Review for 10.1186/1471-230X-8-33 (2008)

Reviewer's report
Title:Epigenetic mechanisms involved in differential MDR1 mRNA expression
between gastric and colon cancer cell lines and rationales for clinical
chemotherapy
Version: 1Date:9 August 2007
Reviewer: Masakazu Yashiro
Reviewer's report:
General
Lee, et al described the comparison between MDR1 mRNA expression and
methylation status at promoter region in gastric and colon cancer cell lines to
clarify the reason why chemotherapeutic regimens have been different in gastric
and colon cancer. The authors showed that MDR1 mRNA was not detected in
the 10 gastric cancer cell lines but variable MDR1 mRNA levels in 7 of 9 colon
cancer cell Lines. Then, they examined underlying mechanisms in silencing of
MDR1 expression by inhibiting methyltransferase inhibitor or histone deacetylase
inhibitor. The authors concluded that the MDR1 mRNA levels in gastric cancer
cells are low due to different epigenetic regulations such as DNA methylation
and/or histone deacetylation.
Although the phenomenon itself seems to be interesting, the data is preliminary.
This paper needs a major revise, and is not recommended for publication in this
form.
Comments:
1. The data presented in this study is not enough to conclude that their results
can provide a better understanding of the efficacy of combined chemotherapy as
well as their oral bioavailability.
2. Their findings are not sufficient for definition of chemotherapeutic regimen. No
experimental evidence is provided in the effect on 5-FU, platinum agents and
topoisomerase inhibitors in animal models.
3. More details of the backgrounds of cancer cell lines used in this study should
be addressed. Because the chemo-sensitivity of most cancer cell lines depend
on p53 status, p53 status in each cancer cell lines should be addressed.
4. Why were both of semi-quantitative RT-PCR and real-time RT-PCR
performed? Some of gastric cancer cell lines such as SNU-668,484 showed
relative high expression in semi-quantitative PCR, whereas no expression in
real-time RT-PCR in despite of more than 35 cycles. In addition, why did these
cell lines show almost same expression ratio as COLO320HSR? Data of Pgp
protein expression should be necessary.
5. In the chemo-sensitivity assay, expression of Pgp protein is not associated
with sensitivity for paclitaxel, because IC50 of SNU-668 was more than 10-fold
high compared with SNU-C5 which showed no expression of Pgp protein same
as SNU-668. In addition, there might be lack in sufficient explanation about dose
of paclitaxel in figure 4B. Growth of SNU-668 which IC50 is 200-fold less than
Colo320HSR is not suppressed at all, whereas that of colo320HSR is
dramatically reduced only by adding Pgp inhibitor.
6. Direct sequencing of promoter region with or without bisulfite treatment might
be useful to examine the methylation status at in gastric and colon cancer cell
lines.
7. Discussion about treatment with 5AdC and TSA is relative complicated. How is
the effect of these treatments on Pgp protein expression or chemo sensitivity?
The authors described that MDR1 mRNA expression is differentially regulated in
gastric and colon cancer. However, as shown in Table1, SNU-16 (gastric cancer
cell line) and SNU-C5 (colon cancer) show similar effect on MDR1 expression as
well as SNU-216 and HCT-116.
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Major Compulsory Revisions (that the author must respond to before a decision
on publication can be reached)
What next?: Reject because scientifically unsound
Level of interest: An article whose findings are important to those with closely
related research interests
Quality of written English: Not suitable for publication unless extensively edited
Statistical review: No, the manuscript does not need to be seen by a
statistician.