Comparative evaluation of p53-protein expression and the PCNA and Ki-67 proliferating cell indices in human astrocytomas

Targeting Non-Oncogene Addiction for Cancer Therapy

While Next-Generation Sequencing (NGS) and technological advances have been useful in identifying genetic profiles of tumorigenesis, novel target proteins and various clinical biomarkers, cancer continues to be a major global health threat. DNA replication, DNA damage response (DDR) and repair, and cell cycle regulation continue to be essential systems in targeted cancer therapies. Although many genes involved in DDR are known to be tumor suppressor genes, cancer cells are often dependent and addicted to these genes, making them excellent therapeutic targets. In this review, genes implicated in DNA replication, DDR, DNA repair, cell cycle regulation are discussed with reference to peptide or small molecule inhibitors which may prove therapeutic in cancer patients. Additionally, the potential of utilizing novel synthetic lethal genes in these pathways is examined, providing possible new targets for future therapeutics. Specifically, we evaluate the potential of TONSL as a novel gene for targeted therapy. Although it is a scaffold protein with no known enzymatic activity, the strategy used for developing PCNA inhibitors can also be utilized to target TONSL. This review summarizes current knowledge on non-oncogene addiction, and the utilization of synthetic lethality for developing novel inhibitors targeting non-oncogenic addiction for cancer therapy.

Molecular Pathological Markers Correlated With the Recurrence Patterns of Glioma

Purpose

Glioma is one of the most common tumors of the central nervous system, and many patients suffer from recurrence even after standard comprehensive treatment. However, little is known about the molecular markers that predict the recurrence patterns of glioma. This study aimed to demonstrate the correlations between molecular markers and glioma recurrence patterns, which included local/nonlocal recurrence and paraventricular/nonparaventricular recurrence.

Methods

Immunohistochemical techniques were used to assess the molecular markers of 88 glioma tissues following surgical resection. The recurrence patterns were divided into local recurrence, marginal recurrence, distant recurrence, multirecurrence, and subarachniod recurrence, with the last four recurrence patterns being collectively called nonlocal recurrence. According to whether the recurrence invaded ventricles, the nonlocal recurrence patterns were divided into paraventricular and nonparaventricular recurrence. Then, we compared the different recurrence patterns and their clinical characteristics, focusing on the expression of molecular markers.

Results

More patients in the nonlocal recurrence group received combined radiotherapy and chemotherapy than patients in the local recurrence group (p=0.019). Sex, age, extent of surgery, time to recurrence, tumor location, size, and WHO grade were not different in the defined groups (P>0.05). Recurrent tumor volume and WHO grade were significantly different between the paraventricular and nonparaventricular recurrence groups (p=0.046 and 0.033). The expression of Ki-67, P53, and PCNA in the nonlocal recurrence group was significantly higher than that in the local recurrence group (p=0.015, 0.009, and 0.037), while the expression of S-100 in the nonlocal recurrence group was significantly lower than that in the local recurrence group (p=0.015). Cox regression indicated hazard ratio (HR) for high expression level of PCNA associated with non-local recurrence was 3.43 (95% CI, 1.15, 10.24), and HR for high expression level of MGMT associated with paraventricular recurrence was 2.64 (95% CI, 1.15,6.08).

Conclusions

Ki-67, P53, PCNA, and MGMT might be important clinical markers for nonlocal recurrence and paraventricular recurrence.

PCNA: a silent housekeeper or a potential therapeutic target?

Proliferating cell nuclear antigen (PCNA) is known as a molecular marker for proliferation given its role in replication. Three identical molecules of PCNA form a molecular sliding clamp around the DNA double helix. This provides an essential platform on which multiple proteins are dynamically recruited and coordinately regulated. Over the past decade, new research has provided a deeper comprehension of PCNA as a coordinator of essential cellular functions for cell growth, death, and maintenance. Although the biology of PCNA in proliferation has been comprehensively reviewed, research progress in unveiling the potential of targeting PCNA for disease treatment has not been systematically discussed. Here we briefly summarize the basic structural and functional characteristics of PCNA, and then discuss new developments in its protein interactions, trimer formation, and signaling regulation that open the door to possible therapeutic targeting of PCNA.

Immunohistochemical Expression of Ki-67, PCNA and CD34 in Astrocytomas: A Clinicopathological Study

OBJECTIVES

To assess the immunohistochemical expression of Ki-67 and Proliferating Cell Nuclear Antigen (PCNA) as proliferative markers to study proliferative activity and CD34 as an endothelial cell marker in order to study vascular proliferation in astrocytomas in correlation with some clinicopathological parameters (age, gender, site of the tumor, and tumor grade).

METHODS

A retrospective study wherein a total of 51 formalin-fixed paraffin-embedded brain astrocytoma excisional biopsies covering the period of June 2009 to February 2011 were retrieved from the archival materials of the Specialized Surgical Hospital in Medical City in Baghdad, Iraq. The histopathological diagnosis had been revised and all cases were stained by immunohistochemical technique with Ki-67, PCNA, and CD34 tumor markers. Values were considered statistically significant when p<0.05.

RESULTS

Fibrillary astrocytoma (WHO grade II) was found to be the most common type among astrocytic tumors with the peak age incidence of astrocytomas found in the second and fifth decades of life, and a slight male predominance had been identified. There was a significant correlation between the age of the patients and the grade of the tumor, Ki-67 and PCNA labeling indices, and microvessel density (MVD) detected by CD34 (p<0.05). There was a highly significant correlation between Ki-67 and PCNA labeling indices in astrocytomas (p<0.001).

CONCLUSION

A significant correlation was found between Ki-67, PCNA labeling indices, and MVD (microvessel density) detected by CD34, and between the clinicopathological variables of astrocytomas (age and grade of tumor). Hence, Ki-67 and PCNA, as markers for proliferation, and MVD as a marker of angiogenesis, could be used as ancillary methods in the differentiation of borderline grades of astrocytomas.

Targeting tyrosine phosphorylation of PCNA inhibits prostate cancer growth

The proliferation cell nuclear antigen (PCNA) is a critical protein required for DNA replication in proliferating cells including cancer cells. However, direct inhibition of PCNA in cancer cells has been difficult due to the lack of targetable sites. We previously reported that phosphorylation of tyrosine 211 (Y211) on PCNA is important for the proliferative function of PCNA when this protein is associated with the chromatin in cancer cells. Here, we show that the Y211 phosphorylation of PCNA is a frequent event in advanced prostate cancer. To explore the potential of this signaling event in inhibition of cancer cell growth, we used a synthetic peptide, the Y211F peptide, which when present inhibits phosphorylation of Y211 on endogenous PCNA. Treatment with this peptide, but not a scrambled control peptide, resulted in S-phase arrest, inhibition of DNA synthesis, and enhanced cell death in a panel of human prostate cancer cell lines. In addition, treatment with the Y211F peptide led to decreased tumor growth in PC3-derived xenograft tumors in vivo in nude mice. Our study shows for the first time that PCNA phosphorylation at Y211 is a frequent and biologically important signaling event in prostate cancer. This study also shows a proof of concept that Y211 phosphorylation of PCNA may be used as a therapeutic target in prostate cancer cells, including cells of advanced cancers that are refractory to standard hormonal therapies.

Immunoexpression of tumor suppressor genes p53, p21 WAF1/CIP1 and p27 KIP1 in humam astrocystic tumors

The aim of the present study was to evaluate the tumor suppressor genes p53, p21 WAF1/CIP1 and p27 KIP1 expression in astrocytic tumors, correlating the findings with the histopathological grade (WHO). An immunohistochemical study of the p53, p21 and p27 proteins using the streptavidin-biotin-peroxidase method was performed in fifty-five astrocytomas (13 grade I, 14 grade II, 7 grade III and 21 grade IV) and five samples of non-tumor brain tissue (negative control). p53 positive indices (PI) and labeling indices (LI) showed tendency to increase according to malignant progression. The nuclear expression of p27 presented similar inclination, except for the PI reduction verified in grade IV tumors. Otherwise, the cytoplasmic p27 staining was more evident between high-grade tumors (III and IV). p53 and nuclear p27 expression was correlated with the histological classification (p<0.01; test H). On the other hand, p21 indices revealed a propensity to reduction in agreement with malignant evolution of the astrocytic tumors, except for high scores observed in grade IV tumors. The non-tumor samples did not show any expression of these proteins. These results indicated the p53 mutation as an initial, relevant and potentially predictor of tumor progression event in astrocytomas, with the detection of p21 protein as an important resource for the deduction of functional situation of this gene. Moreover, the activation of p27 KIP1 was preserved in the astrocytic tumors and its cytoplasmic manifestation seems to be resultant of its nuclear expression, not demonstrating a direct impact in astrocytomas tumorigenesis.

Expression of Ki-67, Topoisomerase II? and c-MYC in astrocytic tumors: Correlation with the histopathological grade and proliferative status

Astrocytomas represent the most frequent primary tumors of the central nervous system. Recently, the determination of the proliferative index of astrocytic tumors by different methods has been proposed as a valuable tool for tumor grading and also as a prognostic marker. The aim of the present study was to evaluate the expression of cell proliferation-related proteins in human astrocytic tumors of different histopathological grades (WHO). An immunohistochemical study of the Ki-67, Topoisomerase IIalpha (Topo IIalpha) and c-MYC proteins using the avidin-biotin-peroxidase method was performed in 55 astrocytomas (13 grade I, 14 grade II, 7 grade III and 21 grade IV) and five samples of non-tumor brain tissue (control group). Ki-67, Topo IIalpha and c-MYC positive indices tended to increase according to malignant progression, were absent in non-tumor brain tissue and showed maximum values in high-grade astrocytomas (III and IV). A gradual increase in Ki-67 antigen expression was observed in agreement with mitotic index and histopathological classification. The same was not observed for Topo IIalpha and c-MYC. Ki-67 antigen detection in more than 8.0% of the tumor cells distinguished astrocytoma grade IV, while a labeling index between 1.5 and 8.0% characterized astrocytomas grade III and values below 1.5% discriminated low-grade tumors (I and II). These results indicate that Topo IIalpha and c-MYC expression is associated with cell proliferation in astrocytomas, although not in an exclusive way. Moreover, Ki-67 antigen was found to be the best marker of cellular proliferation, and its expression predicts the grade of astrocytic tumors.

[Astrocytic neoplasms and correlation with mutate p53 and Ki-67 proteins]

The astrocytic neoplasms respond by 60% of the central nervous system tumors, being the study of the molecular biology an important step for the understanding of the genesis and biological behavior of these diseases. The Ki-67 proteins, which are markers of the cellular proliferation, and p53, which is the product of the tumor suppressor gene TP53, are both important tumoral markers. This study intends to identify and quantify the Ki-67 and p53 proteins in astrocytic tumors of different grades of malignancy, as well as to analyze their relations with age and gender. Ki-67 and p53 proteins in 47 patients with surgically resected astrocytic neoplasms were studied through immunohistochemistry. They have been previously classified and reviewed concerning their histological grade, as suggested by the World Health Organization. The immunomarked cellular nuclei were quantified by the program Imagelab-softium for the absolute parametric reason between the nuclei of the positive cells and the total amount of tumoral cells, being counted 1000 cells. The lineation used has been transversal not controlled. For the statistical analysis the variables were divided into groups. For the Ki-67 they were absent, <5% and >5% and for p53 they were absent (0), <25% (1+), between 25 and 50% (2+), between 50 and 75% (3+), and higher than 75% (4+). Ki-67 was present in 37 cases (78.72%) evidencing a correlation with a higher malignancy degree (p<0,001). p53 was present in 14 cases (35.13%) with a higher correlation with astrocytoma grade IV (p=0.59). There has not been a statistically significant correlation between p53 and Ki-67, as well as among these variables, age and gender. The hypotheses of a greater presence of Ki-67 and p53 in astrocytic neoplasms with a higher degree of malignancy, except for the correlation between grade III and p53, is corroborated by the results of this study.

PCNA and Ki-67 in central nervous system tumors: correlation with the histological type and grade

Determination of proteins in the control of proliferation in normal cells helps a better understanding of cellular transformation and proliferation mechanisms. Measurement of proliferative activity is important in determining the tumor grade, recurrence span and malignancy. Proliferating cell nuclear antigen (PCNA) and Ki-67 are two of the nuclear markers used to demonstrate the proliferative phase of the cell cycle. In the present study, 63 central nervous system (CNS) tumors of various histologic types, diagnosed in Cukurova University Medical Faculty. Department of Pathology and graded according to WHO grading system were examined for PCNA and Ki-67 monoclonal antibodies using immunohistochemistry. Results were analyzed with statistical methods. Distribution of PCNA and Ki-67 LI (labeling index) values were determined for different tumor types. The highest PCNA and Ki-67 LI values were detected in medulloblastoma, malignant meningioma, primitive neuroectodermal tumor (PNET) and glioblastoma (GBM) groups, while pilocytic astrocytoma, meningioma, craniopharyngioma and oligodendroglioma showed the lowest values. In such tumors, the correlation between the increasing grade and PCNA and Ki-67 LI values were statistically significant. A correlation between the clinical outcome and Ki-67 and PCNA LI values was also detected. Conclusively, both markers can be used to evaluate the tumor grade and to asses the possibility of recurrence and malignancy in CNS tumors.