Induction of Morphological and Biochemical Apoptosis following Prolonged Mitotic Blockage by Halichondrin B Macrocyclic Ketone Analog E7389

Abstract

E7389, a macrocyclic ketone analog of the marine natural product halichondrin B, currently is undergoing clinical trials for cancer. This fully synthetic agent exerts its highly potent in vitro and in vivo anticancer effects via tubulin-based antimitotic mechanisms, which are similar or identical to those of parental halichondrin B. In an attempt to understand the impressive potency of E7389 in animal models of human cancer, its ability to induce apoptosis following prolonged mitotic blockage was evaluated. Treatment of U937 human histiocytic lymphoma cells with E7389 led to time-dependent collection of cells in the G 2 -M phase of the cell cycle, beginning as early as 2 h and becoming maximal by 12 h. Increased numbers of hypodiploid events were seen beginning at 12 h, suggesting initiation of apoptosis after prolonged E7389-induced mitotic blockage. The identity of hypodiploid events as apoptotic cells under these conditions was confirmed by two additional morphologic criteria: green to orange/yellow shifts on acridine orange/ethidium bromide staining, and cell surface annexin V binding as assessed by flow cytometry. Several biochemical correlates of apoptosis also were seen following E7389 treatment, including phosphorylation of the antiapoptotic protein Bcl-2, cytochrome c release from mitochondria, proteolytic activation of caspase-3 and -9, and cleavage of the caspase-3 substrate poly(ADP-ribose) polymerase (PARP). In LNCaP human prostate cancer cells, treatment with E7389 also led to generation of hypodiploid cells, activation of caspase-3 and -9, and appearance of cleaved PARP, indicating that E7389 can activate cellular apoptosis pathways under anchorage-independent and -dependent cell culture conditions. These results show that prolonged mitotic blockage by E7389 can lead to apoptotic cell death of human cancer cells in vitro and can provide a mechanistic basis for the significant in vivo anticancer efficacy of E7389.

Microtubule inhibitors: Differentiating tubulin-inhibiting agents based on mechanisms of action, clinical activity, and resistance

“…Halichondrins are noncompetitive inhibitors of vinca alkaloids that occupy the vinca-binding domain on tubulin, suppress the growth of microtubules, and inhibit polymerization, thereby inducing cell cycle arrest and apoptosis (75). The halichondrin analog erubilin mesylate (also known as E7389, ER-086526, and NSC 707389) inhibits the polymerization of purified tubulin more potently than the parent compound halichondrin B (76).…”

Improving the outcome of patients with castration-resistant prostate cancer through rational drug development

“…Satraplatin (JM-216), an oral platinum compound, is currently being evaluated in a large international trial (SPARC), in combination with prednisolone as second-line treatment after docetaxel. Novel tubulin binding drugs such as the epothilone B analogue, ixabepilone (BMS-247550) (Galsky et al, 2005) and the halichondrin B analogue, E7389 (Kuznetsov et al, 2004), have demonstrated promise in the post-docetaxel setting and clinical trials are ongoing.…”

Differential Cytotoxic Effects of Jaspine B in Various Cancer Cells

“…Yondelis, isolated from Ecteinascidia turbinate, was approved for clinical use in metastatic soft tissue carcinoma and ovarian cancer in 2009 in Europe [5]. Another approved marine-based drug is Halaven, an analogue of halichondrin B, extracted from the sea sponge Halichondria okadai [11], and was approved for the treatment of metastatic breast cancer in 2010 from FDA. Besides these three marine anti-cancer agents currently being marketed, several marine products and their derivatives such as aplidin, bryostatin-1, and zalypsis are undergoing phase II and III clinical trials [5].…”