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Molecular Biology and Genetics |
Human Genome Center, Institute of Medical Science, University of Tokyo, Tokyo 108-8639, Japan [C. K., Y. F., K. O., O. K., H. Z., R. Y., T. Tak., Y. N.]; Department of Surgery, Kurume University, School of Medicine, Kurume 830-0011, Japan [H. Y.]; First Department of Surgery, Sapporo Medical University, School of Medicine, Sapporo, Hokkaido 060-0061, Japan [C. K., K. H.]; and SNP Research Center, Riken Institute of Physical and Chemical Research, Tokyo 108-8639, Japan [T. Tsu., T. Tan.]
| ABSTRACT |
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| INTRODUCTION |
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| MATERIALS AND METHODS |
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Construction and Analysis of cDNA Microarray.
The fabrication of cDNA microarray slides have been described elsewhere
(9
, 10)
. A set of cDNA microarray slides containing a
duplicate set of 9216 cDNA spots were used for each analysis of
expression profiles to reduce the experimental fluctuation. Total RNA
was extracted from the frozen samples using TRIzol reagent (Life
Technologies, Inc., Rockville, MD) and digested with RNase-free DNase I
(Nippon Gene Co., Tokyo, Japan) according to the recommendations of the
manufacturers. T7-based RNA amplifications and preparations of cDNA
probes were carried out, as described elsewhere, using 5 µg each of
the total RNA (11
, 12)
. Amplified RNA from cancer
tissues (2.5 µg of each) was labeled with Cy5-dCTP (Amersham
Pharmacia Biotech, Uppsala, Sweden), and an equal amount of amplified
RNA from a pool of total RNA of normal esophagus (Invitrogen, Carlsbad,
CA) was labeled with Cy3-dCTP (Amersham Pharmacia Biotech).
Hybridization, washing, and scanning were performed as described
previously (9
, 10)
. The intensity of each duplicated
signal was evaluated photometrically using the ArrayVision computer
program (Imaging Research, Inc., St. Catharines, Canada). To normalize
the amount of mRNA of tumor and normal cells from each patient, the
Cy5:Cy3 ratio of each gene expression was adjusted so that the averaged
Cy5:Cy3 ratio of 60 housekeeping genes was 1.0. Subsequently, the
duplicated spots on each slide were averaged (9
, 10
, 12)
.
In addition, a cutoff value for each expression level was automatically
calculated using a variance analysis, and data with low signal
intensities were excluded from additional investigation.
Selection of Separating Genes.
To select the genes that can contribute to separating the
drug-sensitive group from the drug-nonsensitive group, we calculated
for each gene the U values of the Mann-Whitney test, which
measures a difference of distribution in groups 1 and 3. The
distribution of the Cy5:Cy3 ratio of a gene was measured for the two
groups. Mann-Whitney U value is defined as the number of
combinations of overlapping patients between the two distributions. If
the two groups are completely separated by the value of the Cy5:Cy3
ratio (an ideal gene), the U value becomes 0, because there
is no overlap between these two groups according to the Cy5:Cy3 ratio
of the gene. Therefore, the less the two groups overlap, the smaller
the U value. We selected 52 genes that had
P < 0.1 (U values of
11 for
eight plus six learning samples) as biologically significant.
Calculation of DRS Using Separating Genes.
The DRS of each patient is defined as the sum of the weighted log ratio
of the gene expression profile:
![]() |
i in group Alog2(rik)/nA
and avegroup B =
i in group Blog2(rik)/nB.
Then, we determined the sign for each gene:
Sk = +1 if
avegroup A
avegroup B, and
Sk = -1 if
avegroup A < avegroup B. Applying a set of
Sk to the expression profiles of new
patients, we can calculate the DRS for each patient.
Semiquantitative RT-PCR.
A 2-µg aliquot of total RNA from each tissue sample was
reverse-transcribed for single-stranded cDNAs using
oligo(dT)1218 primer and Superscript II (Life
Technologies, Inc.). Each cDNA mixture was diluted for subsequent PCR
amplification with the same primer sets that were prepared for
construction of the target DNA- or G3PDH-specific primer set
(5'-GACAACAGCCTCAAGATCATCA-3' and 5'-GGTCCACCACTGACACTGTG-3').
Expression of G3PDH served as an internal control. The PCR
reactions were optimized for number of cycles to ensure product
intensity within the linear phase of amplification.
| RESULTS |
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12 months (6 cases; Table 1A
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11, as elements likely to be
associated with patient survival. The expression pattern of all
52 genes according to their characteristics in each tumor is summarized
in Fig. 2
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| DISCUSSION |
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All 26 esophageal cancer patients in our panel were at clinically advanced stages (Tumor-Node-Metastasis stages IIIIV). Such patients usually have poor prognoses; only a small percentage achieves more than a 5-year survival after surgery. For the nine patients of our panel who survived for more than 30 months (group 1), we assume that postoperative anticancer treatment with CDDP and 5-FU was effective in killing residual cancer cells. Hence, we considered the nine patients (group 1) as drug-sensitive patients and the six with short survival (group 3) as nonsensitive patients. Notably, the patients analyzed were treated with anticancer drugs after the surgical resection; the survival period is the only parameter that could estimate drug sensitivity.
Our data from the patients analyzed in this study allowed us to identify not only consistent patterns of gene expression in esophageal cancers but also a set of genes discriminating the outcome of adjuvant chemotherapy after surgical treatment. We detected elevated expression of c-erbB2 in 3 of 26 cases and that of epidermal growth factor receptor, in 8 of 26 (data not shown), which were almost similar to the data previously reported (18 , 19) . These data, together with the consistent results of semiquantitative RT-PCR, corroborated the reliability of our data.
The most advantageous point of the algorithm we have described for establishing the DRS is that, after selecting genes that may influence the drug response, the algorithm sums up the log ratios of genes, each of which is multiplied by the sign determined according to the contributing direction to the group separation. The selection of genes depends only on a difference in expression patterns between drug-sensitive and -nonsensitive individuals. However, this process only selects genes according to their individual behaviors in a given sample set. Because the actual mechanism that leads to each type of cancer implies a rather complicated network of genetic events, differences of phenotype depend not on single genes but on a global expression pattern. We tried several multivariate statistical analyses, e.g., linear discriminant analysis and qualification theory II, and found this simple method of summing up the log ratio of each gene with each sign separated more efficiently the drug-sensitive group from the drug-nonsensitive group. The ability to assess the effectiveness of anticancer drugs in resected cancer materials before treatment would avoid unnecessary treatment as well as the side effects that would add to the patients suffering in the absence of any benefit.
It is apparent that survival periods reflect not only drug sensitivity but also the malignant properties of the tumor cells (the potentiality of invasion or metastasis), the histopathological grade of the tumors, the surgical procedures, and their curativity. However, because clinicopathological characteristics such as Tumor-Node-Metastasis stage, histopathological grade, lymph node dissection, and the condition of residual tumor in the group-1 and group-3 patients were similar, we assume that the former factors seem to contribute largely to the survival of the patients analyzed. Although it may be overstated that DRS predicts only the sensitivity to anticancer drugs, it is a clinically valuable predictive score reflecting the outcome of the adjuvant chemotherapy after surgical resection for patients with advanced esophageal cancer.
Our data from the patients analyzed in this study allowed us to
identify consistent patterns of gene expression in esophageal cancers.
Some of the 52 genes were indicated to be associated in some aspects
with sensitivity to anticancer drugs or with esophageal carcinogenesis.
For example, glutathione S-transferase
and
S-adenosylmethionine were shown to be related to drug resistance
(20
, 21) . Overexpression of heterogeneous nuclear
ribonucleoprotein A2 in lung cancers was reported (22)
.
EMS1, mapped at chromosome 11q13, was sometimes
amplified in breast cancers (23)
. The activity of
ornithine decarboxylase, a rate-limiting enzyme in the
synthesis of polyamines, which are essential for cellular
proliferation, was found to be elevated in colorectal tumors and polyps
(24)
. The human multidrug resistance-associated protein
family currently consists of seven members and has the ability to
transport a wide range of anticancer drugs out of cells
(25)
. Particularly,
MDR1/P-glycoprotein expression was suggested to
be a predictor of response and survival in advanced ovarian cancer
patients (26)
. In our microarray experiment, significant
reduction of MDR1 expression was observed in 3 of 20
patients in groups 1 and 2, although down-regulation was observed in 0
of 6 patients belonging to group 3, suggesting that MDR1
might affect the sensitivity of 5FU and/or CDDP in the adjuvant
chemotherapy for esophageal cancers. However, this gene was not
included in the 52 genes because the correlation between the expression
and the sensitivity was moderate. The usefulness of the prediction of
the outcome of adjuvant chemotherapy using the DRS system with the 52
genes selected from 9216 genes on our cDNA microarray raises a
possibility that extended analyses of expression profiles with an
increased number of genes using a larger number of samples will help in
the development of a more accurate DRS system.
In conclusion, the strategy outlined here should shed light on freeing cancer patients from suffering the side effects of ineffective adjuvant chemotherapy, and, in the near future, would be useful for clinicians to select an optimal, personalized therapy for each patient. It is also certain that products of these currently unidentified genes as well as genes of known functions may become targets of novel anticancer drugs in the future.
| ACKNOWLEDGMENTS |
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| FOOTNOTES |
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1 This work was supported in part by Research for
the Future Program Grant 96L00102 from the Japan Society for the
Promotion of Science. ![]()
2 These authors contributed equally to this
work. ![]()
3 To whom requests for reprints should be
addressed, at Laboratory of Molecular Medicine, Human Genome Center,
Institute of Medical Science, University of Tokyo, 4-6-1, Shirokanedai,
Minato-ku, Tokyo 108-8639, Japan. Phone: 81-3-5449-5372; Fax:
81-3-5449-5433; E-mail: yusuke{at}ims.u-tokyo.ac.jp ![]()
4 The abbreviations used are: SCC, squamous cell
carcinoma; CDDP, cisplatin; 5-FU, 5-fluorouracil; G3PDH,
glyceraldehyde-3-phosphate dehydrogenase; RT-PCR, reverse
transcription-PCR; DRS, drug response score; MDR, multidrug
resistance. ![]()
Received 2/ 7/01. Accepted 7/ 5/01.
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