Biomedical subjects

N Saijo

Publications and source records attributed to N Saijo.

At least 55 records · Page 3Linked to original sources

PubMed2001

Growth-stimulating pathways in lung cancer: implications for targets of therapy.

Growth-stimulating pathways activated independently of their normal tissue environment are critical to the carcinogenesis and progression of lung cancer. These pathways are comprised of extracellular growth factors; their specific receptors on the cellular membrane; signal transduction cascades in the cytosol; and target molecules, including cytoskeletal proteins, metabolic regulators, and transcription factors in the nucleus. Growth factors can be divided into two groups based on their receptors: G-protein-coupled receptors and receptor tyrosine kinases. Growth factors induce clonal expansion of lung cancer cells by autocrine and/or paracrine mechanisms. Signal transduction cascades form an extremely large and complicated network with cross-talk connections. Ras, phosphatidylinositol-3-OH kinase, and phospholipase C are three key regulators involved in the network. Recent progress in our understanding of the oncoproteins functioning in the pathways has led to the development of novel therapeutic agents. Some of the most exciting results have been obtained with inhibitors of receptor tyrosine kinases. Phase I studies of epidermal growth factor-receptor inhibitors demonstrate objective responses without severe toxicity as single agents in patients with non-small-cell lung cancer refractory to conventional chemotherapy. This new strategy might lead to breakthroughs in the treatment of lung cancer with distant metastases not curable by conventional chemotherapy alone.

Journal Article↗

PubMed2001

In vitro synergistic interactions between the cisplatin analogue nedaplatin and the DNA topoisomerase I inhibitor irinotecan and the mechanism of this interaction.

Among the numerous clinical regimens used in combination chemotherapy, synergy is particularly marked in combinations containing cisplatin (CDDP). However, the clinical use of CDDP is sometimes limited due to its nephrotoxicity. Nedaplatin (NDP) is a second-generation platinum complex with reduced nephrotoxicity that may substitute for CDDP or even surpass it for use in combination with other drugs. We investigated the effects of combinations of NDP and other anticancer drugs on the growth of human small cell lung cancer cells (SBC-3) and non-small cell lung cancer cells (PC-14) using a three-dimensional analysis model. Among the combinations tested, the combination of NDP and irinotecan (CPT-11) showed the most marked synergistic interaction, and the synergism has also been observed against PC-14 cells. With regard to treatment schedule, a remarkable synergistic interaction was produced by concurrent exposure to NDP and CPT-11. On the other hand, sequential exposure to the two drugs led only to additivity. To analyze the interaction between the drugs, the effect of NDP on the 7-ethyl-1-hydroxy-CPT (the active form of CPT-11)-induced inhibitory effect on DNA topoisomerase I was examined. The topoisomerase I-inhibitory effect of 7-ethyl-1-hydroxy-CPT was enhanced 10-fold in the presence of NDP at microgram/milliliter concentrations. These biochemical interactions might be responsible for the synergistic interaction between NDP and CPT-11. These results suggest that the combination of NDP with CPT-11 may be clinically useful for the chemotherapy of lung cancer.

Antineoplastic Agents↗

PubMed2001

[Signal transduction inhibitor].

Numerous molecular targets for cancer chemotherapy have been identified based on the progress made in molecular biology, and new categories of anticancer drugs have been developed. They are variously called target-based drugs, non-cytotoxic drugs and cytostatic drugs. These include inhibitors of signal transduction, cyclin-dependent kinase, angiogenesis, and matrix metalloproteinases. Other new therapies include gene therapy and immunotherapy. There are multiple steps in the signal transduction cascade. Growth factor binds to its cognate receptor tyrosine kinase and the phosphotyrosines on the receptor serve as attachment sites for substrates or adapter molecules. Grb2 functions by directly coupling activated receptor tyrosine kinases to the Ras-activating nucleotide exchange factor SOS. Activation of Ras or Ras family members leads to activation of the mitogen-activated protein kinase (MAPK) cascade pathway. This has been implicated as a necessary component of intracellular signaling to elicit a range of cellular responses including mitogenesis, differentiation, and cell survival. We introduce signal transduction inhibitors including, Ras inhibitors, protein kinase C inhibitors, and MAPK cascade inhibitors. Recently, these drugs have been used in clinical trials and some of them have an antitumor effect. In the near future these drugs may play an important role in cancer chemotherapy. However, these drugs are thought to induce a non-cytotoxic effect different from cytotoxic drugs. Therefore correct and efficient clinical evaluation of these drugs is needed. We look forward to developments from future research on signal transduction inhibitors.

Alkyl and Aryl Transferases↗

PubMed2001

[Platinum compounds in cancer therapy--past, present, and future].

Platinum cytotoxics play an important role globally in the management of solid tumours. Cisplatin sets the standard for efficacy in both regions with careful administration to reduce nephrotoxicity. Carboplatin is associated with neurotoxicity, but has become the leading product in the US due largely to the easier to manage toxicity profile. Both agents have been widely used in both registered and non registered indications and are frequently combined with other cytotoxics. In Japan, cisplatin has been used successfully at low doses in combination with 5-FU based regimens and appears to achieve a synergistic effect, but controlled data are not yet available. More recently oxaliplatin (Europe) and nedaplatin (in Japan) have been introduced, but their clinical roles in therapy have yet to be established. One of the limiting features of the first generation of platinum compounds is that a significant proportion of tumours develop cross resistance to platins due to either changes in uptake or excretion, intracellular detoxification or accelerated DNA repair. The forum discussed the possibility for the development of better new platinum compounds, A new platin agent which had lower toxicity and higher efficacy across a wide range of cancers without the development of resistance would be a significant step forward. If the tolerability profile was suitable, an oral formulation may improve the quality of life for patients but this must not be at the expense of efficacy. Even after the introduction of new target based drugs, platinum cytotoxics are likely to be used to reduce the tumour mass and in some cases can be expected to potentiate the effects of the new agents. In preclinical studies, ZD0473 has been shown to by-pass some major mechanisms of resistance and has the potential to achieve these objectives and is now being evaluated in clinical studies in both Japan and the West.

Antineoplastic Combined Chemotherapy Protocols↗

PubMed2001

Concurrent versus sequential radiotherapy for small cell lung cancer.

Two meta-analyses have shown that thoracic radiotherapy plus chemotherapy is superior to chemotherapy alone in the treatment of limited-stage small cell lung cancer. To minimize the likelihood of emergence of chemotherapy resistance, the optimal schedule for integration of the two modalities might be to introduce radiotherapy early in the course of treatment. The Cancer and Leukemia Group B trial performed from 1981 to 1984 failed to show an advantage for early concurrent chemoradiation. However, three recent controlled trials of thoracic irradiation timing (the National Cancer Institute of Canada trial, the Yugoslavian trial, and the Japan Clinical Oncology Group trial) showed that early radiotherapy is superior to delayed radiotherapy. These three trials used the combination of cisplatin/etoposide and showed that a long-term survival rate greater than 20% is achievable using early integrated chemoradiation. For the present, early concurrent administration of thoracic radiotherapy with a cisplatin/etoposide-based regimen should be standard therapy. Semin Oncol 28 (suppl 4):23-26.

Antineoplastic Combined Chemotherapy Protocols↗

PubMed2001

[Issues in cancer treatments--EBM, individuation, and standardization].

This review emphasizes the following conclusions. Every doctor in Japan is required to recognize that individuated treatments of cancer patients are also necessary to be based on the concept of EBM (evidence based medicine). To do so, it is essential for the doctors to conduct or join clinical trials in Japan more and more. This gives us more evidences applicable to our patients, and deeper analysis for foreign clinical trials. In the 90's, the concept of EBM was introduced to the Japanese medical profession. More recently, advances in molecular biology provided possibilities to customize treatments of individual cancer patients. Some of the new approaches became drugs already approved, such as Herceptin (Trastuzumab), Iressa (ZD1839), and Gleevec (ST1571). This trend, however, may justify even experimental treatments without enough evidence, because some Japanese doctors still rarely understand the concept of EBM. This review begins with mention of the origin of EBM and the methodology of EBM. Then topics in the "individuation" are discussed. Lastly, the need for "standardized-individuated-treatments" is argued.

Antibodies, Monoclonal↗

PubMed2000

Mechanism of action of aragusterol a (YTA0040), a potent anti-tumor marine steroid targeting the G(1) phase of the cell cycle.

Aragusterol A (YTA0040), isolated from the Okinawan marine sponge of the genus Xestospongia, is a potent anti-tumor marine steroid that possesses a unique structural component. This compound showed broad-spectrum anti-proliferative activity against a panel of 14 human cancer cell lines (IC(50) = 0.01-1.6 microM). P-glycoprotein-mediated, multidrug-resistant cells showed cross-resistance to YTA0040 cells, whereas cisplatin-resistant non-small-cell lung-cancer (NSCLC) sublines showed a collateral sensitivity to YTA0040. In transplantable murine tumor models, YTA0040 displayed a broad spectrum and high degree of anti-tumor activity when administered i.p. or p.o. (life span T/C = 135-234%). In P388 murine leukemia cells, YTA0040 caused dose- and time-dependent suppression of nucleic acid and protein synthesis, with protein synthesis being more potently and rapidly inhibited than nucleic acid synthesis. Flow-cytometric analysis revealed that YTA0040 blocked the entry of human NSCLC-derived A549 cells into S phase, leading to arrest in the G(1) phase of the cell cycle. Western blot analysis demonstrated that YTA0040 caused a dose-dependent decrease in the levels of expression of hyperphosphorylated pRb and cyclin A in A549 cells. The level of p53 protein expression was decreased by YTA0040 treatment. A higher concentration of YTA0040 down-regulated the levels of expression of CDK2, CDK4, cyclin D1 and cyclin E. These findings indicated that YTA0040 arrested human NSCLC cells in late G(1) phase of the cell cycle through inhibition of pRb phosphorylation. Inhibition of pRb phosphorylation by YTA0040 resulted from down-regulation of levels of expression of the CDKs and cyclins involved in the G(1)/S transition and not from induction of p53 and/or the CDK inhibitor p21.

Animals↗

PubMed2000

Ectopic p16(ink4) expression enhances CPT-11-induced apoptosis through increased delay in S-phase progression in human non-small-cell-lung-cancer cells.

A tumor-suppressor gene, p16(INK4), which is deleted or mutated in tumors, regulates cell-cycle progression through a G(1)-S restriction point by inhibiting CDK4(CDK6)/cyclin-D-mediated phosphorylation of pRb. We have found that ectopic p16(INK4) expression increased cellular sensitivity of human non-small-cell-lung-cancer (NSCLC) A549 cells to a selective growth-inhibitory effect induced by the topoisomerase-I inhibitor 11, 7-ethyl-10-[4-(1-piperidino)-1-piperidino] carbonyloxy camptothecin (CPT-11) in vitro. In this study, we observed enhanced apoptosis characterized by DNA fragmentation in A549 cells transfected with p16(INK4) cDNA (A549/p16-1) and treated with CPT-11. This apoptosis was suppressed by the inhibitor of interleukin-1beta-converting enzyme (ICE/caspase-1) or ICE-like proteases, Z-Asp-CH2-DCB, as determined by DNA fragmentation and proteolytic cleavage of poly(ADP-ribose) polymerase, a natural substrate for CPP32/caspase-3. In A549/p16-1 cells, cytosolic peptidase activities that cleaved Z-DEVD-7-amino-4-trifluoromethylcoumarin increased during CPT-11-induced apoptosis and were suppressed by a highly specific caspase-3 and caspase-3-like inhibitor, Z-DEVD-fluoromethylketone. These findings indicate that p16(INK) is positively involved in the activation pathway of the caspase-3 induced by CPT-11. The increased delay in S-phase progression and subsequent induction of apoptosis were observed in CPT-11-treated A549/p16-1 cells on the basis of DNA histograms. Specific down-regulation of the cyclin-A protein level in A549/p16-1 cells was observed after CPT-11-treatment, whereas cyclin B, cdk2, and cdc2 protein levels were unaffected. These results suggest that ectopic p16(INK4) expression inappropriately decreases cyclin A and thereby terminates CPT-11-induced G(2)/M accumulation, which is followed by increased apoptosis in p16(INK4)-expressing A549 cells.

Antineoplastic Agents, Phytogenic↗

PubMed2000

Detailed structural analysis on both human MRP5 and mouse mrp5 transcripts.

The multidrug-resistant phenotype in tumor cells is attributed in part to anti-cancer drug efflux transporters such as the MRP family. The amino-terminal structure of MRP5 has not been refined. To determine the amino-terminal structure of a major transcript of the MRP5 gene, we performed primer extension analysis to determine a major transcriptional start site of this gene and compared the structure of human MRP5 and that of mouse mrp5. We successfully determined the structures of human MRP5 and mouse mrp5. Estimated amino acid sequences are 1437 and 1436 amino acids for human MRP5 and mouse mrp5 respectively, and were highly conserved (94.1%). We further showed that our previously identified SMRP mRNA was a splicing variant of the MRP5 gene, which was expressed in various human tissues, suggesting that a short form of MRP5 protein encoded by the SMRP mRNA may have a physiological role.

ATP-Binding Cassette Transporters↗

PubMed2000

Molecular determinants of UCN-01-induced growth inhibition in human lung cancer cells.

UCN-01 (7-hydroxystaurosporine) inhibits the growth of various malignant cell lines in vitro and in vivo. In this study, a human small cell lung carcinoma subline resistant to UCN-01, SBC-3/UCN, was established and characterized. SBC-3/UCN cells showed 8-fold greater resistance to the UCN-01-induced growth-inhibitory effect than the parent cells, SBC-3. No UCN-01-induced G1 accumulation in SBC-3 cells was observed in SBC-3/UCN cells and decreased expression of phosphorylated RB protein was found in SBC-3 cells. Neither basal expression nor induction of p21(Cip1) by UCN-01 treatment was detected in the SBC-3/UCN cell line. An inhibitory effect of UCN-01 on CDK2 activity, which is mediated by p21(Cip1)/CDK2 complex formation upon UCN-01 treatment, was observed in SBC-3 but not in SBC-3/UCN cells. SBC-3/UCN showed higher CDK6 activity than SBC-3 cells. UCN-01 did not inhibit the CDK4 and CDK6 activities in both cells. We screened the cell cycle regulatory molecules associated with G(1)/S progression and found a remarked decrease in interferon regulatory factor 1 (IRF-1), which is known to cooperate with p53 in p21(Cip1) induction. Our results suggest that p21(Cip1) regulation via the IRF-1-associated pathway may represent a major determinant of UCN-01-induced growth inhibition in human lung cancer cells.

Alkaloids↗

PubMed2000

Problems in the development of target-based drugs.

Numerous molecular targets of cancer chemotherapy have been identified based on progress made in molecular biology, and new categories of anticancer drugs have been developed. These include inhibitors for signal transduction, cyclin-dependent kinase, angiogenesis, and matrix metalloproteinase, gene therapy, etc. They are variously called target-based drugs, noncytotoxic drugs, or cytostatic drugs. Such drugs have interesting mechanisms of action and appear promising. However, preclinical and clinical evaluations are difficult. Some drugs have a direct antitumor effect, with demonstrated tumor shrinkage. Others show no direct cytotoxicity. The majority of recent phase I trials have evaluated the maximum tolerated dose, pharmacokinetics, adverse events, and antitumor effect. Unusual, unacceptable toxicities have been noted with some target-based drugs. Few phase I trials or preclinical studies have attempted to demonstrate target inhibition. So far very few studies has shown that there is a correlation between target inhibition and antitumor effect. In general, phase II studies are undertaken with compounds such as trastuzumab which have direct antitumor activity. Phase III trials of most target-based drugs are undertaken immediately after phase I studies since the design of appropriate phase II studies is difficult. The ultimate endpoint of phase III trials of target-based drugs is the same as that for cytotoxic drugs, such as improved cure and survival rates.

Antineoplastic Agents↗

PubMed2000

Retrospective comparison of toxicity and efficacy in phase II trials of 3-h infusions of paclitaxel for patients 70 years of age or older and patients under 70 years of age.

PURPOSE: To evaluate the safety and efficacy of paclitaxel in elderly patients with advanced non-small-cell lung cancer (NSCLC). METHODS: We compared the toxicity, response, survival and pharmacokinetic parameters between patients between 70 and 75 years of age (elderly group) and those under 70 years of age (younger group) who were enrolled in two phase II trials of 3-h infusions of paclitaxel. RESULTS: A total of 120 patients were eligible for the studies, of whom 28 were in the elderly group and 92 in the younger group. Neutropenia was the most prominent toxicity. Grade 3-4 neutropenia was recorded in 89.3% of the elderly group and in 73.9% of the younger group (P = 0.13). Other hematological and non-hematological toxicities were mild regardless of age. Tumor response (46.4% vs 32.2%) and median survival time (9.8 months vs 6.8 months) did not differ between the elderly and younger groups. Pharmacokinetic studies failed to detect any difference between the two groups. CONCLUSION: Intravenous 3-h infusions of paclitaxel are as safe and effective in elderly patients with NSCLC as in younger patients.

Age Factors↗

PubMed2000

Phase II study of concurrent chemotherapy and radiotherapy for unresectable stage III non-small-cell lung cancer: long-term follow-up results. Japan Clinical Oncology Group Protocol 8902.

BACKGROUND: Although chemoradiotherapy is standard treatment for unresectable stage III non-small-cell lung cancer (NSCLC), few long-term survival data exist. PATIENTS AND METHODS: Between October 1989 and December 1991, 74 patients with histologically or cytologically proven NSCLC, unresectable stage IIIA or IIIB, were entered into this study. Seventy patients were eligible and evaluable for response, toxicity, and survival analysis. Chemotherapy consisted of cisplatin (100 mg/m2 on days 1, 29, and 57) and vindesine (3 mg/m2 on days 1, 8, 29, 36, 57, and 64). Thoracic radiotherapy was administered for two weeks (2 Gy given 10 times, five fractions per week), and after a 14-day rest period, the previous schedule of radiotherapy was repeated for two weeks. A 10-Gy to 20-Gy dose of radiotherapy was administered during the third cycle of chemotherapy. RESULTS: Of the 70 evaluable patients, 1 (1.4%) had a complete response (CR) and 51 (72.9%) had a partial response (PR). The median survival time was 14.8 months, and the five-year survival rate was 14.8%. The major toxicity was leukopenia (> or = grade 3, 93%). Other toxicities > or = grade 3 included anemia (34%), nausea/vomiting (27%), alopecia (7%), thrombocytopenia (4%), and serum creatinine elevation (1%). Treatment related death occurred in two patients (2.8%). One patient died of pneumonia and pneumothorax, and the other of hemoptysis. CONCLUSIONS: Concurrent chemotherapy and radiotherapy has the potential to provide long-term survival with acceptable toxicities.

Adult↗

PubMed2000

Pharmacokinetic and pharmacodynamic analysis of bis-acetato-ammine-dichloro-cyclohexylamine-platinum(IV) (JM216) administered once a day for five consecutive days: a phase I study.

BACKGROUND: Bis-acetato-ammine-dichloro-cyclohexylamine-platinum(IV) (JM216) is the first orally given platinum complex that shows in vitro cytotoxicity comparable to that of cisplatin and in vivo cytotoxicity superior to those of cisplatin and carboplatin. METHODS: We conducted an escalating-dose (50, 75, 100, 120 mg/m2) phase I study of JM216 administered orally once a day for five consecutive days in patients with solid tumors to establish the toxicity profile, maximum tolerated dose (MTD) and pharmacokinetic profile. Twenty-three patients were enrolled and all were assessable for toxicity. RESULTS: The MTD was 120 mg/m2/day and the dose-limiting toxicities were leukopenia, thrombocytopenia, anemia and diarrhea. Because of the delayed hematological toxicities, it was difficult to repeat cycles every 26 days in some patients. Tumor shrinkage was observed in two patients with breast cancer, both of whom were resistant to doxorubicin. A pharmacokinetic study showed that the areas under the concentration-time curve (AUC) and peak plasma concentrations (Cmax) for total platinum (Pt) on days 1 and 5 and ultrafiltered Pt (UF-Pt) on day 1 increased in proportion to the dose of JM216. The AUCs for both total and UF-Pt on day 5 were higher than the AUCs on day 1. The AUC for UF-Pt on day 5 showed the best correlation with percentage reduction in leukocyte count and in absolute neutrophil count. CONCLUSION: The recommended dose for phase II studies is 100 mg/m2/day every 4-6 weeks. The observation of tumor shrinkage in previously heavily treated breast cancer patients supports a phase II investigation.

Administration, Oral↗

PubMed2000

Bacterial meningitis observed in a phase I trial of vinorelbine, cisplatin and thoracic radiotherapy for non-small cell lung cancer: report of a case and discussion on dose-limiting toxicity.

Although neutropenia increases the risk of life-threatening infections, bacterial meningitis is rarely encountered as a complication during cancer chemotherapy in adults with a solid tumor. A 66-year-old male with adenosquamous carcinoma of the lung, cT2N3M0, stage IIIB, was enrolled in a phase I trial of chemoradiotherapy and treated with cisplatin 80 mg/m2 (122 mg/ body) on day 1, vinorelbine 20 mg/m2 (32 mg/body) on days 1 and 8 and thoracic radiotherapy 30 Gy/15 fractions, beginning on day 2, with dexamethasone administered for antiemesis at a dose of 16 mg on day 1, 8 mg on days 2 and 3, 4 mg on day 4 and 2 mg on day 5. The patient developed headache and fever on day 6 of the second cycle of the treatment and bacterial meningitis was diagnosed based on the findings of consciousness disturbance, an elevated peripheral blood leukocyte count and numerous leukocytes in the cerebrospinal fluid. In spite of the doctor's delay in establishing the exact diagnosis, the bacterial meningitis in this case was successfully treated with intensive antibiotic therapy. This life-threatening complication, equivalent to a grade 4 non-hematological adverse reaction, was not counted as dose-limiting toxicity in the current phase I trial, because there are only a few reports of bacterial meningitis associated with cancer chemotherapy and it developed in this case without any associated decrease in the peripheral blood leukocyte count.

Aged↗

PubMed2000

Platinum-based chemotherapy with or without thoracic radiation therapy in patients with unresectable thymic carcinoma.

BACKGROUND: Thymic carcinoma is a rare mediastinal neoplasm with poor prognosis. Although the clinical benefit of chemotherapy for thymic carcinoma is controversial, cisplatin-based chemotherapy with or without radiation therapy is ordinarily adopted in advanced cases. We evaluated the clinical outcome of platinum-based chemotherapy with or without radiation therapy in unresectable thymic carcinoma patients. METHODS: Ten patients with unresectable thymic carcinoma were treated with platinum-based chemotherapy with or without radiation therapy in the National Cancer Center Hospital between 1989 and 1998. We reviewed the histological type, treatment, response and survival of these patients. RESULTS: Four of the 10 patients responded to chemotherapy and both the median progression-free survival period and the median response duration were 6.0 months. The median survival time was 11.0 months. There was no relationship between histological classification and prognosis. CONCLUSIONS: Platinum-based chemotherapy with or without thoracic radiation is, regardless of tumor histology, marginally effective in advanced thymic carcinoma patients, giving only a modest tumor response rate and short response duration and survival.

Adult↗

PubMed2000

Phase I study of a weekly infusion of irinotecan hydrochloride (CPT-11) and a 14-day continuous infusion of etoposide in patients with lung cancer: JCOG trial 9408.

BACKGROUND: The aim was to determine the maximum tolerated dose (MTD) and recommended dose of irinotecan hydrochloride (CPT-11) in combination with a 14-day continuous infusion of etoposide in patients with refractory advanced lung cancer (LC), especially small cell lung cancer (SCLC). METHODS: Etoposide was administered continuously at 25 mg/m2/day for 14 days. The initial dose of CPT-11 was 40 mg/m2 given as a 90 min intravenous infusion on days 1, 8 and 15 and the dose escalation of CPT-11 was planned in increments of 20 mg/m2 until severe or life-threatening toxic effects were observed. RESULTS: Nine refractory or advanced LC patients (eight at level 1, one at level 2) were entered in this study, of whom two at level 1 were not assessable for toxicity because of patient's refusal and progressive disease. One treatment-related death due to pulmonary toxicity and one patient with hypotension who needed catecholamine for more than 48 h were observed at level 1, a CPT-11 dose of 40 mg/m2. The MTD of CPT-11 was 40 mg/m2. Therapeutic efficacy could be assessed in seven patients, of whom two achieved a partial response. CONCLUSIONS: This regimen was too toxic and the recommended dose was outside the levels in this study. One has to consider pulmonary toxicity when using CPT-11, especially for patients previously treated with cytotoxic agents for which pulmonary toxicity has been reported.

Adenocarcinoma↗

PubMed2000

A computational model for quantitative analysis of cell cycle arrest and its contribution to overall growth inhibition by anticancer agents.

Most anticancer agents induce cell cycle arrest (cytostatic effect) and cell death (cytotoxic effect), resulting in the inhibition of population growth of cancer cells. When asynchronous cells are to be examined, the currently used flow cytometric method can not provide checkpoint-specific and quantitative information on the drug-induced cell cycle arrest. Hence, despite its significance, no good method to analyze in detail the mechanism of cell cycle arrest and its contribution to overall growth inhibition induced by an anticancer agent has yet been established. We describe in this study the development of a discrete time (Markov model)-based computational model for cell cycle progression / arrest with transition probability (TP(i)) as a model parameter. TP(i) was calculated using model equations that include easily measurable parameters such as the fraction of cells in each cell cycle phase and population doubling time. The TP(i) was then used to analyze checkpoint-specific and quantitative changes in cell cycle progression. We also used TP(i) in a Monte-Carlo simulation to predict growth inhibition caused by cell cycle arrest only. Human SCLC cells (SBC-3) exposed to UCN-01 were used to validate the model. The model-predicted growth curves agreed with the observed data for SBC-3 cells not treated or treated at a cytostatic concentration (0.2 mM) of UCN-01, indicating validity of the present model. The changes in TP(i) indicated that UCN-01 reduced the G(1)-to-S transition rate and increased the S-to-G(2) / M and G(2) / M-to-G(1) transition rates of SBC-3 cells in a concentration- and time-dependent manner. When the model-predicted growth curves were compared with the observed data for cells treated at a cytotoxic concentration (2 mM), they suggested that 22% out of 65% and 32% out of 73% of the growth inhibition could be attributed to the cell cycle arrest effect after 48 h and 72 h exposure, respectively. In conclusion, we report here the establishment of a novel method of analysis that can provide checkpoint-specific and quantitative information about cell cycle arrest induced by an anticancer agent and that can be used to assess the contribution of cell cycle arrest effect to the overall growth inhibition.

Alkaloids↗