Abstract
In the course of screening for anticancer agents, a novel active compound, F3-2-5, was isolated from culture broth of Streptomyces sp., KACC91015. Its structure was identified using nuclear magnetic resonance, mass spectrometry, and molecular modeling experiments, and confirmed by total synthesis. The growth of various human cancer cell lines was inhibited in a dose-dependent manner by 0.06-0.48 mM F3-2-5 over 24 h. Its IC(50) values were estimated at 37 microM on HeLa, 72 microM on A549, and 190 microM on HT-29 cells. However, F3-2-5 had no antiproliferative effect on normal lymphocytes and normal fibroblasts used as controls. Moreover, it affected cell cycle regulation and caused apoptosis of the HeLa cells; chromatin condensation and DNA fragmentation were observed in cells exposed to 80 microM F3-2-5. Western blot analysis revealed that F3-2-5 inhibited phosphorylation of retinoblastoma protein (pRb) and reduced expression of cyclin-dependent kinase-4 and -6, and cyclin D1 and E, while levels of p53 and p21(WAF1/CIP1) increased. Taken together, these findings show that F3-2-5 inhibits proliferation of HeLa cells by inducing G(1) phase arrest as a consequence of inhibition of pRb phosphorylation following up-regulation of p21(WAF1/CIP1) and p53. Furthermore, apoptosis in HeLa cells treated with F3-2-5 was associated with an increase in Bax and p53, leading to release of cytochrome c, activation of caspase-3, and -8, and cleavage of poly (ADP-ribose) polymerase.