Phthalascidin, a synthetic antitumor agent with potency and mode of action comparable to ecteinascidin 743

Abstract

A series of totally synthetic molecules that are structurally related to the marine natural product ecteinascidin 743 (Et 743) has been prepared and evaluated as antitumor agents. The most active of these, phthalascidin, is very similar to Et 743 with regard to in vitro potency and mode of action across a variety of cell types. The antiproliferative activity of phthalascidin (IC 50 ‫؍‬ 0.1-1 nM) is greater than that of the agents Taxol, camptothecin, adriamycin, mitomycin C, cisplatin, bleomycin, and etoposide by 1-3 orders of magnitude, and the mechanism of action is clearly different from these currently used drugs. Phthalascidin and Et 743 induce DNA-protein cross-linking and, although they seem to interact with topoisomerase (topo) I (but not topo II), topo I may not be the primary protein target of these agents. Phthalascidin and Et 743 show undiminished potency in camptothecin-and etoposide-resistant cells. Phthalascidin is more readily synthesized and more stable than Et 743, which is currently undergoing clinical trials. The relationship of chemical structure and antitumor activity for this class of molecules has been clarified by this study.Ecteinascidin 743 (Et 743) is an exceedingly potent antitumor agent isolated from extracts of the marine tunicate Ecteinascidia turbinate that is currently undergoing phase II clinical trials as a result of its promising efficacy in preclinical antitumor tests (1-5). Although the detailed molecular mechanism of action still remains unclear, Et 743 has been reported to yield DNA sequence-selective alkylation of guanine N2 in the minor groove of duplex DNA (6). Additionally, bioassays for antimetabolic activities and enzyme inhibitions revealed Et 743 showed potent inhibition of DNA and RNA synthesis and of RNA polymerase activity but much less inhibition of DNA polymerase activity (7). Despite the minute human dosage of Et 743 currently being used in the clinic, Ϸ2 mg per person by i.v. infusion, the supply of this rare natural product is inadequate for large-scale studies. Consequently, a multistep total chemical synthesis has been developed to provide the amounts of Et 743 required for medical use (8). The availability of this synthetic process and the desirability of finding simpler and more stable structural relatives of Et 743 has led us to synthesize and evaluate new members of this class of substances. Described herein is the discovery of a number of compounds that significantly exhibit antitumor activity. The most potent of these, phthalascidin (Pt 650, Fig. 1

Oncostatin M stimulates proliferation, induces collagen production and inhibits apoptosis of human lung fibroblasts

“…At the end of each incubation period, proliferation was assessed using an MTS assay. This assay measures mitochondrial activity through the formation of an insoluble formazan salt and has been shown to correlate to cell density (Martinez et al, 1999). MTS was diluted 1 : 20 with serum free DMEM and 300 ml was added to each well.…”

Identification of GAPDH as a protein target of the saframycin antiproliferative agents

“…Other studies have shown that Et743 may activate more than one signaling pathway in cancer cells; these include a transcription-coupled process leading to cell-cycle arrest, and another transcription-independent pathway leading to apoptosis (16). In studies of the Et743 analog Pt650, drug exposure was shown to produce DNA-protein crosslinks, but the identities of bound proteins were not established (17). Here, we show that GAPDH is a common protein target of SafA-, QAD-, and Pt650-DNA adducts by using a DNA-linked affinity chromatography technique.…”

Ecteinascidin 743, a transcription-targeted chemotherapeutic that inhibits MDR1 activation

“…97 ͉ no. 12 ͉ 6775-6779 bule disruption (13), and target topoisomerase I (14,15), its mechanism of action in vivo is unknown. A recent study showed that ET-743 interfered with the interaction of minor-groove-binding proteins, particularly NF-Y, with their cognate DNA elements in vitro (16).…”