Mutations in the ras protooncogenes are rare events in renal cell cancer

Evidence for aldosterone-dependent growth of renal cell carcinoma

The aim if this study was to investigate the hypothesis that K-RAS 4A is upregulated in a mineralocorticoid-dependent manner in renal cell carcinoma and that this supports the proliferation and survival of some renal cancers. Expression of the K-RAS in renal tumour tissues and cell lines was examined by real-time PCR and Western blot and mineralocorticoid receptor, and its gatekeeper enzyme 11β-hydroxysteroid dehydrogenase-2 was examined by immunocytochemistry on a tissue microarray of 27 cases of renal cell carcinoma. Renal cancer cells lines 04A018 (RCC4 plus VHL) and 04A019 (RCC4 plus vector alone) were examined for the expression of K-RAS4A and for the effect on K-RAS expression of spironolactone blockade of the mineralocorticoid receptor. K-RAS4A was suppressed by siRNA, and the effect on cell survival, proliferation and activation of the Akt and Raf signalling pathways was investigated in vitro. K-RAS4A was expressed in RCC tissue and in the renal cancer cell lines but K-RAS was downregulated by spironolactone and upregulated by aldosterone. Spironolactone treatment and K-RAS suppression both led to a reduction in cell number in vitro. Both Akt and Raf pathways showed activation which was dependent on K-RAS expression. K-RAS expression in renal cell carcinoma is at least partially induced by aldosterone. Aldosterone supports the survival and proliferation of RCC cells by upregulation of K-RAS acting through the Akt and Raf pathways.

Microvessel density is high in clear-cell renal cell carcinomas of Ukrainian patients exposed to chronic persistent low-dose ionizing radiation after the Chernobyl accident

During the 25-year period subsequent to the Chernobyl accident, the morbidity of malignant renal tumors in Ukraine has increased from 4.7 to 10.7 per 100,000 of the total population. Recent studies of our group have shown that increases in morbidity, aggressiveness, and proliferative activity of renal cell carcinomas (RCCs), especially clear-cell renal cell carcinoma (CCRCC), in Ukrainian patients continuously inhabiting the radio-contaminated areas could be explained by specific molecular changes influenced by the so-called "chronic persistent low-dose ionizing radiation" (CPLDIR) exposure. This study aimed to examine the role of angiogenesis in CCRCC carcinogenesis associated with CPLDIR in patients living more than 20 years in cesium 137 ((137)Cs) contaminated areas after the Chernobyl accident in Ukraine. Paraffin-embedded specimens of 106 CCRCs were studied: Control cases were 18 tumors from Spanish patients (group 1), 25 tumors from Ukrainian patients from so-called clean areas without known radio-contamination (group 2), and 63 tumors from Ukrainian patients from radio-contaminated areas (group 3). For intratumoral microvessel density (MVD) determination, anti-CD31 antibody was used. A computerized image analysis program was used to quantitatively calculate the vascular density. Seventy-three percent of group 3 and 72 % of group 2 CCRCCs displayed the highest MVD. A striking increase in MVD was seen in group 3 CCRCCs, in comparison with groups 1 and 2 (p < 0.001). The majority of the hot spot vessels in group 3 was poorly differentiated. Moreover, MVD values for total vessels as well as for capillaries and tumor grade were strongly correlated. When we compared only tumor-node-metastasis tumor stages I and II, the differences remained statistically significant (p < 0.1). The ratio of the average total vessels and capillaries in the Ukrainian groups combined was 1.65:1 in comparison to the Spanish group. Our results provide evidence that CPLDIR exposure increases MVD (particularly capillary) in CCRCCs and is associated with a higher histological grade.

mTOR inhibitors in advanced renal cell carcinoma

Better understanding of the molecular biology of renal cell carcinoma (RCC) has led to the development of several targeted anti-cancer agents, several of which have since received approval for treatment of advanced disease. Two of these, the intravenous agent temsirolimus and the oral everolimus, exhibit antitumor effects through inhibition of the mammalian target of rapamycin (mTOR) pathway. This article reviews their mechanisms of action in the context of the current understanding of RCC pathophysiology, the clinical data leading to their approval, class-specific toxicities, potential molecular mechanisms behind treatment resistance and novel treatment approaches for RCC that incorporate mTOR blockade.

VHL and HIF signalling in renal cell carcinogenesis

Hypoxia-inducible factor (HIF) plays an important role in renal tumourigenesis. In the majority of clear cell RCC (ccRCC), the most frequent and highly vascularized RCC subtype, HIF is constitutively activated by inactivation of the von Hippel-Lindau gene. Of the HIF subunits, HIF-2alpha appears to be more oncogenic than HIF-1alpha, in that HIF-2alpha activates pro-tumourigenic target genes. In addition, recent studies indicate that HIF-1alpha, more than HIF-2alpha, can undergo proteasomal degradation in VHL - /- RCC cells. A more detailed understanding of the molecular basis of hypoxia and angiogenesis in renal carcinogenesis has set the stage for the development of targeted therapies, inhibiting multiple HIF-related pathways, such as the phosphatidylinositol 3-kinase-AKT-mTOR, RAS/RAF/MAP, and VEGF signalling routes. However, despite the positive results of these targeting agents in progression-free survival, clinical resistance remains an issue. Recent pre-clinical studies have suggested new targeting approaches such as inhibition of HIF-driven key metabolic enzymes and have introduced new HIF targeting agents, such as histone deacetylase inhibitors, with successful anti-neoplastic effects. In this review, we discuss existing and novel findings about RCC carcinogenesis, with subsequent clinical implications.

mTOR pathway in renal cell carcinoma

After decades of therapeutic nihilism in the treatment of advanced renal cell carcinoma, remarkable therapeutic strides have been made over the last few years. Early forays into molecularly targeted therapy for this difficult-to-treat disease were based around the inhibition of gene products of the hypoxia-inducible factor (HIF) transcription factor (i.e., VEGF). Recent data suggest that inhibition of mTOR results in clinical benefit in patients with poor prognostic features, and in preclinical models this therapeutic effect involves downregulation of HIF. Intriguingly, patients with nonclear cell histology appeared to obtain clinical benefit when treated with mTOR inhibitors. This review will highlight the mTOR pathway, its relevance to both clear cell and nonclear cell renal cell carcinoma, and its place in the host of quickly expanding treatment options.

Vascular endothelial growth factor-targeted therapy in renal cell carcinoma: current status and future directions

Renal cell carcinoma is a highly vascular tumor associated with expression of vascular endothelial growth factor (VEGF). Recently, VEGF-targeted therapies have been identified as a promising therapeutic approach. Three agents targeting the VEGF pathway have shown clinical activity as monotherapy in metastatic renal cell carcinoma: the anti-VEGF monoclonal antibody, bevacizumab, and small-molecule VEGF receptor tyrosine kinase inhibitors, sorafenib and sunitinib. This article explores these agents in terms of their mechanisms of action, clinical efficacy, and toxicity profiles. This article also reviews future development strategies, including combination regimens and drug sequencing, trial design considerations, and patient selection opportunities.

Molecular pathogenetics of renal cancer

Recent developments in genetics and molecular biology have led to an increased understanding of the pathobiology of renal cancer. Thorough knowledge of the molecular pathways associated with renal cancer is a prerequisite for novel potential therapeutic interventions. Studies are ongoing to evaluate novel anticancer agents that target specific molecular entities. This article reviews current knowledge on the genetics and molecular pathogenesis of sporadic and inherited forms of renal cancer.

Biology and clinical development of vascular endothelial growth factor-targeted therapy in renal cell carcinoma

PURPOSE

To review the biology of renal cell carcinoma (RCC) leading to vascular endothelial growth factor (VEGF) overexpression and the clinical results of VEGF blockade in metastatic RCC.

METHODS

A review of relevant published literature regarding VEGF, von Hippel-Lindau (VHL) gene inactivation and VEGF overexpression in RCC was performed. Further, a review of the mechanism, toxicity, and clinical development of VEGF-targeted therapy in metastatic RCC was undertaken.

RESULTS

VEGF is the major proangiogenic protein that exerts a biologic effect through interaction with cellular receptors. The majority of sporadic clear-cell RCC tumors are characterized by VHL tumor suppressor gene inactivation. The resulting VHL gene silencing leads to VEGF overexpression. An antibody to VEGF (bevacizumab) has demonstrated a significant prolongation of time to disease progression compared with placebo in patients with metastatic RCC. Small molecules with inhibitory effects against the VEGF receptor have undergone initial clinical testing in metastatic RCC with substantial objective response rates.

CONCLUSION

Therapeutic targeting of VEGF in RCC has strong biologic rationale and preliminary clinical efficacy. Further investigation will determine the optimal timing, sequence, and utility of these agents in RCC.

Frequent allelic changes at chromosome 7q34 but lack of mutation of the BRAF in papillary renal cell tumors

We have analyzed the BRAF locus on chromosome 7q34 with microsatellites for allelic changes and exons 11 and 15 of the BRAF with sequencing for mutations in 50 kidney cancers including 20 papillary, 15 conventional and 15 chromophobe renal cell carcinomas (RCC). Allelic changes at the BRAF locus were seen in 16 of the 20 papillary, 3 of the 15 conventional RCCs and 2 of the 15 chromophobe RCCs. Sequencing failed to disclose mutations in exons 11 and 15 of the BRAF gene in any of the tumors. Our data indicate that BRAF mutation does not play a role in the development of renal cell tumors.

[Expression of p21ras in locally confined renal adenocarcinoma and its prognostic implications]

OBJECTIVE

The p21ras protein is encoded by the three ras genes (H-, K- and N-ras) and participate in the regulation of normal cell growth and cell differentiation. The objective of this study is to determine the expression of this protein in locally confined renal cell carcinoma, as well as its relations with different histopathological variables and their prognostic implications.

METHOD

58 renal cell carcinomas, in pT1-T3a N0 M0 (TNM 1997) stages, treated by radical or partial nephrectomy with curative intention. We analysed different clinical and anatomopathological variables, as well as expression of p21ras in paraffinated tissue, using immunohistochemical techniques.

RESULTS

The mean percentage of stained nuclei was 6.1%, with a range lying between 0 and 45%. We did not obtain statistically significant association between expression of p21ras and the tumour size (p = 0.698), the nuclear grade (p = 0.676) or the histopathological stage (p = 0.095). The survival analysis also did not show significant differences when we stratified the patients using the mean value of the sample as reference point (p = 0.134).

CONCLUSIONS

Expression of p21ras was not demonstrated to be related to any of the histopathological variables analysed: size, grade and stage, or with survival. Therefore, this protein does not appear to be related to the evolution of renal cell carcinoma.

Molecular genetics of renal cell carcinoma

Renal cell carcinoma (RCC) is an important clinical problem for which an effective treatment has yet to be developed. Importantly, the 5-year survival is below 50%. A better understanding of the underlying biological mechanisms could result in improvements in the prevention and treatment of this disease. The molecular mapping of chromosomal losses in renal cell cancer together with increased resolution of the human gene map will provide targets for therapeutic approaches. In this review, I summarize what is known regarding some tumor suppressor genes and candidate tumor suppressor genes in RCC, with reference to their location and expression.

Molecular analysis of occupational cancer: infrequent p53 and ras mutations in renal-cell cancer in workers exposed to gasoline

Occupational exposure to gasoline has been identified in several studies as a risk factor for renal-cell cancer. Cases of renal-cell cancer with and without work-related exposure to gasoline or gasoline and diesel fuel were studied for the presence of mutations in the tumour-suppressor gene p53 (n = 23 exposed and 30 non-exposed cases studied) and ras oncogene (n = 30 exposed and 36 non-exposed cases studied). An average cumulative exposure was estimated at 10 ppm-years benzene among the exposed. Three p53 mutations were detected by denaturing-gradient gel electrophoresis (DGGE) among the 23 exposed cases (3/23, 13%). Of the non-exposed referent cases, 4 had a mutation (4/30, 13%). All but one of the cases with a p53 mutation had smoked. A ras gene (K-ras or N-ras) mutation was found in 3 (3/66, 4.5%) cases, all of whom were smoker referents. We conclude that p53 and ras mutations are infrequent in renal-cell cancer associated with occupational exposure to gasoline. However, the majority of the mutations (6/7 for p53, and 3/3 for ras genes) were seen in smokers.

What's new in ras genes? Physiological role of ras genes in signal transduction and significance of ras gene activation in tumorigenesis

Ras gene mutations have been found with variable prevalence in different tumor types. While during the past decade a lot of information has been accumulated on the frequency of ras oncogene activation in tumors, the last two years brought considerable progress in elucidating molecular mechanisms of signal transduction for which cellular ras proteins are key elements. They transmit signals from upstream tyrosine kinases to downstream serine/threonine kinases ultimately leading to changes of gene expression cytoskeletal architecture, cell-to-cell interactions and metabolism. These signalling pathways are of interest for the physiological regulation of proliferation and differentiation in normal, as well as in cancer tissue. Mutational activation of cellular ras genes to transforming oncogenes is thought to promote cell growth even in the absence of extracellular stimuli, and may thereby contribute to the initiation and/or progression of tumors.

Proliferative heterogeneity of human renal cell carcinomas and prevalence of ras gene point mutations

The variable prevalence and a possible stage-dependent increase of ras gene point mutations in human tumors might correspond to clonal growth advantages of ras-activated cells. Tumor areas with activated ras genes might thus differ in proliferative activity from those lacking ras gene activation. This hypothesis is studied in a series of human renal cell carcinomas that had been used previously for an analysis of proliferative compartments after post-operative vascular [3H]/[14C]thymidine perfusion [Rabes et al. (1979) Cancer 44: 799-813]. The growth fraction of different subcompartments of these tumors was studied by immunohistochemistry with mib1 antibody, recognizing a fixation- and embedding-resistant epitope of Ki-67 protein. Thirty subpopulations of 14 human renal cell carcinomas that exhibited a broad spectrum of proliferative activity were chosen for an analysis of the prevalence of K-ras point mutations in exon 1 by a mutation-enriching primer-mediated restriction-fragment-length-polymorphism analysis and/or direct sequencing of polymerase-chain-reaction-amplified material. The combined autoradiographic and immunohistochemical analysis confirmed the intra- and intertumoral proliferative heterogeneity. Compared to [3H]/[14C]thymidine labeling indices, mib1 labeling indices are higher. The ratio of mib1 to [3H]/[14C]thymidine labeling indices varies from 1.9 to 4.1 for the individual tumor subcompartments. However, neither in K-ras codons 12/13 nor in adjacent codons did we detect any mutations in the various tumor compartments. The results suggest that neither mode of proliferation nor type of differentiation is related to K-ras exon 1 point mutations in human renal cell carcinomas.