The phosphatidyl inositol 3-kinase/AKT signaling pathway in breast cancer

The phosphatidyl inositol 3-kinase (PI3K)/Akt pathway mediates the effects of a variety of extracellular signals in a number of cellular processes including cell growth, proliferation, and survival. The alteration of integrants of this pathway through mutation of its coding genes increases the activation status of the signaling and can thus lead to cellular transformation. The frequent dysregulation of the PI3K/Akt pathway in breast cancer (BC) and the mediation of this pathway in different processes characteristically implicated in tumorigenesis have attracted the interest of this pathway in BC; however, a more comprehensive understanding of the signaling intricacies is necessary to develop clinical applications of the modulation of this pathway in this pathology. We review a series of experiments examining the contribution of alteration of integrants of this signaling network to human BC and we make an update of the information about the effect of the modulation of this pathway in this cancer.     

Targeting the phosphatidylinositol 3-kinase signaling pathway in breast cancer

The phosphatidylinositol 3-kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) network plays a key regulatory function in cell survival, proliferation, migration, metabolism, angiogenesis, and apoptosis. Genetic aberrations found at different levels, either with activation of oncogenes or inactivation of tumor suppressors, make this pathway one of the most commonly disrupted in human breast cancer. The PI3K-dependent phosphorylation and activation of the serine/threonine kinase AKT is a key activator of cell survival mechanisms. The activation of the oncogene PIK3CA and the loss of regulators of AKT including the tumor suppressor gene PTEN are mutations commonly found in breast tumors. AKT relieves the negative regulation of mTOR to activate protein synthesis and cell proliferation through S6K and 4EBP1. The common activation of the PI3K pathway in breast cancer has led to the development of compounds targeting the effector mechanisms of the pathway including selective and pan-PI3K/pan-AKT inhibitors, rapamycin analogs for mTOR inhibition, and TOR-catalytic subunit inhibitors. The influences of other oncogenic pathways such as Ras-Raf-Mek on the PI3K pathway and the known feedback mechanisms of activation have prompted the use of compounds with broader effect at multiple levels and rational combination strategies to obtain a more potent antitumor activity and possibly a meaningful clinical effect. Here, we review the biology of the network, its role in the development and progression of breast cancer, and the evaluation of targeted therapies in clinical trials.     

Phosphoinositide 3-kinase signaling is critical for ErbB3-driven breast cancer cell motility and metastasis

Many malignancies show increased expression of the epidermal growth factor (EGF) receptor family member ErbB3 (HER3). ErbB3 binds heregulin β-1 (HRGβ1) and forms a heterodimer with other ErbB family members, such as ErbB2 (HER2) or EGF receptor (EGFR; HER1), enhancing phosphorylation of specific C-terminal tyrosine residues and activation of downstream signaling pathways. ErbB3 contains six YXXM motifs that bind the p85 subunit of phosphoinositide 3 (PI3)-kinase. Previous studies demonstrated that overexpression of ErbB3 in mammary tumor cells can significantly enhance chemotaxis to HRGβ1 and overall metastatic potential. We tested the hypothesis that ErbB3-mediated PI3-kinase signaling is critical for heregulin-induced motility, and therefore crucial for ErbB3-mediated invasion, intravasation and metastasis. The tyrosines in the six YXXM motifs on the ErbB3 C-terminus were replaced with phenylalanine. In contrast to overexpression of the wild-type ErbB3, overexpression of the mutant ErbB3 did not enhance chemotaxis towards HRGβ1 in vitro or in vivo. We also observed reduced tumor cell motility in the primary tumor by multiphoton microscopy, as well as a dramatically reduced ability of these cells to cross the endothelium and intravasate into the circulation. Moreover, whereas mutation of the ErbB3 C-terminus had no effect on tumor growth, it had a dramatic effect on spontaneous metastatic potential. Treatment with the PI3-kinase inhibitor PIK-75 similarly inhibited motility and invasion in vitro and in vivo. Our results indicate that stimulation of the early metastatic steps of motility and invasion by ErbB3 requires activation of the PI3-kinase pathway by the ErbB3 receptor.     

Dysregulation of phosphatidylinositol 3-kinase and downstream effectors in human breast cancer

Phosphatidylinositol 3-kinase (PI3-K) is a growth factor-activated transforming lipid (and protein) kinase, involved in cell motility and invasion, that has multiple effectors. Relatively little is known about its expression and enzymatic activity in human breast cancer. Since growth factor receptors are amplified in breast cancer, and the tumor suppressor PTEN may be mutated in human breast cancer, it was hypothesized that PI3-K and its downstream effectors would be activated in this disease. In 11 resected tumors analyzed for expression of this kinase, a mean 3-fold increase in protein expression was observed over the corresponding adjacent control tissue. Using an in vitro lipid kinase assay of the immunoprecipitated PI3-K protein, a greater than 2-fold increase in activation was observed. These changes were observed in the absence of an activation of either protein kinase B (PKB, akt1) or p70 S6 kinase (p70 S6K). However, p21-activated kinase (Pak), p38 mitogen-activated protein kinase (p38 MAPK) and mitogen-activated protein kinase-activated protein kinase 2 (MAPKAPK 2) were all overexpressed and demonstrated increased enzyme activity. It may be concluded that aberrant mitogenic signaling in human breast cancer in vivo involves Pak, p38 MAPK and MAPKAPK2 downstream of PI3-K, but neither of PKB or p70 S6K. It is proposed that this pathway may serve as a useful targeting nexus for investigation of small molecule inhibitors in human breast cancer.     

Class IA phosphoinositide 3-kinase isoforms and human tumorigenesis: implications for cancer drug discovery and development

PURPOSE OF REVIEW: The phosphoinositide 3-kinases are lipid kinases that are activated in response to external factors. They regulate a number of intracellular signaling pathways involved in cell motility, metabolism, survival, and growth. This review summarizes the current knowledge about specific contributions of Class IA phosphoinositide 3-kinases to tumorigenesis and presents a rationale for the development of isoform-specific inhibitors. RECENT FINDINGS: In the last decade, the Class IA phosphoinositide 3-kinases have gained considerable attention as drug targets for the treatment of cancer. Indeed, pan-phosphoinositide 3-kinase inhibitors are being evaluated in early phases of clinical trials for the treatment of multiple human malignancies. Accumulating evidence suggests that selectively targeting individual isoforms is also possible. However, the patient population that is most likely to benefit from such selective compounds remains to be elucidated. SUMMARY: Given the importance of the phosphoinositide 3-kinase pathway in the initiation and maintenance of human tumors, drugs that effectively target its constituents will be an invaluable addition to the arsenal of anticancer therapeutics. However, to fully capitalize on the central role of this pathway in malignancy, we must first fully understand the nuances of its multiple players.     

Phosphoinositide 3-kinase/Akt signaling pathway and its therapeutical implications for human acute myeloid leukemia.

The phosphoinositide 3-kinase (PI3K)/Akt signaling pathway is crucial to many aspects of cell growth, survival and apoptosis, and its constitutive activation has been implicated in the both the pathogenesis and the progression of a wide variety of neoplasias. Hence, this pathway is an attractive target for the development of novel anticancer strategies. Recent studies showed that PI3K/Akt signaling is frequently activated in acute myeloid leukemia (AML) patient blasts and strongly contributes to proliferation, survival and drug resistance of these cells. Upregulation of the PI3K/Akt network in AML may be due to several reasons, including FLT3, Ras or c-Kit mutations. Small molecules designed to selectively target key components of this signal transduction cascade induce apoptosis and/or markedly increase conventional drug sensitivity of AML blasts in vitro. Thus, inhibitory molecules are currently being developed for clinical use either as single agents or in combination with conventional therapies. However, the PI3K/Akt pathway is important for many physiological cellular functions and, in particular, for insulin signaling, so that its blockade in vivo might cause severe systemic side effects. In this review, we summarize the existing knowledge about PI3K/Akt signaling in AML cells and we examine the rationale for targeting this fundamental signal transduction network by means of selective pharmacological inhibitors.     

The role of Notch signaling in human cervical cancer: implications for solid tumors

The detection of intracellular forms of Notch1 in human cervical cancers more than a decade ago prompted an investigation into the possible role of this pathway in driving these cancers. These tumors are consistently characterized by features of deregulated ligand-dependent signaling. Although Notch signaling complements the function of papillomavirus oncogenes in transformation assays of human keratinocytes, there are dose-dependent effects, which inhibit growth of established cervical cancer cell lines. Two pro-oncogenic effector mechanisms that have been suggested to operate in this context by Notch signaling are the activation of PI3K/Akt pathway and the upregulation of c-Myc. Collectively, there is a complex interplay between Notch signaling and papillomaviruses in the context of cervical carcinogenesis. Better animal model systems and identification of human cervical cancer stem cells should help clarify the possible stage specific and pleiotropic effects and regulation of Notch signaling.     

Notch信号在人类乳腺癌中的作用

目的观察Notch1和JAG1在乳腺癌中的表达及其与乳腺癌相关因素的关系,探讨Notch信号在人类乳腺癌中的作用。方法应用逆转录聚合酶链反应(RT-PCR)检测62例乳腺癌组织及22例癌旁正常乳腺组织中Notch1和JAG1的表达,对乳腺癌组织与癌旁正常乳腺组织进行表达率和表达强度标准化系数的统计学比较,并在不同的腋窝淋巴结转移情况间、不同的临床分期间进行Notch1表达强度标准化系数的统计学比较。结果乳腺癌组织Notch1的表达率和标准化系数分别为98.0%和0.91,均明显高于癌旁正常乳腺组织,乳腺癌组织中JAG1的表达率为15.0%,癌旁组织中无JAG1表达;伴腋窝淋巴结转移的病例Notch1标准化系数高于无腋窝淋巴结转移的病例;乳腺癌Ⅰ期病例Notch1标准化系数(0.66)低于Ⅱ期(1.20),Ⅱ期高于Ⅲ期(0.62),Ⅰ期与Ⅲ期差异无统计学意义。结论人类乳腺癌中存在Notch1和JAG1的异常高表达,提示Notch1的异常表达与活化人能与人类乳腺癌的形成有关,Notch1在人类乳腺癌不同发展阶段的作用可能不同。     

Activation of inositol phospholipid signaling and Ca2+ efflux in human breast cancer cells by bombesin

Members of the bombesin-related family of peptides (BRPs) are mitogenic for a variety of cell types; however, a role for these peptides has not been previously described in human breast cancer. Early membrane receptor signal transduction mechanisms associated with bombesin action include phospholipase C-mediated inositol phospholipid hydrolysis and the elevation of cytosolic Ca2+ levels. We have investigated a potential role for BRPs in breast cancer by studying their effect on phospholipid hydrolysis, 45Ca2+ efflux, and cell growth in the human breast cancer cell line MCF-7. Bombesin stimulated a dose-dependent increase in the hydrolysis product inositol monophosphate during 1 h with a half-maximal effect around 1 nM. A transient increase in inositol trisphosphate in response to bombesin was also apparent at 2 min. Two distinct bombesin receptor antagonists inhibited this bombesin-induced phospholipid hydrolysis. Both bombesin- and gastrin-releasing peptide also stimulated a dose-related increase in inositol phosphate production in T47D cells, a different human breast cancer cell line. The efflux of 45Ca2+ from prelabeled MCF-7 cells was also stimulated by bombesin. This apparent cellular Ca2+ mobilization was partly dependent on extracellular Ca2+ and was inhibited by Ni2+. Despite this activation of putative mitogenic signaling pathways, bombesin had no effect on either proliferation or DNA synthesis in MCF-7 cells. These data implicate a functional role for BRPs in human breast cancer.     

A novel imidazopyridine analogue as a phosphatidylinositol 3-kinase inhibitor against human breast cancer

Potentiation of anti-breast cancer activity of an imidazopyridine-based PI3Kα inhibitor, HS-104, was investigated in human breast cancer cells. HS-104 shows strong inhibitory activity against recombinant PI3Kα isoform and the PI3K signaling pathway, resulting in anti-proliferative activity in breast cancer cells. It also induced cell cycle arrest at the G(2)/M phase as well as apoptosis. Furthermore, oral administration of HS-104 significantly inhibited the growth of tumor in SkBr3 mouse xenograft models. Therefore, HS-104 could be considered as a potential candidate for the treatment of human breast cancer.     

磷脂酰肌醇3-激酶在人乳腺癌中的活化

背景与目的：磷脂酰肌醇3-激酶（phosphatidylinsitol 3-kinase,P13-K)可被多种有丝分裂信号刺激活化,它参与有关细胞生长信号的调控,但其在人类肿瘤中的作用尚不清楚。本研究旨在探讨人乳腺癌中P13-K的蛋白表达、mRNA表达和激酶活性变化情况。方法：应用Western blot、免疫沉淀、激酶活性测定和RT-PCR方法检测了37例人乳腺癌及其周围非癌组织中P13-KP85亚单位的表达及P13-K活性变化。结果：与周围非癌组织相比,37例人乳腺癌中,32例（86.49%)P13-Kp85亚单位蛋白表达显著增加;35例（94.59%)P13-Kp85亚单位mRNA水平明显增高;25例（67.57%)p13-k激酶活性亦显著增高。结论：人乳腺癌中P13-K被活化,提示P13-K参与乳腺癌细胞的信号转导;它有可能成为人乳腺癌治疗的新靶点。     

Targeting the PI3-kinase pathway in triple-negative breast cancer

Triple-negative breast cancer (TNBC) is characterised by poor outcomes and a historical lack of targeted therapies. Dysregulation of signalling through the phosphoinositide 3 (PI3)-kinase and AKT signalling pathway is one of the most frequent oncogenic aberrations of TNBC. Although mutations in individual genes occur relatively rarely, combined activating mutations in PIK3CA and AKT1, with inactivating mutations in phosphatase and tensin homologue, occur in ∼25%‒30% of advanced TNBC. Recent randomised trials suggest improved progression-free survival (PFS) with AKT-inhibitors in combination with first-line chemotherapy for patients with TNBC and pathway genetic aberrations. We review the evidence for PI3K pathway activation in TNBC, and clinical trial data for PI3K, AKT and mammalian target of rapamycin inhibitors in TNBC. We discuss uncertainty over defining which cancers have pathway activation and the future overlap between immunotherapy and pathway targeting.     

Phosphatidylinositol 3-kinase pathway activation in breast cancer brain metastases

Introduction

Activation status of the phosphatidylinositol 3-kinase (PI3K) pathway in breast cancer brain metastases (BCBMs) is largely unknown. We examined expression of phospho(p)-AKT, p-S6, and phosphatase and tensin homologue (PTEN) in BCBMs and their implications for overall survival (OS) and survival after BCBMs. Secondary analyses included PI3K pathway activation status and associations with time to distant recurrence (TTDR) and time to BCBMs. Similar analyses were also conducted among the subset of patients with triple-negative BCBMs.

Methods

p-AKT, p-S6, and PTEN expression was assessed with immunohistochemistry in 52 BCBMs and 12 matched primary BCs. Subtypes were defined as hormone receptor (HR)+/HER2-, HER2+, and triple-negative (TNBC). Survival analyses were performed by using a Cox model, and survival curves were estimated with the Kaplan-Meier method.

Results

Expression of p-AKT and p-S6 and lack of PTEN (PTEN-) was observed in 75%, 69%, and 25% of BCBMs. Concordance between primary BCs and matched BCBMs was 67% for p-AKT, 58% for p-S6, and 83% for PTEN. PTEN- was more common in TNBC compared with HR+/HER2- and HER2+. Expression of p-AKT, p-S6, and PTEN- was not associated with OS or survival after BCBMs (all, P > 0.06). Interestingly, among all patients, PTEN- correlated with shorter time to distant and brain recurrence. Among patients with TNBC, PTEN- in BCBMs was associated with poorer overall survival.

Conclusions

The PI3K pathway is active in most BCBMs regardless of subtype. Inhibition of this pathway represents a promising therapeutic strategy for patients with BCBMs, a group of patients with poor prognosis and limited systemic therapeutic options. Although expression of the PI3K pathway did not correlate with OS and survival after BCBM, PTEN- association with time to recurrence and OS (among patients with TNBC) is worthy of further study.     

mTOR signaling: implications for cancer and anticancer therapy

Mounting evidence links deregulated protein synthesis to tumorigenesis via the translation initiation factor complex eIF4F. Components of this complex are often overexpressed in a large number of cancers and promote malignant transformation in experimental systems. mTOR affects the activity of the eIF4F complex by phosphorylating repressors of the eIF4F complex, the eIF4E binding proteins. The immunosuppressant rapamycin specifically inhibits mTOR activity and retards cancer growth. Importantly, mutations in upstream negative regulators of mTOR cause hamartomas, haemangiomas, and cancers that are sensitive to rapamycin treatment. Such mutations lead to increased eIF4F formation and consequently to enhanced translation initiation and cell growth. Thus, inhibition of translation initiation through targeting the mTOR-signalling pathway is emerging as a promising therapeutic option.