Targeting the HGF/c-Met axis: state of play

Recent advances in c-Met-based dual inhibitors in the treatment of cancers

The cellular-mesenchymal epithelial transition factor (c-Met) is a receptor tyrosine kinase (RTK) located on the 7q31 locus encoding the Met proto-oncogene and plays a critical role in regulating cell proliferation, metastasis, differentiation, and apoptosis through various signaling pathways. However, its aberrant activation and overexpression have been implicated in many human cancers. Therefore, c-Met is a promising target for cancer treatment. However, the anticancer effect of selective single-targeted drugs is limited due to the complexity of the signaling system and the involvement of different proteins and enzymes. After inhibiting one pathway, signal molecules can be transmitted through other pathways, resulting in poor efficacy of single-targeted drug therapy. Dual inhibitors that simultaneously block c-Met and another factor can significantly improve efficacy and overcome some of the shortcomings of single-target inhibitors, including drug resistance. In this review, We introduced c-Met kinase and the synergism between c-Met and other anti-tumor targets, then dual-target inhibitors based on c-Met for the treatment of cancers were summarized and their design concepts and structure-activity relationships (SARs) were discussed elaborately, providing a valuable insight for the further development of novel c-Met-based dual inhibitors.

Tumor biomarkers for diagnosis, prognosis and targeted therapy

Tumor biomarkers, the substances which are produced by tumors or the body's responses to tumors during tumorigenesis and progression, have been demonstrated to possess critical and encouraging value in screening and early diagnosis, prognosis prediction, recurrence detection, and therapeutic efficacy monitoring of cancers. Over the past decades, continuous progress has been made in exploring and discovering novel, sensitive, specific, and accurate tumor biomarkers, which has significantly promoted personalized medicine and improved the outcomes of cancer patients, especially advances in molecular biology technologies developed for the detection of tumor biomarkers. Herein, we summarize the discovery and development of tumor biomarkers, including the history of tumor biomarkers, the conventional and innovative technologies used for biomarker discovery and detection, the classification of tumor biomarkers based on tissue origins, and the application of tumor biomarkers in clinical cancer management. In particular, we highlight the recent advancements in biomarker-based anticancer-targeted therapies which are emerging as breakthroughs and promising cancer therapeutic strategies. We also discuss limitations and challenges that need to be addressed and provide insights and perspectives to turn challenges into opportunities in this field. Collectively, the discovery and application of multiple tumor biomarkers emphasized in this review may provide guidance on improved precision medicine, broaden horizons in future research directions, and expedite the clinical classification of cancer patients according to their molecular biomarkers rather than organs of origin.

Combination therapy with pazopanib and tivantinib modulates VEGF and c-MET levels in refractory advanced solid tumors

The vascular endothelial growth factor (VEGF)/VEGFR and hepatocyte growth factor (HGF)/c-MET signaling pathways act synergistically to promote angiogenesis. Studies indicate VEGF inhibition leads to increased levels of phosphorylated c-MET, bypassing VEGF-mediated angiogenesis and leading to chemoresistance. We conducted a phase 1 clinical trial with 32 patients with refractory solid tumors to evaluate the safety, pharmacokinetics, and pharmacodynamics of combinations of VEGF-targeting pazopanib and the putative c-MET inhibitor ARQ197 (tivantinib) at 5 dose levels (DLs). Patients either took pazopanib and tivantinib from treatment initiation (escalation phase) or pazopanib alone for 7 days, with paired tumor sampling, prior to starting combination treatment (expansion phase). Hypertension was the most common adverse event. No more than 1 dose limiting toxicity (DLT) occurred at any DL, so the maximum tolerated dose (MTD) was not determined; DL5 (800 mg pazopanib daily and 360 mg tivantinib BID) was used during the expansion phase. Twenty of 31 evaluable patients achieved stable disease lasting up to 22 cycles. Circulating VEGF, VEGFR2, HGF, and c-MET levels were assessed, and only VEGF levels increased. Tumor c-MET levels (total and phosphorylated) were determined in paired biopsies before and after 7 days of pazopanib treatment. Total intact c-MET decreased in 6 of 7 biopsy pairs, in contrast to previously reported c-MET elevation in response to VEGF inhibition. These results are discussed in the context of our previously reported analysis of epithelial-mesenchymal transition in these tumors.

Overcoming resistance to targeted therapy using MET inhibitors in solid cancers: evidence from preclinical and clinical studies

Targeted therapy is a hallmark of cancer treatment that has changed the landscape of cancer management and enabled a personalized treatment approach. Nevertheless, the development of cancer resistance is a major challenge that is currently threatening the effective utilization of targeted therapies. The hepatocyte growth factor receptor, MET, is a receptor tyrosine kinase known for its oncogenic activity and tumorigenic potential. MET is a well-known driver of cancer resistance. A growing body of evidence revealed a major role of MET in mediating acquired resistance to several classes of targeted therapies. Deregulations of MET commonly associated with the development of cancer resistance include gene amplification, overexpression, autocrine activation, and crosstalk with other signaling pathways. Small-molecule tyrosine kinase inhibitors of MET are currently approved for the treatment of different solid cancers. This review summarizes the current evidence regarding MET-mediated cancer resistance toward targeted therapies. The molecular mechanisms associated with resistance are described along with findings from preclinical and clinical studies on using MET inhibitors to restore the anticancer activity of targeted therapies for the treatment of solid tumors.

Targeting MET in cancer therapy

MET encodes a receptor tyrosine kinase c-MET for hepatocyte growth factor (HGF). The specific combination of c-MET and HGF activates downstream signaling pathways to trigger cell migration, proliferation, and angiogenesis. MET exon 14 alterations and MET gene amplification play a critical role in the origin of cancer. Several monoclonal antibodies and small-molecule inhibitors of c-MET have been evaluated in clinical trials. In patients with advanced non-small cell lung cancer, cabozantinib and crizotinib showed clear efficacy with a generally tolerable adverse events profile. In gastrointestinal cancers, most phase III trials of MET inhibitors showed negative results. In hepatocellular carcinoma, based on the encouraging results of some phase II studies, a series of phase III trials are currently recruiting patients to access the efficacy and safety of MET inhibitors.

Recent advances in the development of dual VEGFR and c-Met small molecule inhibitors as anticancer drugs

Vascular endothelial growth factor receptor (VEGFR) is a very important receptor tyrosine kinase (RTK) that can induce angiogenesis, increase cell growth and metastasis, reduce apoptosis, alter cytoskeletal function, and affect other biologic changes. Moreover, it is identified to be deregulated in varieties of human cancers. Therefore, VEGFR turn out to be a remarkable target of significant types of anticancer drugs in clinical trials. On the other side, c-Met is the receptor of hepatocyte growth factor (HGF) and a receptor tyrosine kinase. Previous studies have shown that c-Met elicits many different signaling pathways mediating cell proliferation, migration, differentiation, and survival. Furthermore, the correlation between aberrant signaling of the HGF/c-Met pathway and aggressive tumor growth, poor prognosis in cancer patients has been established. Recent reports had shown that c-Met/HGF and VEGFR/VEGF (vascular endothelial growth factor) can act synergistically in the progression of many diseases. They were also found to be over expressed in many human cancers. Thus, in a variety of malignancies, VEGFR and c-Met receptor tyrosine kinases have acted as therapeutic targets. With the development of molecular biology techniques, further understanding of the human tumor disease pathogenesis and interrelated signaling pathways known to tumor cells, using a single target inhibitors have been difficult to achieve the desired therapeutic effect. At this point, with respect to the combination of two inhibitors, a single compound which is able to inhibit both VEGFR and c-Met may put forward the advantage of raising anticancer activity. With the strong interest in these compounds, this review represents a renewal of previous works on the development of dual VEGFR and c-Met small molecule inhibitors as novel anti-cancer agents. Newly collection derivatives have been mainly describing in their biological profiles and chemical structures.

New molecularly targeted therapies against advanced hepatocellular carcinoma: From molecular pathogenesis to clinical trials and future directions

Hepatocellular carcinoma (HCC) can be lethal due to its aggressive course and lack of effective systemic therapies for advanced disease. Sorafenib is the only systemic therapy that has demonstrated an overall survival benefit in patients with advanced HCC, and new agents for treatment of advanced HCC are needed. The multiple pathways involved in HCC oncogenesis, proliferation and survival provide many opportunities for the development of molecularly targeted therapies. Molecular targets of interest have expanded from angiogenesis to cancer cell-directed oncogenic signaling pathways for treatment of advanced HCC. Agents targeting vascular endothelial growth factor receptor, epidermal growth factor receptor, fibroblast growth factor receptor, platelet-derived growth factor receptor, c-mesenchymal-epithelial transition factor-1 and mammalian target of rapamycin signaling have been actively explored. This article focuses on the evaluation of molecular agents targeting pathogenic HCC and provides a review of recently completed phase III drug studies (e.g. involving sorafenib, sunitinib, brivanib, linifanib, erlotinib, everolimus, ramucirumab or orantinib) and ongoing drug studies (e.g. involving lenvatinib, regorafenib, tivantinib or cabozantinib) of molecularly targeted agents in advanced HCC, including a brief description of the biologic rationale behind these agents.

Co-expression of MET and CD47 is a novel prognosticator for survival of luminal breast cancer patients

Although luminal-type primary breast cancer can be efficiently treated, development of metastatic disease remains a significant clinical problem. We have previously shown that luminal-type circulating tumor cells (CTCs) co-expressing the tyrosine-kinase MET and CD47, a ligand involved in cancer cell evasion from macrophage scavenging, are able to initiate metastasis in xenografts. Here, we investigated the clinical relevance of MET-CD47 co-expression in 255 hormone receptor positive breast tumors by immunohistochemistry and found a 10.3-year mean overall-survival difference between MET-CD47 double-positive and double-negative patients (p<0.001). MET-CD47 co-expression defined a novel independent prognosticator for overall-survival by multivariate analysis (Cox proportional hazards model: HR: 4.1, p<0.002) and CD47 expression alone or in combination with MET was strongly associated with lymph node metastasis. Furthermore, flow cytometric analysis of metastatic patient blood revealed consistent presence of MET⁺CD47⁺ CTCs (range 0.8 – 33.3% of CTCs) and their frequency was associated with increased metastatic spread. Finally, primary uncultured CTCs with high MET⁺CD47⁺ content showed an enhanced capacity to initiate metastasis in mice. Detection and targeting of MET and CD47 may thus provide a rational basis for risk stratification and treatment of patients with luminal-type breast cancer.

CYP2C19 genotype-based phase I studies of a c-Met inhibitor tivantinib in combination with erlotinib, in advanced/metastatic non-small cell lung cancer

Background:

A previous clinical study in non-small cell lung cancer (NSCLC) patients in Western countries suggested the potential for combination of a first-in-class non-ATP-competitive c-Met inhibitor tivantinib with an epidermal growth factor receptor-tyrosine kinase inhibitor erlotinib. Polymorphisms of CYP2C19, the key metabolic enzyme for tivantinib, should be addressed to translate the previous Western study to Asian population, because higher incidence of poor metabolisers (PMs) is reported in Asian population.

Methods:

Japanese patients with advanced/metastatic NSCLC received tivantinib in combination with erlotinib to evaluate safety and pharmacokinetics. Doses of tivantinib were escalated separately for extensive metabolisers (EMs) and PMs.

Results:

Tivantinib, when combined with erlotinib, was well tolerated up to 360 mg BID for EMs and 240 mg BID for PMs, respectively. Among 25 patients (16 EMs and 9 PMs), the adverse events (AEs) related to tivantinib and/or erlotinib (>20%, any grade) were rash, diarrhoea, dry skin and nausea. Grade ⩾3 AEs were leukopenia, anaemia and neutropenia. No dose-limiting toxicity was observed. Pharmacokinetics profile of tivantinib was not clearly different between the combination and monotherapy. Three partial response and three long-term stable disease (⩾24 weeks) were reported.

Conclusion:

Two doses of tivantinib in combination with erlotinib were recommended based on CYP2C19 genotype: 360 mg BID for EMs and 240 mg BID for PMs.

Molecular targeted therapy for hepatocellular carcinoma: current and future

Hepatocellular carcinoma (HCC) is one of the most frequent tumors worldwide. The majority of HCC cases occur in patients with chronic liver disease. Despite regular surveillance to detect small HCC in these patients, HCC is often diagnosed at an advanced stage. Because HCC is highly resistant to conventional systemic therapies, the prognosis for advanced HCC patients remains poor. The introduction of sorafenib as the standard systemic therapy has unveiled a new direction for future research regarding HCC treatment. However, given the limited efficacy of the drug, a need exists to look beyond sorafenib. Many molecular targeted agents that inhibit different pathways involved in hepatocarcinogenesis are under various phases of clinical development, and novel targets are being assessed in HCC. This review aims to summarize the efforts to target molecular components of the signaling pathways that are responsible for the development and progression of HCC and to discuss perspectives on the future direction of research.

Celastrol exerts synergistic effects with PHA-665752 and inhibits tumor growth of c-Met-deficient hepatocellular carcinoma in vivo

PHA665752 (PHA), a selective small molecule c-Met Inhibitor, potently inhibited HGF-stimulated and constitutive c-Met phosphorylation, as well as HGF and c-Met-driven phenotypes of a variety of tumor cells including hepatocellular carcinoma cells. However, these effects were impaired in c-Met-deficient cancer cells. In the present study, we investigated the potential anti-human c-Met-deficient hepatocellular carcinoma effects of Celastrol, a novel triterpene, and its combination with PHA. Human hepatocellular carcinoma cells BEL-7402 (c-Met-positive) and Huh7 (c-Met-deficient) were treated with different dose of PHA with or without equal dose of Celastrol, and cell growth, cell cycle and apoptosis were evaluated, respectively, by MTT assay, flow cytometry and Caspase3/7 activity. Nude mice bearing Huh7 xenografts were used to assess the in vivo anti-tumor activity. Our results showed that Celastrol at high concentration (>1.0 μM) induced G2/M arrest and apoptosis with the activation of Caspase3/7 in Huh7 cells whereas at low concentration (<1.0 μM) had no obvious effects. Low concentration Celastrol presented significant combined effects with PHA on Huh7 cells and Huh7 xenografts in terms of growth inhibition, migration inhibition and apoptosis induction. These results suggest that Celastrol and its combination with PHA present the therapeutic potential on c-Met-deficient hepatocellular carcinoma, and deserve further preclinical and clinical studies.

Ligand-independent activation of MET through IGF-1/IGF-1R signaling

The receptor tyrosine kinase, MET, has been implicated in tumorigenesis and metastasis of many solid tumors, by multiple mechanisms, including cross talk with epidermal growth factor receptor. In this study, we examined the role of insulin-like growth factor receptor-1 (IGF-1R) signaling in MET activation, focusing on prostate cancer cells. Stimulation of the prostate cancer cell line PC3 with IGF-1 induces a delayed phosphorylation of MET at multiple sites (indicative of full activation), reaching a maximum 18 hr after IGF-1 addition. MET activation does not require the sole MET ligand hepatocyte growth factor (HGF), but does require transcription to occur. Furthermore, direct injection of IGF-1 is sufficient to induce MET activation in vivo, in a PC3 xenograft model. Pharmacologic or genetic inhibition of the tyrosine kinase, Src, abolishes MET phosphorylation, and expression of activated Src is sufficient to induce Met phosphorylation in the absence of IGF-1 stimulation. Activated MET is essential for IGF-1-mediated increased migration of PC3 cells, demonstrating an important biologic effect of IGF-1-mediated MET activation. Finally, we demonstrate that IGF-1-induced delayed MET activation occurs in multiple cell lines which express both the receptors, suggesting that IGF-1R-mediated MET activation may contribute to tumorigenic properties of multiple cancer types when both growth factor receptors are expressed. The results further suggest that MET may be activated by multiple receptor tyrosine kinase receptors, and dual targeting of these receptors may be important therapeutically.

Development of therapeutic combinations targeting major cancer signaling pathways

Signaling networks play key homeostatic processes in living organisms but are commonly hijacked in oncogenesis. Prominent examples include genetically altered receptor tyrosine kinases and dysregulated intracellular signaling molecules. The discovery and development of targeted therapies against such oncogenic proteins has imparted clinical benefit. Nevertheless, concerns remain about the limited single-agent efficacy and narrow therapeutic indices of many of these antitumor agents. Moreover, it is apparent that oncogenic proteins comprise complex signaling networks that interact through crosstalk and feedback loops, which modify therapeutic vulnerability. These complexities mandate the study of drug combinations, which will also become necessary to reverse tumor drug resistance. Here, we outline the challenges associated with rational drug codevelopment strategies, with a focus on the importance of analytically validated biomarkers for patient selection and pharmacokinetic-pharmacodynamic (PK-PD) studies. Overall, the most informative clinical studies of novel combinations will have the following characteristics: robust scientific hypotheses leading to their selection; supportive preclinical data from contextually appropriate preclinical model systems; sufficient preclinical PK data to inform on the risk of drug-drug interactions; and detailed PD studies to determine the biologically active dose range for each agent. Toward this end, several novel clinical trial designs may be envisioned to accelerate successful drug combination development while minimizing the risk of late drug combination attrition. Although considerable challenges remain, these efforts may enable important steps to be taken toward more durable therapeutic control of many cancers.

Anthraquinone Derivatives as Potent Inhibitors of c-Met Kinase and the Extracellular Signaling Pathway

The aberrant function of c-Met kinase signaling pathway is ubiquitously involved in a broad spectrum of human cancers; thus, a strong rationale exists for targeting the kinase pathway in cancer therapy. Via integration of computational and experimental studies, anthraquinone derivatives were identified for the first time as potent c-Met kinase inhibitors in this research. The aberrant activation of the c-Met kinase pathway results from (TPR)-Met, MET gene mutation, or amplification and a hepatocyte growth factor (HGF)/scatter factor-dependent autocrine or paracrine mechanism. However, anthraquinone derivatives exclusively suppressed c-Met phosphorylation stimulated by HGF in A549 cells, indicating that the compounds possess the ability to block the extracellular HGF-dependent pathway. A surface plasmon resonance assay revealed that the most potent compound, 2a, shows a high binding affinity for HGF with an equilibrium dissociation constant of 1.95 μM. The dual roles of compound 2a demonstrate the potency of anthraquinone derivatives and provide a new design solution for the c-Met kinase signaling pathway.

The effect of CYP2C19 polymorphism on the safety, tolerability, and pharmacokinetics of tivantinib (ARQ 197): results from a phase I trial in advanced solid tumors

BACKGROUND

Tivantinib (formerly ARQ 197) is a selective inhibitor of c-Met mainly metabolized by CYP2C19. CYP2C19 is known for genetic polymorphisms, and ~20% of Asians are poor metabolizers (PMs), while others are extensive metabolizers (EMs). In this study, we examined the safety, pharmacokinetics (PK), and preliminary efficacy of tivantinib as a single agent to determine recommended phase II doses (RPIIDs).

PATIENTS AND METHODS

Forty-seven patients (EMs, 33; PMs, 14) with solid tumors were orally treated with tivantinib, from 70 to 360 mg bid in a 3 + 3 dose-escalation scheme. EMs and PMs were separately enrolled at the doses >120 mg bid.

RESULTS

Tivantinib was well tolerated up to 360 mg bid for EMs and 240 mg bid for PMs. Neutropenia, leukopenia, anemia, fatigue, and anorexia were the frequent adverse events related to tivantinib and were commonly observed in both EMs and PMs. PMs had 1.9-fold higher AUC(0-12) compared with EMs at 240 mg bid. Regardless of CYP2C19 phenotype, Gr.4 neutropenia occurred in patients with relatively high exposure to tivantinib. A confirmed partial response was achieved in two non-small-cell lung cancer (NSCLC) patients.

CONCLUSION

Two different settings of RPIIDs, 360 mg bid for EMs and 240 mg bid for PMs, were determined.

Development of a metastatic fluorescent Lewis Lung carcinoma mouse model: identification of mRNAs and microRNAs involved in tumor invasion

Cancer metastasis is the foremost cause of death in cancer patients. A series of observable pathological changes takes place during progression and metastasis of cancer, but the underlying genetic changes remain unclear. Therefore, new approaches are required, including insights from cancer mouse models. To examine the mechanisms involved in tumor metastasis, we first generated a stably transfected Lewis Lung carcinoma cell line expressing a far-red fluorescent protein, called Katushka. After in vivo growth in syngeneic mice, two fluorescent Lewis Lung cancer subpopulations were isolated from primary tumors and lung metastases. The metastasis-derived cells exhibited a significant improvement in in vitro invasive activity compared to the primary tumor-derived cells, using a quantitative invasion chamber assay. Moreover, expression levels of 84 tumor metastasis-related mRNAs, 88 cancer-related microRNAs as well as Dicer and Drosha were determined using RT-qPCR. Compared to the primary Lewis Lung carcinoma subculture, the metastasis-derived cells exhibited statistically significantly increased mRNA levels for several matrix metalloproteinases as well as hepatocyte growth factor (HGF) and spleen tyrosine kinase (SYK). A modest decrease in Drosha and Dicer mRNA levels was accompanied by significant downregulation of ten microRNAs, including miR-9 and miR-203, in the lung metastatic Lewis Lung carcinoma cell culture. Thus, a tool for cancer metastasis studies has been established and the model is well suited for the identification of novel microRNAs and mRNAs involved in malignant progression. Our results suggest that increases in metalloproteinase expression and impairment of microRNA processing are involved in the acquirement of metastatic ability.

Seminars in clinical pharmacology: an introduction to MET inhibitors for the medical oncologist

MET is a tyrosine kinase receptor for hepatocyte growth factor (HGF), primarily expressed on epithelial cells; the activation of MET induces several biological responses relevant for the development and growth of many human cancers. Several human malignancies present altered expression of MET and this is usually associated with poor prognosis and aggressive phenotype. The majority of MET inhibitors in clinical development target directly the receptor through the use of monoclonal antibodies (MAbs) or through small molecule inhibitors of MET kinase activity; small molecule inhibitors are very potent but less specific than MAbs. MET inhibitors are of great clinical interest because of the extensive crosstalk of the HGF/MET axis with many other signaling pathways, including growth factor-dependent pathways (like PI3K/AKT/mTOR,RAS/RAF/ERK) and vascular endothelial growth factor (VEGF) axis. In preclinical studies, the treatment with MET inhibitors could prevent or reverse resistance to inhibitors of growth factor-dependent signaling; this hypothesis is currently tested in phase III trials with anti-epidermal growth factor receptor (EGFR) inhibitors in non-small-cell lung cancer (NSCLC). Based on preclinical and preliminary clinical results, a rational strategy for the clinical development of MET antagonists should include a selection of the tumors with MET overexpression, the identification of prognostic/predictive biomarkers, the evaluation of combinations with anti-VEGF compounds.

MET signaling regulates glioblastoma stem cells

Glioblastomas multiforme (GBM) contain highly tumorigenic, self-renewing populations of stem/initiating cells [glioblastoma stem cells (GSC)] that contribute to tumor propagation and treatment resistance. However, our knowledge of the specific signaling pathways that regulate GSCs is limited. The MET tyrosine kinase is known to stimulate the survival, proliferation, and invasion of various cancers including GBM. Here, we identified a distinct fraction of cells expressing a high level of MET in human primary GBM specimens that were preferentially localized in perivascular regions of human GBM biopsy tissues and were found to be highly clonogenic, tumorigenic, and resistant to radiation. Inhibition of MET signaling in GSCs disrupted tumor growth and invasiveness both in vitro and in vivo, suggesting that MET activation is required for GSCs. Together, our findings indicate that MET activation in GBM is a functional requisite for the cancer stem cell phenotype and a promising therapeutic target.

Associations between hepatocyte growth factor, c-Met, and basic fibroblast growth factor and survival in endometrial cancer patients

Background:

Hepatocyte growth factor (HGF), c-Met, and basic fibroblast growth factor (bFGF) are molecular markers that contribute to angiogenesis and proliferation in numerous cancers. We assessed the prognostic significance of these factors in tumour and stroma of endometrial cancer (EC) patients (n=211).

Methods:

Immunohistochemistry (IHC) was used to detect tumour and stromal protein expression of the biomarkers. Associations between expression and clinicopathological factors were assessed using Chi-square tests. Kaplan–Meier curves, log-rank tests, and Cox regression were used to summarise associations between biomarker expression and overall survival (OS) and recurrence-free survival (RFS).

Results:

Tumour bFGF was significantly associated with high-grade endometrioid and clear cell histology (P<0.001), advanced stage (P=0.008), positive lymph-node involvement (P=0.002), poor OS (log-rank test, P=0.009), and poor RFS (P<0.001). In multivariable analyses, cases with HGF-positive, stromal bFGF-positive tumours had a lower risk of death compared with cases with HGF-positive, stromal bFGF-negative tumours (hazard ratio (HR): 0.14, 95% CI: 0.03, 0.60). Cases with HGF-positive, bFGF-positive tumours had a higher risk of recurrence compared with cases with negative expression of both markers (HR: 9.88, 95% CI: 2.63, 37.16).

Conclusion:

These IHC data show that tumour and stromal bFGF expression have opposite associations with survival outcomes in EC patients. If confirmed in larger studies, tumour-derived bFGF could be an attractive target in EC therapy.

Comprehensive predictive biomarker analysis for MEK inhibitor GSK1120212

The MEK1 and MEK2 inhibitor GSK1120212 is currently in phase II/III clinical development. To identify predictive biomarkers, sensitivity to GSK1120212 was profiled for 218 solid tumor cell lines and 81 hematologic malignancy cell lines. For solid tumors, RAF/RAS mutation was a strong predictor of sensitivity. Among RAF/RAS mutant lines, co-occurring PIK3CA/PTEN mutations conferred a cytostatic response instead of a cytotoxic response for colon cancer cells that have the biggest representation of the comutations. Among KRAS mutant cell lines, transcriptomics analysis showed that cell lines with an expression pattern suggestive of epithelial-to-mesenchymal transition were less sensitive to GSK1120212. In addition, a proportion of cell lines from certain tissue types not known to carry frequent RAF/RAS mutations also seemed to be sensitive to GSK1120212. Among these were breast cancer cell lines, with triple negative breast cancer cell lines being more sensitive than cell lines from other breast cancer subtypes. We identified a single gene DUSP6, whose expression was associated with sensitivity to GSK1120212 and lack of expression associated with resistance irrelevant of RAF/RAS status. Among hematologic cell lines, acute myeloid leukemia and chronic myeloid leukemia cell lines were particularly sensitive. Overall, this comprehensive predictive biomarker analysis identified additional efficacy biomarkers for GSK1120212 in RAF/RAS mutant solid tumors and expanded the indication for GSK1120212 to patients who could benefit from this therapy despite the RAF/RAS wild-type status of their tumors.

Tumor-targeted drug delivery with aptamers

Cancer is one of the leading causes of death around the world. Tumor-targeted drug delivery is one of the major areas in cancer research. Aptamers exhibit many desirable properties for tumor-targeted drug delivery, such as ease of selection and synthesis, high binding affinity and specificity, low immunogenicity, and versatile synthetic accessibility. Over the last several years, aptamers have quickly become a new class of targeting ligands for drug delivery applications. In this review, we will discuss in detail about aptamer-based delivery of chemotherapy drugs (e.g. doxorubicin, docetaxel, daunorubicin, and cisplatin), toxins (e.g. gelonin and various photodynamic therapy agents), and a variety of small interfering RNAs. Although the results are promising which warrants enthusiasm for aptamer-based drug delivery, tumor homing of aptamer-based conjugates after systemic injection has only been achieved in one report. Much remains to be done before aptamer-based drug delivery can reach clinical trials and eventually the day-to-day management of cancer patients. Therefore, future directions and challenges in aptamer-based drug delivery are also discussed.

Exploring c-Met kinase flexibility by sampling and clustering its conformational space

It is now widely recognized that the flexibility of both partners has to be considered in molecular docking studies. However, the question how to handle the best the huge computational complexity of exploring the protein binding site landscape is still a matter of debate. Here we investigate the flexibility of c-Met kinase as a test case for comparing several simulation methods. The c-Met kinase catalytic site is an interesting target for anticancer drug design. In particular, it harbors an unusual plasticity compared with other kinases ATP binding sites. Exploiting this feature may eventually lead to the discovery of new anticancer agents with exquisite specificity. We present in this article an extensive investigation of c-Met kinase conformational space using large-scale computational simulations in order to extend the knowledge already gathered from available X-ray structures. In the process, we compare the relevance of different strategies for modeling and injecting receptor flexibility information into early stage in silico structure-based drug discovery pipeline. The results presented here are currently being exploited in on-going virtual screening investigations on c-Met.

Targeting c-Met as a promising strategy for the treatment of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a severe condition that is found worldwide. Liver transplantation, surgical resection, and local-regional therapy such as transarterial chemoembolization have made great progress and play a dominant role in HCC management. However, the high frequency of tumor recurrence and/or metastasis after those treatments acquires systematic drug intervention. The approval of sorafenib, an agent that targets receptor tyrosine kinases (RTKs), as the first effective drug for systemic treatment of HCC represents a milestone in treatment of this disease. As a typical member of the RTK family, c-Met represents an intriguing target for cancer therapy. However, the role of the c-Met signal transduction pathway is less unambiguous in HCC pathology, giving rise to concerns about the feasibility of utilizing c-Met targeting approaches for HCC treatment. Recently, studies on des-γ-carboxy prothrombin, an abnormal cytokine secreted by HCC cells, by the current authors and other researchers have highlighted the critical role of c-Met signaling in HCC progression. This review takes a second look at the c-Met signal transduction pathway and discusses the possibility of targeting c-Met as a therapeutic strategy for HCC treatment.

Future directions in the evaluation of c-MET-driven malignancies

The c-MET (mesenchymal-epithelial transition factor) receptor tyrosine kinase is an exciting novel drug target in view of its key role in oncogenesis, as well as its association with disease prognosis in a number of malignancies. Several drugs targeting c-MET are currently showing promise in clinical trials and will hopefully validate positive observations from preclinical studies. The potential efficacy of these different therapeutic agents is expected to be influenced by the mechanism of aberrant hepatocyte growth factor (HGF)/c-MET signaling pathway activation in a particular cancer, but presents a promising strategy for cancer treatment either as a single agent or as part of a combination therapeutic approach. However, there is an ongoing need to improve and accelerate the transition of preclinical research into improved therapeutic strategies for patients with cancer. The main challenges facing the development of HGF/c-MET-targeted agents for cancer treatment include the discovery of rationally designed anticancer drugs and combination strategies, as well as the validation of predictive biomarkers. This paper discusses these issues, with a particular focus on future directions in the evaluation of c-MET-driven malignancies.

Targeting angiogenesis for controlling neuroblastoma

Neuroblastoma, a progressive solid tumor in childhood, continues to be a clinical challenge. It is highly vascular, heterogeneous, and extracranial tumor that originates from neural crest. Angiogenesis, genetic abnormalities, and oncogene amplification are mainly responsible for malignant phenotype of this tumor. Survivability of malignant neuroblastoma patients remains poor despite the use of traditional therapeutic strategies. Angiogenesis is a very common and necessary pre-requisite for tumor progression and metastasis. Angiogenesis is also a major factor in making malignant neuroblastoma. Thus, prevention of angiogenesis can be a highly significant strategy in the treatment of malignant neuroblastoma. Here, we summarize our current understanding of angiogenesis in malignant neuroblstoma and describe the use of experimental anti-angiogenic agents either alone or in combination therapy. This review will clearly indicate the importance of angiogenesis in the pathogenesis of malignant neuroblastoma, its prevention as a promising therapy in preclinical models of malignant neuroblastoma, and prospective clinical trials.

Bypassing glycosylation: engineering aglycosylated full-length IgG antibodies for human therapy

In recent years a number of aglycosylated therapeutic antibodies have entered the clinic. The clinical evaluation of these antibodies has served to dispel concerns that the absence of the ubiquitous N297 glycan in the Fc of IgG might result in immunogenicity, poor in vivo stability or unfavorable pharmacokinetics. Importantly, recent studies have now demonstrated that aglycosylated antibodies can be engineered to display novel effector functions and mechanisms of action that do not appear to be possible with their glycosylated counterparts. Moreover, the ability to manufacture aglycosylated antibodies in lower eukaryotes or in bacteria provides significant bioprocessing advantages in terms of shorter bioprocess development and running times and by completely bypassing the problems associated with the glycan heterogeneity of conventional antibodies. These advantages are poised to catapult aglycosylated antibodies to the forefront of protein therapeutics.

Phase I trial of a selective c-MET inhibitor ARQ 197 incorporating proof of mechanism pharmacodynamic studies

PURPOSE

The hepatocyte growth factor/c-MET axis is implicated in tumor cell proliferation, survival, and angiogenesis. ARQ 197 is an oral, selective, non-adenosine triphosphate competitive c-MET inhibitor. A phase I trial of ARQ 197 was conducted to assess safety, tolerability, and target inhibition, including intratumoral c-MET signaling, apoptosis, and angiogenesis.

PATIENTS AND METHODS

Patients with solid tumors amenable to pharmacokinetic and pharmacodynamic studies using serial biopsies, dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI), and circulating endothelial cell (CEC) and circulating tumor cell (CTC) enumeration were enrolled.

RESULTS

Fifty-one patients received ARQ 197 at 100 to 400 mg twice per day. ARQ 197 was well tolerated, with the most common toxicities being grade 1 to 2 fatigue, nausea, and vomiting. Dose-limiting toxicities included grade 3 fatigue (200 mg twice per day; n = 1); grade 3 mucositis, palmar-plantar erythrodysesthesia, and hypokalemia (400 mg twice per day; n = 1); and grade 3 to 4 febrile neutropenia (400 mg twice per day, n = 2; 360 mg twice per day, n = 1). The recommended phase II dose was 360 mg twice per day. ARQ 197 systemic exposure was dose dependent and supported twice per day oral dosing. ARQ 197 decreased phosphorylated c-MET, total c-MET, and phosphorylated focal adhesion kinase and increased terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-biotin nick-end labeling (TUNEL) staining in tumor biopsies (n = 15). CECs decreased in 25 (58.1%) of 43 patients, but no significant changes in DCE-MRI parameters were observed after ARQ 197 treatment. Of 15 patients with detectable CTCs, eight (53.3%) had ≥ 30% decline in CTCs after treatment. Stable disease, as defined by Response Evaluation Criteria in Solid Tumors (RECIST), ≥ 4 months was observed in 14 patients, with minor regressions in gastric and Merkel cell cancers.

CONCLUSION

ARQ 197 safely inhibited intratumoral c-MET signaling. Further clinical evaluation focusing on combination approaches, including an erlotinib combination in non-small-cell lung cancer, is ongoing.

Heparanase plays a dual role in driving hepatocyte growth factor (HGF) signaling by enhancing HGF expression and activity

Hepatocyte growth factor (HGF) is a heparin-binding cytokine that enhances growth, motility, and angiogenesis of many tumor types, including multiple myeloma where it is often highly expressed. However, little is known regarding what controls HGF level and activity in these tumors. Evaluation of bone marrow biopsies from myeloma patients revealed a strong positive correlation between the levels of HGF and heparanase, an endoglucuronidase known to promote aggressive tumor behavior. In vitro, addition of recombinant heparanase to myeloma cells or transfection of myeloma cell lines with the cDNA for heparanase significantly increased tumor cell expression and secretion of biologically active HGF. Shed syndecan-1, whose levels in myeloma are also enhanced by heparanase expression, binds to secreted HGF. This syndecan-1-HGF complex is active as shown by its ability to stimulate paracrine signaling via c-Met, the cell surface receptor for HGF. Surprisingly, heparanase enzyme activity was not required for up-regulation of HGF expression by the tumor cells. This is in contrast to the heparanase-mediated enhanced syndecan-1 shedding, which does require activity of the enzyme. This suggests that two different functional domains within the heparanase enzyme (the enzyme active site and a separate site) contribute to events leading to enhanced HGF signaling. These findings demonstrate a novel mechanism driving the HGF pathway whereby heparanase stimulates an increase in both HGF expression and syndecan-1 shedding to enhance HGF signaling. This work also provides further mechanistic insight into the dynamic role of heparanase in driving aggressive tumor progression.

Envisioning the future of early anticancer drug development

The development of novel molecularly targeted cancer therapeutics remains slow and expensive with many late-stage failures. There is an urgent need to accelerate this process by improving early clinical anticancer drug evaluation through modern and rational trial designs that incorporate predictive, pharmacokinetic, pharmacodynamic, pharmacogenomic and intermediate end-point biomarkers. In this article, we discuss current approaches and propose strategies that will potentially maximize benefit to patients and expedite the regulatory approvals of new anticancer drugs.