Discovery of natural apigenin analogues as lysine-specific demethylase 1 inhibitors against tumoral testicular germ cells

Testicular germ cell tumors (TGCT) pose a threat to men's health, discovery of small molecule compounds with potent antiproliferative activity against testicular germ cells is of great significance. Lysine-specific demethylase 1 (LSD1) is overexpressed in tumoral testicular germ cell lines, and it is a promising target for developing agents against TGCT. A series of natural apigenin analogues were evaluated for their inhibitory activity against LSD1, and their structure activity relationships (SARs) were explored. Among them, 8,3'-diprenylapigenin exhibited the most potent inhibitory activity against LSD1 with an IC₅₀ value of 3.60 µM. 7-hydroxy of 8,3'-diprenylapigenin formed a hydrogen bond with Ala809 of LSD1, demonstrating that 7-hydroxy was a dominant group. In addition, 8,3'-diprenylapigenin reversibly and selectively inhibited LSD1 in a concentration-dependent and time-dependent manner. It inhibited proliferation against tumoral testicular germ cell lines NCCIT and NTERA-2 with IC₅₀ values of 9.37 µM and 5.26 µM, respectively. Mechanism studies revealed that 8,3'-diprenylapigenin induced the generation of ROS, inhibited the activity of catalase and decreased the level of ATP in NTERA-2 cells. Meanwhile, it also activated the release of LDH, increased the activity of SOD and enhanced the level of MDA in NTERA-2 cells. These findings indicated that 8,3'-diprenylapigenin is a novel reversible LSD1 inhibitor and deserves further exploration to treat testicular germ cell tumors.