The inefficiency of incisions of ecteinascidin 743-DNA adducts by the UvrABC nuclease and the unique structural feature of the DNA adducts can be used to explain the repair-dependent toxicities of this antitumor agent

HMGB3 and SUB1 Bind to and Facilitate the Repair of N2-Alkylguanine Lesions in DNA

N2-Alkyl-2'-deoxyguanosine (N2-alkyl-dG) is a major type of minor-groove DNA lesions arising from endogenous metabolic processes and exogenous exposure to environmental contaminants. The N2-alkyl-dG lesions, if left unrepaired, can block DNA replication and transcription and induce mutations in these processes. Nevertheless, the repair pathways for N2-alkyl-dG lesions remain incompletely elucidated. By utilizing a photo-cross-linking coupled with mass spectrometry-based quantitative proteomic analysis, we identified a series of candidate N2-alkyl-dG-binding proteins. We found that two of these proteins, i.e., high-mobility group protein B3 (HMGB3) and SUB1, could bind directly to N2-nBu-dG-containing duplex DNA in vitro and promote the repair of this lesion in cultured human cells. In addition, HMGB3 and SUB1 protected cells against benzo[a]pyrene-7,8-diol-9,10-epoxide (BPDE). SUB1 exhibits preferential binding to both the cis and trans diastereomers of N2-BPDE-dG over unmodified dG. On the other hand, HMGB3 binds favorably to trans-N2-BPDE-dG; the protein, however, does not distinguish cis-N2-BPDE-dG from unmodified dG. Consistently, genetic ablation of HMGB3 conferred diminished repair of trans-N2-BPDE-dG, but not its cis counterpart, whereas loss of SUB1 conferred attenuated repair of both diastereomers. Together, we identified proteins involved in the cellular sensing and repair of minor-groove N2-alkyl-dG lesions and documented a unique role of HMGB3 in the stereospecific recognition and repair of N2-BPDE-dG.

Convergent Formal Synthesis of Ecteinascidin 743

A concise formal synthesis of ecteinascidin 743 is described. Key features involve the coupling of the multisubstituted tetrahydroisoquinoline and phenylalaninol moieties via a regio- and stereoselective Pictet-Spengler cyclization as well as the subsequent chemoselective MOM protection of the phenol group, which opens a rapid access to the desirable pentacycle. The synthesis successfully delivered the advanced intermediate with the characteristic macrolactone from sesamol in 23 steps.

The Impact of Minor-Groove N2-Alkyl-2'-deoxyguanosine Lesions on DNA Replication in Human Cells

Endogenous metabolites and exogenous chemicals can induce covalent modifications on DNA, producing DNA lesions. The N² of guanine was shown to be a common alkylation site in DNA; however, not much is known about the influence of the size of the alkyl group in N²-alkyldG lesions on cellular DNA replication or how translesion synthesis (TLS) polymerases modulate DNA replication past these lesions in human cells. To answer these questions, we employ a robust shuttle vector method to investigate the impact of four N²-alkyldG lesions (i.e., with the alkyl group being a methyl, ethyl, n-propyl, or n-butyl group) on DNA replication in human cells. We find that replication through the N²-alkyldG lesions was highly efficient and accurate in HEK293T cells or isogenic CRISPR-engineered cells with deficiency in polymerase (Pol) ζ or Pol η. Genetic ablation of Pol ι, Pol κ, or Rev1, however, results in decreased bypass efficiencies and elicits substantial frequencies of G → A transition and G → T transversion mutations for these lesions. Moreover, further depletion of Pol ζ in Pol κ- or Pol ι-deficient cells gives rise to elevated rates of G → A and G → T mutations and substantially decreased bypass efficiencies. Cumulatively, we demonstrate that the error-free replication past the N²-alkyldG lesions is facilitated by a specific subset of TLS polymerases, and we find that longer alkyl chains in these lesions induce diminished bypass efficiency and fidelity in DNA replication.

Loss of CUL4A expression is underlying cisplatin hypersensitivity in colorectal carcinoma cells with acquired trabectedin resistance

Background:

Colorectal carcinoma (CRC) is the third most common cancer worldwide. Platinum-based anticancer compounds still constitute one mainstay of systemic CRC treatment despite limitations due to adverse effects and resistance development. Trabectedin has shown promising antitumor effects in CRC, however, again resistance development may occur. In this study, we aimed to develop strategies to circumvent or even exploit acquired trabectedin resistance in novel CRC treatment regimens.

Methods:

Human HCT116 CRC cells were selected for acquired trabectedin resistance in vitro and characterised by cell biological as well as bioinformatic approaches. In vivo xenograft experiments were conducted.

Results:

Selection of HCT116 cells for trabectedin resistance resulted in p53-independent hypersensitivity of the selected subline against cisplatin. Bioinformatic analyses of mRNA microarray data suggested deregulation of nucleotide excision repair and particularly loss of the ubiquitin ligase CUL4A in trabectedin-selected cells. Indeed, transient knockdown of CUL4A sensitised parental HCT116 cells towards cisplatin. Trabectedin selected but not parental HCT116 xenografts were significantly responsive towards cisplatin treatment.

Conclusions:

Trabectedin selection-mediated CUL4A loss generates an Achilles heel in CRC cancer cells enabling effective cisplatin treatment. Hence, inclusion of trabectedin in cisplatin-containing cancer treatment regimens might cause profound synergism based on reciprocal resistance prevention.

DNA Repair Endonucleases: Physiological Roles and Potential as Drug Targets

Genomic DNA is constantly exposed to endogenous and exogenous damaging agents. To overcome these damaging effects and maintain genomic stability, cells have robust coping mechanisms in place, including repair of the damaged DNA. There are a number of DNA repair pathways available to cells dependent on the type of damage induced. The removal of damaged DNA is essential to allow successful repair. Removal of DNA strands is achieved by nucleases. Exonucleases are those that progressively cut from DNA ends, and endonucleases make single incisions within strands of DNA. This review focuses on the group of endonucleases involved in DNA repair pathways, their mechanistic functions, roles in cancer development, and how targeting these enzymes is proving to be an exciting new strategy for personalized therapy in cancer.

Ecteinascidins. A review of the chemistry, biology and clinical utility of potent tetrahydroisoquinoline antitumor antibiotics

The ecteinascidin family comprises a number of biologically active compounds, containing two to three tetrahydroisoquinoline subunits. Although isolated from marine tunicates, these compounds share a common pentacyclic core with several antimicrobial compounds found in terrestrial bacteria. Among the tetrahydroisoquinoline natural products, ecteinascidin 743 (Et-743) stands out as the most potent antitumor antibiotics that it is recently approved for treatment of a number of soft tissue sarcomas. In this article, we will review the backgrounds, the mechanism of action, the biosynthesis, and the synthetic studies of Et-743. Also, the development of Et-743 as an antitumor drug is discussed.

Cancer wars: natural products strike back

Natural products have historically been a mainstay source of anticancer drugs, but in the 90's they fell out of favor in pharmaceutical companies with the emergence of targeted therapies, which rely on antibodies or small synthetic molecules identified by high throughput screening. Although targeted therapies greatly improved the treatment of a few cancers, the benefit has remained disappointing for many solid tumors, which revitalized the interest in natural products. With the approval of rapamycin in 2007, 12 novel natural product derivatives have been brought to market. The present review describes the discovery and development of these new anticancer drugs and highlights the peculiarities of natural product and new trends in this exciting field of drug discovery.

Comparison of in vitro and in vivo biological effects of trabectedin, lurbinectedin (PM01183) and Zalypsis® (PM00104)

This study: (i) investigated the in vitro cytotoxicity and mode of action of lurbinectedin (PM01183) and Zalypsis® (PM00104) compared with trabectedin in cell lines deficient in specific mechanisms of repair, (ii) evaluated their in vivo antitumor activity against a series of murine tumors and human xenografts. The antiproliferative activity, the DNA damage and the cell cycle perturbations induced by the three compounds on tumor lines were very similar. Nucleotide Excision Repair (NER) deficient cells were approximately fourfold more resistant to trabectedin, lurbinectedin and Zalypsis®. Cells deficient in non-homologous end joining (NHEJ), MRN complex and translesion synthesis (TLS) were slightly more sensitive to the three compounds (approximately fivefold) while cells deficient in homologous recombination (HR) were markedly more sensitive (150-200-fold). All three compounds showed a good antitumor activity in several in vivo models. Lurbinectedin and trabectedin had a similar pattern of antitumor activity in murine tumors and in xenografts, whereas Zalypsis® appeared to have a distinct spectrum of activity. The fact that no relationship whatsoever was found between the in vitro cytotoxic potency and the in vivo antitumor activity, suggests that in addition to direct cytotoxic mechanisms other host-mediated effects are involved in the in vivo pharmacological effects.

Analysis of DNA repair-related genes in breast cancer reveals CUL4A ubiquitin ligase as a novel biomarker of trabectedin response

Trabectedin is more active in nucleotide excision repair (NER)-efficient and homologous recombination repair (HRR)-deficient cells. As up to 25% of sporadic breast tumors present somatic inactivation of the HRR pathway (BRCAness phenotype), we sought to characterize trabectedin effect in BRCA1-proficient and BRCA1-null breast cancer cell lines. We evaluated whether HRR and NER gene expression correlates with trabectedin sensitivity and explored the response predictive value of the CUL4A ubiquitin ligase, which ubiquitinates NER pathway members. We characterized trabectedin cytotoxicity, cell-cycle effects, and BRCA1, BRCA2, XRCC3, XPG, ERCC1, and CUL4A expression in 10 breast cancer cell lines. Gene expression and trabectedin sensitivity association were determined in cell lines. Survival assays after trabectedin treatment were conducted in CUL4A-silenced BRCA1-proficient and -deficient cells. Because of limited phase II clinical trials evaluating trabectedin efficacy in patients with breast cancer, we assessed CUL4A immunohistochemical staining in a retrospective series of 118 sarcomas from trabectedin-treated patients to validate in vivo our in vitro observations. In cell lines, greater trabectedin sensitivity was associated with higher CUL4A expression and lower BRCA1/ERCC5, BRCA1/CUL4A, and XRCC3/CUL4A expression ratios. In agreement, BRCA1-deficient CUL4A-knockdown cells presented higher cell survival after trabectedin exposure than did scramble control cells. Lack of effect in BRCA1-proficient cells suggests that HRR impairment is key in CUL4A-mediated trabectedin sensitivity. High CUL4A expression in nontranslocation-related patients with sarcoma predicted improved progression-free survival [PFS; HR, 0.37; 95% confidence interval (CI), 0.20-0.68, P = 0.001] and overall survival (OS; HR, 0.44; 95% CI, 0.21-0.93, P = 0.026). Our observations support the notion of greater trabectedin activity in tumors exhibiting BRCAness and reveal CUL4A as a potential biomarker for definition of trabectedin target patients.

XPF-dependent DNA breaks and RNA polymerase II arrest induced by antitumor DNA interstrand crosslinking-mimetic alkaloids

Trabectedin and Zalypsis are two potent anticancer tetrahydroisoquinoline alkaloids that can form a covalent bond with the amino group of a guanine in selected triplets of DNA duplexes and eventually give rise to double-strand breaks. Using well-defined in vitro and in vivo assays, we show that the resulting DNA adducts stimulate, in a concentration-dependent manner, cleavage by the XPF/ERCC1 nuclease on the strand opposite to that bonded by the drug. They also inhibit RNA synthesis by: (1) preventing binding of transcription factors like Sp1 to DNA, and (2) arresting elongating RNA polymerase II at the same nucleotide position regardless of the strand they are located on. Structural models provide a rationale for these findings and highlight the similarity between this type of DNA modification and an interstrand crosslink.

Characterization of a new trabectedin-resistant myxoid liposarcoma cell line that shows collateral sensitivity to methylating agents

Myxoid Liposarcomas (MLS), characterized by the expression of FUS-CHOP fusion gene are clinically very sensitive to the DNA binding antitumor agent, trabectedin. However, resistance eventually occurs, preventing disease eradication. To investigate the mechanisms of resistance, a trabectedin resistant cell line, 402-91/ET, was developed. The resistance to trabectedin was not related to the expression of MDR related proteins, uptake/efflux of trabectedin or GSH levels that were similar in parental and resistant cells. The 402-91/ET cells were hypersensitive to UV light because of a nucleotide excision repair defect: XPG complementation decreased sensitivity to UV rays, but only partially to trabectedin. 402-91/ET cells showed collateral sensitivity to temozolomide due to the lack of O(6) -methylguanine-DNA-methyltransferase (MGMT) activity, related to the hypermethylation of MGMT promoter. In 402-91 cells chromatin immunoprecipitation (ChIP) assays showed that FUS-CHOP was bound to the PTX3 and FN1 gene promoters, as previously described, and trabectedin caused FUS-CHOP detachment from DNA. Here we report that, in contrast, in 402-91/ET cells, FUS-CHOP was not bound to these promoters. Differences in the modulation of transcription of genes involved in different pathways including signal transduction, apoptosis and stress response between the two cell lines were found. Trabectedin activates the transcription of genes involved in the adipogenic-program such as c/EBPα and β, in 402-91 but not in 402-91/ET cell lines. The collateral sensitivity of 402-91/ET to temozolomide provides the rationale to investigate the potential use of methylating agents in MLS patients resistant to trabectedin.

Ecteinascidin 743 interferes with the activity of EWS-FLI1 in Ewing sarcoma cells

ET-743 (trabectedin; Yondelis) is approved in Europe for the treatment of soft tissue sarcomas. Emerging phase 1 and 2 clinical data have shown high response rates in myxoid liposarcoma in part owing to the inhibition of the FUS-CHOP transcription factor. In this report, we show that modulation of specific oncogenic transcription factors by ET-743 may extend to other tumor types. We demonstrate that, among a panel of pediatric sarcomas, Ewing sarcoma family of tumors (ESFTs) cell lines bearing the EWS-FLI1 transcription factor are the most sensitive to treatment with ET-743 compared with osteosarcoma, rhabdomyosarcoma, and synovial sarcoma. We show that ET-743 reverses a gene signature of induced downstream targets of EWS-FLI1 in two different ESFT cell lines (P = .001). In addition, ET-743 directly suppresses the promoter activity of a known EWS-FLI1 downstream target NR0B1 luciferase reporter construct without changing the activity of a constitutively active control in ESFT cells. Furthermore, the effect is specific to EWS-FLI1, as forced expression of EWS-FLI1 in a cell type that normally lacks this fusion protein, HT1080 cells, induces the same NR0B1 promoter, but this activation is completely blocked by ET-743 treatment. Finally, we used gene set enrichment analysis to confirm that other mechanisms of ET-743 are active in ESFT cells. These results suggest a particular role for ET-743 in the treatment of translocation-positive tumors. In addition, the modulation of EWS-FLI1 makes it a novel targeting agent for ESFT and suggests that further development of this compound for the treatment of ESFT is warranted.

The roles of DNA polymerases κ and ι in the error-free bypass of N2-carboxyalkyl-2'-deoxyguanosine lesions in mammalian cells

To counteract the deleterious effects of DNA damage, cells are equipped with specialized polymerases to bypass DNA lesions. Previous biochemical studies revealed that DinB family DNA polymerases, including Escherichia coli DNA polymerase IV and human DNA polymerase κ, efficiently incorporate the correct nucleotide opposite some N(2)-modified 2'-deoxyguanosine derivatives. Herein, we used shuttle vector technology and demonstrated that deficiency in Polk or Poli in mouse embryonic fibroblast (MEF) cells resulted in elevated frequencies of G→T and G→A mutations at N(2)-(1-carboxyethyl)-2'-deoxyguanosine (N(2)-CEdG) and N(2)-carboxymethyl-2'-deoxyguanosine (N(2)-CMdG) sites. Steady-state kinetic measurements revealed that human DNA polymerase ι preferentially inserts the correct nucleotide, dCMP, opposite N(2)-CEdG lesions. In contrast, no mutation was found after the N(2)-CEdG- and N(2)-CMdG-bearing plasmids were replicated in POLH-deficient human cells or Rev3-deficient MEF cells. Together, our results revealed that, in mammalian cells, both polymerases κ and ι are necessary for the error-free bypass of N(2)-CEdG and N(2)-CMdG. However, in the absence of polymerase κ or ι, other translesion synthesis polymerase(s) could incorporate nucleotide(s) opposite these lesions but would do so inaccurately.

Modern natural products drug discovery and its relevance to biodiversity conservation

Natural products continue to provide a diverse and unique source of bioactive lead compounds for drug discovery, but maintaining their continued eminence as source compounds is challenging in the face of the changing face of the pharmaceutical industry and the changing nature of biodiversity prospecting brought about by the Convention on Biological Diversity. This review provides an overview of some of these challenges and suggests ways in which they can be addressed so that natural products research can remain a viable and productive route to drug discovery. Results from International Cooperative Biodiversity Groups (ICBGs) working in Madagascar, Panama, and Suriname are used as examples of what can be achieved when biodiversity conservation is linked to drug discovery.

Synthetic study toward ecteinascidin 743: concise construction of the diazabicyclo[3.3.1]nonane skeleton and assembly of the pentacyclic core

Synthesis of the pentacyclic core of ecteinascidin 743 is described. This synthesis features concise construction of the diazabicyclo[3.3.1]nonane skeleton using gold(I)-catalyzed one-pot keto amide formation, acid-promoted enamide formation, and oxidative Friedel-Crafts cyclization as the key steps.

Wide-spectrum characterization of trabectedin: biology, clinical activity and future perspectives

Ecteinascidin-743 (trabectedin, Yondelis®; PharmaMar, Madrid, Spain), a 25-year-old antineoplastic alkylating agent, has recently shown unexpected and interesting mechanisms of action. Trabectedin causes perturbation in the transcription of inducible genes (e.g., the multidrug resistance gene MDR1) and interaction with DNA repair mechanisms (e.g., the nucleotide excision repair pathway) owing to drug-related DNA double strand breaks and adduct formation. Trabectedin was the first antineoplastic agent from a marine source (namely, the Caribbean tunicate Ecteinascidia turbinata) to receive marketing authorization. This article summarizes the mechanisms of action, the complex metabolism, the main toxicities, the preclinical and clinical evidences of its antineoplastic effects in different types of cancer and, finally, the future perspectives of this promising drug.

Large, sequence-dependent effects on DNA conformation by minor groove binding compounds

To determine what topological changes antiparasitic heterocyclic dications can have on kinetoplast DNA, we have constructed ligation ladders, with phased A5 and ATATA sequences in the same flanking sequence context, as models. Bending by the A5 tract is observed, as expected, while the ATATA sequence bends DNA very little. Complexes of these DNAs with three diamidines containing either furan, thiophene or selenophene groups flanked by phenylamidines were investigated along with netropsin. With the bent A5 ladder the compounds caused either a slight increase or decrease in the bending angle. Surprisingly, however, with ATATA all of the compounds caused significant bending, to values close to or even greater than the A5 bend angle. Results with a mixed cis sequence, which has one A5 and one ATATA, show that the compounds bend ATATA in the same direction as a reference A5 tract, that is, into the minor groove. These results are interpreted in terms of a groove structure for A5 which is largely pre-organized for a fit to the heterocyclic amidines. With ATATA the groove is intrinsically wider and must close to bind the compounds tightly. The conformational change at the binding site then leads to significant bending of the alternating DNA sequence.

Zalypsis (PM00104) is a potent inducer of gamma-H2AX foci and reveals the importance of the C ring of trabectedin for transcription-coupled repair inhibition

Zalypsis (PM00104) is a novel tetrahydroisoquinoline alkaloid related to trabectedin [ecteinascidin 743 (Et743)]. Et743 and PM00104 have similar A and B rings but differ in their C rings. The present study shows that Et743 and PM00104 differ in at least two ways: in their DNA binding properties and nucleotide excision repair (NER) dependency for cellular targeting. DNase I footprinting shows that the two drugs bind DNA differentially. We also found that, in contrast to Et743, the antiproliferative activity of PM00104 does not depend on transcription-coupled NER. Accordingly, PM00104 induces gamma-H2AX foci with the same efficiency in NER-deficient or NER-proficient cells. Moreover, the formation of gamma-H2AX foci is replication dependent for PM00104, whereas it is both transcription and replication dependent in the case of Et743. These findings show the importance of the C ring structure of tetrahydroisoquinoline ecteinascidin derivatives for NER targeting. Finally, PM00104 exerts antiproliferative activity at nanomolar concentrations and induces gamma-H2AX response in two Ewing's sarcoma cell lines, suggesting that gamma-H2AX could serve as a pharmacodynamic biomarker for the clinical development of PM00104.

Induction of glutathione-dependent DNA double-strand breaks by the novel anticancer drug brostallicin

Brostallicin is a DNA minor groove binder in phase II clinical trials. Here, we show that brostallicin induces gamma-H2AX nuclear foci that colocalize with 53BP1 and are dependent on glutathione, as shown by inhibition of those gamma-H2AX foci by l-buthionine sulfoximine. To differentiate brostallicin from the clinically approved minor groove binder trabectedin (ecteinascidin 743), we tested whether the brostallicin-induced gamma-H2AX and antiproliferative responses were dependent on nucleotide excision repair and found that, unlike trabectedin, they are not. Additionally, brostallicin retained activity in the trabectedin-resistant HCT116-ER5 cell line. Induction of gamma-H2AX foci by brostallicin was partially dependent on the repair nuclease Mre11. Pretreatment with aphidicolin partially reduced brostallicin-induced gamma-H2AX foci, suggesting that brostallicin induces both replication-associated and replication-independent DNA damage. Replication-associated DNA damage was further shown by the colocalization of gamma-H2AX foci with replication foci and by the rapid inhibition of DNA synthesis and accumulation of cells in S phase in response to brostallicin. In addition, brostallicin was able to induce lower intensity gamma-H2AX foci in human circulating lymphocytes. Together, our results indicate that brostallicin induces DNA double-strand breaks and suggest gamma-H2AX as a pharmacodynamic biomarker for brostallicin.

Nucleotide excision repair is a predominant mechanism for processing nitrofurazone-induced DNA damage in Escherichia coli

Nitrofurazone is reduced by cellular nitroreductases to form N(2)-deoxyguanine (N(2)-dG) adducts that are associated with mutagenesis and lethality. Much attention recently has been given to the role that the highly conserved polymerase IV (Pol IV) family of polymerases plays in tolerating adducts induced by nitrofurazone and other N(2)-dG-generating agents, yet little is known about how nitrofurazone-induced DNA damage is processed by the cell. In this study, we characterized the genetic repair pathways that contribute to survival and mutagenesis in Escherichia coli cultures grown in the presence of nitrofurazone. We find that nucleotide excision repair is a primary mechanism for processing damage induced by nitrofurazone. The contribution of translesion synthesis to survival was minor compared to that of nucleotide excision repair and depended upon Pol IV. In addition, survival also depended on both the RecF and RecBCD pathways. We also found that nitrofurazone acts as a direct inhibitor of DNA replication at higher concentrations. We show that the direct inhibition of replication by nitrofurazone occurs independently of DNA damage and is reversible once the nitrofurazone is removed. Previous studies that reported nucleotide excision repair mutants that were fully resistant to nitrofurazone used high concentrations of the drug (200 microM) and short exposure times. We demonstrate here that these conditions inhibit replication but are insufficient in duration to induce significant levels of DNA damage.

Mechanisms of drug combinations: interaction and network perspectives

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

Drug development from marine natural products

Drug discovery from marine natural products has enjoyed a renaissance in the past few years. Ziconotide (Prialt; Elan Pharmaceuticals), a peptide originally discovered in a tropical cone snail, was the first marine-derived compound to be approved in the United States in December 2004 for the treatment of pain. Then, in October 2007, trabectedin (Yondelis; PharmaMar) became the first marine anticancer drug to be approved in the European Union. Here, we review the history of drug discovery from marine natural products, and by describing selected examples, we examine the factors that contribute to new discoveries and the difficulties associated with translating marine-derived compounds into clinical trials. Providing an outlook into the future, we also examine the advances that may further expand the promise of drugs from the sea.

Von Hippel-Lindau-coupled and transcription-coupled nucleotide excision repair-dependent degradation of RNA polymerase II in response to trabectedin

PURPOSE

Ecteinascidin 743 (Et743; trabectedin, Yondelis) has recently been approved in Europe for the treatment of soft tissue sarcomas and is undergoing clinical trials for other solid tumors. Et743 selectively targets cells proficient for TC-NER, which sets it apart from other DNA alkylating agents. In the present study, we examined the effects of Et743 on RNA Pol II.

EXPERIMENTAL DESIGN AND RESULTS

We report that Et743 induces the rapid and massive degradation of transcribing Pol II in various cancer cell lines and normal fibroblasts. Pol II degradation was abrogated by the proteasome inhibitor MG132 and was dependent on TC-NER. Cockayne syndrome (CS) cells and xeroderma pigmentosum (XP) cells (XPD, XPA, XPG, and XPF) were defective in Pol II degradation, whereas XPC cells whose defect is limited to global genome NER in nontranscribing regions were proficient for Pol II degradation. Complementation of the CSB and XPD cells restored Pol II degradation. We also show that cells defective for the VHL complex were defective in Pol II degradation and that complementation of those cells restores Pol II degradation. Moreover, VHL deficiency rendered cells resistant to Et743-induced cell death, a similar effect to that of TC-NER deficiency.

CONCLUSION

These results suggest that both TC-NER-induced and VHL-mediated Pol II degradation play a role in cell killing by Et743.

Transcription-coupled DNA double-strand breaks are mediated via the nucleotide excision repair and the Mre11-Rad50-Nbs1 complex

The cellular activity of Yondelis (trabectedin, Ecteinascidin 743, Et743) is known to depend on transcription-coupled nucleotide excision repair (TCR). However, the subsequent cellular effects of Et743 are not fully understood. Here we show that Et743 induces both transcription- and replication-coupled DNA double-strand breaks (DSBs) that are detectible by neutral COMET assay and as gamma-H2AX foci that colocalize with 53BP1, Mre11, Ser(1981)-pATM, and Thr(68)-pChk2. The transcription coupled-DSBs (TC-DSBs) induced by Et743 depended both on TCR and Mre11-Rad50-Nbs1 (MRN) and were associated with DNA-PK-dependent gamma-H2AX foci. In contrast to DNA-PK, ATM phosphorylated H2AX both in NER-proficient and -deficient cells, but its full activation was dependent on H2AX as well as DNA-PK, suggesting a positive feedback loop: DNA-PK-gamma-H2AX-ATM. Knocking-out H2AX or inactivating DNA-PK reduced Et743's antiproliferative activity, whereas ATM and MRN tended to act as survival factors. Our results highlight the interplays between ATM and DNA-PK and their impacts on H2AX phosphorylation and cell survival. They also suggest that gamma-H2AX may serve as a biomarker in patients treated with Et743 and that molecular profiling of tumors for TCR, MRN, ATM, and DNA-PK might be useful to anticipate tumor response to Et743 treatment.

Relevance of the Fanconi anemia pathway in the response of human cells to trabectedin

Trabectedin (Yondelis; ET-743) is a potent anticancer drug that binds to DNA by forming a covalent bond with a guanine in one strand and one or more hydrogen bonds with the opposite strand. Using a fluorescence-based melting assay, we show that one single trabectedin-DNA adduct increases the thermal stability of the double helix by >20 degrees C. As deduced from the analysis of phosphorylated H2AX and Rad51 foci, we observed that clinically relevant doses of trabectedin induce the formation of DNA double-strand breaks in human cells and activate homologous recombination repair in a manner similar to that evoked by the DNA interstrand cross-linking agent mitomycin C (MMC). Because one important characteristic of this drug is its marked cytotoxicity on cells lacking a functional Fanconi anemia (FA) pathway, we compared the response of different subtypes of FA cells to MMC and trabectedin. Our data clearly show that human cells with mutations in FANCA, FANCC, FANCF, FANCG, or FANCD1 genes are highly sensitive to both MMC and trabectedin. However, in marked contrast to MMC, trabectedin does not induce any significant accumulation of FA cells in G2-M. The critical relevance of FA proteins in the response of human cells to trabectedin reported herein, together with observations showing the role of the FA pathway in cancer suppression, strongly suggest that screening for mutations in FA genes may facilitate the identification of tumors displaying enhanced sensitivity to this novel anticancer drug.

Role of homologous recombination in trabectedin-induced DNA damage

Trabectedin (ET-743, Yondelis) is a natural marine compound with antitumour activity currently undergoing phase II/III clinical trials. The mechanism of the drug's action is still to be defined, even though it has been clearly demonstrated the key role of Nucleotide Excision Repair (NER). To get further insights into the drug's mode of action, we studied the involvement of the DNA-double strand break repair (DNA-DSB) pathways: homologous and non-homologous recombination, both in budding yeasts and in mammalian cells and the possible cross-talk between NER and these repair pathways. Budding yeasts and mammalian cells deficient in the non-homologous end-joining pathway were moderately sensitive to trabectedin, while systems deficient in the homologous recombination pathway were extremely sensitive to the drug, with a 100-fold decrease in the IC50, suggesting that trabectedin-induced lesions are repaired by this pathway. The induction of Rad51 foci and the appearance of gamma-H2AX were chosen as putative markers for DNA-DSBs and were studied at different time points after trabectedin treatment in NER proficient and deficient systems. Both were clearly detected only in the presence of an active NER, suggesting that the DSBs are not directly caused by the drug, but are formed during the processing/repair of the drug- induced lesions.

Dynamics of cell cycle phase perturbations by trabectedin (ET-743) in nucleotide excision repair (NER)-deficient and NER-proficient cells, unravelled by a novel mathematical simulation approach

OBJECTIVES

Trabectedin (ET-743, Yondelis) is a natural marine product, with antitumour activity, currently in phase II/III clinical trials. Previous studies have shown that cells hypersensitive to ultraviolet (UV)-rays because of nucleotide excision repair (NER) deficiency, were resistant to trabectedin. The purpose of this study was to investigate whether this resistance was associated with different drug-induced cell cycle perturbations.

MATERIALS AND METHODS

An isogenic NER-proficient cellular system (CHO-AA8) and a NER-deficient one (CHO-UV-96), lacking functional ERCC-1, were studied. Flow cytometric assays showed progressive accumulation of cells in G2 + M phase in NER-proficient but not in NER-deficient cells. Applying a computer simulation method, we realized that the dynamics of the cell cycle perturbations in all phases were complex.

RESULTS

Cells exposed to trabectedin during G1 and G2 + M first experienced a G1 block, while those exposed in S phase were delayed in S and G2 + M phases but eventually divided. In the presence of functional NER, exit from the G1 block was faster; then, cells progressed slowly through S phase and were subsequently blocked in G2 + M phase. This G2 + M processing of trabectedin-induced damage in NER-proficient cells was unable to restore cell cycling, suggesting a difficulty in repairing the damage.

CONCLUSIONS

This might be due either to important damage left unrepaired by previous G1 repair, or that NER activity itself caused DNA damage, or both. We speculate that in UV-96 cells repair mechanisms other than NER are activated both in G1 and G2 + M phases.

Replication and homologous recombination repair regulate DNA double-strand break formation by the antitumor alkylator ecteinascidin 743

Adducts induced by the antitumor alkylator ecteinascidin 743 (ET-743, Yondelis, trabectedin) represent a unique challenge to the DNA repair machinery because no pathway examined to date is able to remove the ET adducts, whereas cells deficient in nucleotide excision repair show increased resistance. We here describe the processing of the initial ET adducts into cytotoxic lesions and characterize the influence of cellular repair pathways on this process. Our findings show that exposure of proliferating mammalian cells to pharmacologically relevant concentrations of ET-743 is accompanied by rapid formation of DNA double-strand breaks (DSBs), as shown by the neutral comet assay and induction of focalized phosphorylated H2AX. The ET adducts are stable and can be converted into DSBs hours after the drug has been removed. Loss of homologous recombination repair has no influence on the initial levels of DSBs but is associated with the persistence of unrepaired DSBs after ET-743 is removed, resulting in extensive chromosomal abnormalities and pronounced sensitivity to the drug. In comparison, loss of nonhomologous end-joining had only modest effect on the sensitivity. The identification of DSB formation as a key step in the processing of ET-743 lesions represents a novel mechanism of action for the drug that is in agreement with its unusual potency. Because loss of repair proteins is common in human tumors, expression levels of selected repair factors may be useful in identifying patients particularly likely to benefit, or not, from treatment with ET-743.

Characterization of SafC, a catechol 4-O-methyltransferase involved in saframycin biosynthesis

Members of the saframycin/safracin/ecteinascidin family of peptide natural products are potent antitumor agents currently under clinical development. Saframycin MX1, from Myxococcus xanthus, is synthesized by a nonribosomal peptide synthetase, SafAB, and an O-methyltransferase, SafC, although other proteins are likely involved in the pathway. SafC was overexpressed in Escherichia coli, purified to homogeneity, and assayed for its ability to methylate a variety of substrates. SafC was able to catalyze the O-methylation of catechol derivatives but not phenols. Among the substrates tested, the best substrate for SafC was L-dihydroxyphenylalanine (L-dopa), which was methylated specifically in the 4'-O position (k(cat)/K(m) = 5.5 x 10(3) M(-1) s(-1)). SafC displayed less activity on other catechol derivatives, including catechol, dopamine, and caffeic acid. The more labile l-5'-methyldopa was an extremely poor substrate for SafC (k(cat)/K(m) = approximately 2.8 x 10(-5) M(-1) s(-1)). L-dopa thioester derivatives were also much less reactive than L-dopa. These results indicate that SafC-catalyzed 4'-O-methylation of L-dopa occurs prior to 5'-C-methylation, suggesting that 4'-O-methylation is likely the first committed step in the biosynthesis of saframycin MX1. SafC has biotechnological potential as a methyltransferase with unique regioselectivity.

Cross-Talk between Nucleotide Excision and Homologous Recombination DNA Repair Pathways in the Mechanism of Action of Antitumor Trabectedin

Trabectedin (Yondelis) is a potent antitumor drug that has the unique characteristic of killing cells by poisoning the DNA nucleotide excision repair (NER) machinery. The basis for the NER-dependent toxicity has not yet been elucidated but it has been proposed as the major determinant for the drug's cytotoxicity. To study the in vivo mode of action of trabectedin and to explore the role of NER in its cytotoxicity, we used the fission yeast Schizosaccharomyces pombe as a model system. Treatment of S. pombe wild-type cells with trabectedin led to cell cycle delay and activation of the DNA damage checkpoint, indicating that the drug causes DNA damage in vivo. DNA damage induced by the drug is mostly caused by the NER protein, Rad13 (the fission yeast orthologue to human XPG), and is mainly repaired by homologous recombination. By constructing different rad13 mutants, we show that the DNA damage induced by trabectedin depends on a 46-amino acid region of Rad13 that is homologous to a DNA-binding region of human nuclease FEN-1. More specifically, an arginine residue in Rad13 (Arg961), conserved in FEN1 (Arg314), was found to be crucial for the drug's cytotoxicity. These results lead us to propose a model for the action of trabectedin in eukaryotic cells in which the formation of a Rad13/DNA-trabectedin ternary complex, stabilized by Arg961, results in cell death.

Inhibition of RecBCD enzyme by antineoplastic DNA alkylating agents

To understand how bulky adducts might perturb DNA helicase function, three distinct DNA-binding agents were used to determine the effects of DNA alkylation on a DNA helicase. Adozelesin, ecteinascidin 743 (Et743) and hedamycin each possess unique structures and sequence selectivity. They bind to double-stranded DNA and alkylate one strand of the duplex in cis, adding adducts that alter the structure of DNA significantly. The results show that Et743 was the most potent inhibitor of DNA unwinding, followed by adozelesin and hedamycin. Et743 significantly inhibited unwinding, enhanced degradation of DNA, and completely eliminated the ability of the translocating RecBCD enzyme to recognize and respond to the recombination hotspot chi. Unwinding of adozelesin-modified DNA was accompanied by the appearance of unwinding intermediates, consistent with enzyme entrapment or stalling. Further, adozelesin also induced "apparent" chi fragment formation. The combination of enzyme sequestering and pseudo-chi modification of RecBCD, results in biphasic time-courses of DNA unwinding. Hedamycin also reduced RecBCD activity, albeit at increased concentrations of drug relative to either adozelesin or Et743. Remarkably, the hedamycin modification resulted in constitutive activation of the bottom-strand nuclease activity of the enzyme, while leaving the ability of the translocating enzyme to recognize and respond to chi largely intact. Finally, the results show that DNA alkylation does not significantly perturb the allosteric interaction that activates the enzyme for ATP hydrolysis, as the efficiency of ATP utilization for DNA unwinding is affected only marginally. These results taken together present a unique response of RecBCD enzyme to bulky DNA adducts. We correlate these effects with the recently determined crystal structure of the RecBCD holoenzyme bound to DNA.

ET-743: a novel agent with activity in soft-tissue sarcomas

PURPOSE OF REVIEW

ET-743 (ecteinascidin-743, trabectedin, Yondelis) is a natural marine product that has shown clinical activity in sarcoma. This paper reviews the current knowledge on this compound.

RECENT FINDINGS

ET-743 interferes with several transcription factors, traps protein from the nucleotide-excision repair system, thus resulting in DNA damage, modulates gene expression, and blocks cells in the G2-M phase. In the clinical setting, after failure of standard treatment, ET-743 at 1.5 mg/m2 in 24 h continuous infusion every 21 days yielded an overall response rate close to 8% and stabilization rates of 30-40%, some lasting beyond 3 years. Leiomyosarcomas, liposarcomas, and synovial sarcomas may be the more sensitive histotypes. The major toxicities of ET-743 are hepatic--through biliary duct destruction--and hematologic. They are not cumulative and a significant number of patients may receive 12 courses or more. In a randomized Phase II study testing weekly ET-743 with treatment every 3 weeks, an improved progression-free survival rate was observed in the 3-weekly arm; the results of the follow-up Phase III trial should be available at the American Society of Clinical Oncology meeting of 2006. Phase I combination studies are in currently progress.

SUMMARY

ET-743 is a novel active drug for sarcoma which yields prolonged disease-free survival in subsets of patients.

A single amino acid governs enhanced activity of DinB DNA polymerases on damaged templates

Translesion synthesis (TLS) by Y-family DNA polymerases is a chief mechanism of DNA damage tolerance. Such TLS can be accurate or error-prone, as it is for bypass of a cyclobutane pyrimidine dimer by DNA polymerase eta (XP-V or Rad30) or bypass of a (6-4) TT photoproduct by DNA polymerase V (UmuD'2C), respectively. Although DinB is the only Y-family DNA polymerase conserved among all domains of life, the biological rationale for this striking conservation has remained enigmatic. Here we report that the Escherichia coli dinB gene is required for resistance to some DNA-damaging agents that form adducts at the N2-position of deoxyguanosine (dG). We show that DinB (DNA polymerase IV) catalyses accurate TLS over one such N2-dG adduct (N2-furfuryl-dG), and that DinB and its mammalian orthologue, DNA polymerase kappa, insert deoxycytidine (dC) opposite N2-furfuryl-dG with 10-15-fold greater catalytic proficiency than opposite undamaged dG. We also show that mutating a single amino acid, the 'steric gate' residue of DinB (Phe13 --> Val) and that of its archaeal homologue Dbh (Phe12 --> Ala), separates the abilities of these enzymes to perform TLS over N2-dG adducts from their abilities to replicate an undamaged template. We propose that DinB and its orthologues are specialized to catalyse relatively accurate TLS over some N2-dG adducts that are ubiquitous in nature, that lesion bypass occurs more efficiently than synthesis on undamaged DNA, and that this specificity may be achieved at least in part through a lesion-induced conformational change.

DNA structural similarity in the 2:1 complexes of the antitumor drugs trabectedin (Yondelis) and chromomycin A3 with an oligonucleotide sequence containing two adjacent TGG binding sites on opposing strands

Yondelis (trabectedin) is an antitumor ecteinascidin that binds covalently to the 2-amino group of the central guanine in the minor groove of selected DNA pyrimidine-G-G and purine-G-C triplets. Chromomycin A3 is an aureolic acid derivative that binds noncovalently to the DNA minor groove in G/C-rich triplet sites as a metal-chelated dimer. Despite their different binding modes, the cytotoxicity profiles of these two drugs, as assessed in the COMPARE analysis carried out by the National Cancer Institute on data from 60 human tumor cell lines, are highly correlated (Pearson's correlation coefficient of 0.96). We now report that in an oligonucleotide containing the "natural bending element" TGGCCA, the structural distortions inflicted by the tail-to-tail bonding of two trabectedin molecules to adjacent target sites on opposing strands are strikingly similar to those observed in a crystal containing d(TTGGCCAA)2 and two bound chromomycin A3 molecules arranged in a head-to-tail orientation in the minor groove. In both complexes, the double helix is characterized by being considerably unwound and possessing a notably widened minor groove. Binding of the drugs to this sequence could be favored by the distinct bends at each of the TpG steps that are already present in the free oligonucleotide. Simultaneous drug binding to the two strands in the manner described here is proposed to stabilize the helical structure of duplex DNA to prevent or hamper strand separation and stall replication and transcription forks.

ET‐743: A Novel Agent with Activity in Soft Tissue Sarcomas

Ecteinascidin-743 (ET-743) is a natural product derived from the marine tunicate Ectenascidia turbinate. ET-743 binds in the minor groove of DNA, blocks transcription factors activity, and traps protein from the nucleotide excision repair system, thus blocking cells in G2-M phase. ET-743 demonstrated cytotoxic activity at very low concentrations against sarcoma cell lines in pre-clinical studies. In several phase II clinical studies in patients with advanced sarcoma failing conventional doxorubicin- and ifosfamide-based chemotherapy, ET-743 delivered by continuous intravenous 24-hour infusion at a dose of 1,500 microg/m2 every 21 days yielded 8% overall response and 30%-40% stabilization rates for a clinical benefit rate close to 40%. Interestingly, long-term stabilizations over more than 3 years have been described. In vivo, ET-743 has a specific toxicity profile, the major toxicity of this product being hepatic, through biliary duct destruction, and hematologic. ET-743 has also been evaluated in first-line treatment for these patients. Finally, due to its original mode of action and the lack of cross-resistance with other chemotherapy agents, ET-743 was tested in a preclinical model in combination with other drugs. Synergy was reported in vitro with doxorubicin and cisplatin; phase I combination studies are in progress.

Low cytotoxicity of ecteinascidin 743 in yeast lacking the major endonucleolytic enzymes of base and nucleotide excision repair pathways

Ecteinascidin 743 (ET-743) is a promising antitumoral drug for the treatment of soft tissues sarcomas, becoming a good candidate for clinical trials. However, the molecular mechanism of how ET-743 induces cells death is poorly understood. The chemical structure of ET-743 suggests that it can form cytotoxic cross-links with proteins and DNA. Experiments with Escherichia coli and mammalian cells indicate that the nucleotide excision repair (NER) pathway promotes ET-743 cytotoxicity. We therefore analyzed cytotoxicity and tolerance to ET-743 in the yeast Saccharomyces cerevisiae, defective for NER and/or base excision repair (BER), either in single mutants or in combination with mutant alleles of genes encoding proteins involved in DNA translesion synthesis (TLS) and homologous recombination (HR). Treatment of haploid and diploid S. cerevisiae strains with ET-743 led to induced mutagenesis, mitotic gene conversion, and crossing-over. The results indicated that yeast strains lacking endonucleases of the NER and BER pathways are especially resistant for ET-743. The mutagenesis data points to a weak mutagenic activity of ET-743 in both WT and strains lacking BER/NER endonuclease, and that a mutant blocked in both BER and TLS totally lacks induced mutagenesis. The diploid strain shows an increase in the frequencies of crossing-over and mitotic recombination. These data lead us to propose a model for ET-743 action in eukaryotic cells, where the presence of BER and NER endonucleases results in cell death. However, ET-743 damage can be tolerated in BER and/or NER mutants by TLS (error-prone) or in combination with HR (error-free).

Synthetic studies toward ecteinascidin 743

An efficient synthesis of a fully functionalized tetracycle (A-B-C-H) 7 containing a 1,4-bridged 10-membered lactone was developed. Phenolic aldol condensation between 2-methylsesamol (15) and Garner's aldehyde provided the protected amino diol 16, which was converted to free amine 11 in excellent yield. A Pictet-Spengler reaction between 11 and ethyl glyoxylate under carefully controlled conditions (LiCl, toluene, 1,1,1,3,3,3-hexafluoro-2-propanol, room temperature) provided the acid-sensitive tetrahydroisoquinoline (18) in high yield, which was converted to the amino alcohol 9. Enantioselective alkylation of a glycine template in the presence of a catalytic amount of chiral cinchonidium salt was the key step for the access of enantiomerically pure amino aldehyde 10. Union of the two fragments 9 and 10 via oxazolidine intermediate afforded amino nitrile 39, which upon esterification of the primary alcohol with (R)-N-(S-4,4',4' '-trimethoxyltrityl) Cys (42) afforded 43. Cyclization of 43 (1% trifluoroacetic acid in trifluoroethanol) provided compound 44 by a domino process involving (a) unmasking of the S-trimethoxytrityl group, (b) fragmentation of dioxane assisted by an electron-rich aromatic ring, and (c) formation of a 1,4-bridged 10-membered lactone via formation of a sulfide linkage. Treatment of 7, obtained in two steps from 44b, under acidic conditions (0.5% methyl sulfonic acid in acetonitrile) afforded the pentacyclic compound 51 via fragmentation of the 10-membered cyclic sulfide followed by an intramolecular Pictet-Spengler reaction.

Marine pharmacology in 2001-2: antitumour and cytotoxic compounds

During 2001 and 2002, marine antitumour pharmacology research aimed at the discovery of novel antitumour agents was published in 175 peer-reviewed articles. The purpose of this paper is to present a structured Review of the antitumour and cytotoxic properties of 97 marine natural products, many of them novel compounds that belong to diverse structural classes, including polyketides, terpenes, steroids, and peptides. The organisms yielding these bioactive compounds comprise a taxonomically diverse group of marine invertebrate animals, algae, fungi and bacteria. Antitumour pharmacological studies were conducted with 30 structurally characterised natural marine products in a number of experimental and clinical models which further defined their mechanisms of action. Particularly potent in vitro cytotoxicity data generated with murine and human tumour cell lines was reported for 67 novel marine chemicals with as yet undetermined mechanisms of action. Noteworthy, is the fact that marine anticancer research was sustained by a collaborative effort, involving researchers from Australia, Brazil, Canada, Denmark, Egypt, France, Germany, Italy, Japan, Netherlands, New Zealand, The Philippines, Russia, Singapore, South Korea, Thailand, Taiwan, Turkey, Spain, Switzerland, Taiwan, Thailand, Turkey, and the United States. Finally, this 2001-2 overview of the marine pharmacology literature highlights the fact that the discovery of novel marine antitumour agents has continued at the same pace as during 1998, 1999 and 2000.

Irofulven cytotoxicity depends on transcription-coupled nucleotide excision repair and is correlated with XPG expression in solid tumor cells

BACKGROUND

Irofulven is a novel alkylating agent with promising clinical activity, particularly toward ovarian and hormone-refractory prostate cancers. To facilitate additional clinical development, we have aimed to identify biological markers associated with sensitivity to the compound.

METHODS

Fibroblasts derived from patients with xeroderma pigmentosum or Cockayne's syndrome along with a panel of 20 human cancer cell lines (eight different tumor types) were examined to establish the importance of nucleotide excision repair proteins in the sensitivity to irofulven.

RESULTS

Human cells deficient in nucleotide excision repair are up to 30-fold more sensitive to the cytotoxic effects of irofulven compared with repair-proficient controls, clearly indicating that nucleotide excision repair plays a crucial role in the sensitivity to the drug. Interestingly, our results show that irofulven-induced lesions are recognized by transcription-coupled repair but not by global genome repair. Another unique feature is the pronounced sensitivity of XPD and XPB helicase-deficient cells to the drug. Comparison of the IC50 values for irofulven, cisplatin, and ecteinascidin 743 with the expression levels of ERCC1, XPD, and XPG genes in different solid tumor cell lines shows no correlation between the expression levels of any of the three nucleotide excision repair proteins and the sensitivity to ecteinascidin 743. In contrast, expression of the XPG endonuclease was correlated with the cytotoxicity for irofulven and, to a lesser degree, for cisplatin. Importantly, XPG expression was also correlated with cellular nucleotide excision repair activity.

CONCLUSIONS

Increasing evidence indicates that compromised nucleotide excision repair activity is frequent in several solid tumor types. The results presented here suggest that XPG expression in such tumors may be a useful marker to predict their sensitivity to irofulven.

Marine natural products and related compounds in clinical and advanced preclinical trials

The marine environment has proven to be a very rich source of extremely potent compounds that have demonstrated significant activities in antitumor, antiinflammatory, analgesia, immunomodulation, allergy, and anti-viral assays. Although the case can and has been made that the nucleosides such as Ara-A and Ara-C are derived from knowledge gained from investigations of bioactive marine nucleosides, no drug directly from marine sources (whether isolated or by total synthesis) has yet made it to the commercial sector in any disease. However, as shown in this review, there are now significant numbers of very interesting molecules that have come from marine sources, or have been synthesized as a result of knowledge gained from a prototypical compound, that are either in or approaching Phase II/III clinical trials in cancer, analgesia, allergy, and cognitive diseases. A substantial number of other potential agents are following in their wake in preclinical trials in these and in other diseases.

In vitro interaction between ecteinascidin 743 (ET-743) and radiation, in relation to its cell cycle effects

Ecteinascidin 743 (ET-743) is a new marine-derived agent with promising activity against a number of solid tumours. In four human tumour cell lines, the interaction between ET-743 and radiation was investigated in relation to the effects of ET-743 on the cell cycle, in vitro. Cell survival was measured based on quantitative staining of cellular protein by sulforhodamine B. A 24 h treatment with ET-743 before radiation resulted in a moderate increase in radiosensitivity in three out of four cell lines. Dose enhancement factors > or =1.8 were observed for concentrations resulting in 52, 46 and 30% cell kill in ECV304, H292 and CAL-27, respectively, whereas in A549 no radiosensitisation was observed (no significant increase in radiosensitivity). According to the combination index analysis, synergism was observed only in ECV304 and CAL-27 cells. A 24 h incubation with ET-743 resulted in a concentration-dependent G2/M block, which might explain the moderate radiosensitising effects in ECV304 and H292. The lack of radiosensitisation in A549 might be due to the S phase delay preceding the G2/M block at the moment of radiation, which only occurred in this cell line. In conclusion, ET-743 has moderate cell line-dependent radiosensitising properties; however, only when cytotoxic concentrations of ET-743 are used. In one of the four cell lines tested, no radiosensitisation was observed.

The combination of yondelis and cisplatin is synergistic against human tumor xenografts

Yondelis (trabectidin, ET-743) is a marine natural product that has shown activity both in preclinical systems and in human malignancies such as soft tissue sarcoma and ovarian cancers that are resistant to previous chemotherapies. Molecular pharmacological studies indicated that Yondelis interacts with DNA and DNA repair systems in a way that is different from Cisplatin (DDP). The current study was designed to investigate the effects of the combination of Yondelis and DDP in human cancer cell lines and in xenografts derived from different tumours. The in vitro studies performed in human TE-671 rhabdomyosarcoma, Igrov-1 and 1A9 human ovarian carcinoma cell lines showed additive effects or slight synergism. Several human tumour xenografts, such as TE-671 rhabdomyosarcoma, SK-N-DX neuroblastoma, FADU head and neck, LX-1 non-small cell lung cancer (NSCLC), H-187 melanoma and SKOV HOC 8 ovarian carcinoma, showed an antitumour effect for the combination that was greater than that of each drug when given as a single agent. No consistent changes in the activity were observed if Yondelis and DDP were given 1 h apart in sequence or simultaneously. An orthotopically transplanted human ovarian cancer HOC 8 growing in the peritoneal cavity of nude mice was used that is insensitive to Yondelis alone and only moderately sensitive to DDP alone. The combination of the two drugs produced a dramatic increase of survival lasting several months. In conclusion, the combination of Yondelis and DDP is synergistic in vivo (i.e. the antitumour effect is greater than that of each drug used as a single agent at the maximum tolerated dose (MTD)) in different human tumour xenografts. The two drugs can be combined at the MTD of each drug, thus indicating there are no overlapping toxicities. These results provide a rationale for testing the combination of Yondelis and DDP in the clinic.