Agent Topotecan Research Articles

Design, synthesis, and evaluation of 3,4-dihydro-2H-[1,4]diazepino[6,7,1-hi]indol-1-ones as inhibitors of poly(ADP-ribose) polymerase.

The design, synthesis, and biological evaluation of potent inhibitors of poly(ADP-ribose) polymerase-1 (PARP-1) are reported. A novel series of 3,4-dihydro-2H-[1,4]diazepino[6,7,1-hi]indol-1-ones were designed using a combination of protein structure-based drug design, molecular modeling, and structure-activity relationships (SAR). These novel submicromolar inhibitors possess a tricyclic ring system conformationally restricting the benzamide in the preferred cis orientation. The compounds were designed to optimize space-filling and atomic interactions within the NAD+ binding site of PARP-1. Previously described and newly adapted methods were applied to syntheses of these tricyclic inhibitors. Various modifications were made to the diazepinoindolones at the 6- and 7-positions in order to study this region of the active site and optimize noncovalent interactions. The electron density of derivative 28 bound to chicken PARP-1 revealed that the oxime makes a tight hydrogen bond with the catalytic gamma-carboxylate of glutamic acid (Glu) 988 in accordance with our original designs and models. Most of the compounds have been evaluated for inhibition of human PARP-1. Selected inhibitors were also tested for the ability to potentiate the cytotoxic effect of the DNA-damaging agent Topotecan.

Mrp4 confers resistance to topotecan and protects the brain from chemotherapy.

The role of the multidrug resistance protein MRP4/ABCC4 in vivo remains undefined. To explore this role, we generated Mrp4-deficient mice. Unexpectedly, these mice showed enhanced accumulation of the anticancer agent topotecan in brain tissue and cerebrospinal fluid (CSF). Further studies demonstrated that topotecan was an Mrp4 substrate and that cells overexpressing Mrp4 were resistant to its cytotoxic effects. We then used new antibodies to discover that Mrp4 is unique among the anionic ATP-dependent transporters in its dual localization at the basolateral membrane of the choroid plexus epithelium and in the apical membrane of the endothelial cells of the brain capillaries. Microdialysis sampling of ventricular CSF demonstrated that localization of Mrp4 at the choroid epithelium is integral to its function in limiting drug penetration into the CSF. The topotecan resistance of cells overexpressing Mrp4 and the polarized expression of Mrp4 in the choroid plexus and brain capillary endothelial cells indicate that Mrp4 has a dual role in protecting the brain from cytotoxins and suggest that the therapeutic efficacy of central nervous system-directed drugs that are Mrp4 substrates may be improved by developing Mrp4 inhibitors.

A mathematical model for the in vitro kinetics of the anti-cancer agent topotecan

In this paper a compartmental modelling approach is applied to provide a mathematical description of the activity of the anti-cancer agent topotecan, and delivery to its nuclear DNA target following administration. The activity of topotecan in defined buffers is first modelled using a linear two compartment model that then forms the basis of a cell based model for drug activity in live cell experiments. An identifiability analysis is performed before parameter estimation to ensure that the model output (i.e., continuous, perfect and noise-free data) uniquely determines the parameters. Parameter estimation is performed using experimental data which offers concentrations of active and inactive forms of topotecan from high performance liquid chromatography methods.

A phase II study of liposomal lurtotecan (OSI-211) in patients with topotecan resistant ovarian cancer

Objective. To determine the safety and efficacy of a novel topoisomerase I inhibitor, liposomal lurtotecan, in patients with topotecan resistant ovarian cancer. Methods. The trial was an open-label phase II study for patients stratified by resistance to either single agent topotecan or to a prior topotecan-containing regimen. Liposomal lurtotecan was delivered at a dose of 2.4 mg/m 2 on Days 1 and 8 of a 21-day cycle. Dose escalations and reductions were allowed based on hematologic toxicity. Patients were evaluated every two cycles for response to liposomal lurtotecan. Results. Twenty-two women were accrued, with 16 women resistant to single agent topotecan and 6 women resistant to topotecan given in combination with a second chemotherapy agent. Hematologic toxicity consisted of mild to moderate thrombocytopenia, anemia, and neutropenia with mild to moderate gastrointestinal toxicity and fatigue. There were no responses, although eight patients had stable disease. Conclusions. Liposomal lurtotecan at this schedule demonstrates moderate hematologic toxicity and no evidence of clinical activity in a group of heavily pretreated women previously exposed to the topoisomerase I inhibitor topotecan. The study of this agent in alternative patient populations or with alternative schedules is ongoing.

Factors affecting pharmacokinetic variability of oral topotecan: a population analysis

The aim of this study was to characterise the pharmacokinetics of the anticancer agent topotecan, and explore the influence of patient covariates and interoccasion variability on drug disposition. Data were obtained from 190 patients who received the drug as a 30-min infusion (N=72) or orally (N=118). The population model was built with the use of NONMEM to identify candidate covariates, and obtain models for clearance (CL) and volume of distribution. The final models were based on first-order absorption with lag-time (oral data), and a two-compartment model with linear elimination from the central compartment. The Cockcroft–Gault creatinine clearance (CrCl) and WHO performance status (PS) were the only significant covariates: CL=(12.8+2.1 × CrCl) × (1−0.12 × PS). For the volume of distribution, a correlation was found between body weight and the central volume (V1)=0.58 × body weight. Based on the structural models, a limited-sampling strategy was developed with minor bias and good precision that can be applied a posteriori using timed samples obtained at 1.5, and 6 h after the administration of topotecan. In conclusion, a population pharmacokinetic model for topotecan has been developed that incorporates measures of renal function and PS to predict CL. In combination with drug monitoring, the limited sampling strategy allows individualised treatment for patients receiving oral topotecan.

Compartmental modelling to assess stability of topotecan bound to DNA

In this paper, a compartmental model is proposed for describing the in vitro kinetics of the anti-cancer agent topotecan following administration into a culture medium containing human lymphoma cells in suspension. The model extends one previously proposed by including an extra dissociation pathway, with the objective of describing the effect of DNA binding on the stability of bound topotecan. The structural identifiability and steady states of the model are analysed. The model is fitted to high performance liquid chromatography data and it is found that there is a qualitative difference between the predicted behaviour of the new model and that of the previous model.

Hematological side-effect profiles of individualized chemotherapy regimen for recurrent ovarian cancer.

The long-term results for patients with recurrent ovarian cancer (ROC) are poor. There is a need to optimize treatment strategies to improve outcome by avoiding ineffective regimens which are often associated with exacerbated side-effects. Individualized chemotherapy regimens guided by a chemosensitivity assay (ATP-tumor chemosensitivity assay) have already been used successfully to direct chemotherapy. Taking the results of this assay into account, application of drug combinations appears more advisable. Here we present a systematic evaluation of toxicities seen with individualized chemotherapy for ROC. A total of 62 patients who received 314 cycles of antineoplastic therapies were evaluated. Three single agents (topotecan, paclitaxel and gemcitabine) and five combinations (cisplatin/gemcitabine, carbopatin/gemcitabine, gemcitabine/treosulfan, mitoxantrone/paclitaxel and carboplatin/paclitaxel) were examined. With respect to myelotoxicity, most single agents except topotecan revealed favorable results in comparison to drug combinations. However, this observation lacks statistical significance. Generally, severe myelosuppression was rare. The highest incidence of leukopenia was seen in regimens with mitoxantrone/paclitaxel or gemcitabine/treosulfan, respectively. Thrombocytopenia accompanied most commonly a topotecan therapy. In the present study combination regimens tend to be more toxic than monotherapies. When response rates are comparable, empirically chosen treatment combination therapies should only be practiced in carefully planned clinical studies.

Tracking the cell cycle origins for escape from topotecan action by breast cancer cells.

The anticancer agent topotecan is considered to be S-phase specific. This implies that cancer cells that are not actively replicating DNA could resist the effects of the drug. The cycle specificity of topotecan action was investigated in MCF-7 cells, using time-lapse microscopy to link the initial cell cycle position during acute exposures to topotecan with the antiproliferative consequences for individual cells. The bioactive dose range (0.5–10 μM) for 1-h topotecan exposures was defined by rapid drug delivery and topoisomerase I trapping. Topotecan caused pan-cycle induction and activation of p53. Lineage analysis of the time-lapse sequences identified cells initially in S-phase and G2, and defined the time to mitosis for cells originating from G2, S-phase and G1. Topotecan prevented all mitoses from S-phase cells and G1 cells (half-maximal effects at 0.14 μM and 0.96 μM, respectively). No dose of topotecan completely prevented mitosis among G2 cells, and at saturating doses of topotecan about half the cells of G2 origin continued dividing (the half-maximal effects was at 0.31 μM). Overall, topotecan differentially targeted G1-, S- and G2-phase cells, but many G2 cells were resistant to topotecan, presenting a clear route for cell cycle-mediated drug resistance.

The mechanism of topoisomerase I poisoning by a camptothecin analog.

We report the x-ray crystal structure of human topoisomerase I covalently joined to double-stranded DNA and bound to the clinically approved anticancer agent Topotecan. Topotecan mimics a DNA base pair and binds at the site of DNA cleavage by intercalating between the upstream (-1) and downstream (+1) base pairs. Intercalation displaces the downstream DNA, thus preventing religation of the cleaved strand. By specifically binding to the enzyme-substrate complex, Topotecan acts as an uncompetitive inhibitor. The structure can explain several of the known structure-activity relationships of the camptothecin family of anticancer drugs and suggests that there are at least two classes of mutations that can produce a drug-resistant enzyme. The first class includes changes to residues that contribute to direct interactions with the drug, whereas a second class would alter interactions with the DNA and thereby destabilize the drug-binding site.

Novel use of an established agent: Topotecan is anti-angiogenic in experimental Wilms tumor

Background/Purpose: Antiangiogenic agents offer a new approach to the treatment of aggressive neoplasms, yet very few agents are available for current use. The authors have shown previously the efficacy of antiangiogenic therapy in experimental Wilms tumor, using an investigative antibody. They hypothesized that topotecan, administered in a regimen targeting endothelial cells, would suppress tumor growth and angiogenesis in experimental Wilms tumor. Methods: Experimental tumors were induced in the left kidneys of athymic mice by injection of cultured Wilms tumor cells. Topotecan (0.36, 0.6, 1.0, 2.0, and 3.0 mg/kg) or vehicle was injected intraperitoneally in 2 cycles over a 6-week period. Fluorescein angiograms and platelet endothelial cell adhesion molecule-1 staining of primary tumors were performed to ascertain vascular architecture. Endothelial apoptosis was assessed by TdT-mediated dUTP nick end labeling assay. Results: Tumor weights were reduced significantly in treated versus control animals, even in the lowest-dose group. Endothelial cell staining and angiography results showed relatively sparse vascularity in treated xenografts. Endothelial apoptosis was observed in treated but not control tumors. Conclusions: Topotecan, delivered in an “antiangiogenic” regimen, even at very low doses, significantly inhibited growth of experimental Wilms tumors. No adverse effects were noted at low doses. Thus, the established chemotherapy agent topotecan may be useful in a novel role: as antiangiogenic therapy. J Pediatr Surg 36:1781-1784. Copyright © 2001 by W.B. Saunders Company.

Phase I and pharmacological study of increased dose oral topotecan in combination with intravenous cisplatin

Based on in vitro observations showing more pronounced antitumour efficacy with protracted exposure of topoisomerase I inhibitors at low concentration, and since oral delivery is a more convenient method for prolonged drug administration, and preferred by patients [1, 2], an oral formulation of topotecan was developed. Topotecan, supplied in gelatin capsules, has an absolute bioavailability of 42% ± 13% [3]. The maximally tolerated dose for oral topotecan, administered for 5 days every 21 days as a single agent was defined as 2.3 mg/m/day, with myelosuppression (in particular neutropenia) as the dose limiting toxicity [4]. Two randomised studies on single agent topotecan suggested that the oral formulation is equipotent to the intravenous formulation in patients with ovarianand small-cell lung cancer, whilst associated with less grade 3 and 4 neutropenia [5, 6]. Recently, a phase I study combining oral topotecan (T) given for five days every three weeks with cisplatin (C) at 75 mg/m on day 1 (sequence CT) or day 5 (sequence TC) was completed [7], In congruency with the results of the study by Rowinsky with i.v. topotecan [8], the maximum tolerated dose (MTD) for topotecan in the CT sequence of 1.25 mg/m/day x 5 was considerably lower than that for the alternate sequence (2 mg/m/day x 5). Cisplatin was not observed to have an effect on the pharmacokinetics of topotecan [7]. Finally, topotecan systemic exposure was directly associated with antitumour activity in in vivo studies [9]. Given this apparent relationship between topotecan systemic exposure and clinical response, we tried to increase the topotecan dose in the combination cisplatinoral topotecan by using a lower cisplatin dose. We performed a phase I study in patients with solid tumours with oral topotecan preceded by a fixed dose of i.v. cisplatin at 50 mg/m. Patients and methods

Topotecan in Squamous Cell Carcinoma of the Cervix: A Phase II Study of the Gynecologic Oncology Group

Purpose. The activity and toxicity of topotecan were evaluated in a multicenter Phase II study for patients with previously treated squamous cell carcinoma of the uterine cervix.Patients and methods. Histologic confirmation of the primary diagnosis was required, as well as adequate performance status and vital organ function and the presence of measurable disease. Patients were allowed one prior regimen of systemic therapy, usually platinum-based. A two-stage accrual design was utilized with early stopping criteria and monitoring of toxicity. Topotecan was administered at 1.5 mg/m2 per day for 5 consecutive days on a 21-day cycle with modifications based on hematologic toxicity.Results. Forty-five patients were entered. Two patients were ineligible (incorrect tumor type) and 2 were inevaluable (never received therapy). One additional patient was not evaluable for response (nonmeasurable disease). A median of 2 cycles was administered to each patient (range: 1–17 cycles) with grade 4 neutropenia in 68% and grade 4 thrombocytopenia in 39% of patients, but without treatment-related deaths. Nonhematologic toxicity was generally mild and not dose-limiting. The overall (complete and partial) response rate among evaluable patients with measurable disease was 12.5% with stable disease in an additional 37.5%. Median progression-free survival was 2.1 months.Conclusions. As a single agent topotecan shows modest antitumor activity, with manageable hematologic and nonhematologic toxicity, in patients with previously treated squamous cell carcinoma of the cervix. Further evaluation in chemotherapy-naive patients or in combination with cisplatin and/or radiation may be indicated.

Reversal of MDR1-associated resistance to topotecan by PAK-200S, a new dihydropyridine analogue, in human cancer cell lines.

Recent data suggest that expression of the membrane P170-glycoprotein (P-gp) may confer resistance to the topoisomerase- I-interactive agent topotecan. The present study describes the cellular effects of a new dihydropyridine analogue, PAK-200S, on P-gp-mediated resistance to topotecan in human breast and ovarian tumour cells. PAK-200S at a non-cytotoxic concentration of 2.0 μM completely reversed resistance to topotecan in P-gp-expressing MCF-7/adr (breast) and A2780/Dx5 (ovarian) tumour cells, respectively, with no effects on parental cells. Cellular pharmacokinetic studies by reversed-phase high-performance liquid chromatography analysis showed significantly lower cellular drug concentrations of the pharmacologically active closed-ring lactone of topotecan in multidrug-resistant cells than in parental cells. PAK-200S was effective in restoring the cellular lactone concentrations of topotecan in resistant MCF-7/adr cells to levels comparable to those obtained in parental cells. Furthermore, exposure of MCF-7/adr cells to topotecan in the presence of PAK-200S significantly increased the induction of protein-linked DNA breaks. PAK-200S did not alter nuclear topoisomerase I-mediated ex vivo pBR322 DNA plasmid unwinding activity and topoisomerase-I protein expression. These results suggest that reversal of P-gp-mediated resistance to topotecan by PAK-200S was related to the restoration of cellular drug concentrations of the active lactone form of topotecan rather than a direct effect on topoisomerase-I function. © 1999 Cancer Research Campaign

Topotecan: Incorporating It Into the Treatment of Solid Tumors

This issue of The Oncologist provides the reader with two useful reviews of the new chemotherapeutic agent topotecan, one of a class of topoisomerase I inhibitors that is being studied and incorporated into the treatment of various malignancies. Topotecan was approved for the treatment of refractory ovarian cancer in 1996, and has shown promising activity against a variety of solid tumors, as well as hematologic malignancies. One paper discusses clinical guidelines for managing topotecan-related hematologic toxicities, and centers on data derived from ovarian cancer studies. The other focuses on the role of topotecan in the treatment of small cell lung cancer (SCLC), where it has consistently shown encouraging results and for which definitive trials are now being conducted. As front-line therapy for ovarian cancer and small cell lung cancer is dominated by platinum-based regimens, the dosing guidelines and management issues discussed are pertinent for both tumor types.

New drugs in therapy of breast carcinoma: current status and outlook

In breast cancer the results of the meta-analysis of the Early Breast Cancer Collaborative Trialists' Group clearly proved a significant improvement of overall survival after systemic adjuvant treatment. These therapy benefits of the years 1970-1990 are significant but still remain unsatisfactory concerning the high recurrence rates and low overall survival rates. Since 1990 many new active drugs and innovative therapy concepts have been developed. At present the new cytotoxic agents gemcitabine, vinorelbine and topotecan are being tested. Paclitaxel and docetaxel are being examined in combination therapy and in the adjuvant setting. Selective aromatase inhibitors and new antigestagens and antiestrogens are endocrine drugs under investigation in advanced breast cancer. Dose intensity concepts are performed safely due to growth factors and peripheral stem cell support. A new therapeutic approach is the application of the humanized monoclonal antibody against the CerbB-2 receptors of breast cancer cells. These new promising therapeutic approaches are under clinical investigation at present and are discussed in detail.

The impact of column temperature in the high performance liquid chromatographic analysis of topotecan in rat and dog plasma

A sensitive high performance liquid chromatographic (HPLC) assay has been developed and validated for the quantitation of the novel anticancer agent topotecan and topotecan as its lactone plus carboxylate forms in rat and dog plasma. Linear responses in analyte standard peak areas were observed over the concentration ranges 0.10–10 ng ml −1 using 100 μl of rat plasma and 0.2–100 ng ml −1 using 100 μl of dog plasma. Due to the instability of the drug in the biological matrix it was necessary to obtain the plasma fraction within 5 min after blood sampling by centrifugation, immediately followed by protein precipitation with cold methanol (−30°C). For the determination of total drug levels (lactone plus lactone ring-opened form), plasma samples were deproteinated with methanol and subsequently acidified with 2% (v/v) perchloric acid. The samples were analysed by HPLC using a Zorbax SB-C18 Stable Bond column and methanol-0.1 M hexane-1-sulfonic acid in methanol-0.01 M N, N, N′, N′-tetramethylethylenediamine in distilled water pH 6.0 (25:10:65, v/v/v) as the mobile phase. The detection was performed fluorimetrically. The analytical column was thermostated at 19–21°C to obtain baseline resolution between an interfering endogenous compound in rat and dog plasma and topotecan. This endogenous peak was absent in human plasma. Variation of chromatography temperature appeared to be a very useful tool in the bioanalysis of topotecan. It allowed optimization of the separation between the endogenous compound and the analyte; different mechanisms of solute interactions are apparently involved in this reversed-phase ion-pair chromatographic system.

Do topotecan concentrations in saliva reflect plasma concentrations?

Purpose. There is an increasing interest to use saliva as biological fluid for drug monitoring as it reflects adequately, in some cases, drug concentrations in plasma. A great advantage is that it can be obtained conveniently by a noninvasive method. We describe our experience with respect to the practical use of saliva for pharmacokinetic monitoring of the novel anticancer agent topotecan. Patients and Methods. Eighty-one saliva sam ples and corresponding plasma samples were ob tained 2 hours after the end of infusion from 15 patients with either ovarian cancer or small cell lung cancer, receiving 1.5 mg/m 2 per day topotecan for 5 consecutive days every 3 weeks. Saliva was obtained by a citric-acid containing dental cotton roll which stimulated the saliva flow. Results. The plasma topotecan concentrations varied between 3.67 and 24.4 ng/mL, with an intrapa tient (day-to-day) variation of only 9.8%, and an inter patient variation of 27.2%. The saliva concentrations varied between 5.34 and 74.2 ng/mL, with an intrapa tient variation of 25.3%, and an interpatient variation of 53.5%. The mean plasma/saliva topotecan ratio was 0.66 (range 0.21 to 1.58) and was both patient dependent and dependent on the sampling time. The day-to-day variation of the plasma/saliva concentra tion ratio in this daily times five schedule was 27.6%, and the interpatient variation was 45.5%. The saliva concentrations of topotecan were not related to the occurrence of mucositis, which was noted in some patients. Conclusion. Based on the large variability in the plasma/saliva ratios, we conclude that in our investi gational setting saliva is not a reliable matrix for topotecan analysis and that plasma sampling is to be preferred.

High-performance liquid chromatographic determination of the novel antitumour drug topotecan and topotecan as the total of the lactone plus carboxylate forms, in human plasma.

A sensitive high-performance liquid chromatographic (HPLC) assay has been developed and validated for the quantitation of the novel anticancer agent topotecan and topotecan as the total of its lactone and carboxylate forms in human plasma. Linear response in analyte standard peak area were observed over the concentration range 0.05-10 ng/ml using 100-microliters plasma samples. The instability of the drug in the biological matrix necessitated that the plasma fraction was obtained within 5 min after blood sampling by centrifugation, immediately followed by protein precipitation with cold methanol (-30 degrees C). Stability studies have indicated that topotecan is stable in these methanolic extracts for at least 4.5 months at -30 degrees C and 2 months at -70 degrees C. For the total determination of the lactone plus lactone ring-opened forms of the drug as topotecan, plasma samples were deproteinated with methanol and, subsequently, acidified with 7% (v/v) perchloric acid. Plasma samples for the measurement of total levels of the lactone and the ring-opened forms of topotecan were stable for at least 4.5 months when stored at -30 degrees C. After centrifugation, the supernatants were analysed by HPLC using a Zorbax SB-C18 Stable Bond column and methanol-0.1 M hexane-1-sulfonic acid in methanol-0.01 M N,N,N',N'-tetramethylethylenediamine (TEMED) in distilled water pH 6.0 (25:10:65, v/v) as the mobile phase. Detection was performed fluorimetrically. Within-run and between-run precision was always less than 12.1% in the concentration range of interest (0.05-10.0 ng/ml). The limit of quantitation is 0.05 ng/ml. Accuracy measurements ranged between 87.6 and 113.5%.