In vitro schedule-dependency of myelotoxicity and cytotoxicity of Ecteinascidin 743 (ET-743)

The Most Important Microtubule Natural Inhibitors

Natural microtubule inhibitors represent chemically very variegated family of structures with strong effect on cytoskeletal functions and the use of them is one of the most frequent therapeutic strategies for carcinoma treatment. The survey of the most important natural microtubule inhibitors is summarized in this paper.

Radiosensitizing effects of trabectedin on human A549 lung cancer cells and HT-29 colon cancer cells

Background and Purpose Trabectedin is a unique alkylating agent with promising effects against a range of solid tumors. In this study, we aimed to examine the cytotoxic and radiosensitizing effects of trabectedin on two human epithelial tumor cell lines in vitro, and its effects on DNA repair capacity. Methods Cancer cells (A549: human lung cancer cells, HT-29: colon cancer cells) were treated with either trabectedin alone for the determination of their growth, or in combination with radiation for the determination of their metabolic activity, proliferation, and clonogenic survival. Besides, the γH2AX foci assay was performed for the assessment of ionizing radiation-induced DNA damage and to evaluate the influence of trabectedin on DNA damage repair. Results Treatment with trabectedin resulted in a growth-inhibiting effect on both cell lines, with the IC₅₀ values remaining within a low nanomolar range. Analyses of metabolic activity confirmed a cytotoxic influence of trabectedin and a BrdU assay demonstrated an antiproliferative effect. When combined with radiation, incubation with trabectedin was found to enhance the radiosensitivity of the tumor cells. The γH2AX foci assay resulted in an increased number of DNA double-strand breaks (DSBs) in cells treated with trabectedin. Conclusion The results of this study underline the antitumor activity of trabectedin at low nanomolar concentrations. We demonstrated that trabectedin enhanced radiation response in human lung (A549) cancer cells and colon (HT-29) cancer cells. Further studies are necessary to examine trabectedin as a potential candidate for future applications in radiotherapy.

Marine Microalgae with Anti-Cancer Properties

Cancer is the leading cause of death globally and finding new therapeutic agents for cancer treatment remains a major challenge in the pursuit for a cure. This paper presents an overview on microalgae with anti-cancer activities. Microalgae are eukaryotic unicellular plants that contribute up to 40% of global primary productivity. They are excellent sources of pigments, lipids, carotenoids, omega-3 fatty acids, polysaccharides, vitamins and other fine chemicals, and there is an increasing demand for their use as nutraceuticals and food supplements. Some microalgae are also reported as having anti-cancer activity. In this review, we report the microalgal species that have shown anti-cancer properties, the cancer cell lines affected by algae and the concentrations of compounds/extracts tested to induce arrest of cell growth. We also report the mediums used for growing microalgae that showed anti-cancer activity and compare the bioactivity of these microalgae with marine anticancer drugs already on the market and in phase III clinical trials. Finally, we discuss why some microalgae can be promising sources of anti-cancer compounds for future development.

Multidrug-resistant cancer cells and cancer stem cells hijack cellular systems to circumvent systemic therapies, can natural products reverse this?

Chemotherapy is one of the most effective and broadly used approaches for cancer management and many modern regimes can eliminate the bulk of the cancer cells. However, recurrence and metastasis still remain a major obstacle leading to the failure of systemic cancer treatments. Therefore, to improve the long-term eradication of cancer, the cellular and molecular pathways that provide targets which play crucial roles in drug resistance should be identified and characterised. Multidrug resistance (MDR) and the existence of tumor-initiating cells, also referred to as cancer stem cells (CSCs), are two major contributors to the failure of chemotherapy. MDR describes cancer cells that become resistant to structurally and functionally unrelated anti-cancer agents. CSCs are a small population of cells within cancer cells with the capacity of self-renewal, tumor metastasis, and cell differentiation. CSCs are also believed to be associated with chemoresistance. Thus, MDR and CSCs are the greatest challenges for cancer chemotherapy. A significant effort has been made to identify agents that specifically target MDR cells and CSCs. Consequently, some agents derived from nature have been developed with a view that they may overcome MDR and/or target CSCs. In this review, natural products-targeting MDR cancer cells and CSCs are summarized and clustered by their targets in different signaling pathways.

Finding chemo: the search for marine-based pharmaceutical drugs active against cancer

OBJECTIVES

Cancer affects the health of many people globally. The most common treatment that is used for cancer is chemotherapy, which has shown promising results but not without side effects. Some of these side effects jeopardise further treatment, and this eventually leads to advanced stages of malignancy and mortality. As a result, there is a need for better and safer anticancer compounds such as those found naturally. One of the most abundant natural environments to find such compounds is the sea, and this vast resource has been biomined since the 1950s.

KEY FINDINGS

There are currently three marine anticancer agents marketed (Yondelis, Cytosar-U and Halaven), with several others undergoing clinical trials. This review discusses marine-derived products in clinical use and in clinical trials, and discusses available literature on the growth suppression or pro-apoptotic properties of these compounds, and the molecular mechanisms underpinning these cell biological phenomena.

SUMMARY

The marine environment may hold promising anticancer compounds within its depths, warranting further research to be performed in this area, albeit with respect for the natural ecosystems that are being explored for drug discover and subsequently used for drug development.

The impairment of the High Mobility Group A (HMGA) protein function contributes to the anticancer activity of trabectedin

Trabectedin (Ecteinascidin-743 or ET-743) is a novel antitumour agent of marine origin with potent antitumour activity both in vitro and in vivo. It interacts with the minor groove of DNA, interfering with transcriptional activity and DNA repair pathways. Here, we report a novel mechanism by which trabectedin exerts its cytotoxic effects on carcinoma cells. It is based on its ability to impair the function of the High-Mobility Group A (HMGA) proteins. These proteins have a key role in cell transformation, and their overexpression is a common feature of human malignant neoplasias, representing a poor prognostic index often correlated to anti-cancer drug resistance. They bind the minor groove of DNA, alter chromatin structure and, thus, regulate the transcription of several genes by enhancing or suppressing the activity of transcription factors. We first report that trabectedin has a higher cytotoxic effect on thyroid and colon carcinoma cells expressing abundant levels of HMGAs in comparison with cells not expressing them. Then, we have shown that trabectedin treatment displaces HMGA proteins from the HMGA-responsive promoters, including ATM promoter, impairing their transcriptional activity. Finally, we report a synergism between Ionising Radiations and trabectedin treatment restricted to the HMGA-overexpressing cancer cells. This result might have important clinical implications since it would suggest the use of trabectedin for the treatment of neoplasias expressing abundant HMGA levels that are frequently associated to chemoresistance and poor prognosis.

Trabectedin has promising antineoplastic activity in high-grade meningioma

BACKGROUND

Meningiomas are common intracranial tumors arising from the meninges and usually are benign. However, a few meningiomas have aggressive behavior and, for such patients, effective treatment options are needed. Trabectedin is a novel, marine-derived, antineoplastic agent that has been approved and is used routinely as therapy for advanced soft tissue sarcoma and ovarian cancer.

METHODS

The authors investigated the in vitro effects of trabectedin alone and in combination with hydroxyurea, cisplatin, and doxorubicin in primary cell cultures of benign (n = 9), atypical (n = 6), and anaplastic (n = 4) meningiomas using chemosensitivity assays (3-[4,5dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide [MTT]), Western blot analysis, cell cycle analysis, and immunofluorescent staining.

RESULTS

Strong antimeningioma activity of trabectedin was observed and was characterized by distinct cell cycle arrest, down-regulation of multiple cyclins, deregulated expression of cell death-regulatory genes, and massive apoptosis induction. Cytotoxic activity was especially intense in higher grade meningiomas with a half-maximal inhibitory concentration <10 nM. Combination with trabectedin synergistically enhanced the antimeningioma activity of hydroxyurea but also enhanced the activity of doxorubicin and cisplatin. On the basis of these findings, trabectedin was given to 1 patient who had heavily pretreated, anaplastic meningioma, and a favorable response was observed with radiologic disease stabilization, marked reductions in brain edema and requirement for corticosteroids, and improvement of clinical symptoms. However, treatment had to be discontinued after 5 cycles because of adverse drug effects.

CONCLUSIONS

The current results indicated that trabectedin may represent a promising new therapeutic option for patients with aggressive meningioma and should be evaluated in prospective clinical studies.

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.

Mechanism-based Pharmacokinetic/Pharmacodynamic Meta-analysis of Trabectedin (ET-743, Yondelis) Induced Neutropenia

Myelosuppression was found to be one of the main toxicities of trabectedin (ET-743, Yondelis) during phase I/II studies. Our objective was to develop a pharmacokinetic-pharmacodynamic (PK/PD) model that describes the time course of the absolute neutrophil counts (ANCs) in cancer patients receiving trabectedin. Data from 699 patients who received intravenous trabectedin as monotherapy (dose range: 0.006-1.8 mg/m2) as a 1-, 3-, or 24-h infusion every 21 days; 1- or 3-h infusion on days 1, 8, and 15 every 28 days; or a 1-h infusion daily for 5 consecutive days every 21 days were used to develop (N=405; ANCs=7,291) and validate (N=294; ANCs=5,029) the model. The PK/PD model comprised a trabectedin-sensitive progenitor cell compartment, linked to the peripheral blood compartment, through three transition compartments representing the maturation chain in the bone marrow. To capture the rebound effect due to endogenous growth factors, the model included a feedback mechanism. The model estimated three system-related parameters: ANC at baseline (Circ0), mean transit time in bone marrow (MTT), and a feedback parameter (gamma). A first-order process quantified by the rate constant k(e0) described the trabectedin concentrations at the effect compartment (C(e)), which were assumed to reduce the proliferation rate and/or to increase the killing rate of the progenitor cells according to the function alphaC(e)beta. The model was qualified and simulations were undertaken to evaluate the neutropenia schedule dependency and the effects of selected covariates. NONMEM software was used to perform the modeling and simulation analyses. For a typical man of 70 kg, the mean values (between-subject variability; %) of the Circ0, MTT, gamma, k(e0), alpha, and beta were estimated to be 4.46 x 10(9)/l (37.9%), 4.0 days (37.5%), 0.218 (41.8%), 2.09 h(-1) (77.9%), 2.00 l/microg (85.1%), and 1.26, respectively. Although in women, k(e0) was reduced by 29% and a 25% increase in body weight resulted in a 12.6% reduction in the beta parameter, the clinical relevance of these effects is limited. The model evaluation procedure indicated accurate prediction of the observed incidence of neutropenia grades 3 and 4 across the dosing regimens evaluated. Simulations indicated that trabectedin dose and interdose interval, but not infusion duration, are the main determinants of the neutropenia severity. The model-predicted time course of the ANC and its variability confirmed that neutropenia is reversible, of short duration, and non-cumulative. The extent and time course of neutropenia following six different dosing regimens of trabectedin were well predicted by the semiphysiological PK/PD model.

Phase II Study of Trabectedin in Pretreated Patients with Advanced Colorectal Cancer

PURPOSE

This open-label, nonrandomized, phase II study was aimed at evaluating the efficacy and toxicity of trabectedin over a 3-hour intravenous infusion every 3 weeks in patients with pretreated advanced colorectal cancer.

PATIENTS AND METHODS

Twenty-one patients were enrolled: 5 patients (23.8%) were treated with 1650 microg/m(2), 10 patients (47.6%) with 1300 microg/m(2), and 6 patients (28.6%) with 1100 microg/m(2). Response to treatment was assessed according to World Health Organization criteria, and toxicities were graded according to National Cancer Institute Common Toxicity Criteria, version 2.0.

RESULTS

The median number of treatment cycles per patient was 2 (range, 1-6 cycles). No objective responses were reported. Four patients (19%; 95% confidence interval [CI], 5.5%-41.9%) exhibited stable disease lasting for a median of 3.6 months (range, 2.4-4.9 months). The median time to progression was 1.5 months (95% CI, 1.3-1.6 months), and the median overall survival was 4.4 months (95% CI, 3-7.5 months; n=2 censored). The main grade 3/4 toxicities were transient asymptomatic transaminase increase (alanine aminotransferase, 66.7% of patients; aspartate aminotransferase, 57.1%) and neutropenia (42.8%). No toxic deaths were reported.

CONCLUSION

Trabectedin 1300 microg/m(2) given as a 3-hour intravenous infusion every 3 weeks was well tolerated but lacked activity in pretreated advanced-stage colorectal cancer. Therefore, further clinical trials with this trabectedin schedule as a single agent are not warranted.

Trabectedin

Trabectedin [Ecteinascidin 743, Yondelis, ET 743, NSC 684766] is a tetrahydroisoquinoline alkaloid derived from the Caribbean marine tunicate, Ecteinascidia turbinata. The drug is being developed by PharmaMar (Zeltia) in partnership with Johnson & Johnson Pharmaceutical Research & Development LLC. It was synthetically isolated and developed by the University of Illinois and licensed to PharmaMar; the company has completed the hemisynthesis of agent. Trabectedin interacts with the minor groove of DNA and alkylates guanine at the N2 position, which bends towards the major groove. In this manner, it is thought that the drug affects various transcription factors involved in cell proliferation, particularly via the transcription-coupled nucleotide excision repair system. Trabectedin blocks the cell cycle at the G(2) phase, while cells at the G(1 )phase are most sensitive to the drug. It also inhibits overexpression of the multidrug resistance-1 gene (MDR-1) coding for the P-glycoprotein that is a major factor responsible for cells developing resistance to cancer drugs. The agent is also thought to interfere with the nucleotide excision repair pathways of cancer cells, suggesting that it could be effective in the treatment of many cancer types including melanoma and sarcoma, as well as lung, breast, ovarian, endometrial and prostate cancers; clinical evaluations are underway in these indications. PharmaMar and Ortho Biotech Products (Johnson & Johnson) entered into an agreement in August 2001 for the joint development and commercialisation of trabectedin. PharmaMar retains commercialisation rights in Europe, including Eastern Europe. Ortho Biotech will market the product in the US, Japan and the rest of the world; Tibotec Therapeutics (a division of Ortho Biotech) will commercialise it in the US. PharmaMar will receive an initial payment from Ortho Biotech plus future milestone and royalty payments linked to development targets and sales; the upfront payment would be approximately 20 million US dollars with royalties contributing 10-20% of total sales of the drug. Although details of the licensing transaction for trabectedin were undisclosed, analysts estimate the figure to be around 100 million US dollars. Previously, PharmaMar signed an agreement granting Bristol-Myers Squibb the option to evaluate and develop as many as 12 of PharmaMar's marine-derived anticancer compounds on an exclusive worldwide basis. However, it appears that Bristol-Myers Squibb had chosen not to exercise the option. Trabectedin is undergoing clinical trials in soft tissue sarcoma (Sarcoma in the Phase table), ovarian, breast, endometrial, prostate and non-small-cell lung cancers. PharmaMar indicated in January 2004 that it intends to launch trabectedin in one of these indications in 2006. PharmaMar raised funds from a round of financing in June 2005 that will be used to fund further clinical trials of its anticancer products, including trabectedin. The US FDA granted trabectedin orphan drug status for ovarian cancer in April 2005. Trabectedin also received orphan drug status from the European Commission for the treatment of ovarian cancer in October 2003. This followed a positive opinion by the Committee for Orphan Medicinal Products (COMP) of the EMEA. Trabectedin has undergone a phase II study for the second- or third-line treatment of ovarian cancer in Europe (England and Belgium), the US and Canada. The trial was initiated in October 2002 and evaluated a weekly schedule of trabectedin (0.58 mg/m(2)) via IV infusion for 3 weeks followed by a week of rest. Final results from this study have been presented. A separate phase II trial evaluating the antitumour activity of trabectedin as a second-line therapy in advanced ovarian cancer was conducted by researchers at the Southern Europe New Drugs Organization (SENDO) in Milan, Italy. PharmaMar and Johnson & Johnson are conducting a pivotal (STS-201) trial to compare a weekly and daily dosing regimen of trabectedin among patients with advanced or metastatic soft tissue sarcoma who are unresponsive to standard chemotherapy of doxorubicin and ifosfamide. The randomised, multicentre, open-label trial has completed enrolment of 270 patients during the second quarter of 2005. Positive data from the STS-201 trial have been announced. An independent data monitoring committee has found that interim data supports a positive trend in time to disease progression favouring patients receiving the daily dosing regimen. Consequently, all patients have been offered the option of switching to the daily regimen. Final results from the STS-201 trial will form the basis of MAA re-submission with European regulatory authorities. PharmaMar has held a pre-submission meeting with the EMEA and has presented a formal letter of intent to file for approval of trabectedin for soft tissue sarcoma. Previously, PharmaMar first filed for EU registration of trabectedin for treatment of advanced soft tissue sarcoma in November 2001, which was accepted for review by the EMEA and Swiss Health Authorities. However, the CPMP confirmed its recommendation not to grant trabectedin marketing authorisation in November 2003 following PharmaMar's appeal against the CPMP's negative opinion first announced in July 2003; the opinion was adopted by a majority vote rather than by consensus. Trabectedin was granted orphan drug status in Europe for recurrent soft tissue sarcoma in 2001. It was also granted orphan drug status by the FDA for the same indication in October 2004. Phase I studies are being conducted to evaluate trabectedin in combination with doxorubicin and liposomal doxorubicin for the treatment of soft tissue sarcoma. PharmaMar is also conducting a phase I study of sequential paclitaxel followed by trabectedin in patients with soft tissue sarcoma. At additional dose levels, patients with other tumour types will be enrolled to assess the antitumour activity of the combination. The US NCI has approved and is partially funding a phase I clinical programme to determine the feasibility of using trabectedin to treat children with soft tissue sarcoma and bone sarcoma who are resistant to conventional therapies. PharmaMar has reported that trabectedin can be safely administered to children at doses up to 1100mg given as a 3-hour infusion, and that this dose will be used in further paediatric studies. Trabectedin has completed phase II studies for small round cell sarcoma and rhabdomyosarcoma, which are aggressive tumours occurring predominantly in children. A phase II study evaluating two dosing schedules of trabectedin has been conducted in patients with leiomyosarcomas or liposarcomas refractory to standard doxorubicin + ifosfamide chemotherapy. The study was conducted in Australia, Canada, Russia and the US.

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.

Phase I and pharmacokinetic study of Yondelis (Ecteinascidin-743; ET-743) administered as an infusion over 1 h or 3 h every 21 days in patients with solid tumours

Yondelis (ET-743) is a novel anticancer agent isolated from the marine ascidian Ecteinascidia turbinata. ET-743 possesses potent antitumour activity and a novel mechanism of action at the level of gene transcription. We conducted two sequential phase I dose escalation and pharmacokinetic studies of ET-743 given as a 1- or a 3-h intravenous (i.v.) infusion. Seventy-two adults with metastatic or advanced solid tumours received ET-743 in escalating doses between 50 and 1100 microg/m(2), initially as a 1-h infusion, and later at doses between 1000 and 1800 microg/m(2) as a 3-h infusion every 3 weeks. The maximum tolerated dose (MTD) of ET-743 was 1100 microg/m(2) for the 1-h infusion schedule and 1800 microg/m(2) when given as a 3-h infusion. Dose-limiting toxicities (DLTs) were fatigue, neutropenia and thrombocytopenia. Transient non-cumulatives grade 3-4 increase in transaminases (not considered DLT) and grades 3-4 nausea and vomiting were frequently observed. Other toxicities (maximum grade 3) included anaemia, increased lactate dehydrogenase (LDH), bilirubin and alkaline phosphatase serum levels, and phlebitis; there were no toxic deaths. One pCR (melanoma), CR (uterine leiomyosarcoma), one PR (colon stromal sarcoma) and a MR (37% tumour shrinkage, gastric stromal sarcoma) were observed. A further 9 patients with colorectal, mesothelioma, bile duct carcinoma and bladder cancer had SD which lasted for six or more treatment cycles. ET-743 pharmacokinetics were linear with the 3-h infusion schedule. The haematological and hepatic toxicities of ET-743 were dose-dependent and not cumulative. Based on the current trial, the recommended dose of ET-743 for phase II studies is 1650 microg/m(2) given as a 3-h infusion.

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.

Phase II study of ecteinascidin 743 in heavily pretreated patients with recurrent osteosarcoma

BACKGROUND

Recurrent osteosarcoma is a drug-resistant disease with a dismal prognosis. The objective of this Phase II study was to evaluate the activity of ecteinascidin 743 (ET-743) as a salvage therapy in these patients.

METHODS

Patients with recurrent osteosarcoma who had received standard chemotherapeutic agents were eligible. ET-743 was administered at a dose of 1500 microg/m(2) as a 24-hour infusion every 3 weeks. Pharmacokinetic studies were performed during the first cycle.

RESULTS

Twenty-five patients were enrolled, 23 of whom were assessable for response (median age of 18 years; range, 12-67 years). The median number of previous chemotherapeutic agents was five (range, three to eight previous agents). Sixty-one cycles were administered (median number of cycles per patient was 2; range, 1-9 cycles per patient). Three patients (12%) achieved minor responses (49% 36% and 25%, respectively). Fifteen patients (60%) developed a transient elevation of hepatic transaminases (Grade 3 or 4 [according to the National Cancer Institute Common Toxicity Criteria]), which was not cumulative. Grade 3 or 4 neutropenia and thrombocytopenia were observed in 12 patients (48%) and 6 patients (24%), respectively. The mean area under the curve (AUC) in 4 patients experiencing Grade 4 toxicity (76.4 +/- 29.3 ng x hr/mL) was significantly greater (P = 0.034) than that in those for whom the most severe toxicity was Grade 3 (39.5 +/- 17.2 ng x hr/mL [n = 12]) or Grade 1-2 (52.6 +/- 15.6 ng x hr/mL [n = 5]). There were no other significant correlations found between pharmacokinetic variables and patient characteristics, toxicity, or therapeutic response.

CONCLUSIONS

ET-743 was found to be well tolerated in heavily pretreated osteosarcoma patients but had limited antitumor activity as a single agent. The combination of ET-743 with cisplatin or doxorubicin should be considered.

Marine-derived anticancer agents in clinical trials

Anticancer agents may be derived either from the isolation of an active lead compound occurring spontaneously in nature or by novel chemical synthesis in the laboratory. There are examples of successful drugs being derived from both sources, which have had a profound impact on the natural history of various types of cancer. The treatment of lymphomas and acute leukaemias with the use of combination chemotherapy, including anthracyclines and vinca alkaloids, are examples of the contribution of nature. In contrast, agents such as 5-fluorouracil, methotrexate and more recently, the humanised anti-CD20 antibody rituximab and the tyrosine kinase inhibitor imatinib are examples of synthetic compounds, which were designed with a clear rationale, that are routinely used in patients with solid tumours and haematological malignancies. Until recently, the tradition in natural product-derived anticancer drug development was to rely almost exclusively on the screening of terrestrial sources (plant extracts and fermentation products) for their cytotoxic properties. Although C-nucleosides obtained from Caribbean sponge were the initial inspiration for the synthesis of antiviral substituted nucleosides and the successful anticancer agent citarabine, active against leukaemias and lymphomas, the contribution of marine compounds as a source of anticancer agents was modest. In recent years, the improvements in the technology of deep-sea collection and aquaculture added to the growing recognition of the tremendous biodiversity present in the marine world, and has contributed to the growing interest of exploring the oceans as a potential source of new anticancer candidates. This is reflected in the number of marine-derived compounds undergoing preclinical and early clinical development. In this paper, the authors discuss the available literature on anticancer agents that have reached clinical trials, such as didemnin B, aplidine, dolastatin-10, bryostatin-1 and ecteinascidin-743 (ET-743, trabectedin), as well as other promising compounds still undergoing tests in the laboratory.

Yondelis (trabectedin, ET-743): the development of an anticancer agent of marine origin

Yondelis (trabectedin, ET-743) is a novel antitumor agent derived from a marine source, the Caribbean tunicate Ecteinascidia turbinata. Preclinical studies demonstrated activity at low concentrations against a variety of tumors. The mechanism by which ET-743 exerts its antitumor activity has not been completely elucidated yet. Binding to the minor groove of DNA which causes a bend towards the major groove has been demonstrated. Furthermore, ET-743 interferes with DNA binding proteins and transcription factors. Clinical studies have been initiated as phase I dose-finding studies at four different treatment regimens. Dose-limiting toxicities were hematological, including neutropenia and thrombocytopenia. Furthermore, significant liver toxicity was observed, especially as a rise in transaminase levels. Antitumor activity in phase I and phase II trials was studied in multiple tumor types, including soft tissue sarcomas, melanomas and breast cancer. ET-743 is currently being extensively investigated in advanced soft tissue sarcomas. The present review describes the development of ET-743, highlighting chemical properties, mode of action, metabolism and preclinical and clinical studies.

Cytotoxic agents in the era of molecular targets and genomics

Cancer treatment is evolving due to the development of molecularly targeted agents and the utilization of pharmacogenomics and pharmacogenetics to identify patients who are at an increased risk for toxicity or may be uniquely responsive to cytotoxic therapies. By identifying polymorphisms in the human genome that confer changes in the ability to metabolize or activate cancer agents, a more patient-specific treatment approach can be initiated. Molecularly targeted therapies such as PS-341, flavopiridol, Iressa, and anti-vascular endothelial growth factor antibodies may help to overcome resistance to cytotoxic therapies by lowering the apoptotic threshold and increasing cytotoxicity. Using molecularly targeted agents in combination with traditional cytotoxic agents may increase the percentage of patients who achieve disease stabilization and prolonged survival. With the development of genetic tools and genotyping of tumor and patient prior to initiating treatment, antitumor efficacy may be increased with a substantial reduction in toxicity.

DNA: still a target worth aiming at? A review of new DNA-interactive agents

DNA acts as the final target for most clinically effective cytotoxic agents, but the lack of selectivity for tumor cells has raised questions about the value of developing new DNA-interactive agents. Three new classes of cytotoxic agents are reviewed; each interacts directly with DNA but cytotoxicity appears to be mediated through novel mechanisms, including the interaction with specific proteins by DNA-bound drug molecules. Irofulven is the lead compound of the illudin family of molecules. It causes a novel type of DNA damage whose repair is dependent on functioning DNA helicases. Pre-clinical and clinical synergy between irofulven and agents which inhibit topoisomerases has been observed. Clinical trials with irofulven have shown significant activity and phase II studies in pancreatic, ovarian and prostatic cancer are ongoing. Toxicity in the form of myelosuppression and fatigue have been shown to be schedule dependent, with intermittent administration appearing to significantly reduce toxicity. DNA-interacting agents which alkylate bases exposed in the minor groove have been derived from a number of natural sources. The minor groove alkylation appears to be sequence specific; although the significance of this specificity for cytotoxicity is unclear, one proposed mechanism is through inhibition of expression of particular genes. Three cyclopropylpyrroloinole analogues which cause sequence specific minor groove alkylation are currently under clinical assessment. Myelosuppression is the dose limiting toxicity and is biphasic in its time course. Moderate activity in phase I trials has been observed. Ecteinascidins represent one of the increasing number of groups of drugs isolated from marine organisms. Ecteinascidin-743 (ET-743) is the most advanced in its clinical development. Binding to the minor groove of DNA occurs, although with a different base specificity from other compounds. The cytotoxic effects of ET-743 may occur by inhibition of the inducible transcription of a number of genes by sequestration of specific transcription factors. Clinical trials of ET-743 have shown significant activity, and phase II trials are underway in soft tissue sarcoma and breast cancer. Hepatic toxicity and myelosuppression are predictable and appear associated with peak plasma concentrations, whereas efficacy seems to be improved with prolonged infusion.

In vitro toxicity of ET-743 and aplidine, two marine-derived antineoplastics, on human bone marrow haematopoietic progenitors. comparison with the clinical results

Ecteinascidine-743 (ET-743) and aplidine are two marine-derived antineoplastics currently in phase II development. With the aim of evaluating whether in vitro haematopoietic studies can predict the toxicity of these two drugs in patients, human bone marrow (BM) samples were incubated with these drugs under conditions which mimicked the administration exposures used in the clinics. As it was observed in different cancer cell lines, ET-743 was more toxic on an equimolar basis in human hematopoietic progenitors (inhibitory concentration reducing the viability to 50% after 24 h exposures; IC50(24h): 10-50 nM) compared with doxorubicin (IC50(24h) values: 280-460 nM), used as a control anticancer drug. In contrast to the high haematotoxic effects observed for ET-743, similar IC values were obtained for aplidine (IC50(24h): 150-530 nM) compared with doxorubicin. For both ET-743 and aplidine, the megakaryocytic progenitor was the most sensitive, compared with the other haematopoietic progenitors (IC50 values were 3- to 5-fold lower in the CFU-Megs compared with the CFU-GMs). The observation that the Cmax observed in patients treated with the aplidine maximum tolerated dose (MTD) (7.1 nM) was 21-75 fold lower than the IC50(24h) value observed for the different haematopoietic progenitors is highly consistent with the lack of haematotoxicity observed in patients treated with this drug. In the case of ET-743, differences between the Cmax value corresponding to the MTD (2.6 nM) and the in vitro IC50 values corresponding to the different progenitors were much lower (4-19-fold), also consistent with the haematotoxicity that was observed in patients treated at recommended doses (RDs) and MTDs. Although CFU-Megs were more sensitive than CFU-GM progenitors to ET-743 in vitro, clinical data showed that neutropenic events were more frequent than thrombocytopenic episodes. Aiming to further improve the predictive value of in vitro IC values corresponding to the different haematopoietic progenitors, additional refinement parameters derived from pharmacokinetic and animal studies are proposed.

Clinical pharmacology of the novel marine-derived anticancer agent Ecteinascidin 743 administered as a 1- and 3-h infusion in a phase I study

Ecteinascidin 743 (ET-743) is an anticancer agent derived from the Caribbean tunicate Ecteinascidia turbinata. In the present article, the pharmacokinetics and pharmacodynamics of ET-743 are described within a phase I study. Forty patients with solid tumors initially received ET-743 as a 1-h i.v. infusion every 21 days at nine dose levels (50-1100 microg/m(2)). The maximal tolerated dose (MTD) was 1100 microg/m(2), with thrombocytopenia and fatigue as dose-limiting toxicities (DLTs). As this MTD was substantially lower than in parallel phase I studies, dose escalation continued using a prolonged, 3-h infusion. Thirty-two patients were entered at five dose levels (1000-1800 microg/m(2)). The MTD was 1800 microg/m(2) with pancytopenia and fatigue as DLTs. The recommended phase II dose was 1650 microg/m(2) given over 3 h at which 12 patients were treated. Pharmacokinetic monitoring was performed for both treatment schedules. Non-compartmental pharmacokinetic parameters at the recommended dose with the 3-h infusion were (mean value+/-SD): clearance 87+/-30 l/h and mean elimination half-life 26+/-7 h. Pharmacokinetics were linear at the dose range tested with this schedule. The percentage decrease in platelets, white blood cells and neutrophils correlated with the area under the plasma concentration versus time curve (AUC), dose and maximal plasma concentration (C(max)). Hepatic toxicity increased with dose, AUC and C(max). Administration of 1650 microg/m(2) ET-743 over 3 h seemed clinically feasible; pharmacokinetics were linear with this schedule. Hepatic and hematological toxicities correlated with exposure to ET-743.

Search for metabolites of ecteinascidin 743, a novel, marine-derived, anti-cancer agent, in man

Ecteinascidin 743 (ET-743) is a potent anti-tumoral agent of a marine origin. It is currently being tested in phase II clinical trials using a 3-weekly 24-h i.v. infusion of 1500 microg/m(2) and 3-h infusions of 1650 microg/m(2). Knowledge of the metabolism of ET-743 is, however, still scarce. In the present study, a qualitative chromatographic discovery of metabolites of ET-743 in man is reported. ET-743 and its demethylated analog ET-729 were incubated at 37 degrees C in the presence of enzyme systems, pooled human microsomes, pooled human plasma and uridine 5'-diphosphoglucuronyltransferase, respectively, in appropriate media. Reaction products were investigated chromatographically using photodiode array and ion spray-mass spectrometric detection (LC-MS). The main reaction products in microsomal incubations of ET-743 resulted from a remarkable breakdown of the molecule. In plasma the drugs were deacetylated, and the transferase did actually yield a glucuronide of both ET-743 and ET-729. In contrast, screening of urine, plasma and bile, collected from patients treated with ET-743 at the highest dose levels, using a sensitive LC-MS assay, did not result in detection of ET-729 and metabolites which were generated in vitro. The urinary excretion of ET-743 in man was lower than 0.7% of the administered dose for a 24-h infusion.

Phase I and pharmacokinetic study of ecteinascidin-743, a new marine compound, administered as a 24-hour continuous infusion in patients with solid tumors

PURPOSE

To define the maximum-tolerated dose (MTD) and the phase II recommended dose (RD) of ecteinascidin-743 (ET-743) given as a 24-hour continuous infusion every 3 weeks to patients with treatment-refractory solid tumors.

PATIENTS AND METHODS

Fifty-two patients received a total of 158 cycles of ET-743 at one of nine dose levels (DLs) ranging from 50 to 1,800 microg/m(2).

RESULTS

The MTD was defined as 1,800 microg/m(2) (DL 9), and the phase II RD was 1,500 microg/m(2) (DL 8) for moderately pretreated patients with performance status (PS) 0 to 1 and good hepatobiliary function. Neutropenia and thrombocytopenia were the dose-limiting toxicities (DLTs) and were severe at the MTD (1,800 microg/m(2)) in 94% and 25% of cycles, respectively. At the RD (1,500 microg/m(2)), neutropenia and thrombocytopenia were present in 33% and 10% of cycles, respectively. Transient acute elevated transaminase levels occurred in almost all cycles and was severe in 38% of cycles. Severe toxicities and DLTs were observed in patients with poor PS or abnormal liver function or who had received a large number of previous chemotherapy regimens. Antitumor activity was observed at the three highest DLs, including three partial responses (breast cancer, osteosarcoma, and liposarcoma), and four patients (all with progressing soft tissue sarcomas) had stable disease lasting > or = 3 months. Pharmacokinetic studies were performed on all patients for at least the first cycle, giving a linear pharmacokinetic profile; this showed a relationship between area under the curve (AUC) and transaminitis grade and a clear correlation between AUC and severe hematologic toxicity likelihood.

CONCLUSION

The RD for a 24-hour continuous intravenous infusion of ET-743 is 1,500 microg/m(2), with the most prevalent DLTs being hematologic. Patients with minor baseline hepatobiliary function abnormalities have a higher likelihood of severe hematologic toxicities and AUC-related DLTs, requiring dose adjustments or delays.

Ecteinascidin-743 (ET-743), a natural marine compound, with a unique mechanism of action

The mode of action of Ecteinascidin-743 (ET-743), a marine tetrahydroisoquinoline alkaloid isolated from Ecteinascidia turbinata, which has shown very potent antitumour activity in preclinical systems and encouraging results in Phase I clinical trials was investigated at a cellular level. Both SW620 and LoVo human intestinal carcinoma cell lines exposed for 1 h to ET-743 progress through S phase more slowly than control cells and then accumulate in the G2M phase. The sensitivity to ET-743 of G1 synchronised cells was much higher than that of cells synchronised in S phase and even higher than that of cells synchronised in G2M. ET-743 concentrations up to four times higher than the IC(50) value caused no detectable DNA breaks or DNA-protein cross-links as assessed by alkaline elution techniques. ET-743 induced a significant increase in p53 levels in cell lines expressing wild-type (wt) (p53). However, the p53 status does not appear to be related to the ET-743 cytotoxic activity as demonstrated by comparing the drug sensitivity in p53 (-/-) or (+/+) mouse embryo fibroblasts and in A2780 ovarian cancer cells or the A2780/CX3 sub-line transfected with a dominant-negative mutant TP53. The cytotoxic potency of ET-743 was comparatively evaluated in CHO cell lines proficient or deficient in nucleotide excision repair (NER), and it was found that ET-743 was approximately 7-8 times less active in ERCC3/XPB and ERCC1-deficient cells than control cells. The findings that G1 phase cells are hypersensitive and that NER-deficient cells are resistant to ET-743 indicate that the mode of action of ET-743 is unique and different from that of other DNA-interacting drugs.

Isolation and characterization of an IGROV-1 human ovarian cancer cell line made resistant to Ecteinascidin-743 (ET-743)

By exposing Igrov-1 human ovarian cancer cells to increasing concentrations of Ecteinascidin-743 (ET-743), either for a short or prolonged time, we obtained sublines resistant to ET-743 which overexpress Pgp. The most resistant clone (Igrov-1/25 ET) was evaluated for biological and pharmacological characterizations. The increased Pgp levels of Igrov-1/25 ET were not due to amplification of the mdr-1 gene but to increased mRNA levels. No increase in other multidrug resistance-related proteins such as MRP or LRP was observed in Igrov-1/25 ET. The IC50 values of ET-743 against Igrov-1/25 ET was approximately 50 times higher than the parental cell line. Resistance was not reversed while maintaining the cell line in drug-free medium for at least 24 months. Igrov-1/25 ET was cross-resistant to Doxorubicin and VP16 while it was equally sensitive to L-PAM, MNNG, CPT and only marginally less sensitive to Cis-DDP and Oxaliplatin compared to the parental cell line. Igrov-1/25 ET exposed to Doxorubicin retained this drug much less, mainly because of a more efficient drug efflux. The cyclosporine analogue SDZ PSC-833 reversed the resistance of Igrov-1/25 ET to ET-743, without any enhancement of the drug activity against the parental Igrov-1 cell line. Igrov-1/25 ET exhibits typical features of cell lines overexpressing the mdr-1 gene and can be a potentially useful tool in selecting ET-743 non-cross-resistant analogues as well as to investigate methods to counteract resistance to this drug.

High antitumour activity of ET743 against human tumour xenografts from melanoma, non-small-cell lung and ovarian cancer

BACKGROUND

Ecteinascidin-743 (ET743) is a novel antitumour agent originating from the Caribbean tunicate Ecteinascidia turbinata. It has potent cytotoxic and antitumour activity and a potential new mechanism of action. The aim of the present study was to further explore the antitumour activity of ET743 in human tumour xenografts from melanoma, non-small-cell lung and ovarian cancer.

DESIGN

As the antitumour profile of ET743 was largely unknown a chemo-sensitive and a marginal chemo-resistant human tumour xenograft were selected for each tumour type. ET743 was administered intravenously using two administration schedules (days 0, 4, 8 and 0-2, 13-15).

RESULTS

ET743 was very active at the maximum tolerated dose (MTD) in the chemo-sensitive xenograft melanoma MEXF 989, non-small-cell lung cancer LXFL 529, and ovarian cancers HOC22 and (marginally resistant to cisplatin) HOC18. Activity was also seen at 1/2 MTD. Apart from HOC18, ET743 caused complete remissions in the responding xenografts. The compound was inactive in the chemo-resistant xenograft melanoma MEXF 514 and non-small-cell lung cancer LXFA 629. In terms of antitumour activity the days 0, 4, 8 schedule had advantages over the days 0-2, 13-15 schedule.

CONCLUSIONS

ET743 is a very effective agent in chemo-sensitive and marginal chemo-resistant xenografts, but inactive in chemo-resistant tumour xenografts. The activity of ET743 in the marginally cisplatin-resistant ovarian cancer HOC18 might indicate absence or incomplete cross-resistance against cisplatin. It is recommended to include melanoma, non-small-cell lung cancer, and ovarian cancer in phase II clinical trials and to use an intermittent schedule.