Combined inhibition of the phosphatidylinositol 3-kinase/Akt and Ras/mitogen-activated protein kinase pathways results in synergistic effects in glioblastoma cells

Systematic Review of Molecular Targeted Therapies for Adult-Type Diffuse Glioma: An Analysis of Clinical and Laboratory Studies

Gliomas are the most common brain tumor in adults, and molecularly targeted therapies to treat gliomas are becoming a frequent topic of investigation. The current state of molecular targeted therapy research for adult-type diffuse gliomas has yet to be characterized, particularly following the 2021 WHO guideline changes for classifying gliomas using molecular subtypes. This systematic review sought to characterize the current state of molecular target therapy research for adult-type diffuse glioma to better inform scientific progress and guide next steps in this field of study. A systematic review was conducted in accordance with PRISMA guidelines. Studies meeting inclusion criteria were queried for study design, subject (patients, human cell lines, mice, etc.), type of tumor studied, molecular target, respective molecular pathway, and details pertaining to the molecular targeted therapy-namely the modality, dose, and duration of treatment. A total of 350 studies met the inclusion criteria. A total of 52 of these were clinical studies, 190 were laboratory studies investigating existing molecular therapies, and 108 were laboratory studies investigating new molecular targets. Further, a total of 119 ongoing clinical trials are also underway, per a detailed query on clinicaltrials.gov. GBM was the predominant tumor studied in both ongoing and published clinical studies as well as in laboratory analyses. A few studies mentioned IDH-mutant astrocytomas or oligodendrogliomas. The most common molecular targets in published clinical studies and clinical trials were protein kinase pathways, followed by microenvironmental targets, immunotherapy, and cell cycle/apoptosis pathways. The most common molecular targets in laboratory studies were also protein kinase pathways; however, cell cycle/apoptosis pathways were the next most frequent target, followed by microenvironmental targets, then immunotherapy pathways, with the wnt/β-catenin pathway arising in the cohort of novel targets. In this systematic review, we examined the current evidence on molecular targeted therapy for adult-type diffuse glioma and discussed its implications for clinical practice and future research. Ultimately, published research falls broadly into three categories-clinical studies, laboratory testing of existing therapies, and laboratory identification of novel targets-and heavily centers on GBM rather than IDH-mutant astrocytoma or oligodendroglioma. Ongoing clinical trials are numerous in this area of research as well and follow a similar pattern in tumor type and targeted pathways as published clinical studies. The most common molecular targets in all study types were protein kinase pathways. Microenvironmental targets were more numerous in clinical studies, whereas cell cycle/apoptosis were more numerous in laboratory studies. Immunotherapy pathways are on the rise in all study types, and the wnt/β-catenin pathway is increasingly identified as a novel target.

Crosstalk between protein kinases AKT and ERK1/2 in human lung tumor-derived cell models

There is no doubt that cell signaling manipulation is a key strategy for anticancer therapy. Furthermore, cell state determines drug response. Thus, establishing the relationship between cell state and therapeutic sensitivity is essential for the development of cancer therapies. In the era of personalized medicine, the use of patient-derived ex vivo cell models is a promising approach in the translation of key research findings into clinics. Here, we were focused on the non-oncogene dependencies of cell resistance to anticancer treatments. Signaling-related mechanisms of response to inhibitors of MEK/ERK and PI3K/AKT pathways (regulators of key cellular functions) were investigated using a panel of patients' lung tumor-derived cell lines with various stemness- and EMT-related markers, varying degrees of ERK1/2 and AKT phosphorylation, and response to anticancer treatment. The study of interactions between kinases was the goal of our research. Although MEK/ERK and PI3K/AKT interactions are thought to be cell line-specific, where oncogenic mutations have a decisive role, we demonstrated negative feedback loops between MEK/ERK and PI3K/AKT signaling pathways in all cell lines studied, regardless of genotype and phenotype differences. Our work showed that various and distinct inhibitors of ERK signaling - selumetinib, trametinib, and SCH772984 - increased AKT phosphorylation, and conversely, inhibitors of AKT - capivasertib, idelalisib, and AKT inhibitor VIII - increased ERK phosphorylation in both control and cisplatin-treated cells. Interaction between kinases, however, was dependent on cellular state. The feedback between ERK and AKT was attenuated by the focal adhesion kinase inhibitor PF573228, and in cells grown in suspension, showing the possible role of extracellular contacts in the regulation of crosstalk between kinases. Moreover, studies have shown that the interplay between MEK/ERK and PI3K/AKT signaling pathways may be dependent on the strength of the chemotherapeutic stimulus. The study highlights the importance of spatial location of the cells and the strength of the treatment during anticancer therapy.

The discovery of indolone GW5074 during a comprehensive search for non-polyamine-based polyamine transport inhibitors

The native polyamines putrescine, spermidine, and spermine are essential for cell development and proliferation. Polyamine levels are often increased in cancer tissues and polyamine depletion is a validated anticancer strategy. Cancer cell growth can be inhibited by the polyamine biosynthesis inhibitor difluoromethylornithine (DFMO), which inhibits ornithine decarboxylase (ODC), the rate-limiting enzyme in the polyamine biosynthesis pathway. Unfortunately, cells treated with DFMO often replenish their polyamine pools by importing polyamines from their environment. Several polyamine-based molecules have been developed to work as polyamine transport inhibitors (PTIs) and have been successfully used in combination with DFMO in several cancer models. Here, we present the first comprehensive search for potential non-polyamine based PTIs that work in human pancreatic cancer cells in vitro. After identifying and testing five different categories of compounds, we have identified the c-RAF inhibitor, GW5074, as a novel non-polyamine based PTI. GW5074 inhibited the uptake of all three native polyamines and a fluorescent-polyamine probe into human pancreatic cancer cells. GW5074 significantly reduced pancreatic cancer cell growth in vitro when treated in combination with DFMO and a rescuing dose of spermidine. Moreover, GW5074 alone reduced tumor growth when tested in a murine pancreatic cancer mouse model in vivo. In summary, GW5074 is a novel non-polyamine-based PTI that potentiates the anticancer activity of DFMO in pancreatic cancers.

Integrin β1, myosin light chain kinase and myosin IIA are required for activation of PI3K-AKT signaling following MEK inhibition in metastatic triple negative breast cancer

The effectiveness of targeted therapies against the Ras-ERK signaling pathway are limited due to adaptive resistance of tumor cells. Inhibition of the Ras-ERK pathway can result in activation of the PI3K-AKT pathway, thereby diminishing the therapeutic effects of targeting ERK signaling. Here we investigated the crosstalk between the Ras-ERK and PI3K-AKT pathways in MDA-MB-231 breast cancer cell lines that have a preference to metastasize to lung (LM2), brain (BrM2) or bone (BoM2). Inhibition of the Ras-ERK pathway reduced motility in both parental and BoM2 cells. In contrast, inhibition of the Ras-ERK pathway in BrM2 and LM2 cells resulted in activation of PI3K-AKT signaling that was responsible for continued cell motility. Analysis of the cross talk between Ras-ERK and PI3K-AKT signaling pathways revealed integrin β1, myosin light chain kinase (MLCK) and myosin IIA are required for the activation of PI3K-AKT following inhibition of the Ras-ERK pathway. Furthermore, feedback activation of the PI3K-AKT pathway following MEK suppression was independent of the epidermal growth factor receptor. Thus, integrin β1, MLCK, and myosin IIA are factors in the development of resistance to MEK inhibitors. These proteins could provide an opportunity to develop markers and therapeutic targets in a subgroup of triple negative breast cancer (TNBC) that exhibit resistance against MEK inhibition.

Dual Inhibition of PI3K/AKT and MEK/ERK Pathways Induces Synergistic Antitumor Effects in Diffuse Intrinsic Pontine Glioma Cells

Diffuse intrinsic pontine glioma (DIPG) is a devastating disease with an extremely poor prognosis. Recent studies have shown that platelet-derived growth factor receptor (PDGFR) and its downstream effector pathway, PI3K/AKT/mTOR, are frequently amplified in DIPG, and potential therapies targeting this pathway have emerged. However, the addition of targeted single agents has not been found to improve clinical outcomes in DIPG, and targeting this pathway alone has produced insufficient clinical responses in multiple malignancies investigated, including lung, endometrial, and bladder cancers. Acquired resistance also seems inevitable. Activation of the Ras/Raf/MEK/ERK pathway, which shares many nodes of cross talk with the PI3K/AKT pathway, has been implicated in the development of resistance. In the present study, perifosine, a PI3K/AKT pathway inhibitor, and trametinib, a MEK inhibitor, were combined, and their therapeutic efficacy on DIPG cells was assessed. Growth delay assays were performed with each drug individually or in combination. Here, we show that dual inhibition of PI3K/AKT and MEK/ERK pathways synergistically reduced cell viability. We also reveal that trametinib induced AKT phosphorylation in DIPG cells that could not be effectively attenuated by the addition of perifosine, likely due to the activation of other compensatory mechanisms. The synergistic reduction in cell viability was through the pronounced induction of apoptosis, with some effect from cell cycle arrest. We conclude that the concurrent inhibition of the PI3K/AKT and MEK/ERK pathways may be a potential therapeutic strategy for DIPG.

A Potential Role for the Inhibition of PI3K Signaling in Glioblastoma Therapy

Glioblastoma multiforme (GBM) is the most common primary brain tumor and among the most difficult to treat malignancies per se. In almost 90% of all GBM alterations in the PI3K/Akt/mTOR have been found, making this survival cascade a promising therapeutic target, particular for combination therapy that combines an apoptosis sensitizer, such as a pharmacological inhibitor of PI3K, with an apoptosis inducer, such as radio- or chemotherapy. However, while in vitro data focusing mainly on established cell lines has appeared rather promising, this has not translated well to a clinical setting. In this study, we analyze the effects of the dual kinase inhibitor PI-103, which blocks PI3K and mTOR activity, on three matched pairs of GBM stem cells/differentiated cells. While blocking PI3K-mediated signaling has a profound effect on cellular proliferation, in contrast to data presented on two GBM cell lines (A172 and U87) PI-103 actually counteracts the effect of chemotherapy. While we found no indications for a potential role of the PI3K signaling cascade in differentiation, we saw a clear and strong contribution to cellular motility and, by extension, invasion. While blocking PI3K-mediated signaling concurrently with application of chemotherapy does not appear to be a valid treatment option, pharmacological inhibitors, such as PI-103, nevertheless have an important place in future therapeutic approaches.

Inhibition of integrin-linked kinase expression by emodin through crosstalk of AMPKα and ERK1/2 signaling and reciprocal interplay of Sp1 and c-Jun

Despite the anti-cancer effect of emodin observed in several cancers, the underlying molecular mechanism remains to be elucidated. In this study, we showed that emodin-inhibited NSCLC cell growth and increased phosphorylation of AMPKα and ERK1/2. In addition, emodin-inhibited ILK protein expression. The overexpression of ILK reversed the effect of emodin on cell growth inhibition. Furthermore, the blockade of AMPK by compound C abrogated, while metformin, an activator of AMPK, strengthened the effect of emodin on the inhibition of ILK expression. Interestingly, the inhibitor of MAPK extracellular signaling-regulated kinase (ERK) kinase (MEK)/ERK1/2 (PD98059) attenuated emodin-induced phosphorylation of AMPKα. Moreover, emodin reduced the protein expression of Sp1 and AP-1 subunit c-Jun. Exogenous expression of Sp1 and c-Jun diminished emodin-reduced ILK protein expression. Emodin suppressed ILK promoter activity, which was not observed in cells overexpression of Sp1 and treated with compound C. Intriguingly, exogenous expression of c-Jun overcame the emodin-inhibited Sp1 protein expression. Collectively, our results demonstrate that emodin inhibits ILK expression through AMPKα-mediated reduction of Sp1 and c-Jun. Metformin enhances the effects of emodin. Exogenous expression of Sp1 and c-Jun resists emodin-inhibited ILK promoter activity and protein expression. In addition, the overexpression of c-Jun diminishes emodin-induced AMPKα signaling. Thus, the crosstalk of AMPKα and MEK/ERK1/2 signaling and the reciprocal interaction between Sp1 and c-Jun proteins contribute to the overall responses of emodin. This novel signaling axis may be a therapeutic potential for prevention and treatment of NSCLC.

Molecularly targeted therapies for malignant gliomas: advances and challenges

The identification of molecular markers associated with tumor but not with normal tissue has allowed the development of highly specific, targeted therapies for the treatment of cancer. Over the last several years, tremendous advances in our understanding of the genetic and molecular changes involved in the progression of malignant gliomas have triggered a large effort in the development of targeted therapies to treat these tumors. However, to date only a modest clinical benefit, limited to subsets of patients, has been demonstrated. Furthermore, despite a high degree of target selectivity, the use of targeted therapies often has systemic toxicity. The reasons behind this limited clinical success are complex and include the intricacy of the signaling pathways in gliomas and the heterogeneity of the disease process, compounded by existing limitations in assessing the efficacy of these novel agents when conventional end points and clinical trial designs are utilized. However, despite these difficulties targeted therapies remain a very attractive avenue of treatment for malignant gliomas. Three basic approaches are needed to overcome the hurdles associated with targeted therapies: first, further development of genetic profiling techniques will help to better determine the genetic changes and molecular pathways involved in gliomas and will potentially allow the design of individualized therapies based on the genetic and molecular signature of each tumor. Second, there is a need for the development of better combination strategies (complementary targeted agents or targeted agents with chemotherapy drugs) directed towards disease heterogeneity. Third, we need to optimize the design of preclinical and clinical trials to obtain the maximum amount of information in the shortest period of time.

Epidermal growth factor receptor variant type III markedly accelerates angiogenesis and tumor growth via inducing c-myc mediated angiopoietin-like 4 expression in malignant glioma

Background

Expression of the constitutively activated mutant EGFR variant III (EGFRvIII), the most common mutation in glioblastoma multiforme (GBMs), has been clinically correlated with tumor proliferation, invasion, and angiogenesis. In this study, we examined the role of EGFRvIII on the tumor microenvironment, especially on angiogenesis.

Methods

To study the role of EGFRvIII in tumor angiogenesis, we prepared LN229 glioblastoma transfected with enhanced green fluorescent protein (EGFP), wild-type EGFR, or EGFRvIII (LN229-WT or -vIII), and examined tumor growth and microvessel density in the tumors. Additionally, the potential angiogenic factors were identified by real-time PCR analysis, and the functions in LN229-vIII cells were examined.

Results

LN229-vIII cells showed more aggressive tumor growth and higher vascularity as compared to LN229-WT cells in vivo, although there was no significant difference in the cell growth rates in vitro. We next investigated the expression of 60 angiogenesis-related factors to clarify the mechanisms underlying the difference in vascularity between tumor xenografts of LN229-vIII and LN229-WT. We found that the mRNA and protein expressions of angiopoietin-like 4 (Angptl4), a secreted protein involved in angiogenesis and metabolism regulation, were significantly induced by EGFRvIII overexpression, both in vitro and in vivo. Constitutive knockdown of Angptl4 in LN229-vIII using shRNA significantly decreased the microvessel density in the tumor xenografts and suppressed tumor growth. To clarify the regulatory mechanisms of Angptl4 by EGFRvIII, we analyzed the signaling pathways and transcription factors by pharmacological inhibition and RNA interference. U0126, an ERK signal inhibitor dramatically suppressed Angptl4 expression. The transcription factor c-Myc, which is regulated by ERK, was activated in the LN229-vIII cells and knockdown of c-Myc using siRNA also attenuated Angptl4 expression in the LN229-vIII cells. Furthermore, chromatin immunoprecipitation (ChIP) assay revealed increased recruitment of c-Myc to the promoter region of Angptl4 in the LN229-vIII cells.

Conclusions

In summary, we demonstrated that EGFRvIII induces Angptl4 expression through the ERK/c-Myc pathway and promotes tumor angiogenesis in malignant gliomas.

Evaluation of tyrosine kinase inhibitor combinations for glioblastoma therapy

Glioblastoma multiforme (GBM) is the most common intracranial cancer but despite recent advances in therapy the overall survival remains about 20 months. Whole genome exon sequencing studies implicate mutations in the receptor tyrosine kinase pathways (RTK) for driving tumor growth in over 80% of GBMs. In spite of various RTKs being mutated or altered in the majority of GBMs, clinical studies have not been able to demonstrate efficacy of molecular targeted therapies using tyrosine kinase inhibitors in GBMs. Activation of multiple downstream signaling pathways has been implicated as a possible means by which inhibition of a single RTK has been ineffective in GBM. In this study, we sought a combination of approved drugs that would inhibit in vitro and in vivo growth of GBM oncospheres. A combination consisting of gefitinib and sunitinib acted synergistically in inhibiting growth of GBM oncospheres in vitro. Sunitinib was the only RTK inhibitor that could induce apoptosis in GBM cells. However, the in vivo efficacy testing of the gefitinib and sunitinib combination in an EGFR amplified/ PTEN wild type GBM xenograft model revealed that gefitinib alone could significantly improve survival in animals whereas sunitinib did not show any survival benefit. Subsequent testing of the same drug combination in a different syngeneic glioma model that lacked EGFR amplification but was more susceptible to sunitinib in vitro demonstrated no survival benefit when treated with gefitinib or sunitinib or the gefitinib and sunitinib combination. Although a modest survival benefit was obtained in one of two animal models with EGFR amplification due to gefitinib alone, the addition of sunitinib, to test our best in vitro combination therapy, did not translate to any additional in vivo benefit. Improved targeted therapies, with drug properties favorable to intracranial tumors, are likely required to form effective drug combinations for GBM.

Ras/Raf/MEK/ERK and PI3K/PTEN/Akt/mTOR inhibitors: rationale and importance to inhibiting these pathways in human health

The Ras/Raf/MEK/ERK and PI3K/PTEN/Akt/mTOR cascades are often activated by genetic alterations in upstream signaling molecules such as receptor tyrosine kinases (RTK). Integral components of these pathways, Ras, B-Raf, PI3K, and PTEN are also activated/inactivated by mutations. These pathways have profound effects on proliferative, apoptotic and differentiation pathways. Dysregulation of these pathways can contribute to chemotherapeutic drug resistance, proliferation of cancer initiating cells (CICs) and premature aging. This review will evaluate more recently described potential uses of MEK, PI3K, Akt and mTOR inhibitors in the proliferation of malignant cells, suppression of CICs, cellular senescence and prevention of aging. Ras/Raf/MEK/ERK and Ras/PI3K/PTEN/Akt/mTOR pathways play key roles in the regulation of normal and malignant cell growth. Inhibitors targeting these pathways have many potential uses from suppression of cancer, proliferative diseases as well as aging.

Targeting Ras-RAF-ERK and its interactive pathways as a novel therapy for malignant gliomas

Malignant gliomas are the most common and the deadliest brain malignancies in adults. Despite the lack of a complete understanding of the biology of these tumors, significant advances have been made in the past decades. One of the key discoveries made in the area of malignant gliomas is that these tumors can be induced and maintained by aberrant signaling networks. In this context, the Ras pathway has been extensively exploited, from both basic and translational perspectives. Although somatic oncogenic mutations of Ras genes are frequent in several cancer types, early investigations on gliomas revealed disappointing facts that the Ras mutations are nearly absent in malignant gliomas and that the BRAF mutations are present in a very small percentage of gliomas. Therefore, the observed deregulation of the Ras-RAF-ERK signaling pathway in gliomas is attributed to its upstream positive regulators, including, EGFR and PDGFR known to be highly active in the majority of malignant gliomas. In contrast to the initial negative results on the somatic mutations of H-Ras, K-Ras and BRAF, recent breakthrough studies on pediatric low-grade astrocytomas uncovered genetic alterations of the BRAF gene involving copy number gains and rearrangements. The 7q34 rearrangements result in a novel in-frame KIAA1549:BRAF fusion gene that possesses constitutive BRAF kinase activity resembling oncogenic BRAF (V600E). In light of the earlier findings and recent breakthroughs, this review summarizes our current understanding of the Ras-RAF-ERK signaling pathway in gliomas and the outcome of preclinical and clinical studies that evaluated the efficacy of Ras-targeted therapy in malignant gliomas.

Anti-angiogenic therapy induces integrin-linked kinase 1 up-regulation in a mouse model of glioblastoma

Background

In order to improve our understanding of the molecular pathways that mediate tumor proliferation and angiogenesis, and to evaluate the biological response to anti-angiogenic therapy, we analyzed the changes in the protein profile of glioblastoma in response to treatment with recombinant human Platelet Factor 4-DLR mutated protein (PF4-DLR), an inhibitor of angiogenesis.

Methodology/Principal Findings

U87-derived experimental glioblastomas were grown in the brain of xenografted nude mice, treated with PF4-DLR, and processed for proteomic analysis. More than fifty proteins were differentially expressed in response to PF4-DLR treatment. Among them, integrin-linked kinase 1 (ILK1) signaling pathway was first down-regulated but then up-regulated after treatment for prolonged period. The activity of PF4-DLR can be increased by simultaneously treating mice orthotopically implanted with glioblastomas, with ILK1-specific siRNA. As ILK1 is related to malignant progression and a poor prognosis in various types of tumors, we measured ILK1 expression in human glioblatomas, astrocytomas and oligodendrogliomas, and found that it varied widely; however, a high level of ILK1 expression was correlated to a poor prognosis.

Conclusions/Significance

Our results suggest that identifying the molecular pathways induced by anti-angiogenic therapies may help the development of combinaatorial treatment strategies that increase the therapeutic efficacy of angiogenesis inhibitors by association with specific agents that disrupt signaling in tumor cells.

Prognostic significance of integrin-linked kinase1 overexpression in astrocytoma

Integrin-linked kinase 1 (ILK1), a member of the serine/threonine kinases, has been demonstrated to be associated with numerous biological and pathological processes. However, the clinical and functional significance of ILK1 expression has not been characterized previously in human astrocytoma. In this study, we found that ILK1 was overexpressed, at both mRNA and protein levels, in astrocytoma cell lines as compared with normal human astrocytes. The ILK1 mRNA and protein were significantly increased up to 5.6-fold and 10.1-fold, respectively, in primary astrocytoma in comparison with the paired adjacent noncancerous brain tissues obtained from the same patient. Furthermore, immunohistochemical analysis revealed that ILK1 protein was positive in 208 of 228 (91.2%) paraffin-embedded archival astrocytoma specimens. Statistical analysis suggested that the upregulation of ILK1 was significantly correlated with the histological grading of astrocytoma (p = 0.000), and that patients with high ILK1 level exhibited shorter survival time (p < 0.001). Multivariate analysis revealed that ILK1 upregulation might be an independent prognostic indicator for the survival of patients with astrocytoma. Taken together, our results suggest that ILK1 might represent a novel and useful prognostic marker for astrocytoma and play a role during the development and progression of the disease.

Combination therapy for malignant glioma based on PTEN status

The phosphatidylinositol 3-kinase (PI3K)/Akt pathway is a central regulator of cell proliferation, migration, tumor growth, survival, angiogenesis and metabolism, contributing to the malignant phenotype of gliomas. Trials using targeted therapeutics against growth factor receptors and downstream signal mediators of the PI3K pathway have demonstrated only modest clinical benefit. Although recent clinical data suggests that malignant gliomas with PTEN are more likely to respond to EGF receptor inhibitors, gliomas have multiple concomitantly activated pathways, making them highly resistant to single-targeted therapy. This review discusses the importance of the PI3K pathway in glioma, the potential role of PTEN status in directing specific therapies, discusses clinical trial development of drug combinations to treat malignant gliomas and offers strategies for trial design that will be necessary to fully understand the successes and failures of current approaches to glioma therapy.

siRNA-mediated integrin-linked kinase suppression: nonspecific effects of siRNA/cationic liposome complexes trigger changes in the expression of phosphorylated-AKT and mTOR independently of ILK silencing

Short interfering RNA targeting ILK (ILK siRNA) could be used to treat patients with cancers where constitutive activation of the AKT/PI3K pathway is prominent (e.g., those cancers lack functional PTEN). It is generally believed that siRNA therapeutics will require the use of delivery systems and lipid-based formulations containing cationic lipids (CLs) are a viable option. However, CLs are known to be toxic and exposure to CLs can influence cell survival pathways. This study characterized how CLs combine with ILK siRNA to influence the AKT/PI3K pathway. Using PTEN-negative cell lines (PC3 castration-insensitive prostate cancer cells and U251 glioma cancer cells), the influence of CLs on the downstream consequences of ILK silencing was determined. When comparing nucleofection (an electroporation method that does not require the use of CLs) and CLs as means to deliver ILK siRNA, a 12- to 30-fold increase in siRNA delivery was achieved when using a CL formulation, yet ILK suppression was less efficient. Importantly, time-dependent signaling consequences associated with ILK silencing, including suppression of phosphorylated (serine 473)-AKT and changes in mTOR expression, were observed independently of ILK suppression when the target cells were exposed to cationic lipids following nucleofection-based delivery of ILK siRNA.

QLT0267, a small molecule inhibitor targeting integrin-linked kinase (ILK), and docetaxel can combine to produce synergistic interactions linked to enhanced cytotoxicity, reductions in P-AKT levels, altered F-actin architecture and improved treatment outcomes in an orthotopic breast cancer model

Introduction

Substantial preclinical evidence has indicated that inhibition of integrin linked-kinase (ILK) correlates with cytotoxic/cytostatic cellular effects, delayed tumor growth in animal models of cancer, and inhibition of angiogenesis. Widely anticipated to represent a very promising therapeutic target in several cancer indications, it is increasingly evident that optimal therapeutic benefits obtained using ILK targeting strategies will only be achieved in combination settings. The purpose of this study was to investigate the therapeutic potential of the ILK small molecule inhibitor, QLT0267 (267), alone or in combination with chemotherapies commonly used to treat breast cancer patients.

Methods

A single end-point metabolic assay was used as an initial screen for 267 interactions with selected chemotherapeutic agents. These in vitro assays were completed with seven breast cancer cell lines including several which over-expressed human epidermal growth factor receptor 2 (Her2). One agent, docetaxel (Dt), consistently produced synergistic interactions when combined with 267. Dt/267 interactions were further characterized by measuring therapeutic endpoints linked to phosphorylated protein kinase B (P-AKT) suppression, inhibition of vascular endothelial growth factor (VEGF) secretion and changes in cytoarchitecture. In vivo efficacy studies were completed in mice bearing orthotopic xenografts where tumor growth was assessed by bioluminescence and calliper methods.

Results

The combination of 267 and Dt resulted in increased cytotoxic activity, as determined using an assay of metabolic activity. Combinations of cisplatin, doxorubicin, vinorelbine, paclitaxel, and trastuzumab produced antagonistic interactions. Further endpoint analysis in cell lines with low Her2 levels revealed that the 267/Dt combinations resulted in: a three-fold decrease in concentration (dose) of 267 required to achieve 50% inhibition of P-AKT; and a dramatic disruption of normal filamentous-actin cellular architecture. In contrast to Her2-positive cell lines, three-fold higher concentrations of 267 were required to achieve 50% inhibition of P-AKT when the drug was used in combination with Dt. In vivo studies focusing on low Her2-expressing breast cancer cells (LCC6) implanted orthotopically demonstrated that treatment with 267/Dt engendered improved therapeutic effects when compared with mice treated with either agent alone.

Conclusions

The findings indicate that the 267/Dt drug combination confers increased (synergistic) therapeutic efficacy towards human breast cancer cells that express low levels of Her2.

Chloroquine inhibits colon cancer cell growth in vitro and tumor growth in vivo via induction of apoptosis

The present study was to investigate the anticancer effect of chloroquine on proliferation of mouse colon cancer cell line CT26 in vivo and in vitro and the possible mechanism. We found that chloroquine inhibited CT26 proliferation by concentration- and time-dependent manner. This effect was associated with apoptosis induction and decreased level of phosphorylated p42/44 mitogen-activated protein kinase and phosphorylated Akt. The in vivo study showed chloroquine-reduced tumor volume and prolonged survival time in CT26-bearing mice. These observations indicated chloroquine could inhibit CT26 proliferation by inducing apoptosis both in vitro and in vivo, providing its chemotherapeutic potential of human cancers.

Targeting the EGFR and the PKB pathway in cancer

The EGFR and PKB pathways are frequently activated in cancer, so are prime targets for cancer therapy. To this end, new inhibitors are being tested. EGFR inhibitors as single therapy have little benefit, although therapies that evoke an antitumor immune response are more effective. Resistance mutations within the EGFR are common, as is activation of the antiapoptotic PKB pathway via alternative tyrosine kinase receptors, especially other EGFR family members or IGF1R. To combat resistance, multitargeted EGFR inhibitors and combined inhibition of the EGFR and PKB are being investigated. Inhibition of the EGFR and PKB pathways also sensitizes cancer cells to chemotherapy. Thus, EGFR and PI3K/PKB inhibitors will be most effective when used in rational combinations of targeted inhibitors and traditional chemotherapy.

Designer therapies for glioblastoma multiforme

Primary brain tumors account for less than 2% of all cancers in adults; however, they are often associated with neurologic morbidity and high mortality. Glioblastoma multiforme (GBM) has been a focus of new therapy development in neurooncology because it is the most common primary brain tumor in adults. Standard-of-care therapy for newly diagnosed GBM includes surgical resection, radiotherapy, and temozolomide, administered both during and after radiotherapy. However, most patients develop tumor recurrence or progression after this multimodality treatment. Repeat resection and stereotactic radiosurgery upon recurrence may improve outcome only in selected patients. Most salvage chemotherapies offer only palliation. Recent advances in our understanding of the molecular abnormalities of GBM have generated new therapeutic venues of molecularly targeted agents (designer drugs) against key components of cellular pathways critical for cancer initiation and maintenance. Such drugs may offer the potential advantage to increase therapeutic efficacy and decrease systemic toxicity compared with traditional cytotoxic agents. Nonetheless, first-generation targeted agents have failed to demonstrate survival benefits in unselected GBM patient populations. Several mechanisms of treatment failure of the first-generation designer drugs have been proposed, whereas new strategies have been developed to increase effectiveness of these agents. Here we will discuss the recent development and the strategies to optimize the effectiveness of designer therapy for GBM.

Integrin-linked kinase--essential roles in physiology and cancer biology

Integrin-linked kinase (ILK) is a multifunctional intracellular effector of cell-matrix interactions and regulates many cellular processes, including growth, proliferation, survival, differentiation, migration, invasion and angiogenesis. The use of recently developed Cre-lox-driven recombination and RNA-interference technologies has enabled the evaluation of the physiological roles of ILK in several major organ systems. Significant developmental and tissue-homeostasis defects occur when the gene that encodes ILK is deleted, whereas the expression of ILK is often elevated in human malignancies. Although the cause(s) of ILK overexpression remain to be fully elucidated, accumulating evidence suggests that its oncogenic capacity derives from its regulation of several downstream targets that provide cells with signals that promote proliferation, survival and migration, supporting the concept that ILK is a relevant therapeutic target in human cancer. Furthermore, a global analysis of the ILK 'interactome' has yielded several novel interactions, and has revealed exciting and unexpected cellular functions of ILK that might have important implications for the development of effective therapeutic agents.

Alphavbeta3 and alphavbeta5 integrins control glioma cell response to ionising radiation through ILK and RhoB

Integrins are extracellular matrix receptors involved in tumour invasion and angiogenesis. Although there is evidence that inhibiting integrins might enhance the efficiency of radiotherapy, little is known about the exact mechanisms involved in the integrin-dependent modulation of tumor radiosensitivity. The purpose of this study was to investigate the role of alphavbeta3 and alphavbeta5 integrins in glioblastoma cell radioresistance and overall to decipher the downstream biological pathways. We first demonstrated that silencing alphavbeta3 and alphavbeta5 integrins with specific siRNAs significantly reduced the survival after irradiation of 2 glioblastoma cell lines: U87 and SF763. We then showed that integrin activity and integrin signalling pathways controlled the glioma cell radiosensitivity. This regulation of glioma cell response to ionising radiation was mediated through the integrin-linked kinase, ILK, and the small GTPase, RhoB, by two mechanisms. The first one, independent of ILK, consists in the regulation of the intracellular level of RhoB by alphavbeta3 or alphavbeta5 integrin. The second pathway involved in cell radiosensitivity consists in RhoB activation by ionising radiation through ILK. Furthermore, we demonstrated that the alphavbeta3/alphavbeta5 integrins/ILK/RhoB pathway controlled the glioma cells radiosensitivity by regulating radiation-induced mitotic cell death. This work identifies a new biological pathway controlling glioblastoma cells radioresistance, activated from the membrane through alphavbeta3 and/or alphavbeta5 integrins via ILK and RhoB. Our results are clues that downstream effectors of alphavbeta3 and alphavbeta5 integrins as ILK and RhoB might also be promising candidate targets for improving the efficiency of radiotherapy and thus the clinical outcome of patients with glioblastoma.

Advances in targeting the Ras/Raf/MEK/Erk mitogen-activated protein kinase cascade with MEK inhibitors for cancer therapy

The identification of intracellular signaling cascades important for the growth and survival of cancer cells has led to the development of targeted cancer therapeutics aimed at blocking these signals. The mitogen-activated protein kinase (MAPK) pathway has a well-defined role in cancer biology and has been an important target in the development of targeted therapies. Recently, several small-molecule inhibitors of MAPK/extracellular signal-regulated kinase kinase (MEK), a key intermediary of MAPK signaling, have been developed and are currently being tested in clinical trials. Herein, we review the MAPK pathway, the development of small-molecule MEK inhibitors, and the results obtained to date with MEK inhibitors in human cancer trials.

Targeted agents: the rules of combination

The success of molecularly targeted agents (MTA) in the treatment of cancer has led to the investigation of their use in combination with other MTAs and with conventional chemotherapies. An overview of the MTAs that have emerged as Food and Drug Administration-approved drugs is presented, along with a framework for the consideration of how MTAs can best be combined to maximize therapeutic effect.

Selective Raf inhibition in cancer therapy

Over the past 5 years, the Raf kinase family has emerged as a promising target for protein-directed cancer therapy development. The goal of this review is to first provide a concise summary of the data validating Raf proteins as high-interest therapeutic targets. The authors then outline the mode of action of Raf kinases, emphasizing how Raf activities and protein interactions suggest specific approaches to inhibiting Raf. The authors then summarize the set of drugs, antisense reagents and antibodies available or in development for therapeutically targeting Raf or Raf-related proteins, as well as existing strategies combining these and other therapeutic agents. Finally, the authors discuss recent results from systems biology analyses that have the potential to increasingly guide the intelligent selection of combination therapies involving Raf-targeting agents and other therapeutics.

Inhibition of Raf-1 alters multiple downstream pathways to induce pancreatic beta-cell apoptosis

The serine threonine kinase Raf-1 plays a protective role in many cell types, but its function in pancreatic beta-cells has not been elucidated. In the present study, we examined whether primary beta-cells possess Raf-1 and tested the hypothesis that Raf-1 is critical for beta-cell survival. Using reverse transcriptase-PCR, Western blot, and immunofluorescence, we identified Raf-1 in human islets, mouse islets, and in the MIN6 beta-cell line. Blocking Raf-1 activity using a specific Raf-1 inhibitor or dominant-negative Raf-1 mutants led to a time- and dose-dependent increase in cell death, assessed by real-time imaging of propidium iodide incorporation, TUNEL, PCR-enhanced DNA laddering, and Caspase-3 cleavage. Although the rapid increase in apoptotic cell death was associated with decreased Erk phosphorylation, studies with two Mek inhibitors suggested that the classical Erk-dependent pathway could explain only part of the cell death observed after inhibition of Raf-1. An alternative Erk-independent pathway downstream of Raf-1 kinase involving the pro-apoptotic protein Bad has recently been characterized in other tissues. Inhibiting Raf-1 in beta-cells led to a striking loss of Bad phosphorylation at serine 112 and an increase in the protein levels of both Bad and Bax. Together, our data strongly suggest that Raf-1 signaling plays an important role regulating beta-cell survival, via both Erk-dependent and Bad-dependent mechanisms. Conversely, acutely inhibiting phosphatidylinositol 3-kinase Akt had more modest effects on beta-cell death. These studies identify Raf-1 as a critical anti-apoptotic kinase in pancreatic beta-cells and contribute to our understanding of survival signaling in this cell type.

Integrin-linked kinase: dispensable for radiation survival of three-dimensionally cultured fibroblasts

PURPOSE

Cancer treatment by conventional radiotherapy is limited by normal tissue side-effects. Fibroblasts as "non-target" stromal cell type are considered as strong promoter of tumor growth and for developing a therapy resistant phenotype. Regarding application of novel molecular therapeutics combined with radiotherapy, evaluation of a specific targeted molecule in both tumor and normal cells is mandatory for efficacy and tolerability assessment. Previous work showed integrin-linked kinase (ILK), a mediator of beta-integrin signals and putative phosphorylator of AKT, as potent anti-survival regulator in human cancer cell lines.

MATERIALS AND METHODS

To evaluate the role of ILK in normal fibroblast survival, ILK-wild-type (ILK(fl/fl)), ILK(-/-) and ILK(N-terminal) and ILK(C-terminal) domain expressing fibroblasts were irradiated with X-rays on different substrata or in three-dimensional laminin-rich extracellular matrix (lrECM).

RESULTS

On control substrata, ILK-deficient and ILK-mutant fibroblasts showed significant increase in radiation survival relative to ILK-wild-type cells. This effect was compensated by growth on ECM proteins and in 3D lrECM. ILK regulated AKT activity in a phosphatidylinositol-3 kinase (PI3K)-dependent manner. Upon PI3K inhibition, only ILK-wild-type fibroblasts showed significant radiosensitization.

CONCLUSIONS

These findings obtained in 3D cell cultures suggest ILK to be dispensable for the radiation survival response of normal fibroblasts. However, targeting the PI3K/AKT signaling axis pharmacologically might be critical for survival of normal fibroblasts exposed to ionizing radiation.

Apoptotic Epidermal Growth Factor (EGF)-Conjugated Block Copolymer Micelles as a Nanotechnology Platform for Targeted Combination Therapy

The overexpression of epidermal growth factor receptor (EGFR) in human epithelial cancers has been associated with aggressive disease, poor patient prognosis, and a high incidence of metastases. In the present study, block copolymer micelles are conjugated with epidermal growth factor (EGF), which acts as both a targeting ligand for the drug carrier and an apoptotic factor against EGFR-overexpressing cancers. Drug-free EGF-conjugated micelles are shown to result in cell-cycle arrest at the G 1 phase and subsequent induction of cell-type-specific apoptosis in EGFR-overexpressing breast cancer cells as demonstrated by flow cytometric analysis. EGF delivered as EGF-conjugated micelles was found to be 13-fold more potent than free EGF; the IC 50 was decreased from 0.98 +/- 0.1 nM for free EGF to 0.076 +/- 0.01 nM for EGF micelles. The apoptotic micelles, however, are non-antiproliferative to cells expressing a low level of EGFR, suggesting that the apoptotic micelles have minimal or no toxicity against normal healthy tissues. Ellipticine, a chemotherapeutic agent, was loaded into the EGF-micelles after it had been shown, using the combination index-isobologram equation, to act synergistically with EGF. A 10-fold increase in EGF content in the ellipticine-loaded micelles lowered the IC 50 of ellipticine in EGFR-overexpressing breast cancer cells by more than 18-fold. The EGF-micelles have the potential to be further pursued as a versatile nanotechnology platform for targeted delivery of a wide range of chemotherapeutic agents as a combination therapy for the treatment of EGFR-overexpressing cancers.

The combination of novel low molecular weight inhibitors of RAF (LBT613) and target of rapamycin (RAD001) decreases glioma proliferation and invasion

Monotherapies have proven largely ineffective for the treatment of glioblastomas, suggesting that increased patient benefit may be achieved by combining therapies. Two protumorigenic pathways known to be active in glioblastoma include RAS/RAF/mitogen-activated protein kinase and phosphatidylinositol 3-kinase/AKT/target of rapamycin (TOR). We investigated the efficacy of a combination of novel low molecular weight inhibitors LBT613 and RAD001 (everolimus), which were designed to target RAF and TOR, respectively. LBT613 decreased phosphorylation of extracellular signal-regulated kinase 1 and 2, downstream effectors of RAF, in a human glioma cell line. RAD001 resulted in decreased phosphorylation of the TOR effector S6. To determine if targeting RAF and TOR activities could result in decreased protumorigenic glioma cellular behaviors, we evaluated the abilities of LBT613 and RAD001 to affect the proliferation, migration, and invasion of human glioma cells. Treatment with either LBT613 or RAD001 alone significantly decreased the proliferation of multiple human glioma cell lines. Furthermore, LBT613 and RAD001 in combination synergized to decrease glioma cell proliferation in association with G(1) cell cycle arrest. Glioma invasion is a critical contributor to tumor malignancy. The combination of LBT613 and RAD001 inhibited the invasion of human glioma cells through Matrigel to a greater degree than treatment with either drug alone. These data suggest that the combination of LBT613 and RAD001 reduces glioma cell proliferation and invasion and support examination of the combination of RAF and TOR inhibitors for the treatment of human glioblastoma patients.

In vitro and in vivo synergy of MCP compounds with mitogen-activated protein kinase pathway- and microtubule-targeting inhibitors

An important clinical task is to coherently integrate the use of protein-targeted drugs into preexisting therapeutic regimens, with the goal of improving treatment efficacy. Constitutive activation of Ras-dependent signaling is important in many tumors, and agents that inhibit this pathway might be useful in numerous therapeutic combinations. The MCP compounds were identified as inhibitors of Ras-Raf interactions and previously shown to inhibit multiple Ras-dependent transformation phenotypes when used as monoagents in cell culture analyses. In this study, we investigate the ability of the MCP110 compound to synergistically enhance the activity of other therapeutic agents. In both a defined K-Ras-transformed fibroblast model and in human tumor cell lines with mutationally activated Ras, MCP110 selectively synergizes with other agents targeting the mitogen-activated protein kinase pathway, and with multiple agents (paclitaxel, docetaxel, and vincristine) targeting the microtubule network. The synergistic activity of MCP110 and paclitaxel was further established by experiments showing that in Kaposi's sarcoma oncogenically transformed cell lines, cellular models for tumors treated with taxanes in the clinic and in which Raf-dependent signaling plays an important role, MCP110 synergizes with paclitaxel and limit growth. Finally, in vivo testing indicate that MCP110 is bioavailable, inhibits the growth of LXFA 629 lung and SW620 colon carcinoma cells in xenograft models, and again strongly synergizes with paclitaxel. Together, these findings indicate that MCP compounds have potential to be effective in combination with other anticancer agents.

A novel small molecule that selectively inhibits glioblastoma cells expressing EGFRvIII

Background

Mutations of the epidermal growth factor receptor (EGFR) are a possible molecular target for cancer therapy. EGFR is frequently amplified in glioblastomas and 30 to 40% of glioblastomas also express the deletion mutation EGFRvIII. This frequent oncogenic mutation provides an opportunity for identifying new anti-glioblastoma therapies. In this study, we sought small molecule inhibitors specific for cancer cells expressing EGFRvIII, using isogenic parental cells without EGFRvIII as a control.

Results

A screen of the NCI small molecule diversity set identified one compound, NSC-154829, which consistently inhibited growth of different human glioblastoma cells expressing EGFRvIII, but permitted normal growth of matched control cells. NSC-154829 had no previously established medicinal use, but has a purine-like structural component. Further experiments showed this compound increased apoptosis in cells with EGFRvIII, and moderately affected the expression of p21, independent of any changes in p53 levels or in Akt phosphorylation.

Conclusion

These initial results suggest that NSC-154829 or a closely related structure might be further investigated for its potential as an anti-glioblastoma drug, although its precise molecular mechanism is still undefined.

An essential role for the integrin-linked kinase-glycogen synthase kinase-3 beta pathway during dendrite initiation and growth

Multiple cues, including growth factors and circuit activity, signal to regulate the initiation and growth of mammalian dendrites. In this study, we have asked how these environmental cues regulate dendrite formation, and in particular, whether dendrite initiation and growth requires integrin-linked kinase (ILK) or its downstream effector, glycogen synthase kinase-3beta (GSK-3beta). In cultured sympathetic neurons, NGF and neuronal depolarization activated ILK and promoted dendrite initiation and growth, and inhibition of ILK (either pharmacologically, with a dominant-negative form of ILK, or by genetic knockdown) reduced depolarization-induced dendrite formation. In sympathetic neurons, ILK phosphorylated and inhibited GSK-3beta, and inhibition of GSK-3beta (either pharmacologically, with dominant-negative GSK-3beta, or by genetic knockdown) caused robust dendrite initiation. GSK-3beta inhibition also caused dendrite initiation in cultured cortical neurons and growth of hippocampal neurons in slice cultures. GSK-3beta functioned downstream of ILK to regulate dendrite formation, because inhibition of GSK-3beta promoted dendrite initiation even when ILK was simultaneously inhibited. Moreover, GSK-3beta promoted dendrite formation in sympathetic neurons by regulating the activity of a key dendrite formation effector, the MAP (microtubule-associated protein) kinase kinase (MEK)-extracellular signal-regulated protein kinase (ERK) pathway. Specifically, inhibition of GSK-3beta led to increased ERK phosphorylation, and inhibition of MEK completely blocked the effects of GSK-3beta inhibition on dendrite initiation and growth. Thus, the ILK-GSK-3beta pathway plays a key role in regulating dendrite formation in developing mammalian neurons.

Signalling via integrins: implications for cell survival and anticancer strategies

Integrin-associated signalling renders cells more resistant to genotoxic anti-cancer agents like ionizing radiation and chemotherapeutic substances, a phenomenon termed cell adhesion-mediated radioresistance/drug resistance (CAM-RR, CAM-DR). Integrins are heterodimeric cell-surface molecules that on one side link the actin cytoskeleton to the cell membrane and on the other side mediate cell-matrix interactions. In addition to their structural functions, integrins mediate signalling from the extracellular space into the cell through integrin-associated signalling and adaptor molecules such as FAK (focal adhesion kinase), ILK (integrin-linked kinase), PINCH (particularly interesting new cysteine-histidine rich protein) and Nck2 (non-catalytic (region of) tyrosine kinase adaptor protein 2). Via these molecules, integrin signalling tightly and cooperatively interacts with receptor tyrosine kinase signalling to regulate survival, proliferation and cell shape as well as polarity, adhesion, migration and differentiation. In tumour cells of diverse origin like breast, colon or skin, the function and regulation of these molecules is partly disturbed and thus might contribute to the malignant phenotype and pre-existent and acquired multidrug resistance. These issues as well as a variety of therapeutic options envisioned to influence tumour cell growth, metastasis and resistance, including kinase inhibitors, anti-integrin antibodies or RNA interference, will be summarized and discussed in this review.