Biomarkers of Renal Tumors: the Current State and Clinical Perspectives.

Renal cell carcinoma (RCC) ranks the first death rate among the urogenital tumors, whereas its incidence follows the incidences of prostate and bladder cancer. The diagnosis of RCC at early stages allows immediately undertaking appropriate treatment, which significantly increases patients' survival rate. Early and accurate diagnosis avoids inadequate treatment, provides the disease progression forecast, and permits to apply more efficient therapy. Unfortunately, the small renal tumors are usually asymptomatic resulting in the late diagnosis and, therefore, low efficacy of treatment. Thus, sensible and preventive biomarkers are essential for early RCC detection and monitoring of its progression. So far, many attempts were performed aimed at recognizing novel informative kidney tumor biomarkers applicable for early detection of the disease and possessing prognostic and predictive capabilities. This review summarizes recent advances in renal tumor biomarkers recognition, their diagnostic and prognostic values, and clinical feasibility.

The cancer-retina antigen recoverin as a potential biomarker for renal tumors.

The renal cell carcinoma is the ninth most common cancer with an increasing occurrence and mortality. Recoverin is the first retina-specific photoreceptor protein that was shown to undergo aberrant expression, due to its promoter demethylation, as a cancer-retina antigen in a number of malignant tumors. In this work, we demonstrated that recoverin is indeed expressed in 68.4 % of patients with different subtypes of renal cell carcinoma, and this expression has tendency to correlate with tumor size. Interestingly, 91.7 % of patients with the benign renal tumor, oncocytoma, express recoverin as well in their tumor. Epigenetic analysis of the recoverin gene promoter revealed a stable mosaic methylation pattern with the predominance of the methylated state, with the exception of -80 and 56 CpG dinucleotides (CpGs). While the recoverin expression does not correlate withoverall survival of the tumor patients, the methylation of the recoverin gene promoter at -80 position is associated with better overall survival of the patients. This work is the first report pointing towards the association of overall survival of renal cell carcinoma (RCC) patients with promoter methylation of a cancer-retina antigen. Taken together, these data allow to consider recoverin as a potential therapeutic target and/or marker for renal tumors.

Aberrant demethylation of the recoverin gene is involved in the aberrant expression of recoverin in cancer cells.

The Ca(2+) -binding protein recoverin is normally specific for the retina. Recoverin aberrantly expressed in lung and melanoma tumors can trigger the host immune response followed by the development of a paraneoplastic neurological syndrome represented by cancer- and melanoma-associated retinopathy, respectively. The mechanisms, underlying the aberrant expression of recoverin in tumor cells, have remained unknown. The data obtained in this study suggest that (i) DNA methylation participates in the repression of synthesis of mRNA for recoverin in normal tissues and (ii) aberrant hypomethylation of the recoverin gene region, overlapping the promoter up-stream of the first exon and the first exon itself, is involved in the aberrant expression of recoverin in tumor cells.

Autoantibody against arrestin-1 as a potential biomarker of renal cell carcinoma.

Renal cell carcinoma (RCC) is the second-most common uronephrological cancer. In the absence of specific symptoms, early diagnosis of RCC is challenging. Monitoring of the aberrant expression of tumour-associated antigens (TAAs) and related autoantibody response is considered as a novel approach of RCC diagnostics. The aim of this study was to examine the aberrant expression of arrestin-1 in renal tumours, to investigate the possible epigenetic mechanism underlying arrestin-1 expression, and to assess the frequency of anti-arrestin-1 autoantibody response. Immunohistochemistry was used to assess the presence of arrestin-1 in primary tumours and metastases of 39 patients with RCC and renal oncocytoma. Bisulfite sequencing was employed to analyse the methylation status of the promoter of the SAG gene encoding arrestin-1. Western blot analysis was performed to detect autoantibodies against arrestin-1 in serum samples of 36 RCC and oncocytoma patients. Arrestin-1 was found to be expressed in RCC (58.7% of cases) and renal oncocytoma (90% of cases) cells, while being absent in healthy kidney. The expression of arrestin-1 in RCC metastases was more prominent than in primary tumours. Hypomethylation of the SAG gene promoter is unlikely to be the mechanism for the aberrant expression of arrestin-1. Autoantibodies against arrestin-1 were detected in sera of 75% of RCC patients. Taken together, our findings suggest employment of autoantibody against arrestin-1 as biomarker of RCC.

Mitochondria-Targeted Antioxidant SkQ1 Prevents Anesthesia-Induced Dry Eye Syndrome.

Dry eye syndrome (DES) is an age-related condition increasingly detected in younger people of risk groups, including patients who underwent ocular surgery or long-term general anesthesia. Being a multifactorial disease, it is characterized by oxidative stress in the cornea and commonly complicated by ocular surface inflammation. Polyetiologic DES is responsive to SkQ1, a mitochondria-targeted antioxidant suppressing age-related changes in the ocular tissues. Here, we demonstrate safety and efficacy of topical administration of SkQ1 at a dosage of 7.5 µM for the prevention of general anesthesia-induced DES in rabbits. The protective action of SkQ1 improves clinical state of the ocular surface by inhibiting apoptotic and prenecrotic changes in the corneal epithelium. The underlying mechanism involves the suppression of the oxidative stress supported by the stimulation of intrinsic antioxidant activity and the activity of antioxidant enzymes, foremost glutathione peroxidase and glutathione reductase, in the cornea. Furthermore, SkQ1 increases antioxidant activity and stability of the tear film and produces anti-inflammatory effect exhibited as downregulation of TNF-α and IL-6 and pronounced upregulation of IL-10 in tears. Our data suggest novel features of SkQ1 and point to its feasibility in patients with DES and individuals at risk for the disease including those subjected to general anesthesia.

Anti-tumor properties of the cGMP/protein kinase G inhibitor DT3 in pancreatic adenocarcinoma.

Pancreatic ductal adenocarcinoma (PDAC) is one of the deadliest cancers in the world. Therefore, new therapeutic options are urgently needed to improve the survival of PDAC patients. Protein kinase G (PKG) conducts the interlude of cGMP signaling which is important for healthy as well as for cancer cells. DT3 is a specific inhibitor of PKG, and it has been shown to possess an anti-tumor cytotoxic activity in vitro. The main aim of this work was to investigate anti-tumor effects of DT3 upon PDAC in vivo.Expression of PKG was assessed with real-time PCR analysis in the normal and tumor pancreatic cells. In vitro cell viability, proliferation, apoptosis, necrosis, migration, and invasion of the murine PDAC cell line Panc02 were assessed after DT3 treatment. In vivo anti-tumor effects of DT3 were investigated in the murine Panc02 orthotopic model of PDAC. Western blot analysis was used to determine the phosphorylation state of the proteins of interest.Functional PKGI is preferentially expressed in PDAC cells. DT3 was capable to reduce viability, proliferation, and migration of murine PDAC cells in vitro. At the same time, DT3 treatment did not change the viability of normal epithelial cells of murine liver. In vivo, DT3 treatment reduced the tumor volume and metastases in PDAC-bearing mice, but it was ineffective to prolong the survival of the tumor-bearing animals. In addition, DT3 treatment decreased phosphorylation of GSK-3, P38, and CREB in murine PDAC.Inhibition of PKG could be a potential therapeutic strategy for PDAC treatment which should be carefully validated in future pre-clinical studies.

Interlude of cGMP and cGMP/protein kinase G type 1 in pancreatic adenocarcinoma cells.

OBJECTIVE: cAMP and cGMP signaling is important both for normal and cancer cells. This signaling is controlled by adenylyl and guanylyl cyclases and cyclic nucleotide phosphodiesterases. One of the direct targets for cGMP is protein kinase G (PKG). The main aim of this work was to investigate cGMP and PKG signaling in pancreatic adenocarcinoma (PDAC) cells. METHODS: The PKG activity, cGMP, and calcium level were measured with the CycLex Cyclic GMP dependent protein kinase (cGK) Assay Kit, the DetectX Cyclic GMP Colorimetric EIA Kit, and the Fluo-4 NW Calcium Assay Kit, respectively. The Proteome Profiler Array was done using Human Phospho-Kinase Array and Human Phospho-MAPK Array Kits. RESULTS: This study shows for the first time that functional PKG1 is expressed in PDAC cells. It demonstrates that the specific PKG1 inhibitor, DT3, induces cytotoxicity through necrosis and reduces proliferation and migration of PDAC cells. Moreover, ERK1/2 and p38 can be considered as potential targets for PKG1 in PDAC cells. In addition, the study shows that phosphodiesterases and nitric oxide-guanylyl cyclases regulate the cGMP level in PDAC cells, affecting the proliferation of the cells. CONCLUSIONS: The cGMP and PKG signaling may be a target for developing new therapeutic approaches for PDAC.