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Dear Editor in Chief,
Thanks considering our manuscript "Drug Metabolism and Pancreatic Cancer". I have
c9onsideered all the suggestions and revised the paper accordingly. Hopefully now it will
be accepted for publication.
Once again, we appreciate for your consideration.
Sincerely yours,
M. Wasif Saif, MD
Reviewer A:
Flores et al. reviewed nicely the available data on predictive biomarkers for several
chemotherapeutic agents in a early and metastatic pancreatic cancer. This is a well-written
article by a group with experience in the field. I have some suggestions, however, that I
believe will of be benefit both for the article and the readers.
1) The authors based their work mostly on reviewing the biomarker detection by IHC.
There is available data on DNA polymorphisms for the genes that encode the same
proteins. Please discuss the most important studies and report a summary of the data in a
table form (e.g. gene, polymorphism, clinical outcome and reference).
RESPONSE: though such data is beyond the scope of this paper but added few other
related markers in this paper, such as
Microsatellite Instability (MSI)
Studies have also suggested that 5-fluorouracil (FU) may be less effective in patients with
MSI pancreatic cancers, similar to data seen in the treatment of colon cancer, especially in
the adjuvant setting. In a study by Nakata et al. 46 patients with pancreatic cancer who had
undergone resection were evaluated for microsatellite variations 34. Univariate analysis
showed that patients with MSI-positive tumors had significantly longer survival than those
with MSI-negative tumors, although there were no significant differences in
clinicopathological factors between the two groups (median survival, 62 months versus 10
months, respectively; p=0.011). Multivariate survival analysis indicated that MSI status had
an independent predictive value (HR=5.577; p=0.007). The tumor-infiltrating leukocyte
intensity in MSI-positive tumors was stronger than that in MSI-negative tumors, suggesting
that MSI-positive tumors may induce stronger antitumor immunity. However, more data is
needed to confirm its role as a marker in these patients.
2) A table that summarizes the presented data (in a similar fashion) will also be helpful for
the readers.
RESPONSE:
Table 1: Potential Markers and Relevant Chemotherapeutic agents
Chemotherapy
agent
Gemcitabine
Representative candidate gene
Irinotecan







Cisplatin

Oxaliplatin
Erlotinib




Fluorouracil
Nab-paclitaxel
Cytidine deaminase
Deoxycytidine kinase
Ribonucleotide reductase M1 subunit (RRM1)
Dihydropyrimidine dehydrogenase (DPD)
Thymidylate synthetase (TS)
5, 10-methylenetetrahydrofolate reductase (MTHFR)
UDP glucuronosyltransferase 1 family, polypeptide A1
(UGT1A1)
Excision repair cross complementation group 1 and 2
(ERCC1 and ERCC2)
Excision repair cross complementation group 1 (ERCC1)
EGFR
K-ras
SPARC
3) Given that the readers of the journal are mostly GI specialists, I suggest an introduction
on biomarkers (eg. definition, characteristics that a biomarker should have and some
examples like HER2 in breast cancer).
RESPONSE: We added a Figure in the beginning to self explain them.
Biomarkers are generally considered as predictive or prognostic (Figure 1). Biomarkers
can be measured in tumor tissue or other body fluids, such as plasma.
Figure 1: How are biomarkers defined?
4) The biomarkers associated with 5FU (DPYD) and irinotecan (UGT1A1) toxicity need to
be discussed.
RESPONSE:
Dihydropyrimidine dehydrogenase DPD:
Dihydropyrimidine dehydrogenase (DPD) is a key enzyme in the degradation of 5-FU. It is
thought that intratumor expression of DPD may correlate with possible 5-FU resistance.
The first study of DPD in pancreatic cancer was done by Nakayama et al. (15492566)
retrospectively in 68 patients with resectable pancreatic adenocarcinoma 30 of which
received 5-FU via a liver perfusion technique. They measured DPD by IHC and found that
those with negative staining had longer survival if treated with intrahepatic 5-FU compared
to those with positive staining. Intrahepatic 5-FU had no effect on survival in the DPD
positive group.
DPD was also studied in patients receiving S-1 by Kuramochi et al31. They evaluated DPD
expression in patients with recurrent pancreatic cancer measured by RT-PCR. In 33
patients treated with S-1 and cisplatin after recurrence, they found that patients who
responded to therapy (as measured by CA 19-9) had a mean lower intratumoral DPD
expression.
A larger study of DPD in the adjuvant setting was done by Kondo et al.32 in which 106
patients treated with adjuvant treatment were evaluated retrospectively. They observed
high DPD expression in 37 percent of patients as measured by IHC. Those with low DPD
expression were found to have increased median overall survival if they received S-1 (all
these patients also received gemcitabine). No differences in survival were seen based on
treatment in the high DPD group or in the group not treated by S-1 when divided by DPD
expression. Interestingly, they also evaluated TS expression and did not find any
correlation to OS by treatment.
A similar study done by Kondo et al. evaluated both DPD and hENT1 by IHC in 86 patients
treated with adjuvant S-1 and gemcitabine33. Low DPD and high hENT1 expression were
observed as favorable factors in this study. Those with one or two favorable factors had an
OS benefit when compared to those patients with no favorable factors.
Like TS, DPD may be a useful marker to guide therapy with 5-FU based treatments, but
prospective data are lacking for validation.
5) I would suggest a comment on the potential future role of BRCA1/2 mutations as
predictive biomarkers for PARP inhibitors. This is not related to drug metabolism but since
ERCC1 data was discussed, I will suggest so for BRCA1/2.
RESPONSE:
BRCA2 mutations:
BRCA2 mutations are found in up to 17% of patients with familial pancreatic cancer. The
protein product of the BRCA2 gene plays an important role in the repair of DNA crosslinking damage. It is located on chromosome 13q and is inactivated in fewer than 10
percent of pancreatic cancers. The gene is almost always inactivated by a germline
(inherited) mutation coupled with somatic loss of the second allele 42. It has been suggested
that this function of BRCA2 can be exploited therapeutically. In vitro studies suggest that
pancreatic cancers with genetically inactivated BRCA2 are significantly more susceptible to
DNA cross-linking agents then are pancreatic cancers with a genetically intact BRCA2.
Indeed, several reports have documented remarkable therapeutic responses to DNA crosslinking agents such as mitomycin, cisplatin, or to poly ADP-ribose polymerase (PARP)
43,44.
inhibitors
in
patients
whose
cancers
have
inactivated
BRCA2
6) Irinotecan is being widely used in good PS patients (FOLFORINOX regimen) and some
discussion
on
biomarkers
will
be
appreciated.
RESPONSE:
Uridine diphosphate-glucuronosyltransferase 1A1 (UGT1A1):
Irinotecan as a part of FOLFIRINOX regimen as well as a single agent or with 5-FU
(FOLFIRI) is used by oncologists to treat patients with pancreatic cancer. A novel form of
irinotecan, nanoliposomal irinotecan combined with fluorouracil/folinic acid is recently
approved by FDA for second line treatment of patients who have failed gemcitabine-based
chemotherapy 45. After intravenous administration, irinotecan is converted to its active
metabolite, 7-ethyl-1 o-hydroxycamptothecin (SN-38) by a carboxylesterase. SN-38 is then
detoxified by UGT1A1 enzyme to its inactive form SN-38 glucuronide (SN-38G) which is
excreted into the bile and urine. UGT1A1 is found to be polymorphic and resulted in wide
inter-individual variation in patient's response as well as toxic side effects. Based on this
information, FDA had first approved irinotecan label with pharmacogenetics information in
2005. In 2010, new pharmacogenetic information was added to the label regarding the risk
of neutropenia in patients who had genetic defect of (UGT1A1).
Over 30 genetic variants in the promoter region and exon 1 of UGT1A1 have been identified
which can decrease enzyme activities. These genetic variants have been linked to few
syndromes, such as Gilbert syndrome and Criegler-Najjar. UGT1A1*28 has been reported to
cause approximately 70 per cent reduction of UGT1A enzyme activity. Under-expression of
UGT1A1 enzyme impaired the metabolism of SN-38 to its inactive form (SN-38G) and
caused an excessive accumulation of toxic SN-38.
The French Joint Work group developed a review on the impact of the deficient UGT1A1*28
variant on irinotecan efficacy and toxicity 46. In addition, there are inter-ethnicity
variations. Therefore, physicians caring for these patients should be aware of these genetic
abnormalities. The practical point is that normally we administer irinotecan doses at least
equal to 180 mg/m2, but this dose should be reduced in patients who are known to be
homozygous for theUGT1A1*28 allele.
Reviewer B:
Flores et al. present a review manuscript that addresses the role of tumor’s genomic profile
and drug metabolism as predictive markers for response to each regimen. There are no
major comments.
Minor comment:
1) Introduction, lines 18-19: The phrase “...in the 2nd line setting after gemcitabine alone”
should be corrected to “after gemcitabine-based therapy”, as more than half of the patients
had received gemcitabine combination regimens, in the 1st line.
RESPONSE: Most recently, nanoliposomal irinotecan plus fluorouracil and folinic acid has
shown a survival benefit in the 2nd line setting after gemcitabine-based therapy.
2) It would be useful, if the authors will comment on irinotecan toxicity in relation to the
genetic variations in UGT1A.
RESPONSE:
Uridine diphosphate-glucuronosyltransferase 1A1 (UGT1A1):
Irinotecan as a part of FOLFIRINOX regimen as well as a single agent or with 5-FU
(FOLFIRI) is used by oncologists to treat patients with pancreatic cancer. A novel form of
irinotecan, nanoliposomal irinotecan combined with fluorouracil/folinic acid is recently
approved by FDA for second line treatment of patients who have failed gemcitabine-based
chemotherapy 45. After intravenous administration, irinotecan is converted to its active
metabolite, 7-ethyl-1 o-hydroxycamptothecin (SN-38) by a carboxylesterase. SN-38 is then
detoxified by UGT1A1 enzyme to its inactive form SN-38 glucuronide (SN-38G) which is
excreted into the bile and urine. UGT1A1 is found to be polymorphic and resulted in wide
inter-individual variation in patient's response as well as toxic side effects. Based on this
information, FDA had first approved irinotecan label with pharmacogenetics information in
2005. In 2010, new pharmacogenetic information was added to the label regarding the risk
of neutropenia in patients who had genetic defect of (UGT1A1).
Over 30 genetic variants in the promoter region and exon 1 of UGT1A1 have been identified
which can decrease enzyme activities. These genetic variants have been linked to few
syndromes, such as Gilbert syndrome and Criegler-Najjar. UGT1A1*28 has been reported to
cause approximately 70 per cent reduction of UGT1A enzyme activity. Under-expression of
UGT1A1 enzyme impaired the metabolism of SN-38 to its inactive form (SN-38G) and
caused an excessive accumulation of toxic SN-38.
The French Joint Work group developed a review on the impact of the deficient UGT1A1*28
variant on irinotecan efficacy and toxicity 46. In addition, there are inter-ethnicity
variations. Therefore, physicians caring for these patients should be aware of these genetic
abnormalities. The practical point is that normally we administer irinotecan doses at least
equal to 180 mg/m2, but this dose should be reduced in patients who are known to be
homozygous for theUGT1A1*28 allele.
Editor's comments:
1. Please consider to add tables as suggested by reviewer A as well as 1-2
figures
RESPONSE: All considered; please see response above
2. The references are not according to Journal's style. Please check
RESPONSE: Revised
3. The abstract could be improved, some more information is needed.
RESPONSE: Revised