Tetsuya Toge

Current status of the molecular mechanisms of anticancer drug-induced apoptosis. The contribution of molecular-level analysis to cancer chemotherapy.

Abstract. Apoptosis is an important phenomenon in cytotoxicity induced by anticancer drugs. Here, we review the current status of the molecular mechanisms of anticancer drug-induced apoptosis in order to assess the contribution of molecular-level analysis to cancer chemotherapy. It is apparent that the molecular mechanisms by which anticancer drugs induce apoptosis are mediated by death receptor-dependent and -independent pathways, which are related to the release of cytochrome c through voltage-dependent anion channels in the mitochondrial inner membrane. The release of cytochrome c is the central gate in turning on/off apoptosis, and is regulated by the interaction of proapoptotic proteins, including Bid, Bax and Bak, and antiapoptotic proteins including Bcl-2 and Bcl-XL, and a specific class of inhibitors of apoptosis proteins (IAPs) including Akt, survivin, and heat-shock proteins. The caspase cascade is activated by the release of cytochrome c, which is initiated by the formation of apoptosomes consisting of procaspase-9, Apaf-1 and cytochrome c in the presence of dATP, and results in the activation of caspase-9 and caspase-3, thereby leading to apoptosis. Drug sensitivity can be enhanced by the introduction of proapoptotic genes and the inhibition of antiapoptotic proteins. The latter process is mediated by antisense oligonucleotides and is associated with apoptosis. The signal transduction pathways that are triggered by the central gate in mitochondria play a critical role in anticancer drug-induced apoptosis. The modulation of signal transduction pathways targeting the proteins involved in these signal transduction pathways using antisense IAPs, and growth factor antibodies may be a good strategy for enhancing therapeutic efficacy of anticancer drugs in cancer chemotherapy.

Clinical significance of the expression of epidermal growth factor and its receptor in esophageal cancer

The epidermal growth factor receptor (EGFR) level in 56 esophageal cancer tissues was measured by 125I‐EGF binding assay to elucidate its role in tumor progression. The survival rate of patients with high EGFR level (more than 50 fmol/mg protein) was significantly lower than that of patients with low EGFR level (less than 50 fmol/mg protein, P less than 0.01), although a correlation between EGFR level and the pathologic findings was not observed. The expression of EGF was examined immunohistochemically using anti‐EGF monoclonal antibody in 100 esophageal cancer tissues; EGF‐positive tumor cells were detected in 92.0%. The immunoreactivity of EGF was classified arbitrarily into four grades according to the number of stained tumor cells. The expression of EGF significantly correlated with the differentiation of esophageal squamous cell carcinoma (P less than 0.01, by chi‐square test). The survival rate of patients with high EGF immunoreactivity (Grade 2 or 3) was much lower than in those with lower grade (0 or 1) tumors, (P less than 0.01). Patients with both high EGFR level and EGF immunoreactivity had a much worse prognosis than if both were low. Furthermore, the mitotic index was higher in groups with both high EGFR and EGF than if both were low (16.39 ± 5.35 versus 6.90 ± 3.31). These results suggest that EGF and EGFR in the autocrine system may play an important role in tumor progression in esophageal cancer and their expression could be of prognostic significance.

Therapeutic potential of antisense Bcl‐2 as a chemosensitizer for cancer therapy

Bcl‐2 protein plays a critical role in inhibiting anticancer drug‐induced apoptosis, which is mediated by a mitochondria‐dependent pathway that controls the release of cytochrome c from mitochondria through anion channels. Constitutive overexpression of Bcl‐2 or unchanged expression after treatment with anticancer drugs confers drug resistance not only to hematologic malignancies but also to solid tumors. The down‐regulation of Bcl‐2 protein by the antisense (AS) Bcl‐2 (oblimesen sodium) may be a useful method for targeting the antiapoptotic protein and thereby increasing the chemotherapeutic effect of anticancer drugs. Several randomized, controlled, Phase III trials have compared standard chemotherapy with a combination of AS Bcl‐2 and standard chemotherapy for the treatment of patients with chronic lymphocytic leukemia, multiple myeloma, malignant melanoma, and nonsmall cell lung carcinoma. Nonrandomized clinical trials and preclinical evaluations of AS Bcl‐2 also are underway for patients with other malignancies. Here, the authors review the current clinical and preclinical evaluations of AS Bcl‐2 and discuss its potential to act as a chemosensitizer and to enhance the therapeutic effect of cancer chemotherapy. Cancer 2004.

The Role of Fas Ligand and Transforming Growth Factor in Tumor Progression Molecular Mechanisms of Immune Privilege via Fas-Mediated Apoptosis and Potential Targets for Cancer Therapy

Despite the fact that expression of Fas ligand (FasL) in cytotoxic T lymphocytes (CTLs) and in natural killer (NK) cells plays an important role in Fas‐mediated tumor killing, During tumor progression FasL‐expressing tumor cells are involved in counterattacking to kill tumor‐infiltrating lymphocytes (TILs). Soluble FasL levels also increase with tumor progression in solid tumors, and this increase inhibits Fas‐mediated tumor killing by CTLs and NK cells. The increased expression of FasL in tumor cells is associated with decreased expression of Fas; and the promoter region of the FASL gene is regulated by transcription factors, such as neuronal factor κB (NF‐κB) and AP‐1, in the tumor microenvironment. Although the ratio of FasL expression to Fas expression in tumor cells is not strongly related to the induction of apoptosis in TILs, increased expression of FasL is associated with decreased Fas levels in tumor cells that can escape immune surveillance and facilitate tumor progression and metastasis. Transforming growth factor β (TGF‐β) is a potent growth inhibitor and has tumor‐suppressing activity in the early phases of carcinogenesis. During subsequent tumor progression, the increased secretion of TGF‐β by both tumor cells and, in a paracrine fashion, stromal cells, is involved in the enhancement of tumor invasion and metastasis accompanied by immunosuppression. Herein, the authors review the clinical significance of FasL and TGF‐β expression patterns as features of immune privilege accompanying tumor progression in the tumor microenvironment. Potential strategies for identifying which molecules can serve as targets for effective antitumor therapy also are discussed. Cancer 2004.

Epidermal growth factor receptor expression as a prognostic indicator in breast cancer

The significance of epidermal growth factor receptor (EGFR) status as a prognostic indicator was investigated by a competitive binding assay in 135 primary breast cancer patients. 55 patients (41%) were EGFR positive and EGFR status was negatively correlated with oestrogen receptor (ER) status (P less than 0.01). 5-year postoperative follow-up showed that relapse-free survival for EGFR positive patients was significantly worse than that for EGFR negative patients (P less than 0.05). There was no difference between the two groups in tumour size, axillary node involvement, age and menopausal status. Analysis by axillary node status demonstrated the poor prognosis of the EGFR positive group in node positive patients. As yet, no difference in prognosis has been seen in node negative patients. A higher frequency of haematopoietic relapse was observed in EGFR positive patients. Simultaneous or sequential EGFR measurements in primary tumour and metastatic sites of 34 patients showed that expression of EGFR was more enhanced in metastatic sites.

Relationship between epidermal growth factor receptor status and various prognostic factors in human breast cancer

Relationship between epidermal growth factor receptor (EGFR) status and various prognostic factors was investigated in 91 human breast cancer tissues. Epidermal growth factor receptor was measured by biochemical competitive binding assay using iodine 125 epidermal growth factor (125I)‐EGF. The EGFR status was not correlated with axillary lymph node involvement, tumor size, stage, and histologic type, but significantly correlated with histologic grading (P < 0.05) and lymphatic invasion (P < 0.01). Between EGFR and estrogen receptor (ER) status, a clear inverse relationship was observed (P < 0.01). The Ki‐67‐positive stained cell rate, which reveals the proportion of cycling cells, was significantly higher in EGFR‐positive tumor tissues than in EGFR‐negative cases. Furthermore, preliminary postoperative survey demonstrated a high tendency of recurrence rate of patients with EGFR‐positive tumors as compared with those with EGFR‐negative tumors. These data suggest that EGFR status may be important for the prediction of biologically high malignant potential.

Targeted therapy against Bcl-2-related proteins in breast cancer cells.

IntroductionBcl-2 and Bcl-xL confer resistance to apoptosis, thereby reducing the effectiveness of chemotherapy. We examined the relationship between the expression of Bcl-2 and Bcl-xL and chemosensitivity of breast cancer cells, with the aim of developing specific targeted therapy.MethodsFour human breast cancer cell lines were examined, and the effects of antisense (AS) Bcl-2 and AS Bcl-xL phosphorothioate oligodeoxynucleotides (ODNs) on chemosensitivity were tested in vitro and in vivo. Chemosensitivity was evaluated by the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide) assay, and the antitumor effect was assessed in vivo by the success of xenograft transplantation into athymic mice.ResultsTreatment with AS Bcl-2 and Bcl-xL ODNs resulted in a sequence-specific decrease in protein expression, compared with controls. Treatment of BT-474, ZR-75-1, and MDA-MB-231 cells with AS Bcl-2 increased chemosensitivity to doxorubicin (DOX), mitomycin C (MMC), paclitaxel (TXL), and docetaxel (TXT). Transfection of the Bcl-2 gene into MDA-MB-453 cells decreased sensitivity to DOX and MMC. Treatment of MDA-MB-231, BT-474, and ZR-75-1 cells with AS Bcl-xL increased chemosensitivity to DOX, MMC and taxanes to a smaller extent than AS Bcl-2. This occurred in the setting of increased Bax and cleaved poly(ADP-ribose) polymerase, as well as decreased Bcl-2 and pAkt. AS Bcl-2 ODNs induced splenomegaly in association with increased serum IL-12, which was attenuated by methylation of the CpG motifs of AS Bcl-2; however, methylated CpG failed to negate the increased antitumor effect of AS Bcl-2. Bcl-2 and Bcl-xL, to a smaller extent, are major determinants of chemosensitivity in breast cancer cells.ConclusionTargeted therapy against Bcl-2 protein with the use of AS ODNs might enhance the effects of chemotherapy in patients with breast cancer.

Establishment of two cell lines from human gastric scirrhous carcinoma that possess the potential to metastasize spontaneously in nude mice

Few experimental studies have been conducted to clarify the mechanism of development of metastasis in scirrhous carcinoma of the stomach. In the present study, we attempted to establish gastric carcinoma cell lines by incubation of cancer cells collected from the body fluids of patients with gastric cancer. At the same time, xenografting of these cells to nude mice was performed. It was found that, of the gastric carcinoma cell lines thus established, two cell lines, designated as HSC‐44PE and HSC‐58, formed s.c. tumors with a high infiltrative potential (often invading the lymphatics around the cancer tissue) when implanted. Metastasis to the lymph nodes and lungs was observed in 20–40% of all the animals, indicating that the two cell lines are also capable of metastasizing spontaneously. Through repeated selection, i.e., repeated cycles of removal, culture, and implantation of the HSC cancer cells from metastatic lesions, we obtained 5 subclones of HSC‐44PE and HSC‐58 (designated as m2509, m2615, m2792, m2917, and m2691), which, when implanted orthotopically, exhibited the following characteristics as compared to the parent cells: (1) a higher percentage take (survival), similar frequency of metastasis, shorter time to metastasis (less than 100 days), and consistent metastasizing potential; (2) a relatively high frequency of metastasis to lymph nodes, including distant metastasis to axillary lymph nodes; (3) the potential to cause occasional bloody ascites; (4) enhanced expression of dysadherin, CD44, and other molecules. This is the first report of cultured scirrhous gastric carcinoma cells showing the potential for spontaneous metastasis.

POOR PROGNOSIS IN ESOPHAGEAL CANCER PATIENTS WITH POSTOPERATIVE COMPLICATIONS

We investigated the relationship between postoperative complications and prognosis in esophageal cancer patients. Two hundred five patients with esophageal cancer were divided into three case groups. Group A (n = 100) consisted of cases without postoperative complications. Groups B (n = 58) and C (n = 47) consisted of cases with minor and major postoperative complications. The 5-year survival rates were 41.8%, 21.3%, and 20.2% in groups A, B, and C, respectively. There was a significant difference in the prognosis between groups A and B, and also between groups A and C. Any patients who died within 5 years without a relapse their cases were excluded from the study; the 5-year survival rates were 46.7%, 32.3%, and 22.5% in groups A, B, and C, respectively, with a significant difference between groups A and B. There were no significant differences between the three groups regarding the patient characteristics. These results therefore indicate that postoperative complications might contribute to a poor prognosis in cancer patients.

Prognostic significance of co-expression of c-erbB-2 oncoprotein and epidermal growth factor receptor in breast cancer patients

The expression of c-erbB-2 oncoprotein and epidermal growth factor receptor (EGFR) was examined by immunocytochemical and radioreceptor assays in 115 patients with primary breast cancer. In 48 of 115 patients (42%), the assays were found to be positive for the expression of c-erbB-2 oncoprotein, and, in 44 of 115 (35%) patients, the assays were positive for the expression of EGFR. There was no correlation between the expression of c-erbB-2 oncoprotein and EGFR. Clinical survey demonstrated that both c-erbB-2 oncoprotein expression and EGFR expression have independent prognostic values. Furthermore, when patients were divided into three groups on the basis of the expression of both c-erbB-2 oncoprotein and EGFR, those who were found to be positive for the expression of both c-erbB-2 oncoprotein and EGFR showed a worse prognosis than other groups. These results suggest that the combination of the expression of both c-erbB-2 oncoprotein and EGFR may be important in selecting patients who have a poor prognosis.