Applications of array technology: melanoma research and diagnosis

Gene network analyses point to the importance of human tissue kallikreins in melanoma progression

Background

A wide variety of high-throughput microarray platforms have been used to identify molecular targets associated with biological and clinical tumor phenotypes by comparing samples representing distinct pathological states.

Methods

The gene expression profiles of human cutaneous melanomas were determined by cDNA microarray analysis. Next, a robust analysis to determine functional classifications and make predictions based on data-oriented hypotheses was performed. Relevant networks that may be implicated in melanoma progression were also considered.

Results

In this study we aimed to analyze coordinated gene expression changes to find molecular pathways involved in melanoma progression. To achieve this goal, ontologically-linked modules with coordinated expression changes in melanoma samples were identified. With this approach, we detected several gene networks related to different modules that were induced or repressed during melanoma progression. Among them we observed high coordinated expression levels of genes involved in a) cell communication (KRT4, VWF and COMP); b) epidermal development (KLK7, LAMA3 and EVPL); and c) functionally related to kallikreins (EVPL, KLK6, KLK7, KLK8, SERPINB13, SERPING1 and SLPI). Our data also indicated that hKLK7 protein expression was significantly associated with good prognosis and survival.

Conclusions

Our findings, derived from a different type of analysis of microarray data, highlight the importance of analyzing coordinated gene expression to find molecular pathways involved in melanoma progression.

Multiplexing molecular diagnostics and immunoassays using emerging microarray technologies

Enzyme-linked immunosorbent assays (ELISA) are frequently used for quantitative measurement of the presence of protein, for single-analyte testing, in a sample. The application of ELISA in a microarray format has the potential to simultaneously measure the presence and/or concentrations of numerous proteins, in multiplex testing, all contained in a small drop of test fluid. Microspot microarray technology, in combination with protein biomarkers and nucleic acid diagnostics, appears to be the future high-performance analytical platform of choice. Validation of a large number of disease markers in both molecular and protein diagnostics has paved the way for the emergence of the multiplex assay. Initially, simple low-throughput multiplex assays were tested using the immunoassay format. These were followed by low-level multiplexing and high-throughput array-based immunoassays. More recently, two types of high-level multiplexing and high-throughput diagnostic methods using microspot arrays and bead arrays have been successfully developed to complement single-analyte assays. The value in rapid diagnostic evaluation for high-throughput multiplex, diagnostic test systems based on sound assay design must take into account data screening, normalization and statistical evaluation of possible concentration measurement, data errors and automated operation. Benefits of using multiplex array platforms include improved-quality patient care, as well as cost effectiveness and time saving. These multiplex methods also set the stage for future protein/nucleic acid codetection. Currently, the one analyte at a time test scheme is still dominant; nonetheless, the multiplex microspot microarray tests evaluated in a single multiassay analyzer are expected to become a significant part of clinical diagnostic testing within the next 5-10 years. This review is focused on microspot array and bead array methods for providing high throughput and a high degree of multiplexing in diagnostic testing.

Introduction: array technology - an overview

Microarray technology has its roots in high-throughput parallel synthesis of biomacromolecules, combined with combinatorial science. In principle, the preparation of arrays can be performed either by in situ synthesis of biomacromolecules on solid substrates or by spotting of ex situ synthesized biomacromolecules onto the substrate surface. The application of microarrays includes spatial addressing with target (macro) molecules and screening for interactions between immobilized probe and target. The screening is simplified by the microarray format, which features a known structure of every immobilized library element. The area of nucleic acid arrays is best developed, because such arrays are allowed to follow the biosynthetic pathway from genes to proteins, and because nucleic acid hybridization is a most straightforward screening tool. Applications to genomics, transcriptomics, proteomics, and glycomics are currently in the foreground of interest; in this postgenomic phase they are allowed to gain new insights into the molecular basis of cellular processes and the development of disease.

Analysis of differential gene expression in human melanocytic tumour lesions by custom made oligonucleotide arrays

Melanoma is one of the most aggressive types of cancer and resection of the tumour prior to dissemination of tumour cells is still the most effective treatment. Therefore, early diagnosis of melanocytic lesions is important and identification of novel (molecular) markers would be helpful to improve diagnosis. Moreover, better understanding of molecular targets involved in melanocytic tumorigenesis could possibly lead to development of novel interventions. In this study, we used a custom made oligonucleotide array containing 298 genes that were previously found to be differentially expressed in human melanoma cell lines 1F6 (rarely metastasising) and Mel57 (frequently metastasising). We determined differential gene expression in human common nevocellular nevus and melanoma metastasis lesions. By performing nine dye-swap array experiments, using individual as well as pooled melanocytic lesions, a constant differential expression could be detected for 25 genes in eight out of nine or nine out of nine array analyses. For at least nine of these genes, namely THBD, FABP7, H2AFJ, RRAGD, MYADM, HR, CKS2, NCK2 and GDF15, the differential expression found by array analyses could be verified by semiquantitative and/or real-time quantitative RT–PCR. The genes that we identified to be differentially expressed during melanoma progression could be potent targets for diagnostic, prognostic and/or therapeutic interventions.

Discovery and development of biomarkers of neurological disease

The identification of clinically relevant biomarkers for neurological diseases poses unique challenges. These include an historical lack of availability of relevant tissues from the site of pathology, relatively poorly matured techniques for disease diagnosis, the complexity and cellular heterogeneity of the brain, and a clear deficiency of models for functional validation of candidate biomarkers. Here, the unique challenges that neurological disorders introduce to biomarker discovery are described and how modern technological advances in genomics, proteomics and metabolomics are overcoming these obstacles and are driving the discovery of novel biomarkers to improve early diagnosis and therapeutic treatment is discussed.