Successful local regional therapy with topotecan of intraperitoneally growing human ovarian carcinoma xenografts

Improved therapy for neuroblastoma using a combination approach: superior efficacy with vismodegib and topotecan

Aberrant activation/expression of pathways/molecules including NF-kB, mTOR, hedgehog and polo-like-kinase-1 (PLK1) are correlated with poor-prognosis neuroblastoma. Therefore, to identify a most efficacious treatment for neuroblastoma, we investigated the efficacy of NF-kB/mTOR dual-inhibitor 13-197, hedgehog inhibitor vismodegib and PLK1 inhibitor BI2536 alone or combined with topotecan against high-risk neuroblastoma. The in vitro efficacy of the inhibitors alone or combined with topotecan on cell growth/apoptosis and molecular mechanism(s) were investigated. Results showed that as single agents 13-197, BI2536 and vismodegib significantly decreased neuroblastoma cell growth and induced apoptosis by targeting associated pathways/molecules. In combination with topotecan, 13-197 did not show significant additive/synergistic effects against neuroblastoma. However, BI2536 or vismodegib further significantly decreased neuroblastoma cell growth/survival. These results clearly showed that vismodegib combination with topotecan was synergistic and more efficacious compared with BI2536 in combination. Together, in vitro data demonstrated that vismodegib was most efficacious in potentiating topotecan-induced antineuroblastoma effects. Therefore, we tested the combined efficacy of vismodegib and topotecan against neuroblastoma in vivo using NSG mice. This resulted in significantly (p<0.001) reduced tumor growth and increased survival of mice. Together, the combination of vismodegib and topotecan showed a significant enhanced antineuroblastoma efficacy by targeting associated pathways/molecules which warrants further preclinical evaluation for translation to the clinic.

Targeting MCT-1 oncogene inhibits Shc pathway and xenograft tumorigenicity

Overexpression of Shc adaptor proteins is associated with mitogenesis, carcinogenesis and metastasis. Multiple copies in T-cell malignancy 1 (MCT-1) oncoprotein promotes cell proliferation, survival and tumorigenic effects. Our current data show that MCT-1 is a novel regulator of Shc-Ras-MEK-ERK signaling and MCT-1 is significantly co-activated with Shc gene in human carcinomas. The knockdown of MCT-1 enhances apoptotic cell death accompanied with the activation of caspases and cleavage of caspase substrates under environmental stress. The cancer cell proliferation, chemo-resistance and tumorigenic capacity are proved to be effectively suppressed by targeting MCT-1. Accordingly, an important linkage between MCT-1 oncogenicity and Shc pathway in tumor development has now been established. Promoting MCT-1 expression by gene hyperactivation may be recognized as a tumor marker and MCT-1 may serve as a molecular target of cancer therapy.

Potent therapeutic activity of folate receptor-targeted liposomal carboplatin in the localized treatment of intraperitoneally grown human ovarian tumor xenograft

Intraperitoneal (IP) therapy with platinum (Pt)-based drugs has shown promising results clinically; however, high locoregional concentration of the drug could lead to adverse side effects. In this study, IP administration was coupled with a folate receptor-targeted (FRT) liposomal system, in an attempt to achieve intracellular delivery of the Pt-based drug carboplatin in order to increase therapeutic efficacy and to minimize toxicity. In vitro and in vivo activity of FRT carboplatin liposomes was compared with the activity of free drug and nontargeted (NT) carboplatin liposomes using FR-overexpressing IGROV-1 ovarian cancer cells as the model. Significant reduction in cell viability was observed with FRT liposomes, which, compared with the free drug, provided an approximately twofold increase in carboplatin potency. The increase in drug potency was correlated with significantly higher cellular accumulation of Pt resulting from FRT liposomal delivery. Further evaluation was conducted in mice bearing intraperitoneally inoculated IGROV-1 ovarian tumor xenografts. A superior survival rate (five out of six animals) was achieved in animals treated with FRT carboplatin liposomes, injected intraperitoneally with a dose of 15 mg/kg and following a schedule of twice-weekly administration for 3 weeks. In contrast, no survivors were observed in the free drug or NT carboplatin liposome groups. The presence of cancer cells in lung and liver tissues was observed in the saline, free carboplatin, and NT carboplatin liposome groups. However, there was no sign of cancer cells or drug-related toxicity detected in tissues from the animals treated with FRT carboplatin liposomes. The results of this study have demonstrated for the first time that the approach of coupling IP administration with FRT liposomal delivery could provide significantly improved therapeutic efficacy of carboplatin in the treatment of metastatic ovarian cancer.

Eradication of ovarian tumor xenografts by locoregional administration of targeted immunotherapy

PURPOSE

Oligodeoxynucleotides containing unmethylated CpG motifs (CpG-ODN) are potent activators of innate and adaptive immunity. Recognition of CpG-ODN is mediated by Toll-like receptor 9 expressed by immune cells, endothelial and epithelial cells, and fibroblasts. We examined the antitumor effect of CpG-ODN and the role of administration route on human ovarian cancers growing in the peritoneal cavity of nude mice.

EXPERIMENTAL DESIGN

Mice implanted i.p. with human ovarian carcinoma cells were treated i.p., s.c., or i.v. and assessed for survival and tumor-free incidence. Peritoneal washings were analyzed for keratinocyte chemokine production and for functional and phenotypic profiles as indicators of the cell types involved in mediating the antitumor effects.

RESULTS

IGROV-1-bearing mice treated i.p. survived significantly longer than those treated i.v. or s.c. (P=0.0005), and nearly half of them (8 of 17) were tumor-free by the end of the experiment, a rate never achieved using a variety of chemotherapeutic drugs. High rates of tumor-free mice were observed in three other ovarian tumor xenografts treated i.p. Compared with peritoneal washings of mice treated s.c. or i.v., those from mice treated i.p. showed the highest level of serum and tissue keratinocyte chemokine, the highest number of natural killer cells and neutrophils, and the highest antiproliferative activity in vitro.

CONCLUSIONS

The superior antitumor effect obtained by locoregional administration of CpG-ODN in i.p. tumor-bearing mice with a limited adaptive immune response points to the importance of innate effector cells amplification at the site of tumor growth and suggests the promise of i.p. CpG-ODN in clinical trials for ovarian cancer.

Phase I clinical trial of topotecan and pegylated liposomal doxorubicin

BACKGROUND

The objective of this study was to determine the feasibility and maximum tolerated dose (MTD) of combination topotecan and pegylated liposomal doxorubicin (PLD) administered in 4- or 3-week cycles in patients with advanced or refractory solid tumors.

PATIENTS AND METHODS

Patients were treated with intravenous topotecan (0.75-1.25 mg/m2) for 3 days followed by PLD (25-40 mg/m2) on Day 4. The following dose combinations (topotecan/PLD, mg/m2) were explored: 0.75/40, 1.0/40, and 1.25/40 every 28 days; and 1.0/25 and 1.0/30 every 21 days.

RESULTS

Thirty-two patients were enrolled, and all had received prior chemotherapy. Most (84 percent) patients had ovarian cancer. A total of 157 cycles (median, 4 cycles; range, 1-19 cycles) of chemotherapy were administered. Dose-limiting toxicities were Grade 4 neutropenia and death at dose level 3 (1.25/40 mg/m2 every 28 days), and neutropenic fever, Grade 3 stomatitis, and Grade 3 peripheral neuropathy (all in one patient) at dose level 5 (1/30 mg/m2 every 21 days). Myelosuppression was the most common serious toxicity. Twenty-six patients were evaluable for response and 7 (27 percent) had partial responses. All responses were seen in patients with ovarian cancer.

CONCLUSIONS

This combination is feasible and well tolerated; encouraging activity was observed in heavily pretreated patients with ovarian cancer. The recommended regimens for a Phase II study are topotecan 1.0 mg/m2 on Days 1-3 followed by PLD 40 mg/m2 on Day 4 of a 28-day cycle, and topotecan 1.0 mg/m2 on Days 1-3 and PLD 30 mg/m2 on Day 4 of a 21-day cycle.

Lysophosphatidic Acid Acyltransferase-β Is a Prognostic Marker and Therapeutic Target in Gynecologic Malignancies

Lysophosphatidic acid, the substrate for lysophosphatidic acid acyltransferase beta (LPAAT-beta), is a well-studied autocrine/paracrine signaling molecule that is secreted by ovarian cancer cells and is found at elevated levels in the blood and ascites fluid of women with ovarian cancer. LPAAT-beta converts lysophosphatidic acid to phosphatidic acid, which functions as a cofactor in Akt/mTOR and Ras/Raf/Erk pathways. We report that elevated expression of LPAAT-beta was associated with reduced survival in ovarian cancer and earlier progression of disease in ovarian and endometrial cancer. Inhibition of LPAAT-beta using small interfering RNA or selective inhibitors, CT32521 and CT32228, two small-molecule noncompetitive antagonists representing two different classes of chemical structures, induces apoptosis in human ovarian and endometrial cancer cell lines in vitro at pharmacologically tenable nanomolar concentrations. Inhibition of LPAAT-beta also enhanced the survival of mice bearing ovarian tumor xenografts. Cytotoxicity was modulated by diacylglycerol effectors including protein kinase C and CalDAG-GEF1. LPAAT-beta was localized to the endoplasmic reticulum and overexpression was associated with redistribution of protein kinase C-alpha. These findings identify LPAAT-beta as a potential prognostic and therapeutic target in ovarian and endometrial cancer.

Camptothecin and its analogues: a review on their chemotherapeutic potential

Topoisomerase I (Topo-I) is a major target for anticancer drug discovery and design. As a result, Topo-I inhibitors constitute an important class of the current anticancer drugs. To date, all of the Topo-I inhibitors that have been clinically evaluated are analogues of camptothecin (CPT), an extract of the Chinese tree Camptotheca acuminata. CPT has shown significant antitumor activity to lung, ovarian, breast, pancreas and stomach cancers. In this article the, phytochemical aspect, and various structural modifications are comprehensively reviewed as in rings A, B, C, D and E. Biological activity of camptothecin, other than anticancer, reported till the year 2003 has also been discussed.

Topotecan, an active new antineoplastic agent: review and current status

Topotecan (Hycamtin) is a water soluble semisynthetic analogue of the alkaloid camptothecin which has antitumour activity in preclinical models in vitro and in vivo. A range of Phase I studies has been performed and a daily x 5 iv. schedule, which showed most promising evidence of activity, was selected for extensive clinical evaluation. To date, topotecan has been shown to be active in a number of malignancies, including metastatic ovarian cancer, recurrent small cell lung cancer (SCLC), non-small cell lung cancer (NSCLC), breast cancer, colorectal cancer and myelodysplastic syndrome. In ovarian cancer, response rates of around 15% were identified in patients who had failed standard chemotherapy, and in a randomised, comparative study with paclitaxel response rates of 20% (topotecan) and 13% (paclitaxel) were observed. In addition, overall time to progression was impressive at 23 weeks (topotecan) compared with 14 weeks (paclitaxel). In recurrent SCLC, topotecan has shown good activity in sensitive patients with a response rate of 39%, although the response rate in refractory patients was considerably lower (7%). Median survival of all patients was 5.4 months, acceptable for this difficult clinical scenario. Topotecan is well-tolerated in the majority of patients and subjective toxicities are uncommon. The principal side-effect is myelosuppression, mainly neutropenia. Serious clinical sequelae are relatively uncommon and non-cumulative. Nonhaematological toxicities are generally mild and not dose-limiting. In clinical use, topotecan has exhibited activity in multiple tumour types, with a side-effect profile that is predictable and manageable. The drug is under evaluation in other tumour types and in combination chemotherapy regimens.

The camptothecins

Supported by detailed understanding of their mechanism of action, and facilitated by chemical manipulations that have amplified their solubility, the camptothecins have advanced to the forefront of several areas of therapeutic and developmental chemotherapy. Additive and synergistic laboratory interactions with other cytotoxic drugs have been exploited to allow development of camptothecin-based multidrug regimens, which are showing important activity in several malignancies. Topotecan and irinotecan are already in widespread use in clinical practice, and newer agents with promising preclinical activity are in various stages of clinical assessment. As knowledge of molecular and biochemical mechanisms of action and resistance continues to expand, newer and better camptothecin-based strategies for treatment of malignant disease are likely to evolve.

Phase II trial of irinotecan in patients with metastatic epithelial ovarian cancer or peritoneal cancer

PURPOSE

To evaluate the efficacy and toxicity of irinotecan in patients with metastatic platinum-resistant or platinum-refractory epithelial ovarian cancer or primary peritoneal cancer.

PATIENTS AND METHODS

Thirty-one patients with measurable disease were enrolled in our study at The University of Texas M.D. Anderson Cancer Center. Twenty-five of these patients were treated with irinotecan at a dose of 300 mg/m2 intravenously for 90 minutes every 3 weeks; the remaining six patients were treated with 250 mg/m2 because their age was greater than 65 years. Median age was 57 years (range, 38 to 74 years). The majority (84%) had a Zubrod performance status of 0. All patients were evaluated for irinotecan toxicity, and 29 (94%) were evaluable for response.

RESULTS

The overall response rate was 17.2%. One patient (3%) had a complete response, four (14%) had partial responses, 14 (48%) had stable disease, and 10 had (35%) disease progression. Median progression-free survival was 2.8 months (range, 1.1 to 16 months), median duration of response was 1.4 months (range, 0.7 to 10.1 months); median survival from primary diagnosis was 24.3 months (range, 6.5 to 85.7 months); and median survival from initiation of irinotecan was 10.1 months (range, 2.3 to 34 months). Major toxicities included fatigue (16 patients), neutropenia (11 patients), diarrhea (nine patients), nausea (10 patients), and anorexia (seven patients). Eleven patients required dose reductions because of these toxicities. No treatment-related deaths occurred.

CONCLUSION

Irinotecan has moderate efficacy and substantial toxicity in patients with metastatic platinum-resistant or platinum-refractory epithelial ovarian or primary peritoneal cancer.

Successful therapy of subcutaneously growing human hepatoblastoma xenografts with topotecan

BACKGROUND

Human hepatoblastoma is an infrequent liver tumor in children. Although many hepatoblastomas can be treated adequately with well-defined treatment regimens, problems still persist with advanced and non-resectable tumors; in these cases, an effective chemotherapy is necessary to improve the patients' prognosis. This underlines the need for alternative anti-tumor agents in the treatment of human hepatoblastoma. The aim of this study was to investigate the therapeutic effects of topotecan, a water-soluble camptothecin analog (topoisomerase-I-antagonist), in an in vivo model of three human hepatoblastomas xenografted subcutaneously into nude mice.

PROCEDURE

Hepatoblastoma cell suspensions from three children were transplanted subcutaneously into nude mice NMRI (nu/nu). Treatment with topotecan was initiated when the tumors reached a volume between 50 and 80 mm(3). A dose of 6.6 mg/kg of topotecan were given intraperitoneally every 4 days on four occasions. The tumor volume development and alpha-fetoprotein alterations were measured and statistically analyzed. After the treatment, the tumors were investigated histologically and by immunohistochemistry.

RESULTS

There was a significant reduction of tumor growth in all treated tumor xenografts vs. untreated control groups (mean relative volume 3.1 vs. 47.4; P = 0,0015-0,0079). Serum alpha-fetoprotein levels were reduced in all three cell lines, in two of them significantly (mean 44,535 kU/l vs. 228,883 kU/l; P = 0.005-0.246). Histologically, the tumor necrosis rates were higher and immunohistochemistry showed lower proliferation activities in the treated tumor xenografts vs. the control groups.

CONCLUSION

The data show that topotecan is an effective agent in the treatment of human hepatoblastoma xenografts. From these results, treatment with topotecan appears to be a promising alternative in the pre- and postoperative therapy of patients suffering from human hepatoblastoma

A phase I and pharmacokinetic study of intraperitoneal topotecan

PURPOSE

To evaluate the feasibility and pharmacology of intraperitoneal (IP) topotecan.

PATIENTS AND METHODS

Fifteen patients with recurrent ovarian cancer in a phase I trial were treated with escalating IP topotecan doses (5-30 mg/m(2)) for pharmacokinetic analysis.

RESULTS

Dose limiting toxicity (DLT) was acute hypotension, chills and fever at the 30 mg/m(2) dose level. Haematological toxicity and abdominal pain were mild for all dose levels studied.

PHARMACOKINETICS

Peak plasma levels of total topotecan were reached at 2.7 +/- 1.1 h after IP instillation. The apparent V(ss) was 69.9 +/- 25.4 L/m(2), plasma clearance 13.4 +/- 2.5 L/h/m(2) and plasma T1/2 3.7 +/- 1.3 h. The plasma AUC was correlated with the dose (R = 0.95, P < 0.01). The plasma AUC ratio of lactone versus total topotecan (lactone + carboxy-forms) increased with the dose from 16% to 55%, (R = 0.84, P < 0.01). Peritoneal total topotecan was cleared from the peritoneal cavity at 0.4 +/- 0.3 L/h.m(2) with a T1/2 = 2.7 +/- 1.7 h. The mean peritoneal/plasma AUC ratio for total topotecan was 54 +/- 34.

CONCLUSION

A substantial dose of topotecan can be delivered by the IP route, achieving cytotoxic plasma levels of topotecan, with acceptable toxicity. The recommended dose for further phase II trials is 20 mg/m(2) IP, which enables combination with active doses of other cytotoxic drugs, in view of its limited myelotoxicity when given by this route.

Topoisomerase I inhibition with topotecan: pharmacologic and clinical issues

Topoisomerase I (topo-I) inhibitors are a new class of anticancer agents with a mechanism of action aimed at interrupting DNA replication in cancer cells, the result of which is cell death. Most, if not all, topo-I inhibitors are derivatives of the plant extract camptothecin. Topotecan is a derivative of camptothecin which has been structurally modified to increase water solubility. The pharmacokinetic profile of topotecan is usually characterised by a two-compartment model and is linear in the dose range of 0.5 - 3.5 mg/m(2). Current clinical trials suggest antitumour activity against a variety of human tumour types, including ovarian cancer, non-small cell lung cancer (NSCLC) and non-lymphocytic haematologic malignancies. The main dose-limiting toxicity (DLT) is non-cumulative myelosuppression. Non-haematologic toxicities are usually mild. Based on several Phase I studies, the recommended Phase II dose was 1.5 mg/m(2)/day iv. for 5 days. Current Phase I and Phase II trials are evaluating the combination of topotecan with other chemotherapeutic agents to increase the therapeutic benefits of topotecan. The DLT in these trials is mainly myelosuppression.

Alternative administration of camptothecin analogues

The binding of camptothecin (CPT) to the DNA-topoisomerase complex is reversible, but it needs to be maintained for maximal inhibitory activity. It is also dependent on the chemical structure of CPT. The lactone form is thought to be necessary for the activity. In human serum, the equilibrium between lactone and carboxylate is in favor of the latter. For these reasons, alternative administration of CPT analogues is being evaluated. The ideal compound would remain in lactone form and would expose the host for long periods of time to its effects. Oral administration of irinotecan (CPT-11) and topotecan (TPT) is discussed by other investigators. We studied oral rubitecan and reported a low lactone to total drug area under the plasma concentration-time curve (AUCP) ratio (14.7%), with low plasma concentration over time despite repeated administrations and the presence of an enterohepatic cycle. Aerosolization of a liposomal formulation of rubitecan is currently under study. Six patients have been treated once a day for 5 days every 3 weeks. The dose was 6.7 micrograms/kg/day. Plasma levels are dose for dose higher than those after oral administration, but the ratio of lactone versus total drug is low. No toxicity was observed. The study will continue with increasing doses and lengths of administration. Intrathecal administration of topotecan has been studied in a phase I trial in children. Doses of 0.4 mg are tolerated without toxicity, and clinical responses have been seen in patients with refractory meningial carcinomatosis. Phase II studies are planned. Intraperitoneal (i.p.) administration of topotecan has been studied in a phase I trial as a 24-hour infusion in 5% dextrose at pH 3.5 every 21 days. Dose-limiting toxicity is 4 mg/m2. Toxic effects are neutropenia, anemia, emesis, fever, and pain. Five of 10 patients with ascites had symptomatic relief. Pharmacokinetic analysis demonstrates a second-order kinetics with elimination half-lives of 0.49 and 2.7 hours. The peritoneal to plasma AUC ratio was 31.2. Intramuscular, transdermal, and subcutaneous administrations have been extensively studied in the mouse.

Efficacy and toxicity profile of oral topotecan in a panel of human tumour xenografts

On the basis of their mechanism of action (cell killing during DNA replication) and the potential reversibility of the drug effects, protracted therapy with camptothecins is reported to provide optimal antitumour effects. Furthermore, oral administration may be a useful modality for optimisation of treatment. The aim of this study was to compare the therapeutic profile of topotecan given orally or intravenously in human tumours xenografted into athymic nude mice. The drug topotecan was given according to an intermittent (every fourth day, four times) or daily (qdx5/weeklyx5-10 weeks; only orally) schedule. Tumour growth inhibition and persistence of drug effects were assessed and compared with untreated mice. In a panel of seven tumour xenografts, oral topotecan was at least as effective on three and significantly more effective on four tumours. Using the intermittent schedule, the maximum tolerated dose (MTD) was comparable for the two routes (15 mg/kg), but the toxicity profile suggested a better tolerability in terms of lethal effects after oral administration. The daily oral treatment of low drug doses allowed a higher cumulative dose to be delivered with improved antitumour efficacy (2/10 cured in a large cell lung cancer) and no evidence of toxicity. In spite of the low bioavailability of oral topotecan (23.5%), the persistent plasma levels of the drug suggest that the time of exposure to the drug is more critical than the plasma concentrations for antitumour efficacy. This interpretation is consistent with the increased efficacy of prolonged daily treatment with low-dose levels. The results may have implications for the future design of clinical studies.

In vitro sensitivity of fresh ovarian carcinoma specimens to CPT-11 (irinotecan)

OBJECTIVE

Irinotecan (CPT-11) is a DNA topoisomerase I inhibitor which has shown activity in vitro against several cancer cell lines and some promising clinical responses in phase I and II trials in various solid tumors. The cytotoxicity of CPT-11 on human ovarian epithelial malignancies was tested in vitro utilizing the ATP chemosensitivity assay. Flow cytometry was also performed on the fresh carcinoma specimens.

METHODS

Fresh tumor samples were obtained at laparotomy from 20 patients with primary adenocarcinoma of the ovary and 1 patient with heavily pretreated recurrent ovarian carcinoma. Tumors were plated in an in vitro system and treated with varying doses of both CPT-11 and its active metabolite SN-38 (7-ethyl-10-hydroxycamptothecin), in addition to a panel of standard chemotherapeutic agents used in treating ovarian cancer. On the sixth day after incubation, ATP levels in remaining cells were measured using a luminometer as an indication of the amount of cell kill compared to untreated controls.

RESULTS

Twelve of the 21 tumors were evaluable for a response to CPT-11. Of the 12 tumors tested, 7 were found to have median effect doses of CPT-11 significantly under the clinically achievable peak plasma concentration (range 1.00 x 10(-4) to 44.67 microM) and 11 of the 12 tumors showed sensitivity to the active metabolite SN38 with median effect doses ranging from 2.00 x 10(-4) to 0.147 microM. Some of these tumors showed resistance to the standard agents, such as platinum, based on our assay. The heavily pretreated recurrent tumor tested was very sensitive to both CPT-11 and SN38 by our assay. The results of flow cytometry showed that the tumors were composed of heterogeneous populations of cells with mean S phase fractions varying from 7.0 to 17.3%. The only tumor not sensitive to SN38 showed the highest mean S phase activity of 17.3%.

CONCLUSIONS

Overall, these results suggest that CPT-11 deserves further investigation as a clinically useful chemotherapeutic agent for ovarian cancer.

Intraperitoneal chemotherapy strategies in the treatment of epithelial ovarian carcinoma

The intraperitoneal delivery of chemotherapeutic agents is presently being investigated as a part of salvage treatment for epithelial ovarian cancer. There are several promising new agents that appear to demonstrate a benefit in selected patients.

Topotecan. A review of its potential in advanced ovarian cancer

The topoisomerase I inhibitor topotecan has shown antitumour activity against a variety of tumour types in vitro and in vivo. Topotecan in combination with drugs that induce DNA damage generally results in synergistic killing of tumour cells in vitro. As the activity of topotecan is related to exposure time, the drug is administered by intravenous infusion either continuously or once daily over a 30-minute period for several consecutive days. A 30-minute infusion of topotecan 1.5 mg/m2 on 5 consecutive days every 3 weeks produced response rates of up to approximately 20% in patients with advanced ovarian cancer who had failed to respond to platinum-based regimens or relapsed after initial response to such regimens. No significant differences in efficacy were apparent between topotecan and paclitaxel in a phase III study in patients with recurrent ovarian cancer, although a trend in favour of topotecan was evident for all major efficacy parameters. Non-cumulative myelosuppression, including neutropenia, thrombocytopenia and anaemia, is the dose-limiting toxicity associated with topotecan. Myelo-suppression was significantly more common with topotecan than with paclitaxel in a single comparative study. Non-haematological adverse events in topotecan recipients are generally mild and include alopecia, nausea, vomiting, and other gastrointestinal problems. Thus, topotecan has modest efficacy in the treatment of recurrent advanced ovarian cancer, with clinical activity similar to that of paclitaxel in a large randomised phase III study in this setting. Combinations of paclitaxel and a platinum compound are being used increasingly for first-line therapy, although relapse rates remain significant. Topotecan is therefore a suitable second-line option, providing antitumour response for some patients whose disease has relapsed after, or is refractory to, platinum-based therapy. Its wider potential when used either alone or in combination regimens should become clearer from ongoing studies.

Clinical pharmacology of camptothecins

Camptothecins (CPTs) are a unique class of chemotherapeutic agent which inhibit DNA synthesis by inhibiting topoisomerase I activity. Structure-activity studies on the original CPT alkaloid led to the development of the new analogues irinotecan (CPT-11), topotecan, and 9-aminocamptothecin, which have improved water solubility and lower toxicity. CPT analogues exhibit interesting pharmacokinetic/pharmacodynamic and metabolic properties that are of major research and clinical interest. This review describes the clinical pharmacology of these 3 CPT analogues. Specific areas such as absorption after extravascular administration, pharmacokinetic/pharmacodynamic variability, metabolism, and administration in special populations are discussed.

Intratumoral infusion of topotecan prolongs survival in the nude rat intracranial U87 human glioma model

Topotecan is a topoisomerase (topo) I inhibitor with promising activity in preclinical studies. We hypothesized that low-dose intratumoral delivery of topotecan would be highly effective for gliomas. Human glioma cell lines (U87, U138 and U373) displayed different sensitivities to topotecan (IC50 range: 0.037 microM to 0.280 microM) in cell culture. The most resistant of the glioma cell lines (U87) was implanted stereotactically into the brains of nude rats. Twelve days later, at which time tumor diameter measured 2 to 2.5 mm, animals were randomized to three groups: group I, intratumoral topotecan infused via osmotic pump (n = 12); group II, intratumoral saline infusion (n = 7); and group III, no treatment (n = 10). Animals were sacrificed when signs of deterioration developed, or at 60 days. Animals in group I had a mean survival time (MST) of > 55 days (range = 40-60); whereas, those in groups II and III had MST of 26.1 (range = 21-31) and 26.5 (range = 20-30) days, respectively. The differences in survival between group I and each of the other groups were statistically significant (p < 0.0001; Logrank Mantel-Cox). None of the animals that survived 60 days had histological evidence of residual tumor at sacrifice. Measurement of topotecan levels in normal brain revealed cytotoxic concentrations up to 4.5 mm from the site of infusion. This study demonstrates that intratumoral topotecan delivered via an osmotic pump prolongs survival in the U87 human glioma model.

In vivo behaviour of rat band 3 cross-linked carrier erythrocytes

Rat band 3 cross-linked carrier erythrocytes have been prepared. Iodinated carbonic anhydrase has been encapsulated into rat erythrocytes. Then, carrier erythrocytes were labeled with 51chromium. Eventually, these doubly labeled rat RBCs were treated with a band 3 cross-linking reagent, namely bis(sulfosuccinimidyl)suberate (BS3). 51Chromium labeling and 125I CA showed to have cytosolic localization in cross-linked carrier erythrocytes. Estimation of the band 3 cross-linking induced by BS3 on rat carrier erythrocytes has been done rendering values around 25% of band 3 monomer reduction. BS3-cross-linked carrier erythrocytes when injected into rats are mainly targeted to liver as shown by chromium labeling localization. Also, encapsulated CA radioactivity carried by cross-linked carrier rat erythrocytes when injected into rats is localized predominantly in liver as shown by in vivo experiments. Accordingly, cross-linked carrier erythrocytes are highly recognized by peritoneal macrophages as detected by in vitro analyses of macrophage recognition. Thus, our data revealed a targeting of carrier rat erythrocytes induced by cross-linking of band 3 protein by BS3. These results support claims in favor of this animal model as a feasible system to analyze cross-linked carrier erythrocytes survival and targeting as well as the in vivo efficacy of targeting of loaded compounds to liver.

In vitro properties and organ uptake of rat band 3 cross-linked erythrocytes

Chemical conditions for cross-linking rat erythrocytes with bis(sulfosuccinimidyl)suberate (BS3) and 3,3' dithiobis(sulfosuccinimidyl propionate) (DTSSP) have been studied. These two cross-linking reagents seem to react with band 3 proteins in rat erythrocyte membrane. Two different conditions have been assayed using different cell/cross-linker concentration ratios. Similar cell volumes were observed in cross-linked rat erythrocytes compared to rat control erythrocytes. Cell yields after cross-linking account for about 65% when a high ratio of cell-to-cross-linker was used. Slightly lower cell yields (about 62%) were obtained when this ratio was reduced. Estimation of band 3 cross-linking by gel electrophoresis revealed a level of cross-linking of around 45% and 50% at the different conditions used. In vivo behavior of these modified rat erythrocytes revealed that they do not circulate, showing a predominant localization in the liver. This effect is evident from the concentration (5 mM BS3 or DTSSP) used. Based on these results, BS3 and DTSSP can be considered as useful tools to cross-link rat erythrocyte band 3 and to target rat erythrocytes to the liver.

Characterization of a xenograft model of human ovarian carcinoma which produces intraperitoneal carcinomatosis and metastases in mice

A new xenograft model for human epithelial ovarian carcinoma, with extensive intraperitoneal (i.p.) carcinomatosis as the predominant disease manifestation, is described. Cells from the established NIH:OVCAR-5 cell line were injected i.p. into 6- to 8-week-old Swiss nude mice. Comparative analyses between cells cultured in vitro and tumor cells derived ex vivo were performed to assess histologic features, immunohistochemical cell markers, hormonal receptor expression, adhesion to extracellular matrix molecules and chromosomal constitution. Macroscopically, the extent of tumor development appeared to be site-dependent and tumor cell survival was dose-dependent. Advanced disease was characterized by extensive solid tumor burden and ascites with parenchymal invasion, lymphatic metastases and vascular dissemination. Individual tumor nodules exhibited developing neovasculature characterized by the absence of mature basement membrane. Despite some histologic loss of cellular differentiation in advanced disease, antigenic expression was preserved, distinguishing these cells as epithelial in origin. Karyotyping of tumor cells demonstrated multiple numeric and structural chromosomal abnormalities. Serum and ascites CA 125 levels were consistently elevated only in tumor-bearing mice. This new murine model closely resembles the aggressive disease process of human epithelial ovarian carcinoma, in which the efficacy of i.p. and systemic therapeutic modalities can be investigated.

Targeting of mouse erythrocytes by band 3 crosslinkers

Chemical conditions of crosslinking mouse erythrocytes with BS3 and DTSSP have been studied. These two crosslinking reagents seem to react with band 3 protein in mouse erythrocytes membrane. Extent of crosslinking is dependent on the concentration of the reagent used. Similar cell volumes were observed in crosslinked erythrocytes with respect to control erythrocytes. In vivo behaviour of these modified erythrocytes revealed prominent targeting of crosslinked erythrocytes to liver. This effect is clearly evident when concentrations of 5 mM BS3 or DTSSP were used and can be dependent of reagent concentration. Consequently, from our results BS3 and DTSSP can be considered as very useful tools to control and modulate targeting of crosslinked erythrocytes.

Interaction of ionizing radiation with topotecan in two human tumor cell lines

The effect of topotecan, a topoisomerase I inhibitor, on ionizing radiation-induced cytotoxicity was studied in 2 human tumor cell lines characterized by a different expression of the target enzyme. The cytotoxicity of topotecan alone or in combination with radiation was assessed in exponentially growing non-small-cell lung cancer (H460) and glioblastoma (GBM) cells using the colony-forming assay. An isobologram method was used to evaluate the treatment interaction. An apparent supra-additive effect in cell killing following drug-radiation-combined treatment was observed only in GBM cells exposed to topotecan for 24 hr. In the case of H460 cells, interaction varied from a strong infra-additive effect at low radiation doses to a slight supra-additive effect when cells were exposed to radiation doses greater than 3 Gy. Northern blot analysis indicated that topoisomerase I expression in H460 cells was 8-fold higher than that of GBM cells. Although the H460 cell line exhibited an increased sensitivity to topotecan, only in the GBM cell line (which expressed a lower level of topoisomerase I) did the drug potentiate the radiation cytotoxicity. The observation that the radiosensitization by topotecan was related to topoisomerase I level is consistent with a putative role of the enzyme in processes involved in the repair of radiation damage. It is conceivable that the modulation of enzyme function results in an effective reduction of cellular capability for repair of radiation damage only if the enzyme is not over-expressed. Although a precise role of topoisomerase I in the cellular response to ionizing radiations (in particular, in DNA repair) remains to be documented, such results suggest the potential interest of topoisomerase I inhibitors in combination with radiation therapy for tumors expressing low topoisomerase I levels.