13-Acetoxysarcocrassolide Exhibits Cytotoxic Activity against Oral Cancer Cells through the Interruption of the Keap1/Nrf2/p62/SQSTM1 Pathway: The Need to Move Beyond Classical Concepts

Abstract

13-Acetoxysarcocrassolide (13-AC), a marine cytotoxic product isolated from the alcyonacean coral Lobophytum crassum, exhibited potent antitumor and immunostimulant effects as reported in previous studies. However, the 13-AC antitumor mechanism of action against oral cancer cells remains unclear. The activity of 13-AC against Ca9-22 cancer cells was determined using MTT assay, flow cytometric analysis, immunofluorescence, immunoprecipitation, Western blotting, and siRNA. 13-AC induced apoptosis in oral cancer cells Ca9-22 through the disruption of mitochondrial membrane potential (MMP) and the stimulation of reactive oxygen species (ROS) generation. It increased the expression of apoptosis- and DNA damage-related proteins in a concentration- and time-dependent manner. It exerted potent antitumor effect against oral cancer cells, as demonstrated by the in vivo xenograft animal model. It significantly reduced the tumor volume (55.29%) and tumor weight (90.33%). The pretreatment of Ca9-22 cells with N-acetylcysteine (NAC) inhibited ROS production resulting in the attenuation of the cytotoxic activity of 13-AC. The induction of the Keap1-Nrf2 pathway and the promotion of p62/SQSTM1 were observed in Ca9-22 cells treated with 13-AC. The knockdown of p62 expression by siRNA transfection significantly attenuated the effect of 13-AC on the inhibition of cell viability. Our results indicate that 13-AC exerted its cytotoxic activity through the promotion of ROS generation and the suppression of the antioxidant enzyme activity. The apoptotic effect of 13-AC was found to be mediated through the interruption of the Keap1/Nrf2/p62/SQSTM1 pathway, suggesting its potential future application as an anticancer agent.

Soft Coral-Derived Dihydrosinularin Exhibits Antiproliferative Effects Associated with Apoptosis and DNA Damage in Oral Cancer Cells

“…In 2003, the IC 50 values of human lung cancer (A549), colon cancer (HT-29), and leukemia (HL-60) cells were reported as greater than 0.15 mM [27]. However, the detection time of the MTT assay and the cytotoxic mechanisms of DHS were not investigated in that study [28].…”

“…To examine the oxidative stress function of DHS-induced antiproliferation, pretreatment with the reactive oxygen species (ROS) scavenger N-acetylcysteine (NAC) [28] was applied before DHS posttreatment. NAC pretreatment alleviated the DHS-induced antiproliferative effect on Ca9-22 and SCC-9 cells (Figure 1B), suggesting that DHS induces antiproliferation of oral cancer cells in a ROS-dependent manner.…”

“…By following the procedure described in our previous study [18], the crude product yielded from the ethyl acetate extraction of the lyophilized bodies of the soft coral S. manaarensis was chromatographed to produce DHS at a high purity, as proven by 1 H and 13 C NMR spectra (Supplementary Figures S2 and S3). The inhibitor, NAC (Sigma-Aldrich, St. Louis, MO, USA) [28,[52][53][54], was pretreated before DHS treatment.…”

Cembranoids of Soft Corals: Recent Updates and Their Biological Activities

“…It also exerted potent anti-tumor effect against oral cancer cells, as demonstrated by the in vivo xenograft animal model. This compound reduced the tumor volume by 55.29% and tumor weight by 90.33% [ 68 ]. In 2019, Roy et al, isolated three cembranoids, 262 – 264 , from Okinawa, Japan, which showed anti-proliferation activity against various cancer cell lines.…”

“…Two compounds were new (culobophylin D 250, and culobophylin E 251) while the others were known compounds including lobocrassin C 252, lobophylin 253, crassocolide E 254, sarcocrassocolide 255, 13-acetoxysarcocrassocolide 256, sarocrassocolide M 257, (R)-14-deoxycrassin 258, lobocrassin B 259, sarcocrassocolides F-G 260-261[67]. Recently, a known compound 13-acetoxysarcocrassocolide 256 was also reported from the same aquacultured Lobophytum crassum by Liu et al[68].…”