Didemnin B in favourable histology non-Hodgkin's lymphoma. A phase II study of the National Cancer Institute of Canada Clinical Trials Group

Cyclic depsipeptides as potential cancer therapeutics

Cyclic depsipeptides are polypeptides in which one or more amino acid is replaced by a hydroxy acid, resulting in the formation of at least one ester bond in the core ring structure. Many natural cyclic depsipeptides possessing intriguing structural and biological properties, including antitumor, antifungal, antiviral, antibacterial, anthelmintic, and anti-inflammatory activities, have been identified from fungi, plants, and marine organisms. In particular, the potent effects of cyclic depsipeptides on tumor cells have led to a number of clinical trials evaluating their potential as chemotherapeutic agents. Although many of the trials have not achieved the desired results, romidepsin (FK228), a bicyclic depsipeptide that inhibits histone deacetylase, has been shown to have clinical efficacy in patients with refractory cutaneous T-cell lymphoma and has received Food and Drug Administration approval for use in treatment. In this review, we discuss antitumor cyclic depsipeptides that have undergone clinical trials and focus on their structural features, mechanisms, potential applications in chemotherapy, and pharmacokinetic and toxicity data. The results of this study indicate that cyclic depsipeptides could be a rich source of new cancer therapeutics.

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.

Natural products as probes of cell biology: 20 years of didemnin research

The discovery of the didemnin family of marine depsipeptides launched an exciting and intriguing chapter in natural product chemistry. The unusual structure of the didemnin congeners has led to several total syntheses by research groups from around the world. The impressive in vitro and in vivo biological activities of the didemnins resulted in the first human clinical trials in the U.S. of a marine natural product against cancer, and additional clinical trials of a second-generation didemnin, dehydrodidemnin B (aplidine), are underway. As we mark the 20-year anniversary of the discovery of the didemnins, this class of natural products continues to stimulate active research in fields ranging from synthetic and medicinal chemistry to clinical oncology and cell biology. While some progress was made in dissecting the molecular mechanism of action and in establishing structure-activity relationships, there are still more questions than answers. This review covers the recent didemnin literature, highlighting the work directed towards understanding how this group of natural products interact with fundamental processes such as cell proliferation, protein biosynthesis, and apoptosis. The didemnin field illustrates how natural product chemistry may be used as a critical tool for the study of cell biology.

Pharmaceutical development of anticancer agents derived from marine sources

The marine ecosystem is more and more acknowledged as a source of potential anticancer agents. After the identification of a potential substance several hurdles have to be overcome before a marine candidate can enter the clinic. Amongst these are the establishment of a method which ensures sufficient supply and, which is the focus of this review, the development of a clinically useful pharmaceutical formulation. General issues with respect to the pharmaceutical development of marine anticancer agents will be discussed, which will be illustrated by highlighting aspects of the pharmaceutical development and clinical use of some representative compounds.

Phase II trail of didemnin B in previously treated non-Hodgkin's lymphoma: an Eastern Cooperative Oncology Group (ECOG) Study

Patients with non-Hodgkin's lymphoma (NHL) who fail initial therapy have a poor prognosis. We conducted a phase II study to determine the efficacy and toxicity of didemnin B, a non-myelosuppressive marine compound, in patients with NHL who relapsed or progressed after receiving one or two previous chemotherapy regimens. Fifty-one eligible patients were registered on this phase II study. Twenty-nine patients had intermediate or high grade (IG/HG) disease and 22 patients had low grade (LG) disease. Twenty-five patients received didemnin B at a dose of 6.3 mg/m2 and the remainder received 5.6 mg/m2, administered intravenously every 28 days. The patients had an Eastern Cooperative Oncology Group (ECOG) performance status of 0-2 and biopsy-proven relapsed disease. Objective responses were observed in two (7%) patients (one complete remission [CR] and one partial remission [PR]) with IG/HG disease and five (23%) patients (one CR and four PR) with LG disease. Patients with IG/HG disease had a median time to treatment failure (TTF) of 1.6 months and a median survival of 8.0 months. In contrast, the group with LG disease had a median TTF of 4.6 months and a median survival of 2.7 years. There were five grade V, 12 grade IV, and 57 grade III toxicities. Didemnin B appears to have modest activity in low grade NHL. However, the drug has considerable toxicity in this population of patients.

Phase II clinical trial of didemnin B in patients with recurrent or refractory anaplastic astrocytoma or glioblastoma multiforme (NSC 325319)

The activity of didemnin B, a natural product derived from the Caribbean Tunic was assessed in 16 patients with Glioblastoma multiforme. Didemnin B was administered intravenously by a short infusion at a dose of 4.3 mg/m2 and subsequently escalated to 6.3 mg/m2. No anti-tumor activity was observed. Toxicity consisted of fatigue, weakness, stomatitis, mild blood count changes, nausea and vomiting and occasional fever. Based on these results further studies with didemnin B in patients with Glioblastoma multiforme are not recommended.

Tamandarins A and B: new cytotoxic depsipeptides from a Brazilian ascidian of the family Didemnidae

The structures of two new, naturally occurring cytotoxic depsipeptides, tamandarins A and B (1 and 2), are presented. The tamandarins were isolated from an unidentified Brazilian marine ascidian of the family Didemnidae. The structures of the new cytotoxins were assigned by interpretation of FABMS data and by extensive 2D NMR analyses. The absolute configurations of the tamandarins were assigned by acid and alkaline hydrolysis to yield their corresponding amino acids, which were then analyzed as their Marfey derivatives. The cytotoxicity of tamandarin A (1) was evaluated against various human cancer cell lines and shown to be slightly more potent than didemnin B. A qualitative discussion of the conformation of tamandarin A (1) in solution, obtained from NMR J-value data, variable temperature experiments, and NOESY/ROESY data, is included.

Analysis of Ecteinascidin 743, a new potent marine-derived anticancer drug, in human plasma by high-performance liquid chromatography in combination with solid-phase extraction

A reversed-phase high-performance liquid chromatographic method has been developed and validated for the quantification of the novel anticancer drug Ecteinascidin 743 in human plasma. The sample pretreatment of the plasma samples involved a solid-phase extraction (SPE) on cyano columns. Propyl-p-hydroxybenzoate was added after the sample pretreatment to correct for variability in injection volumes. The separation was performed on a Zorbax SB-C18 column (75x4.6 mm I.D., particle size 3.5 microm) with acetonitrile-25 mM phosphate buffer, pH 5.0 (70:30, v/v) as the mobile phase. The flow-rate was 1.0 ml/min and the eluent was monitored at 210 nm. The accuracies and precisions of the assay fall within +/-15% for all quality control samples and within +/-20% for the lower limit of quantitation, which was 1.0 ng/ml using 500 microl of plasma. The overall recovery of the sample pretreatment procedure for Ecteinascidin 743 was 87.0+/-5.9%. The drug was found to be stable in human plasma at -30 degrees C for at least 2 months. At room temperature Ecteinascidin 743 was stable in human plasma for 5 h at most.