Low incidence of H-, K- and N-ras oncogene mutations in cytological specimens of laryngeal tumours

Impact of K-Ras Over-expression in Laryngeal Squamous Cell Carcinoma

BACKGROUND/AIM

Oncogene up-regulation combined with suppressor gene down-regulation is a crucial genetic combination that promotes cell neoplastic phenotype and progressively malignant transformation in solid malignancies, including laryngeal squamous cell carcinoma (LSCC). Among oncogenes, the Kirsten ras oncogene homolog (K-Ras) is involved in LSCC onset and progression.

PATIENTS AND METHODS

Sixty (n=60) primary LSCC tissue sections were analyzed by immunohistochemistry (IHC). Digital image analysis (DIA) was also implemented for measuring K-Ras protein expression levels.

RESULTS

High K-Ras protein expression levels were observed in 20/60 (33.3%) LSCC tissue sections, whereas the rest of the cases (n=40; 66.7%) demonstrated low expression. Overall K-Ras expression was borderline significantly associated to the grade of the examined malignancies (p=0.048), whereas no other strong statistical correlations were identified. A progressive K-Ras overexpression was observed in all grades of the examined cases.

CONCLUSION

K-Ras over expression is correlated to a progressive dedifferentiation in LSCC.

Prevalence of K-ras Codon 12 Mutations in Indian Patients with Head and Neck Cancer

In human tumors, somatic mutation frequently occur in K-ras gene at codon 12, which makes the K-ras protein hyper active leading to uncontrolled signaling for cell division: one of the important hall mark of cancer. In order to correlate mutations in K-ras to cause, response to treatment, disease progression and recurrence of Head and Neck Squamous Cell Carcinoma (HNSCC) the following study was undertaken. By using PCR-RFLP method prevalence of codon 12 in K-ras gene was studied in 56 HNSCC patients. High frequency of K-ras mutation was detected in codon 12 (60.71%). The result of this study helps us in understanding the role of K-ras somatic mutations in HNSCC patients and in designing novel treatment protocols for HNSCC patients.

The sensitivity of head and neck carcinoma cells to statins is related to the expression of their Ras expression status, and statin-induced apoptosis is mediated via suppression of the Ras/ERK and Ras/mTOR pathways

Statins induce apoptosis of tumour cells by inhibiting the prenylation of small G-proteins. However, the details of the apoptosis-inducing mechanisms remain poorly understood. The present study showed that the induction of apoptosis by statins in four different human head and neck squamous cell carcinoma (HNSCC) cell lines, HSC-3, HEp-2, Ca9-22, and SAS cells was mediated by increased caspase-3 activity. Statins induced apoptosis by the suppression of geranylgeranyl pyrophosphate biosynthesis. Furthermore, statins decreased the levels of phosphorylated ERK and mTOR by inhibiting the membrane localization of Ras and enhancing Bim expression in HSC-3 and HEp-2 cells. We also found that in all the cell types analyzed, the IC₅₀ values for fluvastatin and simvastatin were highest in HEp-2 cells. In addition, HSC-3, Ca9-22, and SAS cells had higher Ras expression and membrane localization, higher activation of ERK1/2 and mTOR, and lower levels of Bim expression than HEp-2 cells. Our results indicate that statins induce apoptosis by increasing the activation of caspase-3 and by enhancing Bim expression through inhibition of the Ras/ERK and Ras/mTOR pathways. Furthermore, the sensitivity of HNSCC cells to statin treatment was closely related to Ras expression and prenylation levels, indicating that statins may act more effectively against tumours with high Ras expression and Ras-variability. Therefore, our findings support the use of statins as potential anticancer agents.

Anti-epidermal growth factor receptor therapy in head and neck squamous cell carcinoma: focus on potential molecular mechanisms of drug resistance

Targeted therapy against the epidermal growth factor receptor (EGFR) is one of the most promising molecular therapeutics for head and neck squamous cell carcinoma (HNSCC). EGFR is overexpressed in a wide range of malignancies, including HNSCC, and initiates important signal transduction pathways in HNSCC carcinogenesis. However, primary and acquired resistance are serious problems and are responsible for low single-agent response rate and tumor recurrence. Therefore, an improved understanding of the molecular mechanisms of resistance to EGFR inhibitors may provide valuable indications to identify biomarkers that can be used clinically to predict response to EGFR blockade and to establish new treatment options to overcome resistance. To date, no predictive biomarker for HNSCC is available in the clinic. Therapeutic resistance to anti-EGFR therapy may arise from mechanisms that can compensate for reduced EGFR signaling and/or mechanisms that can modulate EGFR-dependent signaling. In this review, we will summarize some of these molecular mechanisms and describe strategies to overcome that resistance.

Prevalence of K-RAS Codons 12 and 13 Mutations in Locally Advanced Head and Neck Squamous Cell Carcinoma and Impact on Clinical Outcomes

Background. RAS gene mutations have an impact on treatment response and overall prognosis for certain types of cancer. Objectives. To determine the prevalence and impact of K-RAS codons 12 and 13 mutations in patients with locally advanced HNSCC treated with primary or adjuvant chemo-radiation. Methods. 428 consecutive patients were treated with chemo-radiation therapy and followed for a median of 37 months. From these, 199 paraffin embedded biopsy or surgical specimens were retrieved. DNA was isolated and analyzed for K-RAS mutational status. Results. DNA extraction was successful in 197 samples. Of the 197 specimens, 3.5% presented K-RAS codon 12 mutations. For mutated cases and non-mutated cases, complete initial response to chemoradiation therapy was 71 and 73% (P = 0.32). LRC was respectively 32 and 83% (P = 0.03), DFS was 27 and 68% (P = 0.12), distant metastasis-free survival was 100 and 81% (P = 0.30) and OS was 57 and 65% (P = 0.14) at three years. K-Ras codon 13 analysis revealed no mutation. Conclusion. K-RAS codon 12 mutational status, although not associated with a difference in response rate, may influence the failure pattern and the type of therapy offered to patients with HNSCC. Our study did not reveal any mutation of K-RAS codon 13.

Genomic dissection of the epidermal growth factor receptor (EGFR)/PI3K pathway reveals frequent deletion of the EGFR phosphatase PTPRS in head and neck cancers

Activation of the PI3K and epidermal growth factor receptor (EGFR) pathway is able to drive oncogenesis in multiple human cancers, including head and neck squamous cell carcinoma. Targeted agents such as cetuximab and erlotinib are currently used in patients with head and neck squamous cell carcinoma, but, in this disease, the genomic alterations that cause pathway activation and determine response to pharmacologic inhibition remain ill-defined. Here, we present a detailed dissection of the EGFR/PI3K pathway, composed of sequencing of the core pathway components, and high-resolution genomic copy number assessment. Mutations were found in PIK3CA (6%), but no point mutations were observed in other pathway genes such as PTEN and EGFR. In contrast, we observed frequent copy number alterations of genes in the pathway, including PIK3CA, EGFR, protein tyrosine phosphatase receptor S (PTPRS), and RICTOR. In total, activating genetic pathway alterations were identified in 74% of head and neck tumors. Importantly, intragenic microdeletions of the EGFR phosphatase PTPRS were frequent (26%), identifying this gene as a target of 19p13 loss. PTPRS loss promoted EGFR/PI3K pathway activation, modulated resistance to EGFR inhibition, and strongly determined survival in lung cancer patients with activating EGFR mutations. These findings have important implications for our understanding of head and neck cancer tumorigenesis and for the use of targeted agents for this malignancy.

Mechanisms of acquired androgen independence during arsenic-induced malignant transformation of human prostate epithelial cells

BACKGROUND

Prostate cancer progression often occurs with overexpression of growth factors and receptors, many of which engage the Ras/mitogen-activated protein MAP kinase (MAPK) pathway.

OBJECTIVES

In this study we used arsenic-transformed human prostate epithelial cells, which also show androgen-independent growth, to study the possibility that chronic activation of Ras/MAPK signaling may contribute to arsenic-induced prostate cancer progression.

METHODS

Control and chronic arsenic-transformed prostate epithelial cells (CAsE-PE) were compared for Ras/MAPK signaling capacities using reverse transcription-polymerase chain reaction and Western blot analyses.

RESULTS

We found activation of HER-2/neu oncogene in transformed CAsE-PE cells, providing molecular evidence of androgen independence in the transformed cells. CAsE-PE cells displayed constitutively increased expression of unmutated K-Ras (6-fold), and the downstream MAP kinases A-Raf and B-Raf (2.2-fold and 3.2-fold, respectively). There was also increased expression of phosphorylated MEK1/2 and Elk1 in the transformant cells. The MEK1/2 inhibitor, U0126, blocked PSA overexpression in CAsE-PE cells.

CONCLUSION

Thus, arsenic-induced malignant transformation and acquired androgen independence are linked to Ras signaling activation in human prostate epithelial cells. Chronic activation of this pathway can sensitize the androgen receptor to subphysiologic levels of androgen. This may be important in arsenic carcinogenesis and provide a mechanism that may be common for prostate cancer progression driven by diverse agents.

TP53 mutations and S-phase fraction but not DNA-ploidy are independent prognostic indicators in laryngeal squamous cell carcinoma

To prospectively evaluate the prognostic significance of TP53, H-, K-, and N-Ras mutations, DNA-ploidy and S-phase fraction (SPF) in patients affected by locally advanced laryngeal squamous cell carcinoma (LSCC). Eight-one patients (median follow-up was 71 months) who underwent resective surgery for primary operable locally advanced LSCC were analyzed. Tumor DNA was screened for mutational analysis by PCR/SSCP and sequencing. DNA-ploidy and SPF were performed by flow cytometric analyses. Thirty-six patients (44%) had, at least, a mutation in the TP53 gene. Of them, 22% (8/36) had double mutations and 3% (1/36) had triple mutations. In total, 46 TP53 mutations were observed. The majority (41%) of these occur in exon 5 (19/46), while the mutations in exons 6, 7, and 8 were represented in 14, 7, and 6 patients, respectively (31%, 15%, and 16%). Five LSCC patients (6%) showed a mutation in H-Ras gene. Sixty-three percent of the cases (51/81) were DNA aneuploidy, 14% of these (7/51) were multiclonal. Thirty-nine patients (48%) had an high SPF value. At Univariate analysis, the DNA aneuploidy, high SPF (>15.1%), TP53 mutations and, in particular, the mutations that occur in exons 5 and 8 were significantly related to quicker disease relapse and short OS. At Multivariate analysis, the major significant predictors for both disease relapse and death were high SPF and any TP53 mutations. While histological grade G3 was an independent factor only for relapse. In conclusions, any TP53 mutations and high SPF are important biological indicators to predict the outcome of LSCC patients.

Unraveling the chromosomal aberrations of head and neck squamous cell carcinoma: a review

Information from the genetic analysis of head and neck cancer has grown enormously in the last 20 years. The advent of high-resolution genetic analysis techniques such as microarray technology will further expand this field in the future. Here we review the data on chromosomal aberrations of head and neck squamous cell carcinoma, focusing on the data generated by comparative genomic hybridization analysis, and suggest how such findings will be taken forward over the next decade. With the search engine PUBMED, the key words "comparative genomic hybridisation," "head and neck," "oral," "hypopharyngeal," "laryngeal," and "squamous cell carcinoma" were used. Publications unavailable in English were excluded.

Molecular events associated with arsenic-induced malignant transformation of human prostatic epithelial cells: aberrant genomic DNA methylation and K-ras oncogene activation

Numerous studies link arsenic exposure to human cancers in a variety of tissues, including the prostate. Our prior work showed that chronic arsenic exposure of the non-tumorigenic, human prostate epithelial cell line, RWPE-1, to low levels of (5 microM) sodium arsenite for 29 weeks resulted in malignant transformation and produced the tumorigenic CAsE-PE cell line. The present work focuses on the molecular events occurring during this arsenic-induced malignant transformation. Genomic DNA methylation was significantly reduced in CAsE-PE cells. A time course experiment showed that during malignant transformation DNA methyltransferase activity was markedly reduced by arsenic. However, DNA methyltransferase mRNA levels were not affected by arsenic exposure. Microarray screening showed that K-ras was highly overexpressed in CAsE-PE cells, a result further confirmed by Northern blot and Western blot analyses. Since ras activation is thought to be a critical event in prostate cancer progression, further detailed study was performed. Time course experiments also showed that increased K-ras expression preceded malignant transformation. Mutational analysis of codons 12, 13, and 61 indicated the absence of K-ras mutations. The K-ras gene can be activated by hypomethylation, but our study showed that CpG methylation in K-ras promoter region was not altered by arsenic exposure. Arsenic metabolism studies showed RWPE-1, CAsE-PE, and primary human prostate cells all had a very poor capacity for arsenic methylation. Thus, inorganic arsenic-induced transformation in human cells is associated with genomic DNA hypomethylation and K-ras overexpression. However, overexpression of K-ras occurred without mutations and through a mechanism other than promoter region hypomethylation.

p53 Codon 72 polymorphism is linked to the development and not the progression of benign and malignant laryngeal tumours

The p53 codon 72 polymorphism, resulting in either an arginine or a proline residue has been proposed to affect the susceptibility of p53 protein to human papilloma virus (HPV) E6-mediated degradation in vitro. However, there are controversial results from several clinical studies in various human tumours. The purpose of our study was to investigate the significance of this p53 genotype with respect to the risk of neoplasia development in Greek patients with benign and malignant laryngeal tumours. Furthermore, we searched for an association between p53 alleles and the presence of HPV in the same series of samples. We found a significant statistical association in the distribution of p53 genotypes between laryngeal lesions and normal samples (P<0.001). Allelic analysis of the patients with both benign and malignant tumours revealed a striking over-representation of the homozygous p53Arg allele compared to normal population (P<0.0003). HPV was detected in only 3 laryngeal samples (1 benign and 2 malignant tumours). This is the first study correlating the p53 codon 72 polymorphism in laryngeal tumours. Our results provide evidence that this p53 polymorphism may be implicated at the early stages of the disease and concerns predisposition to premalignant laryngeal lesions rather than to progression from benign tumour toward malignancy. Moreover, we demonstrate that the p53Arg homozygous genotype affects the predisposition for laryngeal tumours while the heterozygous status does not. The low incidence of HPV infection suggests that it is not a major oncogenic factor in the development of laryngeal tumours but may have synergistic action with specific genotypes of p53 gene.