Targeted therapy in advanced colon cancer: the role of new therapies

Impact of protamine I on colon cancer proliferation, invasion, migration, diagnosis and prognosis

This paper investigates protamine I (PRM1) expression and its effects on proliferation, invasion and migration of colon cancer cells as well as its function in clinical diagnosis and prognosis. Gene chips were used to screen differentially expressed genes. PRM1 expression was detected by Western blotting and quantitative real time-polymerase chain reaction (qRT-PCR). Hematoxylin and eosin (HE) staining and immunohistochemistry were utilized to compare the expression of PRM1 from multiple differentiation levels of colon cancer tissues. Cell viability, cell apoptosis and cell cycle were tested using the MTT assay and flow cytometry. Cell invasion and migration capability were tested using the Transwell assay and wound healing. In vivo effects of PRM1 on colon cancer were explored using a xenograft model. PRM1 expression in serum was detected by enzyme-linked immunosorbent assay (ELISA). The expression level of PRM1 was significantly higher in colon cancer tissues and the staining degree of PRM1 in poorly-differentiated was stronger. pcDNA3.1-PRM1 decreased cell apoptosis while it increased the proliferation, cell invasion and migration. The si-PRM1 group displayed an opposite tendency. The serum PRM1 level was significantly higher and could serve as a diagnostic biomarker for colon cancer.

Ixazomib promotes CHOP-dependent DR5 induction and apoptosis in colorectal cancer cells

BACKGROUND

Ixazomib (Ninlaro), a novel proteasome inhibitor, has been developed for the treatment of many cancers and has demonstrated anti-tumor efficacy against various malignancies. However, the mechanism of the anti-tumor effect of ixazomib in colorectal cancer (CRC) cells remains unclear.

METHODS

MTS and flow cytometry were performed to determine the effect of ixazomib on CRC cells. Western blotting and real-time RT-PCR were performed to detect ixazomib-induced DR5 upregulation. ChIP was performed to detect CHOP binding to DR5 promoter. Finally, xenograft experiments were carried out to measure the antitumor effect of ixazomib in vivo.

RESULTS

In this study, we revealed the mechanism by which ixazomib inhibits the growth of CRC cells. Our findings indicated that ixazomib treatment induces CHOP-dependent DR5 induction, irrespective of p53 status. Furthermore, DR5 is necessary for ixazomib-mediated apoptosis. Ixazomib also synergized with TRAIL to induce marked apoptosis via DR5 in CRC cells.

CONCLUSIONS

Our findings further suggested that ixazomib sensitizes TRAIL/death receptor signaling pathway-targeted CRC and suggested that DR5 induction could be a valuable indicator of ixazomib sensitivity.

An EGFR and AKT Signaling Pathway was Identified with Mediation Model in Osteosarcomas Clinical Study

Identification of correlation pattern and signal pathway among biomarkers in patients has become increasingly interesting for its potential values in diagnosis, treatment and prognosis. EGFR and p-AKT signaling in osteosarcoma (OS) patients were analyzed for its relationship with cancer cell proliferation maker, Ki-67, using causal procedures and statistical tests. A total of 69 patients were collected who present to Vanderbilt University Medical Center with newly diagnosed, previously untreated osteosarcomas during the clinical study period 1994 through 2003. Tissue microarrays were constructed for EGFR, p-AKT and Ki-67. The mediation model was constructed with structural equation model (SEM) for the causal analysis of the three biomarkers in osteosarcoma patients. The results suggested a mediating effect of p-AKT for the causal relationship between EGFR and Ki-67. The study also found significant associations between EGFR and Ki-67 (p = 0.002), EGFR and p-AKT (p = 0.027), and p-AKT and Ki-67 controlling EGFR (p = 0.004). After the impact of EGFR on Ki-67 was accounted for by p-AKT, the relation between EGFR and Ki-67 was no longer significant (p = 0.381). The mediating effect was confirmed with Sobel test (p < 0.001) and Goodman (I) test (p < 0.001). The study indicated that a mediation model could be an approach to exploring the correlation pattern of EGFR and AKT signal pathway for cancer cell proliferation in OS patients in clinical study.

Primary tumor location is an important predictive factor for wild-type KRAS metastatic colon cancer treated with cetuximab as front-line bio-therapy

INTRODUCTION

Left- and right-sided colon cancers were significantly different in epidemiologic, clinical and histological parameters. However, the impact of primary tumor location in metastatic colon cancer treated with front-line targeted triplet regimens is unclear, particularly in Asian populations.

METHODS

A total of 121 patients with KRAS exon 2 codon 12/13 wild-type metastatic colon cancer were enrolled between January 2007 and December 2013. All patients received one target agent, such as cetuximab or bevacizumab, as a front-line targeted triplet regimen. The impact of primary tumor location for cetuximab and bevacizumab groups was analyzed, respectively.

RESULTS

In cetuximab group, left-sided metastatic colon cancer was superior to right-sided metastatic colon cancer in objective response rate (70.1% vs 33.3%, P = 0.024), progression-free survival (15.0 vs 5.3 months, P < 0.001) and overall survival (35.8 vs 14.4 months, P = 0.031). Primary tumor location was an independent prognostic factor for progression-free survival (hazard ratio 0.240, 95% confidence interval 0.114-0.508, P < 0.001). However, in the bevacizumab group, there were no differences in outcomes for either side. Primary tumor location was insignificant for progression-free survival and overall survival in univariate analysis.

CONCLUSION

Left-sided primary tumors were favored in cetuximab-based front-line targeted triplet regimen for metastatic colon cancer.

Cellular inhibitor of apoptosis protein 1 (cIAP1) stability contributes to YM155 resistance in human gastric cancer cells

YM155, which blocks the expression of survivin, a member of the inhibitor of apoptosis (IAP) family, induces cell death in a variety of cancer types, including prostate, bladder, breast, leukemia, and non-small lung cancer. However, the mechanism underlying gastric cancer susceptibility and resistance to YM155 is yet to be specified. Here, we demonstrate that cIAP1 stability dictates resistance to YM155 in human gastric cancer cells. Treatment of human gastric cancer cells with YM155 differentially induced cell death dependent on the stability of cIAP1 as well as survivin. Transfection with cIAP1 expression plasmids decreased cell sensitivity to YM155, whereas knockdown of endogenous cIAP1 using RNA interference enhanced sensitivity to YM155. In addition, double knockdown of survivin and cIAP1 significantly induced cell death in the YM155-resistant cell line, MKN45. We also showed that YM155 induced autoubiquitination and proteasome-dependent degradation of cIAP1. Surprisingly, survivin affected the stability of cIAP1 through binding, contributing to cell sensitivity to YM155. Thus, our findings reveal that YM155 sensitizes human gastric cancer cells to apoptotic cell death by degrading cIAP1, and furthermore, cIAP1 in gastric cancer cells may act as a PD marker for YM155 treatment.

Application of reductive ¹³C-methylation of lysines to enhance the sensitivity of conventional NMR methods

NMR is commonly used to investigate macromolecular interactions. However, sensitivity problems hamper its use for studying such interactions at low physiologically relevant concentrations. At high concentrations, proteins or peptides tend to aggregate. In order to overcome this problem, we make use of reductive ¹³C-methylation to study protein interactions at low micromolar concentrations. Methyl groups in dimethyl lysines are degenerate with one ¹³CH₃ signal arising from two carbons and six protons, as compared to one carbon and three protons in aliphatic amino acids. The improved sensitivity allows us to study protein-protein or protein-peptide interactions at very low micromolar concentrations. We demonstrate the utility of this method by studying the interaction between the post-translationally lipidated hypervariable region of a human proto-oncogenic GTPase K-Ras and a calcium sensor protein calmodulin. Calmodulin specifically binds K-Ras and modulates its downstream signaling. This binding specificity is attributed to the unique lipidated hypervariable region of K-Ras. At low micromolar concentrations, the post-translationally modified hypervariable region of K-Ras aggregates and binds calmodulin in a non-specific manner, hence conventional NMR techniques cannot be used for studying this interaction, however, upon reductively methylating the lysines of calmodulin, we detected signals of the lipidated hypervariable region of K-Ras at physiologically relevant nanomolar concentrations. Thus, we utilize ¹³C-reductive methylation of lysines to enhance the sensitivity of conventional NMR methods for studying protein interactions at low concentrations.

Targeted therapies and predictive markers in epithelial malignancies of the gastrointestinal tract

CONTEXT

In recent years, there has been a tremendous amount of interest in the development of targeted therapies for the treatment of human cancers. Increased understanding of the specific molecular pathways and driver mutations critical to cancer cell growth have allowed the development of these advanced therapeutics. Among these, inhibitors of the epidermal growth factor receptor and HER2/neu pathways now play a major role in the management of gastrointestinal cancers in addition to other solid malignancies. In colorectal and gastric cancers, the use of epidermal growth factor receptor inhibitors and HER2/neu inhibitors has increased the available treatment options for patients with advanced disease.

OBJECTIVE

To focus on the current targeted therapies and predictors of response in malignancies of the gastrointestinal tract.

DATA SOURCES

Medical literature searchable on PubMed (US National Library of Medicine) as well as older studies revealed by the literature review were used as the source of data.

CONCLUSION

Gene testing of critical elements of the pathways targeted by these agents (such as KRAS mutational analysis in colorectal tumors and HER2/neu testing in gastric cancers) allows the ability to predict which patients will respond to these treatments. As the molecular profiling of tumors and our understanding of cancer genomics and epigenetic alterations continues to grow, it is expected that these personalized targeted therapies will form one of the mainstays of gastrointestinal cancer treatment.

Increased epidermal growth factor receptor expression at the invasive margin is a negative prognostic factor in colorectal cancer

The receptor tyrosine kinase epidermal growth factor receptor (EGFR) is often expressed in solid malignant tumours, and the expression has been correlated to disease progression. Multiple new agents targeted against the EGFR have been developed during the last decade, but treatment selecting criteria are still not clear. This immunohistochemical study includes 386 colorectal cancer patients and focuses on EGFR expression variations within the tumour, comparing central parts to the invasive margin. Positive immunostaining for EGFR was evident in the central part in 176/386 (46%) of analyzed primary tumours. The invasive margin was positive in 222/386 (58%). A similar expression in both the central part and the invasive front was evident in 286/386 (74%). An increased score at the invasive margin compared to central parts (EGFR(i) ) was evident in 97/386 (25%) of the tumours. Moreover, the results show a significant survival disadvantage for the EGFR(i) group, both in potentially curatively resected colon cancer patients (n = 170, p = 0.01) and in potentially curatively resected colon and rectal cancer patients combined (n = 273, p = 0.013). Multivariate survival analysis adjusted for age, gender, bowel localisation, grade, stage and tumour type showed an increased risk of cancer death for EGFR(i) tumours (HR, 1.53; 95% CI, 1.04-2.23; p = 0.029). A significant correlation between EGFR expression at the invasive margin and the presence of budding was seen (p = 0.0001). This investigation of a large patient material implies that EGFR immunohistochemical analysis still has a role in risk evaluation of colorectal cancer patients.

Practical and molecular evaluation of colorectal cancer: new roles for the pathologist in the era of targeted therapy

CONTEXT

Colorectal cancer is the third most common cancer and the fourth most common cause of cancer death worldwide. Patient cases are discussed in multidisciplinary meetings to decide on the best management on an individual basis. Until recently, the main task of the pathologist in such teams was to provide clinically useful reports comprising staging of colorectal cancer in surgical specimens. The advent of total mesorectal excision and the application of anti-epidermal growth factor receptor (EGFR)-targeted therapies for selected patients with metastasized colorectal cancer have changed the role of the pathologist.

OBJECTIVES

To present the traditional role of the pathologist in the multidisciplinary team treating patients with colorectal cancer, to address the technique of total mesorectal excision and its implications for the evaluation of surgical specimens, to offer background information on the various EGFR-targeted therapies, and to review the currently investigated tissue biomarkers assumed to be predictive for efficacy of such therapies, with a focus on the role of the pathologist in determining the status of such biomarkers in individual tumors.

DATA SOURCES

This article is based on selected articles pertaining to biopsy evaluation of colorectal carcinoma and reviews of EGFR-targeted therapies for this cancer. All references are accessible via the PubMed database (US National Library of Medicine and the National Institutes of Health).

CONCLUSIONS

Pathologists play an increasingly important role in the diagnosis and management of colorectal cancer because of the advent of new surgical techniques and of targeted therapies. It is expected that this role will increase further in the near future.

Flavonoids as RTK inhibitors and potential anticancer agents

Tyrosine kinase receptors (RTKs) play a crucial role in the regulation of the cell division cycle. Currently more than 50 RTKs divided into several subfamilies have been described. The inhibition of these enzymes has emerged as an important research-area. Compounds able to inhibit the activity of these enzymes are expected to display antiproliferative properties. Flavonoids are representative of various small molecules acting as RTK inhibitors. These naturally occurring compounds are able to bind to the ATP-binding site of several kinases. The most plausible current hypothesis explaining the action of these substances on kinases is that the chromenone moiety of the flavonoid acts as a mimetic of the adenine moiety of ATP, the receptor co-factor. In this review, we report recent results on the activity of natural and synthetic derivatives of flavonoids as inhibitors of RTKs. Mechanistic aspects, the therapeutic usefulness, and the potential clinical use are discussed.

Epidermal growth factor receptor blockade in combination with conventional chemotherapy inhibits soft tissue sarcoma cell growth in vitro and in vivo

PURPOSE

The epidermal growth factor receptor (EGFR) is highly expressed in many human soft tissue sarcomas (STS). However, EGFR blockade has not apparently been used for human STS therapy; therefore, we examined the in vitro and in vivo effects and the underlying mechanisms before considering EGFR blockade as a therapy for STS patients.

EXPERIMENTAL DESIGN

Human STS tissues and cell lines were used to study EGFR expression and activation. Western blot analysis was used to evaluate effects of EGFR activation on downstream signaling. Cell culture assays were used to assess the effect of EGF stimulation as well as EGFR blockade (using an EGFR tyrosine kinase inhibitor, Iressa; AstraZeneca) on STS cell growth, apoptosis, and chemosensitivity. An in vivo study (HT1080 human fibrosarcoma cell line in nude/nude mice: Iressa, doxorubicin, Iressa + doxorubicin, vehicle) was used to examine tumor growth; pEGFR, proliferating cell nuclear antigen, and terminal deoxyribonucleotide transferase-mediated nick-end labeling staining helped assess the effect of therapy in vivo on STS EGFR activation, proliferation, and apoptosis.

RESULTS

EGFR was expressed and activated in STS cell lines and tumors, probably due to ligand binding rather than EGFR mutation. Stimulation caused activation of AKT and mitogen-activated protein kinase pathways. EGFR blockade inhibited these effects and also caused increased apoptosis, a p53-independent G(0)-G(1) cell cycle arrest, and decreased cyclin D1 expression. In vivo, Iressa + doxorubicin had markedly synergistic anti-STS effects.

CONCLUSION

EGFR blockade combined with conventional chemotherapy results in anti-human STS activity in vitro and in vivo, suggesting the possibility that combining these synergistic treatments will improve anti-STS therapy.

VEGF-D expression correlates with colorectal cancer aggressiveness and is downregulated by cetuximab

AIM: To gain mechanistic insights into the role played by epidermal growth factor receptor (EGFR) in the regulation of vascular endothelial growth factors (VEGFs) in colorectal cancer (CRC).

METHODS: The impact of high-level expression of the growth factor receptors EGFR and VEGF receptor (VEGFR)3 and the VEGFR3 ligands VEGF-C and VEGF-D on disease progression and prognosis in human CRC was investigated in 108 patients using immunohistochemistry. Furthermore, the expression of the lymphangiogenic factors in response to the modulation of EGFR signalling by the EGFR-targeted monoclonal antibody cetuximab was investigated at the mRNA and protein level in human SW480 and SW620 CRC cell lines and a mouse xenograft model.

RESULTS: Human CRC specimens and cell lines displayed EGFR, VEGF-C and VEGF-D expression with varying intensities. VEGF-C expression was associated with histological grade. Strong expression of VEGF-D was significantly associated with lymph node metastases and linked to a trend for decreased survival in lymph node-positive patients. EGFR blockade with cetuximab resulted in a significant decrease of VEGF-D expression in vitro and in vivo.

CONCLUSION: In conclusion, the expression of VEGF-D in colorectal tumours is significantly associated with lymphatic involvement in CRC patients and such expression might be blocked effectively by cetuximab.

Differential sensitivity of human colon cancer cell lines to the nucleoside analogs ARC and DRB

Recently, we identified a nucleoside analog named ARC (4-amino-6-hydrazino-7-beta-D-ribofuranosyl-7H-Pyrrolo[2,3-d]pyrimidine-5-carboxamide), which has the properties of a general transcriptional inhibitor. Here, we report the characterization of ARC on a panel of colorectal cancer (CRC) cell lines. Cell death induced by ARC in CRC cells was accompanied by caspase-3 cleavage and correlated with the downregulation of antiapoptotic proteins, survivin and Mcl-1 and with the inhibition of Akt phosphorylation. At the same time, colon cancer cell lines were resistant to the well-known nucleoside analog DRB (5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole), which failed to downregulate Mcl-1 or survivin. Overall, ARC could represent an attractive candidate for anti-cancer drug development that targets multiple survival pathways in colon cancer cells.

Novel therapies in advanced renal cell carcinoma: management of adverse events from sorafenib and sunitinib

INTRODUCTION

Sorafenib and Sunitinib are the first tyrosine kinase inhibitors licensed for the treatment of advanced renal cell carcinoma. In contrast to conventional chemotherapy, targeted therapies have distinct and specific side effects.

METHODS

Selective review in Medline and the data base of the American Society of Clinical Oncology on the treatment and side effects of tyrosine kinase inhibitors in renal cell carcinoma, drawing on the authors' own experience.

RESULTS AND DISCUSSION

Tyrosine kinase inhibitors are characterized by a variety of uncommon side effects, such as lassitude, mucosal inflammation and skin changes. The detection and treatment of adverse events are critical for interdisciplinary cancer treatment in order to ensure patients' safety. This article offers an overview of the unwanted effects of drug therapy in the management of renal cell carcinoma.

Immunotherapy and immunoescape in colorectal cancer

Immunotherapy encompasses a variety of interventions and techniques with the common goal of eliciting tumor cell destructive immune responses. Colorectal carcinoma often presents as metastatic disease that impedes curative surgery. Novel strategies such as active immunization with dendritic cells (DCs), gene transfer of cytokines into tumor cells or administration of immunostimulatory monoclonal antibodies (such as anti-CD137 or anti-CTLA-4) have been assessed in preclinical studies and are at an early clinical development stage. Importantly, there is accumulating evidence that chemotherapy and immunotherapy can be combined in the treatment of some cases with colorectal cancer, with synergistic potentiation as a result of antigens cross-presented by dendritic cells and/or elimination of competitor or suppressive T lymphocyte populations (regulatory T-cells). However, genetic and epigenetic unstable carcinoma cells frequently evolve mechanisms of immunoevasion that are the result of either loss of antigen presentation, or an active expression of immunosuppressive substances. Some of these actively immunosuppressive mechanisms are inducible by cytokines that signify the arrival of an effector immune response. For example, induction of 2, 3 indoleamine dioxygenase (IDO) by IFNγ in colorectal carcinoma cells. Combinational and balanced strategies fostering antigen presentation, T-cell costimulation and interference with immune regulatory mechanisms will probably take the stage in translational research in the treatment of colorectal carcinoma.

Chemotherapeutic agents for colorectal cancer with a defective mismatch repair system: The state of the art

Mismatch repair (MMR) proteins are capable of recognizing and processing not only single base-pair mismatches and insertion-deletion loops that occur during DNA replication, but also adducts in DNA resulting from treatment with cancer chemotherapy agents. MMR deficiency leads to microsatellite instability (MSI) and results in resistance to antimetabolites, alkylating and platinating agents, DNA minor groove binders, and inhibitors of topoisomerases. Therefore, anticancer agents that can be recommended for use in MMR deficient colorectal cancers are those that exert their cytotoxicity regardless of the MMR status. These include some alkylating drugs, brostacillin, gemcytabine, photodynamic therapy, taxanes. An approach that is currently receiving much attention is the use of agents such as 5-azacytidine, an inhibitor of the DNA methyltransferases, in combination with inhibitors of histone de-acetylation, to restore the MMR function. A strong anti-proliferative efficacy with a relatively low direct cytotoxicity, obtainable with oloumicine and roscovitine (selective cyclin-dependent kinases inhibitors) can represent a new expedient for the therapeutic treatment of MMR deficient colorectal cancers. The question of how MMR defects modulate the response to chemotherapeutics deserves further investigation, to enable a more aware choice of cancer treatment.

Radioimmunotherapy of human colon cancer xenografts by using 131I labeled-CAb1 F(ab')2

PURPOSE

Therapeutic efficacy, suitable dose, and administration times of 131I-CAb1 F(ab')2, a new monoclonal antibody therapeutics specifically directed against a cell surface-associated glycoprotein of colon cancer, were investigated in this article.

METHODS AND MATERIALS

In human colon cancer xenografts, 131I-CAb1 F(ab')2 at the dose of 125 muCi, 375 muCi, and 1125 muCi were administrated intraperitoneally on Days 6 and 18 after implantation of HR8348 cells with CAb1 high reactivity. Survival time and tumor growth inhibition rate were used to evaluate the efficacy and safety of 131I-CAb1 F(ab')2 in treatment of colon cancer xenografts.

RESULTS

Treatment of 125, 375, and 1125 muCi 131I-CAb1 F(ab')2 did not significantly decrease the mean survival time of nude mice when compared with nontreated groups (p = 0.276, 0.865, 0.582, respectively). Moreover, the mean survival times of nude mice receiving 375 muCi and 1125 muCi 131I-CAb1 F(ab')2 were significantly longer than that of 5-FU-treated groups (p = 0.018 and 0.042). Tumor growth inhibition rates of the first therapy were 35.67% and 41.37%, with corresponding 131I-labeled antibody dosage of 375 muCi and 1125 muCi. After single attack dosage, second reinforcement therapy may rise efficacy significantly. Tumor growth inhibition rates of 125 muCi, 375 muCi, and 1125 muCi 131I-labeled antibody on Day 20 posttherapy were 42.65%, 56.56%, and 84.41%, respectively. Histopathology examination revealed that tissue necrosis of various degrees was found in 131I-CAb1 F(ab')2-treated groups.

CONCLUSION

131I-CAb1 F(ab')2 is safe and effective for colon cancer. It may be a novel and potentially adjuvant therapeutics for colon cancer.

Recent advances in targeted therapies for colorectal cancer

BACKGROUND

Recent advances in the molecular biology and genetics of colorectal cancer have led to the identification of potential therapeutic targets such as epidermal growth factor receptor, vascular endothelial growth factor and endothelial receptors.

OBJECTIVE

This review will examine the major therapeutic advances along with the preclinical basis justifying their combination with conventional therapeutic tools. This review will also critically consider current possibilities offered to identify responding patients.

DATA SOURCES

Preclinical and primary clinical trial results published in peer-review journals. The authors examined the relevance and subsequent inclusion of the data.

CONCLUSIONS

Cetuximab and bevacizumab provide new benefits in terms of the response rate and survival. There remain, however, important questions concerning, for instance, optimal combinations between conventional cytotoxic agents and targeted therapies and also between targeted drugs themselves. These new targeted treatments are costly and in this context the question of the identification of the right drug for the right patient is particularly relevant. Adequate tools in predicting the efficacy of targeted treatments are still needed.

Prognostic significance of epidermal growth factor receptor expression in colon cancer patients undergoing curative surgery

BACKGROUND

To investigate the role of epidermal growth factor receptor (EGFR) expression as a prognostic marker for prediction of cancer behavior and clinical outcomes in colon cancer patients undergoing potentially curative surgery.

METHODS

EGFR determination using a commercially available immunohistochemistry kit was performed in tissues from 149 colon cancer patients receiving primary surgical treatment and in 25 normal colon mucosa specimens from noncancer patients. EGFR positivity was correlated in univariate and multivariate analyses with disease recurrence and survival. In addition, p27, p53, and vascular endothelial growth factor expression were assessed by immunohistochemistry in 104 patients and correlated with EGFR tumor expression and clinical outcome.

RESULTS

EGFR expression was detected in approximately one third of colon cancer patients (53 of 149; 35.6%). In 126 curatively treated patients, EGFR expression was correlated with disease recurrence and worse survival in both univariate and multivariate analyses. In a multivariate model for predicting recurrence and survival, Dukes' staging, p27, and EGFR expression were the only independent covariates. In particular, in Dukes' A and B patients the 5-year survival probability was 96% for EGFR-negative and high p27 expression cases and was 30.7% for EGFR-positive and low p27 expression cases.

CONCLUSIONS

EGFR expression was an independent prognostic indicator of disease recurrence and poor survival in colon cancer patients undergoing curative surgery. In the context of novel therapeutic options such as molecularly targeted therapies, these findings suggest that anti-EGFR drugs could be evaluated in the adjuvant treatment of EGFR-positive colon cancer patients.

K-ras as a target for cancer therapy

The central role K-, H- and N-Ras play in regulating diverse cellular pathways important for cell growth, differentiation and survival is well established. Dysregulation of Ras proteins by activating mutations, overexpression or upstream activation is common in human tumors. Of the Ras proteins, K-ras is the most frequently mutated and is therefore an attractive target for cancer therapy. The complexity of K-ras signaling presents many opportunities for therapeutic targeting. A number of different approaches aimed at abrogating K-ras activity have been explored in clinical trials. Several of the therapeutic agents tested have demonstrated clinical activity, supporting ongoing development of K-ras targeted therapies. However, many of the agents currently being evaluated have multiple targets and their antitumor effects may not be due to K-Ras inhibition. To date, no selective, specific inhibitor of K-ras is available for routine clinical use. In this review, we will summarize the structure and function of K-ras with attention to its role in tumorigenesis and discuss the successes and failures of the various strategies designed to therapeutically target this important oncogene.