The Dual ErbB1/ErbB2 Inhibitor, Lapatinib (GW572016), Cooperates with Tamoxifen to Inhibit Both Cell Proliferation- and Estrogen-Dependent Gene Expression in Antiestrogen-Resistant Breast Cancer

IQ Motif Containing GTPase Activating Proteins (IQGAPs), A-Kinase Anchoring Proteins (AKAPs) and Kinase Suppressor of Ras Proteins (KSRs) in Scaffolding Oncogenic Pathways and Their Therapeutic Potential

Scaffolding proteins colocalize interacting partners on their surface and facilitate complex formation. They have multiple domains and motifs, which provide binding sites for various molecules. This property of scaffolding proteins helps in the orderly transduction of signals. Abnormal signal transduction is frequently observed in cancers, which can also be attributed to the altered functionality of scaffolding proteins. IQ motif containing GTPase activating proteins (IQGAPs), kinase suppressor of Ras (KSR), and A-kinase anchoring proteins (AKAPs) tether oncogenic pathways RAS/RAF/MEK/ERK, PI3K/AKT, Hippo, Wnt, and CDC42/RAC to them. Scaffolding proteins are attractive drug targets as they are the controlling hub for multiple pathways and regulate crosstalk between them. The first part of this review describes the human scaffolding proteins known to play a role in oncogenesis, pathways altered by them, and the impact on oncogenic processes. The second part provides information on the therapeutic potential of scaffolding proteins and future possibilities. The information on the explored and unexplored areas of the therapeutic potential of scaffolding proteins will be equally helpful for biologists and chemists.

Enhancement of Sensitivity to Tamoxifen by Berberine in Breast Cancer Cells by Inhibiting ER-α36 Expression

Berberine, an isoquinoline alkaloid purified from Chinese herbs, was verified to have antitumor effects. It has also been reported that berberine can enhance the anticancer effect of tamoxifen (TAM) in estrogen receptor (ER)-positive breast cancer cells; however, the involved underlying mechanism is still unclear. In the present study, the role of one variant of ER-α, ER-α36, in the TAM sensitizing effect of berberine was explored in TAM-resistant breast cancer cells. This study demonstrated that berberine potently sensitized TAM-resistant breast cancer cells, including TAM-resistant MCF7 and BT-474 cells, to TAM treatment. Additionally, this study showed that berberine could simultaneously suppress ER-α36 expression in TAM-resistant cells. However, when ER-α36 was knocked down in TAM-resistant cells, there was no significant TAM-sensitizing effect by berberine. Therefore, this study indicated that ER-α36 is involved in berberine's TAM-sensitizing effect on ER-positive breast cancer cells, which provided supporting data for the application of berberine in cancer therapy as an adjuvant agent for TAM treatment.

Pan-HER-targeted approach for cancer therapy: Mechanisms, recent advances and clinical prospect

The Human Epidermal Growth Factor Receptor family is composed of 4 structurally related receptor tyrosine kinases that are involved in many human cancers. The efficacy and safety of HER inhibitors have been compared in a wide range of clinical trials, suggesting the superior inhibitory ability of multiple- HER-targeting blockade compared with single receptor antagonists. However, many patients are currently resistant to current therapeutic treatment and novel strategies are warranted to conquer the resistance. Thus, we performed a critical review to summarize the molecular involvement of HER family receptors in tumour progression, recent anti-HER drug development based on clinical trials, and the potential resistance mechanisms of anti-HER therapy.

Crosstalk between ERα and Receptor Tyrosine Kinase Signalling and Implications for the Development of Anti-Endocrine Resistance

Although anti-endocrine therapies have significantly advanced the treatment of breast cancer, they pose the problem of acquired drug resistance. The oestrogen receptor (ER)-expressing breast cancer cell lines MCF-7 and T47D alongside their in vitro derived resistant counterparts MCF-7-TR (tamoxifen-resistant) and T47D-FR (fulvestrant-resistant) showed dual resistance to fulvestrant and tamoxifen in the presence of upregulated HER1 and HER2 growth factor receptors. Our study demonstrated that tamoxifen resistance and fulvestrant resistance are associated with collateral sensitivity to the tyrosine kinase inhibitors (TKIs) lapatinib (p < 0.0001) and afatinib (p < 0.0001). Further, we found that over time, the TKIs reactivated ER&alpha; protein and/or mRNA in tamoxifen- and fulvestrant-resistant cells. Combinations of anti-endocrine agents with afatinib gave rise to significantly enhanced levels of apoptosis in both T47D-FR and MCF-7-TR in a synergistic manner versus additive effects of agents used singly. This was associated with p27^kip1 induction for anti-endocrine-resistant cells versus parental cells. Our data supports the use of combination treatment utilising dual HER1/2 inhibitors in breast cancer patients showing resistance to multiple anti-endocrine agents.

Estrogen can restore Tamoxifen sensitivity in breast cancer cells amidst the complex network of resistance

Breast cancer-related deaths have been on the decline ever since the application of systemic therapies. Chiefly, endocrine therapy, such as Tamoxifen, enhances the survival of estrogen receptor (ER)-positive patients. More than a decade has passed since the introduction of Tamoxifen, however, drug resistance, particularly to Tamoxifen, still remains a major challenge. It has been shown that not only does chronic Tamoxifen exposures induce resistance, but estrogen deprivation can as well. There are two Tamoxifen resistant cell lines, long term estrogen deprived (LTED) cells and cells that have acquired resistance due to long-term exposure to Tamoxifen (Tam-R). Despite having similar cytosolic pathways over-activated in Tam-R and LTED-R cells during the development of resistance, the administration of receptor tyrosine kinases (RTKs) inhibitors fail to restore Tamoxifen sensitivity in LTED-Rs. This alludes to existing differences in the underlying molecular mechanisms of resistance. Surprisingly, despite estrogen being recognized as a breast cancer stimulator; it has recently been introduced as an apoptotic inducer in unresponsive cells. Furthermore, the addition of estrogen to the media of LTED and Tam-R cells triggers cell death, perhaps is functioning as an anti-proliferative agent. In this review, we outline the molecular pathways potentially facilitating estrogen-induced apoptosis in resistant cells.

Post-transcriptional regulation of ERBB2 by miR26a/b and HuR confers resistance to tamoxifen in estrogen receptor-positive breast cancer cells

Tamoxifen-resistant (TAMR) estrogen receptor-positive (ER+) breast cancer is characterized by elevated Erb-B2 receptor tyrosine kinase 2 (ERBB2) expression. However, the underlying mechanisms responsible for the increased ERBB2 expression in the TAMR cells remain poorly understood. Herein, we reported that the ERBB2 expression is regulated at the post-transcriptional level by miR26a/b and the RNA-binding protein human antigen R (HuR), both of which associate with the 3'-UTR of the ERBB2 transcripts. We demonstrated that miR26a/b inhibits the translation of ERBB2 mRNA, whereas HuR enhances the stability of the ERBB2 mRNA. In TAMR ER+ breast cancer cells with elevated ERBB2 expression, we observed a decrease in the level of miR26a/b and an increase in the level of HuR. The forced expression of miR26a/b or the depletion of HuR decreased ERBB2 expression in the TAMR cells, resulting in the reversal of tamoxifen resistance. In contrast, the inactivation of miR26a/b or forced expression of HuR decreased tamoxifen responsiveness of the parental ER+ breast cancer cells. We further showed that the increase in HuR expression in the TAMR ER+ breast cancer cells is attributable to an increase in the HuR mRNA isoform with shortened 3'-UTR, which exhibits increased translational activity. This shortening of the HuR mRNA 3'-UTR via alternative polyadenylation (APA) was observed to be dependent on cleavage stimulation factor subunit 2 (CSTF2/CstF-64), which is up-regulated in the TAMR breast cancer cells. Taken together, we have characterized a model in which the interplay between miR26a/b and HuR post-transcriptionally up-regulates ERBB2 expression in TAMR ER+ breast cancer cells.

Synergistic disruption of ERα/HER2 crosstalk by endoxifen and lapatinib in breast cancer cells

BACKGROUND

Despite decades of clinical success, tamoxifen therapy is complicated by inter-individual variability due to CYP450 polymorphism and resistance attributed to ERα/HER2 crosstalk. Direct administration of endoxifen shows promise in circumventing obligatory CYP450 bioactivation while maintaining efficacy. Separately, disruption of the crosstalk using probe antagonists against ERα (tamoxifen) and HER2 (e.g., lapatinib) has been explored clinically. However, the efficacy of this combination may be confounded by lapatinib, a potent inactivator of CYP3A4/5 which could negate the bioactivation of tamoxifen to the active metabolite endoxifen. Additionally, in a manner analogous to tamoxifen, endoxifen is similarly not immune to the development of ERα/HER2 crosstalk that could result in resistance. Simultaneous antagonism of ERα and HER2 using endoxifen and lapatinib could overcome these problems.

METHODS

Metabolism studies were performed in human liver microsomes to determine the extent of inhibition of tamoxifen bioactivation by lapatinib. Synergism of endoxifen and lapatinib was assessed using the combination index design in a panel of cell models exhibiting either a priori ERα/HER2 crosstalk (BT474) or acquired ERα/HER2 crosstalk (TAM-R and MCF-7/HER2).

RESULTS

Lapatinib inhibited tamoxifen bioactivation by up to 1.8-fold. Synergistic activity was uncovered for lapatinib and endoxifen against BT474, TAM-R and MCF-7/HER2 models of ERα/HER2 crosstalk. Western blot confirmed that endoxifen and lapatinib disrupted this crosstalk.

CONCLUSION

This forward-looking study extends the success of tamoxifen by exploring the effectiveness of combining the next-generation tamoxifen derivative, endoxifen with an anti-HER2 agent to combat ERα/HER2 crosstalk, and at the same time provides a solution to the predicted pharmacokinetic antagonism between lapatinib and tamoxifen.

Approaches to modernize the combination drug development paradigm

Recent advances in genomic sequencing and omics-based capabilities are uncovering tremendous therapeutic opportunities and rapidly transforming the field of cancer medicine. Molecularly targeted agents aim to exploit key tumor-specific vulnerabilities such as oncogenic or non-oncogenic addiction and synthetic lethality. Additionally, immunotherapies targeting the host immune system are proving to be another promising and complementary approach. Owing to substantial tumor genomic and immunologic complexities, combination strategies are likely to be required to adequately disrupt intricate molecular interactions and provide meaningful long-term benefit to patients. To optimize the therapeutic success and application of combination therapies, systematic scientific discovery will need to be coupled with novel and efficient clinical trial approaches. Indeed, a paradigm shift is required to drive precision medicine forward, from the traditional "drug-centric" model of clinical development in pursuit of small incremental benefits in large heterogeneous groups of patients, to a "strategy-centric" model to provide customized transformative treatments in molecularly stratified subsets of patients or even in individual patients. Crucially, to combat the numerous challenges facing combination drug development-including our growing but incomplete understanding of tumor biology, technical and informatics limitations, and escalating financial costs-aligned goals and multidisciplinary collaboration are imperative to collectively harness knowledge and fuel continual innovation.

Resistance to therapy in estrogen receptor positive and human epidermal growth factor 2 positive breast cancers: progress with latest therapeutic strategies

In this article, we focus on the subtype of estrogen receptor (ER)-positive, human epidermal growth factor 2 (HER2)-positive breast cancer (BC). Preclinical and clinical data indicate a complex molecular bidirectional crosstalk between the ER and HER2 pathways. This crosstalk probably constitutes one of the key mechanisms of drug resistance in this subclass of BC. Delaying or even reversing drug resistance seems possible by targeting pathways implicated in this crosstalk. High-risk patients currently receive anti-HER2 therapy, chemotherapy and endocrine therapy in the adjuvant setting. In metastatic cases, most patients receive a combination of anti-HER2 therapy and chemotherapy. Only selected patients presenting more indolent disease are candidates for combinations of anti-HER2 therapy and endocrine therapy. However, relative improvements in progression-free survival by chemotherapy-based regimens are usually lower in ER-positive patients than the ER-negative and HER2-positive subgroup. Consequently, new approaches aiming to overcome endocrine therapy resistance by adding targeted therapies to endocrine therapy based regimens are currently explored. In addition, dual blockade of HER2 or the combination of trastuzumab and phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin (mTOP) inhibitors targeting the downstream pathway are strategies to overcome resistance to trastuzumab. This may lead in the near future to the less frequent use of chemotherapy-based treatment options in ER-positive, HER2-positive BC.

Lower Beclin 1 downregulates HER2 expression to enhance tamoxifen sensitivity and predicts a favorable outcome for ER positive breast cancer

Tamoxifen(TAM) is one of the most effective endocrine treatment for estrogen receptor(ER)-positive breast cancer, however drug resistance greatly limits benefit of it. Our purpose is to uncover the role of Beclin 1 in tamoxifen resistance and prognosis of ER positive breast cancer. We established a tamoxifen resistant ER-positive breast cancer cell subline MCF-7R presenting with higher Beclin 1 and human epidermal growth factor receptor 2(HER2) levels than MCF-7. Silencing Beclin 1 decreased levels of HER2 and significantly promoted TAM sensitivity of MCF-7 and MCF-7R in vitro. Overexpression of HER2 could reverse TAM sensitivity, which was formerly increased in Beclin 1 downregulated cell. Beclin 1 level was not only positively correlated with level of HER2 but also negatively correlated with overall survival of ER-positive breast cancer patients. Using bioinformatic methods, Beclin 1 mRNA was found to be negatively correlated with overall survival in breast cancer patients receiving TAM treatment. This study indicated for the first time that lower HER2 expression by Beclin 1 downregulation contributes to alteration of tamoxifen sensitivity and low Beclin 1 predicts favorable outcome in ER-positive breast cancer.

Lapatinib (Tykerb, GW572016) reverses multidrug resistance in cancer cells by inhibiting the activity of ATP-binding cassette subfamily B member 1 and G member 2

Lapatinib is active at the ATP-binding site of tyrosine kinases that are associated with the human epidermal growth factor receptor (Her-1 or ErbB1) and Her-2. It is conceivable that lapatinib may inhibit the function of ATP-binding cassette (ABC) transporters by binding to their ATP-binding sites. The aim of this study was to investigate the ability of lapatinib to reverse tumor multidrug resistance (MDR) due to overexpression of ABC subfamily B member 1 (ABCB1) and ABC subfamily G member 2 (ABCG2) transporters. Our results showed that lapatinib significantly enhanced the sensitivity to ABCB1 or ABCG2 substrates in cells expressing these transporters, although a small synergetic effect was observed in combining lapatinib and conventional chemotherapeutic agents in parental sensitive MCF-7 or S1 cells. Lapatinib alone, however, did not significantly alter the sensitivity of non-ABCB1 or non-ABCG2 substrates in sensitive and resistant cells. Additionally, lapatinib significantly increased the accumulation of doxorubicin or mitoxantrone in ABCB1- or ABCG2-overexpressing cells and inhibited the transport of methotrexate and E(2)17betaG by ABCG2. Furthermore, lapatinib stimulated the ATPase activity of both ABCB1 and ABCG2 and inhibited the photolabeling of ABCB1 or ABCG2 with [(125)I]iodoarylazidoprazosin in a concentration-dependent manner. However, lapatinib did not affect the expression of these transporters at mRNA or protein levels. Importantly, lapatinib also strongly enhanced the effect of paclitaxel on the inhibition of growth of the ABCB1-overexpressing KBv200 cell xenografts in nude mice. Overall, we conclude that lapatinib reverses ABCB1- and ABCG2-mediated MDR by directly inhibiting their transport function. These findings may be useful for cancer combinational therapy with lapatinib in the clinic.

Tamoxifen resistance in breast tumors is driven by growth factor receptor signaling with repression of classic estrogen receptor genomic function

Not all breast cancers respond to tamoxifen, and many develop resistance despite initial benefit. We used an in vivo model of estrogen receptor (ER)-positive breast cancer (MCF-7 xenografts) to investigate mechanisms of this resistance and develop strategies to circumvent it. Epidermal growth factor receptor (EGFR) and HER2, which were barely detected in control estrogen-treated tumors, increased slightly with tamoxifen and were markedly increased when tumors became resistant. Gefitinib, which inhibits EGFR/HER2, improved the antitumor effect of tamoxifen and delayed acquired resistance, but had no effect on estrogen-stimulated growth. Phosphorylated levels of p42/44 and p38 mitogen-activated protein kinases (both downstream of EGFR/HER2) were increased in the tamoxifen-resistant tumors and were suppressed by gefitinib. There was no apparent increase in phosphorylated AKT (also downstream of EGFR/HER2) in resistant tumors, but it was nonetheless suppressed by gefitinib. Phosphorylated insulin-like growth factor-IR (IGF-IR), which can interact with both EGFR and membrane ER, was elevated in the tamoxifen-resistant tumors compared with the sensitive group. However, ER-regulated gene products, including total IGF-IR itself and progesterone receptor, remained suppressed even at the time of acquired resistance. Tamoxifen's antagonism of classic ER genomic function was retained in these resistant tumors and even in tumors that overexpress HER2 (MCF-7 HER2/18) and are de novo tamoxifen-resistant. In conclusion, EGFR/HER2 may mediate tamoxifen resistance in ER-positive breast cancer despite continued suppression of ER genomic function by tamoxifen. IGF-IR expression remains dependent on ER but is activated in the tamoxifen-resistant tumors. This study provides a rationale to combine HER inhibitors with tamoxifen in clinical studies, even in tumors that do not initially overexpress EGFR/HER2.

Identification of cyclin D1- and estrogen-regulated genes contributing to breast carcinogenesis and progression

Tumors can become lethal when they progress from preinvasive lesions to invasive carcinomas. Here, we identify candidate tumor progression genes using gene array analysis of preinvasive and invasive tumors from mice, which were then evaluated in human cancers. Immediate early response protein IEX-1, small stress protein 1 (HSPB8), and tumor necrosis factor-associated factor-interacting protein mRNAs displayed higher expression levels in invasive lesions than in preinvasive lesions using samples obtained by laser capture microdissection (LCM) from transgenic erbB2, ras, and cyclin D1 mice. LCM-isolated tissues from patient-matched normal, ductal carcinoma in situ, and invasive ductal carcinoma revealed similar increased expression in invasive human cancers compared with preinvasive and normal samples. These genes induced anchorage independence, increased cell proliferation, and protected against apoptosis, singly or in collaboration with erbB2. Surprisingly, they were all up-regulated by 17beta-estradiol and cyclin D1, and cyclin D1 overexpression increased p300/CBP binding to their promoters, supporting the model that cyclin D1-estrogen receptor (ER) coactivator interactions may be important to its role in ER-positive breast cancer. Additionally, an irreversible dual kinase inhibitor of ErbB signaling inhibited expression of the same genes. The up-regulation of genes contributing to increased invasiveness of ER-positive cancers offers a novel explanation for the contribution of cyclin D1 to a worse prognosis in ER-positive cancers. As targets of estrogen, cyclin D1, and erbB2 signaling, these candidates offer insights into the nature of the second events involved in breast cancer progression, regulatory events contributing to invasion, and potential targets of combined inhibition of hormone and growth factor signaling pathways.

Blockade of EGFR and ErbB2 by the novel dual EGFR and ErbB2 tyrosine kinase inhibitor GW572016 sensitizes human colon carcinoma GEO cells to apoptosis

Coexpression of the epidermal growth factor receptor (EGFR) family receptors is found in a subset of colon cancers, which may cooperatively promote cancer cell growth and survival, as heterodimerization is known to provide for diversification of signal transduction. Recently, efforts have been made to develop novel 4-anilinoquinazoline and pyridopyrimidine derivatives to inhibit EGFR and ErbB2 kinases simultaneously. In this study, we tested the efficacy of a novel reversible dual inhibitor GW572016 compared with the selective EGFR and ErbB2 tyrosine kinase inhibitors (TKI) AG1478 and AG879 and their combination, using the human colon adenocarcinoma GEO mode. GEO cells depend on multiple ErbB receptors for aberrant growth. A synergistic effect on inhibition of cell proliferation associated with induction of apoptosis was observed from the combination of AG1478 and AG879. Compared with AG1478 or AG879, the single TKI compound GW572016 was a more potent inhibitor of GEO cell proliferation and was able to induce apoptosis at lower concentrations. Western blot analysis revealed that AG1478 and AG879 were unable to suppress both EGFR and ErbB2 activation as well as the downstream mitogen-activated protein kinase (MAPK) and AKT pathways as single agents. In contrast, GW572016 suppressed the activation of EGFR, ErbB2, MAPK, and AKT in a concentration-dependent manner. Finally, in vivo studies showed that GW572016 treatment efficiently blocked GEO xenograft growth at a dose range of 30 to 200 mg/kg with a twice-daily schedule. In summary, our study indicates that targeting both EGFR and ErbB2 simultaneously could enhance therapy over that of single agents directed at EGFR or ErbB2 in cancers that can be identified as being primarily heterodimer-dependent.