatinib is severely limited by drug resistance. We previously found that brief treatment with lapatinib induced both apoptosis and autophagy in HER2-positive breast cancer cells. Additionally, the apoptosis induced by lapatinib was dependent on autophagy. In our current study, however, we used extended treatment of HER2-positive breast cancer cells with lapatinib to confirm the presence of protective autophagy in the previously established lapatinib-resistant cells. Specifically, we found that inhibition of autophagy could reduce the proliferation, DNA synthesis, and colony-forming capacity of resistant cells. Thus, autophagy is a potential novel therapeutic target for reversing lapatinib resistance of HER2-positive breast cancer cells. Our data provide clear, novel evidence of both anti-apoptotic and pro-apoptotic functions of autophagy in breast cancer during lapatinib treatment.

Efficacy and mechanism of action of the tyrosine kinase inhibitors gefitinib, lapatinib and neratinib in the treatment of HER2-positive breast cancer: preclinical and clinical evidence

An increasing number of tumors, including breast cancer, overexpress proteins of the epidermal growth factor receptor (EGFR) family. The interaction between family members activates signaling pathways that promote tumor progression and resistance to treatment. Human epidermal growth factor receptor type II (HER2) positive breast cancer represents a clinical challenge for current therapy. It has motivated the development of novel and more effective therapeutic EGFR family target drugs, such as tyrosine kinase inhibitors (TKIs). This review focuses on the effects of three TKIs mostly studied in HER2- positive breast cancer, lapatinib, gefitinib and neratinib. Herein, we discuss the mechanism of action, therapeutic advantages and clinical applications of these TKIs. To date, TKIs seem to be promising therapeutic agents for the treatment of HER2-overexpressing breast tumors, either as monotherapy or combined with other pharmacological agents.

Hematopoietic cell kinase (HCK) as a therapeutic target in immune and cancer cells

The hematopoietic cell kinase (HCK) is a member of the SRC family of cytoplasmic tyrosine kinases (SFKs), and is expressed in cells of the myeloid and B-lymphocyte cell lineages. Excessive HCK activation is associated with several types of leukemia and enhances cell proliferation and survival by physical association with oncogenic fusion proteins, and with functional interactions with receptor tyrosine kinases. Elevated HCK activity is also observed in many solid malignancies, including breast and colon cancer, and correlates with decreased patient survival rates. HCK enhances the secretion of growth factors and pro-inflammatory cytokines from myeloid cells, and promotes macrophage polarization towards a wound healing and tumor-promoting alternatively activated phenotype. Within tumor associated macrophages, HCK stimulates the formation of podosomes that facilitate extracellular matrix degradation, which enhance immune and epithelial cell invasion. By virtue of functional cooperation between HCK and bona fide oncogenic tyrosine kinases, excessive HCK activation can also reduce drug efficacy and contribute to chemo-resistance, while genetic ablation of HCK results in minimal physiological consequences in healthy mice. Given its known crystal structure, HCK therefore provides an attractive therapeutic target to both, directly inhibit the growth of cancer cells, and indirectly curb the source of tumor-promoting changes in the tumor microenvironment.

ShRNA-mediated knock-down of CXCR7 increases TRAIL-sensitivity in MCF-7 breast cancer cells

This study aims to investigate the effects of CXCR7-shRNA on TRAIL-mediated apoptosis and suppression of invasive migration and the underlying mechanisms. (1) We constructed CXCR-7-shRNA lentiviral vectors and confirmed their silencing efficiency in MCF-7 cells by RT-PCR analysis. (2) The effects of CXCR7 and/or TRAIL on cell proliferation were examined by MTT assay. (3) Trans well invasion assay was used to examine the effects of CXCR7 silencing and/or TRAIL on MCF-7 cell invasive migration. (4) Expression of Caspase-3, and Caspase-8, and MMP-2 and MMP-9 proteins was examined by Western blot analysis. (1) Viral titers were 2.95 × 10(8) TU/ml, 3.01 × 10(8) TU/ml, 3.26 × 10(8) TU/ml, and 3.08 × 10(8) TU/ml, respectively. (2) CHXR7 shRNAs markedly decreased CXCR7 mRNA expression in MCF-7 cells, among which CXCR7-shRNA-1 showed significantly higher rate of inhibition (P < 0.05). (3) Combination of TRAIL and CXCR7-shRNA-1 resulted in marked suppression of cell proliferation in time-dependent manner (P < 0.05). (4) Cell invasion capacity was inhibited in each experimental group as compared to blank control group at 48 h post treatments (P < 0.05). Among them, combination of TRAIL and CXCR7-shRNA had the highest inhibitory effect (P < 0.05). (5) Western blot analysis indicated that TRAIL alone does not affect CXCR7 expression, but either TRAIL + CXCR7 shRNA or CXCR7 shRNA alone markedly suppressed CXCR7 protein expression. Furthermore, combination of TRAIL and CXCR-7-shRNA significantly increased Caspase-3 and Caspase-8 expression and decreased MMP-2 and MMP-9 expression (P < 0.05). Knock-down of CXCR-7 expression leads to augmented TRAIL-mediated suppression of MCF-7 cell proliferation and invasion.

Src mutation induces acquired lapatinib resistance in ERBB2-amplified human gastroesophageal adenocarcinoma models

ERBB2-directed therapy is now a routine component of therapy for ERBB2-amplified metastatic gastroesophageal adenocarcinomas. However, there is little knowledge of the mechanisms by which these tumors develop acquired resistance to ERBB2 inhibition. To investigate this question we sought to characterize cell line models of ERBB2-amplified gastroesophageal adenocarcinoma with acquired resistance to ERBB2 inhibition. We generated lapatinib-resistant (LR) subclones from an initially lapatinib-sensitive ERBB2-amplified esophageal adenocarcinoma cell line, OE19. We subsequently performed genomic characterization and functional analyses of resistant subclones with acquired lapatinib resistance. We identified a novel, acquired SrcE527K mutation in a subset of LR OE19 subclones. Cells with this mutant allele harbour increased Src phosphorylation. Genetic and pharmacologic inhibition of Src resensitized these subclones to lapatinib. Biochemically, Src mutations could activate both the phosphatidylinositol 3-kinase and mitogen activated protein kinase pathways in the lapatinib-treated LR OE19 cells. Ectopic expression of SrcE527K mutation also was sufficient to induce lapatinib resistance in drug-naïve cells. These results indicate that pathologic activation of Src is a potential mechanism of acquired resistance to ERBB2 inhibition in ERBB2-amplified gastroesophageal cancer. Although Src mutation has not been described in primary tumor samples, we propose that the Src hyperactivation should be investigated in the settings of acquired resistance to ERBB2 inhibition in esophageal and gastric adenocarcinoma.

Targeting death receptors for TRAIL by agents designed by Mother Nature

Selective killing of cancer cells is one of the major goals of cancer therapy. Although chemotherapeutic agents are being used for cancer treatment, they lack selectivity toward tumor cells. Among the six different death receptors (DRs) identified to date, DR4 and DR5 are selectively expressed on cancer cells. Therefore, unlike chemotherapeutic agents, these receptors can potentially mediate selective killing of tumor cells. In this review we outline various nutraceuticals derived from 'Mother Nature' that can upregulate DRs and thus potentiate apoptosis. These nutraceuticals increase tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL)-induced apoptosis of cancer cells through different mechanisms. First, nutraceuticals have been found to induce DRs through the upregulation of various signaling molecules. Second, nutraceuticals can downregulate tumor cell-survival pathways. Third, nutraceuticals alone have been found to activate cell-death pathways. Although both TRAIL and agonistic antibodies against DR4 and DR5 are in clinical trials, combination with nutraceuticals is likely to boost their anticancer potential.

Therapeutic targeting of ERBB2 in breast cancer: understanding resistance in the laboratory and combating it in the clinic

ERBB2 gene amplification occurs in about one quarter of breast carcinomas (BCs) and identifies a distinct clinical subset of BC. The introduction in the clinic of Trastuzumab, a humanized monoclonal antibody (mAb) directed to the ERBB2 extracellular domain, has had a great impact on the therapeutic management of ERBB2+ BC. Yet, not all patients respond to Trastuzumab and resistance develops also among patients that initially benefit from Trastuzumab-based regimens. Pre-clinical studies have discovered several mechanisms through which tumor cells may escape from Trastuzumab-mediated ERBB2 inhibition. These include rewiring of the ErbB signaling network, loss of ERBB2 expression, expression of ERBB2 isoforms refractory to Trastuzumab inhibition, vicarious signaling by non-ErbB tyrosine kinases and constitutive activation of downstream signaling routes, such as the PI3K pathway. While the relative contribution of each of these mechanisms to establishing Trastuzumab resistance in the clinical setting is not fully understood, much attention has been focused on abating resistance by achieving complete blockade of ERBB2-containing dimers. This approach, propelled by the development of novel anti-ERBB2 therapeutics, has led to the recent approval of Lapatinib, Pertuzumab and T-DM1 as additional anti-ERBB2 therapeutics in BC. However, full success is far from being achieved and resistance to ERBB2 targeting remains a relevant problem in the clinical management of BC. Herein, we provide an overview of biological and molecular bases underpinning resistance to ERBB2 therapeutics in BC, discuss outstanding issues in the field of ERBB2 therapeutic targeting and elaborate on future directions of translational research on ERBB2+ breast cancer.

Src/caveolin-1-regulated EGFR activation antagonizes TRAIL-induced apoptosis in gastric cancer cells

Gastric cancer cells are insensitive to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), and we recently showed that lipid raft-regulated epidermal growth factor receptor (EGFR) activation antagonized TRAIL-induced apoptosis. However, it is not clear whether caveolin-1, an essential structural constituent of lipid rafts, regulates lipid raft-mediated EGFR activation. We report here that TRAIL induced the translocation of EGFR into lipid rafts and its activation in gastric cancer SGC-7901 and MGC-803 cells. Simultaneously, caveolin-1 was also activated. Knockdown of caveolin-1 partially prevented EGFR activation and increased TRAIL sensitivity. Moreover, TRAIL promoted the translocation of Src into lipid rafts and its activation, as well as the interaction of Src with both EGFR and caveolin-1. A Src inhibitor prevented these interactions and the activation of caveolin-1 and EGFR, and thus enhanced TRAIL-induced apoptosis. These data suggest that Src activates EGFR through the interaction of both Src-EGFR and Src-caveolin-1, and then antagonizes TRAIL-induced apoptosis in gastric cancer cells.

Epidermal growth factor-receptor activation modulates Src-dependent resistance to lapatinib in breast cancer models

Introduction

Src tyrosine kinase overactivation has been correlated with a poor response to human epidermal growth factor receptor 2 (HER2) inhibitors in breast cancer. To identify the mechanism by which Src overexpression sustains this resistance, we tested a panel of breast cancer cell lines either sensitive or resistant to lapatinib.

Methods

To determine the role of Src in lapatinib resistance, we evaluated the effects of Src inhibition/silencing in vitro on survival, migration, and invasion of lapatinib-resistant cells. In vivo experiments were performed in JIMT-1 lapatinib-resistant cells orthotopically implanted in nude mice. We used artificial metastasis assays to evaluate the effect of Src inhibition on the invasiveness of lapatinib-resistant cells. Src-dependent signal transduction was investigated with Western blot and ELISA analyses.

Results

Src activation was higher in lapatinib-resistant than in lapatinib-sensitive cells. The selective small-molecule Src inhibitor saracatinib combined with lapatinib synergistically inhibited the proliferation, migration, and invasion of lapatinib-resistant cells. Saracatinib combined with lapatinib significantly prolonged survival of JIMT-1-xenografted mice compared with saracatinib alone, and impaired the formation of lung metastases. Unexpectedly, in lapatinib-resistant cells, Src preferentially interacted with epidermal growth factor receptor (EGFR) rather than with HER2. Moreover, EGFR targeting and lapatinib synergistically inhibited survival, migration, and invasion of resistant cells, thereby counteracting Src-mediated resistance. These findings demonstrate that Src activation in lapatinib-resistant cells depends on EGFR-dependent rather than on HER2-dependent signaling.

Conclusions

Complete pharmacologic EGFR/HER2 inhibition is required to reverse Src-dependent resistance to lapatinib in breast cancer.