Predicting response to epidermal growth factor receptor-targeted therapy in colorectal cancer

Efficacy and safety of panitumumab in a cohort of patients with metastatic colorectal cancer in France: PANI OUEST, a post-EMA-approval descriptive study with a geriatric oncology focus

BACKGROUND/AIMS

The Bretagne-Pays de la Loire cancer observatory, an oncology network created by the French Ministry of Health, is specifically dedicated to assess the use of new targeted anticancer therapies in routine practice. In line with the French National Cancer III program, our cancer network set up a real-life cohort, which is independent of the pharmaceutical industry, for patients with colorectal cancer to monitor patient safety and quality of care and promote pharmacovigilance.

MATERIALS AND METHODS

Panitumumab monotherapy was assessed in 243 patients with wild-type Kirsten rat sarcoma who were treated for metastatic colorectal cancer (mCRC) between July 2008 and December 2010 after prior chemotherapy using oxaliplatine and irinotecan. This was a post-European medicine agency marketing (EMA-M) study Results: This study shed light on the best practices, strategic adaptations, clinical results (treatment objective responses, 13%; progression free survival, 2.99 months [2.73-3.15]; and overall survival, 6.8 months [5.49-8.38]) as well as expected or unexpected (grade 3 or 4: 11.5%) secondary effects in the phase IV panitumumab treatment of mCRC.

CONCLUSION

Our results are similar to those by Amado whose phase III study led to obtaining EMA-M for panitumumab and tend to confirm the antitumor activity of this antiepidermal growth factor receptor antibody in the treatment of mCRC. In addition, our results opened avenues to further assessment of panitumumab use as monotherapy as well as its benefit-risk ratio while taking into account the patients' general and clinical characteristics. In 2012, the French National Authority for Health appended these data to the panitumumab transparency committee report.

Colorectal Cancer: Why Does Side Matter?

Colorectal cancer (CRC) is a heterogeneous disease, and the search for clinical and molecular prognostic and predictive factors is thus necessary to better tailor each individual patient's management. Primary tumor location (PTL) seems to act as a master prognostic factor pooling different clinical, pathological, and molecular poor prognostic factors. In fact, right-sided (RS) CRC patients are more frequently female and elderly with microsatellite unstable, BRAF mutated, CpG island methylator phenotype (CIMP)-high, poorly differentiated tumors, compared to left-sided (LS) CRC patients. PTL does not seem to clearly influence disease-free survival (DFS) in localised colon cancer even though the opposite prognostic value of RS tumors on DFS depending on RAS/BRAF mutational status has been recently suggested in these patients. In metastatic CRC (mCRC), the poor prognosis associated with RS tumors is confirmed in the most recent publications in the era of double and triple chemotherapeutic regimens and targeted agents. Concerning the predictive value of PTL, in patients with RAS wild-type mCRC in the first-line setting, anti-epidermal growth factor receptor (EGFR) therapy combined with chemotherapy appears to be more effective than bevacizumab in LS CRC, while patients with RS CRC benefit less from anti-EGFR therapy, and intensive chemotherapy plus bevacizumab may be more appropriate but EGFR antibodies remain an option if objective response is needed. Due to the limitation of the current data (unplanned and retrospective analyses), these conclusions must be interpreted with caution. Clinical trials in RS CRC may be of interest to clarify what is the best treatment strategy in these patients.

Panitumumab for the treatment of metastatic colorectal cancer: a review

In recent years, the treatment of metastatic colorectal cancer (mCRC) has evolved significantly with the increase of new therapeutic options, leading to an improved median survival for these patients. In particular, the identification of molecular targets in tumor cells has led to the introduction of biological drugs for the treatment of mCRC. Panitumumab is a fully human monoclonal antibody that binds the EGF receptor of tumor cells and inhibits downstream cell signaling with antitumor effect on inhibition of tumor growth. Its use has been approved by randomized clinical trials as monotherapy in chemorefractory patients or combined with chemotherapy in the treatment of RAS wild-type mCRC, where it demonstrated a significant improvement in survival and response rate. The purpose of this review is to analyze the use and efficacy profile of panitumumab, particularly focusing on recently reported data on its use, and future perspectives in patients with mCRC.

Label-Free Raman Spectroscopic Imaging Monitors the Integral Physiologically Relevant Drug Responses in Cancer Cells

Predictions about the cellular efficacy of drugs tested in vitro are usually based on the measured responses of a few proteins or signal transduction pathways. However, cellular proteins are highly coupled in networks, and observations of single proteins may not adequately reflect the in vivo cellular response to drugs. This might explain some large discrepancies between in vitro drug studies and drug responses observed in patients. We present a novel in vitro marker-free approach that enables detection of cellular responses to a drug. We use Raman spectral imaging to measure the effect of the epidermal growth factor receptor (EGFR) inhibitor panitumumab on cell lines expressing wild-type Kirsten-Ras (K-Ras) and oncogenic K-Ras mutations. Oncogenic K-Ras mutation blocks the response to anti-EGFR therapy in patients, but this effect is not readily observed in vitro. The Raman studies detect large panitumumab-induced differences in vitro in cells harboring wild-type K-Ras as seen in A in red but not in cells with K-Ras mutations as seen in B; these studies reflect the observed patient outcomes. However, the effect is not observed when extracellular-signal-regulated kinase phosphorylation is monitored. The Raman spectra show for cells with wild-type K-Ras alterations based on the responses to panitumumab. The subcellular component with the largest spectral response to panitumumab was lipid droplets, but this effect was not observed when cells harbored K-Ras mutations. This study develops a noninvasive, label-free, in vitro vibrational spectroscopic test to determine the integral physiologically relevant drug response in cell lines. This approach opens a new field of patient-centered drug testing that could deliver superior patient therapies.

Phase II trial of cetuximab plus cisplatin and irinotecan in patients with cisplatin and irinotecan-refractory metastatic esophagogastric cancer

INTRODUCTION

Cetuximab in combination with irinotecan has shown clinically significant activity in patients with irinotecan-refractory colon cancer. We evaluated the efficacy of cetuximab in combination with cisplatin and irinotecan in patients with metastatic esophagogastric cancer refractory to cisplatin and irinotecan.

PATIENTS AND METHODS

Patients with disease progression within 3 months of treatment with prior cisplatin and irinotecan received weekly cetuximab and cisplatin/irinotecan for 2 weeks, followed by a 1-week rest period. The primary endpoint was objective response rate. Secondary endpoints included progression-free and overall survival.

RESULTS

Sixteen patients were enrolled (87% with adenocarcinoma). The median prior exposure to cisplatin/irinotecan was 3.6 months. The addition of cetuximab to cisplatin and irinotecan was well tolerated and there were no unexpected toxicities. One of 16 patients treated on study experienced durable RECIST partial response lasting 10 months. The median progression-free survival was 1.4 months (range, 0.5 to 10 mo).

CONCLUSIONS

The addition of cetuximab did not overcome irinotecan resistance in patients with metastatic esophagogastric cancer. Further investigation of this strategy in esophagogastric cancer is not justified. The limited activity observed for cetuximab is consistent with other studies evaluating single-agent cetuximab.

Final results from PRIME: randomized phase III study of panitumumab with FOLFOX4 for first-line treatment of metastatic colorectal cancer

BACKGROUND

The Panitumumab Randomized trial In combination with chemotherapy for Metastatic colorectal cancer to determine Efficacy (PRIME) demonstrated that panitumumab-FOLFOX4 significantly improved progression-free survival (PFS) versus FOLFOX4 as first-line treatment of wild-type (WT) KRAS metastatic colorectal cancer (mCRC), the primary end point of the study.

PATIENTS AND METHODS

Patients were randomized 1:1 to panitumumab 6.0 mg/kg every 2 weeks + FOLFOX4 (arm 1) or FOLFOX4 (arm 2). This prespecified final descriptive analysis of efficacy and safety was planned for 30 months after the last patient was enrolled.

RESULTS

A total of 1183 patients were randomized. Median PFS for WT KRAS mCRC was 10.0 months [95% confidence interval (CI) 9.3-11.4 months] for arm 1 and 8.6 months (95% CI 7.5-9.5 months) for arm 2; hazard ratio (HR) = 0.80; 95% CI 0.67-0.95; P = 0.01. Median overall survival (OS) for WT KRAS mCRC was 23.9 months (95% CI 20.3-27.7 months) for arm 1 and 19.7 months (95% CI 17.6-22.7 months) for arm 2; HR = 0.88; 95% CI 0.73-1.06; P = 0.17 (68% OS events). An exploratory analysis of updated survival (>80% OS events) was carried out which demonstrated improvement in OS; HR = 0.83; 95% CI 0.70-0.98; P = 0.03 for WT KRAS mCRC. The adverse event profile was consistent with the primary analysis.

CONCLUSIONS

In WT KRAS mCRC, PFS was improved, objective response was higher, and there was a trend toward improved OS with panitumumab-FOLFOX4, with significant improvement in OS observed in an updated analysis of survival in patients with WT KRAS mCRC treated with panitumumab + FOLFOX4 versus FOLFOX4 alone (P = 0.03). These data support a positive benefit-risk profile for panitumumab-FOLFOX4 for patients with previously untreated WT KRAS mCRC. KRAS testing is critical to select appropriate patients for treatment with panitumumab.

Molecular markers of chemotherapeutic response and toxicity in colorectal cancer

Outcomes in colorectal cancer have improved over the last 15 years; this is in part due to the optimization of 5-fluorouracil schedules and the introduction of new and effective chemotherapeutic agents, such as irinotecan and oxaliplatin. However, not all patients respond to these agents and a proportion may suffer severe side effects from particular chemotherapy drugs. These observations have resulted in a concerted research effort to identify markers of chemotherapy efficacy and toxicity. Here we review the evidence for using molecular markers to individualize chemotherapy treatment in colorectal cancer.

New and potential clinical applications of KRAS as a cancer biomarker

IMPORTANCE OF THE FIELD

KRAS mutation is the most common oncogenic alteration in various human cancers. Recently, KRAS has emerged as an important predictive biomarker in common malignancies such as metastatic colorectal cancer (mCRC) and non-small cell lung cancer (NSCLC). This work aims to discuss the clinical impact of the KRAS mutation status on state-of-the-art treatment approaches, including epidermal growth factor receptor (EGFR)-targeted therapies.

AREAS COVERED IN THIS REVIEW

This review considers the potential of KRAS to serve as a diagnostic, prognostic or predictive biomarker in various cancers, including those of the lung, colon/rectum, pancreas, ovary and endometrium.

WHAT THE READER WILL GAIN

KRAS mutations in mCRC and NSCLC primary tumors predict resistance to EGFR-targeted therapy. In pancreatic cancer, KRAS may prove useful as a diagnostic biomarker to screen for early neoplasia. Furthermore, quantitative KRAS mutation analysis could have the potential to distinguish pancreatic cancer from other conditions such as chronic pancreatitis. With respect to ovarian and endometrial cancer, further studies should focus on determining reliable biomarkers for predicting response to EGFR-targeted therapy. Besides EGFR inhibition, KRAS may also serve as a diagnostic and predictive biomarker for evolving therapies directed against mutant RAS proteins.

TAKE HOME MESSAGE

KRAS has been recognized as an outstanding predictive biomarker to select mCRC and NSCLC patients for EGFR-targeted therapies; however, multi-determinant approaches including other molecular markers should facilitate the identification of patients likely to respond to such therapies.

Novel drugs targeting the epidermal growth factor receptor and its downstream pathways in the treatment of colorectal cancer: a systematic review

Colorectal cancer is the second most common malignancy among men and women in the United States, and the 5-year survival rate remains poor despite recent advances in chemotherapy and targeted agents. The mainstay of therapy for advanced disease remains the cytotoxic chemotherapy including 5-FU, irinotecan, and oxaliplatin. The USFDA approval and introduction of targeted therapies, including cetuximab and panitumumab (monoclonal antibodies targeting the epidermal growth factor receptor (EGFR)) and bevacizumab (monoclonal antibody targeting the vascular epithelial growth factor (VEGF)), has improved the median survival of patients with metastatic colorectal cancer to around 24 months. Clearly, better and more efficacious drugs are needed, and target-specific agents remain the future of cancer treatment. On this front, rapid advances are being made, which are likely to change the future of the management of metastatic colorectal cancer. However, absence of specific biomarkers for the use of targeted agents, in the subset of population who will benefit from the treatment, remains a major drawback. In this paper, we review agents that are in phases 1 and 2 clinical development, specifically targeting the EGFR and its subsequent downstream pathways.

Panitumumab: a summary of clinical development in colorectal cancer and future directions

Panitumumab is a fully human, monoclonal antibody targeting the EGF receptor with proven clinical activity in KRAS wild-type metastatic colorectal carcinoma. Treatment with panitumumab has been shown to significantly improve response rate and progression-free survival in this subgroup of patients, with a manageable toxicity profile. Panitumumab's first worldwide indication was as a single agent in chemorefractory patients. Recently, the EMA approved its use as part of a chemotherapy regimen in first- and second-line settings, following the encouraging results of large randomized Phase III trials. In order to identify patients with higher chances of benefiting from the treatment, additional molecular aberrations in the EGF receptor signaling pathway are being investigated as predictive biomarkers. In this article we review 10 years of drug development, focusing on the clinical evidence for panitumumab's indication in metastatic colorectal cancer and future strategies of investigation.

Quantifying factors for the success of stratified medicine

Co-developing a drug with a diagnostic to create a stratified medicine - a therapy that is targeted to a specific patient population on the basis of a clinical characteristic such as a biomarker that predicts treatment response - presents challenges for product developers, regulators, payers and physicians. With the aim of developing a shared framework and tools for addressing these challenges, here we present an analysis using data from case studies in oncology and Alzheimer's disease, coupled with integrated computational modelling of clinical outcomes and developer economic value, to quantify the effects of decisions related to key issues such as the design of clinical trials. This illustrates how such analyses can aid the coordination of diagnostic and drug development, and the selection of optimal development and commercialization strategies. It also illustrates the impact of the interplay of these factors on the economic feasibility of stratified medicine, which has important implications for public policy makers.

A flexible approach for highly multiplexed candidate gene targeted resequencing

We have developed an integrated strategy for targeted resequencing and analysis of gene subsets from the human exome for variants. Our capture technology is geared towards resequencing gene subsets substantially larger than can be done efficiently with simplex or multiplex PCR but smaller in scale than exome sequencing. We describe all the steps from the initial capture assay to single nucleotide variant (SNV) discovery. The capture methodology uses in-solution 80-mer oligonucleotides. To provide optimal flexibility in choosing human gene targets, we designed an in silico set of oligonucleotides, the Human OligoExome, that covers the gene exons annotated by the Consensus Coding Sequencing Project (CCDS). This resource is openly available as an Internet accessible database where one can download capture oligonucleotides sequences for any CCDS gene and design custom capture assays. Using this resource, we demonstrated the flexibility of this assay by custom designing capture assays ranging from 10 to over 100 gene targets with total capture sizes from over 100 Kilobases to nearly one Megabase. We established a method to reduce capture variability and incorporated indexing schemes to increase sample throughput. Our approach has multiple applications that include but are not limited to population targeted resequencing studies of specific gene subsets, validation of variants discovered in whole genome sequencing surveys and possible diagnostic analysis of disease gene subsets. We also present a cost analysis demonstrating its cost-effectiveness for large population studies.

Panitumumab: the evidence for its use in the treatment of metastatic colorectal cancer

Panitumumab is the first fully human monoclonal antibody to Epidermal Growth Factor Receptor (EGFR) to enter clinical trials for the treatment of solid tumors. The anti-tumor activity of panitumumab has been tested in vitro and in vivo, and inhibition of tumor growth has been observed in numerous cancer models, particularly lung, kidney and colorectal (CRC). Preclinical and clinical studies have established a role for panitumumab in metastatic colorectal cancer (mCRC) refractory to multiple chemotherapeutic regimens. Based on these encouraging findings, panitumumab was approved by the US Food and Drug Administration for the treatment of patients with epidermal growth factor receptor-expressing mCRC refractory to fluoropyrimidine-, oxaliplatin-, and/or irinotecan-containing chemotherapeutic regimens. The improvement in progression free survival (PFS) and response rate (RR) produced by panitumumab monotherapy was significantly greater in patients with non mutated (wild-type) K-RAS than in those with mutant K-RAS. Therefore implementing routine K-RAS screening and limiting the use of EGFR inhibitors to patients with wild-type K-RAS appears the better strategy for select only the patients who could benefit from the therapy with panitumumab and also may have the potential for cost savings. The purpose of this review was to evaluate the patient-related, disease-related and economic-related evidence for the use of panitumumab in the treatment of metastatic colorectal cancer in clinical practice.

Panitumumab: a new frontier of target therapy for the treatment of metastatic colorectal cancer

Panitumumab is a fully human monoclonal IgG(2) antibody targeting the EGF receptor (EGFR). This agent represents a new class of drug owing to its fully human nature, and no need for premedication and loading dose. Panitumumab selectively binds to EGFR, blocking the extracellular domain of the receptor, and has not been associated with the formation of any antibodies directed against it. The drug is indicated as monotherapy for the treatment of patients with EGFR-expressing metastatic colorectal carcinoma with non-mutated (wild-type) KRAS after failure of fluoropyrimidine-, oxaliplatin- and irinotecan-containing chemotherapy regimens. The safety profile is favorable and is generally well tolerated; the most common toxicities are skin rashes and diarrhea. Therefore, panitumumab's hypersensitivity reaction rate is lower when compared with a chimeric monoclonal antibody such as cetuximab. Panitumumab increases the clinician's repertoire of agents to treat metastatic colorectal carcinoma. The available clinical data are the most promising for a single-agent anti-EGFR monoclonal antibody in this disease at the present time. These new data open different clinical scenarios in metastatic colorectal carcinoma patients and encourage clinicians and basic researchers to investigate new therapeutic approaches for this patient subset.

KRAS, BRAF, EGFR and HER2 gene status in a Spanish population of colorectal cancer

To evaluate the KRAS, BRAF, EGFR, and HER2 gene status in colorectal cancer by novel techniques and evaluate whether anti-HER2 therapies could be offered in the treatment of these patients. There are conflicting data on the prevalence of BRAF mutations and EGFR and HER2 gene amplification in colorectal KRAS wild type patients. In our study we tried to evaluate these expressions and their relationship to future treatment assays. Clinical-pathological data and paraffin-embedded specimens were collected from 186 patients who underwent colorectal resections at General Yagüe Hospital in Burgos, Spain. KRAS and BRAF status was analyzed by real-time PCR in all patients. EGFR and HER2/NEU gene amplification was detected using fluorescent in situ hybridisation technique (FISH) in 38 KRAS and BRAF wild type patients. KRAS mutations were present in 48% of the colorectal cancer patients. BRAF mutations were present in 6.25% of the KRAS wild type patients. EGFR and HER2 gene amplification was observed in 5.3% and 26.3%, respectively, of KRAS and BRAF wild type colorectal cancer patients. HER2, but not EGFR gene amplification, was frequently observed in KRAS and BRAF wild type colorectal cancer patients. These data indicate that HER2 amplification could be one of the genes to be considered in the therapeutic management of colorectal cancer.

KRAS testing in metastatic colorectal cancer: implications on the use of biologic agents

Colorectal cancer is a significant healthcare problem in the United States, with meaningful improvement in survival over the past few years. Much of that improvement is attributable to the availability of molecularly targeted therapies, such as inhibitors of the vascular endothelial growth factor (bevacizumab) and epidermal growth factor receptor (cetuximab and panitumumab), in addition to active cytotoxic agents. KRAS mutations have long been described to play an adverse prognostic role in colorectal cancer. KRAS is downstream from EGFR, and oncogenic mutations will yield a constitutively active protein that will override EGFR control of downstream signaling. Such mutations in KRAS would therefore confer resistance to anti-EGFR antibodies. The cumulative results of several trials incorporating more than a thousand patients in studies of cetuximab and panitumumab confirm that the presence of KRAS mutation in tumors is highly predictive of resistance to anti-EGFR therapy. These findings are likely to change the landscape of metastatic CRC treatment by providing an improved patient-tailored approach.

Low-dose metronomic chemotherapy of paclitaxel synergizes with cetuximab to suppress human colon cancer xenografts

Low-dose metronomic (LDM) chemotherapy represents a new strategy to treat solid tumors by stronger antiangiogenic activity and lower side effects, especially in combination with other antiangiogenic agents. This study aims to investigate whether LDM chemotherapy of paclitaxel could synergize with cetuximab, an antiangiogenic agent to suppress HT-29 human colon tumors in BALB/c nude mice. To explore its possible mechanism, the tumor vascular status was detected by staining with anti-CD31 Ab and the tumoral expression of thrombospondin-1 was examined by immunohistochemistry, western blot analysis, and real-time PCR. Our results showed that empirical metronomic paclitaxel regimens in combination with cetuximab induces significant and durable antitumor responses without overt toxicity. Paclitaxel LDM chemotherapy displayed stronger antiangiogenic activity than maximum tolerable dose (MTD) chemotherapy, whereas MTD chemotherapy induced more apoptotic cells. The combinational therapy with LDM and cetuximab showed the strongest antiangiogenic activity among all the groups. Paclitaxel LDM chemotherapy also dramatically upregulated the expression of thrombospondin-1, but MTD chemotherapy did not. These results suggest that the combination of paclitaxel LDM chemotherapy and cetuximab represents a potent strategy to combat colon cancers.

Update in antiepidermal growth factor receptor therapy in the management of metastatic colorectal cancer

The approval of anti-epidermal growth factor receptor (EGFR) monoclonal antibodies in the treatment of metastatic colorectal cancer (CRC) has expanded the armamentarium against this disease. This paper will review the historical progress and recent clinical developments of anti-EGFR therapies in the treatment of metastatic CRC. Novel strategies of targeting the EGFR pathway to improve efficacy as well as ongoing research in identifying specific molecular predictors of response will be discussed.

Clinical use of anti-epidermal growth factor receptor monoclonal antibodies in metastatic colorectal cancer

Abstract Cetuximab and panitumumab, monoclonal antibodies used to target the epidermal growth factor receptor (EGFR), were recently approved by the United States Food and Drug Administration for use as single agents or in combination with other chemotherapy drugs in the treatment of metastatic colorectal cancer. The anti-EGFR monoclonal antibodies, either as single agents or in combination with chemotherapy, have demonstrated clinical activity in this setting. When combined with standard cytotoxic chemotherapy or other targeted agents (e.g., bevacizumab, an anti-vascular endothelial growth factor monoclonal antibody), anti-EGFR monoclonal antibodies have been well tolerated and produced minimal toxicities. However, cetuximab and panitumumab appear to benefit only select patients. Predictive markers of efficacy, including EGFR overexpression, development of skin rash, and the absence of a K-ras mutation, have been evaluated in clinical studies to identify patients likely to respond to anti-EGFR monoclonal antibody therapy. This review discusses recent clinical studies of anti-EGFR monoclonal antibodies in the treatment of metastatic colorectal cancer, predictive markers of their efficacy, and common toxicities associated with their use.

Association of K-ras mutational status and clinical outcomes in patients with metastatic colorectal cancer receiving panitumumab alone

BACKGROUND

Identifying predictive biomarkers is important to optimally treat patients. This analysis evaluated the association of K-ras, BRAF, and PIK3CA gene mutations with tumor resistance to panitumumab alone.

PATIENTS AND METHODS

From 3 phase II panitumumab metastatic colorectal cancer (mCRC) studies, 62 of 533 patient samples were available. Mutations were identified from genomic DNA by sequencing.

RESULTS

Of the 62 samples, 24 (38.7%) harbored a K-ras mutation, and 38 (61.3%) were wild type. In the wild-type K-ras group, 11% of patients had a partial response (PR), 53% had stable disease (SD), and 37% had progressive disease (PD). In the mutant K-ras group, 21% of patients had SD, and 79% of patients had PD; there were no responses. The absence of a K-ras mutation was associated with response to panitumumab (PR vs. SD vs. PD; P = .0028). The hazard ratio for wild-type versus mutant K-ras was 0.4 (95% CI, 0.2-0.7) for progression-free survival and 0.5 (95% CI, 0.3-0.9) for overall survival. Four patients had a V600E BRAF mutation, and 2 patients had a PIK3CA mutation.

CONCLUSION

These data suggest that patients with mCRC with activating K-ras mutations are less likely to respond to panitumumab alone. The small sample size limits us from defining a predictive role of PIK3CA and BRAF mutations for panitumumab treatment.

Nuclear epidermal growth factor receptor (EGFR) interacts with signal transducer and activator of transcription 5 (STAT5) in activating Aurora-A gene expression

Loss of the maintenance of genetic material is a critical step leading to tumorigenesis. It was reported that overexpression of Aurora-A and the constitutive activation of the epidermal growth factor (EGF) receptor (EGFR) are implicated in chromosome instability. In this study, we examined that when cells treated with EGF result in centrosome amplification and microtubule disorder, which are critical for genetic instability. Interestingly, the expression of Aurora-A was also increased by EGF stimulus. An immunofluorescence assay indicated that EGF can induce the nuclear translocation of EGFR. Chromatin immunoprecipitation (ChIP) and re-ChIP assays showed significant EGF-induced recruitment of nuclear EGFR and signal transducer and activator of transcription 5 (STAT5) to the Aurora-A promoter. A co-immunoprecipitation assay further demonstrated that EGF induces nuclear interaction between EGFR and STAT5. A small interfering (si)RNA knockdown assay also showed that EGFR and STAT5 are indeed involved in EGF-increased Aurora-A gene expression. Altogether, this study proposes that the nuclear EGFR associates with STAT5 to bind and increase Aurora-A gene expression, which ultimately may lead to chromosome instability and tumorigenesis. The results also provide a novel linkage between the EGFR signaling pathway and overexpression of Aurora-A in tumorigenesis and chromosome instability.

Wild-type KRAS is required for panitumumab efficacy in patients with metastatic colorectal cancer

PURPOSE

Panitumumab, a fully human antibody against the epidermal growth factor receptor (EGFR), has activity in a subset of patients with metastatic colorectal cancer (mCRC). Although activating mutations in KRAS, a small G-protein downstream of EGFR, correlate with poor response to anti-EGFR antibodies in mCRC, their role as a selection marker has not been established in randomized trials.

PATIENTS AND METHODS

KRAS mutations were detected using polymerase chain reaction on DNA from tumor sections collected in a phase III mCRC trial comparing panitumumab monotherapy to best supportive care (BSC). We tested whether the effect of panitumumab on progression-free survival (PFS) differed by KRAS status.

RESULTS

KRAS status was ascertained in 427 (92%) of 463 patients (208 panitumumab, 219 BSC). KRAS mutations were found in 43% of patients. The treatment effect on PFS in the wild-type (WT) KRAS group (hazard ratio [HR], 0.45; 95% CI: 0.34 to 0.59) was significantly greater (P < .0001) than in the mutant group (HR, 0.99; 95% CI, 0.73 to 1.36). Median PFS in the WT KRAS group was 12.3 weeks for panitumumab and 7.3 weeks for BSC. Response rates to panitumumab were 17% and 0%, for the WT and mutant groups, respectively. WT KRAS patients had longer overall survival (HR, 0.67; 95% CI, 0.55 to 0.82; treatment arms combined). Consistent with longer exposure, more grade III treatment-related toxicities occurred in the WT KRAS group. No significant differences in toxicity were observed between the WT KRAS group and the overall population.

CONCLUSION

Panitumumab monotherapy efficacy in mCRC is confined to patients with WT KRAS tumors. KRAS status should be considered in selecting patients with mCRC as candidates for panitumumab monotherapy.