A specific binding site in Nb2 node lymphoma cells mediates the effects of didemnin B, an immunosuppressive cyclic peptide.
ABSTRACT Didemnin B (DB) is a cyclic depsipeptide with a variety of biologic effects, including potent antiviral, antitumor, and immunosuppressive activities. Although its mechanism of action has been attributed to inhibition of DNA and protein synthesis, the exact cellular site of interaction has not been previously defined. Since DB is strongly antiproliferative in Nb2 node lymphoma cells, we investigated potential DB binding sites in these cells, using [3H]-DB (2.7 mCi/mg) as the radiolabeled ligand. Time course studies with Nb2 cells showed that steady state [3H]-DB binding was attained after 4 h. Scatchard analysis with resting cells yielded a Kd of 180 nM (200 ng/ml), and 7 x 10(6) binding sites/cell. The IC50 of DB inhibition of ongoing protein and DNA synthesis in Nb2 cells, measured 24 h after prolactin (PRL) stimulation, was also in the range of 100 ng/ml. Didemnin analogs, with alterations at critical amino acid residues, inhibited the synthesis of DNA and protein and competed with [3H]-DB binding with the same rank order of potency. This implies that this binding site may mediate the inhibition of macromolecule synthesis. Subcellular fractionation of [3H]-DB labeled Nb2 cells revealed that specific binding occurred predominantly in the 100,000 g cytosolic fraction. Comparison with cyclophilin and the FK506 binding protein, both cytosolic receptors, suggests that the DB binding site may also belong to the family of immunophilins.
Article: Didemnin B induces apoptosis in proliferating but not resting peripheral blood mononuclear cells.[show abstract] [hide abstract]
ABSTRACT: We have previously shown that didemnin B, a branched cyclic depsipeptide composed of seven amino acids and two hydroxy acids, can induce rapid and complete apoptosis in HL-60 cells (Grubb, D.R. et al. (1995) Biochem. Biophys. Res. Commun. 215, 1130-1136). We now report that didemnin B can induce apoptosis in a wide range of transformed cell lines. Resting normal lymphocytes, however, are apparently unaffected by exposure to the drug. To investigate whether cell transformation, and/or cell proliferation is necessary for didemnin B to induce apoptosis, we examined the effect of didemnin B on freshly harvested human lymphocytes before and after stimulation with concanavalin A. Didemnin B induced apoptosis in normal lymphocytes only after mitogenic stimulation and therefore warrants further examination for its potential as a chemotherapeutic agent, especially for treatment of leukemia.APOPTOSIS 11/2002; 7(5):407-12. · 4.79 Impact Factor