Utility of antiphosphorylated H2AX antibody (gamma-H2AX) in diagnosing metastatic renal cell carcinoma

Factors to Consider for the Correct Use of γH2AX in the Evaluation of DNA Double-Strand Breaks Damage Caused by Ionizing Radiation

People exposed to ionizing radiation (IR) both for diagnostic and therapeutic purposes is constantly increasing. Since the use of IR involves a risk of harmful effects, such as the DNA DSB induction, an accurate determination of this induced DNA damage and a correct evaluation of the risk-benefit ratio in the clinical field are of key relevance. γH2AX (the phosphorylated form of the histone variant H2AX) is a very early marker of DSBs that can be induced both in physiological conditions, such as in the absence of specific external agents, and by external factors such as smoking, heat, background environmental radiation, and drugs. All these internal and external conditions result in a basal level of γH2AX which must be considered for the correct assessment of the DSBs after IR exposure. In this review we analyze the most common conditions that induce H2AX phosphorylation, including specific exogenous stimuli, cellular states, basic environmental factors, and lifestyles. Moreover, we discuss the most widely used methods for γH2AX determination and describe the principal applications of γH2AX scoring, paying particular attention to clinical studies. This knowledge will help us optimize the use of available methods in order to discern the specific γH2AX following IR-induced DSBs from the basal level of γH2AX in the cells.

Immunohistochemical Expression Pattern of Mismatch Repair Genes in the Short-term Streptozotocin-induced Diabetic Rat Kidneys

We studied the expression of mismatch repair genes (MMRs)-mutS protein homolog 2 (MSH2), PMS2, MutL homolog 1 (MLH1), and yH2AFX in diabetic rat kidneys. Streptozotocin-induced diabetes mellitus type 1 rat model (DM1) was used. Renal samples were collected 2 weeks and 2 months after DM1 induction and immunohistochemical expression of MMR genes in the renal cortex was analyzed. Diabetic animals showed lower MSH2 and higher yH2AFX kidney expression both 2 weeks and 2 months after DM1 induction. MLH1 expression significantly increased 2 weeks after DM1 induction (P<0.0001). The most substantial differences were observed in the period 2 weeks after induction, with lower MSH2 and higher MLH1 expression in the proximal convoluted tubules and distal convoluted tubules (DCT) of diabetic animals (P<0.001). yH2AFX expression significantly increased in the DCT of diabetic animals at both time points (P<0.001; P<0.01). PMS2 expression changed only in the glomeruli, where it significantly decreased 2 months after DM1 induction (P<0.05). We concluded that the most substantial changes in renal expression of MMRs are happening already 2 weeks after diabetes induction, predominantly in the proximal convoluted tubules and DCT. Moreover, DCT could have a critical role in the pathophysiology of diabetic nephropathy (DN) and might be a future therapeutic target in this condition. The obtained results point to the MMRs as a potential factor in the development and progression of DN, as well as the possible link between DN and renal carcinogenesis.

Expression of DNA doublestrand repair proteins in oral leukoplakia and the risk of malignant transformation

The present study assessed the expression of the DNA doublestrand repair (DDR) proteins ATM serine/threonine kinase (ATM), checkpoint kinase 2 (CHEK2) and γH2A histone family member X (γH2AFX) in oral leukoplakia (OL) and evaluated their clinical significance and usefulness as biomarkers for predicting OL transformation. Retrospectively, ATM, CHEK2 and γH2AFX protein levels were evaluated using immunohistochemical analysis in 61 OL, 33 oral squamous cell carcinoma (OSCC) and 15 normal oral mucosa tissues. OL tissues were classified into two groups according to the epithelial dysplasia pathology: The low risk dysplasia group (n=41) and the high-risk dysplasia group (n=20). The results of the present study revealed that the expression of ATM and γH2AFX in OSCC was significantly increased compared with that in OL with low-risk dysplasia and normal oral mucosa tissues. There was no statistically significant difference in CHEK2 expression among the groups. ATM expression was correlated with that of γH2AFX in OSCC tissue. The prognostic values of the DDR proteins and their correlation with clinical and pathological parameters were evaluated further in 99 OL patients with low risk dysplasia. Multivariate analysis revealed that increased expression of ATM and γH2AFX was significantly associated with an increased risk of malignant transformation. Immunohistochemical analysis of ATM and γH2AFX protein expression provided useful prognostic information on the carcinogenesis of OL. Increased ATM and γH2AFX expression may indicate a poor prognosis.

PAKs in Human Cancer Progression: From Inception to Cancer Therapeutic to Future Oncobiology

Since the initial recognition of a mechanistic role of p21-activated kinase 1 (PAK1) in breast cancer invasion, PAK1 has emerged as one of the widely overexpressed or hyperactivated kinases in human cancer at-large, allowing the PAK family to make in-roads in cancer biology, tumorigenesis, and cancer therapeutics. Much of our current understanding of the PAK family in cancer progression relates to a central role of the PAK family in the integration of cancer-promoting signals from cell membrane receptors as well as function as a key nexus-modifier of complex, cytoplasmic signaling network. Another core aspect of PAK signaling that highlights its importance in cancer progression is through PAK's central role in the cross talk with signaling and interacting proteins, as well as PAK's position as a key player in the phosphorylation of effector substrates to engage downstream components that ultimately leads to the development cancerous phenotypes. Here we provide a comprehensive review of the recent advances in PAK cancer research and its downstream substrates in the context of invasion, nuclear signaling and localization, gene expression, and DNA damage response. We discuss how a deeper understanding of PAK1's pathobiology over the years has widened research interest to the PAK family and human cancer, and positioning the PAK family as a promising cancer therapeutic target either alone or in combination with other therapies. With many landmark findings and leaps in the progress of PAK cancer research since the infancy of this field nearly 20 years ago, we also discuss postulated advances in the coming decade as the PAK family continues to shape the future of oncobiology.

PET imaging of DNA damage using (89)Zr-labelled anti-γH2AX-TAT immunoconjugates

PURPOSE

The efficacy of most anticancer treatments, including radiotherapy, depends on an ability to cause DNA double-strand breaks (DSBs). Very early during the DNA damage signalling process, the histone isoform H2AX is phosphorylated to form γH2AX. With the aim of positron emission tomography (PET) imaging of DSBs, we synthesized a (89)Zr-labelled anti-γH2AX antibody, modified with the cell-penetrating peptide, TAT, which includes a nuclear localization sequence.

METHODS

(89)Zr-anti-γH2AX-TAT was synthesized using EDC/NHS chemistry for TAT peptide linkage. Desferrioxamine conjugation allowed labelling with (89)Zr. Uptake and retention of (89)Zr-anti-γH2AX-TAT was evaluated in the breast adenocarcinoma cell line MDA-MB-468 in vitro or as xenografts in athymic mice. External beam irradiation was used to induce DSBs and expression of γH2AX. Since (89)Zr emits ionizing radiation, detailed radiobiological measurements were included to ensure (89)Zr-anti-γH2AX-TAT itself does not cause any additional DSBs.

RESULTS

Uptake of (89)Zr-anti-γH2AX-TAT was similar to previous results using (111)In-anti-γH2AX-TAT. Retention of (89)Zr-anti-γH2AX-TAT was eightfold higher at 1 h post irradiation, in cells expressing γH2AX, compared to non-irradiated cells or to non-specific IgG control. PET imaging of mice showed higher uptake of (89)Zr-anti-γH2AX-TAT in irradiated xenografts, compared to non-irradiated or non-specific controls (12.1 ± 1.6 vs 5.2 ± 1.9 and 5.1 ± 0.8%ID/g, respectively; p < 0.0001). The mean absorbed dose to the nucleus of cells taking up (89)Zr-anti-γH2AX-TAT was twofold lower compared to (111)In-anti-γH2AX-TAT. Additional exposure of neither irradiated nor non-irradiated cells nor tissues to (89)Zr-anti-γH2AX-TAT resulted in any significant changes in the number of observable DNA DSBs, γH2AX foci or clonogenic survival.

CONCLUSION

(89)Zr-anti-γH2AX-TAT allows PET imaging of DNA DSBs in a tumour xenograft mouse model.

Dysregulation of PAK1 Is Associated with DNA Damage and Is of Prognostic Importance in Primary Esophageal Small Cell Carcinoma

Primary esophageal small cell carcinoma (PESCC) is a rare, but fatal subtype of esophageal carcinoma. No effective therapeutic regimen for it. P21-activated kinase 1 (PAK1) is known to function as an integrator and an indispensable node of major growth factor signaling and the molecular therapy targeting PAK1 has been clinical in pipeline. We thus set to examine the expression and clinical impact of PAK1 in PESCC. The expression of PAK1 was detected in a semi-quantitative manner by performing immunohistochemistry. PAK1 was overexpressed in 22 of 34 PESCC tumors, but in only 2 of 18 adjacent non-cancerous tissues. Overexpression of PAK1 was significantly associated with tumor location (p = 0.011), lymph node metastasis (p = 0.026) and patient survival (p = 0.032). We also investigated the association of PAK1 with DNA damage, a driven cause for malignancy progression. γH2AX, a DNA damage marker, was detectable in 18 of 24 (75.0%) cases, and PAK1 expression was associated with γH2AX (p = 0.027). Together, PAK1 is important in metastasis and progression of PESCC. The contribution of PAK1 to clinical outcomes may be involved in its regulating DNA damage pathway. Further studies are worth determining the potentials of PAK1 as prognostic indicator and therapeutic target for PESCC.

γH2AX as a marker of DNA double strand breaks and genomic instability in human population studies

DNA double strand breaks (DSB) are the gravest form of DNA damage in eukaryotic cells. Failure to detect DSB and activate appropriate DNA damage responses can cause genomic instability, leading to tumorigenesis and possibly accelerated aging. Phosphorylated histone H2AX (γH2AX) is used as a biomarker of cellular response to DSB and its potential for monitoring DNA damage and repair in human populations has been explored in this review. A systematic search was conducted in PubMed for articles, in English, on human studies reporting γH2AX as a biomarker of either DNA repair or DNA damage. A total of 68 publications were identified. Thirty-four studies (50.0%) evaluated the effect of medical procedures or treatments on γH2AX levels; 20 (29.4%) monitored γH2AX in specific pathological conditions with a case/control or case/case design; 5 studies (7.4%) evaluated the effect of environmental genotoxic exposures, and 9 (13.2%) were descriptive studies on cancer and aging. Peripheral blood lymphocytes (44.6%) or biopsies/tissue specimens (24.3%) were the most commonly used samples. γH2AX was scored by optical microscopy as immunostained foci (78%), or by flow cytometry (16%). Critical features affecting the reliability of the assay, including protocols heterogeneity, specimen, cell cycle, kinetics, study design, and statistical analysis, are hereby discussed. Because of its sensitivity, efficiency and mechanistic relevance, the γH2AX assay has great potential as a DNA damage biomarker; however, the technical and epidemiological heterogeneity highlighted in this review infer a necessity for experimental standardization of the assay.

Changes in γ-H2AX expression in irradiated feline sarcoma cells: an indicator of double strand DNA breaks

Feline injection site sarcoma (ISS) is a highly invasive soft tissue tumor that is commonly treated with radiation. Cellular deoxyribonucleic acid (DNA) is the principal target for the biologic effects of radiation with cell killing correlating to the number of double stranded DNA breaks (DSBs). The objective of this study was to determine if radiation-induced damage to feline ISS cells could be detected using a commercially available DNA DSB detection kit. Feline ISS cells were irradiated and evaluated for extent of DSB induction with a γ-H2AX chemiluminescent kit; results were validated by Western Blot analysis. Irradiated cells showed a significant increase in double strand break induction compared to control cells, which was supported by Western Blot. DNA damage in feline sarcoma cells following single exposure of radiation can be indirectly detected using a commercially available mouse anti-human monoclonal antibody for γ-H2AX.

Imaging the clear cell renal cell carcinoma proteome

PURPOSE

A key barrier to identifying tissue biomarkers of clear cell renal cell carcinoma is the heterogeneity of protein expression in tissue. However, by providing spectra for every 0.05 mm(2) area of tissue, imaging mass spectrometry reveals the spatial distribution of peptides. We determined whether this approach could be used to identify and map protein signatures of clear cell renal cell carcinoma.

MATERIALS AND METHODS

We constructed 2 tissue microarrays with 2 cores each of matched tumor and normal tissue from the nephrectomy specimens of 70 patients with clear cell renal cell carcinoma. Samples were analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. In each tissue microarray peptide signatures were identified that differentiated cancer from normal tissue. The signatures were then cross validated. Mass spectrometry/mass spectrometry sequencing was performed to determine the identity of select, differentially expressed peptides. Immunohistochemistry was used for validation.

RESULTS

In each tissue microarray peptide signatures were identified that had 94.7% to 98.5% classification accuracy for each 0.05 mm(2) spot (spectrum) and 96.9% to 100% accuracy for each tissue core. Cross validation across tissue microarrays revealed a classification accuracy of 82.6% to 84.7% for each spot and 88.9% to 92.4% for each core. We identified vimentin, histone 2A.X and α-enolase as proteins with greater expression in cancer tissue. This was validated by immunohistochemistry.

CONCLUSIONS

Imaging mass spectrometry identified and mapped specific peptides that accurately distinguished malignant from normal renal tissue. This demonstrates its potential as a novel, high throughput approach to clear cell renal cell carcinoma biomarker discovery. Given the multiple pathways and known heterogeneity involved in tumors such as clear cell renal cell carcinoma, multiple peptide signatures that maintain their spatial relationships may outperform traditional protein biomarkers.

γ-H2AX and other histone post-translational modifications in the clinic

Chromatin is a dynamic complex of DNA and proteins that regulates the flow of information from genome to end product. The efficient recognition and faithful repair of DNA damage, particularly double-strand damage, is essential for genomic stability and cellular homeostasis. Imperfect repair of DNA double-strand breaks (DSBs) can lead to oncogenesis. The efficient repair of DSBs relies in part on the rapid formation of foci of phosphorylated histone H2AX (γ-H2AX) at each break site, and the subsequent recruitment of repair factors. These foci can be visualized with appropriate antibodies, enabling low levels of DSB damage to be measured in samples obtained from patients. Such measurements are proving useful to optimize treatments involving ionizing radiation, to assay in vivo the efficiency of various drugs to induce DNA damage, and to help diagnose patients with a variety of syndromes involving elevated levels of γ-H2AX. We will survey the state of the art of utilizing γ-H2AX in clinical settings. We will also discuss possibilities with other histone post-translational modifications. The ability to measure in vivo the responses of individual patients to particular drugs and/or radiation may help optimize treatments and improve patient care. This article is part of a Special Issue entitled: Chromatin in time and space.

Utility of PAX8 and PAX2 immunohistochemistry in the identification of renal cell carcinoma in diagnostic cytology

The diagnosis of metastatic renal cell carcinoma (RCC) in cytology specimens may be difficult to confirm on the basis of cytomorphology alone. Often, immunohistochemistry serves as an important adjunct in confirming this diagnosis. Recently, PAX2 was shown to be useful in this regard. In this study, we sought to compare the utility of PAX8 to that of PAX2 immunohistochemistry in the diagnosis of RCC in cytology specimens. First, we verified the performance of PAX8 immunohistochemistry on a tissue microarray (TMA) composed of 54 cases of RCC; PAX8 immunoreactivity was seen in at least 10% of the tumor cells in all cases. Next, we applied PAX8 immunohistochemistry to cell block sections prepared from 24 cases of RCC, obtained from fine-needle aspirates and effusion specimens. PAX2 immunohistochemistry was performed for comparison. Immunopositivity was defined as the presence of nuclear staining in at least 10% of tumor cell nuclei. Immunoreactivity for PAX8 and PAX2 was seen in 21 (88%) and 20 (83%) of the 24 cases, respectively. The presence of either PAX8 or PAX2 immunostaining was present in 22 of 24 cases, thus showing a total sensitivity of 92%. Overall, the results indicate that PAX8 and PAX2 are diagnostically useful adjuncts in confirming the diagnosis of RCC in cytology specimens.

Histone gammaH2AX and poly(ADP-ribose) as clinical pharmacodynamic biomarkers

Tumor cells are often deficient in DNA damage response (DDR) pathways, and anticancer therapies are commonly based on genotoxic treatments using radiation and/or drugs that damage DNA directly or interfere with DNA metabolism, leading to the formation of DNA double-strand breaks (DSB), and ultimately to cell death. Because DSBs induce the phosphorylation of histone H2AX (γH2AX) in the chromatin flanking the break site, an antibody directed against γH2AX can be employed to measure DNA damage levels before and after patient treatment. Poly(ADP-ribose) polymerases (PARP1 and PARP2) are also activated by DNA damage, and PARP inhibitors show promising activity in cancers with defective homologous recombination (HR) pathways for DSB repair. Ongoing clinical trials are testing combinations of PARP inhibitors with DNA damaging agents. Poly(ADP-ribosylation), abbreviated as PAR, can be measured in clinical samples and used to determine the efficiency of PARP inhibitors. This review summarizes the roles of γH2AX and PAR in the DDR, and their use as biomarkers to monitor drug response and guide clinical trials, especially phase 0 clinical trials. We also discuss the choices of relevant samples for γH2AX and PAR analyses.

GammaH2AX and cancer

Histone H2AX phosphorylation on a serine four residues from the carboxyl terminus (producing gammaH2AX) is a sensitive marker for DNA double-strand breaks (DSBs). DSBs may lead to cancer but, paradoxically, are also used to kill cancer cells. Using gammaH2AX detection to determine the extent of DSB induction may help to detect precancerous cells, to stage cancers, to monitor the effectiveness of cancer therapies and to develop novel anticancer drugs.