Cancer Research in Biotechnology

عبدالرحمن حسن علي
مؤســس المنتدى
مؤســس المنتدى
الجنسية :
عدد المشاركات عدد المشاركات : 16016
تقييم المشترين تقييم المشترين : 49
واتساب واتساب : 201289700022
معاينة صفحة البيانات الشخصي للعضو

في الإثنين أغسطس 22, 2011 11:42 pm

Progress in cancer research requires the discovery of novel
biochemical and molecular targets for targeted treatments, novel
biomarkers for early cancer detection and diagnosis, and improved
classification and subtyping of cancers for prognostication and
treatment selection.
To facilitate these goals, efforts have focused on understanding the molecular basis and cellular biology of human cancer.
examination of multiple expressed genes and/or proteins provides useful
information for both classification and prognostication of individual
tumors. The development of microarray methodology, which permits the
expression of thousands of genes to be assayed simultaneously,
represents a powerful technique to read the "molecular signature" of an
individual patient's tumor. This process is termed gene expression
profiling (GEP). Analyzing gene expression patterns across individual
patients with the "same" disease may reveal molecular differences. Such
classification may allow better treatment selection and prognostication.
description of the methods used for GEP will be presented here. More
detailed discussion of the applications of these techniques to specific
tumor types is discussed in the appropriate tumor topics.
DNA MICROARRAY ANALYSIS - The traditional method of measuring the level
of expression of a single gene is by assaying RNA by Northern blot
analysis. DNA microarray analysis uses the same principles to
simultaneously measure the expression level of thousands of genes on a
platform called a microarray.
There are several stages to performing a microarray analysis:

  • Preparation of the microarray
  • Generation of fluorescent targets from the RNA of the samples
  • Hybridization to the probes
  • Data acquisition: scanning of the signal intensity emanating from the hybridized labeled probes
  • Data analysis: the extraction of biologically useful information
    from the vast quantity of data that is generated from microarray
    analysis. This aspect is often the most challenging component of GEP.
Preparation of the microarray - The DNA array consists of an
orderly arrangement of DNA spots on a glass slide or chip. In its
simplest form, a few dozen complementary DNAs (cDNAs) or
oligonucleotides corresponding to particular genes are immobilized onto
the substrate in a known order within the grid.
highly-sophisticated microarray "chips", up to hundreds of thousands of
unique oligonucleotide probes, representing thousands of known genes or
expressed sequence tags (ESTs), are synthesized in a microgrid on a
glass substrate about the size of a thumbnail. ESTs are segments of
expressed genes that have been sequenced, but do not correspond to known
Each oligonucleotide probe, which is specific for a
particular gene, is located on a precise place within the microgrid;
this is the probe cell. Each probe cell is very small, about 24 microns
by 24 microns, and contains millions of copies of each specific
oligonucleotide. A particular gene (eg, the gene encoding thymidylate
synthetase) may be represented on the microgrid by 20 or more probe
cells, called a probe set. The oligonucleotide probes (usually 15 to 25
nucleotides in length) in each probe cell of the probe set may differ
from each other, some corresponding to the 5' end of the mRNA sequence,
some the middle, and some the 3' end. This gives the sample RNA a broad
range of sequences with which to hybridize.
In summary, the
rapidly evolving field of DNA microarray analysis and gene expression
profiling has wide-ranging implications for the molecular classification
of tumors, refinement of prognostic estimates, and prediction of
response to therapy. Despite its exciting potential and significant
recent advances, this field remains relatively new, and it is premature
to conclude that microarray data can be used as a sole means of
classifying cancers or predicting outcomes of treatment.
Among the
specific challenges that must be met are the need for larger studies
with appropriate validation, standardization of methods and
establishment of guidelines for the conduct and reporting of studies,
and the formation of repositories and registries where research
institutions may deposit data for comparison with independent works
involving the same malignant disorder. Finally, DNA microarray-based
tests must demonstrate utility in prospectively designed clinical trials
before this technology is considered a routine part of clinical
These studies may eventually establish a new treatment paradigm in personalized cancer therapy in the future.

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