CPT-11 is a semisynthesized derivative of camptothecin that has a potent antitumor activity by inhibiting DNA topoisomerase I. Leukopenia (mainly neutropenia) is DLF (dose limiting factor) and MTD (maximum tolerated dose) is higher than 250 mg/m2 in CPT-11 from the results of clinical phase I study. Now we are going on phase II study of CPT-11. We are seeing the cases responded to the drug in cancer of the lung, ovary, uterus, stomach, colorectum, pancreas, breast, malignant lymphoma etc.

The mechanisms of acquired resistance to mammalian DNA topoisomerase I inhibitor, camptothecin or its derivative (CPT-11) were described. Tumor cell lines containing altered or reduced topoisomerase I were reviewed. It might be necessary to further study on reduced inhibitor uptake and other unknown mechanism.

CPT-11, a derivative of camptothecin, has drawn attention to cancer chemotherapy because of the specific mode of action, and the clinical study is now under progress. Liu et al. proved that camptothecin was a DNA topoisomerase I inhibitor, and some kinds of antitumor agents have been recognized as DNA topoisomerase II inhibitors. Based on these findings, DNA topoisomerases have emerged as target enzymes of antitumor agents in cancer chemotherapy. This paper dealt with investigation on the cytotoxic effects induced by combined use of DNA topoisomerase targeting antitumor agents, especially using CPT-11 as a core antitumor agent. Synchronous administration of CPT-11 with other antitumor agents induced cytotoxic effects less than metachronous administration of CPT-11 with other antitumor agents, especially preceding use of CPT-11. Dose of antitumor agents was not necessarily correlated to the cytotoxic effects. In some instances, small doses of the agents showed better therapeutic effects than large doses. The cytotoxic effects of vincristine, vindesine, and hydroxyurea were reduced by combination with CPT-11. On the other hand, non-cytotoxic agents such as aphidicolin, novobiocin, propentofylline, pentoxifylline, norfloxacin, and tosufloxacin enhanced the cytotoxic effects of CPT-11. Hypothetical consideration of cell killing and acquisition of drug resistance was proposed.

Topoisomerase II is now viewed as an important cellular target of antitumor drugs including both DNA intercalators (m-AMSA, ellipticine and Adriamycin) and the nonintercalator epipodophyllotoxin derivatives (VP-16 and VM-26). Topoisomerase I is also shown to be the cellular target of camptotecin. These drugs targeting topoisomerase have been used to establish a relationship between drug-induced cleavable complex formation and cytotoxicity. Mechanistically oriented screening based on the identification of these chemotherapeutic targets have identified a number of antitumor agents that induce topoisomerases mediated DNA cleavage. The new antitumor drugs targeting topoisomerases are reviewed.

For the elucidation of the mode of action of anti-tumor agents, the cell cycle analysis of etoposide and podophyllotoxin was examined by means of the multiparameter flow cytometry using an anti-p-105 monoclonal antibody. The p-105 is one of the proliferation associated nuclear antigens and its expression increases with a cell cycle progression, especially in mitotic phase. Thus, we have applied its anti-monoclonal antibody to the discrimination between M and G2 phases of the gastric cancer cells. The results revealed that etoposide caused a G2 block and retarded an S phase transition, and podophyllotoxin caused both G2 and M phase blocks in the gastric cancer cells. This cell cycle analysis using an anti-p-105 monoclonal antibody would be a useful analysis of the antitumor agents, especially for M phase analysis of human cancer cells because of its rapidity and convenience.

Clinical predictability of preclinical test for antitumor agents has not been significantly improved even after the use of a human tumor/nude mouse model. Such different antitumor activities between preclinical and clinical tests probably due to the fact that therapeutic used in both tests usually each maximum tolerated dose (MTD), are pharmacokinetically not equivalent. Therefore, we introduced a new concept of "clinically equivalent dose (CED)", which can reproduce in the nude mouse the blood level of a given drug observed with human patients received its therapeutic dose. Treatment of human tumors implanted in the nude mice with CEDs of several drugs exhibited much better correlation with their clinical efficacies than those with MTDs. The feasibility of use of CED predicted by animal scale-up procedure as a therapeutic dose in the preclinical test was discussed.

Routinely, phase I clinical study starts with 1/10 of MELD10, provided dog does not produce toxicity. This is empirical method depend upon previous agents. In these days, many new agents appear to clinical study and some of them require so many steps to reach MTD. This is mainly depends upon differences of ADME between animals and human, which is possible to eliminate by pharmacokinetic studies. On the other hand, some of agents exceed MTD with initial dose of 1/10 MECL10. This is mainly due to difference of target organ sensitivity, and could be eliminated by assay of tissue enzyme activities. Another point should be emphasized is the existence of plasma peak level toxicity. This should be eliminated to perform preclinical study of LD10 by continuous infusion rather than iv bolus injection. Since some of new agents have DLF of neuro, hepato or cardiac toxicity rather than bone marrow, those would show quite different behaviors, therefore a special attention should be given for further studies.

The purpose of this report is to review the problems in the evaluation of new drugs in SCLC and phase II testing of analogues in lung cancer. SCLC is one of the most chemotherapy-sensitive solid tumours and patients (pts) who relapse after their first-line treatment are likely to have resistant tumors, precluding the appropriate evaluation of new drugs, especially analogues. However, it is ethically difficult to evaluate new drugs in untreated pts with SCLC. Based on many issues, We recommended that new drugs should be evaluated in "good" pts with extensive-stage SCLC and that the trial design should include early stopping rules as well as a crossover to an active alternative regimen such as etoposide and cisplatin for non-responders. Also, I recommended that the endpoint for a positive phase II study with an analogue depends upon which of the following four ways the analogue's superiority is hope for; (1) superior efficacy in responsive tumors; (2) broader spectrum; (3) cross-over resistance to the parent structure; (4) diminished toxicity.

KB-5424 (ab-(3-aminopyrrolidine)-cd-[glycolato (2-)-0, 0'] platinum (II) is a newly developed antitumor platinum compound which was synthesized at Kanebo Institute for Cancer Research. When the antitumor activity of KB-5424 was evaluated using several rodent tumors, no significant differences were observed between the antitumor activities of KB-5424, cisplatin (CDDP) and DWA-2114 R (DWA). KB-5424 was divided into two kinds of optical isomers, KB-5424 R and KB-5424 S, of which antitumor activity was compared each other. The maximum increased life span (ILSmax) on L 1210 of KB-5424 R was almost equal to that of CDDP and better than those of KB-5424 S and carboplatin (CBDCA). The antitumor activity of KB-5424 R on a human tumor xenograft MX-1 was almost identical to those of CDDP and CBDCA and better than that of DWA. Since the nephrotoxicity of KB-5424 R was significantly reduced comparing with CDDP, this newly developed antitumor platinum compound was thought to be a promising agent for the clinical application.

A phase II clinical trial of SM-5887, a new totally synthesized anthracycline derivative, was carried out in 13 patients with inoperable or recurrent gastric cancer. No patient had been given anthracycline previously. SM-5887 was administered by I.V. bolus with a dose of 100 mg/m2 every three weeks. Twelve of 13 cases were eligible and evaluable for the response. Of the 12 evaluated cases, 6 showed no change (NC), including one minor response (MR). The remaining 6 cases showed progressive disease (PD). Adverse effects were relatively mild in most cases and included anemia, leukocytopenia, thrombocytopenia, nausea/vomiting, phlebitis, hair loss and fever. Among them, leukocytopenia was observed most frequently.

A Phase II study of CPT-11, a new camptothecin, was performed in patients with primary lung cancer. Patients with previously untreated non-small cell carcinomas (group A), or previously treated non-small cell carcinomas (group B), and with small cell carcinomas (group C), were enrolled in this study. CPT-11 was given at a dose of 100 mg/m2 i.v. infusion once a week for three weeks or more. Out of 153 patients enrolled, 128 (A: 67; B: 26; C: 35) were assessed to be evaluable for response by an extramural review committee. Response rates were 34.3% (23/67) for A, 0% (0/26) for B and 37.1% (13/35) for C. The response rate was 50% for previously untreated patients (4/8), and 33.3% for previously treated patients (9/27) including 2 complete responses in the group C. Major toxicities were leukopenia, nausea/vomiting, diarrhea, anorexia and alopecia. Leukopenia and diarrhea were considered to be dose limiting toxicities, but they were reversible. It was, however, suggested that some patients should be monitored carefully for severe reactions and delay in recovery. The results showed that CPT-11 was highly effective against non-small cell and small cell carcinomas of the lung.

An early Phase II study of CTP-11, a new derivative of Camptothecin, in gynecologic cancers was carried out by a cooperative study group of 9 institutions. Forty-six patients were enrolled, and there were 14 cases of ovarian cancers, 7 of cervical cancer, 6 of uterine body cancers and 1 of endometrial stromal sarcoma which satisfied study criteria. The response rate in ovarian cancers was 21.4%, and in cervical cancers 42.9%, among an overall rate of 21.4%. Three out of 6 patients with objective response had undergone previous chemotherapies including cisplatin, suggesting that CPT-11 was effective for patients with no response or refractory to these therapies. Leukopenia was a major adverse reaction with an incidence of 60.0% (grade 2 or more). Gastrointestinal symptoms such as nausea vomiting, anorexia and diarrhea were frequently observed (grade 2 or more; 13.3-43.3%). These were generally tolerable except in a few cases. Besides these reactions, alopecia was also observed (33.3%), but severe adverse reactions such as nephropathy were not. These results suggested that CPT-11 was effective against ovarian cancer and cervical cancer. The recommended dose regimen for a late phase II study is considered to be 100 mg/m2 once weekly and 150 mg/m2 once every 2 weeks.

Combined effect of N-[4-(5-bromo-2-pyrimidinyloxy)-3-chlorophenyl]-N'-(2-nitrobenzoyl ) urea, HO-221, with various antitumor agents was studied using L 1210 leukemia in vivo and in vitro. Ten anticancer drugs were chosen from alkylating agents, antitumor antibiotics, antimetabolites and plant alkaloids each. The combined effect was assessed by comparing ILS (increase of life span) in the combined group with the sum of ILS of each single agent. Synergistic effect was considered to exist if ILS of the combination-treatment group exceeds the sum of those in 2 single-treatment groups. The two-drug combination of HO-221 with cyclophosphamide (CPA), adriamycin (ADM), mitomycin C (MMC), vindesine (VDS), vincristine (VCR) or etoposide showed remarkable synergistic effects with 60-days survivors. However, the combination chemotherapy with antimetabolites, 5-fluorouracil (5-FU) and methotrexate (MTX) showed competitive effects. Moreover, the synergistic cytocidal effect in vitro by the clonogenic assay was observed in combination of HO-221 with the same drug using in vivo test. The present results indicate that HO-221 seems to be a useful antitumor agent in combination chemotherapy.

An early phase II study of CPT-11 was carried out in patients with primary lung cancer in 15 institutions throughout Japan. The efficacy and safety of CPT-11 were studied at 200 mg/m2 based on the results of the previous phase I study. Thirty-eight of 52 enrolled patients were eligible. CPT-11 proved to be effective for primary lung cancer. The response rates were 20.0% (7/35) for non-small cell lung carcinoma and 33.3% (1/3 for small cell lung carcinoma. Hematological toxicities included leukopenia (less than or equal to 3,000) in 44.7% of the patients. Other major toxicities were nausea/vomiting (greater than or equal to grade 2) in 50.0% and diarrhea (greater than or equal to grade 2) in 47.4%.