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Clinical Trials |
Departments of Surgery [D. K-E., C. L., S. K., E. J., M. G., R. J.], Pathology [M. R.], Internal Medicine [C. W., G. S.], Pharmacology [H. S-W.], and Medical Computer Sciences [M. M.], University of Vienna Medical School, A-1090 Vienna, Austria
| ABSTRACT |
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In a series of 67 breast tumors, 19% had TP53 gene mutations, 40% had a positive p53 IHC, and 12% had both. In the FEC group, treatment failure was related to both the presence of TP53 gene mutations (P = 0.0029) and a positive IHC (P < 0.0001). Apoptosis was almost exclusively found in tumors having normal p53 in both parameters (P < 0.0001). In the paclitaxel group, treatment response was neither related to apoptosis nor to normal p53. Combination of sequencing and IHC results revealed a significant association between abnormal p53 and response to paclitaxel (P = 0.011).
We found TP53 mutations, as well as p53 protein overexpression, to be associated with response to chemotherapy. Whereas clinical response to FEC was found to be dependent on normal p53, the cytotoxicity of paclitaxel was related to defective p53. The efficiency of paclitaxel during mitosis might be supported by lack of G1 arrest due to p53 deficiency. Therefore, patients with p53-deficient tumors may benefit from paclitaxel.
| INTRODUCTION |
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The biological functions of the p53 tumor suppressor make it a potential predictive marker. p53 has been observed to function as a transcription factor that regulates normal cell growth by controlling genes that promote progression through the cycle and by controlling those that cause arrest in G1, when the genome is damaged (3) . Active p53 can further promote apoptosis in growth-arrested cells and has been related to the efficient execution of programmed cell death in response to DNA damage in the presence of oncogenic triggers (4) . Intact p53 has been shown to induce apoptosis in response to ionizing radiation, whereas loss of p53 function has been reported to enhance cellular resistance to a number of chemotherapeutic agents (5 , 6) .
Because p53 has been recognized to influence response to chemotherapy, efforts have been undertaken to study its usefulness as a predictive factor in patients (7 , 8) . The majority of studies performed thus far comprised patients receiving adjuvant treatment regarding overall survival as the end point and using IHC3 for p53 analysis. Most of these studies reported a trend but no significant relationship between positive immunohistochemical staining and overall survival (7, 8, 9, 10) .
The combination therapy of FEC is widely used in the treatment of breast cancer (11) . Alkylating substances (cyclophosphamide) as well as anthracyclines (epirubicin) induce DNA damage by cross-linking DNA strands. This results in apoptosis due to p53 activation (12) . Another substance that exhibits significant activity in human tumors, including breast cancer, is paclitaxel (13) . It stabilizes tubulin polymerization, inhibits formation of the mitotic spindle, and leads to cell death (14) . This mechanism is considered not to require the transcriptional activity of p53.
In our study, we analyzed the value of p53 for predicting response to neoadjuvant chemotherapy, using pathological response and apoptosis as end points. We compared a DNA-damaging therapy (FEC) to a microtubule stabilizing therapy (paclitaxel). p53 function was determined by immunohistochemical staining of p53 protein expression and direct DNA sequencing of the entire p53 gene. The p53 findings were correlated with treatment response, and the linkage between p53 function and cellular response was corroborated by an apoptosis assay.
| MATERIALS AND METHODS |
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Neoadjuvant Therapy.
Thirty-five patients received anthracycline-based combination therapy
(FEC) as first-line treatment (600 mg of 5-fluorouracil per square
meter of body surface as a 15-min infusion, 60 mg of epirubicin per
square meter as a 1-h infusion, 600 mg of cyclophosphamide per square
meter as a 1-h infusion, repeated every 21 days for a total of three or
four cycles). FEC was given in full dose for four cycles in 27 patients
and for three cycles in 8 patients.
Thirty-two breast cancer patients were given monotherapy consisting of paclitaxel in escalating doses from 215300 mg per square meter of body surface administered as a 3-h infusion, repeated every 21 days for a total of four cycles in 26 patients and three cycles in 6 patients. Chemotherapy was followed by local surgical treatment in all patients. The reason for surgery after three cycles was lack of compliance partly in connection with toxicity as well as progressive disease (in one patient in the paclitaxel group and in three patients in the FEC group).
Tumor Response.
Tumor diameter was assessed at time of presentation using measurements
from mammography, clinical examination, and ultrasound. Clinical
assessment was recorded monthly, and complete tumor assessment was
repeated before surgery. All patients had subsequent local surgical
treatment. Pathohistological examination of surgical specimen was used
to determine extent of tumor regression. According to Union
International Contre Cancer criteria, CR corresponds to more than a
95% tumor reduction in the product of the two largest tumor diameters
and PR corresponds to more than a 50% tumor reduction. Stable disease
(SD) corresponds to a <50% reduction or less than a 25% increase,
and PD to more than a 25% increase in tumor size. Patients with CR and
PR were grouped together as responders and compared with patients with
SD and PD grouped together as nonresponders.
Tumor Material.
Needle biopsies were taken routinely from the tumors at the time of
presentation. These formalin-fixed and paraffin-embedded biopsies were
used for histological diagnosis, p53 IHC, and p53 gene
analysis.
For apoptosis assay, paraffin-embedded sections from tumors obtained at surgery were used.
DNA Isolation from Paraffin-embedded Tissue.
Depending on the size of the biopsy, three to five unstained sections
of 4-µm thickness were used for DNA extraction. The sections were
mounted on uncoated slides, and tumor tissue was dissected.
Microdissection was not used because tumor content was already
confirmed by pathohistological diagnosis derived from sections of the
same biopsy. The dissected tumor material was subjected to 200 µl of
Xylol (Merck). The mixture was centrifuged at 12,000 rpm for
10 min, and the supernatant was discarded. The remaining pure tissue
was digested with 20 µg/µl proteinase K (Boehringer Mannheim) for
2 h at 65°C. The enzyme was inactivated by incubation at 95°C
for 10 min. DNA was stored at -20°C.
PCR Amplification.
The obtained DNA was usually diluted 1:5. The p53 gene was
amplified in eight different PCRs using DNA primers of 20 bases in
length, placed in the adjacent intron regions of exons 23, 4, 5, 6,
7, 89,10, and 11, as listed previously (15)
.
Amplification was performed in a volume of 50 µl for 45 cycles using 2 µl of diluted DNA and 20 pmol of each sense and antisense primer including, 1.25 units of AmpliTaq Gold DNA polymerase (Perkin-Elmer Corp., Foster City, CA). For DNA Thermal Cycler 480 (Perkin-Elmer Corp.), the following thermal profiles were used: 10-min denaturation (and activation of AmpliTaq Gold) at 95°C, followed by a 1-min 18 s annealing at 64°C, and a 30-s extension at 74°C with slight modifications for exons 2, 3, and 11. The length of the amplification products ranged from 250350 bases. The relative shortness of PCR products is probably the reason for having encountered no difficulties in obtaining PCR products from DNA extracted of 4- to 5-year-old paraffin-embedded tissue. PCR products were analyzed on precast 6% acrylamide/bis-acrylamide gels (Novex, San Diego, CA).
Sequencing.
Enzymatic pretreatment of PCR products and subsequent sequencing was
performed as described previously (16)
. We used the Thermo
Sequinase radiolabeled terminator cycle sequencing kit (United States
Biochemical, Cleveland, OH) for direct sequencing. The reaction mix was
prepared following the instructions provided by the manufacturer, with
some modifications: we added only 1 pmol of the unique primer and used
the forward strand primer for exons 23, 4, 6, 7, 10, 11 and the
reversed strand primers for exons 5 and 89. Every identified mutation
was confirmed in a separate experiment.
p53 IHC.
Histological sections of 4-µm thickness from paraffin blocks were
incubated overnight at 4°C with a 1:50 dilution of the monoclonal
antibody p1801(Oncogene Science, Inc., Uniondale, NY), which recognizes
both wild-type and mutant forms of the p53 protein. The protocol used
was described previously (17)
. As positive and negative
controls, sections from breast cancers with known p53
mutation and immunoreactivity, as well as normal breast tissue, were
included to confirm the consistency of the analysis. A specimen scored
negative when nuclear staining was rare (below 10%) or absent
(18
, 19)
.
Apoptosis Assay (TUNEL).
The immunohistochemical detection of apoptosis in paraffin-embedded
tumor tissue sections was performed by TUNEL staining (Boehringer
Mannheim, Mannheim, Germany). Terminal deoxynucleotidyl transferase
labeling with fluorescein-dUTP was done according to the
manufacturers recommendations. As negative control, all samples were
incubated with a nucleotide mixture lacking terminal transferase. The
tissue sections were counterstained with DAPI
(4',6-diamidine-2'-phenylindole dihydrochloride; Boehringer Mannheim).
Cells carrying fluorescent signals were counted, and the percentages
were calculated.
Statistical Analyses.
Patients who responded to chemotherapy (CR, PR) were compared with
those who were resistant to chemotherapy (SD, PD). Associations between
chemotherapy responders and p53 parameters coming from two analysis
methods (p53 sequencing, p53 IHC) were tested with Fishers exact test
for each method separately and for the combined p53 parameters called
p53 status. The p53 status was defined as negative in tumors with
normal p53 sequence and negative IHC staining and defined as positive
in tumors with either TP53 mutation or positive staining or both. The
probability of recognizing responders and nonresponders correctly
(sensitivity and specificity) was calculated for p53 sequencing, p53
IHC, and for the two combined parameters (p53 status). The accuracy of
p53 status to predict response and resistance in patients with FEC and
paclitaxel treatment is given.
For correlation of response and apoptosis, the percentage of apoptotic
cells was dichotomized (negative value
1.5% and positive >1.5%)
and calculated with Fishers exact test.
The mean cumulative dose per patient for paclitaxel (considering escalating doses and number of cycles) was 1020 mg/m2 in responders and 1017 mg/m2 in nonresponders. To exclude the actually delivered dose as confounding factor for the relation between p53 status and treatment response, the partial correlation of p53 status and response was calculated.
| RESULTS |
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| DISCUSSION |
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Microtubule-stabilizing paclitaxel is considered to have p53-independent effects. However, in vivo and in vitro data concerning the efficiency of paclitaxel and p53 status are controversial (21 , 22) . Response to paclitaxcel has been observed in experiments with tumors known to have p53 mutations and has also been demonstrated to be compromised in cell lines lacking p53 (23, 24, 25) . In our clinical analysis, a negative (normal) p53 status proved to be associated with resistance to paclitaxel, whereas response was supported by deficient p53. Functional p53 has been found to arrest cell cycle in G1 phase to prevent transition into subsequent phases in the presence of DNA damage (26) . For p53-deficient tumor cells it has been shown that this cell cycle checkpoint is bypassed. In the presence of spindle inhibitors, it has been observed that tumor cells lacking p53 were able to repeatedly enter S phase and become polyploid, abrogating the requirement of mitosis before reinitiation of DNA replication (27) . In summary, we speculate that p53-deficient cell populations have a high cycling fraction and that, therefore, paclitaxel, which preferentially acts during the mitosis phase, is highly efficient in cells without functional p53. However, there is an apparent discrepancy between the effects of p53 status on the response of cells to paclitaxel in vivo versus in vitro.
Apoptosis was rarely present in our patients responding to paclitaxel. We did not observe apoptosis in 87% of patients responding to paclitaxel, whereas apoptosis was present in 50% of patients with treatment failure. Thus, we found that treatment resistance was not associated with the absence of apoptosis and treatment response was not related to the presence of apoptosis.
The efficiency of paclitaxel has been attributed to cytostatic and apoptotic effects that seem to be independent (21) . It has been reported that low concentrations of paclitaxel result in apoptosis (28) and that the maximum apoptotic effect can be observed at 10-fold lower drug concentrations as compared with the maximum cytostatic effect (29) . These plasma concentrations have been reported to be at or below clinically achievable concentrations. As paclitaxel was applied in escalating doses in our study, high plasma concentrations might have promoted the cytostatic effect of paclitaxel. This might explain why we rarely observed apoptosis in patients responding to paclitaxel.
Overexpression of the p53 protein has been analyzed in various breast cancer studies. The use of different antibodies, staining standards, tumor material, scores for positivity, and the inclusion of variously selected groups of breast cancer patients might be the reason why the frequency of positive p53 staining ranges from 2050% in the literature (30, 31, 32) . The rate of positive IHC was as high as 40% in our study. At our institution, the p53 IHC is routinely performed in operated breast cancers. In these unselected patients, we observe a positive p53 IHC in about 25%, which is in accordance with most published reports. Hence, excluding technical reasons, we tend to attribute the high rate of positive p53 staining in our study to the selection of patients with advanced stages of breast cancer (T3 and T4 tumors).
The lack of concordance between immunoreactivity and TP53 gene mutation is a matter of discussion and growing interest because p53 is under evaluation as a predictive factor for response to chemotherapy (33 , 34) . In our study, the TP53 mutation rate was 19%, which is in accordance with the published frequencies of breast cancer (35 , 36) . We found IHC to be positive in 16 patients (23% of the total) without evidence of genetic alterations. Originally, positive p53 staining was thought to indicate TP53 gene mutations. Positive staining in tumors without gene mutations was attributed to stabilization of the protein by interruption of degradation and considered to be "false positive." The correlation of the results of IHC to treatment response and tumor cell apoptosis in our study shows that positive IHC staining without gene mutation is of functional importance. However, the exact mechanism leading to a positive IHC staining is still unclear. On the other hand, IHC can be false negative. This finding is typically associated with insertion or deletion mutations, when the antibody binding site of the mutated protein is lost or no protein is produced (30) . Our study supports this observations because 5 of 13 TP53 gene alterations were not reflected by positive IHC staining. The mutations consisted of a one-base deletion, a two-base deletion, a nine-base deletion, a point mutation affecting the splice site, and a complex deletion.
Response assessment using mammography and clinical evaluation can lead to underestimation of therapeutic response due to interpretation of fibrous reaction or persisting calcification as residual tumor. Additionally overestimation of complete response can occur in case of minimal residual disease (37) . Our retrospective analysis included patients from two neoadjuvant trials with subsequent surgical resection. Pathological examination was used to determine the extent of tumor regression to avoid pitfalls of confounding radiological and clinical features. The use of microscopic criteria to assess treatment response is reflected by the small number of CRs that are twice as high in studies without the information from pathohistology.
We have demonstrated that p53 plays a distinct drug-specific role in chemoresistance. The response to a combination of FEC was directly related to normal p53 and tumor cell apoptosis in breast cancer patients. These results provide clinical evidence of a p53-dependent cytotoxic effect of these DNA-damaging agents. In contrast, response to paclitaxel seemed to be related to p53-deficient tumors. We suggest that loss of cell cycle control (lack of G1 arrest) due to p53 deficiency possibly allows tumor cells to more effectively enter the phase of mitosis, thus supporting the tubulin-specific cytotoxicity of paclitaxel. Because the number of patients in our study was small, the results need to be confirmed in larger groups.
| FOOTNOTES |
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1 Supported by the following medical grants:
Medizinisch wissenschaftlicher Fonds des Bürgermeisters der
Bundeshauptstadt Wien, Nr.1361; Kommission Onkologie, Nr.51; and Anton
Dreher Gedächtnis-Schenkung für medizinische Forschung, Nr.
247. ![]()
2 To whom requests for reprints should be
addressed, at Department of Surgery, University of Vienna, Medical
School, Waehringer Guertel 1820, A-1090 Vienna, Austria. Phone:
43-1-40400-5621; Fax: 43-1-40400-6777; E-mail: Daniela.Kandioler{at}akh-wien.ac.at ![]()
3 The abbreviations used are: IHC,
immunohistochemisty; FEC, fluorouracil, epirubicin, and
cyclophosphamide; CR, complete remission; PR, partial remission; SD,
stable disease; PD, progressive disease; TUNEL, terminal
deoxynucleotidyl transferase-mediated nick end labeling. ![]()
Received 4/12/99; revised 10/ 1/99; accepted 10/ 4/99.
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