Molecular targeted therapy in advanced renal cell carcinoma: A review of its recent past and a glimpse into the near future

Molecular characteristics and markers of advanced clear cell renal cell carcinoma: Pitfalls due to intratumoral heterogeneity and identification of genetic alterations associated with metastasis

OBJECTIVES

To identify clear cell renal cell carcinoma-related gene mutations potentially associated with aggressive disease, sarcomatoid differentiation or poor prognosis.

METHODS

We carried out genomic analysis of 217 tumor foci from 25 patients with conventional clear cell renal cell carcinoma (14 patients), clear cell renal cell carcinoma with sarcomatoid differentiation (six patients) and non-clear cell renal cell carcinoma (five patients). Each tumor nodule on the tissue block that corresponded to the same focus on the slide was separated from the normal parenchyma and other histologically distinct areas of tumor. The isolated tumor foci were used for subsequent analyses and sequencing. Deoxyribonucleic acid from the formalin-fixed paraffin-embedded tissues was extracted. Multiplex bar-coded polymerase chain reaction amplification was carried out using next-generation sequencing libraries.

RESULTS

Overall, 67 protein alterations, including amino acid alterations, frame shifts and splice site mutations in seven genes were identified in the cohort of renal cell carcinoma tumors included in this study. Fewer patients with clear cell renal cell carcinoma with sarcomatoid differentiation had clear cell renal cell carcinoma-related mutations in comparison with patients with conventional clear cell renal cell carcinoma. Additionally, the average number of unique clear cell renal cell carcinoma-related protein alterations per patient was significantly lower in clear cell renal cell carcinoma with sarcomatoid differentiation than in conventional clear cell renal cell carcinoma. Mutations in PBRM1 were identified in a higher proportion of patients with high-grade tumors (World Health Organization/International Society of Urological Pathology grade 4) and in the primary tumors of six of 10 (60%) patients with metastatic disease.

CONCLUSIONS

Although there are pitfalls due to intratumoral heterogeneity and sampling bias, mutations in PBRM1 may be associated with metastasis and aggressive disease in clear cell renal cell carcinoma.

Combination of mTOR and MAPK Inhibitors-A Potential Way to Treat Renal Cell Carcinoma

Renal cell carcinoma (RCC) is the most common neoplasm that occurs in the kidney and is marked by a unique biology, with a long history of poor response to conventional cancer treatments. In the past few years, there have been significant advancements to understand the biology of RCC. This has led to the introduction of novel targeted therapies in the management of patients with metastatic disease. Patients treated with targeted therapies for RCC had shown positive impact on overall survival, however, no cure is possible and patients need to undergo treatment for long periods of time, which raises challenges to manage the associated adverse events. Moreover, many patients may not respond to it and even response may not last long enough in the responders. Many inhibitors of the Mammalian target of Rapamycin (mTOR) signaling pathway are currently being used in treatment of advanced RCC. Studies showed that inhibitions of mTOR pathways induce Mitogen-Activated Protein Kinase (MAPK) escape cell death and cells become resistant to mTOR inhibitors. Because of this, there is a need to inhibit both pathways with their inhibitors comparatively for a better outcome and treatment of patients with RCC.

Increased expression of metastasis-associated in colon cancer-1 in renal cell carcinoma is associated with poor prognosis

Metastasis-associated in colon cancer-1 (MACC1) expression in tumor specimens is an independent prognostic indicator of metastasis, which has recently gained considerable attention in cancer research, due to its overexpression in several types of carcinoma. However, MACC1 expression patterns and its possible role in renal cell carcinoma remain unknown. This study aimed to investigate MACC1 expression in renal cell carcinoma via immunohistochemical analysis and determine the relationship between MACC1 expression and cancer prognosis. Positive MACC1 expression was found to significantly correlate with distant metastasis and TNM stage (P < 0.05). A Kaplan-Meier survival analysis revealed that patients with higher MACC1 expression had a significantly lower disease-free rate (P < 0.05). These results indicate that MACC1 expression is significantly associated with prognosis in patients with renal cell carcinoma. To the best of our knowledge, this is the first study on the significance of MACC1 as a prognostic marker in renal cell carcinoma. MACC1 expression may be a useful target for the development of new therapeutic approaches, including molecular targeted therapeutic agents, for renal cell carcinoma.

Reduced L/B/K alkaline phosphatase gene expression in renal cell carcinoma: plausible role in tumorigenesis

Renal cell carcinoma (RCC) is the most common kidney cancer in adults. Although several genes have been found to be involved in carcinogenesis of RCC, more great efforts are needed to identify new genes which are responsible for the process. Clear cell RCC, originates from proximal tubule cells, is the most common pathological type of RCC. Alkaline phosphatase (ALP) is a marker enzyme of brush border membrane of proximal tubular cells. Our previous studies showed a significant decreased activity of Liver/Bone/Kidney (L/B/K) alkaline phosphatase in RCC. In the present study, we explored the molecular basis of the decreased activity of ALP in RCC. Immunohistochemistry, immunofluorescence and flow cytometry analysis showed decreased ALP protein in RCC. Additionally, real time PCR documented significantly reduced ALP gene expression (P = 0.009). Moreover, RCC cell lines (ACHN and A498) transfected with full length L/B/K cDNA showed decreased migratory property as well as viability of these cells as compared with controls (P = 0.000). Further, L/B/K ALP cDNA transfected cells (ACHN and A498) showed significant increased apoptosis as compared to control (P = 0.000). These findings suggest the new role of ALP in cell viability and apoptosis and involvement in RCC tumorigenesis. However, further studies are needed to explore the exact molecular mechanism.

Identification of pathway deregulation--gene expression based analysis of consistent signal transduction

Signaling pathways belong to a complex system of communication that governs cellular processes. They represent signal transduction from an extracellular stimulus via a receptor to intracellular mediators, as well as intracellular interactions. Perturbations in signaling cascade often lead to detrimental changes in cell function and cause many diseases, including cancer. Identification of deregulated pathways may advance the understanding of complex diseases and lead to improvement of therapeutic strategies. We propose Analysis of Consistent Signal Transduction (ACST), a novel method for analysis of signaling pathways. Our method incorporates information regarding pathway topology, as well as data on the position of every gene in each pathway. To preserve gene-gene interactions we use a subject-sampling permutation model to assess the significance of pathway perturbations. We applied our approach to nine independent datasets of global gene expression profiling. The results of ACST, as well as three other methods used to analyze signaling pathways, are presented in the context of biological significance and repeatability among similar, yet independent, datasets. We demonstrate the usefulness of using information of pathway structure as well as genes’ functions in the analysis of signaling pathways. We also show that ACST leads to biologically meaningful results and high repeatability.

Role of VHL gene mutation in human renal cell carcinoma

The Von Hippel-Lindau (VHL) is an inherited neoplasia syndrome caused by the inactivation of VHL tumor suppressor gene, and somatic mutation of this gene has been related to the development of sporadic clear cell renal carcinoma. The affected individuals are at higher risk for the development of tumor in other organs, which include pheochromocytomas, retinal angioma, pancreatic cysts, and CNS hemangioblastomas. The VHL mRNA encodes a protein (pVHL) that contains 213 amino acid residues which migrate with an apparent molecular weight of 24 to 30 kDa. The VHL gene protein has multiple functions that are linked to tumor suppression, but the best recognized and evidently linked to the development of renal cell carcinoma (RCC) is inhibition of hypoxia-inducible factor (HIF), as well as plays a role in targeting HIF for ubiquitin-mediated degradation. Aberrations in VHL's function, either through mutation or promoter hypermethylation, lead to the accumulation of HIF, which will transcriptionally upregulate a sequence of hypoxia responsive genes, including epidermal growth factor, vascular endothelial growth factor, platelet-derived growth factor, and other proangiogenic factors, resulting in upregulated blood vessel growth, one of the prerequisites of a tumor. HIF plays a critical role in pVHL-defective tumor formation, raising the possibility that drugs directed against HIF or its downstream targets (such as vascular endothelial growth factor) may one day play a role in the treatment of RCC. Moreover, a number of drugs have been developed that target HIF-responsive gene products, many of these targeted therapies have demonstrated significant activity in kidney cancer clinical trials and signify substantive advances in the treatment of this disease.