Camptothecins

Substitution-inert trinuclear platinum complexes efficiently condense/aggregate nucleic acids and inhibit enzymatic activity

The trinuclear platinum complexes (TriplatinNC-A [{Pt(NH3 )3 }2 -μ-{trans-Pt(NH3 )2 (NH2 (CH2 )6 NH2 )2 }](6+) , and TriplatinNC [{trans-Pt(NH3 )2 (NH2 (CH2 )6 NH3 (+) )}2 -μ-{trans-Pt(NH3 )2 (NH2 (CH2 )6 NH2 )2 }](8+) ) are biologically active agents that bind to DNA through noncovalent (hydrogen bonding, electrostatic) interactions. Herein, we show that TriplatinNC condenses DNA with a much higher potency than conventional DNA condensing agents. Both complexes induce aggregation of small transfer RNA molecules, and TriplatinNC in particular completely inhibits DNA transcription at lower concentrations than naturally occurring spermine. Topoisomerase I-mediated relaxation of supercoiled DNA was inhibited by TriplatinNC-A and TriplatinNC at concentrations which were 60 times and 250 times lower than that of spermine. The mechanisms for the biological activity of TriplatinNC-A and TriplatinNC may be associated with their ability to condense/aggregate nucleic acids with consequent inhibitory effects on crucial enzymatic activities.

Super Natural II--a database of natural products

Natural products play a significant role in drug discovery and development. Many topological pharmacophore patterns are common between natural products and commercial drugs. A better understanding of the specific physicochemical and structural features of natural products is important for corresponding drug development. Several encyclopedias of natural compounds have been composed, but the information remains scattered or not freely available. The first version of the Supernatural database containing ∼50 000 compounds was published in 2006 to face these challenges. Here we present a new, updated and expanded version of natural product database, Super Natural II (http://bioinformatics.charite.de/supernatural), comprising ∼326 000 molecules. It provides all corresponding 2D structures, the most important structural and physicochemical properties, the predicted toxicity class for ∼170 000 compounds and the vendor information for the vast majority of compounds. The new version allows a template-based search for similar compounds as well as a search for compound names, vendors, specific physical properties or any substructures. Super Natural II also provides information about the pathways associated with synthesis and degradation of the natural products, as well as their mechanism of action with respect to structurally similar drugs and their target proteins.

A review on anticancer potential of bioactive heterocycle quinoline

The advent of Camptothecin added a new dimension in the field anticancer drug development containing quinoline motif. Quinoline scaffold plays an important role in anticancer drug development as their derivatives have shown excellent results through different mechanism of action such as growth inhibitors by cell cycle arrest, apoptosis, inhibition of angiogenesis, disruption of cell migration, and modulation of nuclear receptor responsiveness. The anti-cancer potential of several of these derivatives have been demonstrated on various cancer cell lines. In this review we have compiled and discussed specifically the anticancer potential of quinoline derivatives, which could provide a low-height flying bird's eye view of the quinoline derived compounds to a medicinal chemist for a comprehensive and target oriented information for development of clinically viable anticancer drugs.

Mechanisms controlling the smooth muscle cell death in progeria via down-regulation of poly(ADP-ribose) polymerase 1

Hutchinson-Gilford progeria syndrome (HGPS) is a severe human premature aging disorder caused by a lamin A mutant named progerin. Death occurs at a mean age of 13 y from cardiovascular problems. Previous studies revealed loss of vascular smooth muscle cells (SMCs) in the media of large arteries in a patient with HGPS and two mouse models, suggesting a causal connection between the SMC loss and cardiovascular malfunction. However, the mechanisms of how progerin leads to massive SMC loss are unknown. In this study, using SMCs differentiated from HGPS induced pluripotent stem cells, we show that HGPS SMCs exhibit a profound proliferative defect, which is primarily caused by caspase-independent cell death. Importantly, progerin accumulation stimulates a powerful suppression of PARP1 and consequently triggers an activation of the error-prone nonhomologous end joining response. As a result, most HGPS SMCs exhibit prolonged mitosis and die of mitotic catastrophe. This study demonstrates a critical role of PARP1 in mediating SMC loss in patients with HGPS and elucidates a molecular pathway underlying the progressive SMC loss in progeria.

Pyrenacantha volubilis Wight, (Icacinaceae) a rich source of camptothecine and its derivatives, from the Coromandel Coast forests of India

Camptothecine, a potent eukaryotic topoisomerase inhibitor, is an important anticancer compound. The global demand for this compound was estimated to be $1 billion in 2003 and is only further expected to increase. Partly to meet the expected increase in demand, in the recent past, several efforts have been made to discover newer and alternative plant and fungal sources of camptothecine. In this study we report a rich source of camptothecine and its natural derivatives, Pyrenacantha volubilis (Icacinaceae) from the eastern coast of peninsular India. Camptothecine and its derivatives were analyzed using high performance liquid chromatography (HPLC) coupled with electrospray mass spectrometry (ESI-MS) in all plant parts such as twigs, leaves, roots, seedling, ripened whole fruit, fruit coat, seed coat and cotyledons. Cotyledons and ripened whole fruits contained the highest amount of camptothecine (1.35% and 0.60% dry weight respectively). LC-MS and ESI-MS/MS analyses revealed besides camptothecine, other derivatives and precursors such as 10-hydroxycamptothecine, 9-methoxycamptothecine, 20-deoxycamptothecine, deoxypumiloside, strictosidine and strictosamide. Pure camptothecine was isolated from fruits and structurally confirmed using NMR. Seed extracts were found to be effective against breast cancer, ovarian, colon and carcinoma cell lines (with IC50 values of 4.0 μg/mL, 6.5 μg/mL, 25.0 μg/mL and 25.0 μg/mL respectively). We discuss the results in the context of exploring alternative sources of camptothecine.

Synthesis and cytotoxicity of novel 20-O-linked homocamptothecin ester derivatives as potent topoisomerase I inhibitors

In an attempt to improve the antitumor activity of homocamptothecins (hCPTs), a series of novel 20-O-linked hCPT ester derivatives were first designed and synthesized based on a synthetic route, by which hCPTs are acylated with different substituted phenoxyacetic acid ester derivatives. Most of the derivatives were assayed for in vitro cytotoxicity against six human cancer cell lines KB, KB/VCR, A549, HCT-8, Bel7402, and A2780, and most of the assayed compounds exhibited good antiproliferative activity on these tumor cell lines especially on KB.

Polymeric micelles with small lipophilic moieties for drug delivery

The aim of this study was to develop a new polymeric micelle delivery system for antitumor drugs. An amphiphile of methoxypoly(ethylene glycol)-histidine-di(cinnamic acid) (PEGHC) with a small lipophilic moiety instead of a hydrophobic biodegradable polymer chain was synthesized and characterized. The PEGHC self-assembled into micelles. The critical micelle concentration (CMC) was tested. 9-Nitro-20(s)-camptothecin (9-NC) was used as a model drug for encapsulation. The size and morphology of both blank and 9-NC loaded micelles were characterized by dynamic light scattering (DLS) and transmission electron microscopy (TEM). The release profile of 9-NC loaded micelles was studied. HepG2 liver cancer cells were incubated with the drug-loaded micelles to investigate the in vitro anticancer efficiency. The results showed that the 9-NC loaded micelles exhibited high accumulated release rate (>85%) and efficient in vitro anticancer activity.

Evaluation of the cytotoxic effect of camptothecin solid lipid nanoparticles on MCF7 cells

Camptothecin (CPT) and its analogs exhibit remarkable anti-tumor activity, due to their ability to inhibit DNA topoisomerase I. However, its use is limited by the lack of solubility and stability of the active lactone form. An attractive alternative is the encapsulation of CPT within liposomes. In this study, CPT was incorporated into solid lipid nanoparticles (SLN) based on the triglyceride, Compritol 888 ATO, using supercritical fluid technology without requiring the use of harmful solvents. This drug delivery system was characterized and its cytotoxicity effect was evaluated by measuring MCF7 and MCF10A cell viability as a function of drug loading during a 48-h treatment. Results showed that after 10 h of treatment, MCF7 cells displayed an IC50 of 0.23±0.034 μM at a 1:5 (CPT:SLN) loading and 0.22±0.027 μM at a 1:10 loading, whereas MCF10A cells displayed an IC50 of 0.40±0.036 μM at 1:5 and 0.60±0.063 μM at 1:10. On the other hand, the IC50 of free CPT was 0.57±0.035 μM and 1.07±0.077 μM for MCF7 and MCF10A cells, respectively. Cellular uptake and retention measurements in both cells displayed a two-fold increase when using the SLN formulation. The results from this study showed that the cytotoxic effects of CPT in a SLN formulation improved when compared with those seen with free CPT. The results of this study showed that delivery of CPT as a SLN formulation could be a promising strategy for enhancing its chemotherapeutic effects.

Prodrug and nanomedicine approaches for the delivery of the camptothecin analogue SN38

SN38 (7-ethyl-10-hydroxy camptothecin) is a prominent and efficacious anticancer agent. It is poorly soluble in both water and pharmaceutically approved solvents; therefore, the direct formulation of SN38 in solution form is limited. Currently, the water soluble prodrug of SN38, irinotecan (CPT-11), is formulated as a low pH solution and is approved for chemotherapy. However, CPT-11, along with most other water-soluble prodrugs shows unpredictable inter-patient conversion to SN38 in vivo, instability in the physiological environment and variable dose-related toxicities. More recently, macromolecular prodrugs (i.e. EZN-2208, IMMU-130) and nanomedicine formulations (i.e. nanoemulsions, polymeric micelles, lipid nanocapsule/nanoparticle, and liposomes) of SN38 have been investigated for improved delivery to cancer cells and tissues. Specifically, these carriers can take advantage of the EPR effect to direct drug preferentially to tumour tissues, thereby substantially improving efficacy and minimising side effects. Furthermore, oral delivery has been shown to be possible in preclinical results using nanomedicine formulations (i.e. dendrimers, lipid nanocapsules, polymeric micelles). This review summarizes the recent advances for the delivery of SN38 with a focus on macromolecular prodrugs and nanomedicines.

Dual-acting histone deacetylase-topoisomerase I inhibitors

Current chemotherapy regimens are comprised mostly of single-target drugs which are often plagued by toxic side effects and resistance development. A pharmacological strategy for circumventing these drawbacks could involve designing multivalent ligands that can modulate multiple targets while avoiding the toxicity of a single-targeted agent. Two attractive targets, histone deacetylase (HDAC) and topoisomerase I (Topo I), are cellular modulators that can broadly arrest cancer proliferation through a range of downstream effects. Both are clinically validated targets with multiple inhibitors in therapeutic use. We describe herein the design and synthesis of dual-acting histone deacetylase-topoisomerase I inhibitors. We also show that these dual-acting agents retain activity against HDAC and Topo I, and potently arrest cancer proliferation.

Hydroxycamptothecin induces apoptosis and inhibits tumor growth in colon cancer by the downregulation of survivin and XIAP expression

BACKGROUND

10-Hydroxycamptothecin (10-HCPT), isolated from a Chinese tree Camptotheca acuminate, inhibits the activity of topoisomerase I and has a broad spectrum of anticancer activity in vitro and in vivo. It has been shown that HCPT is more active and less toxic than conventional camptothecins and can induce cancer cell apoptosis. However, the mechanisms of HCPT-induced apoptosis in colon cancer cells remain unclear. In this study, we investigated the effects of HCPT on apoptosis of colon cancer and underlying mechanism.

METHODS

Cell proliferation was measured by MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide) assay, and apoptosis was measured using terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) assay. Expression of genes was detected using real-time reverse transcription-polymerase chain reaction (real time-PCR) and Western blot. Tumor growth in vivo was evaluated using a nude mouse xenograft model.

RESULTS

HCPT could significantly inhibit cell proliferation and induce apoptosis in colon cancer SW1116 and Colo 205 cells in dose- and time-dependent manners. HCPT treatment activated the activities of caspase 3, 7, 8 and 9, downregulated the expression of survivin, survivinΔEx3, survivin-3B and XIAP, and upregulated expression of surviving 2B. Moreover, the combination of HCPT and 5-fluorouracial (5-FU) synergistically induced apoptosis and downregulated the expression of survivin and XIAP. Knockdown of survivin and XIAP by siRNA sensitized colon cancer to HCTP-induced apoptosis. Furthermore, HCPT treatment significantly inhibited SW1116 xenograft tumor growth.

CONCLUSIONS

Our results elucidate new mechanisms of HCPT antitumor by the downregulation of survivin and XIAP expression. The combination of HCPT with 5-FU or IAP inhibitors may be a potential strategy for colon cancer treatment.

New plant sources of the anti-cancer alkaloid, camptothecine from the Icacinaceae taxa, India

In this study, the production of camptothecine and its derivatives, in thirteen species of the family Icacinaceae, namely, Apodytes dimidiata, Codiocarpus andamanicus, Gomphandra comosa, Gomphandra coriacea, Gomphandra polymorpha, Gomphandra tetrandra, Iodes cirrhosa, Iodes hookeriana, Miquelia dentata, Miquelia kleinii, Natsiatum herpeticum, Pyrenacantha volubilis and Sarcostigma kleinii is reported. Seeds of M. dentata were found to produce the highest content of camptothecine (1.0-1.4% by dry weight of seeds). Full scan LC-MS and ESI-MS/MS analysis of M. dentata revealed, besides camptothecine, a number of other derivatives, namely, 10-hydroxycamptothecine, 9-methoxycamptothecine, 20-deoxycamptothecine. Crude extract preparations of the seeds of M. dentata were effective against a breast cancer cell line (IC50=3.82 μg/ml for MDA MB273 cell lines) and two ovarian cancer cell lines (IC50=2.8 μg/ml for NCI/ADR-RES and 4.5 μg/ml for SKOV). These results are the first reports of camptothecine and its derivatives in these species and offer rich alternative plant sources for the anticancer compound, camptothecine.

Synthesis and evaluation of 7-chloro-4-(piperazin-1-yl)quinoline-sulfonamide as hybrid antiprotozoal agents

A new series of 4-aminochloroquinoline based sulfonamides were synthesized and evaluated for antiamoebic and antimalarial activities. Out of the eleven compounds evaluated (F1-F11), two of them (F3 and F10) showed good activity against Entamoeba histolytica (IC50 <5 μM). Three of the compounds (F5, F7 and F8) also displayed antimalarial activity against the chloroquine-resistant (FCR-3) strain of Plasmodium falciparum with IC50 values of 2 μM. Compound F7, whose crystal structure was also determined, inhibited β-haematin formation more potently than quinine. To further understand the action of hybrid molecules F7 and F8, molecular docking was carried out against the homology model of P. falciparum enzyme dihydropteroate synthase (PfDHPS). The complexes showed that the inhibitors place themselves nicely into the active site of the enzyme and exhibit interaction energy which is in accordance with our activity profile data. Application of Lipinski 'rule of five' on all the compounds (F1-F11) suggested high drug likeness of F7 and F8, similar to quinine.

Association between UGT1A1*28 polymorphisms and clinical outcomes of irinotecan-based chemotherapies in colorectal cancer: a meta-analysis in Caucasians

BACKGROUND

Whether UGT1A1*28 genotype is associated with clinical outcomes of irinotecan (IRI)-based chemotherapy in Colorectal cancer (CRC) is an important gap in existing knowledge to inform clinical utility. Published data on the association between UGT1A1*28 gene polymorphisms and clinical outcomes of IRI-based chemotherapy in CRC were inconsistent.

METHODOLOGY/PRINCIPAL FINDINGS

Literature retrieval, trials selection and assessment, data collection, and statistical analysis were performed according to the PRISMA guidelines. Primary outcomes included therapeutic response (TR), progression-free survival (PFS) and overall survival (OS). We calculated odds ratios (OR) and hazard ratios (HR) with 95% confidence intervals (CI). Twelve clinical trials were included. No statistical heterogeneity was detected in analyses of all studies and for each subgroup. Differences in TR, PFS and OS for any genotype comparison, UGT1A1*28/*28 versus (vs) UGT1A1*1/*1 (homozygous model), UGT1A1*1/*28 vs UGT1A1*1/*1 (heterozygous model), and UGT1A1*28/*28 vs all others (recessive model, only for TR) were not statistically significant. IRI dose also did not impact upon TR and PFS differences between UGT1A1 genotype groups. A statistically significant increase in the hazard of death was found in Low IRI subgroup of the homozygous model (HR = 1.48, 95% CI = 1.06-2.07; P = 0.02). The UGT1A1*28 allele was associated with a trend of increase in the hazard of death in two models (homozygous model: HR = 1.22, 95% CI = 0.99-1.51; heterozygous model: HR = 1.13, 95% CI = 0.96-1.32). These latter findings were driven primarily by one single large study (Shulman et al. 2011).

CONCLUSIONS/SIGNIFICANCE

UGT1A1*28 polymorphism cannot be considered as a reliable predictor of TR and PFS in CRC patients treated with IRI-based chemotherapy. The OS relationship with UGT1A1*28 in the patients with lower-dose IRI chemotherapy requires further validation.

Assessing the regioselectivity of OleD-catalyzed glycosylation with a diverse set of acceptors

To explore the acceptor regioselectivity of OleD-catalyzed glucosylation, the products of OleD-catalyzed reactions with six structurally diverse acceptors flavones- (daidzein), isoflavones (flavopiridol), stilbenes (resveratrol), indole alkaloids (10-hydroxycamptothecin), and steroids (2-methoxyestradiol)-were determined. This study highlights the first synthesis of flavopiridol and 2-methoxyestradiol glucosides and confirms the ability of OleD to glucosylate both aromatic and aliphatic nucleophiles. In all cases, molecular dynamics simulations were consistent with the determined product distribution and suggest the potential to develop a virtual screening model to identify additional OleD substrates.

Pharmacological screening using an FXN-EGFP cellular genomic reporter assay for the therapy of Friedreich ataxia

Friedreich ataxia (FRDA) is an autosomal recessive disorder characterized by neurodegeneration and cardiomyopathy. The presence of a GAA trinucleotide repeat expansion in the first intron of the FXN gene results in the inhibition of gene expression and an insufficiency of the mitochondrial protein frataxin. There is a correlation between expansion length, the amount of residual frataxin and the severity of disease. As the coding sequence is unaltered, pharmacological up-regulation of FXN expression may restore frataxin to therapeutic levels. To facilitate screening of compounds that modulate FXN expression in a physiologically relevant manner, we established a cellular genomic reporter assay consisting of a stable human cell line containing an FXN-EGFP fusion construct, in which the EGFP gene is fused in-frame with the entire normal human FXN gene present on a BAC clone. The cell line was used to establish a fluorometric cellular assay for use in high throughput screening (HTS) procedures. A small chemical library containing FDA-approved compounds and natural extracts was screened and analyzed. Compound hits identified by HTS were further evaluated by flow cytometry in the cellular genomic reporter assay. The effects on FXN mRNA and frataxin protein levels were measured in lymphoblast and fibroblast cell lines derived from individuals with FRDA and in a humanized GAA repeat expansion mouse model of FRDA. Compounds that were established to increase FXN gene expression and frataxin levels included several anti-cancer agents, the iron-chelator deferiprone and the phytoalexin resveratrol.

Dissection of DNA damage responses using multiconditional genetic interaction maps

To protect the genome, cells have evolved a diverse set of pathways designed to sense, signal, and repair multiple types of DNA damage. To assess the degree of coordination and crosstalk among these pathways, we systematically mapped changes in the cell's genetic network across a panel of different DNA-damaging agents, resulting in ~1,800,000 differential measurements. Each agent was associated with a distinct interaction pattern, which, unlike single-mutant phenotypes or gene expression data, has high statistical power to pinpoint the specific repair mechanisms at work. The agent-specific networks revealed roles for the histone acetyltranferase Rtt109 in the mutagenic bypass of DNA lesions and the neddylation machinery in cell-cycle regulation and genome stability, while the network induced by multiple agents implicates Irc21, an uncharacterized protein, in checkpoint control and DNA repair. Our multiconditional genetic interaction map provides a unique resource that identifies agent-specific and general DNA damage response pathways.

Anticancer activities of genistein-topotecan combination in prostate cancer cells

Prostate cancer is one of the leading causes of death in men aged 40 to 55. Genistein isoflavone (4', 5', 7-trihydroxyisoflavone) is a dietary phytochemical with demonstrated anti-tumour activities in a variety of cancers. Topotecan Hydrochloride (Hycamtin) is an FDA-approved chemotherapy drug, primarily used for secondary treatment of ovarian, cervical and small cell lung cancers. This study was to demonstrate the potential anticancer efficacy of genistein-topotecan combination in LNCaP prostate cancer cells and the mechanism of the combination treatment. The LNCaP cells were grown in complete RPMI medium, and cultured at 37°C, 5% CO(2) for 24-48 hrs to achieve 70-90% confluency. The cells were treated with varying concentrations of genistein, topotecan and genistein-topotecan combination and incubated for 24 hrs. The treated cells were assayed for (i) post-treatment sensitivity using MTT assay and DNA fragmentation, (ii) treatment-induced apoptosis using caspase-3 and -9 binding assays and (iii) treatment-induced ROS generation levels. The overall data indicated that (i) both genistein and topotecan induce cellular death in LNCaP cells, (ii) genistein-topotecan combination was significantly more efficacious in reducing LNCaP cell viability compared with either genistein or topotecan alone, (iii) in all cases, cell death was primarily through apoptosis, via the activation of caspase-3 and -9, which are involved in the intrinsic pathway, (iv) ROS generation levels increased significantly with the genistein-topotecan combination treatment. Treatments involving genistein-topotecan combination may prove to be an attractive alternative phytotherapy or adjuvant therapy for prostate cancer.

Synthesis and biological evaluation of 7-alkenyl homocamptothecins as potent topoisomerase I inhibitors

Homocamptothecin (hCPT) is a camptothecin (CPT) derivative with a seven-membered β-hydroxylactone E ring, which shows higher lactone stability and improves topoisomerase I (Topo I) inhibition activity. In an attempt to improve the antitumor activity of homocamptothecins, a series of 7-alkenyl-homocamptothecin derivatives was designed and synthesized based on a semisynthetic route starting from CPT. Most of the synthesized compounds exhibit higher cytotoxic activities on the A-549 tumor cell line than topotecan (TPT). Some compounds such as 2a and 2o show a broad in vitro antitumor spectrum and exhibit superior Topo I-inhibition activity.

Synthesis and biological evaluation of new homocamptothecin analogs

In order to increase the stability of E-ring of homocamptothecins, the electron-withdrawing group -OH or -OAc was induced to α position of ring-E lactone. Ten new homocamptothecin analogs were synthesized. Most compounds showed potent in vitro anticancer activity and potent Topo I inhibition, which was equal or superior to that of CPT, SN-38 and 10-HCPT. The stability studies of this series also displayed significant improvement of the stability.

A high-content biosensor-based screen identifies cell-permeable activators and inhibitors of EGFR function: implications in drug discovery

Early success of kinase inhibitors has validated their use as drugs. However, discovery efforts have also suffered from high attrition rates due to lack of cellular activity. We reasoned that screening for such candidates in live cells would identify novel cell-permeable modulators for development. For this purpose, we have used our recently optimized epidermal growth factor receptor (EGFR) biosensor assay to screen for modulators of EGFR activity. Here, we report on its validation under high-throughput screening (HTS) conditions displaying a signal-to-noise ratio of 21 and a Z' value of 0.56-attributes of a robust cell-based assay. We performed a pilot screen against a library of 6912 compounds demonstrating good reproducibility and identifying 82 inhibitors and 66 activators with initial hit rates of 1.2% and 0.95%, respectively. Follow-up dose-response studies revealed that 12 of the 13 known EGFR inhibitors in the library were confirmed as hits. ZM-306416, a vascular endothelial growth factor receptor (VEGFR) antagonist, was identified as a potent inhibitor of EGFR function. Flurandrenolide, beclomethasone, and ebastine were confirmed as activators of EGFR function. Taken together, our results validate this novel approach and demonstrate its utility in the discovery of novel kinase modulators with potential use in the clinic.

Eriocalyxin B induces apoptosis and cell cycle arrest in pancreatic adenocarcinoma cells through caspase- and p53-dependent pathways

Pancreatic cancer is difficult to detect early and responds poorly to chemotherapy. A breakthrough in the development of new therapeutic agents is urgently needed. Eriocalyxin B (EriB), isolated from the Isodon eriocalyx plant, is an ent-kaurane diterpenoid with promise as a broad-spectrum anti-cancer agent. The anti-leukemic activity of EriB, including the underlying mechanisms involved, has been particularly well documented. In this study, we demonstrated for the first time EriB's potent cytotoxicity against four pancreatic adenocarcinoma cell lines, namely PANC-1, SW1990, CAPAN-1, and CAPAN-2. The effects were comparable to that of the chemotherapeutic camptothecin (CAM), but with much lower toxicity against normal human liver WRL68 cells. EriB's cytoxicity against CAPAN-2 cells was found to involve caspase-dependent apoptosis and cell cycle arrest at the G2/M phase. Moreover, the p53 pathway was found to be activated by EriB in these cells. Furthermore, in vivo studies showed that EriB inhibited the growth of human pancreatic tumor xenografts in BALB/c nude mice without significant secondary adverse effects. These results suggest that EriB should be considered a candidate for pancreatic cancer treatment.

Cytotoxic activity of withanolides isolated from Tunisian Datura metel L

Withanolide-type steroids, withametelin Q (1) and 12α-hydroxydaturametelin B (2) along with three known withanolides, were isolated from leaves of Datura metel L. (Solanaceae). The respective structures, characterized mainly by NMR spectroscopy, were identified as (20R,22R,24R)-21,24-epoxy-1α,3β-dihydroxywitha-5,25(27)-dienolide-3-O-β-D-glucopyranoside (1) and (20R,22R,24R)-12α,21,27-trihydroxy-1-oxowitha-2,5,24-trienolide-27-O-β-D-glucopyranoside (2). The cytotoxicity of isolated compounds was evaluated against human lung carcinoma cells (A549) and human colorectal adenocarcinoma cells (DLD-1), respectively. Compound 2 exhibited cytotoxicity against A549 and DLD-1 cell lines, with IC50 values of 7 and 2.0 μM, respectively. However, for compounds 6 and 7, cytotoxicities were higher against DLD-1 cells with IC(50) values of 0.6 and 0.7 μM. Both compounds blocked the cell cycle in the S-phase and induced apoptosis.

RNA polymerase I activity is regulated at multiple steps in the transcription cycle: recent insights into factors that influence transcription elongation

Synthesis of the translation apparatus is a central activity in growing and/or proliferating cells. Because of its fundamental importance and direct connection to cell proliferation, ribosome synthesis has been a focus of ongoing research for several decades. As a consequence, much is known about the essential factors involved in this process. Many studies have shown that transcription of the ribosomal DNA by RNA polymerase I is a major target for cellular regulation of ribosome synthesis rates. The initiation of transcription by RNA polymerase I has been implicated as a regulatory target, however, recent studies suggest that the elongation step in transcription is also influenced and regulated by trans-acting factors. This review describes the factors required for rRNA synthesis and focuses on recent works that have begun to identify and characterize factors that influence transcription elongation by RNA polymerase I and its regulation.

Identification and replication of loci involved in camptothecin-induced cytotoxicity using CEPH pedigrees

To date, the Centre d'Etude Polymorphism Humain (CEPH) cell line model has only been used as a pharmacogenomic tool to evaluate which genes are responsible for the disparity in response to a single drug. The purpose of this study was demonstrate the model's ability to establish a specific pattern of quantitative trait loci (QTL) related to a shared mechanism for multiple structurally related drugs, the camptothecins, which are Topoisomerase 1 inhibitors. A simultaneous screen of six camptothecin analogues for in vitro sensitivity in the CEPH cell lines resulted in cytotoxicity profiles and orders of potency which were in agreement with the literature. For all camptothecins studied, heritability estimates for cytotoxic response averaged 23.1 ± 2.6%. Nonparametric linkage analysis was used to identify a relationship between genetic markers and response to the camptothecins. Ten QTLs on chromosomes 1, 3, 5, 6, 11, 12, 16 and 20 were identified as shared by all six camptothecin analogues. In a separate validation experiment, nine of the ten QTLs were replicated at the significant and suggestive levels using three additional camptothecin analogues. To further refine this list of QTLs, another validation study was undertaken and seven of the nine QTLs were independently replicated for all nine camptothecin analogues. This is the first study using the CEPH cell lines that demonstrates that a specific pattern of QTLs could be established for a class of drugs which share a mechanism of action. Moreover, it is the first study to report replication of linkage results for drug-induced cytotoxicity using this model. The QTLs, which have been identified as shared by all camptothecins and replicated across multiple datasets, are of considerable interest; they harbor genes related to the shared mechanism of action for the camptothecins, which are responsible for variation in response.

Carboxyl-terminated PAMAM-SN38 conjugates: synthesis, characterization, and in vitro evaluation

In this work, carboxyl-terminated PAMAM G-3.5 was covalently attached to SN38 via glycine and β-alanine spacers. The conjugates were stable at pH 7.4 and moderately hydrolyzed in cell culture media and rat plasma. Similarly to SN38 but to a lesser extent, both conjugates inhibited proliferation of human colorectal cancer HCT-116 cells, arrested the cell cycle in the G(2)/M phase, and led to nuclear fragmentation. However, activity of the conjugate with glycine spacer (IC(50) = 129 nM) was higher compared to that of the β-alanine linked conjugate (IC(50) = 387 nM). These PAMAM-SN38 conjugates have the potential for targeted therapy of colorectal carcinoma.

Discovery of ortho-Carborane-Conjugated Triazines as Selective Topoisomerase I/II Inhibitors

The cell growth inhibition profile of 2,4-(2-methyl-ortho-carboranyl)-4-(dimethylamino)-1,3,5-triazine (TAZ-6) was found to be similar to that of ICRF-193, a topoisomerase II inhibitor, as revealed by COMPARE analysis (correlation coefficient (r) = 0.724). Various mono- and di-ortho-carborane-substituted 1,3,5-triazines were synthesized based on the structure of TAZ-6 and tested for their ability to inhibit cell growth and the activities of topoisomerases I and II. Among the compounds synthesized, 3c, 4c, and 4f completely inhibited topoisomerase I activity without affecting topoisomerase II activity, whereas 3a and 3d completely inhibited topoisomerase II activity without affecting topoisomerase I activity, at 100 μM.

Synthesis and Pharmacological Evaluation of Novel Homocamptothecin-Dihydropyridine Derivative Conjugates as Potent Topoisomerase I Inhibitors

Homocamptothecins (hCPT) represent a new generation of antitumour agents targeting DNA topoisomerase I. The expanded seven-membered lactone E-ring that characterizes hCPT enhances the plasma stability of the drug and reinforces the inhibition of topoisomerase I (Topo I) compared with conventional six-membered CPT. In an attempt to improve the antitumour activity of hCP, a series of novel hCPT derivatives conjugating with dihydropyridine derivates were designed and synthesized based on a synthetic route that couples 7-formylhomocamptothecin with different dihydropyridine derivates. Most of the synthesized compounds exhibited good cytotoxic activity on tumour cell line A549, MDA-MB-435, and HCT116. Furthermore, this class of compounds showed superior Topo I inhibition activity comparable to or higher than CPT.

Antitumor Activities and Structure - Activity Relationship of Phosphotriester Derivatives of Homocamptothecin Based on a Semisynthetic Route

Based on a new semisynthetic route, a series of phosphotriester 7-alkyl-homocamptothecin derivatives are designed and synthesized. Cytotoxic activity assays show that compounds 12a and 14c with a methyl in position C7 of the homocamptothecin are more potent than the other derivatives and the positive drug irinotecan against A-549, MCF-7, and LOVO cell lines. Moreover, compound 14c shows potent tumour inhibitory activity in a Colo205 xenograft model.

PAMAM-camptothecin conjugate inhibits proliferation and induces nuclear fragmentation in colorectal carcinoma cells

PURPOSE

To synthesize and characterize a poly (amido amine) dendrimer-camptothecin (PAMAM-CPT) conjugate and evaluate its activity on human colorectal carcinoma cells (HCT-116).

METHODS

The attachment of CPT to amine-terminated PAMAM was facilitated through a succinic acid-glycine linker. The conjugate was characterized for absence of small molecular weight impurities, size and drug content. Stability of the conjugate in PBS and growth media and its in vitro activity on HCT-116 were studied. Cell cycle arrest and nuclear fragmentation upon PAMAM-CPT treatment were investigated.

RESULTS

The conjugate was stable under physiological pH (7.4) in PBS and in growth media (with 10% FBS) with minimal release of 4% and 6% drug, respectively, at 48 h. PAMAM-CPT inhibited proliferation of HCT-116 cells with an IC50 value of 1.6  ±  0.3 µM. The conjugate induced signs of cell cycle arrest with up to 68% of cells blocked in the G(2) phase. Confocal images of cells treated with PAMAM-CPT suggest nuclear fragmentation and formation of apoptotic bodies.

CONCLUSIONS

Results show that the PAMAM-CPT conjugate was active against colorectal cancer cells in vitro, inhibiting their growth and inducing nuclear fragmentation. Coupled with the ability to target macromolecular therapeutics to tumors, this conjugate shows promise for cancer chemotherapy.