Identification of brefelamide as a novel inhibitor of osteopontin that suppresses invasion of A549 lung cancer cells

Abstract

The contribution of aberrant osteopontin (OPN) expression to tumor progression and metastasis has been documented in a wide spectrum of malignancies, and targeted inhibition of OPN has therefore emerged as an attractive strategy for cancer therapy. Transcription of OPN is regulated by various transcription factors, and our recently published study demonstrated that downregulation of OPN is an important event in the TGF‑β cytostatic program. We report here that brefelamide exerts an inhibitory effect on OPN expression and function in A549 human lung carcinoma cells. The promoter, RNA, and protein levels of OPN were decreased in brefelamide‑treated A549 cells, which was accompanied by reduced invasive ability in vitro. OPN inhibition by brefelamide was largely abrogated by disruption of a putative TGF‑β inhibitory element in the OPN promoter. Treatment with brefelamide induced Smad4 expression, and knockdown of Smad4 by RNA interference partially diminished the inhibitory effect of brefelamide on OPN. These results indicate that brefelamide inhibited OPN‑mediated cell invasion through restoration of the OPN repression by TGF‑β/Smad signaling. Together with the reported antiproliferative property, our findings suggest that brefelamide might serve as a potential candidate for the development of a new antitumor and antimetastatic agent.

Induction of Osteopontin by Dengue Virus-3 Infection in THP-1 Cells: Inhibition of the Synthesis by Brefelamide and Its Derivative

“…Inhibiting OPN expression has been suggested as a promising therapeutic strategy against malignancies (Zhang et al, 2016b). Transcriptional regulation of OPN is complex and involves many factors, including AP-1, Ets, Myc, and v-Src (Hijiya et al, 1994; Wang et al, 2000).…”

“…High concentrations of both compounds (>30 μM) were toxic to DENV-infected THP-1 and 293T cells (>30 μM), an effect that was dose-dependent, reflecting their original purpose as an anticancer drug that induces cell growth arrest (Zhang et al, 2016b). Between the two compounds, A showed greater potential than B since the concentration at which it was most effective was much lower than its IC 50 value.…”

“…Brefelamide, henceforth referred to as compound A (Kikuchi et al, 2005), is an aromatic amide isolated from methanol extracts of Dictyostelium brefeldianum and D. giganteum slime mold fruiting bodies; its derivative, henceforth referred to as compound B (Kikuchi et al, 2005; Zhang et al, 2016b), contains a methyl ether group (-OCH 3 ). Both compounds were dissolved in dimethyl sulfoxide (DMSO) at a concentration of 50 mM and stored at -20°C.…”

“…Brefelamide and its methyl ether derivative have been reported to inhibit OPN expression (Zhang et al, 2016b) in DENV-infected cells. This was further investigated in the present study using two different human cell lines.…”

Inhibition of Osteopontin Synthesis in THP-1 Cells Stimulated with Phorbol 12-Myristate 13-Acetate by Brefelamide Derivatives

“…Recently, we showed that small amounts of FL-OPN and tr-OPN were detected in the supernatants of non-phorbol 12-myristate 13-acetate (PMA)-stimulated cells by ELISA, with increased levels of all forms, including undefined Ud-OPN, in PMA-stimulated cells [16]. Brefelamide has been reported to inhibit OPN expression in A549 cells at a concentration of 50 µM using an OPN promoter reporter assay [17]. We also reported that brefelamide and its methyl ether derivative (compound B; Figure. 1) suppressed OPN production in DENV-infected THP-1 cells and also inhibited DENV replication [18].…”