The monofunctional platinum(II) compounds, phenanthriplatin and pyriplatin, modulate apoptosis signaling pathways in HEI-OC1 auditory hybridoma cells.

Cisplatin is a platinum(II) chemotherapy drug that can cause the side-effect of ototoxicity and hearing loss. The monofunctional platinum(II) complexes, phenanthriplatin and pyriplatin, have recently been investigated as anti-cancer agents but their side-effects are largely unknown. Here, we used the auditory hybridoma cell line, HEI-OC1, to investigate the ototoxicity of cisplatin, phenanthriplatin and pyriplatin. The effect of these compounds against cellular viability, on reactive oxygen species (ROS) production, mitochondrial membrane polarization, caspase-3/7 activity, DNA integrity and caspase-12 expression were measured using spectrophotometric, flow cytometric and blot analyses. We found that the monofunctional complexes and cisplatin decreased cellular viability. All three compounds increased ROS yield at 24 h, but at 48 h, ROS levels returned to normal. Also, the compounds did not depolarize the mitochondrial membrane. All three compounds reduced caspase-3/7 activity at 24 h; cisplatin increased caspase-3/7 activity and caused apoptosis at 48 h. Caspase-12 expression was associated with all three compounds. In summary, the monofunctional complexes may cause ototoxicity like cisplatin. Phenanthriplatin and pyriplatin may cause ototoxicity initially by inducing ROS production, but they may also signal through distinct apoptotic pathways that do not integrate caspases-3/7, or may act at different time-points in the same pathways.

Molluscicidal activity and physiological toxicity of quaternary benzo[c]phenanthridine alkaloids (QBAs) from Macleaya cordata fruits on Oncomelania hupensis.

Schistosomiasis is a serious worldwide parasitic disease. One of the best ways to control schistosomiasis is to control the population of Oncomelania hupensis snails. We sought to identify a high-efficiency biogenic molluscicide against Oncomelania with low toxicity, to avoid chemical molluscicide contamination and toxicity in aquatic organisms. We extracted quaternary benzo[c]phenanthridine alkaloids (QBAs) from Macleaya cordata fruits. Molluscicidal activity of the QBAs against Oncomelania was determined using bioassay. Our results showed that the extracted QBAs had a strong molluscicidal effect. In treatment of O. hupensis with QBAs for 48 h and 72 h, the lethal concentration (LC50) was 2.89 mg/L and 1.29 mg/L, respectively. The molluscicidal activity of QBAs was close to that of niclosamide (ethanolamine salt), indicating that QBAs have potential development value as novel biogenic molluscicides. We also analyzed physiological toxicity mechanisms by examining the activity of several important detoxification enzymes. We measured the effect of the extracted QBAs on the activities of glutathione S-transferase (GST), carboxylesterase (CarE), acid phosphatase (ACP), and alkaline phosphatase (AKP) in the liver of O. hupensis. We found that the effects of QBAs on detoxification metabolism in O. hupensis were time and concentration dependent. The activities of GST, CarE, AKP, and ACP in the liver of snails increased significantly in the early stage of treatment (24 h), but decreased sharply in later stages (120 h), compared with these activities in controls. GST, CarE, AKP, and ACP activity in the liver of snails treated with LC50 QBAs for 120 h decreased by 62.3%, 78.1%, 59.2%, and 68.6%, respectively. Our results indicate that these enzymes were seriously inhibited by the extracted QBAs and the detoxification and metabolic functions of the liver gradually weakened, leading to poisoning, which could be the main cause of death in O. hupensis snails.

Lycorine Hydrochloride Inhibits the Virulence Traits of Candida albicans.

The human opportunistic fungal pathogen Candida albicans causes a severe health burden while the biofilms formed by C. albicans present a kind of infections that are hard to cure, highlighting the pressing need for new antifungal drugs against C. albicans. This study was to explore the antifungal activities of lycorine hydrochloride (LH) against C. albicans. The minimal inhibitory concentration (MIC) of LH against C. albicans SC5314 was 64 µM. Below its MIC, LH demonstrated antivirulence property by suppressing adhesion, filamentation, biofilm formation, and development, as well as the production of extracellular phospholipase and exopolymeric substances (EPS). The cytotoxicity of LH against mammalian cells was low, with half maximal inhibitory concentrations (IC50) above 256 µM. Moreover, LH showed a synergistic effect with AmB, although its interaction with fluconazole, as well as caspofungin, was indifferent. Thus, our study reports the potential use of LH, alone or in combination with current antifungal drugs, to fight C. albicans infections.

Identification of narciclasine from Lycoris radiata (L'Her.) Herb. and its inhibitory effect on LPS-induced inflammatory responses in macrophages.

Lycoris radiata (L'Her.) Herb. (L. radiata) was traditionally used as a folk medicine in China for treatment of Alzheimer's disease. However, the specific component responsible for its considerable toxicity remained unclear thus restricting its clinical trials. Narciclasine (NCS) was isolated from L. radiata and treatment of NCS for 72 h exhibited significant antiproliferative effects against L02, Hep G2, HT-29 and RAW264.7 cells. However, what needs to be emphasized is that at safe working concentrations of 0.001-0.016 µM, administration of NCS for 24 h inhibited the mRNA expression of inducible nitric oxide synthase (iNOS), interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-ɑ), interleukin-1beta (IL-1ß) and cyclooxygenase-2 (COX-2) in lipopolysaccharide (LPS)-induced macrophages thereby suppressing production of nitric oxide (NO), IL-6, TNF-ɑ and IL-1ß. NCS supplementation also inhibited nuclear factor-kappa B (NF-κB) activation by suppressing NF-κB P65 phosphorylation and nuclear translocation, IκBɑ degradation and phosphorylation, and IκKɑ/ß phosphorylation. The phosphorylation of c-Jun N-terminal kinase (JNK) and P38, and expression of COX-2 was also attenuated by NCS. These results suggested that NCS might exert anti-inflammatory effects through inhibiting NF-κB and mitogen-activated protein kinase (MAPK) pathways even at very low doses.

Effects of ionizing radiation and HLY78 on the zebrafish embryonic developmental toxicity.

The health-related effects of ionizing radiation on embryonic development and their underlying mechanisms are still unclear. The aim of this study was to investigate the role of Wnt signaling in mediating the developmental toxicity induced by heavy ion and proton radiation using zebrafish embryos. Zebrafish embryos were radiated with carbon ions or protons. HLY78, an activator of the Wnt signaling pathway, was added immediately after radiation. Carbon ion radiation induced a significant increase of mortality, and activating Wnt signaling using HLY78 after radiation significantly alleviated this stress. Both carbon ion and proton radiation significantly increased malformation rates and decreased hatching rates. Supplementation with HLY78 significantly reduced the effects induced by carbon ion radiation alone. After irradiation with carbon ions, embryos showed a significant decrease in heart rate, spontaneous movement, and locomotive behavior. The expression of apoptotic genes was significantly increased, while the expression of anti-apoptotic and Wnt-related genes was significantly decreased. Supplementation with HLY78 was able to reduce these effects. However, embryos irradiated with proton radiation did not show significant changes in the expression of Wnt-related genes. The results of this study improve our understanding of the mechanisms of carbon ion radiation-induced developmental toxicity, which potentially involves the inhibition of Wnt signaling.

Anionic Dinuclear Oxidovanadium(IV) Complexes with Azo Functionalized Tridentate Ligands and µ-Ethoxido Bridge Leading to an Unsymmetric Twisted Arrangement: Synthesis, X-ray Structure, Magnetic Properties, and Cytotoxicity.

The synthesis of ethoxido-bridged dinuclear oxidovanadium(IV) complexes of the general formula (HNEt3)[(VOL1-3)2(µ-OEt)] (1-3) with the azo dyes 2-(2'-carboxy-5'-X-phenylazo)-4-methylphenol (H2L1, X = H; H2L2, X = NO2) and 2-(2'-carboxy-5'-Br-phenylazo)-2-naphthol (H2L3) as ligands is reported. The ligands differ in the substituents at the phenyl ring to probe their influence on the redox behavior, biological activity, and magnetochemistry of the complexes, for which the results are presented and discussed. All synthesized ligands and vanadium(IV) complexes have been characterized by various physicochemical techniques, namely, elemental analysis, electrospray ionization mass spectrometry, spectroscopic methods (UV/vis and IR), and cyclic voltammetry. X-ray crystallography of 1 and 3 revealed the presence of a twisted arrangement of the edged-shared bridging core unit. In agreement with the distorted nature of the twisted core, antiferromagnetic exchange interactions were observed between the vanadium(IV) centers of the dinuclear complexes with a superexchange mechanism operative. These results have been verified by DFT calculations. The complexes were also screened for their in vitro cytotoxicity against HeLa and HT-29 cancer cell lines. The results indicated that all the synthesized vanadium(IV) complexes (1-3) were cytotoxic in nature and were specific to a particular cell type. Complex 1 was found to be the most potent against HeLa cells (IC50 value 1.92 µM).

The antithrombotic, anticoagulant activity and toxicity research of ambinine, an alkaloid from the tuber of Corydalis ambigua var. amurensis.

Ambinine, the major alkaloid of the tuber of Corydalis ambigua var. amurensis, has protective effects on H9C2 myocardial cells. In the present paper, we observed that ambinine demonstrates activities of both anticoagulation and thrombolysis in vitro by significantly degrading the blood clot and delaying the plasma recalcification time (PRT) in a dose-dependent manner (0.5-2 mg/mL). We further studied its safety profile of acute and subacute toxicity by repeated-dose intravenous injection. The median lethal dosage (LD50) of mice given by oral and intravenous administration of ambinine were approximate 800, 41.60 mg/kg, respectively. The acute toxicity research results suggested that compared with an intravenous administration, the oral route is safer to administer ambinine as the promising lead compound for thrombosis. In subacute toxicity research, when mice were given ambinine at doses of 1.40 and 2.10 mg/kg for 7 days by injection, significant alteration of the relative kidney weight, the relative liver weight and serum biochemistry parameters and marked histopathological changes of them were found.

One-Step Synthetic Access to Isosteric and Potent Anticancer Nitrogen Heterocycles with the Benzo[c]phenanthridine Scaffold.

A versatile one-step two-component cyclization to build new tetracyclic nitrogen heterocycles is described. Ortho-methylhetarenecarbonitrile components were condensed with aldehydes to access a large library of differently substituted ring systems. The heterocyclic core can be easily modified by variation of the position of the endocyclic nitrogen atom in the o-methylhetarenecarbonitrile substrate. The manner of the nucleophilic attack that leads to the condensation can be triggered by different electron-density distribution in the molecule induced by the position of the nitrogen atom. Taking this into account, there is an electronic preference that leads to either pyridophenanthrolines or the corresponding pyridoazacarbazoles as the main products. We demonstrate the high antitumor potential of some of our synthesized heterocycles, which is strongly dependent on the substitution pattern introduced through the aldehyde component. The position and number of endocyclic nitrogen atoms play an important role regarding cytotoxicity of the studied compounds.

Cytotoxicity studies of lycorine alkaloids of the Amaryllidaceae.

The plant family Amaryllidaceae is renowned for its unique alkaloid constituents which possess a significant array of structural diversity. Several of these alkaloids are known for their interesting biological properties, of which galanthamine and pancratistatin have acquired a privileged status due to their relevance in the pharmaceutical arena. In particular, galanthamine represents the first prescription drug emanating from the Amaryllidaceae after its approval by the FDA in 2001 for the treatment of Alzheimer's disease. Following on this commercial success there have been sustained projections for the emergence of an anticancer agent related to pancratistatin due to the potency, selectivity, low toxicity and high tolerability typifying targets of this series of alkaloids. The lycorine series of alkaloids have also garnered widespread interest as cytotoxic agents and were amongst the earliest of the Amaryllidaceae constituents to exhibit such activity. To date over 100 of such naturally-occurring or synthetically-derived alkaloids have been screened for cytotoxic effects against a number of cancer cell lines. This survey examines the cytotoxic properties of lycorine alkaloids, highlights the outcomes of structure-activity relationship orientated studies and affords plausible insights to the mechanistic rationale behind these effects.

Inhibition of root growth by narciclasine is caused by DNA damage-induced cell cycle arrest in lettuce seedlings.

Narciclasine (NCS) is an Amaryllidaceae alkaloid isolated from Narcissus tazetta bulbs. Its phytotoxic effects on plant growth were examined in lettuce (Lactuca sativa L.) seedlings. Results showed that high concentrations (0.5-5 µM) of NCS restricted the growth of lettuce roots in a dose-dependent manner. In NCS-treated lettuce seedlings, the following changes were detected: reduction of mitotic cells and cell elongation in the mature region, inhibition of proliferation of meristematic cells, and cell cycle. Moreover, comet assay and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay indicated that higher levels NCS (0.5-5 µM) induced DNA damage in root cells of lettuce. The decrease in meristematic cells and increase in DNA damage signals in lettuce roots in responses to NCS are in a dose-dependent manner. NCS-induced reactive oxygen species accumulation may explain an increase in DNA damage in lettuce roots. Thus, the restraint of root growth is due to cell cycle arrest which is caused by NCS-induced DNA damage. In addition, it was also found that NCS (0.5-5 µM) inhibited the root hair development of lettuce seedlings. Further investigations on the underlying mechanism revealed that both auxin and ethylene signaling pathways are involved in the response of root hairs to NCS.

Design, synthesis and evaluation of 6-(4-((substituted-1H-1,2,3-triazol-4-yl)methyl)piperazin-1-yl)phenanthridine analogues as antimycobacterial agents.

Focus in this Letter is made to design and synthesize a series of nineteen new 6-(4-((substituted-1H-1,2,3-triazol-4-yl)methyl)piperazin-1-yl)phenanthridine analogues employing click chemistry and evaluated for their anti-tubercular activity against Mycobacterium tuberculosis H37Rv. Among the tested compounds, 7f and 7 j exhibited good activity (MIC = 3.125 µg/mL), while 8a displayed excellent activity (MIC = 1.56 µg/mL) against the growth of M. tuberculosis H37Rv. In addition, 7f, 7 j and 8a compounds were subjected to cytotoxic studies against mouse macrophage (RAW264.7) cell lines and the selectivity index values are >15 indicating suitability of compounds for further drug development.

Synthesis and antitumor evaluation of 6-aryl-substituted benzo[j]phenanthridine- and benzo[g]pyrimido[4,5-c]isoquinolinequinones.

A variety of novel 6-arylsubstituted benzo[j]phenanthridine- and benzo[g]-pyrimido[4,5-c]isoquinolinequinones were synthesized from 1,4-naphthoquinone, aryl-aldehydes and enaminones via a two-step synthetic approach. The cytotoxic activity of the aminoquinone derivatives was evaluated in vitro against one normal cell line (MRC-5 lung fibroblasts) and three human cancer cell lines (AGS human gastric adenocarcinoma; SK-MES-1 human lung cancer cells, and J82 human bladder carcinoma) in 72-h drug exposure assays using the MTT colorimetric method. Structure-activity relationships within the series of angular quinones reveal that the insertion of pyrrol-2-yl and furan-2-yl groups at the 6-position is more significant for the increase of the potency and selectivity index of the pharmacophores.

In vivo assessment of antiemetic drugs and mechanism of lycorine-induced nausea and emesis.

Lycorine is the main alkaloid of many Amaryllidaceae and known to cause poisoning with still unknown mechanisms. Longer lasting toxicological core symptoms of nausea and emesis may become a burden for human and animal patients and may result in substantial loss of water and electrolytes. To optimise the only empirical symptomatic antiemetic drug treatment at present, it is important to elucidate the causative involved targets of lycorine-induced emesis. Therefore, in the current study, we have tested the actions of a various antiemetic drugs with selective receptor affinities on lycorine-induced nausea and emesis in vivo in dogs. Beagle dogs were pre-treated in a saline vehicle-controlled crossover and random design with diphenhydramine, maropitant, metoclopramide, ondansetron or scopolamine prior lycorine administration (2 mg/kg subcutaneously). In vivo effects were assessed by a scoring system for nausea and emesis as well as by the number and lag time of emetic events for at least 3 h. Moreover, plasma pharmacokinetic analysis was carried out for ondansetron before and after lycorine injection. The data show that histaminergic (H1), muscarinic and dopaminergic (D2) receptors are presumably not involved in lycorine-induced emetic effects. While ondansetron significantly reduced the number of emetic events, lycorine-induced emesis was completely blocked by maropitant. Only ondansetron also significantly decreased the level of nausea and was able to prolong the lag time until onset of emesis suggesting a preferential participation of 5-HT3 receptors in lycorine-induced nausea. Thus, it is the first in vivo report evidencing that predominantly neurokinin-1 (NK1) and to a lesser extent 5-hydroxytryptamine 3 (5-HT3) receptors are involved in lycorine-induced emesis facilitating a target-oriented therapy.

Dose-dependent emetic effects of the Amaryllidaceous alkaloid lycorine in beagle dogs.

Ingestions of plant material from Amaryllidaceae, especially the bulbs of daffodils, are known to be toxic, representing a persistent cause of poisoning in human and animals. Empiric data from case reports suggested, that the alkaloid lycorine could be the toxic constituent of the multi-component mixture responsible for symptoms like nausea and emesis. Systematic studies of the in vivo effects of the amaryllidaceaeous-type alkaloids are not available. Therefore, in an open, prospective, randomized and controlled trial we studied the dose-effect relationship of lycorine-induced nausea and emesis and the toxicokinetics of lycorine in beagle dogs. Subcutaneously administered lycorine-induced nausea and emesis starting at 0.5 mg/kg body weight reaching statistical significance at 1.0 mg/kg. The maximum emetic dose of lycorine (ED(100)) was 2 mg/kg body weight. There was a correlation between dose and nausea score as well as between dose and number of the induced emetic events. Nausea and emesis were short-lasting and occurred not later than 2.5 h post dose. Lycorine showed linear plasma kinetics with a mean elimination half-life of 0.67 and 0.3 h after single s.c. and i.v. administration, compatible with the clinical course of nausea and emesis. The mean oral bioavailability was calculated to be about 40%. Biochemical and haematological parameters of safety showed no pathological signs. The results provide evidence that lycorine can be considered as a main, if not the crucial constituent responsible for nausea and emesis in human and animals in poisoning due to ingestion of plant material of the Amaryllidaceae.

Lycorine, the main phenanthridine Amaryllidaceae alkaloid, exhibits significant antitumor activity in cancer cells that display resistance to proapoptotic stimuli: an investigation of structure-activity relationship and mechanistic insight.

Twenty-two lycorine-related compounds were investigated for in vitro antitumor activity using four cancer cell lines displaying different levels of resistance to proapoptotic stimuli and two cancer cell lines sensitive to proapoptotic stimuli. Lycorine and six of its congeners exhibited potency in the single-digit micromolar range, while no compound appeared more active than lycorine. Lycorine also displayed the highest potential (in vitro) therapeutic ratio, being at least 15 times more active against cancer than normal cells. Our studies also showed that lycorine exerts its in vitro antitumor activity through cytostatic rather than cytotoxic effects. Furthermore, lycorine provided significant therapeutic benefit in mice bearing brain grafts of the B16F10 melanoma model at nontoxic doses. Thus, the results of the current study make lycorine an excellent lead for the generation of compounds able to combat cancers, which are naturally resistant to proapoptotic stimuli, such as glioblastoma, melanoma, non-small-cell-lung cancers, and metastatic cancers, among others.

12-Substituted 2,3-dimethoxy-8,9-methylenedioxybenzo[i]phenanthridines as novel topoisomerase I-targeting antitumor agents.

2,3-Dimethoxy-8,9-methylenedioxybenzo[i]phenanthridine and a few of its 12-substituted analogs are active as TOP1-targeting agents. Studies were performed to further evaluate the potential of this series of non-camptothecin TOP1-targeting agents. The influence of a hydroxymethyl, formyl, N,N-dimethylaminomethyl, 2-(N,N-dimethylamino)ethyl, 3-(N,N-dimethylamino)propyl), and 4-(N,N-dimethylamino)butyl substituent at the 12-position on TOP1-targeting activity and tumor cell growth was evaluated. In addition, the relative pharmacologic activities of the 12-carboxamide analog, as well as its N-methyl and N,N-dimethyl derivatives were assessed.

Dihydroimidazophenanthridinium (DIP)-based DNA binding agents with tuneable structures and biological activity.

We have synthesised a library of dihydroimidazophenanthridinium cations (DIPs) with large structural diversity (1-29) using a "one-pot" approach. The DNA binding constants of DIPs range from 2x10(4) to 1.3x10(5) M(-1), and the free energies for binding range from -5.9 to -6.40 kcal mol(-1). Viscosity measurements demonstrated that the binding of the compounds caused DNA lengthening, thus signifying binding by intercalation. The cytotoxicities of the compounds were determined by tetrazolium dye-based microtitration assays and showed a large range of values (0.09-11.7 microM). Preliminary molecular modelling studies of the DNA-DIP interactions suggested that the DIP moieties can interact with DNA by intercalation, and some R groups might facilitate binding by minor-groove binding. The results provide insight into how to design biologically active DNA binding agents that can interact in these ways.

Sanguinarine activates polycyclic aromatic hydrocarbon associated metabolic pathways in human oral keratinocytes and tissues.

Sanguinarine's use in human clinical applications is currently controversial. While some studies have demonstrated sanguinarine's anti-inflammatory and anti-oxidant properties, other investigations reported sanguinarine's procarcinogenic effects. Like the tobacco-associated carcinogen, benzo(a)pyrene (B(a)P), sanguinarine is a polycyclic aromatic hydrocarbon (PAH). PAH exposure activates the aryl hydrocarbon transcription activating factor (AhR), resulting in nuclear translocation, binding to the aryl hydrocarbon nuclear translocator (ARNT), which thereby increases expression of a pool of carcinogen metabolizing enzymes. The goal of this study was to investigate whether sanguinarine activates this PAH-associated signaling cascade in human oral cells and tissues. Our results demonstrate that sanguinarine: (i) results in formation of the AhR-ARNT complex, (ii) induces AhR-associated gene expression, (iii) inhibits cytochrome P450 1A1 (CYP 1A1) microsomal oxidative activity and (iv) pretreatment upregulates CYP 1A1 function. Collectively, these data provide evidence that sanguinarine activates PAH-associated signaling and metabolic pathways. Notably, previous studies have demonstrated that mammalian hepatic microsomes metabolize sanguinarine to a mutagenic epoxide. Persons who respond to sanguinarine exposure with induction of primarily Phase I relative to Phase II enzymes are, therefore, at risk for sanguinarine bioactivation and its potential mutagenic effects.

Sanguinarine and chelerythrine: assessment of safety on pigs in ninety days feeding experiment.

Sanguinaria canadesis, Chelidonium majus and Macleya cordata have been used for centuries as alternative medicines. Currently the extracts from these medicinal plants are components of veterinary and human phytopreparations, and of oral-hygiene agents. Sanguinarine and chelerythrine (SA/CHE) are biologically active components of these extracts. They display distinct antibacterial and anti-inflammatory properties, but, on the other hand, they have been reported as having adverse effects - genotoxicity and hepatotoxicity. This paper is aimed at evaluation of the effects of daily administration of the extract from Macleya cordata (2 mg and 100 mg in 1 kg feed, sanguinarine:chelerythrine 3:1) in the diet on the health status of swine. After 90-day administration, alkaloids were retained to a different extent in tissues. The highest SA/CHE retention was detected in the gingiva (0.55 microg/g) and liver (0.15 microg/g), no SA/CHE were detected in muscles. Plasma SA levels attained 0.11 microg/ml. Treated animals did not display any results of hematological, biochemical or histological assay different from controls. A (32)P-postlabeling assay proved that no DNA-adducts with SA/CHE were detected in pig livers. We did not observe any symptom linked to epidemic dropsy syndrome often attributed to sanguinarine. In conclusion, an average daily oral dose of alkaloids up to 5 mg per 1 kg animal body weight proved to be safe.

8,9-methylenedioxybenzo[i]phenanthridines: topoisomerase I-targeting activity and cytotoxicity.

Substituted benzo[i]phenanthridines that have incorporated within their structure an 8,9-methylenedioxy group can exhibit topoisomerase I-targeting activity. Structure-activity studies were performed to examine the influence of saturation at the 11,12-positions of several substituted 8,9-methylenedioxybenzo[i]phenanthridines. The activities of these dihydro analogues were compared to those of their unsaturated analogues. In addition, the influence of varying substituents at the 2- and 3-positions within the A-ring of these 8,9-methylenedioxybenzo[i]phenanthridines on their relative potency as topoisomerase I-targeting agents and cell proliferation as determined using the MTT assay was investigated. 2,3-Dimethoxy-8,9-methylenedioxybenzo[i]phenanthridine and its 11,12-dihydro derivative were among the more potent analogues evaluated with regard to topoisomerase I-targeting activity and cytotoxicity.