Aaptamines from the marine sponge Aaptos sp. display anticancer activities in human cancer cell lines and modulate AP-1-, NF-κB-, and p53-dependent transcriptional activity in mouse JB6 Cl41 cells

Abstract

Aaptamine (8,9-dimethoxy-1H-benzo[de][1,6]naphthyridine) is a marine natural compound possessing antioxidative, antimicrobial, antifungal, and antiretroviral activity. Earlier, we have found that aaptamine and its derivatives demonstrate equal anticancer effects against the human germ cell cancer cell lines NT2 and NT2-R and cause some changes in the proteome of these cells. In order to explore further the mechanism of action of aaptamine and its derivatives, we studied the effects of aaptamine (1), demethyl(oxy)aaptamine (2), and isoaaptamine (3) on human cancer cell lines and on AP-1-, NF-κB-, and p53-dependent transcriptional activity in murine JB6 Cl41 cells. We showed that compounds 1-3 demonstrate anticancer activity in THP-1, HeLa, SNU-C4, SK-MEL-28, and MDA-MB-231 human cancer cell lines. Additionally, all compounds were found to prevent EGF-induced neoplastic transformation of murine JB6 Cl41 cells. Nuclear factors AP-1, NF-κB, and p53 are involved in the cellular response to high and nontoxic concentrations of aaptamine alkaloids 1-3. Furthermore, inhibition of EGF-induced JB6 cell transformation, which is exerted by the compounds 1-3 at low nontoxic concentrations of 0.7-2.1 μM, cannot be explained by activation of AP-1 and NF-κB.

Figure 1

Structures of aaptamine (1), demethyl(oxy)aaptamine (2), and isoaaptamine (3).

Figure 2

Effects of aaptamines 1–3 on the transcriptional activity of AP-1 (a), NF-κB (b), or p53 (c) in JB6 Cl41 cells stably expressing a luciferase reporter gene controlled by AP-1, NF-κB, or p53 DNA binding sequences, respectively. Cells were treated with the indicated concentrations of the substances for 6 h or 24 h. All experiments were performed in triplicate and repeated at least two times. ^“∗”-P < 0.05, statistically significant differences between treated and untreated control cells (Student's t-test).

Figure 3

The induction of apoptosis by aaptamines 1–3 in THP-1 human cancer cells. Cells were treated with the indicated concentrations of the substances for 24 h.

Figure 4

Effects of aaptamines 1–3 on the EGF-induced neoplastic transformation and colony formation of murine epithelial JB6 P⁺ Cl41 cells. Cells in a soft agar were treated with the indicated concentrations of the substances for one week. All experiments were performed in triplicate and repeated at least two times. ^“∗”-P < 0.05, statistically significant differences between treated and untreated control cells (Student's t-test).