
[Cancer Research 61, 6459-6466, September 1, 2001]
© 2001 American Association for Cancer Research
Multidrug Resistance-associated Protein 3 Is a Tumor Rejection Antigen Recognized by HLA-A2402-restricted Cytotoxic T Lymphocytes1
Akira Yamada2,
Kouichiro Kawano,
Makoto Koga,
Tomoko Matsumoto and
Kyogo Itoh
Cancer Vaccine Development Division, Kurume University Research Center for Innovative Cancer Therapy [A. Y., K. K., M. K., T. M., K. I.], and Department of Immunology, Kurume University School of Medicine [A. Y., K. I.], Kurume 830-0011, Japan
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ABSTRACT
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The identification of tumor rejection antigens recognized by CTLs and
its application in peptide-based specific immunotherapy against melanomas have been
extensively investigated in the past decade. However, only a small
number of studies regarding these issues in other epithelial cancers
have been reported. In this study, we show that a multidrug
resistance-associated protein 3 (MRP3) is a tumor rejection antigen
recognized by HLA-A2402-restricted CTLs established from T cells
infiltrating into lung adenocarcinoma. MRP3 is expressed in differing
quantities in tumor cells of various tissue types and origins. Four
dominant MRP3-derived antigenic peptides that are recognized by the
CTLs have been identified, each possessing in vitro
immunogenicity. Namely, these four peptides (MRP3503, MRP3692,
MRP3765, and MRP31293) can induce peptide-specific CTLs after
in vitro stimulation with these peptides in peripheral
blood mononuclear cell cultures of HLA-A24+ cancer
patients, with the CTLs expressing cytotoxicity against
HLA-A2402+ MRP3+ tumor cells but not against
either HLA-A2402- or MRP3- target cells. The
peptide specificity of the cytotoxicity of the CTLs was further
confirmed by using peptide-loaded HLA-A24+ EBV-transformed
B cells. Widespread MRP3 expression in various tumor cell lines and
tumor tissues at the mRNA level was confirmed. Furthermore,
reactivities of the MRP3-peptide-induced CTLs against tumor cells
correlated with MRP3 expression in the tumor cells. These results
suggest that MRP3 and its derived peptides described in the present
paper are potential candidates for cancer vaccines in regard to
HLA-A24+ patients with various tumors, particularly for
those tumors that show anticancer drug resistance.
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INTRODUCTION
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In the past decade, the identification of genes encoding tumor
rejection antigens that can be recognized by CTLs has been extensively
investigated (1
, 2)
. Most of these genes are from
melanomas and belong to a family of genes that encode cancer/testis
antigens or melanoma differentiation antigens (1
, 2)
. The
antigenic peptides of these gene products that can be recognized by
CTLs in a class-I HLA-restricted manner have also been identified, and
some of them have been used as a peptide-based cancer vaccine in
clinical trials for patients with melanomas (1
, 2)
.
Although many studies in the field of melanomas have been performed,
only a small number of studies (3, 4, 5, 6, 7, 8, 9, 10)
regarding these
issues in epithelial cancers other than melanomas have been reported.
SART-1, SART-2, and SART-3 have been identified from the cDNA
libraries of squamous cell carcinoma cells using a CTL line established
from a patient with esophageal cancer (6
, 7
, 9)
. SART-1
and SART-2 are preferentially expressed in squamous cell carcinomas
rather than in adenocarcinomas, whereas the expression of SART-3 is
more widespread in both squamous cell carcinomas and adenocarcinomas.
Cyclophilin B and ART-4 are identified using a CTL line
established from a patient with lung adenocarcinoma (8
, 10)
. Both the molecules are ubiquitously expressed in normal and
cancer tissues at mRNA levels, although the expression of ART4 at
protein levels has been rarely observed in normal cells. These
molecule-derived antigenic peptides that can be recognized by
tumor-specific CTLs in a HLA-A24-restricted manner have been reported
(6, 7, 8, 9, 10)
. Furthermore, Phase I clinical trials using these
peptides as cancer vaccines in patients with various cancers, such as
lung, esophagus, and colon cancers, have begun in Kurume
University Hospital.
At the present time, chemotherapy is one of the major treatment
modalities for patients with cancer. However,
MDR3
is a serious problem associated with this therapy. MDR is a phenomenon
in which cancer cells acquire cross-resistance to a variety of
structurally unrelated cancer chemotherapeutic agents after selection
for resistance to a single anticancer agent (11)
. This
phenomenon is observed not only in vitro but also in
vivo and often results in cancer treatment failure. In the present
study, we report that MRP3 is a tumor rejection antigen recognized by
CTLs in an HLA-A2402-restricted manner. We discuss the potential
application of MRP3-derived peptides as cancer vaccines in specific
immunotherapy.
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MATERIALS AND METHODS
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Cell Lines.
A lung adenocarcinoma cell line, 11-18, was used for preparation of the
cDNA library. COS7, VA13 (fibroblast), 293T, and C1R-A2402 (an
HLA-A2402 transfectant) cells were used for the transfection and
peptide-pulse experiments, respectively. C1R-A2402 cells were kindly
provided by Dr. Masafumi Takiguchi (Kumamoto University,
Kumamoto, Japan). The other cell lines used in this study were as
follows: lung adenocarcinomas (PC-9, A549, LC-1, RERF-LCMS, and 1-87),
lung squamous cell carcinomas (Sq-1, RERF-LCA1, QG56, and LC1-Sq), lung
small cell carcinoma (LK79), renal cell carcinomas (Kur-11, Caki-1,
PC93, RC30-14, PC3, VMRC-RCW, TUHR-4TKB, TUHR-10TKB, RCC-10RGB, and
LNCap), ovarian cancers (KOC-3S, KOC-5C, KOC-7C, TYK-nu, RMUG-S, RMG-I,
TOC-2, MCAS, RTSG, and RKN), bladder carcinoma (HT1376), esophageal
squamous cell carcinoma (KE4), and EBV-transformed B-cell line
(SS-EBB). The origins and HLA genotypes of these cell lines have been
described previously (9
, 10)
.
Identification of the MRP3 Gene.
The expression-gene cloning method was used to identify a gene that
encodes tumor rejection antigens recognized by the CTL line, GK-CTL, as
reported elsewhere (6
, 10)
. Briefly, mRNA of the 11-18
lung adenocarcinoma cells was converted to cDNA, ligated to
SalI adapter, and inserted into the expression vector
pCMV-SPORT2.0 (Life Technologies, Inc., Gaithersburg, MD). A
total of 1 x 105 clones from the
cDNA library of the 11-18 cells was divided into 1000 wells (the
expected number of clones/well was 100) and subjected to the first
screening. Purified DNA from the divided pools and 100 ng of
HLA-A2402 cDNA were cotransfected into VA13 cells and
analyzed for their activity to stimulate IFN-
production by the
GK-CTLs. Nineteen positive pools were obtained from the first screening
and subdivided into smaller pools for further screening. Finally, one
cDNA clone, clone 5, was obtained. DNA sequencing was
performed using the dideoxynucleotide sequencing method employing an
AutoRead Sequencing Kit (Pharmacia Biotech, Uppsala, Sweden) and
analyzed using an ALF express DNA Sequencer (Pharmacia Biotech).
The nt sequence of clone 5 was almost identical to that of
MRP3 (accession nos. Y17151, AF104943, AF085692, AF085690, AF009670,
and NM003786).
Northern Blot Analysis.
Total RNA (5 µg/lane) extracted from various cells or tissue
specimens using RNA zol B (TEL-TEST, Friendswood, TX) was separated on
formaldehyde-agarose gel and transferred to nylon membranes
(Hybond-N+; Amersham, Buckinghamshire, United
Kingdom). The membranes were further hybridized overnight at 65°C in
a hybridization buffer [7% SDS, 1 mM EDTA, and 0.5
M NaH2PO4 (pH
7.2)] containing a 32P-labeled 800-bp fragment
of XhoI and EcoRI cut clone 5 cDNA as
a probe. The membranes were washed three times at room temperature and
once at 65°C with a washing buffer [1% SDS and 40
mM
NaH2PO4 (pH 7.2)] and then
autoradiographed. Human ß-actin cDNA (Clontech,
Tokyo, Japan) was also used as a control probe. The relative expression
of the MRP3 mRNA was calculated using the following formula:
index = (MRP3 density of a
sample/ß-actin density of a sample) x (ß-actin density of the 11-18 cells/MRP3
density of the 11-18 cells).
Peptides and Assays.
Thirty-one different synthetic peptides (purity, >70%) derived from
the deduced aa sequence of MRP3 with binding motifs for HLA-A2402
molecules as described in the literature (12)
, including
motifs of tyrosine or phenylalanine at position 2 and of isoleucine,
leucine, phenylalanine, or tryptophan at position 9, searched using
BIMAS (BioInformatics and Molecular Analysis Section, NIH)
software (Center for Information Technology, NIH, Bethesda, MD) were
obtained from Sawady (Tokyo, Japan). An HIV-derived peptide
(RYPLTFGWCF) capable of binding to HLA-A2402 molecules was used as a
negative control (8)
. Peptides of >95% in purity were
used for experiments regarding dose dependency and CTL induction. The
estimated scores of half-time of dissociation of each MRP3 peptide for
HLA-A24-molecules were calculated using BIMAS software
(13)
. For detection of antigenic peptides recognized by
the GK-CTLs, the peptides were loaded onto C1R-A2402 cells by
incubation at a concentration of 10 µM, unless stated
otherwise. Two h later, the supernatant was removed, and the GK-CTLs
(1 x 105) were added to the
culture, incubated for an additional 18 h, and the concentration
of IFN-
in the culture supernatants was measured by ELISA (the limit
of sensitivity, 10 pg/ml) in triplicate assays. Two-tailed Students
t test was used for statistical analysis.
CTL Induction by Peptides.
PBMCs (1 x 105/well) obtained
from HLA-A2402+ healthy donors or cancer patients
were incubated with 10 µM of the peptide in a 96-well
plate in the presence of 100 units/ml interleukin-2 at day 0 as
reported previously (10)
. At culture days 3, 6, and 9, the
cells were restimulated by 10 µM of the peptide. The
culture supernatant of each well was removed, resuspended in fresh
medium, and separated into two wells. Each of the two wells was
stimulated with the corresponding peptide or control HIV-peptide. After
18 h of culture, the concentration of IFN-
in the culture
supernatants was measured by ELISA in triplicate assays. The
concentration of IFN-
in the supernatant of the assay culture
stimulated by control HIV peptide-loaded C1R-A2402 cells or
HLA-A24+ tumor cells (11-18, Sq-1) was subtracted
from that of specific peptide-loaded C1R-A2402 cells or that of
HLA-A24- QG56 cells, respectively. For
cytotoxicity tests, the cells were further cultured in a 96-well
U-bottomed microculture plate in the presence of irradiated autologous
PBMCs (2 x 106 cells/well) as
antigen-presenting cells that had been pulsed by a corresponding
peptide. The cells were stimulated with the peptide without
antigen-presenting cells at days 3 and 7 of the second culture, and the
cells were further cultured with interleukin-2 alone. The cells were
harvested at culture days 2842, and the cytotoxic activity was
measured using a standard 6-h 51Cr-labeled
release assay at different E:T ratios as reported previously
(10)
.
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RESULTS
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Identification and Characterization of the
MRP3 Gene.
The CTL line used for identification of the MRP3 gene
was the HLA-A24-restricted and tumor-specific CTL (GK-CTL) line with
CD3+CD4-CD8+
phenotype that was established from T cells infiltrating into the lung
adenocarcinoma, and its characteristics have been reported elsewhere
(8)
. Reactivities of the GK-CTLs to various tumor cells
are described previously (8)
. Briefly, the GK-CTLs
recognized HT1376 (HLA-A2402/-A2402) bladder cancer cells and 11-18
(HLA-A0201/-A2402), PC9 (HLA-A0206/-A2402), and Sq-1 (HLA-A1101/-A2402)
lung cancer cells when assessed by an IFN-
production, whereas none
of HLA-A2402- cells, including COS-7 and VA13
cells, stimulated GK-CTLs. The 11-18 lung adenocarcinoma cells were
used as a source of cDNA library. A total of 105
cDNA clones from the cDNA library of the 11-18 cells were tested for
their ability to stimulate IFN-
production by the GK-CTLs after
cotransfection with HLA-A2402 cDNA into the VA13
cells. After repeated cycles of the screening, one clone, clone
5, was confirmed to encode a tumor antigen recognized by the
GK-CTLs when cotransfected with HLA-A2402, but not with
control HLA-A2601 (Fig. 1)
. The vacant vector, pCMVSPORT2, served as a negative
control in this experiment.
Clone 5 contained a 4948-bp-long cDNA insert with 4365 bp of
open reading frame encoding 1455 aas. The obtained nt sequence was
identical to those of MRP3 (European Molecular Biology
Laboratory/GenBank/DNA Data Bank of Japan accession no.
AF085690) but lacked the 5' end; i.e., the nt sequence of
clone 5 corresponds to position 175-5142 of the MRP3 cDNA,
whereas the predicted aa sequence of clone 5 lacked position
1-73 of the MRP3 protein. The reading frame of clone 5 was
identical to that of MRP3, thus indicating that clone
5 encodes a large part of the MRP3 protein. Two alternative
splicing variants of MRP3, MRP3A, and MRP3B have been reported
(14)
. However, the nt sequence of clone 5
differed from those of the two variants.
Identification of MRP3-derived Antigenic Peptides Recognized by the
CTLs.
Each of the 31 different MRP3-derived synthetic peptides with binding
motifs to HLA-A2402 molecules was loaded onto an HLA-A2402 stable
transformant, C1R-A2402 cells, at a concentration of 10
µM, and its ability to induce IFN-
production by
GK-CTL was tested. Four of these peptides, MRP3-503, MRP3-692,
MRP3-765, and MRP3-1293, induced significant levels of IFN-
production (Fig. 2A)
in a dose-dependent manner (Fig. 2B)
. The
optimal concentration of the four peptides for loading C1R-A2402 cells
varied in each peptide ranging from 0.11 µg/ml (compatible to
0.11 µM). The binding affinity of the four
peptides to the HLA-A2402 molecules is relatively intermediate. The
estimated score of half-time of dissociation of each peptide ranged
between 90 to 240 (Fig. 2A)
.
Induction of CTLs by the MRP3-derived Peptides.
The four peptides, MRP3-503, MRP3-692, MRP3-765, and MRP3-1293, were
tested for their ability to induce CTLs in the PBMC cultures of nine
HLA-A24+ patients with cancer (three with lung
adenocarcinomas, four with renal cell carcinomas, and two with colon
adenocarcinomas) and three HLA-A24+ healthy
donors. The PBMCs were stimulated four times every 3 days by one of the
four peptides, and their reactivities to the peptide-loaded C1R-A2402
cells or HLA-A24+ tumor cells were examined.
Representative results are shown in Fig. 3A
. The PBMCs of a patient with lung adenocarcinoma (patient
LC2) cultured with any of the four peptides produced significant levels
of IFN-
in response to the corresponding peptide-loaded C1R-A2402
cells in this case (Fig. 3A
, left). EBV-derived
peptide, which can bind to HLA-A2402 molecules, also induced
EBV-peptide reactive T cells in the culture, whereas HIV-derived
HLA-A2402 binding peptide did not induce the specific T cells after
being stimulated four times. The PBMCs cultured with any of the
MRP-peptides were also reactive to HLA-A24+ lung
cancer cells Sq-1 (Fig. 3A
, right). Reactivity of
the EBV-stimulated PBMCs was similar to that of unstimulated PBMCs (no
peptide). These results suggest that the four MRP3-derived peptides can
induce peptide-specific T cells in the PBMC culture of a lung cancer
patient.

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Fig. 3. Induction of CTLs by the MRP3-derived peptides. The four
peptides, MRP3-503, MRP3-692, MRP3-765, and MRP3-1293, were tested for
their ability to induce CTLs in the PBMC cultures of
HLA-A24+ cancer patients. The PBMCs were stimulated four
times every 3 days with one of the four MRP3-peptides or control
peptides (EBV for positive and HIV for negative controls), and their
reactivities to the peptide-loaded C1R-A2402 cells or
HLA-A24+ tumor cells were examined. Representative results
of the PBMC culture of lung adenocarcinoma patient LC2 are shown.
A, cells of the indicated peptide-stimulated PBMC
culture were restimulated by the same peptide used for the CTL
induction (left) or with HLA-A24+ Sq-1 lung
cancer cells (right), and the culture supernatant was
harvested for the measurement of IFN- production. Values represent
the means of triplicate assays. The background of IFN- production by
the cells in response to peptide-unloaded C1R-A2402 cells
(left) or HLA-A24- QG56 lung cancer cells
(right) was subtracted from the values. Two-tailed
Students t test was used for the statistical analysis
between IFN- production by the cells in response to corresponding
peptide-loaded C1R-A2402 cells or Sq-1 cells and that in response to
unloaded C1R-A240 2 cells or QG56 cells, respectively. *,
P < 0.05. B, specificity
of the peptide-induced CTLs. The MRP3 or control EBV peptide-induced
CTLs were stimulated by the indicated peptides, and the culture
supernatant was harvested for the measurement of IFN- production.
Values represent the means of triplicate assays. Data processing and
statistics are shown in A.
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The specificity of the peptide-induced T cells was further analyzed.
Reactivities of the peptide-induced T cells to C1R-A2402 cells loaded
with each of the four MRP3-peptides or control EBV- and HIV-peptides
were assessed in terms of IFN-
production (Fig. 3B)
. The
MRP3-503 peptide-induced T cells in the PBMC culture of patient LC2
produced significant levels of IFN-
in response to stimulation by
MRP3-503-loaded C1R-A2402 cells. Stimulation by the other
MRP3-peptide-loaded or control EBV- and HIV-peptide-loaded C1R-A2402
cells did not elicit significant levels of IFN-
production by the
MRP3-503-induced T cells. Thus, the T cells were specific for the
MRP3-503 peptide used for the induction. Similar results were also
observed in the other three MRP3-peptide-induced T cells and control
EBV-peptide-induced T cells. HIV-peptide-induced T cells in the PBMCs
did not show reactivity against any of the peptides used in this study
including HIV-peptide.
A summary of the results of CTL induction by the MRP3-peptides in the
PBMC cultures of nine patients with cancer and three healthy donors is
shown in Fig. 4
. The EBV-peptide used as a positive control efficiently induced
peptide-specific T cells in the PBMC cultures of seven of the nine
patients with cancer and one of the three healthy donors (Fig. 4A)
. In contrast, the HIV-peptide used as a negative control
did not induce HIV-peptide-specific T cells in any of the PBMC cultures
used in this experiment. The MRP3-503 induced peptide-specific T cells
in the PBMC cultures of one lung cancer patient (LC2) and three
patients with renal cell carcinomas (RCC1-3). The apparent induction of
peptide-specific T cells was also observed in the PBMC cultures
stimulated by the other three MRP3 peptides. The peptide-reactive T
cells specific for MRP3-692, MRP3-765, and MRP3-1293 were induced in
the PBMC cultures of two (LC2 and RCC2), four (LC2, RCC3, and colon
cancer patients, CC1 and CC2), and three (LC2, RCC1, and CC2) cancer
patients, respectively. The MRP3-765 induced peptide-specific T cells
in the PBMC culture of healthy donor HD1. Reactivities of the
peptide-induced T cells to the HLA-A24+ Sq-1 lung
cancer cells are shown in Fig. 4B
. Similar to the
peptide-specific T cells, MRP3-peptide-induced T cells also reacted to
the Sq-1 cells. In contrast, the EBV- or HIV-peptide-induced T cells
did not react to the Sq-1 lung cancer cells (data not shown).

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Fig. 4. Summary of the results of CTL induction by the MRP3
peptides. PBMCs of nine HLA-A24+ patients with cancer
(three with lung adenocarcinomas, four with renal cell carcinomas, and
two with colon adenocarcinomas) and three HLA-A24+ healthy
donors were subjected to CTL induction by the MRP3 peptides or control
EBV and HIV peptides. The reactivities of the cells to specific
peptide-loaded C1R-A2402 cells (A) or
HLA-A24+ Sq-1 lung cancer cells (B) were
shown. Experimental details are the same as those described in Fig. 3
.
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The cytotoxic activities of the MRP3-peptide-induced T cells were
further examined. The MRP3-peptide-induced T cells specific to the
peptide used for their induction in the PBMC cultures of cancer
patients were restimulated by the specific peptide and
HLA-A24+-irradiated PBMCs and grown to obtain a
sufficient number of cells for the cytotoxicity assay. Representative
results against tumor cells are shown in Fig. 5A
. The MRP3-peptide-induced T cells lysed
HLA-A24+ lung cancer cells, Sq-1, and/or 11-18
cells in an E:T ratio-dependent manner, whereas none of the T cells
induced by the MRP3 peptides killed the
HLA-A-24- QG56 cells. Control
EBV-peptide-induced T cells did not show cytotoxicity against any
target used in this experiment. These results suggest that the
MRP3-peptide-induced T cells not only specifically react to the
original peptide used for their induction, but also recognize
HLA-A24+ tumor cells, and result in lysis of the
tumor cells in an HLA-A24-restricted manner. The cytotoxicity of the
MRP3-peptide-induced CTLs against HLA-A24+
EBV-transformed B-cell line was further examined (Fig. 5B)
.
An HLA-A24+ EBV-transformed B-cell line, SS-EBB,
was used as target cells. None of the MRP3-peptide-induced CTLs lysed
the SS-EBB cells. In contrast, EBV-peptide-induced T cells lysed
SS-EBB. The effect of peptide loading to the SS-EBB on the cytotoxicity
of the peptide-induced CTLs was analyzed. The MRP3-503-induced CTLs
lysed the MRP3-503 peptide-loaded SS-EBB cells only in an E:T
ratio-dependent manner, and MRP3-765 or control HIV-peptide-loaded
SS-EBB cells were not lysed by the CTLs. In an opposite manner, the
MRP3-765-induced CTLs lysed only MRP3-765-loaded SS-EBB cells (Fig. 5B)
. Similar peptide-specific lysis was observed in the
other two MRP3-peptide-induced CTLs (data not shown).

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Fig. 5. Cytotoxic activities of the MRP3 peptide-induced CTLs.
The peptide-induced CTLs shown in Fig. 5
were restimulated by the
specific peptide and HLA-A24+ irradiated PBMCs and grown to
obtain a sufficient number of cells for the assay. Representative
results of PBMC culture of lung cancer patient LC2 (MRP3-503 and
MRP3-765-induced CTLs) and renal cancer patient RCC1 (MRP-692,
MRP-1293, and EBV-induced CTLs) are shown. A,
cytotoxicity of the cells against HLA-A24+ lung cancer
(Sq-1 and 11-18) and HLA-A24- lung cancer (QG56) cells was
measured by a 6-h 51Cr-labeled release assay at different
E:T ratios. Values represent the means of triplicate assays. Two-tailed
Students t test was used for the statistical analysis
between the percentage lysis of Sq-1 or 11-18 cells and that of QG56
cells. *, P < 0.05. B,
effect of peptide loading on the cytotoxicity of the cells against
HLA-A24+ EBV-transformed B-cells (SS-EBB). The MRP3
peptides or control HIV peptide (10 µM) were loaded on
SS-EBB cells and used as target cells for the cytotoxicity assay. A
two-tailed Students t test was used for the
statistical analysis between the percentage lysis of peptide-loaded
SS-EBB cells and that of unloaded SS-EBB cells. *,
P < 0.05. Other details of the
experiment are same as A.
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Expression of MRP3 mRNA in Various Tumor Cell Lines.
The expression of MRP3 in various tumor cell lines and tumor tissues at
the mRNA levels was analyzed by Northern blotting (Fig. 6)
. The relative index of this expression is shown in Table 1
. MRP3 was expressed in all of the tested lung cancer cell lines
(n = 10), ovarian cancer cell lines
(n = 10), and 8 of the 10 renal cancer cell
lines. In contrast, its expression levels were very low in noncancerous
cell lines, COS-7, VA13, and 293T cells, or the EBV-transformed B-cell
line, SS-EBB. Widespread MRP3 expression in tumor cells of various
tissue types and origins was also confirmed in tumor tissue specimens.
Namely, MRP3 was expressed in all of the tested specimens of various
tissue types and origins from patients with different clinical stages;
lung cancers (n = 6), renal cancer
(n = 1), colon cancers
(n = 2), gastric cancers
(n = 4), ovarian cancers
(n = 2), esophageal cancer
(n = 1), and oral cancer
(n = 1).

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Fig. 6. Northern blot analysis of MRP3 expression in various tumor
cell lines (A) and tumor tissues (B).
Total RNA was separated on formaldehyde-agarose gel and transferred to
nylon membranes. The membranes were further hybridized with
32P-labeled fragment of clone 5 and control
ß-actin cDNA. Representative results are shown in this figure.
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Whether the expression of MRP3 in tumor cells correlates with IFN-
production by MRP3-derived peptide-specific CTLs, the reactivity of the
MRP3-peptide-induced CTLs against MRP3+ and
MRP3- tumor cells was further examined.
Representative results of the reactivities of the MRP3-peptide-induced
CTLs against HLA-A24+ MRP3+
(Sq-1, TUHR-10TKB), HLA-A24+
MRP3- (Caki-1), HLA-A24-
MRP3+ (QG56), and HLA-A24-
MRP3- (KUR-11) tumor cells are shown in Fig. 7A
. The MRP3-peptide induced CTLs reacted to
HLA-A24+ MRP3+ (Sq-1,
TUHR-10TKB) tumor cells, whereas the CTLs induced by the MRP3-peptides
recognized neither HLA-A-24- nor
MRP3- tumor cells. Peptide loading of the
MRP3-peptides, but not of the control HIV-peptide, onto
HLA-A24+ MRP3- Caki-1
cells led the CTLs to produce IFN-
in a dose-dependent manner (Fig. 7B)
. These results suggest that MRP3 expression in target
tumor cells correlates to IFN-
production by MRP3-derived
peptide-specific CTLs.

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Fig. 7. Reactivity of the MRP3-peptide-induced CTLs against
MRP3+ and MRP3- tumor cells. A,
representative reactivities of PBMC culture of lung cancer patient LC2
(MRP3-692-, MRP-765-, and MRP-1293-induced CTLs) against
HLA-A24+ MRP3+ (Sq-1, TUHR-10TKB),
HLA-A24+ MRP3- (Caki-1), HLA-A24-
MRP3+ (QG56), and HLA-A24- MRP3-
(KUR-11) tumor cells are shown. Values represent the means of
triplicate assays. The background of IFN- production by the CTLs
alone was subtracted from the values. Two-tailed Students
t test was used for the statistical analysis between
IFN- production by the CTLs in response to indicated cells and that
in response to QG56 cells. *, P < 0.05. MFI, mean fluorescence intensity.
B, effect of peptide-loading onto the target tumor cells
on IFN- production by the CTLs. Representative reactivities of
MRP3-692-induced CTLs against MRP3-692 or control HIV-peptide loaded
tumor cells are shown.
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DISCUSSION
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This study demonstrated that MRP3-derived peptides are tumor
antigenic epitopes recognized by HLA-A24-restricted and tumor-specific
CTLs established from T cells infiltrating into lung adenocarcinoma.
Furthermore, we demonstrated that these MRP3-derived peptides could
induce tumor-specific CTLs in the PBMC cultures of cancer patients in
an HLA-A24-restricted manner.
The MRP family consists of at least seven ABC transporters, several of
which have been demonstrated to transport amphipathic anions and to
confer in vitro resistance to chemotherapeutic agents
(15, 16, 17, 18)
. Two prominent members of the ABC superfamily of
transmembrane proteins, MDR1 P-glycoprotein (ABCB1) and MRP1 (ABCC1),
can mediate the cellular extrusion of xenobiotics and anticancer agents
from normal and tumor cells (11
, 15, 16, 17
, 19)
. MRP1 is a
glutathione conjugate pump or multispecific organic anion transporter
(20)
. MRP1 can mediate the transport of negatively charged
hydrophilic compounds with large hydrophobic moieties such as
glutathione S-, glucuronide, and sulfate conjugates of drugs
(20, 21, 22, 23)
. MRP1 is not only involved in reducing the
passage of drugs across the membrane and some specialized epithelia
(24
, 25)
but is also the major transporter for endogenous
leukotriene C4, an important mediator of inflammatory response
(26
, 27)
. The roles of other members (MRP2-6, ABCC2-6) of
the MRP family in MDR have been reported (28, 29, 30)
. MRP2
has been shown to confer low-level resistance to the anticancer drug
cisplatin, etoposide, vincristine, and methotrexate
(31, 32, 33)
, MRP3 to etoposide, vincristine, and methotrexate
(28
, 34
, 35)
, MRP4 to acyclic nt phosphonates, such
as 9-(2-phosphonylmethoxyethyl) guanine, and anti-HIV drug
9-(2-phosphonylmethoxyethyl) adenine (36)
, and MRP5 to
thiopurine drugs, 6-mercaptopurine and thioguanine, and
9-(2-phosphonylmethoxyethyl) adenine (37)
. No resistance
against anticancer or antiviral drugs has been reported for MRP6 and
MRP7 at the present time.
The expression of several MRP genes at mRNA levels
can be up-regulated after selection by anticancer drugs
(15, 16, 17)
. Up-regulation of MRP3 expression has been
observed in several cell lines after selection with doxorubicin,
regardless of the apparent lack of correlation of the mRNA
levels with resistance to either doxorubicin or cisplatin
(29)
. In the present study, we demonstrated that
MRP3 was expressed in most cell lines derived from lung cancers,
ovarian cancers, and renal cancers at the mRNA levels. In contrast, the
MRP3 message was very low in nontumorous cell lines (COS-7, VA13, and
293T) or EBV-transformed B cells (Table 1)
. MRP1 and MRP5 are
ubiquitously expressed in normal tissues, whereas MRP3 expression in
normal tissues is restricted to the liver, duodenum, colon, and adrenal
gland at relatively high levels and to the lung, kidney, bladder,
spleen, stomach, pancreas, and tonsil at low levels (29)
.
Many genes encoding tumor antigens recognized by CTLs have been
identified from melanoma cDNA (1
, 2)
. CTL-directed tumor
antigens have also been identified from tumors other than melanomas,
including HER2/neu (3
, 4)
, prostate-specific
antigen (5)
, SART-13 (6
, 7
, 9)
, ART4
(10)
, and cyclophilin B (8)
, with some of
these antigen-derived peptides being currently under Phase I clinical
trials for development as cancer vaccines. The results shown in this
study suggest that MRP3-derived peptides are possible candidates for
cancer vaccines. MRP3 is a unique target molecule for cancer vaccines
because the expression of MRP3 is associated with MDR, the most
important problem in chemotherapy. As described above, MRP3 was
expressed in most cancer cell lines tested, and overexpression of the
MRP3 was observed in several tumor cell lines after acquisition of MDR
(29)
. These results suggest that immunotherapy with
MRP3-derived peptide vaccine is advantageous for MDR-acquired tumors.
Patients with renal cancer may be particularly suitable subjects for
the MRP3-peptide vaccine, because renal cancer is generally resistant
to chemotherapy and radiation therapy. Our results regarding CTL
induction by MRP3-peptides in the PBMC cultures of patients with renal
cancer supported this suggestion. Namely, the MRP3-peptides induced
tumor-specific CTLs in the PBMC cultures of three of the four patients
with renal cancer tested. Furthermore, immunotherapy using
MRP3-peptides in combination with chemotherapy might be possible if the
immunosuppression induced by the chemotherapeutic agents is not severe
in the patient. The effectiveness of the combination of humanized
monoclonal antibody-mediated immunotherapy in accompaniment with
chemotherapy for treatment of breast cancer and B-cell lymphoma has
already been reported (38, 39, 40)
.
Because of the relatively high level expression of MRP3 in normal
tissues, particularly the liver, duodenum, colon, and adrenal gland,
these organs are possible targets of adverse effects of specific
immunotherapy. However, it should be noted that no severe adverse
effects in the normal tissues or organs have been reported in the
clinical trials of cancer vaccines specific to the MAGE-1, MAGE-3,
Melan-A, gp100, tyrosinase, and NY-ESO-1 in melanoma patients,
although these molecules are expressed in the normal testis, retina, or
melanocytes at both mRNA and protein levels (41, 42, 43, 44, 45, 46)
.
Similarly, no severe adverse effects on the function of normal organs
have been observed in our clinical trials of peptide cancer vaccines,
although some of the target molecules are ubiquitously expressed in
normal
organs.4
Processing of the antigenic peptides in proteasomes of normal cells may
differ from that of tumor cells in these cases. Alternatively, some
molecules in normal cells, including a family of serpins (a group of
serine-protease inhibitors), might be involved in normal cell
resistance to CTL-mediated lysis (47)
.
The HLA-A24 allele is found in 60% of Japanese (with
95% of these cases being genotypically A2402), in 20% of Caucasians,
and in 12% of Africans (48)
. The four MRP3-derived
peptides were able to induce HLA-A24-restricted and tumor-specific CTLs
in the PBMCs of cancer patients. These MRP3 peptides might be
appropriate molecules for use in specific immunotherapy for
HLA-A24+ patients with various cancers.
 |
FOOTNOTES
|
|---|
The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
1 Supported in part by a Grant-in-Aid from the
Ministry of Education, Science, Sports, and Culture of Japan
(12670583), and a Grant-in-Aid for the Second Term Comprehensive
10-year Strategy for Cancer Control from the Ministry of Health and
Welfare, Japan (H12-cancer-025). 
2 To whom requests for reprints should be
addressed, at Cancer Vaccine Development Division, Kurume University
Research Center for Innovative Cancer Therapy, Asahi-machi 67, Kurume
830-0011, Japan. Phone: 81-942-31-7744; Fax: 81-942-31-7745; E-mail: akiymd{at}med.kurume-u.ac.jp 
3 The abbreviations used are: MDR, multidrug
resistance; MRP, MDR-associated protein; aa, amino acid; nt,
nucleotide; PBMC, peripheral blood mononuclear cell; ABC, ATP-binding
cassette. 
4 Manuscript in preparation. 
Received 3/26/01.
Accepted 6/21/01.
 |
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