Topotecan versus paclitaxel for the treatment of recurrent epithelial ovarian cancer

PURPOSE

Topotecan and paclitaxel were evaluated in a randomized, multicenter study of patients with advanced epithelial ovarian carcinoma who had progressed during or after one platinum-based regimen.

PATIENTS AND METHODS

Patients received either topotecan (1.5 mg/m2) as a 30-minute infusion daily for 5 days every 21 days (n = 112) or paclitaxel (175 mg/m2) infused over 3 hours every 21 days (n = 114). Patients had bidimensionally measurable disease and were assessed for efficacy and toxicity.

RESULTS

Response rate was 23 of 112 (20.5%) in topotecan-treated patients and 15 of 114 (13.2%) in paclitaxel-treated patients (P = .138). Disease stabilization for at least 8 weeks was noted in 30% of patients with topotecan and 33% of patients with paclitaxel. Median durations of response to topotecan and paclitaxel were 32 and 20 weeks, respectively (P = .222) and median times to progression were 23 and 14 weeks, respectively (P = .002). Median survival was 61 weeks for topotecan and 43 weeks for paclitaxel (P = .515). Response rates for topotecan and paclitaxel were 13.3% versus 6.7% (P = .303) in resistant patients (not responded to prior platinum-based therapy or progressed within 6 months of an initial response) and 28.8% versus 20.0% (P = .213) in sensitive patients (progressed > 6 months after response). Neutropenia was significantly more frequent on the topotecan arm 79% versus paclitaxel arm 23% (P < .01). It was short-lasting and noncumulative in both arms. Nonhematologic toxicities were generally mild (grades 1 to 2) for both agents.

CONCLUSION

Topotecan has efficacy at least equivalent to paclitaxel manifested by the higher response rate and significantly longer time to progression.

The current status of camptothecin analogues as antitumor agents

The nuclear enzyme topoisomerase I (topo I) has been recently recognized as the target for the anticancer drug camptothecin (CPT) and its derivatives. Two of the agents that target this enzyme--topotecan (TPT) and CPT-11--appear to be active against a broad range of human tumors. In the following presentation, we review 1) the role of topo I in normal cells, 2) the chemistry and proposed mechanism of action of CPT and its analogues, 3) the results of preclinical and clinical testing of TPT and CPT-11, and 4) mechanisms of resistance to these agents. In normal cells, topo I is thought to be involved in gene transcription and DNA replication. During the course of its normal catalytic cycle, topo I transiently forms a covalent bond with DNA. CPT and its derivatives slow the religation step of the enzyme and stabilize the covalent adduct between topo I and DNA. In S-phase cells, advancing replication forks convert these topo I-DNA adducts into double-strand breaks that appear to be responsible for the cytotoxicity of these agents. Preclinical studies demonstrate antineoplastic activity for TPT and CPT-11 in a variety of tumor models. Phase I studies have identified neutropenia as the dose-limiting toxicity for both drugs. Gastrointestinal effects might also be dose-limiting for CPT-11 administered on some schedules. CPT-11 has shown antitumor activity in phase II trials for patients with carcinomas of lung, cervix, ovary, colon, and rectum and for patients with non-Hodgkin's lymphoma. Phase II studies of TPT are in progress. Resistance to the cytotoxic effects of these agents might result from decreased production of topo I or from production of a mutated form of topo I. In addition, decreased metabolic activation of CPT-11 (which is a pro-drug) and active efflux of TPT by P-glycoprotein-mediated transport might contribute to resistance. As agents with a novel mechanism of action, tolerable toxicity, and encouraging antitumor activity in early clinical trials, TPT and CPT-11 are undergoing further clinical development. If these agents can be successfully combined with other active chemotherapy agents, the topo I-directed agents offer the potential for significant advances in the treatment of patients with a variety of malignancies.

Computerized quantitation of synergism and antagonism of taxol, topotecan, and cisplatin against human teratocarcinoma cell growth: a rational approach to clinical protocol design

BACKGROUND

Cisplatin-based induction chemotherapy may achieve a complete response (i.e., no sign of tumor following treatment) in 70%-80% of patients with germ cell tumors. However, only a minority of patients in whom the firstline regimens fail are cured with the salvage regimens.

PURPOSE

The aim of these studies was to identify new agents or new regimens for the treatment of germ cell tumors by carrying out quantitative assessment in vitro of two promising new antitumor agents (paclitaxel [Taxol] and topotecan) and three more established agents (cisplatin, vincristine, and etoposide). These agents were used singly or in two- and three-drug combinations and were selected because they represent five distinct categories of antineoplastic mechanisms.

METHODS

The combination index-isobologram method, which is based on the median-effect principle developed by Chou and Talalay, was used for computerized data analysis. This method was selected because it takes into account both the potencies of each drug and combinations of these drugs and the shapes of their dose-effect curves.

RESULTS

Synergism against the growth of teratocarcinoma cells resistant to cisplatin (833K/64CP10 cells) was greater than against the growth of parent 833K cells. The degrees of synergism were in the following order: cisplatin + topotecan > or = paclitaxel + cisplatin + topotecan > paclitaxel + topotecan > or = paclitaxel + etoposide > paclitaxel + cisplatin + etoposide > paclitaxel + cisplatin. All other combinations showed nearly additive effects or moderate antagonism. The degrees of antagonism were as follows: cisplatin + etoposide > or = paclitaxel + vincristine > paclitaxel + cisplatin + vincristine > cisplastin + vincristine. The combination of paclitaxel and cisplatin was synergistic against 833K/64CP10 cells and moderately antagonistic against 833K cells. Since the combination of paclitaxel, cisplatin, and topotecan and the two-component combinations of these drugs (cisplatin + topotecan and paclitaxel + topotecan) showed synergism stronger than that of other combinations, these three drugs were selected for illustrating detailed data analysis, using a computer software program developed in this institute.

CONCLUSIONS AND IMPLICATIONS

Our findings suggest that, as a result of synergy, the doses of these agents needed to achieve an antitumor effect may be reduced by twofold to eightfold when these agents are given in combination. The present quantitative data analyses for synergism or antagonism provide a basis for a rational design of clinical protocols for combination chemotherapy in patients with advanced germ cell tumors.

Topotecan, a new active drug in the second-line treatment of small-cell lung cancer: a phase II study in patients with refractory and sensitive disease. The European Organization for Research and Treatment of Cancer Early Clinical Studies Group and New Drug Development Office, and the Lung Cancer Cooperative Group

PURPOSE

To assess activity and toxicity of topotecan in previously treated small-cell lung cancer (SCLC) patients.

PATIENTS AND METHODS

Patients with measurable SCLC, progressive after one first-line regimen, were eligible for the study. Two groups of patients were selected: (1) patients who failed first-line treatment < or = 3 months from chemotherapy discontinuation (refractory group); and (2) patients who responded to first-line treatment and progressed greater than 3 months after chemotherapy discontinuation (sensitive group). Topotecan was administered as a 30-minute daily infusion at a dose of 1.5 mg/m2 for 5 consecutive days, every 3 weeks.

RESULTS

One hundred one patients were entered onto the study and 403 courses were administered. Ninety-two patients (47 refractory and 45 sensitive) were eligible and assessable for response. Among refractory patients, there were two partial responses (PRs) and one complete response (CR), for an overall response rate of 6.4% (95% confidence interval [CI], 1.3% to 17.6%), whereas in the sensitive group, there were 11 PRs and six CRs, for an overall response rate of 37.8% (95% CI, 23.8% to 53.5%). Overall median duration of response was 7.6 months. Median survival was 5.4 months; median survival of refractory patients was 4.7 months, whereas that of sensitive patients was 6.9 months (P = .002). Median survival of responding patients was 12.5 months. Toxicity was mainly hematologic. Leukopenia, although short-lived, was universal, with grade III and IV neutropenia occurring in 28% and 46.8% of cycles, respectively. Nonhematological toxicity was mild. Fatigue/malaise was reported in 39.3% of cycles and transient elevation of liver enzymes in 17%.

CONCLUSION

Topotecan has significant activity in SCLC, particularly in patients sensitive to prior chemotherapy, with predictable and manageable toxicity. The incorporation of topotecan in combination chemotherapy regimens for future treatment of SCLC is warranted.

Efficacy of topoisomerase I inhibitors, topotecan and irinotecan, administered at low dose levels in protracted schedules to mice bearing xenografts of human tumors

The efficacy of protracted schedules of therapy of the topoisomerase I inhibitors 9-dimethyl-aminomethyl-10-hydroxycamptothecin (topotecan) and 7-ethyl-10-[4-(1-piperidino)-1-piperidino]-carbonyloxycamptothecin (irinotecan; CPT-11) were evaluated against a panel of 21 human tumor xenografts derived from adult and pediatric malignancies. Tumors included eight colon adenocarcinomas, representing an intrinsically chemorefractory malignancy, six lines derived from childhood rhabdomyosarcoma (three embryonal, three alveolar) representing a chemoresponsive histiotype, sublines of rhabdomyosarcomas selected in vivo for resistance to vincristine and melphalan, and three pediatric brain tumors. All tumors were grown at the subcutaneous site. Topotecan was administered by oral gavage 5 days per week for 12 consecutive weeks. The maximum tolerated dose (MTD) was 1.5 mg/kg per dose. Irinotecan was given by i.v. administration daily for 5 days each week for 2 weeks [(d x 5)2](one cycle of therapy), repeated every 21 days. The MTD for three cycles was 10 mg/kg per dose. Treatment was started against advanced tumors. Topotecan caused a high frequency of objective regressions in one of eight colon tumor lines, whereas irinotecan caused complete regressions (CR) of all tumors in three colon lines and a high frequency of CRs in three additional lines. Both drugs demonstrated similar activity against rhabdomyosarcoma xenografts. Topotecan caused CR of all tumors in four of six lines, and irinotecan in five of six lines evaluated. Both agents retained full activity against tumors selected for primary resistance to vincristine, but only irinotecan retained activity against a tumor selected for primary resistance to melphalan. Both agents demonstrated good activity against brain tumor xenografts with irinotecan causing CR in two of three lines and topotecan inducing CR in one of three lines. Results indicate that low-dose protracted schedules of daily administration of these topoisomerase I inhibitors is either equi-effective or more efficacious than more intense shorter schedules of administration reported previously.

Topotecan, an active drug in the second-line treatment of epithelial ovarian cancer: results of a large European phase II study

PURPOSE

Topotecan is a topoisomerase I inhibitor with preclinical activity against various tumor types. We conducted a large multicenter phase II study with topotecan in ovarian cancer in patients who had failed to respond to one prior cisplatin-based chemotherapeutic regimen.

PATIENTS AND METHODS

Topotecan 1.5 mg/m2/d was administered intravenously by 30-minute infusion for 5 days repeated every 3 weeks. As the cisplatin-free interval relates to response in subsequent treatment, patients were stratified in subgroups, ie, cisplatin-refractory, cisplatin-resistant, and cisplatin-sensitive.

RESULTS

One-hundred eleven patients entered the study. Nineteen patients were considered to be ineligible; 92 patients were assessable for response. A total of 552 courses were given (median, four per patient; range, one to 17). The major toxicities were leukocytopenia and neutropenia, which were grade 3 to 4 in 54.2% and 69.1% of courses, respectively, but with only 4.3% of these being grade 4 neutropenia plus fever or infectious complications. Prophylactic granulocyte colony-stimulating factor (G-CSF) was given in 20.5% of courses to maintain dose-intensity. Other relatively frequent side effects were alopecia (82%), nausea (36.4%), and vomiting (17.5%). The overall response rate was 16.3%, with one complete response (CR) and 14 partial responses (PRs). In the cisplatin-refractory, cisplatin-resistant, and cisplatin-sensitive strata, the response rates were 5.9%, 17.8%, and 26.7%, respectively. The median duration of time of documented response was 21.7 weeks (range, 4.6 to 41.9).

CONCLUSION

Topotecan in a daily-times-five schedule is an effective regimen as second-line treatment in ovarian cancer. Further investigations of topotecan in ovarian cancer, including first-line use and combination with other active agents, are indicated.

Specific phosphorylation of SR proteins by mammalian DNA topoisomerase I

Several metazoan splicing factors are characterized by ribonucleoprotein (RNP) consensus sequences and arginine-serine repeats (RS domain) which are essential for their function in splicing. These include members of the SR-protein family (SC35, SF2/ASF), the U1 small nuclear (sn) RNP protein (U1-70K) and the U2 snRNP auxiliary factor (U2AF). SR proteins are phosphorylated in vivo and the phosphorylation state of U1-70K's RS domain influences its splicing activity. Here we report the purification of a protein kinase that is specific for SR proteins and show that it is DNA topoisomerase I. This enzyme lacks a canonical ATP-binding motif but binds ATP with a dissociation constant of 50 nM. Camptothecin and derivatives, known to be specific inhibitors of DNA topoisomerase I, strongly inhibit the kinase activity in the presence of DNA and affect the phosphorylation state of SR proteins. Thus, DNA topoisomerase I may well be one of the SR protein kinases operating in vivo.

The structural basis of camptothecin interactions with human serum albumin: impact on drug stability

The intense intrinsic fluorescence emissions from several clinically relevant camptothecin drugs have been exploited in order to study the structural basis of drug binding to human serum albumin. Both HPLC and time-resolved fluorescence spectroscopic methodologies were employed to characterize the associations of camptothecins with HSA in phosphate-buffered saline (pH 7.4) at 37 degrees C. The alpha-hydroxy delta-lactone ring moiety of camptothecin (C), 10-hydroxycamptothecin (HC), 10,11-(methylenedioxy)camptothecin (MC) and 9-chloro-10,11-(methylenedioxy)camptothecin (CMC) was in each case observed to hydrolyze more rapidly and completely in the presence of HSA than in the protein's absence. Binding isotherms constructed by the method of fluorescence lifetime titration showed that HSA bound preferentially the carboxylate forms of C, HC, MC, and CMC over their lactone forms, thereby providing an explanation for the shift to the right in the lactone-carboxylate equilibrium observed for each compound upon HSA addition. In marked contrast, three analogues (SN-38, CPT-11, and topotecan) all displayed enhanced stabilities in the presence of HSA. While the lifetimes of CPT-11, topotecan, and the carboxylate forms of both drugs were insensitive to the addition of HSA, the lifetimes of both SN-38 and its carboxylate form did titrate upon HSA addition. Analysis of binding isotherms constructed for the albumin interactions of SN-38 and its carboxylate form demonstrated a higher overall association constant for the lactone form [640 (M amino acid (aa) residues)-1] relative to the carboxylate form [150 (M aa)-1]. Our studies indicate that specific modifications at the 7- and 9-positions of the quinoline nucleus, such as those contained in CPT-11, topotecan, and SN-38, enhance drug stability in the presence of HSA. In the case of SN-38, the enhanced stability was shown to be due to preferential associations between the drug's lactone form and the blood protein.

Phase I and pharmacologic study of topotecan: a novel topoisomerase I inhibitor

PURPOSE

A phase I and pharmacologic study was undertaken to determine the maximum-tolerated dose (MTD), describe the principal toxicities, and characterize the pharmacologic behavior of topotecan, which is a semisynthetic analog of camptothecin with broad preclinical antitumor activity and the first topoisomerase I-targeting agent to enter clinical development in the United States since studies of sodium camptothecin over 2 decades ago.

PATIENTS AND METHODS

Thirty-minute infusions of topotecan were administered daily for 5 consecutive days every 3 weeks to patients with advanced solid malignancies at doses ranging from 0.5 to 2.5 mg/m2/d.

RESULTS

At doses of 1.5 and 2.0 mg/m2, grade 3 and 4 neutropenia occurred in most courses; however, neutropenia was brief and rarely associated with fevers or treatment delays. Neutropenia was more severe in patients with extensive prior treatment than in minimally pretreated patients, but these differences were not substantial. At 2.5 mg/m2, topotecan induced profound and prolonged neutropenia that was frequently associated with fever and treatment delays in minimally pretreated patients. Topotecan also induced mild depressions in the hematocrit level in the majority of courses; however, precipitous drops requiring transfusional therapy occurred in 14% of courses and suggested a drug-induced hemolytic effect. Unlike sodium camptothecin, hemorrhagic cystitis was not observed. Thrombocytopenia, skin rash, diarrhea, and vomiting occurred infrequently and were modest in severity. Responses were observed in non-small-cell lung carcinoma and platinum-refractory ovarian carcinoma. Drug disposition in plasma was described by a biexponential model, with renal elimination accounting for 38.7% of drug disposition. Topotecan was rapidly hydrolyzed in vivo to a less active, open-ring form.

CONCLUSIONS

Neutropenia is the dose-limiting toxicity, and 1.5 mg/m2 is the recommended starting dose of topotecan for both minimally and heavily pretreated patients in future phase II trials, with escalation to 2.0 mg/m2 if treatment is well tolerated. Non-small-cell lung and platinum-refractory ovarian carcinomas should be among those evaluated in phase II trials of topotecan.

Phase II study of intravenous topotecan as a 5-day infusion for refractory epithelial ovarian carcinoma

PURPOSE

To determine the efficacy and toxicity of topotecan administered as a 5-day intravenous infusion in patients with advanced ovarian cancer refractory to cisplatin-based chemotherapy.

PATIENTS AND METHODS

Thirty patients with advanced epithelial ovarian cancer refractory to cisplatin-based chemotherapy received intravenous infusions of topotecan 1.5 mg/m2 delivered over 30 minutes each day for 5 days. A course was repeated every 21 days. The patient eligibility requirements included age > or = 18 years, Zubrod score < or = 2, measurable disease, adequate hepatic and renal function, neutrophil count > or = 1,500/microL, platelet count > or = 100,000/microL, and anticipated survival > or = 3 months.

RESULTS

Twenty eight patients were assessable for response and toxicity. All patients were assessable for survival. The major toxicity from administration of topotecan at this dose schedule was myelosuppression; 21 patients required dose reductions. Four patients had neutropenic fever that required hospitalization, and seven patients required platelet transfusions. Maculopapular pruritic exanthema occurred in 20% of patients; gastrointestinal side effects were mild. No deaths were reported on the study. At dose levels of 1.5, 1.25, and 1.0 mg/m2, 61%, 31%, and 25% of patients, respectively, required dose reductions. Of 28 assessable patients, four (14%; 95% confidence interval [CI], 4% to 34%) achieved a partial response (PR) at a median of 1.4 months and lasting 8.9 months, and 17 had stable disease (SD). The overall median survival time was 10.0 months (95% CI, 8.1 to 13.5).

CONCLUSION

Topotecan shows modest clinical activity against cisplatin-refractory ovarian cancer, although the dose-intensity is compromised by the depth of the granulocyte nadir and the duration of granulocytopenia. Further studies of topotecan may necessitate a reevaluation of optimal dose schedule, with the possible incorporation of multilineage cytokines, and its activity in taxane-resistant tumors.

Evaluation of 9-dimethylaminomethyl-10-hydroxycamptothecin against xenografts derived from adult and childhood solid tumors

The topoisomerase I inhibitor 9-dimethylaminomethyl-10-hydroxycamptothecin (topotecan) was evaluated against a panel of xenografts comprising four lines of adult colon adenocarcinoma, three colon tumors derived from adolescents, six childhood rhabdomyosarcomas from previously untreated patients as well as sublines selected in vivo for resistance to vincristine and melphalan, and three lines of childhood osteogenic sarcoma. Efficacy was determined at maximal tolerated dose levels using intermittent i.p. administration [every 4 days for 4 doses (q4dx4)] or daily p.o. or i.p. administration 5 days per week for up to 20 courses. On a q4dx4 schedule, the maximum tolerated dose (MTD) was 12.5 mg/kg per administration, which caused marked weight loss and lethality in approximately 5% of the tumor-bearing mice. This schedule caused significant growth inhibition (but no tumor regression) in advanced adult colon adenocarcinomas. The minimal treated/control (T/C) ratios were 0.49, 0.54, and 0.3 for three of the tumor lines and were achieved at 18-21 days after the initiation of treatment. In contrast, rhabdomyosarcomas were considerably more sensitive, with T/C ratios being < 0.1 for three lines, whereas topotecan was less active against two other rhabdomyosarcoma xenografts (minimal T/C ratios, 0.17 and 0.14). As inhibitors of topoisomerase I have been demonstrated to have activity in the replication phase of the cell cycle (S-phase-specific), prolonged administration schedules were examined. Mice received topotecan 5 days per week for 3 weeks either by i.p. injection or by oral gavage (p.o.). In selected experiments, p.o. administration was continued for up to 20 weeks. Oral administration for 3 weeks (2 mg/kg per dose) resulted in complete regression of all six lines of rhabdomyosarcoma, with two lines demonstrating no regrowth during the period of observation (> or = 84 days). Similar results were obtained after i.p. administration, suggesting significant schedule dependency for these tumors. For colon tumors, the daily administration schedule (i.p. or p.o.) demonstrated some advantage over the intermittent schedule, resulting in partial regressions and significant inhibition of the growth of several colon adenocarcinoma lines. In rhabdomyosarcoma Rh12 and VRC5 colon adenocarcinoma, both of which demonstrated intermediate sensitivity to topotecan, and in osteosarcoma OS33, protracted p.o. administration for 13-20 weeks (1.0-1.5 mg/kg per dose given daily x 5 days) caused complete regression without regrowth in Rh12 and OS33 tumors and partial regression of all VRC5 tumors. No toxicity was observed using this schedule of administration. Topotecan demonstrated significant activity against all three osteosarcoma xenografts examined, with optimal schedules causing complete regression in two lines.(ABSTRACT TRUNCATED AT 400 WORDS)

Three inhibitors of type 1 human immunodeficiency virus long terminal repeat-directed gene expression and virus replication

Transcription of type 1 human immunodeficiency virus (HIV-1) provirus is governed by the viral long terminal repeat (LTR). Drugs can block HIV-1 replication by inhibiting activity of its LTR. We report that topotecan, beta-lapachone, and curcumin are potent and selective inhibitors of HIV-1 LTR-directed gene expression, at concentrations that have minor effects on cells. At these concentrations, each drug inhibited p24 antigen production in cells either acutely or chronically infected with HIV-1. Their target is transcriptional function of the LTR.

Phase II study of topotecan in patients with extensive-stage small-cell carcinoma of the lung: an Eastern Cooperative Oncology Group Trial

PURPOSE

To determine the response rate and survival of chemotherapy-naive patients with extensive-stage small-cell lung cancer (SCLC) treated with topotecan, and to determine the relationship of topotecan pharmacokinetics with response and toxicity.

PATIENTS AND METHODS

Forty-eight patients with previously untreated, extensive-stage SCLC received 2.0 mg/m2 of topotecan daily for 5 days. The first 13 patients were treated without colony-stimulating factor (CSF) support; the next 35 patients received 5 micrograms/kg of granulocyte-colony-stimulating factor (G-CSF) for 10 to 14 days starting on day 6. Cycles were repeated every 3 weeks for a maximum of four cycles. Patients who had a partial response to topotecan after four cycles, stable disease after two cycles, or progressive disease at any time received salvage chemotherapy with cisplatin and etoposide. Topotecan pharmacokinetics were measured using a four-point sampling scheme.

RESULTS

Of 48 patients, none had a complete response and 19 had a partial response, for an objective response rate of 39% (95% confidence interval [CI], 25.2% to 53.0%). The median response duration was 4.8 months (95% CI, 3.0 to 7.3). After a median follow-up duration of 18.2 months, the overall median survival time was 10.0 months (95% CI, 8.2 to 12.7); the 1-year survival rate was 39% (95% CI, 25.2% to 53.0%). Eight of 34 patients (24%) who received salvage chemotherapy responded. Four of 17 patients who did not respond to first-line therapy with topotecan responded to cisplatin and etoposide. The most common toxicity was hematologic. Ninety-two percent of patients treated without G-CSF developed grade 3 or 4 neutropenia, compared with 29% who received G-CSF. However, the incidence of neutropenic fevers was similar between the two groups (8% and 11%, respectively), and one patient in each group died of neutropenic fevers. There were no differences in objective tumor response, duration of response, time to treatment failure, or survival between the 13 patients who entered the study before G-CSF administration was mandated and the 35 patients who entered after and received G-CSF. There was poor correlation between the WBC count and absolute neutrophil counts (ANCs) and both the area under the curve (AUC) and maximum concentration++ (Cmx) of total topotecan in plasma. There was no correlation between the tumor response and either AUC or Cmx of total topotecan.

CONCLUSION

The activity of topotecan in extensive-stage SCLC noted in this study warrants further investigation of this agent in phase III clinical trials.

Cytotoxic effects of topotecan combined with various anticancer agents in human cancer cell lines

BACKGROUND

Topotecan (TPT) is a topoisomerase I poison that exhibits antineoplastic activity. Analysis of the cytotoxic effects of combinations of TPT and other anticancer agents has been limited.

PURPOSE

We assessed the cytotoxic effects produced by combinations of TPT and other antineoplastic agents in experiments involving multiple human cancer cell lines of diverse histologic origins.

METHODS

The cytotoxic effects of various antimetabolites (fluorouracil, methotrexate, or cytarabine), antimicrotubule agents (vincristine or paclitaxel [Taxol]), DNA alkylating agents (melphalan, bis[chloroethyl]nitrosourea [BCNU], or 4-hydroperoxycyclophosphamide [4HC]), and a DNA-platinating agent (cisplatin), alone and in combination with TPT, were measured in clonogenic (i.e., colony-forming) assays. HCT8 ileocecal adenocarcinoma, A549 non-small-cell lung carcinoma, NCI-H82ras(H) lung cancer, T98G glioblastoma, and MCF-7 breast cancer cell lines were used in these assays. The data were analyzed by the median effect method, primarily under the assumption that drug mechanisms of action were mutually nonexclusive (i.e., completely independent of one another). For each level of cytotoxicity (ranging from 5% to 95%), a drug combination index (CI) was calculated. A CI less than 1 indicated synergy (i.e., the effect of the combination was greater than that expected from the additive effects of the component agents), a CI equal to 1 indicated additivity, and a CI greater than 1 indicated antagonism (the effect of the combination was less than that expected from the additive effects of the component agents).

RESULTS

When the mechanisms of drug action were assumed to be mutually nonexclusive, virtually all CIs for combinations of TPT and either antimetabolites or antimicrotubule agents revealed cytotoxic effects that were less than additive. The CIs calculated at low-to-intermediate levels of cytotoxicity for combinations of TPT and the DNA alkylating agents melphalan, BCNU, and 4HC also showed drug effects that were less than additive; in most cases, however, nearly additive or even synergistic effects were observed with these same drug combinations at high levels of cytotoxicity (i.e., at > or = 90% inhibition of colony formation). Results obtained with combinations of TPT and cisplatin varied according to the cell line examined. With A549 cells, less than additive effects were seen at low-to-intermediate levels of cytotoxicity, and more than additive effects were seen at high levels of cytotoxicity. With NCI-H82ras(H) cells, synergy was observed over most of the cytotoxicity range.

CONCLUSIONS AND IMPLICATIONS

TPT cytotoxicity appears to be enhanced more by combination with certain DNA-damaging agents than by combination with antimetabolites or antimicrotubule agents. Interactions between TPT and other drugs can vary depending on the cell type examined. Further investigation is required to determine the basis of the observed effects and to determine whether these in vitro findings are predictive of results obtained in vivo.

Activity of topotecan, a new topoisomerase I inhibitor, against human tumor colony-forming units in vitro

BACKGROUND

Topotecan [(S)-9-dimethylaminomethyl(10-hydroxy-camptothecin), NSC 609699, SK&F 104864A], a semisynthetic analogue of the natural product camptothecin, is a cell cycle-specific drug that exerts antineoplastic activity through inhibition of topoisomerase I. Currently, topotecan is undergoing phase I and early phase II clinical trials. The dose-limiting toxicity for topotecan is myelosuppression.

PURPOSE

Our purpose was to determine plasma concentrations and exposure times necessary for optimal clinical activity and tumor types that may be responsive in phase II clinical studies of topotecan.

METHODS

A soft-agar cloning system assay was used to determine the in vitro effects of topotecan against cells from biopsy specimens of colorectal, breast, lung, ovarian, renal cell, and gastric cancers and cancers of unknown primary origin. We studied 141 freshly explanted tumor specimens, using 1-hour exposure to topotecan, and 80 were studied using continuous exposure. A decrease in tumor colony formation resulting from drug exposure was considered an in vitro response if survival of colonies was up to 50% of that in controls.

RESULTS

With 1-hour exposure, in vitro responses were seen in 10% and 25% of assessable tumor specimens at final topotecan concentrations of 1.0 and 10.0 micrograms/mL, respectively. With continuous exposures at concentrations of 0.1 and 1.0 micrograms/mL, in vitro response rates were 34% and 76%, respectively. Specific activity was seen against colorectal, breast, non-small-cell lung, ovarian, and renal cell cancers, with responses observed in 27%, 25%, 32%, 39%, and 83%, respectively, of assessable tumor specimens after continuous exposure to 0.1 micrograms/mL topotecan. A subset of tumor specimens resistant to doxorubicin or fluorouracil was sensitive to topotecan, and the difference in sensitivity was statistically significant. In addition, some of the tumor specimens resistant to cyclophosphamide and etoposide were also sensitive to topotecan.

CONCLUSIONS

Topotecan appears to be active in vitro against a variety of human tumors, including a subgroup resistant in vitro to standard antineoplastic agents. If plasma levels of 0.1 micrograms/mL can be achieved for prolonged periods of time in ongoing clinical trials, topotecan should have substantial clinical activity.

IMPLICATIONS

Further clinical development of topotecan is warranted.

Topoisomerase inhibitors. A review of their therapeutic potential in cancer

The nuclear enzymes topoisomerase I and II are critical for DNA function and cell survival, and recent studies have identified these enzymes as cellular targets for several clinically active anticancer drugs. Topoisomerase II inhibitors (anthracyclines, epipodophyllotoxins, etc.) are active against several types of tumours. However, treatment with these drugs often results in the development of the multi-drug resistance. Because topoisomerase II-active drugs have several different modes of action, different mechanisms of resistance, including decreased activation and increased detoxification by glutathione-dependent enzymes, have also been implicated. Unlike topoisomerase II, topoisomerase I is not a cell cycle-dependent enzyme and, therefore, it is a more desirable cellular target for anticancer drug development. Topoisomerase I inhibitors, such as camptothecin and its derivatives, have shown significant activity against a broad range of tumours and, in general, are not substrates for either the multi-drug-resistance P-170 glycoprotein or the multi-drug-resistance-associated protein. Because of manageable toxicity and encouraging activity against solid tumours, topoisomerase I-active drugs offer promise in the clinical management of human tumours.

Phase I trial of low-dose continuous topotecan infusion in patients with cancer: an active and well-tolerated regimen

PURPOSE

The objective of this trial was to define the maximum-tolerated dose (MTD) of topotecan for a 21-day infusion schedule, repeated every 28 days, in patients with cancer.

PATIENTS AND METHODS

Cohorts of four patients received continuous ambulatory infusions of topotecan in escalated duration with doses beginning at 0.20 mg/m2/d for 7 days. Forty-four patients with a histologic diagnosis of cancer refractory to standard therapy were treated with infusions of topotecan for a total of 115 cycles and 1,780 patient-days of infusion. The median number of treatment cycles per patient was two (range, one to eight). All patients were heavily pretreated with chemotherapy and/or radiation.

RESULTS

The dose-limiting toxicity (DLT) was myelo-suppression, with thrombocytopenia greater than neutropenia seen at the dose level of 0.70 mg/m2/d for 21 days. At the MTD of 0.53 mg/m2, ten patients were treated for a total of 20 courses, resulting in one episode of grade 4 thrombocytopenia and leukopenia, one grade 3 thrombocytopenia, and two grade 3 leukopenias. This dose regimen was well tolerated, with minimal nonhematologic toxicity. Local infusion port complications developed in two patients and two had bacteremia, including one patient with repeated local skin infections. Objective responses were observed in this heavily pretreated population for patients with ovarian cancer (two partial responses and one mixed response in six patients), breast cancer (one partial response and one mixed response in two patients), and for one patient each with renal and non-small-cell lung cancer (two partial remissions).

CONCLUSION

Twenty-one-day topotecan infusion is well tolerated at 0.53 mg/m2, with dose-intensity exceeding other schedules for administration of topotecan. The DLT is hematologic, with thrombocytopenia somewhat exceeding leukopenia. Objective responses were observed in seven patients with breast, ovarian, renal, and non-small-cell lung cancer.

Clinical pharmacokinetics of topotecan

Topotecan (Hycamtin), a semisynthetic water-soluble derivative of camptothecin, is a potent inhibitor of DNA topoisomerase I in vitro and has demonstrated encouraging antitumour activity in a wide variety of tumours, including ovarian cancer and small cell lung cancer. Now approved in the US, topotecan has completed single-agent phase I testing; phase II/III trials are ongoing. Under physiological conditions the lactone moiety of topotecan undergoes a rapid and reversible pH-dependent conversion to a carboxylated open-ring form, which lacks topoisomerase I inhibiting activity. At equilibrium at pH 7.4 the open-ring form predominates. Topotecan is stable in infusion fluids in the presence of tartaric acid (pH < 4.0), but is unstable in plasma, requiring immediate deproteinisation with cold methanol after blood sampling and storage of the extract at -30 degrees C to preserve the lactone form. Topotecan has been administered in phase I trials in several infusion schedules ranging from 30 minutes to 21 days. The plasma decay of topotecan concentrations usually fits a 2-compartment model. Rapid hydrolysis of topotecan lactone results in plasma carboxylate levels exceeding lactone levels as early as 45 minutes after the start of a 30-minute infusion. The peak plasma concentrations and the area under the plasma concentration-versus-time curves (AUC) show linear relationship with increasing dosages. No evidence of drug accumulation is seen with daily 30-minute infusions for 5 consecutive days. Topotecan lactone is widely distributed into the peripheral space, with a mean volume of distribution (Vd) at steady-state of 75 L/m2. The mean total body clearance of the lactone form is 30 L/h/m2, with a mean elimination half-life (t1/2 beta) of 3 hours; renal clearance accounts for approximately 40% of the administered dose with a large interindividual variability. The oral bioavailablity of topotecan is approximately 35%. The low bioavailability may be caused by hydrolysis of topotecan lactone in the gut, yielding substantial amounts of the open-ring form, which is poorly absorbed. Renal dysfunction may decrease topotecan plasma clearance. Creatinine clearance is significantly, but poorly, correlated with topotecan clearance. Hepatic impairment does not influence topotecan disposition. Indices of systemic exposure (steady-state concentrations and AUC) are correlated with the extent of myelotoxicity. Sigmoidal functions adequately describe the relationships between systemic exposure and the percentage decrease in neutrophils.

Biochemical and biophysical analyses of recombinant forms of human topoisomerase I

Amino acid sequence comparisons of human topoisomerase I (Topo I) with seven other cellular Topo I enzymes reveal that the enzyme can be divided into four major domains: the unconserved NH2-terminal domain (24 kDa), the conserved core domain (54 kDa), a poorly conserved linker region (5 kDa), and the highly conserved COOH-terminal domain (8 kDa), which contains the active site tyrosine. To investigate this predicted domain organization, recombinant baculoviruses were engineered to express the 91-kDa full-length enzyme, a 70-kDa NH2-terminally truncated enzyme that is missing the first 174 residues, and a 58-kDa NH2- and COOH-terminally truncated core fragment encompassing residues 175-659. The specific activity of the full-length and Topo70 enzymes are indistinguishable from the native human Topo I purified from HeLa cells. Each protein is inhibited by camptothecin, topotecan, and 9-aminocamptothecin, but not by ATP. Activity is stimulated by Mg2+, Ba2+, Ca2+, Mn2+, spermine, and spermidine. The magnitude of the stimulatory effect of Mg2+ is inversely proportional to the salt concentration. Furthermore, at KCl concentrations of 300 mM or greater, the addition of Mg2+ is inhibitory. The effects of Mg2+ and the polycations spermine and spermidine are partially additive, an indication that the stimulatory mechanisms of the two substances are different. Activity was strongly inhibited or abolished by Ni2+, Zn2+, Cu2+, Cd2+, and Co2+. An examination of the hydrodynamic properties of full-length Topo I, Topo70, and Topo58 demonstrates that the core, linker, and COOH-terminal domains fold into a globular structure, while the NH2-terminal domain is highly extended. A comparison of the circular dichroism spectra of full-length Topo I and Topo70 demonstrates that residues 1-174 (approximately 21 kDa) of Topo I are largely if not completely unfolded. This observation is consistent with the fact that the NH2-terminal domain is dispensable for activity.

Topotecan in platinum- and paclitaxel-resistant ovarian cancer

OBJECTIVE

The purpose of this study was to define the response rate and toxicity of topotecan in patients with ovarian cancer resistant to first-line therapy.

METHODS

Twenty patients with advanced or recurrent ovarian cancer were enrolled in a phase I/II protocol, and an additional 16 patients were treated following protocol closure at Washington University Medical Center. The starting dose of topotecan was 1.25 mg/m2/day given intravenously over 30 min for 5 consecutive days. Patients were eligible for response evaluation if they completed more than one cycle of topotecan. All patients were evaluated for toxicity.

RESULTS

Of 28 patients eligible for response evaluation, 26 were resistant to both platinum and paclitaxel prior to treatment with topotecan. There were four partial responders and no complete responders for a total response rate of 14% (95% confidence interval: 4 to 33%). All responders had exhibited primary resistance to both platinum and paclitaxel. Myelotoxicity was the major toxicity, with 92% of patients experiencing Gynecologic Oncology Group (GOG) grade 3 or 4 neutropenia and 67% experiencing GOG grade 3 or 4 thrombocytopenia. Other toxicity was minimal and easily managed. Fifty percent of patients receiving more than one cycle of topotecan tolerated a dose equal or greater to the starting dose.

CONCLUSIONS

Topotecan exhibits activity in patients with ovarian cancer resistant to both platinum and paclitaxel. Further study is warranted in less heavily pretreated patients and in combination with other chemotherapeutic agents.

Sequences of topotecan and cisplatin: phase I, pharmacologic, and in vitro studies to examine sequence dependence

PURPOSE

A phase I and pharmacologic study was performed to evaluate the feasibility of administering the topoisomerase I (topo I) inhibitor topotecan (TPT) in combination with cisplatin (CDDP) in minimally pretreated adults with solid tumors. The study was designed to evaluate the magnitude of the toxicologic and pharmacologic differences between the two sequences of drug administration.

MATERIALS AND METHODS

TPT was administered as a 30-minute infusion daily for 5 days and CDDP was given either before TPT on day 1 or after TPT on day 5. Each patient was treated with both schedules on an alternating basis every 3 weeks. Sequential dose escalation of TPT or CDDP resulted in three dosage permutation of TPT/CDDP (mg/m2): 0.75/50, 1/50, and 0.75/75. After the maximum-tolerated dose (MTD) level was achieved, the feasibility of using granulocyte colony-stimulating factor (G-CSF) to permit further dose escalation was studied. To examine the interaction of TPT and CDDP in vitro, human A549 lung cancer cells were exposed to these agents concurrently and sequentially.

RESULTS

Dose-limiting neutropenia and thrombocytopenia resulted after the doses of TPT or CDDP were increased to greater than 0.75 and 50 mg/m2, respectively, without and with G-CSF. The sequence of CDDP before TPT induced significantly worse neutropenia and thrombocytopenia than the alternate sequence. In vitro studies failed to provide any evidence for the differences in the cytotoxicity of these two sequences. Instead, pharmacokinetic studies suggested that the differences in toxicity were due, in part, to lower TPT clearance and exposure when CDDP preceeds TPT, possibly due to subclinical renal tubular toxicity induced by CDDP.

CONCLUSION

The sequence of CDDP before TPT at doses of 50 and 0.75 mg/m2, respectively, is recommended for subsequent clinical trials in tumor types in which both agents have significant single-agent activity. The potential for sequence-dependent cytotoxic, toxicologic, and pharmacologic effects should be evaluated in concurrent clinical and laboratory studies in the course of developing combination chemotherapy regimens that consist of topo I-targeting agents and other antineoplastic agents, particularly DNA-damaging agents.

Cerebrospinal fluid pharmacokinetics and penetration of continuous infusion topotecan in children with central nervous system tumors

The purpose of this study was to describe the cerebrospinal fluid (CSF) penetration of topotecan in humans, to generate a pharmacokinetic model to simultaneously describe topotecan lactone and total concentrations in the plasma and CSF, and to characterize the CSF and plasma pharmacokinetics of topotecan administered as a continuous infusion (CI). Plasma and CSF samples were collected from 17 patients receiving 5.5 or 7.5 mg/m2 per day as a 24-h CI (5 patients, 7 courses), or 0.5 to 1.25 mg/m2 per day as a 72-h CI (12 patients, 12 courses). CSF samples were obtained from either a ventricular reservoir (VR) or a lumbar puncture (LP). Topotecan lactone and total (lactone plus hydroxy acid) concentrations were determined by HPLC and fluorescence detection. Using MAP-Bayesian modelling, a three-compartment model was fitted simultaneously to topotecan lactone and total concentrations in the plasma and CSF. The penetration of topotecan into the CSF was determined from the ratio of the CSF to the plasma area under the concentration-time curve. The median CSF ventricular lactone concentrations, obtained prior to the end of infusion (EOI), were 0.86, 1.4, 0.73, 5.3, and 4.6 ng/ml for patients receiving 0.5, 1.0, 1.25, 5.5, and 7.5 mg/m2 per day, respectively. EOI CSF lumbar lactone concentrations measured in three patients were 0.44, 1.1, and 1.7 ng/ml for topotecan doses of 1.0, 5.5, and 7.5 mg/m2 per day, respectively. In two patients receiving 1.25 mg/m2 per day, EOI CSF concentrations were obtained simultaneously from a VR and LP; the lumbar lactone concentrations were 30% and 49% lower than the ventricular concentrations. During a 24-h and a 72-h CI, the median CSF penetration of topotecan lactone was 0.29 (range 0.10 to 0.59) and 0.42 (range 0.11 to 0.86), respectively. A three-compartment model adequately described topotecan lactone and total concentrations in the plasma and CSF. Topotecan was therefore found to significantly penetrate into the CSF in humans. The pharmacokinetic model presented may be useful in the design of clinical studies of topotecan to treat CNS tumors.

Influence of low pH on cytotoxicity of paclitaxel, mitoxantrone and topotecan

The extracellular pH (pHe) of solid tumours is often lower than in normal tissues, and this may influence the uptake and/or activity of anti-cancer drugs. The cytotoxicity of mitoxantrone, paclitaxel and topotecan was therefore assessed at low pHe and after manipulation of intracellular pH (pHi) in murine EMT6 and in human MGH-U1 cells. The cytotoxic efficacy of all three agents was reduced at pHe 6.5 as compared with pHe 7.4. The ionophore nigericin and inhibitors of membrane-based ion exchange mechanisms that regulate pHi (5-[N-ethyl-N-isopropyl] amiloride, EIPA; 4,4-diisothiocyanstilbene 2,2-disulphonic acid, DIDS) were used to cause intracellular acidification. Combined use of the cytostatic drugs with pHi modifiers reduced their cytotoxicity under both physiological and low-pHe conditions. The uptake into cells of mitoxantrone (a weak base) was inhibited at pHe 6.5 as compared with pHe 7.4, and smaller effects of low pHe to inhibit uptake of topotecan were also observed. DNA analysis of cell cycle distribution revealed that intracellular acidification, as observed during incubation at low pHe and/or using pHi modifiers, resulted in accumulation of cells in G1 phase, where they may be more resistant to these drugs. Reduced uptake of weak bases (mitoxantrone) at low pHe and altered cell cycle kinetics upon acidification are the postulated causes of reduced cytotoxicity of the agents investigated.

Current perspectives on camptothecins in cancer treatment

The camptothecins are a new class of chemotherapeutic agents which have a novel mechanism of action targeting the nuclear enzyme topoisomerase I. Knowledge of the structure-activity relationships of the parent compound camptothecin has led to the development of effective soluble analogues with manageable toxicities. Broad anti-tumour activity shown in preclinical studies has been confirmed in phase I/II studies for irinotecan and topotecan. Two other derivatives, 9-aminocamptothecin and GI 147211C, are undergoing phase I and early phase II evaluation. Although camptothecin is a plant extract, it and most of its derivatives are not affected by the classic P-gpMDR1 mechanism of resistance which may allow the development of novel combination chemotherapeutic regimens. Important areas of future endeavour will include the development of rational combination regimens and the pursuit of randomised trials. Based on single agent data, colorectal cancer and non-small-cell lung cancer should be the focus for future irinotecan studies. Small-cell lung cancer and ovarian carcinoma are logical tumour types to pursue with topotecan. Both 9-aminocamptothecin and GI 147211C are too early in their clinical evaluation to make recommendations about their future roles. Finally, the unfolding story of camptothecin analogue development will give important insights into the predictive value of preclinical observations on relative efficacy, schedule dependency, combination strategies and resistance mechanisms which have helped determine the strategies for clinical evaluation of these agents.