Topoisomerase II-␣ Expression in Different Cell Cycle Phases in Fresh Human Breast Carcinomas Kenneth Villman, M.D., Elisabeth Ståhl, M.S., Göran Liljegren, M.D., Ph.D., Ulf Tidefelt, M.D., Ph.D., Mats G. Karlsson, M.D., Ph.D. Departments of Oncology (KV), Pathology (ES, MGK), Surgery (GL), and Medicine (UT), Örebro University Hospital, Örebro, Sweden; and Karolinska Institute (UT), Stockholm, Sweden cluded in most adjuvant chemotherapy regimens Topoisomerase II-␣ (topo II␣) is the key target en- for breast cancer. Anthracyclines belong to the an- zyme for the topoisomerase inhibitor class of anti- ticancer agents called topoisomerase (topo) II cancer drugs. In normal cells, topo II␣ is expressed inhibitors. predominantly in the S/G2/M phase of the cell cycle. Topoisomerases are enzymes, present in the nu- In malignant cells, in vitro studies have indicated clei in mammalian cells, that regulate topological that the expression of topo II␣ is both higher and changes in DNA that are vital for many cellular less dependent on proliferation state in the cell. We processes such as replication and transcription (5). studied fresh specimens from 50 cases of primary They perform their function by introducing tran- breast cancer. The expression of topo II␣ in differ- sient protein-bridged DNA breaks on one (topo- ent cell cycle phases was analyzed with two- isomerase I) or both DNA strands (topoisomerase parameter flow cytometry using the monoclonal II; 6). There are two isoenzymes of topoisomerase antibody SWT3D1 and propidium iodide staining. II, with genetically and biochemical distinct fea- ␣ The expression of topo II was significantly higher tures. Topoisomerase II-␣ (topo II␣), with a molec- in the S/G2/M phase of the cell cycle than in the ular weight of 170 kd, is located on chromosome 17 G0/G1 phase in both DNA diploid and DNA nondip- (7), and topoisomerase II-␤ (topo II␤), with a mo- loid tumors. In 18 of 21 diploid tumors, and in 25 of lecular weight of 180 kd, is located on chromosome ␣ 29 nondiploid tumors, >50% of the topo II –posi- 3 (8). Topo II␣ is the primary drug target for anthra- tive cells were in the G0/G1 phase. This significant cyclines (6, 9). ␣ expression of topo II in the G0/G1 phase of the cell Topoisomerase II inhibitors inhibit the rejoining cycle may have clinically important implications for step in the breakage-rejoining cycle of topo II␣ and treatment efficacy of topoisomerase II inhibitors. thereby shift the equilibrium toward a key covalent reaction intermediate termed the cleavable complex KEY WORDS: Breast cancer, Cell cycle, DNA flow (10). This leads to double-stranded DNA breaks, ␣ cytometry, Topoisomerase II . which can, by a partly unknown mechanism, lead to Mod Pathol 2002;15(5):486–491 cell death (11). In vitro studies on cell lines from different human malignancies has shown that sensi- Breast cancer is the most common cancer among tivity to topoisomerase II inhibitors is dependent on women in Sweden and in the United States, and the the cellular level of topo II␣ (12–14). disease is fatal to every fourth woman despite wide Topo II␤ is expressed relatively constantly through- use of adjuvant chemotherapy (1–3). The limited out the cell cycle in both normal and transformed efficacy of chemotherapy is due to intrinsic or ac- cells (15, 16). In cell lines, it has been shown that in quired resistance to the drugs in use. Anthracy- normal cells, topo II␣ is a marker of proliferation and clines are the most active chemotherapeutic agents that expression is restricted to S and G2/M phases of in advanced breast cancer (4) and are today in- the cell cycle, whereas in transformed cells, the topo II␣ expression is both higher and less dependent on proliferation state in the cell (15, 17–21). The altered Copyright © 2002 by The United States and Canadian Academy of topo II␣ distribution may be caused by prolonged Pathology, Inc. VOL. 15, NO. 5, P. 486, 2002 Printed in the U.S.A. intracellular half-life of topo II␣ associated with the Date of acceptance: January 23, 2002. This study was supported by grants from the Research Committee of malignant transformation (17). This dysregulation of Örebro County Council, Sweden. the expression of topo II␣ in the cell cycle in malig- Address reprint requests to: Kenneth Villman, M.D., Department of On- cology, Örebro University Hospital, S-701 85 Örebro, Sweden; e-mail: nant cells may have implications for the efficacy of [email protected]; fax: 46-19-101768. treatment with topoisomerase II inhibitors. 486 There is today little information regarding topo pared within 18 hours of excision. Fresh breast tis- II␣ expression related to different cell cycle phases sue was mechanically disaggregated with Medima- in human neoplasms. A study on ovarian cancer chine (ConsulT.S., Rivalta di Torino, Italy) in 0.05 M with two-parameter flow cytometric analysis has PBS for 1–2 minutes. The cell suspension was fil- detected topo II␣–positive cells in the G1 phase in tered through a 40-␮m filter and centrifuged at 300 14 of 29 cases (22). ϫ g for 5 minutes. After one wash in PBS the cells The aim of the present study was to examine the were diluted to a concentration of 10 ϫ 106/mL in distribution of topo II␣ in the different cell cycle 0.05 M PBS. phases with two-parameter flow cytometry (FCM) in fresh human breast carcinomas. Determination of S-Phase Fraction and Ploidy A regular DNA staining with DNAcon 3 tubes MATERIALS AND METHODS (ConsulT.S.) was performed. The tubes contained a dehydrated buffer (lysing agent, RNAse and croma- Patients tin stabiliser). Propidium iodide solution (PI) was Material from 50 tumors from 49 women oper- added and the tube left at room temperature for 5 ated on at Örebro University Hospital was used in minutes in the dark. Two different control cells, this study. All breast cancer samples where sent chicken and salmon, were added to 1 ϫ 106 sample fresh from the operation theater to the Department cells and then incubated for 1 hour in an ice bath in of Pathology. Only patients with tumor size big the dark. enough to allow adequate material for routine his- The stained nuclei were analyzed in a FACScan tology, DNA analysis, estrogen receptor and proges- equipped with a 488-nm argon laser (Becton Dick- terone receptor determinations, and FCM for topo inson, Immunocytometry Systems, CA) with II␣ were included. CellQuest (Becton Dickinson) software. The DNA Patient age at operation ranged from 33 to 94 analysis was based on 15 000 events. To calculate years, with a median age of 61 years. All tumors DNA ploidy and S-phase fraction (SPF), Modfit were invasive breast carcinomas. Tumor character- (Becton Dickinson) software was used. Tumors istics are shown in Table 1. No patient had received were defined as either diploid (one stemline) or preoperative chemotherapy, hormonal therapy, or nondiploid (two or more cell populations; 23). The radiotherapy. Patients were given oral and written SPF was compared with that of the total number of information regarding the study, and informed cells expressing topo II␣. SPF was technically feasi- consent was obtained. ble in 82% (41/50) of the tumors. Preparation of Fresh Breast Tumor Tissue Flow Cytometry TopoII␣ Analysis The breast tumor samples were stored at 4° Cin Simultaneous measurement of topo II␣ and DNA ϫ 0.05 M phosphate buffered saline (PBS) and pre- content was done by two-parameter FCM. After 1 106 cells was added to each of two tubes, the tubes TABLE 1. Characteristics of the 50 Breast Carcinomas were incubated with 600-␮L of lysing solution (0.5% Number % Triton X-100 [Sigma Chemical Co, St. Louis, MO], Tumor size 1% BSA [Life Technologies, Paisley, Scotland], and pT1 16 32 0.2 ␮g/mL EDTA [Sigma] in 0.05 M PBS), pH 8.6. The pT2 32 64 cells were incubated for 10 minutes in an ice bath in pT3 2 4 Ϫ Histologic type the dark. The nuclei were fixed in 2 mL of 20° C Ductal 43 86 99.8% methanol pa (J.T. Baker. Deventer, Holland) Lobular 3 6 for 10 minutes in an ice-bath in the dark. After one Other 4 8 M Tumor gradea wash with 0.05 PBS, the tubes were centrifuged 1918for 5 minutes at 300 ϫ g. Topo II␣ clone SWT3D1 22550IgG1␬ (DAKO, Glostrup, Denmark; 1:100) was 31632 Estrogen receptor status added to one of the tubes. After incubation, a FITC- Positive 39 78 conjugated rat anti-mouse (RAM) antibody (DAKO; Negative 11 22 1:50) was added to both tubes and incubated, fol- Ploidy status ␮ Diploid 21 42 lowed by another incubation with 400 LofPI(10 Nondiploid 29 58 ␮g/mL; Sigma), with RNAse (200 ␮g/mL; Sigma). Axillary nodal status The last three incubations were performed for 30 pN0 26 52 pN1 22 44 minutes in an ice bath in the dark. NDb 24The stained nuclei were analyzed in a FACScan a Using the Elston modification of the Bloom and Richardson system. equipped with a 488-nm argon laser (Becton Dick- b ND, axillary node dissection not done. inson) and CellQuest (Becton Dickinson) software. TopoII␣ in Breast Cancer (K. Villman et al.) 487 FIGURE 1. Flow cytometric analysis of topo II␣ and DNA contents in fresh breast carcinomas. The DNA content of the investigated nuclei, reflecting the cell cycle phase, was determined after incubation with propidium iodide and RNAse. (A and D) show DNA histograms used for separation of the different cell cycle phases. A–C, tumor with diploid DNA content showing cells in G0/G1 phase (*) and S/G2/M phase (**).