Synergistic cytotoxicity of cisplatin and topotecan or SN-38 in a panel of eight solid-tumor cell lines in vitro

Sacituzumab govitecan plus platinum-based chemotherapy mediates significant antitumor effects in triple-negative breast, urinary bladder, and small-cell lung carcinomas

Sacituzumab govitecan (SG) is an antibody-drug conjugate composed of an anti-Trop-2-directed antibody conjugated with the topoisomerase I inhibitory drug, SN-38, via a proprietary hydrolysable linker. SG has received United States Food and Drug Administration (FDA) approval to treat metastatic triple-negative breast cancer (TNBC), unresectable locally advanced or metastatic hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative breast cancer, and accelerated approval for metastatic urothelial cancer. We investigated the utility of combining SG with platinum-based chemotherapeutics in TNBC, urinary bladder carcinoma (UBC), and small-cell lung carcinoma (SCLC). SG plus carboplatin or cisplatin produced additive growth-inhibitory effects in vitro that trended towards synergy. Immunoblot analysis of cell lysates suggests perturbation of the cell-cycle and a shift towards pro-apoptotic signaling evidenced by an increased Bax to Bcl-2 ratio and down-regulation of two anti-apoptotic proteins, Mcl-1 and survivin. Significant antitumor effects were observed with SG plus carboplatin in mice bearing TNBC or SCLC tumors compared to all controls (P < 0.0062 and P < 0.0017, respectively) and with SG plus cisplatin in UBC and SCLC tumor-bearing animals (P < 0.0362 and P < 0.0001, respectively). These combinations were well tolerated by the animals. Combining SG with platinum-based chemotherapeutics demonstrates the benefit in these indications and warrants further clinical investigation.

Peptide-Hydrogel Nanocomposites for Anti-Cancer Drug Delivery

Cancer is the second leading cause of death globally, but conventional anticancer drugs have side effects, mainly due to their non-specific distribution in the body in both cancerous and healthy cells. To address this relevant issue and improve the efficiency of anticancer drugs, increasing attention is being devoted to hydrogel drug-delivery systems for different kinds of cancer treatment due to their high biocompatibility and stability, low side effects, and ease of modifications. To improve the therapeutic efficiency and provide multi-functionality, different types of nanoparticles (NPs) can be incorporated within the hydrogels to form smart hydrogel nanocomposites, benefiting the advantages of both counterparts and suitable for advanced anticancer applications. Despite many papers on non-peptide hydrogel nanocomposites, there is limited knowledge about peptide-based nanocomposites, specifically in anti-cancer drug delivery. The aim of this short but comprehensive review is, therefore, to focus attention on the synergies resulting from the combination of NPs with peptide-based hydrogels. This review, which includes a survey of recent advances in this kind of material, does not aim to be an exhaustive review of hydrogel technology, but it instead highlights recent noteworthy publications and discusses novel perspectives to provide valuable insights into the promising synergic combination of peptide hydrogels and NPs for the design of novel anticancer drug delivery systems.

The EMT-activator ZEB1 is unrelated to platinum drug resistance in ovarian cancer but is predictive of survival

The IGROVCDDP cisplatin-resistant ovarian cancer cell line is an unusual model, as it is also cross-resistant to paclitaxel. IGROVCDDP, therefore, models the resistance phenotype of serous ovarian cancer patients who have failed frontline platinum/taxane chemotherapy. IGROVCDDP has also undergone epithelial-mesenchymal transition (EMT). We aim to determine if alterations in EMT-related genes are related to or independent from the drug-resistance phenotypes. EMT gene and protein markers, invasion, motility and morphology were investigated in IGROVCDDP and its parent drug-sensitive cell line IGROV-1. ZEB1 was investigated by qPCR, Western blotting and siRNA knockdown. ZEB1 was also investigated in publicly available ovarian cancer gene-expression datasets. IGROVCDDP cells have decreased protein levels of epithelial marker E-cadherin (6.18-fold, p = 1.58e-04) and higher levels of mesenchymal markers vimentin (2.47-fold, p = 4.43e-03), N-cadherin (4.35-fold, p = 4.76e-03) and ZEB1 (3.43-fold, p = 0.04). IGROVCDDP have a spindle-like morphology consistent with EMT. Knockdown of ZEB1 in IGROVCDDP does not lead to cisplatin sensitivity but shows a reversal of EMT-gene signalling and an increase in cell circularity. High ZEB1 gene expression (HR = 1.31, n = 2051, p = 1.31e-05) is a marker of poor overall survival in high-grade serous ovarian-cancer patients. In contrast, ZEB1 is not predictive of overall survival in high-grade serous ovarian-cancer patients known to be treated with platinum chemotherapy. The increased expression of ZEB1 in IGROVCDDP appears to be independent of the drug-resistance phenotypes. ZEB1 has the potential to be used as biomarker of overall prognosis in ovarian-cancer patients but not of platinum/taxane chemoresistance.

PLGA nanoparticle-reinforced supramolecular peptide hydrogels for local delivery of multiple drugs with enhanced synergism

Localized drug delivery offers great therapeutic efficacy at local tissues while avoiding the systemic toxicity of drugs. Yet it demands the development of structurally-stable drug carrier systems with excellent injectability, as well as the capability to facilitate controlled release of multiple drugs. Herein, we describe the design and synthesis of a supramolecular hydrogel (Cis/Peptide@NP/Irino) for the combined delivery of cisplatin (Cis) and irinotecan (Irino). The self-assembled hydrogel consisted of an inner phase of irinotecan-loaded PLGA nanoparticles (NP/Irino) and an outer phase of cisplatin-loaded peptide nanofibers (Cis/Peptide). Through the structural reinforcement of PLGA nanoparticles, the Cis/Peptide@NP/Irino hydrogel exhibited better mechanical properties than Cis/Peptide or Peptide hydrogels. With excellent shear-thinning properties, it facilitated the development of a localized drug delivery system with an improved retention time in vivo. The hydrogel incorporated two anticancer drugs, Cis and Irino, at the Peptide and PLGA domains, respectively, and exhibited a faster release of Cis prior to the continuous release of Irino in vitro. Furthermore, the Cis/Peptide@NP/Irino formulation showed a better inhibition efficacy against the proliferation of cancerous A549 cells, with the synergism of Cis and Irino exceeding that of the simple solution mixtures, which was plausibly due to the enhanced cellular uptake of drugs through endocytosis. We believe that structurally-stable supramolecular hydrogels show great promise in the local delivery of various drug combinations for cancer therapy.

Double-crosslinked nanocomposite hydrogels for temporal control of drug dosing in combination therapy

Temporal control of drug dosing is indispensable for a successful combination therapy that utilizes cisplatin (CDDP) and irinotecan (IRN), with clinical evidence supporting a higher response rate when CDDP was administered prior to IRN. Herein, a peptide-based nanocomposite hydrogel (CDDP/Pept-AlgNP/IRN) was designed for differential release of CDDP and IRN to maximize synergism of two drugs. First, a double-crosslinking strategy was exploited for structural reinforcement of hydrogel, with integration of coordination interactions between CDDP and hydrogelator (Pept) as well as electrostatic interactions between Pept and alginate nanoparticles (AlgNP/IRN), that afforded nanocomposite hydrogel with 42-fold increase in storage modulus comparing to peptide gel alone. Next, the nanocomposite hydrogel with excellent injectability served as a depot for controlled release of dual drugs, and guaranteed a fast release of CDDP prior to a tunable release of IRN that is dependent on fraction ratios of AlgNP in the composite materials. Comparing to simple mixture of CDDP and IRN solution, CDDP/Pept-AlgNP/IRN hydrogel formulation demonstrated excelling synergism of CDDP and IRN in cell inhibition studies, with efficacious antitumor potency further proved in tumor regression studies in vivo. We believe that the strategy of utilizing co-assembly of multiple pairs of entities (i.e. drug-gelator, nanoparticle-gelator) in composite materials provides a generalized method to design mechanically stable supramolecular hydrogels, and further promises an exact temporal control of drug dosing by packing individual drugs in co-assembled structures/domains to satisfy clinical demands from combination therapy. STATEMENT OF SIGNIFICANCE: This study reports the design of nanocomposite hydrogels with two distinct co-assembling domains for structural reinforcement of hydrogel and differential release of two drugs (CDDP and IRN) in combination therapy. We first investigated the effects of co-assembling processes for the reinforcement of hydrogel. Then we utilized the hydrogel for differential release of CDDP and IRN to achieve better synergistic efficacy of drugs in inhibiting the growth of cancer cell A549 and better anticancer efficacies than single drug formulations or solution mixtures of dual drugs in an A549-xenografted mouse model. We believe that the strategy of packing individual drugs in distinct co-assembling structures promises a paradigm shift for regulating temporal control of drug dosing in combination therapy.

BO-1055, a novel DNA cross-linking agent with remarkable low myelotoxicity shows potent activity in sarcoma models

DNA damaging agents cause rapid shrinkage of tumors and form the basis of chemotherapy for sarcomas despite significant toxicities. Drugs having superior efficacy and wider therapeutic windows are needed to improve patient outcomes. We used cell proliferation and apoptosis assays in sarcoma cell lines and benign cells; γ-H2AX expression, comet assay, immunoblot analyses and drug combination studies in vitro and in patient derived xenograft (PDX) models. BO-1055 caused apoptosis and cell death in a concentration and time dependent manner in sarcoma cell lines. BO-1055 had potent activity (submicromolar IC50) against Ewing sarcoma and rhabdomyosarcoma, intermediate activity in DSRCT (IC50 = 2-3μM) and very weak activity in osteosarcoma (IC50 >10μM) cell lines. BO-1055 exhibited a wide therapeutic window compared to other DNA damaging drugs. BO-1055 induced more DNA double strand breaks and γH2AX expression in cancer cells compared to benign cells. BO-1055 showed inhibition of tumor growth in A673 xenografts and caused tumor regression in cyclophosphamide resistant patient-derived Ewing sarcoma xenografts and A204 xenografts. Combination of BO-1055 and irinotecan demonstrated synergism in Ewing sarcoma PDX models. Potent activity on sarcoma cells and its relative lack of toxicity presents a strong rationale for further development of BO-1055 as a therapeutic agent.

PARP Inhibitors as P-glyoprotein Substrates

The cytotoxicity of PARP inhibitors olaparib, veliparib, and CEP-8983 were investigated in two P-glycoprotein (P-gp) overexpressing drug-resistant cell models (IGROVCDDP and KB-8-5-11). IGROVCDDP and KB-8-5-11 were both resistant to olaparib and resistance was reversible with the P-gp inhibitors elacridar, zosuquidar, and valspodar. In contrast, the P-gp overexpressing models were not resistant to veliparib or CEP-8983. Olaparib and veliparib did not induce protein expression of P-gp in IGROVCDDP or KB-8-5-11 at doses that successfully inhibit PARP. Olaparib therefore appears to be a P-gp substrate. Veliparib and CEP-8983 do not appear to be substrates. Veliparib and CEP-8983 may therefore be more useful in combined chemotherapy regimens with P-gp substrates and may be active in platinum and taxane-resistant ovarian cancer.

Design, modeling, synthesis and biological activity evaluation of camptothecin-linked platinum anticancer agents

The design, modeling, synthesis and biological activity evaluation of two hybrid agents formed by 7-oxyiminomethylcamptothecin derivatives and diaminedichloro-platinum (II) complex are reported. The compounds showed growth inhibitory activity against a panel of human tumor cell lines, including sublines resistant to topotecan and platinum compounds. The derivatives were active in all the tested cell lines, and compound 1b, the most active one, was able to overcome cisplatin resistance in the osteosarcoma U2OS/Pt cell line. Platinum-containing camptothecins produced platinum-DNA adducts and topoisomerase I-mediated DNA damage with cleavage pattern and persistence similar to SN38, the active principle of irinotecan. Compound 1b exhibited an appreciable antitumor activity in vivo against human H460 tumor xenograft, comparable to that of irinotecan at lower well-tolerated dose levels and superior to cisplatin. The results support the interpretation that the diaminedichloro-platinum (II) complex conjugated via an oxyiminomethyl linker at the 7-position of the camptothecin resulted in a new class of effective antitumor compounds.

Resistance to paclitaxel in a cisplatin-resistant ovarian cancer cell line is mediated by P-glycoprotein

The IGROVCDDP cisplatin-resistant ovarian cancer cell line is also resistant to paclitaxel and models the resistance phenotype of relapsed ovarian cancer patients after first-line platinum/taxane chemotherapy. A TaqMan low-density array (TLDA) was used to characterise the expression of 380 genes associated with chemotherapy resistance in IGROVCDDP cells. Paclitaxel resistance in IGROVCDDP is mediated by gene and protein overexpression of P-glycoprotein and the protein is functionally active. Cisplatin resistance was not reversed by elacridar, confirming that cisplatin is not a P-glycoprotein substrate. Cisplatin resistance in IGROVCDDP is multifactorial and is mediated in part by the glutathione pathway and decreased accumulation of drug. Total cellular glutathione was not increased. However, the enzyme activity of GSR and GGT1 were up-regulated. The cellular localisation of copper transporter CTR1 changed from membrane associated in IGROV-1 to cytoplasmic in IGROVCDDP. This may mediate the previously reported accumulation defect. There was decreased expression of the sodium potassium pump (ATP1A), MRP1 and FBP which all have been previously associated with platinum accumulation defects in platinum-resistant cell lines. Cellular localisation of MRP1 was also altered in IGROVCDDP shifting basolaterally, compared to IGROV-1. BRCA1 was also up-regulated at the gene and protein level. The overexpression of P-glycoprotein in a resistant model developed with cisplatin is unusual. This demonstrates that P-glycoprotein can be up-regulated as a generalised stress response rather than as a specific response to a substrate. Mechanisms characterised in IGROVCDDP cells may be applicable to relapsed ovarian cancer patients treated with frontline platinum/taxane chemotherapy.

Resistance to paclitaxel in a cisplatin-resistant ovarian cancer cell line is mediated by P-glycoprotein

The IGROVCDDP cisplatin-resistant ovarian cancer cell line is also resistant to paclitaxel and models the resistance phenotype of relapsed ovarian cancer patients after first-line platinum/taxane chemotherapy. A TaqMan low-density array (TLDA) was used to characterise the expression of 380 genes associated with chemotherapy resistance in IGROVCDDP cells. Paclitaxel resistance in IGROVCDDP is mediated by gene and protein overexpression of P-glycoprotein and the protein is functionally active. Cisplatin resistance was not reversed by elacridar, confirming that cisplatin is not a P-glycoprotein substrate. Cisplatin resistance in IGROVCDDP is multifactorial and is mediated in part by the glutathione pathway and decreased accumulation of drug. Total cellular glutathione was not increased. However, the enzyme activity of GSR and GGT1 were up-regulated. The cellular localisation of copper transporter CTR1 changed from membrane associated in IGROV-1 to cytoplasmic in IGROVCDDP. This may mediate the previously reported accumulation defect. There was decreased expression of the sodium potassium pump (ATP1A), MRP1 and FBP which all have been previously associated with platinum accumulation defects in platinum-resistant cell lines. Cellular localisation of MRP1 was also altered in IGROVCDDP shifting basolaterally, compared to IGROV-1. BRCA1 was also up-regulated at the gene and protein level. The overexpression of P-glycoprotein in a resistant model developed with cisplatin is unusual. This demonstrates that P-glycoprotein can be up-regulated as a generalised stress response rather than as a specific response to a substrate. Mechanisms characterised in IGROVCDDP cells may be applicable to relapsed ovarian cancer patients treated with frontline platinum/taxane chemotherapy.

Resistance to paclitaxel in a cisplatin-resistant ovarian cancer cell line is mediated by P-glycoprotein

The IGROVCDDP cisplatin-resistant ovarian cancer cell line is also resistant to paclitaxel and models the resistance phenotype of relapsed ovarian cancer patients after first-line platinum/taxane chemotherapy. A TaqMan low-density array (TLDA) was used to characterise the expression of 380 genes associated with chemotherapy resistance in IGROVCDDP cells. Paclitaxel resistance in IGROVCDDP is mediated by gene and protein overexpression of P-glycoprotein and the protein is functionally active. Cisplatin resistance was not reversed by elacridar, confirming that cisplatin is not a P-glycoprotein substrate. Cisplatin resistance in IGROVCDDP is multifactorial and is mediated in part by the glutathione pathway and decreased accumulation of drug. Total cellular glutathione was not increased. However, the enzyme activity of GSR and GGT1 were up-regulated. The cellular localisation of copper transporter CTR1 changed from membrane associated in IGROV-1 to cytoplasmic in IGROVCDDP. This may mediate the previously reported accumulation defect. There was decreased expression of the sodium potassium pump (ATP1A), MRP1 and FBP which all have been previously associated with platinum accumulation defects in platinum-resistant cell lines. Cellular localisation of MRP1 was also altered in IGROVCDDP shifting basolaterally, compared to IGROV-1. BRCA1 was also up-regulated at the gene and protein level. The overexpression of P-glycoprotein in a resistant model developed with cisplatin is unusual. This demonstrates that P-glycoprotein can be up-regulated as a generalised stress response rather than as a specific response to a substrate. Mechanisms characterised in IGROVCDDP cells may be applicable to relapsed ovarian cancer patients treated with frontline platinum/taxane chemotherapy.

Phase I Study of Topotecan, Ifosfamide, and Etoposide (TIME) with autologous stem cell transplant in refractory cancer: pharmacokinetic and pharmacodynamic correlates

PURPOSE

To determine the maximum tolerated dose (MTD) of topotecan in combination with ifosfamide, mesna, and etoposide (TIME), followed by autologous hematopoietic cell transplant (HCT), in patients with chemotherapy-refractory malignancies.

EXPERIMENTAL DESIGN

Patients were treated with (in mg/m(2)/d) ifosfamide 3,333, mesna 3,333, and topotecan 3.3 to 28.3 during days -8 through -6 and etoposide 500 (days -5 through -3) followed by HCT on day 0. Once MTD was defined, we expanded this dosing cohort to include patients with high-risk lymphoma due to activity seen during dose escalation. Topotecan pharmacokinetic analyses were carried out, and topoisomerase I levels and activity were measured.

RESULTS

The topotecan MTD in this regimen was 64 mg/m(2) (21.3 mg/m(2)/d). Mucositis was dose limiting and correlated with topotecan dose level and area under the curve (AUC). Dose level was also correlated with length of hospitalization, number of days of parenteral nutrition, and neutrophil and platelet engraftment. Topotecan AUC was significantly correlated with time to platelet recovery. The baseline peripheral blood mononuclear cell topoisomerase I level was found to be a significant positive predictor for overall and progression-free survival. Topotecan AUC was positively correlated with dose level, with a trend toward decreasing clearance with increasing dose.

CONCLUSION

Topotecan can be a useful drug in the high-dose setting given its activity in some malignancies when given in standard dose. Pharmacokinetic monitoring may be a valuable tool for optimizing the use of topotecan and to avoid toxicity seen with high-systemic exposures. Baseline topoisomerase I levels may have an important role in predicting topotecan efficacy.

Plasma and cerebrospinal fluid pharmacokinetics of topotecan in a phase I trial of topotecan, tamoxifen, and carboplatin, in the treatment of recurrent or refractory brain or spinal cord tumors

PURPOSE

This study was designed to ascertain the dose-limiting toxicities (DLT) and maximally tolerated doses of the combination of fixed-dose tamoxifen and carboplatin, with escalating doses of topotecan, and to determine the pharmacokinetics of topotecan in the plasma and cerebrospinal fluid.

METHODS

Tamoxifen 100 mg po bid, topotecan 0.25, 0.5, 0.75, or 1.0 mg/m(2)/d IV, administered as a 72 h continuous infusion on days 1-3, followed by carboplatin AUC = 3, IV on day 3. Cycles were repeated every 4 weeks.

RESULTS

Seventeen patients received 39 cycles of treatment: median 2, (range 1-5). The tumors included glioblastoma (6), anaplastic astrocytoma (2), metastatic non-small cell (3), small cell lung (2), and one each with medulloblastoma, ependymoma, and metastatic breast or colon carcinoma. The median Karnofsky performance status was 70% (range 60-90%) and age: 52 (range 24-75). Eleven patients were female and six male. Toxicities included thrombocytopenia (2), neutropenia without fever lasting 6 days (1), DVT (2), and emesis (1). Topotecan levels, total and lactone, were measured prior to the end of infusion in plasma and cerebrospinal fluid (CSF). At 1.0 mg/m(2)/d, the median CSF/plasma ratio was 19.4% (range 15.1-59.1%). The total plasma topotecan in two pts with DLTs was 4.63 and 5.87 ng/ml, in three without DLTs at the same dose level the mean total plasma topotecan was 3.4 ng/ml (range 3.02-3.83). Plasma lactone levels were 33% of the total; CSF penetration was 20% of the total plasma levels. 4/8 pts with high-grade gliomas had stable disease (median: 3 cycles (range 2-5)). Two had minor responses. One patient with metastatic non-small cell and one with small cell lung cancer had objective PRs.

CONCLUSIONS

The recommended phase II doses are: tamoxifen 100 mg po bid, topotecan 0.75 mg/m(2)/d IV continuous infusion for 72 h, followed by carboplatin AUC = 3 IV on day 3. Measurable topotecan levels, both total and lactone, are observed in the CSF.

Drug ratio-dependent antitumor activity of irinotecan and cisplatin combinations in vitro and in vivo

Irinotecan and cisplatin are two established anticancer drugs, which together constitute an effective combination for treating small-cell lung cancer. We investigated whether the efficacy of this combination could be improved by controlling drug ratios following in vivo administration. Irinotecan and cisplatin combinations were evaluated systematically for drug ratio-dependent synergy in vitro using a panel of 20 tumor cell lines. In vitro screening informatics on drug ratio-dependent cytotoxicity identified a consistently antagonistic region between irinotecan/cisplatin molar ratios of 1:2 to 4:1, which was bordered by two synergistic regions. Liposomal co-formulations of these two agents were developed that exhibited plasma drug half-lives of approximately 6 hours and maintained a fixed drug ratio for more than 24 hours. Drug ratio-dependent antitumor activity was shown in vivo for these liposome formulations, and irinotecan/cisplatin ratios between 5:1 and 10:1 were identified as therapeutically optimal. The relationship between irinotecan/cisplatin ratio and in vivo efficacy was consistent with in vitro drug ratio dependency results. Superior antitumor activity was observed for the liposome-encapsulated 7:1 molar ratio of irinotecan/cisplatin (designated CPX-571) compared with the free-drug cocktail in all models tested. Further efficacy studies in a range of human tumor xenografts, including an irinotecan-resistant model, showed that both liposomal agents contributed to the overall efficacy in a manner consistent with in vivo synergy. These results show the ability of drug delivery technology to enhance the therapeutic activity of irinotecan/cisplatin combination treatment by maintaining synergistic ratios in vivo. CPX-571, a fixed-ratio formulation of irinotecan and cisplatin, is a promising candidate for clinical development.

Phase I trial of autologous hematopoietic SCT with escalating doses of topotecan combined with CY and carboplatin in patients with relapsed or persistent ovarian or primary peritoneal carcinoma

We designed a phase I clinical trial of escalating doses of topotecan with CY and carboplatin in combination with autologous hematopoietic SCT (AHSCT) for the treatment of relapsed or persistent platinum sensitive ovarian or primary peritoneal carcinoma. After stem cell collection, 16 patients received topotecan at 1.5, 2.5, 3.5, 4.5 or 6.0 mg/m(2)/d combined with CY 1.5 g/m(2)/d and carboplatin 200 mg/m(2)/d, all by 4-day continuous infusion. Steady state pharmacokinetics of topotecan and carboplatin were examined. Pre-treatment biopsies were examined for the expression of topoisomerase (topo) I, Ki67 and Bcl-2 family members by immunohistochemistry. One of six patients at a topotecan dose of 4.5 mg/m(2)/d and two of three patients at 6.0 mg/m(2)/d had dose-limiting toxicity of grade 3 stomatitis lasting >2 weeks. There was no treatment-related mortality. As topotecan clearance was constant over the dose range examined, topotecan steady state plasma concentrations increased with dose. Median progression-free survival and overall survival were 6.5 months and 2.7 years, respectively. Shorter progression-free survival was observed in tumors with low topo expression (P=0.04). Topotecan can safely be dose escalated to 4.5 mg/m(2)/d in combination with CY, carboplatin and AHSCT. This trial is registered at ClinicalTrials.gov as NCT00652691.

Phase I pharmacokinetic and pharmacodynamic study of Carboplatin and topotecan administered intravenously every 28 days to patients with malignant solid tumors

PURPOSE

Preclinical studies have shown that the combination of topotecan and carboplatin is synergistic. To evaluate the schedule dependency of this interaction, the following phase I trial was designed to determine the safety and maximum tolerated dose (MTD), pharmacokinetics, and pharmacodynamics of carboplatin and topotecan in patients with malignant solid tumors.

EXPERIMENTAL DESIGN

In part 1, patients received carboplatin on day 1 and topotecan on days 1, 2, and 3 (C-->T schedule). In part 2, topotecan was administered on days 1, 2, and 3, followed by carboplatin on day 3 (T-->C schedule). Pharmacokinetics were determined in plasma and DNA topoisomerase I catalytic activity and Pt-DNA adducts in WBC and tumor tissue.

RESULTS

Forty-one patients were included. Dose-limiting toxicities during the C-->T schedule were grade 4 thrombocytopenia and febrile neutropenia (MTD: carboplatin target area under the free carboplatin plasma concentration versus time curve, 4 min mg/mL; topotecan, 0.5 mg/m(2)/d). Dose-limiting toxicities during the T-->C schedule included grade 4 neutropenia, thrombocytopenia, neutropenic fever, and grade 4 nausea and vomiting (MTD: carboplatin target area under the free carboplatin plasma concentration versus time curve, 6 min mg/mL; topotecan, 0.9 mg/m(2)/d). One complete response and five partial responses were observed. The clearance of and exposure to carboplatin and topotecan did not depend on the sequence of drug administration. No schedule-dependent effects were seen in Pt-DNA levels and DNA topoisomerase I catalytic activity in WBC and tumor tissue. However, myelotoxicity was clearly more evident in the C-->T schedule.

CONCLUSION

The T-->C schedule was better tolerated because both hematologic and nonhematologic toxicities were milder. Other pharmacodynamic factors than the ones investigated must explain the schedule-dependent differences in toxicities.

Paclitaxel, topotecan, and carboplatin in metastatic endometrial cancinoma: a Hellenic Co-operative Oncology Group (HeCOG) study

OBJECTIVE

Taxanes, and platinum compounds represent the chemotherapeutic agents with the greatest activity in metastatic endometrial carcinoma. We administered the combination of paclitaxel, topotecan and carboplatin to patients with metastatic or recurrent carcinoma of the endometrium to evaluate its activity and to define its toxicity.

METHODS

Thirty-nine consecutive patients were treated on an outpatient basis with paclitaxel 150 mg/m(2), administered intravenously over a 3-h period and followed by carboplatin at AUC of 5 on day 3, with both agents proceding topotecan that was given at 0.75 mg/m(2)/day on days 1 through 3. The chemotherapy was repeated every 3 weeks with granulocyte colony-stimulating factor (G-CSF) support for a maximum of six courses.

RESULTS

Twenty-one (60%) patients achieved objective clinical response (95% CI, 42.2-75.7%) including 4 (11.4%) complete and 17 (48.6%) partial responses. The median times to progression and survival for all patients were 8.9 and 17.7 months, respectively. Grade 3 or 4 thombocytopenia and neutropenia occurred in 5 (13%) and 4 (10%) patients, respectively, but only 2 episodes of neutropenic fever were encountered. Grade 2 or 3 neurotoxicity was observed in 23% of patients.

CONCLUSIONS

The combination of paclitaxel, topotecan and carboplatin with G-CSF support appears active with acceptable toxicity in patients with metastatic or recurrent carcinoma of the endometrium.

Synergy of karenitecin and mafosfamide in pediatric leukemia, medulloblastoma, and neuroblastoma cell lines

BACKGROUND

A major barrier to treatment of leptomeningeal disease is the lack of proven combination chemotherapy regimens for intrathecal administration. The purpose of this study was to determine the cytotoxic effects of karenitecin and mafosfamide in vitro against leukemia, medulloblastoma, and neuroblastoma cell lines.

PROCEDURE

A modified methyl tetrazolium (MTT) assay was used to determine the sensitivity of the cells to karenitecin and mafosfamide. Cells were exposed to drug for 72 hr, after which the number of surviving cells was quantitated. For drug combination experiments, cells were exposed to medium alone (controls), single drugs alone (mafosfamide only, karenitecin only) or to different concentrations of the combination of the two drugs (karenitecin + mafosfamide), for a total of 36 concentration pairs per plate. The universal response surface approach (URSA) was used to analyze the cytotoxic effects of the combination of karenitecin and mafosfamide.

RESULTS

The IC(50)s of karenitecin and mafosfamide for the various cell lines were similar. For both drugs nearly complete inhibition of cell growth was demonstrated at higher concentrations in all cell lines. In the neuroblastoma cell lines (SK-N-DZ; SK-N-SH) and the DAOY medulloblastoma cell line, the combination of karenitecin and mafosfamide were synergistic. In the D283 medulloblastoma and both the leukemia cell lines (JM1 and Molt-4), the drug interaction was additive. Antagonism was not seen in any cell line.

CONCLUSIONS

Karenitecin and mafosfamide are additive or synergistic in vitro against tumor types that disseminate to the leptomeninges. These results provide guidance for the choice of potential combination intrathecal regimens.

Antiangiogenic activity of thalidomide in combination with fludarabine, carboplatin, and topotecan for high-risk acute myelogenous leukemia

Forty-two patients with poor prognosis AML were enrolled in a phase II study combining fludarabine, carboplatin, and topotecan (FCT) with thalidomide. Laboratory correlates included serum vascular endothelial growth factor levels (VEGF) and bone marrow microvascular density (MVD). Ten of 42 (24%) patients achieved a complete remission (CR or CRp). Serious thrombotic adverse events were observed in 5 patients suggesting that the combination of cytotoxic chemotherapy and thalidomide may be thrombogenic despite significant thrombocytopenia. VEGF did not correlate with response to therapy, while a trend towards decreased MVD was noted in patients who achieved CR. The addition of thalidomide did not significantly influence angiogenic markers. It is not clear that thalidomide adds any efficacy to the FCT regimen.

A phase I study of paclitaxel, topotecan, cisplatin and Filgrastim in patients with newly diagnosed advanced ovarian epithelial malignancies: a Gynecologic Oncology Group study

OBJECTIVES

To determine a recommended dose level (RDL) of paclitaxel, cisplatin and topotecan in women with previously untreated epithelial ovarian or peritoneal cancer as a possible experimental arm in a future Gynecologic Oncology Group phase III study.

METHODS

Patients with newly diagnosed stage III or IV disease were treated with paclitaxel 175 mg/m2/3 h, followed 2 h later by cisplatin 50 mg/m2 on day 1. Topotecan was administered on consecutive days as a 30-minute infusion, beginning after cisplatin on day 1, receiving either 5 days beginning at 0.3 mg/m2 (cohort 1), or 3 days beginning at 0.5 mg/m2 (cohort 2). Treatment was given every 21 days for a maximum of 8 cycles.

RESULTS

Forty-five evaluable patients were enrolled in the two cohorts. Thrombocytopenia and prolonged neutropenia were the major dose-limiting toxicities. Dose-limiting neutropenia was seen at the first dose level, thus all subsequent dose escalations included Filgrastim. The RDL of cohort 1 was paclitaxel 175 mg/m2/3 h, cisplatin 50 mg/m2 and topotecan 0.5 mg/m2 daily x 5 with Filgrastim. The RDL of cohort 2 was paclitaxel 175 mg/m2/3 h, cisplatin 50 mg/m2 and topotecan 0.75 mg/m2 daily x 3 with Filgrastim.

CONCLUSION

In women with previously untreated epithelial ovarian or peritoneal cancer the combination of paclitaxel, cisplatin and topotecan is feasible. However, this treatment requires the use of Filgrastim and attenuated dosing of topotecan in both a 5-day and 3-day topotecan infusion schedule.

Pooled efficacy analysis from a phase I-II study of biweekly irinotecan in combination with gemcitabine, 5-fluorouracil, leucovorin and cisplatin in patients with metastatic pancreatic cancer

Development of treatments to improve the outcomes achieved with single-agent gemcitabine therapy for metastatic pancreatic cancer remains a research priority. G-FLIP (gemcitabine, 5-fluorouracil, leucovorin and cisplatin) is a four-drug regimen designed to maximize sequence-dependent synergy, while attempting to minimize toxicity among the four drugs. The dose-limiting toxicities and maximum tolerated dose of irinotecan as part of the G-FLIP regimen have been published. For phase II testing, G-FLIP consisted of sequential gemcitabine 500 mg/m2 at a fixed rate of 10 mg/m2/min, irinotecan 120 mg/m2, bolus 5-fluorouracil 400 mg/m2 and leucovorin 300 mg, followed by a 24-h 5-fluorouracil infusion of 1500 mg/m2 on day 1 and cisplatin 35 mg/m2 on day 2. Cycles were repeated every 14 days. Thirty-three patients with metastatic pancreatic cancer (22 men and 11 women) were treated and 31 were evaluable. Median patient age was 63 years (range 44-78 years) and median Karnofsky performance status score was 70-80. Estimated median time to disease progression was 171 days (6.1 months) and Kaplan-Meir-estimated median overall survival was 229 days (8.1 months). Twelve- and 18-month survivals were 33 and 21%, respectively. As per Response Evaluation Criteria in Solid Tumors criteria, 13 patients had stable disease, seven (22%) attained a partial response, and 10 (32%) had disease progression. One patient attained a complete response and two were not evaluable (one withdrew consent and one died suddenly, each after cycle 1). Treatment generally was well tolerated. Grade 3-4 toxicities/patient were thrombocytopenia (3.1%), leukopenia (15%), neutropenia (21%), neutropenic fever (3%), fatigue (18%) and thrombosis (12.5%). Common grade 1-2 toxicities per patient included nausea/vomiting (69%), diarrhea (45%), constipation (21%) and fatigue (39%). In conclusion, G-FLIP is a feasible outpatient regimen with acceptable toxicity for metastatic pancreatic cancer patients. Disease control rate (stable disease rate plus partial or complete responses) and 1-year survival outcomes are encouraging.

The effect of hydroxyurea on P-glycoprotein/BCRP-mediated transport and CYP3A metabolism of imatinib mesylate

PURPOSE

It has been reported that the combination therapy of imatinib mesylate, a tyrosine kinase inhibitor, plus hydroxyurea, a ribonucleotide reductase inhibitor, is associated with remarkable antitumor activity in patients with recurrent glioblastoma multiforme. However, the mechanism of the added activity of hydroxyurea to imatinib is not known. The purpose of this study was to investigate in vitro, whether hydroxyurea could enhance the central nervous system penetration of imatinib, by inhibition of the ATP-dependent transporter proteins P-glycoprotein (ABCB1; MDR1; Pgp) and Breast Cancer Resistance Protein (ABCG2; BCRP), or by inhibition of cytochrome P450 3A (CYP3A) metabolism of imatinib.

METHODS

The effect of hydroxyurea on the Pgp and BCRP mediated transport of imatinib was investigated by the sulforhodamine-B (SRB) drug cytotoxicity assay and transepithelial transport assay. In vitro biotransformation studies with supersomes expressing human CYP3A4 were performed to investigate whether hydroxyurea inhibited CYP3A4.

RESULTS

In both in vitro cytotoxicity and transport assays, hydroxyurea did not affect Pgp and BCRP mediated transport of imatinib. In a biotransformation assay, hydroxyurea had no influence on the metabolic degradation of imatinib either.

CONCLUSION

The results indicate that hydroxyurea does not interact with imatinib by inhibition of Pgp and BCRP mediated transport or by CYP3A4 mediated metabolism of imatinib.

The synergism between Belotecan and cisplatin in gastric cancer

PURPOSE

We wanted to demonstrate the anti-cancer effect and interaction between belotecan and cisplatin on gastric cancer cell line and we evaluated the mechanisms of this synergistic effect in vitro.

MATERIALS AND METHODS

The growth inhibitory effect of belotocan and cisplatin against several gastric cancer cell lines (SNU-5, SNU-16 and SNU-601) was estimated by tetrazolium dye assay. The effect of a combination treatment was evaluated by the isobologram method. The biochemical mechanisms for the interaction between the drugs were analyzed by measuring the formation of DNA interstrand cross-links (ICLs) and DNA topo-I activity.

RESULTS

Belotecan showed synergism with cisplatin for growth inhibitory effect on the gastric cancer cell lines SNU-5, and SNU-16, but this was subadditive on the SNU-601 cell line. The formation of DNA ICLs in SNU-16 cells by cisplatin was increased by combination with belotecan, but this was not affected in SNU-601 cells. The topo-I inhibition by belotecan was enhanced at high concentrations of cisplatin in SNU-16, but not in SNU-601 cells.

CONCLUSION

Belotecan and cisplatin show various combination effect against gastric cancer cells. The synergism between cisplatin and belotecan could be the result of one of the following mechanisms: the modulating effect of belotecan on the repair of cisplatin-induced DNA adducts and the enhancing effect of cisplatin on the belotecan-induced topo-I inhibitory effect.

Irinotecan-cisplatin interactions assessed in cell-based screening assays: cytotoxicity, drug accumulation and DNA adduct formation in an NSCLC cell line

PURPOSE

The use of in vitro drug cytotoxicity assays for the assessment of drug-drug interactions that lead to synergy may not take into account the many cellular determinants responsible for combination effects. Administration of the anticancer drug CPT-11, for example, is associated with rapid conversion of drug from its active lactone form to the inactive carboxylate form. Thus it is difficult to model, in vitro, the behavior of this drug when used as a single agent and when used in a combination setting, this factor may contribute to the interactions measured. Therefore, the objective of this study was to examine the influence of CPT-11 lactone ratio on the cellular accumulation of CPT-11 when used as a single agent and under conditions where it is used in combination with cisplatin.

METHODS

A fixed ratio experimental design was used and drug ratios of CPT-11 and cisplatin were judged to be antagonistic, additive, or synergistic to the non-small cell lung cancer cell line, H460, on the basis of the median effect analysis methodology of Chou and Talalay. The influence of extracellular pH on CPT-11 accumulation was evaluated at pH 7.4 and pH 6.6 when the drug was added immediately to the cells or first pre-equilibrated at the indicated pH. These studies were completed in the presence and absence of cisplatin.

RESULTS

When CPT-11 was added as a single agent to cells in pH = 7.4 media, the drug underwent hydrolysis to the carboxylate form; however, there was a rapid accumulation of the CPT-11 lactone form which peaked at 3,800 pmol/mg protein by 30 min and drops to 570 pmol/mg protein by 24 h. In pH = 6.6 media, accumulation of CPT-11 lactone was substantially lower over a 60 min timecourse; however, the cellular uptake measured at 24 h was comparable to that observed when the drug was added into pH 7.4 media. When evaluating CPT-11 lactone accumulation in a combination setting with cisplatin no significant difference in either CPT-11 lactone accumulation or cisplatin accumulation was observed, suggesting that drug interactions that led to synergy were mechanistically based. Results are presented which suggest that when cisplatin and CPT-11 are used in combination, there was a significant prolongation of platinum association with DNA compared to results obtained when cisplatin was used alone.

CONCLUSION

These results suggest that the CPT-11 lactone to carboxylate ratio does not influence the accumulation of the active CPT-11 lactone form in H460 cells and that CPT-11 does not influence cisplatin uptake when used in combination. It is argued, therefore, that the improved cytotoxicity between CPT-11 and cisplatin, as determined using cell-based assay, has the potential to be preserved in vivo assuming the optimal drug-drug ratio and concentration can be effectively delivered to the tumor.

Antitumor efficacy of edotecarin as a single agent and in combination with chemotherapy agents in a xenograft model

The novel indolocarbazole edotecarin (J-107088, formerly ED-749) differs from other topoisomerase I inhibitors both pharmacokinetically and pharmacodynamically. In vitro, it is more potent than camptothecins and has a variable cytotoxic activity in 31 different human cancer cell lines. Edotecarin also possesses greater than additive inhibitory effects on cell proliferation when used in combination with other agents tested in vitro against various cancer cell lines. The present in vivo studies were done to extend the in vitro findings to characterize the antitumor effects of edotecarin when used either alone or in combination with other agents (i.e., 5-fluorouracil, irinotecan, cisplatin, oxaliplatin, and SU11248) in the HCT-116 human colon cancer xenograft model. Treatment effects were based on the delay in onset of an exponential growth of tumors in drug-treated versus vehicle control-treated groups. In all studies, edotecarin was active both as a single agent and in combination with other agents. Combination therapy resulted in greater than additive effects, the extent of which depended on the specific dosage regimen. Toxicity in these experiments was minimal. Of all 359 treated mice, the six that died of toxicity were in the high-dose edotecarin/oxaliplatin group. The results suggest that edotecarin may serve as effective chemotherapy of colon cancer when used as a single agent, in combination with standard regimens and other topoisomerase inhibitors or with novel agents, such as the multitargeted tyrosine kinase inhibitor SU11248.

Modulation of radiation response by inhibiting topoisomerase II catalytic activity

Due to the essential role played by DNA topoisomerases (topos) in cell survival, the use of topoisomerase inhibitors as chemotherapeutic drugs in combination with radiation has become a common strategy for the treatment of cancer. Catalytic inhibitors of these enzymes would be promising to improve the effectiveness of radiation and therefore, it appears reasonable to incorporate them in combined modality trials. In this work, we have investigated the capacity of both ICRF-193 and Aclarubicin (ACLA), two catalytic inhibitors of topoisomerase II (Topo II), to modulate radiation response in Chinese hamster V79 cell line and its radiosensitive mutant irs2. We also have explored potential mechanisms underlying these interactions. Experiments were performed in the presence and absence of either ICRF-193 or ACLA, and topo II activity was measured using an assay based upon decatenation of kinetoplast DNA (kDNA). For the combined experiments cells were incubated for 3 h in the presence of various inhibitor concentrations and irradiated 30 min prior to the end of treatments and cell survival was determined by clonogenic assay. DNA-damaging activity was measured by single-cell gel electrophoresis. Our results demonstrate that combinations of catalytic inhibitors of topo II and radiation produce an increase in cell killing induced by ionising radiation. The mechanism of radiation enhancement may involve a direct or indirect participation of topo II in the repair of radiation-induced DNA damage.

Sequence dependence of hematologic toxicity using carboplatin and topotecan for primary therapy of advanced epithelial ovarian cancer: a phase I study of the Gynecologic Oncology Group

PURPOSE

Selection of a feasible sequence and schedule of carboplatin in combination with topotecan for evaluation in advanced epithelial ovarian cancer (EOC).

PATIENTS AND METHODS

Women with stages III-IV EOC or primary peritoneal carcinoma without prior chemotherapy were assigned to consecutive cohorts evaluating a "forward" (carboplatin day 1, topotecan days 1-3), "reverse" (carboplatin day 3, topotecan days 1-3), or "extended reverse" sequence (carboplatin day 5, topotecan days 1-5). Patients received 4 cycles carboplatin-topotecan followed by 4 cycles carboplatin-paclitaxel. Feasibility was defined according to the cumulative proportion of patients with dose-limiting events (DLEs) during the first four cycles.

RESULTS

Sixty-eight patients were enrolled across 5 cohorts. The forward sequence demonstrated unacceptable hematologic DLEs at the lowest topotecan dose (0.75 mg/m2/day x 3 days). The reverse sequence was feasible at 1.25 mg/m2/day x 3 days, with only 1/15 patients experiencing a DLE within 4 cycles, and 14/15 patients were able to receive 4 subsequent cycles of carboplatin-paclitaxel. The extended reverse sequence was associated with excessive DLEs at 1.00 mg/m2/day x 5 days. Prophylactic hematopoietic growth factors were not required.

CONCLUSION

Higher doses of topotecan could be safely administered with reduced toxicity over multiple cycles using the reverse sequence, which was selected for phase III evaluation. The relative efficacy of the forward and reverse sequence is unknown.

In-vitro schedule-dependent interaction between oxaliplatin and 5-fluorouracil in human gastric cancer cell lines

In order to define the most effective combination schedule of oxaliplatin (L-OHP) and 5-fluorouracil (5-FU), we investigated the in vitro interaction between these drugs in a panel of four human gastric adenocarcinoma cell lines (MKN-1, NUGC-3, NUGC-5 and AZ-521). Cytotoxic activity was determined by the WST-1 assay. Different schedules of the two drugs were compared and evaluated for synergism, additivity or antagonism with a quantitative method based on the median-effect principle of Chou and Talalay. Cell cycle perturbation and apoptosis were evaluated by flow cytometry. Simultaneous and sequential treatments of L-OHP followed by 5-FU exhibited synergistic effects in all four cell lines, whereas the reverse sequence yielded a clear antagonism. 5-FU exclusively arrested cells at the G0/G1 phase, and L-OHP at the G0/G1 and G2/M phases. Apoptosis was most prominent when cells were treated simultaneously or in a sequence of L-OHP followed by 5-FU, producing apoptosis in the majority of treated cells (55.5-61.5%). In contrast, the reverse sequence yielded only 20% induction of apoptosis, the rate being not significantly different from those induced by each drug singly. Moreover, this sequence dependence was further confirmed by the experiment which compared the total number of NUGC-3 cells 7 days after these combination schedules. These findings suggest that the interaction of 5-FU and L-OHP could be highly schedule dependent, with the most efficacious interaction observed in simultaneous combination and that 5-FU followed by L-OHP would not be recommended in clinical trials for patients with advanced gastric cancer.

Randomized Phase II study of two opposite administration sequences of irinotecan and cisplatin in patients with advanced nonsmall cell lung carcinoma

BACKGROUND

Combined chemotherapy with irinotecan and cisplatin (IP) is active in patients with nonsmall cell lung carcinoma (NSCLC). However, the optimal administration schedule needs to be defined to maximize its synergic effect. The authors evaluated the efficacy, toxicity, and pharmacokinetics (PK) of IP chemotherapy given on two administration sequences in chemotherapy-naive patients with NSCLC.

METHODS

Eighty eligible patients were assigned randomly to receive 1 of 2 irinotecan and cisplatin administration sequences on Day 1: irinotecan followed by cisplatin (I-P) (n = 39 patients) or cisplatin followed by irinotecan (P-I) (n = 41 patients). Treatment was comprised of irinotecan at a dose of 80 mg/m(2) intravenously on Days 1 and 8 and cisplatin at a dose of 60 mg/m(2) intravenously on Day 1 of a 21-day cycle for a maximum of 6 cycles. For PK analysis, serial plasma samples were obtained on Day 1 of the first cycle.

RESULTS

In total, 77 patients were assessable for efficacy. The overall response rate was 47%, and there was a trend in favor of P-I (54%) compared with I-P (39%). In multivariate logistic regression analysis, the P-I sequence and female gender were found to be significant predictors of a better response (P = 0.047 and P = 0.011, respectively). Overall toxicity profiles and PK parameters were similar in both arms.

CONCLUSIONS

IP chemotherapy showed promising activity with a favorable 1-year survival rate. For future clinical use, the authors recommend administering cisplatin first and then irinotecan, because that sequence was associated with a higher response rate.

Phase I and Pharmacologic Study of Infusional Topotecan and Carboplatin in Relapsed and Refractory Acute Leukemia

PURPOSE

To assess the maximum tolerated dose, toxicities, pharmacokinetics, and antileukemic activity of topotecan and carboplatin in adults with recurrent or refractory acute leukemias.

EXPERIMENTAL DESIGN

Patients received topotecan and carboplatin by 5-day continuous infusion at nine dose levels. Patients achieving a complete remission received up to two additional courses for consolidation. Plasma topotecan and ultrafilterable platinum were assayed on days 1 to 5. In addition, pretreatment levels of various polypeptides in leukemic cells were examined by immunoblotting to assess possible correlations with response.

RESULTS

Fifty-one patients received a total of 69 courses of therapy. Dose-limiting toxicity consisted of grade 4/5 typhlitis and grade 3/4 mucositis after one course of therapy or grade 4 neutropenia and thrombocytopenia lasting >50 days when a second course was administered on day 21. Among 45 evaluable patients, there were 7 complete remissions, 2 partial remissions, 1 incomplete complete remission, and 1 reversion to chronic-phase chronic myelogenous leukemia. Topotecan steady-state plasma concentrations increased with dose. No accumulation of topotecan or ultrafilterable platinum occurred between days 1 and 5 of therapy. Leukemic cell levels of topoisomerase I, checkpoint kinase 1, checkpoint kinase 2, and Mcl-1 correlated with proliferating cell nuclear antigen but not with response. In contrast, low Bcl-2 expression correlated with response (P = 0.014, Mann-Whitney U test).

CONCLUSIONS

The maximum tolerated dose was 1.6 mg/m(2)/d topotecan plus 150 mg/m(2)/d carboplatin. The complete remission rate in a heavily pretreated population was 16% (33% at the highest three dose levels). Responses seem to correlate with low pretreatment blast cell Bcl-2 expression.

Phase I trial of intravenous cisplatin-topotecan chemotherapy for three consecutive days in patients with advanced solid tumors: parallel topotecan escalation in two fixed platinum dosing schemes

PURPOSE

We performed a phase I study of two fixed dosing schemes of cisplatin, a DNA cross-linker, with intravenous escalating topotecan, a DNA-topoisomerase I inhibitor.

EXPERIMENTAL DESIGN

40 patients with advanced solid tumors received intravenous cisplatin at a fixed dose of either 25 mg/m2 (schedule A) or 20 mg/m2 (schedule B) daily for 3 days with standard hydration. Topotecan escalation proceeded in 0.75, 0.90, 1.0, 1.15 mg/m2 cohorts in schedule A and 1.0, 1.1, 1.2, 1.3 mg/m2 cohorts in schedule B, administered intravenously at the end of cisplatin infusion daily for 3 days, repeated every 3 weeks. Dose-limiting toxicity (DLT) consisted of protracted grade IV neutropenia, febrile neutropenia, grade IV thrombocytopenia and any grade III/IV non-hematological toxicity. Epoetin and granulocyte colony-stimulating factor support was allowed on severe myeloablation. Endpoints were the identification of maximal tolerated dose (MTD), DLT and other toxicity.

RESULTS

The MTD was reached in cohort 25/1.15 mg/m2 in schedule A and 20/1.2 mg/m2 in schedule B. All DLT seen consisted of three episodes of febrile neutropenia and two of grade IV thrombocytopenia in schedule A, with three episodes of febrile neutropenia and one of protracted neutropenia in schedule B. Myelosuppression was substantial in all cohorts despite granulocyte colony-stimulating factor and epoetin support, peaked on the third week of treatment and resulted in administration of chemotherapy at a median of every 4 weeks. Non-hematologic toxicity was mild. The response rate was 51% with seven complete responses occurring in patients with ovarian cancer, small cell and non-small cell lung cancer and cancer of unknown primary. The recommended dose was 20/ 1.1 mg/m2 for cisplatin and topotecan on schedule B, as the number of responses and administered topotecan dose were higher in schedule B recommended dose with lower cisplatin dose, minimizing problems of nephrotoxicity and vomiting.

CONCLUSIONS

The schedule B daily cisplatin-topotecan x 3 combination with secondary cytokine support is associated with promising activity and schedule convenience. However, substantial myelosuppression undermines its applicability in the palliative setting, stressing the need for less toxic regimens.

In vitro sequence-dependent interaction between nedaplatin and paclitaxel in human cancer cell lines

PURPOSE

To define the most effective combination schedule of paclitaxel and nedaplatin, a new platinum derivative, we investigated the in vitro interaction between these drugs in AZ-521 and NUGC-4 gastric adenocarcinoma and KSE-1 esophageal squamous carcinoma cell lines.

MATERIALS AND METHODS

Cytotoxic activity was determined by the WST-1 assay. Different treatment schedules of the two drugs were compared and evaluated for synergism, additivity, or antagonism using a quantitative method based on the median-effect principle of Chou and Talalay. Cell-cycle perturbation and apoptosis were evaluated by means of flow cytometry.

RESULTS

Upon 24-h sequential exposure, the sequence paclitaxel followed by nedaplatin induced greater than additive effects in all of the cell lines, with synergistic interactions in NUGC-4 and KSE-1 cells. By contrast, antagonistic effects were observed with the reverse sequence. Simultaneous treatment resulted in either a synergistic or antagonistic effect, depending on the cell line. Therefore, the sequence paclitaxel followed by nedaplatin appears most active, at least in these three cell lines. Flow cytometric analyses at IC50 indicated that paclitaxel induced G2/M arrest with subsequent induction of apoptosis (56%) in the sub-G1 phase. When paclitaxel preceded nedaplatin, apoptosis was most prominent (70%) with pronounced G2/M arrest. By contrast, the reverse sequence yielded only 28% induction of apoptotic cells, with almost identical cell-cycle distribution patterns to those observed with nedaplatin alone, indicating that the activity of paclitaxel is abolished by pretreatment with nedaplatin.

CONCLUSIONS

Our findings suggest that the interaction of nedaplatin and paclitaxel is highly schedule dependent and that the sequential administration of paclitaxel followed by nedaplatin should be thus incorporated into the design of a clinical trial.

Ex vivo characterization of XR11576 (MLN576) against ovarian cancer and other solid tumors

XR11576 (MLN576) is a novel monophenazine with a mechanism of action that includes interaction with both topoisomerase (Topo) I and II. The aim of this study was to evaluate its cytotoxicity against fresh tumor cells taken from patients with a variety of solid tumors. Cells were obtained from 89 patients and exposed for 6 days to XR11576 alone, or in combination with doxorubicin, cisplatin, treosulfan, paclitaxel or vinorelbine. Cell survival was measured using the ATP-Tumor Chemosensitivity Assay (ATP-TCA). Immunohistochemical staining of Topo I, Topo IIalpha and MDR1 was performed on paraffin-embedded blocks in those tumors for which tissue was available (n = 49). Overall, the median IC90 and IC50 values of XR11576 in tumor-derived cells were 242 and 110 nM, respectively. In all samples XR11576 was more potent than the other cytotoxics tested. Breast and gynecological malignancies were most sensitive to XR11576, while the potency of this compound was slightly attenuated in gastrointestinal tumors, in which the median IC90 and IC50 values were 308 and 212 nM, respectively. Cases of synergism were identified when combining XR11576 with vinorelbine (nine of 30 samples) and doxorubicin (12 of 38 samples), while the addition of paclitaxel resulted in an antagonistic effect (CI50>1.2) in 38 of 42 tumors. A very modest correlation by linear regression analysis was found between the intensity of MDR1 staining and the IC50 of XR11576 (r = 0.311, p = 0.0312), but not with the IC90 (r = 0.247, NS). These data support the rapid introduction of XR11576 to clinical trials and suggest that it may be effective against a broad spectrum of tumor types.

A phase I and pharmacodynamic study of fludarabine, carboplatin, and topotecan in patients with relapsed, refractory, or high-risk acute leukemia

PURPOSE

A novel regimen designed to maximize antileukemia activity of carboplatin through inhibiting repair of platinum-DNA adducts was conducted in poor prognosis, acute leukemia patients.

EXPERIMENTAL DESIGN

Patients received fludarabine (10 to 15 mg/m(2) x 5 days), carboplatin (area under the curve 10 to 12 by continuous infusion over 5 days), followed by escalated doses of topotecan infused over 72 hours (fludarabine, carboplatin, topotecan regimen). Twenty-eight patients had acute myelogenous leukemia (7 untreated secondary acute myelogenous leukemia, 11 in first relapse, and 10 in second relapse or refractory), 1 patient had refractory/relapsed acute lymphoblastic leukemia, and 2 patients had untreated chronic myelogenous leukemia blast crisis. Six patients had failed an autologous stem cell transplant. Patients ranged from 19 to 76 (median 54) years. Measurement of platinum-DNA adducts were done in serial bone marrow specimens.

RESULTS

Fifteen of 31 patients achieved bone marrow aplasia. Clinical responses included 2 complete response, 4 complete response with persistent thrombocytopenia, and 2 partial response. Prolonged myelosuppression was observed with median time to blood neutrophils >/=200/microl of 28 (0 to 43) days and time to platelets >/=20,000/microl (untransfused) of 40 (24 to 120) days. Grade 3 or greater infections occurred in all of the patients, and there were 2 infection-related deaths. The nonhematologic toxicity profile was acceptable. Five patients subsequently received allografts without early transplant-related mortality. Maximum tolerated dose of fludarabine, carboplatin, topotecan regimen was fludarabine 15 mg/m(2) x 5, carboplatin area under the curve 12, and topotecan 2.55 mg/m(2) over 72 hours. An increase in bone marrow, platinum-DNA adduct formation between the end of carboplatin infusion and 48 hours after the infusion correlated with bone marrow response.

CONCLUSIONS

Fludarabine, carboplatin, topotecan regimen is a promising treatment based on potential pharmacodynamic interactions, which merits additional study in poor prognosis, acute leukemia patients.

In vitro schedule-dependent interaction between paclitaxel and oxaliplatin in human cancer cell lines

PURPOSE

In order to define the most effective administration schedule of the combination of paclitaxel and oxaliplatin, we investigated the in vitro interaction between these drugs in a panel of three human cancer cell lines (AZ-521 gastric adenocarcinoma cell line, HST-1 tongue squamous carcinoma cell line, and KSE-1 esophageal squamous carcinoma cell line).

MATERIALS AND METHODS

Cytotoxic activity was determined by the WST-1 assay. Different administration schedules of the two drugs were compared and evaluated for synergism, additivity, or antagonism with a quantitative method based on the median-effect principle of Chou and Talalay. Cell cycle perturbation and apoptosis were evaluated by flow cytometry.

RESULTS

Simultaneous treatment of cells with paclitaxel and oxaliplatin showed greater than additive effects. Upon 24-h sequential exposure, the sequence of paclitaxel followed by oxaliplatin showed synergistic effects in AZ-521 and HST-1 cells, and greater than additive effects in KSE-1 cells, while the opposite sequence yielded marked antagonistic effects in all three cell lines. Flow cytometric analysis indicated that paclitaxel induced G(2)/M arrest with subsequent induction of apoptosis in the sub-G(1) phase. Apoptosis was most prominent when paclitaxel preceded oxaliplatin, which produced apoptosis in the majority of treated cells (75%). By contrast, the reverse sequence yielded only 39% induction of apoptotic cells, the rate being not different from those induced by each drug singly.

CONCLUSIONS

Our findings suggest that the interaction of paclitaxel and oxaliplatin is highly schedule-dependent and that the sequential administration of paclitaxel followed by oxaliplatin should thus be incorporated into the design of a clinical trial.

Review of the use of topotecan in ovarian carcinoma

Ovarian cancer is the fifth leading cause of cancer deaths in women. The majority of patients present with advanced disease and relapse after first-line platinum-based chemotherapy; therefore, many proceed to treatment with salvage chemotherapy. Currently available treatment options are generally no longer curative in the relapse setting; hence, the emphasis of treatment is towards disease control and palliation of symptoms. There are several agents available for the treatment of relapsed ovarian carcinoma, of which topotecan is one of the most widely studied and characterised. This review aims to evaluate the role of topotecan in the management of this disease by considering the properties of the compound, the clinical efficacy in Phase II and III studies, its role in first- and second-line treatment and alternative dosing strategies to overcome toxicity.

Platinated DNA adducts enhance poisoning of DNA topoisomerase I by camptothecin

Camptothecins constitute a novel class of chemotherapeutics that selectively target DNA topoisomerase I (Top1) by reversibly stabilizing a covalent enzyme-DNA intermediate. This cytotoxic mechanism contrasts with that of platinum drugs, such as cisplatin, which induce inter- and intrastrand DNA adducts. In vitro combination studies using platinum drugs combined with Top1 poisons, such as topotecan, showed a schedule-dependent synergistic activity, with promising results in the clinic. However, whereas the molecular mechanism of these single agents may be relatively well understood, the mode of action of these chemotherapeutic agents in combination necessitates a more complete understanding. Indeed, we recently reported that a functional homologous recombination pathway is required for cisplatin and topotecan synergy yet represses the synergistic toxicity of 1-beta-D-arabinofuranosyl cytidine in combination with topotecan (van Waardenburg, R. C., de Jong, L. A., van Delft, F., van Eijndhoven, M. A., Bohlander, M., Bjornsti, M. A., Brouwer, J., and Schellens, J. H. (2004) Mol. Cancer Ther. 3, 393-402). Here we provide direct evidence for Pt-1,3-d(GTG) poisoning of Top1 in vitro and demonstrate that persistent Pt-DNA adducts correlate with increased covalent Top1-DNA complexes in vivo. This contrasts with a lack of persistent lesions induced by the alkylating agent bis[chloroethyl]nitrosourea, which exhibits only additive activity with topotecan in a range of cell lines. In human IGROV-1 ovarian cancer cells, the synergistic activity of cisplatin with topotecan requires processive DNA polymerization, whereas overexpression of Top1 enhances yeast cell sensitivity to cisplatin. These results indicate that the cytotoxic activity of cisplatin is due, in part, to poisoning of Top1, which is exacerbated in the presence of topotecan.

A novel combination of cisplatin, irinotecan, and capecitabine in patients with advanced cancer

BACKGROUND

We conducted a dose escalation study combining cisplatin, irinotecan, and capecitabine (CIC), aiming to establish the maximum tolerated doses (MTD), side effect profile, and dose-limiting toxicity (DLT) of this novel regimen.

PATIENTS AND METHODS

Intravenous cisplatin and irinotecan were to be administered on days 1 and 8, and oral capecitabine on days 1-14 of a 3-week cycle. The study was conducted in three parts. Part A: escalating doses of irinotecan (40 --> 80 mg/m2) and capecitabine (1000 --> 3300 mg/d) combined with a fixed dose of cisplatin (30 mg/m2). Part B: escalating doses of irinotecan (MTD-A --> MTD-A + 40 mg/m2) with fixed doses of cisplatin (20 mg/m2) and capecitabine (MTD-A level). Part C: escalating doses of capecitabine (1300 mg/d-->2600 mg/d) with fixed doses of cisplatin (20 mg/m2) and irinotecan (60 mg/m2).

RESULTS

Of 51 eligible patients 27 (53%) were male, median age was 58 years and 88% had PS 0-1. Major primary disease sites were colorectal (24%), unknown (14%), stomach (14%), and pancreas (12%). MTD-A was cisplatin 30 mg/m2, irinotecan 60 mg/m2, capecitabine 1000 mg/d and MTD-B was cisplatin 20 mg/m2, irinotecan 90 mg/m2, capecitabine 1000 mg/d. An MTD was not formally established for part C. DLTs consisted of infection with neutropenia (1), diarrhea and fatigue (1), hypokalemia (1), diarrhea and febrile neutropenia (1) and C2 delay of > or = 2 weeks or 25% dose reduction in C1 due to neutropenia or thrombocytopenia (6). Seven patients had a partial response to treatment (four colorectal, one SCLC, one NSCLC, one unknown primary), twenty seven SD (53%), twelve PD (24%) and five NE (10%).

CONCLUSION

CIC was associated with moderate toxicity and only modest antitumor activity. We conclude that this regimen has insufficient activity to justify further study in the phase II setting.

Homologous recombination is a highly conserved determinant of the synergistic cytotoxicity between cisplatin and DNA topoisomerase I poisons

Phase I and II clinical trails are currently investigating the antitumor activity of cisplatin and camptothecins (CPTs; DNA topoisomerase I poisons), based on the dramatic synergistic cytotoxicity of these agents in some preclinical models. However, the mechanistic basis for this synergism is poorly understood. By exploiting the evolutionary conservation of DNA repair pathways from genetically tractable organisms such as budding and fission yeasts to mammalian cells, we demonstrate that the synergism of CPT and cisplatin requires homologous recombination. In yeast and mammalian cell lines defective for RAD52 and XRCC2/3, respectively, the combination of these agents proved antagonistic, while greater than additive activity was evident in isogenic wild-type cells. Homologous recombination appears to mediate a similar interaction of X-rays and CPT, but antagonizes the synergism of cytarabine (Ara-C) with CPT. These findings suggest that homologous recombination comprises an evolutionarily conserved determinant of cellular sensitivity when CPTs are used in combination with other therapeutics.

Cytotoxicity of the organic ruthenium anticancer drug Nami-A is correlated with DNA binding in four different human tumor cell lines

PURPOSE

The cytotoxicity, intracellular accumulation and DNA adduct formation of the ruthenium complex imidazolium trans-imidazoledimethylsulfoxide tetrachlororuthenate (ImH[ trans-RuCl(4)(DMSO)Im], Nami-A) were compared in vitro with those of cisplatin in four human tumor cell lines: Igrov-1, 2008, MCF-7, and T47D.

METHODS

Cytotoxicity was assessed in vitro using a growth inhibition assay. Accumulation was determined by flameless atomic absorption spectroscopy (AAS). GG and AG intrastrand adducts were measured using the (32)P-postlabeling assay.

RESULTS

Nami-A was on average 1053 times less cytotoxic than cisplatin. The cytotoxicity of cisplatin was linearly related to both intracellular platinum accumulation and DNA binding, while the cytotoxicity of Nami-A was significantly related only to DNA binding and not to intracellular ruthenium accumulation. The levels of accumulation of Nami-A measured as ruthenium and of cisplatin measured as platinum were correlated linearly with the incubation concentration over a concentration range of 0 to 600 micro M of both drugs. Ruthenium intracellular accumulation and DNA binding were on average 4.8 and 42 times less, respectively, than those of cisplatin. In addition, the numbers of GG and AG intrastrand adducts induced by Nami-A were 418 and 51 times fewer, respectively. Nami-A and cisplatin had the same binding capacity to calf thymus DNA. Nami-A was 25-40% less bound to cellular proteins than cisplatin.

CONCLUSIONS

There was no saturation of the uptake and DNA binding capacity of either Nami-A or cisplatin. Furthermore, the low binding of Nami-A to cellular DNA cannot simply be explained by a lower capacity to bind to DNA, because the absolute level of binding in vitro to calf thymus DNA was the same for Nami-A and cisplatin. Finally, the lower cytotoxicity of Nami-A on a molar basis than that of cisplatin can at least partly be explained by its reduced reactivity to DNA in intact cells.

Phase I dose-finding study of biweekly irinotecan in combination with fixed doses of 5-fluorouracil/leucovorin, gemcitabine and cisplatin (G-FLIP) in patients with advanced pancreatic cancer or other solid tumors

This phase I trial was initiated based on encouraging clinical data with 5-fluorouracil (5-FU)/leucovorin (LV), gemcitabine and cisplatin (G-FLIP) in the therapy of solid tumors. In this trial, G-FLIP has been modified to facilitate outpatient administration and to optimize sequence-dependent synergistic activity. Treatment consisted of biweekly (once every 14 days) cycles of sequential gemcitabine 500 mg/m, irinotecan per dose escalation schedule, bolus 5-FU 400 mg/m and LV 300 mg on day 1 followed by a 24-h 5-FU infusion 1500 mg/m, followed by cisplatin 35 mg/m on day 2. The irinotecan starting dose was 80 mg/m and escalated by 20 mg/m in cohorts of three patients until the maximum tolerated dose (MTD) was defined. Twenty-three patients were enrolled (13 men/10 women) with the following cancers: 11 pancreatic, five gallbladder, three squamous cell carcinoma of the head and neck, one hepatocellular carcinoma, one melanoma, one gastric, and one breast cancer. Median patient age was 63 years (range 44-78) and median Karnofsky performance status (KPS) was 80. Patients received a median of 8 cycles (range 1-16) over five irinotecan dose levels (80, 100, 120, 140 and 160 mg/m). Dose-limiting toxicity consisting of grade 3 nausea/vomiting despite aggressive anti-emetic therapy occurred in one patient at dose level 1 and three patients at dose level 3. Grade 3-4 hematological toxicities per patient consisted of thrombocytopenia (3%), anemia (6%), thrombosis (23%), neutropenia (16%) and neutropenic fever (10%). Of 18 patients evaluable for response, one complete response (pancreatic) and eight partial responses (three gallbladder, two pancreatic, two head and neck, and one breast) were attained. Seven patients had disease stabilization (five pancreatic, one hepatocellular and one gastric) for a median of 16 weeks (range 10-22). Median time to disease progression among all 23 patients enrolled to the phase I portion of the trial was 20.5 weeks (range 4-37). We conclude that G-FLIP is a novel outpatient chemotherapy regimen with acceptable toxicity at the maximum tolerated irinotecan dose of 120 mg/m. The phase II trial of G-FLIP using an irinotecan dose of 120 mg/m for patients with metastatic pancreatic cancer is ongoing.

Phase II study to topotecan and cisplatin in advanced hepatocellular carcinoma

BACKGROUND

Hepatocellular carcinoma remains a highly chemoresistant neoplasm and is a common malignancy with poor prognosis in Korea. We performed a phase II study to evaluate the efficacy and toxicities of topotecan and cisplatin combination chemotherapy for advanced hepatocellular carcinoma.

METHODS

Between November 1999 and May 2001, ten patients with histologically proven hepatocellular carcinoma were enrolled in this study. The median age was 54 (range: 53-74) years and all were male. Six patients demonstrated stage IV, 1 stage IIIC, 2 stage IIIB and 1 stage IIIA. Six patients showed a ECOG performance status of 1. The treatment regimen consisted of topotecan 1.25 mg/m2 and cisplatin 20 mg/m2 for 5 days. The treatment was repeated every 4 weeks. Toxicities were evaluated according to WHO toxicity criteria.

RESULTS

All ten patients were evaluable for response and toxicity. There was only one patient who achieved partial response. The overall response rate was 10% (95% C.I.) and the response duration was 46 weeks. The median survival of all patients was 21 (range: 17-54+) weeks. During a total of 24 cycles, neutropenia of WHO grade 3 and 4 occurred in 33%, thrombocytopenia in 33% and anemia in 21%. In non-hematologic toxicity, diarrhea and hepatoxicity of grade 3 occurred in 1 and 2 patients, respectively. But there was no treatment-related death.

CONCLUSION

When used in this dose and schedule, topotecan and cisplatin combination chemotherapy does not seem to be effective for patients with advanced hepatocellular carcinoma.

DNA repair mechanisms involved in gemcitabine cytotoxicity and in the interaction between gemcitabine and cisplatin

The influence of DNA repair mechanisms on the interaction between gemcitabine and cisplatin was studied using a panel of Chinese hamster ovary (CHO) cell lines deficient in one of the following repair pathways: base excision repair (BER), nucleotide excision repair (NER), homologous recombination (HR) and non-homologous end joining (NHEJ). NER and HR are known to be involved in platinum-DNA adduct repair. Single agent experiments demonstrated that each of the repair deficient cell lines had a similar sensitivity towards gemcitabine as the parental cell lines, whereas the NER- and HR-deficient lines showed increased sensitivity towards cisplatin. Furthermore, in the parental cell lines, the administration sequence cisplatin followed by gemcitabine was synergistic, whereas the reversed schedule showed additivity and simultaneous administration revealed antagonistic cytotoxicity. In the repair deficient cell lines, using this synergistic schedule of cisplatin followed by gemcitabine, loss of synergy was observed in the NER- and HR-deficient cell lines. However, the magnitude of the effect in the NER-deficient cells was small. The sensitivity to the combination of cisplatin and gemcitabine shown by the BER- and NHEJ-deficient cell lines did not differ significantly from that of the parental cell line. Cellular accumulation of platinum as well as the formation of GG- and AG-intrastrand adducts in the parental line and in the HR-deficient line were not affected by gemcitabine. In conclusion, our results indicate that BER, NER, HR, and NHEJ are most likely incapable of modulating the cytotoxicity of gemcitabine, and that HR is involved in the synergistic interaction between cisplatin and gemcitabine in our cell system.

Emerging role of topotecan in front-line treatment of carcinoma of the ovary

The conventional front-line chemotherapy strategy for advanced epithelial ovarian carcinoma has become adjuvant administration of platinum (carboplatin and cisplatin), either alone or, most often, in combination with a taxane. However, a number of active agents have been identified in phase II/III trials of second-line and salvage ovarian cancer patients that may augment this front-line strategy. One agent, topotecan, has antitumor activity comparable with paclitaxel in patients with recurrent ovarian cancer and is an established treatment in second-line or salvage settings. Additionally, its mechanism of action is different from paclitaxel and is nonoverlapping. These properties, coupled with the in vitro synergy observed in tumor models among topotecan, paclitaxel, and platinum, have provided the rationale for investigators to examine topotecan in front-line ovarian cancer therapy. A number of strategies for incorporating topotecan into front-line therapy are under active investigation, including the replacement of paclitaxel with topotecan, a triplet regimen with cisplatin or carboplatin and paclitaxel, a consolidation regimen consisting of several courses of a platinum agent and paclitaxel followed by several courses of topotecan, and a sequential doublet regimen in which patients receive platinum in every course as part of a doublet with alternating or sequential topotecan and paclitaxel. Preliminary data from ongoing clinical trials of these new regimens show favorable response rates and generally manageable toxicity profiles. This review summarizes the preliminary clinical findings associated with the four strategies and outlines ongoing and future randomized studies of topotecan in front-line ovarian cancer.

DNA-based drug interactions of cisplatin

The interactions of cisplatin with other anti-cancer agents on the DNA level have been studied extensively in pre-clinical experiments. In general, combination of cisplatin with an antimetabolite, taxane, or topoisomerase inhibitor, can result in a modulation of platinum pharmacology on the DNA, for example, enhanced retention of the platinum-DNA adducts. These interactions are mostly sequence and cell type dependent. In cell line models, antimetabolites can enhance the number of platinum-DNA adducts, probably by inhibition of DNA repair pathways. However, in clinical trials, the opposite effect has been observed, with a reduction of these adducts upon combined treatment. For the taxanes it has been shown that they can inhibit the formation of platinum-DNA adducts, whereas topoisomerase I inhibitors increase the number of adducts, resulting in strong synergistic cytotoxicity. For this last interaction a mechanistic model has recently been proposed, in which the topoisomerase I enzyme directly binds to the platinum-DNA adduct. Thereafter, the topoisomerase I inhibitor binds to this complex, which yields large stabilised lesions to the DNA that are probably difficult to repair. Ongoing studies will proceed to elucidate the exact mechanism underlying the interactions between cisplatin and other anti-neoplastic agents on the DNA level. Such increased understanding might help in designing new and more effective treatment regimens for cancer. In this paper, we review the pre-clinical and clinical studies investigating the observed interactions between cisplatin, the antimetabolites, taxanes, and topoisomerase inhibitors on the DNA level.

Contribution of apoptosis in the cytotoxicity of the oxaliplatin-irinotecan combination in the HT29 human colon adenocarcinoma cell line

Interactions between the topoisomerase I inhibitor irinotecan (CPT-11) and the platinum derivative oxaliplatin (L-OHP) were investigated in HT29 colon cancer cell line. Synergism was observed when cells were simultaneously exposed to drugs or when cells were first exposed to CPT-11. Flow cytometric studies showed a G(2)/M accumulation when cells were exposed to the simultaneous and CPT-11-->L-OHP combinations whereas a persistent S phase delay was observed when cells were first exposed to L-OHP. We characterised the cytotoxic effect by assessing the induction of apoptosis. Irinotecan induced substantial DEVDase activity and poly(ADP-ribose) polymerase cleavage while this activity was moderate and delayed after exposure to L-OHP. Combination experiments showed a sequence-dependent onset of apoptosis, the CPT-11-->L-OHP schedule being the earliest and the most effective; on the other hand the apoptotic signaling generated by CPT-11 was partly inhibited in the simultaneous combination and in the L-OHP-->CPT-11 sequence. Cell death studies using a dual staining technique showed a shift from apoptosis to necrosis when combining these drugs at high concentrations. Synergistic interactions observed using CPT-11 before L-OHP may be linked to an early apoptotic signaling while the L-OHP-induced S phase block could account for the observed additive effect in the reverse sequence. An additional phenomenon might work towards synergism for the simultaneous combination.