Strategies to overcome resistance to epidermal growth factor receptor monoclonal antibody therapy in metastatic colorectal cancer

Administration of monoclonal antibodies(mAbs)against epidermal growth factor receptor(EGFR)such as cetuximab and panitumumab in combination with conventional chemotherapy substantially prolongs survival of patients with metastatic colorectal cancer(mCRC).However,the efficacy of these mAbs is limited due to genetic variation among patients,in particular K-ras mutations.The discovery of K-ras mutation as a predictor of non-responsiveness to EGFR mAb therapy has caused a major change in the treatment of mCRC.Drugs that inhibit transformation caused by oncogenic alterations of Ras and its downstream components such as BRAF,MEK and AKT seem to be promising cancer therapeutics as single agents or when given with EGFR inhibitors.Although multiple therapeutic strategies to overcome EGFR mAb-resistance are under investigation,our understanding of their mode of action is limited.Rational drug development based on stringent preclinical data,biomarker validation,and proper selection of patients is of paramount importance in the treatment of mCRC.In this review,we will discuss diverse approaches to overcome the problem of resistance to existing anti-EGFR therapies and potential future directions for cancer therapies related to the mutational status of genes associated with EGFRRas-ERK and PI3K signalings.     

Development of a mouse model for sporadic and metastatic colon tumors and its use in assessing drug treatment

Most genetically engineered mouse (GEM) models for colon cancer are based on tissuewide or germline gene modification, resulting in tumors predominantly of the small intestine. Several of these models involve modification of the adenomatous polyposis coli (Apc) gene and are excellent models for familial cancer predisposition syndromes. We have developed a stochastic somatic mutation model for sporadic colon cancer that presents with isolated primary tumors in the distal colon and recapitulates the entire adenoma–carcinoma–metastasis axis seen in human colon cancer. Using this model, we have analyzed tumors that are either solely mutant in the Apc gene or in combination with another colon cancer-associated mutant gene, the Kras G12D allele. Because of the restricted location in the distal colon, the natural history of the tumors can be analyzed by serial colonoscopy. As the mammalian target of rapamycin (mTOR) pathway is a critical component of the complex signaling network in colon cancer, we used this model to assess the efficacy of mTOR blockade through rapamycin treatment of mice with established tumors. After treatment, Apc mutant tumors were more than 80% smaller than control tumors. However, tumors that possessed both Apc and Kras mutations did not respond to rapamycin treatment. These studies suggest that mTOR inhibitors should be further explored as potential colorectal cancer therapies in patients whose tumors do not have activating mutations in KRAS.     

Mammalian target of rapamycin inhibition in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the leading causes of cancer-related death worldwide. It is associated with a poor prognosis and has limited treatment options. Sorafenib, a multi-targeted kinase inhibitor, is the only available systemic agent for treatment of HCC that improves overall survival for patients with advanced stage disease; unfortunately, an effective second-line agent for the treatment of progressive or sorafenib-resistant HCC has yet to be identified. This review focuses on components of the mammalian target of rapamycin (mTOR) pathway, its role in HCC pathogenesis, and dual mTOR inhibition as a therapeutic option with potential efficacy in advanced HCC. There are several important upstream and downstream signals in the mTOR pathway, and alternative tumor-promoting pathways are known to exist beyond mTORC1 inhibition in HCC. This review analyzes the relationships of the upstream and downstream regulators of mTORC1 and mTORC2 signaling; it also provides a comprehensive global picture of the interaction between mTORC1 and mTORC2 which demonstrates the pre-clinical relevance of the mTOR pathway in HCC pathogenesis and progression. Finally, it provides scientific rationale for dual mTORC1 and mTORC2 inhibition in the treatment of HCC. Clinical trials utilizing mTORC1 inhibitors and dual mTOR inhibitors in HCC are discussed as well. The mTOR pathway is comprised of two main components, mTORC1 and mTORC2; each has a unique role in the pathogenesis and progression of HCC. In phase III studies, mTORC1 inhibitors demonstrate anti-tumor activity in advanced HCC, but dual mTOR (mTORC1 and mTORC2) inhibition has greater therapeutic potential in HCC treatment which warrants further clinical investigation.     

Mammalian target of rapamycin inhibitors and their potential role in therapy in leukaemia and other haematological malignancies

The mammalian target of rapamycin (mTOR) is a serine/threonine kinase that functions as a key regulator of cell growth, protein synthesis, and cell-cycle progression through interactions with a number of signalling pathways, including PI3K/AKT, ras, TCL1, and BCR/ABL. Many haematological malignancies have aberrant activation of the mTOR and related signalling pathways. Accordingly, mTOR inhibitors, a class of signal transduction inhibitors that were originally developed as immunosuppressive agents, are being investigated in preclinical models and clinical trials for a number of haematological malignancies. Sirolimus and second-generation mTOR inhibitors, such as temsirolimus and everolimus, are safe and relatively well-tolerated, making them potentially attractive as single agents or in combination with conventional cytotoxics and other targeted therapies. Promising early clinical data suggests activity of mTOR inhibitors in a number of haematological diseases, including acute lymphoblastic leukaemia, chronic myeloid leukaemia, mantle cell lymphoma, anaplastic large cell lymphoma, and lymphoproliferative disorders. This review describes the rationale for using mTOR inhibitors in a variety of haematological diseases with a focus on their use in leukaemia.     

Targeting phosphoinositide 3-kinase signalling in lung cancer

Lung cancer is the leading cause of cancer-related mortality worldwide and more than 1 million people annually die in consequence of lung cancer. Although an improvement in lung cancer treatment could be achieved, especially in the last decade, the development of additional therapeutic strategies is urgently required in order to provide improved survival benefit for patients. Lung cancer formation is caused by genetic modifications commonly caused by tobacco smoking. Numerous studies have demonstrated the role of extracellular growth factors in lung cancer cell proliferation, metastasis, and chemoresistance. Mutations and amplifications in molecules related to receptor tyrosine signalling, such as EGFR, ErbB2, c-Met, c-Kit, VEGFR, PI3K, and PTEN are only some of the alterations known to contribute to the development of lung cancer. The phosphoinositide 3-kinase (PI3K) pathway, fundamental for cell development, growth, and survival, is known to be frequently altered in neoplasia, including carcinomas of the lung. Based on the high frequency of alterations, which include mutations and amplifications, leading to over-activation of certain upstream/downstream mediators, targeting components of the PI3K signalling pathway is considered to be a promising therapeutic approach in cancer treatment. In this article we will summarize the current knowledge about the involvement of PI3K signalling in lung cancer and discuss the development of targeted therapies involving PI3K pathway inhibitors.     

mTOR信号传导通路及其相关药物与非小细胞肺癌

哺乳动物雷帕霉素靶蛋白(mTOR)处于细胞生长繁殖、细胞周期调控、生物合成、细胞迁移等信号通路调控的中心位置,因此在肿瘤以及肺癌的发生、发展,特别是在治疗和预后中具有重要的作用.mTOR磷酸化激活后,通过调控4EBP和P70S6K两条不同的下游通路,分别控制特定亚组mRNA的翻译,进而影响生物合成.对非小细胞肺癌来讲,mTOR能够加快细胞周期G1-S期的转换,促进细胞增殖.雷帕霉素、西罗莫司、依维莫司等mTOR信号通路的阻断药物在肺癌的治疗中显示出了希望.     

Synergistic anti-tumor effects of RAD001 with MEK inhibitors in neuroendocrine tumors: a potential mechanism of therapeutic limitation of mTOR inhibitor

Mammalian target of rapamycin (mTOR) inhibitors have been clinically used as anticancer agents in several types of human malignancies including neuroendocrine tumor (NET) but the development of clinical resistances or their therapeutic limitations have been also reported. This clinical resistance has been proposed to be partly due to a compensatory activation of an mTOR upstream factor Akt and MEK/ERK pathway in NET cells but its details have not necessarily been reported. Therefore, in this study, we examined the effects of mTOR inhibitors on these activations and of the concomitant treatment of mTOR and MEK inhibitors in two NET cell lines, NCI-H727 and COLO320. We evaluated the effects of RAD001, mTOR inhibitor, and U0126, MEK inhibitor, on cell proliferation and migration of these cells. In addition, an alteration of the factors involved in Akt/mTOR and MEK/ERK pathways was also examined under administration of these agents. RAD001 and U0126 treatment significantly inhibited cell proliferation and their combined treatment synergistically decreased it in both cell lines. Additionally, these treatments above decreased the expression of cell cycle-related factors, suggestive of an involvement of cell cycle arrest in therapeutic effects. The combined treatment also inhibited the cell migration in NCI-H727 via the decrement of MMP2 and 9 in an additive manner. We demonstrated the potential synergistic/combined effects of inhibitors of mTOR and MEK on cell proliferation and migration. These results suggest the potential therapeutic efficacy of the combined therapy of mTOR and MEK inhibitors or a dual inhibitor for the treatment of NET patients.     

Targeting the PI3K/Akt signaling pathway in gastric carcinoma: A reality for personalized medicine?

Frequent activation of phosphatidylinositol-3 kinases (PI3K)/Akt/mTOR signaling pathway in gastric cancer (GC) is gaining immense popularity with identification of mutations and/or amplifications of PIK3CA gene or loss of function of PTEN, a tumor suppressor protein, to name a few; both playing a crucial role in regulating this pathway. These aberrations result in dysregulation of this pathway eventually leading to gastric oncogenesis, hence, there is a need for targeted therapy for more effective anticancer treatment. Several inhibitors are currently in either preclinical or clinical stages for treatment of solid tumors like GC. With so many inhibitors under development, further studies on predictive biomarkers are needed to measure the specificity of any therapeutic intervention. Herein, we review the common dysregulation of PI3K/Akt/mTOR pathway in GC and the various types of single or dual pathway inhibitors under development that might have a superior role in GC treatment. We also summarize the recent developments in identification of predictive biomarkers and propose use of predictive biomarkers to facilitate more personalized cancer therapy with effective PI3K/Akt/mTOR pathway inhibition.     

Molecular target therapy for gastroenteropancreatic endocrine tumours: Biological rationale and clinical perspectives

Gastroenteropancreatic endocrine tumours (GEP ETs) represent a relatively rare and heterogeneous group of neoplasms whose therapy can be challenging. The poorly differentiated, fast-growing cases are treated with chemotherapy. In the slow-growing ones, biotherapy is usually performed. Several categories of targeted therapies have been studied for their treatment in vitro and in vivo. A critical review of molecular alterations suggests a rationale for targeting angiogenesis, and the phosphatidylinositol 3 kinase (PI₃K)/AKT/mammalian target of rapamycin (mTOR) pathway. Accordingly, antiangiogenic agents and mTOR inhibitors are presently the most tested agents in phase II and III studies. Bevacizumab, some multitarget inhibitors, and mTOR inhibitors showed promising results in patients with advanced GEP ETs. A limited activity has been reported for imatinib and epidermal growth factor receptor (EGFR) inhibitors. Combinations of molecular targeted therapies with different sites of action, and somatostatin analogues may be relevant to avoid molecular escape pathways. Future trials should include more homogeneous groups of patients and pay more attention to the subgroup with progressive disease.     

Aspirin inhibits cell viability and mTOR downstream signaling in gastroenteropancreatic and bronchopulmonary neuroendocrine tumor cells

AIM:To investigate the effect of aspirin on neuroendocrine tumor(NET)cell growth and signaling in vitro.METHODS:Human pancreatic BON1,bronchopulmonary NCI-H727 and midgut GOT1 neuroendocrine tumor cells were treated with different concentrations of aspirin(from 0.001 to 5 mmol/L),and the resulting effects on metabolic activity/cell proliferation were measured using cell proliferation assays and SYBR-DNAlabeling after 72,144 and 216 h of incubation.The effects of aspirin on the expression and phosphorylation of several critical proteins that are involved in the most common intracellular growth factor signaling pathways(especially Akt protein kinase B)and mammalian target of rapamycin(mTOR)were determined by Western blot analyses.Propidium iodide staining and flow cytometry were used to evaluate changes in cell cycle distribution and apoptosis.Statistical analysis was performed using a 2-tailed Student’s t-test to evaluate the proliferation assays and cell cycle analyses.The results are expressed as the mean±SD of 3 or 4 independently performed experiments.Statistical significance was set at P<0.05.RESULTS:Treatment with aspirin suppressed the viability/proliferation of BON1,NCI-H727 and GOT1 cells in a time-and dose-dependent manner.Significant effects were observed at starting doses of 0.5-1 mmol/L and peaked at 5 mmol/L.For instance,after treatment with 1 mmol/L aspirin for 144 h,the viability of pancreatic BON1 cells decreased to 66%±13%(P<0.05),the viability of bronchopulmonary NCI-H727 cells decreased to 53%±8%(P<0.01)and the viability of midgut GOT1 cells decreased to 89%±6%(P<0.01).These effects were associated with a decreased entry into the S phase,the induction of the cyclin-dependent kinase inhibitor p21 and reduced expression of cyclindependent kinase 4 and cyclin D3.Aspirin suppressed mTOR downstream signaling,evidenced by the reduced phosphorylation of the mTOR substrates 4E binding protein 1,serine/threonine kinase P70S6K and S6 ribosomal protein and inhibited glycogen synthase kinase3 activity.We observed the(compensatory)activation of tuberous sclerosis 2,the serine/threonine specific protein kinase AKT and extracellular signal-regulated kinases.CONCLUSION:Aspirin demonstrates promising anticancer properties for NETs in vitro.Further preclinical and clinical studies are needed.     

Antileukaemic effect of PI3K‐mTOR inhibitors in acute myeloid leukaemia‐gene expression profiles reveal CDC25B expression as determinate of pharmacological effect

Acute myeloid leukaemia (AML) is a heterogeneous malignancy. Intracellular signalling through the phosphatidylinositol 3‐kinase (PI3K)‐Akt‐mammalian target of rapamycin (mTOR) pathway is important for regulation of cellular growth and metabolism, and inhibitors of this pathway is considered for AML treatment. Primary human AML cells, derived from 96 consecutive adult patients, were examined. The effects of two mTOR inhibitors (rapamycin, temsirolimus) and two PI3K inhibitors (GDC‐0941, 3‐methyladenine) were studied, and we investigated cytokine‐dependent proliferation, regulation of apoptosis and global gene expression profiles. Only a subset of patients demonstrated strong antiproliferative effects of PI3K‐mTOR inhibitors. Unsupervised hierarchical clustering analysis identified two main clusters of patients; one subset showing weak or absent antiproliferative effects (59%) and another group showing a strong growth inhibition for all drugs and concentrations examined (41%). Global gene expression analyses showed that patients with AML cell resistance against PI3K‐mTOR inhibitors showed increased mRNA expression of the CDC25B gene that encodes the cell cycle regulator Cell Division Cycle 25B. The antileukaemic effect of PI3K‐Akt‐mTOR inhibition varies between patients, and resistance to these inhibitors is associated with the expression of the cell cycle regulator CDC25B, which is known to crosstalk with the PI3K‐Akt‐mTOR pathway and mediate rapamycin resistance in experimental models.     

Optimal biologic dose of metronomic chemotherapy regimens is associated with maximum antiangiogenic activity

Low-dose metronomic chemotherapy is a promising therapeutic cancer treatment strategy thought to have an antiangiogenic basis. However, the advantages of reduced toxicity, increased efficacy in some cases, and ability to combine chemotherapy administered long term in this way with targeted therapies can be compromised by the empiricism associated with determining the optimum biologic dose (OBD). Using 4 distinct metronomic chemotherapy regimens in 4 different preclinical tumor models, including a hematologic malignancy, we established the OBD by determining the maximum efficacy associated with minimum or no toxicity. We then found each OBD to be strikingly correlated with the maximum reduction in viable peripheral blood circulating vascular endothelial growth factor receptor 2-positive (VEGFR-2+) endothelial precursors (CEPs). These results suggest that CEPs may serve as a pharmacodynamic biomarker to determine the OBD of metronomic chemotherapy regimens.     

Aberrant STAT5 and PI3K/mTOR pathway signaling occurs in human CRLF2-rearranged B-precursor acute lymphoblastic leukemia

Adults and children with high-risk CRLF2-rearranged acute lymphoblastic leukemia (ALL) respond poorly to current cytotoxic chemotherapy and suffer unacceptably high rates of relapse, supporting the need to use alternative therapies. CRLF2 encodes the thymic stromal lymphopoietin (TSLP) receptor, which activates cell signaling in normal lymphocytes on binding its ligand, TSLP. We hypothesized that aberrant cell signaling occurs in CRLF2-rearranged ALL and can be targeted by signal transduction inhibitors of this pathway. In a large number of primary CRLF2-rearranged ALL samples, we observed increased basal levels of pJAK2, pSTAT5, and pS6. We thus characterized the biochemical sequelae of CRLF2 and JAK alterations in CRLF2-rearranged ALL primary patient samples via analysis of TSLP-mediated signal transduction. TSLP stimulation of these leukemias further induced robust JAK/STAT and PI3K/mTOR pathway signaling. JAK inhibition abrogated phosphorylation of JAK/STAT and, surprisingly, of PI3K/mTOR pathway members, suggesting an interconnection between these signaling networks and providing a rationale for testing JAK inhibitors in clinical trials. The PI3K/mTOR pathway inhibitors rapamycin, PI103, and PP242 also inhibited activated signal transduction and translational machinery proteins of the PI3K/mTOR pathway, suggesting that signal transduction inhibitors targeting this pathway also may have therapeutic relevance for patients with CRLF2-rearranged ALL and merit further preclinical testing.     

m‐TOR inhibitors and their potential role in haematological malignancies

It is widely demonstrated that the PI 3K‐AKT ‐mTOR signalling is critical in normal myeloid and lymphoid development and function. Thus, it is not strange that this pathway is often deregulated in haematological tumours, providing a strong preclinical rationale for the use of drugs targeting the PI 3K‐AKT ‐mTOR axis in haematological malignancies. The main focus of this review is to examine the mammalian target of rapamycin (mTOR , also termed mechanistic target of rapamycin [MTOR ]) signalling pathways and to provide a brief overview of rapalogs and second‐generation mTOR inhibitors used to target its aberrant activation in cancer treatment. We will also discuss the results obtained with the use of these agents in patients with acute leukaemia, Hodgkin lymphoma, non‐Hodgkin lymphomas, multiple myeloma and Waldenström macroglobulinaemia. Ongoing clinical trials in haematological malignancies that are investigating first‐ and second‐generation mTOR inhibitors as single agents and as components of combination regimens are also presented.     

雷帕霉素靶分子在糖尿病肾病发病机制中的作用

哺乳动物雷帕霉素靶分子位于胰岛素/胰岛素样生长因子通路的下游,同时接受营养信号和能量信号,参与细胞、器官和生物体肥胖的调控,引起胰岛素抵抗,促进血管内皮细胞生长因子的表达,可能在2型糖尿病及糖尿病肾病的发生发展中起重要的作用.     

Targeting the Ras signaling pathway: a rational, mechanism-based treatment for hematologic malignancies?

A series of alterations in the cellular genome affecting the expression or function of genes controlling cell growth and differentiation is considered to be the main cause of cancer. These mutational events include activation of oncogenes and inactivation of tumor suppressor genes. The elucidation of human cancer at the molecular level allows the design of rational, mechanism-based therapeutic agents that antagonize the specific activity of biochemical processes that are essential to the malignant phenotype of cancer cells. Because the frequency of RAS mutations is among the highest for any gene in human cancers, development of inhibitors of the Ras-mitogen-activated protein kinase pathway as potential anticancer agents is a very promising pharmacologic strategy. Inhibitors of Ras signaling have been shown to revert Ras-dependent transformation and cause regression of Ras-dependent tumors in animal models. The most promising new class of these potential cancer therapeutics are the farnesyltransferase inhibitors. The development of these compounds has been driven by the observation that oncogenic Ras function is dependent upon posttranslational modification, which enables membrane binding. In contrast to many conventional chemotherapeutics, farnesyltransferase inhibitors are remarkably specific and have been demonstrated to cause no gross systemic toxicity in animals. Some orally bioavailable inhibitors are presently being evaluated in phase II clinical trials. This review presents an overview on some inhibitors of the Ras signaling pathway, including their specificity and effectiveness in vivo. Because Ras signaling plays a crucial role in the pathogenesis of some hematologic malignancies, the potential therapeutic usefulness of these inhibitors is discussed. (Blood. 2000;96:1655-1669)     

Cyclooxygenase-2 as a target for anticancer drug development

The two isoforms cyclooxygenase-1 and -2 catalyze the initial step in the formation of prostaglandins in a variety of pathophysiological processes. More recently their role in carcinogenesis has become more evident. They seem to influence apoptosis, angiogenesis, and invasion, and play a role in the production of carcinogens. Usually, a high level of COX-2 expression is found in cancer cells. However, low COX-2 expression is observed in some cancers like prostate or breast cancer. This phenomenon is quite surprising and should influence on clinical trial designs. Large epidemiological trials studying users and non-users of aspirin have shown that cyclooxygenase (COX) inhibitors and non-steroidal anti-inflammatory drugs (NSAIDs) could be of benefit against the development and growth of malignancies. Moreover, clinical trials in patients with familial adenomatosis polyposis syndrome have shown too the efficacy of non-selective COX inhibitors and recently also of selective COX-2 inhibitors in the reduction of the number and the size of colorectal polyps. However, a primary chemopreventive effect has not been demonstrated yet. NSAIDs are also supposed to have a preventive and growth inhibitory effect in extra-colonic epithelial malignancies. Several preclinical studies show promising results with combination treatments of either chemotherapy or radiotherapy with COX inhibitors. Preclinical studies with the simultaneous use of inhibitors of the epidermal growth factor receptor and COX-2 inhibitors have shown also promising results. Encouraging results with the first clinical trials combining chemotherapy with COX-2 inhibitors in patients with cancer in the advanced and neoadjuvant setting have recently been reported. However, NSAIDs effects in cancer cells are mediated not only by COX enzymes but also by interactions with downstream effectors of COX-2. Hence, we can state that targeting the COX-2 pathway is a promising strategy in the prevention and treatment of solid tumors. Ongoing trials are expected to answer - at least partly - the remaining questions concerning COX-2 and cancer.     

mTOR信号通路与胰岛素抵抗的关系及运动的影响

哺乳动物雷帕霉素靶蛋白(mTOR)是细胞内感受细胞外营养、能量水平以及生长因子等信号变化的一种丝/苏氨酸蛋白激酶,参与凋节细胞生长、分化、增殖以及蛋白质合成等过程,并且与胰岛素抵抗(IR)的发生、发展关系密切.本文对mTOR/S6K1信号通路的调控机制与IR发生、发展过程的关系,以及运动对mTOR信号通路的影响加以综述,以期为探寻合理的运动手段以及药物作用靶点作为治疗由细胞代谢紊乱引起的IR、2型糖尿病等代谢性疾病提供理沦依据.     

Hepatitis B reactivation related to everolimus

Reactivation of hepatitis B virus (HBV) during chemotherapy is a well known complication in patients with chronic hepatitis B and cancer.The clinical manifestations range from subclinical elevation of liver enzymes to severe,potentially fatal fulminant hepatitis.Reactivation can occur in a patient with previous inactive HBV infection;either an inactive carrier or a patient with resolved hepatitis.Everolimus is a mammalian target of rapamycin (mTOR) inhibitor approved in renal cell carcinoma,neuroendocrine tumours and breast cancer.mTOR inhibitors are a new generation of drugs for targeted treatment;therefore,little about their side effects is known.Here,we report a patient with renal cell carcinoma who experienced a flare of hepatitis B infection during treatment with everolimus.Clinicians should be aware of HBV reactivation in patients who are undergoing treatment with everolimus,and screening for hepatitis B infection and prophylactic antiviral treatment should be considered.