Inhibition of tumor growth by S-3-1, a synthetic intermediate of salvianolic acid A

Salvianolic acid A (1) is one of the active components from Salvia miltiorrhiza, which was found to suppress the growth of mouse tumors. S-3-1 (a 2-allyl-3,4-dihydroxybenzaldehyde, 2) is a synthetic intermediate of a salvianolic acid A derivative with strong inhibitory effects on the growth of cancer cells in vitro. The inhibitory effects of 2 on tumor growth and its molecular targets were studied. 2 significantly suppressed the growth of mouse Lewis lung carcinoma, S180 sarcoma and H22 hepatic carcinoma in a dose-dependent manner. With a simple scrape-loading dye transfer method, 20 μg/ml of 2 was found to significantly enhance gap junction intercellular communication (GJIC) in human pancreatic adenocarcinoma PaCa Cells, human lung epithelial carcinoma W₁-38 cells and human lung adenocarcinoma A549 cells, but 2 had no marked effect on GJIC in human colon cancer CACO₂ cells. With Northern blot analysis, 2 was found to inhibit the expression of c-myc gene in A549 cells and have no marked effect on H-ras oncogene expression, and increase the cellular P53 mRNA contents, though it did not affect the expression of RB tumor suppressor gene. 2 also suppressed the P46 (JNK/SAPK) expression in A549 cells. Western blot analysis was applied to visualize the P21^ras protein. Results shows that 2 at concentrations ranging from 10 to 20 μg/ml decreases the contents of the membranous P21^ras and total P21^ras and increases the contents of cytosolic P21^ras protein in a time-dependent manner. However, 2 had no significant effects on farnesyl protein transferase activities at the concentrations that could efficiently decrease the membranous P21^ras content. This suggested that 2 might suppress tumor growth partly through enhancement of GJIC and reversion of the transformed phenotypes. The other mechanisms may be that 2 can suppress the overexpression of c-myc oncogene, inhibit the function of Ras oncoprotein, increase the expression of P53 tumor suppressor gene and interrupt P46-associated mitogen-activated pathway other than farnesylation of Ras protein.