Platinated DNA adducts enhance poisoning of DNA topoisomerase I by camptothecin

Progesterone Enhances Sensitivity of Ovarian Cancer Cells to SN38 Through Inhibition of Topoisomerase I and Inducing Ferroptosis

BACKGROUND

Progesterone rapidly induces ovarian cancer cell death through non-genomic actions mediated by the membrane progesterone receptor (mPR).

AIMS

We investigated the combined effects of progesterone and SN38, an active metabolite of irinotecan, on ovarian cancer cells.

METHODS AND RESULTS

mPR-positive and PR-negative ovarian cancer cell lines were utilized in experiments. Tumor cells were exposed to SN38 or cisplatin for 48 h following exposure to progesterone for 30 min. The viable cell counts were measured using a colorimetric assay and the expression of topoisomerase I (TOPO-I), the direct target of SN38, was observed with or without exposure to progesterone. Moreover, we investigated the relationship between several types of programmed cell death and the SN38 sensitivity enhancement effect of progesterone using specific cell death inhibitors. The chemosensitivity to SN38 was 8.7- to 26.0-fold higher with the administration of progesterone than that without (p < 0.01), but not to cisplatin in ovarian cancer cells. Progesterone suppressed the expression of TOPO-I mRNA by less than 50% (p < 0.01). Furthermore, among various programmed cell death inhibitors, only the ferroptosis inhibitor attenuated the progesterone-induced SN38 chemosensitivity enhancement effect.

CONCLUSIONS

Progesterone increased sensitivity to SN38 by suppressing TOPO-I expression and inducing ferroptosis. The combination of progesterone and irinotecan could be a novel treatment modality for ovarian cancer.

Common Markers and Small Molecule Inhibitors in Golgi Studies

In this chapter, we provide a detailed guide for the application of commonly used small molecules to study Golgi structure and function in vitro. Furthermore, we have curated a concise, validated list of endomembrane markers typically used in downstream assays to examine the consequent effect on the Golgi via microscopy and western blot after drug treatment. This chapter will be useful for researchers beginning their foray into the field of intracellular trafficking and Golgi biology.

Camptothecin compromises transcription recovery and cell survival against cisplatin and ultraviolet irradiation regardless of transcription-coupled nucleotide excision repair

DNA-damaging anti-cancer drugs are used clinically to induce cell death by causing DNA strand breaks or DNA replication stress. Camptothecin (CPT) and cisplatin are commonly used anti-cancer drugs, and their combined use enhances the anti-tumour effects. However, the mechanism underlying this enhanced effect has not been well studied. In this study, we analysed the combined effect of CPT and cisplatin or ultraviolet (UV) and found that CPT suppresses transcription recovery after UV damage and induces the disappearance of the Cockayne syndrome group B (CSB) protein, a transcription-coupled nucleotide excision repair (TC-NER) factor. This CPT-induced disappearance of CSB expression was suppressed by proteasome and transcription inhibitors. Moreover, CSB ubiquitination was detected after CPT treatment in a transcription-dependent manner, suggesting that the transcription stress caused by CPT induces CSB ubiquitination, resulting in CSB undetectability. However, Cockayne syndrome group A (CSA) and CUL4A were not involved in the CPT-induced CSB undetectability, suggesting that CSB ubiquitination caused by CPT is regulated differently from the UV response. However, cisplatin or UV sensitivity was enhanced by CPT even in CSB- or CSA-knockout cells. Furthermore, the excessive CSB expression, which suppressed CSB ubiquitination, did not cancel the combined effect of CPT. These results suggest that CPT blocks the repair of cisplatin or UV-induced DNA damage regardless of TC-NER status. CPT possibly compromised the alternative repair pathways other than TC-NER, leading to the suppression of transcription recovery and enhancement of cell killing.

Human topoisomerases and their roles in genome stability and organization

Human topoisomerases comprise a family of six enzymes: two type IB (TOP1 and mitochondrial TOP1 (TOP1MT), two type IIA (TOP2A and TOP2B) and two type IA (TOP3A and TOP3B) topoisomerases. In this Review, we discuss their biochemistry and their roles in transcription, DNA replication and chromatin remodelling, and highlight the recent progress made in understanding TOP3A and TOP3B. Because of recent advances in elucidating the high-order organization of the genome through chromatin loops and topologically associating domains (TADs), we integrate the functions of topoisomerases with genome organization. We also discuss the physiological and pathological formation of irreversible topoisomerase cleavage complexes (TOPccs) as they generate topoisomerase DNA–protein crosslinks (TOP-DPCs) coupled with DNA breaks. We discuss the expanding number of redundant pathways that repair TOP-DPCs, and the defects in those pathways, which are increasingly recognized as source of genomic damage leading to neurological diseases and cancer.

Topoisomerases have essential roles in transcription, DNA replication, chromatin remodelling and, as recently revealed, 3D genome organization. However, topoisomerases also generate DNA–protein crosslinks coupled with DNA breaks, which are increasingly recognized as a source of disease-causing genomic damage.

Excision repair of topoisomerase DNA-protein crosslinks (TOP-DPC)

Topoisomerases are essential enzymes solving DNA topological problems such as supercoils, knots and catenanes that arise from replication, transcription, chromatin remodeling and other nucleic acid metabolic processes. They are also the targets of widely used anticancer drugs (e.g. topotecan, irinotecan, enhertu, etoposide, doxorubicin, mitoxantrone) and fluoroquinolone antibiotics (e.g. ciprofloxacin and levofloxacin). Topoisomerases manipulate DNA topology by cleaving one DNA strand (TOP1 and TOP3 enzymes) or both in concert (TOP2 enzymes) through the formation of transient enzyme-DNA cleavage complexes (TOPcc) with phosphotyrosyl linkages between DNA ends and the catalytic tyrosyl residue of the enzymes. Failure in the self-resealing of TOPcc results in persistent TOPcc (which we refer it to as topoisomerase DNA-protein crosslinks (TOP-DPC)) that threaten genome integrity and lead to cancers and neurodegenerative diseases. The cell prevents the accumulation of topoisomerase-mediated DNA damage by excising TOP-DPC and ligating the associated breaks using multiple pathways conserved in eukaryotes. Tyrosyl-DNA phosphodiesterases (TDP1 and TDP2) cleave the tyrosyl-DNA bonds whereas structure-specific endonucleases such as Mre11 and XPF (Rad1) incise the DNA phosphodiester backbone to remove the TOP-DPC along with the adjacent DNA segment. The proteasome and metalloproteases of the WSS1/Spartan family typify proteolytic repair pathways that debulk TOP-DPC to make the peptide-DNA bonds accessible to the TDPs and endonucleases. The purpose of this review is to summarize our current understanding of how the cell excises TOP-DPC and why, when and where the cell recruits one specific mechanism for repairing topoisomerase-mediated DNA damage, acquiring resistance to therapeutic topoisomerase inhibitors and avoiding genomic instability, cancers and neurodegenerative diseases.

Tyrosyl-DNA Phosphodiesterase I N-Terminal Domain Modifications and Interactions Regulate Cellular Function

The conserved eukaryotic DNA repair enzyme Tyrosyl-DNA phosphodiesterase I (Tdp1) removes a diverse array of adducts from the end of DNA strand breaks. Tdp1 specifically catalyzes the hydrolysis of phosphodiester linked DNA-adducts. These DNA lesions range from damaged nucleotides to peptide-DNA adducts to protein-DNA covalent complexes and are products of endogenously or exogenously induced insults or simply failed reaction products. These adducts include DNA inserted ribonucleotides and non-conventional nucleotides, as well as covalent reaction intermediates of DNA topoisomerases with DNA and a Tdp1-DNA adduct in trans. This implies that Tdp1 plays a role in maintaining genome stability and cellular homeostasis. Dysregulation of Tdp1 protein levels or catalysis shifts the equilibrium to genome instability and is associated with driving human pathologies such as cancer and neurodegeneration. In this review, we highlight the function of the N-terminal domain of Tdp1. This domain is understudied, structurally unresolved, and the least conserved in amino acid sequence and length compared to the rest of the enzyme. However, over time it emerged that the N-terminal domain was post-translationally modified by, among others, phosphorylation, SUMOylation, and Ubiquitinoylation, which regulate Tdp1 protein interactions with other DNA repair associated proteins, cellular localization, and Tdp1 protein stability.

Combination of baicalein and 10-hydroxy camptothecin exerts remarkable synergetic anti-cancer effects

BACKGROUND

10-Hydroxy camptothecin (HCPT), a naturally occurring alkaloid, is a clinical drug for cancer chemotherapy. Baicalein (BA) is a flavonoid extracted from the root of Scutellaria baicalensis. The synergistic anti-cancer effect of BA and HCPT has not been reported.

PURPOSE

To explore whether and how BA enhances the anti-cancer effect of HCPT in BGC823 cells.

METHODS

Cell viability was measured by MTT assay. Apoptosis and cell cycle were analyzed through flow cytometry and western blotting analysis. DNA damage was determined by a comet assay. The activity of topoisomerase I (Topo I) was detected by the plasmid DNA relaxation assay. The synergistic anti-cancer effect of BA and HCPT in vivo was tested by BGC823 xenografted tumor model.

RESULTS

BA at non-toxic doses prominently enhanced the anti-cancer activities of HCPT in BGC823, MCF7 and SMMC7721 cells. Combination treatment of BA and HCPT induced BGC823 cells apoptosis mainly via intrinsic rather than extrinsic pathways, and preferentially arresting cell cycle in G1 and G2 phases with the aid of p21. Of note, p53, the upstream regulator of cell apoptosis and cycle, was increased by 5 folds in combination group. It helped to further trigger DNA damage and inhibit Topo I catalytic activity after combination treatment of BA and HCPT. Moreover, the BGC823 xenografted tumor growth rate in nude mice was repressed in a greater degree (P< 0.01) in the combinational group than the single-drug group.

CONCLUSION

HCPT and BA, a new and effective combination therapy, synergistically target Topo I and up-regulate p53 to induce cell apoptosis and cell cycle arrest.

Immunodetection of human topoisomerase I-DNA covalent complexes

A number of established and investigational anticancer drugs slow the religation step of DNA topoisomerase I (topo I). These agents induce cytotoxicity by stabilizing topo I-DNA covalent complexes, which in turn interact with advancing replication forks or transcription complexes to generate lethal lesions. Despite the importance of topo I-DNA covalent complexes, it has been difficult to detect these lesions within intact cells and tumors. Here, we report development of a monoclonal antibody that specifically recognizes covalent topo I-DNA complexes, but not free topo I or DNA, by immunoblotting, immunofluorescence or flow cytometry. Utilizing this antibody, we demonstrate readily detectable topo I-DNA covalent complexes after treatment with camptothecins, indenoisoquinolines and cisplatin but not nucleoside analogues. Topotecan-induced topo I-DNA complexes peak at 15-30 min after drug addition and then decrease, whereas indotecan-induced complexes persist for at least 4 h. Interestingly, simultaneous staining for covalent topo I-DNA complexes, phospho-H2AX and Rad51 suggests that topotecan-induced DNA double-strand breaks occur at sites distinct from stabilized topo I-DNA covalent complexes. These studies not only provide new insight into the action of topo I-directed agents, but also illustrate a strategy that can be applied to study additional topoisomerases and their inhibitors in vitro and in vivo.

Tyrosyl-DNA phosphodiesterase I resolves both naturally and chemically induced DNA adducts and its potential as a therapeutic target

DNA is subject to a wide range of insults, resulting from endogenous and exogenous sources that need to be metabolized/resolved to maintain genome integrity. Tyrosyl-DNA phosphodiesterase I (Tdp1) is a eukaryotic DNA repair enzyme that catalyzes the removal of covalent 3'-DNA adducts. As a phospholipase D superfamily member Tdp1 utilizes two catalytic histidines each within a His-Lys-Asn motif. Tdp1 was discovered for its ability to hydrolyze the 3'-phospho-tyrosyl that in the cell covalently links DNA Topoisomerase I (Topo1) and DNA. Tdp1's list of substrates has since grown and can be divided into two groups: protein-DNA adducts, such as camptothecin stabilized Topo1-DNA adducts, and modified nucleotides, including oxidized nucleotides and chain terminating nucleoside analogs. Since many of Tdp1's substrates are generated by clinically relevant chemotherapeutics, Tdp1 became a therapeutic target for molecularly targeted small molecules. Tdp1's unique catalytic cycle allows for two different targeting strategies: (1) the intuitive inhibition of Tdp1 catalysis to prevent Tdp1-mediated repair of chemotherapeutically induced DNA adducts, thereby enhancing their toxicity and (2) stabilization of the Tdp1-DNA covalent reaction intermediate, prevents resolution of Tdp1-DNA adduct and increases the half-life of this potentially toxic DNA adduct. This concept is best illustrated by a catalytic Tdp1 mutant that forms the molecular basis of the autosomal recessive neurodegenerative disease spinocerebellar ataxia with axonal neuropathy, and results in an increased stability of its Tdp1-DNA reaction intermediate. Here, we will discuss Tdp1 catalysis from a structure-function perspective, Tdp1 substrates and Tdp1 potential as a therapeutic target.

Analysis of the active-site mechanism of tyrosyl-DNA phosphodiesterase I: a member of the phospholipase D superfamily

Tyrosyl-DNA phosphodiesterase I (Tdp1) is a member of the phospholipase D superfamily that hydrolyzes 3'-phospho-DNA adducts via two conserved catalytic histidines-one acting as the lead nucleophile and the second acting as a general acid/base. Substitution of the second histidine specifically to arginine contributes to the neurodegenerative disease spinocerebellar ataxia with axonal neuropathy (SCAN1). We investigated the catalytic role of this histidine in the yeast protein (His432) using a combination of X-ray crystallography, biochemistry, yeast genetics, and theoretical chemistry. The structures of wild-type Tdp1 and His432Arg both show a phosphorylated form of the nucleophilic histidine that is not observed in the structure of His432Asn. The phosphohistidine is stabilized in the His432Arg structure by the guanidinium group that also restricts the access of nucleophilic water molecule to the Tdp1-DNA intermediate. Biochemical analyses confirm that His432Arg forms an observable and unique Tdp1-DNA adduct during catalysis. Substitution of His432 by Lys does not affect catalytic activity or yeast phenotype, but substitutions with Asn, Gln, Leu, Ala, Ser, and Thr all result in severely compromised enzymes and DNA topoisomerase I-camptothecin dependent lethality. Surprisingly, His432Asn did not show a stable covalent Tdp1-DNA intermediate that suggests another catalytic defect. Theoretical calculations revealed that the defect resides in the nucleophilic histidine and that the pK(a) of this histidine is crucially dependent on the second histidine and on the incoming phosphate of the substrate. This represents a unique example of substrate-activated catalysis that applies to the entire phospholipase D superfamily.

Alternative cyclin D1 splice forms differentially regulate the DNA damage response

The DNA damage response (DDR) activates downstream pathways including cell cycle checkpoints. The cyclin D1 gene is overexpressed or amplified in many human cancers and is required for gastrointestinal, breast, and skin tumors in murine models. A common polymorphism in the human cyclin D1 gene is alternatively spliced, resulting in cyclin D1a and D1b proteins that differ in their carboxyl terminus. Cyclin D1 overexpression enhances DNA damage-induced apoptosis. The role of cyclin D1 and the alternative splice form in regulating the DDR is not well understood. Herein cyclin D1a overexpression enhanced the DDR as characterized by induction of γH2AX phosphorylation, the assembly of DNA repair foci, specific recruitment of DNA repair factors to chromatin, and G(2)-M arrest. Cyclin D1 deletion in fibroblasts or small interfering RNA-mediated reduction of endogenous cyclin D1 in colon cancer cells reduced the 5-fluorouracil-mediated DDR. Mechanistic studies showed that cyclin D1a, like DNA repair factors, elicited the DDR when stably associated with chromatin.

Phase II trial of oral topotecan and intravenous carboplatin with G-CSF support in previously untreated patients with extensive stage small cell lung cancer: A North Central Cancer Treatment Group Study

OBJECTIVES

The objective of this study was to evaluate the response rate and toxicities of the combination of oral topotecan and carboplatin in patients with untreated extensive stage small cell lung cancer (ES-SCLC). Previous studies have suggested improved outcomes with a topoisomerase I inhibitor in combination with a platinum agent.

METHODS

Twenty-six patients with previously untreated, ES-SCLC were evaluable in this phase II trial. All patients received oral topotecan 2.0 mg/m per day on days 1 through 5 and carboplatin at an area under curve of 5 on day 5. Treatment was repeated every 21 days up to a total of 6 cycles. All patients received G-CSF.

RESULTS

There were no complete responses and 16 partial responses, for an overall response rate of 62% (95% CI: 41-80). Median time to progression was 6.0 months (95% CI: 4-8), with a median overall survival of 12 months (95% CI: 8-16). This study was closed to accrual early with 26 of a planned 39 patients enrolled because of grade 5 adverse events in 4 (15%) patients (3 neutropenic infections, 1 sudden cardiac death). Eighty-five percent of patients experienced grade 3 or higher hematologic events. The most common severe nonhematologic events included diarrhea, vomiting, dyspnea, hypoxia, and hypotension.

CONCLUSIONS

Although this drug regimen has activity as first-line therapy in ES-SCLC, it is associated with excessive hematologic toxicity, which occurred in spite of growth factor support. Despite promising survival estimates, this particular combination and dose level of oral topotecan and carboplatin cannot be recommended.

In vivo bioassay to detect irinotecan-stabilized DNA/topoisomerase I complexes in rats

Irinotecan is an anticancer agent that stabilizes topoisomerase I/DNA complexes. So far, no test system has been reported for directly determining irinotecan-induced stabilization of topoisomerase I/DNA complexes in organs in vivo. We adapted an 'in vivo complexes of enzyme to DNA' (ICE) bioassay to assess irinotecan activity in the stomach, duodenum, colon and liver of male Wistar rats after a single treatment with irinotecan (100 mg/kg body weight, intraperitoneally). This was compared to the control group receiving 0.9% sodium chloride intraperitoneally. In addition, the DNA strand breaking properties of irinotecan were measured in mucosal cells from the distal colon by single-cell gel electrophoresis (comet assay) to investigate the association of topoisomerase poisoning and DNA damage in vivo. A single dose of irinotecan significantly increased amounts of topoisomerase I covalently bound to DNA in stomach, duodenum, colon and liver. Concomitantly, the irinotecan-treated group showed significantly higher amounts of DNA strand breaks in colon mucosa cells compared to the control group. The ICE bioassay and the comet assay represent two test systems for investigating the impact of topoisomerase I poisons on DNA integrity in colon tissues of Wistar rats.

Clinical relevance of human cancer xenografts as a tool for preclinical assessment: example of in-vivo evaluation of topotecan-based chemotherapy in a panel of human small-cell lung cancer xenografts

Prediction of human tumor response based on preclinical data could reduce the failure rates of subsequent new anticancer drugs clinical development. Human small-cell lung carcinomas (SCLC) are characterized by high initial sensitivity to chemotherapy but a low median survival time because of drug resistance. The aim of this study was to evaluate the therapeutic relevance of a panel of human SCLC xenografts established in our laboratory using one compromising drug in SCLC, topotecan (TPT). Six SCLC xenografts derived from six patients were used: three were sensitive to a combination of etoposide (VP16), cisplatin (CDDP), and ifosfamide (IFO), and three were resistant, as published earlier. Growth inhibition was greater than 84% for five xenografts at doses of 1-2 mg/kg/day. TPT was combined with IFO, etoposide (VP16), and CDDP. IFO improved the efficacy of TPT in three of the five xenografts and complete responses were obtained even with the less TPT-sensitive xenograft. VP16 increased the efficacy of two of four xenografts and complete responses were obtained. The combination of TPT and CDDP did not improve TPT responses for any of the xenografts tested. Semiquantitative reverse transcriptase-PCR of genes involved in drug response, such as topoisomerase I, topoisomerase IIalpha, multidrug resistance 1 (MDR1), multidrug resistance-associated protein (MRP), lung resistance-related protein (LRP), and glutathione S-transferase pi (GSTpi), did not explain the variability in drug sensitivity between SCLC xenografts. In conclusion, these preclinical data mirror those from published clinical studies suggesting that our panel of SCLC xenografts represents a useful tool for preclinical assessment of new treatments.

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.

Association of SUMO1 and UBC9 genotypes with tumor response in non-small-cell lung cancer treated with irinotecan-based chemotherapy

Irinotecan induces small ubiquitin-like modifier (SUMO)-1 conjugation to topoisomerase-I, leading to enhanced sensitivity to irinotecan. In this study, we genotyped SUMO1 and UBC9 polymorphisms in 147 non-small-cell lung cancer (NSCLC) treated with irinotecan chemotherapy to investigate the association between genotypes and tumor response rate. Immunohistochemistry for SUMO1 and UBC9 was performed in 42 tumor samples and correlated with genotypes. The UBC9 10920CG genotype was associated with significantly higher response rate than the C/C genotype (81 vs 37%, P=0.0002). This predictive effect on tumor response was also seen in multivariate analysis (odds ratio=8.5, P=0.003). Moreover, tumors arising from the UBC9 10920CG genotype were associated with higher prevalence of SUMO1 overexpression compared with those with CC genotype (78 vs 31%, P=0.021). This finding suggests that the UBC9 10920CG genotype enhances sensitivity to irinotecan chemotherapy in advanced NSCLC through upregulation of SUMO1 in tumor cells.

Mechanistic studies of the modulation of cleavage activity of topoisomerase I by DNA adducts of mono- and bi-functional PtII complexes

Using electrophoresis and replication mapping, we show that the presence of DNA adducts of bifunctional antitumor cisplatin or monodentate [PtCl(dien)]Cl (dien = diethylenetriamine) in the substrate DNA inhibits eukaryotic topoisomerase 1 (top1) action, the adducts of cisplatin being more effective. The presence of camptothecin in the samples of platinated DNA markedly enhances effects of Pt–DNA adducts on top1 activity. Interestingly, the effects of Pt–DNA adducts on the catalytic activity of top1 in the presence of camptothecin differ depending on the sequence context. A multiple metallation of the short nucleotide sequences on the scissile strand, immediately downstream of the cleavage site impedes the cleavage by top1. On the other hand, DNA cleavage by top1 at some cleavage sites which were not platinated in their close proximity is notably enhanced as a consequence of global platination of DNA. We suggest that this enhancement of DNA cleavage by top1 may consist in its inability to bind to other cleavage sites platinated in their close neighborhood; thus, more molecules of top1 may become available for cleavage at the sites where top1 normally cleaves and where platination does not interfere.

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.

Phase 1 study of oxaliplatin and irinotecan in pediatric patients with refractory solid tumors: a children's oncology group study

BACKGROUND

For this report, the authors estimated the maximum tolerated dose (MTD) and investigated the toxicities of oxaliplatin combined with irinotecan in children with refractory solid tumors.

METHODS

Oxaliplatin was administered on Days 1 and 8 in combination with irinotecan on Days 1 through 5 and Days 8 through 12 of a 21-day cycle. An oral cephalosporin was administered daily to ameliorate irinotecan-associated diarrhea. Pharmacokinetic studies of oxaliplatin and uridine diphosphate glucuronosyltransferase 1 family, polypeptide A1 (UGT1A1) genotyping were performed.

RESULTS

Thirteen patients were enrolled. Dose-limiting diarrhea (n = 3), serum lipase elevation (n = 3), serum amylase elevation (n = 2), colitis, abdominal pain, and headache (n = 1 each) occurred at the first dose level (oxaliplatin at a dose of 60 mg/m(2); irinotecan at a dose of 20 mg/m(2)). Only 1 of 7 patients who received reduced doses of both agents (40 mg/m(2)/dose oxaliplatin; 15 mg/m(2)/dose irinotecan) experienced a dose-limiting toxicity (DLT): diarrhea. When the oxaliplatin dose was re-escalated (60 mg/m(2)) with irinotecan at a dose of 15 mg/m(2), 2 of 3 patients had a DLT (1 episode of diarrhea, 1 episode of hypokalemia). Myelosuppression was minimal. One patient had a complete response, and another patient had stable disease for 6 cycles of therapy. The median oxaliplatin area under the concentration versus time curve (AUC(0-->infinity)) was 5.9 microg . hour/mL (range, 1.8-7.6 microg . hour/mL). The frequency of the 6/6, 6/7, and 7/7 UGT1A1 promoter genotypes was 5 of 10, 4 of 10, and 1 of 10, respectively.

CONCLUSIONS

The oxaliplatin MTD was 40 mg/m(2) per dose on Days 1 and 8 in combination with irinotecan 15 mg/m(2) per dose on Days 1-5 and Days 8-12. There was some evidence of antitumor activity; however, severe toxicity, both expected (diarrhea) and unexpected (elevation in pancreatic enzymes), was observed.

Mechanisms of drug combinations: interaction and network perspectives

Understanding the molecular mechanisms underlying synergistic, potentiative and antagonistic effects of drug combinations could facilitate the discovery of novel efficacious combinations and multi-targeted agents. In this article, we describe an extensive investigation of the published literature on drug combinations for which the combination effect has been evaluated by rigorous analysis methods and for which relevant molecular interaction profiles of the drugs involved are available. Analysis of the 117 drug combinations identified reveals general and specific modes of action, and highlights the potential value of molecular interaction profiles in the discovery of novel multicomponent therapies.

Central neurocytoma responsive to topotecan, ifosfamide, carboplatin

A 5-year-old male presented with spinal cord drop metastasis from a recurrent neurocytoma. Topotecan (0.5 mg/m(2)) and carboplatin (250 mg/m(2)) were administered on days 1-3 and ifosfamide (1,800 mg/m(2)) on days 1-5, every 21 days, for three cycles and resulted in complete response without severe complications. A literature review yielded 20 patients with central neurocytoma but no complete responses. The complete response of central neurocytoma to chemotherapy only reported here should be helpful to those caring for patients with this rare tumor.

Predictive biomarkers of chemotherapy efficacy in colorectal cancer: results from the UK MRC FOCUS trial

PURPOSE

Candidate predictive biomarkers for irinotecan and oxaliplatin were assessed in 1,628 patients in Fluorouracil, Oxaliplatin, CPT-11: Use and Sequencing (FOCUS), a large randomized trial of fluorouracil alone compared with fluorouracil and irinotecan and compared with fluorouracil and oxaliplatin in advanced colorectal cancer.

METHODS

The candidate biomarkers were: tumor immunohistochemistry for MLH1/MSH2, p53, topoisomerase-1 (Topo1), excision repair cross-complementing gene 1 (ERCC1), O-6-methylguanine-DNA-methyltranserase (MGMT), and cyclooxygenase 2 (COX2); germline DNA polymorphisms in GSTP1, ABCB1, XRCC1, ERCC2, and UGT1A1. These were screened in more than 750 patients for interaction with benefit from irinotecan or oxaliplatin; two markers (Topo1 and MLH1/MSH2) met criteria to be taken forward for analysis in the full population. Primary end points were progression-free survival (PFS) and overall survival.

RESULTS

One thousand three hundred thirteen patients (81%) were assessable for Topo1 immunohistochemistry (low, < 10%; moderate, 10% to 50%; or high, > 50% tumor nuclei). In patients with low Topo1, PFS was not improved by the addition of either irinotecan (hazard ratio [HR], 0.98; 95% CI, 0.78 to 1.22) or oxaliplatin (HR, 0.85; 95% CI, 0.68 to 1.07); conversely, patients with moderate/high Topo1 benefited from the addition of either drug (HR, 0.48 to 0.70 in all categories; interaction P = .005; overall, P = .001 for irinotecan; P = .05 for oxaliplatin). High Topo1 was associated with a major overall survival benefit with first-line combination chemotherapy (HR, 0.60; median benefit, 5.3 months); patients with moderate or low Topo1 did not benefit (HR, 0.92 and 1.09, respectively; interaction P = .005). MLH1/MSH2 did not show significant interaction with treatment, although the low rate of loss (4.4%) limits the power of the study for this biomarker.

CONCLUSION

Topo1 immunohistochemistry identified subpopulations that did or did not benefit from irinotecan, and possibly also from oxaliplatin. If verified independently, this information will contribute to the individualization of treatment for colorectal cancer.

Mutation of a Conserved Active Site Residue Converts Tyrosyl-DNA Phosphodiesterase I into a DNA Topoisomerase I-dependent Poison

Tyrosyl-DNA phosphodiesterase 1 (Tdp1) catalyzes the resolution of 3' and 5' phospho-DNA adducts. A defective mutant, associated with the recessive neurodegenerative disease SCAN1, accumulates Tdp1-DNA complexes in vitro. To assess the conservation of enzyme architecture, a 2.0 A crystal structure of yeast Tdp1 was determined that is very similar to human Tdp1. Poorly conserved regions of primary structure are peripheral to an essentially identical catalytic core. Enzyme mechanism was also conserved, because the yeast SCAN1 mutant (H(432)R) enhanced cell sensitivity to the DNA topoisomerase I (Top1) poison camptothecin. A more severe Top1-dependent lethality of Tdp1H(432)N was drug-independent, coinciding with increased covalent Top1-DNA and Tdp1-DNA complex formation in vivo. However, both H(432) mutants were recessive to wild-type Tdp1. Thus, yeast H(432) acts in the general acid/base catalytic mechanism of Tdp1 to resolve 3' phosphotyrosyl and 3' phosphoamide linkages. However, the distinct pattern of mutant Tdp1 activity evident in yeast cells, suggests a more severe defect in Tdp1H(432)N-catalyzed resolution of 3' phospho-adducts.

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.

Synthesis and Biological Evaluation of 10,11-Methylenedioxy-14-azacamptothecin

[reaction: see text] 10,11-Methylenedioxy-14-azacamptothecin, a potent analogue of the antitumor agent camptothecin (CPT), has been prepared via a key condensation between AB and DE ring precursors. The biological testing of this compound validated a strategy for modulation of the off-rate of camptothecin analogues from the topoisomerase-DNA-CPT ternary complex via structural modification.

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.

Biochemical and proteomics approaches to characterize topoisomerase IIalpha cysteines and DNA as targets responsible for cisplatin-induced inhibition of topoisomerase IIalpha

Cisplatin was shown to strongly inhibit the decatenation and relaxation activity of isolated human DNA topoisomerase IIalpha. This inhibition was not accompanied by stabilization of a covalent topoisomerase IIalpha-DNA intermediate. Pretreatment of kinetoplast plasmid DNA (kDNA) or pBR322 DNA with submicromolar concentrations of cisplatin quickly rendered these substrates incompetent in the topoisomerase IIalpha catalytic assay. Cisplatin nearly equally inhibited growth of a parental K562 and an etoposide-resistant K/VP.5 cell line that contained decreased topoisomerase IIalpha levels, a result consistent with isolated enzyme experiments demonstrating that cisplatin was not a topoisomerase IIalpha poison. Because cisplatin is known to react with protein sulfhydryl groups, the 13 cysteine groups in the topoisomerase IIalpha monomer were evaluated by mass spectrometry to determine which cysteines were free and disulfide-bonded to identify possible sites of cisplatin adduction. High-pressure liquid chromatography-matrix-assisted laser desorption ionization mass spectrometry showed that topoisomerase IIalpha contained at least five free cysteines (170, 216, 300, 392, and 405) and two disulfide-bonded cysteine pairs (427-455 and 997-1008). Cysteine 733 was also disulfide-bonded, but its partner cysteine could not be identified. Cisplatin antagonized the formation of a fluorescence adduct between topoisomerase IIalpha and the sulfhydryl-reactive maleimide reagent 10-(2,5-dihydro-2,5-dioxo-1H-pyrrol-1-yl)-9-methoxy-3-oxo-3H-naphtho[2,1-b]pyran-2-carboxylic acid methyl ester (ThioGlo-1). Dithiothreitol, which was shown by spectrophotometry to react rapidly with cisplatin (6-min half-time), diminished the capacity of cisplatin to interfere with ThioGlo-1 binding to topoisomerase IIalpha. The results of this study suggest that cisplatin may exert some of its cell growth inhibitory and antitumor activity by inhibition of topoisomerase IIalpha through reaction with critical enzyme sulfhydryl groups and/or by forming DNA adducts that render the DNA substrate refractory to topoisomerase IIalpha.