Camptothecin. Discovery to clinic

Evaluation of Anticancer Activity of 76 Plant Species Collected in Andalusia (Spain) against Lung Cancer Cells

Every year, cancer kills millions of people around the world. Finding more selective anticancer agents is essential to improve the low survival rates of patients with metastatic cancers. Since the research of natural products is a valuable approach to the discovery of new compounds and the Iberian flora offers a rich source of unstudied plants, we have carried out a random screening of 76 plant species from 43 families collected in Andalusia (South of Spain). Using non-malignant cells (HaCaT) and lung cancer cells (A549), we found that the extract from Arum italicum Mill. subsp. italicum (Araceae), Mandragora autumnalis Bertol. (Solanaceae), Rhamnus alaternus L. (Rhamnaceae), and Lomelosia simplex (Desf.) Raf. subsp. dentata (Jord. & Fourr.) Greuter & Burdet (Dipsacaceae) showed selective cytotoxicity against lung cancer cells. Extracts of plant species belonging to the Iridaceae family showed high selective activity against cancer cells, highlighting that the Xiphion xiphium (L.) M.B. Crespo, Mart.-Azorín & Mavrodiev flower extract was more selective against lung cancer cells than the standard anticancer drugs, cisplatin and 5-fluorouracil. This extract also showed modest selective cytotoxicity against bladder carcinoma cells (T24). The number of cells in the G1 phase increased after treatment with the extract from Xiphion xiphium. Our research indicates that various plants are potential sources for the isolation and development of new anticancer drugs.

SK119, a Novel Shikonin Derivative, Leads to Apoptosis in Melanoma Cell Lines and Exhibits Synergistic Effects with Vemurafenib and Cobimetinib

Melanoma is a complex and heterogenous disease, displays the deadliest form of skin cancer, and accounts for approx. 80% of all skin cancer deaths. In this study, we reported on the synthesis and pharmacological effects of a novel shikonin derivative (SK119), which is active in a nano-molar range and exhibits several promising in vitro effects in different human melanoma cells. SK119 was synthesized from shikonin as part of our search for novel, promising shikonin derivatives. It was screened against a panel of melanoma and non-tumorigenic cell lines using XTT viability assays. Moreover, we studied its pharmacological effects using apoptosis and Western blot experiments. Finally, it was combined with current clinically used melanoma therapeutics. SK119 exhibited IC₅₀ values in a nano-molar range, induced apoptosis and led to a dose-dependent increase in the expression and protein phosphorylation of HSP27 and HSP90 in WM9 and MUG-Mel 2 cells. Combinatorial treatment, which is highly recommended in melanoma, revealed the synergistic effects of SK119 with vemurafenib and cobimetinib. SK119 treatment changed the expression levels of apoptosis genes and death receptor expression and exhibited synergistic effects with vemurafenib and cobimetinib in human melanoma cells. Further research indicates a promising potential in melanoma therapy.

The Road so Far in Colorectal Cancer Pharmacogenomics: Are We Closer to Individualised Treatment?

In recent decades, survival rates in colorectal cancer have improved greatly due to pharmacological treatment. However, many patients end up developing adverse drug reactions that can be severe or even life threatening, and that affect their quality of life. These remain a limitation, as they may force dose reduction or treatment discontinuation, diminishing treatment efficacy. From candidate gene approaches to genome-wide analysis, pharmacogenomic knowledge has advanced greatly, yet there is still huge and unexploited potential in the use of novel technologies such as next-generation sequencing strategies. This review summarises the road of colorectal cancer pharmacogenomics so far, presents considerations and directions to be taken for further works and discusses the path towards implementation into clinical practice.

The development and validation of an LC-MS/MS method for the quantification of CZ112, a prodrug of 9-Nitrocamptothecin in rat plasma

9-Nitrocamptothecin-20-O-propionate (CZ112) and 9-Nitrocamptothecin (9NC) are the bioactive derivatives of camptothecin (CPT), an alkaloid isolated from Camptotheca acuminata, and have been confirmed to possess high anti-cancer properties. In the present study, 9NC was identified as the major metabolite of CZ112 in rat plasma through HPLC/photodiode array detection (PDA) and liquid chromatography tandem mass spectrometry (LC-MS/MS) analysis. A highly sensitive LC-MS/MS method was developed and validated for the simultaneous analysis of CZ112 and 9NC in rat plasma, and camptothecin-20-O-acetate (CZ44) was used as an internal standard (IS). The calibration curves were linear (r² > 0.999) over concentrations from 2.5 to 320 ng/mL for both CZ112 and 9NC. The method had an accuracy of 96.7-109.6%, and the intra- and inter-day precision (RSD%) were 10.9% or less for CZ112 and 9NC. The stability data showed no significant degradation occurred under the experimental conditions. This method was successfully applied to the pharmacokinetic study of CZ112 and its metabolite 9NC in rat plasma after intravenous and intragastric administration. The oral bioavailability of CZ112 was 6.2 ± 3.3% (n = 6).

Entrapment of DNA topoisomerase-DNA complexes by nucleotide/nucleoside analogs

Topoisomerases are well-validated targets for cancer chemotherapy and DNA topoisomerase 1 (Top1) is the sole target of the camptothecin (CPT) class of anticancer drugs. Over the last 20 years, multiple studies have shown Top1 activity is modulated by non-native DNA structures and this can lead to trapping of Top1 cleavage complexes (Top1cc) and conversion to DNA double strand breaks. Among the perturbations to DNA structure that generate Top1cc are nucleoside analogs that are incorporated into genomic DNA during replication including cytarabine, gemcitabine, and 5-fluoro-2'-deoxyuridine (FdU). We review the literature summarizing the role of Top1cc in mediating the DNA damaging and cytotoxic activities of nucleoside analogs. We also summarize studies demonstrating distinct differences between Top1cc induced by nucleoside analogs and CPTs, particularly with regard to DNA repair. Collectively, these studies demonstrate that, while Top1 is a common target for both Top1 poisons such as CPT and nucleoside analogs such as FdU, these agents are not redundant. In recent years, studies have shown that Top1 poisons and nucleoside analogs together with other anti-cancer drugs such as cisplatin cause replication stress and the DNA repair pathways that modulate the cytotoxic activities of these compounds are being elucidated. We present an overview of this evolving literature, which has implications for how targeting of Top1 with nucleoside analogs can be used more effectively for cancer treatment.

The Chalcone Lonchocarpin Inhibits Wnt/β-Catenin Signaling and Suppresses Colorectal Cancer Proliferation

The deregulation of the Wnt/β-catenin signaling pathway is a central event in colorectal cancer progression, thus a promising target for drug development. Many natural compounds, such as flavonoids, have been described as Wnt/β-catenin inhibitors and consequently modulate important biological processes like inflammation, redox balance, cancer promotion and progress, as well as cancer cell death. In this context, we identified the chalcone lonchocarpin isolated from Lonchocarpus sericeus as a Wnt/β-catenin pathway inhibitor, both in vitro and in vivo. Lonchocarpin impairs β-catenin nuclear localization and also inhibits the constitutively active form of TCF4, dnTCF4-VP16. Xenopus laevis embryology assays suggest that lonchocarpin acts at the transcriptional level. Additionally, we described lonchocarpin inhibitory effects on cell migration and cell proliferation on HCT116, SW480, and DLD-1 colorectal cancer cell lines, without any detectable effects on the non-tumoral intestinal cell line IEC-6. Moreover, lonchocarpin reduces tumor proliferation on the colorectal cancer AOM/DSS mice model. Taken together, our results support lonchocarpin as a novel Wnt/β-catenin inhibitor compound that impairs colorectal cancer cell growth in vitro and in vivo.

Silicon-containing analogs of camptothecin as anticancer agents

The plant pentacyclic alkaloid camptothecin and its structural analogs were extensively studied. These compounds are interesting due to the antitumor activity associated with their ability to inhibit topoisomerase I in tumor cells. During the last decades of the 20th century, a large number of the silicon-containing camptothecins (silatecans) were synthesized. 7-tert-Butyldimethylsilyl-10-hydroxy-camptothecin (DB-67 or AR-67) has enhanced lipophilicity and demonstrates a antitumor activity superior to its carbon analog. To date, certain silatecans are under clinical trials and their ultimate role in cancer therapy appears promising. In this review, we present chemical methodologies for the synthesis of silicon-containing camptothecins, their chemical properties, biological activity, and results of clinical trials.

Enabling Oral SN38-Based Chemotherapy with a Combined Lipophilic Prodrug and Self-Microemulsifying Drug Delivery System

Oral chemotherapy with SN38 is restricted by its poor solubility in gastrointestinal (GI) fluids and low permeability. Here we report the oral delivery of SN38 by a combined lipophilic prodrug and lipid-based formulation strategy. A lead lipophilic prodrug of SN38, SN38-undecanoate (SN38-unde20), was incorporated into a self-microemulsifying drug delivery system (SMEDDS) for improved in vitro and in vivo performance. The formulation was purposefully designed and optimized with long chain lipids and lipid-based nonionic surfactants to maximize drug solubilization in GI conditions, facilitate trans-membrane permeation, and hence improve oral absorption. SN38-unde20-SMEDDS significantly increased (>7 fold) drug solubilization in the aqueous phase compared to unformulated drug during in vitro lipolysis and drug solubilization studies. In an orally dosed in vivo pharmacokinetics study in a Dark Agouti rat model, the SN38-unde20-SMEDDS formulation confirmed oral absorption of SN38-unde20 and subsequent reconversion to SN38. Importantly, the overall plasma exposure of SN38 (AUC_0→∞) was equivalent for orally dosed SN38-unde20-SMEDDS in comparison with a parenteral dose of SN38-unde20-SMEDDS and SN38 at an identical dose (10 mg/kg). The combination of lipophilic prodrug along with an optimal delivery carrier is demonstrated to enable effective oral delivery of challenging chemotherapeutic compounds that are conventionally dosed by injection.

Feeling Nature's PAINS: Natural Products, Natural Product Drugs, and Pan Assay Interference Compounds (PAINS)

We have previously reported on classes of compounds that can interfere with bioassays via a number of different mechanisms and termed such compounds Pan Assay INterference compoundS, or PAINS. These compounds were defined on the basis of high-throughput data derived from vendor-supplied synthetics. The question therefore arises whether the concept of PAINS is relevant to compounds of natural origin. Here, it is shown that this is indeed the case, but that the context of the biological readout is an important factor that must be brought into consideration.

Folding graft copolymer with pendant drug segments for co-delivery of anticancer drugs

A graft copolymer with pendant drug segments can fold into nanostructures in a protein folding-like manner. The graft copolymer is constructed by directly polymerizing γ-camptothecin-glutamate N-carboxyanhydride (Glu(CPT)-NCA) on multiple sites of poly(ethylene glycol) (PEG)-based main chain via the ring open polymerization (ROP). The "purely" conjugated anticancer agent camptothecin (CPT) is hydrophobic and serves as the principal driving force during the folding process. When exposed to water, the obtained copolymer, together with doxorubicin (Dox), another anticancer agent, can fold into monodispersed nanocarriers (with a diameter of around 50 nm) for dual-drug delivery. Equipped with a PEG shell, the nanocarriers displayed good stability and can be internalized by a variety of cancer cell lines via the lipid raft and clathrin-mediated endocytotic pathway without premature leakage, which showed a high synergetic activity of CPT and Dox toward various cancer cells. In vivo study validated that the nanocarriers exhibited strong accumulation in tumor sites and showed a prominent anticancer activity against the lung cancer xenograft mice model compared with free drugs.

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.

The quest for modernisation of traditional Chinese medicine

Traditional Chinese medicine (TCM) is an integral part of mainstream medicine in China. Due to its worldwide use, potential impact on healthcare and opportunities for new drug development, TCM is also of great international interest. Recently, a new era for modernisation of TCM was launched with the successful completion of the Good Practice in Traditional Chinese Medicine Research in the Post-genomic Era (GP-TCM) project, the European Union's Seventh Framework Programme (FP7) coordination action on TCM research. This 3.5-year project that involved inputs from over 200 scientists resulted in the production of 20 editorials and in-depth reviews on different aspects of TCM that were published in a special issue of Journal of Ethnopharmacology (2012; volume 140, issue 3). In this narrative review, we aim to summarise the findings of the FP7 GP-TCM project and highlight the relevance of TCM to modern medicine within a historical and international context. Advances in TCM research since the 1950s can be characterised into three phases: Phase I (1950s-1970s) was fundamental for developing TCM higher education, research and hospital networks in China; Phase II (1980s-2000s) was critical for developing legal, economic and scientific foundations and international networks for TCM; and Phase III (2011 onwards) is concentrating on consolidating the scientific basis and clinical practice of TCM through interdisciplinary, interregional and intersectoral collaborations. Taking into account the quality and safety requirements newly imposed by a globalised market, we especially highlight the scientific evidence behind TCM, update the most important milestones and pitfalls, and propose integrity, integration and innovation as key principles for further modernisation of TCM. These principles will serve as foundations for further research and development of TCM, and for its future integration into tomorrow's medicine.

Assessment of anti-cytogenotoxic effects of quercetin in animals treated with topotecan

The present investigation was directed to study the possible chemoprotective activity of orally administered quercetin against topotecan-induced cyto- and genotoxicity towards mouse somatic cells in vivo. DNA strand breaks, micronuclei formation, and mitotic activity were undertaken in the current study as markers of cyto- and genotoxicity. Oxidative stress markers such as intracellular reactive oxygen species generation, lipid peroxidation, and reduced and oxidized glutathione were assessed in bone marrow as a possible mechanism underlying this amelioration. Quercetin was neither cytotoxic nor genotoxic in mice at doses tested. Pretreatment of mice with quercetin significantly reduced topotecan-induced genotoxicity and cytotoxicity in bone marrow cells, and these effects were dose dependent. Moreover, prior administration of quercetin ahead of topotecan challenge ameliorated oxidative stress markers. In conclusion, quercetin has a protective role in the abatement of topotecan-induced cyto- and genotoxicity in the bone marrow cells of mice that resides, at least in part, on its antioxidant effects. Based on the data presented, strategies can be developed to decrease the topotecan-induced bone marrow suppression and secondary malignancy in cancer patients and medical personnel exposing to topotecan.

Molecular cytogenetic evaluation of the mechanism of micronuclei formation induced by camptothecin, topotecan, and irinotecan

We used the conventional bone marrow micronucleus test complemented with the fluorescent in situ hybridization with the minor satellite DNA probe to investigate the mechanisms of induction of micronuclei in mice treated with camptothecin and its clinical antineoplastic analogues topotecan and irinotecan. All experiments were performed with male Swiss albino mice. Single doses of 1 mg/kg camptothecin or 0.6 mg/kg topotecan were injected intraperitoneally and bone marrow was sampled at 30 hr (camptothecin) or 24 hr (topotecan) after treatment. A dose of 60 mg/kg irinotecan was injected intravenously, once every fourth day for 13 days and bone marrow was sampled 24 hr after the last treatment. In animals treated with camptothecin, a total of 1.07% micronuclei were found and 70% of them were centromere-negative, indicating their formation by DNA strand breaks and reflecting the predominant clastogenic activity of camptothecin. Exposure to topotecan and irinotecan yielded 1.71 and 0.83% micronuclei, respectively. About 52.7 and 48.8% of the induced micronuclei, respectively, were centromere-positive, indicating their formation by whole chromosomes and reflecting the aneugenic activity of both compounds. Correspondingly, about 47.3 and 51.2% of the induced micronuclei, respectively were centromere-negative, demonstrating that topotecan and irinotecan not only induce chromosome loss but also DNA strand breaks. Both the clastogenic and aneugenic potential of these drugs can lead to the development of secondary tumors and abnormal reproductive outcomes. Therefore, the clinical use of these agents must be weighed against the risks of secondary malignancies in cured patients and persistent genetic damage of their potential offspring.

Structural studies of type I topoisomerases

Topoisomerases are ubiquitous proteins found in all three domains of life. They change the topology of DNA via transient breaks on either one or two of the DNA strands to allow passage of another single or double DNA strand through the break. Topoisomerases are classified into two types: type I enzymes cleave one DNA strand and pass either one or two DNA strands through the break before resealing it, while type II molecules cleave both DNA strands in concert and pass another double strand through the break followed by religation of the double strand break. Here we review recent work on the structure of type I enzymes. These structural studies are providing atomic details that, together with the existing wealth of biochemical and biophysical data, are bringing our understanding of the mechanism of action of these enzymes to the atomic level.

Chimmitecan, a novel 9-substituted camptothecin, with improved anticancer pharmacologic profiles in vitro and in vivo

PURPOSE

This study aimed to evaluate antitumor activities and pharmacologic profiles of chimmitecan, a novel 9-small-alkyl-substituted lipophilic camptothecin, in comparison with irinotecan (CPT-11) and topotecan.

EXPERIMENTAL DESIGN

The in vitro cytotoxities of chimmitecan in human tumor cell lines and multidrug resistance (MDR) cells were evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide and sulforhodamin B assays. DNA relaxation, cleavage assays, and cellular band depletion assay were combined to delineate its effects on topoisomerase I. DNA damage, cell cycle arrest, and apoptosis were assessed using comet assay, flow cytometry, and DNA ladder analysis, respectively. The in vivo antitumor activities were measured in nude mice bearing human tumor xenografts.

RESULTS

Chimmitecan displayed more potent cytotoxicity than SN38 and topotecan. Neither a cross-resistance to chimmitecan in MDR cells nor an influence of human serum albumin in its cytotoxity was observed. Chimmitecan exhibited comparable effects on topoisomerase I compared with the reference drugs, including inhibiting topoisomerase I catalytic activity and trapping and stabilizing covalent topoisomerase I-DNA complexes. Furthermore, nanomolar levels of chimmitecan caused impressive DNA damage, G(2)-M phase arrest, and apoptosis in human leukemia HL60 cells. I.v. administration of chimmitecan inhibited the growth of HCT-116, MDA-MB-435, BEL-7402, and A549 human carcinoma xenografts in nude mice, with greater potency than CPT-11 against the latter two tumors models. Chimmitecan presented potent efficacy in A549 tumor model when given orally.

CONCLUSIONS

Chimmitecan is a potent inhibitor of topoisomerase I and displays outstanding activity in vitro and in vivo. The substitution at the 9-position benefits chimmitecan a salient anti-MDR activity, stability in human serum albumin, improved solubility, and oral availability, which might favorably promise its therapeutic potential in clinical settings.

Cytotoxic and antiproliferative effects induced by a non terpenoid polar extract of A. indica seeds on 3T6 murine fibroblasts in culture

Neem oil is a natural product obtained from the seeds of the tree Azadirachta indica. Its composition is very complex and the oil exhibits a number of biological activities. The most studied component is the terpenoid azadirachtin which is used for its insecticidal and putative antimicrobial properties. In this report we investigate the biological activity of partially purified components of the oil obtained from A. indica. We show that the semi-purified fractions have moderate to strong cytotoxicity. However, this is not attributable to azadirachtin but to other active compounds present in the mixture. Each fraction was further purified by appropriate extraction procedures and we observed a differential cytotoxicity in the various sub-fractions. This led us to investigate the mode of cell death. After treatment with the oil fractions we observed positivity to TUNEL staining and extensive internucleosomal DNA degradation both indicating apoptotic death. The anti-proliferative properties of the neem oil-derived compounds were also assayed by evaluation of the nuclear PCNA levels (Proliferating Cell Nuclear Antigen). PCNA is significantly reduced in cells treated with a specific fraction of neem oil. Finally, our results strongly suggest a possible involvement of the mitochondrial pathway in the apoptotic death.

Camptothecin induces the ubiquitin-like protein, ISG15, and enhances ISG15 conjugation in response to interferon

Interferon (IFN)-stimulated gene (15 kDa) (ISG15) is a ubiquitin-like protein that forms covalent conjugates with cellular proteins. ISG15 is induced by IFN, microbial challenge, and p53, suggesting that it represents a genetic response that is shared among diverse stress stimuli. To investigate the regulation of this posttranslational modification pathway by a genotoxic chemotherapeutic agent, we examined ISG15 induction and conjugation in cells treated with the topoisomerase I (topoI) poison, camptothecin (CPT). CPT induced ISG15mRNA, and induction required protein synthesis and a functional p53 protein. However, IFN and the Jak-Stat components of the IFN signaling pathway were dispensable for CPT induction of ISG15. CPT induced free ISG15 and conjugates in a dose-dependent and time-dependent manner. A single 55-kDa protein was the prominent CPT-induced ISG15 conjugate and localized to the nuclear compartment. CPT-induced ISG15 conjugates were distinct from those induced by IFN; however, CPT treatment dramatically enhanced ISG15 conjugation in response to IFN. These findings provide the first evidence of a stimulus-specific induction of discrete ISG15 conjugate species and demonstrate that treatment with a combination of cancer therapeutic agents can cooperate to enhance ISG15 conjugation. Identification of the specific ISG15 conjugates induced by chemotherapeutic agents may reveal novel molecular targets.

Silatecan DB-67 is a novel DNA topoisomerase I–targeted radiation sensitizer

The silatecan 7-tert-butyldimethylsilyl-10-hydroxy-camptothecin (DB-67) represents a new generation of camptothecin derivatives that exhibits a potent in vitro DNA topoisomerase I (TOP1)–mediated DNA-damaging activity, improved blood stability, and holds significant promise for the treatment of human cancers. In this study, we characterize the role of TOP1 in mediating the radiosensitization activity of DB-67. As examined by clonogenic survival assay, DB-67 exhibited potent radiosensitization activity at a concentration 10-fold lower than camptothecin in the human glioma D54-MG and T-98G cells, which harbor wild-type and mutant p53, respectively. Analyzed by the single-hit multitarget model, DB-67 induced radiosensitization by obliterating the “shoulder” of the radiation survival curve in the D54-MG cells. The in vivo targeting of TOP1 by DB-67 was investigated by immunoblot analysis. In a dose-dependent manner, DB-67 specifically stimulates covalent linking of TOP1 to chromosomal DNA at concentrations 10-fold lower than camptothecin in the D54-MG cells. The potency of in vivo targeting of TOP1 by DB-67 correlates well with its cytotoxicity and radiosensitization activity. Furthermore, DB-67 exhibited substantially less cytotoxicity and radiosensitization activity in the TOP1 mutant Chinese hamster lung fibroblast DC3F/C-10 cells than in their parental DC3F cells. Together, our data show that DB-67 exhibits potent cytotoxicity and radiosensitization activity by targeting TOP1 in mammalian cells and has great potential for being developed to treat human cancers.

Novel camptothecin analogue (gimatecan)-containing liposomes prepared by the ethanol injection method

Small-sized liposomes have several advantages as drug delivery systems, and the ethanol injection method is a suitable technique to obtain the spontaneous formation of liposomes having a small average radius. In this paper, we show that liposomal drug formulations can be prepared in situ, by simply injecting a drug-containing lipid(s) organic solution into an aqueous solution. Several parameters should be optimized in order to obtain a final suitable formulation, and this paper is devoted to such an investigation. Firstly, we study the liposome size distributions determined by dynamic light scattering (DLS), as function of the lipid concentration and composition, as well as the organic and aqueous phases content. This was carried out, firstly, by focusing on POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine) then on the novel L-carnitine derivative PUCE (palmitoyl-(R)-carnitine undecyl ester chloride), showing that it is possible to obtain monomodal size distributions of rather small vesicles. In particular, depending on the conditions, it was possible to achieve a population of liposomes with a mean size of 100 nm, when a 50 mM POPC ethanol solution was injected in pure water; in the case of 50 mM PUCE the mean size was around 30 nm, when injected in saline (0.9% NaCl). The novel anticancer drug Gimatecan, a camptothecin derivative, was used as an example of lipophilic drug loading by the injection method. Conditions could be found, under which the resultant liposome size distributions were not affected by the presence of Gimatecan, in the case of POPC as well as in the case of PUCE. To increase the overall camptothecin concentration in the final liposomal dispersion, the novel technique of "multiple injection method" was used, and up to a final 5 times larger amount of liposomal drug could be reached by maintaining approximately the same size distribution. Once prepared, the physical and chemical stability of the liposome formulations was satisfactory within 24, as judged by DLS analysis and HPLC quantitation of lipids and drug. The Gimatecan-containing liposomes formulations were also tested for in vitro and in vivo activity, against the human nonsmall cell lung carcinoma NCI-H460 and a murine Lewis lung carcinoma 3 LL cell lines. In the in vitro tests, we did not observe any improvement or reduction of the Gimatecan pharmacological effect by the liposomal delivery system. More interestingly, in the in vivo Lewis lung carcinoma model, the intravenously administration of liposomal Gimatecan formulation showed a mild but significant increase of Tumor Volume Inhibition with respect to the oral no-liposomal formulation (92% vs. 86 %, respectively; p < 0.05). Finally, our study showed that the liposomal formulation was able to realize a delivery system of a water-insoluble drug, providing a Gimatecan formulation for intravenous administration with a preserved antitumoral activity.

AK37: the first pyridoacridine described capable of stabilizing the topoisomerase I cleavable complex

Pyridoacridines are marine natural products that contain planar structures. Almost all are cytotoxic and capable of DNA intercalation. Several pyridoacridines have demonstrated anti-cancer activity, being able to generate reactive oxygen species or to inhibit topoisomerase (Topo) II. Synthetic pyridoacridines were characterized and compared to other pyridoacridines as well as the Topo-inhibiting drugs (etoposide, 9-aminocamptothecin and wakayin) in a series of in vitro enzyme systems. We found AK37 was able to stabilize a DNA-Topo I cleavable complex, but not a DNA-Topo II cleavable complex. To our knowledge, this is the first report of a DNA-Topo I cleavable complex stabilizing pyridoacridine. Structure comparison studies demonstrated that this activity was lost when an extra 'F' ring was added, but activity was not affected when the 'D' ring was removed. AK37 inhibited the catalytic activity of both human Topo I and II.

DNA and the chromosome - varied targets for chemotherapy

The nucleus of the cell serves to maintain, regulate, and replicate the critical genetic information encoded by the genome. Genomic DNA is highly associated with proteins that enable simple nuclear structures such as nucleosomes to form higher-order organisation such as chromatin fibres. The temporal association of regulatory proteins with DNA creates a dynamic environment capable of quickly responding to cellular requirements and distress. The response is often mediated through alterations in the chromatin structure, resulting in changed accessibility of specific DNA sequences that are then recognized by specific proteins. Anti-cancer drugs that target cellular DNA have been used clinically for over four decades, but it is only recently that nuclease specific drugs have been developed to not only target the DNA but also other components of the nuclear structure and its regulation. In this review, we discuss some of the new drugs aimed at primary DNA sequences, DNA secondary structures, and associated proteins, keeping in mind that these agents are not only important from a clinical perspective but also as tools for understanding the nuclear environment in normal and cancer cells.

A phase I and pharmacokinetic study of MAG-CPT, a water-soluble polymer conjugate of camptothecin

Polymeric drug conjugates are a new and experimental class of drug delivery systems with pharmacokinetic promises. The antineoplastic drug camptothecin was linked to a water-soluble polymeric backbone (MAG-CPT) and administrated as a 30 min infusion over 3 consecutive days every 4 weeks to patients with malignant solid tumours. The objectives of our study were to determine the maximal tolerated dose, the dose-limiting toxicities, and the plasma and urine pharmacokinetics of MAG-CPT, and to document anti-tumour activity. The starting dose was 17 mg m(-2) day(-1). Sixteen patients received 39 courses at seven dose levels. Maximal tolerated dose was at 68 mg m(-2) day(-1) and dose-limiting toxicities consisted of cumulative bladder toxicity. MAG-CPT and free camptothecin were accumulated during days 1-3 and considerable amounts of MAG-CPT could still be retrieved in plasma and urine after 4-5 weeks. The half-lives of bound and free camptothecin were equal indicating that the kinetics of free camptothecin were release rate dependent. In summary, the pharmacokinetics of camptothecin were dramatically changed, showing controlled prolonged exposure of camptothecin. Haematological toxicity was relatively mild, but serious bladder toxicity was encountered which is typical for camptothecin and was found dose limiting.

The development of camptothecin analogs in childhood cancers

Camptothecin analogs, agents that target the intranuclear enzyme topoisomerase I, represent a promising new class of anticancer drugs for the treatment of childhood cancer. In preclinical studies, camptothecins, such as topotecan and irinotecan, are highly active against a variety of pediatric malignancies including neuroblastomas, rhabdomyosarcomas, gliomas, and medulloblastomas. In this paper, we review the status of completed and ongoing clinical trials and pharmacokinetic studies of camptothecin analogs in children. These and future planned studies of this novel class of cytotoxic agents are critical to defining the ultimate role of topoisomerase I poisons in the treatment of childhood cancer.

Effect of P-glycoprotein modulators on the pharmacokinetics of camptothecin using microdialysis

1. By performing microdialysis, this study investigated the pharmacokinetics of unbound camptothecin in rat blood, brain and bile in the presence of P-glycoprotein mediated transport modulators (cyclosporin A, berberine, quercetin, naringin and naringenin). Pharmacokinetic parameters of camptothecin were assessed using a non-compartmental model. 2. Camptothecin rapidly crosses the blood-brain barrier (BBB) within 20 min after camptothecin administration. The disposition of camptothecin in rat bile appeared to have a slow elimination phase and a peak concentration after 20 min of camptothecin administration. The area under the concentration versus time curve (AUC) for camptothecin in bile significantly surpassed that in blood, suggesting active transport of hepatobiliary excretion. 3. In the presence of cyclosporin A camptothecin AUC, in the brain, was significantly elevated but no significant change in the presence of berberine, quercetin, naringin and naringenin. 4. With treatment by smaller doses of quercetin (0.1 mg x kg(-1)), naringin (10 mg x kg(-1)) and naringenin (10 mg x kg(-1)), they significantly diminished the camptothecin AUC in bile, but was not altered by the treatment of berberine (20 mg x kg(-1)), a higher dose of quercetin (10 mg x kg(-1)), and cyclosporin A treated (20 mg x kg(-1)) and pretreated groups. 5. The distribution ratio (AUC(bile)/AUC(blood)) of camptothecin in bile was decreased in the cyclosporin A, quercetin, naringin and naringenin treated groups. However, the distribution ratio in the brain was increased in the cyclosporin A groups, but was decreased in the groups treated with quercetin, naringin and naringenin. These results revealed that P-glycoprotein might modulate hepatobiliary excretion and BBB penetration of camptothecin.

Structure-activity relationship of alkyl camptothecin esters

The cytotoxicity of camptothecin (CPT) esters 1-6 was measured. Like parental camptothecin, esters 2 and 3, but not 1, 4, 5, and 6, inhibited proliferation of human leukemia cells in culture and induced programmed cell death as assessed by flow cytometry studies. Exhibition of similar levels of antiproliferative activities of CPT 2 and 3 required different incubation time periods in cell cultures, with CPT and 3 requiring the shortest and longest periods, respectively. Both 2 and 3 were inactive against cells resistant to the semisynthetic CPT derivative 9-nitrocamptothecin and unable to stabilize DNA-topoisomerase I (Topo I) "cleavable complexes" in a cell-free system, suggesting that Topo I activity was required but insufficient for the mechanism of action of 2 and 3. Mouse liver homogenate converted esters to parental CPT, but the conversion rates were different with different esters. Of four tested esters in this experiment, ester 2 had the fastest conversion rate. In vivo studies showed that ester 2 had an exceptional lack of toxicity in nude mice, even at enormous doses, and demonstrated extensive activity against human breast and colon tumors grown as xenografts in immunodeficient nude mice, whereas no antitumor activity was observed for the other esters. In conclusion, ester 2 is a prodrug of the antitumor compound CPT, and it can be administered at very high doses in mice with no appearance of toxicity. This study provides a basis for further evaluation of CPT ester 2 as an investigational anticancer agent.

Molecular and biological determinants of the cytotoxic actions of camptothecins. Perspective for the development of new topoisomerase I inhibitors

Camptothecin, originally discovered in 1957 as an antitumor activity in plant extracts, has recently become one of the most promising leads to new anticancer drugs. After lingering for many years, interest in camptothecin was revitalized in 1985 upon discovery of its specific action on topoisomerase I. Detailed elucidation of action mechanisms at the molecular, cellular, and pharmacologic levels has made camptothecin and its congeners perhaps the best understood among clinical anticancer drugs. Promising chemical variants of camptothecin, and recently other chemical categories of topoisomerase I-targeted drugs, provide unusually rich opportunities for rational drug selection and design. This is made possible by current concepts based, for the most part, on a sound experimental foundation, which points the way towards optimally effective therapy.

Propionate and butyrate esters of camptothecin and 9-nitrocamptothecin as antileukemia prodrugs in vitro

Six camptothecin (CPT) alkyl esters and four 9-nitrocamptothecin (9NC) alkyl esters were assayed for ability to inhibit proliferation and induce programmed cell death (apoptosis) in human leukemia HL-60 and U-937 cells, which exhibit differential sensitivity to CPT and 9NC. In general, CPT-propionate and CPT-butyrate demonstrated activities, while the other esters were practically inactive. Similarly, 9NC-propionate and 9NC-butyrate were active, while the other 9NC esters exhibited little or no activity. The biologically active esters required metabolic conversion (i.e., de-esterification) to their parental compounds as demonstrated by the conversion of CPT-propionate to CPT in mouse liver homogenate, and the topoisomerase I-inhibition assay. In conclusion, the propionate and butyrate esters of CPT and 9NC are CPT and 9NC prodrugs, that can develop to important chemotherapeutic agents for the effective treatment of human leukemias and other malignancies.

Water-insoluble camptothecin analogues as potential antiviral drugs

In addition to being causative agents of infectious diseases in animals and humans, DNA viruses have served as models for the study of eukaryotic molecular mechanisms including replication and transcription. Studies of DNA virus functions utilizing cell-free systems and virus-infected cells in culture, in the presence of the anticancer drug camptothecin (CPT), have demonstrated that CPT is a potent inhibitor of replication, transcription and packaging of double-stranded DNA-containing adenoviruses, papovaviruses and herpesviruses, and the single- stranded DNA-containing autonomous parvoviruses. CPT inhibits viral functions by inhibiting topoisomer- ase I, a host cell enzyme required for initiation and completion of the viral functions. These findings indicate that CPT analogues could be developed for use as potent drugs against DNA viruses.

Clinical pharmacokinetics of irinotecan

This article reviews the clinical pharmacokinetics of a water-soluble analogue of camptothecin, irinotecan [CPT-11 or 7-ethyl-10-[4-(1-piperidino)-1-piperidino]-carbonyloxy-camptoth eci n]. Irinotecan, and its more potent metabolite SN-38 (7- ethyl-10-hydroxy-camptothecin), interfere with mammalian DNA topoisomerase I and cancer cell death appears to result from DNA strand breaks caused by the formation of cleavable complexes. The main clinical adverse effects of irinotecan therapy are neutropenia and diarrhoea. Irinotecan has shown activity in leukaemia, lymphoma and the following cancer sites: colorectum, lung, ovary, cervix, pancreas, stomach and breast. Following the intravenous administration of irinotecan at 100 to 350 mg/m2, mean maximum irinotecan plasma concentrations are within the 1 to 10 mg/L range. Plasma concentrations can be described using a 2- or 3-compartment model with a mean terminal half-life ranging from 5 to 27 hours. The volume of distribution at steady-state (Vss) ranges from 136 to 255 L/m2, and the total body clearance is 8 to 21 L/h/m2. Irinotecan is 65% bound to plasma proteins. The areas under the plasma concentration-time curve (AUC) of both irinotecan and SN-38 increase proportionally to the administered dose, although interpatient variability is important. SN-38 levels achieved in humans are about 100-fold lower than corresponding irinotecan concentrations, but these concentrations are potentially important as SN-38 is 100- to 1000-fold more cytotoxic than the parent compound. SN-38 is 95% bound to plasma proteins. Maximum concentrations of SN-38 are reached about 1 hour after the beginning of a short intravenous infusion. SN-38 plasma decay follows closely that of the parent compound with an apparent terminal half-life ranging from 6 to 30 hours. In human plasma at equilibrium, the irinotecan lactone form accounts for 25 to 30% of the total and SN-38 lactone for 50 to 64%. Irinotecan is extensively metabolised in the liver. The bipiperidinocarbonylxy group of irinotecan is first removed by hydrolysis to yield the corresponding carboxylic acid and SN-38 by carboxyesterase. SN-38 can be converted into SN-38 glucuronide by hepatic UDP-glucuronyltransferase. Another recently identified metabolite is 7-ethyl-10-[4-N-(5-aminopentanoic acid)-1-piperidino]-carbonyloxy-camptothecin (APC). This metabolite is a weak inhibitor of KB cell growth and a poor inducer of topoisomerase I DNA-cleavable complexes (100-fold less potent than SN-38). Numerous other unidentified metabolites have been detected in bile and urine. The mean 24-hour irinotecan urinary excretion represents 17 to 25% of the administered dose. Recovery of SN-38 and its glucuronide in urine is low and represents 1 to 3% of the irinotecan dose. Cumulative biliary excretion is 25% for irinotecan, 2% for SN-38 glucuronide and about 1% for SN-38. The pharmacokinetics of irinotecan and SN-38 are not influenced by prior exposure to the parent drug. The AUC of irinotecan and SN-38 correlate significantly with leuco-neutropenia and sometimes with the intensity of diarrhoea. Certain hepatic function parameters have been correlated negatively with irinotecan total body clearance. It was noted that most tumour responses were observed at the highest doses administered in phase I trials, which indicates a dose-response relationship with this drug. In the future, these pharmacokinetic-pharmacodynamic relationships will undoubtedly prove useful in minimising the toxicity and maximise the likelihood of tumour response in patients.